The majority of plasmonic and metamaterials research utilizes noble metals such as gold and silver which commonly operate in the visible region. However, these materials are not well suited for many applications due to their low melting temperature and polarization response at longer wavelengths. A viable alternative is aluminum doped zinc oxide (AZO); a high melting point, low loss, visibly transparent conducting oxide which can be tuned to show strong plasmonic behavior in the near-infrared region. Due to it’s ultrahigh conformality, atomic layer deposition (ALD) is a powerful tool for the fabrication of the nanoscale features necessary for many nanoplasmonic and optical metamaterials. Despite many attempts, high quality, low loss AZO has not been achieved with carrier concentrations high enough to support plasmonic behavior at the important telecommunication wavelengths (ca. 1550 nm) by ALD. Here, we present a simple process for synthesizing high carrier concentration, thin film AZO with low losses via ALD that match the highest quality films created by all other methods. We show that this material is tunable by thermal treatment conditions, altering aluminum concentration, and changing buffer layer thickness. The use of this process is demonstrated by creating hyperbolic metamaterials with both a multilayer and embedded nanowire geometry. Hyperbolic dispersion is proven by negative refraction and numerical calculations in agreement with the effective medium approximation. This paves the way for fabricating high quality hyperbolic metamaterial coatings on high aspect ratio nanostructures that cannot be created by any other method.
Conor T. Riley, Joseph S. T. Smalley, Yeshaiahu Fainman, Donald J. Sirbuly, and Zhaowei Liu, "Conformal plasmonic and hyperbolic metamaterials
(Conference Presentation)," Proc. SPIE 9919, Nanophotonic Materials XIII, 991905 (Presented at SPIE Nanoscience + Engineering: August 30, 2016; Published: 7 November 2016); https://doi.org/10.1117/12.2237347.5159519601001.
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