Probing Dynamically Tunable Localized Surface Plasmon Resonances of Film-Coupled Nanoparticles by Evanescent Wave Excitation

• Published in: Nano letters 2012-04, Vol.12 (4), p.1757-1764
• Main Authors: Mock, Jack J, Hill, Ryan T, Tsai, Yu-Ju, Chilkoti, Ashutosh, Smith, David R
• Format: Article
• Language: English
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electric fields; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Evanescent waves; Exact sciences and technology; Excitation; Gold; Gold - chemistry; Materials science; Membranes, Artificial; Metal Nanoparticles - chemistry; Molecular Dynamics Simulation; Nanocrystalline materials; Nanoparticles; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Particle Size; Physics; Plasmons; Spectra; Surface and interface electron states; Surface Plasmon Resonance; Surface Properties; Thin films
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl204596h

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.