Engineering the broadband spectrum of close-packed plasmonic honeycomb array surfaces

Abstract

Plasmonic nanostructures operating over a wide spectrum are promising candidates for broadband spectroscopic applications. While promising, spectral engineering of close-packed plasmonic honeycomb nanoantenna arrays is challenging due to the strong correlation between the particle geometry and hexagonal grid, particle coupling within unit cells, and interaction between neighboring unit cells. In this study, we demonstrate that the spectral distribution of large scale surfaces can be effectively tailored over a wideband spectral range using close-packed plasmonic honeycomb array surfaces. We discuss coupling-mechanisms responsible for the spectral response of honeycomb arrays and discuss the geometrical restrictions limiting the bandwidth of the spectral response. These limitations can be overcome with a more general honeycomb structure by introducing additional morphological parameters within the Wigner–Seitz unit cell. The proposed morphological parameters provide additional flexibility for manipulating the spectrum by relaxing geometrical restrictions due to a strong correlation between the unit-cell and nanoparticle morphology. Furthermore, we achieve spectral broadening by breaking the symmetry within a Wigner–Seitz unit cell on a hexagonal grid, rather than breaking the symmetry of the hexagonal grid itself via generalized honeycomb arrays. Additionally, we demonstrate the advantages of close-packed arrays in terms of spectral response and electric field enhancement over large surfaces. Finally, radiative far-field properties, absorptance, transmittance, and reflectance of honeycomb structures are investigated.