Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Bachelor of Science in Electrical Engineering

Degree Level

Undergraduate

Department

Electrical Engineering

Advisor

Magda O. El-Shenawee

Reader

Shui Qing (Fisher) Yu

Abstract

Nowadays, the manipulation of light by using metallic nanostructures has wide applications in photonics, optoelectronics and energy conversion. Along with other universities all over the world, the University of Arkansas is researching on nano-antennas’ design, fabrication and applications. Current research in Dr. El-Shenawee’s Terahertz Imaging and Spectroscopy Computational Electromagnetics Group, has computationally investigated the behaviors of plasmonic nanostructures by using the commercial finite element electromagnetic solver Ansys® HFSS. This work reproduced the previous work of spectral absorption enhancement of infinite and finite arrays of silver and gold nanotoroids with sizes of the inner radii: 13nm – 21nm, while outer radius of 42nm and more on an amorphous silicon absorbing layer. There are three significant factors in modeling this configuration such as surface resolution, optical properties of materials, and boundary conditions. A convergence study was performed on a gold sphere dimer with 40 nm radii and 1 nm gap between spheres. This illustrated that an at least surface resolution of 0.02 nm was needed to provide converging results in an acceptable computational time for conducted simulations. Furthermore, the Lorentz- Drude models for silver and gold were studied to obtain the optical properties. In addition, in order to reduce computation time and memory consumption by reduction of computational domain, the appropriate symmetry boundary conditions were applied. In this work, three samples of infinite arrays of gold nanotoroids with the sizes of inner radii: 50nm, 60nm and 100nm, respectively, while outer radius of 150nm were simulated as well. These gold nanotoroids were fabricated on glass substrate and then optically characterized by ellipsometry’s transmission measurement. The optical characterization was performed in Dr. Shui-Qing Yu’s Applied Nano and Bio Photonics Group. The observed differences between compute simulations and experimental results in shifting resonance frequencies were analyzed. This thesis is organized as: Part I is discussing about the finite element method, boundary conditions and Lorentz-Drude Model. Part II involves Lorentz-Drude model for gold and silver, convergence study using HFSS, simulations of infinite silver and gold nanotoroid arrays and ellipsometry transmission measurement on gold nanotoroid arrays. Part III is about conclusions and future research. The Appendix A is providing Matlab codes of Lorentz-Drude model for gold and silver.

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