Single-Molecule Circuits with Well-Defined Molecular Conductance
Author(s):
Latha Venkataraman, Jennifer E. Klare, Iris W. Tam, Colin Nuckolls, Mark S. Hybertsen, Michael L. Steigerwald
Journal:
Nano Letters
Year:
2006
Volume:
6
Pages
458-462
DOI:
10.1021/nl052373+
Abstract:
We measure the conductance of amine-terminated molecules by breaking Au point contacts in a molecular solution at room temperature. We find that the variability of the observed conductance for the diamine molecule−Au junctions is much less than the variability for diisonitrile− and dithiol−Au junctions. This narrow distribution enables unambiguous conductance measurements of single molecules. For an alkane diamine series with 2−8 carbon atoms in the hydrocarbon chain, our results show a systematic trend in the conductance from which we extract a tunneling decay constant of 0.91 ± 0.03 per methylene group. We hypothesize that the diamine link binds preferentially to undercoordinated Au atoms in the junction. This is supported by density functional theory-based calculations that show the amine binding to a gold adatom with sufficient angular flexibility for easy junction formation but well-defined electronic coupling of the N lone pair to the Au. Therefore, the amine linkage leads to well-defined conductance measurements of a single molecule junction in a statistical study.