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Metallic conduction at organic charge-transfer interfaces

Nature Materials volume 7, pages 574–580 (2008)Cite this article

Abstract

The electronic properties of interfaces between two different solids can differ strikingly from those of the constituent materials. For instance, metallic conductivity—and even superconductivity—have recently been discovered at interfaces formed by insulating transition-metal oxides. Here, we investigate interfaces between crystals of conjugated organic molecules, which are large-gap undoped semiconductors, that is, essentially insulators. We find that highly conducting interfaces can be realized with resistivity ranging from 1 to 30 kΩ per square, and that, for the best samples, the temperature dependence of the conductivity is metallic. The observed electrical conduction originates from a large transfer of charge between the two crystals that takes place at the interface, on a molecular scale. As the interface assembly process is simple and can be applied to crystals of virtually any conjugated molecule, the conducting interfaces described here represent the first examples of a new class of electronic systems.

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Figure 1: Charge transfer in the TTF–TCNQ system.
Figure 2: Characterization of TCNQ and TTF single crystals.
Figure 3: Assembly of TTF–TCNQ charge-transfer interfaces.
Figure 4: Room-temperature electrical characteristics of TTF–TCNQ interfaces.
Figure 5: Temperature dependence of the electrical characteristics of TTF–TCNQ interfaces.

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Acknowledgements

A.F.M. gratefully acknowledges a useful conversation with D. van der Marel. H.A. acknowledges FCT for financial support under contract nr. SFRH/BPD/34333/2006. Financial support from NanoNed and NWO is also acknowledged.

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Authors and Affiliations

  1. Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands

    Helena Alves, Anna S. Molinari, Hangxing Xie & Alberto F. Morpurgo

Authors
  1. Helena Alves
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  2. Anna S. Molinari
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  3. Hangxing Xie
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  4. Alberto F. Morpurgo
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Contributions

H.A. grew the molecular crystals, fabricated the devices and took part in the electrical measurements; A.S.M. carried out most of the electrical measurements on TTF–TCNQ interfaces; H.X. did the field-effect transistor characterization of TTF and TCNQ crystals; A.F.M. conceived the experiments, directed the research and wrote the manuscript.

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Correspondence to Alberto F. Morpurgo.

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Alves, H., Molinari, A., Xie, H. et al. Metallic conduction at organic charge-transfer interfaces. Nature Mater 7, 574–580 (2008). https://doi.org/10.1038/nmat2205

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