# 63<sup>rd</sup> ANNUAL CONFERENCE OF THE SA INSTITUTE OF PHYSICS

Africa/Johannesburg
Support
• Monday, 25 June
• 08:30 16:00
SAIP Council meeting
• 09:00 16:10
Winter School: Applications of Luminescence
Convener: Dr Elizabeth Coetsee (University of the Free State)
• 09:00
Opening 10m
Speaker: Dr Elizabeth Coetsee (University of the Free State)
• 09:10
Introduction to Luminescence 45m
Speaker: Prof. Hendrik Swart (University of the Free State)
• 09:55
Light harvesting 45m
Speaker: Prof. Tjaart Krüger (University of Pretoria)
• 10:40
Tea 20m
• 11:00
ZnO-based Photonics 45m
Speaker: Dr David Rogers (Nanovation)
• 11:45
Thermoluminescence: Standards and contemporary developments 45m
Speaker: Prof. Makaiko Chithambo (Rhodes University)
• 12:30
Lunch 1h
• 13:30
Lighting the future: perspectives on solid state lighting, energy efficiency and phototherapy 45m
Speaker: Prof. Odireleng Ntwaeaborwa (University of the Witwatersrand)
• 14:15
Luminescent gas sensors 45m
Speaker: Ms Gugu Mhlongo (CSIR, MSM, Nano Centre)
• 15:00
Tea 15m
• 15:15
Experimental design and characterization of nano-photonic materials through classical and quantum calculations 45m
Speaker: Dr Richard Harris (University of the Free State)
• 16:00
Closing and Thanks 5m
Speaker: Dr Elizabeth Coetsee (University of the Free State)
• 17:00 19:00
Welcome Reception
• Tuesday, 26 June
• 08:30 09:00
Official Opening Auditorium

### Auditorium

• 09:00 10:00
Plenary: Liu
Convener: Prof. Hendrik Swart (University of the Free State)
• 09:00
The Search for High Efficiency Energy Conversion Nanocrystals: A Personal Account 1h
Lanthanide-doped nanoparticles exhibit unique luminescent properties, including a large Stokes shift, a sharp bandwidth of emission, high resistance to optical blinking, and photobleaching. Uniquely, they can also convert long-wavelength stimulation into short- wavelength emission. These attributes offer the opportunity to develop alternative luminescent labels to organic fluorophores and quantum dots. In recent years, researchers have taken advantage of spectral-conversion nanocrystals in many important biological applications, such as highly sensitive molecular detection and autofluorescence-free cell imaging. With significant progress made over the past several years, we can now design and fabricate nanoparticles that display tailorable optical properties. In particular, we can generate a wealth of color output under single-wavelength excitation by rational control of different combinations of dopants and dopant concentration. By incorporating a set of lanthanide ions at defined concentrations into different layers of a core-shell structure, we have expanded the emission spectra of the particles to cover almost the entire visible region, a feat barely accessible by conventional bulk phosphors. In this talk, I will highlight recent advances in the broad utility of upconversion nanocrystals for multimodal imaging, bio-detection, display and photonics.
Speaker: Prof. Xiaogang Liu (Department of Chemistry, National University of Singapore, Singapore 117543 and Institute of Materials Research and Engineering, A*STAR, Singapore 117602)
• 10:00 11:00
Applied Physics
Convener: Dr phil ferrer (wits)
• 10:00
Spectral Resource Management based on VCSEL Wavelength Switching and Allocation 20m
Emerging high bandwidth demanding applications such as cloud computing, 5G wireless, wearable devices for health monitoring and high definition video streaming has brought about a rapid growth of Internet traffic. This calls for upgrade of the traditional fixed grid wavelength division multiplexing (WDM) system, to improve capacity, reliability, cost and simplicity in the network through spectrum flexibility and cost effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub carriers and assigning a number of frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a technique for bandwidth variability and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing. We present wavelength switching using a low cost, high bandwidth and power efficient vertical cavity surface emitting laser (VCSEL) wavelength tenability property. In this study, the driving current of a 1550 nm VCSEL is varied from (2 mA to 8 mA), therefore attaining different channel spacing 0.8 nm (100 GHz), 0.4 nm (50 GHz), 0.2 (25 GHz), 0.1 nm (12.5 GHz) and 0.05 nm (6.25 GHz) at over a constant wavelength range of 5 nm. The majority of the spectrum was utilized at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint was reduced and bandwidth utilization was improved.
Speaker: Ms Phumla Dlamini (optical fibre research unit (nelson mandela metropolitan university))
• 10:20
Aerosol and cloud studies using LIDAR, satellite and model data in South Africa 20m
Atmospheric aerosols are minute particles suspended in the atmosphere. They interact both directly and indirectly with the Earth's radiation budget and climate. The aerosol optical depth (AOD) is the most important parameter used to quantify the impact of aerosols on radiative energy budget. In this study we report on the various aerosol and cloud measurements we have carried out this far. Firstly, we report on the distribution and seasonal variation of various aerosols such as black carbon (BC), sulphate and dust AOD in South Africa using Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) model data. BC aerosols were observed to be dominant in the north eastern parts of South Africa (SA) while sulphate aerosols were observed to be dominant in eastern parts of SA. Secondly, we report on the transport of volcanic aerosols over SA from the Calbuco volcano eruption in Chile that occurred on 21 April 2015. Volcanic aerosols were observed over SA from 28 April 2015 to 16 May 2015 as indicated by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Lastly, we report on the observation of clouds over Durban using the CSIR mobile Light Detection And Ranging (LIDAR) instrument. Low level cloud layers showed high extinction coefficients values ranging between 0.9 and 4.4 km−1, whereas low extinction coefficients for high level clouds were observed at values ranging between 0.001 and 0.002 km−1.
Speaker: Dr Lerato Shikwambana (SANSA)
• 10:40
A predictive approach for vibration analysis in underground mining operation 20m
Mine fatalities, accidents and incidents are often associated with ground, roof, stope or side instability. Attenuation of rock integrity or the presence of (under)ground pockets of gases or ground waters lead to the collapse of the tunnel. Safety sensors and machine learning tools are placed in the underground mine tunnels to alert for emergencies and immediate evacuation. Numerous reported data are found on condition monitoring of mining machineries but scarce are on monitoring of an underground gallery roof, floor or stope prior to the fatality or failure. Additionally, safe mining practices would include a proactive predictive approach instead of waiting for the occurrence of the unfortunate event. While the magnitude of vibrations could be measured with accelerometers, a programming model could assist with the prediction making used of curve fitting. This normally required knowledge of the pre-alarm and alarm standard level in order to assess the severity of the vibration. In this paper, we are discussing a predictive approach for the monitoring and the analysis of the vibration in an underground mining tunnel roof. This approach has been illustrated using the software MATLAB. Ultimately, an immediate action leading to proactively preventing any damage to the structure constitutes the main contribution of this work.
Speaker: Prof. Antoine Floribert Mulaba - Bafubiandi (University of Johannebsurg)
• 10:00 11:00
Astrophysics: Optical Astronomy I
Convener: Dr Alida Odendaal (University of the Free State)
• 10:00
Ultra-diffuse galaxies in Stripe 82 Clusters 20m
Ultra-Diffuse Galaxies(UDGs) are low surface brightness galaxies with a very low stellar mass component but their sizes are comparable to the Milky Way. To survive in the cluster environments where they have been observed these galaxies must contain significant amounts of dark matter as the strong tidal fields would normally tear diffuse low-mass galaxies apart. UDGs are hard to detect and classify as they are very faint and have the appearance of nearby dwarf galaxies. We are developing a pipeline to identify and analyze UDGs within galaxy clusters within the deep Stripe 82 region of the Sloan Digital Sky Survey. Preliminary results show a significant number of UDGs in all 16 clusters in our sample, at redshifts below 0.15. The abundance of these galaxies in clusters has only recently been recognized, therefore identifying and measuring their properties is key in understanding how they are formed and continue to exist. The resulting UDG sample will allow us to constrain how common UDGs are as a function of halo mass and redshift, and to determine their properties and distribution within the host clusters.
Speaker: Mr Nazir-Ahmed Makda (University of Cape Town)
• 10:20
Regulation of star formation in X-ray rich galaxy groups (stellar populations in brightest group galaxies) 20m
An important component of galaxy formation and evolution studies, is to accurately constrain their star formation histories (SFHs). While the SFHs of most massive early-type galaxies can be described using a single passively-evolving stellar component (Single Stellar Population [SSP]), there is a fraction of massive early-type galaxies in the centres of galaxy groups and galaxy clusters where recent star formation is observed and are better described by two or more stellar components (Composite Stellar Population [CSP]). In this project we identify and constrain possible recent star formation episodes in a sample of 23 BGGs (Brightest Group Galaxies), of which most are in the centres of X-ray rich groups and all are closer than 80Mpc, and a sub-sample of the Complete Local-Volume Groups Sample (CLoGS). We use archival spatially-resolved long-slit spectroscopy from the Hobby-Eberly Telescope (HET) at the McDonald Observatory, and determine whether the BGGs are better described by a SSP or a CSP using ULySS. We compare the results with existing X-ray observations of some of the BGGs, obtained by Chandra/XMM-Newton, and the X-ray determined physical properties of the host groups, e.g. cooling time and central entropy. The results of these BGGs can then be compared to a comparable sample of 32 Brightest Cluster Galaxies (BCGs) in rich galaxy clusters at a redshift (z) between 0.05 and 0.3.
Speaker: Mr Okkert Havenga (North-West University)
• 10:00 11:00
Convener: Dr Simon Mullins (iThemba LABS (Gauteng))
• 10:00
Using Monte Carlo Simulations and Experiments to Investigate the Activation of Heavy Metals Using 14.1 MeV Neutrons 20m
The area of Richards Bay is one of the industrialized areas in South Africa and, as a result, it is prone to industrial pollution. Two studies were recently conducted in the area, one of the studies focused on the chemical contamination and radiological risk of water sources in the area and it was found that heavy metals such as As, Mn and Cd were the main contaminants, with Mn being above the target water quality range (TWQR). In this study the aim was to investigate the feasibility of employing the Neutron Activation Analysis (NAA) technique to measure the levels of heavy metals and other trace elements in Richards Bay water and sediments. The technique is known to be sensitive to about 78 elements in the periodic table when employing thermal neutrons, since it decreases with an increase in neutron energy, a Monte Carlo-based code was used to simulate the activation of copper, a matrix consisting of the elements under study and a standard reference sample. Gamma energies identified in the Cu spectrum were 1718 keV, 2097 keV and 2301 keV. The simulations showed that elements are most likely to be activated by 14.1 MeV neutrons if present in higher quantities, due to typically low fast neutron cross-sections in most elements. The simulation results for the matrix of elements were poor due to saturation, and also due to some activation products such as Mg-27, Fe-53 and Al-28 having a half life shorter than the preferred irradiation time.
Speaker: Mr Sizwe Mhlongo (University of the Western Cape)
• 10:20
Efficiency calibration of the laboratory based gamma-ray detector for various sample geometries 20m
Radioactivity has been present on earth since its formation and is part of the environment we live in. Humans are exposed every day to radioactivity through the radioactive elements that occur naturally in the environment. Radionuclides are found naturally in air, water, soil, plants and inside our bodies. In this study, radiometric measurements using various sample holders for environmental samples are performed. Available sample holders under study are Marinelli beaker (1l) and cylindrical pill bottle (100 ml). The gamma-ray spectrometry method is the tool used to analyse samples. For absolute photo peak efficiency measurements IAEA reference material RGU-1, RGTh-1 and potassium chloride powder were prepared for 100 ml pill bottles and the Marinelli beakers (1l) then each measured in HPGe detector for a day. Additionally, certified reference point sources bought from NMISA were also measured. From the known activities of the point sources and the prepared volume sources, photopeak efficiency was calculated and efficiency parameters for these geometries were obtained. Also Monte Carlo simulation was used to benchmark the parameters of the detector used to determine the activity concentration of environmental samples. Later will compare the experimental data of reference samples with correction factors of the simulation data to match the experimental data. For this contribution, the efficiency of the detector as function of gamma-ray energy in various measuring geometries will be known.
Speaker: Ms Avuyile Sisanda Bulala (University of Cape Town / iThemba LABS)
• 10:40
Using reference radiation source to test Monte Carlo simulations 20m
The environments that surround us contains some amount of radioactive (unstable) materials or radionuclides that are derived from primordial and cosmogenic sources. In addition to naturally occurring radioactive materials (NORMs), there are technologically enhanced naturally occurring radioactive material (TENORMs) and man-made radionuclides that have been introduced into ecosystems due to proliferation of different nuclear applications in industry, medicine and research. The main aim of this study is to assess level of concentration of natural and man-made radionuclides in environmental samples. To achieve this goal, we seek to use Monte Carlo simulations and gamma-ray spectroscopy method. For this conference we will be presenting the test result obtained from GEANT4. The trial runs aimed at environmental gamma-ray spectrometry analysis of 60Co and 22Na point source samples on Hyper Pure Germanium detector and are verified using a Monte Carlo simulation code (GEANT4). Preliminary comparison results will be discussed.
Speaker: Ms Mistura Bolaji Ajani (University of the Witwatersrand/iThemba LABS)
• 10:00 11:00
Physics Education
Convener: Mr Paul Molefe (University of Johannesburg)
• 10:00
Student ideas on Vector direction in Kinematics graphs 20m
Understanding graphs is a primary skill in any discipline, physics in particular. Students frequently do not know whether to extract the desired information from the slope or height of a graph. This is a pilot study to understand the interpretation of direction of a vector in a kinematics graph. We used a questionnaire consisting of three graphs to study the understanding of kinematics graphs of first-year university students in various contexts. The study was conducted on Extended Curriculum Students (ECP) and main stream students who were registered for various courses in a UoT. The students were asked to determine the direction of movement of the objects in various graphs within different contexts. The result from the study shows that the students are engaging with the shape of the graphs rather than the variables in each axis. This paper presents the outcome from three different graphs and their reasoning for their responses, and the comparison between the two groups.
Speaker: Dr Ignatius John (CPUT)
• 10:20
The impact of phenomenography and variation theory on students’ understanding of the concept of acceleration. 20m
Challenges in the teaching and learning of physics existed as far as education existed worldwide. During the period, various approaches were continuously suggested and implemented but the learning gains were always disappointing, and physics was labelled as a difficult subject for the chosen few and that idea encouraged instructors accept high failure rate in physics as normal. Departing form that belief that physics is for the chosen few, the current study explored how phenomenography and variation theories from social sciences can help students to understand the concept of acceleration. Google form was initially used to collect data that informed the instructor about students’ prior understanding of the concept of acceleration. Later data gathered informed how activities should be designed guided by variation theory. The study reports about students’ prior understanding of the concept of acceleration, the activities designed and lastly the impact of both phenomenography and variation theory on students’ understanding of acceleration.
Speaker: Mr Mphiriseni Khwanda (University of Johannesburg)
• 10:40
Where does the problem start, in as far as vectors are concerned? 20m
The challenge faced by lectures of first year students at tertiary level is undermined. The perception is the thinking that the subject is a simple and manageable to students. First year students enrolled for pure Bachelor of Science (BSc.) and Bachelor of Engineering (BIng) are mostly expected to undertake some of their Physical Science modules with ease especially since they start with familiar work. The first that the content of their first year Physics involved repetition of the high school work becomes a point of challenge for first year lecturers. This could be the case if assumptions are mostly made about the students understanding those specific topics. An observation was made as an involvement with high school learners, particularly grade 11. The curriculum of grade 11 included and covers vectors and forces extensively. Questions were raised as to where do we or where do our students miss it, especially when they have to undertake these topics at the university level. To try get to the bottom of this challenge, first year level Physics papers which covered forces and vectors was given to grade 11 learners. This work presents the results of both groups (students and grade 11 learners), as we try to go deeper in finding out where the challenge starts.
• 10:00 11:00
Physics of Condensed Matter and Materials
Convener: Mr peace prince mkhonto (University of Limpopo)
• 10:00
Beyond Li-ion: Computational Modelling Studies on Stability of Li-S-Se System 20m
Recent rechargeable batteries are mainly based on conventional lithium intercalation chemistry, using lithium transition metal oxides as cathode material with typical capacities of 120-160 mA.h/g. The low energy density and/ or high cost of these cathode materials have limited their large scale production and application in Li ion batteries. Exploration of new cathode materials is consequently necessary to realise more efficient energy storage systems. Lithium sulphur cells have a promise of providing 2-5 times the energy density of Li-ion cells, however, they suffer poor cycling performance. Improvements that are effected by using Li/SeS x system in different electrolytes have been reported. In the current study we employ computational modelling methods to explore stability, structural and electronic properties of discharge products formed in the Li/SeS x battery, which has potential to offer higher theoretical specific energy and remedies the challenges that Li-S battery encounters. First principle methods were used to calculate thermodynamic properties of Li 2S and Li 2Se, which agreed with available experimental results. A cluster expansion technique generated new stable phases of Li/SSe x system and Monte Carlo simulations determined concentration and temperature ranges in which the systems mix. Interatomic Born Meyer potential models for Li2S and Li2Se were derived and validated and used to explore high temperature structural and transport properties of mixed systems. Our study demonstrated that a combination of different computational techniques could assist in generating new stable phases of materials for future high energy density rechargeable batteries.
Speaker: Mr Cliffton Masedi (UL)
• 10:20
Effect of Li+ ion on the structural, morphological and luminescent properties of Y2O3:Tm3+ nanophosphor 20m
Rare-earth ions doped nanocrystals are increasingly important as an active media for solid-state lasers which efficiently operate under diode pumping. Among them the thulium (Tm3+) ion could be an attractive activator with suitable absorption for commercial diode pumping. In addition to this, it shows long fluorescence life times and it is suitable for large energy storage devices. Tm3+ doped yttrium oxide (Y2O3) and lithium (Li+) co-doped Y2O3:Tm3+ were prepared by the solution combustion technique. The samples were annealed at 900 °C to obtain crystalline phases. X-ray diffraction patterns confirmed the cubic phase of Y2O3. The crystallite sizes were calculated by using the Scherrer formula and was found to be in the order of 20 nm. The particles were found to be spherical in nature and their sizes were estimated to be 37 nm by the scanning electron microscope technique. A sharp andstrong photoluminescence (PL) emission peak at 453 nm was observed in the pristine and in the Li+ co-doped Y2O3:Tm3+ sample. The emission peak at 453 nm was assigned to the 1G4→3H6 transition. It was found that the PL intensity increased with the Li ion concentration up to 4 mol% and then it decreased with a further increase of Li ion concentration. The 4 mol% Li+ co-doped material showed a strong blue emission. The 4 mol% Li+ co-doped material exhibited a long decay. Thermoluminescence (TL) glow curves were obtained for the samples exposed with a UV light at room temperature. These glow curves showed peaks at 323 K, 356 K and 583 K and the intensities linearly increased upto a Li+ concentration of 4 mol%. Whereas, the pristine sample showed low intensity. The detailed TL kinetic parameters were evaluated by a glow curve deconvoluted technique.
Speaker: Dr Shivaramu N J (Department of Physics, University of the Free State, Bloemfontein, ZA-9300, South Africa)
• 10:40
Influence of Mn doping on the Room Temperature Gas Sensing Characteristics of TiO2 nanostructures 20m
Imperative increase has been observed over the years in the need of enhanced performance of gas sensor devices for the detection of toxic and combustible gases in working and living environments. The demand for accurate, fast, stable and portable devices rises with technology advances and wide application fields. Enhanced sensitivity, fast response, total recovery, and good selectivity are the main characteristics of a good sensor. With advances in nanotechnology, titanium dioxide (TiO2) nanostructures display great properties from their bulk characteristics contributing to promising sensor performance. Various processes have been attempted to modify the structure and properties of TiO2 such as sensitizing and metal ion doping in order to enhance its performance, mostly sensitivity. In this study, we report on the ultra-high sensitive and selective Mn doped TiO2 nanoparticles prepared by a microwave assisted hydrothermal method with various amounts of Mn 1.0, 1.5, 2.0, 2.5, 3.0 mol% added. Findings revealed a higher response of the Mn doped samples when exposed to NH3 gas at room temperature. The Mn doped TiO2 nanoparticles contains higher concentration of Ti3+ and singly ionized oxygen vacancies contributing to gas sensing properties. An enhanced UV–Vis emission and a broad shoulder at 540 nm were observed denoting defects induced by the substitution of Ti4+ ions with Mn2+. The Mn2+ ions improved surface activity of the sensing layer resulting in reduced gas surface chemisorption activation energy. The sensing mechanism towards NH3 gas is also proposed.
Speaker: Ms zamaswazi portia Tshabalala (DST/CSIR National Centre for Nano-Structured Materials, Council for Scientific and Industrial Research, Pretoria, 0001, South Africa)
• 10:00 11:00
Physics of Condensed Matter and Materials: Parallel Session
Convener: Dr Setumo Victor Motloung (SMU)
• 10:00
Bandgap tuned Co<sup>2+</sup>-doped ZnO for the photocatalysis of Methylene Blue and Rhodamine B 20m
Water pollution and the insufficiency of proper clean energy sources have resulted in the need for developing environmentally safe technologies and processes to combat this concern. One of the major constituents of wastewater are dyes, that are carcinogenic and immune to conventional physical and chemical remediation techniques. Thus, suitable techniques need to be designed to degrade these pollutants into harmless moieties before discharging them into aquatic systems. In this study, bandgap tuned Co2+-doped ZnO has been used as a UV/visible light photocatalyst on the degradation of methylene blue and rhodamine B, a model organic dye. X-Ray diffraction patterns of the sample annealed at 500°C showed the formation of highly crystalline phase-pure ZnO with no impurities. The bandgap was calculated from diffuse reflectance spectroscopy and the point of zero charge was evaluated using the pH drift method. The rate of degradation was investigated for different pH values and a suitable pH was optimized for the most effective degradation. The performance of this Co2+-doped ZnO photocatalyst under visible light was superior compared to other known reports. The efficiency of degradation was improved significantly by adding H2O2 and the amount of degradation was quantified using a simple methanolic extraction technique. ZnO is an environmentally friendly mineral and this study demonstrates the use of an effective and efficient, eco-friendly technique for combating water pollution.
Speaker: Dr Samvit Menon (University of the Free State)
• 10:20
Highly capable non-rare earth doped LiMgBO<sub>3</sub> phosphor for light emitting diodes 20m
Non- rare earth doped phosphor materials particularly Mn4+ activated nitrides and fluorides are emerging as an alternative to rare earth doped red emitting phosphor materials for light emitting diodes, as these materials are more cost effective. Still it remains a challenge to prepare high purity red light emitting and cost effective non-rare earth doped red phosphors because of the broad emission and challenging synthesis of nitrides and fluorides, respectively. Herein we reported the red emitting Mn4+ doped LiMgBO3 phosphor synthesized by solution combustion and solid state route. The photoluminescence spectrum had two broad bands from 260–410 nm and 420-545 nm, due to the 4A2 → 4T1 and 4T2 transition of Mn4+, respectively. Under UV and visible excitation the phosphor emits at 665 nm with CIE chromaticity coordinates of (0.706, 0.292) and FWHM of 35 nm, which revealed the high purity red light emission from the phosphor. The concentration quenching of Mn4+ was observed at around 0.6 mol%. The predicted mechanism for concentration quenching to be a dipole–dipole interaction among the Mn4+ ions. The results suggests that the phosphor with enough color purity ~62% and stable CIE coordinates could be an eventual choice as the red component for white light emitting diodes.
Speaker: Dr Ankush Kumar Bedyal (Department of Physics, University of Free State)
• 10:40
Size and shape impact on thermal expansion coefficient of nanowires 20m
The properties of bulk crystals depend upon their structure but in case of nanocrysatal, in addition to the structure, size and shape are the significant factor, which affect their properties. The shape factor has been introduced in the bond energy model. The basic idea is that the atomic cohesive energy decides the thermodynamical properties of the crystals. Also, cohesive energy changes with the atomic coordination background. The bond energy model justifies that how the surface dangling bonds depress the melting temperature of the nanomaterials and how the order disorder transition of the nanoparticles varies upon the particle size. The cohesive energy associated with these surface atoms will be unlike from their bulk materials. The excess energy associated with these surface atoms is defined as the surface free energy. On examining the surface effect, a simple model is debated to study the size and shape dependence of thermal expansion coefficient of Se and Si nanowires with different cross sectional shapes. It is projected that the thermal expansion increases with decrease in particle size. Also, it is recognized that the particle shape can impact the thermal expansion of nanoparticles and this effect on the thermal expansion becomes more with decreasing of particle size. Our theoretical predictions approve fairly well with the existing experimental and simulation results for nanowires in different shapes. Due to the modesty and applicability, this model can be stretched to the other nanomayterials and may be the recent attention of the researches engaged in the study of physical properties of nannomaterials.
Speaker: Prof. Madan Singh (National University of Lesotho)
• 10:00 11:00
Space Science
• 10:00 11:00
Theoretical and Computational Physics
Convener: Prof. Alan Cornell (NITheP)
• 10:00
A bond energy model to study the melting point and Debye temperature of nanomaterials 20m
The physical properties of materials change when the size of the material approaches from bulk to nanoscale. The size effect is taken by increasing the fraction of the surface atoms with lower coordination numbers, therefore increasing number of dangling bonds, which results in causing the thermodynamical properties as cohesive energy at nanoscale. The cohesive energy of nanoparticles decreases due to the dangling chemical bonds. On considering the surface effect, using bond energy model, a size dependent theory is discussed to study the melting point and Debye temperature of nanoscale materials. The number of atoms on the surface to the total number of atoms in nanosolid is analysed in terms of shape factor and the size of nanomaterials. The variation of melting point and Debye temperature is reported for spherical, regular tetrahedral, regular hexahedral and regular octahedral nanomaterials. It is found that the melting temperature and Debye temperature decrease as the particle size is reduced. The result reported is compared with the available experimental and simulation data. A good agreement between the present calculated results and the results reported by earlier researcher confirms the validity of the existing theory. Due to the simplicity and applicability, this model can be extended to the other nanomaterials and may be the recent consideration of the scholars engaged in the study of thermodynamical properties of nanosolids.
Speaker: Prof. Madan Singh (National University of Lesotho)
• 10:20
Quantum mechanical ab initio calculations of the structural, electronic,vibrational, mechanical and optical properties of bulk Silicon tellurides 20m
Silicon tellurides are being considered for next-generation non-volatile memory material. For the applications of these materials in electronic devices, it is necessary to provide information on their thermodynamic and mechanical stabilities, structural, electronic and optical properties based on first-principles density-functional theory. The obtained results are compared with experiment and with some available previous calculations.
Speaker: Dr George Manyali (Masinde Muliro University of Science and Technology)
• 10:40
Decade of High Performance Computing in South Africa: Opportunities for Physics Community 20m
The Centre for High Performance Computing (CHPC) is part of the National Integrated Cyber-Infrastructure System of the government of South Africa. It was established in 2007 by Department of Science and Technology and is managed by the Council for Scientific and Industrial Research (CSIR). Its mandate is to provide world class computational resources to research community across different fields of Science and Engineering in the country; and also to drive human capital development in field of high performance computing. Over the past 10 years, the centre managed to significantly grow itself from a flagship project to a more sustainable institution. In this presentation, I will share with you temporal evolution of the CHPC since it was established to date and how it can further benefit the Physics community.
Speaker: Dr Daniel Mojalefa Moeketsi (CSIR Meraka Institute (CHPC))
• 11:00 11:20
Tea 20m
• 11:20 13:00
Applied Physics
Convener: Dr Aletta Karsten (NMISA)
• 11:20
Enhanced photocatalytic degradation of methyl violet on TiO2/N-MWCNTs 20m
Textile industries are amongst the top environs of water polluters. They release complex organic pollutants (such as organic dyes) that are resistant to conventional water purification methods. Lately, TiO2-based photocatalytic degradation method has been successfully used to ravage the organic dye pollutants in aqueous medium at a low cost. However, the efficiency and turnover number of TiO2 is limited due to its low surface area, sintering, and the electron-hole recombination. Thus, multiwalled carbon nanotubes (MWCNTs) can be used to enhance the photocatalytic activity of TiO2 by increasing the catalyst surface area and also acting as photo-generated electron capturers. Moreover, the MWCNTs can be modified with nitrogen dopants to create more defects on the carbon lattice and a net positive charge to strengthen the TiO2-C interaction. We herein report on the competence of CVD-synthesized nitrogen doped MWCNTs (N-MWCNTs) in the enhancement of TiO2 photocatalytic activity for the degradation of methyl violet. Our results showed that N-MWCNTs supported TiO2 photocatalyst exhibit a large surface area, good TiO2-C interaction, and a reduction in the electron-hole recombination. Consequently, the photocatalytic activity of raw TiO2 was drastically increased after the inclusion of N-MWCNTs. Furthermore, the N-MWCNTs showed a great potential of improving the photocatalytic stability of TiO2 and its reusability.
Speaker: Ms Xiluva Mathebula (University Of The Witwatersrand)
• 11:40
Closed loop feedback control of an external cavity diode laser for laser cooling application 20m
Laser cooling of neutral atoms is currently receiving a lot of attention worldwide due to the fact that cold atoms are promising candidates for implementation of quantum information processing elements. To cool neutral atoms, such as Rubidium and Caesium, external cavity diode lasers (ECDL) are commonly used. The laser frequency is finely tuned by adjusting the cavity length as well as the diode current. The ECDL is locked to the appropriate transition, of Rubidium in our case, using a saturated absorption setup in the feedback path together with a proportional-integral-derivative (PID) controller, to control the cavity length and diode current. In this presentation we report on the analysis and performance of the closed loop control system using theoretical and numerical analysis, together with validation using experimental data. We present numerical and experimental results of the system’s response to various input stimuli and provide regions of safe operation.
Speaker: Mr Victory Opeolu (Cape Peninsula University of Technology)
• 12:00
Real-time Vibration Sensing in Renewable Energy Wind Turbine Blades Using a Polarization Based Optical Fibre Device 20m
Energy is essential for achieving sustainable growth among developing countries within Africa. Wind is regarded as one of the most promising types of renewable energy source capable of lowering the effects of greenhouse gases. Vibration monitoring and analysis is essential in the design of wind turbines due to the partially elastic structural property of the blades and because they are required to function in harsh and unsteady environments. This work presents a novel technique for accurately measuring vibrational frequencies as well as monitoring the plane of vibrations in renewable energy wind turbine blades, based on a polarimetric optical fibre sensor. The proposed technique further involves an offline, fast Fourier transform (FFT) digital signal processing (DSP) analysis. We successfully show operation for vibrations from 57-117 Hz. A fibre sensing system capable of measuring vibrational frequencies in one plane was first demonstrated. Frequencies of 56.7 Hz, 84.8 Hz and 90.3 Hz were accurately measured within 99.2 % of the actual value. Thereafter, simultaneous sensing in two orthogonal planes at 99.4 Hz and 116.5 Hz was experimentally achieved.
Speaker: Mr Shukree Wassin (NMMU)
• 12:20
Directly Modulated 850 nm Multimode VCSEL Performance Analysis for Short Reach Optical Communications 20m
Abstract: Short reach optical interconnects must support higher data rates to manage the increasing needs of end users and the commensurate increase in storage and computation within and between data centres. Multimode vertical cavity surface-emitting lasers (VCSELs) and multimode fibre (MMF) links provide a power efficient solution, which is achieved in part by maximizing the data rate per transmission channel. We experimentally analyze the performance of a 10 Gbps 850 nm multimode VCSEL for adoption in high-speed VCSEL-MMF based short range optical interconnects. Results show that an error-free operation at 10 Gbps is achieved at back-to-back (B2B) configuration with less than 0 dBm of received optical power. A successful transmission over OM3 optical fibre is achieved with a clearly open eye diagrams. Results from this work indicate that 850 nm multimode VCSELs have the potential for reliable operation over OM3 optical fibres. They are therefore ideal candidate for bandwidth demanding shor-range applications. Keywords: VCSEL, MMF, OM3, fibre, optical interconnects
Speaker: Dr George Isoe (Centre for Broadband Communication,Nelson Mandela University)
• 12:40
Development and characterization of a micro-controller based two photon correlation interferometer 20m
Quantum properties of light are usually characterized by the measurement of the first and second order correlation functions. These correlation functions are estimated from measurements of difference in arrival times of photons striking two single photon detectors. In this presentation, we describe the design, implementation and results of such a correlation interferometer. The device is capable of measuring time difference between the arrival of photons with a resolution of 110ps or smaller. The two photon correlator discussed here was built using two 16 bit micro-controllers, each having an analogue charge-time-measurement unit. The charge-time-measurement unit is an analogue circuitry within the micro-controller that charges a capacitor for a time period. A pulse from one photon detector starts the capacitor charging while a pulse from the other detector stops the charging. The voltage on the capacitor then is proportional to the charging time, in this case the time between arrival of the start and stop pulses. Our system provides the following features: (1) performs a measurement of time differences via the charge-time-measurement unit and produces a histogram of time differences, (2) counts the number of individual photons detected by each single photon detector, (3) detects coincidence events, i.e. photons arriving at the detectors simultaneously, using additional logic gates and (4) provides an interface between the micro-controllers and a user PC running a dedicated software. The system was tested in a lab using fabricated signals simulating classical chaotic light, single photons and light from a coherent source. The system was also tested using photons from a live quantum entanglement experiment where our system was compared to a commercial product. Measurements of the histograms of difference in photon arrival times are presented for both cases. From these histograms the first and second order correlation functions are extracted. Also presented are measurements of coincidence rates.
Speaker: Dr Kessie Govender (Cape Peninsula University of Technology)
• 11:20 13:00
Astrophysics: Optical Astronomy II / Astronomy for Development
Convener: Ms Helene Szegedi (University of the Free State)
• 11:20
Modelling the Spectral Energy Distribution and Polarisation of Blazars 20m
The optical emission from most blazars is dominated by the polarised synchrotron radiation of relativistic electrons in the jet, but the thermal radiation from the accretion-disk and host galaxy also contributes towards the high and low frequency ends of the optical spectrum. As the accretion-disk and host galaxy emissions are expected to be unpolarised, they reveal their presence in a decrease of the degree of polarisation towards the high- and low-frequency ends of the optical spectrum, respectively. This motivates a target-of-opportunity programme of spectropolarimetry observations of gamma-ray blazars with the Southern African Large Telescope (SALT). A model is constructed that combines modelling of the spectral energy distribution (SED) and of the degree of optical polarisation to constrain the accretion disk contributions in the spectra of blazars. I will present the model fit to the Flat Spectrum Radio Quasar 4C+01.02 in its flare and quiescent state in which degeneracies of parameters such as the electron spectrum energies, accretion disk luminosity, ordering of the magnetic field of the jet and the mass of the black hole are constrained. Presentation keywords: blazar, active galactic nuclei, spectropolarimetry, spectral energy distribution, optical polarisation
