Dispersion of surface acoustic waves in polycrystalline diamond plates

Abstract

Abstract Five free-standing polycrystalline diamond plates were grown by electron-assisted hot filament CVD on molybdenum using different deposition parameters. The homogeneity of the elastic properties was studied for each side of the samples by surface acoustic waves (SAWs) using pulsed laser excitation and piezoelectric detection. From the velocities of the longitudinal acoustic bulk waves (LABWs) and SAWs, values of the Poisson ratio of approximately ν=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 the nucleation side was observed in some samples. In addition the mean velocity of the SAWs was generally higher on the nucleation side than on the growth side. This indicates that the elastic properties changed considerably during the growth process. Measurements of the grain size by scanning electron microscopy (SEM), of the phase purity by Raman spectroscopy, and the texture by X-ray diffraction (XRD) were performed in order to estimate the contribution of different effects to the dispersion and the side dependence of the SAW velocities. In addition Fourier transform infrared (FTIR) spectroscopy was applied to study the influence of the hydrogen content.