title: Observation of Ground- and Excited-State Charge Transfer at the C60/Graphene Interface.
abstract: We examine charge transfer interactions in the hybrid system of a film of C60 molecules deposited on single-layer graphene using Raman spectroscopy and Terahertz (THz) time-domain spectroscopy. In the absence of photoexcitation, we find that the C60 molecules in the deposited film act as electron acceptors for graphene, yielding increased hole doping in the graphene layer. Hole doping of the graphene film by a uniform C60 film at a level of 5.6 × 10(12)/cm(2) or 0.04 holes per interfacial C60 molecule was determined by the use of both Raman and THz spectroscopy. We also investigate transient charge transfer occurring upon photoexcitation by femtosecond laser pulses with a photon energy of 3.1 eV. The C60/graphene hybrid exhibits a short-lived (ps) decrease in THz conductivity, followed by a long-lived increase in conductivity. The initial negative photoconductivity transient, which decays within 2 ps, reflects the intrinsic photoresponse of graphene. The longer-lived positive conductivity transient, with a lifetime on the order of 100 ps, is attributed to photoinduced hole doping of graphene by interfacial charge transfer. We discuss possible microscopic pathways for hot carrier processes in the hybrid system.
authors.affiliation: †Department of Physics, Columbia University, New York, New York 10027, United States.
authors.forename: Giriraj
authors.initials: G
authors.lastname: Jnawali
authors.affiliation: †Department of Physics, Columbia University, New York, New York 10027, United States.
authors.forename: Yi
authors.initials: Y
authors.lastname: Rao
authors.affiliation: §Department of Electrical Engineering, Columbia University, New York, New York 10027, United States.
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Beck
authors.affiliation: ∥Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Petrone
authors.affiliation: §Department of Electrical Engineering, Columbia University, New York, New York 10027, United States.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Kymissis
authors.affiliation: ∥Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: †Department of Physics, Columbia University, New York, New York 10027, United States.|§Department of Electrical Engineering, Columbia University, New York, New York 10027, United States.
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz
keywords: C60; Raman spectroscopy; THz time-domain spectroscopy; graphene; hybrid nanomaterials; interfacial charge transfer; photoconductivity