Atomic and electronic structures of the Au2Sn surface alloy on Au(111)

Atomic and electronic structure investigations of the substitutional ${\mathrm{Au}}₂\mathrm{Sn}$ surface alloy formed on Au(111) are presented. Low energy electron diffraction and scanning tunneling microscopy (STM) reveal a structure with a local $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ periodicity with a superimposed modulation resulting in a $26\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ unit cell. STM images show a striped structure that resembles the herringbone reconstruction of clean Au(111), but with a longer periodicity compared to the $22\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ unit cell of clean Au(111). Angle-resolved photoelectron spectroscopy data along the high-symmetry lines $\overline{\mathrm{\ensuremath{\Gamma}}}\ensuremath{-}{\overline{K}}^{\ensuremath{'}}\ensuremath{-}{\overline{M}}^{\ensuremath{'}}$ and $\overline{\mathrm{\ensuremath{\Gamma}}}\ensuremath{-}{\overline{M}}^{\ensuremath{'}}\ensuremath{-}\phantom{\rule{4pt}{0ex}}{\overline{\mathrm{\ensuremath{\Gamma}}}}^{\ensuremath{'}}$ of a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surface Brillouin zone show two bands from the ${\mathrm{Au}}₂\mathrm{Sn}$ surface alloy layer. The experimental bands are compared to the calculated band structure of the local $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ periodicity. Most of the experimental band dispersions are qualitatively reproduced by the theoretical band structure including a spin split of one of the alloy bands. However, our detailed data reveal a band split, not present in the calculated bands of the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ model, which is a consequence of the striped atomic structure of the ${\mathrm{Au}}₂\mathrm{Sn}$ surface alloy.