Monolayer resolution in medium-energy ion-scattering experiments on theNiSi2(111) surface

The surface structure of the epitaxial ${\mathrm{NiSi}}_2$/Si(111) system has been determined applying a new ion-scattering method. Detecting backscattered ions with ultrahigh energy resolution we resolve the signals from successive atomic layers. From both their intensity and energy, which depends on the specific ion trajectories, we directly deduce the (sub)surface atom coordinates. Applying this new approach, we find that the ${\mathrm{NiSi}}_2$(111) surface has a bulklike topology, i.e., it is terminated by a Si-Ni-Si triple layer. The outermost Ni-Si and Ni-Ni interlayer distances are relaxed from their bulk values.