In situ x-ray scattering study of Ag island growth on Si(111) 7 × 7

We report on the epitaxial relationship between Ag and the Si(111)$7\ifmmode\times\else\texttimes\fi{}7$ substrate where the wetting layer and the emergence of islands was investigated using in situ x-ray scattering with a combination of grazing incidence diffraction, specular reflectivity, and crystal truncation rod measurements. The atomic-scale structure of the wetting layer evolves continuously with coverage until a transition where it ceases to change its structure concomitantly with the appearance of islands. The islands are observed to reside on the Si(111)$7\ifmmode\times\else\texttimes\fi{}7$ and, although the minimum average island height is three atomic layers of face-centered-cubic Ag, the average island height depends on the coverage and temperature. The majority of the Ag islands are oriented along the symmetry-equivalent Si crystallographic axes and a minority population of islands are rotated by $15.{7}^{\ensuremath{\circ}}$. A coincidence-site lattice model is used to show that kinetic considerations lead to the observed island orientations.