The structures and energetics of Ge substitutional defects at the α-Sn/Ge(111) surface were analyzed by using density functional theory molecular dynamics simulations. An isolated Ge defect introduced a very local distortion into the 3 x 3 reconstruction. This was confined to a significant downwards displacement (-0.031nm) at the defect site, and a modest upward displacement (0.005nm) of the three Sn nearest neighbours with partially occupied dangling bonds. Dynamic fluctuations between the 2 degenerate ground states yielded the 6-fold symmetry which was observed around a defect in room-temperature experiments. Defect-defect interactions were controlled by the energetics of 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; thus 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[28], 7147-54