X-ray standing-wave and tunneling-microscope location of gallium atoms on a silicon surface

Abstract

The position of gallium atoms on a silicon (111) surface has been completely determined using the tunneling microscope and x-ray standing-wave methods. The (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} electron diffraction pattern observed with (1/3-monolayer coverages is shown to result from a simple adatom gallium lattice with the adatoms at a distance 1.49 A\r{} above the bulk extrapolated surface (111) plane above the filled threefold silicon surface sites. Total-energy calculations correctly predict the binding site with the Ga 1.33 A\r{} above the bulk (111) plane.