7-11 July 2014
Africa/Johannesburg timezone
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Residual stress in polycrystalline thin Cr films deposited on fused silica substrates

Presented by Ms. Z P MUDAU on 9 Jul 2014 from 14:40 to 15:00
Type: Oral Presentation
Session: DPCMM1
Track: Track A - Division for Physics of Condensed Matter and Materials

Abstract

The Néel temperature (<i>T</i><sub>N</sub>) in thin film Cr coatings is strongly influenced by dimensionality effects, as well as strain and stress [1]. In an investigation of Cr thin films with thickness (<i>t</i>) varied between 20 and 320 nm deposited on fused silica substrates, the <i>T</i><sub>N</sub> values obtained from resistivity measurements indicate an increase with thickness as expected [1]. However, it is noted that the <i>T</i><sub>N</sub> ≈ 460 K obtained for the <i>t</i> = 320 nm sample, is considerably higher than the transition temperature of 311 K obtained in bulk pure Cr. This behavior is unexpected, but incidentally corresponds with <i>T</i><sub>N</sub> = 475 K obtained for the CSDW-P Néel transition in bulk Cr when influenced by stresses introduced by cold working [3,4]. Since stresses are well known to influence the physical properties of materials [1,2], amongst others the magnetic properties, this study is now extended to investigations of the in-plane stresses in these thin films. This is done using the specialised X-ray diffraction sin<sup>2</sup>&psi–method [2,5,6]. With this technique, variations in the lattice plane spacing is accurately determined from the precisely measured (310) Bragg peak position as function of systematically increased tilt angles, &psi, from the surface normal to as close as achievable to the in-plane direction. The in-plane residual strain present in the coating (&epsilon) is determined from the slope of a linear plot through the fractional change in the plane spacing (or Bragg peak position) versus sin<sup>2</sup>&psi plots. Residual stress (&sigma) are calculated from the &epsilon versus sin<sup>2</sup>&psi data by incorporating the elastic properties of the coating material. The results indicate tensile stresses in all the samples. Results will be used to correlate the <i>T</i><sub>N</sub> values to the stresses in the coatings. References: [1] Zabel H 1999 <i>J. Phys. Condens. Matter</i> 11 9303 [2] Genzel CH 2004 <i>J. of Neutron Research</i> 12 233 [3] Fawcett E 1988 <i>Rev. Mod. Phys.</i> 60 209 [4] Prinsloo ARE et al. 2010 <i>J. Magn. Magn. Mat.</i> 322 1126 [5] Society for Automotive Engineering, Residual Stress Measurement by XRD, 2nd edition 1971 SAE J748a [6] Noyan IC, Cohen JB, Residual Stress, Measurement by Diffraction and Interpretation, Springer-Verlag, New York, 1987

Award

YES

Level

MSc

Supervisor

Dr C J Sheppard cjshepppard@uj.ac.za University of Johannesburg

Paper

yes

Place

Room: D Les 201


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