Universal structural dependence of optical properties in 3D nanocolumnar metamaterial platforms*

Due to the complexity of optical anisotropy possessed by highly porous nanostructure systems, performing the growth-time dependent critical dimension analysis and unraveling the correlation between the optical and structural parameters remain challenging.  With this study, we presented and discussed a route to extract a set of optical parameters, depolarization factors, that are extremely sensitive to the changes in critical dimensions of the nanostructure platforms. We pursue a comprehensive methodical series of studies to investigate the effect of column-aspect-ratio on the evolution of anisotropic homogenization parameters of slanted columnar thin films (SCTFs) from wide range of material choices. Hence, we fabricated sets of highly porous, spatially coherent SCTFs from zirconia (ultra-wide band gap), silicon (semiconductor), titanium (zero-band gap), and permalloy (metal alloy) on silicon substrates by using custom-built, ultra-high vacuum glancing-angle deposition technique. Subsequently, we used the anisotropic Bruggeman effective medium approximation to analyze spectroscopic ellipsometry data. We have successfully extracted the anisotropic optical characteristics, including the complex dielectric function, birefringence, and dichroism, for each metamaterial platform.