Zhao Yao, Yang Yang, Wen Huihui, Liu Chao, Huang Xianfu, Liu Zhanwei
School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China.
AECC Beijing Institute of Aeronautical Materials, Beijing 100190, China.
Phys Chem Chem Phys. 2022 May 4;24(17):9848-9854. doi: 10.1039/d1cp05891f.
STEM nano-moiré can achieve high-precision deformation measurement in a large field of view. In scanning moiré fringe technology, the scanning line and magnification of the existing transmission electron microscope (TEM) cannot be changed continuously. The frequency of the crystal lattice is often difficult to match with the fixed frequency of the scanning line, resulting in mostly too dense fringes that cannot be directly observed; thus, the calculation error is relatively large. This problem exists in both the STEM moiré method and the multiplication moiré method. Herein, we propose the STEM secondary nano-moiré method, , a digital grating of similar frequency is superimposed on or sampling the primary moiré fringe or multiplication moiré to form the secondary moiré. The formation principle of the secondary moiré is analyzed in detail, with deduced theoretical relations for measuring the strain of STEM secondary nano-moiré fringe. The advantages of sampling secondary moiré and digital secondary moiré are compared. The optimal sampling interpolation function is obtained through error analysis. This method expands the application range of the STEM moiré method and has better practicability. Finally, the STEM secondary nano-moiré is used to accurately measure the strain field at the Si/Ge heterostructure interface, and the theoretical strain field calculated by the dislocation model is analyzed and compared. The obtained results are more compatible with the P-N dislocation model. Our work provides a practical method for the accurate evaluation of the interface characteristics of heterostructures, which is an important basis for judging the photoelectric performance of the entire device and the optimal design of the heterostructures.
扫描透射电子显微镜（STEM）纳米莫尔条纹能够在大视场下实现高精度变形测量。在扫描莫尔条纹技术中，现有透射电子显微镜（TEM）的扫描线和放大倍数无法连续变化。晶格频率往往难以与扫描线的固定频率匹配，导致条纹大多过于密集而无法直接观察；因此，计算误差相对较大。STEM莫尔条纹法和乘法莫尔条纹法都存在这个问题。在此，我们提出了STEM二次纳米莫尔条纹法，即将频率相近的数字光栅叠加在一次莫尔条纹或乘法莫尔条纹上，或者对其进行采样以形成二次莫尔条纹。详细分析了二次莫尔条纹的形成原理，推导了测量STEM二次纳米莫尔条纹应变的理论关系。比较了采样二次莫尔条纹和数字二次莫尔条纹的优点。通过误差分析获得了最佳采样插值函数。该方法扩展了STEM莫尔条纹法的应用范围，具有更好的实用性。最后，利用STEM二次纳米莫尔条纹准确测量了Si/Ge异质结构界面处的应变场，并对由位错模型计算得到的理论应变场进行了分析和比较。所得结果与P - N位错模型更为吻合。我们的工作为准确评估异质结构的界面特性提供了一种实用方法，这是判断整个器件光电性能以及异质结构优化设计的重要依据。
