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Probing dynamically tunable localized surface plasmon resonances of film-coupled nanoparticles by evanescent wave excitation.

ABSTRACT: The localized surface plasmon resonance (LSPR) spectrum associated with a gold nanoparticle (NP) coupled to a gold film exhibits extreme sensitivity to the nanogap region where the fields are tightly localized. The LSPR of an ensemble of film-coupled NPs can be observed using an illumination scheme similar to that used to excite the surface plasmon resonance (SPR) of a thin metallic film; however, in the present system, the light is used to probe the highly sensitive distance-dependent LSPR of the gaps between NPs and film rather than the delocalized SPR of the film. We show that the SPR and LSPR spectral contributions can be readily distinguished, and we compare the sensitivities of both modes to displacements in the average gap between a collection of NPs and the gold film. The distance by which the NPs are suspended in solution above the gold film is fixed via a thin molecular spacer layer and can be further modulated by subjecting the NPs to a quasistatic electric field. The observed LSPR spectral shifts triggered by the applied voltage can be correlated with angstrom scale displacements of the NPs, suggesting the potential for chip-scale or flow-cell plasmonic nanoruler devices with extreme sensitivity.

SUBMITTER: Mock JJ

PROVIDER: S-EPMC3324644 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Probing dynamically tunable localized surface plasmon resonances of film-coupled nanoparticles by evanescent wave excitation.

Mock Jack J JJ Hill Ryan T RT Tsai Yu-Ju YJ Chilkoti Ashutosh A Smith David R DR

Nano letters 20120323 4

The localized surface plasmon resonance (LSPR) spectrum associated with a gold nanoparticle (NP) coupled to a gold film exhibits extreme sensitivity to the nanogap region where the fields are tightly localized. The LSPR of an ensemble of film-coupled NPs can be observed using an illumination scheme similar to that used to excite the surface plasmon resonance (SPR) of a thin metallic film; however, in the present system, the light is used to probe the highly sensitive distance-dependent LSPR of t ...[more]

PMID: 22429053

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Project description:While the role and manifestations of the localized surface plasmon resonances (LSPRs) in anomalous scattering, like superscattering and invisibility, are quite well explored, the existence, appearance, and possible contribution of localized epsilon-near-zero (ENZ) resonances still invoke careful exploration. In this paper, that is done along with a comparison of the resonances of two types in the case of thin-wall cylinders made of lossy and loss-compensated dispersive materials. It is shown that the localized ENZ resonances exist and appear very close to the zero-permittivity regime, i.e., at near-zero but yet negative permittivity that is similar to the ENZ modes in thin planar films. Near- and far-field characteristics of the superscattering modes are investigated. The results indicate that the scattering regimes arising due to LSPRs and localized ENZ resonances are distinguishable in terms of the basic field features inside and around the scatterer and differ in their contribution to the resulting scattering mechanism, e.g., in terms of the occupied frequency and permittivity ranges as well as the sensitivity to the wall thickness variations. When the losses are either weak or tend to zero due to the doping with gain enabling impurities, the sharp peaks of the scattering cross-section that are yielded by the resonances can be said to be embedded into the otherwise wide invisibility range. In the case of lossy material, a wide and continuous invisibility range is shown to appear not only due to a small total volume of the scatterer in the nonresonant regime, but also because high-Q superscattering modes are suppressed by the losses. For numerical demonstration, indium antimonide, a natural lossy material, and a hypothetical, properly doped material with the same real part of the permittivity but lower or zero losses are considered. In the latter case, variations of permittivity with a control parameter can be adjusted in such a way that transitions from one superscattering mode to another can be achieved. In turn, transition from the strong-scattering to the invisibility regime is possible even for the original lossy material. The basic properties of the studied superscattering modes may be replicable in artificial structures comprising natural low-loss materials.

Dataset Information

Probing dynamically tunable localized surface plasmon resonances of film-coupled nanoparticles by evanescent wave excitation.

Publications

Probing dynamically tunable localized surface plasmon resonances of film-coupled nanoparticles by evanescent wave excitation.

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