Bevel-edge epitaxy of ferroelectric rhombohedral boron nitride single crystal.

Within the family of two-dimensional dielectrics, rhombohedral boron nitride (rBN) is considerably promising owing to having not only the superior properties of hexagonal boron nitride1-4-including low permittivity and dissipation, strong electrical insulation, good chemical stability, high thermal conductivity and atomic flatness without dangling bonds-but also useful optical nonlinearity and interfacial ferroelectricity originating from the broken in-plane and out-of-plane centrosymmetry5-23. However, the preparation of large-sized single-crystal rBN layers remains a challenge24-26, owing to the requisite unprecedented growth controls to coordinate the lattice orientation of each layer and the sliding vector of every interface. Here we report a facile methodology using bevel-edge epitaxy to prepare centimetre-sized single-crystal rBN layers with exact interlayer ABC stacking on a vicinal nickel surface. We realized successful accurate fabrication over a single-crystal nickel substrate with bunched step edges of the terrace facet (100) at the bevel facet (110), which simultaneously guided the consistent boron-nitrogen bond orientation in each BN layer and the rhombohedral stacking of BN layers via nucleation near each bevel facet. The pure rhombohedral phase of the as-grown BN layers was verified, and consequently showed robust, homogeneous and switchable ferroelectricity with a high Curie temperature. Our work provides an effective route for accurate stacking-controlled growth of single-crystal two-dimensional layers and presents a foundation for applicable multifunctional devices based on stacked two-dimensional materials.

Magic Momenta and Three-Dimensional Landau Levels from a Three-Dimensional Graphite Moiré Superlattice.

In this Letter, we theoretically explore the physical properties of a new type of three-dimensional graphite moiré superlattice, the bulk alternating twisted graphite (ATG) system with homogeneous twist angle, which is grown by in situ chemical vapor decomposition method. Compared to twisted bilayer graphene (TBG), the bulk ATG system is bestowed with an additional wave vector degree of freedom due to the extra dimensionality. As a result, when the twist angle of bulk ATG is smaller than twice of the magic angle of TBG, there always exist "magic momenta" which host topological flat bands with vanishing in-plane Fermi velocities. Most saliently, when the twist angle is relatively large, a dispersionless three-dimensional zeroth Landau level would emerge in the bulk ATG, which may give rise to robust three-dimensional quantum Hall effects and unusual quantum-Hall physics over a large range of twist angles.

Pulchinenoside B4 ameliorates oral ulcers in rats by modulating gut microbiota and metabolites.

Pulchinenoside B4, a natural saponin monomer from the Pulsatilla plant, plays an important role as an immunomodulator in the treatment of acute inflammation. Oral ulcer (OU) is a common ulcerative injury disease that occurs in the oral mucosa, including mucosal ulceration and abnormalities of lips and tongue. A close correlation exists between gut microbiota and circulating metabolites in patients with OU. However, the correlation between gut microbiota and serum metabolomics is not clear. Therefore, this study aimed to explore the changes in gut microbiota and metabolites in OU. The 16S ribosomal RNA (16S rRNA) gene sequencing was used to detect the changes in the composition of gut microbiota in OU rat model. Moreover, the endogenous small metabolites were explored by collecting the non-targeted serum metabolomics data. A total of 34 OU-related biomarkers were identified, mainly related to fatty acid metabolism and inflammatory pathways. The administration of B4 effectively reduced the occurrence of OU and restored the levels of multiple endogenous biomarkers and key gut microbial species to the normal level. This study demonstrated that the gut microbiota and metabolites were altered in the OU rat model, which were significantly restored to the normal level by B4, thereby showing good application prospects in the treatment of OU. KEY POINTS: • The first investigating the correlation between OU and gut microbiota. • A close correlation between metabolites and gut microbiota in OU disease was successfully identified. • Pulchinenoside B4 ameliorates oral ulcers in rats by modulating gut microbiota and metabolites.

Atomic Ruthenium-Promoted Cadmium Sulfide for Photocatalytic Production of Amino Acids from Biomass Derivatives.

Amino acids are the building blocks of proteins and are widely used as important ingredients for other nitrogen-containing molecules. Here, we report the sustainable production of amino acids from biomass-derived hydroxy acids with high activity under visible-light irradiation and mild conditions, using atomic ruthenium-promoted cadmium sulfide (Ru1/CdS). On a metal basis, the optimized Ru1/CdS exhibits a maximal alanine formation rate of 26.0 molAla ⋅ gRu -1 ⋅ h-1, which is 1.7 times and more than two orders of magnitude higher than that of its nanoparticle counterpart and the conventional thermocatalytic process, respectively. Integrated spectroscopic analysis and density functional theory calculations attribute the high performance of Ru1/CdS to the facilitated charge separation and O-H bond dissociation of the α-hydroxy group, here of lactic acid. The operando nuclear magnetic resonance further infers a unique "double activation" mechanism of both the CH-OH and CH3-CH-OH structures in lactic acid, which significantly accelerates its photocatalytic amination toward alanine.

