Abstract
Brillouin scattering measurements are presented of guided modes in TiN films on high-speed steel (HSS). Because of its relatively high elastic moduli, TiN has a stiffening effect on the surface wave velocity of HSS. With increasing k∥h (wavevector × film thickness), the Rayleigh surface wave of HSS increases in velocity and then merges into the bulk wave continuum and becomes a highly damped pseudo-surface acoustic wave (p-SAW). Its higher modes can also be observed. It is found that the elastic constants of the TiN film play a crucial role in the acoustic behavior of TiN/HSS. There is a discontinuity in the calculated dispersion curve for normal TiN-HSS - a strong stiffening system, but not for reduced elastic moduli TiN-HSS - a relatively soft stiffening system. However, the acoustic modes in both situations evolve into a 'quasi-Rayleigh' wave of the corresponding systems at large k I h, which are very close to the Rayleigh waves of TiN. Comparison between the measured and calculated dispersion relations indicates that the effective elastic moduli of TiN for film thicknesses d< 500 nm are about 25% smaller than those of bulk TiN. A possible explanation for the lowered elastic moduli of the thinner films could be composition variations at the TiN-HSS interface.
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