| AVS 55th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS2-WeA |
| Session: | Electrons and Electronic Spectra at Surfaces |
| Presenter: | P.S. Bagus, University of North Texas |
| Authors: | P.S. Bagus, University of North Texas Ch. Wöll, Ruhr Universität Bochum, Germany A. Wieckowski, University of Illinois at Urbana-Champagne |
| Correspondent: | Click to Email |
A detailed analysis of the character of the bond of I adsorbed at on-top and three-fold sites of Pt(111) is presented. At both sites, the bonding is dominated by an ionic interaction supplemented with some covalent character due to donation from the adsorbed I anion to Pt. The way in which the I-Pt interaction affects observed properties, including the anomalous work function changes induced by the adsorption of I and the shifts of I core level binding energies, will be described. The surprising fact that a negatively charged adsorbate leads to a work function decrease, rather than the increase expected solely due to the charge of the adsorbate, arises from electronic reorganizations that cancel the dipole due to the charged adsorbate.1 Furthermore, the contributions that lead toward an interface dipole that lowers the work function are larger as the adsorbate moves closer to the surface. Thus, the magnitude of the change in the interface dipole can be directly correlated with the distance of the I adsorbate from the Pt surface. A similar distance dependence is also found for the shifts of the I core level binding energies. In effect, these shifts can be interpreted to indicate adsorbate height. In particular, the shifts provide a new way to distinguish I adsorption at on-top and three-fold sites of Pt(111) since the distance of I from Pt(111) is different for these two sites. Furthermore, the effects important for the shifts of the interface dipole in the simpler case of I/Pt are also relevant for the charge transport barrier between a metal substrate and an organic adsorbate.2 Thus the distance dependence demonstrated here for I/Pt may also provide information helpful for understanding these more complex systems.
1P. S. Bagus, D. Käfer, G. Witte, and C. Wöll, Phys. Rev. Lett., 100, 126101 (2008).
2G. Witte, S. Lukas, P. S. Bagus, and C. Wöll, Appl. Phys. Lett., 87, 263502 (2005).