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Author

Binay Jha

Document Type

Thesis - University Access Only

Award Date

2014

Degree Name

Master of Science (MS)

Department

Electrical Engineering

First Advisor

Mandi Farrokh Baroughi

Abstract

Spherical voids in gold lattices have the ability to concentrate light in subwavelength dimensions resulting in a significant increase in the intensity of the light (field enhancement) near the metal surface. Field enhancement properties of nanostructured metals can significantly enhance efficiency of an upconverter used in solar cells. The objective of this work was to develop an understanding why selfassembled porous and nanoporous spherical voids yield significantly higher field enhancement compared to planar gold and to explore the potential of self-assembled spherical and nanoporous spherical voids through a comprehensive full wave simulation study on geometry dependent field enhancement. Localized surface plasmons (LSPs) are the non-propagating modes excited by the polarization of sub-wavelength metallic structures whereas surface plasmon polaritons (SPPs) are propagating modes evanescently confined at the interface between a dielectric and metals. Three dimensional finite difference time domain method (3D FDTD) is a numerical method for solving Maxwell equations and determine accurate interaction of light. Self-assembled spherical voids in gold films were modeled to study the geometry dependence of reflectance. Their geometry was optimized for maximum intensity enhancement at 980 nm. Four out of five active plasmonic modes of spherical voids in gold films were found to be localized plasmons, less vulnerable to structural defects. Four diameters (between 800 nm and 1600 nm) provided the highest field enhancement at film thickness of 0.26 times their diameter. The underlying mechanisms for maximum field enhancement by spherical voids in gold films were found to be both plasmonic and off angle reflection. The plasmonic resonance of nanoporous voids in gold can be linearly tuned by varying the numbers of nanopores. Simulation reflection spectrum of spherical voids in gold films was in good agreement with experimental measurements. This is the first report of plasmonic properties of nanoporous spherical voids in gold films. Future research includes fabrication of spherical voids of diameter 1200 nm in gold films and thickness 312 nm as indicated by simulation.

Library of Congress Subject Headings

Gold films
Plasmons (Physics)
Photovoltaic cells

Description

Includes bibliographical references (pages 100-110)

Format

application/pdf

Number of Pages

123

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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