Room 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/12423 |
| Date | 14 February 2013 |
| Creators | Sumanya, Clemence |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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