Wang Yan, Zhang Wei
Key Laboratory of Mobile Materials MOE, and School of Materials Science & Engineering, and Electron Microscopy Center, Jilin University, Changchun, 130012, China.
Key Laboratory of Mobile Materials MOE, and School of Materials Science & Engineering, and Electron Microscopy Center, Jilin University, Changchun, 130012, China; Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, 430074, China.
Micron. 2019 Oct;125:102715. doi: 10.1016/j.micron.2019.102715. Epub 2019 Jul 23.
Strain variation within a nanoparticle plays a crucial role in tuning its properties. Geometrical phase analysis (GPA) is typically a powerful tool to investigate the strain in high-resolution transmission electron microscopy (HRTEM) images. It is known that the traditional GPA method measuring the displacement of lattice fringes directly in an HRTEM image is inapplicable to strain measurements on nanoparticles embedded in a matrix, where lattice fringes of nanoparticles are invisible, instead Moiré fringes are present. Furthermore, considering the small size of embedded nanoparticles, generally a few nanometers, no reference region can be chosen and utilized to calculate the relative displacement by GPA. Hence advanced methods need to be developed to break through the barriers of invisible lattice fringes and lack of a reference region. In this work, using α-Fe nanoparticles embedded in sapphire as a test object, we illustrate a GPA method dedicated to embedded nanoparticles. Both the Fourier filter method and the inverse Moiré fringes method were used to reconstruct the invisible lattice fringes of α-Fe nanoparticles. Then a computer-generated image corresponding to an unstrained α-Fe lattice was used as the reference during GPA. The GPA results indicate that there exists a compressive strain in the range of 1.5˜2% within the α-Fe nanoparticles. Our work presents an effective approach to revealing the strain distributions within embedded nanoparticles.
纳米颗粒内部的应变变化在调节其性能方面起着至关重要的作用。几何相位分析（GPA）通常是在高分辨率透射电子显微镜（HRTEM）图像中研究应变的有力工具。众所周知，传统的GPA方法是直接在HRTEM图像中测量晶格条纹的位移，这种方法不适用于测量嵌入基质中的纳米颗粒的应变，因为在这种情况下纳米颗粒的晶格条纹不可见，而是出现了莫尔条纹。此外，考虑到嵌入的纳米颗粒尺寸很小，通常只有几纳米，无法选择参考区域并利用GPA来计算相对位移。因此，需要开发先进的方法来突破不可见晶格条纹和缺乏参考区域的障碍。在这项工作中，我们以嵌入蓝宝石中的α-Fe纳米颗粒为测试对象，展示了一种专门用于嵌入纳米颗粒的GPA方法。我们使用傅里叶滤波法和逆莫尔条纹法重建了α-Fe纳米颗粒不可见的晶格条纹。然后，在GPA过程中，将对应于无应变α-Fe晶格的计算机生成图像用作参考。GPA结果表明，α-Fe纳米颗粒内部存在1.5%至2%的压缩应变。我们的工作提出了一种揭示嵌入纳米颗粒内部应变分布的有效方法。
