Tem Study of Cvd-Grown Bi-Sr-Ca-Cu-0 Thin Films on (001) Mgo Substrates
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TEM STUDY OF CVD-GROWN Bi-Sr-Ca-Cu-O THIN FILMS ON (001) MgO SUBSTRATES 0. UEDA, T. KIMURA, H. YAMAWAKI, M. IHARA and M. OZEKI Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01,
JAPAN
ABSTRACT CVD-grown Bi-Sr-Ca-Cu-O thin films on (001)MgO with T at 110 K have been investigated by transmission electron microscopy. The films are found to consist of large domains oriented along the c-axis, with diameters of 15100 pm. These domains exhibit incommensurate superstructures along the baxis. In addition, we have observed similar superstructure spots in two equivalent directions normal to each other. It has also been found that the interface between the thin film and the substrate is very abrupt. Five different perovskite-related layers along the c-axis with different thickness are present. In the thin film, 80K phases are dominant and 110 K phases are less likely. Three other phases are very rarely observed. Furthermore, boundaries where the layered structure is different on both sides are often found. INTRODUCTION Since
the
discovery of the oxide superconductors of La-Sr-Cuextensive studies have been performed on the structure and various properties of these materials. Recently, Maeda et al. have discovered a new superconducting oxide of Bi-Sr-Ca-Cu-0 with different transition temperatures of 80 K and 110 K[3]. A series of detailed structural evaluations by high resolution transmission electron microscopy(HRTEM) have been performed on sintered Bi-Sr-Ca-Cu-0 superconductors of various compositions regarding atomic structure of the unit cell[4-6]. modulated structures along the b-axis[4-6]. twins[7].and intergrowths[6,7]. For the application of these superconductors to the development of electronic devices, fabrication of thin films of excellent quality, i. e., large domain size, uniformity in thickness, low defect density etc., on the substrate is essential. In previous work, we have reported the successful growth of high Tc superconducting Bi-Sr-Ca-Cu-O thin films with the highest transition temperature of 110 K on (001) MgO substrates by chemical vapor deposition(CVD)[8-10]. However, the crystal quality of these films, e. g., grain size, orientation relationship between the film and the substrate, stacking sequence of different perovskite-related layers and types of defects, has not been clarified yet. In this paper, we describe for the first time a detailed TEM investigation of this system.
O[l] and Y-Ba-Cu-O[2],
EXPERIMENTAL PROCEDURES Thin Bi-Sr-Ca-Cu-O films are grown on (001) MgO substrates by CVD. In the growth system, BiCl , SrI?, CaI 2 and Cul are used as source materials, which are kept at l 0, 82, 800 and 425 0 C, respectively. Helium is used as carrier gas and 02 and/or H2 0 are used for oxidizing agents. In this study, thin films are grown with a substrate temperature of 854°C and 02 concentration of 12.5% of the total gas flow (detailed growth procedures Typical Tc and Jc-values for tje thin are described elsewhere[8-10]). films grown under these conditions are 110 K and 1.7 x 104 A/cm
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