Computational modeling of dispenser cathode emission properties

Work function curves for BaO on W, Os, Os-W, and Pt have been derived from calculated initial surface dipoles and their depolarization at higher coverages. An accurate picture is obtained for the minimum work functions of the different materials. The optimum in emission that is observed for the Os-W alloy substrate has its origin in the small depolarization of the surface dipole on hexagonal-close-packed substrates. This important result provides the microscopic explanation for the emission enhancement in alloy cathodes. An increase in the surface concentration of W for the Os-W substrate leads to an increase in the calculated work function, which is consistent with the observed emission degradation during the life of the cathode.<>