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arXiv · 1403.4266

Large tunable image-charge effects in single-molecule junctions

M. L. Perrin·C. J. O. Verzijl·C. A. Martin·A. J. Shaikh·R. Eelkema·J. H. van Esch·J. M. van Ruitenbeek·J. M. Thijssen·H. S. J. van der Zant·D. Dulić
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Abstract

The characteristics of molecular electronic devices are critically determined by metal-organic interfaces, which influence the arrangement of the orbital levels that participate in charge transport. Studies on self-assembled monolayers (SAMs) show (molecule-dependent) level shifts as well as transport-gap renormalization, suggesting that polarization effects in the metal substrate play a key role in the level alignment with respect to the metal's Fermi energy. Here, we provide direct evidence for an electrode-induced gap renormalization in single-molecule junctions. We study charge transport in single porphyrin-type molecules using electrically gateable break junctions. In this set-up, the position of the occupied and unoccupied levels can be followed in situ and with simultaneous mechanical control. When increasing the electrode separation, we observe a substantial increase in the transport gap with level shifts as high as several hundreds of meV for displacements of a few ångstroms. Analysis of this large and tunable gap renormalization with image-charge calculations based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions.

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M. L. Perrin, C. J. O. Verzijl, C. A. Martin, A. J. Shaikh, R. Eelkema, J. H. van Esch, J. M. van Ruitenbeek, J. M. Thijssen, H. S. J. van der Zant, D. Dulić. 2014-03-17. Large tunable image-charge effects in single-molecule junctions. https://doi.org/10.1038/nnano.2013.26

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