Annealing at 400 °C of one Er monolayer deposited on Si(111) results in a p(1×1) two-dimensional epitaxial silicide with a remarkable degree of perfection. In the present study, Auger and photoelectron diffraction is used to investigate the atomic structure of this surface silicide. The Er MNN Auger-intensity polar profiles as well as the photoemission intensities of the characteristic surface bands measured along the opposite [1¯21¯] and [12¯1] azimuths display a typical asymmetry that implies the formation of one domain of a silicide with p3m1 symmetry. A comparison of the Er MNN polar profiles with single-scattering cluster simulations demonstrates that the hexagonal Er monolayer is accommodated underneath a buckled Si layer similar to a Si(111) double layer in the substrate. The buckling is found to be comparable to Si(111) (0.90 Å, as opposed to 0.78 Å in Si) and the Er-Si interlayer spacing is contracted with respect to bulk ${\mathrm{ErSi}}_{1.7}$ (1.80 Å, as opposed to 2.045 Å).

• Received 14 October 1992

DOI:https://doi.org/10.1103/PhysRevB.47.3677