title: In situ formation of highly conducting covalent Au-C contacts for single-molecule junctions.
abstract: Charge transport across metal-molecule interfaces has an important role in organic electronics. Typically, chemical link groups such as thiols or amines are used to bind organic molecules to metal electrodes in single-molecule circuits, with these groups controlling both the physical structure and the electronic coupling at the interface. Direct metal-carbon coupling has been shown through C60, benzene and π-stacked benzene, but ideally the carbon backbone of the molecule should be covalently bonded to the electrode without intervening link groups. Here, we demonstrate a method to create junctions with such contacts. Trimethyl tin (SnMe(3))-terminated polymethylene chains are used to form single-molecule junctions with a break-junction technique. Gold atoms at the electrode displace the SnMe(3) linkers, leading to the formation of direct Au-C bonded single-molecule junctions with a conductance that is ∼100 times larger than analogous alkanes with most other terminations. The conductance of these Au-C bonded alkanes decreases exponentially with molecular length, with a decay constant of 0.97 per methylene, consistent with a non-resonant transport mechanism. Control experiments and ab initio calculations show that high conductances are achieved because a covalent Au-C sigma (σ) bond is formed. This offers a new method for making reproducible and highly conducting metal-organic contacts.
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Z-L
authors.initials: ZL
authors.lastname: Cheng
authors.forename: R
authors.initials: R
authors.lastname: Skouta
authors.forename: H
authors.initials: H
authors.lastname: Vazquez
authors.forename: J R
authors.initials: JR
authors.lastname: Widawsky
authors.forename: S
authors.initials: S
authors.lastname: Schneebeli
authors.forename: W
authors.initials: W
authors.lastname: Chen
authors.forename: M S
authors.initials: MS
authors.lastname: Hybertsen
authors.forename: R
authors.initials: R
authors.lastname: Breslow
authors.forename: L
authors.initials: L
authors.lastname: Venkataraman
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D004553:Electric Conductivity; D004563:Electrochemistry; D004566:Electrodes; D004581:Electronics; D006046:Gold / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D036103:Nanotechnology / Q000379:methods; D014298:Trimethyltin Compounds / Q000737:chemistry*
chemical_list: D000473:Alkanes; D014298:Trimethyltin Compounds; D002244:Carbon; D006046:Gold