Abstract
Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties.
Highlights
Hyperbolic metamaterials possess unique properties due to extreme anisotropy in the uniaxial permittivity tensor
We have presented a critical comparison of permittivity extraction for multilayered nanolaminated hyperbolic metamaterials utilizing two measurement techniques: polarized reflectometry and spectroscopic ellipsometry
We examined the effect of varying the outer layer (Ag vs. MgF2) on the optical properties of the nanolaminates
Summary
Hyperbolic metamaterials possess unique properties due to extreme anisotropy in the uniaxial permittivity tensor. The hyperbolicity occurs when one of the diagonal tensor components is opposite in sign from the other two components. This unique material dispersion leads to novel optical properties, such as negative refractive index in a waveguiding geometry, nominally unbounded density of photonic states, and the existence of an ENZ (epsilon-near-zero) wavelength range for one of the permittivity components.. There have been recent demonstrations of large-area fabrication of two types of hyperbolic metamaterials: anodized alumina membranes, filled with metal nanocolumns and metallo-dielectric laminates.. The laminated metal/dielectric hyperbolic metamaterials are attractive because their fabrication can be performed in a simple thermal evaporator over large sample areas
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