How Dark Are Radial Breathing Modes in Plasmonic Nanodisks?

Schmidt, Franz; Losquin, Arthur; Hofer, Ferdinand; Hohenau, Andreas; Krenn, Joachim R.; Kociak, Mathieu

doi:10.1021/acsphotonics.7b01060

Cited by 29 publications

(41 citation statements)

References 32 publications

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“…Our experimental data show that dark plasmonic modes, namely RBMs, in Au NDs can not only be detected by EEL but also by CL spectroscopy, despite probing only the radiative part of the LDOS. In contrary to previously reported CL measurements of RBMs in silver NDs [10], this work reveals CL signal from RBMs in Au NDs with much smaller diameters down to 110 nm. This suggests that retardation effects, as proposed by Schmidt et al [10], cannot fully explain our results.…”

Section: Introductioncontrasting

confidence: 99%

“…RBMs do not posses a net dipole moment which is why they are optically inaccessible with light at normal incidence. However, they can be excited by an electron beam in a scanning transmission-electron microscope (STEM), taking advantage of the near-field excitation and detection using electron-energy loss (EEL) spectroscopy [5,10,11]. In conjunction with the electron-energy loss spectrum, this technique allows to probe the electromagnetic local density-of-states (LDOS) of plasmonic nanostructures projected to the swift electron's trajectory [12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

“…EEL spectroscopy is a very powerful tool to study plasmonic nanostructures with a subnanometer spatial and high spectral resolution [16,17], allowing to correlate structural with spectral features at the nanoscale regardless of their "brightness". However, it has recently been shown that dark modes in plasmonic NPs can also be made visible by taking advantage of retardation effects in sufficiently large nanostructures, using cathodoluminescence (CL) or optical spectroscopy at an oblique angle [10,11,18]. Another way to get more insight in dark plasmonic modes has been achieved by breaking the symmetry, either by asymmetrically arranging metallic nanostructures or breaking the symmetry of an individual NP [19,20].…”

Section: Introductionmentioning

confidence: 99%

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Importance of substrates for the visibility of "dark" plasmonic modes

Fiedler¹,

Raza²,

Ai³

et al. 2020

Opt. Express

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Dark plasmonic modes have interesting properties, such as a longer lifetime and a narrower linewidth than their radiative counterpart, as well as little to no radiative losses. However, they have not been extensively studied yet due to their optical inaccessibility. Using electron-energy loss (EEL) and cathodoluminescence (CL) spectroscopy, the dark radial breathing modes (RBMs) in thin, monochrystalline gold nanodisks are systematically investigated in this work. It is found that the RBMs can be detected in a CL set-up despite only collecting the far-field. Their visibility in CL is attributed to the breaking of the mirror symmetry by the high-index substrate, creating an effective dipole moment. The outcoupling into the far-field is demonstrated to be enhanced by a factor of 4 by increasing the thickness of the supporting SiN membrane from 5 nm to 50 nm due to the increased net electric dipole moment in the substrate. Furthermore, it is shown that the resonance energy of RBMs can be easily tuned by varying the diameter of the nanodisk, making them promising candidates for nanophotonic applications.

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Section: Introductioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Importance of substrates for the visibility of "dark" plasmonic modes

Fiedler¹,

Raza²,

Ai³

et al. 2020

Opt. Express

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“…Figure 2(d) illustrates the far field radiation pattern of the RBM. Owing to the charge symmetry, it shows a typical cone-like pattern with a nearly zero radiation at the vertical direction [36], which indicates that this mode cannot be excited by the normal incident plane wave and has an optically dark nature. We further obtain the scattering spectrum of a dual-hexamer with geometry parameters L 1 = 400 nm and L 2 = 620 nm (inter-hexamers gap size of 20 nm) as shown by the red dots in Fig.…”

Section: Resultsmentioning

confidence: 99%

Radial breathing modes coupling in plasmonic molecules

et al. 2019

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Metallic hexamer, very much the plasmonic analog of benzene molecule, provides an ideal platform to mimic modes coupling and hybridization in molecular systems. To demonstrate this, we present a detailed study on radial breathing mode (RBM) coupling in a plasmonic dual-hexamers. We excite RBMs of hexamers by symmetrically matching the polarization state of the illumination with the distribution of electric dipole moments of the dual-hexamer. It is found that the RBM coupling exhibits a nonexponential decay when the inter-hexamer separation is increased, owing to the dark mode nature of RBM. When the outer hexamer is subjected to the in-plane twisting, resonant wavelengths of two coupled RBMs as well as the coupling constant show cosine variations with the twist angle, indicating the symmetry of hexamer structure plays a critical role in the coupling of RBMs. Moreover, it is demonstrated that the coupling of RBMs is dominated by the in-plane interaction as the outer hexamer is under an out-of-plane tilting, causing convergence of resonant wavelengths of the two coupled RBMs with increasing tilt angle. Our results not only provide an insight into the plasmonic RBM coupling mechanism, but also pave the way to systematically control the spectral response of plasmonic molecules.

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“…27 In addition, retardation can also cause the dark mode to radiate, while increasing the effective size of sustained structures. 28 Therefore, the term dark mode cannot be quantitatively linked to nanoscale nonstatic charge configurations, as from the above-mentioned observations.…”

mentioning

confidence: 99%

Radiation of Dynamic Toroidal Moments

et al. 2019

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Dynamic toroidal dipoles, a distinguished class of fundamental electromagnetic sources, receive increasing interest and participate in fascinating electrodynamic phenomena and sensing applications. As described in the literature, the radiative nature of dynamic toroidal dipoles is sometimes confounded, intermixing with static toroidal dipoles and plasmonic dark modes. Here, we elucidate this issue and provide proof-of-principle experiments exclusively on the radiation behavior of dynamic toroidal moments. Optical toroidal modes in plasmonic heptamer nanocavities are analyzed by electron energy loss spectroscopy and energy-filtered transmission electron microscopy supported by finite-difference time-domain numerical calculations. Additionally, their corresponding radiation behaviors are experimentally investigated by means of cathodoluminescence. The observed contrasting behaviors of a single dynamic toroidal dipole mode and an antiparallel toroidal dipole pair mode are discussed and elucidated. Our findings further clarify the electromagnetic properties of dynamic toroidal dipoles and serve as important guidance for the use of toroidal dipole moments in future applications.

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How Dark Are Radial Breathing Modes in Plasmonic Nanodisks?

Cited by 29 publications

References 32 publications

Importance of substrates for the visibility of "dark" plasmonic modes

Importance of substrates for the visibility of "dark" plasmonic modes

Radial breathing modes coupling in plasmonic molecules

Radiation of Dynamic Toroidal Moments

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