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Development of Crystal Structure Analysis due to Convergent-Beam Electron Diffraction

会聚束电子衍射晶体结构分析的发展

基本信息

批准号：
02402055
负责人：
TANAKA Michiyoshi
金额：
$ 18.94万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (A)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

This imaging plate (IP) has the following advantages for the detection of the election beam : (1) High sensitivity to small electron dose, (2) wide dynamic range, (3) linearity of sensitivity, (4) high precision digital images and (5) dry system. We have applied the IP to the convergent-beam electron diffraction (CBED) and obtained the following results.(a) It has been shown that the IP is effective to detect the symmetry of CBED patterns. As an example, very weak 200 and equivalent reflections of GaAs were recorded by the IP at the 001 incidence. These reflections all very important for the symmetry study of the material, and had not been recorded clearly by conventional photo films due to the back ground noise. The IP recording and successive image processing of the reflections enable us to reveal the symmetry formed by the 200 and equivalent reflections.(b) The symmetry of CBED patterns has been quantitatively examined for the first time. The symmetry of CBED pattern has been judged … More by human eyes but has not ever been studied quantitatively. Two reflections which are connected by a symmetry operation were compared. Intensity of one reflection is subtracted from that of the other and the value of R=ROO<SIGMA(I_1-I_2)^2/SIGMAI_1^2> is calculated. It was revealed that a CBED pattern of <111> Si, which is a typical example of good symmetry, showed a value of R<similar or equal>10 %. Human eyes recognize the breakdown of symmetry when CBED patterns which have a value of R beyond 20 %.(c) The displacement vector of a stacking fault can be determined by analyzing the intensity profiles of reflections appearing in CBED patterns. The IP is quite useful to record the intensities of profiles accurately. The displacement vectors of stacking faults in Si and TiO_2 could be reliably determined by applying IP.(d) One of the final goal of CBED is the crystal structure analysis, which requires precise intensity measurements. The IP is indispensable to develop the crystal structure analysis using CBED. Firstly, we tried to solve the crystal structure of the low temperature phase of SrTiO_3, or the rotation angle of the oxygen octahedron and the Debye-Waller factor. The computer analysis program using a nonlinear least-square method (SALS) was developed. Using the intensity data recorded by IP and the analysis program, the rotation angle of the oxygen octahedron was determined to be 1.12 <plus-minus> 0.04ﾟ. The value shows a good agreement with that obtained by the electron-spin resonance method. Secondary, the crystal structure of the intermediate phase of the hexagonal BaTiO_3, which had been remained unsolved, was determined under the guide of the result of the soft-mode analysis. These results strongly promise the success of the crystal structure analysis of a small specimen area using CBED. Less

这种成像板（IP）对电子束的探测具有以下优点：（1）对小剂量电子的灵敏度高，（2）动态范围宽，（3）灵敏度线性，（4）数字图像精度高，（5）系统干燥。我们将IP应用于会聚束电子衍射（CBED），得到了以下结果。(a)实验结果表明，该方法能有效地检测CBED图像的对称性。作为一个例子，非常弱的200和等效的反射GaAs记录的IP在001入射。这些反射对于研究材料的对称性都是非常重要的，但由于背景噪声的影响，传统的照相胶片不能清楚地记录这些反射。IP记录和连续的图像处理的反射，使我们能够揭示对称形成的200和等效的反射。(b)CBED图案的对称性已被首次定量检查。判断了CBED图的对称性 ...更多信息但从未被定量研究过。比较了由对称操作连接的两个反射。从一个反射的强度中减去另一个反射的强度，并计算R= R 00 <SIGMA（I_1-I_2）^2/SIGMAI_1^2>的值。结果表明，<111>作为良好对称性的典型实例的Si的CBED图案显示出R 10%的值<similar or equal>。当R值超过20%时，人眼可以识别对称性的破坏。(c)层错的位移矢量可以通过分析CBED图中出现的反射光的强度分布来确定。IP是非常有用的，以准确地记录剖面的强度。用激电方法可以可靠地测定Si和TiO_2中层错的位移矢量。(d)CBED的最终目标之一是晶体结构分析，这需要精确的强度测量。IP是发展CBED晶体结构分析不可缺少的基础。首先，我们尝试求解SrTiO_3低温相的晶体结构，即氧八面体的旋转角和德拜-沃勒因子。采用非线性最小二乘法（SALS）的计算机分析程序开发。利用IP记录的强度数据和分析程序，确定氧八面体的旋转角为1.12 <plus-minus>± 0.04 °。该值与电子自旋共振法所得结果吻合较好。其次，在软模分析结果的指导下，确定了六方BaTiO_3中未溶解的中间相的晶体结构。这些结果有力地保证了使用CBED的小样品区域的晶体结构分析的成功。少