Characterization of surface damage via surface acoustic waves

The damage introduced by polishing and machining of brittle materials has been evaluated by two techniques: quantitative acoustic microscopy (QAM) and surface Brillouin scattering (SBS), Both methods rely on the generation and detection of surface acoustic waves (SAW), also known as Rayleigh waves. The difference between the two techniques lies in the frequency of the wave generated and hence in the depth of the near-surface region sampled. Results are presented for (i) GaAs samples, polished using a variety of chemical and chemo-mechanical treatments, (ii) float-glass specimens with different levels of tin-contamination in either side, and (iii) alumina samples that have been variously ground and polished. It is shown that both BS and QAM can be used to evaluate the state of damage in a surface and that the varying contributions to the differences in SAW velocity between damaged and undamaged surfaces (viz surface roughness, surface microcracking and residual stresses) can be quantitatively modelled.