Date of Award

8-2023

Document Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Physics, Applied

First Advisor

Chandra Yelleswarapu

Second Advisor

Greg Sun

Third Advisor

Mohamed Gharbi

Abstract

Plasmon resonance refers to the collective oscillation of free electrons in a nanomaterial in response to an incident electromagnetic field. When two plasmonic nanoparticles are placed close together, their localized surface plasmon resonances can couple and interact. The resulting plasmonic coupling leads to the formation of new plasmonic modes in the dimer system, significantly enhancing the electromagnetic fields in the vicinity of the nanoparticles, with various interesting and potentially useful applications. This thesis investigates the optical field enhancement arising from gold nanoparticle dimers in an aqueous dielectric medium, using the Finite Element Method simulation software COMSOL Multiphysics. The simulations provide comparative field strengths for 10 nm radius gold nanosphere (AuNP) dimers parameterized by a separation distance of 0 nm to 20 nm and orientation along the x-axis, y-axis, and z-axis relative to the incident light. Results demonstrate strong coupling when aligned with the incident polarization, and decreased field strength with increasing separation, consistent with existing literature. Additionally, both orientations perpendicular to the incident polarization behaved identically, resembling independent AuNPs. Furthermore, field enhancement of a gold nanorod (AuNR) with a 10 nm radius and 40 nm height was simulated for orientation along the x-axis, y-axis, and z-axis. The simulations showed resonance confined to the outer ring of the circular faces when aligned with the incident polarization and confined to the upper and lower edges of the curved surface in the other orientations. Moreover, the study included simulations of a dimer composed of an AuNR and an AuNP across different orientations of the AuNR, relative positions of the AuNR and AuNP, and separation between them. The results indicated strong coupling enhancement when both the dimer and the AuNR were aligned with the incident polarization, weaker coupling when the AuNR was perpendicular to, but the dimer was aligned with the incident polarization, and evidence of small coupling when the AuNR was aligned with the polarization, but the dimer was aligned with the incident propagation vector, among other findings. These simulations not only explore the field enhancement of various nanoparticle configurations but also enable the determination of particle orientations in a laboratory sample by comparing the relative field enhancements by incident angle to those obtained in the simulations.

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