Speaker: Ms Hester M. Schutte (North-West University)
• 11:40
Improved Photometric Identification Formula for Pulsating Stars 20m
In this talk a detailed review of stellar pulsation and radiative transfer equations are presented. Starting from the radiative transfer equations and by considering appropriate physical conditions and mathematical formulations, we derived a formula that describes the effect of pulsations in the light output of a star. We took into consideration the interaction of light with the different layers of the atmosphere. This is an improvement from previous studies where the atmosphere is treated as a single layer at τ = 2/3. In this talk, we also investigated the depth dependence of eigenfunctions in the atmosphere of pulsating stars. Our results demonstrate that the displacement eigen function δr/r, the temperature eigen function δT/T and the opacity eigenfunction show great variability in the atmosphere of the equilibrium models studied. Our formalism is based on non-grey approximation where the pulsation equation and opacity depends on depth and frequency of observation. We also showed that the observed luminosity, for high overtone pulsators, comes from all the layers above the photosphere and the upper layer contributes the most. Moreover, from the equilibrium models considered in this study, the plots of the temperature eigen function as a function of depth demonstrated that, even with small T_eff, the atmosphere of a pulsating star will not be considered as a solitary and distinct layer as depicted by Watson, (1987) and Watson, (1988). we also show the depth dependence of eigenfunctions in the atmosphere of pulsating stars.
Speaker: Dr Getachew Mekonnen Mengistie (Northwest University)
• 12:00
High speed photometry of a pre-main sequence star HD 68695 using the Mahikeng Astronomical Telescope (MAT) 20m
HD 68695 is a well known pre-main sequence star with well established infrared excess and emission in its hydrogen lines. In this paper we show for the first time that this star pulsates with periods around 23 minutes and the main amplitude of 3 mmag. We present the data collected using the new Mahikeng astronomical Observatory which confirms the frequencies that are found in the KELT data in Sutherland. We show that the MAT is capable of producing photometric data with noise levels of less than 2 mmag. This makes the MAT not only an ideal instrument for performing photometry of pulsating stars, but also a very useful tool in the search and study transits of exoplanets.
Speaker: Mr Thapelo Mokgadi (Department of Physics, North West University)
• 12:20
Science at the Mahikeng Astronomical Observatory 20m
The new observatory of the North West University (MAO) houses a 40-cm MEADE LX200GPS ACF telescope with SBIG STT 8300M electronically cooled camera. It was officially launched on the 21 April 2018. This instrument is capable of detecting mili-magnitude changes in brightness of a star, and is thus suitable for the study of pulsating stars and exoplanet research. In this paper we present light curves and Fourier spectra of the various Pulsating stars observed at the MAO. This demonstrates that MAO is capable of producing high precision photometry.
Speaker: Prof. Thebe Medupe (Department of Physics, North West University, Mafikeng)
• 11:20 13:00
Convener: Prof. Bruce Mellado (University of the Witwatersrand)
• 11:20
Fine structure of the IsoScalar Giant Monopole Resonance (ISGMR) in 40,42,44,48Ca using alpha inelastic scattering at zero degrees 20m
Previous studies have shown that fine structure in the excitation energy spectra of nuclear giant resonances can be attributed to different physical processes. For example, characteristic energy scales of the fine structure for the IsoScalar Giant Quadrupole Resonance (ISGQR) arise mainly from the collective coupling of the ISGQR to low-lying surface vibrations, while on the other hand it has been shown that Landau damping is the main mechanism leading to the fine structure phenomenon in the IsoVector Giant Dipole Resonance (IVGDR). It is important to determine which processes are responsible for the fine structure in the ISGMR, particularly in the 40,42,44,48Ca isotope chain with its systematic increase in neutron number. Moreover, study of the ISGMR is of special significance because knowledge of its excitation energy provides direct information on nuclear incompressibility. Experiments were performed using the Separated Sector Cyclotron of iThemba LABS, together with the K600 magnetic spectrometer using inelastic scattering of 200 MeV alpha particles at zero degrees from 40,42,44,48Ca for measurements in the region of ISGMR with a good energy resolution of 86 keV (FWHM). In addition, following the application of Autocorrelation analysis, J п = 0+ level densities can be extracted also. Preliminary results will be presented.
Speaker: Mr Sunday Olorunfunmi (School of Physics, University of the Witwatersrand, Johannesburg.)
• 11:40
Low Pressure Focal Plane Detectors for the K600 :A design study 20m
Magnetic spectrometers have proven to be very useful in the world of experimental nuclear and astrophysics. The focal plane detection system instrumenting these spectrometers is instrumental in their success. A new focal plane detection system is envisaged for the K600 QDD magnetic spectrometer at iThemba LABS in Cape Town, South Africa. The existing focal plane detection system, consisting of two multi-wire drift chambers (MWDCs) and plastic scintillators, is designed to detect light ions (H and He isotopes) at medium energies (50-200 MeV). To be detected these particles go through a lot of material before reaching the scintillators and an event is registered. This affects the low energy threshold for operation of the K600. This study will quantify the low energy limitations as well as investigate the material budget for a new low energy detector. A conceptual design for a new focal plane detection system will be explored. This work is supported by the National Research Foundation South Africa
Speaker: Ms Thuthukile Khumalo (University of Zululand & iThemba LABS)
• 12:00
Cross section measurements of light ion production using (p,xp) reactions 20m
Neutron-rich beams are being developed at iThemba LABS to study nuclear structure away from stability. This is also the opportunity of deepening our understanding of astrophysical origin of elements. The interest of using (p,xp) reactions in the production of exotic nuclei, lies in the fact that proton beams have a large penetrating power and can be produced with high intensity. Some measurements have been performed at iThemba LABS using, 7Li, 9Be and natB targets with proton projectiles of energy 50 MeV and 66 MeV. The detection setup included two electron spectrometers composed of a 5mm thick plastic scintillator, for energy loss measurement, and a thin window Germanium detector (LEPS) for residual energy measurement. The E- ∆E technique with this combination of detectors allows particle identification and high-resolution measurement simultaneously. Lanthanum Bromide detectors where also used to measure gamma particles. Some preliminary results will be presented. Beryllium and Boron are chosen here because they can be used in oxide, carbide or nitride form that can sustain large temperature amplitudes and therefore can be used in place as Uranium carbide in the current design of the ISOL source of iThemba LABS. This is important as there is no significant cost or resources implications. In addition, light targets produce a lot less species which makes debugging easier. The results of this investigation will be used to evaluate the feasibility of light neutron rich beams at iThemba LABS.
Speaker: Mrs Doris Carole Kenfack Jiotsa (Stellenbosch University/ iThemba LABS)
• 12:20
Production of electron sources at iThemba LABS 20m
An electron spectrometer for the measurement of internal conversion electrons is undergoing development at iThemba LABS. The spectrometer will be used to study the nuclear configuration of multiple excited 0+ states around Z ≈50 region. The purpose of the project is to wider the state of knowledge for electron conversion sources of nuclei with proton number near fifty (Z≈50). In order to accomplish this, a set of different electron sources around this region will be produced (120Sn, 109Cd & 170Yb) 170Yb will be used to calibrate the spectrometer, since this nucleus has lot of discrete states. A proton beam ranging from 11 to 66 MeV will be used to produce sources using(p,n) reaction. The cross sections and activity yield for sources have been calculated, 133Ba and 207Bi will be used to calibrate the spectrometer, and hence their efficiency have been measured. This presentation will describe current progress on this project.
Speaker: Mr Bonginkosi Zikhali (University of wersten cape physics)
• 12:40
OPTIMIZATION OF ELECTRON SPECTROMETER IN LENS-MODE OPERATION 20m
The study of monopole transitions via excited 0+ states requires the measurement of internal conversion electrons and internal pair formation using an electron spectrometer. Such a spectrometer, consisting of a solenoid magnet transporter and a Si(Li) detector with an array of LaBr3, is undergoing development at iThemba LABS. Performance of the electron spectrometer has been investigated using radioactive sources produced at iThemba LABS. The spectrometer has been used in lens mode with the field swept under computer control. Transmission and efficiency, as well as the momentum resolution of the swept lens, are presented. Commissioning experiments are due to take place in July 2018 using an alpha beam at a maximum of Eα = 30 MeV with a beam current of 10enA on isotopically enriched 70Ge which will provide an opportunity to investigate E0 transitions in the target nucleus. This serves as a sensitive probe for the study of shape coexistence in nuclei since the monopole strength parameter is related to the change in mean square radius between the initial and final 0+ states.
Speaker: Mr Abraham Avaa (Wits\iThemba)
• 11:20 13:00
Physics Education
Convener: Dr Ignatius John (CPUT)
• 11:20
Producing introductory videos for student preparation for physics practical work 20m
Experimental work in the physics curriculum is vital to gain practical scientific skills as well as a better understanding of models and measurement. Due to increasing student numbers, limited equipment and laboratory space, students do not have unlimited time to perform experiments during practical sessions. Therefore students need to be increasingly well prepared in order to complete them successfully. Improved access to the internet has made it feasible to use introductory videos for preparation. The aim was not to reduce or replace written instructions or supervision, but rather to allow students to see the actual equipment and setup as well as measurement techniques in practice and hence allow the students to make better use of limited laboratory time. Producing the videos using professional help had significant time and cost implications, so the challenge was set to produce these internally with filming equipment available in the department. To pilot this project, short introductory videos were produced on four experiments dealing with Lissajous figures, Fourier synthesis, standing waves of a string, and diffraction of light. The demonstrator assigned to each experiment gained experience by acting as the presenter in the video to give an outline of the aim, equipment, method and measurement process. A single experiment took approximately 3 h of preparation and filming time, which was done in short segments of a few sentences at a time. It was useful to have two cameras so that an overview and close-up could be captured simultaneously. With the available filming equipment the quality video was excellent while the audio quality was merely sufficient. Editing of the videos was done using free software. The running time and resolution were limited to keep the file size to a minimum for easier access on or off campus. Anonymous feedback on the videos was collected from students e.g. initial results showed that only 39% accessed the videos off-campus, while 50% viewed them on campus and 11% not at all. It has been demonstrated that it is possible to create educational videos at low cost and the experience gained will allow improvement of quality and saving of time for future endeavours. A later phase of this project will include assessment whether the videos improve student practical work performance.
Speaker: Mr Antonie Fourie (University of the Free State)
• 11:40
Can exemption from practical(s) help students to pass physics modules? 20m
Pure BSc major and engineering students at University of Johannesburg undertake a standard calculus-based physics course as an introduction to their degree major. Each module in a semester consists of both theory and a practical component that need to be passed if credit has to be given. Failure to attain 50% pass mark in practical component makes it impossible for a student to sit for a final exam and this renders the students ineligible for promotion. Most of repeating students take the option of exemption from practicals, as a result some fail the module for the second time. This paper presents observations that reflect advantage of passing a module if good practical marks are attained, and the possibility of failing the module for the second time if exemption from practical sessions was chosen.
Speaker: Dr Buyi Sondezi (University of Johannesburg)
• 12:00
How do students use the knowledge of conservative and non-conservative forces when solving work and energy theorem problems? 20m
The concept of conservative force and non-conservative forces play a vital role in solving problems related to the application of the principle of conservation of energy and momentum, but they are generally ignored when solving quantitative problems. First year students usually assumed that the system is isolated even if isolated case has to be proven first before the equation is used. The study explores if students are using the knowledge of conservative and non-conservative forces when approaching problems dealing with work and energy theorem.
Speaker: Mr Paul Molefe (University of Johannesburg)
• 11:20 13:00
Physics of Condensed Matter and Materials
Convener: Mr Bertrand SONE (iThemba LABS-UWC)
• 11:20
Characterisation of Y<sub>2</sub>O<sub>3</sub> co-doped Bi<sup>3+</sup> and Yb<sup>3+</sup> thin films synthesised using pulsed laser deposition and spin coating. 20m
Phosphor materials doped with various rare-earth (RE) elements have been used by the lighting industry in light emitting diodes and mercury free fluorescent tubes due to the wide range of possible luminescence ranging from ultraviolet (UV) through to the near-infrared (NIR) regions. In recent years, phosphor materials have been used to alter the solar spectrum in order to reduce the spectral mismatch and improve the conversion efficiency of solar cells. RE3+ - Yb3+ co-doped phosphors have shown potential for down-converting/shifting UV photons to NIR photons, but due to the parity forbidden 4f transition of RE3+, they are generally inefficient at absorbing photons in the UV and blue regions resulting in a weak NIR Yb3+ emission. Metal donor ions such as Bi3+ have shown to be an alternative to rare-earth ions for enhancing the NIR emission of Yb3+ ions. Y2O3:Bi3+,Yb3+ thin films were prepared using the pulsed laser deposition (PLD) and spin coating techniques. For films prepared through spin coating we found that the molarity of the Y2O3:Bi3+,Yb3+ solution plays an important role in the smoothness of the prepared films. Scanning electron microscopy analysis showed that films prepared at concentrations greater than 0.4 M were rough and dispersed with large agglomerations in the order of 100 μm, while films prepared at 0.2 M were significantly smoother and no agglomerations. Films synthesised using PLD also showed a rough surface, however the size of the agglomerated particles were approximately 1 μm. These small agglomerations were expected due to the laser ablation process which has an explosive-like character. Finally, under UV (325 nm) excitation the photoluminescence analysis for both the PLD and spin coating synthesised thin films yielded good luminescence properties in both the visible and more importantly in the NIR region. The result demonstrated that UV to NIR down-conversion/shifting is possible and may be used to modify the solar spectrum with the aim of improving the efficiency of solar cells.
Speaker: Mr Edward Lee (University of the Free State)
• 11:40
Growth and electronic structure charaterization of 2D germanene/Pt(111) 20m
In the last decade, a new class of solids known as “2D Dirac materials” has led to an outburst of research activities in condensed matter physics and materials science. The low-energy quasiparticles in these materials are described by the relativistic (2+1) Dirac equation rather than Schrodinger’s equation. The relativistic effect in these systems confers to them some unusual properties not observed in the usual Schrodinger-type systems. This makes them very attractive for fundamental research as well as for technological applications. Recently, germanene has been predicted not only to be a 2D Dirac material but also to show some behavior beyond those of other 2D Dirac materials (such as graphene and silicene). In particular Its predicted quantum spin Hall effect makes germanene appealing to semiconductor and spintronics industries. We report on the fabrication of germanene on Pt(111), its characterization by combined X-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED) and its Dirac cone structure by use of angle-resolved photoemission spectroscopy (ARPES). LEED and XPS analysis suggest that germanene forms a (2 x 2) superstructure on Pt(111) and shows strong interaction with Pt substrate. The germanene-substrate interaction is seen to play an important role in the electronic structure revealed by ARPES. This result confirms this interaction to be an important parameter to be exploited in the synthesis of germanene on suitable substrates.
Speaker: Mr Carmel Dansou (Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa.)
• 12:00
Effects of pore size on the electrochemical properties of Li-Mn-O nanoporous cathode material 20m
Nanoporous spinel materials have ignited interest as cathode materials for lithium ion batteries owing to their superior rate capability at ambient temperature, improved electrochemical performance and mechanical stability, compared to the bulk material. However, nanospherical layered-spinel lithium manganese oxides (LMOs) cathodes have demonstrated spontaneously great reversible capacity (302 mAh/g) and superior rate capability due to their composite nature. In this study we simulated the synthesis and investigate the host capability of various Li-Mn-O nanoporous composite materials. The prediction of electrochemical behaviour of these layered-spinel composite cathodes, during the discharge process of a lithium ion battery, is carried out by employing the amorphization and recrystallization technique, using the DL_POLY code. The radial distribution functions (RDFs), X-ray diffraction patterns (XRDs) and structural snapshots of various microstructures for the Li-Mn-O composites showed efficient spontaneous recrystallization (exothermic) and co-existence of spinel and layered components in the nanoporous materials with different pore sizes. Increment of the Li content resulted in more polycrystallization structures and increment of the layered content in the nanostructures.
Speaker: Ms Beauty Shibiri (University of Limpopo)
• 12:20
The thermal quenching process of the La<sub>2</sub>O<sub>2</sub>S:Eu(III) phosphor material 20m
This study is concentrating on the measurement of the emission of commercially available lanthanum oxysulphide doped with europium(III) (La2O2S:Eu(III)) phosphor material at various temperatures. For the thermal quenching process, the average activation energies for the emission from the 5D2, 5D1 and 5D0 excited states were determined as 0.49 eV, 0.55 eV and 0.77 eV, respectively and the average pre-exponential constant was determined as 9.5×107 s-1. The optical band gap of La2O2S:Eu(III) was determined as 2.75 eV. It was also established that the sulphur(II) to europium(III) (Eu(III)) charge transfer band absorbs ultraviolet light and transfers the excited electrons to the excited states of the Eu(III) ions from where emission can take place. The lifetime of the luminescence results indicated that the higher excited states have a double exponential lifetime that results from the emission from both the conventional Eu(III) ions and Eu(III) ions that are in the vicinity of a defect or impurity group. It was determined that in the case of the La2O2S:Eu(III) phosphor material, the presence of defect or impurity groups is due to the hydroxide groups that forms when the material was exposed to water vapour in the atmosphere at room temperature. The average emission decay constants of the 5D2, 5D1 and 5D0 excited states were determined as 10 ns, 80 ns and 340 ns respectively. It was also revealed that La2O2S:Eu(III) can be utilised as a temperature sensor by using the fluorescence intensity ratio of the emission from the 5D1 and 5D0 excited states. This worked well for the temperature range from 80 °C to 180 °C.
Speaker: Mr Lucas Erasmus (University of the Free State)
• 12:40
Computational modelling of binary titanium-based shape memory alloys 20m
Ab initio density functional theory approach was employed to investigate the structural properties, elastic constant and phonon dispersion of B2 binary TiPt, TiCo, TiNi and TiZr shape memory alloys. We employed the plane-wave pseudopotential method within generalized gradient approximation parameterized by Perdew, Burke and Enzerhof using VASP code. These alloys have the ability to remember their shapes after deformation, and this is due to their shape memory effect and super elasticity properties. We found that the lattice parameters are in good agreement with the experimental results within 2%. Furthermore, the TiCo system is more stable B2 and displayed higher transformation temperature. The Pugh’s ratio clearly indicates that TiPt, TiCo and TiNi binary alloys are ductile (B/G>1.75) while TiZr alloy are brittle (B/G<1.75). Phonon dispersion curves shows that TiCo is vibrational stable and there are acoustic modes observed at the gamma directions while TiPt and TiNi are not due to the existence of imaginary frequencies observed along M high symmetry direction, in agreement with the literature.
Speaker: Mr Mphamela Enos Baloyi (UL)
• 11:20 13:00
Physics of Condensed Matter and Materials: Parallel Session
Convener: Ms Mart-Mari Duvenhage (University of the Free State)
• 11:20
Ab-Initio Study of Stability of Discharge Products in Li/Na-Air Batteries 20m
Rechargeable metal-air batteries have attracted a growing interest due to their significantly higher theoretical energy density. It is well recognize that the performance of the battery is governed by the electrochemical reactions that occur at the cathode which result in the formation of discharge products. Different discharge products are produced, through the Oxidation Reduction Reaction (ORR), and among those products some are unstable which might react with other components of the battery contribute to the capacity fading and aging. First principle density functional theory (DFT) was used to investigate the stability of discharge products. We found that LiO2 marcasite is stable and NaO2 is slightly stable due to the absence of soft mode along the Γ-direction in the phonon dispersion curve. Ceder et al. previously investigated the nanoscale stabilization of sodium oxides and found NaO2 to be metastable at standard conditions and also found that LiO2 marcasite is stable. Our results are aimed to give an insight on the stability of major discharge products and give research direction towards controlling the formation of desired Li/Na-O compounds in the batteries.
Speaker: Mr Brian Ramogayana (UL)
• 11:40
Development of a Quantification Software/Programme for Li-Mn-O Composite Nanoarchitectures 20m
The integrated layered-spinel manganese composites are the most desired cathode materials for lithium ion batteries due to their enhanced safety, inexpensive and non-toxic properties. They are preferred over Ni- and Co- containing compounds due to their greater stability (retention of the Oxygen) in their charged state. It has been reported that the spinel and layered integrated composites improve the electrochemical properties of lithium ion batteries, depending on the concentration of the layered Li2MnO3 component and spinel LiMn2O4 component. In this study, we develop a program aimed at quantifying the layered-spinel Li-Mn-O in the layered-spinel composite nanomaterials synthesized computationally using the amorphization and recrystallization technique. The program was developed using C# programming language and helps with better investigation of the impact associated with their respective quantities on the electrochemical performance of the cathode materials. The spinel content in the layered-spinel Li-Mn-O nanomaterial was found to be approximately 30 %. Capabilities of the program is to quantifying the amount of LiMn2O4 in layered-spinel Li-Mn-O composite nanomaterials which will add valuable insights to the design of such electrode materials associated with their performance.
Speaker: Mr DONALD HLUNGWANI (UL)
• 12:00
Computational modelling of graphene mediated sodium air batteries 20m
Rechargeable metal–air batteries are widely regarded as the next best generation of high energy density electrochemical storage devices. The performance and rechargeability of these metal–air batteries is highly dependent on the stability and performance of the positive electrode materials, where oxygen reduction and evolution reactions occur. Due to the high cost and limited resources for lithium-ion batteries, sodium air batteries are a promising alternative because of their high theoretical energy density and low cost to meet the rapidly increasing global energy demands. Graphene has shown a great potential in electrochemical energy storage and conversion due to its remarkable properties. In this work, density functional theory (DFT) methodologies are used to investigate the reaction mechanisms of sodium oxides being adsorbed onto graphene surface. Generalized gradient approximation (GGA) as implemented in density functional theory was used to perform the calculations, employing CASTEP code. The four discharge products namely; Na2O2, NaO2, Na2O and NaO were adsorbed onto graphene layer. Our results show that Na2O is the most stable discharge product due to its lower adsorption energy.
• 12:20
ATOMISTIC SIMULATION STUDY OF SODIUM INTERCALATION IN TITANIUM DIOXIDE NANOSTRUCTURES 20m
Sodium-ion batteries (NIBs) have emerged as a promising candidate for application in large scale energy devices. These batteries have the same battery configuration as lithium–ion batteries (LIBs), however the huge difference in the ionic size, makes it impossible for graphite (anode material in LIBs) to intercalate sodium ions. Therefore it is crucial to develop high-performance anode materials for NIBs. We investigate the potential of titanium dioxide (TiO2) nanosphere as an anode material for NIBs since TiO2 is highly stable with most organic electrolytes, has small structural changes during intercalation, it is nontoxic and inexpensive.TiO2 nanosphere was sodiated with a total of 300 atoms and investigated the structure from amorphous to crystalline phase while varying temperature. Recrystallization was achieved by using molecular dynamics (MD) simulation with the DL_POLY code this was confirmed by the configurational energy plots. The structural rearrangement during cooling to 0K were analysed by radial distribution functions (RDFs) and the microstructures thereof shows the presence of sodium vacancies, rutile and brookite polymorphs, these polymorphs were also observed on the XRDs. Our study shows that sodium ions can be intercalated in Na0.06TiO2 nanosphere, thus TiO2 nanosphere can serve as suitable anode material for sodium ion batteries.
Speaker: Ms Tshidi Malibe (UL)
• 12:40
Effects of annealing time on the structure and photoluminescence properties of Sr3Al2O6:1% Ce3+ nanophosphor synthesize via sol-gel method 20m
Sr3Al2O6:1% Ce3+ nano-powders have been successfully prepared via sol-gel technique. Citric acid was used as a chelating agent. All powder samples were annealed at 950 oC and the annealing time (AT) was varied from 0.5 - 20 hrs. X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with an energy dispersive X-ray spectroscope (EDS), transmission electron microscopy (TEM) and photoluminescence (PL) spectra were used to characterize the samples. The XRD data revealed that all the samples were single phase crystalline structures and the estimated average crystallites size were found to be 20 nm. EDS results confirmed the presence of the expected elementary composition. SEM image presented in Fig. 1 (a) illustrates that the crystals have rods-like morphology structures. The AT was found to influences the phosphor morphology. The TEM results confirmed that the prepared nano-powders are on the nano-scale. PL results showed that the excitation wavelength as a function of emission intensity has the Gaussian behaviour with the maximum at 263 nm. When the samples were excited at 263 nm, four emission peaks at 382, 541, 593 and 620 nm were observed (see Fig. 1 (b)). All of the emissions corresponds to the emissions observed on the un-doped (Sr3Al2O6), which suggest that all of the observed emissions are originating from the defects levels within the Sr3Al2O6 (host) [1,2]. The optimum luminescence for 541 nm emission was found to be for the AT = 8 hrs sample.
Speaker: Dr Setumo Victor Motloung (SMU)
• 11:20 13:00
Space Science
Convener: Dr Du Toit Strauss (Centre for Space Research, North-West University)
• 11:20
SuperDARN radar estimates of thermospheric neutral density 20m
Using the ion-momentum equation in the F-region ionosphere, simplified for field-perpendicular ion motion only, we derive an expression for the ion-neutral collision frequency that depends primarily on the temporal and spatial variability of the ion velocity. The ion-neutral collision frequency is primarily a function of neutral density in the thermosphere. SuperDARN radars are very suited to this type of observation because of their large coverage of the F-region ionosphere, mesoscale range resolution and frequency agility. Multi-frequency observations at one second integration have been performed by the UNIS Longyearbyen radar using natural backscatter, and the University of Leicester CUTLASS-Hankasalmi radar using EISCAT Heater-generated artificial striations. Both show that realistic estimates of thermospheric neutral density, compared to the MSIS model, can be obtained with minute cadence or less. Since HF radio wave propagation refracts in the F-region ionosphere, a functional comparison is only possible with ray tracing. This works well, at least for low geomagnetic activity.
Speaker: Prof. Michael Kosch (SANSA)
• 11:40
Investigation of Pc5 pulsations during a TRINNI event 20m
Pc5 (1-5mHz) pulsations are global magnetohydrodynamic (MHD) events in the magnetosphere. Identification of the causes of Pc5 ULF pulsations has been a challenging problem in the field of MHD physics because of the complex nature of the magnetosphere. Several studies have shown that high speed ionospheric plasma flow in the night side which are mapped to the magnetospheric tail during magnetically quiet periods are associated with releasing of energy from quick reconfiguration of tail magnetic field lines because of reconnection, and these events are referred to as a TRINNI, which is an acronym for “Tail Reconnection during IMF Northward, Non-substorm Interval”. Numerous TRINNI events have been reported using the SuperDARN (acronym for a network of HF radars) and magnetometer data. In this study, we analyse a known TRINNI event for the presence of associated Pc5 pulsations and investigate if TRINNI events could be their driving mechanism. SuperDARN cross-polar cap potential data were used as proxy for a TRINNI. We investigate the relationship between the TRINNI and Pc5 pulsations of this event by using sophisticated Fourier analysis techniques using complex demodulation on the SuperDARN cross-polar cap potential and magnetometer data.
• 12:00
An investigation of the presence of Pc5 oscillations during a TRINNI event 20m
Pc5 ULF pulsations are magnetohydrodynamic (MHD) events in the magnetosphere. To identify the causes of Pc5 ULF pulsations has been a challenging matter in the field of MHD through the complexity of the nature of the magnetosphere. Flow bursts in the magnetotail are known as TRINNIs short for ”tail reconnection during IMF northward, non-substorm intervals. In this study we used the SuperDARN to observe the convection maps with the cross polar cap potential (CPCP) and the Greenland magnetometer stations to investigate the presence of Pc5 pulsations during a TRINNI event which occurred on 20 March 2002 (01:00-12:00 UT). These two instruments measure the resonance from the cavities within the magnetosphere during quiet time magnetosphere. We employed the Fast Fourier Transform (FFT) method to compute the power spectrum . The spectral analysis has shown that there are possible pulsations associated with this TRINNI event. We present results in a graphical form and discuss them in relation to magnetic reconnection in the magnetotail and in the context of magnetohydrodynamic (MHD) theory of magnetic pulsations.
Speaker: Mr Njabulo Mbanjwa (UKZN)
• 12:20
Measuring the mesoscale neutral wind variability near auroral arcs using Fabry-Perot Interferometer (FPI). 20m
Fabry-Perot Interferometers (FPIs) measure the Doppler shift and broadening of the green-line emission from which neutral velocities and temperatures can be derived respectively. The Scanning Doppler Imager (SDI) which is an all sky version of the FPI measures the neutral winds. SDIs are currently located in Alaska, Antarctica and Svalbard Island. This study investigates the E region neutral wind response to the driving force caused by the enhanced electric field upon the occurrence of an aurora. Subsequently, it is intended to study the ion-neutral coupling in the E layer focussing on energy dissipation in the form of Joule heating. Other scientific goals that can be achieved from knowing thermospheric neutral wind velocity include studying the geomagnetic effects on the neutral wind and temperature, direct observation of gravity waves originating in the thermosphere and comparing ion drift measurements. The main scientific thrust is to expand our knowledge on the interaction of neutral thermospheric winds and temperatures with auroral arcs from an initial single publication [Kosch et al., 2010] using existing SDI data from McMurdo and South Pole (projects 1 and 2). The Super Dual Auroral Radar Network (SuperDARN) data set is used as a source of ion velocities to estimate the electric field.
Speaker: Mr Ntlakanipho Ngwane (SANSA/UKZN)
• 12:40
Investigation of traveling ionospheric disturbances (TIDs) using SANAE SuperDARN radar 20m
Travelling Ionospheric Disturbances (TIDs) are an ionospheric manifestation of Atmospheric Gravity Waves (AGWs) that occurs in the neutral atmosphere. They are generated by different sources, such as solar terminators (sunrise and sunset), magnetic storms and substorms, tropospheric weather and mountain turbulence. TIDs appear in power spectra of SuperDARN radars as spatially localized enhancements and as quasi-periodic fluctuations in Doppler velocities and reflection heights. SuperDARN is a network of HF radars designed to study plasma convection and plasma density irregularities in the E and F-regions of the ionosphere at high and mid-latitudes. The continues, large scale nature of SuperDARN observations make them an ideal tool for TID study. Understanding the characteristics and source of mechanisms of TIDs has been of interest since 1960’s. AGWs significantly affect global circulation through their ability to transport energy and momentum vertically through different layers of the atmosphere and horizontally across the globe. Although they have been different studies done on TIDs using ground and space based instruments, very few have used observations in the southern polar hemisphere, in particular, SANAE HF radar. This project aims to investigate TIDs events observed by SANAE SuperDARN radar in more details. This preliminary investigation includes determining possible source of mechanisms of the events. We have performed a survey of TIDs in the SANAE HF radar data. When many events are identified, we also survey other radar data which have common or conjugate field of view.
Speaker: Ms Tsige Atilaw (Rhodes University)
• 11:20 13:00
Theoretical and Computational Physics
Convener: Dr William Horowitz (University of Cape Town)
• 11:20
Phenomenology of 2HDM+S at the LHC 20m
Evidences of new physics begins from the updated data sets at the ATLAS and CMS detectors based at the Large Hadron Collider. Among the noted deviations in multi-lepton final states which leads signatures of the heavy scalars beyond the Standard Model Higgs boson, in this talk we discuss how these deviations can be explained by introducing two scalars of masses around 150 and 270 GeV in an effective filed theory approach and further in a model dependent two-Higgs doublet model with an additional singlet scalar (2HDM+S). Also we explain how the parameter space of this model constrained from the available relevant data sets. Further associated phenomenology of 2HDM+S is discussed.
Speaker: Dr Mukesh Kumar (University of the Witwatersrand)
• 11:40
Commutative/Non-Commutative Dualities 20m
We show that it is in principle possible to construct dualities between commutative and noncommutative theories in a systematic way. This construction exploits a generalization of the exact renormalization group equation (ERG). This link can also be understood as a blocking (coarse graining) transformation of the degrees of freedom. We apply this to the simple case of the Landau problem and then generalize it to the free and interacting non-canonical scalar field theory. In non-canonical quantum field theories, the canonical equal time commutation relations between fields are modified in a similar way to non-commutative quantum mechanics. This differs from usual non-commutative field theories where the space-time labels are non-commutative. This constructive approach offers the advantage of tracking the implementation of the Lorentz symmetry in the non-commutative dual theory. We briefly demonstrate this for the free scalar theory. In principle, we can construct completely consistent non-commutative and non-local theories where the Lorentz symmetry and unitarity are still respected but may be implemented in a highly non-trivial and non-local manner.
Speaker: Mr Paul Henry Williams (Stellenbosch University)
• 12:00
Quantum Control by Self-fullfilling prophecy 20m
We describe a method based on a sequence of measurements combined with feedback that allows us to prepare a quantum system in a target state or smooth target dynamics and protect it against noise. The convergence for arbitrary initial states is based on the gradual increase of information about the post-measurement state in the course of the measurements, which have to be weak in order to yield smooth state trajectories. The mechanism is the same that enables the continuous monitoring of quantum states and is related to the monotonicity of fidelity between any two quantum states under selective (non-trace-preserving) operations, as we will demonstrate.
• 12:20
Quasi-normal modes and absorption probabilities of spin-3/2 fields in D-dimensional Reissner-Nordstrom black hole spacetimes 20m
In this talk we consider spin-3/2 fields in a D-dimensional Reissner-Nordstrom black hole spacetime. As these spacetimes are not Ricci-flat, it is necessary to modify the covariant derivative to the supercovariant derivative, by including terms related to the background electromagnetic fields, so as to maintain the gauge symmetry. Using this supercovariant derivative we arrive at the corresponding Rarita-Schwinger equation in a charged black hole background. As in our previous works, we exploit the spherically symmetry of the spacetime and use the eigenspinor-vectors on an N-sphere to derive the radial equations for both non-transverse-traceless modes and tranverse-traceless modes. We then determine the quasi-normal mode and absorption probabilities of the associated gauge-invariant variables using the WKB approximation and the asymptotic iteration method. We then concentrate on how these quantities change with the charge of the black hole, especially when they reach the extremal limits.
Speaker: Prof. Alan Cornell (NITheP)
• 12:40
f(R) oscillating universes 20m
The purpose of this paper is to investigate the oscillatory behavior of the universe through the Schrödinger equation and a modified gravitational background described by the theory of f(R) gravity. Motivation for this stems from the proven periodic structure of the universe when described within the scope of the general theory of relativity. A further analysis of different f(R) toy models and the equation of state associated with each epoch of interest results in different behaviors for the wave-function of the universe.
Speaker: Mr Neo Namane (North West University)
• 13:00 14:00
Lunch 1h Centenary Complex

