Size-dependent phase transformations during point loading of silicon

Using a unique combination of in situ electrical and acoustical measurement s and ex situ transmission electron microscopy, the phase transformations o f silicon during point loading were shown to exhibit a strong dependence on the size of the deformed volume. For nanometer-size volumes of silicon, th e final phase was the body centered cubic structure BC8, but for larger vol umes it was amorphous. The size dependence was explained by considering how shear stress fields vary with contact size and how interfacial effects bet ween the silicon substrate and the BC8 phase determine its stability. For b oth small and large contacts the presence of a nonmetallic phase (assumed t o be the Rhombohedral structure R8) was observed.