Conductance in nanowires

Abstract

This paper presents a detailed analysis of conductance and atomic structure in metal nanowires under tensile stress. We calculate the variation of conductance with the crossection of the constriction between two reservoirs, that is represented by three-dimensional circularly symmetric potentials. The absence of several observed features in the calculated conductance variations, in particular sudden jumps, suggests that the discontinuous rearrangements of atoms under stretch dominate the electron transport. To analyze the variations of atomic structure, we performed simulations based on the state of the art molecular dynamics simulations and revealed novel structural transformations. It is found that yielding and fracture mechanisms depend on the geometry, size, atomic arrangement and temperature. The elongation under uniaxial stress is realized by consecutive quasi elastic and yielding stages; the neck develops mainly by the implementation of a layer with a smaller crossection at certain stages of elongation. This causes to an abrupt decrease of the tensile force. Owing to the excessive strain at the neck, the original structure and atomic registry are modified; atoms show tendency to rearrange in closed-packed structures. In certain circumstances, a bundle of atomic chains or single atomic chain forms as a result of transition from the hallow site to the top site registry shortly before the break. The origin of the observed "giant" yield strength is explained by using results of present simulations and ab initio calculations of total energy and Young's modulus for an infinite atomic chain.