Photon-assisted electron spectroscopy of nanostructures in the transmission electron microscope

本项目将开发透射电子显微镜（TEM）中的光子辅助电子光谱，这是一种研究纳米材料电子和光学特性的新技术。一个很好的特征光源被用来激发电子跃迁内的纳米结构，和修改后的电子密度探测电子能量损失谱（EELS）在扫描TEM模式。传统的EEL谱表示通过与样品的非弹性相互作用由电子束损失的能量，因此揭示了材料中从占据电子态到未占据电子态的转变。当通过光子吸收填充更高能量的电子能级时，例如带隙态，将在EEL光谱中观察到不同的态密度配置。这种结合的技术可以应用于无机和有机纳米材料中长寿命电子态的研究。连续紫外光源可以用来照射二氧化钛和氧化锌纳米颗粒，以研究它们的响应如何根据它们的相、尺寸、形态而变化。这在技术上是相关的，因为TiO 2和ZnO是强大的光催化剂，可以在紫外线辐射下氧化几乎任何有机分子。了解和提高TiO 2和ZnO纳米颗粒的催化活性将为从环境中去除有毒气体提供更有效的解决方案。当激光被用来激发工作纳米线光伏器件（太阳能电池的纳米级等效物）中的光电子跃迁时，修改后的EELS信号和光生电流可以同时被监测，并且可以与单个纳米线的尺寸、晶相和取向以及表面结构相关联。这项研究将有助于开发更有效的光伏器件，将太阳光转化为电能。激发氧从表征良好的纳米颗粒表面的光解吸将有助于理解电子表面态和催化和传感所基于的一些电荷转移机制。这项技术的发展将分三个阶段进行，其复杂性将不断增加，不仅涉及研究仪器的设计和组装，而且还涉及数据采集和分析方法的设计。光子辅助光谱学将使用FEI Titan TEM/STEM进行，这是新一代单色像差校正显微镜，具有前所未有的能量和空间分辨率，可用于分析工作。该项目代表了一次伟大的冒险，创造了一个新的研究领域的机会，以及纳米计量学的新工具。

This project will develop photon-assisted electron spectroscopy in the transmission electron microscope (TEM), a new technique to study the electronic and optical properties of nanomaterials. A well characterised light source is used to excite electronic transitions within a nanostructure, and the modified electronic density is probed by electron energy loss spectroscopy (EELS) in scanning TEM mode. Conventional EEL spectra represent the energy lost by the electron beam through inelastic interactions with the specimen, and hence reveal transition from the occupied to the unoccupied electronic states in the material. When populating higher energy electronic levels through photon absorption, e.g. band-gap states, a different configuration of the density of states will be observed in the EEL spectrum. This combined technique can be applied to the study of long-lived electronic states in both inorganic and organic nanomaterials. A continuous ultraviolet source can be used to irradiate titanium dioxide and zinc oxide nanoparticles to study how their response changes depending on their phase, size, morphology. This is technologically relevant because TiO2 and ZnO are powerful photocatalysts that can oxidize almost any organic molecule under UV radiation. Understanding and enhancing the catalytic activity of TiO2 and ZnO nanoparticles will provide a more effective solution for the removal of toxic gases from the environment. When a laser is used to excite optical electronic transitions in working nanowire photovoltaic devices (the nanoscale equivalent of a solar cell), the modified EELS signal and the photo-generated current can be monitored at the same time, and can be correlated with the size, crystallographic phase and orientation, as well as surface structure of the individual nanowires. This study will contribute to the development of more efficient photovoltaic devices for the conversion of sun light into electricity. Stimulating the photodesorption of oxygen from the surface of well characterised nanoparticles will help understanding the electronic surface states and some of the charge-transfer mechanisms on which catalysis and sensing are based. The development of the technique will proceed in three stages of increasing complexity, and will involve not only the design and assembling of the research apparatus, but also the devising of a methodology for data acquisition and analysis. Photon-assisted spectroscopy will be carried out using the FEI Titan TEM/STEM, a monochromated aberration corrected microscope of the new generation, with unprecedented energy and spatial resolution for analytical work.This project represents a great adventure, an opportunity to create a new field of research, and a new tool in nanometrology.