The effect of laser excitation on the Raman microspectroscopy of nanoindentation-induced silicon phase transformation

It is well established that silicon undergoes a series of phase transformations when subjected to the pressure of nanoindentation. Phase transformations in silicon are studied using diamond anvil apparatus. The effect of the high pressure is an increase in density in diamond-cubic Si-I and as a result an unstable metallic phase of silicon (Si-II) is formed. This rapidly transforms to other phases upon pressure release. Depending on the rate of pressure release, rhombohedral (r8) Si-XII, body-centered-cubic (bc8) Si-III and/or the amorphous phase (a-Si) can occur. Raman spectroscopy is particularly useful for the characterization of the many different phases of the transformed silicon. A comparison of Raman spectra obtained with different laser wavelength excitations has been undertaken to examine whether source dependent effects occur during the characterization of the silicon phases. Preliminary results are presented here.