Fabrication and superconductivity of very thin Tl2Ba2CaCu2Ox films

Very thin Tl2Ba2CaCu2Ox (Tl-2212) superconducting films with thickness<100 nm have been fabricated on LaAlO3 (001) substrates using dc magnetron sputtering and post-annealing process in pure argon. For a 100 nm thick film, Tc and Jc (77 K, 0 T) show the values of 105.3 K and 2.33×106 A/cm2, respectively. A 30 nm thick film with Tc>100 K shows smooth surface morphology and high quality epitaxy. A 20 nm thick film revealed full transition to superconductivity at temperature of 98.7 K. The superconductivity and surface morphology of the very thin film deteriorated rapidly as the film thickness below 20 nm. A 6 nm thick Tl-2212 film was not found to be superconducting at temperature down to 15 K. In our experiments the critical film thickness leading to degradation of the superconducting properties was 20 nm.