DOMAIN-WALL STRUCTURE OF SI(111) (ROOT-3X-ROOT-3) R30-DEGREES-AU

A characteristic feature of the Si(111) (square-root3 x square-root3)R 30-degrees-Au surface is an intrinsically high density of domain walls . Combining the complementary strengths of scanning tunneling microsco py and X-ray standing waves it was possible to resolve the atomic stru cture of the domain walls and the Si(111) (square-root3 x square-root3 )R30-degree-Au domains. A detailed structural model for the domain wal ls is presented and compared to the experimental results. The model in volves the coexistence of two kinds of Au trimers with different regis tries and a separation of 0.5 angstrom normal to the (111) planes.