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Carbon-film-based Zernike phase plates with smooth thickness gradient for phase-contrast transmission electron microscopy with reduced fringing artefacts
Journal of Microscopy ( IF 2 ) Pub Date : 2022-04-19 , DOI: 10.1111/jmi.13108
M Obermair 1 , S Hettler 1, 2 , M Dries 1 , M Hugenschmidt 1, 3 , R Spiecker 1, 4 , D Gerthsen 1, 3
Affiliation  

Phase plates (PPs) in transmission electron microscopy (TEM) improve the contrast of weakly scattering objects under in-focus imaging conditions. A well-established PP type is the Zernike (Z)PP, which consists of a thin amorphous carbon (aC) film with a microscaled hole in the centre. The mean inner potential of the aC film is exploited to shift the phase of the scattered electrons while the unscattered electrons in the zero-order beam propagate through the hole and remain unaffected. However, the abrupt thickness increase at the hole edge induces an abrupt change of the phase-shift distribution and leads to fringing, that is, intensity oscillations around imaged objects, in TEM images. In this work, we have used focused-ion-beam milling to fabricate ZPPs with abrupt and graded thickness profiles around the centre hole. Depending on the thickness gradient and inner hole radius, graded-ZPP-TEM images of an aC/vacuum interface and bundles of carbon nanotubes (CNTs) show strongly reduced fringing. Image simulations were performed with ZPP-phase-shift distributions derived from measured thickness profiles of graded ZPPs, which show good agreement with the experimental images.

中文翻译:

基于碳膜的 Zernike 相位板具有平滑的厚度梯度,用于相差透射电子显微镜,减少了边缘伪影

透射电子显微镜 (TEM) 中的相位板 (PP) 可提高聚焦成像条件下弱散射物体的对比度。一种成熟的 PP 类型是 Zernike (Z)PP,它由薄的无定形碳 (aC) 薄膜组成,中间有一个微型孔。aC 薄膜的平均内电位被用来改变散射电子的相位,而零级光束中的未散射电子通过孔传播并保持不受影响。然而,孔边缘处厚度的突然增加会导致相移分布的突然变化,并导致 TEM 图像中的边缘,即成像物体周围的强度振荡。在这项工作中,我们使用聚焦离子束铣削来制造在中心孔周围具有陡峭和渐变厚度轮廓的 ZPP。根据厚度梯度和内孔半径,aC/真空界面和碳纳米管 (CNT) 束的渐变 ZPP-TEM 图像显示出显着减少的边缘。图像模拟是使用从分级 ZPP 的测量厚度剖面得出的 ZPP 相移分布进行的,这与实验图像具有良好的一致性。
更新日期:2022-04-19
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