Lattice resonances of lossy transition metal and metalloid antennas

Localized plasmonic resonances in isolated (single) nanoparticles of lossy materials are weak and do not result in resonances or significant field enhancement. In turn, if nanoparticles are arranged in a periodic lattice, collective resonances emerge from the coupling of the localized resonances of each individual nanoparticle. This coupling results in strong lattice resonances even when the nanoparticles are made of material with high optical losses. Here, we study lattice resonances in the arrays of nanoantennas made of lossy materials, such as transition metals, titanium Ti and tungsten W, and metalloid in the carbon group, germanium Ge. We perform both full-wave electromagnetic simulations and proof-of-concept experimental characterization in the near-infrared range, and we study the lattice resonances in lossy nanoantenna arrays and consider various practical scenarios that commonly arise in laboratory measurements and nanofabrication processes. We excite lattice resonance at different wavelengths by changing the refractive index of substrate and superstrate materials. We show lattice resonances in proximity to Rayleigh anomaly wavelength for homogeneous (substrate and superstrate are the same) and inhomogeneous (substrate and superstrate are different) surrounding environments for disk-shaped titanium nanoantennas on top of a substrate. We analyze the case of oblique light incidence with small angles as it often happens in laboratory measurements with a focused light spot. In this work, we observe lattice resonance in different practical conditions, and we show lattice resonances can be tuned for various applications, including sensing, depending on those conditions.