Yun Hwanhui, Ganguly Koustav, Postiglione William, Jalan Bharat, Leighton Chris, Mkhoyan K Andre, Jeong Jong Seok
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
Sci Rep. 2018 Jul 6;8(1):10245. doi: 10.1038/s41598-018-28520-9.
Detailed microstructure analysis of epitaxial thin films is a vital step towards understanding essential structure-property relationships. Here, a combination of transmission electron microscopy (TEM) techniques is utilized to determine in detail the microstructure of epitaxial La-doped BaSnO films grown on two different perovskite substrates: LaAlO and PrScO. These BaSnO films are of high current interest due to outstanding electron mobility at ambient. The rotational disorder of low-angle grain boundaries, namely the in-plane twist and out-of-plane tilt, is visualized by conventional TEM under a two-beam condition, and the degree of twists in grains of such films is quantified by selected-area electron diffraction. The investigation of the atomic arrangement near the film-substrate interfaces, using high-resolution annular dark-field scanning TEM imaging, reveals that edge dislocations with a Burgers vector along [001] result in the out-of-plane tilt. It is shown that such TEM-based analyses provide detailed information about the microstructure of the films, which, when combined with complimentary high-resolution X-ray diffraction, yields a complete structural characterization of the films. In particular, stark differences in out-of-plane tilt on the two substrates are shown to result from differences in misfit dislocation densities at the interface, explaining a puzzling observation from X-ray diffraction.
外延薄膜的详细微观结构分析是理解基本结构-性能关系的关键一步。在此，利用透射电子显微镜（TEM）技术的组合，详细确定了在两种不同的钙钛矿衬底（LaAlO和PrScO）上生长的外延La掺杂BaSnO薄膜的微观结构。这些BaSnO薄膜由于在环境条件下具有出色的电子迁移率而备受关注。低角度晶界的旋转无序，即面内扭曲和面外倾斜，在双束条件下通过传统TEM可视化，并且通过选区电子衍射对这种薄膜晶粒中的扭曲程度进行量化。使用高分辨率环形暗场扫描TEM成像对薄膜-衬底界面附近的原子排列进行研究，结果表明，伯格斯矢量沿[001]的刃型位错导致了面外倾斜。结果表明，这种基于TEM的分析提供了有关薄膜微观结构的详细信息，当与互补的高分辨率X射线衍射相结合时，可对薄膜进行完整的结构表征。特别是，两种衬底上的面外倾斜存在明显差异，这是由界面处失配位错密度的差异导致的，解释了X射线衍射中一个令人困惑的观察结果。
