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Critical Roles of Metal-Molecule Contacts in Electron Transport Through Molecular-wire Junctions

We study the bonding-site dependence of the transmission through metal-molecule contacts at Au-S interfaces in gold-S-benzene-S-gold junctions and related systems. We find that on flat Au(111) surfaces the transmission is rather insensitive to the bonding site. Dramatic differences between measured and calculated conductivities may therefore be due to non-ideal experimental junctions, experiment and theory addressing different systems. In particular, if S is adsorbed in an Au vacancy, or on-top of a small (3-Au-atom) island, sharp spectral features appear near the Fermi level due to essential changes of the level structure and hybridization in the contacts, admitting order-ofmagnitude variations of the conductivity. Possibly such a system, can it be fabricated, will show extremely strong non-linear e ects and might work as uni- or bi-directional voltage-controlled 2-terminal switches and non-linear mixing elements.

nonequilibrium electron transport ; density functional calculations ; organic molecules ; nanostructures ; low index single crystal surface ; gold

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