We have used a combination of dynamical low-energy-electron diffraction and density functional formalism calculations to find a structural model for two-dimensional (2D) ${\mathrm{YSi}}_2$ layers epitaxially grown on Si(111). Both techniques show that the geometric structure of the yttrium silicide is quite similar to other 2D rare-earth silicides. The surface termination consists of a relaxed Si-bilayer and underlying Y atoms on $T_4$ sites [with respect to the Si(111) interface]. The low-energy electron diffraction study shows several occurrences of minima in the R factor. The analysis of diffracted beams measured at non-normal incidence allows us to discriminate the spurious minima.

• Received 12 April 2002

DOI:https://doi.org/10.1103/PhysRevB.66.235421