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A bond-fluctuation mechanism for stochastic switching in wired molecules
Ganesh K Ramachandran1, Theresa J Hopson, Adam M Rawlett
1Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287, USA.
Science (New York, N.Y.)
|May 31, 2003
Summary
Stochastic on-off conductivity switching was observed in simple alkanethiols on gold surfaces. Molecular mobility at the gold interface, not internal electronic changes, likely causes this switching behavior.
Area of Science:
- Materials Science
- Surface Chemistry
- Molecular Electronics
Background:
- Stochastic on-off conductivity switching is a phenomenon observed in molecular electronic devices.
- Previous explanations for this switching in phenylene-ethynylene oligomers involved conformational changes or electron localization.
- The simplest wired molecules, alkanethiols, offer a fundamental system to investigate this behavior.
Purpose of the Study:
- To investigate stochastic on-off conductivity switching in alkanethiols.
- To determine the underlying mechanism responsible for switching in these simple molecular systems.
- To explore the role of molecular mobility at the metal-molecule interface.
Main Methods:
- Utilizing alkanethiols (octanedithiol, decanedithiol, dodecanedithiol) bonded to an Au(111) surface.
- Employing conducting atomic force microscopy (AFM) with a top gold contact pressed at constant force.
- Conducting experiments at room temperature and an elevated temperature of 60 degrees C.
Main Results:
- Stochastic on-off conductivity switching was successfully observed in octanedithiol, decanedithiol, and dodecanedithiol on Au(111).
- Switching persisted even under constant force applied by the AFM tip.
- The rate of switching significantly increased at 60 degrees C.
- Internal molecular electronic changes and top contact breaking were ruled out as primary causes.
Conclusions:
- The observed stochastic switching in alkanethiols is attributed to the inherent mobility of molecules tethered to the gold surface via thiol linkages.
- This molecular mobility at the metal-molecule interface is a key factor in conductivity switching.
- The findings provide a fundamental understanding of switching mechanisms in molecular electronics.
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