Metasurfaces with Dual-Band, Spatially Overlapped Resonances in the Visible and Near-Infrared

Metasurfaces are arrays of subwavelength resonators that demonstrate optical properties that are unobtainable naturally, such as near-perfect absorption of incident light on resonance. In the visible and near-infrared, near-perfect absorption has been previously demonstrated in a number of systems, including nanopatch antennas (NPAs), which are composed of colloidally-synthesized silver nanocubes separated from a metallic film by a polymer spacer layer. However, using colloidal nanocubes results in a random distribution of nanoparticles and does not allow for the creation of two absorption resonances that can be tuned independently. Highly-ordered samples with independently-tunable absorption resonances can be produced by instead using nanolithography techniques. In this work, patterned NPA arrays have been fabricated using electron beam lithography. Arrays of both nanocubes and nanodisks demonstrate strong, tailorable absorption. The resonance bandwidth decreases with increasing particle spacing, allowing for fabrication of absorbing metasurfaces with on-demand bandwidth. Furthermore, nanorectangles have shown double absorption resonances. Two spatially overlapped modes can be accessed via the incident polarization may find application in dual enhancement of optical processes.