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Contact and edge effects in graphene devices


Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level1,2 and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions3,4,5. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics6,7. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.

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Figure 1: Photocurrent response of a graphene device.
Figure 2: Spatially resolved photocurrent maps at various transport regimes of a graphene device.
Figure 3: Quantitative determination of the potential steps at the metal–graphene interface.
Figure 4: Invasive nature of metal contacts to graphene.


  1. 1

    Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004).

    Article  Google Scholar 

  2. 2

    Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183–191 (2007).

    Article  Google Scholar 

  3. 3

    Novoselov, K. S. et al. Two-dimensional gas of massless Dirac fermions in graphene. Nature 438, 197–200 (2005).

    Article  Google Scholar 

  4. 4

    Zhang, Y., Tan, J. W., Stormer, H. L. & Kim, P. Experimental observation of the quantum Hall effect and Berry's phase in graphene. Nature 438, 201–204 (2005).

    Article  Google Scholar 

  5. 5

    Katsnelson, M. I., Novoselov, K. S. & Geim, A. K. Chiral tunneling and the Klein paradox in graphene. Nature Phys. 2, 620–625 (2006).

    Article  Google Scholar 

  6. 6

    Hwang, E. H., Adam, S. & Das Sarma, S. Carrier transport in two-dimensional graphene layers. Phys. Rev. Lett. 98, 186806 (2007).

    Article  Google Scholar 

  7. 7

    Adam, S., Hwang, E. H., Galitski, V. M. & Das Sarma, S. A self-consistent theory for graphene transport. Proc. Natl Acad. Sci. USA 104, 18392–18397 (2007).

    Article  Google Scholar 

  8. 8

    Martin, J. et al. Observation of electron–hole puddles in graphene using a scanning single-electron transistor. Nature Phys. 4, 144–148 (2008).

    Article  Google Scholar 

  9. 9

    Tan, Y. W. et al. Measurement of scattering rate and minimum conductivity in graphene. Phys. Rev. Lett. 99, 246803 (2007).

    Article  Google Scholar 

  10. 10

    Rossi, E. & Das Sarma, S. Ground-state of graphene in the presence of random charge impurities. Preprint at <> (2008).

  11. 11

    Polini, M., Tomadin, A., Asgari, R. & MacDonald, A. H. Density-functional theory of graphene sheets. Preprint at <> (2008).

  12. 12

    Sze, S. M. Physics of Semiconductor Devices (Wiley, New York, 2007).

  13. 13

    Giovannetti, G. et al. Doping graphene with metal contacts. Preprint at <> (2008).

  14. 14

    Golizadeh-Mojarad, R. & Datta, S. Effect of the contact induced states on minimum conductivity in graphene. Preprint at <> (2007).

  15. 15

    Huard, B., Stander, N., Sulpizio, J. A. & Goldhaber-Gordon, D. Evidence of the role of contacts on the observed electron–hole symmetry in graphene. Preprint at <> (2008).

  16. 16

    Balasubramanian, K. et al. Photoelectronic transport imaging of individual semiconducting carbon nanotubes. Appl. Phys. Lett. 84, 2400–2402 (2004).

    Article  Google Scholar 

  17. 17

    Balasubramanian, K., Burghard, M., Kern, K., Scolari, M. & Mews, A. Photocurrent imaging of charge transport barriers in carbon nanotube devices. Nano Lett. 5, 507–510 (2005).

    Article  Google Scholar 

  18. 18

    Lee, E. J. H. et al. Electronic band structure mapping of nanotube transistors by scanning photocurrent microscopy. Small 3, 2038–2042 (2007).

    Article  Google Scholar 

  19. 19

    Freitag, M. et al. Imaging of the Schottky barriers and charge depletion in carbon nanotube transistors. Nano Lett. 7, 2037–2042 (2007).

    Article  Google Scholar 

  20. 20

    Ahn, Y., Dunning, J. & Park, J. Scanning photocurrent imaging and electronic band studies in silicon nanowire field effect transistors. Nano Lett. 5, 1367–1370 (2005).

    Article  Google Scholar 

  21. 21

    Ferrari, A. C. et al. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006).

    Article  Google Scholar 

  22. 22

    Horcas, I. et al. WSxM: a software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 78, 013705 (2007).

    Article  Google Scholar 

  23. 23

    Graf, D. et al. Spatially-resolved Raman spectroscopy of single- and few-layer graphene. Nano Lett. 7, 238–242 (2007).

    Article  Google Scholar 

  24. 24

    Blake, P. et al. Making graphene visible. Appl. Phys. Lett. 91, 063124 (2007).

    Article  Google Scholar 

  25. 25

    Roddaro, S., Pingue, P., Piazza, V., Pellegrini, V. & Beltram, F. The optical visibility of graphene: interference colours of ultrathin graphite on SiO2 . Nano Lett. 7, 2707–2710 (2007).

    Article  Google Scholar 

  26. 26

    Piscanec, S., Lazzeri, M., Mauri, F., Ferrari, A. C. & Robertson, J. Kohn anomalies and electron–phonon interactions in graphite. Phys. Rev. Lett. 93, 185503 (2004).

    Article  Google Scholar 

  27. 27

    Hansen, W. N. & Johnson, K. B. Work function measurements in gas ambient. Surf. Sci. 316, 373–382 (1994).

    Article  Google Scholar 

  28. 28

    Klusek, Z. et al. Local electronic edge states of graphene layer deposited on Ir(111) surface studied by STM/CITS. Appl. Surf. Sci. 252, 1221–1227 (2005).

    Article  Google Scholar 

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The authors gratefully thank J. Smet and D. Obergfell for help with the preparation of the graphene monolayers, and A. Forment-Aliaga and A. Sagar for the Raman spectroscopy measurements.

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Correspondence to Eduardo J. H. Lee.

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Lee, E., Balasubramanian, K., Weitz, R. et al. Contact and edge effects in graphene devices. Nature Nanotech 3, 486–490 (2008).

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