Potential-induced phase transitions in 2,2′-bipyridine and 4,4′-bipyridine monolayers on Au(111) studied by in situ scanning tunneling microscopy and atomic force microscopy

F. Cunha, Nongjian Tao, X. W. Wang, Q. Jin, B. Duong, J. D'Agnese

Research output: Contribution to journalArticle

95 Citations (Scopus)

Abstract

The formation and structure of 2,2′-bipyridine (22BPY) and 4,4′-bipyridine (44BPY) monolayers on Au(111) substrate have been studied as a function of the substrate potential. At high potentials, both molecules adsorb onto the substrate and stand vertically with their nitrogen atoms facing the Au(111). The vertically standing molecules stack, like rolls of coins, into polymer-like chains which pack closely in parallel to form ordered monolayers. Decreasing the potential to a critical value, the 22BPY chains become randomly oriented via a reversible order - disorder phase transition. The phase transition, as revealed by scanning tunneling microscopy, is driven by a potential dependent attractive force between the chains. The attractive force is believed to be a substrate-mediated effective force which arises as an adsorbed 22BPY perturbs its surrounding local surface potential and thus the nearby molecules. This hypothesis is supported by a quantitative investigation of the local surface potential using a self-consistent density functional method. In contrast to 22BPY, the 44BPY chains dissolve instead of becoming randomly oriented at low potentials. This behavior may be due to that 44BPY is not as strongly adsorbed on the surface as 22BPY because it has only one nitrogen facing the surface.

Original languageEnglish (US)
Pages (from-to)6410-6418
Number of pages9
JournalLangmuir
Volume12
Issue number26
StatePublished - Dec 25 1996
Externally publishedYes

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Scanning tunneling microscopy
scanning tunneling microscopy
Monolayers
Atomic force microscopy
Phase transitions
atomic force microscopy
Surface potential
Substrates
Molecules
Nitrogen
Order disorder transitions
Polymers
molecules
Atoms
nitrogen atoms
disorders
nitrogen
polymers

ASJC Scopus subject areas

  • Colloid and Surface Chemistry
  • Physical and Theoretical Chemistry

Cite this

Potential-induced phase transitions in 2,2′-bipyridine and 4,4′-bipyridine monolayers on Au(111) studied by in situ scanning tunneling microscopy and atomic force microscopy. / Cunha, F.; Tao, Nongjian; Wang, X. W.; Jin, Q.; Duong, B.; D'Agnese, J.

In: Langmuir, Vol. 12, No. 26, 25.12.1996, p. 6410-6418.

Research output: Contribution to journalArticle

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