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Accurate geometrical calibration between the scan coordinates and the camera coordinates is critical in four-dimensional scanning transmission electron microscopy (4D-STEM) for both quantitative imaging and ptychographic reconstructions. For atomic-resolved, in-focus 4D-STEM datasets, we propose a hybrid method incorporating two sub-routines, namely a J-matrix method and a Fourier method, which can calibrate the uniform affine transformation between the scan-camera coordinates using raw data, without a priori knowledge of the crystal structure of the specimen. The hybrid method is found robust against scan distortions and residual probe aberrations. It is also effective even when defects are present in the specimen, or the specimen becomes relatively thick. We will demonstrate that a successful geometrical calibration with the hybrid method will lead to a more reliable recovery of both the specimen and the electron probe in a ptychographic reconstruction. We will also show that, although the elimination of local scan position errors still requires an iterative approach, the rate of convergence can be improved, and the residual errors can be further reduced if the hybrid method can be firstly applied for initial calibration. The code is made available as a simple-to-use tool to correct affine transformations of the scan-camera coordinates in 4D-STEM experiments.
The correction of aberrations in the scanning transmission electron microscope (STEM) has simultaneously improved both spatial and temporal resolution, making it possible to capture the dynamics of single atoms inside materials, and resulting in new insights into the dynamic behavior of materials. In this article, we describe the different beam–matter interactions that lead to atomic excitations by transferring energy and momentum. We review recent examples of sequential STEM imaging to demonstrate the dynamic behavior of single atoms both within materials, at dislocations, at grain and interface boundaries, and on surfaces. We also discuss the effects of such dynamic behavior on material properties. We end with a summary of ongoing instrumental and algorithm developments that we anticipate will improve the temporal resolution significantly, allowing unprecedented insights into the dynamic behavior of materials at the atomic scale.
The two current reigning paradigms enabling nanotechnology are scanning probe microscopy and molecular machine devices that date back to seminal experiments by Eigler and visionary work by Drexler, respectively. The nanoscience and nanotechnology community is seeing the emergence of a third paradigm—the use of the atomically focused beam of a scanning transmission electron microscope (STEM) to control and direct matter on the atomic scale. Beam-induced modifications involving one atom or a small group of atoms can be induced and monitored in real time with atomic resolution. Combined with the development of beam-control electronics, big data acquisition, and analytical tools such as artificial intelligence-based feedback systems, electron and ion microscopies are at the brink of a transition from purely imaging tools to tools capable of creating structures with atomic precision and high throughput. In this issue of MRS Bulletin, we present recent advances in electron- and ion-beam-based atomic fabrication on surfaces, in layered materials, and finally in three dimensions—the ultimate dream and possibly the final frontier of nanoscience.
In his famous 1959 lecture “There’s plenty of room at the bottom,” Richard Feynman put out this challenge: “Is there no way to make the electron microscope more powerful?” He called for “improving the electron microscope by a hundred times,” which, given that the resolution then was about 10 Å, meant he was calling for a resolution in the range of 0.1 Å. Today’s aberration-corrected microscopes have come a long way, achieving a resolution of around 0.5 Å. This has enormously improved our ability to see atomic arrangements in crystals, measure ferroelectric displacements, and even determine valence and spin states with electron energy-loss spectroscopy. However, there remain many structures crucial to materials properties that we cannot yet see. Continuing the road toward Feynman’s goal would bring these structures to light, with yet more dramatic impacts on the entire field of materials science.