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

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±0.05 Å to the first and 2.70±0.05 Å 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±0.04 Å to the first- and second-layer Si atoms of the substrate.