title: Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.
abstract: In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.
authors.affiliation: National Institute for Nanotechnology, Edmonton, AB, Canada T6G 2M9.
authors.forename: Haijun
authors.initials: H
authors.lastname: Yan
authors.forename: Adam Johan
authors.initials: AJ
authors.lastname: Bergren
authors.forename: Richard
authors.initials: R
authors.lastname: McCreery
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Della Rocca
authors.forename: Pascal
authors.initials: P
authors.lastname: Martin
authors.forename: Philippe
authors.initials: P
authors.lastname: Lafarge
authors.forename: Jean Christophe
authors.initials: JC
authors.lastname: Lacroix
mesh_terms: D002244:Carbon / Q000737:chemistry; D004581:Electronics / Q000379:methods*; D006358:Hot Temperature; D007474:Ion Exchange; D036103:Nanotechnology / Q000379:methods*; D011789:Quantum Theory; D012666:Semiconductors
chemical_list: D002244:Carbon