Phase transformations, dislocations and hardening behavior in uniaxially compressed silicon nanospheres

Molecular dynamics has been used to simulate the uniaxial compression of single crystal silicon nanospheres using the Tersoff potential. The resulting yield behavior is shown to vary with changes in temperature, sphere size, and crystallographic orientation with respect to the loading direction. Only compression along the [1 0 0] crystallographic direction resulted in the formation of the β-Sn phase. A temperature dependent hardening response is observed in all orientations independent of the β-Sn phase transformation. Dislocation activity is detected at elevated temperatures in the largest sphere indicating a critical temperature and size for nucleation. Consequences of these dislocations to simulating strength properties at the nanoscale are discussed.

Research highlightsObserved yielding mechanisms are orientation and size dependent. Resulting β-Sn has no effect on measured hardness. Room temperature dislocations are observed despite large strain rates.