ETD Collection
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Item Measurement of elastic properties of hard films using Brillouin scattering(1997) Pang, WenjunBrillouin scattering of light is used to study the various surface acoustic modes that are predicted theoretically to be supported by TiN thin films on high speed steel (HSS). Information is thereby obtained on the elastic properties and adhesion of the films, which range in thickness from 20nm to 4180nm. A Green's function method, invoking the surface ripple mechanism for the inelastic scattering of light, is used to calculate the Brillouin spectrum for scattering from the surface acoustic excitations. For the TiN/HSS combination, guided modes take the form of true SAW, highly damped p- SAW, "pre-Rayleigh" and "quasi-Rayleigh" and its higher order modes as the film thickness increases. (Abbreviation abstract)Item Brillouin light scattering of ion-implanted and annealed diamond surfaces(2016) Motochi, IsaacThe sub-surface region of chemical vapour deposition (CVD) diamond was transformed by C+ ion implantation followed by isochronal annealing up to 1200 oC. Different implantation regimes and with different energies at different implantation temperatures would give different thicknesses were studied. This enabled a study in the evolution of the stiffness of the damaged layer as a function of annealing. The technique of choice for this study was the non-destructive Brillouin light scattering (BLS) utilizing two scattering geometries; indirectly scattered phonons (Kr¨uger-type geometry) for temperature anneals up to 600 oC, and the conventional surface ripple mechanism up to 1200 oC. It has been argued that surface acoustic waves (SAW) on a transparent medium are enhanced by applying a thin metallic reflective layer on the surface, this study has showed that opacity of the substrate is key. In fact, bulk modes with SAW-like characteristics emanating from indirect photon scattering off phonons after reflection at the smooth reflective back of the sample dominated down to transmission below 5% which was observed after annealing between 500-600 oC (low annealing temperatures). The other complementing techniques employed to understand the changing structure of the ion implanted diamond were Raman spectroscopy, electromagnetic transmission in the visible range, electron energy loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) in addition to theoretical techniques: transport of ions in matter (TRIM), finite element modelling (FEM) and elastodynamic Green’s functions. Although the electronic techniques showed a structurally changing material at the low annealing temperatures, the optical ones did not show significant changes in the ion-damaged material possibly due to lack of distinct interface between the pristine diamond and the ion irradiated region at these lower annealing temperatures.Item Surface brillouin scattering in opaque thin films and bulk materials(2013-02-14) Sumanya, ClemenceRoom temperature elastic properties of thin supported TiC films, deposited on silicon and silicon carbide substrates and of single Rh-based alloy crystals, Rh3Nb and Rh3Zr, are investigated by the Surface Brillouin Scattering (SBS) technique. Velocity dispersion curves of surface acoustic waves in TiC films of various thicknesses, deposited on each substrate (Si and SiC) were obtained from SBS spectra. Simulations of SBS spectra of TiC thin hard films on germanium, silicon, diamond and silicon substrates have been carried out over a range of film thickness from 5 nm to 700 nm. The simulations are based on the elastodynamic Green's functions method that predicts the surface displacement amplitudes of acoustic phonons. These simulations provide information essential for analysis of experimental data emerging from SBS experiments. There are striking differences in both the simulated and experimental SBS spectra depending on the respective elastic properties of the film and the substrate. In fast on slow systems (e.g. TiC on silicon), the Rayleigh mode is accompanied by both broad and sharp resonances; in slow on fast systems (e.g TiC on SiC), several orders of Sezawa modes are observed together with the Rayleigh mode. The velocity dispersion of the modes has been obtained experimentally for both situations, allowing the elastic constants of the films to be determined. Effects of two deposition conditions, RF power and substrate bias, on the properties of the films are also considered. Platinum metal group alloys are promising candidates for future ultra high temperatures gas turbines materials due to their excellent high-temperature properties. In the present work, room temperature elastic properties of single crystals of Rh3Nb and Rh3Zr are investigated. SBS spectra for a range of wave vector directions from the (001) surface have been acquired in order to determine the angular variation of the surface acoustic wave velocities and the longitudinal wave threshold within the Lamb shoulder. The elastic stiffnesses of the specimens were determined using two approaches; one approach involves a least-square fit of the experimental data to calculated results and the other is an analytical approach which involves the 2 c minimization of secular equations for the Rayleigh surface acoustic wave and the longitudinal wave threshold velocities in the [100] and [110] directions on the (001) surface of a cubic crystal. Results from the two methods were in good agreement.