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Tuning surface d bands with bimetallic electrodes to facilitate electron transport across molecular junctions

Nature Materials volume 20, pages 658–664 (2021)Cite this article

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Abstract

Understanding chemical bonding and conductivity at the electrode–molecule interface is key for the operation of single-molecule junctions. Here we apply the d-band theory that describes interfacial interactions between adsorbates and transition metal surfaces to study electron transport across these devices. We realized bimetallic Au electrodes modified with a monoatomic Ag adlayer to connect α,ω-alkanoic acids (HO2C(CH2)nCO2H). The force required to break the molecule–electrode binding and the contact conductance Gn=0 are 1.1 nN and 0.29 G0 (the conductance quantum, 1 G0 = 2e2/h ≈ 77.5 μS), which makes these junctions, respectively, 1.3–1.8 times stronger and 40–60-fold more conductive than junctions with bare Au or Ag electrodes. A similar performance was found for Au electrodes modified by Cu monolayers. By integrating the Newns–Anderson model with the Hammer–Nørskov d-band model, we explain how the surface d bands strengthen the adsorption and promote interfacial electron transport, which provides an alternative avenue for the optimization of molecular electronic devices.

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Fig. 1: Proposed improvement of ELA by narrow surface d bands.
Fig. 2: Junction conductance of bimetallic UPD electrodes.
Fig. 3: Effect of UPD-modified electrodes on i–Vbias characteristics.
Fig. 4: Derivations of transmission spectrum for AgUPD junction.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

The algorithm that was used to calculate the quantum transport properties is available from the corresponding author upon reasonable request.

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Acknowledgements

The authors are grateful to C.-H. Lin (NTU) and L.-Y. Hsu (IAMS, Academia Sinica) for fruitful discussions and to F.-M. Chen for the graphic drawing. Thanks to S.-J. Ji of the Ministry of Science and Technology (MOST) for the characterization of UPD-modified AFM tips by SEM. This research is supported by MOST (109-2628-M-143-001-MY3, 108-2113-M-002-007-MY3 and 106-2113-M-032-005) and by NTU (108L880115). H.H.P. thanks NTU for a University Fellowship.

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Authors and Affiliations

  1. Department of Chemistry and Centre for Emerging Materials and Advanced Devices, National Taiwan University, Taipei, Taiwan

    Mong-Wen Gu, Hao Howard Peng & Chun-hsien Chen

  2. Department of Applied Science, National Taitung University, Taitung, Taiwan

    I-Wen Peter Chen

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Contributions

C.-h.C. conceived the idea. M.-W.G. developed the theoretical model. M.-W.G. and H.H.P. performed the experiments and the data were analysed by M.-W.G., H.H.P. and I-W.P.C. I-W.P.C. and C.-h.C. supervised the research. The manuscript was written through contributions from all authors.

Corresponding authors

Correspondence to I-Wen Peter Chen or Chun-hsien Chen.

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Peer review information Nature Materials thanks Thomas Frederiksen and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Discussion, Figs. 1–10, Tables 1–5, glossary and refs. 1–75.

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Source Data Fig. 2

Numerical data used to generate the graphs displayed in panels a–c.

Source Data Fig. 3

Numerical data used to generate the graphs displayed in panels a and b.

Source Data Fig. 4

Numerical data used to generate the graphs displayed in panels c–e and h–j.

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Gu, MW., Peng, H.H., Chen, IW.P. et al. Tuning surface d bands with bimetallic electrodes to facilitate electron transport across molecular junctions. Nat. Mater. 20, 658–664 (2021). https://doi.org/10.1038/s41563-020-00876-2

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