THEORY, CHARACTERIZATION AND APPLICATIONS OF INFRARED HYPERBOLIC METAMATERIALS
Analytics
89 views ◎65 downloads ⇓
Abstract
ABSTRACTDANIEL B. FULLAGER. Theory, characterization and applications of infraredhyperbolic metamaterials. (Under the direction of DR. MICHAEL A. FIDDY)Hyperbolic Metamaterials (HMMs) are engineered structures capable of supporting lightmatterinteractions that are not normally observed in naturally occuring material systems.These unusual responses are enabled by an enhancement of the photonic density of states(PDOS) in the material. The PDOS enhancement is a result of deliberately introducedanisotropy via a permittivity sign-change in HMM structures which increases the numberand frequency spread of possible wave vectors that propagate in the material. Subwavelengthstructural features allow effective medium theories to be invoked to constructthe k-space isofrequency quadratic curves that, for HMMs, result in the k-space isofrequencycontour transitioning from being a bounded surface to an unbounded one. Sincethe PDOS is the integral of the differential volume between k-space contours, unboundedmanifolds lead to the implication of an infinite or otherwise drastically enhanced PDOS.Since stored heat can be thought of as a set of non-radiative electromagnetic modes, in thisdissertation we demonstrate that HMMs provide an ideal platform to attempt to modifythe thermal/IR emissivity of a material. We also show that HMMs provide a platform forbroadband plasmonic sensing. The advent of commercial two photon polymerization toolshas enabled the rapid production of nano- and microstructures which can be used as scaffoldsfor directive infrared scatterers. We describe how such directive components can beused to address thermal management needs in vacuum environments in order to maximizeradiative thermal transfer. In this context, the fundamental limitations of enhanced spon-taneous emission due to conjugate impedance matched scatterers are also explored. TheHMM/conjugate scatterer system’s performance is strongly correlated with the dielectricfunction of the negative permittivity component of the HMM. In order to fully understandthe significance of these engineered materials, we examine in detail the electromagneticresponse of one ternary material system, aluminium-doped zinc oxide (AZO), whose tuneableplasma frequency makes it ideal for HMM and thermal transfer applications. Thisstudy draws upon first principle calculations from the open literature utilizing a Hubbard-Ucorrected model for the non-local interaction of charge carriers in AZO crystalline systems.We present the first complete dielectric function of industrially produced AZO samplesfrom DC to 30,000 cm1 and conclude with an assessment of this material’s suitability forthe applications described.