Electron Emission from Low Dimensional Structures.

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Title: Electron Emission from Low Dimensional Structures.
Author: Jaeger, David Lawrence
Advisors: Dr. Victor V. Zhirnov, Committee Co-Chair
Dr. Olga A. Shenderova, Committee Member
Dr. Gerald J. Iafrate, Committee Member
Dr. John J. Hren, Committee Co-Chair
Abstract: A fundamental technological driving force is the search for simpler, more efficient and economical means of accomplishing a task. Nano-scale materials are seen as a means to efficiently emit electrons from a solid under the action of an electric field. The drive to smaller scales is also seen as a means to efficiently and simply produce devices. A thorough understanding of the characteristics of such materials is needed to understand and fully exploit these nano-materials when used as field enhanced electron emitters and efficiently process the devices. The focus of this work was to investigate the effects that morphology, geometry and size can have on the electron emission characteristics of vacuum field emission cathodes. Deviations in surface structure and material strongly impact cathode reliability and performance due to the effect that these deviations have on the local surface electric field. Deterministically coating the cathode surface with material can positively impact cathode reliability and performance by manipulating surface morphology, band structure, thermal conductivity, and surface stability. The local electrostatic field effects of nano-scale metallic and dielectric structures on metallic needles were investigated. The effects of needle arrays, dot size and position were analyzed for both metal and composite structures. Composite metal-insulator needles were investigated for effects of size and geometry of the insulator on electron emission. The field emission characteristics of a proposed electron source, designed for processing simplicity and, was analyzed. Effects of dimensionality and possible quantization of the electron gas from which emission occurs was also analyzed. Electrostatic shielding, triple junctions, multistage effects and geometric field enhancement were determined to be strongly affected by size, shape and morphology of the emitting structure. A condition for the saturation of the coherent tunneling current at high fields was found to be dependent on the band structure of the material. Coherent tunneling from low dimensional electron gases was found to be relatively insensitive to the dimensionality and quantization of the electron gas. Design criteria for a novel efficient microwave field emission cathode utilizing various low dimensional emission structures were also developed.
Date: 2006-09-07
Degree: PhD
Discipline: Materials Science and Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/3841

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