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Molecular diodes with rectification ratios exceeding 105 driven by electrostatic interactions

Abstract

Molecular diodes operating in the tunnelling regime are intrinsically limited to a maximum rectification ratio R of 103. To enhance this rectification ratio to values comparable to those of conventional diodes (R ≥ 105) an alternative mechanism of rectification is therefore required. Here, we report a molecular diode with R = 6.3 × 105 based on self-assembled monolayers with Fc–C≡C–Fc (Fc, ferrocenyl) termini. The number of molecules (n(V)) involved in the charge transport changes with the polarity of the applied bias. More specifically, n(V) increases at forward bias because of an attractive electrostatic force between the positively charged Fc units and the negatively charged top electrode, but remains constant at reverse bias when the Fc units are neutral and interact weakly with the positively charged electrode. We successfully model this mechanism using molecular dynamics calculations.

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Figure 1: The junctions and mechanism of rectification.
Figure 2: Electrical characteristics of the junctions.
Figure 3: Temperature-dependent measurements of the junctions.
Figure 4: Bias-dependent change in contacts in the junctions.
Figure 5: Computed change in the SC15Fc-C≡C-Fc SAM structure as the junction is biased.

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Acknowledgements

The authors thank the Ministry of Education (MOE) for supporting this research under award no. MOE2015-T2-1-050. The Prime Minister's Office, Singapore, under its Medium Sized Centre programme, is also acknowledged for supporting this research. The authors thank T. Wang for assisting in the analysis of the optical data and L. Jiang for providing the Au and Ag substrates. D.T. acknowledges Science Foundation Ireland (SFI) for financial support under grant no. 15/CDA/3491, and for provision of computing resources at the SFI/Higher Education Authority Irish Centre for High-End Computing (ICHEC). E.d.B. acknowledges support from the National Science Foundation (grants numbers NSF-ECCS 1402990 and 1518863). The authors thank Y. Xiaojiang for assisting at the SINS beamline at SSLS under NUS core support C-380-003-003-001.

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X.C. and L.Y. performed electrical characterization and analysed the data. M.R. synthesized the compounds. L.Y. performed the XPS, ultraviolet photoelecton spectroscopy and near-edge X-ray fine structure spectroscopy measurements. W.D. carried out the optical measurement. D.T. computed the molecular dynamics. E.d.B. modelled the junction data. C.A.N. conceptualized and led the study. All authors discussed the results, contributed to writing the paper and commented on the manuscript.

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Correspondence to Christian A. Nijhuis.

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The authors declare no competing financial interests.

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Chen, X., Roemer, M., Yuan, L. et al. Molecular diodes with rectification ratios exceeding 105 driven by electrostatic interactions. Nature Nanotech 12, 797–803 (2017). https://doi.org/10.1038/nnano.2017.110

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