MWA and scanning-probe study of argon-ion irradiation effects on superconducting properties of Bi2Sr2CaCu2O8 thin films

Bi2Sr2CaCu2O8 films with thickness of 200 and 800 nm were irradiated with monovalent argon ions with an energy of 40 keV and a dose ranging between 1014 and 1017 ion/cm2. The dose dependences of (i) the superconducting transition temperature, (ii) the critical current density value and (iii) the irreversibility line position on the magnetic field-temperature phase diagram were determined for two series of samples of different thickness. Atomic force microscopy images of the irradiated samples showed an appearance of defects in the form of surface holes. The obtained data were used to establish conditions for improving properties of thin-film superconducting materials. Firstly, the irradiation dose should be at least 1016 ion/cm2 to form embedded gas bubbles and surface holes serving as artificial pinning centers. Secondly, the film thickness and the average depth of the defect formation should be of a comparable value and sufficiently exceed the thickness of the surface layer sputtered as a result of irradiation.