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Bioceramics for hard tissue repair in the fields of dentistry or orthopedics should have the ability to promote adhesion, proliferation and differentiation of osteoblast cells. In this study, different BaTiO3 (BT) ratio modified 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) discs were prepared by conventional sintering. The specimen surfaces were characterized using scanning electron microscopy (SEM). The wettability of the material surface was measured by the water contact angle. Human osteoblastic cells (MG63) were used for the in vitro experiments. The cytotoxicity of the material was detected by the MTT assay. Cell morphology on the material surface was observed by SEM. The expression of alkaline phosphatase (ALP), and the expression of osteogenic associated genes such as runt-related transcription factor 2 (RUNX2), transforming growth factor beta (TGF-β), bone morphogenetic protein 4 (BMP4) and osteocalcin (OCN) were assessed to detect the osteogenic potential of the ceramic composites. Results showed that the BT ratio influenced the surface porosities of the ceramics. The 5 mol% BT/3Y-TZP group had a higher density and lower open porosity than 3 mol% and 7 mol% BT/3Y-TZP. The different surface porosities further affect the hydrophilicity of the surface. In comparison with the other groups, 5 mol% BT/3Y-TZP ceramic composite also had a significantly lower water contact angle, which demonstrated a superior hydrophilicity of the surface. A fine biocompatibility of the BT/3Y-TZP ceramic composites was confirmed by the MTT assay and cell morphology observations. Both the ALP assay and key osteogenic markers showed the 5 mol% BT/3Y-TZP group significantly promoted the osteogenic differentiation of osteoblasts, indicating that the 5 mol% BT optimized 3Y-TZP ceramics is a prospective candidate to be used in hard tissue repair due to its effective osteogenic properties and biocompatibility.

It remains difficult to control the morphology of two-dimensional (2D) materials via direct chemical vapor deposition (CVD) growth. In particular, off-equilibrium (kinetic) growth may produce flakes with non-Wulff shapes (e.g., high-index edges, symmetrical shapes, etc.), which are potentially useful; however, a general controllable approach for the kinetic growth of 2D materials is currently lacking. In this work, we pushed the CVD growth of 2D MoS2 into deep kinetic regime, by using potassium chloride (KCl) as catalyst and plasma pretreatment on growth substrates. The unprecedented nonequilibrium high-index faceting and unusual high-symmetry shapes in 2D materials have been realized. The growth mechanism of high-index facets is rationalized based on the theory of kinetic instability on crystal surfaces. This new vapor-liquid-adatom-solid (VLAS) growth mechanism-synergistic capture of multiple vapor phase molecules by the catalyst particles on corners and the oversaturated adatom diffusion along adjacent edges can offer great opportunities for shape engineering on 2D materials. The high-quality, rapid, and controllable synthesis of high-index facets (edges) and other non-Wulff shapes of 2D transition metal dichalcogenides will benefit the developments in 2D materials.

Acquired resistance to fulvestrant and palbociclib is a new challenge to treatment of estrogen receptor positive (ER+) breast cancer. ER is expressed in most resistance settings; thus, bromodomain and extra-terminal protein inhibitors (BETi) that target BET-amplified ER-mediated transcription have therapeutic potential. Novel pyrrolopyridone BETi leveraged novel interactions with L92/L94 confirmed by a cocrystal structure of 27 with BRD4. Optimization of BETi using growth inhibition in fulvestrant-resistant (MCF-7:CFR) cells was confirmed in endocrine-resistant, palbociclib-resistant, and ESR1 mutant cell lines. 27 was more potent in MCF-7:CFR cells than six BET inhibitors in clinical trials. Transcriptomic analysis differentiated 27 from the benchmark BETi, JQ-1, showing downregulation of oncogenes and upregulation of tumor suppressors and apoptosis. The therapeutic approach was validated by oral administration of 27 in orthotopic xenografts of endocrine-resistant breast cancer in monotherapy and in combination with fulvestrant. Importantly, at an equivalent dose in rats, thrombocytopenia was mitigated.

Two-dimensional (2D) ferroelectric materials with unique structure and extraordinary optoelectrical properties have attracted intensive research in the field of nanoelectronic and optoelectronic devices, such as optical sensors, transistors, photovoltaics and non-volatile memory devices. However, the transition temperature of the reported ferroelectrics in 2D limit is generally low or slightly above room temperature, hampering their applications in high-temperature electronic devices. Here, we report the robust high-temperature ferroelectricity in 2D α-In2Se3, grown by chemical vapor deposition (CVD), exhibiting an out-of-plane spontaneous polarization reaching above 200 °C. The polarization switching and ferroelectric domains are observed in In2Se3 nanoflakes in a wide temperature range. The coercive field of the CVD grown ferroelectric layers illustrates a room-temperature thickness dependency and increases drastically when the film thickness decreases; whereas there is no large variance in the coercive field at different temperature from the samples with identical thickness. The results show the stable ferroelectricity of In2Se3 nanoflakes maintained at high temperature and open up the opportunities of 2D materials for novel applications in high-temperature nanoelectronic devices.

