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.

Seeded growth of large single-crystal copper foils with high-index facets.

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering1-5. For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically6,7 nor kinetically3 favourable compared to low-index facets6-18. Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30 × 20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation.

Epitaxial growth of a 100-square-centimetre single-crystal hexagonal boron nitride monolayer on copper.

The development of two-dimensional (2D) materials has opened up possibilities for their application in electronics, optoelectronics and photovoltaics, because they can provide devices with smaller size, higher speed and additional functionalities compared with conventional silicon-based devices1. The ability to grow large, high-quality single crystals for 2D components-that is, conductors, semiconductors and insulators-is essential for the industrial application of 2D devices2-4. Atom-layered hexagonal boron nitride (hBN), with its excellent stability, flat surface and large bandgap, has been reported to be the best 2D insulator5-12. However, the size of 2D hBN single crystals is typically limited to less than one millimetre13-18, mainly because of difficulties in the growth of such crystals; these include excessive nucleation, which precludes growth from a single nucleus to large single crystals, and the threefold symmetry of the hBN lattice, which leads to antiparallel domains and twin boundaries on most substrates19. Here we report the epitaxial growth of a 100-square-centimetre single-crystal hBN monolayer on a low-symmetry Cu (110) vicinal surface, obtained by annealing an industrial copper foil. Structural characterizations and theoretical calculations indicate that epitaxial growth was achieved by the coupling of Cu <211> step edges with hBN zigzag edges, which breaks the equivalence of antiparallel hBN domains, enabling unidirectional domain alignment better than 99 per cent. The growth kinetics, unidirectional alignment and seamless stitching of the hBN domains are unambiguously demonstrated using centimetre- to atomic-scale characterization techniques. Our findings are expected to facilitate the wide application of 2D devices and lead to the epitaxial growth of broad non-centrosymmetric 2D materials, such as various transition-metal dichalcogenides20-23, to produce large single crystals.

Visualizing the Anomalous Catalysis in Two-Dimensional Confined Space.

Confined nanospaces provide a new platform to promote catalytic reactions. However, the mechanism of catalytic enhancement in the nanospace still requires insightful exploration due to the lack of direct visualization. Here, we report operando investigations on the etching and growth of graphene in a two-dimensional (2D) confined space between graphene and a Cu substrate. We observed that the graphene layer between the Cu and top graphene layer was surprisingly very active in etching (more than 10 times faster than the etching of the top graphene layer). More strikingly, at a relatively low temperature (∼530 °C), the etched carbon radicals dissociated from the bottom layer, in turn feeding the growth of the top graphene layer with a very high efficiency. Our findings reveal the in situ dynamics of the anomalous confined catalytic processes in 2D confined spaces and thus pave the way for the design of high-efficiency catalysts.

Interfacial engineering in graphene bandgap.

Graphene exhibits superior mechanical strength, high thermal conductivity, strong light-matter interactions, and, in particular, exceptional electronic properties. These merits make graphene an outstanding material for numerous potential applications. However, a graphene-based high-performance transistor, which is the most appealing application, has not yet been produced, which is mainly due to the absence of an intrinsic electronic bandgap in this material. Therefore, bandgap opening in graphene is urgently needed, and great efforts have been made regarding this topic over the past decade. In this review article, we summarise recent theoretical and experimental advances in interfacial engineering to achieve bandgap opening. These developments are divided into two categories: chemical engineering and physical engineering. Chemical engineering is usually destructive to the pristine graphene lattice via chemical functionalization, the introduction of defects, doping, chemical bonds with substrates, and quantum confinement; the latter largely maintains the atomic structure of graphene intact and includes the application of an external field, interactions with substrates, physical adsorption, strain, electron many-body effects and spin-orbit coupling. Although these pioneering works have not met all the requirements for electronic applications of graphene at once, they hold great promise in this direction and may eventually lead to future applications of graphene in semiconductor electronics and beyond.

Fast Growth of Strain-Free AlN on Graphene-Buffered Sapphire.

We study the roles of graphene acting as a buffer layer for growth of an AlN film on a sapphire substrate. Graphene can reduce the density of AlN nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in AlN and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AlN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry.

Unique Transformation from Graphene to Carbide on Re(0001) Induced by Strong Carbon-Metal Interaction.

