二维材料的定量电子衍射及电子显微镜中的自动化数据处理

发布时间：2018-11-28 07:08

【摘要】：纳米科学自上世纪被提出以来已经取得了丰硕的成果,这离不开电子显微镜技术的不断发展。近年来,二维材料因为其新奇的物理特性而得到研究者们广泛的关注,本课题以二维材料为切入点,围绕定量电子显微镜学完成了两部分工作。第一部分:层厚对于二维材料的物理性质有着重要影响,尤其是单原子层厚的二维材料,我们提出了一种定量电子衍射的方法,确定了单原子层厚的二硒化铼及其在垂直方向上的晶体学取向,这对于各向异性的器件的表征也有重要影响;第二部分:原子级分辨的电子显微图像能提供原子尺度上的微观信息,但是缺乏在相对宏观尺度上的统计信息,为了能够高效和准确地分析这两个不同尺度上的信息,我们开发了一套图像处理程序,基于数据科学中的工具,实现了自动化地统计原子级分辨图像中原子的分布情况,最后得到原子局域晶体学环境的信息。在目前对层状二维材料的研究中,与石墨烯,六方氮化硼和二硫化钼等六方结构材料相比,低对称性二维材料在各向异性器件中的应用中显示出了巨大的潜力。体相的二硒化铼属于空间群P1,是畸变的碘化镉结构,即低对称性的三斜晶系。这里我们提出了一种基于定量电子衍射的方法,用来区分二硒化铼的单层与多层,同时还确定了单层的两种不同垂直取向。从我们的原理出发,该方法也可以应用于其他低对称性晶系,包括三斜晶系和单斜晶系,只要它们满足单胞的第三个基矢量不垂直于它们的基底平面。我们从实验结果上,很好地印证了运动学电子衍射理论和多层法模拟的推断。最后,我们讨论了该方法对其他二维材料的推广,例如石墨烯。随着电子显微镜成像技术的不断发展,分辨率的不断提升,原子尺度的结构和功能数据的采集越来越普遍。这些数据为我们提供了丰富的信息,例如功能表征中应用的高维度的谱学数据和结构表征中原子的位置、种类、排列等信息,为了分析这些复杂和海量的数据,数据科学将在后期实验数据分析中发挥越来越重要的作用。原子级分辨的扫描透射电子显微镜直接反映了二维材料的原子结构信息,特别适合用来表征掺杂的过渡族金属硫族化合物,为了从图像中高效地提取信息,我们开发了一套图像处理程序,用来确定合金化二维材料中的原子位置和种类,并在此基础上分析原子的局域环境,并计算合金化程度。
[Abstract]:Nano-science has made great achievements since it was put forward in the last century, which can not be separated from the development of electron microscope technology. In recent years, two-dimensional materials have been widely concerned by researchers because of their novel physical properties. In this paper, two parts of work have been completed by using two-dimensional materials as a breakthrough point and focusing on quantitative electron microscopy (QEM). The first part: layer thickness has an important influence on the physical properties of two-dimensional materials, especially for two-dimensional materials with single atomic layer thickness. We propose a method of quantitative electron diffraction. The uniatomic layer thickness of rhenium diselenide and its crystallographic orientation in the vertical direction are determined, which also has an important effect on the characterization of anisotropic devices. Part two: atomic resolution electron microscopy images can provide microcosmic information on atomic scale, but lack statistical information on relative macro scale, in order to efficiently and accurately analyze the information on these two different scales. We have developed a set of image processing programs. Based on the tools in data science, we have realized the automatic statistics of the atomic distribution in the atom-level resolution image. Finally, we have obtained the information of the atomic local crystallographic environment. Compared with hexagonal materials such as graphene, hexagonal boron nitride and molybdenum disulfide, the application of low symmetry two-dimensional materials in anisotropic devices shows great potential. The bulk rhenium diselenide belongs to the space group P _ 1, which is a distorted structure of cadmium iodide, that is, a low symmetry triclinic crystal system. A method based on quantitative electron diffraction is proposed to distinguish the monolayer and multilayer of rhenium diselenide, and two different vertical orientations of monolayer are also determined. Based on our principle, the method can also be applied to other low symmetry crystal systems, including triclinic and monoclinic systems, as long as they satisfy the third basis vector of the unit cell and are not perpendicular to their base plane. From the experimental results, the theory of kinematic electron diffraction and the inference of multilayer simulation are well confirmed. Finally, we discuss the extension of this method to other two-dimensional materials, such as graphene. With the development of electron microscope imaging technology and the improvement of resolution, the acquisition of atomic scale structure and function data is becoming more and more common. These data provide us with a wealth of information, such as high-dimensional spectroscopic data used in functional representations and information on atomic positions, types, arrangements in structural representations, in order to analyze these complex and massive data. Data science will play a more and more important role in experimental data analysis. Atomic resolved scanning transmission electron microscopy (SEM) directly reflects the atomic structure information of two-dimensional materials and is especially suitable for characterization of doped transition metal sulfur compounds in order to extract information efficiently from images. We have developed a set of image processing programs to determine the position and category of atoms in alloyed two-dimensional materials, and on this basis to analyze the local environment of atoms and to calculate the alloying degree.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1

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