High aspect ratio double insulator plasmonic nanostructures towards gas-sensing applications

In this work, we designed and fabricated high aspect ratio vertical plasmonic nanostructures geared towards gas sensing using infrared absorption. The structures have inner and out Au walls with an aspect ratio of 18.3 and 16.7, respectively. The gap between the walls is partially filled with SiO2. From finite-difference time-domain simulations, we found that the initial resonance frequency of the entire structure is dictated by the overall height of the inner Au walls, while the SiO2/air ratio at the gap can further tune the resonance frequency. This is experimentally demonstrated through the observed Fourier transform infrared measurements.