Ultra-microindentation of silicon at elevated temperatures

Abstract

Ultra-microindentations have been performed on {110} surfaces of silicon single crystals in the temperature range 20–600°C. The indents formed were observed with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The hardness determined from the measured load-displacement curves after correcting for the elastic recovery is almost independent of temperature up to 500°C, as is found for the Vickers hardness in the literature. The TEM images, electron diffraction patterns, SEM images and their variations with temperature are investigated in connection with high-pressure studies and plasticity data. A conclusion consistent with every observation is that below 500°C, the temperature-insensitive hardness is determined by the transformation to the metallic β-tin phase, which amorphizes or nanocrystallizes during unloading while, above 500°C, plastic deformation due to dislocation activity causes temperature-dependent hardness.