Structural analysis of Ge(1 1 1)–3 × 3-Sn surface at low-temperature by reflection high-energy positron diffraction

We have investigated the structure of Ge(1 1 1)–3 × 3-Sn surface using reflection high-energy positron diffraction. From the intensity analysis based on the dynamical diffraction theory, we determined the equilibrium positions of Sn atoms at 110 K. We found that one Sn atom and the other two atoms in the unit cell are displaced upward and downward, respectively. The height difference between the two inequivalent Sn atoms was evaluated to be 0.26 Å, which is in good agreement with those obtained in the previous theoretical and experimental studies. We also found that the first-layer Ge atoms are considerably relaxed downward (∼0.35 Å) as compared with the ideal Ge bulk positions. The large shift is induced by the adsorption of Sn atoms.