Nanometer to micron scale mechanics of [100] silicon nanowires using atomistic simulations at accelerated time steps

Atomistic simulations have a unique capability to reveal the material deformation mechanisms and the corresponding deformation-based constitutive behavior. However, atomistic simulations are limited by the accessible length and time scales. In the present work an equivalent crystal lattice method is used to perform mechanical deformation atornistic simulations of nanometer to micrometer sized silicon (Si) nanowires at accelerated time steps. The equivalent crystal lattice method's validity is verified by comparing the method's results with the results of classical molecular dynamics (MD) simulations at MD strain rates. The simulations predict that when the nanowire cross-sectional size exceeds 50 nm, the dependence of the nanowire Young's moduli values on the changes in nanowire cross-sectional size is considerably reduced. Analyses show a transition in nanowire failure mechanism from being ductile to being brittle with increase in the nanowire cross-sectional size. Examinations of the surface effect reveal that below a critical surface to volume ratio value of 0.05 nm(-1), the peak nanowire strength is independent of further reduction in the surface to volume ratio value. This finding places a size limit on the surface effect observed in Si nanowires. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim