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Nature Research, Nature Communications, 1(6), 2015

DOI: 10.1038/ncomms9788

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Multipole plasmons and their disappearance in few-nanometre silver nanoparticles

Journal article published in 2015 by Søren Raza, Shima Kadkhodazadeh ORCID, Thomas Christensen ORCID, Marcel Di Vece, Martijn Wubs ORCID, N. Asger Mortensen, Nicolas Stenger ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

In electron energy-loss spectroscopy (EELS) of individual silver nanoparticles encapsulated in silicon nitride, we observe besides the usual dipole resonance an additional surface plasmon (SP) resonance corresponding to higher angular momenta. We even observe both resonances for nanoparticle radii as small as 4 nm, where previously only the dipole resonance was assumed to play a role. Electron beams positioned outside of the particles mostly excite the dipole mode, but the higher-order resonance can even dominate the dipole peak when exciting at the particle surface, the usual choice for maximal EELS signal. This allows us to study the radius dependence of both resonances separately. For particles smaller than 4 nm, the higher-order SP mode disappears, in agreement with generalized nonlocal optical response (GNOR) theory, while the dipole resonance blueshift exceeds GNOR predictions. Unlike in optical spectra, multipole surface plasmons are important in EELS spectra even of ultra-small metallic nanoparticles. ; Comment: Supplementary Information is available on request