Aberration Assessment and Correction using High-Resolution Holographic Methods in Electron Microscopy

与其他用于获得材料结构信息的技术相比，高分辨率电子显微镜（HREM）具有很大的优势，它产生关于原子排列的局部信息，沿着电子入射方向以与原子间距离相当的分辨率投影。这使得对复杂结构、晶体缺陷、沉淀物等的研究能够深入到原子水平。随着在材料设计和微结构和纳米结构的控制中对非周期结构处原子排列的精确测定的需求的增加，获得亚埃级的定量结构信息的高分辨率电子显微镜将是不可或缺的。然而，由于电子与物质的强烈相互作用以及显微镜的像差，HREM图像的解释并不简单。后者导致复杂的图像，不能揭示真实的结构。不幸的是，像差不能从传统的电子显微照片中校正，因为在记录期间丢失了相位信息。因此，只有像通过聚焦系列和离轴电子全息术的全息方法在重建过程中恢复振幅和相位才有可能进行后续的像差校正。因此，显微镜像差的校正对于HREM的进一步发展至关重要，特别是当人们想要以定量的方式应用HREM时。德累斯顿和德尔夫特集团有强大的研究计划，重点是离轴电子全息（德累斯顿）和通过焦点系列（德尔夫特），其中都包括仔细校正显微镜像差。通过DFG-NWO赠款，他们可以通过频繁的相互访问进行讨论和实验，以更好的结构化合作加入他们的力量。合作将集中在像差评估和校正的优化（方法和软件开发）上。

Compared to other techniques used to obtain structural information of materials, high resolution electron microscopy (HREM) has the great advantage that it yields local information about the atomic arrangements, projected along the direction of electron incidence at a resolution comparable to the interatomic distances. This enables the study of complicated structures, crystal defects, precipitates, etc. down to the atomic level. With the increasing need of the accurate determination of the atomic arrangements at non-periodic structures in materials design and control of microstructures and nanostructures, the accessibility to a high resolution electron microscope yielding quantitative structural information at the sub-angstrom level will be indispensable. The interpretation of HREM images, however, is not simple due to the strong interaction of electrons with matter and due the aberrations of the microscope. The latter result in complicated images, which do not reveal the real structure. Unfortunately, aberrations cannot be corrected from conventional electron micrographs since the phase information is lost during recording. Only holographic methods like through focus series and off-axis electron holography retrieve - within the reconstruction process - amplitude and phase hence make possible a subsequent correction of aberrations. Thus the correction for the microscope aberration is crucial for the further development of HREM, in particular when one wants to apply HREM in a quantitative manner. The Dresden and Delft groups have strong research programs focussed of off-axis electron holography (Dresden) and through focus series (Delft) which both includes the careful correction for the microscope aberrations. By means of a DFG-NWO grant they can join their forces in a better structured cooperation with frequent mutual visits for discussions und experiments. The cooperation will be focussed on the optimisation (method and software development) of aberration assessment and correction.