AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA5
Factors Influencing Ion Yields and Angular Distributions in Electron Stimulated Desorption

Monday, November 3, 2003, 3:20 pm, Room 326

Session: Stimulated Processes at Surfaces
Presenter: D.O. Kusmierek, Rutgers University
Authors: N.S. Faradzhev, Rutgers University
D.O. Kusmierek, Rutgers University
T.E. Madey, Rutgers University
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The focus of this work is on scattering processes affecting the survival probability and 'depth of origin' of low-energy ions (F@super+@, F@super-@) that pass through condensed ultrathin layers of polar molecules (H@sub2@O, NH@sub3@). The ions are generated by electron stimulated desorption (ESD) of SF@sub6@ adsorbed on Ru(0001) at 25K. Electron stimulated desorption ion angular distribution (ESDIAD) and temperature programmed desorption (TPD) reveal predominantly molecular adsorption of SF@sub6@ on Ru(0001) via three F atoms, with the other three pointing away from the surface. Several characteristic angular distributions of F@super+@ and F@super-@ (halo, hexagon) are observed as a function of temperature, coverage, and electron irradiation. Adsorption of overlayers of polar molecules, e.g. H@sub2@O and NH@sub3@ leads to changes in both the F@super+@ and F@super-@ ion intensities (attenuation and enhancement), as well as dramatic changes in the ion angular distributions. Analysis of these changes gives insight into the role of charge-transfer and elastic scattering processes during the passage of ions through ultrathin polar films. The polar coadsorbate can also influence the ESD process itself by modifying polarization energies, low-energy electron lifetimes, and potential barriers for electron tunneling.