西北工业大学分析测试中心系列讲座（第十一期）

一、报告题目：Processed Electron Illumination used in the TEM: Orientational Mapping, Electron Christallography and Tomography（旋进电子衍射在TEM中的应用：取向图，电子晶体学以及三维重构）

二、报告人：Joaquim Portillo, Doctor of Philosophy

三、讲座时间：2019年5月10日（星期五），14:00-16:00

四、讲座地点：友谊校区研究生西馆XA309

五、报告摘要：

旋进电子衍射PED是采用类似X-射线衍射中的旋进技术，只不过样品不倾斜，而是将电子束小角度倾斜，并沿与透射电镜光轴同锥的锥面在样品表面扫描，在此过程中用软件自动收集每一幅电子衍射图样，并进行合并分析，这样可以大大减少多重散射从而可以大大减弱动力学效应，使得鉴定空间群相对容易，并且通过衍射强度的分析揭示纳米材料的原子排列结构。

与普通选区电子衍射相比，PED具有很多优点，比如利用电子衍射的三维重构技术，可以无需转正晶体的带轴，沿任意带轴进行数据采集，这在处理敏感材料（沸石、药物、蛋白质等）时非常有用。另一方面，近年来旋进电子衍射在纳米晶体结构解析中发展出了新的应用领域，即通过快速的旋进电子衍射数据采集进行纳米晶体取向/相图的绘制，这在透射电镜中相当于扫描电镜中的EBSD技术。

Precession electron diffraction (PED) is an inverted hollow cone illumination technique for electron diffraction pattern collection under quasi-kinematical conditions (as in X-ray Diffraction), which allows solving “ab-initio” crystal structures of nanocrystals. Diffraction patterns are collected while the TEM electron beam is precessing on an inverted cone surface; in this way, only a few reflections are simultaneously excited and, therefore, dynamical effects are strongly reduced.

In comparison with normal selected area electron diffraction, PED has the following advantages:

· Oriented electron diffraction (ED) patterns may be obtained even if the crystal is not perfectly aligned to a particular zone axis. Thus, reliable ED patterns may be collected very quickly without the need to accurately align the observed crystal along a particular zone axis, which is very useful when dealing with beam sensitive materials (zeolites,pharmaceuticals, proteins, etc.)

· Geometry of PED patterns, when including first-order Laue zone excitation, show all symmetry elements necessary to determine the space and point group of the nanocrystal under investigation, without the need of applying further special techniques, such as Convergent Beam Electron Diffraction.

· PED intensities are quasi-kinematical, likewise to X-rays , up to a thickness of 100 nm and may be used to solve the structure of nanocrystals PED has recently gained large recognition in TEM and X-Ray community and several new nanocrystalline structures have been solved with this technique ^[1,2]. On the other hand, a new field of precession diffraction has recently been developed, the orientational/phase mapping through rapid precessed electron diffraction data collection, which may be regarded as the equivalent in the TEM to the Scanning Electron Microscopy (SEM) based EBSD technique (Electron Backscatter Diffraction) ^[3].

[1] T.E.Weirich, J.Portillo, G.Cox, H.Hibst, S.Nicolopoulos, “Ab initio determination of framework structure of CsNbWO from 100KV precession data”, Ultramicroscopy 106 (2007), 164-175

[2] A.Avilov, K.Kuligin, S.Nicolopoulos, M.Nickolsky, K.Boulahya, J.Portillo, G.Lepeshov,B.Sobolev, J.P.Collette, N.Martin, A.C.Robins, P.Fischione, “Precession technique and electron diffractometry as new tools for crystal structure and chemical bonding”, Ultramicroscopy 107 (2007), 431-444

[3] E.F.Rauch, M.Veron, J.Portillo, D.Bultreys, Y.Maniette, S.Nicolopoulos, “Automatic crystal orientation and phase mapping in TEM by precession diffraction”, Microsc. Anal. 93 (2008), 5-8

六、报告人简介：

Joaquim Portillo currently works at the Centres Científics i Tecnològics, Universitat de Barcelona, University of Barcelona, as well as for NANOMEGAS SL "Tools for Electron Diffraction" company. Joaquim does research in Materials Science, Physical Chemistry and Spectroscopy. Current project is Precession NanoDiffraction in STEM and Precession Diffraction Tomography.

https://www.researchgate.net/profile/Joaquim_Portillo

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