Effect of phase transformations on the shape of the unloading curve in thenanoindentation of silicon

Silicon wafers subject to depth-sensing indentation tests have been studied using Raman microspectroscopy. We report a strong correlation between the shape of the load-displacement curve and the phase transformations occurrin g within a nanoindentation. The results of Raman microanalysis of nanoinden tations in silicon suggest that sudden volume change in the unloading part of the load-displacement curve ("pop-out" or "kink-back" effect) correspond s to the formation of Si-XII and Si-III phases, whereas the gradual slope c hange of the unloading curve ("elbow") is due to the amorphization of silic on on pressure release. The transformation pressures obtained in nanoindent ation tests are in agreement with the results of high pressure cell experim ents. (C) 2000 American Institute of Physics. [S0003-6951(00)02916-8].