Correlation between HOMO alignment and contact resistance in molecular junctions: Aromatic thiols versus aromatic isocyanides

Bongsoo Kim, Jeremy M. Beebe, Yongseok Jun, X. Y. Zhu, G. Daniel Frisbie

Research output: Contribution to journalArticle

228 Citations (Scopus)

Abstract

Understanding electron transport in metal-molecule-metal (MMM) junctions is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity in a MMM junction include the nature of metal-molecule contacts and the electronic structure of the molecular backbone. We have studied the electronic transport property and the valence electronic structure on rigid, conjugated oligoacenes of increasing length with either thiol (-S) or isocyanide (-CN) linkers using conducting probe atomic force microscopy (CP-AFM) and ultraviolet photoelectron spectroscopy (UPS). We find that for these conjugated systems the Au-CN contact is more resistive than Au-S. The difference in contact resistance correlates with UPS measurements that show the highest-occupied molecular orbital (HOMO) of the isocyanide series is lower in energy (relative to the Fermi level of Au) than the HOMO of the thiol series, indicating the presence of a higher tunneling barrier at the contact for the isocyanide-linked molecules. By contrast, the difference in the HOMO positions for the two series of molecules does not appear to affect the length dependence of the junction resistance (i.e., the β value = 0.5 Å-1).

Original languageEnglish
Pages (from-to)4970-4971
Number of pages2
JournalJournal of the American Chemical Society
Volume128
Issue number15
DOIs
Publication statusPublished - 2006 Apr 19
Externally publishedYes

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Cyanides
Molecular orbitals
Contact resistance
Sulfhydryl Compounds
Metals
Molecules
Ultraviolet photoelectron spectroscopy
Photoelectron Spectroscopy
Electronic structure
Electron transport properties
Molecular electronics
Atomic Force Microscopy
Electron Transport
Molecular Structure
Fermi level
Atomic force microscopy

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Correlation between HOMO alignment and contact resistance in molecular junctions : Aromatic thiols versus aromatic isocyanides. / Kim, Bongsoo; Beebe, Jeremy M.; Jun, Yongseok; Zhu, X. Y.; Frisbie, G. Daniel.

In: Journal of the American Chemical Society, Vol. 128, No. 15, 19.04.2006, p. 4970-4971.

Research output: Contribution to journalArticle

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AB - Understanding electron transport in metal-molecule-metal (MMM) junctions is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity in a MMM junction include the nature of metal-molecule contacts and the electronic structure of the molecular backbone. We have studied the electronic transport property and the valence electronic structure on rigid, conjugated oligoacenes of increasing length with either thiol (-S) or isocyanide (-CN) linkers using conducting probe atomic force microscopy (CP-AFM) and ultraviolet photoelectron spectroscopy (UPS). We find that for these conjugated systems the Au-CN contact is more resistive than Au-S. The difference in contact resistance correlates with UPS measurements that show the highest-occupied molecular orbital (HOMO) of the isocyanide series is lower in energy (relative to the Fermi level of Au) than the HOMO of the thiol series, indicating the presence of a higher tunneling barrier at the contact for the isocyanide-linked molecules. By contrast, the difference in the HOMO positions for the two series of molecules does not appear to affect the length dependence of the junction resistance (i.e., the β value = 0.5 Å-1).

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