Exploring low energy excitations with electron microscopy

在过去的几年里，电子显微镜硬件的进步使我们有机会在纳米尺度上研究材料的振动特性。晶体材料的振动特性，称为声子，是原子核的集体振荡，并控制热量和声音通过材料传递的方式。分子的振动性质是键的伸缩、弯曲和转动模式。在晶体和分子两种情况下，振动性质都是材料中键合的特征。新一代的电子显微镜能够将联合收割机原子分辨率成像与高分辨率电子能量损失光谱结合起来，从而实现原子分辨率的振动光谱。它使我们能够从体积比任何其他技术小20个数量级的材料中收集振动光谱。这些实验发展使我们能够研究振动模式在空间上如何变化，并将有利于材料设计和优化。欧洲第一台新一代显微镜位于英国SuperSTEM实验室，该实验室是EPSRC国家高级电子显微镜研究设施。为了解释实验光谱中的新特征，开发一个强大的理论框架非常重要。该项目将联合收割机从新的SuperSTEM显微镜与量子力学模拟实验数据相结合，以解决这些新的实验能力所产生的一些基本问题。它将建立在今年早些时候发表在Hage，Nicholls等人的《科学进展》上的工作基础上，其中首次使用透射电子显微镜获得了结晶材料的动量分辨振动光谱。这项工作将超越以前对晶体材料的工作，并解决分子和官能团。它将比较理论光谱模拟与晶体的方法与一种新的分子方法在这个项目中开发。实验工作将用于指导和测试散射理论框架中使用的近似。这些实验将在SuperSTEM进行，并与SuperSTEM合作。首先，原型材料将用于测试理论预测。一旦有一个强大的方法来模拟和解释实验光谱，这种新的知识将被应用于尖端材料问题。这个项目的目的是关注分子官能团，因此这种方法可以用来观察催化剂颗粒的表面。这种特殊的催化剂颗粒用于燃料电池，这是减少道路车辆温室气体排放的一种可行方法。在燃料电池成为主流技术之前，催化剂颗粒是燃料电池需要优化的部分。该项目属于EPSRC物理科学，能源和制造未来研究领域的福尔斯。

In the last few years advances in electron microscopy hardware have given us the opportunity to study the vibrational properties of materials at the nanoscale. The vibrational properties of crystalline materials, known as phonons, are collective oscillations of the atomic nuclei and control the way heat and sound are transferred through a material. The vibrational properties of molecules are the stretching, bending and rotational modes of the bonds. In both the crystalline and molecular cases, the vibrational properties are characteristic of the bonding in the material. A new generation of electron microscopes are able to combine atomic resolution imaging with high resolution electron energy loss spectroscopy, allowing vibrational spectroscopy at atomic resolution. It allows us to collect vibrational spectra from volumes of material up to 20 orders of magnitude smaller than any other technique. These experimental developments allow us to study how the vibrational modes vary spatially and will benefit materials design and optimisation. The first of this new generation of microscopes in Europe is housed at the UK SuperSTEM facility, which is the EPSRC National Research Facility for Advanced Electron Microscopy.In order to interpret the new features in the experimental spectra, it is important to develop a robust theoretical framework. This project will combine experimental data from the new SuperSTEM microscope with quantum mechanical simulations to address some of the fundamental questions rising from these new experimental capabilities. It will build on work published earlier this year in Science Advances by Hage, Nicholls et al. where, for the first time, momentum resolved vibrational spectra from crystalline materials were obtained using a transmission electron microscope. This work will go beyond the previous work on crystalline materials and address molecules and functional groups. It will compare theoretical spectra simulated with the crystalline approach with a novel molecular approach developed in this project. Experimental work will be used to guide and test the approximations used in the scattering theory framework. The experiments will be carried out at, and in collaboration with, SuperSTEM. To start with, prototype materials will be used to test the theoretical predications. Once there is a robust approach to simulating and interpreting experimental spectra, this new knowledge will then be applied to cutting-edge materials problems. The aim of this project is to focus on molecular functional groups, and so this approach be used to look at the surfaces of catalyst particles. The particular catalyst particles are used in fuel cells which are a viable way of reducing the greenhouse gas emissions from road vehicles. The catalyst particles are part of the section of the fuel cell that needs optimising before fuel cells can become a mainstream technology. This project falls within the EPSRC Physical sciences, Energy and Manufacturing the Future research areas.