Structure of a two-dimensional epitaxial Er silicide on Si(111) investigated by Auger-electron diffraction

Abstract

Annealing at 400 \ifmmode^\circ\else\textdegree\fi{}C of one Er monolayer deposited on Si(111) results in a p(1\ifmmode\times\else\texttimes\fi{}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\ifmmode\bar\else\textasciimacron\fi{}21\ifmmode\bar\else\textasciimacron\fi{}] and [12\ifmmode\bar\else\textasciimacron\fi{}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 \AA{}, as opposed to 0.78 \AA{} in Si) and the Er-Si interlayer spacing is contracted with respect to bulk ${\mathrm{ErSi}}_{1.7}$ (1.80 \AA{}, as opposed to 2.045 \AA{}).