Raman imaging of stress-induced phase transformation in transparent ZnSe ceramic and sapphire single crystals

It is known that the polishing of a material can cause pressure-induced phase transformation and modify its surface properties. Indentation was used to apply controlled perturbation on optically clear ZnSe ceramics and on a-alumina single-crystal wafers. New Raman bands are observed at the periphery and/or the centre of the indented area. Confocal. Raman and Rayleigh imaging of the peak intensity, bandwidth and wavenumber shift show complex transformations of the indented area. Peak intensity can be used to map the surface geometry with approximately micrometre resolution. For ZnSe, the new bands (ca 235 and 248 cm(-1)) are assigned to the phases obtained above 5 and 34 GPa under hydrostatic pressure. Comparison is made with zirconia and corundum crystals. Stress-induced modifications are observed on the a-alumina wafer. They seem to be due to an unknown disordered phase rather than to a high remnant stress. The relationship between the Raman parameters and the applied stress is discussed. Copyright (C) 2002 John Wiley Sons, Ltd.