### Centenary Complex

• 14:00 15:00
Plenary: Vestergaard Auditorium

### Auditorium

Convener: Ms Gugu Mhlongo (CSIR/UFS)
• 14:00
Bio-based and Bio-inspired [nano]Technologies: The laboratory, and the field 1h
Development and application of bio-based and bio-inspired technologies to (i) screen for, identify and quantify molecules of interest; (ii) profile and characterize molecular activities/events; and (iii) help elucidate pathophysiological mechanisms is a major field with applications in various sectors including biomedical, environmental, energy, food and agriculture. With students and researchers of Applied Physics in mind, we will highlight the fundamental chemical principles intrinsic in biological and biophysical interactions and their exploitation in development of the technologies. Concrete examples with be discussed, and relations to applied physics drawn. We will focus on the development and application of Biosensors, a bio-based technology; and biomimicry membranes, a bio-inspired technology. These interactions are largely driven by natural affinities between biological molecules such as substrate-enzyme, antibody-antigen, receptor-ligand, and Watson-Crick base-pairing. Advances in science and technology have allowed the inclusion of artificially synthesised molecules that mimic biomolecules of interest, such as peptide nucleic acid (PNA). Biomimicry membranes are cell-sized, lipid vesicles that mimic the biological cell. Since the relative compositions of lipid mixtures used influence molecular self-organization and vesicle properties, preparation for tailored application is possible. Thus, biomimetic membranes enable a researcher to manipulate a 'biological' micro-vesicle under a controlled environment. We will conclude by discussing the challenges in design, development and application at point of use. The latter remains one of the biggest challenges in realizing the potential of bio-based and bio-inspired [nano]technologies.
Speaker: Prof. Mun'delanji C Vestergaard (Kagoshima University)
• 15:00 17:00
Poster Session 1
• 15:00
A Planned Calibration Facility For In-Situ Gamma-Ray Detectors 2h
In-situ measurements are affected by changes in the geometry of the landscape. Due to these challenges, a dedicated calibration facility is required. The calibration facility is best optimized by making use of a combination of Monte Carlo simulations and a dedicated measurement setup, MEDUSA system. With the simulation, one can optimize the dimensions of the calibration facility, the type of material to be used and the geometry. The use of Monte Carlo simulations is used in instances, where measurements would require too much time, expensive or are even impractical to consider and moreover to account for the differences between the calibration and other geometries. Various types of samples of bricks were acquired, crushed and measured using the hyper-pure germanium (HPGe) detector, a laboratory-based setup used to count low-level radiation samples. The results of the HPGe detector system was used to calculate the activity concentrations of 40K, 232Th and 238U decay series. In addition, the type of the brick to be selected will depend amongst others on the homogeneity of the sample. The brick castle is constructed at iThemba LABS, Cape Town, Western Cape, South Africa. The brick castle has dimensions of 121 cm height, 119 cm width and 134 cm depth with a 10 cm PVC tube, facing upwards, for inserting a detector for measurements. Initially, the brick castle is designed to house an 8 cm diameter detector (MEDUSA). It has a wall thickness of 55 cm (width) and 63 cm (depth) to reduce the background radiation from reaching the detector. On completion of the brick castle, activity measurements were taken in order to create spectra of the natural-occurring radionuclides (40K and radionuclides from the 232Th and 238U-series). These spectra were converted to create what we call standard spectra for the castle geometry.
Speaker: Mr Alfred Mogotsi Sehone (Military Academy)
• 15:00
An open quantum systems approach to the radical pair mechanism 2h
The development of the radical pair mechanism has allowed for theoretical explanation of the fact that magnetic fields are observed to have an effect on chemical reactions. The mechanism describes how an external magnetic field can alter chemical yields by interacting with the spin state of a pair of radicals. Since the inception of quantum biology, there has been interest in the application of this mechanism to biological systems, in particular the avian compass. However, one of the pitfalls of attempting to apply the tools of quantum theory to the messy and complex systems that typify living organisms is the risk of oversimplification. To this end, the aim of the research outlined here is twofold. First to develop an open quantum systems approach to a model of the radical pair mechanism that allows for an investigation into the effects of different hyperfine configurations on radical pair dynamics while maintaining the necessary complexity and flexibility of the biological context. This model would allow for the simulation of, for instance, the case in which the electrons interact with a number of nuclei each at different distances from the radical and the distinction between weak or strong coupling with the nuclear environment. And second, this research aims to investigate whether the radical pair model might be applied to other emerging topics of interest within the field of quantum biology.
• 15:00
Analysis of temperature dependent I-V characteristics of Pd/n-4H-SiC Schottky barrier diodes and the determination of the Richardson constant in a wide temperature range 2h
Schottky barrier diodes (SBDs) made on 4H-SiC have been commercially available for a considerable time but their properties and applications are still not thoroughly understood. Consistent control of metal contact properties is yet to be established so as to optimize reliability. As a result, the inability to physically reproduce the Schottky barrier height is a technologically important concern which is continuously being researched. The current voltage (I-V) characteristics of Pd/n-type 4H-SiC Schottky barrier diode in the 300-800 K temperature range have been analysed. Barrier height and ideality factor were found to be strongly temperature dependent. Barrier height was observed to increase whilst ideality factor decreased with an increase in temperature and the conventional activation energy plot showed some deviation from linearity. This was attributed to barrier inhomogeneities at the metal-semiconductor interface which resulted in a distribution of barrier heights at the interface. From the modified Richardson plot, the Richardson constant, A** was found to be 155 A cm-2K-2 and 87 A cm-2K-2 in the 300-525 K and the 550-800 K temperature ranges respectively.
Speaker: Mr Valentine Gora (Mdlands State University)
• 15:00
Angular correlation measurements with the iThemba LABS segmented clover detector 2h
iThemba LABS has purchased a segmented clover detector, a detector that uses the latest achievements in the Ge detectors technology. Contrary to the standard Ge detectors the new detector is segmented on the outer contact, resulting in 8 segments per crystals, or 32 segments for the whole detector. The segments can be run as individual detectors, allowing considerably higher event rates to be handled successfully. In addition, utilising segments allows improved accuracy for all direction-sensitive measurements, such as Doppler correction, angular distributions and correlations, g-factor measurements based on recoil in vacuum technique, linear polarization, lifetime measurements based on Doppler effects, etc. The impact of this improvements increases dramatically with the increase of the opening angle of the detector, i.e. at small detector-to-target distances. In close geometry the face of the detector covers a large opening angle, for instance at 4 cm from the radioactive target the detector subtends a solid angle of approximately 1/8 of 4π. Therefore, it covers the whole range of angles needed for precise angular correlation measurements. Such full coverage in addition to the excellent position sensitivity of the detector (due to its segmentation and its tracking ability) allows very precise spin and parity measurements to be carried out. It should be noted that measurements with such precision cannot be performed at present with the current much larger AFRODITE array. In particular, one would be able to measure (i) high-order multipolarities such as E3, M4, E4, M5, E5, etc, (ii) mixing ratios of M1+E2, M2+E3, etc, (iii) distinguish unstretched dipole from a stretched quadrupole transition, etc. Furthermore, due to the segmentation and the tracking capability, the detector will produce more precise linear polarization results too. We collected data with several gamma-ray sources to evaluate the performance of the detector in close geometry for angular correlations measurements. A few targets were also irradiated with neutrons in the neutron therapy vault to test the activity that can be produced and the performance of the detector. The data are being analysed, but preliminary results look very promising. The results will be presented and discussed.
Speaker: Dr OBED SHIRINDA (iThemba LABS/Stellenbosch University)
• 15:00
ATLAS Tile Calorimeter online software configuration and Perfomance study of the super-drawer components 2h
To operate the Tile Calorimeter, the Tile Online software which is a set of Trigger and Data Acquisition (TDAQ) is required for configuration. The modularity and configurability of TDAQ enables it to be used as data acquisition system for test setups, test beams, detector calibration, ect. Partitions which are the starting point that defines a DAQ configuration are created to readout,transport, and store Physics data originating from proton-proton collisions from the Large Hadron Collider. In ATLAS a partition is a synonym for data taking configuration.Tests are performed on the super-drawer which contains the components of the front-end electronics of the ATLAS detector. The performed tests will enable us to improve the performance of the components that are used for data taking.
Speaker: Mr Thabo Masuku (University of the Witwatersrand)
• 15:00
Background estimation for multilepton and $b$-jets analysis at ATLAS at the LHC 2h
Background estimation is one of the most important aspects for all the analysis at the Large Hadron Collider. This proceeding presents the background estimation for the $A\rightarrow ZH$ search with the heavy scalar, $H$, decaying into a pair of Higgs, or Madala, $S$, bosons. The final state for this search is formed by 3 leptons, $\geq$~2 $b$-jets and low jet multiplicity. The $t\bar{t}Z$ process is the dominant background contribution for this analysis. The second important background is the $WZ$ for which a control region is defined to check the modeling and the normalization of this process. Finally, processes with fake leptons are expected to have a small contribution, estimated using a data-driven techniques.
Speaker: Mr Jeremiah Monnakgotla (University of the Witwatersrand)
• 15:00
Characterization of dopant levels in a III-V molecular beam epitaxial system 2h
Commissioning of the III-V MBE system at the University of Pretoria has started. Doped GaAs layers have been grown and characterised electrically. The resulting carrier densities were used to determine the doping concentration versus cell temperature parameters that are required for controlled growth.
Speaker: Prof. Chris Theron (University of Pretoria)
• 15:00
Comparison of ionospheric scintillation to in situ electron density variations as measured by the Swarm satellites. 2h
Ionospheric scintillation is known to be caused by rapid variations in the electron density of the ionosphere. It manifests as rapid fluctuations in the amplitude and phase of radio signals traversing the ionosphere. In the case of navigation signals transmitted from satellites of the Global Navigation Satellite System (GNSS) ionospheric scintillation can cause a decrease in the accuracy of position estimation. During extreme fluctuations, a loss of lock on the satellites can occur, which can result in data outages. The ability to estimate the likelihood of ionospheric scintillation is of great importance for precision navigation applications such as GNSS assisted aircraft landing systems. The altitude at which the electron density irregularities occur can be inferred from a comparison of the variations in electron density as measured by means of Langmuir probes on the Swarm LEO satellites (Swarm A, B and C) and the L-band scintillations on GPS signals detected both by the scintillation monitors on the Swarm satellites and by dedicated GPS scintillation and total electron content monitors (GISTMs) on the ground. The aim of this research is to derive estimates of the altitudes where electron density irregularities occur and to estimate the spatial extent of the irregularities which give rise to amplitude and phase scintillations on the L-band signals from GNSS satellites. In this paper we present some preliminary results on the characterization of the electron density gradients that lead to ionospheric scintillation through a comparison of conventional scintillation indices derived from GNSS signals recorded by a GPS receiver installed at Pwani University (Geo. Lon: 39.78oE, Geo. Lat: 3.24oS) in Kenya with in-situ measurements of L-band scintillation and electron density on the Swarm satellites during the equinox period March/April 2016.
Speaker: Dr Pierre Cilliers (SANSA Space Science)
• 15:00
Computational investigation of vacancy ordering in gamma-Mn<sub>2</sub>O<sub>3</sub>. 2h
A high energy demand as a result of a growth in living standards and population has stimulated the efforts to develop high energy density power sources which is, metal air batteries. However, the fundamental challenge that limits the use of metal air battery technology is the ability to find a catalyst that will catalyse Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). Density Functional study was employed to investigate the ordered tetragonal structure using a supercell of the cubic structure Mn3O4. We obtain the spectrum of energies of all the ordered configurations which contribute to the partially disordered Mn2O3 structure. The degree of ordering in manganese vacancies in the octahedral sites appears to be more stable than the in tetrahedral manganese.
Speaker: Dr Khomotso Maenetja (University of Limpopo)
• 15:00
Computational Modelling of Platinum Arsenide (PtAs</2>) 2h
Compound such as cooperate, braggite, sperrylite and platarsite are important sources of platinum (Pt) and palladium (Pd) in many of the world’s largest deposits of platinum group minerals (PGM). South Africa is major producer of platinum group elements (PGE), therefore research in understanding the surface chemistry and surface reactivity of this platinum group mineral is central to major mining industrial process. Sperrylite (PtAs</2>) is an important and very rare ore of mineral of platinum, but still by far the best known compound containing platinum. Industrial mineralogical studies have found platinum group minerals, such as Sperrylite (PtAs</2>) to be poorly recovered during flotation. Research on the flotation behaviour of Sperrylite mineral is very limited, due to their small size (<10μm), and also the scarcity of individual grains contribute to the complexity of studying fundamental interactions. We have performed density functional theory calculations within the generalized gradient approximation (GGA) to study bulk, electronic and surface properties of PtAs</2> using CASTEP code. The theoretical calculated lattice constant and bulk modulus compare very well with the available experiment and theoretical calculations. The convergence test of slab thickness and vacuum width for low index surfaces (100), (110) and (111) were carried out and the results are discussed.
Speaker: Mr Kgwajana Barnard Molala (UL)
• 15:00
Computational modelling studies of oxidation and hydration on NiS<sub>2</sub> and NiAs<sub>2</sub> surfaces 2h
The atmospheric oxidation of minerals either by weathering or aging involves physical and chemical adsorption of oxygen on the surfaces and this forms various peroxides and hydroxides. In this study ab-initio computational method was employed to investigate the interaction of oxygen and water molecules at different adsorption sites on the most stable surfaces of NiS2 and NiAs2. Their calculated surface energies showed that the NiS2 (100) and NiAs2 (111) surfaces are more stable. We predicted the order of surface stability as: (100) > (111) > (210) > (110) for NiS2 and (111) > (110) > (100) > (210) for NiAs2. The adsorption of O2 was found to dissociate on mineral surfaces and different bonding mechanisms of the oxygen atoms were depicted. The O2 adsorption on both NiS2 (100) and NiAs2 (111) surfaces was exothermic with adsorption energies of -3.19 eV and -4.83 eV, respectively. The H2O adsorption on both NiS2 (100) and NiAs2 (111) mineral surfaces were found to relax deep into the surface. The H2O adsorption on Ni-top site was more exothermic, suggesting preferential adsorption on Ni atoms than on S and As atoms on both NiS2 and NiAs2. These investigations suggests that the oxidation of NiS2 and NiAs2 prefer adsorbing on S and As atoms than on Ni, while the hydration of NiS2 and NiAs2 prefer adsorbing on Ni atoms than S and As atoms. These investigations provide information on the bonding mechanism and chemistry of oxygen and water molecules onto NiS2 (100) and NiAs2 (111) surfaces that may be applicable to the atmospheric oxidation and during flotation process or mineral extraction.
• 15:00
Computational modelling study of hydrated nickel-rich pentlandite (110) surface 2h
The hydration of minerals is one of the main processes that occur during mineral processing. These include wet grinding of the ore and during flotation of liberated particles. In this study we employed ab-initio density functional theory to investigate the adsorption of water molecules onto nickel-rich pentlandite (110) surface. We considered three adsorption aspects: Fe-top, Ni-top and complete surface coverage adsorptions and explored the bonding geometry, density of states (DOS) and Bader charges which are directly related to the reactivity of the water molecules. The hydrophobicity and hydrophilicity of minerals during mineral processing require detailed understanding in the mineral-water interaction that could give valuable insight during flotation. We found that the adsorption of water molecules on pentlandite (110) surface showed exothermic reaction. The water adsorption energies were more exothermic on Fe-top than Ni-top. This indicates that the water molecule interacts strongly with Fe than Ni atoms. The complete surface coverage revealed a physisorption process on (110) surface. Furthermore, DOS showed orbital shift to lower energy level and their energy states are lowered near EF. This indicates that there are electron/charge transfers from the surface metals to the water molecule. The charge density difference indicated that some charges are localised at the internuclear region. Due to the 1b1-3d orbital mixing, some charges are depleted from the 3d-orbitals to the lower lying manifold 3d-orbitals. These observations gave valuable insights on how the metals (Fe and Ni) react with water during mineral extraction using the flotation process.
Speaker: Dr Peace Mkhonto (University of Limpopo)
• 15:00
Computational study of ZIF with functional groups for CO2 adsorption. 2h
Greenhouse gases, Carbon Dioxide in particular, has been a main concern for climate change. Zeolitic Imidazolate Framework (ZIF), a sub class of Metal Organic Framework (MOFs), is a 3-dimensional nanoparticle consisting of metal ion (Zn2+) and an organic linker (imidazole) with high chemical and thermal stability. The bond angle between the metal and imidazole has the same 145° angle found in zeolites. These cage like structure are porous and have a high surface area (>1600 m2 g-1). The high surface area is advantageous in several applications such as gas storage, gas separation, chemical sensors etc. ZIFs with its organic imidazole counterpart can be easily modified to add or improve functionality of the materials. Additional functional groups on the imidazole linker such as NO2 groups were found to greatly enhance the CO¬2 adsorption capabilities of ZIFs via a ligand exchange process. In this study a series of functional groups on ZIFs were computed with Grand Conical Monte Carlo (GCMC) simulations by Material Studio to determine whether NO2, SH, F, Cl, Br, CH3, OH, NH2, phenyl and H groups will benefit in improving CO2 adsorption. Our results show that ZIFs with electron withdrawing groups can greatly enhance CO2 adsorption and can easily predict which functional group to synthesis experimentally.
Speaker: Dr Chih-Wei Tsai Tsai (University of the Free State)
• 15:00
Computerised Ionospheric Tomography (CIT) for supportive GNSS-derived ionospheric applications. 2h
Computerised Ionospheric Tomography (CIT) is a technique where multiple measurements from signals modulated when passing through an object, are used as inputs to reconstruct the three-dimensional structure of the object by employing mathematical inversion techniques. In CIT the "object" is the spatial distribution of the electron density composition of the Earth's Ionosphere, i.e., the ionised component of Earth's atmosphere extending from about 50-2000 km above Earth. SANSA's Matlab-based TEC imaging system utilizes GPS observations as available from the IGS network (http://www.igs.org/network). RINEX observations files from regional GPS receivers are processed to yield regional 2D TEC maps. The objective of the project is to develop necessary algorithms and software to apply the MIDAS system for ionospheric tomography (developed by the University of Bath) to derive 2D TEC images using data from the African Equatorial region to support other ionospheric applications such as TEC gradient studies for deriving scintillation proxies.
Speaker: Mr Kit Ng (University of Michigan)
• 15:00
Constraining the TeV Gamma-ray Emission Regions with Gamma-Gamma Absorption 2h
Gamma-ray binaries are a class of high-mass binary systems, which are distinguished by having spectral energy distributions which peak above 1 MeV. Gamma-ray binaries consist of a compact object, either a neutron star or black hole, orbiting a massive O or B type star. While there is some debate around how the gamma-rays are produced, in two systems, PSR B1259-63 and PSR J2032+4127, the compact object is known to be a young pulsar, and the gamma-ray production is due to particle acceleration in the shock that forms between the pulsar and stellar winds. It has been suggested by some studies that there may be different sights of particle acceleration in these systems, with the GeV and TeV emission being produced in different locations. Gamma-gamma absorption of the TeV emission could significantly modify the observed emission. This may provide a mechanism to constrain the location of the production of TeV gamma-rays. In this project we plan to model the effect of gamma-gamma absorption in all known gamma-ray binary systems, in order to investigate how this will modify the observed spectrum. This may be used to place constraints on the location when combined with the observations of the TeV emission. We will investigate this for the upcoming Cherenkov Telescope Array (CTA). We present the initial results from this project.
Speaker: Mr Drikus Du Plooy (University of the Free State)
• 15:00
Controlling iron-oxide nanoparticle size with nanometer precision to synthesize monodispersed particles: a theoretical and experimental investigation. 2h
Nanosized iron-based magnets have attracted a great deal of attention in life-sciences and health-care research where they find use in tissue-specific drug delivery, contrast enhancement agents in magnetic resonant imaging (MRI) and cell separation, among others. To improve the efficiency of these nanoparticles (NPs), a very narrow size distribution centering on a small NP size is required, since this directly affects the superparamagnetic behavior. Despite great progress in the synthesis of iron-oxide NPs using thermal decomposition methods, production of NPs with a low polydispersity index is still a challenge. To narrow down the size distribution, size selective precipitation processes have to be performed. In this study we show that, for the first time, the production of monodisperse iron-oxide NPs are indeed possible without employing any post synthesis size-selective procedures. Surfactants oleic acid and oleylamine were used and an experimental and theoretical study on the role of the surfactant ratio to NP size-distribution was carried out. It was observed that at a very specific acid/amine ratio of 3/1, different synthesis procedures may yield truly monodisperse NPs with polydispersity of less than 7%. This acid/amine ratio of 3/1 allowed for the control of the NP size with nanometer precision by simply changing the reaction heating rate. We were able to predict this specific ratio by performing molecular dynamic simulations in advance that revealed a maximization of binding energy at this ratio. HRTEM and XRD were used to confirm the narrow size distribution and hysteresis loops recorded at 300 K and 2 K confirmed the superparamagnetic character of the NPs.
Speaker: Dr Richard Harris (University of the Free State)
• 15:00
Crystal structure and thermodynamic properties of the non-centrosymmetric PrRu<sub>4</sub>Sn<sub>6</sub> caged compound 2h
PrRu4Sn6 is a tetragonal, non-centrosymmetric structure compound [1]. It is isostructural to the extensively studied Kondo insulator CeRu4Sn6 [2, 3, 4] which crystallizes in the YRu4Sn6-type structure with space group I-42m. In this structure, the Pr atom fills the void formed by the octahedral Ru4Sn6 units which results in a tetragonal body centered arrangement [1, 5]. Here we present the physical and magnetic properties of PrRu4Sn6. The specific heat, Cp(T), electrical resistivity, &rho(T) and magnetic susceptibility, &chi(T) results collected between 300 K and 2 K do not show any phase transition in the temperature range. &chi(T) follows Curie-Weiss behavior above 100 K with effective magnetic moment, &mueff = 3.34 &muB/Pr which is close to the expected free ion value of 3.58 &muB/Pr and paramagnetic Weiss temperature, &thetap = –19.47 K indicating a dominant antiferromagnetic interaction. The magnetization, M(H) at 2 K is quasi-linear in nature and attains a value of 0.86 &muB/Pr at 7 T which is well reduced compared to the free ion saturation moment of 3.32 &muB/Pr possibly due to magnetocrystalline anisotropy in the polycrystalline sample. The low-temperature analysis of Cp(T) gives a Sommerfeld coefficient, &gamma = 38.60 mJ/(K2 mol). &rho(T) follows a typical metallic behavior down to low-temperatures in contrast to the semi-metallic behavior observed in CeRu4Sn6. The thermal conductivity, &kappa of PrRu4Sn6 shows a glassy behavior above 30 K possibly due to the interactions of the low-frequency “rattling” vibrations of the guest atom with the acoustic phonons of the host lattice resulting in heat dissipation.
Speaker: Mr Michael Ogunbunmi (University of Johannesburg)
• 15:00
Data Processing Procedure for the Time-of-Flight Spectrometer of Heavy Ions in the wide range of Energies. 2h
At the present moment it is well known that detecting fission fragments from a decay of heavy nuclei using silicon detectors comes with two experimental challenges, namely Pulse Height Defect and Plasma delay. The negative effect of the Pulse Height Defect (PHD) is observed when registering the energy of the fission fragment and the one of Plasma Delay (PD) is observed when registering time of the fission fragments using the silicon detectors. Finding a solution to these experimental challenges is critical to the investigation of the decay of low excited heavy nuclei called “Collinear Cluster Tri-partition” (CCT)[1]. A precise but rather complicated procedure that takes into account the above mentioned experimental challenges (PHD and PD) has been successfully developed. This procedure involves an iterative process where the correct masses of fission fragment are calculated taking into account both PHD and PD in the measurement of energy and Time-Of-Flight (TOF) respectively. This procedure is divided into 3 stages. The first stage is the first approximation where the energies of the fission fragment is calculated without taking into account the PHD and the PD. The second stage is the calculation of the PHD value using an empirical formula derived by Mulgin et al [2]. The last stage involves using a special equation suggested by Neidel and Henschel [3] to calculate the PD. In this way, the correct PD values are obtained and are then used to calculate the correct TOF for fission fragments. A special code to perform the abovementioned procedures was first designed in Fotran 95 programming language. At the moment a newly improved and modern code is currently being developed in C++ programming language. This modern code also includes a design of an easy to use graphical interface that runs the iteration used to find the parameters without compiling. In this paper we present both the description of this analysis procedure and a detailed explanation of this modern code. References: 1. Pyatkov Yu.V. et al.,Eur. Phys. J. A 48 (2010) p 94 2. Mulgin S. et al., NIM A 388 (1997) p 254-259. 3. Neidel H, Henschel H., Nucl. Instr. Meth. 178 (1980) p137 - 148
Speaker: Mr Vusi Malaza (Stellenbosch University, Faculty of Military Science)
• 15:00
Deconvolution method for obtaining directly the original in-depth distribution of composition from the measured sputter depth profile 2h
It is shown that the original in-depth distribution of composition can be directly obtained by the deconvolution of measured depth profiling data using the MRI (Mixing-Roughness-Information) depth resolution function, as demonstrated for the case that the original depth-concentration distribution is either a smooth function or a square wave function. To overcome the ill-conditioned problem that is often experienced in the deconvolution procedure, the regularization method and the TV-Tikhonov algorithm are applied. The noise influences from measured data points on the deconvolution procedure are discussed quantitatively.
Speaker: Dr Xin Liang Yan (Shantou university, China)
• 15:00
Deriving thermospheric neutral density from SuperDARN radar data 2h
Knowledge of thermospheric neutral density, above 200 km altitude, is important for applications such as satellite drag, which give satellite lifetime, and long-term climatic trends such as global warming. We have successfully applied theory (ion momentum equation) to incoherent scatter radar (ISR) data (e.g., EISCAT) to extract the thermospheric neutral density above 300 km. However, ISRs provide poor coverage and are expensive to operate. Hence, we now focus on coherent scatter radars, which provide great coverage and are cheap to operate. Simplification of the ion momentum equation applied to the ionosphere shows that from the rate of change in ion velocity we can derive the ion-neutral collision frequency, and from this we can calculate the neutral density if the atmosphere is a mono-species or of known composition. The SuperDARN radar global network of 35 radars covers much of the northern and southern hemisphere polar regions. Normally, the radars observe each beam at a cadence of once per minute. For this novel experiment, we operated selected radars on a single beam with a cadence of one second. This project consists of applying the theory to selected radar data sets, all of which are available. The resultant thermospheric neutral density estimate will be compared to the standard MSIS model.
Speaker: Ms Eva Gnegy (University of Michigan)
• 15:00
Effect of domain transformation on the magnetic properties of NixCo1-xFe2O4 2h
In this study, nanoparticles of NixCo1-xFe2O4 (x = 0, 0.1, 0.2, 0.3, 0.8 and 1.0) were produced by glycol thermal process and characterized by several techniques such as XRD, TEM, SEM, FTIR, Mössbauer spectroscopy and magnetization measurements. The as-prepared fine powders show transformation from single- to multi-domain behaviour at a critical particle size dependent on sample chemical composition. The effect of domain transformation on the magnetic properties has been investigated. 57Fe Mössbauer spectral studies and magnetization data show significant differences between single- and multi-domain particles. The results are explained on the basis of crystallite size and constituent atoms. The variation of the magnetic parameters such coercive fields and saturation magnetization revealed by hysteresis loop measurements in the temperature range 4 – 300 K is also reported.
Speaker: Mr Amos Nhlapo (University of KwaZulu-Natal)
• 15:00
Effect of temperature on the structure and dynamic properties of metal sulphide nanostructures via molecular dynamics simulation 2h
Metal sulphide nanostructures via molecular dynamics (MD) simulations at different temperatures are presented and discussed in order to understand their structure and dynamic properties. Nanostructured metal sulphides have attracted the attention of researchers in the fields of materials science, physics and chemistry. They have enhanced structure and dynamic properties due to their large surface-to-volume ratio; hence making them desirable to a wide range of industries. They are promising materials for catalysis, batteries and photovoltaic, however the understanding on the structure and dynamic conditions of large-scale nanostructures are still to be explored more. Computational modelling technique, MD was performed to provide atomic or molecular level insights of the structure and dynamic properties of nanostructured metal sulphides. The effect of temperature on different sizes of nanostructures are analysed in a form of structure and dynamic properties; namely radial distribution functions, potential energy and diffusion coefficient. The results showed that temperature associated with the melting transition and stability increased with an increase in the nanoparticle size. New insight into MD study of nanostructured metal sulphides is obtained and providing guidance to experiments.
Speaker: Dr Mofuti Mehlape (University Of Limpopo)
• 15:00
Electronic and Optical Properties of Lead-free Hybrid Perovskite CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> from first principles calculations 2h
Organic-inorganic halide perovskites have recently emerged as promising candidates for low cost, high-efficiency solar cells. In this work, the electronic and optical properties of the lead-free hybrid halide perovskite CH3NH3SnI3 as a solar cell absorber has been investigated using first-principles density functional theory calculations and many body perturbation theory. Our calculated electronic band gaps are 0.77, 1.23 and 1.40 eV using the Perdew, Burke and Ernzerhof, the modified Becke-Johnson and the hybrid functional HSE06, respectively. CH3NH3SnI3 has been reported to have a band gap of 1.21 and 1.35 eV depending on the preparation method. Our calculated band gap using the modified Becke-Johnson and hybrid functional HSE06 agree well with experimental results. The investigated compound (CH3NH3SnI3) is found to be a direct band gap semiconductor with fundamental band gap (1.44 eV). In order to obtain optical spectra, we carried out Bethe-Salpeter equation calculations on top of non-self-consistent G0W0 calculations. Our calculated band gap using Bethe-Salpeter equation calculations is 1.22 eV, within the experimentally reported range, confirming that CH3NH3SnI3 has potential as a solar cell absorber.
Speaker: Mr Ibrahim Omer Abdallah Ali (The National Institute for Theoretical Physics, School of Physics and Mandelstam Institute for Theoretical Physics, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa.)
• 15:00
Enhanced Photocatalytic Activity of TiO2 Nanoparticles by Copper and Silver Codoping 2h
The large band-gap of Titania, and the high recombination of photogenerated charge carriers that limit its overall photocatalytic efficiency, prompted the systematic investigation of copper and silver, doped and codoped, TiO2 nanocatalysts. In the study, four different TiO2 nanopowder species, namely undoped, Cu-doped, Ag-doped and Cu+Ag-doped, were fabricated via the sol-gel route for the activity assessment. After drying at 100oC, the powder samples were annealed for one hour at temperatures of 300oC, 600oC, 900oC and 1100oC. Analysis by XRD revealed that TiO2 was effectively doped, and that the anatase – rutile mixed-phase occurred around 600oC. Brookite-bearing, mixed‐phases (anatase – brookite, brookite – rutile) appeared in the 300oC and 600oC of the codoped samples. UV-vis indicated a shift of the absorption edge to a lower energy and a stronger absorption in the visible light region for these two samples, the highest quantum efficiency being induced by the former. Photoluminescence (PL) spectroscopy suggests that these high activity photocatalysts produced lower PL spectra intensities. The visible emission observed were attributed to the enhancement of oxygen and Ti vacancies by the presence of the brookite phase.
Speaker: Mr Olatunbosun Nubi Nubi (University of Limpopo)
• 15:00
Extensions of THERMUS and its Applications in High Energy Particle collisions 2h
We have analyzed and discussed the hadronic abundances measured in Au-Au, p-p and Pb-Pb collisions at RHIC and LHC experiments using THERMUS. The results were obtained with two particle data tables, and their differences were explained. In particular, the data from the RHIC experiment for Au-Au collisions at 130 GeV and 200 GeV were discussed and analyzed. Similarly, using the preliminary particle yield results of p-p collisions at 0.9 TeV and 7 TeV as well as Pb-Pb collision at 2.76 TeV particle yield calculations were presented and the thermodynamic parameters were obtained from the fits.
Speaker: Dr DAWIT WORKU (Cape Peninsula University of Technology)
• 15:00
First principles studies of Palladium nanoparticles on TiO<sub>2</sub> surfaces for catalytic application 2h
Palladium-based catalyst are being developed as an alternative to the commonly used and high cost platinum catalyst because of their similar electronic configurations, lattice constants and they are cheaper than platinum with a high methanol-tolerance. In this study, first principle density functional theory was used to study the catalytic properties of Pd/TiO2, in particular the interaction and electronic behaviour of palladium nano-clusters on a stable titanium dioxide surface using the plane-wave pseudo-potential method. Titanium dioxide is used as a metal support to develop the palladium catalyst, and is the most important transition metal oxide since its photo-catalytic activity was discovered. This transition metal oxide was used in many catalytic processes in the industries such as metal catalysts, which include the platinum group metals such as Pd, Pt, and Rh. These metals are involved in processes such as fuel cells, methane oxidation, catalysis, and in emission control technology. Firstly, the stability of titanium dioxide polymorphs was deduced from elastic properties and in good agreement with the experimental values to within 3%. The observation made was based on the shear modulus of rutile being higher and positive compared to that of the other polymorphs suggesting that rutile is more stable. The order of surface stabilities is given as (110)> (100)> (101)> (001)> (111), and in good agreement with previous work. Adsorption of water on the stable (110) surface showed that the (110) surface was more preferred(exothermic). Secondly, the interaction of Palladium clusters with titanium dioxide surface showed that Pd13 prefers the bridging adsorption site, and as predicted it’s the least negative D2E energy value. The findings of this work suggests that palladium-based catalysts may play a significant role in future developments and applications in emission control technologies.
Speaker: Ms Andile Mazibuko (yes)
• 15:00
Gadolinium doped and undoped silicon detectors for radiation sensing in high energy physics experiments 2h
Speaker: Mr THOKOZANE MOSES SITHOLE (UNIVERSITY OF SOUTH AFRICA)
• 15:00
Global ionospheric vertical drift studies 2h
Electrodynamic and dynamic processes mainly control low and equatorial latitude ionospheric electron density changes. The transportation of plasma to high altitudes where recombination rate is lower over the equatorial regions results in the formation of the equatorial ionization anomaly characterized by enhancement of electron density at approximately 15 degrees latitude on both sides of the geomagnetic equator. Magnitudes of vertical ExB drifts influence the extent of development of ionospheric irregularities and hence useful to understand for communication and navigation applications. Despite the critical importance of vertical ExB drift (Lorenz force), long-term direct observations of low latitude electric field data remains scarce in a number of longitude sectors. As a result, a number of studies rely on Low Earth satellite data that are more appropriate for climatological studies. A useful complimentary data is daytime observations from ground-based magnetometers. Ground-based magnetometer data have advantage of being continuous with high temporal resolution and are available in a number of longitude sectors, thus increasing the probability of getting coincidental observations when the satellite is within the vicinity of the magnetometer location. It is established that the difference between horizontal components of the Earth’s magnetic field observations (ΔH) from magnetometer locations at the equator and about 6- 9 degrees away from the equator is a proxy of EEJ, which has a linear relationship with vertical ExB drift. The framework of the current project involves performing climatological studies of vertical drifts observed by the Communications and Navigation Outage Forecasting System (C/NOFS) satellite and EEJ data with the ultimate aim of developing a global model of low latitude vertical drifts.
Speaker: Ms Gabriel Lefebvre (University of Michigan)
• 15:00
High-resolution confocal Raman microscopy analysis of the transparent hematite films prepared on fluorine-doped tin oxide coated glass substrates by spray pyrolysis 2h
Hematite (Fe2O3) is a promising material that is being studied immensely for its application in solar water splitting. It has attractive properties such as a narrow bandgap that allows for absorption of visible light, earth-abundant and is an easily processable photocatalytic material. In this study, we report hematite thin films prepared by spray pyrolysis on fluorine-doped tin oxide (FTO) coated glass substrates; it has been shown in literature that films prepared by ultrasonic spray pyrolysis allow for better light harvesting than those prepared by conventional spray pyrolysis. Amongst other characterization techniques, Raman micro-spectroscopy is a preferred method for hematite analysis since it is non-destructive. This work demonstrates the characterization of the as-prepared hematite thin films using the confocal Raman technique (with three different laser sources, i.e. 488, 532 and 633 nm) combined with an integrated atomic force microscopy (AFM) and force-distance curves measurements. Raman imaging/spectroscopy confirmed the characteristic Raman spectrum of the hematite. In addition, the less rough surface of the films seen from the Raman optical microscope images as well as AFM 3D surface images confirmed the uniform and conformal coverage across the substrate with surface roughness in the order of <10 nm. The force-distance curves (approach and retract) have shown an average adhesion force of about 10.4 nN for hematite on FTO substrates. Moreover, from Raman depth profiles the thicknesses of the films were estimated.
Speaker: Mr Sipho Congolo (University of Pretoria)
• 15:00
Hα images of nearby galaxy groups; NGC 193 and NGC 940 2h
A significant fraction of the baryons in galaxy groups and clusters is not locked up in stars and the interstellar medium (ISM), but exists in the form of extended multi-phase gas. The advantage of nearby galaxy groups is that this multi-phase gas can be studied via hot X-ray (≈Hα filaments) via optical emission line observations. Another advantage of groups is that the galaxies' heating process effects are more visible due to lower density and mass, containing few galaxies, as opposed to rich clusters. Interaction between the different phases is important for galaxy formation and evolution due to the fact that at least 50% of galaxies can be found in groups and clusters. The Complete Local-Volume Groups Sample (CLoGS) is an optically selected sample of 53 groups within 80 Mpc of which the X-ray observations (Chandra / XMM-Newton) have already been done and can be used to infer important physical properties of galaxy groups, such as gas temperature and X-ray luminosity. In this project the Hα images, observed using the WIYN 0.9m telescope on Kitt Peak, are analysed with the aim to compare the Hα filaments to the X-ray emission images. Here we present preliminary results and a multi-wavelength comparison for two rich galaxy groups , where the central member is an X-ray bright radio galaxy with a powerful central jet, and , where the brightest member is an X-ray faint radio galaxy with only a weak radio point source.
Speaker: Ms Sumari Hattingh (North-West University)
• 15:00
Influence of citric acid on LiMn2O4 nanostructures prepared by modified chemical bath method 2h
LiMn2O4 powders were prepared by modified chemical bath method using citric acid solution (CA) a catalyst. The volume ratio (VR) of Li and Mn on LiMn2O4 was kept constant and the volumes of CA were varied. The effect of CA on structure, morphology and optical properties of LiMn2O4 nanostructures were investigated. The VR’s of CA were varied from 1 mL≤ VR ≤120 mL. The X-ray diffraction (XRD) patterns of the LiMn2O4 nanostructures correspond to the various planes of a spinel LiMn2O4 phase. The diffraction peaks increase in intensity up to 40 mL of CA. The estimated average crystallite sizes calculated using the XRD spectra were found to be in the order of 63 ± 1 nm. It was observed that the estimated average crystallite sizes increases with an increase in CA up to 40 mL. The surface morphology study revealed the polygon shape. By varying CA solution morphology changed from polygon to irregular shape. The UV-Vis spectra showed a red shift with an increase in the amount of CA. The band gap energy of LiMn2O4 was also found to decrease. The best VR of CA on LiMn2O4 nanopowders were obtained at Li:Mn:CA ratio of 1:1:4. Lithium ion batteries are widely used in portable equipment, such as mobile phone, notebook computer, electron instrument, and so on.