During graphene growth on various transition metals in the periodic table, metal carbides always emerge to behave as complex intermediates. On VIII metals, metastable carbides usually evolve and then transform into graphene along the phase interfaces, and even no metal carbides can form on IB-IIB metals. In contrast, during graphene growth on group IVB-VIB metals, carbides are usually generated even before the evolution of graphene and stably exist throughout the whole growth process. However, for the remaining transition metals, e.g., group VIIB, located in between IVB-VIB and VIII, the interplay between graphene and carbide is still vague. Herein, on Re(0001) (VIIB), we have revealed a novel transition from graphene to metal carbide (reverse to that on VIII metals) for the first time. This transition experienced graphene decomposition, dissolution, and carbon segregation processes, as evidenced by scanning tunneling microscopy (STM) and on-site, variable-temperature low electron energy diffraction (LEED) characterizations. This work thus completes the picture about the interplay between graphene and carbide on/in transition metals in the periodic table, as well as discloses a new territory for the growth of carbon-related materials, especially the metal carbide.

[Analysis of treatment efficacy for congenital hypothyroidism in some regions of Yunnan Province, China].

OBJECTIVE: To observe the effects of initial doses and treatment timing of levothyroxine (L-T4) on the clinical efficacy in children with congenital hypothyroidism (CH). METHODS: This study included 98 children who had an abnormal level of thyroid stimulating hormone (TSH) in neonatal screening in four regions of Yunnan Province and who finally had a confirmed diagnosis of CH. They received treatment with L-T4 and were divided into standard dose group (10-15 µg/kg per day) and low dose group (<10 µg/kg per day) by the therapeutic dose of L-T4. Meanwhile, these patients were also classified into two treatment groups based on the starting time of L-T4 treatment, namely under 2 months old group and more than 2 months old group. The thyroid function and physical and neural development were examined before and after treatment. RESULTS: Compared with the low dose group, the standard dose group had a significantly lower TSH level and a significantly higher free thyroxine (FT4) level at 2 weeks after treatment (P<0.05). There were no significant differences in TSH and FT4 levels at other time points after treatment between the standard and low dose groups (P>0.05). The physical and neural development were not significantly different between the two dose groups before and at all time points after treatment (P>0.05). At all time points after treatment, the levels of TSH and FT4 and physical development were not significantly different between the different starting time groups (P>0.05). However, the Gesell score was significantly higher in the under 2 months old group than in the more than 2 months old group at all time points after treatment (P<0.05). CONCLUSIONS: The standard dose group has a better treatment outcome than the low dose group, whereas the symptoms of hyperthyroidism deserve close attention. The treatment timing is vital to the neurodevelopment of children with CH. Once diagnosed, the patients should receive treatments immediately.

Direct observation of ordered configurations of hydrogen adatoms on graphene.

Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated, and searched for. Here, we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. Scanning tunneling spectroscopy measurements revealed a substantial gap in the local density of states in H-contained regions as well as in-gap states below the conduction band due to the incompleteness of H ordering. These findings can be well explained by density functional theory calculations based on double-sided H configurations. In addition, factors that may influence H ordering are discussed.

The role of cGAS/STING signaling in ophthalmological diseases.

The eye is one of the most vulnerable parts of the human body. There are many kinds of ophthalmic diseases, which are caused by multiple factors. Generally, ophthalmic diseases have the characteristics of complicated etiology and difficult therapy. With the development of the times, ophthalmic diseases have become a major problem that affects people's lives. Inflammation, a major factor inducing ocular diseases, is one of the most popular research directions. The cGAS/STING pathway is a recently discovered inflammatory signaling pathway, which recognizes double-stranded DNA (dsDNA) as an activation signal to promote the expression of downstream cytokines that promote inflammatory response or autoimmune response. Since most of the current treatments for ophthalmic diseases mainly rely on surgery, it is of positive significance to explore the pathogenesis for the discovery of drug targets. This review summarize the research progress of the cGAS/STING pathway in major ophthalmic diseases by introducing the correlation between classical inflammatory pathway and ophthalmic diseases, in order to predict the research direction and methods targeting the cGAS/STING pathway in the pathogenesis of ophthalmic diseases, and also provide guidance for the mechanism as well as molecular targets of ophthalmic diseases.