Tin (Sn)‐based perovskites with favorable optoelectronic properties and ideal bandgaps have emerged as promising alternatives to toxic lead (Pb)‐based perovskites for photovoltaic applications. However, it is challenging to obtain high‐quality Sn‐based perovskite films by solution process. Here, liquid‐exfoliated 2D transition‐metal dichalcogenides (i.e., MoS2, WS2, and WSe2) with smooth and defect‐free surfaces are applied as growth templates for spin‐coated FASnI3 perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The authors find that WSe2 has better energy alignment with FASnI3 than MoS2 and WS2 and results in a cascade band structure in resultant perovskite solar cells (PSCs), which can facilitate hole extraction and suppress interfacial charge recombination in the devices. The WSe2‐modified PSCs show a power conversion efficiency up to 10.47%, which is among the highest efficiency of FASnI3‐based PSCs. The appealing solution phase epitaxial growth of FASnI3 perovskite on 2D WSe2 flakes is expected to find broad applications in optoelectronic devices., Liquid‐exfoliated 2D transition‐metal dichalcogenides (MoS2, WS2, and WSe2) are introduced as growth templates for spin‐coated FASnI3 perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The good energy alignment in the NiOx/WSe2/FASnI3 structure facilitates hole extraction and suppresses interfacial charge recombination, leading to the best PCE of 10.47% for the PSC.

Discovering low-cost, durable and highly active electrocatalysts with reduced use of precious platinum group metals (PGM) as catalysts for the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the oxygen evolution reaction (OER) is a key step for large-scale adaptation of fuel cells, electrolyzers, and metal-air batteries. Here we explore the stability and reaction mechanisms of synthesized one-dimensional transition metal dithiolene wire (TM-DWs, TM = Cr – Cu, Rh, Ir, Pt, Pd) for the ORR and the OER in acid solution by density functional theory (DFT) calculations. Our calculations reveal that Co-DW intrinsically exhibits high catalytic activity for bi-functional ORR/OER with low limiting overpotentials (η) of 0.46/0.45 V via four-electron reactions. These low limiting overpotentials arise from modified scaling relations by strengthening the binding free energy of OOH* compared to OH* on TM-DWs, yielding universal minimum ORR/OER overpotentials of η = 0.28/0.22 V, remarkably decreased compared to both metal and oxide surfaces (ηideal = 0.37 V). By applying uni-axial strain, the adsorption strength of reaction intermediates on TM reactive sites can be optimized due to shifts in d-band centers. Our findings provide valuable insight into rational design of non-precious metals based electrocatalysts, and demonstrate a new strategy of tuning adsorptions via uni-axial strain to develop efficient bifunctional electrocatalysts of ORR/OER under optimal conditions.

Atomic lattice reconstruction and postcrack edge stacking behavior are observed during the fracture of 2D ReS2., Low-dimensional materials usually exhibit mechanical properties from those of their bulk counterparts. Here, we show in two-dimensional (2D) rhenium disulfide (ReS2) that the fracture processes are dominated by a variety of previously unidentified phenomena, which are not present in bulk materials. Through direct transmission electron microscopy observations at the atomic scale, the structures close to the brittle crack tip zones are clearly revealed. Notably, the lattice reconstructions initiated at the postcrack edges can impose additional strain on the crack tips, modifying the fracture toughness of this material. Moreover, the monatomic thickness allows the restacking of postcrack edges in the shear strain–dominated cracks, which is potentially useful for the rational design of 2D stacking contacts in atomic width. Our studies provide critical insights into the atomistic processes of fracture and unveil the origin of the brittleness in the 2D materials.

In this paper, we propose a linear optical implementation scheme of the quantum router. A programming unit is designed. The quantum router makes use of devices which are experimentally realized easily. The signal can be routed into a superposition of output modes through the routing operation, and the spatial degree of freedom of each output mode is related to the control parameter. In addition, the strategy of multistage routing is also exploited on the basis of this router model, and it can exponentially expand the number of output ports. The quantum router is deterministic, rather than probabilistic, no matter how many output ports the quantum router has.

In bulk crystals, the kinetics of dislocations is usually hindered by the twining boundaries (TB) or grain boundaries (GB), rendering the well‐known grain boundary strengthening effects. Nevertheless, here it is found that in 2D rhenium disulfide (ReS2), twinning is much easier than dislocation slip. Consequently, the highly mobile TBs or GBs are inversely pinned by the relatively immobile dislocations. Due to the strong in‐plane covalent bonding, the GBs in high‐symmetry 2D materials such as graphene which consists of defects are immobile at room temperature. In contrast, in monoclinic 2D ReS2 several types of GBs (including TBs) can be readily generated and driven by mechanical loading. A complete library of the GBs in 2D ReS2 is established by the (in situ) atomic‐scale transmission electron microscopy (TEM) characterizations and density functional theory (DFT) calculations. The twinning (shear) stresses for 2D ReS2 are estimated as low as 4–30 MPa, one or two orders of magnitude lower than the traditional bulk materials. Full elucidation on the GB structures and especially the intriguing GB kinetics in such anisotropic 2D materials are of fundamental importance to understand the structure–property relationships and develop strain‐tunable applications for 2D materials in future., A complete library of grain boundaries in 2D rhenium disulfide, classified by the mobile and pinned nature, is established. In 2D rhenium disulfide twinning is much easier than dislocation slip. As a result, the highly mobile twining boundaries (TBs) or grain boundaries (GBs) can be inversely pinned by the relatively immobile dislocations.

This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg–8Li–3Al–2Zn–0.5Y (wt%) alloy, which was prepared by casting, and then homogenized and rolled at 200 °C. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg–8Li–3Al–2Zn–0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al2Y phases. After rolling process, anisotropic microstructure was observed. α-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.

