Exploring the frontiers of electron ptychography

点击翻译按钮获取中文摘要

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.