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We report on the three-dimensional (3D) structure determination of a twisted hexagonal boron nitride (h-BN) heterointerface from a single-view dataset using multislice ptychography. We identify the buried heterointerface between two twisted h-BN flakes with a lateral resolution of 0.57 Å and a depth resolution of 2.5 nm. The latter represents a significant improvement (∼2.7 times) over the aperture-limited depth resolution of incoherent imaging modes, such as annular-dark-field scanning transmission electron microscopy. This improvement is attributed to the diffraction signal extending beyond the aperture edge, with the depth resolution set by the curvature of the Ewald sphere. Future advancements in this approach could enhance the depth resolution to the subnanometer level and enable the identification of individual dopants, defects, and color centers in twisted heterointerfaces and other materials.

Hexagonal boron nitride (hBN), also known as white graphite, is a transparent layered crystal with a wide bandgap. Its crystal structure resembles graphite, featuring layers composed of honeycomb lattices held together through van der Waals forces. The layered crystal structure of hBN facilitates exfoliation into thinner flakes and makes it highly anisotropic in in-plane and out-of-plane directions. Unlike graphite, hBN is both insulating and transparent, making it an ideal material for isolating devices from the environment and acting as a waveguide. As a result, hBN has found extensive applications in optical devices, electronic devices, and quantum photonic devices. This comprehensive tutorial aims to provide readers with a thorough understanding of hBN, covering its synthesis, lattice and spectroscopic characterization, and various applications in optoelectronic and quantum photonic devices. This tutorial is designed for both readers without prior experience in hBN and those with expertise in specific fields seeking to understand its relevance and connections to others.

We report the development of deep-learning coherent electron diffractive imaging at subangstrom resolution using convolutional neural networks (CNNs) trained with only simulated data. We experimentally demonstrate this method by applying the trained CNNs to recover the phase images from electron diffraction patterns of twisted hexagonal boron nitride, monolayer graphene, and a gold nanoparticle with comparable quality to those reconstructed by a conventional ptychographic algorithm. Fourier ring correlation between the CNN and ptychographic images indicates the achievement of a resolution in the range of 0.70 and 0.55 Å. We further develop CNNs to recover the probe function from the experimental data. The ability to replace iterative algorithms with CNNs and perform real-time atomic imaging from coherent diffraction patterns is expected to find applications in the physical and biological sciences.

Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-Ångstrom spatial resolution. These electric field maps represent the integrated effect of the nucleus, core electrons and valence electrons, and separating their contributions is non-trivial. In this paper, we utilized simultaneously acquired 4D-STEM center of mass (CoM) images and annular dark field (ADF) images to determine the projected electron charge density in monolayer MoS2. We evaluate the contributions of both the core electrons and the valence electrons to the derived electron charge density; however, due to blurring by the probe shape, the valence electron contribution forms a nearly featureless background while most of the spatial modulation comes from the core electrons. Our findings highlight the importance of probe shape in interpreting charge densities derived from 4D-STEM and the need for smaller electron probes.

The engineering of atomically-precise nanopores in two-dimensional materials presents exciting opportunities for both fundamental science studies as well as applications in energy, DNA sequencing, and quantum information technologies. The exceptional chemical and thermal stability of hexagonal boron nitride (h-BN) suggest that exposed h-BN nanopores will retain their atomic structure even when subjected to extended periods of time in gas or liquid environments. Here we employ transmission electron microscopy to examine the time evolution of h-BN nanopores in vacuum and in air and find, even at room temperature, dramatic geometry changes due to atom motion and edge contamination adsorption, for timescales ranging from one hour to one week. The discovery of nanopore evolution contrasts with general expectations and has profound implications for nanopore applications of two-dimensional materials.

The colour centre platform holds promise for quantum technologies, and hexagonal boron nitride has attracted attention due to the high brightness and stability, optically addressable spin states and wide wavelength coverage discovered in its emitters. However, its application is hindered by the typically random defect distribution and complex mesoscopic environment. Here, employing cathodoluminescence, we demonstrate on-demand activation and control of colour centre emission at the twisted interface of two hexagonal boron nitride flakes. Further, we show that colour centre emission brightness can be enhanced by two orders of magnitude by tuning the twist angle. Additionally, by applying an external voltage, nearly 100% brightness modulation is achieved. Our ab initio GW and GW plus Bethe-Salpeter equation calculations suggest that the emission is correlated to nitrogen vacancies and that a twist-induced moiré potential facilitates electron-hole recombination. This mechanism is further exploited to draw nanoscale colour centre patterns using electron beams.

Substituting heteroatoms into graphene can tune its properties for applications ranging from catalysis to spintronics. The further recent discovery that covalent impurities in graphene can be manipulated at atomic precision using a focused electron beam may open avenues towards sub-nanometer device architectures. However, the preparation of clean samples with a high density of dopants is still very challenging. Here, we report vacancy-mediated substitution of aluminium into laser-cleaned graphene, and without removal from our ultra-high vacuum apparatus, study their dynamics under 60 keV electron irradiation using aberration-corrected scanning transmission electron microscopy and spectroscopy. Three- and four-coordinated Al sites are identified, showing excellent agreement with ab initio predictions including binding energies and electron energy-loss spectrum simulations. We show that the direct exchange of carbon and aluminium atoms predicted earlier occurs under electron irradiation, although unexpectedly it is less probable than the same process for silicon. We also observe a previously unknown nitrogen-aluminium exchange that occurs at Al─N double-dopant sites at graphene divacancies created by our plasma treatment.

