Effect of electric field on the electron field emission current densities of Cu and Cu-O systems: A First-Principle Approach

In this study we investigated the electron field emission current densities for the 100, 110, and 111 surfaces of Cu and Cu with an oxygen adlayer. Using density functional theory (DFT), we calculated the potential energies and work functions to show the effect of the electric field for the various surface orientations. Predicted trends of current densities for the Cu surfaces were found to be J₁₁₁ < J₁₀₀ < J₁₁₀. This relation was not shown for the Cu-O surfaces and resulted in little change with increasing field for each surface. To explain these trends, we calculated the density of states (DOS), without and with an external field, and charge densities for both materials. The Cu surfaces included a broadening over the entire spectrum of the DOS indicating a delocalization of electrons, especially near the Fermi level. This broadening is absent from the Cu-O surfaces because the Cu-O bonding is able to overcome the external electric field resulting in the lack of current density change.