Three-dimensional visualization of dislocations in a ferromagnetic material by magnetic-field-free electron tomography
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Three-dimensional visualization of dislocations in a ferromagnetic material by magnetic-field-free electron tomography

机译：通过无磁场电子断层扫描的铁磁材料中位错的三维可视化

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Highlights?Low-Mag STEM imaging with a spherical aberration correction for electron tomography observation of ferromagnetic materials.?Electron channeling contrast imaging in STEM-LAADF to achieve sharp and clear dislocation strain contrast.?3D visualization of dislocations in α-Fe.AbstractIn conventional transmission electron microscopy, specimens to be observed are placed in between the objective lens pole piece and therefore exposed to a strong magnetic field about 2?T. For a ferromagnetic specimen, magnetization of the specimen causes isotropic and anisotropic defocusing, deflection of the electron beam as well as deformation of the specimen, which all become more severe when the specimen tilted. Therefore electron tomography on a ferromagnetic crystalline specimen is highly challenging because tilt-series data sets must be acquired without changing the excitation condition of a specific diffraction spot. In this study, a scanning transmission electron microscopy (STEM) tomography method without magnetizing a ferromagnetic specimen has been developed for three-dimensional (3D) visualization of dislocations in α-Fe, which is a typical ferromagnetic material. Magnetic-field-free environment down to 0.38?±?0.07?mT at the specimen position is realized by demagnetizing the objective lens pole piece of a commercial STEM instrument. By using a spherical aberration corrector with the magnetic-field-free environment, an “aberration corrected Low-Mag STEM mode” with no objective lens field reaches a convergence semi angle ～1?mrad and a spatial resolution ～5?nm, and shows an adequate performance of imaging dislocations under a two-beam excitation condition for a low-index diffracted beam. The illumination condition for the aberration corrected Low-Mag STEM mode gives no overlap between the direct beam disk (spot) and neighboring diffraction disks. An electron channeling contrast imaging technique, in which an annular detector was located at a doughnut area between the direct beam and the neighboring diffracted beams, was effectively employed with the aberration corrected Low-Mag STEM mode to keep image intensity high enough even at large specimen-tilt angles. The resultant tomographic observation visualized 3D dislocation arrangements and active slip planes in a deformed α-Fe specimen.]]>
机译：<！[cdata [ 突出显示 ？ 低mar step成像，具有用于电子断层摄影术的球面像差校正的铁磁材料。 ？ 茎Laadf中的电子信道对比度成像实现尖锐和明确的错位应变对比度。 ？ α-fe脱位的3D可视化。 < / ce：抽象 - 秒> 抽象 在传统的透射电子显微镜中，要观察的样品被放置在物镜杆杆之间，因此暴露于强磁场2？t。对于铁磁性试样，样品的磁化导致各向同性和各向异性散焦，电子束的偏转以及样本的变形，当样品倾斜时，所有变得更加严重。因此，铁磁晶体标本上的电子断层扫描具有高度挑战，因为必须在不改变特定衍射点的激励条件的情况下获得倾斜序列数据集。在该研究中，已经开发了一种扫描透射电子显微镜（茎）断层扫描方法，但是对于α-Fe的脱位的三维（3D）可视化已经开发了α-Fe的脱位，这是典型的铁磁性材料。通过将商业干燥仪器的物镜极杆块退磁来实现磁场场位置下降至0.38Ω·λ±0.07μmt。通过使用具有磁场环境的球面像差校正器，没有物镜场的“像差校正的低音杆模式”达到了趋同半角〜1？MRAD和空间分辨率〜5？NM，并显示在双光束激发条件下对低折射率衍射光束的成像脱位进行成像的足够性能。像差校正的低MAT杆模式的照明条件在直接梁盘（点）和相邻的衍射盘之间没有重叠。电子通道对比度成像技术，其中环形检测器位于直接梁和相邻衍射梁之间的甜甜圈区域，有效地采用了像差校正的低MAT杆模式，使图像强度甚至在大型标本中保持高度-ttilt角度。所得到的断层观察可视化3D位错布置和在变形的α-Fe标本中的主动滑坡。 ]]>

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