title: Probing the chemistry of molecular heterojunctions using thermoelectricity.
abstract: Thermopower measurements offer an alternative transport measurement that can characterize the dominant transport orbital and is independent of the number of molecules in the junction. This method is now used to explore the effect of chemical structure on the electronic structure and charge transport. We interrogate junctions, using a modified scanning tunneling microscope break junction technique, where: (i) the 1,4-benzenedithiol (BDT) molecule has been modified by the addition of electron-withdrawing or -donating groups such as fluorine, chlorine, and methyl on the benzene ring; and (ii) the thiol end groups on BDT have been replaced by the cyanide end groups. Cyanide end groups were found to radically change transport relative to BDT such that transport is dominated by the lowest unoccupied molecular orbital in 1,4-benzenedicyanide, while substituents on BDT generated small and predictable changes in transmission.
authors.affiliation: Department of Chemistry, University of California Berkeley, California 94720, USA.
authors.forename: Kanhayalal
authors.initials: K
authors.lastname: Baheti
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Malen
authors.forename: Peter
authors.initials: P
authors.lastname: Doak
authors.forename: Pramod
authors.initials: P
authors.lastname: Reddy
authors.forename: Sung-Yeon
authors.initials: SY
authors.lastname: Jang
authors.forename: T Don
authors.initials: TD
authors.lastname: Tilley
authors.forename: Arun
authors.initials: A
authors.lastname: Majumdar
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Segalman
mesh_terms: D004553:Electric Conductivity; D004563:Electrochemistry / Q000379:methods*; D008422:Materials Testing / Q000379:methods; D008839:Microelectrodes; D016252:Microscopy, Scanning Tunneling / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D012666:Semiconductors; D013817:Thermography / Q000379:methods*