Yamasaki Jun, Shimaoka Yuki, Sasaki Hirokazu
Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki 567-0047, Japan.
Department of Electronic Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan.
Microscopy (Oxf). 2018 Feb 1;67(1):1-10. doi: 10.1093/jmicro/dfx093.
We have developed a method to precisely measure spatial coherence in electron beams. The method does not require an electron biprism and can be implemented in existing analytical transmission electron microscopes equipped with a post-column energy filter. By fitting the Airy diffraction pattern of the selector aperture, various parameters such as geometric aberrations of the lens system and the point-spread function of the diffraction blurring are precisely determined. From the measurements of various beam diameters, components that are attributed to the partial spatial coherence are successfully separated from the point-spread functions. A linear relationship between the spatial coherence length and beam diameter is revealed, thus indicating that a wide range of coherence lengths can be determined by our proposed method as long as the coherence length remains >80% of the aperture diameter. A remarkable feature of this method is its ability to simultaneously determine diffraction blurring and lens aberrations. Possible applications of this method are also discussed.
我们已经开发出一种精确测量电子束空间相干性的方法。该方法不需要电子双棱镜，并且可以在配备有柱后能量过滤器的现有分析型透射电子显微镜中实现。通过拟合选择器孔径的艾里衍射图样，可以精确确定诸如透镜系统的几何像差和衍射模糊的点扩散函数等各种参数。通过对各种束径的测量，成功地从点扩散函数中分离出归因于部分空间相干性的成分。揭示了空间相干长度与束径之间的线性关系，这表明只要相干长度保持大于孔径直径的80%，我们提出的方法就可以确定很宽范围的相干长度。该方法的一个显著特点是能够同时确定衍射模糊和透镜像差。还讨论了该方法的可能应用。
