AVS 50th International Symposium
    Contacts to Organic Materials Topical Conference Monday Sessions
       Session OM-MoM

Paper OM-MoM4
Molecule on Metal versus Metal on Molecule: The Sexiphenyl/Al Interfaces

Monday, November 3, 2003, 9:20 am, Room 318/319

Session: Contacts to Molecules and Molecular Films (I)
Presenter: M.G. Ramsey, Karl-Franzens University, Austria
Authors: B. Winter, Karl-Franzens University, Austria
J. Ivanco, Karl-Franzens University, Austria
F.P. Netzer, Karl-Franzens University, Austria
M.G. Ramsey, Karl-Franzens University, Austria
Correspondent: Click to Email
Here the formation of both the organic/metal and metal/organic interfaces has been investigated with particular attention given to both their electronic and geometric structure as elucidated by angle resolved UV- photoemission and low energy electron diffraction. Despite the weak electrostatic bond found, a dense well ordered wetting monolayer results for sexiphenyl (6P) on single crystal Al(111), irrespective of growth temperature. The interface dipole of this layer determines the band alignment for the subsequent films that develop. For the converse, Al on 6P, a similarly weak bonding interaction is observed with no evidence for the commonly invoked scenarios of either a strong chemical bond formation or diffusion into the organic film. Under UHV growth conditions a wetting layer is impossible to achieve and the Al balls-up on the organic film. In spite of this weak interaction the evaporation of Al disturbs the surface of the crystalline 6P film, changing the conformation of the molecules at the surface and thereby effecting a 0.6 eV change in the HOMO binding energy and concomitantly the band alignment. If oxygen is introduced at the interface a change of up to 2 eV in the band alignment results, due to both a change in the interface dipole and in the ionisation potential of the interfacial molecules brought about by an increase in their conjugation. Not only does the oxygen improve the electron injection ability at the Al interfaces, the changes in surface energy allows the formation of a metallic wetting layer. Acknowledgments: Supported by the Austrian Science Foundation SFB Electroactive Materials