Toward a Detailed Understanding of Si(111)-7×7Surface and Adsorbed Ge Nanostructures: Fabrications, Structures, and Calculations

Abstract

Firstly, both the rest atoms and the adatoms of Si(111)-7×7surface are observed simultaneously by scanning tunneling microscopy (STM) when the sample bias voltages are kept less than − 0.7 V. The visibility of the rest atoms is rationalized by first-principle calculations and a very sharper tip can resolve them. Secondly, the behaviors of various Ge nanostructures fabricated on Si(111)-7×7, ranging from the initial adsorption sites of individual Ge atoms to the aggregation patterns of Ge nanoclusters, and then to 2D extended Ge islands, are comprehensively investigated by STM. The individual Ge atoms tend to substitute for Si adatoms at Si(111)-7×7with the preference of corner adatoms in the faulted half unit when keeping substrate at150∘C. With increasing Ge coverage, individual Ge atoms and Ge nanoclusters coexist on the substrate. Subsequently, the density of Ge nanoclusters increase and cluster-distribution becomes gradually regular with the formation of final 2D extended hexagonal configuration. When keeping the substrate at300∘C, Ge islands consisting of more complicated reconstructions with intermixing Ge/Si components are present on the substrate. The detail structural characterizations and the bonding nature of the observed Ge nanostructures are enunciated by the first-principle calculations.