Ciston J, Deng B, Marks L D, Own C S, Sinkler W
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
Ultramicroscopy. 2008 May;108(6):514-22. doi: 10.1016/j.ultramic.2007.08.004. Epub 2007 Aug 8.
Precession electron diffraction (PED) is a technique which is gaining increasing interest due to its ease of use and reduction of the dynamical scattering problem in electron diffraction. To further investigate the usefulness of this technique, we have performed a systematic study of the effect of precession angle on the mineral andalusite where the semiangle was varied from 6.5 to 32 mrad in five discrete steps. The purpose of this study was to determine the optimal conditions for the amelioration of kinematically forbidden reflections, and the measurement of valence charge density. We show that the intensities of kinematically forbidden reflections decay exponentially as the precession semiangle (varphi) is increased. We have also determined that charge density effects are best observed at moderately low angles (6.5-13 mrad) even though PED patterns become more kinematical in nature as the precession angle is increased further.
进动电子衍射（PED）是一种因其易于使用以及减少了电子衍射中的动力学散射问题而越来越受到关注的技术。为了进一步研究该技术的实用性，我们对进动角对半宝石红柱石的影响进行了系统研究，其中半角以五个离散步骤从6.5毫弧度变化到32毫弧度。本研究的目的是确定改善运动学禁阻反射以及测量价电荷密度的最佳条件。我们表明，随着进动半角（φ）的增加，运动学禁阻反射的强度呈指数衰减。我们还确定，即使随着进动角进一步增加，PED图案在本质上变得更具运动学特征，但电荷密度效应在中等低角度（6.5 - 13毫弧度）下观察效果最佳。
