Ab initio calculation of work functions of ZrO/W(100) and YO/W(100) surfaces

The work functions of ZrO/W(100) and YO/W(100) surfaces are investigated by the ab initio calculation based on the density-functional theory. The work function of the W(I 00) surface is markedly decreased owing to the adlayers of ZrO and YO, which is in good agreement with experimental observations. The energetically stable configuration of ZrO and YO on the W(100) surface is found not to be perpendicular to the surface but to lie on the surface, which cannot be derived from the phenomenological surface-dipole model. We found from the detailed analysis of surface electronic structures that the lying configuration lowers the work function appreciably, particularly for ZrO, owing to an 0 atom going into the hollow site of the W(100) surface. The present study emphasizes the crucial role of ab initio calculation for clarifying the electronic-state-based origin of the work function.