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Using the concept of surface stress, we developed a model that is able to predict Young’s modulus of nanowires as a function of nanowire diameters from the calculated properties of their surface and bulk materials. We took both equilibrium strain effect and surface stress effect into consideration to account for the geometric size influence on the elastic properties of nanowires. In this work, we combined first-principles density functional theory calculations of material properties with linear elasticity theory of clamped-end three-point bending. Furthermore, we applied this computational approach to Ag, Au, and ZnOnanowires. For both Ag and Aunanowires, our theoretical predictions agree well with the experimental data in the literature. For ZnOnanowires, our predictions are qualitatively consistent with some of experimental data for ZnO nanostructures. Consequently, we found that surface stress plays a very important role in determining Young’s modulus of nanowires. Our finding suggests that the elastic properties of nanowires could be possibly engineered by altering the surface stress of their lateral surfaces.