Bias-induced forces in conducting atomic force microscopy and contact charging of organic monolayers

X. D. Cui, X. Zarate, J. Tomfohr, A. Primak, Ana Moore, Thomas Moore, D. Gust, G. Harris, O. F. Sankey, Stuart Lindsay

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

Contact electrification, a surface property of bulk dielectric materials, has now been observed at the molecular scale using conducting atomic force microscopy (AFM). Conducting AFM measures the electrical properties of an organic film sandwiched between a conducting probe and a conducting substrate. This paper describes physical changes in the film caused by the application of a bias. Contact of the probe leads to direct mechanical stress and the applied electric field results in both Maxwell stresses and electrostriction. Additional forces arise from charge injection (contact charging). Electrostriction and contact charging act oppositely from the normal long-range Coulomb attraction and dominate when a charged tip touches an insulating film, causing the tip to deflect away from the film at high bias. A bias-induced repulsion observed in spin-coated PMMA films may be accounted for by either mechanism. In self-assembled monolayers, however, tunnel current signals show that the repulsion is dominated by contact charging.

Original languageEnglish (US)
Pages (from-to)67-76
Number of pages10
JournalUltramicroscopy
Volume92
Issue number2
DOIs
StatePublished - 2002

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Instrumentation

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