Vapor-liquid-solid tri-phase pulsed-laser epitaxy of RBa₂Cu ₃O_7-y single-crystal films

We report on the fabrication of single-crystalline thin films of RBa ₂Cu₃O_7-y (R: rare-earth element, R123) using an approach of vapor-liquid-solid tri-phase epitaxy. This method is based on application of pulsed-laser deposition under appropriate compositions and conditions predetermined from the relevant thermodynamic phase diagram. The laser-ablated gases of R, Ba, and Cu, and their oxides dissolve into a liquid Ba₃Cu₅O_x(3BaCuO₂+2CuO) layer placed on the film/substrate surface, penetrate to reach the liquid-solid interface with a seed R123, and are condensed into the solid R123 phase under a quasiequilibrium state. The uniform single-crystalline nature of the film was verified by x-ray diffraction, atomic-force microscopy, and transmission electron microscopy by the observation of giant grain size and atomic-scale surface smoothness.