Brillouin scattering measurements are presented of surface acoustic waves in TiN films of various thicknesses on high speed steel. Because of its relatively high elastic moduli as compared with those of steel, TiN has a stiffening effect on the surface, causing the surface acoustic wave (SAW) to increase in velocity, merge into the bulk wave continuum, and become a pseudo-SAW. In the limit of large film thickness this pseudo-SAW evolves into the Rayleigh wave for TiN. 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 these surface acoustic modes, and reveals details of the acoustic excitations of stiffening thin films not previously appreciated. A comparison between the measured and calculated dispersion relation for TiN thicknesses ranging from 20 to 4180 nm reveals that the elastic moduli of the thicker films are close to those of bulk TiN, but the effective elastic moduli of the thinner films are found to decrease with reducing film thickness. This conclusion is reinforced by backscattering measurements of Brillouin spectra at incident angles between 50° and 80° for a film thickness of 350 nm. Compositional variations at the interface have been investigated using x-ray photoelectron spectroscopy in an effort to understand this reduction in the elastic constants.
Surface Brillouin scattering ͑SBS͒ has been used to monitor a structural transition during high-temperature annealing of silicon previously bombarded at ambient temperature with 100 keV carbon ions with a fluence of 5ϫ10 17 ions/cm 2 . It was observed that a significant change of the Rayleigh surface wave peak frequency occurred during annealing at 600°C; thereafter the frequency remained essentially constant to 900°C. Raman and SBS measurements of the sample after annealing and recooling to ambient temperature show that the significant change in the Rayleigh mode frequency results from recrystallization of the amorphous silicon layer near the sample surface produced by the ion bombardment. The work demonstrates the potential of SBS to study in situ the structural phase transitions of opaque materials.
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