Energetic Deposition of Niobium Thin Film in Vacuum

Abstract

(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-to-day 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. Fig. 2-3 The illustration of the surface atom nucleation process to show the columnar forming and atom mobility relation………………………………………………………………………………………………………….16 Fig. 2-4 Energetic deposition or condensation is a coating process with the deposition energy well defined in a range above the thermal deposition process and below the ion implantation process. List of TablesThe energy involved in the energetic deposition is variable and depends on the material.Typically, the energy for energetic deposition ranges between 10 and 100 eV. In the energy range well above 200 eV, niobium atoms tend to induce back sputtering resulting in lower deposition rate, thus offering less opportunity to explore energetic deposition. 1-2. Current Implementations in Particle AcceleratorsIt is absolutely not an exaggeration to say that radio frequency superconductivity is the fastest growing technology for particle accelerators. Numerous particle accelerators constructed around the world use or have used accelerating structures based on RF ...

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