Two-dimensional (2D) materials and soft materials are both susceptible to mechanical instabilities, such as buckling, wrinkling, folding and creasing, especially when located on surfaces. Here, we report that weak van der Waals interactions cause the interface between 2D molybdenum disulphide (MoS2) and a soft poly(methyl methacrylate) coating to demonstrate mechanical instability and delamination. The resulting non-uniform and buckled interface greatly hampers the ability of the coating to protect the MoS2 substrate. Also, the corrosion rate of 2D MoS2 and quench rate of intrinsic luminescence in 2D MoS2 were significantly accelerated by the soft coating. Owing to the formation of corrosive cavities at the interface, the geometry and size of the flakes became the dominating factor, and a critical size of 2D flakes for such interfacial instability was determined based on elasticity theory. Such hazardous corrosion in a 2D material caused by a soft coating raises concern for their use in electronic packaging, and for the processing of van der Waals-layered materials for future applications. The interface between a 2D material and a soft polymer coating may suffer from mechanical instabilities and delamination. A team led by Thuc Hue Ly at City University of Hong Kong investigated the role of soft coating layers like Poly methyl methacrylate (PMMA) in the protection of atomically thin transition metal dichalcogenides. A combination of experimental techniques including atomic force microscopy, photoluminescence and Raman spectroscopy indicated formation of corrosive cavities at the interface between PMMA and the chalcogenide monolayers. The enhanced corrosion behaviour of 2D materials in the presence of soft polymer coatings resembles the corrosion under insulation (CUI) phenomenon known in industry. As the geometry and size of flakes dominate the corrosion rate, a rational design of such interfaces should be employed to avoid CUI events.

Two-dimensional (2D) materials have been emerging as potential candidates for the next-generation materials in various technology fields. The performance of the devices based on these 2D materials depends on their intrinsic band structures as well as the extrinsic (doping) effects such as surrounding chemicals and environmental oxygen/moisture, which strongly determines their Fermi energy level. Herein, we report the UV treatments on the 2D transition-metal dichalcogenides, to controllably dope the samples without damaging the crystal structures or quenching the luminescence properties. More surprisingly, both n-type and p-type doping can be achieved depending on the initial status of the sample and the UV treatment conditions. The doping mechanisms were elaborated on the atomic scale with transmission electron microscopy and ab initio calculations. The facile doping by UV light has potential to be integrated with photolithography processes, aiming for the large-scale integrated device/circuits design and fabrications.

Layered transition-metal dichalcogenides (TMDCs) have received great interest due to their potential applications in many fields including electronics, optoelectronics, electrochemical hydrogen production and so on. Recent research effort on the development of effective hydrogen evolution reaction (HER) is to modulate the active edge sites through controlling surface structure at the atomic scale. Here we firstly demonstrate a facile strategy to synthesize large-area and edge-rich platinum diselenide (PtSe 2 ) via selenization of Pt films by magnetron sputtering physical deposition method. The edge site density of the PtSe 2 can be effectively controlled by tuning the thickness of Pt films. The HER activity of the PtSe 2 can be enhanced significantly as the active edge site density increases. The maximum cathodic current density of 227 mA/cm 2 can be obtained through increasing the edge density, which well agrees with the density functional theory calculations. Our work provides a fundamental insight on the effect of active edge site density towards HER.

The conversion of chalcogen atoms to other types in transition metal dichalcogenides has significant advantages for tuning bandgaps and constructing in-plane heterojunctions; however, difficulty arises from the conversion of sulfur or selenium to tellurium atoms owing to the low decomposition temperature of tellurides. Here, we propose the use of sodium for converting monolayer molybdenum disulfide (MoS2) to molybdenum ditelluride (MoTe2) under Te-rich vapors. Sodium easily anchors tellurium and reduces the exchange barrier energy by scooting the tellurium to replace sulfur. The conversion was initiated at the edges and grain boundaries of MoS2, followed by complete conversion in the entire region. By controlling sodium concentration and reaction temperature of monolayer MoS2, we tailored various phases such as semiconducting 2H-MoTe2, metallic 1T′-MoTe2, and 2H-MoS2−xTex alloys. This concept was further extended to WS2. A high valley polarization of ~37% in circularly polarized photoluminescence was obtained in the monolayer WS2−xTex alloy at room temperature., Two dimensional monolayer transition metal ditellurides and their alloys are interesting but their growth has been difficult. Herein, Yun et al. demonstrate the use of sodium salts to convert transition metal disulfide to ditelluride and alloys in tellurium vapor at low temperature.

Metals have the best dielectric screening capability among all materials; however, it is usually difficult to fabricate continuous and uniform ultrathin (few-atomic-layer thickness) metal films. Conversely, high-quality atomic-thick semiconductor or semimetal materials (so called two-dimensional materials) such as graphene or MoS2 can be readily obtained and robust in ambient conditions; however, their dielectric screening capabilities are greatly reduced by their reduced dimensionality. Particularly, in the vertical direction, the dielectric screening of two-dimensional materials is insufficient; thus, the performances of devices by two-dimensional materials were easily affected by the coulomb-scattering or other kind of sources. Herein, we propose that with a screw dislocation connecting the van der Waals layers in two-dimensional MoS2 spiral structures, excellent dielectric screening in the vertical direction can be achieved. Our Kelvin force microscopy directly demonstrates that the external impurity ...

