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Light Scattering Techniques Applied to Materials Science

Professor J D Comins

Materials Physics Research Institute, School of Physics & DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, Johannesburg, South Africa

3:30 pm Friday, 19 November 2010,
EN413 (EN Building), Hawthorn.

Raman and Brillouin light scattering techniques are powerful laser-based methods to study the properties of materials. Laser light interacts with the vibrating atoms of the material investigated and a very small fraction of the scattered light emerging from the sample undergoes a change in frequency.
      Raman scattering (RS) refers to the atoms within unit cells or within molecules moving with respect to one another.  RS can identify the nature of a material, its state of crystalline perfection or disorder, changes of phase, the presence of defects and inclusions, and the effects of temperature, pressure and strain. Experimental studies to be discussed include stress mapping in single crystal and polycrystalline diamond, recrystallisation of ion beam induced amorphised layers, studies of the passivation and pitting of iron during in-situ corrosion studies and the temperature dependence of the vibrational modes of single-walled carbon nanotubes.
      Brillouin scattering (BS)refers to the coupled movement of the unit cells constituting both bulk and surface acoustic waves in the GHz region. BS measurements determine the elastic stiffnesses that characterize the resistance of a material to deformation. The stiffnesses depend on temperature and pressure, microstructure, composition and strain, and are sensitive to solid-state phase transitions.  Examples are given of surface BS studies of the elastic properties of bulk solids and thin supported films at both ambient and high temperatures. These include platinum group alloys, iron pyrite, and thin supported films including carbides and nitrides. Theoretical methods using surface Green’s functions used in the analysis are briefly discussed. 

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