Energetic Deposition of Niobium Thin Film in Vacuum

(Abstract) Niobium thin films are expected to be free of solid inclusions commonly seen in solid niobium. For particle accelerators, niobium thin film has the potential to replace the solid niobium in the making of the accelerating structures. In order to understand and improve the superconducting performance of niobium thin films at cryogenic temperature, an energetic vacuum deposition system has been developed to study deposition energy effects on the properties of niobium thin films on various substrates. The system directly uses microwave power to create a pure niobium plasma, which can be used to extract niobium ion flux with controllable kinetic energy for direct deposition. The ultra high vacuum avoids the gaseous inclusions in thin films. A retarding field energy analyzer is developed and used to measure the kinetic energy of niobium at the substrate location. A systematic process for thin film characterization is developed and used to analyze the niobium thin films made by this energetic condensation. The properties of niobium thin films at several deposition energies are obtained, and the results show that there exists a preferred deposition energy around 115eV. Acknowledgement iii Acknowledgement Prof. Ron Sundelin has supported me through out the dissertation work at Jefferson Lab. His guidance and help extended beyond the scientific scope, and probably will influence through out my lifetime. Dr. Larry Phillips, as my day-today supervisor, looked after many technical details during the system development. Many times, Larry helped to expedite the work requests and material acquisitions. Both Ron and Larry's extensive scientific knowledge made my student life enviable by others. Beside their mentorship, Ron and Larry are also the best friends I can have. They helped me in many ways to settle into the American cultures. Julie Oyer and Chris Thomas helped me in every administrative detail, in a way that I felt " spoiled ". I am grateful for their help that I can focus on my dissertation. I also got encouragement from other committee members like Prof. Ficenec provided many writing suggestions. Many staff members at Jefferson Lab are supportive and helpful. Dr. Peter Kneisel and John Musson are first two staff I want to express lot of appreciations. Their support and encouragement were countless and critical for my dissertation work. Charlie Reece, Larry Doolittle and Ganapati Myneni are also supportive and shared their scientific knowledge. Viet Nguyen helped me with HFSS program. lot of help in machining, instrumentation …