Recent achievements in ultra-high vacuum arc deposition of superconducting Nb layers

摘要

The properties of niobium films obtained by cathodic arc deposition in ultra high vacuum (UHVCA) using constant and pulsed bias are discussed and compared. UHVCA-produced Nb films are found to have structural and transport properties closer to Nb bulk ones, providing a promising alternative for niobium coated, high voltage, high Q, copper RF cavities with respect to the standard magnetron sputtering technique. A series of sapphire substrate coatings with niobium has been performed at pulsed bias and compared with the films deposited at cd bias. Using pulsed bias resulted in increasing an average deposition ratio by a factor of 2-3 up to a value of 0.9 um/min. The layers coated with pulsed bias reached higher RRR values. Their microstructure is characterized by much larger, randomly oriented grains, compared to the layers obtained with constant bias, with no evidence of epitaxial growth and a lattice parameter identical to that of bulk niobium. The apparatus for coating of a cavity using planar UHVCA sources is presented and discussed. First results on plasma transport into a cavity cell are presented showing that it is possible to guide the plasma generated by a planar arc source inside it. Several magnetic configurations have been analyzed and different voltage bias used