Direct In- and Out-of-Plane Writing of Metals on Insulators by Electron-Beam-Enabled, Confined Electrodeposition with Submicrometer Feature Size.

Additive microfabrication processes based on localized electroplating enable the one-step deposition of micro-scale metal structures with outstanding performance, e.g., high electrical conductivity and mechanical strength. They are therefore evaluated as an exciting and enabling addition to the existing repertoire of microfabrication technologies. Yet, electrochemical processes are generally restricted to conductive or semiconductive substrates, precluding their application in the manufacturing of functional electric devices where direct deposition onto insulators is often required. Here, the direct, localized electrodeposition of copper on a variety of insulating substrates, namely Al2O3, glass and flexible polyethylene, is demonstrated, enabled by electron-beam-induced reduction in a highly confined liquid electrolyte reservoir. The nanometer-size of the electrolyte reservoir, fed by electrohydrodynamic ejection, enables a minimal feature size on the order of 200 nm. The fact that the transient reservoir is established and stabilized by electrohydrodynamic ejection rather than specialized liquid cells can offer greater flexibility toward deposition on arbitrary substrate geometries and materials. Installed in a low-vacuum scanning electron microscope, the setup further allows for operando, nanoscale observation and analysis of the manufacturing process.

Metabolomic analysis to understand the mechanism of Ti3C2Tx (MXene) toxicity in Daphnia magna.

Due to their potential release into the environment, the ecotoxicity of Ti3C2Tx (MXene) nanomaterials is a growing concern. Unfortunately, little is known about the toxic effects and mechanisms through which Ti3C2Tx induces toxicity in aquatic organisms. The aim of this study is thus to investigate the toxic effects and mechanisms of Daphnia magna upon exposure to Ti3C2Tx with different sheet sizes (100 nm [Ti3C2Tx-100] and 500 nm [Ti3C2Tx-500]) by employing conventional toxicology and metabolomics analysis. The results showed that exposure to both Ti3C2Tx-100 and Ti3C2Tx-500 at 10 µg/mL resulted in a significant accumulation of Ti3C2Tx in D. magna, but no effects on the mortality or growth of D. magna were observed. However, the metabolomics results revealed that Ti3C2Tx-100 and Ti3C2Tx-500 induced significant changes in up to 265 and 191 differential metabolites in D. magna, respectively, of which 116 metabolites were common for both. Ti3C2Tx-100-induced metabolites were mainly enriched in phospholipid, pyrimidine, tryptophan, and arginine metabolism, whereas Ti3C2Tx-500-induced metabolites were mainly enriched in the glycerol-ester, tryptophan, and glyoxylate metabolism and the pentose phosphate pathway. These results indicated that the toxicity of Ti3C2Tx to D. magna has a size-dependent effect at the metabolic level, and both sheet sizes of Ti3C2Tx can lead to metabolic disturbances in D. magna by interfering with lipid and amino acid metabolism pathways.

Unraveling the Nanoscale Segregation Mechanism in N-Doped Niobium for Enhanced SRF Performance.

The nitrogen doping (N-doping) treatment for niobium superconducting radio-frequency (SRF) cavities is one of the key enabling technologies that support the development of more efficient future large accelerators. However, the N-doping results have diverged due to a complex chemical profile under the nitrogen-doped surface. Particularly, under industrial-scale production conditions, it is difficult to understand the underlying mechanism thus hindering performance improvement. Herein, a combination of spatially resolved and surface-sensitive approaches is employed to establish the detailed near-surface phase composition of thermally processed niobium. The results show that intermediate phase segregations, particularly the nanometric carbon-rich phase, can impede the nitridation process and limit the interactions between nitrogen and the niobium sub-surface. In comparison, the removal of the carbon-rich layer at the Nb surface leads to enhanced nitrogen binding at the Nb surface. Combining the RF test results, it is shown that the complex uniformity and grain boundary penetrations of impurity elements have a direct correlation with the mid-field quench behavior in the N-doped Nb cavities. Therefore, proper control of the nanometric intermediate phase formation in discrete thermal steps is critical in improving the ultimate performance and production yield of the Nb cavities.

