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 nano-gap 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.

Broad electrical tuning of plasmonic nanoantennas at visible frequencies

“…In turn, these modifications to the thickness and dielectric constant of the material in the gap between the metal film and the silver nanocubes lead to a modified plasmon resonance of the sample structure. 21,40 As seen from Fig. 3, a negative bias voltage is observed to induce a much larger shift in the plasmon resonance than a positive bias.…”

“…19 However, for on-chip integration and future practical applications, electrical tunability is highly desirable. While there have been several recent demonstrations of electrical tuning of plasmonic structures, [20][21][22][23][24][25][26][27] they either show a very limited tuning range around 10 nm, 21,22,25 are restricted to the infrared spectral region, 20,23,24,27 or require the application of a large voltage $100 V. 26 In this paper, we experimentally demonstrate electrical tuning of the plasmon resonance of an ensemble of nanopatch antennas from 613 nm to 713 nm by the application of a small external bias voltage of less than 3 V. The nanopatch antennas consist of colloidally synthesized silver nanocubes with a side length of $75 nm placed over a gold film with an 8 nm dielectric polymer spacer layer sandwiched in between. This structure supports a transmission line mode and highly enhanced electric fields in the gap region up to a 100-fold for the fundamental mode centered at 646 nm.…”

Gold Nanoparticle Arrays Spectroscopy: Observation of Electrostatic and Radiative Dipole Interactions

“…29 Mock et al measured the LSPR of gold nanoparticles arrays,¯nding a red shift of the spectral position as the interparticle spacing reduces. 30,31 Haynes et al showed the importance of radiative dipole coupling in 2D nanoparticles arrays of different size, shape, arrangement and material. 19 The present paper studies the e®ect of electromagnetic coupling on LSPR of 2D arrays of cylindrical gold nanoparticle fabricated by electron beam lithography (EBL).…”

Compound resonance-induced coupling effects in composite plasmonic metamaterials

“…In the last few years, great attention has been devoted to studying systems composed of not only localized metallic nanostructures or a conductive film, but rather composed of both [17]. The interaction and hybridization of localized surface plasmon resonances (LSPRs) and propagating surface plasmon resonances (SPPs) in such systems results in a variety of rich and interesting optical phenomena [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33].…”