Combinedab initioand LEEDI∕Vstudy of submonolayer adsorption of In on W(110)

Abstract

The atomic structure of various indium adlayers at submonolayer coverages on W(110) is investigated by a density functional theory (DFT) approach as well as by analysis of low-energy electron diffraction intensities (LEED $I∕V$). Single-atom adsorption is studied by DFT, with the result that adsorption at the pseudo-fourfold coordinated sites of the W(110) is most preferable, followed by bonding to the pseudo-threefold and twofold short-bridge sites. Both theory and experiment reveal that for the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure, which corresponds to a coverage of 0.33 monolayer (ML), indium atoms occupy exclusively pseudo-fourfold coordinated sites, while for the $(1\ifmmode\times\else\texttimes\fi{}4)$ phase (0.75 ML coverage) and $(1\ifmmode\times\else\texttimes\fi{}5)$ phase (0.80 ML coverage), pseudo-threefold and twofold short-bridge sites are also occupied. According to DFT, the $(1\ifmmode\times\else\texttimes\fi{}4)$ structure is the most stable one, closely followed by the $(1\ifmmode\times\else\texttimes\fi{}5)$ structure. Analysis of DFT studies on free monolayers of In reveals the significant influence of In-In bonding on the formation of these adlayer structures. The low-coverage $(3\ifmmode\times\else\texttimes\fi{}1)$ structure is energetically the least favorable one, in agreement with the experimental finding that the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure is only metastable and transforms with increasing time or upon annealing into islands of $(1\ifmmode\times\else\texttimes\fi{}4)$ patterns. In order to investigate whether the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure might be stabilized by contaminants, DFT calculations were also performed for coadsorbing hydrogen and oxygen with indium on W(110). However, the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure always remains metastable. Furthermore, we find that phase separated regions of oxygen patches and $(1\ifmmode\times\else\texttimes\fi{}4)$ In islands are stabilized by about $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$/atom relative to mixed $(3\ifmmode\times\else\texttimes\fi{}1)$ $\mathrm{In}+\mathrm{O}$ configurations. This is in very good agreement with the experimental observation that the $(3\ifmmode\times\else\texttimes\fi{}1)\ensuremath{\rightarrow}(1\ifmmode\times\else\texttimes\fi{}4)$ transition can be triggered by additional oxygen.