AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP23
Low Energy Li Ion Scattering from Iodine Adatoms on Si and SiO@sub 2@ Surfaces

Tuesday, November 4, 2003, 5:30 pm, Room Hall A-C

Session: Poster Session
Presenter: Y. Yang, University of California, Riverside
Authors: Y. Yang, University of California, Riverside
J.A. Yarmoff, University of California, Riverside
Correspondent: Click to Email
We recently showed that the neutralization of alkali ions backscattered from halogens adsorbed on metal surfaces depends sensitively on the internal polarization of the adatom. Charge-resolved time-of-flight spectra collected from backscattered @super 7@Li@super +@ ions display consistently larger neutral fractions for scattering from the halogen adatoms than that from the substrate. An increased neutral fraction indicates that the potential at the halogen site is reduced from that of the substrate, which is surprising considering that the halogen adatom is overall negatively charged. We thus propose that there is a region of positive charge at the very top of the adatom, which is consistent with the results of density functional theory. The positive region is presumably formed as the electron charge is attracted to its image in the metal substrate. This internal electronic structure of the halogen adatom was verified by measurements of the angular dependence of the neutralization. The neutral fraction of Li scattered from the halogens decreases as the exit beam moves off-normal, demonstrating that the charge associated with the adsorbate is non-uniform and that ion scattering is sensitive to this internal structure. Surprisingly, we found the same behavior for iodine adsorbed on Si surfaces, although the image charge in the substrate and the consequent charge rearrangement might be expected to be weaker. This implies that the iodine adatoms above a Si substrate are internally polarized. We are currently exploring the role of the substrate by investigating the neutralization of alkali ions scattered from Si wafers that are oxidized in situ prior to iodine exposure. This will allow us to determine how the conductivity of the substrate is involved in facilitating the internal charge rearrangement.