Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Gregory J. Salamo

Committee Member

Morgan Ware

Second Committee Member

Hugh Churchill

Keywords

nanotechnology, optical behavior of materials, quantum well, surface plasmon

Abstract

Due to the advanced focusing ability, characterization methods based on the electron-beam excitation have been broadly applied to investigate nanomaterials. Structural or compositional information is commonly acquired using electron microscopes. Moreover, taking advantage of the super spatial resolution of the focused electron beam, optical properties of nanomaterials can be also obtained. Herein, general concepts and processes of the interaction between electrons and materials are studied. Two specific optical nanomaterials, including plasmonic nanostructures and semiconductor quantum layers, are investigated by the cathodoluminescence (CL) measurement.

Surface plasmonic resonance can be generated when high-energy electrons strike the interface between the dielectric medium and plasmonic nanomaterials. It is found in our research that a special hybridized plasmonic resonance can be achieved by using a combination of multiple materials. Furthermore, a hybridized Au/Ag bullseye nanostructure has been designed and fabricated by the focused ion beam milling. Investigated by the CL process, we find that the hybridized plasmonic emission can be manipulated by the excitation position of the electron beam and the geometry of the bullseye pattern. Finally, we move forward to apply the electron-beam excitation to investigate topological insulators, which are possible to support surface plasmonic waves. A new tip plasmon emission is excited due to the charge oscillation in Bi2Te3 nanotips. Plasmonic properties of Bi2Te3 nanostructures relate to the lateral size, excitation location and resonant wavelength. Finally, based on the application of hybrid plasmonic structures and resonance between edges, nanosphere heterodimers are expected to broaden the usage of plasmonic materials. Investigated by the numerical simulation, an enhanced hotspot emission is observed with a broad wavelength range. The plasmonic behaviors depend on the composition and structural size.

As high energy incident electrons excite electrons from valence bands to conduction bands by secondary processes, we investigated high quality ultrathin InAs layers in InAs/GaAs heterostructures. The CL measurement reveals the formation of In rich clusters for sub monolayers. The electron beam excitation provides a better spatial resolution to observe the variation of CL signal at different locations. The CL peak position, linewidth, and intensity relate to the thickness and roughness of ultrathin layers.

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