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

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 I D22文件D20 etching and high-temperature annealing，c-axis oriented YBCO thin films were grown on such substrates by sputtering and observed the earststages of the films by AFM。3D island structures were observed along the step edges for 3unit 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 was3u.c.Growth mode on such substrates changed from2D 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。

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.