Web Release Date: January 29,
Mechanical and Charge Transport Properties of Alkanethiol Self-Assembled Monolayers on a Au(111) Surface: The Role of Molecular Tilt
and
Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Applied Science and Technology Graduate Group, University of California Berkeley, The Molecular Foundry, Lawrence Berkeley National Laboratory, and Materials Science and Engineering, University of California Berkeley, Berkeley California 94720
Received October 10, 2007
In Final Form: November 14, 2007
Abstract:
The relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers
(SAMs) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular
tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant 
=
0.57 ± 0.03 Å-1 was found for the current passing through the film as a function of tip-substrate separation due to
this molecular tilt. This is significantly smaller than the value of ~1 Å-1 found when the separation is varied by
changing the length of the alkanethiol molecules. Calculations indicate that, for isolated dithiol molecules S-bonded
to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of
S-Au bonding on SAM conductance is discussed.
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