Effective Nonlinear Susceptibilities of Metal-Insulator and Metal-Insulator-Metal Nanolayered Structures

Date of Award

2020

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics

Advisor/Chair

Advisor: Imad Agha

Abstract

Nonlinear electromagnetic radiation (second and third harmonic) from the metal-insulator and metal-insulator-metal structures were measured and compared against predictions from the hydrodynamic models of plasmonics. This model incorporated higher-order terms stemming from electron tunneling and nonlocality. This study shows that, besides the linear optical parameter like permittivity, conductivity etc, changes in the nonlinear optical parameters, namely, second and third order susceptibilities (?(2) and ?(3), respectively) can also be used to probe and compare the higher-order terms of the hydrodynamic model of plasmonics. Two insulator materials (ZnO and Al2O3) were used in two separate sets of experiments, and atomic layer deposition was used to cover the gold substrate with variable thicknesses of these insulator films (nanometer to sub-nanometer range). Large reduction in second and third harmonic signals was measured after the insulator film was deposited over the gold substrate revealing the spilled-out electronic states in the insulator region at the vicinity of the metal-insulator interface, which are dubbed metal insulator gap states. Then, the metal-insulator samples were spin-coated with Au-nanoparticle solution to prepare a metal-insulator-metal structures. For these structures, saturation and quenching of the third harmonic efficiencies were observed which were indicative of the capping of E-field enhancement due to the existence of higher order terms in the hydrodynamic model that accounts for nonlocality and quantum tunneling of electrons. A generalized 4 ╫ 4 matrix method was utilized to calculate the effective ?(2) and ?(3) parameters that confirm the changes of effective material properties for ultra-thin films. These nonlinear coefficients, besides the linear permittivity ? and conductivity ?, can be a useful material parameter to study the effects of higher-order terms of hydrodynamic model.

Keywords

Electromagnetics, Engineering, Optics, Transfer-Matrix-Method with Nonlinearity, Nonliear Optics, Nanoplasmonics, Nanolayered Structures, Effective Nonloinear Susceptibility, Second-Harmonic, Third-Harmonic, 4-by-4-Transfer-Matrix-Method, Hydrodynamic-modeling, nonlocality, quantum-tunneling

Rights Statement

Copyright © 2020, author

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