Molecular Dynamics Simulation of Nanoindentation-induced Mechanical Deformation and Phase Transformation in Monocrystalline Silicon

This work presents the molecular dynamics approach toward mechanical deformation and phase transformation mechanisms of monocrystalline Si(100) subjected to nanoindentation. We demonstrate phase distributions during loading and unloading stages of both spherical and Berkovich nanoindentations. By searching the presence of the fifth neighboring atom within a non-bonding length, Si-III and Si-XII have been successfully distinguished from Si-I. Crystallinity of this mixed-phase was further identified by radial distribution functions

Structure and properties of silicon XII: A complex tetrahedrally bonded phase.

Angle-dispersive powder diffraction using an image-plate area detector and synchrotron radiation have been used in conjuction with first-principles pseudopotential calculations to examine the structural, electronic, and vibrational properties of the recently discovered phase XII of silicon (the R8 phase). The R8 phase is synthesized by decompression of the high-pressure β-Sn phase and exists over a relatively wide pressure range of 2–12 GPa. Although there are structural similarities between BC8 and R8, the latter phase exhibits substantially greater local deviations from ideal tetrahedral bonding and is the most distorted crystalline structure containing fourfold-coordinated silicon. We present a detailed investigation of the pressure response of the BC8 structure, suggest plausible atomic trajectories for the β-Sn to R8 transition, and we investigate the energy of R8 silicon relative to those of other tetrhedral forms

Tetrahedral structures and phase transitions in III-V semiconductors.

The BC8 structure (body-centered cubic with eight atoms per cell) is a known pressure-induced modification of both silicon and germanium. However, its diatomic analogue [the SC16 structure (a simple cubic lattice with a basis of 16 atoms)] has never been found in compound semiconductors. We find from total-energy pseudopotential calculations that the SC16 structure is a stable high-pressure polymorph of the III-V semiconductors GaAs, InAs, and AlSb. We report ab initio calculations of the structural, electronic, and vibrational properties of SC16-GaAs. The wurtzite structure is found to be unstable at all pressures for each compound considered. We consider possible transition routes consistent with our high-pressure x-ray diffraction results and propose that the formation of the SC16 structure in compounds is kinetically inhibited by the formation of wrong bonds at the structural transition