A molecular dynamics study of phase transformations in mono-crystalline Si under nanoindentation

A molecular dynamics (MD) simulation is adopted to examine the deformation behavior and phase transformation of mono-crystalline Si in nanoindentation with a spherical indenter. The techniques of coordination number and radial distribution function are used to monitor and elucidate the detailed mechanism of the phase transformation throughout the whole process in which the evolution of structural phase change and the relevant distributions of bonding length can be traced and exhibited. In this article, the phases of BC8 and R8, which have the same coordinate number as the phase Si-I and were difficult to distinguish from each other in previous studies, are successfully identified and extracted from the deformed region during unloading. Moreover, the effect of the indenter-radius size on the structural phase transformation of mono-crystalline Si for three different crystallographically oriented surfaces is investigated. It is found that the onset of the plastic deformation tends to take place only as the ratio of the indentation depth to the tip radius is larger than 0.7. Under this condition the structural phase transformation can be easily observed in the residual deformed region after unloading.