Plasmon Coupling of Gold Nanorods at Short Distances and in Different Geometries

Funston, Alison M.; Novo, Carolina; Davis, Timothy J.; Mulvaney, Paul

doi:10.1021/nl900034v

Cited by 712 publications

(852 citation statements)

References 45 publications

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“…In contrast to previous work [20][21][22] we demonstrate full control over symmetric and anti-symmetric optical modes by means of white-light scattering experiments. We experimentally demonstrate the presence of atomic-scale light confinement in these structures by observing an extreme > 800 meV hybridization splitting of corresponding symmetric and antisymmetric dimer modes.…”

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confidence: 73%

Atomic-Scale Confinement of Resonant Optical Fields

Kern¹,

Großmann²,

Tarakina³

et al. 2012

Nano Lett.

139

157

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2The interaction of light and matter, i.e. absorption and emission of photons, can be considerably enhanced in the presence of strongly localized and therefore highly intense optical near fields 1 .Plasmonic antennas consisting of pairs of closely spaced metal nano particles have gained much attention in this context since they provide the possibility to strongly concentrate optical fields into the gap between the two metal particles [2][3][4] . Pairs of closely spaced metal nanoparticles supporting plasmonic gap resonances consequently find broad applications, e.g. in single-emitter surfaceenhanced spectroscopy 5,6 , quantum optics 7 , extreme nonlinear optics 8-10 , optical trapping 11 , metamaterials 12, 13 and molecular opto-electronics 14 .The success of metal-insulator-metal structures is based on two fundamental properties of their anti-symmetric electromagnetic gap modes. (i) As a direct consequence of the boundary conditions, the dominating field components normal to the metal-dielectric interfaces are sizable only inside the dielectric gap. This means that for anti-symmetric gap modes the achievable field confinement is not limited by the skin depth of the metal, but is solely determined by the actual size of the gap. (ii) Since the free electrons of the metal respond resonantly to an external optical frequency field, enormous surface charge accumulations, accompanied by ultra-intense optical near fields, will occur. In addition, with decreasing gap width, stronger attractive coulomb forces 4 across the gap lead to further surface-charge accumulation and a concomitantly increased near-field intensity enhancement. We therefore conclude that an experimental realization of atomic-scale concentration of electromagnetic fields at visible frequencies is possible but it requires atomic-scale shape control of the field-confining structure, i.e. the gap, as well as a careful assignment and selection of suitable optical modes.Here we achieve atomic-scale confinement of electromagnetic fields at visible frequencies by combining for the first time both atomic-scale shape control of the field confining structure 15 as well as a careful selection and assignment of suitable optical modes [16][17][18] . We study single-crystalline nanorods which self-assemble into side-by-side aligned dimers with gap widths below 0.5 nm. Sideby-side aligned nanorod dimers possess various distinguishable symmetric and anti-symmetric 3 modes in the visible range 19 . In contrast to previous work 20-22 we demonstrate full control over symmetric and anti-symmetric optical modes by means of white-light scattering experiments. We experimentally demonstrate the presence of atomic-scale light confinement in these structures by observing an extreme > 800 meV hybridization splitting of corresponding symmetric and antisymmetric dimer modes. Our results open new perspectives for atomically-resolved spectroscopic imaging, deeply nonlinear optics and attosecond physics, cavity optomechanics and ultra-sensing as well as quantum optics.To obtain nano...

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contrasting

confidence: 73%

Atomic-Scale Confinement of Resonant Optical Fields

Kern¹,

Großmann²,

Tarakina³

et al. 2012

Nano Lett.

