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Observation of inhomogeneous plasmonic field distribution in a nanocavity


The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1,2,3,4,5,6. Plasmon-enhanced applications include advanced spectroscopies7,8,9,10, optomechanics11, optomagnetics12 and biosensing13,14,15,16,17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.

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Fig. 1: Probing the plasmon field in a nanocavity.
Fig. 2: Longitudinal plasmon field distribution within the nanocavity.
Fig. 3: Measurement of longitudinal plasmon field distribution using an alternative probe and nanocavity size.

Data availability

The data that support this study are available from the corresponding authors upon reasonable request.

Code availability

The codes that support this study are available from the corresponding authors upon reasonable request.


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We thank X. S. Zhou, Z. L. Yang, L. W. Ye, Z. Lu, Y. H. Wang and Q. Y. Dai for helpful discussions. This work was supported by the National Natural Science Foundation of China (grant nos. 21925404, 21775127, 21427813 and 21790350), the National Key Research and Development Programme of China (grant nos. 2019YFA0705400 and 2017YFA0303500), and the Anhui Initiative in Quantum Information Technologies (grant no. AHY090000). The Swedish National Infrastructure for Computing is acknowledged for computer time. S.D. is sponsored by Shanghai Pujiang Programme (grant no. 19PJ1400600).

Author information




J.-F.L., Y.L., C.-Y.L. and S.D. conceived and designed the project. C.-Y.L., B.-Y.W., S.-B.L., K.M., L.-Q.X., B.-W.M. and J.-F.L. performed the experiments. S.D. and Y.L. performed the DFT and MIM calculations. S.C. performed the FEM simulations. J.-F.L., Y.L., Z.-Q.T., C.-Y.L., S.D. and J.R.A. analysed the results and wrote the manuscript. All authors contributed to the interpretation of data.

Corresponding authors

Correspondence to Yi Luo or Jian-Feng Li.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Javier Garcia de Abajo and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Notes I–III, Figs. 1–9 and Tables 1 and 2.

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Li, CY., Duan, S., Wen, BY. et al. Observation of inhomogeneous plasmonic field distribution in a nanocavity. Nat. Nanotechnol. 15, 922–926 (2020).

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