Molecular-scale and wide-energy-range tunneling spectroscopy on self-assembled monolayers of alkanethiol molecules

Masato Nakaya, Masaya Shikishima, Masahiro Shibuta, Naoyuki Hirata, Toyoaki Eguchi, Atsushi Nakajima

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The electronic properties of alkanethiol self-assembled monolayers (alkanethiolate SAMs) associated with their molecular-scale geometry are investigated using scanning tunneling microscopy and spectroscopy (STM/STS). We have selectively formed the three types of alkanethiolate SAMs with standing-up, lying-down, and lattice-gas phases by precise thermal annealing of the SAMs which are conventionally prepared by depositing alkanethiol molecules onto Au(111) surface in solution. The empty and filled states of each SAM are evaluated over a wide energy range covering 6 eV above/below the Fermi level (E F) using two types of STS on the basis of tunneling current-voltage and distance-voltage measurements. Electronic states originating from rigid covalent bonds between the thiol group and substrate surface are observed near E F in the standing-up and lying-down phases but not in the lattice-gas phase. These states contribute to electrical conduction in the tunneling junction at a low bias voltage. At a higher energy, a highly conductive state stemming from the alkyl chain and an image potential state (IPS) formed in a vacuum gap appear in all phases. The IPS shifts toward a higher energy through the change in the geometry of the SAM from the standing-up phase to the lattice-gas phase through the lying-down phase. This is explained by the increasing work function of alkanethiolate/Au(111) with decreasing density of surface molecules.

Original languageEnglish
Pages (from-to)8728-8734
Number of pages7
JournalACS Nano
Volume6
Issue number10
DOIs
Publication statusPublished - 2012 Oct 23
Externally publishedYes

Keywords

  • alkanethiol
  • image potential state
  • scanning tunneling microscopy
  • scanning tunneling spectroscopy
  • self-assembled monolayer

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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  • Cite this

    Nakaya, M., Shikishima, M., Shibuta, M., Hirata, N., Eguchi, T., & Nakajima, A. (2012). Molecular-scale and wide-energy-range tunneling spectroscopy on self-assembled monolayers of alkanethiol molecules. ACS Nano, 6(10), 8728-8734. https://doi.org/10.1021/nn302405r