| Paper | Title | Page |
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| TUPPO068 | Energetic Condensation Growth of MgB2 Thin-Films for SRF Applications | 391 |
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We report single-step vacuum growth of a stoichiometric superconducting thin film of MgB2, using AASC’s cathodic arc deposition process. Energetic condensation using cathodic arcs produces non-equilibrium fast ions (~50-100eV) that allow growth modes on relatively low temperature substrates. We have demonstrated a film Tc of 34K with MgB2 by depositing at 275 °C in a single step, from a stoichiometric, solid MgB2 source. In a subsequent experiment, the single-step coated samples (on c-plane sapphire) were ex-situ annealed. Post-deposition anneal temperature ranged from 825900K, for 15 minutes. The annealed film also showed a transition at 30K. An MgB2 film was also deposited over a 50mm diameter circle on a Buffered Chemically Polished Niobium substrate for future RF evaluation in a cavity. The depositions spanned a range of substrate temperatures from 550-675 K. The films began to change in appearance form silver to black as substrate temperature was increased, indicating a decreasing magnesium content in the films. Future plans are to reduce oxygen contamination and to use our filtered cathodic arc to deposit smoother films |
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| TUPPO069 | Energetic Condensation Growth of Nb Thin-Films for SRF Applications | 396 |
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AASC, JLab and NSU conduct research into SRF thin-film coatings by first characterizing properties such as morphology, grain size, crystalline structure, defects, and impurities, then measuring Tc and RRR, and following this with ‘in-cavity’ RF measurements of the Surface Impedance of the films at cryogenic temperatures. These progressive steps are essential to eventual design and measurement of SRF accelerator structures at high fields. We have recently produced Nb superconducting thin-films with crystal grain sizes ~50μm using our proprietary CED^TM cathodic arc technique. RRR of ~129 at Tc of 9.2K was measured in a film grown on a-plane sapphire heated to 400oC. At 20oC, the RRR dropped to ~4. Energetic condensation using cathodic arcs produces non-equilibrium fast ions (~50-100eV). These ion energies are much higher than typical sputtering energies. When such energetic condensation is complemented by substrate biasing (to ~200-300eV) the incident ion energy is further increased, allowing growth modes that would otherwise require much higher substrate temperatures. Data are presented for pure Nb films using SEM, EBSD, XRD and a Surface Impedance Characterization RF cavity. |
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| TUPPO080 | X-ray Pole Figure Analysis on Fiber Textured Epitaxial Niobium Films for SRF Cavities | 418 |
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Single and large grain Nb films are of interest to reduce the cost of SRF cavities. The structural properties and SRF potential of Nb films obtained by coaxial energetic deposition (CEDTM) in an ultra-high vacuum process are compared and discussed. The CEDTM is a hybrid technique with both energetic ion deposition and implantation phases based on cathodic arc plasma sources, which are copious generators of condensable energetic (20-200 eV), multiply charged ions from metal or alloy cathodes. The X-ray pole figure of the thin films revealed grain orientations on Nb films grown at different substrate temperatures that indicate good structural and electrical properties. Single crystalline 110 epilayers of Nb films are grown on a-plane sapphire substrates at 400 degreeC, but at lower temperature, there are two kinds of twins in which the grains are rotated by ~45 degree about the film normal. RRR of ~129 and Tc=9.2K were measured on a Nb film on a-plane sapphire substrate at 400 degreeC, dropping to ~4 on a room temperature substrate. |