Deformation behaviors and inverse Hall-Petch effect in nanoindentation of silicon: An atomistic simulation study with experimental validation

Abstract

In this research, the unique perspectives on deformation behaviors of monocrystalline and polycrystalline silicon materials in nanoindentation are studied by the atomistic simulation approach. First, the validity of molecular dynamics (MD) simulation model for nanoindentation is verified by comparing the indentation morphology and force of simulation with those of nanoindentation experiment on monocrystalline silicon using atomic force microscopy (AFM). Further simulation on nanoindentation of polycrystalline silicon reveals the intriguing phenomena such as phase transformation and the effect of grain size. The indentation force with respect to indentation depth is analyzed for the monocrystalline silicon and polycrystalline silicon with grain size ranging from 20.48 nm to 6.45 nm. Inverse Hall-Petch effect, which indicates that stress decreases with the decrease of grain size, is observed in the nanoindentation process of silicon. The grain boundary-induced stress during indentation process hardly affects the formation of bct-5 silicon significantly, but it is responsible for the reduced formation of β‑silicon. The amount of bct-5 silicon atoms at the maximum indentation depth is not significantly different among the polycrystalline cases. On the other hand, the amount of bct-5 atoms of monocrystalline silicon is 14–18% less than that of polycrystalline silicon. In addition, it is discovered that residual indentation morphology and residual phase transformation are not significantly affected by the grain size. As such, this research reflects the rare efforts that bring direct validation to atomistic simulation of nanomanufacturing and provide analysis on deformation and phase transformation under various grain sizes for silicon nanoindentation.