In the present work, the atomic structure of the Si(111)(√3 × √3 )R30°-Ag surface is investigated with the quasikinematic low-energy electron-diffraction approach in conjunction with the constant-momentum-transfer-averaging technique. Our results support the honeycomb-chained-triangle model. The topmost layer of the model consists of Ag atoms arranged as ‘‘honeycomb chained trimers.’’ Below the Ag layer is a Si-trimer layer and then bulklike Si double layers follow. In the optimized model of this work the √3 × √3 reconstruction extends down to the fifth Si layer, and there is an oscillatory multilayer relaxation in the selvage region. We give all structural parameters of the model.

• Received 26 July 1993

DOI:https://doi.org/10.1103/PhysRevB.48.18109