Revealing the mechanisms of electronic transport through metal–molecule interfaces is of central importance for a variety of molecule-based devices. A key method for understanding these mechanisms is based on the study of conductance versus molecule length in molecular junctions. However, previous works focused on transport governed either by coherent tunnelling or hopping, both at low conductance. Here, we study the upper limit of conductance across metal–molecule–metal interfaces. Using highly conducting single-molecule junctions based on oligoacenes with increasing length, we find that the conductance saturates at an upper limit where it is independent of molecule length. With the aid of two prototype systems, in which the molecules are contacted by either Ag or Pt electrodes, we find two different possible origins for conductance saturation. The results are explained by an intuitive model, backed by ab initio calculations. Our findings shed light on the mechanisms that constrain the conductance of metal–molecule interfaces at the high-transmission limit.
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T.Y. and O.T. thank L. Goffer, B. Pasmantirer and K. L. Narasimhan for their valuable help in developing the measurement set-ups and O. Yaffe for his assistance with molecule resources. O.T. thanks the H. Perlman family for their support and acknowledges funding by the Israel Science Foundation (Grant No. 1089/15), and the Minerva Foundation (Grant No. 711136). R.K. and F.E. gratefully acknowledge the Steinbuch Centre for Computing (SCC) for providing computing time on the computer HC3 at Karlsruhe Institute of Technology (KIT). Part of the computational work was performed on the bwUniCluster resources funded by the Ministry of Science, Research and Arts and the Universities of the State of Baden-Wuerttemberg, Germany, within the framework programme bwHPC.
The authors declare no competing financial interests.
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Yelin, T., Korytár, R., Sukenik, N. et al. Conductance saturation in a series of highly transmitting molecular junctions. Nature Mater 15, 444–449 (2016). https://doi.org/10.1038/nmat4552
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