Study on shock compression phase transition of single crystal siliconbased on molecular dynamics simulation

Abstract

Crystalline silicon has a complicated phase transition mechanism, which has received extensive attention in the research field of phase diagram, and the deformation mechanism of silicon crystals under dynamic loading is the current research hotspot. In order to reveal its deformation and phase transition behaviors under intensive dynamic loading, molecular dynamics method was used to simulate the shock compression behavior of single crystal silicon along the crystal directions [001], [110] and [111] at an initial ambient temperature of 300 K, respectively. All simulations were carried out basing on the classical open-source codes LAMMPS and a Tersoff interatomic potential was adopted to describe the material responses of silicon under dynamic compression. Before shock loading, periodic boundary conditions were applied along the three independent directions, and an NPT ensemble was used to equilibrate the systems; then shock compression was applied by using the piston method, where a virtual piston wall impinges the sample such that the particle velocity in the sample is the same as the piston speed after the shock reaches a steady state. The shock particle velocities varied from 0.3 km/s to 3.2 km/s, and a timestep of 0.001 ps was adopted. During the stress wave formation and propagation, the simulation system was in the NVE ensemble with the absence of temperature control. The loading method and effect are similar to typical plane impact experiments. The results show that with the increase of shock particle velocity, the shear stress of single crystal silicon increases gradually and then decreases sharply due to the structural phase change. Both the phase transition threshold and the phase transition mechanism are anisotropic. Among them, a variety of solid-solid phase transitions and solid-liquid phase transitions are observed under shock compression along the [001] crystal direction. The phenomenon of solid-liquid coexistence is highly consistent with the recent international experiments. The research results provides new nano-scale results to support the study of phase transition of crystalline silicon under dynamic loading.