Arrays of nanotubes/rods made of appropriate materials can yield unique radiative properties, such as large absorption and optical anisotropy, with broad applications from high-efficiency emitters and absorbers for energy conversion to the polarization conversion via anisotropic responses. The objective of this dissertation is to investigate the radiative properties (including reflection, absorption, and scattering) of arrays formed by aligned carbon nanotubes (CNTs) and silver nanorods (AgNRs).

The CNT arrays used in the present study consist of multi-walled CNTs synthesized vertically on silicon substrates using thermal chemical vapor deposition. Their close-to-unity absorptance is demonstrated by measuring the directional-hemispherical reflectance (DHR) within the visible and near-infrared spectral ranges using an integrating sphere (IS). The bidirectional reflectance distribution function (BRDF) and angle-resolved reflectance were measured with a three-axis automated scatterometer (TAAS) at the 635-nm wavelength. The results demonstrate that high-absorptance CNT arrays may be diffusely or specularly reflecting and have important applications in radiometry. Compared with the commercially available specular blacks, the specular CNT sample investigated in this dissertation has an even higher absorptance while maintaining similar specularity. By treating the vertically aligned CNT array as an effective homogenous and uniaxial medium, the effective medium theory (EMT) is used to elucidate the mechanism of the high absorption for this high-aspect-ratio configuration. The anisotropic reflectance and transmittance coefficients are developed from the basic Maxwell equation to explain the high absorption and polarization dependence. The effective ordinary and extraordinary optical constants of the specular CNT sample are determined by fitting the angle-resolved reflectance from theoretical prediction with those obtained from measurements.

The AgNR array used in the present study was fabricated using oblique angle deposition, which results in inclined Ag nanorods that can be modeled as an effective homogenous and optically anisotropic thin film. This AgNR thin layer has either a dielectric or metallic response for a given polarization. The spectral and directional radiative properties of AgNRs grown on different substrates, including a glass slide with a silver film and compact disc gratings, were characterized with the IS and TAAS at the 635-nm and 977-nm wavelengths for different polarizations. The results are analyzed with theoretical modeling based on the EMT, rigorous coupled-wave analysis, and anisotropic thin-film optics. The theoretical investigation not only provides a better understanding of the optically anisotropic responses of nanostructures but also allows their effective properties to be quantitatively determined, which in turn can be used to optimize the parameters of material fabrication. The results of this dissertation help gain a better understanding of the radiative properties of anisotropic nanostructures for potential applications in high-efficiency energy conversion, radiometric devices, and optical system.