In situ observation of photon-stimulated hydrogen removal on a HF-passivated Si(111) surface by ultraviolet photoelectron spectroscopy using synchrotron radiation

Photon-stimulated hydrogen removal on a HF-passivated Si(111) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation (SR). Vacuum ultraviolet (VUV) light, which was tuned to a photon energy of ∼23eV and an incidence angle of ∼45° to maximize the efficiency of hydrogen removal due to irradiation, was employed as a light source for UPS measurement as well as for irradiation. This enabled us to observe in situ the changes in the adsorption state and the amount of surface hydrogen during irradiation without probe-beam induced disturbance of hydrides and the need to position a probe beam within an irradiated area on the surface. UPS spectra for the HF-passivated Si(111) surface, which was composed primarily of trihydride with a small amount of dihydride and monohydride prior to irradiation, showed that the amount of each kind of hydride varied with irradiation time in a different manner. The variation is interpreted in terms of a kinetics model proposed for the photon-stimulated hydrogen removal reaction, in which monohydride and dihydride are produced via photon-stimulated hydrogen removal in dihydride and trihydride, respectively. Based on the reaction kinetics model, it was clarified that the order of magnitude in the rate of photon-stimulated hydrogen removal R is R(monohydride) > R(dihydride) > R(trihydride).