This study was undertaken to evaluate the effect of extrusion ratio on the microstructure and mechanical properties of Mg–8Li–3Al–2Zn–0.5Y (wt%) alloy, which was prepared by casting and then deformed by hot extrusion at 200 ℃ with four different ratios of 4:1, 9:1, 16:1 and 25:1, respectively. It was identified that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy is composed of α -Mg, β -Li, AlLi, MgLi 2 Al and Al 2 Y phases. After hot extrusion with all four ratios, the microstructure was significantly refined. The mechanical properties of Mg–8Li–3Al–2Zn–0.5Y alloy at room temperature were improved, mainly caused by grain refinement and precipitation strengthening. As the extrusion ratio increases from 4 to 25, the grains of the alloy become elongated and refined, and the tensile properties first increase and then decline. Among all the tested alloys, the alloy with the extrusion ratio of 16 exhibits the highest yield strength, ultimate tensile strength and elongation of 214 MPa, 243 MPa and 41%. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically.

Despite numerous studies on two-dimensional van der Waals heterostructures, a full understanding of the charge transport and photoinduced current mechanisms in these structures, in particular, associated with charge depletion/inversion layers at the interface remains elusive. Here, we investigate transport properties of a prototype multilayer MoS2/WSe2 heterojunction via a tunable charge inversion/depletion layer. A charge inversion layer was constructed at the surface of WSe2 due to its relatively low doping concentration compared to that of MoS2, which can be tuned by the back-gate bias. The depletion region was limited within a few nanometers in the MoS2 side, while charges are fully depleted on the whole WSe2 side, which are determined by Raman spectroscopy and transport measurements. Charge transport through the heterojunction was influenced by the presence of the inversion layer and involves two regimes of tunneling and recombination. Furthermore, photocurrent measurements clearly revealed recombina...

Despite recent advances in the use of porous materials as efficient heterogeneous catalysts which operate through effectively trapping reagents in a well-defined space, continuously uptaking reagents to substitute products in the cavity for efficient product turnover still remains challenging. Here, a porous catalyst is endowed with ‘breathing’ characteristics by thermal stimulus, which can enable the efficient exchange of reagents and products through reversible stacking from inflated aromatic hexamers to contracted trimeric macrocycles. The contracted super-hydrophobic tubular interior with pyridine environment exhibits catalytic activity towards a nucleophilic aromatic substitution reaction by promoting interactions between concentrated reagents and active sites. Subsequent expansion facilitates the exchange of products and reagents, which ensures the next reaction. The strategy of mesoporous modification with inflatable transition may provide a new insight for construction of dynamic catalysts. Porous materials are efficient heterogeneous catalysts, but the continuous uptake of reagents to substitute products in the cavities remains unsettled. Here the authors fabricate a self-assembled tubular structure with breathing characteristics for efficient exchange of reactants and products in a nucleophilic substitution reaction.

The emergent two-dimensional (2D) materials are atomically thin and ultraflexible, promising for a variety of miniaturized, high-performance, and flexible devices in applications. On one hand, the ultrahigh flexibility causes problems: the prevalent wrinkles in 2D materials may undermine the ideal properties and create barriers in fabrication, processing, and quality control of materials. On the other hand, in some cases the wrinkles are used for the architecturing of surface texture and the modulation of physical/chemical properties. Therefore, a thorough understanding of the mechanism and stability of wrinkles is highly needed. Herein, we report a critical length for stabilizing the wrinkles in 2D materials, observed in the wrinkling and wrinkle elimination processes upon thermal annealing as well as by our in situ TEM manipulations on individual wrinkles, which directly capture the evolving wrinkles with variable lengths. The experiments, mechanical modeling, and self-consistent charge density functional tight binding (SCC-DFTB) simulations reveal that a minimum critical length is required for stabilizing the wrinkles in 2D materials. Wrinkles with lengths below a critical value are unstable and removable by thermal annealing, while wrinkles with lengths above a critical value are self-stabilized by van der Waals interactions. It additionally confirms the pronounced frictional effects in wrinkles with lengths above critical value during dynamical movement or sliding.

Owing to their high robustness and conductivity, 2D transition metal carbides and nitrides known as MXenes are considered as a promising material class for electrochemical catalysis, energy conversion, and storage applications. Nevertheless, conventional hazardous fluoride‐based synthesis routes and the intense intralayer bonding restrict the development of MXenes. Herein, a fluoride‐free, facile, and rapid method for synthesizing self‐assembled 1D architecture from an MXene‐based compound is reported. The MXene nanowire (NW) not only provides a robust connection to the flexible substrate but also effectively increases the electrochemically active surface area. The kinetics‐favorable structure yields a boosted performance for the hydrogen/oxygen evolution reaction and the intake of the zinc ion. The 1D NW based on MXene compound maintains high stability in a quite low overpotential of 236 mV for 24 h without detachment from the substrate and manifests an exceptional high‐power density of 420 W kg−1 over 150 cycles as a flexible aqueous zinc ion battery. This work paves a novel and non‐toxic synthesis method for the 1D nanofiber structure from MXene composition and demonstrates its multifunctional applications for energy conversion and storage., With the facile technique in alkali hydrolysis and HF‐free electrochemical etching, MXene nanowire is fabricated in a shortened etching time without the utilization of hazardous HF acid. The MXene NW@3D substrate not only renders a boosted kinetics and shortened diffusion length, but also offers a stable hydrogen evolution activity and flexible zinc ion battery application even during the deformation progress.

