On the Tensile Strength of a Solid Nanowire

Abstract

The present paper is concerned with the mechanical characterization of the measured tensile strength of a solid nanowire. As miniaturization is a general trend in nanotechnology, a variety of nanowires have been successfully fabricated/synthesized, including but not limited to Si, C, polymer DNA, MoSe, Au, Cu, TiC, Fe, Mo, NiAl and W. Mechanical strength is essential to maintaining the structural integrity in the multi-functional performance of those nanowires. A simple derivation in mechanics principle, without relying on tedious ab initio molecular dynamics calculations, is given which shows that the measured tensile strength contains two terms: the material’s intrinsic bond breaking strength and the surface stress (or surface tension) contribution. It further shows that as the size of the nanowire diminishes, the surface stress effect is enhanced, such that a simple functional relationship can be established in the nanscale regime: σ α 1/D where is strength and D is the diameter of the nanowire. Generally speaking, depending on the ratio of surface stress to the intrinsic strength, the apparent tensile strength can be enhanced up to one order of magnitude in the nanometer size range. In addition to the mechanical strength, the surface tension plays a role in: tension/compression asymmetry; helical shapes of a nanobelt if surface stress is anisotropic; reduced melting point; stress-induced phase transformation under free external loading conditions. These phenomena will be discussed as direct evidence of the existence of the surface stress.