Brittle and ductile fracture of semiconductor nanowires – molecular dynamics simulations

Abstract

Fracture of silicon and germanium nanowires in tension at room temperature is studied by molecular dynamics simulations using several interatomic potential models. While some potentials predict brittle fracture initiated by crack nucleation from the surface, most potentials predict ductile fracture initiated by dislocation nucleation and slip. A simple parameter based on the ratio between the ideal tensile strength and the ideal shear strength is found to correlate very well with the observed brittle versus ductile behaviours for all the potentials used in this study. This parameter is then computed by ab initio methods, which predict brittle fracture at room temperature. A brittle-to-ductile transition (BDT) is observed in MD simulations at higher temperature. The BDT mechanism in semiconductor nanowires is different from that in the bulk, due to the lack of a pre-existing macrocrack that is always assumed in bulk BDT models.

Acknowledgement

We appreciate the kind help from Dr. M. I. Baskes, who provided us with the source codes of the MEAM potential. We would like to thank Prof. W. D. Nix and Prof. J. K. Hsia for helpful discussions, Dr. B. Sadigh for helping us with the Lenosky potential, and Dr. J. Marian for helping us with the MEAM potential. We would also like to thank Prof. H. Dai and Dr. R. Grow for stimulating our interest in the fracture of semiconductor NWs by sharing with us their experimental data on NW bending and fracture. This work is partly supported by NSF grant CMS-0556032.

Notes

†MD++ code is available at http://micro.stanford.edu/∼caiwei/Forum

†The Vienna Ab-initio Simulation Package (VASP), http://cms.mpi/univie.ac.at/vasp/

†http://micro.stanford.edu /∼caiwei/Forum