SUDDEN BEGINNING OF METALLIC BEHAVIOR AT AG/SI(100) INTERFACE - A REAL-TIME PHOTOREFLECTANCE-SPECTROSCOPY INVESTIGATION

The Ag growth of Si(100)-2 X 1 has been investigated by real-time in situ photoreflectance spectroscopy, in the spectral range 1. 1-5.4 eV. For the lowest coverages, the interface displays a nonmetallic character, due to the covalent bonding between the Ag atoms and the Si atoms. When the Ag coverage increases, the additional deposits become suddenly metallic and the differential reflectance spectra display typical features: rapid increase of the signal in the red and near-infrared range because of the optical response of the conduction electrons; appearance and growing of a plasma resonance in the thin Ag deposits. Moreover, the following of the signal during the Ag growth permits accurate determination of the beginning of the metallic behavior.