Effect of crystal orientation on the formation of bct-5 silicon

The five-coordinated body-centred tetragonal (bct-5) silicon is conductive, and can be generated under external stresses. This work explores the effect of crystal plane orientation on the nanofabrication of bct-5 silicon by means of nanoscratching using a diamond tip. With the aid of the molecular dynamics analysis, the study reveals the deformation behaviours of three typical monocrystalline silicon surfaces with crystallographic orientations of {001}, {110} and {111}. It was found that amorphous silicon always appears on the scratched surface, irrespective of the crystal orientation and scratching direction. However, the amount of amorphous silicon produced varies when scratched on different surfaces along different directions. Stable bct-5 silicon beneath the amorphous silicon can only be generated by scratching on {001} along <110> direction ({001}/<110>) and {110}/<100> at a depth of cut >1 nm. Scratching on {001}/<100> would introduce frequent dislocations in the subsurface through nanotwinning; while that on {110}/<110>, {111}/<011> and {111}/<211> would only produce amorphous silicon. The investigation concluded that the bct-5 initiation on various crystal planes is mainly governed by the application of a sudden hydrostatic stress associated with nanoscratching at a speed 106–108 times higher than the speed that is used in nanoscratching experiments.