In situ characterization of formation and growth of high-pressure phases in single-crystal silicon during nanoindentation

Pressure-induced intermediate phases of silicon exhibit unique characteristics in mechanics, chemistry, optics, and electrics. Clarifying the formation and growth processes of these new phases is essential for the preparation and application of them. For in situ characterization of the formation and growth of high-pressure phases in single-crystal silicon, a quantitative parameter, namely displacement change of indenter (Δh) during the unloading holding process in nanoindentation, was proposed. Nanoindentation experiments under various unloading holding loads and loading/unloading rates were performed to investigate their effects on Δh. Results indicate that Δh varies significantly before and after the occurrence of pop-out; for the same maximum indentation load, it tends to increase with the decrease in the holding load and to increase with the increase in the loading/unloading rate. Thus, the value of Δh can be regarded as an indicator that reflects the formation and growth processes of the high-pressure phases. Using Δh, the initial position for the nucleation of the high-pressure phases, their growth, and their correlation to the loading/unloading rate were predictable.