Professor Darrell Comins graduated with a BSc (Honours) degree in Physics cum laude from the University of Natal and a Ph D degree from the University of the Witwatersrand (Wits), Johannesburg. He was a Postdoctoral Fellow at Queen’s University, Kingston, Canada and was subsequently appointed as a lecturer at at Wits in 1971. During his career at Wits he was ad hominem Professor of Optical Spectroscopy of Solids, Professor of Solid State Physics, Head of the Department of Physics, Executive Chairman of the Materials Physics Research Institute and Director of the DST/NRF Centre of Excellence in Strong Materials. He is presently Emeritus Research Professor. He enjoyed extended research visits in the Universities of Oxford and Bath (UK), Nantes (France) and Kaiserslautern (Germany) and has been the recipient of the Science for Society Gold Medal of the Academy of Science of South Africa, the Gold Medal of the South African Institute of Physics and research awards from the South African National Research Foundation and the University of the Witwatersrand.

Abstract

Light Scattering Techniques Applied to NDE

Brillouin and Raman light scattering techniques are powerful laser-based methods to perform non-destructive evaluation of materials in the solid state. Laser light interacts with the vibrating atoms of the material under study and a very small fraction of the scattered light that emerges from the sample is changed in frequency.

Brillouin scattering refers to the coupled movement of the unit cells constituting both bulk and surface waves in the GHz region. Hence, the elastic properties of materials in bulk form and as thin films and coatings are determined. The characteristic elastic stiffnesses determine the resistance of the material to deformation and depend on variables such as temperature and pressure, microstructure, composition and strain, and are sensitive to solid-state phase transitions. In order to resolve the very small changes in frequency and provide sufficient contrast, a (3+3) pass tandem Fabry-Pérot interferometer system is used in combination with a frequency-stabilised laser.

Recent surface Brillouin scattering studies of the elastic properties of bulk solids are considered. These include platinum-group alloys and iron pyrite, and thin supported films such as carbides and nitrides at both ambient and high temperatures. Theoretical methods using surface Green’s functions are employed in the analyses.

Raman scattering refers to the atoms within the unit cells or within molecules moving with respect to one another in various ways. Raman scattering is used to identify the nature of a material, its state of crystalline perfection or disorder, changes of phase, the presence of inclusions, and the effects of temperature, pressure and strain. A triple grating spectrograph is used to resolve spectral features and our instrument is fitted with a Raman microscope with 2-and 3-dimensional mapping being possible. Low and high temperature stages, and high-pressure cells are available. The same equipment is used for photo-luminescence studies.

Experimental studies using Raman scattering to be discussed include stress mapping in single crystal and polycrystalline diamond, studies of the passivation and pitting of iron using a special cell for in-situ corrosion studies and recrystallisation of ion beam induced amorphised layers.