Yamasaki Jun, Mutoh Michihiro, Ohta Shigemasa, Yuasa Syuichi, Arai Shigeo, Sasaki Katsuhiro, Tanaka Nobuo
Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
Microscopy (Oxf). 2014 Oct;63(5):345-55. doi: 10.1093/jmicro/dfu020. Epub 2014 Jun 2.
To obtain the correct tomographic reconstruction of micron-sized materials, the nonlinear intensity attenuation of bright-field transmission electron microscopy (BF-TEM) images was analyzed as a function of the sample thickness using a high-voltage electron microscope. The intensity attenuation was precisely measured relative to the projection thickness of carbon microcoils (CMCs) at acceleration voltages of 400-1000 kV using objective apertures (OAs) with radii of 2.1-28 nm(-1). The results show that the nonlinearity is strongly dependent on the OA size and the acceleration voltage. The influence of nonlinearity on tomographic reconstructions was also examined using a specially developed 360°-tilt sample holder. Sliced images of the reconstructed volumes indicated that an increase in the nonlinearity caused artificial fluctuations in the internal density of materials and inaccurate shapes of the objects in more significant cases. Conditions sufficient for reconstruction with the correct density have been estimated to be 0.67 of the minimum electron transmittance, and for reconstructions with correct shapes, 0.4. This information enables foreseeing the quality of the reconstruction from a single BF-TEM image prior to the tilt-series acquisition. As a result to demonstrate the appropriateness of these conditions, a CMC with a diameter of 3.7 µm was reconstructed successfully; i.e. not only the shape but also the internal density were correctly reproduced using electron tomography.
为了获得微米级材料的正确断层图像重建，使用高压电子显微镜分析了明场透射电子显微镜（BF-TEM）图像的非线性强度衰减与样品厚度的函数关系。在400-1000 kV的加速电压下，使用半径为2.1-28 nm⁻¹的物镜光阑（OA），相对于碳微线圈（CMC）的投影厚度精确测量强度衰减。结果表明，非线性强烈依赖于物镜光阑尺寸和加速电压。还使用专门开发的360°倾斜样品架研究了非线性对断层图像重建的影响。重建体积的切片图像表明，在更显著的情况下，非线性增加会导致材料内部密度出现人为波动以及物体形状不准确。据估计，对于具有正确密度的重建，足够的条件是最小电子透射率的0.67，对于具有正确形状的重建，是0.4。此信息能够在倾斜系列采集之前从单个BF-TEM图像预测重建质量。作为证明这些条件适用性的结果，成功重建了直径为3.7 µm的CMC；也就是说，使用电子断层扫描不仅正确再现了形状，还正确再现了内部密度。
