title: Molecular electronic level alignment at weakly coupled organic film/metal interfaces.
abstract: Electronic level alignment at interfaces of molecular materials with inorganic semiconductors and metals controls many interfacial phenomena. How the intrinsic properties of the interacting systems define the electronic structure of their interface remains one of the most important problems in molecular electronics and nanotechnology that can be solved through a combination of surface science experimental techniques and theoretical modeling. In this article, we address this fundamental problem through experimental and computational studies of molecular electronic level alignment of thin films of C(6)F(6) on noble metal surfaces. The unoccupied electronic structure of C(6)F(6) is characterized with single molecule resolution using low-temperature scanning tunneling microscopy-based constant-current distance-voltage spectroscopy. The experiments are performed on several noble metal surfaces with different work functions and distinct surface-normal projected band structures. In parallel, the electronic structures of the quantum wells (QWs) formed by the lowest unoccupied molecular orbital state of the C(6)F(6) monolayer and multilayer films and their alignment with respect to the vacuum level of the metallic substrates are calculated by solving the Schrödinger equation for a semiempirical one-dimensional (1D) potential of the combined system using input from density functional theory. Our analysis shows that the level alignment for C(6)F(6) molecules bound through weak van der Waals interactions to noble metal surfaces is primarily defined by the image potential of metal, the electron affinity of the molecule, and the molecule surface distance. We expect the same factors to determine the interfacial electronic structure for a broad range of molecule/metal interfaces.
authors.affiliation: Department of Physics and ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and §Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhao
authors.forename: Min
authors.initials: M
authors.lastname: Feng
authors.forename: Daniel Barker
authors.initials: DB
authors.lastname: Dougherty
authors.forename: Hao
authors.initials: H
authors.lastname: Sun
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Petek
keywords: energy level alignment; image potential; quantum well state