Speaker: Mr Lehlohonolo Koao (UFS (Qwa Qwa Campus))
• 15:00
Interpreting features of the LHC data with a second complex doublet and a singlet 2h
Based on a number of features of the LHC data in Run I, that have re-emerged in Run II, the HEP group at Wits formulated a hypothesis. This hypothesis entails the existence of a heavy boson with a mass around twice the mass of the SM Higgs boson and a single scalar with a mass around 150 GeV. Data reported recently displays discrepancies with the SM that are consistent with the decay of a boson of a mass around 600 GeV that decays into the above mentioned bosons. We interpret these effects in the context of a second scalar complex doublet and a singlet. The parameters of the model that fit the data are extracted.
Speaker: Mr Elie Danien RAJAOBELINA IARILALA (Wits University)
• 15:00
Investigating the relationship between Ground level enhancement events and radiation enhancement at aviation altitude 2h
Cosmic particle flux is significantly higher on-board aircraft than at ground level. The radiation field at aviation altitude is very complex in terms of particle composition and particle energies and as such, the dose assessment is a very difficult task. The dose is usually estimated using numerical codes validated by experimental data. Ground‐level enhancements (GLEs) are sudden, sharp, and short‐lived increases in cosmic ray intensities registered by neutron monitors. These enhancements are known to take place during powerful solar eruptions such as solar flares, coronal mass ejections (CMEs), and solar energetic particle (SEP) fluxes. In this project, the idea is to analyze neutron monitor data during a solar storms that lead to a Forbush decrease and subsequently a GLE. The idea is to see how much these series of events can influence or contribute to increasing dose at aviation altitude. The Dose rate will be computed along certain chosen route by using Model for Atmospheric Ionization Radiation Effects (MAIRE), the Sievert and EpCard online calculator, to see if during an events there is a significant increase. The neutron monitor data (from four neutron monitors in Southern Africa: Hermanus (oldest in the world), Potchefstroom, Sanae (Antarctica), and Tsumeb (Namibia)) will also be utilized as this data gives the information about GLEs. The standard geomagnetic activity parameters (Kp, Bz the southward component, Solar wind data and Dst) will be used as an indicator to show the level of disturbance.
Speaker: Mr Kyle Webster (University of Michigan)
• 15:00
Ion-Implanted Polyaniline thin films for radiation sensing applications 2h
Polymer based electronics is an emerging technology that is focused on developing electronic devices using semiconducting polymers that can potentially replace silicon based electronics. Polymer based electronics materials are relatively cheaper to synthesize and are mechanically flexible compared to silicon. Metal-polymer nanocomposites, for example, have distinctive electrical, optical and morphological properties that can be useful for device applications. However, fabrication-structure-property relationships of these materials are not yet fully understood, and this warrants further investigative studies. In this work, Polyaniline (PANI) was dissolved in dimethyl sulfoxide and spun cast on an ITO/PET substrate to obtain PANI thin films. Prepared films were then implanted with 10 keV Ti+ ions to a fluence of 5x1015 ions/cm2 to form a Ti-PANI nanocomposite material. Rutherford Backscattering Spectrometry (RBS), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis spectroscopy, Current-Voltage (I-V)and Capacitance-Voltage (C-V) measurements were used for structural, optical and electrical characterization of the films before and after ion implantation. This presentation describes and explains the results of the characterisation measurements, with a view to modifying material properties of Ti-PANI nanocomposites for nuclear radiation sensor applications.
Speaker: Mr maloba matome (University of South Africa)
• 15:00
Ionospheric Diurnal Double Peak Structures 2h
The study of ionospheric disturbances and irregularities is beneficial to both the scientific advancement of knowledge as well as the practical applicability to high frequency (HF) communications, navigation, surveying and understanding various aspects of space weather effects on technological systems. Studies have shown that ionospheric disturbances have characteristic features, such as diurnal double peak structures, that differ from effects associated with major geomagnetic storm, Pi et al (1995). Diurnal double peak structures have been observed to have varying magnitudes with respect to the background ionosphere. In addition there has not been convincing evidence that these structures are caused solely by geomagnetic disturbances, Katamzi et al (2012). In fact, a study by Katamzi et al. (2016) in a case study showed evidence of tides having an influence on their generation, from the observations of sporadic E layer. However, this needs further investigation. Therefore the student will use long-term ionosonde and GPS data to investigate the relationship between sporadic E layer and double peak structures over South Africa.
Speaker: Mr Joe Taylor (University of Michigan)
• 15:00
LaAlO<sub>3</sub> sheet-like nanostructures synthesized through microwave-assisted method and their gas sensing characteristics 2h
Lanthanum (La) based perovskite oxides such as LaFeO3, LaCoO3 and LaAlO3 have stimulated great interest in the gas sensing technology world as promising candidates for gas sensing towards different gases. This is due to their unique electrical and electrocatalytic properties, providing good response with high selectivity and stability. Out of all the La based perovskite oxides, LaAlO3 is a quite new perovskite that has mostly been used as an additive to other materials such as ZnO and SrTiO3 due to its good electron gas conductivity. However, there are only a few reports on the application of LaAlO3 for gas sensing. In this work, LaAlO3 nanostructures have been synthesized using metal nitrate salts through the hydrothermal microwave-assisted method. Characterizations of the synthesized materials by means of X-ray diffraction, scanning electron microscopy and nitrogen adsorption confirmed the formation of high purity hexagonal 2D sheet-like structures LaAlO3 with high surface area. The sheet-like structures were assessed for gas sensing towards several test gases namely CO, CH3, C2 H5 OH, NH3 and NO2 at different working temperatures ranging from room temperature to 400 &#176C.
Speaker: Ms Katekani Shingange (CSIR/UFS)
• 15:00
Magnetic and Mössbauer studies of Ca_xZn_{1-x }Fe_2O_4 nanoferrites 2h
A one-step synthesis of Ca_xZn_{1-x }Fe_2O_4 (x=0, 0.5 and 1) nanoferrites and nanocomposites by the glycol-thermal method is reported. The structural, morphological and magnetic properties were studied using XRD, HRTEM/SEM, VSM and Mössbauer spectroscopy. The XRD patterns show a single phase cubic spinel structure of ZnFe_2O_4 at x=0. A composite phase of a spinel and hematite structure of Ca_{0.5}Zn_{0.5}Fe_2O_4/Fe_2O_3 was observed for x=0.5 and CaFe_2O_4/Fe_2O_3 for x=1. The addition of Ca2+ increased the particle size due to large ionic radius of Ca2+ ions. This was also evident from the HRTEM/SEM images. The images show that the particles are almost spherical in shape. The Mössbauer results showed a higher percentage of the α-Fe_2O_3 phase for x=1 and only the presence of Fe3+ ions was detected in all the samples. The small coercivity and high magnetization of the samples reveal the superparamagnetic nature of the samples and the saturation magnetization decreases as the percentage of the α-Fe_2O_3 phase increases.
Speaker: Ms Kemi Adewale (School of Chemistry and Physics, University of KwaZulu-Natal, Durban, South Africa)
• 15:00
Mesospheric Ozone Monitoring 2h
SANSA has built a low-cost (USD 100-) mesospheric ozone radiometer based on a BeagleBone micro-controller running Linux. This presentation describes the development of a real-time data viewer and algorithm that analyses the ozone spectrum to infer ozone density. A spectrum is generated roughly every 5 minutes, and one data file per day. Results examining ozone density as a function of day-of-year will be presented along with a description of the code development.
Speaker: Mr Ed Lopez (University of Michigan)
• 15:00
Microstructural and Electrical Properties of Graphene-Oxide (GO) Functionalized with Gold Nanoparticles (Au: NPs) 2h
We have synthesized Graphene-Oxide (GO) by the modified hummer’s process and functionalized with gold-nanoparticles (Au-NPs) for the study of microstructure and electrical properties. We have observed from the Raman spectroscopy that the intensity of D-peak (disorder) reduced with respect to G (graphite-cluster) when GO is functionalizes with Au-NPs (r-GO: Au). Reduction of D-peak (increase of G-peak) implies the reduction of ID/IG ratio that are obtained from the Raman spectra. The reduction of ID/IG ratio (GO: 1.17 to rGO-Au: 0.95) clearly indicates that the sp2-cluster is reduced through functionalization of GO with Au-NPs. The reduction of sp2-cluster and/or enhancement of sp3-cluster is due to replacement of sp2-cluster by the Au-NPs. The reduction of sp2-cluster in the film networks are also observed from the Fourier transform infrared (FTIR) spectroscopy and are consistent with reduction of conductivity as we observe from the voltage (V) – Current (I) characteristics measurement curve. We believe that the reduction of conductivity of r-GO:Au would be most suitable Ferro-electric materials for memory storage device applications.
Speaker: Mr David Omoefe Idisi (Department of Physics, College of Science, Engineering and Technology, University of South Africa)
• 15:00
Multi-wavelength variability and correlation studies of flaring Fermi-LAT blazars. 2h
We aim to place constraints on the size and location of the radiation production regions in flaring Fermi-LAT blazars. Multi-wavelength data will be obtained from a selection of BL Lacs and FSRQ sources, from available archival data and new observations. The Fermi-LAT gamma-ray data will be analysed using the Fermi Pass 8 data reduction, which provides a significant improvement in terms of background rejection, event reconstruction and photon acceptance. We aim to investigate the time-domain relationship between several wavelength regimes. From high signal-to-noise light curves, multi-wavelength cross-correlation studies will be performed in order to characterize and compare variability and time-lags. By fitting exponential rise and decay functions to the light-curves, variability times and time gaps between flaring events from different wavelengths will be extracted. The time scale of the variability will be used to place constraints on the size of the emission.
Speaker: Mr Tekano Mbonani (UFS)
• 15:00
Persistent luminescence excitation of BaAl2O4:Eu2+,Dy3+ 2h
BaAl2O4:Eu2+,Dy3+ is the heaviest but the least efficient persistent luminescent material in the MAl2O4:Eu2+,R3+ series. Low efficiency may be due to the hygroscopic host material and/or polymorphic crystal structure [1]. Both may deteriorate the persistent excitation and emission through a change in the trap structure thus shortening the persistent duration. Charging of BaAl2O4:Eu2+,Dy3+ is rather slow, a steady state was achieved only after 30 s. Deconvolution of the thermoluminescence (TL) curves yielded a single trap with a depth of 0.8 eV after UV irradiation. Results agree well with studies on BaAl2O4:Eu2+,Dy3+ prepared with solid state and combustion methods [2]. 3D persistent excitation spectroscopy used in this study gives more detailed information than the simple TL measurements. The irradiation of BaAl2O4:Eu2+,Dy3+ with 200 to 500 nm UV-vis radiation has no effect on the shape of the TL glow curves consisting of a single band at 57 °C. The excitation spectra show little fine structure: at least two bands at 280 and 330 nm (max) with a shoulder at 380 nm. This structure may be due to the splitting of the 2D excited level of Eu2+. The use of free solar energy for excitation is thus limited. The 3D TL emission spectra show only one broad band at 500 nm despite two Ba2+ sites. The BaAl2O4:Eu2+,Dy3+ materials are interesting persistent phosphors though UV excitation is required. The shallow trap at 0.8 eV yields weak and short persistent luminescence at room temperature, as well. A stable crystal structure would be an advantage, too. References [1] J. Hölsä, H.C. Swart, L.C.V. Rodrigues, H.F. Brito, M. Lahtinen, M. Lastusaari, ESTAC-11, Aug. 17-21, 2014, Espoo, Finland. [2] L.C.V. Rodrigues, R. Stefani, H.F. Brito, M.C.F.C. Felinto, J. Hölsä, M. Lastusaari, T. Laamanen, M. Malkamäki, J. Solid State Chem. 183 (2010) 2365.
Speaker: Prof. Hendrik Swart (University of the Free State)
• 15:00
Probing the intergalactic magnetic field through observations of high energy gamma-rays produced by electromagnetic cascades. 2h
Currently there is limited knowledge of the origin of the intergalactic magnetic fields (IGMF) that lie between galaxies, galaxy clusters and cosmic voids. Understanding the origin of the IGMF is a crucial component in models of galaxy and galaxy clusters formation. This magnetic field can be probed indirectly by its effect on electromagnetic cascades initiated by gamma-gamma absorption of very high energy (VHE) gamma-rays, produced in blazars, due to its interaction with the extragalactic background light (EBL). The electron-positron pairs produced via the gamma-gamma absorption interact with the intergalactic magnetic field (IGMF) and can be deviated from their original trajectory path. These pairs can then Compton-scatter off the cosmic microwave background (CMB) to produce high energy gamma-rays that may be detected with Fermi-LAT. The strength of this signal strongly depends on the IGMF strength (B) and the coherence length (L). This secondary gamma-ray emission would be superimposed on the blazar’s intrinsic gamma-ray spectrum. A selection of bright blazars will be re-analysed using the upgraded Pass 8 analysis pipeline, to search for this secondary component. This will be used to place constraints on the IGMF strength. The initial results from this project will be presented.
Speaker: Mr Brandon Bisschoff (University of the Free state)
• 15:00
Quantum efficiency of visible-light photochemical water splitting for hydrogen production by photocatalysis 2h
: Hydrogen has been labeled as the cleanest energy carrier, which can be used for fuel cells. However, the use of clean and renewable energy has been largely hindered by the low efficiency of photocatalysts. An efficient and cheap photocatalyst is required to produce energy from hydrogen in large quantities to meet the ever-increasing demand. Water splitting photocatalysts have attracted a lot of interest because of the environmental friendliness of the technique, however, most of these use only 4 % (UV-region) of the solar energy. In this study CdS, nanoparticles for photocatalytic water splitting were synthesized by using a chemical precipitation method. One of the aims of this investigation was to see to what degree bandgap engineering over a large spectral range could be conducted through particle size manipulation. It is well known that the capping agent, as well as the surfactant concentration, largely contribute to the final nanoparticle size. As such, in this study, we investigated to what degree thioglycerol (TG) could be used as a capping agent (to this end). Structural and morphological properties of the synthesized material were conducted with transmission electron microscopy (TEM), scanning electron microscopy (SEM) as well as Scherrer analysis of the x-ray diffraction patterns (XRD). We showed that the particle sizes and band gap energy could be successfully controlled with the TG capping agent and particle sizes were varied between 6.8 ±1 nm and 1.8 ±1 nm. The quantum-confinement effect was also visually observed in a change in the color of the CdS NP’s from dark yellow to light green with increasing TG concentration was noted. Small sized particles have a high surface-to-volume ratio, this shortens the distance the electrons travel during separation, leading to a large number of electrons reaching the surface without recombination. An increase in the bandgap from 2.5 eV (500 nm) to 3.2 eV (384 nm) was observed with UV-vis spectroscopy. Furthermore, annealing studies revealed that an enhancement in the crystallinity of the material may lead to a reduction in the recombination rates of the electron-hole pair during photocatalytic water splitting. Photoluminescence (PL) studies show a change in luminescence centers with increasing annealing temperature and crystallinity.
Speaker: Mr Sibusiso Nqayi (ufs)
• 15:00
Quantum optical implementation of open quantum walks – a generalized approach 2h
Open quantum walks (OQWs) are a new type of quantum walks, where the “walker” is driven by dissipation [J. Stat. Phys. 147 (2012) 832]. Recently, a quantum optical scheme for the experimental realization of OQWs was proposed [Int. J. Quant. Info. 12, 1461010 (2014)]. In the proposed quantum optical scheme, a two level atom plays the role of the “walker’’ and the Fock states of the cavity mode correspond to the lattice sites of the OQW. Using the small unitary rotations approach and rotating wave approximation the effective dynamics of the system is shown to be an OQW. The presence of spontaneous emission in the system was the key ingredient for obtaining an OQW. However, the spontaneous emission leads to an uncompensated and continuous loss of energy by the system, which is reflected in the relatively poor dynamics of the “walker’’. To overcome this problem, an external driving term of the cavity mode or two level systems was added to the system to pump in energy and drive the “walker” in both directions. Keywords: Open quantum walks; quantum optics; quantum dynamics engineering.
Speaker: Mr Ayanda Zungu (Sol Plaatje University / University of KwaZulu-Natal)
• 15:00
Radiological risk assessment of water sources from the Serule area of Botswana 2h
Abstract. Environmental radioactivity studies involving water sources are essential for the monitoring of the quality of drinking water for public consumption. Natural water sources generally contain some level of concentration of alpha and beta emitters. Radiological examination of these sources becomes necessary to determine their contribution to internal radiation exposure by ingestion. Most villages in Botswana use untreated natural water for human consumption. The recent discovery of uranium in the Serule village of Botswana has established the need for analysis of water samples from the area. Twenty water samples were collected from various sources such as boreholes, wells, rivers and local ditches in Serule. These will set a baseline that currently does not exist in Botswana with regard to radiological concentrations of both surface and ground water. Screening of water samples was carried out using a liquid scintillation counter (Quantulus 1220) to determine the gross alpha and beta activity of the water samples. A presentation will be made on the application of the liquid scintillation counting method for measurement of gross alpha and beta activities in spiked water samples from Serule, Botswana. This includes sample preparation, radiation detection and analysis techniques.
Speaker: Mr Donovan Botlhole (Botswana International University of Science and Technology)
• 15:00
Search for gamma-ray emission from the newly discovered close binary system AR Scorpii 2h
Detailed multi-frequency studies of the white dwarf pulsar AR Scorpii (AR Sco) revealed a Spectral Energy Distribution (SED) that showed optically thin synchrotron emission between IR and X-ray energies. This implies that AR Sco is a site of particle acceleration and associated pulsar-like synchrotron emission, which makes AR Sco an interesting source to search for possible gamma-ray emission in available Fermi-LAT data (100 MeV – 100 GeV). The focus of this MSc project is to do a complete analyses of the total Fermi-LAT data (2008-2018) by utilizing the upgraded Fermi-LAT Pass 8 data analysis pipeline to search for pulsed and un-pulsed gamma-ray emission. The possible detection of gamma-rays from AR Sco will be a strong motivation for possible CTA and H.E.S.S. follow-up studies. A positive detection will also be invaluable to the field of gamma-ray astronomy, establishing close binaries containing fast rotating, highly magnetic white dwarfs, as a new class of gamma-ray source.
Speaker: Mr Quinton Kaplan (University of the Free State)
• 15:00
Spectroscopic follow up of TESS observations to study new Pulsating Pre-Main Sequence stars 2h
Scientific rationale The NASA KEPLER Mission sent a 1.0 m telescope into space to search for planets around other stars. Tremendous amount of photometric data was produced and was used to study pulsating stars of the different types. Many of the observed pulsators had multiple frequencies which were used to determined detailed physics of these stars. For example, solar like oscillations were detected in highly evolved stars and used to determine their masses, radii and even mass loss rates. Follow-up spectroscopic observations were used to provide further constraints in the properties of these Kepler stars. The only stars that were not found in the KEPLER data were the pulsating Pre-main sequence stars (also called pulsating Herbig AeBe stars). This is largely because the region of the sky that KEPLER telescope was pointing at is away from star forming regions where Herbig stars are usually found. Herbig AeBe are very young stars (several million years old, compared to our Sun which is 5 billion years old for example). These stars derive most of their energy from gravitational contraction. Furthermore, the region of interest for the KEPLER mission was in the northern sky, and thus was not suitable for follow-up observations with telescopes in the Southern Hemisphere. In April 2018, NASA is launching a new mission called TESS to search for earth-like planets around other stars. TESS will take photometric observations of stars and their exo-planets. It will similarly produce tremendous amount of data of high precision. The main advantage of TESS is that it observe stars in both the Northern and Southern Hemisphere, and will thus be within reach of our telescopes in Sutherland. We will thus be able to perform follow-up spectroscopic observations of the TESS targets. Our Phd proposal aims to observe Herbig pulsating Ae stars that have been observed by TESS with spectrograph attached to the 1.9 metre telescope at Sutherland. The aim being to make detailed studies of the Herbig Ae stars in order to learn more about their internal physics from their pulsations and spectroscopy. The light curves extracted from the TESS simulated data allows us to search and study to detail for Young Pre-main sequence stars.
Speaker: Mr Papi Lekwene (North West University)
• 15:00
SQUID Magnetometer Data Analysis 2h
The observation of very low magnetic fields is of primary importance for a better understanding of Earth and environment, as well as for early warning of potential hazards coming from space. Recent scientific studies have shown that magnetometers based on Superconducting QUantum Interference Devices (SQUID’s) are able to detect P waves emitted during earthquakes or magnetic storms in the upper atmosphere with sensitivity far better than that of conventional magnetometers. During thunderstorms there are several types of TLEs (Transient Luminous Events), the most common being sprites. Sprites are flashes of bright red light that occur above thunderstorm systems, and can be observed with ultrasensitive high-speed cameras. During January and February 2018 SANSA embarked on a sprite campaign in the centre of South Africa. Significant sprites were identified during at least 3 nights and these occurrences are GPS time stamped. During the same time SQUID data were recorded from the SQUID located at SANSA Space Science in Hermanus. The aim of this project will be to correlate data from the sprite observations with data from the SQUID in Hermanus to establish if the magnetic signature of sprites can be identified in SQUID data. During a previous study the magnetic signatures of sprites were identified in the data from a low-Tc SQUID, located underground at the Low Noise Laboratory (LSBB), France, and partially shielded. The SQUID operating in Hermanus is a High Tc SQUID, with higher intrinsic noise levels, and operating completely unshielded in the geomagnetic field. The main aim of the project would be identification of magnetic sprite signatures in SANSA Squid data.
Speaker: Mrs Abigail Huff (University of Michigan)
• 15:00
Statistical properties of 180,181,182Ta and their implications for 180Ta nucleosynthesis 2h
Most stable and extremely low abundance proton-rich nuclei with A>110 are thought to be produced by the photodisintegration of s- and r- process seed nuclei. However, this so-called p-process is insufficient to explain the observed low abundance (0.012%) of the 180Ta isotope. Hence combinations of several processes are considered to reproduce the observed abundance of 180Ta in the cosmos, provoking debates and making it a unique case study. Significant uncertainties in the predicted reaction rates in p-nuclei arise due to large uncertainties in nuclear properties such as the nuclear level densities (NLD) and gamma-ray strength functions (γSF) (S. Goriely et al., 2001), as well as the actual astrophysical environments. An experiment was performed in October 2014 to extract the NLD and γSF below the neutron threshold (Sn) in 180,181,182Ta isotopes which provide important input parameters for nuclear reaction models. In the present case study, these parameters were measured using the 181Ta(3He,3He’γ) and 181Ta(3He,4Heγ) reactions with 34MeV beam, 181Ta(d,d'γ) and 181Ta(3He,tγ) reactions with 15 MeV beam , and 181Ta(d,d'γ) and 181Ta(d,pγ) reactions with 12.5 MeV beam at the Oslo Cyclotron Laboratory (OCL). Using the SiRi array at backward angles (64 silicon particle telescopes) and the CACTUS array (26 NaI(Tl) detectors), the NLD and γSF were simultaneously extracted below Sn from particle-γ coincidence matrices through iterative procedures using the Oslo method (A. Schiller et al., 2000). The experimental results have been used to determine the corresponding neutron capture cross sections, which in turn were utilized to extract Maxwellian averaged cross sections. The latter were further used in astrophysical s- and p-process network calculations to investigate the galactic production mechanism of 180Ta. In this talk I will present final results on the statistical properties of 180,181,182Ta and their implications for the nucleosynthesis of 180Ta. This work is based on the research supported in part by the National Research Foundation of South Africa Grant Number 92600 and the IAEA under research grant number 20454.
Speaker: Mr Kgashane Malatji (iThemba LABS / Stellenbosch University)
• 15:00
Status of the ECR ionizer for polarized ion source at iThemba LABS 2h
The polarized ion source at iThemba LABS has been in operation for over two decades using Electron Beam (EB) ionizer. The source has been used to deliver beam for nuclear physics research. Due to its disadvantages which are producing beam with large energy spread and having complicated extraction system,the EB ionizer was replaced by Electron Cylotron Resonance (ECR) ionizer. The ECR ionizer has better plasma confinement due to its higher magnetic mirror fields as well as low energy spread of which nuclear physics require. The use of ECR ionizer recently installed at iThemba LABS is under investigation.
Speaker: Mr Ndumiso Mnikathi (student)
• 15:00
Structural and optical properties of NiO nanopowders prepared by co-precipitation method for gas sensing applications 2h
Prompt technological and industrial advances uninterruptedly cause the release of hazardous and toxic gases that are harmful to human life; as a result sensing devices that are sensitive and selective to such gases are desirable. Presently, gas sensors based on semiconductor metal oxide (SMO) materials are pleasing more consideration, because of their evident change in electrical resistance when exposed to the target gases such as reducing and oxidizing gases [1]. Amongst the semiconductor metal oxide, p-type nickel oxide (NiO) was found to be promising candidate for gas sensing applications due to its wide bandgap (~ 3.6 - 4 eV) [2], high specific surface area, excellent structural stability. Therefore, we report on the gas sensing characteristics of NiO nanostructures prepared by co-precipitation method at various reaction times ranging from 2 to 24 hours. X-ray diffraction patterns revealed that nanostructures are polycrystalline, displaying average crystallite sizes of ~ 10 - 12 nm. The physical variation of colour from green to black after heat treatment was assigned with the non-stoichiometric property of NiO which was confirmed from photoluminescence and electron paramagnetic resonance studies. The effects of non-stoichiometry and energy bandgap on the gas sensing properties of NiO based sensor have been investigated towards various oxidizing and reducing gases at various operating temperatures. Keywords: surface area, adsorption, desorption, gas sensing. References [1]. T.-H. Kim, J.-W. Yoona, Y.C. Kang, F. Abdel-Hady, A.A. Wazzan, J.-H. Lee, Sensors and Actuators B 240 (2017) 1049–1057. [2]. A. Yazdani, H. Zafarkish, K. Rahimi, Materials Science in Semiconductor Processing, 74 (2018) 225 – 231.
Speaker: Mr Teboho Mokoena (University of the Free State)
• 15:00
Structural and optical properties of spin coated graphene oxide thin films 2h
Graphene oxide (GO) is a derivative of graphene, consisting of an atomic layer of carbon bonded to oxygen functional groups such as hydroxyl and epoxide, which make it insulating and hydrophilic. This novel material it has attracted much research recently, although there is varying information in the literature because the properties may depend on the synthesis technique and form (powder, thin film, solution). An investigation of the structural and optical properties of spin coated GO thin films was made. GO powder was purchased from Sigma Aldrich (15-20 sheets, 4-10% edge-oxidized) and used to prepare a GO suspension in distilled water (1 mg/ml) which was ultrasonicated and centrifuged. The supernatant black solution was spin coated on silicon substrates to produce thin films. The solution was characterized using photoluminescence (PL) and UV-vis absorption measurements, while the GO powder and thin films were assessed using X-ray diffraction (XRD). A broad absorption band was observed at 273 nm, although subsequent PL measurements showed that this was not an efficient excitation wavelength. Instead, the weak blue luminescence observed at 444 nm could be excited at 325 nm. Blue luminescence has been attributed to thoroughly exfoliated GO suspensions while red emission (not observed here) to poorly dispersed suspensions. The Raman peak of water was observed on the short wavelength side of this emission. The XRD pattern for the commercial GO powder had a peak near 2θ = 13.3°. This low angle, compared to the corresponding peak of graphite (27°), indicates much wider spaced interplanar layers as a result of oxidation, but showed that the GO was stacked in multiple layers. A weak band near 30° suggested that the powder probably also contained a small amount of graphite. This was absent for the thin film since it was likely removed by centrifuging. The XRD peak of the thin film was shifted to 2θ = 13.8°, indicating a small reduction in the interplanar spacing. Although the XRD data corresponded to stacked GO, the optical properties suggest that significant reduction was present in the commercial powder.
• 15:00
Structural, electronic and optical properties of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> 2h
Organic-inorganic halide perovskites are promising candidates for low cost, high-efficiency solar cells. We examined the structural, electronic, and optical properties of the low temperature tetragonal phase of the halide peroviskite CH3NH3PbI3 using Density Functional Theory (DFT). Our numerically predicted structure is in agreement with existing experimental data. DFT electronic structure calculations show that relativistic effects are important for the heavy lead atom and spin-orbit coupling has to be included for accurate results. The experimental band gap of 1.63 to 1.66 eV is similar in magnitude to the DFT direct gap of 1.72 eV, which suggests that many-body and relativistic effects cancel in this compound. Our calculated fundamental gap, at the G0W0 level of approximation, is 2.48 eV. Optical anisotropy of tetragonal CH3NH3PbI3 was investigated by including many-body effects at the time dependent Hartree Fock and the Bethe-Salpeter equation level of approximation, with input data from a range separated Heyd-Scuseria-Ernzerhof DFT functional calculation. The optical edge for radiation polarised parallel to the a- and b-axes differ by about 0.15 eV and for polarisation parallel to the b- and c-axes the difference is about 0.05 eV.
Speaker: Mrs Aya Alsadig (Sudan University of Science and Technology)
• 15:00
Study the impact of pile-up jets in the MET reconstruction for the forward region at the ATLAS experiment 2h
In 2017 and 2018 data taking in the ATLAS detector at LHC, the average bunch crossing per collision is much higher than before. Thus the pile-up effect is much stronger, which will significantly affect the MET reconstruction. In the MET reconstruction, the forward jet, which is hardly distinguished from the pile-up jet, will cause a large MET resolution. This presentation will introduce the study that how the transverse momentum threshold and the jet vertex fraction tagger (JVT) can improve the MET resolution in the high pile-up situation.
Speaker: Ms Esra Shrif (University of the Witwatersrand)
• 15:00
Studying the effects of pileup on the leptonic properties for the H-> ZZ -> 4l channel with the ATLAS detector at the LHC 2h
The background composition and shapes are studied in spectral control regions which are constructed inverting selections or lepton identification requirements. I will be looking at the effect of pileup for the H -> ZZ -> 4l channel with weighted histograms, normalized to the expected luminosity. The background considered is the qq -> ZZ reducible background which is from a dominant quark-antiquark initial state. Comparisons between mc16a, mc16d and mc16e samples for the pile effect and the expected yield will be studied for all channels. I will also look at studies on the high mass qq->ZZ samples.
Speaker: Ms Onesimo Mtintsilana (University of Witwatersrand)
• 15:00
Surface chemical characterization of ZnO-Eu3+/Yb3+ thin films on Si (100) substrates using TOF‐SIMS 2h
Mixed Nitrates of Zn, Eu and Yb were deposited on Si (100) substrates using the sol-gel spin coating method under optimized deposition conditions using monoethanolamine as stabilizing component. This paper reports on the morphology and topographical images of ZnO:Eu3+,Yb3+(7%) thin films. The surface composition of the annealed ZnO films were investigated by using Field emission Scanning Electron Microscopy (FE-SEM) and Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). The presence of various types of particles on the surface of the spin coating thin films as well as the differences in the film structure, played an important role to induce artificial topographical effects on the ZnO:Eu3+,Yb3+ thin films. The presence of H on the surface and throughout the entire thickness of the thin films was confirmed by TOF-SIMS. Furthermore, it was found that the near surface region of the as-grown thin films was Zn-rich, and annealing at higher temperatures (1000 °C) removed the H-related defects from the surface of the thin films and affect the balance of the Zn and O concentrations. Both the positive and negative ion depth profiles of the ZnO:Eu3+,Yb3+(7%) thin films were measured. The two and three-dimensional (2D and 3D) images have also been recorded in the positive and negative ion mode. Analysis of the 3D images showed big agglomerated particles on the surface of the Si substrate that appears to be embedded in the substrate and the substrate appears to be on the same level as the particles. This phenomenon was due to the artificial topographic effects which are attributed to the experimental setup of the TOF-SIMS system. The details of these features will be discussed. Key words: Spin coating, Tof-SIMS, 2D and 3D images.
Speaker: Dr Balakrishna Avula (University of The Free State)
• 15:00
Synthesis and characterization of Zn<sub>(1-x)</sub>S:Cu<sub>x</sub> nanoparticle thin films by using spin-coating for enhancement of UV-LEDs and Solar Cells 2h
Efficient enhancement of solar cells has become more important due to the need for environmentally friendly renewable energy sources. Using thioglycerol as the capping agent and concentrated HCl as the catalyst, ZnS:Cu sol-gels with different Cu concentrations were successfully used to grow nanoparticle thin films on ultrasonically cleaned glass substrates. The as-deposited films were spin-coated at room temperature for 30 s at different spin speeds, heat-treated at 275 °C for 10 minutes and annealed at different temperatures in air. The x-ray diffraction studies revealed that both the un-doped and Cu-doped ZnS films were amorphous when annealed at 300 °C and possess a hexagonal wurzite crystal structure with preferred orientations at higher temperatures. The films were optically characterized at room temperature using a Cary Eclipse spectrophotometer and UV-visible spectroscopy. Photoluminescence (PL) spectra showed green and red emissions which may be due to excited electron transitions from both the shallow donor level and the deep donor level (sulphur vacancies) to the t2 level of Cu2+, respectively. The Zn0.05S:Cu0.05 film yielded the highest PL intensity when excited at 237nm and was used to study the effect of annealing temperature and spin speed. Optical absorbance and reflectance measurements revealed that changing both the Cu concentration, annealing temperature and spin speed tunes the band gap of the ZnS:Cu thin films. Copper doped zinc sulphide nanoparticle thin films with a hexagonal wutzite crystal structure were successfully synthesized using the spin coating method and can be used for efficient enhancement of solar cells.
Speaker: Mr Molise Jan Mphuthi (University of the Free State)
• 15:00
Synthesis and characterization of ZnS prepared by Co-precipitation method 2h
Zinc Sulphide is an important optoelectronic device material with a wide band gap and it is used for violet to blue light applications. Zinc Sulphide (ZnS) nanoparticles doped with Manganese and Copper have been synthesized with the chemical co-precipitation method using Polyvinylpyrrolidone (PVP) as a capping agent to control the particle growth. The crystal structure and particle size were studied utilising X-ray diffraction and it was found that the un-doped ZnS, the Mn-doped ZnS and the Cu-doped ZnS powders all have the cubic zinc blende crystal structure with a (111) preferred orientation. The crystallite sizes were in the order of 4 nm. UV-visible spectroscopy was used to characterize the powders at room temperature and reflectance measurements were performed on all samples. From these measurements the band gap of the un-doped ZnS, the Mn-doped ZnS and the Cu doped ZnS powders was found to be 3.3 eV, 3.2 eV and 3.1 eV, respectively. Photoluminescence (PL) measurements were performed on all samples with a Cary Eclipse spectrophotometer. From the PL measurements it was found that the un-doped ZnS had a broad emission peak at 480 nm (blue). Both doped samples had the same broad emission peak at 480 nm (blue) with a stronger second emission peak at 605 nm (orange) for Mn-doped ZnS while for the Cu-doped ZnS the second emission peak was at 580 nm (yellow). The broad blue emission is attributed to Zinc or Sulphur vacancies while the orange and yellow emission can be attributed to the Mn and Cu dopants respectively.
Speaker: Ms Tshegofatso Modungwe (University of Free State)
• 15:00
Synthesis, structural and magnetic properties of Ni0.5Ti0.5Fe2O4 2h
Nickel base ferrites of the spinel structure have been reported to have interesting properties such as low coercivity, high saturation magnetization, chemical and thermal stability. These qualities allow the materials to be used in applications such as gas sensors, magnetic fluids, magnetic storage systems. The properties of NiFe2O4 can be tuned by doping in the A or B sites of the spinel structure. Furthermore, the synthesis technique used has great influence on the resulting properties. Hence, we have successfully synthesized a polycrystalline Ni0.5Ti0.5Fe2O4 compound by high energy ball milling. To our surprise the phase quickly takes form as early as 0.25 hours. The sample was milled for 10 hours. Prolonged milling destroyed the phase. From the structural analysis it is evidence that starting precursors for a chemical reaction are of vital importance as they have great influence on the reaction product. The mean particle size was obtained to be 45.2±9.4 nm. Particle size reduces with milling time whilst the strain increases. The density is inversely proportional to the lattice parameters. Intriguingly, The coercivity and saturation magnetization followed Stoner Wohlfarth model with two distinct regions at high temperature (300-100) and low temperature (50 -10) with approximately equal anisotropy. Saturation magnetization was obtained to be between 38.73 to 38.84 ± 0.03 emu/g and the coercivity is between 820 to 407 ± 32 Oe. Room temperature Mossbauer revealed hyperfine fields of 446 ± 1 kOe and 480 ± 1 kOe for A and B sites respectively. Isomer shift values revealed co-existence of both F3+ and Fe2+. The interesting and intriguing properties displayed by the material serves as great potential and open room for further investigation.
Speaker: Mr Sanele Dlamini (UKZN)
• 15:00
Systematic uncertainties in the search for a high mass scalar decaying to 4 leptons in the ATLAS detector at the LHC 2h
Searches for heavy scalars beyond the Standard Model are ongoing endeavours at the LHC. One particularly interesting method of doing this is through the hypothetical decay of the heavy scalar to two Z bosons, which subsequently decay to four leptons. In this work, the ATLAS high mass four lepton search is discussed with emphasis on its experimental systematic uncertainties. The background statistical framework is explained and applied to the Run 2 ATLAS data. Prospects and implications are discussed in the context of searches for new heavy bosons at the LHC.
Speaker: Mr Stefan von Buddenbrock (University of the Witwatersrand)
• 15:00
The \textbf{{\textbf{ $H \to h h, S h, S S\to 4W\to 4\ell + 4\nu$} analysis with the ATLAS detector: optimization and prospects for the full Run-2 data}} 2h
The $H \to h h, S h, S S\to 4W\to 4\ell + 4\nu$ analysis using \ensuremath{36.1 fb^{-1}} of $pp$ collision data at a center-of-mass energy of 13~TeV recorded with the ATLAS detector at the Large Hadron Collider is presented. The analysis introduces the new Higgs-like scalar, $S$, as well as the Standerd Model Higgs boson, $h$, through the decay of the heavy scalar, $H$. The search is characterized by four lepton and missing transverse momentum carried out by the neutrinos in the final state. This is a very clean signature with low expected background. The analysis strategy relies on the invariant mass of the four leptons and also uses dilepton kinematics to reject $ZZ$ background. The paper discusses the published results with \ensuremath{36.1 fb^{-1}} of the Run-2 data. The analysis optimization and also the prospects for the full Run-2 data are also presented.
Speaker: Mr Lehumo Mashishi (Wits)
• 15:00
The effect of different annealing period intervals on BaAl2O4:0.2% Ce3+ nano-phosphor’ structure, morphology and luminescent properties synthesized by citrate sol-gel method. 2h
Cerium-doped Barium Aluminate (BaAl2O4:0.2%Ce3+) nano-powders were prepared by citrate sol-gel method to overcome the flickering luminescence in signage and displays by offsetting dark duration with persistent luminescence. The effects of annealing period (AP) at a constant temperature of 900 ⁰C and dopant concentration of 0.2% Ce3+ on the structure, particle morphology and photoluminescent properties of nano-powders were investigated. The X-ray powder diffraction (XRD) patterns showed that the 0.2% Ce3+ dopant did not have a major influence on the crystalline structure of the host BaAl2O4. The crystalline quality and size of the nano-powders ware influenced by varying the AP. The scanning electron microscope (SEM) together with the energy dispersive spectra (EDS) images revealed the increase in AP affects the morphology of the prepared phosphor. There is a presence of hexagonal platelets with well-developed faces that dominate the morphology of the doped samples. The emission peaks at 427 nm, 538 nm and 727 nm are attributed to band-gap defects in the host material at λex = 299 nm. The emission peaks at 481 nm, 549 nm and 612 nm are attributed to the 5d⟶4f emission of Ce3+. The commision internationale de l’eclairage (CIE) results showed the there is a slight change in the emission color of 0.2% Ce3+ doped BaAl2O4 when varying the AP.
Speaker: Ms Kgomotso Modisakeng (Sefako Makgatho Health Science University)
• 15:00
Use of machine learning techniques in high energy physics 2h
The large and complex dataset from Large Hadron Collider (LHC) at CERN has led to the application of Machine Learning (ML) techniques in analysing the data. Up until now, most of the methods used to extract useful information from the large datasets have been based on physics intuition built from existing models. By applying advanced data science methodology, we have developed tools for determining achievable classification performance for a variety of relevant physics processes. In this talk, I will review the recent developments, focussing on optimising trigger, object identification and reconstruction, and tagging jets based on initiating particle using ML methods. Applied to searches for new physics processes, these show significant improvement in sensitivity. I will also summarise the challenges faced in implementing these algorithms in experiments.
Speaker: Deepak Kar (University of Witwatersrand)
• 17:00 20:00
Excursions to Planetarium Naval Hill Planetarium

