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Conductance saturation in a series of highly transmitting molecular junctions

Abstract

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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Figure 1: Characterization of Ag/oligoacene molecular junctions.
Figure 2: The characteristic conductance of Ag/oligoacene and Pt/oligoacene junctions as a function of molecule length.
Figure 3: Calculated transmission curves and the corresponding single-Lorentzian model for the Ag/oligoacene junctions.
Figure 4: A single-level model explaining the conductance trend along the Ag/oligoacene series.
Figure 5: Experimental and theoretical conductance characterization of the Pt/oligoacene molecular junctions.

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Acknowledgements

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.

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O.T. and T.Y. conceived the project and designed the experiments; T.Y. performed the experiments with assistance from N.S. and R.V.; T.Y. analysed the data; R.K. and F.E. performed the calculations and participated together with T.Y. and O.T. in the overall analysis of the results; B.K. and C.N. synthesized the final precursor for hexacene. T.Y. and O.T. wrote the paper and all co-authors commented on the manuscript.

Corresponding author

Correspondence to O. Tal.

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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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