Bonding Configurations and Collective Patterns of Ge Atoms Adsorbed on Si(111)-7x7

TL;DR

This study uses scanning tunneling microscopy and density functional theory to analyze how germanium atoms adsorb and form patterns on the Si(111)-7x7 surface, revealing preferred substitution sites and stable configurations.

Contribution

It provides new insights into the atomic-scale bonding configurations and collective patterns of Ge atoms on Si(111)-7x7, combining experimental observations with theoretical calculations.

Findings

Ge atoms replace Si adatoms in preferred sites

Distinct patterns emerge with increasing coverage

Substituted atoms are more thermodynamically stable

Abstract

We report scanning tunneling microscopy observations of Ge deposited on the Si(111)-7x7 surface for a sequence of sub-monolayer coverages. We demonstrate that Ge atoms replace so-called Si adatoms. Initially, the replacements are random, but distinct patterns emerge and evolve with increasing coverage, till small islands begin to form. Corner adatom sites in the faulted half unit cells are preferred. First-principles density functional calculations find that adatom substitution competes energetically with a high-coordination bridge site, but atoms occupying the latter sites are highly mobile. Thus, the observed structures are indeed more thermodynamically stable.