IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Monday Sessions
       Session SS2-MoP

Paper SS2-MoP21
Anomalous Growth of Ba on Ag(111)

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: Surfaces and Interfaces Poster Session
Presenter: O.M.N.D. Teodoro, New University of Lisbon, Portugal
Authors: O.M.N.D. Teodoro, New University of Lisbon, Portugal
J. Los, FOM- Institute for Atomic and Molecular Physics, NL
A.M.C. Moutinho, New University of Lisbon, Portugal
Correspondent: Click to Email
The deposition of alkalis or earth alkali elements on other metals often produce a well-known decrease of the surface's work function. Such films make possible to achieve work function values lower than 2 eV. These surfaces found applications, for example, in long life cathodes or in negative ion converters. When these electropositive elements are adsorbed the work function drops steeply and reaches a minimum at coverage lower than 1 monolayer. Then, it increases slightly and the work function converges to the value of the deposited element. In this work, we report an anomalous behavior found during the deposition of barium on an Ag(111) surface. After the minimum of about 2.4 eV the work function did not increase up to 2.7 eV, the bulk barium work function, no matter the amount of barium deposited. These results were corroborated by Auger Electron Spectroscopy where we measured a permanent and constant intensity of the Ag MNN peak for high coverages of barium. To explain this anomalous growth of barium on Ag(111) we propose a model based in the diffusion of silver atoms to the barium film. Details of this model will be presented. Further experiments, showed that co-adsorption of oxygen before a second deposition of barium blocked the diffusion allowing the work function to reach the value of 2.7 eV.