STRUCTURE OF A 2-DIMENSIONAL EPITAXIAL ER SILICIDE ON SI(111) INVESTIGATED BY AUGER-ELECTRON DIFFRACTION

Annealing at 400-degrees-C of one Er monolayer deposited on Si(111) results in a p (1 X 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 [121BAR] and [121BAR] azimuths display a typical asymmetry that implies the formation of one domain of a silicide with p3m 1 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 angstrom, as opposed to 0.78 angstrom in Si) and the Er-Si interlayer spacing is contracted with respect to bulk ErSi1.7 (1.80 angstrom, as opposed to 2.045 angstrom).