Photon-stimulated desorption (PSD) experiments on oxidized Si(111) surfaces were performed to study the adsorption of hydrogen at the SiO2/Si(111) interface using synchrotron radiation. H+ is found to be the only ion product desorbing in significant quantities from the oxidized surfaces at photon energies above 20 eV. PSD spectra of H+ ions, i.e., the H+ ion desorption yield as a function of photon energy, exhibit two peaks at 23 eV and 33 eV. These peaks are interpreted in terms of Si-H bond and O-H bond breaking in a Si-H and Si-OH complex, respectively. The observed dependence of the H+ ion yield on oxidation temperature implies that the peak at 23 eV originates from hydrogen atoms adsorbed onto the so-called Pb centers at the SiO2/Si(111) interface. A comparison between the PSD and the total photoelectric yield spectra, the latter of which corresponds to the photoabsorption spectrum, is also made.
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