On line digital manipulation process of elastically and inelastically scattered electron signals in scanning transmission electron microscopy

1. 对不同厚度的传统粉末荧光粉闪烁体进行了高灵敏度电子探测器的研究。厚度为0.07mm的闪烁体在10kv时灵敏度最高。同时发现，厚度为1mm的YAG单晶闪烁体的灵敏度是粉末状荧光粉闪烁体的4倍。为避免X射线和杂散电子的影响，通过安装信号电子偏转磁铁和孔径隔膜，实现了非弹性散射和非弹性散射电子的高精度检测。图像信号数字处理系统研制了一种能够高精度记录多达三种电子信号的系统。在采样过程中特别注意采集误差，采用巴特沃斯滤波器避免混叠，将采集误差控制在0.2%以内。采用滤波和反卷积相结合的方法，研究了合适的低通滤波器窗口，以提高无伪影的分辨率。实验发现，在适当的条件下，分辨率提高了40%。对入射电子对信号电子的归一化过程进行了定量评价，发现SN比的提高与理论相符。通过对弹性散射电子和非弹性散射电子的处理，可以得到与原子序数成正比的对比，而在差像中，通过适当的差因子可以减弱或增强特定元素的结构对比。

1. Improvement of electron detection An electron detector of high sensitivity was investigated for conventional powdered phosphor scintillator of various thicknesses. The scintillator of 0.07mm thickness was found to give the maximum sensitivity at 1OOkV. It was found as well that a YAG single crystal scintillator of lmm thickness gives the sensitivity 4 times as much as the powdered phosphor scintillator. A high-accuracy detection of inelastically scattered and unscattered electroits was realized by installation of a deflection magnet for signal electrons and an aperture diaphragm, to avoid the influence of X ray and stray electrons.2. Digital processing system of image signals A system was developed to record electron signals of up to three kinds with high- accuracy. Special attentions were paid to acquisition error in sampling and the error was reduced within 0.2% by using a Butterworth filter to avoid aliasing.3. Digital manipulation process A proper window of low-pass filter was investigated for improvement of resolution without artifacts by using a method combined by filtering and deconvolution. It was found that the resolution is improved by 40% under the appropriate condition. The quantitative evaluation of normalization process of signal electrons by incident electrons was carried out and it was found that the SN ratio is improved in accordance with the theory. The manipulation among elastically scattered and inelastically scattered electrons revealed that the contrast in proportion to atomic number is obtained in the ratio image and that the contrast of structure of specific element is diminished or enhanced in the difference image by taking an appropriate difference factor.