Vapor–liquid–solid tri-phase pulsed-laser epitaxy of $RBa2Cu3O7−y$ single-crystal films

We report on the fabrication of single-crystalline thin films of $RBa2Cu3O7−y$ (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 $Ba3Cu5Ox (3BaCuO2+2CuO)$ 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.