INTERFACIAL STRUCTURE OF 2-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 descripti on of the atomic structure of a two-dimensional epitaxial Er silicide layer on Si(111). AED reveals that a monolayer of Er is located undern eath 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 angstrom to the first and 2.70+/ -0.05 angstrom to the second Si top layer. Er near-neighbor bond lengt hs and coordination numbers are obtained independently from polarizati on-dependent SEXAFS. The SEXAFS data, when combined with the Si top-la yer geometry inferred from AED, permit the determination of the atomic positions at the silicide/Si(111) interface. The Er is found to resid e in relaxed T4 sites of Si(111) with a single Er-Si distance of 3.09/-0.04 angstrom to the first-and second-layer Si atoms of the substrat e.