高分辨率透射电子显微镜(HRTEM或HREM)是相衬(高分辨率的电子显微镜图像的对比度是由合成的投射波和衍射波之间的相位差形成的,称为相衬)。给出大多数晶体材料的原子排列。
High-resolution transmission electron microscopy began in the 1950s. In 1956, JWMenter directly observed parallel strips of 12 Å copper phthalocyanine with a resolution of 8 Å transmission electron microscope, and opened high-resolution electron microscopy. The door to surgery. In the early 1970s, in 1971, Iijima Chengman used a TEM with a resolution of 3.5 Å to capture the phase contrast image of Ti2Nb10O29, and directly observed the projection of the atomic group along the incident electron beam. At the same time, the research on high resolution image imaging theory and analysis technology has also made important progress. In the 1970s and 1980s, the electron microscope technology was continuously improved, and the resolution was greatly improved. Generally, the large TEM has been able to guarantee a crystal resolution of 1.44 Å and a dot resolution of 2 to 3 Å. HRTEM can not only observe the lattice fringe image reflecting the interplanar spacing, but also observe the structural image of the atom or group arrangement in the reaction crystal structure. Recently, Professor David A. Muller’s team at Cornell University in the United States used laminated imaging technology and an independently developed electron microscope pixel array detector to achieve a spatial resolution of 0.39 Å under low electron beam energy imaging conditions.
当前,透射电子显微镜通常能够执行HRTEM。这些透射电子显微镜分为两种:高分辨率和分析型。高分辨率TEM配有高分辨率的物镜极靴和光阑组合,使样品台的倾斜角较小,从而减小了物镜的球差系数;而分析型TEM需要大量进行各种分析。样品台的倾斜角度,因此物镜极靴的使用与高分辨率类型不同,从而影响了分辨率。通常,200 kev的高分辨率TEM的分辨率为1.9Å,而200 kev的分析TEM的分辨率为2.3Å。但这不影响解析TEM拍摄高分辨率图像。

As shown in Fig. 1, the optical path diagram of the high-resolution electron microscopy imaging process, when an electron beam with a certain wavelength (λ) is incident on a crystal with a crystal plane spacing d, the Bragg condition (2dsin θ = λ) is satisfied, A diffracted wave is generated at an angle (2θ). This diffracted wave converges on the back focal plane of the objective lens to form a diffraction spot (in an electron microscope, a regular diffraction spot formed on the back focal plane is projected onto the phosphor screen, which is a so-called electron diffraction pattern). When the diffracted wave on the back focal plane continues to move forward, the diffracted wave is synthesized, an enlarged image (electron microscopic image) is formed on the image plane, and two or more large objective lens pupils can be inserted on the back focal plane. Wave interference imaging, called high-resolution electron microscopy, is called a high-resolution electron microscopic image (high-resolution microscopic image).
如上所述,高分辨率电子显微图像是由于物镜的相位相干性而使物镜的焦平面的透射光束和若干衍射束通过物镜而形成的相衬显微图像。由于参与成像的衍射束的数量不同,因此获得了不同名称的高分辨率图像。由于不同的衍射条件和样品厚度,具有不同结构信息的高分辨率电子显微照片可分为五类:晶格条纹,一维结构图像,二维晶格图像(单细胞图像),二维结构图像(原子尺度图像:晶体结构图像),特殊图像。
格子条纹:如果通过物镜选择了后焦平面上的透射光束,并且衍射光束相互干扰,则会获得强度周期性变化的一维条纹图案(如图中的黑色三角形所示)图2(f))这是晶格条纹与晶格图像和结构图像之间的差异,它不需要电子束与晶格平面完全平行。实际上,在观察微晶,析出物等时,经常通过投射波和衍射波之间的干涉而获得晶格条纹。如果拍摄诸如微晶之类的物质的电子衍射图,则会出现如图2(a)所示的礼拜环。

一维结构图:如果样品具有一定的倾斜度,使得电子束平行于晶体的某个晶面入射,则可以满足图2(b)所示的一维衍射衍射图样(相对于透射光点的对称分布)(衍射图样)。在该衍射图案中,在最佳聚焦条件下拍摄的高分辨率图像不同于晶格条纹,并且一维结构图像包含晶体结构信息,即所获得的一维结构图像,如图所示。在图3中(示出了Bi基超导氧化物的高分辨率一维结构图像。
Two-dimensional lattice image: If the electron beam is incident parallel to a certain crystal ribbon axis, a two-dimensional diffraction pattern can be obtained (two-dimensional symmetric distribution with respect to the central transmission spot, shown in Fig. 2(c)). For such an electron diffraction pattern. In the vicinity of the transmission spot, a diffraction wave reflecting the crystal unit cell appears. In the two-dimensional image generated by the interference between the diffracted wave and the transmitted wave, a two-dimensional lattice image showing the unit cell can be observed, and this image contains information on the unit cell scale. However, information that does not contain an atomic scale (into atomic arrangement), that is, a two-dimensional lattice image is a two-dimensional lattice image of single crystal silicon as shown in Fig. 3(d).
Two-dimensional structure image: A diffraction pattern as shown in Fig. 2(d) is obtained. When a high-resolution electron microscope image is observed with such a diffraction pattern, the more diffraction waves involved in imaging, the information contained in the high-resolution image is also The more. A high-resolution two-dimensional structure image of the Tl2Ba2CuO6 superconducting oxide is shown in Fig. 3(e). However, the diffraction of the high-wavelength side with higher resolution limit of the electron microscope is unlikely to participate in the imaging of the correct structure information, and becomes the background. Therefore, within the range allowed by the resolution. By imaging with as many diffracted waves as possible, it is possible to obtain an image containing the correct information of the arrangement of atoms within the unit cell. The structure image can only be observed in a thin region excited by the proportional relationship between the wave participating in imaging and the thickness of the sample.

特殊图像:在后焦平面的衍射图上,光圈的插入仅选择特定的波成像即可观察特定结构信息的对比度图像。一个典型的例子是有序结构。相应的电子衍射图显示在图2(e)中,作为Au,Cd有序合金的电子衍射图。有序结构基于其中Cd原子按顺序排列的面心立方结构。图2(e)的电子衍射图谱很弱,除了指数(020)和(008)的基本晶格反射。有序晶格反射,使用物镜提取基本晶格反射,使用透射波和有序晶格反射成像,只有Cd原子具有亮点或暗点,例如高分辨率,如图4所示。

如图4所示,所示的高分辨率图像随着样品的厚度在最佳高分辨率欠聚焦附近而变化。因此,当我们获得高分辨率图像时,我们不能简单地说出高分辨率图像是什么。我们必须首先进行计算机模拟,以计算不同厚度下材料的结构。物质的高分辨率图像。将计算机计算出的一系列高分辨率图像与通过实验获得的高分辨率图像进行比较,以确定通过实验获得的高分辨率图像。将图5所示的计算机模拟图像与通过实验获得的高分辨率图像进行比较。
This article is organized by the material person column technology consultant.

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