Strain rate is a critical parameter in the mechanical application of nano-devices. A comparative atomistic study on both perfect monocrystalline silicon crystal and silicon nanowire was performed to investigate how the strain rate affects the mechanical response of these silicon structures. Using a rate response model, the strain rate sensitivity and the critical strain rate of two structures were given. The rate-dependent dislocation activities in the fracture process were also discussed, from which the dislocation nucleation and motion were found to play an important role in the low strain rate deformations. Finally, through the comparison of five equivalent stresses, the von Mises stress was verified as a robust yield criterion of the two silicon structures under the strain rate effects.

In nano-crystalline and multi-crystalline silicon, grain boundaries (GBs) and their properties may dominate the overall material performance. With a hybrid Monte Carlo and molecular dynamics (MC/MD) approach capable of reproducing the natural formation process of silicon (001) small angle twist GBs, the misorientation and temperature dependence of GB properties were examined at the atomic level. The GB structures and energies show various transition characteristics around three critical misorientation angles. Structure–property correlations are established by converting the three critical misorientation angles to the corresponding dislocation spacings, which are equal to 6-, 2-, and 1-times dislocation core radius. Stress fields and elastic strain energies agree well with the Continuum theory, and their effects on the dislocation structures and defect sink are discussed. This work also reports the variations of GB structures and energies are governed by a critical temperature at around 800 K, where the GB energies reach the minimum and the dislocation dissociations are suppressed.