An LEED and STM study of the structures formed by sulfur on the Rh(111) surface

The structures formed by sulfur adsorbed on the Rh(111) surface have been studied with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Five differently ordered overlayer structures were observed to form as a function of coverage. These are: (root 3 x root 3)R30 degrees, c(root 3 x 7)rect, c(4 x 2), (4 x 4) and (7 x 7). The first structure forms up to 0.33 monolayers, with S occupying fee hollow sites. Above 0.33, hcp hollow sites are occupied as well. In the c(4 x 2) structure, at 0.5 monolayer coverage, there is equal occupation of fee and hcp hollow sites. The transition from the (root 3 x root 3)R30 degrees to c(4 x 2) overlayer occurs by formation of dense domain boundaries containing both fee and hcp sites. The S in the hcp sites is metastable and, upon heating, it moves to nearest fee sites to produce the (4 x 4) structure. (C) 1998 Elsevier Science B.V.