Measurement of the chemical composition of nanostructures by quantification of Z-contrast in scanning-transmission electron microscopy

通过扫描透射电子显微镜中 Z 对比度的量化来测量纳米结构的化学成分

• 批准号: 134655250
• 负责人: Professor Dr. Andreas Rosenauer
• 金额: --
• 依托单位: Institut für Festkörperphysik (IFP)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2009
• 资助国家: 德国
• 起止时间: 2008-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/134655250?language=en
• 关键词: Measurement; chemical; composition; nanostructures; quantification

In project we developed a method to precisely analyse the chemical composition in a sample using scanning-transmission electron microscopy (STEM). The method wich is based on a direct comparsion of the experimental high-angle annular dark field (HAADF) intensity with simulations was already applied to many different materials.So far, the intensity was measured by integrating the scattered intensity over a certain angular range which is defined by the camera length and the geometry of the detector. In this renewal proposal we aim at a measurement of STEM intensity as a function of the scattering angle. The angle-dependence of the scattered intensity is not only influenced by the chemical concentration but also by the type of the scattering process (e.g. thermal-diffuse scattering or scattering at static atomic displacements) and by distortions of the crystal lattice. Therefore, the scattering intensity measured with selected detection angles contains additional information which allows for measuring two or more experimental parameters (e.g. thickness and chemical concentration) at the same time. For this purpose we suggest to install a motor-driven diaphragm directly above the HAADF detector in the microscope.The new method will be able to measure the local chemical concentration of a single element (e.g. In in InGaN) and the local specimen thickness or the local chemical concentrations of two elements (e.g. In and Al in InAlGaN) at the same time. Our priliminary studies using a prototype diaphragm show that our method allows for either making strain fields visible or performing quantitative chemical analyses without strain-induced artifacts. The studies further show a difference in the angle-dependend intensity distribution between experiment and simulation at angles smaller than 40 mrad. A main topic of this proposal is the quantification of the small-angle scattering intensity, which includes the investigation of plasmon scattering and its implementation into our simulation software using different apporaches.The method will contribute to various cooperations and projects by its application to investigate quantum dots, quaternary layers, segregation effects, nano particles of non-homogeneous composition, nano-pourous gold and SiGe MOSFETs. Thus, the project will significantly contribute to the understanding of semiconductor nanostructures and catalysists by the suggested method.

在项目中，我们开发了一种使用扫描透射电子显微镜 (STEM) 精确分析样品中化学成分的方法。该方法基于实验高角度环形暗场 (HAADF) 强度与模拟的直接比较，已应用于许多不同的材料。到目前为止，强度是通过对一定角度范围内的散射强度进行积分来测量的，由相机长度和探测器的几何形状定义。在这个更新提案中，我们的目标是测量 STEM 强度作为散射角的函数。散射强度的角度依赖性不仅受到化学浓度的影响，而且还受到散射过程类型（例如热扩散散射或静态原子位移处的散射）以及晶格畸变的影响。因此，用选定的检测角度测量的散射强度包含附加信息，允许同时测量两个或多个实验参数（例如厚度和化学浓度）。为此，我们建议在显微镜中的 HAADF 探测器正上方安装一个电机驱动隔膜。新方法将能够测量单个元素（例如 InGaN 中的 In）的局部化学浓度以及局部样本厚度或同时计算两种元素（例如 InAlGaN 中的 In 和 Al）的局部化学浓度。我们使用原型隔膜进行的初步研究表明，我们的方法可以使应变场可见或进行定量化学分析，而不会产生应变引起的伪影。研究进一步表明，在角度小于 40 mrad 时，实验与模拟之间的角度相关强度分布存在差异。该提案的一个主要主题是小角度散射强度的量化，其中包括等离子体激元散射的研究及其使用不同方法在我们的模拟软件中的实现。该方法将通过其应用来研究量子点、四元层、偏析效应、非均匀成分的纳米颗粒、纳米多孔金和 SiGe MOSFET。因此，该项目将通过建议的方法极大地促进对半导体纳米结构和催化剂的理解。