Article | Published:

Metallic conduction at organic charge-transfer interfaces

Nature Materials volume 7, pages 574580 (2008) | Download Citation

Subjects

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    et al. Electrical conductivity in doped polyacetylene. Phys. Rev. Lett. 39, 1098–1101 (1977).

  2. 2.

    et al. Conducting films of C60 and C70 by alkali-metal doping. Nature 350, 320–322 (1991).

  3. 3.

    et al. Superconductivity at 18 K in potassium-doped C60. Nature 350, 600–601 (1991).

  4. 4.

    & Organic conductors and superconductors. Adv. Phys. 31, 299–490 (1982).

  5. 5.

    , , , & Electronic functionalization of the surface of organic semiconductors with self-assembled monolayers. Nature Mater. 7, 84–89 (2008).

  6. 6.

    & A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004).

  7. 7.

    et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007).

  8. 8.

    et al. Magnetic effects at the interface between non-magnetic oxides. Nature Mater. 6, 493–496 (2007).

  9. 9.

    , , & Electron-transfer in a new highly-conducting donor–acceptor complex. J. Am. Chem. Soc. 95, 948–949 (1973).

  10. 10.

    Organic conductors: from charge density wave TTF–TCNQ to superconducting (TMTSF)2PF6. Chem. Rev. 104, 5565–5591 (2004).

  11. 11.

    , & Organic Superconductors 2nd edn (Springer, Berlin, 1998).

  12. 12.

    & Organic Molecular Crystals (American Institute of Physics, New York, 1994).

  13. 13.

    & Electrical properties of powdered or pure TCNQ and TTF: Evidence for a strong solid-state charge-transfer reaction. Physica 143B, 324–326 (1986).

  14. 14.

    , , & Organic single-crystal field-effect transistors. Phys. Status Solidi. A 201, 1302–1331 (2004).

  15. 15.

    , , , & Mobility studies of field-effect transistor structures based on anthracene single crystals. Appl. Phys. Lett. 84, 5383–5385 (2004).

  16. 16.

    , & Field-effect transistors on tetracene single crystals. Appl. Phys. Lett. 83, 4345–4347 (2003).

  17. 17.

    et al. Field-induced charge transport at the surface of pentacene single crystals: A method to study charge dynamics of two dimensional electron systems in organic crystals. J. Appl. Phys. 94, 5800–5804 (2003).

  18. 18.

    et al. Tunable Frohlich polarons in organic single-crystal transistors. Nature Mater. 5, 982–986 (2006).

  19. 19.

    et al. Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors. Appl. Phys. Lett. 86, 262109 (2005).

  20. 20.

    , , , & Field-effect transistor made with a sexithiophene single crystal. Adv. Mater. 8, 52–54 (1996).

  21. 21.

    et al. Elastomeric transistor stamps: Reversible probing of charge transport in organic crystals. Science 303, 1644–1646 (2004).

  22. 22.

    , , , & Bias-dependent contact resistance in rubrene single-crystal field-effect transistors. Appl. Phys. Lett. 90, 212103 (2007).

  23. 23.

    , , & Ambipolar organic field-effect transistors based on rubrene single crystals. Appl. Phys. Lett. 88, 033505 (2006).

  24. 24.

    , , & Gate dielectric materials for high-mobility organic transistors of molecular semiconductor crystals. Solid State Electron. 51, 1338–1343 (2007).

  25. 25.

    et al. Nanoscale surface morphology and rectifying behavior of a bulk single-crystal organic semiconductor. Adv. Mater. 18, 1552–1556 (2006).

  26. 26.

    , & Electronic transport in single-crystal organic transistors. Rev. Mod. Phys. 78, 973–989 (2006).

  27. 27.

    , , & Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes. Appl. Phys. Lett. 88, 113512 (2006).

  28. 28.

    , , , & Orientation control of pentacene and transport anisotropy of the thin film transistor by photoaligned polyimide film. Appl. Phys. Lett. 90, 102117 (2007).

  29. 29.

    & Disordered electronic systems. Rev. Mod. Phys. 57, 287–337 (1985).

  30. 30.

    , , , & Current saturation and Coulomb interactions in organic single-crystal transistors. New J. Phys. 10, 033031 (2008).

  31. 31.

    et al. Control of carrier density by self-assembled monolayers in organic field-effect transistors. Nature Mater. 3, 317–322 (2004).

  32. 32.

    , & Excitonic insulator. Phys. Rev. 158, 462–475 (1967).

  33. 33.

    , , & Physical vapor growth of organic crystals. J. Cryst. Growth 187, 449–454 (1998).

  34. 34.

    , & The crystal structure of the 1:1 radical cation-radical anion salt of 2-2-bis-1,3-dithiole (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Acta Crystallogr. B 30, 763–768 (1974).

  35. 35.

    et al. Crystal and molecular structure of aromatic sulphur compound 2,2-bi-1,3-dithiole—evidence for d-orbital participation in bonding. J. Chem. Soc. D 16, 889–890 (1971).

  36. 36.

    , & The crystal and molecular structure of 7,7,8,8-tetracyanoquinodimethane. Acta Crystallogr. 18, 932–939 (1965).

  37. 37.

    et al. High-performance n- and p-type single-crystal organic transistors with free-space gate dielectrics. Adv. Mater. 16, 2097–2101 (2004).

Download references

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.

Author information

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. Search for Helena Alves in:

  2. Search for Anna S. Molinari in:

  3. Search for Hangxing Xie in:

  4. Search for Alberto F. Morpurgo in:

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.

Corresponding author

Correspondence to Alberto F. Morpurgo.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nmat2205

Further reading