Quantum plasmon resonances of individual metallic nanoparticles


The plasmon resonances of metallic nanoparticles have received considerable attention for their applications in nanophotonics, biology, sensing, spectroscopy and solar energy harvesting. Although thoroughly characterized for spheres larger than ten nanometres in diameter, the plasmonic properties of particles in the quantum size regime have been historically difficult to describe owing to weak optical scattering, metal–ligand interactions, and inhomogeneity in ensemble measurements. Such difficulties have precluded probing and controlling the plasmonic properties of quantum-sized particles in many natural and engineered processes, notably catalysis. Here we investigate the plasmon resonances of individual ligand-free silver nanoparticles using aberration-corrected transmission electron microscope (TEM) imaging and monochromated scanning TEM electron energy-loss spectroscopy (EELS). This technique allows direct correlation between a particle’s geometry and its plasmon resonance. As the nanoparticle diameter decreases from 20 nanometres to less than two nanometres, the plasmon resonance shifts to higher energy by 0.5 electronvolts, a substantial deviation from classical predictions. We present an analytical quantum mechanical model that describes this shift due to a change in particle permittivity. Our results highlight the quantum plasmonic properties of small metallic nanospheres, with direct application to understanding and exploiting catalytically active and biologically relevant nanoparticles.

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Figure 1: Aberration-corrected TEM images of silver nanoparticles synthesized free of stabilizing ligands.
Figure 2: STEM image of a 20-nm-diameter silver particle and the associated deconvoluted EELS data.
Figure 3: Correlating Ag nanoparticle geometry with plasmonic EELS data.
Figure 4: Analytic quantum theory of particle permittivity and spectra.
Figure 5: Comparison of experimental data with quantum theory.


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We thank S. Sheikholeslami, A. Atre, A. García-Etxarri and A. Baldi for discussions. This research was supported by the National Science Foundation Graduate Research Fellowship Program. J.A.D. acknowledges support from a Stanford Terman Fellowship and a Robert N. Noyce Family Faculty Fellowship.

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J.A.S. performed the experiment, analysed the data, and developed the model. A.L.K. provided substantial assistance with the STEM EELS procedure. J.A.D. guided and supervised the experiments and analysis. All authors contributed to writing and editing the manuscript.

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Correspondence to Jonathan A. Scholl or Jennifer A. Dionne.

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The authors declare no competing financial interests.

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Scholl, J., Koh, A. & Dionne, J. Quantum plasmon resonances of individual metallic nanoparticles. Nature 483, 421–427 (2012). https://doi.org/10.1038/nature10904

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