Structure of Sn/Ge(111) from low-energy electron-diffraction and photoemission studies

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Abstract
High-resolution photoemission measurements (ΔE≊200–250 meV) have been made on Ge 3d and Sn 4d core levels using synchrotron radiation from the National Synchrotron Light Source at Brookhaven National Laboratory. Systematic analysis using nonlinear least-squares fits has shown evidence for three different Ge components and two different Sn components. The selective modification of one Ge component as a function of Sn coverage leads to some quantitative restrictions on structural models for the Sn-induced 7×7 and 5×5 reconstructed superlattices. In particular, simple adatom models, vacancy models, and buckling models are not fully consistent with our results. A multilayer adatom model, such as the ‘‘tripedal’’ model of Aono et al. [Phys. Rev. Lett. 51, 801 (1983)] is found to be the most plausible one to interpret our results.