Characterization of electron emission from diamond surfaces for energy conversion devices

Abstract

The aim of this thesis is towards a solar thermal type of energy converter, using a plasmonically-enhanced diamond based thermionic converter. The approach was to first form a strong fundamental basis of understanding on the diamond electronic properties, including its electron emission behavior and the use of ultra-high vacuum techniques to analyze them. Modification of the diamond surface was then studied to find an optimum structure for thermionic emission, along with possible emission enhancement mechanisms. Finally, plasmonic structures were added by different methods where their feasibility was investigated.

Angle-resolved photoemission spectroscopy was employed to analyze the diamond electronic band structure. This allowed the valence band width of diamond to be determined at approximately $18.3$ eV, which has significant implications for photoelectron spectroscopy with lab-based light sources. And from the electron emission perspective, low energy electron emission was found to originate from unoccupied electronic states which gave well defined and ordered emission structure, meaning that unoccupied states can be directly mapped using secondary electrons. The emission behavior was also determined to have no preferential perpendicular momentum selection. As thermionic emission occurs in this region, its behavior can be predicted and studied in detail using the proposed model. These methods then supported the study of surface functionalization and graphene application on diamond, where the general electronic effects and interactions on diamond from surface modifications, such as band bending and work function are inferred.

Thermionic emission from diamond was found to be readily enhanced through various mechanisms, which strongly points to further enhancements via surface plasmonic resonances. Plasmonic structure generation on diamond surfaces was then studied using application of atomic gold layers. Surface characterizations of the gold-diamond structure along with optical responses were considered to determine the most suitable approaches. With this approach, a highly efficient diamond-based electron emitter can be realized for thermionic energy conversion applications.

Date of Award	23 Mar 2021
Original language	English
Awarding Institution	University of Bristol
Sponsors	Renewtec, Al Hamad Group
Supervisor	Neil A Fox (Supervisor)