We report the development of deep learning coherent electron diffractiveimaging at sub-angstrom resolution using convolutional neural networks (CNNs)trained with only simulated data. We experimentally demonstrate this method byapplying the trained CNNs to directly recover the phase images from electrondiffraction patterns of twisted hexagonal boron nitride, monolayer graphene anda Au nanoparticle with comparable quality to those reconstructed by aconventional ptychographic method. Fourier ring correlation between the CNN andptychographic images indicates the achievement of a spatial resolution in therange of 0.70 and 0.55 angstrom (depending on different resolution criteria).The ability to replace iterative algorithms with CNNs and perform real-timeimaging from coherent diffraction patterns is expected to find broadapplications in the physical and biological sciences.

Epitaxial heterostructures based on oxide perovskites and III-V, II-VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics1-7. Halide perovskites-an emerging family of tunable semiconductors with desirable properties-are attractive for applications such as solution-processed solar cells, light-emitting diodes, detectors and lasers8-15. Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration16,17. Atomically sharp epitaxial interfaces are necessary to improve performance and for device miniaturization. However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility, which leads to interdiffusion and large junction widths18-21, and owing to their poor chemical stability, which leads to decomposition of prior layers during the fabrication of subsequent layers. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance22-26. Here we report an effective strategy to substantially inhibit in-plane ion diffusion in two-dimensional halide perovskites by incorporating rigid π-conjugated organic ligands. We demonstrate highly stable and tunable lateral epitaxial heterostructures, multiheterostructures and superlattices. Near-atomically sharp interfaces and epitaxial growth are revealed by low-dose aberration-corrected high-resolution transmission electron microscopy. Molecular dynamics simulations confirm the reduced heterostructure disorder and larger vacancy formation energies of the two-dimensional perovskites in the presence of conjugated ligands. These findings provide insights into the immobilization and stabilization of halide perovskite semiconductors and demonstrate a materials platform for complex and molecularly thin superlattices, devices and integrated circuits.

Chip capacitors used in pulsed filed can offer extraordinary discharge energy under elevated electric fields which can be used in high power pulse. However, the low energy density for dielectric ceramic limits the total discharge energy, instead, multilayer-structured design needs to be developed. The ensuing problem is to develop low-temperature sintered ceramics which can be used for the fabrication of multilayered ceramics by cofiring with low-cost Cu electrode. The present study aims to lower sintering temperature and tailors antiferroelectric performances of Cd-doped (Pb, La)(Sn, Zr, Ti)O3 (PCLSZT) ceramics by phase regulation. The case indicates that the modification of Cd largely reduces the sintering temperature, while Ti regulation can gradually induce an orthorhombic-tetragonal phase transition to optimize dielectric energy storage. The promising energy properties can be obtained (Pb0.955Cd0.015La0.02)(Sn0.5Zr0.45Ti0.05)O3 under a low field of 260 kV/cm with a charge energy density of 3.52 J/cm3, an energy efficiency of 85%, respectively, accompanied by a rapid discharge speed of t0.9 = 0.74 μs. This indicates the tunability of energy property in AFE Cd-doped PCLSZT ceramics, thereby providing a potential alternative to develop emerging materials for multilayered pulsed power components. [ABSTRACT FROM AUTHOR]

Systemic sclerosis (SSc) is an autoimmune connective tissue disease with skin fibrosis being the first and most common manifestation. Patients with SSc have a higher risk of developing malignant tumors than the general population. However, the sequence and underlying mechanisms linking SSc to malignancy remain controversial. This article presents the case of a 59-year-old woman who was diagnosed with SSc after developing skin fibrosis during neoadjuvant therapy for breast cancer. Despite aggressive antitumor treatments, including targeted therapy, SSc did not improve and progressed rapidly with increasing dermatofibrosis. Remarkably, the SSc entered remission following the cessation of antitumor therapy. Additionally, we reviewed the literature on SSc and malignant tumors, examined their relationship, and discussed key points regarding their identification and potential for adverse drug reactions. [ABSTRACT FROM AUTHOR]

Author(s): Pin-Chun Shen [sup.1] , Cong Su [sup.2] [sup.3] [sup.4] [sup.5] , Yuxuan Lin [sup.1] [sup.6] , Ang-Sheng Chou [sup.7] [sup.8] , Chao-Ching Cheng [sup.7] , Ji-Hoon Park [sup.1] , [...], Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered.sup.1,2. Atomically thin two-dimensional semiconductors have great potential for realizing high-performance electronic devices.sup.1,3. However, owing to metal-induced gap states (MIGS).sup.4-7, energy barriers at the metal-semiconductor interface--which fundamentally lead to high contact resistance and poor current-delivery capability--have constrained the improvement of two-dimensional semiconductor transistors so far.sup.2,8,9. Here we report ohmic contact between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where the MIGS are sufficiently suppressed and degenerate states in the TMD are spontaneously formed in contact with bismuth. Through this approach, we achieve zero Schottky barrier height, a contact resistance of 123 ohm micrometres and an on-state current density of 1,135 microamps per micrometre on monolayer MoS.sub.2; these two values are, to the best of our knowledge, the lowest and highest yet recorded, respectively. We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS.sub.2, WS.sub.2 and WSe.sub.2. Our reported contact resistances are a substantial improvement for two-dimensional semiconductors, and approach the quantum limit. This technology unveils the potential of high-performance monolayer transistors that are on par with state-of-the-art three-dimensional semiconductors, enabling further device downscaling and extending Moore's law. Electric contacts of semimetallic bismuth on monolayer semiconductors are shown to suppress metal-induced gap states and thus have very low contact resistance and a zero Schottky barrier height.