Graduate Studies, UNL

 

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

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First Advisor

Timothy Gay

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Eva Schubert, Herman Batelaan, Marcel Ngoko

Department

Physics and Astronomy

Date of this Version

4-24-2026

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy

Major: Physics and Astronomy

Under the supervision of Professor Timothy Gay

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, William Truslow Newman. Used by permission

Abstract

Spin-polarized electrons are commonly emitted from GaAs photocathodes with treated surfaces in a process called negative electron affinity activation. These sources require stringent vacuum conditions that are often hard to achieve and lead to significant downtimes in experiments. In this dissertation, I present new investigations of electron emission from unactivated GaAs towards the development of novel sources of spin-polarized electrons. The work entails two primary directions. The first is the investigation of electron emission using multiphoton ionization processes enhanced by nanoscale surface structures. We explore GaAs electron sources including, shards, nanotip arrays of pyramid structures, wedges, and ion-milled tips. The second direction is the investigation of the effects of photoexcitation on the secondary electron emission from GaAs. We explore the secondary electron emission from p-doped, n-doped, and intrinsic GaAs both with and without photoexcitation. In this investigation, a paucity of research on secondary electron emission from unactivated GaAs is filled and a newly discovered large effect on the secondary electron emission from intrinsic GaAs with photoexcitation is discussed. These results progress the development of a source of spin-polarized electrons from an unactivated GaAs improving accessibility for the scientific community.

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