Interfacial structure of two-dimensional epitaxial Er silicide on Si(111).

Abstract

Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) have been used to obtain a complete description of the atomic structure of a two-dimensional epitaxial Er silicide layer on Si(111). AED reveals that a monolayer of Er is located underneath a buckled Si double layer. The relevant Er-Si interlayer spacings are determined by means of single scattering cluster simulations and a R-factor analysis to be 1.92\ifmmode\pm\else\textpm\fi{}0.05 \AA{} to the first and 2.70\ifmmode\pm\else\textpm\fi{}0.05 \AA{} to the second Si top layer. Er near-neighbor bond lengths and coordination numbers are obtained independently from polarization-dependent SEXAFS. The SEXAFS data, when combined with the Si top-layer geometry inferred from AED, permit the determination of the atomic positions at the silicide/Si(111) interface. The Er is found to reside in relaxed ${\mathit{T}}_{4}$ sites of Si(111) with a single Er-Si distance of 3.09\ifmmode\pm\else\textpm\fi{}0.04 \AA{} to the first- and second-layer Si atoms of the substrate.