Using scanning-tunnelling microscopy and first-principles total-energy calculations, the atomic geometry of the superstructures formed by the adsorption of up to 0.5 monolayer of indium on Ge(001) and annealing at temperatures above 200C was determined. A strong interaction between indium adatoms and the germanium substrate atoms led to the formation of two different In-Ge sub-units on the Ge(001) surface. In the sub-saturation regime separate (n x 4) subunits were observed where n could be either 3 or 4 and the scanning tunnelling microscopic images resemble those of the Si(001)-(3 x 4)-In and -Al reconstructions. An ordered arrangement of the sub-units into a (7 x 4) reconstruction could be prepared at saturation coverage. The (3 x 4) sub-units were well described by the pyramid-like model introduced by Bunk et alia (1998) for In on Si(001). For the (4 x 4) sub-unit, a model was proposed that includes the main features of the (3 x 4) sub-unit together with additional mixed Ge-In dimers. The atomic positions were optimized using ab initio total-energy calculations. The calculated local densities of states were in excellent agreement with the scanning tunnelling microscopic images.

Atomic Structure of the Indium-Induced Ge(001)(n x 4) Surface Reconstruction Determined by Scanning Tunnelling Microscopy and ab initio Calculations. G.Falkenberg, O.Bunk, R.L.Johnson, J.A.Rodriguez, N.Takeuchi: Physical Review B, 2002, 66[3], 035305 (8pp)