Structural studies of Schottky barrier formation by means of surface EXAFS: Pd and Ag on Si(111) 7×7

Abstract

The initial stages of Schottky barrier formation for Pd and Ag on Si(111) 7×7 have been investigated by means of surface extended x-ray absorption fine structure (SEXAFS) measurements above the metal L2 absorption edges. For Pd deposition at room temperature (RT) and 1.5 monolayer coverage the local structure around the Pd atoms is found to closely resemble that of a thick (∠300 Å) Pd2Si layer grown on Si(111). The Ag/Si system exhibits a distinctly different interface formation. At RT and around 2.5 monolayers Ag coverage the SEXAFS spectrum is found to be identical to Ag metal. Upon heating to 500 °C a √3×√3 LEED pattern is observed and the polarization dependent SEXAFS signal reveals that the LEED pattern is due to Ag atoms in a threefold site on Si(111) with a Ag–Si distance of 2.45±0.05 Å. At higher Ag coverage the periodic √3×√3 Ag sites on the annealed (500 °C) surface are accompanied by large Ag clusters. The derived structural models are discussed in comparison with various models suggested previously.