Interaction of voids and nano-ductility in single crystal silicon

This paper investigates void growth and interaction in a single crystal silicon cubic box under hydrostatic tension by performing three-dimensional strain-controlled molecular dynamics simulations. Two types of fracture behaviors are observed: brittle cleavage on void surface and ductile void coalescence in the inter-void ligament. A critical initial inter-void ligament distance is suggested to be the transition criterion for distinguishing the two behaviors. When the distance between the voids is less than the critical initial inter-void ligament distance, the silicon cube tends to fracture via void coalescence. We demonstrate that the nano-ductility of single crystal silicon is due to vacancy diffusion triggered by void surfaces, which is different from that of metals. In addition, the effect of temperature on the nano-ductility is also investigated. Single crystal silicon becomes ductile at high temperature due to the thermal activated vacancy diffusion.