STM study of gold on Ge (111)

The gold-induced reconstructions of Au on Ge(111 ) were investigated with STM, LEED and RHEED in the coverage region up to one monolayer. The STM images of the (√3 × √3)R30° Au structure are compared with those of other noble metal-semiconductor adsorbate systems. Two types of √3 reconstructed islands were found on terraces either above or below the top double layer of the original c(2 × 8) reconstructed surface. The ratio of the areas of the two different √3 reconstructed islands allowed us to determine that the number density of Ge atoms in the √3 reconstruction corresponds to a coverage of one monolayer and provides convincing evidence for a missing top layer model. In the low coverage regime it was found that small amounts of Au stabilize single √3 unit cells which lead to the formation of a hexagonal domain wall phase. The results obtained from the Au stabilized domain wall phase are compared to those of the high temperature I(2 × 2) phase of clean Ge(111).