| Abstract: | Surface studies of BaO on W---Ir alloy substrates of different composition show work functions lower for the alloys than on either pure W or pure Ir. In particular, the lowest work function ( 1.8 eV) appears near the 50% W, 50% Ir concentration. Peak height characterizations and energy shifts of interatomic Auger lines indicate an adsorbate-substrate interaction is responsible for the function lowering. The interaction consists of the O of the adsorbed Ba+O− molecule receiving electrons from the W and the Ba from the same molecule contributing electrons to the Ir. The resulting increase in surface dipole (as observed from interatomic O 2p and Ba 6s peak heights) is in very good agreement with the actual work function lowering. If the substrate consists of significant “patches” of W and Ir, then the Ba and O from the same molecule cannot interact with the different substrate components. When this happens, neither is the adsorbate-substrate interaction seen in the interatomic Auger spectra nor is any work function-lowering observed. The minimum in work function near 50% W, 50% Ir is the point where the dipole lowering (i.e., charge transfer) is most efficient because at thatconcentration there is one Ir atom available for each Ba atom and one W atom available for each O atom on the surface. |
