title: Too Hot for Photon-Assisted Transport: Hot-Electrons Dominate Conductance Enhancement in Illuminated Single-Molecule Junctions.
abstract: We investigate light-induced conductance enhancement in single-molecule junctions via photon-assisted transport and hot-electron transport. Using 4,4'-bipyridine bound to Au electrodes as a prototypical single-molecule junction, we report a 20-40% enhancement in conductance under illumination with 980 nm wavelength radiation. We probe the effects of subtle changes in the transmission function on light-enhanced current and show that discrete variations in the binding geometry result in a 10% change in enhancement. Importantly, we prove theoretically that the steady-state behavior of photon-assisted transport and hot-electron transport is identical but that hot-electron transport is the dominant mechanism for optically induced conductance enhancement in single-molecule junctions when the wavelength used is absorbed by the electrodes and the hot-electron relaxation time is long. We confirm this experimentally by performing polarization-dependent conductance measurements of illuminated 4,4'-bipyridine junctions. Finally, we perform lock-in type measurements of optical current and conclude that currents due to laser-induced thermal expansion mask optical currents. This work provides a robust experimental framework for studying mechanisms of light-enhanced transport in single-molecule junctions and offers tools for tuning the performance of organic optoelectronic devices by analyzing detailed transport properties of the molecules involved.
authors.affiliation: Department of Applied Physics and Applied Mathematics and ‡Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: E-Dean
authors.identifier: 0000-0001-6996-0243
authors.initials: ED
authors.lastname: Fung
authors.affiliation: Department of Applied Physics and Applied Mathematics and ‡Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Olgun
authors.initials: O
authors.lastname: Adak
authors.affiliation: Department of Applied Physics and Applied Mathematics and ‡Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Lovat
authors.affiliation: Department of Applied Physics and Applied Mathematics and ‡Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Diego
authors.initials: D
authors.lastname: Scarabelli
authors.affiliation: Department of Applied Physics and Applied Mathematics and ‡Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Latha
authors.identifier: 0000-0002-6957-6089
authors.initials: L
authors.lastname: Venkataraman
mesh_terms: D004553:Electric Conductivity; D004566:Electrodes; D004579:Electron Transport; D004583:Electrons; D006046:Gold / Q000737:chemistry; D008029:Lighting; D008962:Models, Theoretical; D017785:Photons; D011725:Pyridines / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
chemical_list: D011725:Pyridines; D006046:Gold; C034306:4,4'-bipyridyl
keywords: Photon-assisted transport; Tien-Gordon; hot-electron; single-molecule; surface plasmon