Energy Level Alignment in Molecular Tunnel Junctions by Transport and Spectroscopy: Self-Consistency for the Case of Alkyl Thiols and Dithiols on Ag, Au, and Pt Electrodes

Zuoti Xie, Ioan Baldea, C. Daniel Frisbie

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

We report here an extensive study of transport and electronic structure of molecular junctions based on alkyl thiols (CnT; n = 7, 8, 9, 10, 12) and dithiols (CnDT; n = 8, 9, 10) with various lengths contacted with different metal electrodes (Ag, Au, Pt). The dependence of the low-bias resistance (R) on contact work function indicates that transport is HOMO-assisted (p-type transport). Analysis of the current-voltage (I-V) characteristics for CnT and CnDT tunnel junctions with the analytical single-level model (SLM) provides both the HOMO-Fermi energy offset h trans and the average molecule-electrode coupling (I") as a function of molecular length (n), electrode work function (φ), and the number of chemical contacts (one or two). The SLM analysis reveals a strong Fermi level (EF) pinning effect in all the junctions, i.e., h trans changes very little with n, φ, and the number of chemical contacts, but I" depends strongly on these variables. Significantly, independent measurements of the HOMO-Fermi level offset (h) by ultraviolet photoelectron spectroscopy (UPS) for CnT and CnDT SAMs agree remarkably well with the transport-estimated This result provides strong evidence for hole transport mediated by localized HOMO states at the Au-thiol interface, and not by the delocalized σ states in the C-C backbones, clarifying a long-standing issue in molecular electronics. Our results also substantiate the application of the single-level model for quantitative, unified understanding of transport in benchmark molecular junctions.

Original languageEnglish (US)
Pages (from-to)18182-18192
Number of pages11
JournalJournal of the American Chemical Society
Volume141
Issue number45
DOIs
StatePublished - Nov 13 2019

Bibliographical note

Funding Information:
C.D.F. acknowledges financial support from the U.S. National Science Foundation (CHE-1708173). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC program. I.B. acknowledges financial support from the Deutsche Forschungsgemeinschaft (grant BA 1799/3-2) and computational support from the State of Baden-Württemberg through bwHPC and the German Research Foundation (DFG) through grant no. INST 40/467-1 FUGG. (80)

Publisher Copyright:
Copyright © 2019 American Chemical Society.

How much support was provided by MRSEC?

  • Shared

PubMed: MeSH publication types

  • Journal Article

Fingerprint

Dive into the research topics of 'Energy Level Alignment in Molecular Tunnel Junctions by Transport and Spectroscopy: Self-Consistency for the Case of Alkyl Thiols and Dithiols on Ag, Au, and Pt Electrodes'. Together they form a unique fingerprint.

Cite this