Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

Anshuma Pathak, Achyut Bora, Kung Ching Liao, Hannah Schmolke, Antje Jung, Claus Peter Klages, Jeffrey Schwartz, Marc Tornow

Research output: Contribution to journalArticle

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Abstract

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlOx) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current-voltage (J-V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β mono = 0.85 ± 0.03 per carbon atom, a surprisingly high value, β bis = 1.40 ± 0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of 'through-space' tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices.

Original languageEnglish (US)
Article number094008
JournalJournal of Physics Condensed Matter
Volume28
Issue number9
DOIs
StatePublished - Feb 12 2016

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics

Keywords

  • aluminum oxide
  • bis-phosphonic acids
  • conformational disorder
  • monolayer
  • though-space tunneling

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    Pathak, A., Bora, A., Liao, K. C., Schmolke, H., Jung, A., Klages, C. P., Schwartz, J., & Tornow, M. (2016). Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers. Journal of Physics Condensed Matter, 28(9), [094008]. https://doi.org/10.1088/0953-8984/28/9/094008