Structure ofO/Fe(001)-p(1×1)studied by surface x-ray diffraction

Abstract

The geometric structure of $\text{O}/\text{Fe}(001)\text{-p}(1\ifmmode\times\else\texttimes\fi{}1)$ is studied by surface x-ray diffraction (SXRD). After dosing of about 4 L $(1\text{ }\text{L}={10}^{\ensuremath{-}6}\text{ }\text{Torr}\text{ }\text{s})$ of oxygen at room temperature we find approximately one monolayer (ML) of oxygen in an FeO-like structure forming two layer thick islands covering about 40% of a roughened Fe(001) surface. Subsequent annealing up to $500\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ results in surface flattening leading to a highly ordered structure. Very precise SXRD data reveal the presence of 1 ML of oxygen atoms located in fourfold hollow sites at ${d}_{(\text{O}\text{\ensuremath{-}}\text{Fe})}=0.48\ifmmode\pm\else\textpm\fi{}0.08\text{ }\text{\AA{}}$ above the first Fe layer. The first Fe--Fe-interlayer spacing is expanded to ${d}_{12}=1.66\ifmmode\pm\else\textpm\fi{}0.02\text{ }\text{\AA{}}$ corresponding to an increase of 16% relative to the bulk spacing $(1.43\text{ }\text{\AA{}})$. Density-functional calculations confirm our findings and indicate a strong dependence of the (local) layer expansion on the oxygen coverage. Our results are important for understanding the surface magnetic properties of the $\text{O}/\text{Fe}(001)\text{-p}(1\ifmmode\times\else\texttimes\fi{}1)$ surface in general.