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Energy and angular distribution of low energy H/sup +/ and D/sup +/ backscattered from polycrystalline carbon

Description: The energy distributions of H/sup +/ and D/sup +/ backscattered from a polycrystalline graphite sample were recorded as a function of total scattering angle, angle of incidence, and for incident beam energies 200 < E/sub i/ < 3000 eV. The general shapes of the distributions are discussed qualitatively, and their variation with incident energy and total scattering angle are explained and compared with theoretical and other experimental results. The average energies E/sup - +/, of the distributions are found to increase relative to the single scattering energy, E/sub k/, with decreasing incident energy, E/sup - +//E/sub k/ also increases with increasing exit angle from the solid in a way which is slightly dependent upon the angle of incidence. The integrated intensities of the distributions are found to depend strongly upon the angle of incidence, with a normally incident beam producing a nearly cosine distribution of backscattered ions and grazing angles of incidence producing an intensity which peaks at an angle forward of the specular direction. Using charge fractions obtained previously for surface scattering from graphite and transmission through thin carbon foil, values of the particle reflection coefficient R/sub N/ are obtained as a function of energy.
Date: January 1, 1980
Creator: Overbury, S.H.; Dittner, P.F.; Datz, S. & Thoe, R.S.
Partner: UNT Libraries Government Documents Department

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

Electron emission from the interaction of multiply charged ions with a Au(110) surface

Description: We have measured energy distributions of electrons produced during slow glancing collisions of H-like and He-like N and O projectiles with a clean Au(110) surface. For the case of the H-like incident projectiles, two peaks, at 250 and 350 eV, and 250 and 490 eV for incident N/sup +6/ and O/sup +7/, respectively, are observed. Both peaks are associated with Auger transitions to the K-shell vacancy brought into the collision by the incident H-like multicharged ions: from the higher lying shells of the projectile in the case of the high energy peaks, and from the target inner shells in the case of the low energy peaks. 10 refs., 3 figs.
Date: January 1, 1986
Creator: Zehner, D.M.; Overbury, S.H.; Havener, C.C.; Meyer, F.W. & Heiland, W.
Partner: UNT Libraries Government Documents Department

Low-energy collisions of multiply charged ions with electrons, atoms and surfaces

Description: Results are presented from recent experiments at the ORNL-ECR Multicharged Ion Research Facility which have addressed low-energy interactions of multiply charged ions with electrons, hydrogen atoms and metal surfaces. The specific processes for which results are reported are electron-impact excitation, electron capture and ion neutralization. The objective of these studies is a more detailed understanding of the mechanisms which govern the interactions of multicharged ions at low (or near-threshold) collision energies. 18 refs., 8 figs.
Date: January 1, 1991
Creator: Phaneuf, R.A.; Meyer, F.W.; Gregory, D.C.; Havener, C.C.; Zeijlmans van Emmichoven, P.A.; Overbury, S.H. et al.
Partner: UNT Libraries Government Documents Department