Microscopic and spectroscopic investigation of phase evolution within static and dynamic indentations in single-crystal silicon

Silicon undergoes multiple phase transformations during indentation, and its final phase depends primarily upon the rate of unloading. In this study, single-crystal silicon was subjected to static and dynamic indentations in order to evaluate the propensity for particular phase transformations as a function of unloading strain rate. Raman spectroscopy and transmission electron microscopy were employed to map the phase distribution within and beneath the indent impression. It was found that silicon behavior is strongly dependent on unloading strain rate, with the preferred final phase switching from crystalline polytypes to nanocrystalline Si. The manuscript provides data in the intermediate strain rate range (103-105 s−1) that is not currently available in literature and links published nanoindentation to shock testing results, crucial to predicting material response at a range of strain rates.