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

锰氧化物由于其金属到绝缘体的转变，伴随着巨大的磁阻（CMR），近年来得到了广泛的研究。CMR效应与材料中Mn的化学成分和氧化状态有关。基于对磁场的敏感性，这些材料在设备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。薄膜的磁输运特性对衬底类型、空位和应变等各种薄膜特性都很敏感，这些特性可以通过使用与生长薄膜晶格不同的衬底来诱导。采用脉冲反应交叉束激光烧蚀技术在SrTiO3衬底上制备了高取向（002）La0.6Ca0.4MnO3薄膜。通过XRD、高分辨TEM和电子衍射分析，我们成功地获得了在STO衬底上生长LCMO薄膜的初步结果。分析结果表明，双畴外延生长与钙钛矿结构密切相关。由于衬底与薄膜之间的晶格不匹配，在界面上形成错配位错。为了优化这种CMR薄膜，重要的是获得关于错配位错对界面结构和局部化学计量的影响的更详细的信息，以及关于薄膜中的La/Ca/Mn和空位分布的信息。校正了像差的Daresbury SuperSTEM可以获得原子柱空间分辨率的信息。在不同材料系统的试点研究中，即缺氧的La/Ca钴酸盐（通过上述方法生长），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的结合使用可以实现：这使我们能够识别出两种类型的平面断层（“Brownmillerite”和“Ruddleston-Popper”缺陷），其中一种由有序的o空位平面组成，另一种由1/2单元宽的岩盐构造域组成，断层中Ca富集较强。这些都是前所未有的测量结果，如果没有SuperSTEM是不可能获得这些数据的。

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.