The clinical steroidal selective estrogen receptor (ER) degrader (SERD), fulvestrant, is effective in metastatic breast cancer, but limited by poor pharmacokinetics, prompting the development of orally bioavailable, nonsteroidal SERDs, currently in clinical trials. These trials address local breast cancer as well as peripheral metastases, but patients with brain metastases are generally excluded because of the lack of blood-brain barrier penetration. A novel family of benzothiophene SERDs with a basic amino side arm (B-SERDs) was synthesized. Proteasomal degradation of ERα was induced by B-SERDs that achieved the objectives of oral and brain bioavailability, while maintaining high affinity binding to ERα and both potency and efficacy comparable to fulvestrant in cell lines resistant to endocrine therapy or bearing ESR1 mutations. A novel 3-oxyazetidine side chain was designed, leading to 37d, a B-SERD that caused endocrine-resistant ER+ tumors to regress in a mouse orthotopic xenograft model.

Developing metallic co-catalysts is an effective way to enhance the photocatalytic activity of semiconductor by forming the Schottky junction, but it remains challenging to unveil the design principle. Herein, a novel nanocomposite is prepared by coupling ultra-small WP nanoparticles embedded on N-doped carbon (WP NC) with 2D graphitic C3N4 (g-C3N4). The WP NC and g-C3N4 form an intimate interface via PN chemical bonds at atomic level, which facilitates the flow of photoexcited electrons from g-C3N4 to WP NC. Moreover, the Schottky junction formed at the interface can prevent the charge-carrier recombination in the WP NC/g-C3N4 composite and thus significantly enhance the photocatalytic CO production rate from 29 (bare g-C3N4) to 376 μmol g−1 h−1. As the first example of WP applied on the photocatalytic CO2 reduction, this work demonstrates the potential of metallic WP as a co-catalyst in photocatalysis and provides a useful guide on the phosphide-based material designing.

Dislocations are one-dimensional line defects in three-dimensional crystals or periodic structures. It is common that the dislocation networks made of interactive dislocations be generated during plastic deformation. In van der Waals layered materials, the highly anisotropic nature facilitates the formation of such dislocation networks, which is critical for the friction or exfoliation behavior for these materials. By transmission electron microscopy analysis, we found the topological defects in such dislocation networks can be perfectly rationalized in the framework of traditional dislocation theory, which we applied the name "hyperdislocations". Due to the strong pinning effect of hyperdislocations, the state of exfoliation can be easily triggered by 1° twisting between two layers, which also explains the origin of disregistry and frictionlessness for all of the superlubricants that are widely used for friction reduction and wear protection.

Two-dimensional (2D) hexagonal boron nitride (h-BN) is a thin insulating material that can be used to enhance the electrical and optical properties of other 2D materials when used as a substrate or a capping layer, owing to its absence of dangling bonds on the surface. The use of multilayer h-BN films is often required in such applications to realize high material performance. However, previous works have focused mostly on the synthesis of monolayer or few-layer h-BN films. Herein we report a method to control the thickness of h-BN film up to the centimeter scale by means of plasma-enhanced chemical vapor deposition (PECVD). The thickness of the h-BN film is controlled by varying the deposition time of borazine precursor onto a monolayer h-BN film on a Pt foil substrate at room temperature. The resultant film is then annealed at high temperature (1050 °C) to increase the crystallinity of the h-BN. Monolayer h-BN film grown on Pt foil used as a buffer layer is of importance to improve uniformity and smooth surface of the multilayer h-BN film over the whole area. We further demonstrate that our multilayer h-BN film is very useful in graphene/h-BN/SiO2 heterostructures as a charge-blocking layer between graphene and SiO2.

The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2 is locally converted into metallic 1T-MoS2 through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T' phases coexisting in Li-treated MoS2, which result in unusual transport phenomena. Although multiphase MoS2 shows no transistor-gating response, the channel resistance decreases in proportion to the temperature, similar to the behavior of a typical semiconductor. Transmission electron microscopy images clearly show that the 1T and 1T' phases are randomly distributed and intervened with 2H-MoS2, which is referred to as the 1T and 1T' puddling phenomenon. The resistance curve fits well with 2D-variable range-hopping transport behavior, where electrons hop over 1T domains that are bounded by semiconducting 2H phases. However, near 30 K, electrons hop over charge puddles. The large temperature coefficient of resistance (TCR) of multiphase MoS2, -2.0 × 10(-2) K(-1) at 300 K, allows for efficient IR detection at room temperature by means of the photothermal effect.

Single-crystalline artificial AB-stacked bilayer graphene is formed by aligned transfer of two single-crystalline monolayers on a wafer-scale. The obtained bilayer has a well-defined interface and is electronically equivalent to exfoliated or direct-grown AB-stacked bilayers.

In this study, the microstructure evolution and mechanical properties of as-cast Mg–8Li–3Al–2Zn–0.5Y alloy during solid solution treatment from 300 °C to 450 °C were firstly investigated, and then the effect of Y content (from 0.5 wt% to 1.5 wt%) on the age softening of solid solution treated Mg–8Li–3Al–2Zn alloy was also analyzed. The results show that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy mainly consists of α -Mg, β -Li, Al 2 Y and AlLi phases. With the increase of solid solution temperature from 300 °C to 450 °C for as-cast Mg–8Li–3Al–2Zn–0.5Y alloy, the AlLi phase is decomposed and the atoms of Al and Li dissolve into the matrix gradually. The hardness, yield strength and ultimate tensile strength of the tested alloy are increased dramatically; however, the ductility is relatively decreased. Meanwhile, the room temperature aging treated Mg–8Li–3Al–2Zn–0.5Y has age hardening during initial time, and the addition of Y is helpful to the thermal stability of Mg–8Li–3Al–2Zn alloy. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically.

