A single-molecule diode
- Mark Elbing*,
- Rolf Ochs*,
- Max Koentopp*,
- Matthias Fischer*,
- Carsten von Hänisch*,
- Florian Weigend*,
- Ferdinand Evers*,†,
- Heiko B. Weber‡,§, and
- Marcel Mayor*,¶,∥
- *Institute for Nanotechnology, Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, D-76021 Karlsruhe, Germany; ‡University of Erlangen-Nürnberg, D-91058 Erlangen, Germany; and ¶Department of Chemistry, University of Basel, St. Johannsring 19, CH-4056 Basel, Switzerland
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Edited by Mark A. Ratner, Northwestern University, Evanston, IL, and approved May 10, 2005 (received for review November 30, 2004)
Abstract
We have designed and synthesized a molecular rod that consists of two weakly coupled electronic π -systems with mutually shifted energy levels. The asymmetry thus implied manifests itself in a current–voltage characteristic with pronounced dependence on the sign of the bias voltage, which makes the molecule a prototype for a molecular diode. The individual molecules were immobilized by sulfur–gold bonds between both electrodes of a mechanically controlled break junction, and their electronic transport properties have been investigated. The results indeed show diode-like current–voltage characteristics. In contrast to that, control experiments with symmetric molecular rods consisting of two identical π -systems did not show significant asymmetries in the transport properties. To investigate the underlying transport mechanism, phenomenological arguments are combined with calculations based on density functional theory. The theoretical analysis suggests that the bias dependence of the polarizability of the molecule feeds back into the current leading to an asymmetric shape of the current–voltage characteristics, similar to the phenomena in a semiconductor diode.
Footnotes
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↵ † To whom correspondence regarding theory should be addressed. E-mail: ferdinand.evers{at}int.fzk.de. §To whom correspondence regarding conductance experiments should be addressed. E-mail: heiko.weber{at}physik.uni-erlangen.de. ∥To whom correspondence regarding molecules should be addressed. E-mail: marcel.mayor{at}unibas.ch.
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Author contributions: F.E., H.B.W., and M.M. designed research; M.E., R.O., M.K., M.F., F.E., H.B.W., and M.M. performed research; M.E., R.O., M.K., M.F., C.v.H., F.W., F.E., H.B.W., and M.M. contributed new reagents/analytic tools; M.E., R.O., M.K., C.v.H., F.E., H.B.W., and M.M. analyzed data; and F.E., H.B.W., and M.M. wrote the paper.
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This paper was submitted directly (Track II) to the PNAS office.
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Abbreviations: A, acceptor; D, donor; MCB, mechanically controlled break junction.
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Data deposition: The atomic coordinates have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, Cambridge CB2 1EZ, United Kingdom (CSD reference no. 241632).
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↵ ** 11: a = 520.9(1), b = 1238.7(3), c = 2309.5(5) pm, α = 96.58(3), β = 90.77(3), γ = 97.75(3)°, V = 1466.4(5) × 106 pm3; triclinic
, Z = 2, ρcalc = 1.369 g/cm3, μ(MoKα) = 0,237 mm–1, STOE IPDS2, MoKα-radiation, λ = 0.71073 Å, T = 200 K, 2θmax = 52°; 6,316 reflections measured, 4,591 independent reflections (R
int = 0.0301), 3,232 independent reflections with F
obs > 4σ(F
obs). The structure was solved by direct methods and refined by full-matrix least square techniques against F
2, 379 parameters (S, O, F, and C were refined anisotropically; H atoms were calculated at ideal positions); R1 = 0.0567; wR2 = 0.1737 (all data); Gof: 1.067; maximum peak, 0.238 eÅ–3. Cambridge Crystallographic Data Centre entry 241632 contains the crystallographic data for this paper.
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↵ †† |U| =1.5 V is a compromise of being well above the threshold voltage, which is affected by sample-to-sample fluctuations, and still being at a voltage, which allows for stable conditions for all junctions. The absolute current values scattered within a factor of two to three for all molecules. No correlation between the current level and the rectification ratios were observed.
- Copyright © 2005, The National Academy of Sciences