### Naval Hill Planetarium

• Wednesday, 27 June
• 08:50 09:00
Announcements Auditorium

### Auditorium

• 09:00 10:00
Plenary: Hanlon
Convener: Dr Brian van Soelen (University of the Free State)
• 09:00
Welcome to the Dome - Three surprising things a Robot Telescope can do 1h
Small robot telescopes occupy a particular niche in the astronomy ecosystem by virtue of their autonomous scheduling capabilities, rapid response times and flexible operations. These characteristics offer a wealth of use cases, three examples of which are explored in this talk. Located at Boyden Observatory, Watcher is a robotic telescope owned by University College Dublin, developed and operated in collaboration with University of the Free State. Gamma-ray bursts are the most luminous electromagnetic events in the universe, the signal of the collapse of distant massive stars, or the mergers of two neutron stars. Gamma-ray bursts only last seconds to minutes, producing rapidly fading visible light in some cases. The discovery of a gamma-ray transient by the Fermi and INTEGRAL satellites, coincident with the LIGO/VIRGO binary neutron star merger event of August 17th 2017, has revealed the connection between short gamma-ray bursts and the gravitational wave universe in spectacular fashion. Watcher's main scientific goal is the rapid follow-up of newly discovered transient astrophysical sources such as gamma-ray bursts. Upon receipt of a new trigger, Watcher can be on target within 30 seconds. Despite their vast distances, the incredible luminosities of gamma-ray bursts render them detectable even by a small telescope, once it is fast enough. The crude localisations of gravitational wave events provided by LIGO/VIRGO pose challenges to narrow field telescopes such as Watcher that must be addressed to ensure the continued relevance of such systems in this exciting new era of multi-messenger astrophysics. When it is not chasing gamma-ray bursts, Watcher conducts a diverse and rich observing programme that has impact beyond research, supporting learning in astronomy and astrophysics by providing bespoke data to students without requiring them to travel to the telescope. Beyond the traditional academic boundaries, collaboration with an artist has led to Watcher data being used in work exploring the role of women in astronomy.
Speaker: Prof. Lorraine Hanlon (University College Dublin)
• 10:00 11:00
Applied Physics
Convener: Dr Mmantsae Diale (University of Pretoria)
• 10:00
A preliminary study of the impact of metal-induced CT artifacts on Monte Carlo dose calculations in a pelvic prosthesis phantom 20m
Computed tomography (CT) images of patients undergoing radiation therapy form the basis of 3D radiotherapy treatment planning. But in the presence of metallic implants, metal streak artifacts are produced in CT images which could provide inaccurate electron density information (due to incorrect Hounsfield units (HU) values) needed for accurate calculation of patient radiation dose. In this study, the dosimetric impact of metal-induced CT streak artifacts on Monte Carlo dose calculations in a pelvic phantom that contains unilateral hip Ti implant is evaluated. Correct HU values were assigned to known materials of the pelvic prosthesis phantom to create an artifact-free phantom model in contrary to HU values generated through the original artifact-induced CT images. DOSXYZnrc Monte Carlo dose calculations were then computed in the artifact-free phantom model created from the exact geometry of the phantom with known materials and the phantom model made from the original CT images containing the metal artifacts. The dose calculations were benchmarked against Gafchromic EBT3 film measurements using 10 × 10 cm2 15 MeV electron and 10 MV photon beams. The average discrepancies between film and MC dose data decreased from 4±2% to 2±1% and from 5±3% to 3±2% in the two phantom models for the electron and photon fields, respectively. The study shows that Monte Carlo calculated dose data in the artefact-free phantom model were closer to film measurements compared to dose data computed in the original phantom model containing the metal-induced CT artifacts.
Speaker: Dr Nicholas Ade (University of the Free State)
• 10:20
Photodynamic Therapy using Sulfonated Aluminum Phthalocyanine Mix for the eradication of Cervical Cancer, An in vitro Study 20m
The use of phthalocyanines in Photodynamic Therapy (PDT) has greatly altered the difficulties associated with the treatment of cancer. PDT is a treatment modality that uses photo-physical properties of a photosensitizer (PS), in the presence of light and molecular oxygen to eradicate cancer cells. The correct choice of PS used maximizes its therapeutic potential and efficacy. This study, therefore, investigates the effectiveness of Sulfonated Aluminum phthalocyanine Mix (AlPcSmix) in PDT for the treatment of cervical cancer, which in developing countries, South Africa included, is a common type of cancer among women, and the leading cause of cancer-related deaths. A working solution of AlPcSmix was prepared in Dimethyl Sulfoxide. Cervical cancer HeLa cells (ATCC® CCL2™) were cultured in liquid medium, Dulbecco’s Minimum Eagle’s Medium supplemented with 10% Foetal Bovine Serum and incubated at 37 °C, 5% CO2 and 85% humidity. The cells were treated with varying concentrations of AlPcSmix. The treated cells were then irradiated using 673 nm diode laser at fluences of 5, 10 and 15 J/cm2. Cellular responses were evaluated 24h post-irradiation using Trypan blue viability assay, Adenosine Triphosphate assay for proliferation, Lactate Dehydrogenase cytotoxicity assay for membrane integrity, and fluorescent microscopy for cellular localization. Results indicated that AlPcSmix localized in the mitochondria and lysosomes, and cellular responses showed dose-dependent structural changes, with increasing cytotoxicity and decreased cell viability and proliferation. Results obtained indicate AlPcSmix as an excellent choice of PS for use in PDT and the eradication of cervical cancer cells in vitro.
Speaker: Mr Elvin Chizenga (Laser Research Center, University of Johannesburg)
• 10:40
ANALYSIS OF TYPE 1 DIABETES WITH MACHINE LEARNING METHODS 20m
ANALYSIS OF TYPE 1 DIABETES WITH MACHINE LEARNING METHODS ABSTRACT Big data is a term that we can use for data sets with large, diverse and complex data structures that are difficult to analyse or visualize using traditional computing methods and approaches. Health care sectors rely on interpreting data gathered from patients, which ranges from graphic scans to medical images of which there is a limitation on its analysis by medical practitioners. It is this same limitation for datasets and advances in big-data methodology that sparked interest an interest in this sector as well. We proposed to use the Type 1 Diabetes (T1DM) data from INDEPTH VA as a test case for applying modern machine learning (ML) methods to analyse the data. Due to a high prevalence of Type 1 Diabetes (T1DM) it has huge amounts of data available from on-going researches, and there are possible misclassifications of such data in past researches. In collaboration with Dr Alisha Wade(DG,Johannesburg) and a study by Prof Justine Davies (KCL,London,UK) which aimed to estimate the numbers of deaths in people with T1DM and the causes of those deaths by using VA data in the under 40 age-group across all INDEPTH sites. The same data will be processed by classification algorithms based on machine learning. The basic idea is that the algorithm automatically learns to make accurate predictions based on past observations. For this particular case, it will learn the features present in diabetic patients, thereby able to identify patients with high chances of unidentified T1DM. One of the advantages of this approach is that it can avoid human bias, but to not fall prey to any training bias, and understand the correlation between different properties, inputs from medical experts will also be necessary. The feasibility of this approach will be studied to see if accuracy obtained with current methods can be reached or bettered. If this preliminary study is successful, the scope can be expanded. For this study, we will use Tensorflow [2] or Scikit Learning [3], two of the most popular deep learning libraries to classify the dataset. They are both open source software.
Speaker: Ms Thokozile MANAKA (University of the Witwatersrand)
• 10:00 11:00
Astrophysics: Gamma-ray / Multi-wavelength Astronomy I
Convener: Dr Brian van Soelen (University of the Free State)
• 10:00
Constraining star formation history with Fermi-LAT observations of the gamma-ray opacity of the Universe 20m
The star formation history (SFH) of the Universe is of fundamental importance to cosmology, not only to galaxy formation itself, but also for ongoing efforts to determine cosmological parameters and matter content of the universe. Measurement of the extragalactic background light (EBL) as a function of redshift can constrain models of the SFH, including the initial mass function(IMF) and dust extinction. The gamma-ray spectra of AGN allow us to study the extragalactic background light (EBL) through absorption of high-energy photons. In this work, we present constraints on models of SFH using a sample of AGN observed by the Fermi-LAT instrument by investigating the imprint of the EBL on the observed spectra of high-redshift Fermi-LAT AGN above ~ 10 GeV.
Speaker: Ms Ashlynn Le Ray (University of the Witwaterstrand)
• 10:20
Lorentz Invariance Violation in high energy astrophysics 20m
Several quantum-gravity theories predict that familiar concepts such as Lorentz symmetry can be broken at energies approaching the Planck energy scale. Such extreme energies are currently unreachable by experiments on Earth, but for photons traveling over cosmological distances the accumulated deviations from the Lorentz symmetry may be measurable using the Cherenkov Telescope Array (CTA). Considering the Lorentz Invariance Violation (LIV) effect, we found that the cosmic opacity for VHE gamma rays with energy more than 10 TeV can be strongly reduced. I will further discuss the impact of LIV on the Compton scattering process, and how future CTA observations may open an exciting window on studies of the fundamental physics.
Speaker: Mr Hassan Abdalla (Centre for Space Research, North-West University, Potchefstroom 2520, South Africa)
• 10:40
Radiation from relativistic particles accelerated at shear layers in relativistic jets. 20m
The supermassive black holes in the centers of some active galaxies (AGN) eject powerful relativistic jets which propagate over kpc scales, showing no significant momentum loss. Both observational evidence as well as theoretical considerations from MHD simulations of jets suggest that they are radially stratified, with a fast inner spine surrounded by a slower-moving outer sheath. The resulting relativistic shear layers are a prime candidate for the site of relativistic particle acceleration in the jets of AGN and gamma-ray bursts (GRBs). In this talk, we will present results of particle-in-cell simulations of magnetic-field generation and particle acceleration in the relativistic shear boundary layers of jets in AGN and GRBs. We outline future plans to include self-consistent calculation of radiation produced by the particles accelerated at these shear boundary layers.
Speaker: Mr Tej Chand (Center for Space Research, North-West University Potchefstroom South Africa)
• 10:00 11:00
Convener: Mr Muneer Sakildien (iThemba LABS)
• 10:00
A review of nuclear clustering formulation 20m
Nuclear cluster models are a means to describe complex many body systems, specifically to predict nuclear structure properties within strongly correlated subsystem of nucleons. The binary cluster model has shown some success in predicting the alpha decay and spontaneous fission half-lives. A relativistic description of the Binary Cluster Model using the Dirac formulation treats spin correlations in a more natural way. The objective of this study is to develop a fully microscopic description of the nuclear clustering based on a relativistic mean field theory. So doing, extending the application of the model to a greater range of observables, testing it in scattering phenomena and Colinear Cluster Tri-Partition (CCT). This presentation which gives an overview of binary clustering model and the formalism used identify the core-cluster partition and corresponding nuclear cluster observables. A comparison with existing phenomenological and non-relativistic Brueckner G-Matrix model predictions will be done.
Speaker: Mr Timothy Gary Carolus (Stellenbosch University)
• 10:20
Investigating the candidate 5-alpha cluster state in 20Ne at Ex = 22.5 MeV with the 22Ne(p, t)20Ne reaction. 20m
The study of alpha-cluster in light nuclei have been well documented with experimental evidences. Meanwhile, in the recent experiments performed at iThemba LABS using (p,t) reaction on 22Ne with the K600 magnetic spectrometer, a 22.5 MeV state was found, which accounts for 5-alpha cluster situated at 3.3 MeV above the 5-alpha break-up threshold. However, this state could not be accounted for by theoretical shell-model calculations and angular distribution data taken at forward angles including zero degrees. In the present project, (p, t) reaction on 22Ne will be carried out at zero degrees, to ascertain whether this state exist or not. A proton beam with an energy of Elab= 80 MeV from the Separated Sector Cyclotron (SSC) facility impinged on a 22Ne gas target at lab angles of Θlab= 00 was considered. Preliminary results of these experiments will be discussed.
Speaker: Ms Lerato Baloyi (University of the Witwatersrand)
• 10:40
The first-excited 2+ state in 14C 20m
B(E2: 2+→0+) values of neutron-rich even-even carbon isotopes have been reported up to 20C and do not only provide important information on the evolution of the underlying structural mechanism towards the drip line but also provide critical constraints for theoretical models. The B(E2: 2+→0+) value in 14C can be indispensable to advance our understanding of the Carbon isotopic chain. However, the experimentally determined B(E2: 2+→0+) value for 14C exhibits persistent inconsistencies with that obtained from theoretical models, including the no-core shell model. The attempted safe Coulomb excitation experiment of 14C at Florida State University took advantage of the unique beam capabilities and the availability of high-efficiency large volume LaBr3 detectors and the S3 double sided silicon strip detector. The preliminary results from the experiment to attempt the Coulomb excitation of 14C will be presented. This work was supported by the National Research Foundation of South Africa under grant number 105205 and by the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
Speaker: Mr Christiaan Brits (University of Stellenbosch)
• 10:00 11:00
Photonics: Spectroscopy
Convener: Prof. Tjaart Krüger (University of Pretoria)
• 10:00
Contrast enhancement in spectral domain optical coherence tomography. 20m
Optical Coherance Tomography (OCT) is an interferometric technique, which allows for non-invasive in vivo diagnostic medical imaging. It is a powerful tool in ophthalmology since it is able to produce high-resolution 2D profiles or 3D reconstructions of ocular structures to aide in the early diagnosis of ocular diseases. The main advantages associated with OCT are its high resolution and depth of penetration, which are in the micron and millimeter ranges respectively. OCT typically makes use of a low coherence light source, in order to obtain high depth resolution. Typical light sources found in commercial systems include super luminescent diodes and super continuum pulsed sources based on anomalous dispersion photonic crystal fibers. The phase instabilities associated with these sources contribute to noise and diminish the signal to noise ratio. The University of Stellenbosch are currently developing a multimodal laser microscopy setup, which will make use of an All Normal Dispersion Photonic Crystal Fibre (ANDi-PCF) developed at the Laser Research Institute (LRI). This source does not suffer from the inherent phase instabilities found in conventional OCT sources, which makes it the ideal source for OCT applications. The main purpose of this research is to observe the effects of the critical parameters, identified using our SD-OCT system simulation, has on the system resolution and signal to noise ratio. In this presentation, results from the setup using the ANDi-PCF will be compared to those from conventional LED sources, thereby highlighting the expected improvement in signal to noise obtained from using the ANDi-PCF.
Speaker: Mr Wendall Coenraad (Stellenbosch University)
• 10:20
A Heat Pipe Setup for Resonant Ionisation Spectroscopy of Zinc 20m
Resonant Ionisation Spectroscopy (RIS) is a technique to selectively ionise a particular element or even isotope. It has applications in the production and quality assurance of isotopes for medical applications. It is also applied for the production and study of beams of exotic nuclei in large nuclear physics facilities such as CERN. We report on the development of a heat pipe based setup for atomic spectroscopy that will be used to investigate and optimise resonant ionisation schemes for Zinc (Zn). RIS is a multi-step process of which the first 1 or 2 photons are resonant, and the last photon ionises the atom. We apply a novel setup for atomic absorption spectroscopy using multiple laser beams and time-delayed pulses to investigate and characterise the different steps in the RIS scheme. A python program was created to analyse the data that will be obtained. The design and development of the setup and preliminary results are presented. The results are relevant to inform the design of an optimised resonant ionisation scheme that could be applied in industry within the limitations posed by a production environment.
Speaker: Mr Brandon Hattingh (University of Stellenbosch)
• 10:40
Enhancement of signal to noise ratio through temporal pulse shaping 20m
The quest to probe deeper into biological tissue has led to the development of many microscopic techniques ranging from the linear regime, such as bright-field microscopy, to higher order nonlinear optical microscopy (NLOM) techniques. These NLOM permit intrinsic 3D imaging with submicron spatial resolution, decreased photodamage to tissue, increased depth of penetration, as well as the ability to perform label-free imaging. This research focuses on the enhancement of signal to noise ratio obtained in NLOM through temporal pulse shaping and phase manipulation of the excitation pulses. The application and effects of this pulse shaping and manipulation on contrast enhancement, as applied to examples including nonlinear crystals and biological tissues, will be discussed.
Speaker: Mr George Okyere Dwapanyin (Stellenbosch University)
• 10:00 11:00
Physics Education
• 10:00 11:00
Physics of Condensed Matter and Materials
Convener: Dr Madan Singh (National university of Lesotho, Roma, Lesotho)
• 10:00
ZnO nanoparticles doped with cobalt and indium mechano-chemically for methane gas sensing application 20m
The mechano-chemical technique was employed to synthesise the undoped zinc oxide (ZnO), 5% cobalt (Co) and indium (In) single doped ZnO nanoparticles and Co-In double doped ZnO nanoparticles. The diffraction pattern for In-ZnO nanoparticles obtained from the X-ray diffraction (XRD) reveals an additional peak that is associated with the In+3 dopant. The scanning electron microscope (SEM) images shows the spherical morphology of the nanoparticles for all the prepared samples. The gas sensing properties of ZnO nanoparticles were probed using the kenosistec station equipment. The response and sensitivity of ZnO nanoparticles to methane (CH4) gas were investigated at different temperatures and gas concentrations. The Co-In double doped ZnO and Co-ZnO nanoparticles show great sensitivity to CH4 gas at the concentration of 20 and 40 ppm, respectively.The CH4 gas sensor seems to work better at lower temperatures and higher gas concentrations, which is good for monitoring the environment.
Speaker: Ms Mahlatse Manamela (University of Limpopo)
• 10:20
A numerical study of heterogeneous annealing in a finite one-dimensional geometry 20m
The irradiation of a material with high-energy particles causes the formation of different types of defects in its crystalline lattice. At any temperature above absolute zero, the defects anneal spontaneously and the rate of annealing increases with temperature. The thermal energy released in the process of annealing contributes to the temperature of the material, and creates a positive feedback effect referred to as the thermal-concentration feedback. The non-homogeneous distribution of defects or of temperature in the material, along with the thermal-concentration feedback, may lead to the appearance of a self-sustaining annealing wave. Conditions for the formation of the annealing wave are currently not well established. In this study numerical modelling of the heterogeneous annealing in a finite one-dimensional geometry was performed. To this end, a finite difference solver was implemented, verified and applied in our numerical experiments. The self-sustaining annealing process was initialized by adding heat to a localized region near the material surface at the initial moment. Evolution of temperature and defect distributions during the process of annealing was obtained for different initiating heat distributions and initial defect concentrations. It was demonstrated that for large values of initiating energy, the annealing process develops as a wave, which propagates at a constant speed. For more moderate values of initiating energy, the interplay of the heterogeneous initial heat distribution and the spontaneous annealing leads to the appearance of the wave regime in the terminal part of the process.
Speaker: Mr Jeremiah Lethoba (Department of Physics, University of Pretoria)
• 10:40
Quantification of Ag in Ag doped glass based metamaterials using XPS analysis. 20m
Quantification in XPS is not easy, more especially if the concentrations of the substituents in the sample are not homogeneous on the sample surface or with depth. In this study the Quases-Tougaard Software analyses approach was used to quantify Ag nano clusters in a Ag doped glass host. The specimens were synthesized by a simple molten bath ion exchange method and then annealed at different temperatures. A XPS-spectrum of the Ag 3d peaks were isolated from a survey spectrum of the specimen and compared to a spectrum generated from a pure Ag reference. The morphology was changed until there was a good match between the two spectra. The results shows that the QUASES Software can be a vital tool in determining the morphology of elements in a sample.These results are then compared with results from TEM data.
Speaker: Ms Rethabile Makole (University of the Free State)
• 10:00 11:00
Space Science
• 10:00 11:00
Theoretical and Computational Physics
• 10:00
Full phase space simulation of the relativistic Boltzmann equation in the context of heavy-ion collisions 20m
Relativistic hydrodynamics has been the tool of choice to simulate the dynamics of the quark-gluon plasma produced in heavy-ion collisions. Despite the success of hydrodynamics, it has several shortcomings stemming from the fact that it assumes a system close to equilibrium. An alternative to hydrodynamics is solving the Boltzmann equation, which describes the evolution of the full distribution function of the system without the close to equilibrium requirement. The Boltzmann equation, however, has hitherto proved computationally intractable. By using a novel algorithm, and leveraging the computational power, we numerically integrate the Boltzmann equation in the relaxation time approximation.
Speaker: Mr Ernst Grunow (University of Cape Town)
• 10:20
Quantitative Predictions of Heavy Flavor Photon Bremsstrahlung in Heavy Ion Collisions from AdS/CFT 20m
We present quantitative predictions for the spectra of photon bremsstrahlung from heavy quarks propagating through a strongly-coupled quark-gluon plasma using the techniques of AdS/CFT. The spectra are the result of including both drag and diffusion terms in the heavy flavor propagation in the plasma. The predictions show that future experimental upgrades and high-luminosity runs at the Large Hadron Collider at CERN will allow for a quantitative comparison between data and our calculations, providing novel insight into the non-trivial, emergent many-body dynamics of a non-Abelian gauge theory.
Speaker: Dr William Horowitz (University of Cape Town)
• 10:40
Using the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model to extract the thermal conductivity transport coefficient of hadron gas. 20m
Thermal conductivity of hadron matter is studied using a microscopic transport model, which can support the newly Large Hadron Collider (LHC) energy of up to √s = 14 TeV, namely the Ultra-relativistic Quantum Molecular Dynamics (UrQMD). The molecular dynamics simulation is performed for a system of light mesons species (pions, rhos, Kaons) in a box with periodic boundary conditions. Equilibrium state is investigated by studying chemical equilibrium and thermal equilibrium of the system. Particle multiplicity equilibrates with time, and the energy spectra of different light mesons species have the same slopes and com- mon temperatures when thermal equilibrium is reached. Thermal conductivity transport coefficient is calculated from the heat current - current correlations using the Green-Kubo relations.
Speaker: Mr Thendo Emmanuel Nemakhavhani (University of Johannesburg)
• 11:00 11:20
Tea 20m
• 11:20 13:00
Applied Physics
Convener: Dr phil ferrer (wits)
• 11:20
Corrosive Sulphur in Transformers 20m
The failure of many power transformers have been linked to the presence of an additive, Dibenzyl disulphide (DBDS) in transformer oil. The additive degrades the insulation system of the transformer resulting in untimely breakdown. Most studies have focused on laboratory oil testing, however, the interaction between DBDS and the copper windings of the transformer are still not fully understood. We present experimental results that were obtained from monitoring DBDS formation by varying the temperature of an active oil-filled transformer. It was observed that at high temperatures, the DBDS concentration reached equilibrium. The activation energy for the DBDS reacting with copper and the formation of copper sulphide was determined. It was established that a significant amount of the initial concentration of DBDS was needed in order to react with copper. The interaction of DBDS with the copper surface of the windings was also modelled using density functional theory (DFT). The most stable interaction configuration was determined by comparing different adsorption energies. This configuration was the starting point for further DFT analysis. The respective interacting molecule/additive and surface was optimized to allow maximum interaction between the additive and the surface. These results are compared to our experimental results.
Speaker: Ms Sharlene-Asia Naicker (University of KwaZulu-Natal)
• 11:40
Wireless Mesh Data Communications and Reliability Analysis for Anti-theft Application Deployment in Educational Institutions 20m
This research is a continuation of a security application to protect portable computer devices against theft in educational institutions of South Africa. The project is an initiative from the School of Physics with the goal of in-house development of a low-cost anti-theft system where devices require secure communication to a wireless mesh network. Hundreds of thousands of packets were transmitted and logged between interconnected nodes to analyze the quality of the network's service in harsh indoor building environments. Similar methodologies in big data analysis as found in particle physics at the Large Hadron Collider were adopted between multiple point data communications to analyze the network's performance and reliability. Network development is further extended consisting of hardware and software development for transceiving encrypted messages between interconnected nodes using the User Datagram Protocol. Finally, the anti-theft application will focus on proprietary firmware and Android application development to render the device inoperable using the encrypted messaging scheme as a medium for communication to devices. Results thus far indicate reliable data transmissions in noisy indoor environments and between multiple asynchronous transmitting nodes in the network. The distance vector routing algorithm adopted by the Thread networking protocol is simulated to determine hop routing distances between source and destination routers. The results are compared with the network's multipoint data to determine coverage in large geographical areas.
Speaker: Mr Roger van Rensburg (Wits)
• 12:00
Flame retardants in City of Johannesburg EMS fire fighters bunker gear 20m
Fire fighting protective garment (bunker gear) is the main shield that fire fighters use for protection against heat, flame and other hazards during fires. The bunker gear’s thermal protection is enhanced by the addition of flame retardants, which resist ignition and or reduces the rate of fire spread. Initial investigation of the bunker gear used by the City of Johannesburg EMS fire fighter is found to contain brominated flame retardants, that have been found to be harmful to human and the environment and have been banned or restricted in most parts of the world. Five (5) new and three (3) used bunker gears were investigated. X-ray fluorescence (XRF) scanning measurements showed that all the samples contained significant amount of brominated flame retardants. Comparison of the old (used in fire fighting events) and new samples showed no significant difference in brominated flame retardant content. The fire retardants effects of the samples were investigated using the Cone Calorimeter under 50 and 75 kW.m-2 external heat fluxes. Heat release rate, smoke release rate and fire spread measurements on the samples showed low values attributed to the retardants in the bunker gear. The average fire growth rate index (FIGRA) for the samples were found to be 1.88  0.44 kW.s-1 (5 new bunker gear) and 2.63  0.37 kW.s-1 (3 old/used bunker gear) for external irradiation flux of 50 kW.m-2. FIGRA values for external heat flux 75 kW.m-2 were 5.07  1.12 kW.s-1 and 6.17  0.99 kW.s-1 for new and old respectively. In the case of smoke growth rate (SMOGRA), values found were 3.12  0.34 and 4.96  0.59 m2.s-2, respectively for new and used gears under 50 kW.m-2 irradiation and 13.26  3.63 and 14.60  2.37 m2.s-2under 75 kW.m-2 heat flux.
Speaker: Mr Vincent Mokoana (Tshwane University of Technology)
• 12:20
Experimental thermal performance of a domestic latent heat medium temperature storage system during charging 20m
Thermal energy storage (TES) helps alleviate the mismatch between energy supply and demand by using the stored energy during peak demand periods when it is required. The two most appropriate types of TES systems for domestic applications are sensible heat and latent heat TES. Latent heat TES systems have larger thermal energy storage densities as compared to sensible heat TES systems thus reducing the space requirements for TES. An experimental investigation for a domestic latent TES system is presented in this paper. The latent heat TES system consists of a packed bed of encapsulated adipic acid in spherical aluminium spheres. The TES system is charged electrically using Sunflower Oil as the heat transfer fluid (HTF). Charging experiments are done with three different flow-rates (4 ml/s, 8 ml/s and 12 ml/s). Charging results are presented in terms of the HTF temperatures, phase change material (PCM) temperatures, charging energy rates and charging exergy rates. Results show that increasing the flow-rate reduces the temperature difference between the top and the bottom of the storage thus reducing the degree of thermal stratification. This reduction in thermal stratification results in the lowest peak charging energy and exergy rates with the highest flow-rate (12 ml/s). Energy and exergy rate profiles peak and drop for all flow-rates as the temperature difference between the top and bottom of the storage tank reduces as charging progresses. Charging with lowest flow-rate (4 ml/s) shows the best thermal performance and more pronounced phase change characteristics for adipic acid.
Speaker: Mr Katlego Lentswe (NWU)
• 12:40
Analyses of the Pore Structure Formation of Activated Carbon from Compactivation of Plant Biomass Waste for Electrochemical Device Electrodes 20m
The formation mechanism of the porous framework in nanostructured carbon materials is important in a wide variety of applications such as in supercapacitors, gas storage, adsorbents and catalyst supports etc. The accessibility to the pore sites by electrolyte ions and gases are highly determined by the precise synthesis techniques adopted for these materials. As such, biomass waste materials are a good choice for synthesis as they are available in abundance and cheap, while containing high carbon content and giving high specific surface area for electrochemical supercapacitor applications. In this study, activated carbon (AC) was synthesized from renewable plant biomass waste using a chemical vapour deposition (CVD) technique via a pre-hydrothermal conversion step and compactivation along with the fine-tuning of key growth parameters, such as activating agent and carrier gas. The textural, structural and morphological features were investigated by the Brunauer-Emmett-Teller (BET) technique, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Scanning/Transmission electron microscopy (SEM/TEM) characterization. The material tested in a three-electrode configuration exhibited electric double-layer capacitor (EDLC) behaviour in different electrolytes and working comfortably in KNO3 electrolyte in both negative and positive operating widow of 0.80 V. The results from this study provide the pathway into designing hierarchically porous materials from cheap and sustainable sources suitable in high power energy storage devices.
Speaker: Mr Tjatji Tjebane (Necsa/UP)
• 11:20 13:00
Astrophysics: Cosmology / Dark Matter
Conveners: Prof. Christo Venter (North-west University, Potchefstroom Campus) , Mr Geoff Beck (University of Witwatersrand)
• 11:20
Dark Matter gets DAMPE 20m
The Dark Matter Particle Explorer (DAMPE) satellite mission recently announced an excess is the observed electron/positron spectrum occurring around the TeV scale. This has been conjectured to be explicable in terms of the annihilation of a heavy leptophilic WIMP particle. Additionally, this hypothesis requires the presence of a dense clump of dark matter within 1 kpc of the Earth, in order for the required WIMP annihilation cross-section to fall into territory that is largely unconstrained by experiments like Fermi-LAT. We will explore the astrophysical consequences of this model, the impact of current data on its parameter space, the observability of the conjectured dark matter clump, and the projections for up-coming experiments like KM3NET. We confirm the inability of Fermi-LAT to probe the required parameter space and show that the LOFAR array is well positioned to hunt for the nearby dark matter clump in radio frequencies and that KM3NET can deeply probe the muon coupling of such a dark matter model.
Speaker: Dr Geoff Beck (University of Witwatersrand)
• 11:40
Did Dark Matter Kill the Dinosaurs? 20m
Potential links between astrophysical sources, such as gamma ray bursts and supernovae, and mass extinction events on Earth are of interest in the historical trajectory of life on our planet. There are strong arguments to suggest that these astrophysical sources can have several destructive effects, including depletion of atmospheric ozone and an increase in the radiation dose received by living organisms. Recently, the possibility of galactic Dark Matter (DM) clumps having an affect life on Earth has been of some interest in the literature. In this work, it is shown that when the Earth passes through clumpy DM composed of WIMPs, there is an equivalent dose of ~15.9 μSv imparted to organic tissue when the WIMPs are treated as mutagenic radiation. There will also be an increase to the internal heat flow of the Earth of as much as ~3700 TW, leading to increased flood-basalt volcanism. It is also shown that when a clump of DM with ~1 M passes through the solar system, the annihilation and decay of WIMPs can produce a gamma ray flux strong enough to deplete parts of the ozone layer. If WIMPs are found to be a major constituent of DM, these effects (or a combination thereof) could provide an explanation for mass extinction events on Earth.
Speaker: Mr Michael Sarkis (University of the Witwatersrand)
• 12:00
Fast algorithm for the computation of the CMB polarization <i>TE</i> power spectrum using non-circular beam 20m
A precise measurement of the Cosmic Microwave Background (CMB) anisotropy has been one of the foremost concerns in modern cosmology as it provides a valuable information on the cosmology of the Universe. The estimation of the CMB power spectrum is complicated by different systematics. For the polarization experiments, the signals are rather fainter in comparison with the CMB total intensity, which may lead to an important bias in the estimation of the angular power spectrum. One of the most important source of bias in CMB polarization experiment is the beam asymmetry. We present a semi-analytical framework using the pseudo-Cl estimator to compute the power spectrum TE of the temperature anisotropy and the E-component of the polarization radiation field using non-circular beams. We assume that the beam is non-rotating. We adopt a model of beams obtained from a perturbative expansion of the beam around a circular (axisymmetric) beam in harmonic space. We compute the resulting bias matrix which relates the true power spectrum with the observed one by using an efficient algorithm for rapid computation. We show that for a multipole up to lmax=500, the bias matrix can be computed in less than one second with a single CPU processor at 2.53 GHz. We find that the systematic effect induced by the beam asymmetry in the temperature and polarization power spectrum at the peak of the bias matrix for the WMAP and Planck experiments can be as large as a few 10 to 20%.
Speaker: Dr Fidy Andriamanankasina Ramamonjisoa (University of the Free State)
• 12:20
Probing Quantum Gravity through the Radio and Gamma Regimes 20m
What is the fate of a collapsing star? One possibility is that they evaporate due to Hawking radiation. The problem with this decay channel is that this perturbative phenomenon takes place on time scales far too large to be of astrophysical concern. We consider the exciting and exotic proposal of Planck stars put forth by Carlo Rovelli and others which posits new ways of probing quantum gravity using radio and gamma astronomy. It also provides an alternative end point for black holes. A Planck star is the end result of a collapsing star that forms a black hole but does not ever reach the singularity at r = 0. Instead the matter that had collapsed into the black hole is released in an explosion as the black hole quantum tunnels to a white hole. This tunneling process is similar to that which triggers nuclear decay. These Planck stars are modelled using primordial black holes, at least those of interest to us, since they will be exploding today. Larger black holes will only be exploding at times larger than the Hubble time. We study two primordial black hole models and compare whether, given certain assumptions about the spectrum of an exploding black hole, these models might lead to reasonable observations in the radio and gamma regime. We then discuss whether the proposal by Rovelli, that these signals may correspond to fast radio and gamma ray bursts, is plausible.
Speaker: Mr Geoff Beck (University of Witwatersrand)
• 12:40
Shear-free Dust Cosmological Models in Gravitational Scalar-Tensor Theories 20m
Theoretical physics in general and cosmology in particular have faced some challenges due to the recent observations in cosmology and astronomy, such as the discovery of the accelerated cosmic expansion and the existence of dark matter and dark energy. Einstein’s theory of General Relativity (GR) together with the standard model of cosmology fall short of giving any explanations for these problems. Higher-order gravitational theories such as f(R) and scalar-tensor theories of gravity have been suggested to provide an answer to these shortcomings. In this work, we investigate the cosmological implications of such theories such as the background expansion history as well as the evolution of cosmological density perturbations. We present the equivalence between f(R) and scalar-tensor theories of gravity. Although GR is a generalization of Newtonian gravity in the presence of strong gravitational fields, there is no properly defined Newtonian limit of GR on cosmological scales. Recently, general relativistic quasi-Newtonian cosmologies have been studied in the context of large-scale structure formation and nonlinear gravitational collapse in the late-time universe. This despite the general covariant inconsistency of these cosmological models except in some special cases such as the spatially homogeneous and isotropic, spherically symmetric, expanding FLRW spacetimes. f(R) models have been shown to exhibit more shared properties with Newtonian gravitation than does GR. We investigate the existence and integrability conditions of quasi-Newtonian cosmological spacetimes of classes of shear-free cosmological dust models with irrotational fluid flows in the context of scalar-tensor theories of gravity. We also derive the covariant density and velocity propagation equations of such models and analyse the corresponding solutions to these perturbation equations.
Speaker: Ms Heba Abdulrahman (North-West University)
• 11:20 13:00
Convener: Dr Iyabo Usman (WITS)
• 11:20
Performance of missing transverse energy reconstruction in pp collisions at 13 TeV in the diphoton channel with ATLAS 20m
A good measurement of missing transverse energy (MET) is pre-eminent for many searches for new physics carried out by the ATLAS experiment at the LHC. The measurement of MET in the ATLAS detector makes use of the full event reconstruction and a calibration based on reconstructed physics objects. The performance of MET reconstruction is evaluated using data collected in proton-proton collisions at a centre-of-mass energy of 13 TeV in Run 2 of data taking in the diphoton channel. Regrettably, these high luminosities achieved lead to undesirable backgrounds due to additional proton-proton collisions occurring at the same bunch crossing as the collision of interest (pile-up). As a result of this downside, several methods have been implemented in an effort to alleviate the effects of pile-up on the reconstruction and performance of MET. Some of these methods and the consequent performance of MET reconstruction at ATLAS in events with two photons are deliberated.
Speaker: Ms Shell-may Liao (University of the Witwatersrand, School of Physics, 1 Jan Smuts Avenue, Braamfontein, Johannesburg, 2000, South Africa”)
• 11:40
Mitigating the effect of fake missing energy using Machine learning in the ATLAS experiment 20m
The missing transverse momentum in the ATLAS experiment is the momentum imbalance in the plane transverse to the beam axis. That is the resultant of the negative vectorial sum of the momenta of all particles that are involved in the proton-proton collision. A precise measurement of the missing transverse energy is essential for many physics studies at the LHC, such as Higgs boson measurements and dark matter search. The result presented in this study are from the implementation of Boosted Decision tree (BDTs) based on vertex variables and fake/real missing samples. The preliminary results show the BDTs classifiers can improve signal purity to about 50% as compared to the nominal selection.
Speaker: Mr Kehinde Tomiwa (University of the Witwatersrand)
• 12:00
Event Selection and Signal Optimization of Three-Lepton and $b$-jets Search in ATLAS 20m
A study is performed to investigate the phenomenological signatures of additional scalar bosons at the LHC. This talk summarizes an overview of the ATLAS detector results for events observing excesses in multi-lepton events with three-leptons and at least two b-jets and number of jets, two and three. The channel investigated is that of $A \rightarrow ZH[250] \rightarrow Z(\rightarrow\ell^{\pm}\ell^{\mp}) + hh, SS, Sh(\rightarrow b\bar{b}, VV)$, The final state is a very clean signature with low expected background processes. In the CMS measurement of the cross section for top quark pair production in association with a $W$ or $Z$ boson in proton-proton collisions at 13~TeV, the production in three-lepton channels for the expected and the observed significances is found to be in excess of 5 standard deviations. This further enforces the high interest in performing multi-lepton with $b$-jet searches. The strategy of the event selection is described in this talk and leads to the signal optimization strategy.
Speaker: Mr Lebohang Mokoena (University of the Witwatersrand)
• 12:40
Signal and background ATLAS Monte Carlo Comparison studies in the H→ZZ→4l Channel. 20m
The search for new heavy particles in the H→ZZ→4l decay channel represents one of the most promising searches in High Energy Physics. This study focuses on the hadronic properties of this channel which leads to the final state consisting of four isolated leptons plus at least two light flavor jets. gg→H signal and qq→ZZ background studies using High mass (m4l > 140 GeV) ATLAS Monte Carlo samples with different pile-up conditions are conducted. Comparisons of the shapes of the distributions are made between two sets of qq→ZZ background as well as two sets of gg→H (m4l = 200 GeV) signal Monte Carlo samples. Expected yields in each of the two sets of qq→ZZ background and signal efficiencies in each set of the gg→H signal Monte Carlo samples are also calculated and compared.
Speaker: Mr Mzwandile Thabede (University of the Witwatersrand)
• 11:20 13:00
Photonics: Lasers and Optics
Convener: Dr Pieter Neethling (Laser Research Institute, University of Stellenbosch)
• 11:20
Output power stability of an all-fibre Erbium doped fibre laser 20m
Stable and single-longitudinal-mode Erbium-doped fiber ring lasers (EDFRLs) have been studied intensively due to their wide range application in field like optical communication and fiber sensors. Because of the fiber vulnerability to perturbation of temperature and vibration, it has been demonstrated that the output power of the conventional fiber ring lasers are unstable. In this report, the output power and stability of a narrow linewidth Erbium-doped fiber ring lasers as a function of the laser parameters was experimentally investigated. The fiber laser configuration include two narrow spectral bandwidth optical filters namely, fiber Bragg grating and fiber Fabry-Perot tunable filter. Without changing the basic scheme of the fiber laser, the study focuses on the optimization of key parameters of the fiber laser cavity namely, Erbium-doped fiber length, pump power, output coupling ratio and Erbium ions concentration. We have demonstrated that the output power as well as the power stability of the fiber laser increase as the output coupling ratio increase. The maximum power fluctuation of the output power of 7.52 %, corresponding to 0.24 dB is observed for 10 % output coupling. The power stability of 0.71 % and 0.8 % were observed for 80 % and 90 % coupling ratio respectively. To improve the power stability we have introduced 1.5 m umpumped Erbium-doped fiber into the fiber laser system. A stable output power was obtained for all coupling ratio during a measurement period of 120 min.
Speaker: Mr jean jacques monga kaboko (university of johannesburg)
• 11:40
Vector vortex beams through amplifiers 20m
Vector beams are spatial modes of light in which the polarization and spatial degree of freedom are inseparable. Such beams have widely been used in applications ranging from optical tapping and tweezers to optical communications. Yet, these vector beams have been only generated in low power due to limitation in the tools used to generate them. Here, we show the amplification of vector beams through birefringent amplifier. Since the beam purity is important key that determines the efficiency of the beam in specific applications. We measured the perturbation of the vector beam purity throughout the amplification process. Our result shows that the purity of the vector beams can be modified while increasing the power which is a significant step toward the high brightness lasers.
Speaker: Ms Hend SROOR (University of The Witwatersrand)
• 12:00
Spontaneous Parametric Down-Conversion Beam Shaping 20m
Spontaneous parametric down-conversion (SPDC) has been (and continues to be) a very popular mechanism for generating entangled biphotons for applications in fields ranging from quantum key distribution and quantum computing to quantum imaging. In a nutshell, if ones impinges a crystal (characterised by a nonlinear, second-order susceptibility tensor) with a pump photon, there is a small probability that the crystal will spontaneously down-convert the pump photon into 2 new photons (called signal and idler photons) subject to conservation of energy. There are other conserved quantities as well, notably orbital angular momentum (OAM). It has been observed that the OAM of the signal and idler photons violate Bell's inequality and so SPDC can be used to generate entangled biphotons in the OAM degree of freedom. Typically, one only observes entanglement in a 2-dimensional OAM subspace. We study whether it's possible to engineer arbitrary entangled qudit states by changing the spatial profile of the pump beam.
Speaker: Mr Jonathan Pinnell (University of the Witwatersrand)
• 12:20
Observation of local entanglement oscillation in free space 20m
It is well known that the entanglement of a quantum state is invariant under local unitary transfor- mations. It dictates, for example, that the degree of entanglement of a photon pair in a Bell state remains maximally entangled during propagation in free-space. Here we outline a scenario where this paradigm does not hold. Using local Bell states engineered from classical vector vortex beams with non-separable degrees of freedom, so-called classically entangled states, we demonstrate that the en- tanglement evolves during propagation, oscillating between maximally entangled (purely vector) and product states (purely scalar). We outline the theory behind these novel propagation dynamics and confirm the results experimentally. Crucially, our approach allows delivering a tunable degree of local entanglement to a distant receiver by simply altering a modal phase delay holographically, or, in essence, a tractor beam for entanglement. This demonstration highlights a hitherto unnoticed property of classi- cal entanglement and offers at the same time a device for on-demand delivery of vector states to targets, e.g., for dynamic laser materials processing as well as switchable resolution within STED systems.
Speaker: Dr Carmelo Rosales-Guzman (University of the Witwatersrand, Johannesburg)
• 12:40
Generating high quality spatial modes of light at a high rate 20m
Digital micro-mirror devices (DMDs) are composed of arrays of micro-mirrors that are able to reflect incident light in ways based on the binary operational state of each mirror. Traditionally used in digital light processing, its importance in research aspects has increased. The operational states of the mirrors make the DMD an amplitude-only light modulating device at high speeds, insensitive to polarisation states and significantly cheaper compared to traditional liquid crystal spatial light modulators. We have employed a DMD to create and switch between different modes of light at a rate of 400 Hz, and as such demonstrated arbitrary control of the amplitude and phase of light. We show a high quality in the generated beams, with correlation factors of more than 90\%.
Speaker: Mr Ravin Kara (University of the Witwatersrand)
• 11:20 13:00
Physics Education
• 11:20 13:00
Physics of Condensed Matter and Materials
Convener: Dr Deon Marais (The South African Nuclear Energy Corporation (Necsa))
• 11:20
Cation distribution and mixing thermodynamics in Li(Mn<sub>1-x</sub>Ni<sub>x</sub>)O<sub>4</sub> spinel via tuning of the Ni concentration 20m
Spinel LiMn2O4 is a promising cathode material for secondary lithium-ion batteries which, despite its high average voltage of lithium intercalation, suffers crystal symmetry lowering due to the Jahn-Teller active six-fold Mn3+ cations. LiMn2 O4 is a low-cost, environmentally friendly, and highly abundant material used as a cathode in Li-ion batteries. Although Ni has been proposed as a suitable substitutional dopant to improve the structural and mechanical stability of LiMn2O4 and enhance the average lithium intercalation voltage, the thermodynamics of the Ni incorporation and its effect on the electrochemical properties of spinel LiMn2O4 is not known yet. In this paper we have implemented two approaches; the cluster expansion which determined stable multi-component crystal structures and ranks metastable structures by the enthalpy of formation, while maintaining the accuracy of first-principles density functional methods. In the second approach we employed density functional theory calculations with a Hubbard Hamiltonian (DFT+U) to investigate the thermodynamics of mixing of the Li(Mn1-xNix)O4 solid solution. The results suggest that LiMn1.5Ni0.5 O4 is the most stable composition at temperatures ranging from room temperature to 1000K. The configurational entropy is much lower at low temperatures. It was also found that the mechanical properties of Ni-doped LiMn2O4 are stable at 0K. The calculated maximum average lithium intercalation voltage was found to be 4.8 V for LiMn1.5Ni0.5O4 composition and is in agreement with the experimental value of 4.7 V. The temperature was found to have a negligible effect on the Li intercalation voltage of the most stable composition.
Speaker: Mr kemeridge Tumelo Malatji (University of Limpopo)
• 11:40
Fluence enhanced optical response of ion implanted stripper foil carbon thin films 20m
Silver nanoparticles (NPs) are known to exhibit a strong interaction with light because the conduction electrons on the metal surface undergo a collective oscillation once excited by light at specific wavelengths; the so-called surface plasmon resonance (SPR). However, their incorporation into amorphous carbon is shown to greatly influence the overall optical response of the nanomaterial due to aggregation of the NPs in the host amorphous carbon. In this paper, we studied the optical response of silver irradiated amorphous carbon films due to varying fluence of the NPs. Stripper foil amorphous carbon films were irradiated by 25kV Ag ions at different fluences ranging from 2.5 to 3.4 x 1016 ions/cm2. Optical absorption studies revealed that the SPR of Ag NPs on quartz substrate occurs at wavelength ⁓410 nm but shows a blue shift (⁓60 nm) in the irradiated film with increasing ion fluence up to 3.4 x 1016 ions/cm2. Transmission electron microscopy (TEM) was used to investigate the particle size and aggregation. The blue shift response in plasmonic wavelength is explained with respect to the increase in particulate density due to increasing fluence of irradiation as confirmed by TEM.
Speaker: Mr Abdulsalam Ismaila (WITS)
• 12:00
Analysis of Nd3+ concentration on the structure, morphology and photoluminescence of sol-gel Sr3ZnAl2O7 nanophosphor 20m
Neodymium activated strontium zinc aluminate (Sr3ZnAl2O7:x%Nd3+) nanophosphor was synthesized using the sol-gel technique whereby the Nd3+ concentration was varied in the range 0 ≤ x ≤ 2. The effect of Nd3+ concentration on the structure, particle morphology and photoluminescence properties of Sr3ZnAl2O7 were investigated. The X-ray diffraction (XRD) results revealed that all samples resembled the mixture of both ZnAl2O4 and Sr3Al2O6 cubic structures. Nd3+ doping influenced the crystallite sizes of the prepared phosphor materials. The energy dispersive X-ray spectroscopy (EDS) results confirmed the presence of all expected elements in the composition. Scanning electron microscopy (SEM) revealed that as the Nd3+ concentration increased the surface morphology changed to smooth mountain like structures. The ultraviolet-visible (UV-Vis) diffuse reflection spectroscopy showed that the band gap of Sr3ZnAl2O7 can be tuned from 2.74 to 2.95 eV by increasing the Nd3+ concentration. When the host is excited above the bandgap (374 nm), broad emission attributed to defects occurs with the maximum near 585 nm. Doped samples excited in this manner do not exhibit additional luminescence due to the Nd3+ ions, but in contrast there is a small dip in the defect emission band near 585 nm due to absorption attributed to Nd3+ ions. Characteristic infrared emissions of Nd3+ ions at 885, 1064 and 1340 nm were observed by directly exciting the Nd3+ ions at 585 nm (4I9/2 → 5G5/2+2G7/2) and were attributed to 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 transitions, respectively. The Commission Internationale de l’Eclairage (CIE) coordinates results showed that the emission colour cannot be tuned by varying the Nd3+ concentration.
Speaker: Mrs Motlalepula Rebecca Mhlongo (Sefako Makgatho Health Sciences University)
• 12:20
La<sup>3+</sup> doped ZnO nanofibers obtained through electrospinning: Influence of La<sup>3+</sup> doping concentration on the structural, optical and gas sensing properties 20m
ZnO has been used as a gas sensing material for different reducing and oxidizing gases, however; poor sensitivity and slow response and recovery times are hindering its commercial application. Doping of ZnO with different metallic ions such as rare earth and noble metals have proven to be one of the efficient ways of modifying its gas sensing performance. In this study, ZnO nanofibers with different La3+ doping concentration (0, 0&#1831, 0&#1833 and 0&#1835 wt.%) were successfully obtained through electrospinning and subsequent annealing at 500 &#176C. The effect of La3+ concentration on the structural, morphological, surface area and optical properties were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) and Photoluminescence (PL) spectroscopy. XRD results revealed a single phase of hexagonal wurtzite ZnO that showed poor crystallinity, shifted peaks to higher two theta and changes in lattice parameters with La3+ doping, confirming the substitution of Zn2+ by La3+ in the ZnO lattice. Morphological studies revealed fibers structures that were made of tiny particles of ̴20-40 nm adjoined together and no change in morphology was induced by the La3+ doping. BET indicated that the surface area of ZnO was improved by La3+ doping. The PL emissions quenched with increasing La3+ concentration. Gas sensing performance of these samples to different test gases was performed at different temperatures ranging from room temperature to 400 &#176C at different gas concentrations ranging from 5-100 ppm.
Speaker: Ms Katekani Shingange (CSIR/UFS)
• 12:40
Colloidal Synthesis of Molybdenum Diselenide Nanomaterials for Supercapacitor Applications 20m
Molybdenum diselenide(MoSe2) is a layered material that has attracted a lot of interest in the scientific community; the 2D nanomaterials derived from the bulk crystals of these materials have been found to have exceptional electronic and optical properties. These properties include a high surface to volume ratio, high carrier mobility, relatively high stability and a band-gap in the visible region of the electromagnetic spectrum. One possible application for these materials is as electrode materials in supercapacitors. Supercapacitors are energy storage devices that have high power densities, high cycle stability, large operational temperature range and a higher energy density than conventional capacitors. Unfortunately, these devices suffer from low energy densities compared to batteries. To circumvent this major drawback nanomaterials are being explored as alternatives to activated carbon for use as electrode materials in supercapacitors. In this work a novel colloidal synthetic method has been developed to synthesize 2H hexagonal phase MoSe 2 nanomaterials with a nanosheets and nanoflower morphology for supercapacitor applications. The electrochemical performance of the two morphologies were compared to determine the best suitable MoSe2 nanomaterials morphology for the application. The MoSe2 nanomaterials displayed electric double capacitance. The specific capacitance of the MoSe2 nanosheets and nanoflowers was determined to be 30 Fg-1 and 81 Fg-1 respectively. The impedance MoSe2 nanosheets and nanoflowers was determined to be 57.1 Ω and 34.0 Ω respectively. The nanoflowers morphology has superior electrochemical performance because the 3D interconnected nature of the nanoflowers gives them higher surface area and pore volume.
Speaker: Mr Zakhele Ndala (Wits university)
• 11:20 13:00
Space Science
Convener: Prof. Michael Kosch (SANSA)
• 11:20
Modelling the acceleration of energetic particles at travelling heliospheric shocks 20m
Propagating shocks are observed to form ahead of the solar material expelled into interplanetary space following coronal mass ejections (CMEs). During the passage of these CME-driven shocks, spacecraft often observe energetic particle enhancements commonly associated with particle acceleration. In this study, the acceleration of energetic particles at halo-CME-driven shocks is investigated, with a particular focus on the acceleration of particles from the suprathermal solar wind (SW). A set of stochastic differential equations, derived from the Parker transport equation and including the effects of diffusive shock acceleration (DSA), is solved numerically to model this process. The SW particle velocity distribution is described by a Kappa distribution in the solar wind frame and prescribed as a source function at the shock. The injection energy is calculated from first principles, but can also be changed to investigate the effect thereof on model solutions. With the further application of physically representative transport coefficients, the model results are presented and their accuracy evaluated against how well they reproduce observations of protons and heavier ions during selected shock passage events. The results illustrate the significance of the DSA mechanism in accelerating energetic particle populations in the near-Earth environment.
Speaker: Mr Phillip Prinsloo (Centre for Space Research, North-West University)
• 11:40
Towards an ab initio model for the radiation dose rate of cosmic rays on and near various planetary surfaces is our solar system: solar cycle-dependent modulation of galactic cosmic-ray intensities 20m
With the advent of commercial space travel and the proposed colonization of Mars and other planets, it has become even more important to study the cosmic ray radiation environment on, and near the surface of these bodies, in order to plan for future manned missions. Galactic cosmic rays, with a well-known 11 year cycle pose the primary radiation risk. Solar energetic particles that are frequent during solar maximum periods are sporadic and highly variable in terms of intensities, are a secondary radiation risk. In this study we explore an approach to model cosmic-ray radiation based on spacecraft data inputs and existing models for galatic cosmic rays, which will have implications for the future modelling of solar energetic particle transport as well.
Speaker: Mr KATLEGO MOLOTO (NORTH WEST UNIVERSITY)
• 12:00
Investigate ionizing radiation in the troposphere using ground-based neutron monitor, ACE/DSCVR satellite and RBSP satellite data for aviation radiation forecasting. 20m
The aviation altitude is continuously bombarded with high-energy ionizing cosmic radiation. The two main sources of ionizing radiation at the aviation altitude are the omnipresent background galactic cosmic rays which originate from outside our solar system and the transient solar energetic particle events which are associated with space weather events such as solar flares and coronal mass ejections. The passengers and aircraft crew are exposed to high-energy ionizing cosmic radiation during the flight. In this work, we will investigate the correlation between Neutron Monitor counts rates and solar wind speed and proton density from the Advanced Composition Explorer (ACE) satellite, as well as Neutron Monitor count rates and radiation belt density from the Radiation Belt Storm Probes (RBSP) satellites, during the coronal mass ejection (CME) events and quiet time. If the correlation exists, then it may be possible to use Neutron Monitor data in the future for the forecast the timing and level of ionizing radiation in the troposphere.
Speaker: Mr Golekamang Thaganyana (South Africa National Space Agency)
• 12:20
High Altitude Radiation Monitor (HARM) 20m
Speaker: Mr Godfrey Moshe Mosotho (.)
• 12:40
Including Variometers in Geomagnetic Field Interpolation 20m
One of the best tools we have in geophysical modelling is the ability to interpolate the horizontal geomagnetic field at the surface of the Earth. This is especially useful in regions, such as southern Africa, where there is a sparse array of absolute magnetometers available for geomagnetic field measurements. In terms of geomagnetic field interpolation, the spherical elementary current systems (SECS) spatial interpolation scheme has shown to be very successful, and the planar approximation of this method adequate for modelling at mid-latitudes. The SECS interpolation scheme is physics based, making use of the Biot-Savart law and equivalent ionospheric currents to interpolate measured geomagnetic field data. As with most interpolation methods, more data points result in lower error. Therefore, we adapt the SECS method to work with variometers. These instruments measure variations in magnetic field and are more abundant in southern Africa. Merging the two resulting interpolated datasets, the initial absolute geomagnetic field interpolation can be significantly improved. This improved interpolation scheme is incredibly useful locally where a sparse magnetometer array is a challenge, but can be applied just as effectively in other cases across the globe where there are numerous magnetometers and variometers available.
Speaker: Mr Michael Heyns (UCT/SANSA)
• 11:20 13:00
Theoretical and Computational Physics
Convener: Dr Konstantin Zloshchastiev (Durban University of Technology)
• 11:20
Bose Einstein Condensation from a Gluon Transport Equation 20m
We present a novel numerical scheme to solve the QCD Boltzmann equation in the small-scattering angle approximation, for the quenched limit of QCD. Using this we can investigate the evolution of spatially homogeneous systems of gluons distributed isotropically in momentum space. We numerically confirm results of Blaizot et al, in particular that for certain “overpopulated” initial conditions, a transient Bose-Einstein condensate emerges during equilibriation in a finite time. We further analyse the dynamics of the formation of this condensate. The scheme can be extended to systems with cylindrically symmetric momentum distributions, in order to investigate the effects of anisotropy. In particular we compare the rates at which isotropization and equilibriation occur. We also compare our results from the small-scattering angle scheme to the relaxation-time approximation.
Speaker: Mr Brent Harrison (University of Cape Town)
• 11:40
QCD Boltzmann Equation: Beyond the Soft-Scattering Approximation 20m
Using the case study of a spatially homogeneous many-gluon system, distributed isotropically in momentum space, we will investigate more thoroughly than in the existing literature the evolution of a hot (quark-) gluon plasma from an initial state towards equilibrium. To that end we will investigate the QCD Boltzmann Equation beyond the popular soft-scattering approximation, thereby shedding light on the applicability of previous results in the field.
Speaker: Ms Nicole Moodley (University of Cape Town)
• 12:00
Fluctuating Open Heavy Flavour Energy Loss in a Strongly Coupled Plasma 20m
Heavy ion collisions at RHIC and at the LHC produce an enormous amount of energy that enables the nuclei and its constituent particles to melt, thus releasing gluons, quarks and antiquarks, travelling in different directions with different momenta. Studies of these collisions have shown that low transverse momentum observables describe a strongly coupled plasma (quark-gluon plasma), an almost perfect liquid that evolves hydrodynamically and flows with almost no viscosity. Focusing on observables related to high mass and high momentum particles, we numerically integrate the Langevin equation that describes the motion of unbound heavy quarks propagating in a strongly-coupled quark-gluon plasma. We present predictions for the suppression of the heavy flavor mesons that these heavy quarks decay to; we show that these predictions are in good agreement with experimental data. We outline future valuable measurements that will provide a vital consistency check for the assumed dynamics of the strongly-coupled quark-gluon plasma.
Speaker: Mr Blessed Ngwenya (University of Cape Town)
• 12:20
Theoretical and Computational Physics Division Meeting 40m
Speaker: Prof. Alan Cornell (NITheP)
• 13:00 14:00
Lunch 1h Centenary Complex

