ENERGETIC CONDENSATION GROWTH OF MgB2 THIN-FILMS FOR SRF APPLICATIONS*

We report single-step vacuum growth of stoichiometric superconducting thin films 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 MgB2 films with Tc of 34K 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 sealed into small stainless steel containers prior to ex-situ annealing, to create a small volume that would quickly achieve a high partial pressure of Mg vapor upon heating to minimize loss of Mg from the films. Post-deposition anneal steps varied in temperature from 825–900K with duration of 15 minutes. This annealed films also showed a transition at 30K. Subsequently, an MgB2 film was successfully deposited over a 50mm diameter circular area on a 63mm Buffered Chemically Polished (BCP) 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 decrease in magnesium content in the films. Future plans are to reduce oxygen contamination and to use our filtered cathodic arc to deposit smoother films.