Optical Characterisation of Plasmonic Indium Lattices Fabricated Via Electrochemical Deposition

Indium is an emerging plasmonic material that offers to extend the plasmonic applications given by gold and silver from the visible to the ultraviolet spectral range, with applications in imaging, sensing, and lasing. However, due to the high-vapor pressure/low melting temperature of indium, nanofabrication of pre-defined metallic indium nanostructures is non-trivial. In this work, we show the potential of selective area electrochemical deposition for the manufacturing of large-area arrays of indium pillars, which can be used for plasmonic applications. We combine electrochemical deposition with substrate-conformal imprint lithography to realize these large-scale indium nanoparticle arrays, having well-defined dimensions. This template growth results into well-defined hexagonal array of pillars with a mean height of 235 nm having a standard deviation of 60 nm. To highlight the potential of this electrochemical-based technique for plasmonic applications, we have performed angle-dependent extinction measurements using s-polarized light and using a RI matching oil. We found that these indium nanopillar arrays exhibit a strong plasmonic response due to the coupling to the plasmonic surface lattice resonances (SLRs). Furthermore, we have simulated the optical response of this indium nanopillar array using finite difference time domain (FDTD) simulations. In these simulations, we included the morphology obtained from SEM and the electrical permittivity of elemental indium. We found that the simulated extinction spectra agree well with the experimentally obtained spectra at 0˚ and 8˚ incidence, despite the polydispersity of the indium pillar height and defects in the hexagonal array. Our results therefore demonstrate the possibility of realizing large-area fabrication of indium plasmonic nanoparticles, which can be used for plasmonic applications. Given the low-cost and scalable nature of this technique, this work opens new possibilities in the design and fabrication of large-area plasmonic metasurfaces that operate in the UV spectral range. Future extensions of this work may leverage the indium mask-constrained growth to tailor even further the shape of the nanoparticle and hence give a powerful tuning knob to tailor plasmonic resonances.