Date of Award

3-26-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Tansel Karabacak

Abstract

Metallic nanostructures can exhibit different optical properties compared to bulk materials mainly depending on their shape, size, and separation. Vertically aligned arrays of aluminum (Al) nanorods of different lengths and morphologies were fabricated by DC sputtering using the glancing angle deposition (GLAD) method. Detailed structural and optical properties of GLAD Al nanorod were investigated and compared to those of conventional flat Al thin film coatings. Optical characterization results show that total reflectance is inversely proportional to nanorod length in the wavelength range 200-1800 nm, due to the enhanced surface plasmon resonance and light trapping among the nanorods. In addition, we present the results from an optical modeling study on ordered arrays of Al nanorods with a hexagonal periodic geometry. We used a finite-difference time-domain (FDTD) method to solve the Maxwell's equations and predict the reflectance of the nanorod arrays. In FDTD simulations, height and nanorod center-to-center periodicity were varied and reflectance profiles were calculated in the wavelength range 200-1800 nm. In addition, we calculated spatial electric field intensity distributions around the nanorods for some wavelengths. Our results show that average reflectance of Al nanorods can drop down to as low as ~50%, which is significantly lower than the ~90% reflectance of conventional flat Al film at similar wavelengths. In addition to the overall decrease in reflectance, Al nanorod arrays manifest multiple resonant modes (higher-order modes) indicated by several dips in their reflectance spectrums (i.e. multiple attenuation peaks in their absorption profiles). Positions of these dips in the reflectance spectrum and spatial EM field distribution vary with nanorod height and diameter. Multiple reflectance peaks are explained by cavity resonator effects. Spatial EM field distribution profiles indicate enhanced light trapping among the nanorods, which can be useful especially in optoelectronic and solar cell applications. Preliminarily results from organic solar cells that utilize GLAD Al nanorods are presented in this study.

Download

Share

COinS