139

157

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“…35 Aggregates of nanorods usually produce broad non-Lorentzian spectra, often with more than one longitudinal peak or with a plasmon resonance well shifted from the expected resonance position of a single nanorod. 36,37 Figure 3d shows a fluorescence time trace recorded on the single gold nanorod highlighted in Figure 3c excited with a circularly polarized 633 nm laser. The fluorescence time trace shows bursts that are due to the enhanced fluorescence from the CV molecules passing close to the tips, through the near-field volume of the nanorod.…”

Section: Articlementioning

confidence: 99%

Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods

et al. 2014

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Enhancing the fluorescence of a weak emitter is important to further extend the reach of single-molecule fluorescence imaging to many unexplored systems. Here we study fluorescence enhancement by isolated gold nanorods and explore the role of the surface plasmon resonance (SPR) on the observed enhancements. Gold nanorods can be cheaply synthesized in large volumes, yet we find similar fluorescence enhancements as literature reports on lithographically fabricated nanoparticle assemblies. The fluorescence of a weak emitter, crystal violet, can be enhanced more than 1000-fold by a single nanorod with its SPR at 629 nm excited at 633 nm. This strong enhancement results from both an excitation rate enhancement of ∼130 and an effective emission enhancement of ∼9. The fluorescence enhancement, however, decreases sharply when the SPR wavelength moves away from the excitation laser wavelength or when the SPR has only a partial overlap with the emission spectrum of the fluorophore. The reported measurements of fluorescence enhancement by 11 nanorods with varying SPR wavelengths are consistent with numerical simulations.

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“…As sketched in Fig. 1, the energy splitting of the modes in a linear dipole antenna increases with reduced feedgap size, revealing the distance dependent interparticle coupling [8,[28][29][30][31][32].Even in presence of strong coupling, anti-bonding antenna modes are not always observed in whitelight scattering experiments since their excitation is symmetry-forbidden for normally-incident plane wave sources [33]. The antibonding antenna mode can, however, be excited if the symmetry of the system is broken either by the shape of the structure [34,35] or by the excitation geometry [6,27,36,37].…”

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confidence: 99%

Mode Imaging and Selection in Strongly Coupled Nanoantennas

et al. 2010

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The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the "bonding" and "antibonding" plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-qualityfactor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad "bonding" resonance, in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the "bonding" mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices. IntroductionPlasmonic nanostructures consisting of particular arrangements of closely spaced resonant particles are of great interest since they offer a variety of eigenmodes that evolve due to mode hybridization [1]. Characterization and well-defined excitation of such eigenmodes is important in order to achieve welldefined functionality in devices [2,3] and to successfully apply techniques of coherent control [4][5][6][7]. Nanoantennas consisting of two strongly coupled particles can serve as a model system to study the impact of mode selectivity [6,8,9]. Upon illumination nanoantennas confine and enhance optical fields [10,11] and can therefore be used to tailor the interaction of light with nanomatter [12]. Various applications of nanoantennas have been proposed and experimentally demonstrated, including enhanced single-emitter fluorescence [13][14][15], enhanced Raman scattering [16,17], near-field polarization engineering [18][19][20], high-harmonic generation [21,22], as well as applications in integrated optical nanocircuitry [23,24]. The longitudinal resonances of a symmetric dipole antenna can be understood in terms of hybridization of the longitudinal resonances of individual antenna arms, caused by the coupling over the narrow feedgap [25,26]. Such coupling causes a mode splitting into a lower-energy "bonding" mode and a higher-energy "antibonding" mode, respectively (Fig. 1). Limited by the uncertainty of conventional nanofabrication, it is often difficult to fabricate antenna arrays with a reproducible gap size below 20 nm, which is necessary to achieve significant energy splitting between the bonding and the antibonding mode. As a result, the existence of the antibonding antenna resonance has hardly been considered, although it may offer interesting opportunities, such as impedance tunability, a high quality factor due to its weakly radiative nature, the launching of propagating plasmon modes with increased propagation lengths [27] and spatial select...

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Plasmon Coupling of Gold Nanorods at Short Distances and in Different Geometries

Cited by 712 publications

References 45 publications

Atomic-Scale Confinement of Resonant Optical Fields

Atomic-Scale Confinement of Resonant Optical Fields

Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods

Mode Imaging and Selection in Strongly Coupled Nanoantennas

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