Recent Advances in Layered-Double-Hydroxide-Based Separation Membranes.

The use of two-dimensional materials shows great promise for the development of next-generation membrane materials, thanks to their atomic thinness and the ease with which precise nanochannels can be constructed. Among these materials, layered double hydroxides (LDHs) stand out as an important class, possessing many features that make them ideal for constructing high-performance membranes. LDHs offer many advantages, such as their abundant and tunable interlayer anions, which enable the preparation of membranes with adjustable sub-nanometer pore sizes. Additionally, their hydrophilicity and positive charge characteristics afford them unique benefits. LDHs have been found to be effective in gas separation, ion sieving, and nanofiltration. This review provides a summary of the latest progress in using LDHs for membrane separation. It begins by introducing the basic properties of LDHs, followed by the assembly strategy for LDH membranes. Furthermore, the review presents the research status of LDHs membranes in various fields in a systematic manner. Lastly, the paper highlights some challenges and future prospects for preparing and applying LDHs membranes.

Phase-selective in-plane heteroepitaxial growth of H-phase CrSe2.

Phase engineering of two-dimensional transition metal dichalcogenides (2D-TMDs) offers opportunities for exploring unique phase-specific properties and achieving new desired functionalities. Here, we report a phase-selective in-plane heteroepitaxial method to grow semiconducting H-phase CrSe2. The lattice-matched MoSe2 nanoribbons are utilized as the in-plane heteroepitaxial template to seed the growth of H-phase CrSe2 with the formation of MoSe2-CrSe2 heterostructures. Scanning tunneling microscopy and non-contact atomic force microscopy studies reveal the atomically sharp heterostructure interfaces and the characteristic defects of mirror twin boundaries emerging in the H-phase CrSe2 monolayers. The type-I straddling band alignments with band bending at the heterostructure interfaces are directly visualized with atomic precision. The mirror twin boundaries in the H-phase CrSe2 exhibit the Tomonaga-Luttinger liquid behavior in the confined one-dimensional electronic system. Our work provides a promising strategy for phase engineering of 2D TMDs, thereby promoting the property research and device applications of specific phases.

Electro-oxidation of Ibuprofen using carbon-supported SnOx-CeOx flow-anodes: The key role of high-valent metal.

Exploiting electrochemically active materials as flow-anodes can effectively alleviate mass transfer restriction in an electro-oxidation system. However, the electrocatalytic activity and persistence of the conventional flow-anode materials are insufficient, resulting in limited improvement in the electro-oxidation rate and efficiency. Herein, we reported a rational strategy to substantially enhance the electrocatalytic performance of flow-anodes in electro-oxidation by introducing the redox cycle of high-valent metal in a suitable carbon substrate. The characterization suggested that the SnOx-CeOx/carbon black (CB) featured well-distributed morphology, rapid charge transfer, high oxygen evolution potential, and strong water adsorption, and stood out among three kinds of SnOx-CeOx loaded carbon materials. Mechanistic analysis indicated that the redox cycle of Ce species played a key role in accelerating the electron transfer from SnOx to CB directionally and could continuously create the electron-deficient state of the SnOx, thereby sustainably triggering the generation of ·OH. All these features enabled the resulting SnOx-CeOx/CB flow-anode to accomplish a calculated maximum kinetic constant of 0.02461 1/min, a higher current efficiency of 47.1%, and a lower energy consumption of 21.3 kWh/kg COD compared with other conventional flow-anodes reported to date. Additionally, SnOx-CeOx/CB exhibited excellent stability with extremely low leaching concentrations of Sn and Ce ions. This study provides a feasible manner for efficient water decontamination using the electro-oxidation system with SnOx-CeOx/CB.

AKT2 deficiency alleviates doxorubicin-induced cardiac injury via alleviating oxidative stress in cardiomyocytes.

