Length-dependent conductance of molecular wires and contact resistance in metal–molecule–metal junctions
Boey, Freddy Yin Chiang
Date of Issue2008
School of Materials Science and Engineering
Molecular wires are covalently bonded to gold electrodes—to form metal–molecule–metal junctions—by functionalizing each end with a SH group. The conductance of a wide variety of molecular junctions is studied theoretically by using first-principles density functional theory (DFT) combined with the nonequilibrium Green′s function (NEGF) formalism. Based on the chain-length-dependent conductance of the series of molecular wires, the attenuation factor β is obtained and compared with the experimental data. The β value is quantitatively correlated to the molecular HOMO–LUMO gap. Coupling between the metallic electrode and the molecular bridge plays an important role in electron transport. A contact resistance of 6.0±2.0 KΩ is obtained by extrapolating the molecular-bridge length to zero. This value is of the same magnitude as the quantum resistance.
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.