Microstructure of La(0.6)Ca(0.4)MnO3 thin films grown on StTiO3

锰氧化物由于其金属-绝缘体转变和巨磁电阻效应而受到广泛关注。CMR效应与材料中Mn的化学组成和氧化态有关。基于对磁场的敏感性，这些材料在器件应用中的可能集成代表了工业应用（例如磁记录）的主要任务之一。磁输运性质对各种膜性质（例如衬底类型、空位和应变）敏感，这可以通过使用具有与生长膜不同的晶格的衬底在薄膜中诱导。采用脉冲反应交叉束激光烧蚀技术在SrTiO_3衬底上生长了高度取向的（002）La_（0.6）Ca_（0.4）MnO_3薄膜。利用XRD、高分辨TEM和电子衍射等方法对STO基片上生长的LCMO薄膜进行了初步研究。分析揭示了具有与钙钛矿结构特别相关的孪晶畴的外延生长。由于衬底和薄膜之间的晶格失配，在界面处形成失配位错。为了优化这种膜的CMR，重要的是要获得更详细的信息失配位错的界面结构和局部化学计量的影响，以及有关La/Ca/Mn-和空位分布在膜中。通过像差校正的达雷斯伯里SuperSTEM，可以获得具有原子柱空间分辨率的此类信息。在对不同材料系统，即缺氧La/Ca钴酸盐的初步研究中，我们已经证明了原子分辨率高角度环形暗场（HAADF）成像和原子柱EELS的组合使用可以实现什么：它使我们能够识别两种类型的平面断层（“Brownmillerite”和“Ruddleston-Popper”缺陷），其中一个缺陷由有序的O空位面组成，另一个缺陷由1/2晶胞宽的岩盐结构域组成。这些都是前所未有的测量，如果没有SuperSTEM，就不可能获得这些。

Manganese oxides have been intensively studied recently due to their metal to insulator transition, accompanied by colossal magnetoresistance (CMR). The CMR effect is related to the chemical composition and oxidation state of Mn in the material. A possible integration of those materials in device applications based on the sensitivity to magnetic fields represents one of the major tasks for industrial applications, such as magnetic recording.The magneto- transport properties are sensitive to various film properties, such as substrate type, vacancies and strain, which can be induced in thin films by using substrates with a lattice different to the growing film. Highly oriented (002) La0.6Ca0.4MnO3 films can be grown on SrTiO3 substrates using Pulsed Reactive Crossed Beam Laser Ablation. We have succeeded to obtain preliminary results for LCMO films grown on STO substrates by XRD, high resolution TEM analysis and electron diffraction. The analysis revealed epitaxial growth with twin domains specifically related to the perovskite structure. Due to the lattice mismatch between the substrate and the film, misfit dislocations form in the interface. In order to optimise such films for CMR it is important to obtain more detailed information about the influence of misfit dislocations on the interface structure and the local stoichiometry as well as about La/Ca/Mn- and vacancy-distributions in the film. With the aberration corrected Daresbury SuperSTEM it is possible to gain such information with atomic column spatial resolution. In a pilot study on a different materials system, namely oxygen deficient La/Ca cobaltates (grown by the above method) we have already demonstrated what combined use of atomic resolution high angle annular dark field (HAADF) imaging and atomic column EELS can achieve: it enabled us to identify two types of planar faults ('Brownmillerite' and 'Ruddleston-Popper' defects) consisting of ordered O-vacancy planes in one case and of 1/2 unit cell-wide rocksalt-structure domains with strong enrichment in Ca on in the fault. These are unprecedented measurements, and it would have been impossible to obtain these without the SuperSTEM.