Doxorubicin (DOX), a widely used chemotherapy agent in cancer treatment, encounters limitations in clinical efficacy due to associated cardiotoxicity. This study aims to explore the role of AKT serine/threonine kinase 2 (AKT2) in mitigating DOX-induced oxidative stress within the heart through both intracellular and extracellular signaling pathways. Utilizing Akt2 knockout (KO) and Nrf2 KO murine models, alongside neonatal rat cardiomyocytes (NRCMs), we systematically investigate the impact of AKT2 deficiency on DOX-induced cardiac injury. Our findings reveal that DOX administration induces significant oxidative stress, a primary contributor to cardiac injury. Importantly, Akt2 deficiency exhibits a protective effect by alleviating DOX-induced oxidative stress. Mechanistically, Akt2 deficiency facilitates nuclear translocation of NRF2, thereby suppressing intracellular oxidative stress by promoting the expression of antioxidant genes. Furthermore, We also observed that AKT2 inhibition facilitates superoxide dismutase 2 (SOD2) expression both inside macrophages and SOD2 secretion to the extracellular matrix, which is involved in lowering oxidative stress in cardiomyocytes upon DOX stimulation. The present study underscores the important role of AKT2 in mitigating DOX-induced oxidative stress through both intracellular and extracellular signaling pathways. Additionally, our findings propose promising therapeutic strategies for addressing DOX-induced cardiomyopathy in clinic.

Cardiac injury activates STING signaling via upregulating SIRT6 in macrophages after myocardial infarction.

AIMS: This work sought to investigate the mechanism underlying the STING signaling pathway during myocardial infarction (MI), and explore the involvement and the role of SIRT6 in the process. MAIN METHODS: Mice underwent the surgery of permanent left anterior descending (LAD) artery constriction. Primary cardiomyocytes (CMs) and fibroblasts were subjected to hypoxia to mimic MI in vitro. STING expression was assessed in the infarct heart, and the effect of STING inhibition on cardiac fibrosis was explored. This study also evaluated the regulatory effect of STING by SIRT6 in macrophages. KEY FINDINGS: STING protein was increased in the infarct heart tissue, highlighting its involvement in the post-MI inflammatory response. Hypoxia-induced death of CMs and fibroblasts contributed to the upregulation of STING in macrophages, establishing the involvement of STING in the intercellular signaling during MI. Inhibition of STING resulted in a significant reduction of cardiac fibrosis at day 14 after MI. Additionally, this study identified SIRT6 as a key regulator of STING via influencing its acetylation and ubiquitination in macrophages, providing novel insights into the posttranscriptional modification and expression of STING at the acute phase after myocardial infarction. SIGNIFICANCE: This work shows the key role of SIRT6/STING signaling in the pathogenesis of cardiac injury after MI, suggesting that targeting this regulatory pathway could be a promising strategy to attenuate cardiac fibrosis after MI.

Remote epitaxy of single-crystal rhombohedral WS2 bilayers.

Compared to transition metal dichalcogenide (TMD) monolayers, rhombohedral-stacked (R-stacked) TMD bilayers exhibit remarkable electrical performance, enhanced nonlinear optical response, giant piezo-photovoltaic effect and intrinsic interfacial ferroelectricity. However, from a thermodynamics perspective, the formation energies of R-stacked and hexagonal-stacked (H-stacked) TMD bilayers are nearly identical, leading to mixed stacking of both H- and R-stacked bilayers in epitaxial films. Here, we report the remote epitaxy of centimetre-scale single-crystal R-stacked WS2 bilayer films on sapphire substrates. The bilayer growth is realized by a high flux feeding of the tungsten source at high temperature on substrates. The R-stacked configuration is achieved by the symmetry breaking in a-plane sapphire, where the influence of atomic steps passes through the lower TMD layer and controls the R-stacking of the upper layer. The as-grown R-stacked bilayers show up-to-30-fold enhancements in carrier mobility (34 cm2V-1s-1), nearly doubled circular helicity (61%) and interfacial ferroelectricity, in contrast to monolayer films. Our work reveals a growth mechanism to obtain stacking-controlled bilayer TMD single crystals, and promotes large-scale applications of R-stacked TMD.

Universal epitaxy of non-centrosymmetric two-dimensional single-crystal metal dichalcogenides.

