Nanoindentation-Induced Phase Transformation in Silicon

Nanoindentation-induced phase transformation in silicon has been studied. A series of nanoindentations were made with the sharp diamond Berkovich tip. During nanoindentations, maximum load ranged from 2000 $\mu$N to 5000 $\mu$N, with a 1000 $\mu$N/sec loading rate. Slow unloading rate at 100$\mu$N/sec was chosen to favor the formation of the crystalline end phases, high pressure phase (Si-III and Si-XII). Fast unloading rate at 1000$\mu$N/sec was used to obtain amorphous phase. The phase transformation was examined by Raman spectroscopy and plan-view transmission electron microscopy (TEM). HPP have been identified even if no "pop-in" and "pop-out" observed in load-depth characteristics curves. HPP appeared in c-Si when the maximum load up to 3000 $\mu$N. TEM images have been revealed that the optimization HPP transformation in c-Si at the nanoscale occurred when the maximum load applied at 5000 $\mu$N.