Coupling of epsilon-near-zero and plasmonic modes in ALD-AZO coated nanoantenna array*

Recently, there has been a revival of the interests in the optical properties of materials near their Epsilon-near-zero (ENZ) (real part of material permittivity crosses zero) regions. By integrating ENZ thin films into plasmonic nanoantenna arrays, hybrid ENZ-plasmonic systems can be formed. Most of the hybrid systems reported so far include ENZ thin film layers as substrates, which restrict the control of the coupling strength. Here, we study the optical response of gold nanoantenna arrays conformally coated with ENZ Al-doped zinc oxide (AZO) thin films. We grow the AZO nano-layers on top of gold nanoantennae by using the atomic layer deposition (ALD) technique. Both the simulated (finite-difference-time-domain) and the measured transmission spectra show resonance splitting due to the coupling between the localized surface plasmon and the Ferrell-Berreman modes. These plasmonic antenna arrays with ENZ AZO conformal coatings can support novel hybrid plasmonic-ENZ modes and may pave a way towards a completely new type of plasmonic devices.