Conductance and geometry of pyridine-linked single-molecule junctions.
We have measured the conductance and characterized molecule-electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine-gold bond allows two distinct conductance states that are accessed as the gold-molecule-gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the pi* orbital.
Kamenetska
M
M
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
Quek
Su Ying
SY
Whalley
A C
AC
Steigerwald
M L
ML
Choi
H J
HJ
Louie
Steven G
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Nuckolls
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Hybertsen
M S
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Neaton
J B
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Venkataraman
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