Kossel-Möllenstedt衍射花样特征及薄晶体厚度测定

Kossel-Möllenstedt衍射花样特征及薄晶体厚度测定

娄艳芝

(中国航发北京航空材料研究院，北京100095)

摘  要  本文利用会聚束电子衍射(CBED)技术测定了晶体Si的局部厚度和消光距离ξ，讨论了关键参数n₁取不同值时的数据特点及对分析结果的影响规律，明确了n₁的确定方法，总结了Kossel-Möllenstedt（K-M）衍射花样特征及影响因素，给出了Si晶体(400)晶面K-M衍射花样的暗纹暗条纹位置预测图。结论如下：当n₁<真值时，在数据点较少(≤5)的情况下，数据近似符合直线关系且拟合直线斜率为正；当n₁=真值时，拟合直线斜率为负；当n₁>真值时，在数据点较少(≤5)的情况下，数据近似符合直线关系且拟合直线斜率为负，数据点较多时，远离衍射盘中心的数据会落在拟合直线的上方；如果n₁的取值偏大，会导致消光距离的分析结果偏小，同时试样厚度的分析结果偏大；加速电压的差异会影响K-M花样的衬度；K-M花样暗条纹之间的距离随着距离衍射盘中心距离的增大而逐渐减小；第一暗条纹距衍射盘中心的距离Δθ₁和第一暗条纹对应的n₁值均与消光距离ξ和试样厚度t有关。

关键词 透射电子显微术；会聚束电子衍射；Kossel-Möllenstedt（K-M）衍射花样；薄晶体厚度；消光距离

中图分类号：TB303；TG115.21⁺5.3   文献标识码：A   doi:10.3969/j.issn.1000-6281.2021.03.004

Characteristics of Kossel-Möllenstedtdiffraction pattern and measurement of thin crystal thickness

LOU Yan-zhi

(AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China)

Abstract  In this paper, the siliconSi crystal thickness and extinction distance were are determined by the method of convergent-beam electron diffraction (CBED) at electron beam energy of 200kV. At the same time,and the influence ofthe order of the first dark stripe nearest to the center of the diffraction disk, i.e. the value of n_1, value on the analysis results is discussed. The extinction distance and thin foil thickness t is are analyzed and the determination method of n₁value is defined. In addition, the characteristics of K-M diffraction patterns are summarized, and the influence of accelerating voltage and sample thickness on K-M diffraction patterns is discussed.The results show that if the value of n₁ is smaller than the true value, the data approximately conforms to the linear relationship and the slope of the fitting line is positive when the number of measured data points is less than 5.If n₁is equal to the true value, the slope of the fitting line is negative. If the value of n₁ is larger than the true value, the data approximately conforms to the linear relationship and the slope of the fitting line is negative when the number of measured datapoints is less than 5.If the value of n₁ is larger than the true value,the data points corresponding to the dark stripe far away from the center of the diffraction disk will be concentrated above the fitting line.，and tThis characteristic can be used to determine the value of n₁. If the value of n₁ is larger greater than the true value, the larger the value of n₁is, the smaller the extinction distance and the larger the samplethickness. The value of the accelerating voltage will affect the contrast of theK-Mdiffraction patterns. In a K-Mdiffraction patterns, ，the distance between the dark strips decreases with the increase of the distance between the dark stripe and the center of the diffraction disk. The distance between the first dark stripe and the center of the diffraction disk is related to the extinction distance and the thickness of the sample. Finally, a model for predicting the position of dark stripeson K-Mdiffraction patterns of silicon crystal (400) plane is given at an electron beam energy of 200kV and itwhich can be used to predict the K-Mdiffraction patterns of other crystals or crystal planes.

Keywords   transmission electron microscopy；convergent-beam electron diffraction；Kossel-Möllenstedt（K-M）diffraction patterns；thin foil thickness；extinction distance

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