2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Mechanics of silicon nanowires: size-dependent elasticity from first principles

R.E. Rudd and B. Lee
Lawrence Livermore National Laboratory, US

Keywords:
nanowire, Young's modulus, ab initio, nanomechanics, silicon, elasticity

Abstract:
We have conducted a detailed study of the size dependence of the mechanical properties of silicon nanowires using first principles quantum mechanical calculation together with continuum mechanics theory and atomistic simulation based on empirical potentials. This size dependence largely arises from surface effects. We have used density functional theory to calculate the Young's modulus, residual stress and equilibrium elongation of hydrogen-terminated Si nanowires. An extensive array of first-principles total energy calculations were conducted on supercomputers for two series of nanowire geometries (differing in the passivated surfaces) with a range of wire diameters in each series. We have compared the results to continuum mechanical models of these properties in which the parameters of the models (surface energies, stresses and moduli) are calculated in much less computationally expensive calculations based on bulk and slab systems. The principal goals of this research have been to establish an understanding of the relevant physics for the mechanics of silicon nanowires from first principles. The first-principles calculations are extremely expensive in terms of computer time, so we have also assessed the extent to which less expensive atomistic and continuum models capture the relevant physics.

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