IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS3-TuP

Paper SS3-TuP12
Negative Ion Formation in Electron-Stimulated Desorption of CF@sub2@Cl@sub2@ Co-adsorbed with Polar and Non-polar Gases on Ru(0001)

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Adsorption/Desorption Poster Session
Presenter: S.M Solovev, A. F. Ioffe Physico-Technical Inst., Russia
Authors: S.M Solovev, A. F. Ioffe Physico-Technical Inst., Russia
D. Kusmierek, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
Photon-induced dissociation of CF@sub2@Cl@sub2@ (freon-12) in the stratosphere contributes substantially to atmospheric ozone depletion. We report recent results on dissociation and negative ion formation in electron-stimulated desorption of CF@sub2@Cl@sub2@ on Ru(0001), when CF@sub2@Cl@sub2@ is coadsorbed with a polar gas ( NH@sub3@) and non polar Xe, for electron energies from 50 eV to 300 eV. Two different time-of-flight methods were used in this investigation : (a) an ESD ion angular distribution (ESDIAD) detector with wide collection angle, and (b) a quadrupole mass spectrometer with narrow collection angle and high mass resolution. Many negative ESD fragments are seen (F@super-@, Cl@super-@, FCl@super-@, CF@super-@, F@sub2@@super-@, Cl@sub2@@super-@, CFCl@sub2@@super-@, whose intensities depend on the surface preparation. Using both detectors we observe a giant enhancement of Cl@super-@ and F@super-@ yields for ESD of CF@sub2@Cl@sub2@ coadsorbed with ~1ML of NH@sub3@; this enhancement ( > 10@super3@ for Cl@super-@) is specific to certain ions, and is attributed to an increased probability of dissociative electron attachment due to "trapped" low-energy secondary electrons.@footnote 1@ The magnitude of Cl@super-@ yield enhancement as a function of electron energy scales with the secondary electron yield, demonstrating the role of low-energy secondaries. In further studies, the influence of polar NH@sub3@ and non-polar Xe space layers (1-10 ML) on ESD of top-layer CF@sub2@Cl@sub2@ is determined, and compared with thick films of condensed CF@sub2@Cl@sub2@. The magnitudes and energy-dependences of the Cl@super-@ yields are different in these cases, due to several contributing factors. @FootnoteText@ @footnote 1@ Q. - B. Lu and T. E. Madey, Surf. Sci. 451(2000) 238.