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Electron ptychography has recently attracted considerable interest for high resolution phase-sensitive imaging. However, to date studies have been mainly limited to radiation resistant samples as the electron dose required to record a ptychographic dataset is too high for use with beam-sensitive materials. Here we report defocused electron ptychography using a fast, direct-counting detector to reconstruct the transmission function, which is in turn related to the electrostatic potential of a two-dimensional material at atomic resolution under various low dose conditions.

A technique capable of detecting the electric field associated with individual atoms is now demonstrated. Atomic-resolution differential phase-contrast imaging using aberration-corrected scanning transmission electron microscopy provides a sensitive probe of the gradient of the electrostatic potential in a crystal lattice. Differential phase-contrast (DPC) imaging enhances the image contrast of weakly absorbing, low-atomic-number objects in optical and X-ray microscopy 1 , 2 , 3 , 4 . In transmission electron microscopy 5 , this same imaging mode can image magnetic fields in magnetic materials at medium resolution 6 , 7 . Atomic-resolution imaging of electromagnetic fields, however, is still a major challenge. Here, we demonstrate atomic-resolution DPC imaging of crystals using aberration-corrected scanning transmission electron microscopy. The image contrast reflects the gradient of the electrostatic potential of the atoms; that is, the atomic electric field, which is found to be sensitive to the crystal ionicity. Both the mesoscopic polarization fields within each domain and the atomic-scale electric fields induced by the individual electric dipoles within each unit cell can be sensitively detected in ferroelectric BaTiO 3 . The realization of atomic-resolution DPC microscopy opens a new dimension of microscopy from crystalline materials through to biological molecules.

The resolution of electron microscopy has increased through the years, and scientists have been able to measure progressively lighter elements. The ultimate goal has now been reached with the imaging of hydrogen atoms. Enhancing the imaging power of microscopy to identify all chemical types of atom, from low- to high-atomic-number elements,would significantly contribute for a direct determinationof material structures. Electron microscopes have successfully provided images of heavy-atom positions, particularly by the annular dark-field method 1 , 2 , but detection of light atoms was difficult owing to their weak scattering power. Recent developments of aberration-correction electron optics 3 , 4 , 5 have significantly advanced the microscope performance, enabling identification of individual light atoms such as oxygen 6 , 7 , 8 , 9 , nitrogen 7 , 9 , carbon 9 , 10 , 11 , boron 9 and lithium 12 , 13 . However, the lightest hydrogen atom has not yet been observed directly, except in the specific condition of hydrogen adatoms on a graphene membrane 14 . Here we show the first direct imaging of the hydrogen atom in a crystalline solid YH 2 , based on a classic ‘hollow-cone’ illumination theory 15 , 16 , 17 , 18 combined with state-of-the-art scanning transmission electronmicroscopy. The optimizedhollow-cone condition derived from the aberration-corrected microscope parameters confirms that the information transfer can be extended to 22.5 nm −1 , which corresponds to a spatial resolution of about 44.4 pm. These experimental conditions can be readily realized with the annular bright-field imaging in scanning transmission electron microscopy 19 , 20 according to reciprocity 21 , revealing successfully the hydrogen-atom columns as dark dots, as anticipated from phase contrast of a weak-phase object 22 .

Precise measurement and characterization of electrostatic potential structures and the concomitant electric fields at nanodimensions are essential to understand and control the properties of modern materials and devices. However, directly observing and measuring such local electric field information is still a major challenge in microscopy. Here, differential phase contrast imaging in scanning transmission electron microscopy with segmented type detector is used to image a p-n junction in a GaAs compound semiconductor. Differential phase contrast imaging is able to both clearly visualize and quantify the projected, built-in electric field in the p-n junction. The technique is further shown capable of sensitively detecting the electric field variations due to dopant concentration steps within both p -type and n -type regions. Through live differential phase contrast imaging, this technique can potentially be used to image the electromagnetic field structure of new materials and devices even under working conditions.

One of the most attractive applications of carbon nanomaterials is as catalysts, due to their extreme surface-to-volume ratio. The substitution of C with heteroatoms (typically B and N as p- and n-dopants) has been explored to enhance their catalytic activity. Here we show that encapsulation within weakly doping macrocycles can be used to modify the catalytic properties of the nanotubes towards the reduction of nitroarenes, either enhancing it (n-doping) or slowing it down (p-doping). This artificial regulation strategy presents a unique combination of features found in the natural regulation of enzymes: binding of the effectors (the macrocycles) is noncovalent, yet stable thanks to the mechanical link, and their effect is remote, but not allosteric, since it does not affect the structure of the active site. By careful design of the macrocycles’ structure, we expect that this strategy will contribute to overcome the major hurdles in SWNT-based catalysts: activity, aggregation, and specificity. Doping carbon nanomaterials with heteroatoms is the most common way to change their catalytic activity. Here, the authors show that the catalytic properties of single-walled carbon nanotubes can be modified by non-covalently encapsulating them within electron-accepting or electron-donating macrocycles to form rotaxane-like structures.

The interactions between magnetic skyrmions and structural defects, such as edges, dislocations, and grain boundaries (GBs), which are all considered as topological defects, will be important issues when magnetic skyrmions are utilized for future memory device applications. To investigate such interactions, simultaneous visualization of magnetic skyrmions and structural defects at high spatial resolution, which is not feasible by conventional techniques, is essential. Here, taking advantages of aberration-corrected differential phase-contrast scanning transmission electron microscopy, we investigate the interaction of magnetic skyrmions with a small-angle GB in a thin film of FeGe 1−x Si x . We found that the magnetic skyrmions and the small-angle GB can coexist each other, but a domain boundary (DB) was formed in the skyrmion lattice along the small-angle GB. At the core of the DB, unexpectedly deformed magnetic skrymions, which appear to be created by joining two portions of magnetic skyrmions in the adjacent lattices, were formed to effectively compensate misorientations between the two adjacent magnetic skyrmion lattices. These observations strongly suggest the flexible nature of individual magnetic skyrmions, and also the significance of defect engineering for future device applications.

A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene.

A method for measurement of the aberration status from high-resolution dark-field images is developed using scanning transmission electron microscopy (STEM), called the Segmented Image Autocorrelation function Matrix (SIAM). The method employs an autocorrelation function from the segmented area in the defocused STEM images from an aligned crystalline specimen to measure the defocus and twofold astigmatism for the probe-forming system. The values measured using this method can be fed directly back to the instrument by changing the strength of the stigmator and the objective lens of the microscope. It is successfully demonstrated that the feedback system can automatically correct the defocus and twofold astigmatism of the microscope after several iterations using practical STEM images from an actual crystalline specimen.