An electron microscopic study on the incipient crystal growth of Bi-Sr-Ca-Cu-O superconducting thin films on a MgO(001) substrate

Abstract

Several types of growth modes of superconducting BiSrCaCuO thin films on a MgO(001) single crystal substrate have been clarified by means of electron diffraction and moiré imaging techniques. Both Bi₂Sr₂CaCu₂O_x (2212-phase) and Bi₂Sr₂Ca₂Cu₃O_y (2223-phase) were investigated, and all of them had “c-axis up” microstructures. It is remarkable that the films contain many grains rotated about the c-axis, and the authors have revealed that such rotations tend to appear with low-angle tilt boundaries near the growth modes of [100]_substrate//[100]_film and [100]_substrate//[110]_film. It is also an interesting phenomenon that the [230]_substrate//110]_film growth mode was frequently observed in the films presently examined, and this mode is considered to have a favorable lattice coincidence between the film and substrate. A possibility of the formation of special grain boundaries connected with the coincidence site lattice theory (CSL theory) is also discussed. The determination of the above-mentioned several types of growth mode can be achieved using transmission electron microscopy (TEM), and the authors note that the moiré patterns are very useful in measuring the rotation angle between the film and substrate precisely for individual small-size domains.