Electronic structure of energy materials

材料的电子结构是可再生能源的基础。例如，价带/导带的带隙和排列决定光伏性能。只有少数实验技术可以测量电子结构，例如扫描隧道光谱学，角分辨光电子能谱学和电子-正电子湮灭。这些方法有几个缺点，例如需要高质量的单晶样品、放射源和有限的空间分辨率。开发新能源材料需要适用于薄膜和多晶材料的通用表征方法。 我的小组最近在TEM中开发了电子康普顿散射（Talmantaite等人，J Microscopy 2019，Mendis和Talmantaite，Microsc. Microanal，in press）.它测量电子态的动量密度分布。我们已经成功地使用康普顿散射来分析二维材料的带隙跃迁和金属-绝缘体相变。本计画将利用康普顿散射及上级透射电子显微镜的空间解析度来分析能源材料中的一些基本电子结构问题，例如光伏中界面及晶界的带隙分级及电子结构，以及发光二极管中的量子威尔斯。这是一个独特的机会，让学生开拓一套新的分析技术，具有广泛的用途。学生将获得先进的电子显微镜和DFT模拟的技能，并接触到外部合作者（利物浦和剑桥）提供的几种不同的能源材料和设备（PV，LED）。由于该方法的多功能性，还可以用于其他ReNU项目，例如电池材料。

Electronic structure of materials is fundamental to renewable energy. For example, the band gap and alignment of valence/conduction bands govern photovoltaic performance. There are only a handful of experimental techniques that measure electronic structure, such as scanning tunnelling spectroscopy, angle resolved photoemission spectroscopy and electron-positron annihilation. These have several drawbacks, such as the need for high quality single crystal samples, radioactive sources and limited spatial resolution. Developing new energy materials requires versatile characterisation methods that are applicable in both thin-film and polycrystalline material. My group has recently developed electron Compton scattering in the TEM (Talmantaite et al, J Microscopy 2019, Mendis and Talmantaite, Microsc. Microanal, in press). This measures the momentum density distribution of electronic states. We have successfully used Compton scattering to analyse band gap transitions in 2D materials and metal-insulator phase changes. This project will exploit Compton scattering and the superior TEM spatial resolution to analyse some fundamental electronic structure problems in energy materials, such as band gap grading and electronic structure of interfaces and grain boundaries in PV, as well as quantum wells in LEDs. This is a unique opportunity for a student to pioneer a new set of analytical techniques that has widespread use. The student will gain skills in advanced electron microscopy and DFT simulations, and be exposed to several different energy materials and devices (PV, LED) provided by external collaborators (Liverpool and Cambridge). Due to the versatility of the method there is also scope to work on other ReNU projects, e.g. battery materials.