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Impact of junction formation process on single molecular conductance

Abstract

We have investigated electric conductance and atomic structure of single molecular junctions of pyrazine (Py), 4,4’-bipyridine (BiPy), fullerene (C60), and 1,4-diaminobutane (DAB). The single molecular junctions were fabricated by breaking Au contacts between a Au tip and Au electrode surface in the presence of the target molecules (breaking process) or approaching the Au tip to the Au electrode surface covered by the molecules (making process). In the making process, no major conductance state was observed in the conductance histogram for DAB, while single conductance states were observed for the π-conjugated molecules of Py (10 mG0, G0~ 77.45 μ/Ω), BiPy (3 mG0), and C60 (5 mG0). In contrast to the making process, two major conductance states were observed for Py (1 mG0 and 0.3 mG0), BiPy (0.6 mG0 and 0.2 mG0), and C60 (30 mG0 and 3 mG0) in the breaking process. The observed conductance behavior could be explained by the characters of anchoring unit of molecules. In the making process, the localized lone pair on the N atom of DAB, Py, and BiPY hardly find a Au atom and cannot make a contact to the Au electrode surface, while the delocalized π electrons in the aromatic ring of Py, BiPY, and C60 make contact with the Au electrode surface, which explains the difference in the observed conductance behavior between DAB and the π conjugated molecules of Py, BiPY, and C60 in the making process. In the breaking process, the delocalized π-electrons of Py, BiPY, and C60 can make contact with the Au electrode surface and the lone pair on the N atom of DAB as well as Py and BiPY can bind to Au atoms, and therefore, the single molecular junctions were formed for all systems. The present results indicates that the π-plane is important for making metal-molecule contacts and for the formation of the single molecular junction in the making process.

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Publication details

The article was received on 16 Jan 2018, accepted on 15 Feb 2018 and first published on 15 Feb 2018


Article type: Paper
DOI: 10.1039/C8CP00317C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Impact of junction formation process on single molecular conductance

    Y. Isshiki, S. Fujii, T. Nishino and M. Kiguchi, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP00317C

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