TEMPERATURE DEPENDENCE OF SILICON HARDNESS: EXPERIMENTAL EVIDENCE OF PHASE TRANSFORMATIONS

The hardness of silicon is known to be nearly independent of temperature below a certain transition point, and to decrease steeply thereafter. Based on high-temperature Berkovich nanoindentation at 25-500 deg C and Raman microanalysis of Vickers indentations produced in single-crystal silicon at 25-750 deg C, we present evidence of a transformation into a high-pressure metallic Si phase during indentation at temperatures up to about 350 deg C. We show that this transformation pressure determines silicon hardness below the transition temperature. We also report the temperature stability ranges of different metastable phases of silicon, including a new Si-X111 phase.