Field emission of metal nanowires studied by first-principles methods

We study the field-emission properties of an ultrathin silver nanowire using first-principles methods. The simulation and analysis of the field emission are carried out based on density-functional theory using a localized basis scheme. Through the explicit time evolution of wavefunctions, we obtain the emission currents and spatial distributions of emitted electrons from a silver nanowire. In contrast to carbon nanotubes, the localized states are not found. Instead, pronounced emission currents are observed for s-like extended states that are free of nodes in a plane normal to the field direction, and the total emission currents of a silver nanowire are found to be significantly larger than those of carbon nanotubes. A quantum-mechanical analysis is presented to explain the observed current enhancement. On the other hand, an ultrathin gold nanowire gives much smaller emission currents than the silver nanowire due to a larger work function.