THE MECHANISM OF ION DESORPTION FROM H2O/SI(100) BY O 1S ELECTRON-EXCITATION

The photon stimulated ion desorption (PSID) of H2O on the Si(100) surface has been studied in the photon energy region of 500-750 eV. Not only H+ but also O+ ion was observed. PSID yield curves of these ions indicate characteristic behavior near and above the 0 K edge; H+ ion exhibits sharp rises at ca. 530 eV and two broad peaks below (ca. 533 eV) and above (ca. 555 eV) the O K-edge, O+ exhibits a delayed threshold at ca. 570 eV and gradual increase up to 700 eV. The O KVV auger electron yield curve, the photoion-photoion coincidence spectrum and the gas-phase photofragment ion spectrum have also been obtained and compared with the PSID curves. The results are consistent with a mechanism of formation of multiple charged OH(m+) (m greater-than-or-equal-to 3) ions followed by reneutralization of the excess of charge with strong interactions with the substrate and finally desorption as single charged H+ and O+ ions.