A medium-energy ion scattering investigation of the structure and surface vibrations of two-dimensional YSi2 grown on Si(1Â 1Â 1)

Medium-energy ion scattering has been used to determine the atomic structure of two-dimensional yttrium silicide on silicon (1 1 1). A full quantitative analysis of the atomic positions of the Si atoms in the top bilayer yields a model similar to that previously suggested in the literature with a Si1-Si2 vertical spacing of 0.80 ± 0.03 Å, but with the Si bilayer relaxed slightly further away from the Y layer (Si2-Y vertical spacing of 1.89 ± 0.02 Å). Observing the effects of the top bilayer vibrations yields a model with significant enhancements.