Year: 2008
Type: dissertation
Abstract: In recent years, carbon nanotubes (CNTs) have emerged as one of the \nbest field emitters for a variety of technological applications. \nThe field emitting cathodes have several advantages over the \nconventional thermionic cathodes: (i) current density from field \nemission would be orders of magnitude greater than in the \nthermionic case, (ii) a cold cathode would minimize the need for \ncooling, and (iii) a field emitting cathode can be miniaturized. \nIn spite of good performance of such cathodes, the procedure to \nestimate the device current \nis not straight forward and the required insight towards \ndesign optimization is not well understood. In addition, the current \nin CNT-based thin film devices shows fluctuation. Such fluctuation \nin field emission current is not desirable for many biomedical \napplications such as x-ray devices. \n \nThe CNTs in a thin film undergo complex dynamics during \nfield emission, which includes processes such as (i) evolution, \n(ii) electromechanical interaction, (iii) thermoelectric heating, \n(iv) ballistic transport, and (v) electron gas flow. \nThese processes are coupled and \nnonlinear. Therefore, they must be analyzed accurately from the \nstability and long-term performance point of view. In this research, \nwe develop detailed physics-based models of CNTs considering \nthe aspects mentioned above. The models are integrated in a systematic manner \nto calculate the device current by using the Fowler-Nordheim \nequation. Using the models, we were able to capture the fluctuations \nin the field emission current, which have been \nobserved in actual experiments. A detailed analysis of the results \nreveals the deflected shapes of the CNTs \nin an ensemble and the extent to which the initial state of \ngeometry and orientation angles affect the device current. \n \nIn addtion, investigations on the influence of defects \nand impurities in CNTs on their field emission properties have been \ncarried out. By inclusion of defects and impurities, the field emission \nproperties of CNTs can be tailored for specific device applications \nin future. For stable performance of CNT-based field emission devices, such \nas x-ray generators, design optimization studies have been presented. \nIt has been found that the proposed design minimizes transience in \nfield emission current. In this \nthesis, it has been demonstrated that phonon-assisted \ncontrol of field emission current in CNT based thin film is possible. \nFinally, experimental studies pertaining to crosstalk phenomenon in \na multi-pixel CNT array are presented.
Source: UWSpace (University of Waterloo)
Author: Niraj Sinha
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1679155948