### Centenary Complex

• 13:00 14:00
WiPiSA lunch Scaena

### Scaena

Convener: Dr Buyi Sondezi (University of Johannesburg)
• 13:20
South African Women in Physics- Progress 20m
The landscape of Women in Physics in South Africa has change dramatically since launch of WIPISA in 2005. PhD graduates have increased with at least one female staff member in various institutions and research centres.Research groups led by female professors are visible but few. While there is such progress, women are still found to occupy invisible positions in their institutions and some get completely lost. This presentation will show the statistical progress and possible solutions to visible issues.
Speaker: Dr Mmantsae Diale (University of Pretoria)
• 14:00 15:20
Applied Physics
Convener: Dr Shukree Wassin (student)
• 14:00
Applied Physics Division Meeting 40m
Speaker: Dr phil ferrer (wits)
• 14:40
Synthesis of MXene nanoribbons with Onion-like carbons for supercapacitors 20m
A new family of 2D materials called MXenes have recently been discovered, which can be synthesized from MAX phases via chemical etching of the A group elements. The properties of MXenes can be tuned by changing their terminal functional groups, and they further allow for the easy creation of thin films, increasing their versatility. Their 2D structure allows for fast redox reactions at their surface, which creates an excellent candidate for supercapacitor electrode material for high power density applications. We doped Ti2C with onion-like carbons, a material known for excellent conductivity and highly accessible surface area, and studied its physical properties as a cathode for applications in supercapacitor storage. We will further comment on its applicability in conjunction with photovoltaic panels.
Speaker: Mr Irfan Habib (Wits University)
• 15:00
Effects of Ion Implantantion on Energy Storage Properties of Bulk Molybdenum Disulphide 20m
We report the effects of implanted molybdenum and tungsten ions on the capacitance of electrodes made from bulk molybdenum disulphide (MoS2). Six samples of crystalline MoS2, were modified by ion implanted. Three samples with Mo ions and three with W ions, at varying fluences and an acceleration voltage of 10 keV. The ion implantation process first simulated using the Stopping and Range for Ions in Matter (SRIM) software. This provided us with the simulated defect density in terms of vacancies and ion penetration depth. Raman Spectroscopy (RS) and Photoluminescence (PL) Spectroscopy have been used to give some insight into vibrational and optical properties respectively, before and after the ion implantation. Pseudocapacitance properties, specific capacities, performance and stability of the electrodes were measured using Electrochemistry techniques. Coulombic efficiencies, retention capabilities as well as the knee frequencies are measured as well. All our modified electrodes showed remarkable improvement on performance, especially in terms of specific capacity and % capacitance retention after 1000 cycles of charge and discharge, with reference to the pristine (as received) MoS2 electrodes.
Speaker: Mr Patrick Mwonga (University of the Witwatersrand)
• 14:00 15:20
Astrophysics: Gamma-ray / Multi-wavelength Astronomy II / Non-specialist Talk
Convener: Prof. Christo Venter (North-west University, Potchefstroom Campus)
• 14:00
Spectral and Morphological Fitting of Young Pulsar Wind Nebulae using a Markov-Chain-Monte-Carlo Procedure 20m
We present results from a spatio-temporal leptonic emission code that models the spectral energy distribution (SED) from and the radiation spectrum at different positions in a pulsar wind nebula (PWN). The model includes a time- and spatially-dependent magnetic field, spatially-dependent bulk particle speed implying convection and adiabatic losses, diffusion, as well as radiative losses and can predict the SED, surface brightness vs. radius and thus the nebular size as function of energy. We apply the code to PWN G0.9+0.1 and a fit for both the SED and PWN size as a function of energy. We use a Markov-chain-Monte-Carlo (MCMC) method to find not only the best fit but also errors on these best-fit model parameters. We will investigate the error behaviour when only fitting the SED vs. concurrently fitting both the SED and energy-dependent size. Our model will contribute to interpreting results by the future Cherenkov Telescope Array (CTA) that will yield many more morphological details.
Speaker: Carlo van Rensburg (North West University Potchefstroom)
• 14:20
Modelling the polarisation signatures detected from the first white dwarf pulsar AR SCO. 20m
Marsh et al. (2016) detected radio and optical pulsations from the binary system AR Scorpii(AR Sco). This system, with a orbital period of 3.55h, is composed of a cool, low-mass companion star and a white dwarf with a spin period of 1.97min. Optical observations by Buckley et al. (2017) showed that the polarimetric emission from the white dwarf is strongly linearly polarised (~ 40%) with periodically changing intensities. This periodic emission is thought to be powered by the highly magnetised (5*108 G) white dwarf that is spinning down. The morphology of the polarisation signal is similar to that seen in the Crab pulsar. All these observations plus the lack of any obvious sign of accretion lead us to believe that this is the first observed white dwarf pulsar, bringing a lot of excitement to the field of pulsar physics. A next step is to investigate if known neutron star pulsar models are applicable to describe the white dwarf pulsar's polarimetric signatures. We applied the Rotating Vector Model (RVM; Radhakrishnan and Cooke 1969) to model the polarisation swing of the white dwarf pulsar. We also conducted a parameter study using a Markov chain Monte Carlo method, making it possible to constrain the magnetic inclination angle &alpha and the impact angle &beta = &zeta - &alpha, with &zeta the observer angle. Here, we present first results of such constraints. In the future, we will apply more detailed models to the polarisation swing data.
Speaker: Mr Louis Du Plessis (NWU, Potchefstroom, Department of Physics)
• 14:40
Non-specialist talk: GW170817 - The South African Perspective 40m
The joint detection of a gravitational-wave event from a binary-neutron-star merger, GW170817, by LIGO/VIRGO and a short gamma-ray burst, GRB170817A, by Fermi-GBM and INTEGRAL, ushers in a new era of true multi-messenger astronomy. It triggered the most intensive, world-wide multi-wavelength follow-up observing campaign ever conducted to date, involving almost 3,700 astronomers around the world. This talk will review the observations of this event, highlighting the contributions by southern African observatories (e.g., H.E.S.S., SALT, MeerKAT). These will be put into the broader context of recent developments in multi-messenger astronomy, including the possible association of high-energy neutrinos detected by IceCube, with flaring gamma-ray sources. Future prospects for multi-messenger astronomy and the Southern African involvement in these exciting developments will be discussed.
Speaker: Dr Markus Bottcher (North-West University)
• 14:00 15:20
Convener: Dr Pete Jones (iThemba LABS)
• 14:00
ATLAS Monte Carlo studies for the search of heavy resonances in the H->ZZ->4l decay channel. 20m
The search of a heavy resonance denoted H, decaying into four-leptonic final states through a pair of Z bosons is discussed. This study mainly focuses on the high mass region of the H->ZZ->4l decay channel with the ATLAS detector. Two different sets of signal Monte Carlo (MC) samples produced with different pileup conditions were studied for the gluon-gluon fusion production mode. For the MC comparisons, signal efficiency studies are presented at selected mass points. Also, shape comparisons of selected mass and kinematic (H, Z, leptons) variables were performed at the same time.
Speaker: Mampionona Ralaimiaramanana RAJAOFERASON (Wits-University of Witwatersrand)
• 14:20
Electrons inside jets in ATLAS: not an isolated problem 20m
The standard electron and jet reconstruction processes in ATLAS happen independently, as a result energy deposits from electrons in Electromagnetic calorimeter often end up reconstructed as a jet close to the electron. Also, real jets can end up being reconstructed as a "fake" electron. Therefore, an overlap removal procedure is applied during analysis in ATLAS, where a jet close to an electron is removed as a physics object, and further if the electron has any more jets closer to it, the electron is discarded. This procedure results in using electrons which is isolated from nearby hadronic activity. In fact, even during the reconstruction of the electron, some isolation from hadronic activity is demanded. Where for most of the scenarios, this works as intended, there are situations when this causes a problem. For example, in top antitop pair production and semi-leptonic decay, if the system is boosted and decay products overlap, then the electron can land up close to jet. Certain models of new physics can also result in a similar situation, for example in ATLAS heavy neutrino analysis, for certain configurations, the heavy neutrino can be reconstructed as large-radius jet containing the electron inside where the electron is close to a real jet and we want to keep them both. Then the standard electron reconstruction and overlap removal procedure results in a large fraction of real signal events being discarded, thereby severely hampering the search. Additionally, the events which are kept, the performance of electron reconstruction is likely to adversely affected. Currently, a larger systematic uncertainty is applied to account for this effect. This presentation proposes how we can deal with the reconstruction of such electrons that are close to the real jets. This work further aims at identifying such electrons in the midst of dense hadronic activity without removing either the electron or the jet which will highly benefit many analyses in ATLAS
Speaker: Mr Lawrence Christopher (University of the Witwatersrand)
• 14:40
Search for a heavier Higgs like boson and a dark force boson using ATLAS experiment results 20m
A search is described for a new boson that lies beyond the standard model is conducted where the progenitor 125 GeV Higgs Boson decays ultimately to four leptons (electrons or muons). The Higgs boson provides a portal into the hidden sector, which contains dark particles. The processes under consideration include H → ZX→ 4l and H → XX → 4l where X is the dark vector boson Zd or the pseudoscalar boson <it>a</it>, which are part of the two benchmark models used in the analysis. The mass range under consideration for the dark vector boson or the pseudoscalar boson are 1 < X < 60 GeV. The data under analysis is collected from p-p collisions at the LHC from the ATLAS detector using a centre of mass energy of √s=14 TeV with an integrated luminosity of 36-1 fb. Upper limits at the 95% confidence level are imposed on the fiducial cross sections for the processes under consideration. The subsequent work considers relaxing the Higgs Boson mass constraint upwards, introducing improved filtering and also improvements in the background estimation.
Speaker: Mr Xolani Mapekula (University of Johannesburg)
• 15:00
Search for W'->tb using the 2017 and 2018 in the hadronic final states with ATLAS 20m
A previous search for W'->tb decays in the hadronic final state using collisions at sqrt(s) = 13 TeV with luminosity of 36.1 fb^-1 of the data collected by the ATLAS detector in 2015 and 2016 at the Large Hadron Collider was conducted. At 1-5 TeV mass range the search was interpreted for both left-handed and right-handed chiral W' boson. It was observed that the top and bottom quark masses were consistent with background prediction. The limits on the cross-section were set at high $W'$-boson masses, the W' boson with right left-handed couplings of masses below 3 TeV, 2 TeV are excluded respectively at 95% confidence level. Since this relies on identifying a large-radius jet from boosted top quarks, jet substructure techniques are employed. The current signal samples are generated using a Geant4 based full simulation, which needs a significant amount of resources to produce. So in order to increase number of signal points probed, a simpler fast simulation is being investigated. The first step is to check the modelling of jet substructure observables relevant for this search between full simulation and fast simulation, and derive appropriate correction factors if necessary.
Speaker: Mr Fortune Mhlanga (Wits student)
• 14:00 15:20
Photonics: Beam Shaping & Meeting
Convener: Prof. Andrew Forbes (U. Witwatersrand)
• 14:00
Modelling Crosstalk and Propagation of LG Beams in Turbulence 20m
The use of higher order modes in optical communications is topical due to their versatility and in particular their ability to conveniently increase the number of degrees of freedom in a communications system. This enables multiplexing for higher bandwidth communications as well as diversity for improving the robustness of a link. One of the main reasons why we do not see commercial systems making use of Mode Division Multiplexing is because the channel has not been accurately modelled and so it is impossible to engineer a reliable system. Accurate models exist for flat and spherical wave-fronts, but are not suitable for higher order modes and do not take into account crosstalk effects which is critical for multiplexing. Experimental measurements of the intensity fluctuations and crosstalk of Laguerre-Gauss modes in various conditions was performed on a 150 m free space link at the CSIR in Pretoria. Statistical modes based on the data as well as some example mechanisms for how the models may be used in future will be presented.
Speaker: Mr Mitchell Cox (University of the Witwatersrand)
• 14:20
Creation, characterization and analysis of propagation invariant vector flat-top beams 20m
Laser beams structured to have a uniform peak intensity profile (flat-top) have become ubiquitous and a topic of interest in many research fields. However, such beams alter their intensity profile as they propagate in free space. This problem can be overcome by generating vector flat-top beams. Here, we present theoretical simulations and demonstrate experimentally the creation of propagation invariant vector flat-top beams. By utilizing the spatial light modulator’s polarization dependent efficiency, we coaxially superimpose a Gaussian and donut beam with orthogonal polarization states. We employ a classical and quantum toolkit to characterize and analyse the vector state of the resulting vector flat-top beam during propagation. As an example, we demonstrate the adaptability of these beams in an optical tweezer system however these beams can be of impact in a wide range of applications.
Speaker: Mr NKOSIPHILE ANDILE BHEBHE (UNIVERSITY OF THE WITWATERSRAND)
• 14:40
Photonics Division Meeting 40m
Speaker: Prof. Andrew Forbes (U. Witwatersrand)
• 14:00 15:20
Physics Education
• 14:00 15:20
Physics of Condensed Matter and Materials
Convener: Dr Rapela Maphanga (CSIR)
• 14:00
Sol-gel combustion synthesis and stability of La<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup> powder phosphor 20m
Bismuth (Bi) ions exhibit interesting optical properties, yet have been less intensively studied compared to rare earth ions. Bi doped lanthanum oxide (La2O3:Bi3+) phosphor was synthesized via the sol-gel combustion method at 250 °C using citric acid as the fuel. The product powder was annealed at different temperatures between 800 °C to 1400 °C in air for 2 h. X-ray diffraction (XRD) data confirmed that the La2O3 host as well as doped phosphor crystallized in a hexagonal lattice. For photoluminescence spectroscopy (PL) an excitation wavelength of 308 nm, the phosphor powder produced a blue emission band centered at 462 nm. The maximum intensity was obtained for the sample doped with 0.2 mol% Bi which was annealed at 1200 °C. It was observed that the luminescence from the samples decreased after storage of several weeks. XRD measurements revealed that the La2O3 had changed to La(OH)3, which does not give luminescence when doped with Bi. It has been reported that La2O3 can absorb moisture from the air and transform to La(OH)3. This was observed to occur completely in about 6 days. The poorly emitting samples were re-annealed between 500 °C and 800 °C for 2 h. For the highest temperature it was found that the structure reverted completely to La2O3 and the blue PL emission was once again observed at about the same intensity as for freshly prepared samples. Although La2O3:Bi3+ can be used as a blue emitting phosphor, it is only suitable for applications where it will not be exposed to moisture in the atmosphere. For samples stored in a vacuum desiccator for one week, no change for XRD and PL were observed. Therefore, it may have an application as a moisture sensor, because while the luminescence remains high it is evidence that it has not been exposed to the atmosphere.
Speaker: Mr Babiker Jaffar (ufs)
• 14:20
Modeling of a Resonant Tunneling Transistor under Uniaxial Strain 20m
Graphene is an atomically thin two-dimensional (2-D) crystal with unique thermal, mechanical, and electronic transport properties such as the high mobility of carriers, perfect 2-D confinement, and linear dispersion, etc., has been attracted many interests as a promising candidate for nano-scale devices over the past decades. Multilayer stacks of graphene and other stable, atomically thin, 2-D materials offer the prospect of creating a new class of heterostructure materials. Hexagonal boron- nitride (hBN), is a great candidate to be stacked with graphene due to an atomically 2-D layered structure with a lattice constant very similar to graphene (1.8% mismatch), large electrical band gap (∼ 4.7eV ), and excellent thermal and chemical stability. The graphene/hBN based tunneling transistors show the resonant tunneling and strong negative differential resistance (NDR). These devices which have the potential for future high-frequency and logic applications such as high-speed IC circuits, signal generators, data storage, etc., has been studied both theoretically and experimentally recently. The aim of this paper has been to study the effect of the uniaxial strain on the graphene nanoribbon resonant tunneling transistors (RTTs). The uniaxial strain may be induced either by an external stress applied to the graphene in a particular direction or by a substrate due to deposition of graphene on top of the other materials. The strain modifies distances between carbon atoms which leading to different hopping amplitudes among neighboring sites. A resonant tunneling transistor consisting of armchair graphene nanoribbon (AGNR) electrodes with three layers of hBN tunnel barrier between them has been considered. By using the nearest-neighbor tight-bind (TB) method and the nonequilibrium Green function (NEGF) formalism, the electronic transport characteristics of RTT is calculated. In this work, we focus on how the strain affects the current-voltage characteristics of AGNR/hBN RTT. The results demonstrated that the strain decreased the amount of the current in both cases; however, the quantitative behavior of the I-V plot turned out to be different for the strain in different directions. The current collapsed more rapidly when the strain was applied in the armchair direction.
Speaker: Mr Mahmood Akbari (University of Cape Town)
• 14:40
Cryogenic ion implantation of polyethylene terephthalate (PET) thin films: structural and electrical properties 20m
Organic polymer based electronics have attracted attention in the semiconductor industry for many different applications which include solar cells, lighting, display, and so on. Since polymers are naturally insulating materials, enhancing their electrical properties through modification of their conductance using ion implantation is a focal research area in the semiconductor industry. Previous research shows that structural, optical and electrical properties of Polyethylene Terephthalate (PET) can be modified through ion implantation. However, most of the PET implantations reported in the literature are under room temperature conditions; not much has been done to investigate the effects of temperature on the target material during implantation. In this study, ITO coated PET is implanted with 80keV metal (Ti+) and non-metal (Ar+) ions at three different ion fluences (5 x 10^14, 5 x 10^15 and 5 x 10^16 ions/cm^2), at both room and cryogenic (liquid nitrogen) temperatures. Implanted samples are characterized using the Elastic Recoil Detection Analysis (ERDA) technique to determine the depth profiles of implanted species. Additionally, SEM, FTIR and UV-Vis are carried out to determine the morphology, chemical and molecular structure, and the electronic band gap respectively. The electrical properties of the implanted PET are investigated through current-voltage (I-V) and capacitance-voltage (C-V) measurements. This presentation describes and explains results of the characterization measurements with a view to establishing structure-property relationships of the cryogenically implanted PET.
Speaker: Ms Gaopalelwe Motaung (University of South Africa)
• 15:00
Diffusion study of metal precursor layers for CZTS solar cell 20m
The core of a CZTS solar cell is the p-type absorber layer that gives this type of solar cell its name. It consists of copper, tin, zinc and sulfur in a single crystal structure: Cu2ZnSnS4. In this study two methods are investigated to deposit the copper, zinc and tin as precursor layers for the formation of the Cu2ZnSnS4 layer, namely electroplating and electron beam evaporation. One of the advantages of CZTS solar cells is that the constituent elements are a lot more common and less toxic than what are usually used in other types of solar cells. The elements used in the solar cell itself is only one half of the picture, one also needs careful consideration of the methods and chemicals used during the manufacturing. This is why reline, an environmentally friendly deep eutectic solvent, is used as the electrolyte during electroplating. The 3 metals were deposited in the correct stoichiometric ratio in different sequences on Mo coated glass, and then annealed in vacuum. To estimate annealing times and temperatures, Fick’s diffusion equation was solved [1] for a finite diffusion region with finite diffusion source: C(x,t) = ½ C 0 Σ n=-∞ erf ((h+2nL -x)/(2√Dt)) + erf ((h-2nL+x)/(2√Dt) ) ] From the calculated depth profiles the annealing times and temperatures were chosen 500 K, 550 K, 650 K and 725 K, all for 1 hour. The annealed samples were characterised using Auger Electron Spectroscopy depth profiling, and from these depth profiles the inter-diffusions were calculated. . [1] J Crank, The Mathematics of Diffusion, 2nd edition, (1975)
Speaker: Mr Antonie Fourie (University of the Free State)
• 14:00 15:20
Space Science
Convener: Dr John Bosco Habarulema (South African National Space Agency)
• 14:00
Sprites over South Africa 20m
Sprites observations were recorded in South Africa for the first time on the 11th of January 2016 from Sutherland using a night-vision TV camera from SANSA's Optical Space Research laboratory. Sprites are middle atmosphere optical emissions produced by large positive cloud-to-ground lightning discharges which have an average peak value of ~74 kA. Sprites appear in different forms, such as carrot, jellyfish, column or disk-shaped, typically in the height range ~40-90 km above the thunderstorm. Sprites also contribute to the global electric circuit. Lightning strikes and sprites produce unique Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio wave signatures that can be detected remotely on the ground by using ELF receiver. South Africa has large convective thunderstorms typically in January and February of every year. Lightning strength, time and position data is obtained from the SA Weather Service and may also be tracked in real time using the World Wide Lightning Locating Network (WWLLN). The aim of this research is to determine the maximum altitude of sprites, and the altitude of maximum brightness, as a function of the lightning magnitude. The cameras' spatial pointing geometry was calibrated using stars. The algorithm for distance and height triangulation in spherical coordinates (latitude, longitude, altitude) was developed. The data from 2016 Sprites campaign was processed and we found that the average maximum altitude, and altitude of maximum brightness, of sprites is approximately 85 and 69 km, respectively. We also found the correlation between the sprites maximum altitude and charge moment change (CMC).
Speaker: Mr Dakalo Mashao (South Africa National Space Agency)
• 14:20
Multi-spectral observations of sprites: N2(1PG) and N2+(2PG) Emissions 20m
We present a series of simultaneous ground-based observations of sprite events over convective thunderstorms in southern Africa. These observations were made at the South African Astronomical Observatory in Sutherland during the austral summer of 2016/17 and 2017/18, using multiple cameras to record unfiltered images in white light and filtered images at 426-438 nm and 640 – 675 nm, which correspond to the N2+ and N2 emission spectra of sprites. The orientation of the camera (azimuth and elevation angle) was determined during the analysis by identifying the stars recorded in the image, which was done to single-pixel accuracy. The sprite locations were compared with the lightning locations derived from the lightning detection network operated by the South African Weather Service (SAWS). Low-Frequency radio waveforms associated the observed events were inferred from Extremely Low-Frequency electric field measurements recorded at Sutherland simultaneously with the optical measurements. The results are presented and discussed.
Speaker: Mr Stanislaus Nnadih (SpaceLab, Electrical Engineering Department,University of Cape Town)
• 14:00 15:20
Theoretical and Computational Physics
Convener: Dr Daniel Mojalefa Moeketsi (CSIR Meraka Institute (CHPC))
• 14:00
Logarithmic nonlinearity in theory of quantum and classical liquids 20m
Wave equation with logarithmic nonlinearity find fruitful applications in different branches of physics - from nuclear physics and condensed-matter theory to particle physics, theory of quantum gravity and models of physical vacuum. In order to derive this nonlinearity from basic principles, we apply statistical mechanics and Madelung hydrodynamical presentation for an effective description of strongly-interacting many-body systems, such as Bose liquids or Korteweg-type materials. We show the relationship between the “logarithmic” fluids and those described by polynomially nonlinear wave equations, such as the Gross-Pitaevskii equation.
Speaker: Dr Konstantin Zloshchastiev (Durban University of Technology)
• 14:20
Solutions of Einstein-Klein-Gordon equations with logarithmic phantom field 20m
We study Einstein-Klein-Gordon equations with a phantom, which is a scalar field with a negative sign in front of the kinetic energy term of its Lagrange density. Such equations can find applications in approximate cosmological models based on a low-energy limit of the superfluid vacuum theory. We show that they have spherically symmetric solutions, and perform their stability analysis.
• 14:40
Hyperon-nucleon and hyperon-hyperon interactions constructed via Marchenko inversion approach: Application to hypernuclear spectroscopy 20m
The knowledge of the hyperon-nucleon (YN) and hyperon-hyperon (YY) interactions is vital toward our deeper understanding of the nature of the nucleon-nucleon interaction. However, the direct study of the YN and YY interactions is practically impossible due to the limited or no data available. This is because the hyperon has a very short lifetime, making experiments with hyperon beams extremely difficult. Currently the study of the nonzero strangeness hypernuclear spectroscopy proceeds via theoretically constructed models. For example, the YN and YY interactions can be constructed ab initio via the Chiral Effective Field Theory (χEFT). This method has been extensively studied and is based on the chiral power counting of Weinberg. That is, starting with the field theoretical Lagrangian for the interacting particles, one reduce the infinite dimensional equation of motion to a finite and solvable one in the particles’ degrees of freedom. That is the reduced or effective Schrodinger equation is the one to solve. The process of power counting can be laborious and in general requires large computer power. On the other hand, one may employ the Marchenko Inversion method to construct the interactions. In this work, we constructed the YN and YY potentials from the limited available YN experimental data and simulated YY data to study the structure and dynamics of selected hypernuclear systems within the three-particle model. We employ the differential Faddeev equations to construct the wave functions with the constructed YN and YY potentials as input and study the dynamics of the systems.
Speaker: Mr Emile Meoto (Department of Physics, University of South Africa)
• 15:20 15:40
Tea 20m
• 15:40 17:00
Applied Physics
Convener: Dr Timothy Gibbon (NMMU Physics Department)
• 15:40
A scheme to analyze the decay time of rare earth ions using a square wave technique 20m
Three samples La2O3:Er3+/Yb3+ (LEY), La2O3:Ho3+/Yb3+ (LHY) and La2O3:Er3+ (LE) were synthesized via the combustion method. Urea was used as a fuel and reducing agent. The samples were annealed at 800 oC for 4 hours in order to get good crystallization. The phase confirmation of the samples was carried out by using X-ray diffraction analysis. Surface morphology of the sample was done by field emission scanning electron microscopy analysis with spherical particles. Fourier transformed infra-red transmittance of the samples was done in order to investigate the impurities. The annealed samples (800 oC) were further used for optical measurements. Upconversion emission of all the samples were measured and three prominent bands were monitored at 522, 548 and 662 nm corresponding to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, manifolds, respectively. The decay time measurements were done using a monochromator coupled with a Cathode ray oscilloscope (CRO). A continuous laser beam (976 nm) was chopped using a mechanical chopper (1000 Hz). Thus the data acquired by using the CRO was plotted as a square wave and this wave was further used to analyze the decay time with fixing different fitting parameters. This technique of decay time measurements is very inexpensive and easy handled. Thus the calculated decay time of the samples were found to be 252 ms, 102 ms and 54 ms, for LEY, LHY and LE, respectively.
Speaker: Dr S P Tiwari (Department of Physics University of Free State)
• 16:00
Upconversion luminescence of NaGdF4 : Yb3+, Ho3+ phosphors for potential biomedical applications 20m
Lanthanide ions (Ln3+) doped upconversion (UC) materials show great potential applications in optical and optoelectronic devices owing to their novel optical properties.Yb3+, Ho3+ co-doped NaGdF4 materials were synthesized by a simple co-precipitation method. Powder X-ray diffraction and X-ray photoelectron spectroscopy analysis demonstrated successful formation and incorporation of ions in NaGdF4: Yb3+, Ho3+ materials. The UC luminescence properties of NaGdF4 materials co- doped with different Yb3+, Ho3+ concentrations were investigated, and the related UC mechanisms of Yb3+, Ho3+ co-doped NaGdF4 depending on pump power were studied in detail.The intense green UC emission bands at 540, 549 nm, red emission at 645 nm and 752 nm signals in the emission spectra could be assigned to the 5S2, 5F4→5I8, 5F5 →5I8 and 5F4→5I7 transitions of Ho3+ via 980 nm near infrared excitation along with energy transfer from the Yb3+, respectively. It was confirmed that the green UC emission was generated via a two-photon process from a quadratic dependence of the emission intensity on the pumping power. The chromaticity coordinate (0.276, 0.708) of the optimized NaGdF4: 15 mol% Yb3+, 2 mol% Ho3+ upconversion material was located in the green region and hardly changed due to the negligible red emission. The present Yb3+, Ho3+ co-doped NaGdF4 phosphor is an interesting UC material with a stable crystal structure, good cytocompatibility and bioactivity possesses great potential for biomedical applications.
Speaker: Dr ASHWINI SHARMA (UNIVERSITY OF THE FREE STATE)
• 16:20
The MinPET diamond discovery technique – an update 20m
MinPET is a novel technology that provides the first ever high-throughput 3D quantitative imaging of locked diamonds within kimberlite rocks presented as a close packed run-of-mine stream. It is a patented technique that combines two existing technologies in a novel way. The ore is activated by an electron accelerator which produces a high-energy photon beam of some tens of MeV via bremsstrahlung. PET isotope production is the most significant source of photons for delay times of the order of 30 minutes. After this delay time, scanners based on medical PET (Positron Emission Tomography) technology image the activated rocks for diamond. Essentially a carbon density distribution map is created and analysed. This presentation will look at MinPET performance results based on a Full Dress Rehearsal of Activation, Detection, Analysis using experimental datasets with statistics that would typically be collected in a run-of-mine scenario at 700 tons per hour of rock throughput. The data was collected using the PET detectors optimized by the Research Group and Net Instruments and various spiked kimberlite samples at the electron injector microtron of the ASTRID storage ring of the ISA, Centre of Storage Ring Facilities at the Department of Physics in Aarhus University, Denmark.
Speaker: Mr Thendo Emmanuel Nemakhavhani (University of Johannesburg)
• 16:40
Temperature-dependent gas sensing study of chemically prepared CeO<sub>2</sub>-CuO nanoparticles 20m
The combination of nanosized cerium dioxide (CeO2) with transition metal oxides, like copper oxide (CuO), containing Ce1-xCuxO2-y, have received significant attention for their catalytic application due to their economic, environmental, and catalytically favourable properties.[1] These systems proved efficient for selective CO oxidation the water-gas shift (WGS) reactions and the hydrogen combustion reactions.[2] Even though the surface and catalytic properties of the Ce1-xCuxO2-y systems can be translated to the field of gas sensors, the gas sensing performance of these systems have not yet been investigated. Therefore, herein, we report for the first time, the gas sensing performance of Ce1-xCuxO2-y systems towards various gases such as CO, H2S, H2, CH4, NH3, ethanol, NO2 and toluene at various operating temperatures and relative humidity. The influence of the crystallize size, point defects and adsorbed surface oxygen species on the response, selectivity and sensitivity of Ce1-xCuxO2-y nanoparticles was investigated using X-ray diffraction, transmission electron microscopy attached with electron energy loss spectroscopy, X-ray photo-electron spectroscopy and photoluminescence spectroscopy. The underlying gas sensing mechanism was also examined and discussed. [1] (a) Putla, S., M.H. Amin, B.M. Reddy, A. Nafady, K.A. Al Farhan, and S.K. Bhargava, ACS Applied Materials & Interfaces, 7, 16525-16535 (2015); DOI: 10.1021/acsami.5b03988; (b) Qin, J., J. Lu, M. Cao, and C. Hu, Nanoscale, 2, 2739-2743 (2010); DOI: 10.1039/c0nr00446d [2] (a) Bernardi, M.I.B., A. Mesquita, F. Beron, K.R. Pirota, A.O. de Zevallos, A.C. Doriguetto, and H.B. de Carvalho, Physical Chemistry Chemical Physics, 17, 3072-3080 (2015); DOI: 10.1039/c4cp04879b; (b) Elias, J.S., N. Artrith, M. Bugnet, L. Giordano, G.A. Botton, A.M. Kolpak, and Y. Shao-Horn, 6, 1675-1679 (2016); DOI: 10.1021/acscatal.5b02666
Speaker: Ms Dina N. Oosthuizen (CSIR and University of the Free State)
• 15:40 17:00
Astrophysics: Division Meeting
Convener: Prof. Christo Venter (North-west University, Potchefstroom Campus)
• 15:40
Astrophysics and Space Science - joint meeting 1h 20m
Speakers: Prof. Christo Venter (North-west University, Potchefstroom Campus) , Dr Du Toit Strauss (Centre for Space Research, North-West University)
• 15:40 17:00
Convener: Dr Simon Mullins (iThemba LABS (Gauteng))
• 15:40
NPRP Division Meeting 1h 20m
Speaker: Dr Simon Mullins (iThemba LABS (Gauteng))
• 15:40 17:00
Photonics: Applied Photonics
Convener: Dr Carmelo Rosales-Guzman (University of the Witwatersrand, Johannesburg)
• 15:40
Continuation of Photonics Division Meeting (if required) 20m
Speaker: Prof. Andrew Forbes (U. Witwatersrand)
• 16:00
Using optical tweezers to measure the forces exerted by molecular motors in onion cells 20m
Optical tweezers demonstrate how light can be applied to exert piconewton forces on a microscopic particle. This allows for the particle to be spatially manipulated in three dimensions. Optical tweezing is achieved by creating an optical trap. In this work, a single beam optical trap is created using a high numerical aperture microscope objective to focus a near infrared laser into a sample. The sample used for calibration of the setup is micron sized, dielectric particles suspended in a fluid. The particles have a higher refractive index than the fluid in which the particles are suspended. After the light refracts through a particle, a net force is applied to the particle that causes it to move into the focus of the beam due to conservation of momentum. When moving the trap position relative to the sample, the optical trap acts as optical tweezers moving the particle(s) currently in trap relative to the sample. Optical tweezers have been developed for various applications. However, here the optical tweezers is used to investigate the forces needed to stall the motion of molecular motors in onion (Allium cepa) cells. To do this, the optical tweezers were constructed and the forces applied to micron sized particles in the trap were calibrated. An integrated microscopy imaging setup was used to see and trap vesicles transported by molecular motors in the cells. The force calibration was then used to determine the intracellular forces of the molecular motors.
Speaker: Ms Anneke Erasmus (Stellenbosch University)
• 16:20
Robust quantum key distribution with spatial modes 20m
Quantum key distribution (QKD) allows the secure sharing of information by exploiting the laws of physics. Traditionally demonstrated with polarisation, there has been novel avenues of research whereby the spatial degree of freedom is employed to increase the bandwidth; that is because spatial modes allow access to a larger state space beyond the qubit, unlike polarisation. However, unlike polarisation, spatial modes are not resilient to atmospheric perturbations; the random fluctuations in of refractive index cause wavefront aberrations that broadens the spectrum of a single mode OAM state. In the context of quantum key distribution, the broadening leads to measurement errors that decrease or compromise the security of the QKD link. Here we present a study of the deleterious effects of atmospheric turbulence on orbital angular momentum- based quantum key distribution protocols. We show that the impact of turbulence on the secret key rate can be mitigated by using spatial modes with high orbital angular momentum content. We attribute the resilience of high OAM states (labelled with l) to the separation in OAM space; the further apart the modes are, i.e., the higher Δlℏ, the lower the overlap for given turbulence conditions. Consequently, the range of real-world quantum communication link that employ spatial modes can be significantly extended without compromise on security.
Speaker: Mr Bienvenu Ndagano (University of the Witwatersrand)
• 16:40
Single molecule fluorescence microscopy- An application in thin polymer film dynamics. 20m
With worldwide production of polymers pegged at over 300 million tonnes (2017), there’s need for sustainable options for production, waste management and recycling of polymers [1]. This high demand of polymers has made them become one of the most important materials in various industrial and biomedical sectors. These materials have shown interesting and unique physical properties that change drastically such as conductivity, viscosity and thermal expansion below, near and above the glass transition temperature which originate from complicated relaxation processes of polymer chains [2]. However these unique properties have not yet been fully understood despite experimental and theoretical studies of the glass transition temperature of polymers over the past decades. Thus there has been a need in polymer research to further understand the dynamics connecting the macroscopic and microscopic properties of polymers. Different experimental methods have been used to try and understand the nano-environment of polymers. One of these methods also used in this research is single molecule fluorescence microscopy. It is a powerful imaging tool that enables the direct observation of single fluorescent molecules in their nano-environment [3]. For this research, the diffusion of single fluorescent dye molecules embedded in thin polystyrene and poly (isobutyl methacrylate) films was used to study and investigate the dynamics of the thin polymer films. In this presentation, dynamics of the thin polymer films below and near the glass transition temperature as derived from the probe molecule diffusion will be discussed. [1]. Plastics Europe, PEMRG,2017. [2]. B. Flier, et al. “Heterogeneous Diffusion in Thin Polymer-Films as observed by High-Temperature Single Molecule Fluorescence Microscopy”; J. Am. Chem. Soc.,134,480-488, 2012. [3]. Dominik Woll et al, “Polymers and single molecule fluorescence microscopy, what can we learn?”,Chem.Soc.Rev,vol 38,pp313-328, 2009.
Speaker: Ms charmaine sibanda (stellenbosch university)
• 15:40 17:00
Physics Education
• 15:40 17:00
Physics of Condensed Matter and Materials
Convener: Dr Mmantsae Diale (University of Pretoria)
• 15:40
The Dependence of Raman Signal Enhancements on Chain-lengths of Alkanethiols functionalized on gold nanoparticles 20m
Surface-enhanced Raman spectroscopy (SERS) has been widely studied for decades and has attracted many researchers in various fields due to its advantageous characteristics such as a low limit of detection, easy sample preparation, non-destructive nature and high sensitivity. Recent studies have focused more on enhancing the Raman signal by manipulating various parameters of SERS. SERS signals are heavily dependent on the substrates and molecules (Raman reporters) adsorbed on a substrate. Recently the focus has been on trying to develop materials with different and enhanced properties to be employed as SERS substrate. As such, gold nanoparticles (AuNPs) are a type of material that has received much attention. Unlike most transition metals, AuNPs are biocompatible, stable in the harsh environment and most importantly they can provide extremely strong electromagnetic field around the hot spots due to the excitation of surface plasmons. However, the effect of chain-length of Raman reporter molecules functionalized on SERS substrates has not been investigated in a wide range. Herein we investigate the effect of the chain-lengths of 1-alkanethiols (1-pentanethiol, 1-decanethiol, and 1-pentadacanethiol) functionalized AuNPs on the Raman signal enhancement. AuNPs were synthesized using chloroauric acid (HAuCl4) as a precursor and trisodium citrate as a capping and reducing agent. The nanoparticles were then functionalized with 1-pentanethiol, 1-decanethiol, and 1-pentadecanethiol, thus resulting in the formation of self-assembled monolayers. UV-Vis spectroscopy confirmed the plasmon resonance of gold nanoparticles at 520 nm; HR-TEM illustrated monodispersed spherical nanoparticles with an average diameter of 14 nm. The SERS experiments revealed the increase in Raman signal as the chain-length of alkanethiol decreases.
Speaker: Mr Ndivhuwo Shumbula (university of witwatersrand)
• 16:00
The synthesis, characterization and application of different morphologies of ZnO in the photocatalytic degradation of Rhodamine B 20m
Speaker: Mr Siyabonga Nkabinde (University of the Witwatersrand)
• 16:20
First principle study of structural, magnetic, electronic and mechanical properties of A15 X3Ru alloys 20m
Ruthenium based alloys have excellent properties which makes them good candidates for high temperature applications. A large number of equipment such as turbine and spacecraft engines operates at high temperatures in aggressive chemical environments. Therefore there is a need to search for materials that can withstand extreme thermal, chemical and mechanical conditions for these applications. This study aims to develop high temperature materials with good oxidation and corrosion resistance. We discuss trends in structural, magnetic, electronic and mechanical properties of 3d transition A15 X3Ru alloys (X = Sc, Ti, V, Cr, Mn, Co, Cu, Ni, Fe and Zn) observed using First principle density functional theory calculations. The heats of formation predict an increase in stability in the following trend: Ti3Ru > V3Ru > Cr3Ru > Mn3Ru. We find that Ni3Ru, Fe3Ru, Co3Ru and Mn3Ru compounds have magnetic moments of 1.0, 1.6, 1.7 and 2.6 µB/atom. The density of states indicates that Sc3Ru, Ti3Ru, V3Ru and Cr3Ru systems are metallic due to valence-conduction overlap in the Fermi energy level, whilst X3Ru (Mn, Fe, Co and Ni) are half-metallic with 100% spin polarization at the Fermi level. Furthermore, the ratio of bulk to shear modulus indicates ductility in X3Ru (X = Sc, Ti, V, Cu, Ni, Mn, Cr and Zn) suggesting that these systems are mechanically stable. Doping the X3Ru (X = Sc, Ti, V, Cr, Mn, Co, Cu, Ni, Fe and Zn) alloys with transition metals such as Nb, Ta, Pd or Pt improves their structural, electronic and mechanical properties.
Speaker: Mr BHILA OLIVER MNISI (University of South Africa, Department of Physics)
• 16:40
Magnetic and physical properties of new hexagonal PrPt<sub>4</sub><i>X</i> (<i>X</i> = Ag, Au) compounds 20m
We have synthesized PrPt4Ag and PrPt4Au compounds for the first time and report their crystal structure, as well as magnetic and physical properties in the temperature range between 2 K and 300 K. Both compounds are derived from the substitution of Pt with Ag and Au respectively in the parent compound PrPt5 which crystallizes in the hexagonal CaCu5-type structure [1, 2]. Here, we observed the preservation of the hexagonal CaCu5-type structure under such substitutions which is in contrast to the observations in PrCu4Ag and PrCu4Au [3, 4] adopting the cubic MgCu4Sn-type structure upon substitution on parent hexagonal PrCu5. The temperature dependence of specific heat, Cp(T) and electrical resistivity, &rho(T) of PrPt4Ag show an anomaly at 7.6 K but which is absent in the magnetic susceptibility, &chi(T) and thus suggesting a possible multipolar ordering of the Pr3+ magnetic moment. PrPt4Au on the other hand does not show any anomaly but an upturn in Cp(T)/T below about 10 K and reaching a value of 1.23 J/(K2mol) at 2 K. In addition, &rho(T) ~ T and &chi(T) ~ T-1/3 for nearly a decade in temperature. These observations in PrPt4Au are the hallmark of a non-Fermi liquid (nFL) behavior and is characteristic of a system with a low lying order parameter. The analysis of the low temperature Cp(T) for PrPt4Ag and PrPt4Au give values of the Sommerfeld coefficient, &gamma = 728.5 mJ/(K2mol) and 509.1 mJ/(K2mol) respectively indicating a significant enhancement of the quasiparticle mass in the two compounds.
Speaker: Mr Michael Ogunbunmi (University of Johannesburg)
• 15:40 17:00
Space Science: Division meeting
Convener: Dr Du Toit Strauss (Centre for Space Research, North-West University)
• 15:40 17:00
Theoretical and Computational Physics
• 17:00 18:00
Physics Bowl
Conveners: Dr Brian van Soelen (University of the Free State) , Ms Helene Szegedi (University of the Free State)
• 18:00 20:00
Council meeting with HODs EBW

