(Georgia Institute of Technology, 2009-08-07)
Shaw, David
We investigate a novel method of fabricating a network of graphene nanoribbon structures. The process is a sharp departure from conventional nanolithographic techniques in both method and amount of time required. Epitaxial graphene prepared on single crystal 4H-SiC was etched with O2 plasma through 0.2 ìm porous filters adhered to the surface of the sample. Thickness measurements using ellipsometry and topological mappings using atomic force microscopy were conducted to ascertain the extent of graphene nanoribbon formation. Sheet resistance of the samples was measured using the four-point van der Pauw method to ensure the existence of electrical conductivity in the etched samples. Furthermore, the etch-rate of multilayer epitaxial graphene was determined.
(Georgia Institute of Technology, 2009-05-04)
Campbell, Jenna
This study develops a one-step anodization separation process (OSS) after examining two step and multi step liftoff procedures in which porous silicon (PS) films lift off from their substrates. This lift-off process provides a means to produce silicon filters, a worthy alternative to alumina filters that cannot withstand high temperatures as well as silicon and whose pore diameter has yet to reach into the order of microns. By electrochemical etching of p-type silicon wafers in a hydrofluoric acid-based solution, microporous filters with pore diameters varying from 1 to 2 microns whose depths range from 3 to 70 micrometers are fabricated. Using wafers with a resistivity of 14-22 Ω-cm, mobile filters with consistent structural qualities can be reproduced.
(Georgia Institute of Technology, 2008-05-05)
Seltzman, Andrew
Traditional inertial electrostatic confinement (IEC) fusion reactor designs utilize an ion accelerating grid fabricated out of a refractory metal capable of operating at high temperatures to radiate off heat imparted by ion-grid collisions. Unfortunately, the high gird temperature allows for a substantial thermionic electron emission current, requiring a high power draw and significantly reducing reactor efficiency. Further, electrons emitted from the grid are accelerated into the reactor shell where they generate a significant amount of bremsstrahlung x-rays requiring additional shielding and increasing system size and weight.
Presented is a novel modification to the traditional implementation of IEC fusion reactor, designed to improve operating efficiency by reducing electron emission from the grid. A liquid cooled grid design is utilized to reduce thermionic electron emission, allowing for higher plasma densities, and greater input power while improving system efficiency and reducing x-ray output. The resulting low grid temperatures substantially reduce thermionic electron emission and greatly improve reactor efficiency by reducing current draw from the central grid. The reduction of thermionic electron emission will eliminate the majority of bremsstrahlung x-ray generation thereby reducing shielding requirements.
By measuring the heat deposited into the coolant, the grid cooling system may also be used as a diagnostic tool to study the physics involved in IEC reactors. In this manner, grid transparency may be directly measured as a function of ion bombardment heating. By modifying the confinement scheme of the reactor and subsequently evaluating the energy flux to the grid through ion collisions, greater energy and particle confinement times may be obtained.