| AVS 56th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS2-WeM |
| Session: | Surface Chemistry and Dynamics |
| Presenter: | P.S. Bagus, University of North Texas |
| Authors: | P.S. Bagus, University of North Texas Ch. Wöll, Ruhr-Universitaet Bochum, Germany A. Wieckowski, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
We present detailed theoretical analyses of nominally anionic Iodine and nominally cationic Cs adsorbed on Cu(111) and Pt(111) surfaces. We consider the consequences of the coverage, the choice of on-top or three-fold sites, and the differences between Cu and Pt substrates on the degree of ionicity and on other properties of the interaction. This work extends our earlier studies of I and Cs on Cu(111)1 and of I/Pt(111).2 There we demonstrated that, although both Cs and I were dominantly ionic adsorbates, the properties of the adsorption, including work function changes, ΔΦ, and photoemission binding energy shifts, ΔBE, depended on other factors besides the adsorbate ionicity. However in this earlier work, only a single I or Cs adsorbate was explicitly treated and we neglected both direct and indirect, substrate mediated, adsorbate-adsorbate interactions. Now, we use models where several adsorbates are included, thus explicitly modeling lower and higher coverages. In particular, we examine whether the coverage dependent departures from ideal ionicity are different for cations and anions. Furthermore, we examine how ΔΦ depends on the adsorbate-adsorbate interaction and compare our predictions with measurements of ΔΦ as a function of coverage. This is relevant for the modification of charge transport barriers, which is key for the design of organic electronics.3 The distance of I above Pt(111) is quite different for on-top and three-fold sites,2 which has important consequences for ΔΦ and ΔBE. Here, we examine the generality of different heights of ionic adsorbates at these sites and how this difference is affected by the sign of the ionicity and the substrate. Our theoretical methodology uses wavefunctions for cluster models of the surface since this allows us to determine the quantitative importance of the individual physical and chemical mechanisms that contribute to the interaction. Our present work marks the first time that these methods have been applied to study the influence of coverage for halogen and alkali metal adsorbates.
1P. S. Bagus, D. Käfer, G. Witte, and C.Wöll, Phys. Rev. Lett., 100, 126101 (2008).
2P. S. Bagus, C. Wöll, and A. Wieckowski, Surf. Sci. 603, 273 (2009).
3G. Witte, S. Lukas, P. S. Bagus, and C. Wöll, Appl. Phys. Lett., 87,263502 (2005).