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Near-unity Raman β-factor of surface-enhanced Raman scattering in a waveguide

Nature Nanotechnology volume 17, pages 1251–1257 (2022)Cite this article

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Abstract

The Raman scattering of light by molecular vibrations is a powerful technique to fingerprint molecules through their internal bonds and symmetries. Since Raman scattering is weak1, methods to enhance, direct and harness it are highly desirable, and this has been achieved using optical cavities2, waveguides3,4,5,6 and surface-enhanced Raman scattering (SERS)7,8,9. Although SERS offers dramatic enhancements2,6,10,11 by localizing light within vanishingly small hot-spots in metallic nanostructures, these tiny interaction volumes are only sensitive to a few molecules, yielding weak signals12. Here we show that SERS from 4-aminothiophenol molecules bonded to a plasmonic gap waveguide is directed into a single mode with >99% efficiency. Although sacrificing a confinement dimension, we find a SERS enhancement of ~103 times across a broad spectral range enabled by the waveguide’s larger sensing volume and non-resonant waveguide mode. Remarkably, this waveguide SERS is bright enough to image Raman transport across the waveguides, highlighting the role of nanofocusing13,14,15 and the Purcell effect16. By analogy to the β-factor from laser physics10,17,18,19,20, the near-unity Raman β-factor we observe exposes the SERS technique to alternative routes for controlling Raman scattering. The ability of waveguide SERS to direct Raman scattering is relevant to Raman sensors based on integrated photonics7,8,9 with applications in gas sensing and biosensing.

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Fig. 1: Illustration of plasmonic gap waveguides, their linear characterization and observation of W-SERS.
Fig. 2: Imaging and spectroscopy of W-SERS.
Fig. 3: Imaging of Raman-scattering transport in W-SERS.
Fig. 4: Experimental evaluation of the Raman β-factor.

Data availability

The data that support the findings of this study have been deposited in the Research Data Repository of Imperial College London and are available online at https://doi.org/10.14469/hpc/10981. Any additional materials and data are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the EPSRC Reactive Plasmonics Programme (EP/M013812/1, R.F.O. and S.A.M.), the EPSRC Catalysis Plasmonics Programme (EP/W017075/1, R.F.O. and S.A.M.) and the Leverhulme Trust (RPG-2016-064, R.F.O. and S.A.M.). In addition, S.A.M. acknowledges the Lee-Lucas Chair in Physics. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under a Marie Skłodowska-Curie Fellowship (grant agreement no. 844591, M.F.). M.F. thanks R. Hoggarth for his support on laser maintenance and alignment. N.A.G. thanks the German National Academy of Sciences Leopoldina for their support via the Leopoldina Postdoc Fellowship (LPDS2020-12).

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Authors and Affiliations

  1. Blackett Laboratory, Imperial College London, London, UK

    Ming Fu, Mónica P. dS. P. Mota, Xiaofei Xiao, Andrea Jacassi, Nicholas A. Güsken, Yuxin Chen, Huaifeng Xiao, Yi Li, Ahad Riaz, Stefan A. Maier & Rupert F. Oulton

  2. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, USA

    Nicholas A. Güsken

  3. School of Microelectronics, MOE Engineering Research Center of Integrated Circuits for Next Generation Communications, Southern University of Science and Technology, Shenzhen, China

    Yi Li

  4. School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia

    Stefan A. Maier

  5. Chair in Hybrid Nanosystems, Nanoinstitute Munich, Faculty of Physics, Ludwig-Maximilians-Universität München, Munich, Germany

    Stefan A. Maier

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Contributions

M.F., M.P.dS.P.M., N.A.G. and R.F.O. developed the idea and designed the experiments. M.P.dS.P.M., N.A.G. and X.X. designed and simulated the waveguide structures and their mode properties. A.J., X.X. and Y.L. fabricated the waveguides and performed the structural characterization. M.F., M.P.dS.P.M. and Y.L. prepared samples with 4-ATP molecules. M.F., M.P.dS.P.M., Y.C. and H.X. conducted the experiments and analysed the data. A.R. and R.F.O. developed the waveguide Raman model and analysed this in the context of the experimental data. All authors contributed to the writing of the manuscript.

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Correspondence to Rupert F. Oulton.

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Nature Nanotechnology thanks Jeremy Baumberg, Reuven Gordon and Jacob Khurgin for their contribution to the peer review of this work.

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Supplementary discussion, Figs. 1–10 and Table 1.

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Fu, M., Mota, M.P.d.P., Xiao, X. et al. Near-unity Raman β-factor of surface-enhanced Raman scattering in a waveguide. Nat. Nanotechnol. 17, 1251–1257 (2022). https://doi.org/10.1038/s41565-022-01232-y

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