Exploring the frontiers of electron ptychography

电子平版印刷术正在成为一种重要的新成像工具，它可以提高光元素的图像对比度，降低辐射敏感材料的剂量，能够校正光学系统中的缺陷，并能够检索3D信息。这项技术已经被用于一系列材料应用，很可能是我们进行材料原子分辨率表征的方式的一场革命。这个项目的目的是探索这项技术可以推进到什么程度，以及如何对材料进行新的测量。大体上，可以用两种不同的配置进行层析。样品可以用会聚的光束照射，然后在样品上扫描。使用快速相机记录每个照明位置的衍射图，以形成4D数据集。或者，平行照明光束可以倾斜，并在常规的瞬变显微镜中记录一系列图像。该项目的一个特别重点是确定在低电子辐照剂量(通量)下可以进行的测量的精确度。许多与能量转换和存储相关的材料，如催化剂、有机-无机混合光伏材料和电池材料，在电子辐照下会迅速降解。层析成像固有的降噪特性使其非常适合于研究此类材料。由于降噪在互易空间中不是均匀的，图像表现出相关的噪声效应。这种相关噪声对测量的影响以前没有被考虑过，这里将讨论它。这项工作的一个重要部分将是开发方法，允许将成像数据反演为材料的有意义的测量，如键长和由于成键而可能产生的电荷重新分布。一个特别的焦点将是2D材料中的掺杂剂和其他缺陷的影响，如石墨烯、六边形氮化硼和过渡金属二卤化物。然后，该项目将转移到更强散射的样品上，如过渡金属氧化物。这项工作与研究基础设施EPSRC的主题密切相关，因为它将允许使用先进的电子显微镜进行增强的测量，这是英国研究基础设施的一部分。将使用材料系和哈维尔钻石光源的领先电子显微镜。它还创造了可以应用于能源主题中的材料的方法，更广泛地说，这项工作符合物理科学主题。

Electron ptychography is emerging as an important new imaging tool allowing greater image contrast of light elements, lower doses for radiation sensitive materials, the ability to correct for imperfections in the optics and the retrieval of 3D information. The technique is already being used for a range of materials applications and is likely to be revolution in the way we perform atomic resolution characterisation of materials. The aims of this project are to explore how far the technique can be pushed and how new measurements of materials can be made. Broadly, ptychography can be performed in two different configurations. The sample can be illuminated by a converged beam which is then scanned over the sample. Fast cameras are used to record diffraction patterns for each illuminating position, to form a 4D data set. Alternatively, a parallel illuminating beam can be tilted and a series of images recorded in a conventional TEM. A particular focus of this project is to determine the precision of measurements that can be made under low electron irradiation doses (fluences). Many materials associated with energy conversion and storage, such as catalysts, hybrid organic-inorganic photovoltaic materials and battery materials, degrade rapidly under electron irradiation. The inherent noise-reduction that occurs in ptychographic imaging makes it highly suitable for investigating such materials. Because the noise reduction is not uniform in reciprocal space, images show correlated noise effects. The effect of such correlated noise on measurements has not previously been considered, and will be addressed here. An important part of the work will be developing methods that allow inversion of the imaging data to meaningful measurements of materials such as bond-lengths and potentially charge redistribution due to bonding. A particular focus will be the effects of dopants and other defects in 2D materials such as graphene, hexagon boron nitride and transition metal dichalcogenides. The project will then move onto sample that scatter more strongly such as transition metal oxides.The work fits closely with the Research Infrastructure EPSRC theme as it will allow enhanced measurements to be made using advanced electron microscopes that form part of the UK research infrastructure. Leading electron microscopes in the Department of Materials and at the Diamond Light Source at Harwell will be used.It also creates methods that can be applied to materials within the Energy theme and more generally the work fits in the Physical Sciences theme.