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New Silicon (111) Surface (7×7) Reconstruction Benzene-Like Ring Model
Published online by Cambridge University Press: 25 February 2011
Abstract
A new silicon (111) surface (7×7) reconstruction model is proposed. The model for the unit mesh consists of 13 benzene like rings formed by lowering triples of top layer atoms and 12 raised top layer atoms, with three of the rings combining to give depressed corners. The construction of the model is based on some considerations of the physical properties of the surface and on cluster calculations using the semi-empirical MNDOgeometrical optimization method. A cluster calculations with 9 silicon atoms gave the ring structure as an energy minimized result and also gives evidence that the two halves of the unit mesh should be at different height levels. A 13 silicon atom “flower” cluster calculation gave the height of the raised atoms to be .851A. The structure of the unit mesh resembles two types of (2×2) structure which can be formed from the rings and raised atoms (“flowers”), one of which is readily transformed into pi-bonded chain or molecular structures. The model gives a good qualititative account of the various hills and valleys seen in scanning tunneling microscopy, and since lateral displacement is small, it agrees with low energy channeling experiments. In addition good agreement with Cardillo s helium atom scattering experiment and Yang et al. s LEED experiment is found as the model has different heights for the two halves of the unit mesh and characteristics of a mixture of two types of structure.
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