Extremely large magnetoresistance in twisted intertwined graphene spirals.

Extremely large magnetoresistance (XMR) is highly applicable in spintronic devices such as magnetic sensors, magnetic memory, and hard drives. Typically, XMR is found in Weyl semimetals characterized by perfect electron-hole symmetry or exceptionally high electric conductivity and mobility. Our study explores this phenomenon in a recently developed graphene moiré system, which demonstrates XMR owing to its topological structure and high-quality crystal formation. We investigate the electronic properties of three-dimensional intertwined twisted graphene spirals (TGS), manipulating the screw dislocation axis to achieve a rotation angle of 7.3°. Notably, at 14 T and 2 K, the magnetoresistance of these structures reaches 1.7 × 107%, accompanied by a metal-insulator transition as the temperature increases. This transition becomes noticeable when the magnetic field exceeds a minimal threshold of approximately 0.1 T. These observations suggest the possible existence of complex, correlated states within the partially filled three-dimensional Landau levels of the 3D TGS system. Our findings open up possibilities for achieving XMR by engineering the topological structure of 2D layered moiré systems.

WS2 ribbon arrays with defined chirality and coherent polarity.

One-dimensional transition metal dichalcogenides exhibiting an enhanced bulk photovoltaic effect have the potential to exceed the Shockley-Queisser limit efficiency in solar energy harvest within p-n junction architectures. However, the collective output of these prototype devices remains a challenge. We report on the synthesis of single-crystalline WS2 ribbon arrays with defined chirality and coherent polarity through an atomic manufacturing strategy. The chirality of WS2 ribbon was defined by substrate couplings into tunable armchair, zigzag, and chiral species, and the polarity direction was determined by the ribbon-precursor interfacial energy along a coherent direction. A single armchair ribbon showed strong bulk photovoltaic effect and the further integration of ~1000 aligned ribbons with coherent polarity enabled upscaling of the photocurrent.

Phylogenetic diversity of functional genes in deep-sea cold seeps: a novel perspective on metagenomics.

BACKGROUND: Leakages of cold, methane-rich fluids from subsurface reservoirs to the sea floor are termed cold seeps. Recent exploration of the deep sea has shed new light on the microbial communities in cold seeps. However, conventional metagenomic methods largely rely on reference databases and neglect the phylogeny of functional genes. RESULTS: In this study, we developed the REMIRGE program to retrieve the full-length functional genes from shotgun metagenomic reads and fully explored the phylogenetic diversity in cold seep sediments. The abundance and diversity of functional genes involved in the methane, sulfur, and nitrogen cycles differed in the non-seep site and five cold seep sites. In one Haima cold seep site, the divergence of functional groups was observed at the centimeter scale of sediment depths, with the surface layer potentially acting as a reservoir of microbial species and functions. Additionally, positive correlations were found between specific gene sequence clusters of relevant genes, indicating coupling occurred within specific functional groups. CONCLUSION: REMIRGE revealed divergent phylogenetic diversity of functional groups and functional pathway preferences in a deep-sea cold seep at finer scales, which could not be detected by conventional methods. Our work highlights that phylogenetic information is conducive to more comprehensive functional profiles, and REMIRGE has the potential to uncover more new insights from shotgun metagenomic data. Video Abstract.

iNAP: An integrated network analysis pipeline for microbiome studies.

Integrated network analysis pipeline (iNAP) is an online analysis pipeline for generating and analyzing comprehensive ecological networks in microbiome studies. It is implemented in two sections, that is, network construction and network analysis, and integrates many open-access tools. Network construction contains multiple feasible alternatives, including correlation-based approaches (Pearson's correlation and Spearman's rank correlation along with random matrix theory, and sparse correlations for compositional data) and conditional dependence-based methods (extended local similarity analysis and sparse inverse covariance estimation for ecological association inference), while network analysis provides topological structures at different levels and the potential effects of environmental factors on network structures. Considering the full workflow, from microbiome data set to network result, iNAP contains the molecular ecological network analysis pipeline and interdomain ecological network analysis pipeline (IDENAP), which correspond to the intradomain and interdomain associations of microbial species at multiple taxonomic levels. Here, we describe the detailed workflow by taking IDENAP as an example and show the comprehensive steps to assist researchers to conduct the relevant analyses using their own data sets. Afterwards, some auxiliary tools facilitating the pipeline are introduced to effectively aid in the switch from local analysis to online operations. Therefore, iNAP, as an easy-to-use platform that provides multiple network-associated tools and approaches, can enable researchers to better understand the organization of microbial communities. iNAP is available at http://mem.rcees.ac.cn:8081 with free registration.