Electron Microscopy for Materials Research (EMAT), University of Antwerp, Department of Physics, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
Ultramicroscopy. 2013 Oct;133:50-61. doi: 10.1016/j.ultramic.2013.05.008. Epub 2013 May 23.
The concept of resolution in high-resolution electron microscopy (HREM) is the power to resolve neighboring atoms. Since the resolution is related to the width of the point spread function of the microscope, it could in principle be determined from the image of a point object. However, in electron microscopy there are no ideal point objects. The smallest object is an individual atom. If the width of an atom is much smaller than the resolution of the microscope, this atom can still be considered as a point object. As the resolution of the microscope enters the sub-Å regime, information about the microscope is strongly entangled with the information about the atoms in HREM images. Therefore, we need to find an alternative method to determine the resolution in an object-independent way. In this work we propose to use the image wave of a crystalline object in zone axis orientation. Under this condition, the atoms of a column act as small lenses so that the electron beam channels through the atom column periodically. Because of this focusing, the image wave of the column can be much more peaked than the constituting atoms and can thus be a much more sensitive probe to measure the resolution. Our approach is to use the peakiness of the image wave of the atom column to determine the resolution. We will show that the resolution can be directly linked to the total curvature of the atom column wave. Moreover, we can then directly obtain the resolution of the microscope given that the contribution from the object is known, which is related to the bounding energy of the atom. The method is applied on an experimental CaTiO₃ image wave.
高分辨率电子显微镜（HREM）中的分辨率概念是指分辨相邻原子的能力。由于分辨率与显微镜的点扩散函数的宽度有关，因此原则上可以从点物体的图像中确定分辨率。然而，在电子显微镜中没有理想的点物体。最小的物体是单个原子。如果原子的宽度远小于显微镜的分辨率，则该原子仍可被视为点物体。随着显微镜的分辨率进入亚埃范围，显微镜的信息与 HREM 图像中原子的信息强烈纠缠在一起。因此，我们需要找到一种替代方法来以独立于物体的方式确定分辨率。在这项工作中，我们建议使用晶轴取向的晶态物体的图像波。在这种条件下，列中的原子充当小透镜，使得电子束周期性地穿过原子列。由于这种聚焦，柱的图像波可以比构成原子更加尖锐，因此可以成为更敏感的探针来测量分辨率。我们的方法是使用原子柱的图像波的尖锐度来确定分辨率。我们将表明分辨率可以直接与原子柱波的总曲率相关联。此外，只要知道物体的贡献，就可以直接获得显微镜的分辨率，这与原子的束缚能有关。该方法应用于实验性 CaTiO₃ 图像波上。
