M.S. Thesis Presentation by Brian Thomas Fuhrman
Friday, August 18, 2000

(Dr. Jack Lackey, advisor)

"Fabrication of Advanced Thermionic Emitters Using LCVD-RP"

Abstract

The goal of this thesis was to determine the feasibility of using Laser Chemical Vapor Deposition-Rapid Prototyping (LCVD-RP) as a manufacturing method for fabricating an integrated-grid thermionic emitter.  Integrated-grid thermionic emitters are composed of wagon wheel-like grid structures of alternating layers of boron nitride and molybdenum deposited on tungsten.  They are utilized as the electron source for such devices as cathode ray tubes and microwave sources.  Their performance is dependent on the distance between the control grid (the molybdenum layers) and the cathode (the tungsten).  LCVD-RP is the process of using the thermal energy from a laser to thermally react special reagent gases to deposit various metals and ceramics.  Boron trichloride (BCl3) and ammonia (NH3) were used as reagents for the deposition of boron nitride.  Molybdenum pentachloride (MoCl5) and hydrogen (H2) were used to deposit molybdenum. To determine what the effects of the reagents used for depositing boron nitride had on the molybdenum, tungsten, or each other, a thermodynamic model of the reaction was created.  The results from the experiments and the thermodynamic model are used to determine whether or not LCVD-RP can be used to fabricate integrated-grid thermionic emitters.

In addition to the feasibility study, an automation program was developed to monitor and control the experimental system.  This program was utilized to regulate the reagents, regulate the pressure in the reaction chamber, control the laser power, and move the substrate.