  Applying direct growth and deposition of optical surfaces holds great promise
for the advancement of future nanophotonic technologies. Here, we report on a
chemical vapor deposition (CVD) technique for depositing amorphous selenium
(a-Se) spheres by desorption of selenium from Bi2Se3 and re-adsorption on the
substrate. We utilize this process to grow scalable, large area Se spheres on
several substrates and characterize their Mie-resonant response in the
mid-infrared (MIR) spectral range. We demonstrate size-tunable Mie resonances
spanning the 2-16 um spectral range, for single isolated resonators and large
area ensembles, respectively. We further demonstrate strong absorption dips of
up to 90% in ensembles of particles in a broad MIR range. Finally, we show that
ultra-high-Q resonances arise in the case where Se Mie-resonators are coupled
to low-loss epsilon-near-zero (ENZ) substrates. These findings demonstrate the
enabling potential of amorphous Selenium as a versatile and tunable
nanophotonic material that may open up avenues for on-chip MIR spectroscopy,
chemical sensing, spectral imaging and large area metasurface fabrication.
