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) surf ace has been studied in the photon energy region of 500-750 eV. Not on ly H+ but also O+ ion was observed. PSID yield curves of these ions in dicate characteristic behavior near and above the 0 K edge; H+ ion exh ibits 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 elect ron yield curve, the photoion-photoion coincidence spectrum and the ga s-phase photofragment ion spectrum have also been obtained and compare d 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) i ons followed by reneutralization of the excess of charge with strong i nteractions with the substrate and finally desorption as single charge d H+ and O+ ions.