SODIUM-INDUCED H+ ION RESONANCE ON SILICON SURFACES

We present the first observation of an ion resonance, H+, desorbed from Na overlayers on Si(100)2 X 1 and Si(111)2 x 1 surfaces by means of photon stimulated ion desorption (PSD). This resonance occurs at a photon energy corresponding to the excitation of the Na 2p core level and is much stronger than the corresponding interband electronic excitations initiating the PSD process. This H+ ion resonance, which is unique to Na on Si surfaces, is quenched by coadsorption of other alkali metals, while it is strongly enhanced by the presence of an electron acceptor specie as oxygen. It is associated with the dielectric response of the near surface region including a spectator photoelectron within the Si-Na-H interface complex) at the Na 2p core level threshold.