Web Release Date: September 27,
Amine-Gold Linked Single-Molecule Circuits: Experiment and Theory
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Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Applied Physics, Columbia University, New York, New York 10027, Center for Electron Transport in Nanostructures, Columbia University, New York, New York 10027, Department of Physics and IPAP, Yonsei University, Seoul 120-749, Korea, Department of Physics, University of California, Berkeley, Berkeley, California 94720, and Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973
Received August 15, 2007
Revised September 6, 2007
Abstract:
A combination of theory and experiment is used to quantitatively understand the conductance of single-molecule benzenediamine-gold junctions. A newly developed analysis is applied to a measured junction conductance distribution, based on 59 000 individual conductance traces, which has a clear peak at 0.0064 G0 and a width of ±47%. This analysis establishes that the distribution width originates predominantly from variations in conductance across different junctions rather than variations in conductance during junction elongation. Conductance calculations based on density functional theory (DFT) for 15 distinct junction geometries show a similar spread. We show explicitly that differences in local structure have a limited influence on conductance because the amine-Au bonding motif is well-defined and flexible, explaining the narrow distributions seen in the experiments. The minimal impact of junction structure on conductance permits an unambiguous comparison of calculated and measured conductance values and a direct assessment of the widely used DFT theoretical framework. The average calculated conductance (0.046 G0) is found to be seven times larger than experiment. This discrepancy is explained quantitatively in terms of electron correlation effects to the molecular level alignments in the junction.
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