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Biography:
Education:
North Carolina State University
- Ph.D. Candidate, Physics August 2002 to present
- B.S. Physics, May 2002
- B.S. Mathematics, May 2002
Current Research:
In my research, I have dealt with two main projects: studying a direct-energy
conversion device known as a thermionic energy converter (TEC), and developing
a process to hydrogen terminate tetrahedral amorphous carbon (ta:C) facets for
the IBEX program. My work ranges from theory and modeling on the TEC project to
experimental work on the IBEX project.
TEC's are a type of heat engine which convert heat directly to electrical
work. These devices have a configuration similar to a vacuum diode: they
consist of two electrodes separated by an evacuated interelectrode space. The
emitter electrode is heated and electrons are boiled off, traverse the
interelectrode space, and are collected at the collector. This current travels
out of the device and can do useful work at an external load.
My work has focused on the two main issues which affect the performance of
these devices: decreasing the emission barrier height of the emitter, and
mitigating the negative space charge effect. We have investigated the effect of
employing geometric field enhancing structures on the emitter surface in order
to locally decrease the emission barrier height via Schottky barrier lowering
(SBL). We approached this problem by calculating the electric field inside the
thermionic cell using the finite element method. From this data, we calculated
the local field enhancement on all points on the emitter's surface and were
able to calculate the total increased output current. We showed that the
geometric field enhancement structures increased the output current as a result
of two effects: the increased emitter surface area due to the nonplanar
features, and the decreased emission barrier height at the tips of the
structures. (Reference)
I have also been involved in studying methods to mitigate the negative space
charge effect. We approached this problem by developing a space charge theory
of operation of a TEC employing an emitter with a negative electron affinity
(NEA). This NEA occurs when the vacuum level of the surface falls below the
conduction band minimum. The NEA essentially changes the electrostatic boundary
conditions of the emitter, reducing the additional barrier the electron current
produces. The theory shows that a TEC with an NEA emitter will outperform a TEC
with a conventional emitter. (Reference)
Finally, I have worked on the IBEX program
through a partnership with Lockheed Martin. In this project, I developed a
process to hydrogen terminate ta:C facets which will be used in the IBEX-Lo
detector. In order to develop the H-termination process, I used x-ray
photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy
(UPS) to characterize test samples. Once it was determined that the process was
H-terminating the samples and the samples weren't being significantly roughened,
I processed the thirty flight facets that will be included in the IBEX
satellite.
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