Phase purity and surface morphology of high-Jc superconducting Bi2Sr2Ca1Cu2O8+d thin films

Bi2Sr2Ca1Cu2O8+d (Bi-2212) thin films with thicknesses less than 50 nm (<20 unit cells) are grown by pulsedlaser deposition (PLD) onto (001) LaAlO3 (LAO) single crystal substrates. Phase-pure and smooth c-axis oriented Bi-2212 films with optimal oxygen doping, critical temperature T-c0 up to 86 K, and critical current density J(c)(60 K) above 1 MA/cm(2) are obtained for samples that are annealed in situ at temperatures below 700 degrees C. At higher temperature Bi-2212 films on LAO substrates partially decompose to non-superconducting impurity phases, while films on MgO and SrTiO3 substrates are stable. The broadening T-Delta(c) of the metal-to-superconductor resistive phase transition in magnetic fields is much larger for thin films of Bi-2212 as compared to YBa2Cu3O7. The magnetic field-induced suppression of T-c0 is stronger for Bi-2212 films containing impurity phases as compared to the phase-pure Bi-2212 films. The degradation of LAO substrate crystals after several steps of deposition and chemical removal of the Bi-2212 layer is investigated. New, commercially prepared substrates provide Bi-2212 films with smallest surface roughness (3 nm) and strong out-of-plane texture. However, thin films of almost the same quality are obtained on re-used LAO substrates that are mechanically polished after the chemical etching.

Automated summary

Bi2Sr2Ca1Cu2O8+d (Bi-2212) thin films with thicknesses less than 50 nm are grown on (001) LaAlO3 substrates by pulsed laser deposition (PLD). Phase-pure and smooth c-axis oriented Bi-2212 films with optimal oxygen doping and high Tc0 and Jc(60K) are obtained. The films on LAO substrates decompose at high temperatures, while films on MgO and SrTiO3 substrates are stable. The magnetic field-induced suppression of Tc0 is stronger for films with impurity phases compared to phase-pure films.