Fabrication of the oxide single crystal film by Tri-phase Epitaxy

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Tri-phase epitaxy (TPE) is a new approach in vapor phase epitaxy for a single crystal oxide film based on a flux method primarily developed in a bulk single crystal process. That is, the film is grown through a liquid layer of the flux at a high temperature enough to attain a thermodynamic steady-state condition between the growing film and the flux. We have verified the capability of the TPE by fabricating a single crystal film of NdBa_2Cu_3O_<7-d> (Nd123).In the first year for this project (H14), we attempted to apply the TPE to the fabrications of Ca doped Nd123 and ferroelectric Bi_4Ti_3O_<12> (BIT) single crystal films. In parallel, we also developed a new combinatorial system for a ternary composition spread to speed up the experimental work.In the next year (H15), a new impurity flux of Bi-Cu-O for the BIT single crystal film was successfully found from a high-throughput screening by the ternary composition spread technique. The additional CuO_x flux could suppress an evaporation of the BiO_x flux during the growth. As a result, the single crystal quality of the BIT film was achieved, which was evidenced by no sliding dislocations and defects inherited from steps of a substrate and/or the lattice mismatching in the film. In addition, we found that the PLD grown BIT film with its surface capped with the BiO_x became single crystalline after annealing at high temperature. This preliminary result suggests a new possibility of "solid phase flux epitaxy" by applying the TPE to the solid phase reaction.