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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. 10. 2. At 0. 750. 07 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.
Katayama et al. (Mon,) studied this question.