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

1.电子探测的改进研究了一种适用于不同厚度的常规粉状荧光粉闪烁体的高灵敏度电子探测器。发现0.07 mm厚度的闪烁体在100okV时灵敏度最高。实验还发现，厚度为1 mm的YAG单晶闪烁体的灵敏度是粉状荧光粉闪烁体的4倍。通过安装信号电子偏转磁铁和孔径膜片，避免了X射线和杂散电子的影响，实现了对非弹性散射和非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高精度记录多达三种电子信号的系统。特别注意了采样过程中的采集误差，通过使用巴特沃斯滤波器避免混叠，使采样误差减小到0.2%以内。数字处理过程采用滤波和反褶积相结合的方法，研究了适当的低通滤波窗口，以提高分辨率而不产生伪影。结果表明，在合适的条件下，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，发现信噪比得到了理论上的改善。对弹性散射和非弹性散射电子的处理表明，在比值图像中获得了与原子序数成正比的对比度，而在差值图像中采取适当的差异因子可以减小或增强特定元素结构的对比度。

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.