Structure analysis of the Si(111)√3 × √3 R30°-Ag surface

The structure of the Si(111)√3 × √3 R30°-Ag surface has been analyzed with a novel form of low-energy ion-scattering spectroscopy and energy-minimization calculations. The topmost layer of the surface is formed by Ag atoms with a honeycomb-chained-trimer arrangement in which the intratrimer Ag-Ag distance is 5.1±0.2 Å. At 0.75±0.07 Å below the Ag layer there exists a Si layer with three Si atoms per surface unit cell. The lower layer of the subsequent bulklike Si double layers is split into a honeycomb and a √3 × √3 layer with a large interlayer distance of about 0.6 Å.