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

该项目将在透射式电子显微镜(TEM)中开发光子辅助电子光谱，这是一种研究纳米材料电子和光学性质的新技术。利用特性良好的光源激发纳米结构中的电子跃迁，并在扫描电子显微镜模式下用电子能量损失谱(EELS)探测修正后的电子密度。传统的鳗鱼光谱表示电子束通过与样品的非弹性相互作用而损失的能量，从而揭示了材料中从被占据的电子态到未被占据的电子态的转变。当通过光子吸收来填充较高能级的电子态时，例如带隙状态，在鳗鱼光谱中将观察到不同组态的态密度。这种组合技术可以应用于研究无机和有机纳米材料中的长寿命电子态。连续的紫外光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随着它们的物相、尺寸和形貌的变化而变化。这在技术上是有意义的，因为二氧化钛和氧化锌是强大的光催化剂，在紫外线照射下几乎可以氧化任何有机分子。了解和提高纳米二氧化钛和氧化锌的催化活性，将为环境中有毒气体的去除提供更有效的解决方案。当使用激光激发工作的纳米线光伏器件(相当于太阳能电池的纳米级)中的光电子跃迁时，可以同时监测修正的EELS信号和光生电流，并可以与单个纳米线的尺寸、晶体相和取向以及表面结构相关联。这项研究将有助于开发更高效的将太阳光转化为电能的光伏设备。激发氧从具有良好特性的纳米颗粒表面的光解吸将有助于理解电子表面状态以及催化和传感所基于的一些电荷转移机制。这项技术的开发将分三个日益复杂的阶段进行，不仅将涉及研究仪器的设计和组装，还将涉及数据采集和分析方法的设计。光子辅助光谱分析将使用FEI Titan TEM/STEM，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用于分析工作。这个项目代表着一次伟大的冒险，一个创造一个新的研究领域的机会，一个新的纳米计量学工具。

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.