MoS2 spirals grown by the chemical vapor deposition method, driven by a threading dislocation, has a peculiar rhombohedral-like structure. This threading dislocation can carry helical current in the vertical direction and greatly enhances the vertical conductance in the MoS2 multilayer samples.

The identification of catalytically active and stable bifunctional electrocatalysts for the oxygen reduction and evolution reaction (ORR/OER) would revolutionize rechargeable metal-air batteries and regenerative fuel cell technologies. In this study, we use density functional theory (DFT) calculations to systemically investigate 2D transition metal based tetracyanoquinodimethane (TM–TCNQ, TM = Cr-Cu, Ru-Ag, Pt, Ir) monolayers with single TM atoms catalysts (SACs) distributed periodically with high density. We calculate a lower limiting overpotential of ηlim = 0.33 V for Fe-TCNQ yielding a higher expected activity than that of Pt metal (0.48 V) for the ORR under acidic conditions. The catalytic performance of Fe-TCNQ for OER is, however, surpassed by Ni-TCNQs (ηlim = 0.46 V), which is identified as the highest among the candidates. By applying grafting axial ligands and external strain, the adsorption strength of reaction intermediates on TM reactive sites can be further optimized and enhances the activities of Mn-, Fe- and Ni-TCNQs for the ORR or the OER. Here, Fe-TCNQ-Cl (ηlim = 0.27/0.55 V), followed by Fe-TCNQ-CO (ηlim = 0.67/0.43 V), are predicted as novel, high-performance bifunctional ORR/OER catalysts with comparable limiting overpotentials to those of the best commercially used electrocatalysts, Pt (ORR: ηlim = 0.48 V) and RuO2 (OER: ηlim = 0.42 V). In addition, the recently synthesized Fe-TCNQ possess excellent conductivity with fast electron transfer during the catalytic reactions. These results show 2D TM-TCNQ monolayers are durable, low-cost, and efficient catalysts for the ORR and the OER in metal-air batteries and fuel cells.

Layered van der Waals materials have recently attracted attention owing to their exceptional electrical and optical properties in thin layer form. One way to extend their utility is to form a heterostructure which combines various properties of layered materials to reveal intriguing behavior. Conventional heterostructure synthesis methods are difficult to develop and the heterostructure formed can be limited to a small area. Here, we investigate the phase transformation of SnS2 to SnS by removing sulfur atoms at the top surface using Ar plasma. By varying the plasma power and exposure time, we observed that SnS is subsequently formed on top of the mogul-like structure of SnS2. Since SnS is a p-type semiconductor and SnS2 is an n-type semiconductor, we naturally formed a vertical p-n junction. By using graphene at the top and bottom as transparent electrodes, a vertical p-n diode device is constructed. The device demonstrates good rectifying behavior and large photocurrent generation under white light. This method can be applied to large-area heterostructure synthesis using plasma via phase transformation of various metal dichalcogenides to metal monochalcogenides.

In this study, effect of Y on microstructure and mechanical properties of as-cast Mg–8Li–3Al–2Zn alloy was investigated. The results show that microstructure of the Mg–8Li–3Al–2Zn alloy mainly consists of α -Mg, β -Li, AlLi and MgLiAl 2 phases. With addition of Y, the Al 2 Y compound forms and increases gradually, the AlLi phase decreases and the β -Li phase increases, meanwhile, the microstructure is significantly refined and equiaxed. The addition of 1 wt% Y produces the smallest grain size. Mg–8Li–3Al–2Zn–0.5Y alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 153.0 MPa, 218.5 MPa and 16.9%, which are improved by about 6.4%, 13.2% and 13.4% compared with those of Mg–8Li–3Al–2Zn alloy (143.8 MPa, 193.0 MPa and 14.9%), respectively. The mechanisms of improvement are related to grain refinement and second phase strengthening.

The polar edges of two-dimensional monolayer transition metal dichalcogenides (TMD) and their alloys are examined by combined theoretical (density functional theory) and experimental approaches. For these polar edges, the growth reaction energies between different edge terminations are considered instead of the surface free energies. Due to different energy evolutions during growth on the zigzag edges between MoS2 and WS2, the S-ZZ edges in the WS2 monolayer flakes more easily decompose into sawtooth-like edges in M-ZZ type as compared to the MoS2 monolayer; thus, the hexagonal morphology can be seen more often in WS2. Moreover, the observed anisotropic short-range order in the MoS2/WS2 alloys is originated from the freezed edge configurations during growth, explainable by the growth kinetics and thermodynamics of the Mo-ZZ-edges. The determination of the growing edge terminations is of great importance for the controllable synthesis of the emergent two-dimensional TMD materials.

Despite the recent development of highly efficient and stable metal catalysts, conferral of regulatory characteristics to the catalytic reaction in heterogeneous systems remains a challenge. Novel supramolecular nanotubules were prepared by alternative stacking from trimeric macrocycles, which was found to be able to coordinate with Pd cations. The Pd complexes exhibited a high catalytic performance for C-C coupling reaction. Notably, the tubular catalyst was observed to be controlled by supramolecular reversible assembly and showed superior heterogeneous catalytic activity, which was maintained for a number of cycles or reuse under an aerobic environment. Furthermore, the supramolecular catalyst showed unprecedented selectivity for the multifunctional coupling reaction and was able to serve as a new constructor of asymmetrical compounds.

