Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

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.

Similar content being viewed by others

References

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  4. Jerome, D. & Schulz, H. J. Organic conductors and superconductors. Adv. Phys. 31, 299–490 (1982).

    Article  CAS  Google Scholar 

  5. Calhoun, M. F., Sanchez, J., Olaya, D., Gershenson, M. E. & Podzorov, V. Electronic functionalization of the surface of organic semiconductors with self-assembled monolayers. Nature Mater. 7, 84–89 (2008).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  9. Ferraris, J., Walatka, V., Perlstei, J. H. & Cowan, D. O. Electron-transfer in a new highly-conducting donor–acceptor complex. J. Am. Chem. Soc. 95, 948–949 (1973).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  11. Ishiguro, T., Yamaji, K. & Saito, G. Organic Superconductors 2nd edn (Springer, Berlin, 1998).

    Book  Google Scholar 

  12. Silinsh, E. A. & Capek, V. Organic Molecular Crystals (American Institute of Physics, New York, 1994).

    Google Scholar 

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

    Google Scholar 

  14. de Boer, R. W. I., Gershenson, M. E., Morpurgo, A. F. & Podzorov, V. Organic single-crystal field-effect transistors. Phys. Status Solidi. A 201, 1302–1331 (2004).

    Article  CAS  Google Scholar 

  15. Aleshin, A. N., Lee, J. Y., Chu, S. W., Kim, J. S. & Park, Y. W. Mobility studies of field-effect transistor structures based on anthracene single crystals. Appl. Phys. Lett. 84, 5383–5385 (2004).

    Article  CAS  Google Scholar 

  16. de Boer, R. W. I., Klapwijk, T. M. & Morpurgo, A. F. Field-effect transistors on tetracene single crystals. Appl. Phys. Lett. 83, 4345–4347 (2003).

    Article  CAS  Google Scholar 

  17. Takeya, J. 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).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  19. de Boer, R. W. I. et al. Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors. Appl. Phys. Lett. 86, 262109 (2005).

    Article  Google Scholar 

  20. Horowitz, G., Garnier, F., Yassar, A., Hajlaoui, R. & Kouki, F. Field-effect transistor made with a sexithiophene single crystal. Adv. Mater. 8, 52–54 (1996).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  22. Molinari, A., Gutierrez, I., Hulea, I. N., Russo, S. & Morpurgo, A. F. Bias-dependent contact resistance in rubrene single-crystal field-effect transistors. Appl. Phys. Lett. 90, 212103 (2007).

    Article  Google Scholar 

  23. Takahasi, T., Takenobu, T., Takeya, J. & Iwasa, Y. Ambipolar organic field-effect transistors based on rubrene single crystals. Appl. Phys. Lett. 88, 033505 (2006).

    Article  Google Scholar 

  24. Takeya, J., Yamagishi, M., Tominari, Y. & Nakazawa, Y. Gate dielectric materials for high-mobility organic transistors of molecular semiconductor crystals. Solid State Electron. 51, 1338–1343 (2007).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  26. Gershenson, M. E., Podzorov, V. & Morpurgo, A. F. Electronic transport in single-crystal organic transistors. Rev. Mod. Phys. 78, 973–989 (2006).

    Article  CAS  Google Scholar 

  27. Hulea, I. N., Russo, S., Molinari, A. & Morpurgo, A. F. Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes. Appl. Phys. Lett. 88, 113512 (2006).

    Article  Google Scholar 

  28. Guo, D., Sakamoto, K., Miki, K., Ikeda, S. & Saiki, K. Orientation control of pentacene and transport anisotropy of the thin film transistor by photoaligned polyimide film. Appl. Phys. Lett. 90, 102117 (2007).

    Article  Google Scholar 

  29. Lee, P. A. & Ramakrishnan, T. V. Disordered electronic systems. Rev. Mod. Phys. 57, 287–337 (1985).

    Article  CAS  Google Scholar 

  30. Fratini, S., Xie, H., Hulea, I. N., Ciuchi, S. & Morpurgo, A. F. Current saturation and Coulomb interactions in organic single-crystal transistors. New J. Phys. 10, 033031 (2008).

    Article  Google Scholar 

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

    Article  CAS  Google Scholar 

  32. Jerome, D., Rice, T. M. & Kohn, W. Excitonic insulator. Phys. Rev. 158, 462–475 (1967).

    Article  CAS  Google Scholar 

  33. Laudise, R. A., Kloc, C., Simpkins, P. G. & Sigriest, T. Physical vapor growth of organic crystals. J. Cryst. Growth 187, 449–454 (1998).

    Article  CAS  Google Scholar 

  34. Kistenmacher, T. J., Phillips, T. E. & Cowan, D. O. 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).

    Article  CAS  Google Scholar 

  35. Cooper, W. F. 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).

    Article  Google Scholar 

  36. Long, R. E., Sparks, R. A. & Trueblood, K. N. The crystal and molecular structure of 7,7,8,8-tetracyanoquinodimethane. Acta Crystallogr. 18, 932–939 (1965).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

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
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Anna S. Molinari
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Hangxing Xie
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Alberto F. Morpurgo
    View author publications

    You can also search for this author in PubMed Google Scholar

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.

Rights and permissions

Reprints and permissions

About this article

Cite this article

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

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat2205

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing