title: Ultrafast Bidirectional Charge Transport and Electron Decoherence at Molecule/Surface Interfaces: A Comparison of Gold, Graphene, and Graphene Nanoribbon Surfaces.
abstract: We investigate bidirectional femtosecond charge transfer dynamics using the core-hole clock implementation of resonant photoemission spectroscopy from 4,4'-bipyridine molecular layers on three different surfaces: Au(111), epitaxial graphene on Ni(111), and graphene nanoribbons. We show that the lowest unoccupied molecular orbital (LUMO) of the molecule drops partially below the Fermi level upon core-hole creation in all systems, opening an additional decay channel for the core-hole, involving electron donation from substrate to the molecule. Furthermore, using the core-hole clock method, we find that the bidirectional charge transfer time between the substrate and the molecule is fastest on Au(111), with a 2 fs time, then around 4 fs for epitaxial graphene and slowest with graphene nanoribbon surface, taking around 10 fs. Finally, we provide evidence for fast phase decoherence of the core-excited LUMO* electron through an interaction with the substrate providing the first observation of such a fast bidirectional charge transfer across an organic/graphene interface.
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
authors.forename: Olgun
authors.initials: O
authors.lastname: Adak
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana , Ljubljana, Slovenia.|Department of Physics, University of Trieste , Trieste, Italy.
authors.forename: Gregor
authors.initials: G
authors.lastname: Kladnik
authors.affiliation: Faculty of Education, University of Ljubljana , Ljubljana, Slovenia.
authors.forename: Gregor
authors.initials: G
authors.lastname: Bavdek
authors.affiliation: CNR-IOM Laboratorio Nazionale TASC , Basovizza SS-14, km 163.5, I-34012 Trieste, Italy.
authors.forename: Albano
authors.initials: A
authors.lastname: Cossaro
authors.affiliation: Department of Physics, University of Trieste , Trieste, Italy.|CNR-IOM Laboratorio Nazionale TASC , Basovizza SS-14, km 163.5, I-34012 Trieste, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Morgante
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana , Ljubljana, Slovenia.|CNR-IOM Laboratorio Nazionale TASC , Basovizza SS-14, km 163.5, I-34012 Trieste, Italy.
authors.forename: Dean
authors.initials: D
authors.lastname: Cvetko
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.|Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Latha
authors.initials: L
authors.lastname: Venkataraman
keywords: Charge transfer dynamics; charge decoherence; core−hole clock; molecule−graphene interface; molecule−metal interface; photoemission spectroscopy