Simulations of field emission from copper electrodes with inclusion of oxygen surface layer and work function changes based on first-principles calculations

Abstract

Analysis of field emission requires the inclusion of the internal potentials that shape the electronic wavefunctions and tunneling probabilities; details of the work function that are dependent on material quality and defects; and the role of the density of states (DOS) that influences the electronic supply. Here, these factors are collectively included on the basis of density functional theory to obtain predictions of field-dependent electron tunneling current densities. Results are obtained in copper for three different orientations. The DOS is predicted to be broadened by an externally applied electric field. The (100) copper is shown to yield the largest current density, and the (111) orientation is the lowest. The presence of an oxide surface monolayer is shown to increase the work function, leading to the emission of current reductions. The technique is general and can be applied to other materials (e.g., carbon fibers) that have shown promise as cathode emitters.