Environmental Control of Single-Molecule Junction Transport

• Published in: Nano letters Vol. 11; no. 5; pp. 1988 - 1992
• Main Authors: Fatemi, V, Kamenetska, M, Neaton, J. B, Venkataraman, L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11-05-2011
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Methods of electronic structure calculations; Physics; Solid surfaces and solid-solid interfaces; Surface double layers, schottky barriers, and work functions; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); solvent effects; ρ-phenylenediamine; Metal–organic interface; tunnel coupling; density functional theory; single-molecule conductance; Molecular arrangement; Molecular orbital; Point contacts; Scanning tunneling microscopy; Gold; Work functions; Transport properties; Adsorption; Density functional method; Binding site; Molecular junction
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl200324e

The conductance of individual 1,4-benzenediamine (BDA)–Au molecular junctions is measured in different solvent environments using a scanning tunneling microscope based point-contact technique. Solvents are found to increase the conductance of these molecular junctions by as much as 50%. Using first principles calculations, we explain this increase by showing that a shift in the Au contact work function is induced by solvents binding to undercoordinated Au sites around the junction. Increasing the Au contact work function reduces the separation between the Au Fermi energy and the highest occupied molecular orbital of BDA in the junction, increasing the measured conductance. We demonstrate that the solvent-induced shift in conductance depends on the affinity of the solvent to Au binding sites and also on the induced dipole (relative to BDA) upon adsorption. Via this mechanism, molecular junction level alignment and transport properties can be statistically altered by solvent molecule binding to the contact surface.