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Sub-nanometre resolution in single-molecule photoluminescence imaging

Abstract

Ambitions to reach atomic resolution with light have been a major force in shaping nano-optics, whereby a central challenge is achieving highly localized optical fields. A promising approach employs plasmonic nanoantennas, but fluorescence quenching in the vicinity of metallic structures often imposes a strict limit on the attainable spatial resolution, and previous studies have reached only 8 nm resolution in fluorescence mapping. Here, we demonstrate spatially and spectrally resolved photoluminescence imaging of a single phthalocyanine molecule coupled to nanocavity plasmons in a tunnelling junction with a spatial resolution down to 8 Å and locally map the molecular exciton energy and linewidth at sub-molecular resolution. This remarkable resolution is achieved through an exquisite nanocavity control, including tip-apex engineering with an atomistic protrusion, quenching management through emitter–metal decoupling and sub-nanometre positioning precision. Our findings provide new routes to optical imaging, spectroscopy and engineering of light–matter interactions at sub-nanometre scales.

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Fig. 1: Sub-nanometre-resolved single-molecule TEPL imaging.
Fig. 2: Evolution of spatial resolution for photon images at different gap distances.
Fig. 3: Revealing the photophysics of ZnPc in a plasmonic nanocavity by tracking the evolution of TEPL intensities at different tip–molecule distances.
Fig. 4: Revealing subtle plasmon–molecule interactions at the sub-molecular level by spectroscopic imaging.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

Code availability

The MATLAB codes used for the electromagnetic calculations in this study are available from the corresponding authors on reasonable request.

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Acknowledgements

We thank B. Wang for helpful discussions. This work was supported by the National Key R&D Program of China (grant numbers 2016YFA0200600 and 2017YFA0303500), the National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences (grant number XDB36000000) and the Anhui Initiative in Quantum Information Technologies. J.A. acknowledges project IT1164-19 of the consolidated university groups from the Basque Government.

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Z.D. and J.G.H. conceived and supervised the project. B.Y., A.G., Yufan Zhang and Yang Zhang performed experiments and analysed data. G.C. and Yao Zhang derived the theory and performed theoretical simulations. B.Y., G.C., Yao Zhang, Yang Zhang, Y.L., J.Y., V.S., J.A., Z.D. and J.G.H contributed to the data interpretation. Z.D., B.Y., G.C., Yang Zhang, J.A., V.S. and J.G.H. co-wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Yang Zhang or Zhenchao Dong or J. G. Hou.

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Extended data

Extended Data Fig. 1 Schematic drawing of our custom-built experimental setup for TEPL measurements.

This setup is composed of four sub-systems: a laser source for light excitation, a dark-box for optical filtering, polarization control and alignment, a low-temperature UHV STM for sample preparation and characterization with a built-in lens for both light excitation and collection, and a photon detection sub-system containing a SPAD for PL intensity measurements and a spectrometer equipped with a highly sensitive CCD detector for PL spectral measurements.

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Supplementary Sections 1–7.

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Yang, B., Chen, G., Ghafoor, A. et al. Sub-nanometre resolution in single-molecule photoluminescence imaging. Nat. Photonics 14, 693–699 (2020). https://doi.org/10.1038/s41566-020-0677-y

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