Exploring the limits of analytical electron microscopy

自从1930年S发明以来，电子显微镜在揭示远低于光学显微镜的长度尺度上的材料结构方面发挥了无价的作用。最近的发展(包括校正电子透镜的像差)使透射式电子显微镜(TEM)能够将结构分辨到原子尺度。此外，分光仪还可以安装在电子显微镜上，把它变成一个分析显微镜。能量色散X射线光谱学(EDX)可以进行原子水平的化学分析，而电子能量损失谱(EELS)可以提供任何其他技术无法比拟的分辨率的化学和结构信息。为了实现这些目标，分析型瞬变电磁波必须非常稳定，但也有几个物理因素限制了它的空间分辨率。其中之一是电子的非弹性散射的离域，这是光谱技术所依赖的。这种离域可以从波动光学(将电子视为物质波)中估计出来，但要精确地考虑离域需要对其点扩散函数(PSF)有准确的了解。我建议使用目前在加拿大和其他地方可以买到的最先进的TEM来测量这种PSF到原子尺度。此外，我将与一位经验丰富的理论家合作，计算PSF在各种实验条件下的变化情况。这一知识将提高从分析透射电子显微镜获得的分辨率，并有助于解决材料科学中的几个重要问题。例如，EELS可以测量半导体器件的局域电子性质，但受到离域的严重限制。*分析电子显微镜的另一个局限性是电子在样品中造成的损害，这构成了生物研究和其他领域的实际分辨率极限，如化学工业所需的改进催化剂的开发。我计划继续研究如何在透射电子显微镜中将辐射损害降至最低。*改进的分析技术将增强加拿大一流电子显微镜设施的能力，如麦克马斯特大学的CCEM，这对加拿大的研究和工业发展具有潜在的好处，并将有助于保持加拿大在先进电子显微镜领域的声誉。

Ever since their invention in the 1930's, electron microscopes have been invaluable for revealing the structure of materials on a length scale far below what is possible with the light microscope. Recent developments (including correction of the aberrations of electron lenses) enable the transmission electron microscope (TEM) to resolve structure down to the atomic scale. Also, spectrometers can be attached to the TEM, turning it into an analytical microscope. Energy-dispersive x-ray (EDX) spectroscopy allows chemical analysis down to the atomic level, while electron energy-loss spectroscopy (EELS) can provide both chemical and structural information at a resolution unmatched by any other technique. ******To achieve these goals, the analytical TEM must be very stable but there are also several physical factors that limit its spatial resolution. One of these is the delocalization of the inelastic scattering of electrons, upon which the spectroscopy techniques depend. This delocalization can be estimated from wave optics (treating the electrons as matter waves) but making precise allowance for delocalization requires an accurate knowledge of its point spread function (PSF). I propose to measure this PSF down to the atomic scale, using state-of-the art TEMs that are now available in Canada and elsewhere. In addition, I will collaborate with an experienced theoretician to calculate how the PSF may vary under various experimental conditions. This knowledge will improve the resolution obtainable from analytical TEM and help towards solving several important problems in materials science. For example, EELS can measure the local electronic properties of semiconductor devices but is severely limited by delocalization. ******Another limitation of analytical TEM is the damage that electrons create in the specimen, which forms the practical resolution limit in biological research and other fields, such as the development of improved catalysts required by the chemical industry. I plan to continue my study into how radiation damage can be minimized in the TEM.******Improved analysis techniques will enhance the capability of Canada's premier electron microscope facilities, such as the CCEM at McMaster University, with potential benefits to Canadian research and industrial development, and will help to maintain Canada's reputation at the frontier of advanced electron microscopy.