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Growth of High-Temperature Oxide Superconductor Thin Films on Ultrasmooth Substrates and Elucidation of Their Growth Mechanism.

超光滑基底上高温氧化物超导体薄膜的生长及其生长机制的阐明。

基本信息

批准号：
10650016
负责人：
SUZUKI Toshimasa
金额：
$ 1.34万
依托单位：
Nippon Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

It is very important to know the growth mechanism of oxide superconductors to obtain high-quality films with atomic surface flatness. In this study, we deposited YBCO thin films on MgO(100) ultra smooth step substrates by sputtering and investigated the early stages of the growth by atomic force microscopy (AFM). And discussed the influence of the surface structure of the substrates on the growth mechanism and surface structure of YBCO films.Atomically flat surface of MgO(100) step substrates with different terrace width and step height have been obtained by HィイD22ィエD20 etching and high-temperature annealing, c-axis oriented YBCO thin films were grown on such substrates by sputtering and observed the early stages of the films growth by AFM. 3D island structures were observed along the step edges for 3 unit cell(u.c.) thick YBCO films when grown on wide terrace width and high step height. It is considered that the deposited species of YBCO are preferentially captured at the step edges and form island structures there when the terrace width is wider than diffusion length of deposition species and the step height is much higher than the unit cell length of YBCO. On the other hand, 2D grains and no island were observed on the films grown on the substrates with narrow terrace width and low step height when the film thickness was 3u.c. Growth mode on such substrates changed from 2D layer-by-layer growth to 3D ledge growth at the film thickness around 7u.c. The initiation of spiral structures was observed when the film thickness is lOu.c. It is concluded that the growth mechanisms of YBCO film changed from 3D ledge growth to spiral growth when the film thickness is thicker than lOu.c.Ultra smooth sapphire step substrates were also obtained by chemical etching using sulfuric and phosphoric acids and ZnO and GaN thin films were grown on them by sputtering. The crystal quality of thin films grown on step substrate was better than that on non-treated substrates.

了解氧化物超导体的生长机理对获得高质量的原子表面平整的薄膜具有重要意义。在本研究中，我们利用溅镀法在MgO（100）超光滑阶梯基底上沉积YBCO薄膜，并利用原子力显微镜（AFM）研究薄膜生长的早期阶段。通过H_（100）D_22 ~（100）D_20刻蚀和高温退火，获得了不同台阶宽度和台阶高度的MgO（100）台阶衬底原子级平整表面，通过溅射法在这种衬底上生长了c轴取向的YBCO薄膜，并通过原子力显微镜观察了薄膜生长的早期阶段。对于3个晶胞（u.c.）在宽台阶宽度和高台阶高度上生长YBCO薄膜时，研究认为，当台阶宽度大于沉积物种的扩散长度，台阶高度远大于YBCO的晶胞长度时，YBCO的沉积物种优先被捕获在台阶边缘，并在那里形成岛状结构。另一方面，当膜厚为3 μ c时，在具有窄平台宽度和低台阶高度的衬底上生长的膜上观察到2D晶粒，并且没有岛。在这种衬底上的生长模式从2D逐层生长转变为3D台阶生长，膜厚度约为7 μ c。当膜厚为10u.c时，观察到螺旋结构的开始。当YBCO薄膜厚度大于10 u.c时，YBCO薄膜的生长机制由3D台阶生长转变为螺旋生长。采用硫酸和磷酸化学腐蚀法制备了超光滑的蓝宝石台阶衬底，并在其上溅射生长了ZnO和GaN薄膜。在台阶衬底上生长的薄膜的结晶质量优于未处理衬底上生长的薄膜。