CONTROLLING THE THERMAL TRANSMITTANCE OF GLASS BY COATING WITH A BROAD-BAND HYPERBOLIC MATERIAL

Abstract

Hyperbolic metamaterials are nano-engineered materials with dielectric function components of opposite signs, allowing them to function as metals in some directions and as dielectrics or insulators in others. They are expected to play an important role in future optical, electrical, and thermal applications. Some natural anisotropic materials or combinations of natural materials, such as transparent conducting oxides or nitrides, function as potential hyperbolic metamaterials over a narrow infrared spectral range. Due to the fact that the structure of ZnO thin films obtained by pulsed laser deposition is columnar and often contains a high density of free electrons, these films can exhibit strong anisotropy and hyperbolic behavior in a wide spectral range. This process can be of utmost importance to control solar infrared radiation and prevent heating of the vehicle interior. The main objective of this thesis is to study the planar and transverse dielectric constants of ZnO thin films grown on glass over a wide infrared spectral range and to investigate the potential application of coating glass with ZnO films to reduce the transfer of solar radiation to absorbing materials in the vehicle. Using the pulsed laser deposition methods, thin ZnO thin films of different thicknesses were deposited on glass substrates of different thicknesses. The obtained samples were analyzed using XRD, UV-VIS spectroscopy, SEM, and FTIR spectroscopy. XRD and SEM measurements indicated that the produced films are granular, but well oriented along the c-axis. Spectroscopic measurements in the UV-VIS-NIR range showed that the samples ellaborated transparent in the visible spectrum, which is crucial to maintain the vehicle glasses transparent. The in-plane and cross-plane complex infrared dielectric functions of the samples ellaborated were investigated using accurate analysis of the infrared reflectivity spectrum. It was demonstrated that thin ZnO films deposited on glass exhibit hyperbolic behavior over a wide infrared spectral range and the ratio of the cross-plane to the in-plane dielectric constant can be tuned through the film thickness. The results of this thesis would allow controlling the direction of the solar radiation incident on the vehicle glass when it is coated by a ZnO film of a specific thickness