Ag on the Si(001) surface: Growth of the first monolayer at room temperature

Growth of the first monolayer (ML) of Ag on the Si(001) surface at room temperature has been studied by means of scanning tunneling microscopy (STM) and low-energy electron diffraction. Ag atoms form single-layer islands with a density of one Ag atom per Si surface atom. These Ag islands exhibit both local 2×{}1 and 2×{}2 order. As the Ag coverage approaches 1 ML, the 2×{}1 order disappears in favor of the 2×{}2 order. One ML of Ag is required to complete the first full surface layer. There is no evidence of three-dimensional Ag growth up to 1 ML. Models of the 2×{}1 and 2×{}2 surface structures are proposed on the basis of the STM images.