Ab initio study of indium clusters on the Ge(5 × 5) wetting layer of Si(111)-7 × 7

An ab initio study of In adsorbed on the Ge(111)-5 × 5 wetting layer, which forms on top of a Si(111)-7 × 7 substrate, is reported. A recent experiment showed that small In clusters form on this surface with some regularity but their exact size and structure are still unknown. Results are presented of a detailed investigation of the structural and electronic properties of a single adsorbed In atom and small candidate In clusters, carried out using density-functional calculations. Using density difference plots and population analysis, the mechanisms of bonding for different In structures are explained. Comparison of total energies shows that for a single In atom the faulted half cell is marginally preferred to the unfaulted half, and little tendency for clustering of In is found for low coverages. Both of these conclusions seem to be at odds with the experimental results and possible explanations are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)