プラズマ制御型スパッタ法によるセラミックス多積層膜の作製と界面の構造

抄録

For artificial construction of new high Tc superconducting structures, the preparation of compositionally modulated films has been studied by using such processes as the laser ablation 1), multi-targets sputtering 2), and plasma-controlled sputtering 3). Here, we report on the syntheses of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O multilayered films by plasma controlled sputtering.
The apparatus used for the film preparation has two solenoid coils which can work for varying the shape of the plasma above the targets. The sputtered area can be controlled by changing the coil current. Binary targets consisting of a smaller Ca₁Cu_1.5O_x(φ40mm) and a larger Bi_1.6Sr₁O_y(φ70mm) disks were used for the preparation of Bi-Sr-Ca-Cu-O modulated film. In case of the synthesis of Y-Ba-Cu-O modulated film, a smaller Y₁Cu_1.25O_x(φ50mm) and a larger Ba₁Cu₁O_y(φ70mm) disks were employed. The substrates, MgO(100), were. eated from 450°C to 550°C.
In case of the preparation of compositionally modulated Bi-Sr-Ca-Cu-O film, the periodicity of 20A was designed in view of c-axis length of 18A between two Bi₂O₂ layers in the Bi₂Sr₂Ca₂Cu₃O_x structure. By the low angle X-ray diffraction, peaks attributed to planar spacing of 19.9A appeared. Annealing the as-grown amorphous film in a PbO atmosphere made it superconductor whose T_conset of 113K and T_czero of 103K. Auger electron spectroscopy revealed the existence of Pb in the film.
X-ray diffraction patterns of Y₂Cu₂O₅ and BaCuO₂ were observed for the films prepared from Y-Cu-O and Ba-Cu-O targets, respectively. When we designed the multilayered film with periodicity of 12A, peaks identified to (003) and (006) planes of Ba₂YCu₃O_7-δ were observed for the as-grown film prepared at the substrate temperature of 500°C. Increase of substrate temperature up to 550°C made their intensities high. The as-grown film deposited at the substrate temperature of 450°C was annealed to be strongly c-axis oriented Ba₂YCu₃O_7-δfilm. Planar-like crystals texture was observed in the annealed film by SEM measurement. Its T_conset and T_czero were 65K and 49K, respectively.