The great challenge for the growth of non-centrosymmetric 2D single crystals is to break the equivalence of antiparallel grains. Even though this pursuit has been partially achieved in boron nitride and transition metal dichalcogenides (TMDs) growth, the key factors that determine the epitaxy of non-centrosymmetric 2D single crystals are still unclear. Here we report a universal methodology for the epitaxy of non-centrosymmetric 2D metal dichalcogenides enabled by accurate time sequence control of the simultaneous formation of grain nuclei and substrate steps. With this methodology, we have demonstrated the epitaxy of unidirectionally aligned MoS2 grains on a, c, m, n, r and v plane Al2O3 as well as MgO and TiO2 substrates. This approach is also applicable to many TMDs, such as WS2, NbS2, MoSe2, WSe2 and NbSe2. This study reveals a robust mechanism for the growth of various 2D single crystals and thus paves the way for their potential applications.

Stamped production of single-crystal hexagonal boron nitride monolayers on various insulating substrates.

Controllable growth of two-dimensional (2D) single crystals on insulating substrates is the ultimate pursuit for realizing high-end applications in electronics and optoelectronics. However, for the most typical 2D insulator, hexagonal boron nitride (hBN), the production of a single-crystal monolayer on insulating substrates remains challenging. Here, we propose a methodology to realize the facile production of inch-sized single-crystal hBN monolayers on various insulating substrates by an atomic-scale stamp-like technique. The single-crystal Cu foils grown with hBN films can stick tightly (within 0.35 nm) to the insulating substrate at sub-melting temperature of Cu and extrude the hBN grown on the metallic surface onto the insulating substrate. Single-crystal hBN films can then be obtained by removing the Cu foil similar to the stamp process, regardless of the type or crystallinity of the insulating substrates. Our work will likely promote the manufacturing process of fully single-crystal 2D material-based devices and their applications.

Dual-coupling-guided epitaxial growth of wafer-scale single-crystal WS2 monolayer on vicinal a-plane sapphire.

The growth of wafer-scale single-crystal two-dimensional transition metal dichalcogenides (TMDs) on insulating substrates is critically important for a variety of high-end applications1-4. Although the epitaxial growth of wafer-scale graphene and hexagonal boron nitride on metal surfaces has been reported5-8, these techniques are not applicable for growing TMDs on insulating substrates because of substantial differences in growth kinetics. Thus, despite great efforts9-20, the direct growth of wafer-scale single-crystal TMDs on insulating substrates is yet to be realized. Here we report the successful epitaxial growth of two-inch single-crystal WS2 monolayer films on vicinal a-plane sapphire surfaces. In-depth characterizations and theoretical calculations reveal that the epitaxy is driven by a dual-coupling-guided mechanism, where the sapphire plane-WS2 interaction leads to two preferred antiparallel orientations of the WS2 crystal, and sapphire step edge-WS2 interaction breaks the symmetry of the antiparallel orientations. These two interactions result in the unidirectional alignment of nearly all the WS2 islands. The unidirectional alignment and seamless stitching of WS2 islands are illustrated via multiscale characterization techniques; the high quality of WS2 monolayers is further evidenced by a photoluminescent circular helicity of ~55%, comparable to that of exfoliated WS2 flakes. Our findings offer the opportunity to boost the production of wafer-scale single crystals of a broad range of two-dimensional materials on insulators, paving the way to applications in integrated devices.

High-efficiency CO2 separation using hybrid LDH-polymer membranes.

Membrane-based gas separation exhibits many advantages over other conventional techniques; however, the construction of membranes with simultaneous high selectivity and permeability remains a major challenge. Herein, (LDH/FAS)n-PDMS hybrid membranes, containing two-dimensional sub-nanometre channels were fabricated via self-assembly of unilamellar layered double hydroxide (LDH) nanosheets and formamidine sulfinic acid (FAS), followed by spray-coating with a poly(dimethylsiloxane) (PDMS) layer. A CO2 transmission rate for (LDH/FAS)25-PDMS of 7748 GPU together with CO2 selectivity factors (SF) for SF(CO2/H2), SF(CO2/N2) and SF(CO2/CH4) mixtures as high as 43, 86 and 62 respectively are observed. The CO2 permselectivity outperforms most reported systems and is higher than the Robeson or Freeman upper bound limits. These (LDH/FAS)n-PDMS membranes are both thermally and mechanically robust maintaining their highly selective CO2 separation performance during long-term operational testing. We believe this highly-efficient CO2 separation performance is based on the synergy of enhanced solubility, diffusivity and chemical affinity for CO2 in the sub-nanometre channels.