Current-Voltage Characteristics of Metal-Electrode-Linked Molecular Wires: Examination of Basic Assumptions and Extension of Analytical Formulations
Lachlan E. Halla, Jeffrey R. Reimers*, b, Noel S. Husha, c, and Kia Silverbrooka
aMolecular Electronics Research, 393 Darling Street. Balmain,Sydney N.S.W. 2041 Australia bChemistry School, University of Sydney,
N.S.W. 2006, Australia cBiochemistry Department, University of Sydney,
N.S.W. 2006, Australia
The current-voltage characteristics of a molecular wire linked to metallic electrodes has been the subject of much recent study. In particular, the extensive work of Mujica, Ratner et al. (1-4) and of Datta et al. (5) provides explicit formalisms in the low-temperature ballistic limit. In the first part of this work, we examine the consequences of some of the simplifying assumptions of these approaches, with particular reference to the system of p-thioquinone linked to Au electrodes at the 111 faces. We proceed by considering the electrode to be represented by a supramolecular cluster, an approach also used by Emberly and Kirczenow (6) and by Datta et al. (5). Only a small number of surface Au atoms, those nearest the binding sites, need to be explicitly included in the supramolecular cluster. The topics considered include the following:
The consequences of using Newns-Anderson semi-elliptical model densities of states or constant densities, rather than actual bulk state densities.
The consequences of ignoring p and d band states
The consequences of ignoring the real component in the Green's function self-energy terms
The consequences of using one-electron tight-binding models of electronic structure: comparisons with density functional and related approaches.
Examination of the form of scaling of current with magnitude of molecule-electrode coupling.
In the second part of this work, analytical models are developed for the conductance of linear molecules which both simplify earlier expressions and bring out fundamental relationships in a particularly transparent fashion.
Mujica, V.; Kemp, M.; Ratner, M. A. J. Chem. Phys.1994, 101, 6849.
Mujica, V.; Kemp, M.; Ratner, M. A. J. Chem. Phys.1994, 101, 6856.
Mujica, V.; Kemp, M.; Roitberg, A.; Ratner, M. A. J. Chem. Phys.1996, 104, 7296.
Ratner, M. A.; Davis, B.; Kemp, M.; Mujica, V.; Roitberg, A.; Yaliraki, S. Ann. N.Y. Acad. Sci.1998, 852, 22.
Tian, W.; Data, S.; Hong, S.; Reifenberger, R.; Henderson, J. I.; Kubiak, C. I. J. Chem. Phys.1998, 109, 2874.
Emberly, E. G.; Kirczenow, G. Phys. Rev. B1998, 58, 10911.