| dc.description.abstract | In recent years, carbon nanotubes (CNTs) have emerged as one of the
best field emitters for a variety of technological applications.
The field emitting cathodes have several advantages over the
conventional thermionic cathodes: (i) current density from field
emission would be orders of magnitude greater than in the
thermionic case, (ii) a cold cathode would minimize the need for
cooling, and (iii) a field emitting cathode can be miniaturized.
In spite of good performance of such cathodes, the procedure to
estimate the device current
is not straight forward and the required insight towards
design optimization is not well understood. In addition, the current
in CNT-based thin film devices shows fluctuation. Such fluctuation
in field emission current is not desirable for many biomedical
applications such as x-ray devices.
The CNTs in a thin film undergo complex dynamics during
field emission, which includes processes such as (i) evolution,
(ii) electromechanical interaction, (iii) thermoelectric heating,
(iv) ballistic transport, and (v) electron gas flow.
These processes are coupled and
nonlinear. Therefore, they must be analyzed accurately from the
stability and long-term performance point of view. In this research,
we develop detailed physics-based models of CNTs considering
the aspects mentioned above. The models are integrated in a systematic manner
to calculate the device current by using the Fowler-Nordheim
equation. Using the models, we were able to capture the fluctuations
in the field emission current, which have been
observed in actual experiments. A detailed analysis of the results
reveals the deflected shapes of the CNTs
in an ensemble and the extent to which the initial state of
geometry and orientation angles affect the device current.
In addtion, investigations on the influence of defects
and impurities in CNTs on their field emission properties have been
carried out. By inclusion of defects and impurities, the field emission
properties of CNTs can be tailored for specific device applications
in future. For stable performance of CNT-based field emission devices, such
as x-ray generators, design optimization studies have been presented.
It has been found that the proposed design minimizes transience in
field emission current. In this
thesis, it has been demonstrated that phonon-assisted
control of field emission current in CNT based thin film is possible.
Finally, experimental studies pertaining to crosstalk phenomenon in
a multi-pixel CNT array are presented. | en |
