Microstructure and superconducting properties of Nb-Ti thin films

Investigation results of interconnection between microstructure and superconducting characteristics of Nb-Ti-thin films with Ti content from 30 to 66 at. % are presented. For all the films investigated the mean grain size of 100-250 nm is characteristic. The density of the defects observed (the grain boundaries, deposition, dislocations) depends greatly on the sample composition. The structure of the films, deposited upon the copper sublayer, differ from the structure of films deposited upon silicon mainly by greater dislocation density (approximately by an order). In films with Ti content higher than 60 at. % separations of the α-Ti phase are observed (with the size of approximately 100 nm), which are in some triple points of the structure (in the junction of three boundaries of grains). Conclusion is made on the effect of the structure defects upon the pinning force