Control of Radiative Processes Using Tunable Plasmonic Nanopatch Antennas

• Published in: Nano letters Vol. 14; no. 8; pp. 4797 - 4802
• Main Authors: Rose, Alec, Hoang, Thang B, McGuire, Felicia, Mock, Jack J, Ciracì, Cristian, Smith, David R, Mikkelsen, Maiken H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13-08-2014
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Fullerenes and related materials; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Surface and interface electron states; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Visible and ultraviolet spectra; Purcell factor; nanocube; nanoantennas; plasmon resonance; Plasmonics; fluorescence enhancement; metasurface; Digital simulation; Fluorescence; Nanostructures; Thin films; Finite element method; Nanoparticles; Nanometer scale; Spontaneous emission; Fluorophore; Local field; Detectors; Plasmons; Resonance; Absorption spectra; Nanostructured materials; Antennas
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl501976f

The radiative processes associated with fluorophores and other radiating systems can be profoundly modified by their interaction with nanoplasmonic structures. Extreme electromagnetic environments can be created in plasmonic nanostructures or nanocavities, such as within the nanoscale gap region between two plasmonic nanoparticles, where the illuminating optical fields and the density of radiating modes are dramatically enhanced relative to vacuum. Unraveling the various mechanisms present in such coupled systems, and their impact on spontaneous emission and other radiative phenomena, however, requires a suitably reliable and precise means of tuning the plasmon resonance of the nanostructure while simultaneously preserving the electromagnetic characteristics of the enhancement region. Here, we achieve this control using a plasmonic platform consisting of colloidally synthesized nanocubes electromagnetically coupled to a metallic film. Each nanocube resembles a nanoscale patch antenna (or nanopatch) whose plasmon resonance can be changed independent of its local field enhancement. By varying the size of the nanopatch, we tune the plasmonic resonance by ∼200 nm, encompassing the excitation, absorption, and emission spectra corresponding to Cy5 fluorophores embedded within the gap region between nanopatch and film. By sweeping the plasmon resonance but keeping the field enhancements roughly fixed, we demonstrate fluorescence enhancements exceeding a factor of 30 000 with detector-limited enhancements of the spontaneous emission rate by a factor of 74. The experiments are supported by finite-element simulations that reveal design rules for optimized fluorescence enhancement or large Purcell factors.