Self-Assembly of carboranethiol isomers on Au{111}: Intermolecular interactions determined by molecular dipole orientations

J. Nathan Hohman, Pengpeng Zhang, Elizabeth I. Morin, Patrick Han, Moonhee Kim, Adam R. Kurland, Patrick D. McClanahan, Viktor P. Balema, Paul S. Weiss

Research output: Contribution to journalArticlepeer-review

82 Citations (Scopus)


Self-assembled monolayer (SAM) structures and properties are dominated by two interactions: those between the substrate and adsorbate and those between the adsorbates themselves. We have fabricated self-assembled monolayers of m-1-carboranethiol (M1) and m-9-carboranethiol (M9) on Au{111}. The two isomers are nearly identical geometrically, but calculated molecular dipole moments show a sizable difference at 1.06 and 4.08 D for M1 and M9 in the gas phase, respectively. These molecules provide an opportunity to investigate the effect of different dipole moments within SAMs without altering the geometry of the assembly. Pure and codeposited SAMs of these molecules were studied by scanning tunneling microscopy (STM). The molecules are indistinguishable in STM images, and the hexagonally close-packed adlayer structures were found to have (√19 ×√19)R23.4° unit cells. Both SAMs display rotational domains without the protruding or depressed features in STM images associated with domain boundaries in other SAM systems. Differing orientations of molecular dipole moments influence SAM properties, including the stability of the SAM and the coverage of the carboranethiolate in competitive binding conditions. These properties were investigated by dynamic contact angle goniometry, Kelvin probe force microscopy, and grazing incidence Fourier transform infrared spectroscopy.

Original languageEnglish
Pages (from-to)527-536
Number of pages10
JournalACS Nano
Issue number3
Publication statusPublished - 2009 Mar 24
Externally publishedYes


  • Carboranethiol
  • Contact angle
  • Dipole moment
  • Fourier transform infrared spectroscopy
  • Kelvin probe
  • Scanning tunneling microscopy
  • Self-assembled monolayers
  • Self-assembly

ASJC Scopus subject areas

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


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