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Direct measurement of electrical conductance through a self-assembled molecular layer

Nature Nanotechnology volume 4, pages 373–376 (2009)Cite this article

Abstract

The self-assembly of organic molecules on surfaces is a promising approach for the development of nanoelectronic devices1,2. Although a variety of strategies have been used to establish stable links between molecules2,3,4,5,6,7,8,9,10,11, little is known about the electrical conductance of these links. Extended electronic states, a prerequisite for good conductance, have been observed for molecules adsorbed on metal surfaces12,13,14,15,16. However, direct conductance measurements through a single layer of molecules are only possible if the molecules are adsorbed on a poorly conducting substrate. Here we use a nanoscale four-point probe17 to measure the conductivity of a self-assembled layer of cobalt phthalocyanine on a silver-terminated silicon surface as a function of thickness. For low thicknesses, the cobalt phthalocyanine molecules lie flat on the substrate, and their main effect is to reduce the conductivity of the substrate. At higher thicknesses, the cobalt phthalocyanine molecules stand up to form stacks and begin to conduct. These results connect the electronic structure and orientation of molecular monolayer and few-layer systems to their transport properties, and should aid in the rational design of future devices.

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Figure 1: Conductance, structure and model of CoPc.
Figure 2: Photoemission spectra from different CoPc systems.

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Acknowledgements

We acknowledge useful discussions with P. Petersen, M. Balslev, J. Hansen, T. Hansen and P. Bøggild. Ph.H. thanks the Leverhulme Foundation and the Danish National Research Council for supporting a stay at the University of Liverpool. K.S. acknowledges support from an Anne McLaren Fellowship from the University of Nottingham, and support from the European Community – Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’ Programme (through the Integrated Infrastructure Initiative ‘Integrating Activity on Synchrotron and Free Electron Laser Science’). M.A.-T. received funding through NANOCAGE (MEST-CT-2004-506854), a Marie Curie Early Stage Training Network, part of EC-FP6. We thank F. Bondino, E. Magnano and A. Preobrajenski for their help during synchrotron measurements.

Author information

Author notes

  1. K. Schulte, J. C. Swarbrick & Ph. Hofmann

    Present address: Present address: MAX-lab, Lund University, P.O. Box 118, 22100 Lund, Sweden (K.S.), European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble cedex 9, France (J.C.S.), Surface Science Research Centre, University of Liverpool, Liverpool L69 3BX, UK (Ph.H.),

Authors and Affiliations

  1. Institute for Storage Ring Facilities (ISA) and Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, Aarhus C, 8000, Denmark

    F. Song, J. W. Wells, K. Handrup, E. W. Perkins & Ph. Hofmann

  2. Department of Physics, Zhejiang University, Hangzhou, 310027, China

    F. Song & S. N. Bao

  3. Norwegian University of Science and Technology (NTNU), Trondheim, Norway

    J. W. Wells

  4. Institute for Storage Ring Facilities (ISA), University of Aarhus, Aarhus C, 8000, Denmark

    Z. S. Li

  5. School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK

    K. Schulte, L. C. Mayor, J. C. Swarbrick & E. W. Perkins

  6. Department of Physics and Astronomy, University of Turku, Turku, 20014, Finland

    M. Ahola-Tuomi

  7. Capres A/S, 2800 Kgs, Lyngby, Denmark

    L. Gammelgaard

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Contributions

F.S., J.W.W., S.N.B. and Ph.H. conceived the conductance experiments and F.S., K.H. and J.W.W. designed and performed these experiments and analysed the data. F.S., J.W.W., Z.S.L., K.S., M.A.-T., L.C.M., J.C.S. and E.W.P. performed the photoemission (PES) and NEXAFS experiments. K.S. analysed the NEXAFS and lithium-doping PES, F.S. the thickness-dependent PES. L.G. fabricated the nanoscale four-point probes. Ph.H., J.W.W. and K.S. co-wrote the initial draft of the paper. All authors discussed the results and significantly commented on the manuscript.

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Correspondence to Ph. Hofmann.

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Song, F., Wells, J., Handrup, K. et al. Direct measurement of electrical conductance through a self-assembled molecular layer. Nature Nanotech 4, 373–376 (2009). https://doi.org/10.1038/nnano.2009.82

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