ePDF tools, a processing and analysis package of the atomic pair distribution function for electron diffraction

We present a new processing & analysis package of the atomic pair distribution function (PDF) for the electron diffraction (ED) pattern based on the total scattering theory which has been broadly used in the X-ray or neutron diffraction to reveal the local atomic structures, but PDF analysis based on the electron diffraction is still rarely used for the lack of an efficient PDF tool. The program was written as a package of DigitalMicrograph, a very popular software to record and analyze the data of transmission electron microscopes (TEM) in the most of TEM laboratories. The azimuthal rotation-average projection algorithm was implemented to enhance the signal-noise ratio of the intensity profile. In order to obtain the reduced structure function, the cubic spline fitting method was utilized to subtract the background scattering. The real-time displayed PDF makes data normalization easier and more accurate, and results of coordination numbers and averaged bond angles can be extracted from calibrated PDFs in real time.我们报道了一款基于总散射理论（total scattering theory）的电子衍射（electron diffraction, ED）图谱原子对分布函数（atomic pair distribution function, PDF）处理与分析新工具包。总散射理论已广泛应用于X射线或中子衍射领域以揭示材料的局域原子结构，但由于缺乏高效的PDF分析工具，基于电子衍射的PDF分析仍鲜有报道。本程序被封装为DigitalMicrograph插件——该软件是目前绝大多数透射电子显微镜（transmission electron microscope, TEM）实验室中用于记录与分析透射电镜数据的主流商用软件。工具包采用方位角旋转平均投影算法，以提升强度分布曲线的信噪比；为获取约化结构函数（reduced structure function），采用三次样条拟合法扣除背景散射信号；实时展示的PDF图谱可使数据归一化操作更为简便精准，同时支持从已校准的PDF图谱中实时提取配位数（coordination numbers）与平均键角（averaged bond angles）等结构参数。