Recently electrical conductance of a single molecule sandwiched between two gold electrodes has been measured by repeated formation of gold break junctions in the presence of molecules by STM in liquids, air or UHV. As binding groups to gold electrodes, thiolates have been most widely used. During the break junction formation, a thiolate group may bind surface gold atoms in the hollow, the bridge, or the top site. Depending upon the binding modes of two thiolate groups to the two gold electrodes, two [1] or three [2] different contact resistances of the molecular junctions have been reported. In the case of the amino binding group, only one contact resistance was observed and the result was attributed to a single binding mode of the amine to a single surface gold atom [3]. However, it was reported recently [4] that the two different contact resistances could be also observed for the amino binding groups.
To solve the controversial problem of the contact between the amine and the gold electrode, we measured electrical conductance of single molecular junctions of diamines sandwiched between two gold protrusions by STM and analyzed data by a recently proposed robust statistical analysis method [5]. After the careful analysis, we found that there are three different contact resistances, and we attributed these three contact resistances to three different contact modes as previously [2].
References
[1] X. Li et al., J. Am. Chem. Soc. 128, 2135 (2006).
[2] M. Fujihira et al., Phys. Chem. Chem. Phys. 8, 3876 (2006).
[3] L. Venkataraman et al., Nano Lett. 6, 458 (2006).
[4] F. Chen et al., J. Am. Chem. Soc. 128, 15874 (2006).
[5] M. T. Gonzalez et al., Nano Lett. 6, 2238 (2006).
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