Tomita Masato, Nagatani Yukinori, Murata Kazuyoshi, Momose Atsushi
National Institute for Physiological Sciences, 38 Nishigonaka Myodaiji, Okazaki, Aichi, 444-8585, Japan.
National Institute for Physiological Sciences, 38 Nishigonaka Myodaiji, Okazaki, Aichi, 444-8585, Japan; KEK, High Energy Accelerator Research Organization, 4 Shirane Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195 Japan.
Ultramicroscopy. 2020 Nov;218:113089. doi: 10.1016/j.ultramic.2020.113089. Epub 2020 Aug 5.
Electron microscopy is a powerful tool for visualizing the shapes of sub-nanometer objects. However, Contrast Transfer Function (CTF) principally restricts lower frequency components in the image. To overcome this problem, phase-plate techniques have been proposed and currently Hole Free Phase Plate (HFPP) and Volta Phase Plate (VPP) are widely used especially for biological specimens to retrieve low frequency information of the sample's potential distributions. In this report, we have developed a new phase-contrast scanning transmission electron microscope (STEM) in which a probe beam including side robes is formed with an amplitude Fresnel zone plate (FZP) and the interference patterns produced by the zero and first order diffracted waves generated by the FZP are detected. We name it FZP Phase Contrast STEM (FZP-PC-STEM) hereinafter. The amplitude FZP was manufactured by using focused ion beam (FIB) equipment, and the diffraction data were collected by using diffraction imaging technique. The validity of our proposed optical model was confirmed by comparing experimental and simulated images. Observations of carbon nanotube (CNT) bundles by using this method showed that the contrast of low-spatial-frequency components in the CNT image was significantly enhanced. This method does not, in principle, require the post-image processing used in the diffraction imaging method, and it can be easily introduced into pre-existing equipment without major modifications. The stability and robustness of the FZP inserted in condenser system were also confirmed during long-time operation. We expect that the FZP-PC-STEM will be widely applicable to high-contrast observations of low-Z samples with simple and easy operation.
电子显微镜是一种用于可视化亚纳米级物体形状的强大工具。然而，对比度传递函数（CTF）主要限制了图像中的低频成分。为了克服这个问题，人们提出了相板技术，目前无孔相板（HFPP）和伏打相板（VPP）被广泛使用，特别是用于生物样本以获取样本电势分布的低频信息。在本报告中，我们开发了一种新的相衬扫描透射电子显微镜（STEM），其中利用振幅菲涅耳波带片（FZP）形成包含旁瓣的探测束，并检测由FZP产生的零阶和一阶衍射波所产生的干涉图案。我们将其简称为FZP相衬STEM（FZP-PC-STEM）。通过聚焦离子束（FIB）设备制造了振幅FZP，并使用衍射成像技术收集了衍射数据。通过比较实验图像和模拟图像，证实了我们所提出光学模型的有效性。使用这种方法对碳纳米管束的观察表明，碳纳米管图像中低空间频率成分的对比度得到了显著增强。原则上，这种方法不需要衍射成像方法中使用的图像后处理，并且可以很容易地引入到现有设备中而无需进行重大修改。在长时间运行过程中，还证实了插入聚光镜系统中的FZP的稳定性和耐用性。我们期望FZP-PC-STEM将以简单易操作的方式广泛应用于低原子序数样品的高对比度观察。
