Dispersion of surface acoustic waves in polycrystalline diamond plates

Five free-standing polycrystalline diamond plates were grown by electron-as sisted hot filament CVD on molybdenum using different deposition parameters . The homogeneity of the elastic properties was studied for each side of th e samples by surface acoustic waves (SAWs) using pulsed laser excitation an d piezoelectric detection. From the velocities of the longitudinal acoustic bulk waves (LABWs) and SAWs, values of the Poisson ratio of approximately v = 0.14 +/- 0.06 were obtained. The Young's modulus varied between E = 928 +/- 40 GPa and E = 1098 +/- 43 GPa. Anomalous dispersion of the SAWs on th e nucleation side was observed in some samples. In addition the mean veloci ty of the SAWs was generally higher on the nucleation side than on the grow th side. This indicates that the elastic properties changed considerably du ring the growth process. Measurements of the grain size by scanning electro n microscopy (SEM), of the phase purity by Raman spectroscopy, and the text ure by X-ray diffraction (XRD) were performed in order to estimate the cont ribution of different effects to the dispersion and the side dependence of the SAW velocities. In addition Fourier transform infrared (FTIR) spectrosc opy was applied to study the influence of the hydrogen content. (C) 2001 El sevier Science B.V. All rights reserved.