Phase separation of binary self-assembled thiol monolayers composed of 1-hexadecanethiol and 3-mercaptopropionic acid on Au(111) studied by scanning tunneling microscopy and cyclic voltammetry

Daisuke Hobara, Masayuki Ota, Shinichiro Imabayashi, Katsumi Niki, Takashi Kakiuchi

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The mixing characteristics of binary self-assembled monolayers composed of 1-hexadecanethiol (HDT) and 3-mercaptopropionic acid (MPA) on Au(111) have been studied by cyclic voltammetry and scanning tunneling microscopy. Two distinctive peaks, ∼ 0.45V apart, are observed over the entire range of surface composition on cyclic voltammograms for the reductive desorption of the adsorbed thiol molecules, which reflects the presence of two different types of phase-separated domains greater than several tens of nm2 which can be imaged by scanning tunneling microscopy. The peak potential of 1-hexadecanethiol is nearly independent of the surface composition whereas a slight shift of the peak potential is observed in the case of MPA, suggesting that the HDT is slightly soluble in the MPA domains, while MPA is insoluble in the HDT domains. The minimum number of the adsorbed thiol molecules required for exhibiting two distinctive peaks (i.e. two-dimensional bulk properties) is estimated to be ca. 50 by comparing the cyclic voltammograms with the distribution of the domain size observed by scanning tunneling microscopy.

Original languageEnglish
Pages (from-to)113-119
Number of pages7
JournalJournal of Electroanalytical Chemistry
Issue number1
Publication statusPublished - 1998 Mar 5
Externally publishedYes



  • 1-Hexadecanethiol
  • 3-Mercaptopropionic acid
  • Binary self-assembled monolayers
  • Scanning tunneling microscopy

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Analytical Chemistry
  • Electrochemistry

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