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

Paper OM-MoM3
Long Range Electronic Coupling at Molecule-metal Interfaces: C60/Cu(111)

Monday, November 3, 2003, 9:00 am, Room 318/319

Session: Contacts to Molecules and Molecular Films (I)
Presenter: X.-Y. Zhu, University of Minnesota
Authors: G. Dutton, University of Minnesota
X.-Y. Zhu, University of Minnesota
Correspondent: Click to Email
It is well-recognized that electronic interaction at molecule-metal interface is one of the key factors governing the performance of molecular-semiconductor devices. The efficiency or rate of injection at such an interface is determined by (1) the energet ic alignment of molecular orbitals to the metal Fermi level, (2) the electronic coupling strength (wavefunction mixing) between molecular orbitals and metal bands, and (3) the dynamics of charge carrier localization at the interface. While energetic align ment has been probed by photoemission spectroscopies, electronic coupling strength and charge localization dynamics remain largely unknown at the present time. We attempt to address these issues in the present study using the model system of C60/Cu(111) a nd the experimental technique of time-resolved two-photon photoemission (2PPE) spectroscopy. The lowest unoccupied molecular orbital (LUMO) and LUMO+1 levels in C60 are transiently populated via the creation of charge-transfer excitons, with lifetimes < 1 00 fs. The lifetimes decrease substantially as film thickness decreases, due to quenching by the Cu substrate; this effect is seen for films as thick as 50 @Ao@. Such a long-range effect is attributed to charge transfer between the Cu substrate and electronic bands in C60.