In situ growth of epitaxial TlBa2CaCu2O7 thin films

Epitaxial TlBa2CaCu2O7 thin films have been grown on single-crystal LaAlO3 and NdGaO3 substrates by in situ off-axis magnetron sputtering in the presence of Tl2O vapor. X-ray diffraction shows that the films are highly epitaxial with the c axis perpendicular to the substrate surface and [100] TlBa2CaCu2O7 aligned with pseudo-cubic [100] NdGaO3 and LaAlO3. The full width at half maximum of the rocking curve for the best films is 0.2°. X-ray diffraction finite size effects show that the film surface is smooth to within several unit cells (∼40 Å). The films are superconducting as deposited with a Tc (onset) of about 80 K and a Tc (R=0) of about 8 K. In situ oxygen treatment of the films at 675 °C has produced films with a Tc(R=0) as high as 40 K. Ex situ annealing in O2 and Tl2O vapor at 800 °C has produced films with a Tc(R=0) as high as 97 K while still retaining a very smooth surface.