Density functional theory was used to investigate H adsorption and diffusion on a W(110) surface. The H adsorption structures were examined from a low coverage, up to 1 monolayer, and a three-fold hollow site was found to be the most stable site at all coverages. In contrast to previous claims, the work function decrease was not due to electron transfer from H atoms to the W surface, but due to electron depletion in the vacuum region above the H atoms. The H atoms could diffuse via short-bridge sites and long-bridge sites at a coverage of 1.0. Although the calculated activation energy for H diffusion via a short-bridge site could be as small as 0.05eV, field-emission microscopy had shown that the activation energy for H diffusion was about 0.20eV. This agreed fairly well with the calculated value of the activation energy via a long-bridge site. This discrepancy could be related to a H delocalization, on the W(110) surface, which was suggested by electron energy loss spectroscopy data.

A Theoretical Study of Hydrogen Adsorption and Diffusion on a W(110) Surface. A.Nojima, K.Yamashita: Surface Science, 2007, 601[14], 3003-11