Development of new methods for the characterization of bio and nanomaterials

通常使用场发射透射电子显微镜（FE-TEM）对材料的微观结构进行表征，其空间分辨率为1nm。这种表征包括使用x射线微分析的定量化学分析，使用电子衍射确定晶体结构以及使用电子能量损失光谱（EELS）确定原子键的性质。FE-TEM要求样品必须对电子束透明。制备用于FE-TEM观察的薄片是一个漫长而繁琐的过程。然而，由于有报道称快速二次电子（FSE）会降低FE-TEM中用于量化轻元素的x射线微分析的分辨率，因此该技术的最终分辨率仍然是一个问题。最近有报道称俄歇电子可能具有同样的效果。自20世纪90年代中期以来，场发射扫描电子显微镜（FE-SEM）在市场上上市。低压FE-SEM的图像分辨率为2 nm。由于在FE-SEM中制备样品比在FE-TEM中更容易，这解释了低压FE-SEM越来越受欢迎的原因。此外，用于FE-TEM观察的透明薄膜的可观察面积为0.25，而插入FE-SEM中的抛光样品的面积为1cm2数量级。因此，在FE-SEM中观察到的面积比在TEM中观察到的面积大4亿，这导致了关于给定材料微观结构的大量优越的统计信息。然而，FE-TEM可以利用电子断层扫描技术在三维空间上确定纳米材料的微观结构，需要开发软件来提高其空间分辨率。该项目将开发科学软件，使FE-SEM能够对非均质材料进行化学定量x射线分析，通过模拟电子背散射衍射模式确定其晶体结构，并开发用于软x射线光谱的新型x射线探测器。FSE和俄歇电子对x射线微观分析的影响，以及一种新的FE-TEM层析成像方法。

Characterization of the microstructure of materials with a spatial resolution of the order of 1 nm is normally performed using field emission transmission electron microscopy (FE-TEM). This characterization includes quantitative chemical analysis using x-ray microanalysis, the determination of the crystalline structure with electron diffraction and the nature of the atomic bonds using electron energy loss spectroscopy (EELS). FE-TEM requires specimens that must be transparent to the electron beam. Preparing thin foils for FE-TEM observation can be a long and tedious process. However, since it was reported that Fast Secondary Electrons (FSE) can degrade the resolution of X-Ray microanalysis in FE-TEM for the quantification of light elements, the ultimate resolution of this technique is still an issue. Auger electrons were reported recently to have potentially the same effect. Since the mid 1990's, the Field Emission Scanning Electron Microscope (FE-SEM) are available on the market. Low voltage FE-SEM has an image resolution of 2 nm. Since specimen preparation is easier in FE-SEM than in FE-TEM, this explains the increasing popularity of low voltage FE-SEM. Also, transparent thin films for FE-TEM observations have an observable area of 0.25 where polished specimens inserted in the FE-SEM have area of the order of 1cm2. Therefore the area observable in the FE-SEM is 400,000,000 greater than in the TEM, leading to vastly superior statistical information about the microstructure of a given material. However, FE-TEM can determine the microstructure of nanomaterials in three dimension using electron tomography and software development is needed to improve its spatial resolution. This project will develop the scientific software that will allow FE-SEM to perform chemical quantitative x-ray analysis of heterogeneous materials, to determine their crystalline structure by simulating electron backscattered diffraction patterns and to develop a new x-ray detector for soft x-ray spectroscopy. The effect of FSE and Auger electrons on x-ray microanalysis and a new tomography method will also be developed for the FE-TEM.