SCANNING TUNNELING MICROSCOPE OBSERVATION OF SI(111)-3X1-AG STRUCTURE

A scanning tunneling microscope has been used to study the Si(111)-3 x 1-Ag surface. The 3 x 1-Ag surface has been observed to consist of a bright row and small protrusions; the bright row points in the [1BAR10 ] direction and the protrusions point in the [123BAR] and [213BAR] dir ections. The width of 3 x 1-Ag domains, nucleated on the Si-7 x 7 terr aces, has been found to be (21n - 2)a, where n is an integer (n = 1, 2 , ...) and a is the lattice constant of Si (a=3.84 angstrom). Detailed investigation on domain boundaries reveals that both sides of the 3 x 1-Ag domain face the unfaulted halves of the 7 x 7 structure. Moreove r, two types of domain boundaries have been observed: one which runs a cross the corner holes, and another is that runs apart from the corner holes, leaving a narrow 7 x 7 terrace of one adatom width. Possible s tructural models for the 3 x 1-Ag surface are proposed based on the pr esent STM results.