With the growing depletion of fossil energy and the unceasing joint efforts to maintain sustainable development, bio-based materials are appealing for academic and industrial researchers because they possess the merits of environmental friendliness and renewability. In this study, a tung-oil-based derivative, tung-maleic anhydride (TMA), which was prepared from methyl eleostearate and maleic anhydride, reacted with epichlorohydrin to synthesize epoxidized tung-maleic anhydride (ETMA) after the hydrolysis of anhydride. Furthermore, ETMA was chemically modified by pentaerythritol triacrylate to obtain hexa-functional epoxidized tung-maleic anhydride acrylate prepolymers (PETMA). The chemical structure of the resultant prepolymers was confirmed by FT-IR and 1H NMR, while the rheological behavior of prepolymers was investigated by using a rheometer. Also, the curing efficiency of different photoinitiators on PETMA prepolymers was investigated, and the result revealed that the tung oil-based prepolymers could be rapidly cured with 3.0 wt% photoinitiator PI-819 under a UV lamp with 5 kW light intensity within 45 s. Furthermore, various reactive diluents were used to be cured with PETMA prepolymers, and the thermomechanical properties, mechanical properties, volume shrinkage, swelling property, and general performances of the resultant UV-cured films were investigated. DMA results revealed that, among the films cured by the reactive diluents with same functionality, reactive diluents with a higher Tg resulted in a higher Tg toward the resultant cured films. The crosslinking density (νe) of the films cured with various reactive diluents was determined by the double bond density, leading to the fact that the films cured with bi-functional reactive diluents exhibited a higher crosslinking density than the ones cured with mono-functional reactive diluents. TGA results showed that high crosslinking density facilitated improving the thermal stability of the cured films, while the steric structure in film matrix exerted adverse effect on thermal stability. Besides, tensile test indicated that high crosslinking density and steric structure facilitated the enhancement of mechanical properties toward the resultant films. More strikingly, all UV-cured films possessed excellent hardness, high glossiness and remarkable water resistance, and these high-performance bio-based UV-curable films are promising for widespread applications.

The quality of perovskite films is critical to the performance of perovskite solar cells. However, it is challenging to control the crystallinity and orientation of solution-processed perovskite films. Here, solution-phase van der Waals epitaxy growth of MAPbI3 perovskite films on MoS2 flakes is reported. Under transmission electron microscopy, in-plane coupling between the perovskite and the MoS2 crystal lattices is observed, leading to perovskite films with larger grain size, lower trap density, and preferential growth orientation along (110) normal to the MoS2 surface. In perovskite solar cells, when perovskite active layers are grown on MoS2 flakes coated on hole-transport layers, the power conversion efficiency is substantially enhanced for 15%, relatively, due to the increased crystallinity of the perovskite layer and the improved hole extraction and transfer rate at the interface. This work paves a way for preparing high-performance perovskite solar cells and other optoelectronic devices by introducing 2D materials as interfacial layers.

Whether and how fracture mechanics needs to be modified for small length scales and in systems of reduced dimensionality remains an open debate. Here, employing in situ transmission electron microscopy, atomic structures and dislocation dynamics in the crack tip zone of a propagating crack in two-dimensional (2D) monolayer MoS2 membrane are observed, and atom-to-atom displacement mapping is obtained. The electron beam is used to initiate the crack; during in situ observation of crack propagation the electron beam effect is minimized. The observed high-frequency emission of dislocations is beyond previous understanding of the fracture of brittle MoS2. Strain analysis reveals dislocation emission to be closely associated with the crack propagation path in nanoscale. The critical crack tip plastic zone size of nearly perfect 2D MoS2 is between 2 and 5 nm, although it can grow to 10 nm under corrosive conditions such as ultraviolet light exposure, showing enhanced dislocation activity via defect generation., How well the linear elastic fracture picture holds at small length scales and systems with reduced dimensionality remains an active area of inquiry. Here authors use in situ electron microscopy to study fracture in MoS2 monolayers and report dislocation emission rates greater than expected accompanying crack propagation.

Delamination of thin films from the supportive substrates is critical issues in thin film industry and technology. The emergent two-dimensional materials, atomic layered materials, such as transition metal dichalcogenides are highly flexible thus the buckles and wrinkles can be easily generated and play vital effects on the physical properties. Here we introduce one kind of patterned buckling behavior caused by the delamination from substrate initiated at the edges of the chemical vapor deposition synthesized monolayer transition metal dichalcogenides, mainly due to the thermal expansion mismatch. The atomic force microscopy and optical characterizations clearly showed the puckered structures associated with strains, whereas the transmission electron microscopy revealed the special sawtooth shaped edge structures which break the geometrical symmetry of the buckling behavior of hexagonal samples. The condition of this edge delamination is in accordance with the fracture theory. This edge delamination process and buckling upon synthesis is universal for most of the ultrathin two dimensional materials, and it is definitely noteworthy in their future applications., Comment: 18 pages, 6 figures

A Pt-free nanoreactor, consisting of N-doped hollow carbon nanocapsules with encapsulated Ni nanoparticles, is developed for high-performance oxygen reduction reaction (ORR) catalyst. The nanoreactor effect improves its catalytic activity for ORR mainly in a 4e- pathway. The presence of Ni nanoparticles within the nanoreactor significantly enhances the stability with a current retention of 90% after 40 h.

