Bekarevich Raman, Mitsuishi Kazutaka, Ohnishi Tsuyoshi, Uesugi Fumihiko, Takeguchi Masaki, Inaguma Yoshiyuki, Ohno Takahisa, Takada Kazunori
Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Materials Science, 1-1, Namiki, Tsukuba, Ibaraki305-0044, Japan.
Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Materials Science, 1-1, Namiki, Tsukuba, Ibaraki 305-0044, Japan.
Microscopy (Oxf). 2018 Mar 1;67(suppl_1):i142-i149. doi: 10.1093/jmicro/dfx121.
Unlike X-ray diffraction or Raman techniques, which suffer from low spatial resolution, transmission electron microscopy can be used to obtain strain maps of nanoscaled materials and devices. Convergent-beam electron diffraction (CBED) and nanobeam electron diffraction (NBED) techniques detect the deviation of a lattice constant (i.e. an indicator of strain) within 0.01%; however, their use is restricted to beam-insensitive samples. Selected-area electron diffraction (SAED) does not have such limitations but has low spatial resolution and precision. The use of a spherical aberration corrector and a nanosized selected-area aperture improves the spatial resolution, but the precision is still low. In this study, a two-dimensional stage-scanning system is used to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with iterative nonlinear least-squares fitting enabled the spot displacement for each point of the scan area to be measured with precision comparable to that of the CBED or NBED technique. The precise strain determination, in combination with the simplicity of the measurement process, makes the nanosized SAED technique competitive with other methods for strain mapping at nanoscale dimensions.
与X射线衍射或拉曼技术不同，这两种技术存在空间分辨率低的问题，而透射电子显微镜可用于获取纳米级材料和器件的应变图。会聚束电子衍射（CBED）和纳米束电子衍射（NBED）技术可检测晶格常数的偏差（即应变指标），偏差在0.01%以内；然而，它们的应用仅限于对电子束不敏感的样品。选区电子衍射（SAED）不存在此类限制，但空间分辨率和精度较低。使用球差校正器和纳米尺寸的选区光阑可提高空间分辨率，但精度仍然较低。在本研究中，使用二维样品台扫描系统在固定电子束条件下获取样品不同位置的衍射图案阵列。通过迭代非线性最小二乘法拟合进行数据处理，能够精确测量扫描区域每个点的斑点位移，其精度与CBED或NBED技术相当。精确的应变测定，再加上测量过程的简便性，使得纳米级SAED技术在纳米尺度应变映射方面与其他方法具有竞争力。
