Electron tomography imaging methods with diffraction contrast for materials research

Abstract

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable the visualization of three-dimensional (3D) microstructures ranging from atomic to micrometer scales using 3D reconstruction techniques based on computed tomography algorithms. This 3D microscopy method is called electron tomography (ET) and has been utilized in the fields of materials science and engineering for more than two decades. Although atomic resolution is one of the current topics in ET research, the development and deployment of intermediate-resolution (non-atomic-resolution) ET imaging methods have garnered considerable attention from researchers. This research trend is probably not irrelevant due to the fact that the spatial resolution and functionality of 3D imaging methods of scanning electron microscopy (SEM) and X-ray microscopy have come to overlap with those of ET. In other words, there may be multiple ways to carry out 3D visualization using different microscopy methods for nanometer-scale objects in materials. From the above standpoint, this review paper aims to (i) describe the current status and issues of intermediate-resolution ET with regard to enhancing the effectiveness of TEM/STEM imaging and (ii) discuss promising applications of state-of-the-art intermediate-resolution ET for materials research with a particular focus on diffraction contrast ET for crystalline microstructures (superlattice domains and dislocations) including a demonstration of in situ dislocation tomography.

Reconstructing dual-phase nanometer scale grains within a pearlitic steel tip in 3D through 4D-scanning precession electron diffraction tomography and automated crystal orientation mapping

“…The effects of dynamical diffraction were reduced by beam precession during the experiment, whereas the latter two effects are intrinsic to the sample and material studied. As a result, there are contrast fluctuations within each grain, which are visible in Figure 5, and, despite the use of precession, the FTVDF images do not exactly satisfy the projection criteria that the projected object intensity is proportional to the thickness of the object [39]. These effects, however, do not prevent a well-defined reconstruction of the grain contour.…”

A new method for obtaining the magnetic shape anisotropy directly from electron tomography images

“…Filtering utility: Handling the diffraction contrast in electron tomography is still an ongoing issue [ 28 – 29 ]. In this regard, the Magn3t software is accompanied by an in-house developed novel image filtering tool, which can be applied on well-aligned experimental tomography tilt series, prior to the tomographic reconstruction.…”

Semi-Automated, Object-Based Tomography of Dislocation Structures

“…Although complex arrangements of dislocations are well-resolved by diffraction contrast techniques in transmission electron microscopy (TEM), particularly under weak-beam imaging conditions (Cockayne et al, 1969), information regarding feature height position is mostly lost in any single image since TEM is a projection technique. This challenge has motivated much interest in developing diffraction-contrast tomographic techniques suitable for dislocation imaging, as has been the subject of several recent reviews (Liu et al, 2014; Feng et al, 2020; Hata et al, 2020 a , 2020 b ).…”

“…Although complex arrangements of dislocations are wellresolved by diffraction contrast techniques in transmission electron microscopy (TEM), particularly under weak-beam imaging conditions (Cockayne et al, 1969), information regarding feature height position is mostly lost in any single image since TEM is a projection technique. This challenge has motivated much interest in developing diffraction-contrast tomographic techniques suitable for dislocation imaging, as has been the subject of several recent reviews (Liu et al, 2014;Feng et al, 2020;Hata et al, 2020aHata et al, , 2020b. One widely employed approach, which was pioneered by co-workers (Barnard et al, 2006a, 2006b), is to apply intensity-based reconstruction algorithms, such as weighted back projection (WBP) or the sequential iterated reconstruction technique (SIRT), to diffraction contrast images collected over a wide tilt range but with finely spaced tilt increments.…”