Saturation of tungsten surfaces with hydrogen: A density functional theory study complemented by low energy ion scattering and direct recoil spectroscopy data

Herein, we investigate the saturation limits of hydrogen on the (110) and (100) surfaces of tungsten via Density Functional Theory (DFT) and complement our findings with experimental measurements. We present a detailed study of the various stable configurations that hydrogen can adopt upon the surfaces at coverage ratios starting below 1.0, up to the point of their experimental coverage ratios, and beyond. We provide the many low-energy configurations that exist at all coverages along with the energy landscape they form. Our findings allow us to estimate that the saturation limit on each surface exists with one monolayer of hydrogen atoms adsorbed. In the case of (110) this corresponds to a coverage ratio of one hydrogen atom per tungsten atom, while in the case of (100) a full monolayer is present at a coverage ratio of 2.0 hydrogen atoms per tungsten atoms. Preliminary Low Energy Ion Scattering (LEIS) and Direct Recoil Spectroscopy (DRS) measurements complement this work on the W(110) surface. These results and some previously published measurements obtained on the W(100) surface confirm the findings obtained by DFT. In particular, the saturation limits on each surface, the preferred adsorption sites on both surfaces up to saturation, and the reconstruction of the bare and unsaturated (100) surface. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.