Spectral tuning of double resonant nanolaminate plasmonic nanoantennas with a fixed size

Abstract

Multiresonant plasmonic nanoantennas can enhance nanolocalized multiphoton processes or enable wavelength-multiplexed nano-optic operations by supporting multiple spatially overlapped plasmonic modes. Nevertheless, current multiresonant plasmonic nanoantenna designs do not consider engineering multiresonant spectral responses with strict size and footprint constraints. Developing a strategy to engineer fixed-size nanoantennas with tunable multiresonant responses is highly desirable for maintaining controlled cellular responses at the nano-bio interface and achieving seamless integration with other nanodevices with predefined footprints. Here, we report that fixed-size tapered nanolaminate nanoantennas (TNLNAs) can achieve a wide double-resonance spectral tunability by only changing the metal-to-insulator thickness ratio (t/h). Three separate TNLNAs' samples (8/38 , 20/20, and 28/8 nm) with a nominal total height of ∼100 nm are created from a high-throughput nanofabrication technique. Specifically, we fabricated TNLNAs' samples by exploiting a nanohole array membrane from soft interference lithography as a deposition mask for electron-beam evaporation of alternating Au and SiO2 layers. Transmission and dark field scattering measurements show that TNLNAs support two distinct resonant features with t/h-dependent tunable resonant wavelengths in the range of 730–850 and 840–1050 nm, respectively. Numerical simulations reveal that (i) a bianisotropy-induced magnetoelectric response in top and bottom nanogaps due to the asymmetric tapered shape can enhance light trapping and achieve optical near-field intensity enhancements up to 1000-fold and (ii) while TNLNAs consisting of thin Au nanodisks at low t/h primarily support spatial overlap between modes with enhanced electric polarizability, TNLNAs consisting of thick Au nanodisks at high t/h support spatial overlap between modes with enhanced magnetic polarizability, evoking higher-order multipolar behaviors.