Metal oxide nanoparticles decorating graphene have attracted abundant interest in the scientific community owing to their significant application in various areas such as batteries, gas sensors, and photocatalysis. In addition, metal and metal oxide nanoparticles are of great interest for the etching of graphene, for example, to form nanoribbons, through gasification reactions. Hence it is important to have a good understanding of how nanoparticles interact with graphene. In this work we examine, in situ, the behavior of CuO and ZnO nanoparticles on graphene at room temperature while irradiated by electrons in a transmission electron microscope. ZnO is shown to etch graphene through gasification. In the gasification reaction C from graphene is released as CO or CO2. We show that the reaction can occur at room temperature. Moreover, CuO and ZnO particles trapped within a graphene fold are shown to effuse out of a fold through small ruptures. The mass transport in the effusion process between the CuO and ZnO particles is fundamentally different. Mass transport for CuO occurs in an amorphous phase, while for ZnO mass transport occurs through the short-lived gliding of vacancies and dislocations. The work highlights the potential and wealth of electron beam driven chemical reactions of nanomaterials, even at room temperature.

One well-known argument about one dimensional(1D) system is that 1D phase transition at finite temperature cannot exist, despite this concept depends on conditions such as range of interaction, external fields and periodicity. Therefore 1D systems usually have random fluctuations with intrinsic domain walls arising which naturally bring disorder during transition. Herein we introduce a real 1D system in which artificially created defects can induce a well-defined 1D phase transition. The dynamics of structural reconstructions at graphene zigzag edges are examined by in situ aberration corrected transmission electron microscopy (ACTEM). Combined with an in-depth analysis by ab-initio simulations and quantum chemical molecular dynamics (QM/MD), the complete defect induced 1D phase transition dynamics at graphene zigzag edge is clearly demonstrated and understood on the atomic scale. Further, following this phase transition scheme, graphene nanoribbons (GNR) with different edge symmetries can be fabricated, and according to our electronic structure and quantum transport calculations, a metal-insulator-semiconductor transition for ultrathin GNRs is proposed., 6 pages, 4 figures

Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS2 by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5–7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles, Grain boundaries can degrade the performance of electronic devices made from single atomic layers of transition metal dichalcogenides. Here, the authors combine transport measurements and transmission electron microscopy to find a correlation between field-effect mobility and grain misorientation angle.

Synthesis of monolayer transition metal dichalcogenides (TMDs) via chemical vapor deposition relies on several factors such as precursor, promoter, substrate, and surface treatment of substrate. Among them, the use of promoter is crucial for obtaining uniform and large-area monolayer TMDs. Although promoters have been speculated to enhance adhesion of precursors to the substrate, their precise role in the growth mechanism has rarely been discussed. Here, we report the role of alkali metal promoter in growing monolayer TMDs. The growth occurred via the formation of sodium metal oxides which prevent the evaporation of metal precursor. Furthermore, the silicon oxide substrate helped to decrease the Gibbs free energy by forming sodium silicon oxide compounds. The resulting sodium metal oxide was anchored within such concavities created by corrosion of silicon oxide. Consequently, the wettability of the precursors to silicon oxide was improved, leading to enhance lateral growth of monolayer TMDs.

Single-crystalline monolayer hexagonal WS2 is segmented into alternating triangular domains: sulfur-vacancy (SV)-rich and tungsten-vacancy (WV)-rich domains. The WV-rich domain with deep-trap states reveals an electron-dedoping effect, and the electron mobility and photoluminescence are lower than those of the SV-rich domain with shallow-donor states by one order of magnitude. The vacancy-induced strain and doping effects are investigated via Raman and scanning photoelectron microscopy.

Defects in bulk crystals can be classified into vacancies, interstitials, grain boundaries, stacking faults, dislocations, and so forth. In particular, the vacancy in semiconductors is a primary defect that governs electrical transport. Concentration of vacancies depends mainly on the growth conditions. Individual vacancies instead of aggregated vacancies are usually energetically more favorable at room temperature because of the entropy contribution. This phenomenon is not guaranteed in van der Waals 2D materials due to the reduced dimensionality (reduced entropy). Here, it is reported that the 1D connected/aggregated vacancies are energetically stable at room temperature. Transmission electron microscopy observations demonstrate the preferential alignment direction of the vacancy chains varies in different 2D crystals: MoS2 and WS2 prefer 〈2¯11〉 direction, while MoTe2 prefers 〈1¯10〉 direction. This difference is mainly caused by the different strain effect near the chalcogen vacancies. Black phosphorous also exhibits directional double-chain vacancies along 〈01〉 direction. Density functional theory calculations predict that the chain vacancies act as extended gap (conductive) states. The observation of the chain vacancies in 2D crystals directly explains the origin of n-type behavior in MoTe2 devices in recent experiments and offers new opportunities for electronic structure engineering with various 2D materials.

Among various transition metal dichalcogenides, MoTe2 has drawn attention due to its capability of robust phase engineering between semiconducting (2H) and semi-metallic distorted octahedral (1T') phase. In particular, 1T'-MoTe2 has been predicted to have intriguing physics such as quantum spin Hall insulator, large magnetoresistance, and superconductivity. Recent progress showed weak antilocalization behavior in 1T'-MoTe2 which is the one of representative characteristics in topological insulator. Here, we grow centimeter-scale monolayer 1T'-MoTe2 on SiO2/Si substrate via chemical vapordeposition and demonstrate dichroism in visible range. Ribbon-like 1T'-MoTe2 flakes were initially nucleated randomly on SiO2 substrate and at a later stage merged to form a continuous monolayer film over the entire substrate. Each flake revealed one dimensional Mo–Mo dimerization feature and anisotropic absorption behavior in visible range (400–600 nm). This allowed us to detect the grain boundary due to stark contrast difference among flakes in different orientations.