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Applications of SXPS for studying surface structure, reaction mechanisms and kinetics

Description: Soft x-ray photoelectron spectroscopy (SXPS) from the S 2p core level has been used to study adsorbate induced reconstruction, identify reaction intermediates and study reaction kinetics on the Ni(111) surface. The S 2p binding energy is affected by the nature of the surface adsorption site. It has been determined from the number of S 2p states and their relative binding energies that adsorbed S induces a reconstruction of the Ni(111) surface and that the S adsorbs in fourfold sites on terraces and in troughs. S 2p SXPS has also been used to identify adsorbed species during the thermal decomposition of methanethiol on Ni(111). CH{sub 3}SH adsorbs as CH{sub 3}S{minus} at low temperatures. Above 200 K, the CH{sub 3}S{minus} changes adsorption site and the C-S bond begins to cleave. The relative concentrations of CH{sub 3}S{minus} in the two different sites and of atomic S have been monitored as a function of temperature and initial coverage. As a result of the sensitivity and resolution available in SXPS, reaction rates and kinetic parameters have been obtained for the decomposition of benzenethiol on Ni(111) by monitoring the changes in the surface composition continuously as a function of temperature and time.
Date: December 31, 1994
Creator: Mullins, D. R.; Huntley, D. R. & Overbury, S. H.
Partner: UNT Libraries Government Documents Department

Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy

Description: Laser irradiated Si(100) surfaces were studied with an ultrahigh-vacuum scanning tunneling microscopy (STM) system. Our observations indicate that only the dimerized outermost atomic layer is removed if the laser fluence is below the melting threshold with a photon energy larger than the band gap. The newly exposed layer, surprisingly, did not have a dimerized atomic structure, but rather, resembled that of a bulk-terminated structure. The uncovered layer remained atomically smooth (no vacancies) even after 90% of the outermost layer was removed. A possible explanation of these observations is that atom removal occurs by a preferential breakage of the atomic bonds in defect sites. When the laser fluence was increased to levels above the melting threshold, extensive surface roughening occurs.
Date: July 1, 1995
Creator: Xu, Jun; Overbury, S.H. & Wendelken, J.F.
Partner: UNT Libraries Government Documents Department