Structure and width of Au-adsorbed narrow Si(111) terraces

The structure and width of Au-adsorbed narrow terraces on a vicinal Si(111) surface misoriented reward the [(112) over bar] direction are studied by scanning tunneling microscopy. We find that, at a coverage of 0.15 ML, narrow Au-adsorbed bunched steps are separated by wide 7 x 7 terraces. The An-adsorbed terraces are classified into three types according to the structures on the neighboring terraces. Where the Au-adsorbed terrace is next to the 7 x 7 terrace. the boundary facing the 7 x 7 terrace has a characteristic structure depending on whether it faces the faulted or the unfaulted halves. On the other hand, where the Au-adsorbed structure is sandwiched by the other Au-adsorbed terraces. the width of the An-adsorbed terrace along the [(112) over bar] direction can be expressed by (5N + 5 + 2/3) root 3/2, where the length is represented in units of the lattice constant of the 1 x 1 surface, and the N is the number of the 5 x 2 unit cells along the [(112) over bar] direction. For N = 0, the terrace width is equal to that of a (755) facet. On this terrace, 5 x 2 reconstruction cannot be observed although the size of the terrace is sufficient to form 5 x 2 reconstruction. We propose a model for the boundaries between the 7 x 7 terrace and the Au adsorbed structure on the narrow (111) terraces.