Issue 36, 2018, Issue in Progress

Bottom-electrode induced defects in self-assembled monolayer (SAM)-based tunnel junctions affect only the SAM resistance, not the contact resistance or SAM capacitance

Abstract

In large area molecular junctions, defects are always present and can be caused by impurities and/or defects in the electrode materials and/or SAMs, but how they affect the electrical characteristics of junctions has rarely been studied. Usually, junctions are characterized by two-terminal current–voltage measurements where only the total current across the junction is measured, but with these methods one cannot distinguish how the individual components of the junctions are altered by the defects. Here we show that the roughness of the bottom-electrode is a crucial factor in determining the electrical properties of self-assembled monolayer (SAM)-based junctions. We used potentiodynamic impedance spectroscopy to reveal which components of the junctions are altered by defective bottom electrodes because this method allows for direct determination of all components that impede charge transport in the equivalent circuit of the junctions. We intentionally introduced defects via the roughness of the bottom electrode and found that these defects lower the SAM resistance but they do not alter the capacitance of the SAM or the contact resistance of the junction. In other words, defective junctions can be seen as “leaky capacitors” resulting in an underestimation of the SAM resistance of two orders of magnitude. These results help to improve the interpretation of data generated by SAM-based junctions and explain in part the observed large spread of reported tunneling rates for the same molecules measured across different platforms.

Graphical abstract: Bottom-electrode induced defects in self-assembled monolayer (SAM)-based tunnel junctions affect only the SAM resistance, not the contact resistance or SAM capacitance

Supplementary files

Article information

Article type
Paper
Submitted
19 Feb 2018
Accepted
14 May 2018
First published
30 May 2018
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2018,8, 19939-19949

Bottom-electrode induced defects in self-assembled monolayer (SAM)-based tunnel junctions affect only the SAM resistance, not the contact resistance or SAM capacitance

C. S. S. Sangeeth, L. Jiang and C. A. Nijhuis, RSC Adv., 2018, 8, 19939 DOI: 10.1039/C8RA01513A

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