Through the interplay of noncontact atomic force microscopy studies and density functional theory calculations, an atomistic model for the ${\mathrm{Al}}_2{\mathrm{O}}_3(0001)\mathrm{\text{−}}\sqrt{31}\times \sqrt{31}R9°$ surface reconstruction is revealed. The surface is found to consist of an Al adlayer on the ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate, and the driving force for the formation of the reconstruction is related to a detailed balance between strain in the adlayer and the preference for Al atoms to be located on distinct substrate sites.

• Received 23 April 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.076103