### EBW

• 18:30 19:30
Public Lecture
Convener: Prof. Pieter Meintjes (University of the Free State)
• 18:30
The Multimessenger Universe - A New Era of Astronomy 1h
Speaker: Dr Markus Bottcher (North-West University)
• Thursday, 28 June
• 08:50 09:00
Announcements Auditorium

### Auditorium

• 09:00 10:00
Plenary: Leach
Convener: Prof. Andrew Forbes (U. Witwatersrand)
• 09:00
Quantum Imaging Technologies Using Single Photon Detectors 1h
Technology at the quantum limit promises significant advances in computing, communication, sensing and metrology, and imaging. The UK and many other countries around the world have recently provided significant investment in the development and realisation of such technologies. In this talk, I will discuss the UK’s quantum technology landscape and highlight my group's activities in applied and fundamental quantum science, specifically focussing on advances in communication, imaging, and metrology. Much of our work relies on the detection of single photons via single-photon detectors, either in single-point or array formats. Such detectors enable unprecedented sensitivity to light and allow precise detection of arrival times, down to picosecond timescales. This is the key enabling feature that allows us to see around corners, detect objects through scattering media, and generate entanglement between photons that have never interacted. Our work highlights the progress in single-photon detection technologies and showcases a range of applied and fundamental applications of the science.
Speaker: Dr Jonathan Leach (Heriot-Watt University)
• 10:00 11:00
Applied Physics: PHYSICS IN INDUSTRY
Convener: Mr Brian Masara (SAIP)
• 10:00
Physics in Industry: Overview 10m
Speaker: Mr Brian Masara (SAIP)
• 10:10
Physics in Industry: Nanotechnology 25m
Speaker: Prof. Odireleng Ntwaeaborwa (University of the Witwatersrand)
• 10:35
Physics in Industry: Photovoltaics 25m
Speaker: Prof. Ernest van Dyk (Mandela University)
• 10:00 11:00
Astrophysics: Gamma-ray / Multi-wavelength Astronomy III / Radio Astronomy I
Convener: Dr Markus Bottcher (North West University)
• 10:00
Investigating the difference in FRI and FRII AGN jet morphology with relativistic hydrodynamic simulations 20m
Relativistic hydrodynamic simulations have become a powerful tool used to simulate the dynamics of jets produced in radio-loud Active Galactic Nuclei (AGN). These AGN jets consist of plasma ejected by a central engine moving at relativistic velocities. Observational studies of AGN jets have shown that they emit variable emission over the whole of the electromagnetic spectrum. The spectral energy distribution (SED) of these sources show dominant components of synchrotron and Inverse-Compton emission produced within relativistic jets originating from the nucleus. While simulations of AGN jets have been able to reproduce many of the observed structures (e.g. radio lobes, hot spots and super-luminal emission components) the physical properties relating to the FRI/FRII division are not well understood. In this study the PLUTO RHD code was used to investigate the parameters required to reproduce structures consistent with both FR I and FRII jets. In the first simulation a Lorentz factor of 10 and supersonic flow of Mach 300 were chosen, while for the second simulation a Lorentz factor of 1.0014 with a supersonic flow of Mach 4 were used. Over similar distances scales the first case shows a well collimated beam with a strong shock at the interface between the jet and ambient medium while the second case shows a less stable beam and larger cocoon. To determine whether the physical structures simulated by the PLUTO code are consistent with the observable FR I/II structures, the synchrotron emission has been calculated to produce radio maps at a single frequency of 1.5 GHz. The first case showed emission structures similar to that of FR II radio galaxies with hotspots at the head of the jet while the second case was more consistent to that of an FR I source with the highest intensity occurring within the beam of the jet. Calculating the multi-wavelength (radio - gamma-ray) SED of a synchrotron self-Compton model for these simulations is very computationally intensive. We are, therefore, currently investigating the use of Monte-Carlo codes in conjunction with the hydrodynamical simulations. These codes can provide us with a time-dependent, multi-zone emission model to compare to observations. Our progress thus far is also presented.
Speaker: Mr Izak van der Westhuizen (University of the Free State)
• 10:20
Estimating the Modulated Inverse-Compton Flux Level from a Black Widow System 20m
The Fermi Large Area Telescope has detected more than 200 gamma-ray pulsars. Many of them are in binary systems, and a subset of these comprise the "spider binary" class, including black widows and redbacks. The latter systems consists of energetic pulsars and companion stars that are in tight binary orbits. The two stellar winds interact with each other, forming an intrabinary shock and leading to particle acceleration. Observed double-peaked X-ray light curves from these systems are attributed to Doppler-boosted synchrotron emission by relativistic particles flowing out along the shock. Additionally, radio eclipses reflect the presence of the shock enshrouding the companion in the black-widow case. Although energetic arguments suggest that these systems may be detectable by ground-based Cherenkov telescopes, detailed calculations remain to be done rigorously. Given the non-trivial geometry and particle dynamics, we first attempt a simple approach to estimate the level of inverse Compton flux that should result from nearby black-widow systems. We normalise the injected particle spectrum to the pulsar current and spin-down luminosity and approximately take into account the processes of diffusion, convection, and radiative energy losses in an axially-symmetric, steady-state approach. Future work will build on these first estimates and will include more detailed particle transport in a relativistic 2D approach.
Speaker: Prof. Christo Venter (North-west University, Potchefstroom Campus)
• 10:40
Bayesian TiRiFiC 20m
The tilted-ring model describes a galaxy as a set of rotating rings, each of which is parameterized by a set of parameters representing surface brightness, rotation speed, and orientation of the disk. Our implementation of the tilted-ring model, TiRiFiC ("Tilted-Ring-Fitting-Code") works by directly fitting galaxy models to spectroscopic data cubes (as observed with the SKA and its progenitors) and is most suitable to be used for radio surveys of emission lines, e.g. with the SKA and its progenitors. While the method is well tested, it currently lacks a solid approach to quantify statistical errors and correlations between parameters. We attempt to overcome this problem by making use of a robust Bayesian statistical framework, which enables a full exploration of the posterior probability distribution and can be used to estimate errors and quantify the correlation between parameters. This forms a report of the implementation of this technique.
Speaker: Mr Eric Maina (Rhodes University)
• 10:00 11:00
Convener: Dr Simon Mullins (iThemba LABS (Gauteng))
• 10:00
Measurement of fundamental ion beam – matter interaction parameters for heavy ion nuclear analytical techniques 20m
The use of heavy ion beams (Z>2) in ion beam materials analysis (IBA) techniques has been shown to enhance the sensitivity of these techniques when compared to using light ions (H, He). The development of theoretical models to describe various ion beam-matter interaction phenomena for use in IBA analytical software is strongly dependent on the availability of experimental data to test these models. One of the factors inhibiting widespread implementation of heavy ion IBA techniques is the scarcity of experimental data of basic parameters such as stopping force and X-ray production cross sections. This contribution describes measurements carried out to determine heavy ion induced X-ray production cross sections and stopping force in solid matter for applications in Heavy Ion ERDA and Heavy Ion PIXE. Stopping force data is compared to predictions by the ab initio CasP code and the semi-empirical SRIM, and X-ray production cross section measurement results are compared to the plane wave Born approximation (PWBA) and ECPSSR-UA calculations.
Speaker: Prof. Mandla Msimanga (Tshwane University of Technology)
• 10:20
Measurement of heavy ion induced X-ray production cross sections in metallic targets at MeV energies. 20m
Experimental X-Ray production cross sections (i.e. probability of X-ray generation in a target by an incoming MeV heavy ion beam) are useful not just for fundamental ion beam-matter interaction studies,but also for the development of new ion beam materials analysis techniques such as the Heavy Ion Particle Induced X-Ray Emission (HI-PIXE) spectroscopy. Unfortunately, while theoretical predictions of X-ray production cross sections due to light (Z <6) projectile ions are generally in good agreement with experiment, this is not the same for heavier projectiles. There is therefore need for substantial experimental data to improve theoretical models. This presentation describes measurements carried out to determine X-ray production cross sections in zirconium (Zr), Tin (Sn) and Vanadium (V) metal oxide films due to carbon and chlorine MeV ion beams. The measured cross sections are compared to predictions by the modified Plane Wave Born Approximation (PWBA) and the ECPSSR theory that takes into account the energy loss and coulomb deflection of the projectile and the pertubed-stationary state and relativistic nature of the target's inner shell. The observed agreements and discrepancies between experiment and theory are discussed in terms of the atomic ionization mechanisms for each projectile-target collision.
Speaker: Mr Masedi Masekane (University of South Africa)
• 10:40
Measurement of the cosmogenic isotope 10-Be at iThemba LABS and applications of cosmogenic isotopes in South Africa 20m
10Be is an important isotope for accelerator mass spectrometry system of iThemba LABS in Johannesburg, because of local demand for cosmogenic radionuclide dating methods in the local earth science and paleosciences community. This demand also meets a very suitable basic AMS setup with its ion-source based on a version of the Cesium Sputter source of the Lawrence Livermore National Laboratories, which delivers significantly higher output of BeO- than commercially available ion sources. The measurement of 10Be by accelerator mass spectrometry requires the effective suppression of 10B before the detector, which is either done by using an gas absorber cell for full stopping of 10B, or by differential energy loss of 10B versus 10Be in an absorber foil (post-stripping) followed by a high-resolution magnet or electrostatic analyser. The latter method has proven effective in that the 2+ charge state can be utilized, which has in excess of 40% charge state transmission at 4MV terminal voltage, but there are charge state losses from the absorber foil. Using gas absorber cell employing havar windows usually requires higher energies, requiring the 3+ charge state and higher terminal voltage, resulting in additional interference from the 10B(p,)7Li reaction that is not fully separated in the detector. Recently it has been shown that low stress silicone nitride membranes can be used as absorber for full stopping with particle energies of 6MeV for 10-Be. This allows for the use of the 2+ charge state, avoids the charge state losses of the post-stripping method, and – provided the chosen terminal voltage is low enough – it avoids incurring massive interference from the nuclear reaction. We implemented this method in lieu of the traditional gas absorber cell, thus cashing in on the efficiency gain from using the 2+ charge state. Together with the efficiency benefits of our ion-source we have a high detection efficiency AMS system for 10Be. We applied the foilstack methods successfully in test runs and recently in first projects of our cosmogenic isotope programme.
Speaker: Dr Stephan Winkler (NRF/iThemba LABS)
• 10:00 11:00
Physics Education
• 10:00 11:00
Physics of Condensed Matter and Materials
Convener: Dr Ganga Babu Geetha (University of Johannesburg)
• 10:00
Synthesis and characterization of Halide Perovskite Materials for Photovoltaic Application 20m
Among all the components of perovskite solar cells (PSCs), the perovskite materials play a central role in light absorption and photoelectric conversion. The optimization of the materials and structures is a key to enhancing the conversion efficiency. The perovskite materials for inclusion into solar cells were prepared by one and two-steps solution fabrication process to generate polycrystalline structures with diverse grain sizes. PbI2, PbCl2 and MAI were used in the synthesis of organic-inorganic hybrid perovskite , as they facilitate the formation of well-organised perovskite layer. In a quest to improve the performance of these devices, the effect of synthesis approach on the properties of the material have been investigated. Our fundamental objective therefore was to determine how synthesis influences the structure and the properties of perovskite material for the application in photovoltaic cell. Samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis spectrometry and thermogravic analysis (TGA). Subsequent to the characterization the light harvesting efficiencies of these materials have been investigated which is significant for photovoltaic materials. Key words: Hybrid perovskite, solar cells, synthesis, properties, characterization
Speaker: Mr Akin Olaleru (University of venda, South Africa)
• 10:20
Structure and dynamics of noble gas temperature control on Ti metal clusters 20m
Titanium clusters is one of the central theme in cluster science to investigate the evolution of the electronic, structural and magnetic properties of the metal clusters as a function of cluster size. The atomic structures and dynamics of nanoclusters have been of crucial importance in both experimental and theoretical studies owing to their useful physical and chemical properties in various industrial applications. In particular, the titanium metal clusters have been shown to strongly dependent on their internal clusters energy which dictate the geometrical arrangement and growth patterns. In this study, molecular dynamics simulation was used to investigate the temperature effects on pure Ti metal nanoclusters in both vacuum and under pressure of Argon gas. The effect of gas phase environment on the structural growth and dynamical properties was interrogated by subjecting the nanoclusters to various temperatures in the range of 300K – 2000K. The radial distribution functions and diffusivity were examined to study the structural changes as a function of temperature. It was found that the gas phase and the vacuum structures melting point correspond well with the experimental data. Furthermore, the diffusivity of both the gas phase and vacuum increases as the temperature is increased. This observations is important in the production of titanium metal and development of titanium metal components for industrial and aerospace applications
Speaker: Mr Tshegofatso Michael Phaahla (University of Limpopo)
• 10:40
Sampling of P91 base metal for in-situ neutron powder diffraction and dilatometer evaluation / characterisation 20m
ASTM SA-335 Grade P91 / T91, a 9%Cr creep strength enhanced ferritic (CSEF) steel, is commonly used in modern power industry for manufacturing critical pressure components and vessels, tubing, piping and headers. The objective of the current study is to determine the temperatures at which transformation of BCC ferrite to FCC austenite starts and finishes on heating (the so-called Ac1 and Ac3 temperatures). In addition, the transformation of austenite to delta ferrite (a BCC structure) at higher temperatures must be characterized. As reported previously, neutron powder diffraction and dilatometry were selected to characterize these phase transformations. A small number of isothermal heat treatments, followed by water quenching was also done, to verify neutron diffraction results at temperatures that could not be achieved using the dilatometer. The objective of the current paper is to describe calibration and sampling methods in P91 base metal for such phase transformation.Temperatures in the dilatometer and neutron furnace were verified by comparing the experimentally measured phase transformation temperatures of pure iron rod with the theoretical temperatures.By using room temperature neutron powder diffraction, the crystallographic preferred orientation in a tubular sample of P91 base metal was established along the longitudinal, through-thickness and tangential direction by comparison of intensity ratios of the diffraction peaks with those of Fe powder. It was found that the tangential sample machined exhibited intensity ratios closer to those of Fe powder. The longitudinal sample presented severe preferred orientation. Dilatometer results were insensitive to the orientation of the sample. The Ac1 and Ac3 temperatures in the different oriented samples were determined in the range 809-811°C and 875-811°C respectively in the dilatometer. The quenching methods revealed that at 1150°C, the onset of delta ferrite in P91 base metal has already commenced, which agrees with previous temperature range obtained by in-situ neutron diffraction (between 1140 and 1160°C). The calibration results indicate that the error in temperature (between published and experimentally determined temperatures, and between neutron diffraction and dilatometry results) was less than 5°C, and that the combination of neutron diffraction, dilatometry and isothermal heat treatments resulted in an assessment of the phase transformation behavior over a wide range of temperatures, not achievable using only one characterization technique.
Speaker: Ms zeldah sentsho (necsa)
• 10:00 11:00
Space Science
• 10:00 11:00
Theoretical and Computational Physics
• 11:00 11:20
Tea 20m
• 11:20 13:00
Applied Physics: PHYSICS IN INDUSTRY
Convener: Mr Brian Masara (SAIP)
• 11:20
Physics in Industry: Nuclear 25m
Speaker: Dr M Mkhosi (Centre for Nuclear Safety and Security, South African National Nuclear Regulator)
• 11:45
Physics in Industry: Photonics 25m
Speaker: Dr Darryl Naidoo (Council for Scientific and Industrial Research)
• 12:10
Partnership Opportunities in Hosting Business/Industry Events, Meetings and Conferences 25m
Speaker: SA National Convention Bureau
• 12:35
Physics in Industry: Discussion 25m
Speaker: Dr Iyabo Usman (University of the Witwatersrand, Johannesburg.)
• 11:20 13:00
Astrophysics: Radio Astronomy II / Gamma-ray / Multi-wavelength Astronomy IV
Convener: Prof. Pieter Meintjes (University of the Free State)
• 11:20
Radio observation of diffuse radio emission in Abell 773 galaxy cluster 20m
A fraction of galaxy clusters host diffuse,Mpc-scale,low surface brightness emissions named "radio halos",that spatially correlate with the diffuse X-ray emission. Current models indicate that radio halos are connected to the galaxy cluster merger history: radio emission is due to particles that are re-accelerated to relativistic energies via turbulence induced via cluster mergers. Here we present radio observations of the A773 galaxy cluster taken with the Westerbork telescope aimed to study the physical properties(morphology, size and spectral index, polarization) of its radio halo and characterize their radio emissions at different frequencies.
Speaker: Mr Gift Sichone (Rhodes University)
• 11:40
Radio Intereformetric Calibration using a Complex Student-t distribution and Wirtinger derivatives 20m
Calibration in radio astronomy is the step during which all systematic errors and ionospheric curruptions, are estimated and removed from the observed data. This consists of solving for all propagation effects, i.e.~Jones matrices, which minimizes the difference between the measured and the model data using a mathematical framework known as the Radio Interferometric Measurement Equation (RIME). The model data is constructed based on our existing knowledge of the observed field using a Gaussian likelihood function. However various outliers in the data and errors in the model cause deviations from the assumed likelihood function. This leads to “poor”' calibration solutions and formation of various artefacts in the calibrated images. These include generation of spurious sources, suppression in the flux of real structures and an increase in images' rms that reduces the detection probability of faint sources. Recently some authors (Kazemi and Yatawatta (2013); Ollier, Virginie, et al.~2016) have proposed using a different statistical noise model that better fits the noise as well, as unmodelled data and errors, in order to improve calibration. Kazemi and Yatawatta (2013) used a Student-t likelihood in place of a Gaussian likelihood and obtained considerable improvement in flux’ suppression of the faint unmodelled sources. The algorithm implemented by Kazemi and Yatawatta (2013) requires us to separate the complex visibilities data in to real and imaginary parts, and independently solve for the real and imaginary parts of the gains. We derive and implement an analogue algorithm using a complex student-t distribution, which evicts the need of separating the data in their real and imaginary parts. This is achieve by exploiting the recent developments in optimization theory and particularly the Wirtinger calculus as explained by Smirnov and Tasse (2015) for gain calibration. We show results from simulations and the improvements obtained using the latter approach.
Speaker: Mbou Sob Ulrich Armel (Rhodes University)
• 12:00
All Sky Imaging with PAPER 20m
The Precision Array to Probe the Epoch of Reionization (PAPER, http://eor.berkeley.edu) was built to measure the redshifted 21-cm line from cosmic reionization. Here, I will present the analysis of the last season of PAPER observations, with particular focus to image and characterize the foreground emission, a crucial task in order to detect the much fainter 21-cm emission.
Speaker: Mr James Chege (Rhodes University)
• 12:20
A Practical Survey of Novel and Legacy Radio Interferometry Imaging Algorithms and Packages 20m
Radio interferometry software packages have grown sophisticated enough that we can now begin to address some of the imaging issues that are posed by the next generation of radio telescopes, most notably the MeerKAT and Square Kilometre Array (SKA). The main objective of this project is to develop a framework that allows the evaluation of deconvolution algorithms and imaging techniques using a platform independent pipelining tool. We use MeerKAT L-band simulated visibility data to perform the evaluation of the radio interferometric packages. Using the framework, we compare the performance of imaging tools such as CASA, DDFacet, LWImager and WSClean. Using these images we recovered source flux density, morphology, angular position and spectral index. Therefore, by comparing the model inputs and the recovered source properties with their corresponding measured uncertainties, we can infer how well each imager performs the deconvolution process for a given set of observational parameters. It was found that at flux densities below 20σ, there is a significant scatter in the measured properties as a result of the decrease in signal to noise ratios of the sources, and at higher source flux densities there is a clear correlation which was simply described statistically.
Speaker: Mr Athanaseus Ramaila (Rhodes University)
• 12:40
Updated orbital parameters for LMC P3 with SALT/HRS 20m
LMC P3 is the most recently discovered, and the most luminous, γ-ray binary. The source was discovery with Fermi-LAT γ-ray observations which showed a 10.301 ± 0.002 day period. The γ-ray emission is associated with the previously detected point-like X-ray source CXOU J053600.0-67350, within the supernova remnant DEM L241, and this binary was previously classified as a high mass X-ray binary where the optical companion is a O5III(f) star. The source has also been detected at very high energies with the H.E.S.S. gamma-ray telescope, though in only one phase bin. We have used the High Resolution Spectrograph (HRS) with the Southern African Large Telescope (SALT) to obtain the best binary solution so far for this source, showing that source is slightly eccentric (~0.4) and constrained the phases of superior and inferior conjunction. The Fermi-LAT and H.E.S.S. results are discussed in relation to the new binary solution.
Speaker: Dr Brian van Soelen (University of the Free State)
• 11:20 13:00
Convener: Dr Stephan Winkler (NRF/iThemba LABS)
• 11:20
Lifetime measurements in <sup>44</sup>Sc excited states using LaBr<sub>3</sub> :(Ce) detectors coupled with the AFRODITE Array 20m
The progressive development of the scintillator detectors has made it possible to do direct electronic lifetime determination. The 2” x 2” LaBr3:(Ce) detectors provide a combination of excellent time resolution and good energy resolution. With these detectors it is possible to do direct lifetime measurements of excited nuclear states up to a few hundred nanoseconds. Six 2” x 2” LaBr3:(Ce) detectors were coupled to the AFRODITE array as their first in-beam experiment. AFRODITE consisted of eight HPGe clover detetectors as well two 3.5” x 8” LaBr3 (Ce) detectors. A particle telescope was used to select the desired reaction channel. The reaction of interest 45Sc(p,d) 44Sc was carried out at a beam energy of 27MeV. Through this reaction, excited states that have lifetimes which are apt for the characterization of the 2” x 2” LaBr3:(Ce) detectors were populated. One of the nuclei of interest in this work, 44Sc, has states with a wide range of lifetimes at low to moderate energies.
Speaker: Mr Lumkile Msebi (iThemba Labs, UWC)
• 11:40
Structure of <sup>33</sup> Si, <sup>35</sup> S and <sup>36</sup> S nuclei and the N=20 shell gap 20m
The project focuses on studying the evolution of the N=20 shell gap. The shell gaps have been previously investigated through studies of nuclear levels, using various experimental approaches namely: Coulomb excitation, knockout reactions, transfer reactions and g-factor measurements. In exotic nuclei with an imbalanced number of neutrons and protons, significant modifications of the nuclear structure have been observed. A detailed study of the evolution of the shell gaps will lead to a comprehensive understanding of the structure of atomic nuclei. In order to investigate the evolving shell structure it is necessary to determine single particle observables such as spectroscopic factors of the states involving the active orbitals at these shells gaps. A knockout reaction is the first set of data for this project, the experiment was performed at MSU/NSCL laboratory using the GRETINA gamma-ray tracking array and S800 spectrometer. The knockout reaction was performed using inverse kinematics with a 36S secondary beam incident on a 9Be target. The nuclei of interest studied are 33Si, 35S and 36S. Various transitions in these nuclei have been identified from the analysis of add-back Doppler corrected spectra and a level scheme has been built from the resulting analysis. In addition parallel momentum distributions have been constructed to investigate the possible nature of the different states. This work is supported by the National Research Foundation of South Africa .
Speaker: Ms Sandile Jongile (Stellenbosch/ iThemba LABS)
• 12:00
Potential Human Risk of Dissolved Heavy Metals in Gold Mine Waters of Gauteng Province, South Africa 20m
This paper evaluates the health risk caused by heavy metals in water around a gold mining area. In this study, samples of water were collected around the mining area. After appropriate preparation, all samples were analyzed for As, Pb, Hg, Cd, Cr, Cu, Zn, Co and Ni using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Measured concentrations of the various heavy metals were then used to calculate the average daily intake (ADI) for the inhabitants of the area through ingestion and dermal contact. This ADI was then used to calculate the hazard quotient (HQ) and hazard index (HI) leading to the determination of carcinogenic and non-carcinogenic effects of these heavy metals. The average concentrations of heavy metals decreased in the order of Ni>Cu> Zn>As> Cr>Co>Pb. In mg.L-1 the average concentrations were as follows: Ni (0.39); Cu(0.38); Zn (0.33); As (0.19); Cr (0.14); Co (0.08); Pb (0.01), respectively. Hg and Cd were not detectable. For the non-carcinogenic risk assessment, calculated values of HQ showed an HI value of 3.38×10-1, a value less than 1, which is potentially safe according to USEPA and South Africa guidelines. When the carcinogenic risk assessment was carried out, the results showed that the total cancer risk due to the heavy metals was 2.94×10-6 mainly due to dermal contact. The US Environmental Protection Agency considers a cancer risk in the range of 1 × 10-6 to 1 × 10-4 acceptable for regulatory purposes. From the findings presented, it was concluded that dissolved heavy metal levels in mine water were within permissible limits in the mining area.
Speaker: Dr Caspah Kamunda (Rusangu University)
• 12:20
Statistical Properties of highly-deformed Samarium isotopes 20m
The rare-earth isotopic chain of Samarium provides an excellent opportunity to systematically investigate the evolution of nuclear structure effects from the near spherical (β2=0.09) 144Sm isotope to the highly-deformed system 154Sm (β2=0.34). As the nuclear shape changes, statistical properties such as the nuclear level density (NLD) and γ-strength function (γSF) are expected to be affected. In particular resonance modes, such as the Pygmy Dipole (PDR), Scissors Resonances (SR) and the recently discovered Low-Energy Enhancement (LEE) in rare-earth region may reveal interesting features when their evolution is investigated across several nuclei in an isotopic chain. Most reliable knowledge can be obtained when results from several different experiments are compared. An experiment was performed in September 2016 at Oslo Cyclotron Laboratory (OCL) where the NaI(Tl) γ-ray array, silicon particle telescopes and 6 high-efficiency LaBr3:Ce detectors were utilized to measure particle-γ coincidence events from which the NLDs and γSFs will be extracted below the neutron separation energy threshold, Sn, using the Oslo Method (A. Schiller et al. 2000). The deuteron beam with 13 and 15 MeV energies was used to populate excited states in 154,155Sm through the inelastic scattering (d,d’γ) and the transfer reaction (d,p). Based on the results from these measurements, the extracted NLDs and γSFs will be used to investigate the evolution of nuclear structure effects in 154,155Sm and provide complementary information to the 154Sm(p,p’)154Sm and 154Sm(α,α’γ)154Sm data on resonance features that lie on the low-energy tail of the GDR. In addition, the results will further provide a near-complete picture on the evolution of the PDR, SR and/or the LEE as the isotopic chain transitions from near spherical to very deformed. In this talk I will present preliminary results of this investigation of statistical properties for 154,155Sm in comparison to the previous and recent measurements of 148,149Sm and 151,153Sm isotopes, respectively, and ongoing measurements of 152,153Sm at OCL. This work is based on the research supported in part by the National Research Foundation of South Africa, the IAEA under research grant number: 20454 and by the DFG under contract SFB 1245.
Speaker: Mr Kgashane Malatji (iThemba LABS / Stellenbosch University)
• 12:40
Microwave induced electron losses from an ECR Ion Source 20m
To enhance high charge state ion beam production it is imperative to maximize the electron confinement time of the heated electron populations of an Electron Cyclotron Resonance Ion Source (ECRIS). A key loss mechanism for heated electrons are induced by the injected microwaves which heats the plasma electrons of an ECRIS. This electron loss mechanism is thought to limit ultimate source performance. With this investigation a number of plasma diagnostics were combined to study this plasma process. Here we will report on the results of preliminary measurements on the JYFL 14 GHz ECRIS.
Speaker: Mr Muneer Sakildien (iThemba LABS)
• 11:20 13:00
Physics Education
• 11:20 13:00
Physics of Condensed Matter and Materials
Convener: Dr Raesibe Sylvia Ledwaba (University of Limpopo)
• 11:20
Effect of substrate temperature on photoluminescence properties of Eu<sup>3+</sup> doped BaZrO<sub>3</sub> thin films deposited by PLD 20m
Perovskite type (A2+B4+O2-3) structures are significantly important host for rare earth (RE) doping because they offer promising luminescence properties for light emitting diode, field emission display and all solid compact laser devices. Eu(3+ doped BaZrO3 thin films with cubic structure were prepared on Si(100) substrates by using the pulse laser deposition (PLD) technique, using an Eu3+ doped BaZrO3 target at 10 mTorr oxygen pressure. The substrate temperature was varied from 400°C to 700℃. The thicknesses of the films were calculated from transmittance spectra. The thickness of all the films were around 300 nm. The phase identification and structural properties of the films were characterized by X-ray diffractometry. Surface morphology were studied by Scanning Electron Microscopy. Elemental analysis was performed using X-ray photoelectron spectroscopy (XPS). The oxidation states were also confirmed from XPS analysis. With the increase in substrate temperature, the growth of the films changed. Intense red emission was observed by the excitation of UV light. Emission spectra showed peaks at 577, 597 and 615 nm corresponding to the 5D07F0 , 5D07F1 and 5D07F2 transitions of Eu3+, respectively. It was observed that the emission at 597 nm which was due to the magnetic dipole transition (5D07F1) was the dominating emission. This confirms that Eu3+ ion occupied the centro-symmetric Zr(4+ site. Emission properties and defects involved within the films were investigated via photoluminescence. Keywords: PLD, Thin film, Photoluminescence
Speaker: Dr ARUP KUNTI (University of the Free State)
• 11:40
Searching for Majorana Zero Modes Using Model-free Reinforcement Learning 20m
Majorana fermions are particles which are their own antiparticles; hence they have zero charge. They are governed by non-Abelian statistics. For a Majorana fermionic operator &gamma, and the Hamiltonian of a system H, Majorana fermions satisfy fermionic anti-commutation relation (that is, for a pair of Majorana operators &gammai, &gammaj; {&gammai, &gammaj} = 2&deltaij) and a Majorana fermion squares to 1 (that is, &gamma2 = 1). If, in addition to this, the fermionic operator commutes with the Hamiltonian of the system (that is, [H,&gamma] = 0), then such an operator is a Majorana zero mode (MZM). Majorana zero modes are Majorana fermions bound to zero energy. MZMs have applications in both topological quantum computation and spintronics. However, Majorana zero modes are yet to be conclusively demonstrated experimentally. In this work, we report the algorithm that searches for MZMs using reinforcement learning. Reinforcement learning is a machine learning paradigm where the learner is a decision-maker (agent) that takes action in an environment and receives rewards or penalties for the actions taken. Results obtained from this work demonstrate the significance of using reinforcement learning in the quest for Majorana zero modes.
Speaker: Dr Makhamisa Senekane (Department of Physics and Electronics, National University of Lesotho, Roma, Lesotho)
• 12:00
Magnetic properties studies of Fe-substituted La0.67Sr0.33MnO3 20m
The magnetic phase transitions for pure ceramic La0.67Sr0.33FexMn1-xO3 (x = 0, 0.05, 0.1, 0.2, 0.3 and 0.5) perovskites are investigated. The understanding of the magnetic interactions that occur in these perovskites manganite afford the opportunity to tune their properties for practical applications. The double exchange interactions in Mn3+-O-Mn4+ was found to be suppressed by the superexchange interactions in Mn3+(4+)-O-Mn3+(4+) as the Fe content x increases. The samples were found to be a mixed phase of ferromagnetism FM and antiferromagnetism AFM with a paramagnetic component. The saturation magnetization decreased from 52 emu/g to 1 emu/g at 300 K and from 80 emu/g to 5 emu/g at 2 K due to antiferromagnetic interactions. Exchange bias effect was observed at low temperatures especially at 240 K and 260 K with maximum values of 190 Oe and 194 Oe respectively. 57Fe Mössbauer spectroscopy measurements show a transition from a paramagnetic state to a mixed spectra of FM-AFM and paramagnetic components. The percentage contributions of the magnetic phases and their hyperfine magnetic field values were estimated from the 57Fe Mössbauer results.
Speaker: Mr Itegbeyogene Ezekiel (University of KwaZulu-Natal)
• 12:20
Effect of Hf and Cu on the cubic B2 TiPt shape memory alloys 20m
Computational modelling approach has been used to investigate the effect of hafnium and copper on the B2 TiPt shape memory alloys. The calculations were performed using the CASTEP code embedded in materials studio. Cubic B2 TiPt is known to be thermodynamically unstable at 0 K as compared to the B19 orthorhombic phase with it having the highest heats of formations and soft modes in the lowest frequency. Moreover, the C´ of the structure was previously found to be negative as compared to the commercialised B2 NiTi which is positive. With the recent increasing demand on shape memory alloys that can be used at high temperatures in aerospace and automobiles, TiPt is found to be one of the promising alloys with the transformation temperature of 1300 K. These alloys are known to remember their original shape when a certain temperature or pressure is exerted on them upon cooling. In order to enhance the elastic properties of the B2 TiPt alloy, Hf and Cu elements are substituted in the TiPt to form ternary and quaternary alloys. The stability of these structures are investigated with respect to their heats of formation, elastic constants and density of states. Interestingly, the addition of these elements increases the C´ of the structures with all the elastic constants being positive for the hafnium addition.
Speaker: Dr Rosinah Modiba (CSIR)
• 12:40
DPCMM Meeting 20m
Speaker: Dr Rudolph Erasmus (University of the Witwatersrand)
• 11:20 13:00
Space Science
Convener: Dr Shimul Kumar Maharaj (South African National Space Agency (Space Science) (formerly NRF Hermanus Magnetic Observatory))
• 11:40
Climatology of thermospheric meridional winds derived from South African ionosonde network during extended solar minimum of 2007-2009. 20m
Thermospheric winds play an important role in the dynamics of the mean behaviour of the midlatitude ionosphere especially during quiet conditions, which are dominant during low solar activity. This study will present equivalent meridional winds derived from ionospheric F2 peak parameters using the servo and Liu et al. (2003) methods during the solar minimum period of 2007-2009. Midlatitude ionosonde data over Grahamstown (33.3˚S, 26.5˚E), Hermanus (34.4˚S, 19.2˚E), and Madimbo (22.9˚S, 30.9˚E) are used to derive the winds. For the first time, local time and seasonal dependency of the derived winds over this region are explored and compared to global trends. The equivalent winds are compared to the winds predicted from the horizontal wind model 2014 (HWM14) and the coupled middle atmosphere thermosphere model (CMAT2) to test the validity of these methods.
Speaker: Dr Zama Thobeka Katamzi-Joseph (South African National Space Agency)
• 12:00
Estimation of ionospheric vertical drifts based on magnetometer and satellite data 20m
This work presents the development of a mathematical relationship between ground-based magnetometer and satellite data to estimate long-term values of ionospheric vertical drift during local daytime. The expression is developed based on a relatively long-term data set during 2008-2014 and validated with radar observations. The obtained correlation coefficient values computed using observed and derived vertical drift velocities are 0.78 and 0.83 for two different sets of radar measurements during 2008-2014 when data was available. In this talk, we will show that this approach is applicable during both quiet and disturbed conditions; and forms a basis for development of high resolution vertical drift models in equatorial latitudes.
Speaker: Dr John Bosco Habarulema (South African National Space Agency)
• 12:20
Storm-time TEC mapping over Africa and surrounding areas 20m
Based on storm-time ionospheric total electron content (TEC) derived from Global Positioning Systems (GPS) measurements over the African sector and surrounding areas, TEC maps will be developed based on data assimilation technique. The region of interest extends from -40 to 40 and -20 to 60 latitude and longitude degrees, respectively, and the Kalman filtering technique with the International Reference Ionosphere (IRI) as a background model will be used during data assimilation process. A statistical analysis of the results will also be presented.
Speaker: Dr John Bosco Habarulema (South African National Space Agency & Rhodes University)
• 12:40
The ionospheric response to HILDCAA events over the African mid-latitude sector 20m
The response of the ionosphere to High-intensity, long-duration, continuous AE activity (HILDCAA) events that occurred during the solar cycle 23 and 24 will be presented. HILDCAA are magnetospheric/ionospheric events that occur during high-speed solar wind streams. During solar minimum, the corotating interaction regions (CIRs) are followed by lengthy (days to weeks) periods of HILDCAA intervals characterised by low Disturbance storm time (Dst) index. The HILDCAA events were selected based on the high intensity, long duration, continuous Auroral electrojet (AE) activity where AE peak values exceed 1000 nT, the duration were greater than 2 days and the AE values never drop to 200 nT for more than two hours at a time. The HILDCAA must occur outside the main phases of the geomagnetic storms. The critical frequency of F2 layer (foF2) and Global Navigation Satellite System (GNSS) Total electron Content (TEC) over the African mid-latitude region will be used to analyse the ionospheric responses. Some physical processes responsible for the ionospheric responses will be discussed.
Speaker: Mrs Tshimangadzo Merline Matamba (SANSA Space Science)
• 11:20 13:00
Theoretical and Computational Physics
• 13:00 14:00
Lunch 1h Centenary Complex

