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

1.电子探测器的改进本文研究了一种适用于各种厚度的常规粉末荧光体的高灵敏度电子探测器。0.07mm厚的闪烁体在100 kV处具有最大的灵敏度。还发现，厚度为1 mm的YAG单晶闪烁体的灵敏度是粉末状磷光体闪烁体的4倍。通过安装信号电子偏转磁铁和孔径光阑，避免了X射线和杂散电子的影响，实现了非弹性散射和非散射电子的高精度探测.图像信号的数字处理系统开发了一种系统，可以高精度记录多达三种电子信号。在采样过程中，特别注意了采集误差，采用巴特沃思滤波器消除混叠，使误差降低到0.2%以内.数字处理过程采用滤波与反卷积相结合的方法，研究了合适的低通滤波窗口，以提高分辨率而不产生伪影。实验结果表明，在适当的条件下，分离度提高了40%。对入射电子对信号电子的归一化过程进行了定量评价，发现信噪比得到了提高，与理论相符。弹性散射和非弹性散射电子之间的操纵揭示了在比值图像中获得与原子序数成比例的对比度，并且通过采取适当的差异因子，在差异图像中减小或增强特定元素的结构对比度。

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.