Resonant Far- to Near-Field Channeling in Synergetic Multiscale Antennas

Abstract

Enhancing light-molecule interactions requires the efficient transfer of energy between the laboratory macroscale and the molecule nanoscale. Multiscale designs have been proposed as a means to efficiently connect these two worlds. Metallic sphere-segment void (SSV) cavities constitute plasmonic substrates in which light wavelength scale cavity-like modes and nanoscale roughness operate in conjunction as a multiscale antenna to provide larger surface-enhanced Raman scattering efficiency than the two mechanisms considered separately. We study the selective resonant coupling to cavity modes with different spatial distributions in SSV arrays with tailored nanoscale roughness. Cavity modes that are spatially more confined to the surface are demonstrated to lead to more efficient channeling of energy from the far to the near field, a synergy that scales with the degree of roughness. Finite-element modeling of the spatially varying local fields in rough SSV arrays allows for a microscopic description of the results, opening promising paths for the design of spatially and spectrally optimized multiscale antennas for efficient sensing with far- to near-field channeling of light.