A MODEL FOR NUCLEATION AND GROWTH-MECHANISM OF SI(111)-7X7 DOMAINS IN THE SI(111)-1X1 MATRIX

On the basis of the more important role of the corner holes with respect to the adatoms in characterizing the Si(111)-7 x 7 reconstructed surface, a model for nucleation and growth of the Si(111)-7 x 7 domains in the Si(111)-1 x 1 matrix has been proposed for the first time. The strained twelve-membered ring of a corner hole can never be stable around the transition temperature, 1100 K. This, in conjunction with high oxygen fluxes from bulk and ambient of a standard UHV, leads us to assume that the corner holes are stabilized with oxygen atoms in the bridge sites. During thermal vibration the surrounding oxygen atoms would take stacking fault (SF) sites sequentially with the oxygen site as a foothold. In-phase merging of the SF fronts would stabilize an SF triangle. The reason for the n x n structures with odd n is successfully been given by the in-phase merging of the SF fronts. This leads eventually to the nucleation of the 7 x 7 domains. The growth of 7 x 7 domains with triangular shapes from the step edges can be explained quite well by assembling the SF triangles and the unfaulted triangles.