### Centenary Complex

• 14:00 15:00
Plenary: Rogers
Convener: Prof. Odireleng Ntwaeaborwa (University of the Witwatersrand)
• 14:00
Emergent Property Sets & Applications of Beta-Gallium Oxide 1h
Recently, there has been a surge in interest for the wide bandgap (Eg ~ 4.9 eV) semiconductor gallium oxide (Ga2O3). A key driver for this boom is that single crystal wide area bulk β-Ga2O3 substrates have become commercially available [1] and a variety of methods have been shown to give high quality epitaxial growth [2,3]. Although Ga2O3 has a number of polymorph forms (α-, β-, γ-, δ- and ε) the more stable monoclinic phase (β-Ga2O3) has attracted the most attention. Amongst a whole range of potential applications power electronics, solar-blind photodetectors and UVC transparent electrodes offer exciting perspectives [3-5]. In this talk we give an overview of these applications illustrated with examples from the β-Ga2O3 development work carried out at the French oxide epiwafer start-up, Nanovation [4-7]. [1] http://www.tamura-ss.co.jp/en/products/gao/index.html [2] http://nanovation.com/en/products/ [3] M. Razeghi, D. J. Rogers et al. Proc. SPIE 15330 (2018) 15330 O R-1 [4] D. J. Rogers et al. Proc. SPIE 15330 (2018) 15330 O R-1 [5] A. Perez-Tomas, D. J. Rogers et al. Proc. SPIE 15330 (2018) 15330 1 Q-1 [6] F. H. Teherani, D. J. Rogers et al. Proc. SPIE 10105 (2017) 10105 1 P-1 [7] E. Chikoidze et al. Materials Today Physics 3 (2017) 118
Speaker: Dr David Rogers (Nanovation)
• 15:00 17:00
Poster Session 2
• 15:00
4fN energy level schemes for the di-, tri-, and tetravalent lanthanides 2h
Since the refinement of the famous Dieke diagram (DD) [1] to include all higher energy levels, not much progress has been made in this field. It is now clear, though, that the purely theoretical methods have still a long way to go to yield the 4fN (or 5fN) energy levels in any accuracy. This is because the new applications, e.g. up- and down-conversion, require energy levels that are ever more accurate. In fact, these processes are the most efficient when quasi-resonant condition is reached. The proven phenomenological methods to calculate the energy level schemes (and wave functions required by many applications) are still the most reliable, accurate and fastest way. Unfortunately, some of the published data [2] are so inaccurate that they are of little or no use. In this work, the energy level schemes for the di-, tri-, and tetravalent lanthanides were calculated taking into account the crystal field effects as well. The effect of the host was synchronised for both the R2+ and R3+ series by the use of isomorphic crystal structures (BaFCl and ROCl, respectively) facilitating the comparison between them. Utmost care was taken to compare the calculated data with the experimental one which was easy for the R3+ but much more scarce for the R2+ series. For the RIV series, experimental data is virtually inexistent. The energy level schemes for the R3+ are the most useful ones whilst the 4fN levels of the R2+ series are often masked in practice by the low-energy 4fN-15d1 configuration. The 4fN levels of the RIV series are practically inaccessible because of the low-energy charge transfer transitions and the initial low-energy positions of the 4fN levels of RIV species. References [1] R.H.T. Wegh, A. Meijerink, R.-J. Lamminmäki, J. Hölsä, J. Lumin. 87-89 (2000) 1002. [2] C.-G. Ma, M.G. Brik, D.-X. Liu, B. Feng, Ya Tian, A. Suchocki, J. Lumin. 170 (2016) 369.
Speaker: Prof. Hendrik Swart (University of the Free State)
• 15:00
A Mechanism for (&epsilon, &delta)-differential privacy using Student's t distribution 2h
The proliferation of data and data analysis has resulted in a need to pay more attention to the security of the the data being analyzed. Different options have been pursued to guarantee privacy of these statistical databases generated. However, most of such options cannot offer guarantee of security of the statistical databases. On the other hand, differential privacy is able to meet such a requirement of security definition. It guarantees privacy of an individual against an adversary with arbitrary auxiliary information. Differential privacy can be categorized as either &epsilon- or (&epsilon, &delta)-differential privacy. In this work, we report a mechanism for (&epsilon, &delta)-differential privacy using Student's t probability distribution. Our results guarantee the privacy and the utility of the mechanism, and this underlines the utility of this mechanism.
Speaker: Dr Makhamisa Senekane (Department of Physics and Electronics, National University of Lesotho, Roma, Lesotho)
• 15:00
An evaluation of the Newton-Raphson iteration method in the prediction of leaf temperature 2h
A knowledge of the temperature of leaves is of enormous significance particularly from a plant physiological point of view. A study was conducted under field conditions to evaluate Newton-Raphson iterative method as an alternative approach in the indirect determination of leaf temperature from meteorological data. Three field experiments were performed at two different sites at Cape Peninsula University of Technology (CPUT), Bellville Campus in Cape Town, using three different plants. Leaf temperatures predicted from the iteration method were compared with field measurements of leaf temperatures obtained from a local tree, potted Strelitzia Nicolai flower plant and Agapanthus Praecox, another flower growing at CPUT nursery complex. The strongest relation, characterized by reasonable precision (R2 = 0.89), high accuracy (D = 0.96) and a fairly high value of the confidence index (C = 0.91) was obtained when Agapanthus Praecox was used, whilst Strelitzia Nicolai yielded a poorer relationship (R2 = 0.71; D = 0.77; C = 0.64). The tree had the worst correlation. Leaf temperature computed by the iteration process showed a tendency of underestimation in all the field experiments.
Speaker: Dr Martin Kudinha (CPUT)
• 15:00
Are Bessel beams resilient to aberrations and turbulence? 2h
It is understood from the conical wave picture that Bessel beams may self-heal after certain opaque obstructions, but the extrapolation to transparent phase screens is not self-evident. We demonstrate that self-healing is not guaranteed when the Bessel beam is propagated through transparent obstacles with aberrations but is rather dependent on the strength of the aberrations. Finally we combine aberrations to simulate the Bessel beam passing through turbulence and debunk the myth that Bessel beams are resilient to such perturbations.
Speaker: Ms Nokwazi Purity Mphuthi (Hartebeesthoek Radio Astronomy Observatory: Space Geodesy)
• 15:00
Cathodoluminescence degradation of Bi doped SrO phosphor powder 2h
Speaker: Mr Mogahid Abdelrehman (University of the Free State)
• 15:00
Charactarisation of the solar resource at the Fort Hare Institute of Technology 2h
The sun is the primary source of energy on earth as almost all the sources of energy emanate either directly or indirectly from the sun. It is also at the center of the photovoltaic technology in which case, sunlight is directly converted to electricity with the use of solar cells. An in-depth knowledge of the sun and the various factors that affect its intensity are very vital for photovoltaic system manufacturers and operators. This will improve the efficiency of an already efficiency-limited photovoltaic energy technology. However, solar characterization for locations in the Southern hemisphere are not common in literature. Attention is mostly paid to locations in the Northern hemisphere. Here, existing mathematical models were used to perform a holistic solar characterization at the Fort Hare Institute of Technology which is located in the southern hemisphere. The variation of solar parameters such as solar declination, elevation, zenith and azimuth angles as well as air mass ratio were examined. Also the variation of different components of solar radiation such as; direct beam, diffuse and reflected components were evaluated. These results were compared to the results obtained from an onsite weather station. The comparison between the calculated and the on-site measured values yielded just a 1.1% difference. This means in the absence of weather stations, mathematical models can be used to evaluate various solar radiation parameters with a high degree of certainty. Finally, the results obtained from the computations and measurements were compared with data from nearby weather stations.
Speaker: Ms Carine Buma (University of Fort Hare)
• 15:00
Characterization of aluminium Schottky junction diode fabricated on nickel oxide thin film synthesized through sol-gel method 2h
Nickel oxide (NiO) thin films were deposited on glass substrates through the sol-gel spin coating technique. Structural, optical and electrical characteristics of the films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Uv-vis spectrophotometery and linear four point probe resistivity measurement. The films were found to be polycrystalline, uniform, conducting and transparent. NiO film was also deposited on p-type silicon substrates and aluminium contacts of 0.6 mm diameter were deposited on the film to form an Al/NiO/p-Si structure. Indium-gallium was used as ohmic contact on the silicon and current-voltage characteristics of the Al/NiO schottky junction were investigated. The junction showed good rectification and the parameters of the junction were determined.
• 15:00
Characterization of stirred calibration bath from -80 to 550 °C 2h
This paper describes the methods of characterizing stirred liquid bath at the National Metrology Institute of South Africa (NMISA) in maintenance and dissemination of the international temperature scale of 1990 (ITS-90). In practice, methods of characterizing stirred liquid baths varies from institution to another as well as manufacturer. This results in either over estimation or under estimation of uncertainty in calibration of thermometers. Generally, the criteria for choosing stirred calibration baths depends on the manufacturer stated stability of time and temperature gradients over the working volume of the bath. The methods used by manufacturer in most specifications are not clearly defined or even stated. As a result, most laboratories develop their own accredited procedures in estimation the effect of the stirred liquid baths in overall uncertainty of thermometer calibration, which in turn differ amongst them. Through a practical example, the paper describes for three different methods in characterizing stirred liquid baths from -80 °C to 550 °C. Axial or radial temperature gradients were observed as thermometers were placed in different locations in the bath. Furthermore, since the reading of the thermometer(s) changes over time, the methods used are independent of the variation of the bath temperature over time. Hence the uncertainty due to the bath is not over estimated or under estimated. Through these methods, uncertainty in calibration thermometers due to stirred calibration liquid baths were found to be in the range of sub mK to 100 mK from -80 °C to 550 °C. .
Speaker: Mr Tshifhiwa Madiba (National Metrology Institute of South Africa)
• 15:00
Collinear ptychographic pulse reconstruction of ultrashort laser pulses 2h
Reconstruction of the phase and amplitude of ultrashort pulses are needed since no detector is fast enough to measure these pulses directly. Many methods to do so exists each with its own set of advantages and disadvantages. The only pulse reconstruction methodology which allows one to reconstruct the electric field at the sample plane in the focus of a collinear pulsed laser source, is the multiphoton intrapulse interference phase scan (MIIPS). The technique requires rescanning a specific phase pattern for multiple steps and thereby allowing extraction of the phase from the measurement. The process is repeated several times to improve the extracted phase until the deviation from the previous extracted phase is small enough to stop. We have adapted the time-domain ptychographic reconstruction algorithm to take a MIIPS trace as an input and reconstruct the full electric field with the advantage that only a single scan needs to be taken where after the measure spectrogram is passed to the Ptycho-MIIPS reconstruction algorithm. Ptycho-MIIPS has the advantage that it returns not only the phase but also the amplitude of the electric field, unlike MIIPS which only returns the phase.
Speaker: Mr Ruan Viljoen (Stellenbosch University)
• 15:00
Computational Modelling of FeS<sub>2</sub> Nanoparticles 2h
Nanoparticles have been the area of active research in the recent years due to their unique material properties, which distinguish them from the bulk materials due to the high surface atom ratio. Pyrite (FeS2) structures at a nanoscale are considered to be one of few materials for photovoltaics capable of bridging the cost and performance gap of solar batteries. It also holds promise for energy storage applications as the material for high-performance cathodes. Computational modelling technique, molecular dynamics (MD) was performed to provide atomic or molecular level insights of the structural and dynamics of iron sulphide (FeS2) nanoparticles (NP’s). NP’s of different sizes ranging from approximately 1 nm to 4.5 nm were considered. The effect of temperature on different sizes of NP’s was determined via radial distribution functions (RDF’s), energy as a function of temperature and structural changes. At low temperatures the RDF’s have many and sharp peaks (the structure is still compact), at higher temperature the peaks are few and smooth which is an indicative of phase transition. Density Functional based Tight-Binding (DFTB+) code was utilized to study the electronic properties of the different sizes of nanoparticles, whereby the effect of temperature on the electronic properties. Band structures have indicated at low temperature there is a low band gap but at high temperature the material become metallic. Our findings have demonstrated that nanotechnology is the future for energy storage especially utilizing pyrite materials.
Speaker: Dr Thabo Letsoalo (University of Limpopo)
• 15:00
Current Status of the Technology of Light Emitting Diodes from Silicon Carbide: A Review. 2h
Light-emitting diodes (LEDs) are semiconductor devices that emit light in a narrow-band spectrum with wavelengths ranging from the infrared to the ultraviolet. This paper will look at current state of the art of the fabrication techniques and characterisation of LEDs from silicon carbide (SiC). SiC has a wide band gap and high thermal conductivity. These unique properties make SiC an ideal candidate for fabricating high-temperature operating semiconductor devices. Most of the LED technology at present uses gallium nitride (GaN) with phosphors. Phosphors have a short life-time and contain rare-earths which are very expensive. In order to overcome these shortcomings, the technology of producing highly efficient SiC-based LEDs has to be explored so as to make them a viable alternative to GaN-based LEDs.
Speaker: Dr Kinnock Vundawaka Munthali (University of Namibia)
• 15:00
Data Analysis and Security Development of a Wireless Mesh Network 2h
A multiple router, low-power mesh wireless network with multi-hopping networking capabilities was developed at the Physics building ground floor. Multi-point data between routers was collected over an extended period of time. This study contributes to the analysis of the data for an anti-theft application, based on the future work of the research 'System Control Applications of Low-power Radio Frequency Devices' (S.A.I.P 2017). Data packets were sent between multiple mesh routers and quantitative experimental data was collected consisting of latency delays and packet losses. The network performance, based on statistical analysis, has indicated reliable interconnected node communications even in the presence of physical obstacles in the environment. To extend the study, an algorithm is proposed for implementation on an Android application of the device and application layer of the routers. This is to ensure secure communications within the mesh components. Secure communications between the device and the network will result in normal device operation while device locations outside the coverage perimeter may render the device inoperable. The added security feature allows secure communications of devices connected to the network and prevents unauthorized connections such as black-hat hacking.
Speaker: Mr Rorisang Sitoboli (University of the Witwatersrand)
• 15:00
Data extraction techniques for terahertz time-domain ellipsometry 2h
Terahertz(THz) radiation is a powerful tool for non-destructive spectroscopy and has the potential of being useful in analysing biological materials. Due to the strong absorption of THz radiation by water, a reflection-based geometry is required when investigating samples in an aqueous medium. Due to the relatively low alignment tolerance in THz time-domain spectroscopy it is preferable to implement a technique that does not depend on the need for a reference measurement when performing reflection-based measurements. Ellipsometry has been implemented to this end. The construction of a THz ellipsometer has been completed, but to make use of the measured data, analysis algorithms need to be implemented and tested. The development of these algorithms, which are model dependent and are applicable to specific cases, will be discussed. The cases investigated are bulk isotropic samples, single-layer isotropic samples and two-layer isotropic systems where the second layer is a bulk isotropic layer.
Speaker: Mr Shane Smith (Student Member)
• 15:00
Defects in diamond created by NO<sup>+</sup> ion implantation 2h
The formation of shallow n-type dopants in diamond is one of the major challenges for the electronic application of diamond. n-type behavior in diamond is observed for substitutional phosphorus and nitrogen, with activation energies of ~0.62 and 1.7 eV respectively. It has been theoretically found that the substitution of N-O molecule into the diamond lattice induces a shallow defects below the conduction band edge which may lead to n-type conductivity. In this project we are exploring the possibility of achieving n-type conductivity in diamond by conducting an experimental investigation on the interaction between nitrogen and oxygen in the diamond as well as the related defects. This involves placing nitrogen and oxygen impurities close to each other into the diamond lattice by means of ion implantation; which has the advantage to provide greater accuracy of depth and location of ions in the host material. Optical spectroscopy and electrical characterization techniques are used to investigate the nature and behavior of the defects induced by the implantation of N-O ions into type IIa CVD diamond samples. In this presentation the experimental results of photoluminescence, Raman spectroscopy and cathodoluminescence will be discussed.
Speaker: Mr Tresor MATINDI (University of the Witwatersrand)
• 15:00
Design, development and characterization of a magneto-optical trap for laser cooling of Rubidium atoms: a project at the Cape Peninsula University of Technology 2h
Laser cooling of neutral atoms have opened up a new area of research into ultra-low temperature physics of quantum systems. These systems have shown potential in many areas of quantum information processing, such as single photon sources, entangled photon generation, quantum simulations using cold atoms in optical lattices etc. We describe in this presentation the theory of laser cooling and the development and characterization of a device to cool and trap neutral Rubidium atoms. The system consists of an octagonal vacuum chamber having a number of view ports, vacuum pumps, piping, vacuum gauge and valves. Three stages of pumping (i.e. rotary, turbo and ion pumping,) are used to reduce the pressure from atmospheric down to ~ 10^(-10) mbar. Rubidium atoms stored in a getter material are released into the vacuum chamber by means of electrical heating. Three pairs of counter propagating laser beams, each pair positioned on opposite sides of the chamber along three orthogonal axes are used for cooling of the atoms in the chamber. The lasers are frequency locked, using a saturated absorption setup and incorporating a PID controller, to the 5S1/2(F=2) to 5P3/2(F=3) transition of Rb87. Because the atoms eventually move out of the cooling transition cycle a re-pumping laser is also incorporated and tuned to 5S1/2(F=1) to 5P3/2(F=2) transition. The cooled atoms will be trapped using a pair of anti-Helmholtz magnetic coils positioned on either side of the vacuum chamber. Measurements will be conducted using optical sensors such as CCD cameras and avalanche photo detectors for measuring the light emitted by the trapped atoms. By measuring the fluorescence of the cooled atoms, the number density, size of the atomic cloud, and temperature can be inferred. We provide preliminary measurements of these, in addition to details of the performance of the saturated absorption setup and of the laser control for Doppler cooling.
Speaker: Dr Kessie Govender (Cape Peninsula University of Technology)
• 15:00
DFT study of Modifications of Pt-doped TiO2 using N, for application in DSSCs 2h
Doping has found to be one of the most promising method to in increasing photocatalytic activity of various materials. The location and nature of the doping elements strongly affect the structural, electronic and optical properties of TiO2. To tailor the band structure and modify the photocatalytic activity of TiO2 brookite (210) surface, a pair of dopants is selected. Platinum and Nitrogen atoms are inserted in the TiO2 network as substitutional and N was also doped through absorption on the surface. The main objective behind the different locations and methods of the dopant elements are to banish the isolated unoccupied states from the forbidden region that normally annihilates the photogenerated carriers. Pt replaced Ti, N replaced O and N was also absorbed and bond with 2 coordinated O in the TiO2 brookite (210) surface network. N absorbed Pt\N TiO2 provided a suitable configuration of dopant atoms in terms of geometry and band structure. Moreover, the optical properties showed a notable shift to the visible regime. Individual dopants either introduced isolated unoccupied states in the band gap or disturbed the Fermi level and structural properties. Furthermore, the other co-doped configurations showed no remarkable band shift, as well as exhibiting a suitable band structure. Resultantly, comparing the band structure and optical properties, it is argued that Pt (at Ti) and N absorbed (at O) doped would strongly improve the photocatalytic activity of TiO2 brookite (210) surface.
Speaker: Mr Ratshilumela Steve Dima (University of venda)
• 15:00
DFT STUDY OF SELECTED NEAR INFRARED (NIR) FREE METAL DYE MOLECULES FOR APPLICATION IN DYE SENSITIZED SOLAR CELLS 2h
Dye‐sensitized solar cells (DSSCs) have attracted considerable attention in recent years as they offer the possibility of low‐cost conversion of photovoltaic energy. DSSCs use the dye molecules adsorbed on the TiO2 semiconductor in nano architecture with the role of absorbing photon from the sun. The electronic structure and excitation properties of dye sensitizer determine the efficiency of the DSSCs. The dye molecule is sensitizer that absorbs the photon from the sun and inject an excited electron on the TiO2 semiconductor. The study focuses on the understanding of different properties (electronic optical properties) of NIR-dye molecules employing density functional theory (DFT) calculations. The calculations are based on the determinations of Absorption spectrum, UV-Vis spectrum and Light Harvesting Efficiency of the dye molecules. The results obtained shows that NIR-dye molecules can improve the efficiency of DSSCs as there is a shift of absorption to the near infrared, which increase the absorption range from visible on the solar spectrum. Keywords: Dye Sensitized Solar Cells, Dye,Efficiency
Speaker: Mr Tshifhiwa Steven Ranwaha (University of Venda)
• 15:00
Elastic and Thermal Properties of Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> by Surface Brillouin Scattering 2h
Ge2Sb2Te5 (GST225) is a chalcogenide phase change alloy widely used in optical storage media and electronic memory devices. It has been studied in the past two decades due to its optical and electrical properties driven by fast and reversible structural phase transformation. However, its elastic properties have not been thoroughly investigated. Since thermal energy can be stored in vibrational modes, surface Brillouin scattering (SBS) has been used to determine the elastic properties and correlate them with thermal properties. RF-magnetron sputtering was used to deposit films of thickness varying from 50-500 nm on a Si/Si1O2 substrate. The crystalline (c) phase was obtained by annealing the samples at a temperature of 150 ֯C for one hour. Since the transition between the amorphous (a) and crystalline phases is associated with a volume change, we studied this by measuring the densities of the two phases using x-ray reflectivity. Rutherford Backscattering was used to investigate the films chemical composition and atomic density, which was found to be n~3.05×〖10〗^22 and 3.01×〖10〗^22 atoms cm^(-3) for a-GST225 and c-GST-225. The elastic constants for the amorphous (a) and crystalline (c) phases obtained are C11=37.9/37.0 GPa, C12=17.6/13.1 GPa and C44=10.2/12.0 GPa respectively. The corresponding longitudinal and transverse velocities are vl=2558/2499 m/s and vt=1325/1421 m/s. Lastly the calculated minimum lattice thermal conductivities of a- and c-GST225 were found as κmin=0.283 and 0.287 Wm^(-1) K^(-1). Such low thermal conductivities are desirable for improving thermal management in memory devices during programming.
Speaker: Ms Mmapula Baloi (University of the Witwatersrand)
• 15:00
Elastic constants of as-deposited amorphous SiC thin films by Brillouin Spectroscopy 2h
Silicon carbide (SiC) has proven to be the future of Micro-electromechanical systems. Previous research has dwelled on the properties of SiC thin films on Si or silicon-on-insulator substrates and it has been a success in realising the potential of SiC (van Rijn, 2013). However, due to the difficult micromachining process and high density of defects when dealing with the SiC substrate , the elastic properties of a-SiC thin film on 3C-SiC and glass substrates remain a subject of tremendous scientific interest. In this study, a complete set of elastic constants of amorphous SiC thin films were determined by Surface Brillouin Scattering. The films were deposited by RF magnetron sputtering using a commercial SiC target. Subsequently the films were characterized using scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to study the surface morphology and structural properties. Raman showed a strong randomization of Si-Si (500 cm-1), Si-C (780-800 cm-1) and C-C (1400 cm-1) modes suggesting the films were amorphous. Velocity dispersion curves of surface acoustic waves in SiC films deposited on glass, were obtained, from which the dispersive Rayleigh mode was measured at 5120 m/s. Simulations of SBS spectra of SiC thin films on silicon and glass substrates were carried out to inversely extract the elastic constants of the films. The simulations were based on the elasto-dynamic Green's functions method that predicts the surface displacement amplitudes of acoustic phonons. Sound velocities for both transverse and longitudinal waves were determined along with the elastic constants C11, C12, C13, C33 and C44.
Speaker: Hlosani Dube (Wits Masters Student)
• 15:00
Electrically active induced energy levels and metastability of B and N vacancy-complexes in 4H-SiC 2h
Electrically active induced energy levels in semiconductor devices could be beneficial to the discovery of an enhanced p or n-type semiconductor. N implanted into 4H-SiC is a high energy process that produced high defect concentrations which could be removed during dopant activation annealing. On the other hand, B substituted for silicon in SiC leads to a decrease in the dielectric properties and induced deep donor and shallow acceptor levels. Complexes formed by the N, such as the nitrogen-vacancy centre, have been reported to play a significant role in the application of quantum bits. The results of charge states thermodynamic transition level of the N and B vacancy-complexes in 4H-SiC are presented. The energies of formation of the N related vacancy-complexes shown the NCVC to be energetically stable close to the valence band maximum in its double positive charge state. The NCVSi is more energetically stable in the double negative charge state close to the conduction band minimum. The NSi VC on the other hand, induced double donor level and the NCVSi induced a double acceptor level. For B related complexes, the BCVC and BSiVC were energetically stable in their single positive charge state closed to the valence band maximum. As the Fermi energy is varied across the band gap, the neutral and single negative charge states of the BSiVC become more stable at different energy levels. B and N related complexes exhibited charge state controlled metastability behaviour.
Speaker: Dr Emmanuel Igumbor (University of Pretoria)
• 15:00
Elemental analysis and Activation in Kimberlite using delayed gammas after GDR photon induced activation. 2h
Element analysis as a nuclear activation analysis technique (gamma,x) using photons above the Giant Dipole Resonance and the (gamma,x) reactions is a novel development. In these studies the excited nuclei decay by photon emission and these photons can be detected using time stamped event-by-event data acquisition with multiple gamma detectors. In this way, the resulting spectra can be multi-dimensional as (energy, time) or (energy, energy). The ambiguity in the identification of the decaying nuclide is well resolved considering unique sequential decay chains or using the extracted lifetime for a given gamma energy. The data was acquired on a time scale of minutes to weeks following activation, so that a wide range of activated nuclide lifetimes could be identified. The samples were various kinds of kimberlite rocks. A benchmark analysis using XRF was also performed. The elemental analysis technique is potentially of interest for non-destructive geochemical analysis. The study had a dual purpose in that it is also relevant to the study of nuclide activation that is of importance to the MinPET technique as elaborated in companion presentations. The experiments were carried out at the electron injector microtron of the ASTRID storage ring of the ISA, Centre of Storage Ring Facilities at the Department of Physics in Aarhus University, Denmark.
Speaker: Mr Thendo Emmanuel Nemakhavhani (University of Johannesburg)
• 15:00
Extracting a vibrational Raman spectrum from a broadband Coherent Anti-Stokes Raman Scattering measurement 2h
Probing the vibrational energy states of molecules can be done by Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy. Traditionally two or three different laser beams are employed to pump and probe the vibrational spectrum of molecules, probing the molecules one wavelength at a time. With the introduction of a coherent broadband light source it is possible to pump and probe multiple states simultaneously, with a single broadband beam. Increasing the pump bandwidth has the disadvantage of increasing the non-resonant CARS signal which drowns out and masks the spectrum-containing resonant signal. For broadband single beam CARS, the question is: how does one extract the Raman spectrum from the mix of resonant and non-resonant CARS? In this presentation we introduce novel techniques that answer this question. We simulate these techniques to illustrate the expected single beam CARS measurements and how a vibrational Raman spectrum can be extracted. Comparisons are made between these simulations and experiments on liquid and crystalline samples to prove the techniques.
Speaker: Mr Ruan Viljoen (Stellenbosch University)
• 15:00
Fabrication and characterization of Au and ZnO nanowires on silicon substrate spin coated with poly(methylmethacrylate) resist. 2h
One of the goals of nanoscience and nanotechnology is to synthesize and manufacture nanodevices that are multifunctional, exceptionally small and sensitive with low power consumption. In the past five decades, numerous investigations resulted in novel nanodevices with applications such as resonators, biosensors, logic devices, transistors, optoelectronics and even in situ biomedical monitoring and detection. Real-time energy harvesting from the environment to power these nanosystems and devices is an essential requirement. As such solar-energy harvesting technologies for nanoscale devices have been an emerging field of research. For example, a singular silicon nanowire has been demonstrated to fabricate a photovoltaic cell that is effective to drive a nanowire-based logic gate or even pH sensor. As an added incentive, these technologies may further be scaled up to deliver more efficient green energy sources, by manipulating the current solar-energy harvesting technologies on the nanoscale to increase their efficiencies. In this study it is shown that metal (Au) and semiconductor (ZnO) nanowires can be fabricated by a combination of pulsed laser deposition (PLD) and electron beam lithography (EBL). EBL was conducted using the electron beam from the auger electron spectroscopy (AES) system to produce grooves trenched on poly (methyl methacrylate) (PMMA). This polymer was spin coated on oxidized silicon (110) substrates. PMMA thickness for each specimen was then measured using atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) and the relationship of the thickness to spin speed and PMMA composition was established. The morphology of the fabricated nanowires was examined by utilization of scanning electron microscope (SEM). The changes in optical and electrical properties with respect to nanowires dimensions were investigated through characterization by photoluminescence (PL), UV absorption and solar simulation techniques.
Speaker: Mr Sekhants'o Lara (University of the Free State, Department of Physics)
• 15:00
First principles investigation of structural, dynamic, electronic and optical properties of Barium seleno-germanate Ba<sub>2</sub>GeSe<sub>4</sub> 2h
Ternary and quaternary chalco-germanates and stannates have a rich structural chemistry. Experimental studies of their nonlinear optical properties have been reported, but there are few published computational studies on their structural, dynamic, electronic and optical properties. In this work, we investigate the structural, dynamic, electronic and optical properties of Ba2GeSe4 using Density Functional Theory (DFT) and post-DFT many body perturbation theory. The ground state energy and properties, including equilibrium lattice parameters, bulk modulus, band gap and phonon dispersion were calculated at the DFT level of approximation. The fundamental gap was determined at the post DFT G0W0 level of approximation while optical absorption was determined within the Bether-Salpeter Equation approximation. The ground state energy, mechanical and phonon dispersion results show that Ba2GeSe4 is a stable compound while the calculated optical absorption results show that it is a wide band gap material that is well-situated for photon absorption in visible range.
Speaker: Abdu Barde (The National Institute for Theoretical Physics, School of Physics and Mandelstam Institute for Theoretical Physics, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa.)
• 15:00
First principles studies of Palladium nanoparticles on TiO<sub>2</sub> surfaces. 2h
Precious metal catalysts, which include the platinum group metals (PGMs), find their way into processes such as in emission control technology. Metal nanoparticles supported on metal oxides are being considered as catalysts in the emission control technology, with the most used catalysts being the Pt and Pt-based catalysts. However, Pd-based catalysts are being developed since they have similar electronic configurations and lattice constants as Pt but are cheaper and show other interesting properties which find them suitable for use in catalytic converters. Here it is shown that the rutile (110) surface is stable and thus a suitable support material to be used in this type of catalysis, whereas previously anatase was suggested. The palladium clusters show that Pd13 is stable from its least negative second order difference (D2E) energy value. Furthermore, we found that the interactions of the Pd13/TiO2 gave the most favourable site to be the one where Pd13 adsorbs on the bridging oxygen. This suggests that adsorption is likely to be more effective when the catalyst and support material are configured in that order. Our results demonstrate how the interaction of the stable components of Pd13/TiO2 will result in more carbon monoxide emissions being controlled when used in catalytic converters because of the high affinity to hydrogen that the Pd13-catalyst has which will subsequently result in the conversion of carbon monoxide into carbon dioxide and water.
Speaker: Ms Andile Mazibuko (yes)
• 15:00
Graphene/Transition metal oxides thin films using first principle approaches 2h
Since the effectively increase in the efficiency of dye sensitized solar cells (DSSCs) by O’Regan and Gratzel in 1991, the research in the string of DSSCs has grown rapidly. The preparation of the mesoporous oxide (typically, titanium dioxide) film is a key factor in the optimization of DSSCs because of its enormous influence on the anchoring of dye molecules, and the transfer and separation of charge carriers. However charge recombination is a main negative factor that limits DSSCs performance. It is predicted that improving the conduction from the location of the photo-generated carriers to the collecting electrode would considerably enhance the DSSC efficiency. One way to slow recombination is by use of composite semiconductor photoanode with different bandgaps. Recently, carbonaceous nanomaterials such as carbon nanotubes and two-dimensional graphene sheet have attracted the attention of the scientific community in probe to improve energy conversion and storage technologies. The graphene sheet is more preferred due to its large specific area, flexible structure, high transparency and also excellent mobility of charge carriers and is expected to be able to slow the charge recombination. Graphene/Transition metal oxides nanocomposite study has become much of a wide interest recently with metal oxides like titanium dioxide, zinc oxide, Chalcopyrite, etc in search to improve the DSSCs performance. The final composite embodies both the transport properties of the former and the semiconducting properties of the latter species. This talk gives preliminary results of electronic and optical properties of the final composite studied using the Density Functional Theory in application to DSSCs.
Speaker: Mr Lutendo Phuthu (University of Venda)
• 15:00
Growth and Characterization of Metallic Film Precursors for the Synthesis of CZTS Thin Films for Photovoltaic Applications 2h
Copper Zinc Tin Sulphide (CZTS) thin films are materials of interest for low cost solar cells due to their suitable direct band gap of between 1.4 and 1.5eV, large absorption coefficient of over 104 cm-1, abundance and low toxicity of the elements in the CZTS compound compared to the currently used compounds, such as copper indium selenide (CIS), copper indium gallium selenide (CIGS) and cadmium telluride (CdTe), which are rare and toxic. However, the suitability of CZTS materials under different radiation environments has not yet been tested. In this work, i.e., the first phase of CZTS synthesis, Cu-Zn-Sn film precursors, were deposited on glass substrate using electron beam deposition. The crystal structure of the synthesised film precursors were characterised by X- ray Diffraction (XRD) and elemental identification performed using Rutherford Backscattering Spectrometry (RBS). Moreover, ion beam energies and fluences to be used to study the radiation hardness capability of the grown CZTS thin films were simulated using the Transport of Ions in Matter (TRIM) code. The synthesis results obtained are in agreement with those presented in the literature indicating that the metallic CZT film precursors were successfully synthesised.
Speaker: Ms Tshegofatso Moipolai (University of South Africa)
• 15:00
Growth of zinc oxide nanostructures using block copolymer templates 2h
Growth of zinc oxide nanostructures using block copolymer templates A.Talla, S. R. Dobson, Z. N. Urgessa and J. R. Botha Department of Physics, Nelson Mandela University, P O Box 77000, Port Elizabeth, 6031, South Africa s217063969@Mandela.ac.za Keywords: nano template, diblock copolymer, wet etching, zinc oxide nanorods, Abstract The growth of ZnO nanorods on a lattice mismatched substrate, using solution methods, typically results in a random orientation of the rods.. In this paper, the use of block copolymer films as a template for the oriented growth of ZnO nanorods is presented. These rods can be used for solar cells or as templates for the growth of TiO2 nanotubes. Poly (styrene-block-methylmethacrylate) (PS-b-PMMA) has been investigated as a potential nano-mask for semiconductor growth. For this study, diblock copolymer thin films were spun onto a zinc oxide seed layer-coated silicon substrate and on an aluminium doped zinc oxide (AZO) substrate. Thermal annealing of PS-b-PMMA having an appropriate thin film thickness led to vertically oriented cylinders of PMMA within a PS matrix. Samples were then processed by wet etching in acetic acid after ultraviolet (UV) exposure of the polymer film at a specific dose.. This resulted in the removal of the PMMA cylindrical nano-domains from the polymer films,, leaving an array of ordered nanoscopic pores in which ZnO nanorods were subsequently grown. Samples were characterized using X-ray reflectometry to determine the thicknesses of the annealed PS-b-PMMA thin films. Scanning probe microscopy was used to view the phase morphology and characterize the selective removal of the PMMA. Scanning electron microscopy was used to view the zinc oxide rods grown on the polymer templates produced on the two different substrates.
Speaker: Mr Assane Talla (Nelson Mandela University)
• 15:00
Hardware optimization and open-source for learning and research 2h
Open hardware and software are intensively used in academia, for research and teaching due to the affordable costs. Most famous open hardware devices like Arduino and RaspberryPi are fully accessorised with several shields able to perform general tasks. In this work we propose methods to optimise the existing Open-source platforms with non-existing shields which are easy to explain to entry level students in applied physics subjects. These devices are designed to avoid the use of Surface Mounting Device (SMD) in order to be built by the students and anybody with scarce technical skills .
Speaker: Mr SENZO HLONGWANE