Towards robust and reliable short-range order measurement using electron spectroscopy

非晶材料的原子结构是许多应用的关键，无论是干涉仪的光学涂层，窄带光电探测器的滤光片，金属玻璃还是玻璃。但是，可靠地确定玻璃的结构仍然是一个主要的发展领域，特别是当它们是薄膜形式时。对于大块玻璃，光束线技术，如使用短波长X射线的X射线PDF（XPDF）测量，给出了所有原子的总散射的良好图像。将其与扩展X射线吸收精细结构（EXAFS）相结合，可以提供对局部原子环境的更具原子特异性的探测。对于薄膜，透射电子显微镜更合适，因为亚纳米电子束可以容易地形成。基于衍射的技术，如来自高角电子衍射的径向分布函数测量（类似于XPDF）或用于检查中程有序（约1-3 nm）的波动显微镜，是研究所有原子的总散射的有用方法。原则上，EXAFS与电子的类比是可能的，扩展的能量损失精细结构。然而，虽然EXELFS的影响是众所周知的电子能量损失光谱的背景上的干扰，它还没有被广泛用于确定特定原子周围的短程有序。这有几个原因：电子枪和显微镜设计的各种功能可能会导致光谱中连续背景的扰动，从而阻止准确的背景拟合，显微镜光学设计中关于色彩效应的缺点也可能在较高的能量损失下扰动背景，并且检测器可能会有噪音，并且在其范围内给出不均匀的读数。近年来的重大进展意味着这些问题现在可以在很大程度上被克服，并且有可能在将EXELFS从有趣的可能性转换为广泛可用的技术方面取得重大进展。这将包括在格拉斯哥的电子显微镜光学系统中使用色效应补偿的新发展，更好地理解如何与枪杂散散射一起工作，以及EELS检测技术的新发展（与宾夕法尼亚州费城德雷克塞尔大学的研究人员合作）。我们将利用这一点来了解玻璃的结构含有Si，Ti和其他可能的阳离子的材料，如SiO2，和含Ti的混合氧化物玻璃，以及调查是否O原子环境也可以通过这种技术进行调查。由此产生的出版物将有助于理解这种材料的薄膜结构，并推动该技术应用于各种玻璃质材料的方法学发展。这项工作涉及以下EPSRC研究领域：功能陶瓷和无机物-特别是光学涂层用玻璃化学结构-固体结构的测定生物材料-特别是微晶玻璃光电器件和电路，传感器和仪器仪表-都在了解玻璃过滤器的波长选择性超导-非晶超导薄膜结构

The atomic structure of amorphous materials is a key to many applications, whether optical coatings for interferometers, filters for narrow-band photodetectors, metallic glasses, or bioglasses. But reliable determination of the structure of glasses is still a major area for development, especially when they are in thin film form. For bulk glasses, beamline techniques like X-ray PDF (XPDF) measurement using short wavelength X-rays gives a good picture of the total scattering from all atoms. Combining that with Extended X-ray Absorption Fine Structure (EXAFS) gives a more atom-specific probe of local atomic environments. For thin films, transmission electron microscopy is more appropriate because of the ease with which sub-nanometre electron beams can be formed. Diffraction-based techniques like radial distribution function measurement from high angle electron diffraction (analogous to XPDF) or fluctuation microscopy for examining medium-range order (to about 1-3 nm) are useful methods for investigating the total scattering from all atoms. In principle, an analogy to EXAFS is possible with electrons, EXtended Energy Loss Fine Structure. However, whilst the effects of EXELFS are well known as a disturbance on the background in Electron Energy Loss Spectroscopy, it has not been extensively used for the determination of short range order around specific atoms. There are several reasons for this: various features of electron gun and microscope design can lead to perturbations of the continuum background in the spectrum that prevent accurate background fitting, shortcomings in the optical design of microscopes with regard to chromatic effects can also perturb the background at higher energy losses, and detectors can be noisy and give non-uniform readings across their range. Major advances in recent years mean that these problems can now be largely overcome and it may be possible to make significant progress in converting EXELFS from an intriguing possibility into a widely useable technique. This will include the use of new developments in the compensation of chromatic effects in electron microscope optics at Glasgow, a better understanding of how to work with gun stray scattering, and new developments in detection technologies for EELS (in collaboration with researchers at Drexel University, Philadelphia, PA). We will use this to understand the structure of glasses containing Si, Ti and possibly other cations in materials like SiO2, and mixed oxide glasses containing Ti, as well as investigating as to whether O atom environments can also be investigated by this technique. The resulting publications will both aid the understanding of structures in thin films of such materials, as well as driving the methodological development of the technique for application to a wide variety of glassy materials.This work relates to the following EPSRC research areas:Functional Ceramics and Inorganics - Especially glasses for optical coatingsChemical Structure - Determination of structure in solidsBiomaterials - Especially bioglassesOptoelectronic Devices and Circuits, Sensors and Instrumentation - both in understanding glasses for filters for wavelength selectivitySuperconductivity - amorphous superconducting thin film structure