The structure and energetics of Ge substitutional defects on the α-Sn/Ge(111) surface were analysed using density functional theory molecular dynamics simulations. An isolated Ge defect induced a very local distortion of the 3 x 3 reconstruction, confined to a significant downwards displacement (−0.31Å) at the defect site and a modest upward displacement (0.05Å) of the three Sn nearest neighbours with partially occupied dangling bonds. Dynamical fluctuations between the two degenerate ground states yield the sixfold symmetry observed around a defect in the experiments at room temperature. Defect–defect interactions were controlled by the energetics of the deformation of the 3 x 3 structure: they were negligible for defects on the honeycomb lattice and quite large for a third defect on the hexagonal lattice, explaining the low-temperature defect ordering.

Ge Substitutional Defects and the √3 x√3 ↔ 3 x 3 Transition in α-Sn/Ge(111). J.Ortega, R.Pérez, L.Jurczyszyn, F.Flores: Journal of Physics - Condensed Matter, 2002, 14[30], 7147-54