Large tunable image-charge effects in single-molecule junctions
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 \aa ngstroms. 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.
Cite
@article{arxiv.1403.4266,
title = {Large tunable image-charge effects in single-molecule junctions},
author = {M. L. Perrin and C. J. O. Verzijl and C. A. Martin and A. J. Shaikh and R. Eelkema and J. H. van Esch and J. M. van Ruitenbeek and J. M. Thijssen and H. S. J. van der Zant and D. Dulić},
journal= {arXiv preprint arXiv:1403.4266},
year = {2014}
}