Volumetric and timescale analysis of phase transformation in single-crystal silicon during nanoindentation

Clarifying the phase transformation process and mechanism of single-crystal silicon induced by high pressure is essential for preparation of new silicon phases. Although many previous researches have focused in this area, the volume of high-pressure phases and the duration of phase transformation are still unclear. In this paper, the volume change and the duration of phase transformation from Si-II phase into Si-XII/Si-III phases were investigated quantitatively by introducing a holding process in the unloading stage of a nanoindentation test. Experimental results indicate that the high-pressure phase volume is dependent strongly on the maximum indentation load and independent of the loading/unloading rate and the holding time at the maximum indentation load, while phase transformation duration is independent of the aforementioned experimental parameters. By analyzing the results, a critical volume of Si-XII/Si-III phases was identified which determines the occurrence of sudden phase transformation, and a modified nucleation and growth mechanism of high-pressure phases was proposed. These results provide new insights into high-pressure phase transformations in single-crystal silicon.