Pressure-Induced Structural Transformations in Si Nanocrystals: Surface and Shape Effects

The kinetics of solid-solid phase transitions are explored using pressure-induced structural transformations in Si nanocrystals. In agreement with the predictions of homogeneous deformation theories, large elevations in phase transition pressure are observed in nanocrystals as compared to bulk Si, and high pressure x-ray diffraction peak widths indicate an overall change in nanocrystal shape upon transformation. In addition, unlike the BC8 phase recovered in bulk Si, amorphous Si nanoclusters are obtained upon release of pressure, providing an example of kinetic size control over solid phases.