Anisotropic mechanical properties of α-MoO3 nanosheets.

The mechanical behaviors of 2D materials are fundamentally important for their potential applications in various fields. α-Molybdenum trioxide (α-MoO3) crystals with unique electronic, optical, and electrochemical properties, have attracted extensive attention for their use in optoelectronic and energy conversion devices. From a mechanical viewpoint, however, there is limited information available on the mechanical properties of α-MoO3. Here, we developed a capillary force-assisted peeling method to directly transfer α-MoO3 nanosheets onto arbitrary substrates. Comparatively, we could effectively avoid surface contamination arising from the polymer-assisted transfer method. Furthermore, with the help of an in situ push-to-pull (PTP) device during SEM, we systematically investigated the tensile properties of α-MoO3. The measured Young's modulus and fracture strengths along the c-axis (91.7 ± 13.7 GPa and 2.1 ± 0.9 GPa, respectively) are much higher than those along the a-axis (55.9 ± 8.6 GPa and 0.8 ± 0.3 GPa, respectively). The in-plane mechanical anisotropy ratio can reach ∼1.64. Both Young's modulus and the fracture strength of MoO3 show apparent size dependence. Additionally, the multilayer α-MoO3 nanosheets exhibited brittle fracture with interplanar sliding due to poor van der Waals interaction. Our study provides some key points regarding the mechanical properties and fracture behavior of layered α-MoO3 nanosheets.

Strain-restricted transfer of ferromagnetic electrodes for constructing reproducibly superior-quality spintronic devices.

Spintronic device is the fundamental platform for spin-related academic and practical studies. However, conventional techniques with energetic deposition or boorish transfer of ferromagnetic metal inevitably introduce uncontrollable damage and undesired contamination in various spin-transport-channel materials, leading to partially attenuated and widely distributed spintronic device performances. These issues will eventually confuse the conclusions of academic studies and limit the practical applications of spintronics. Here we propose a polymer-assistant strain-restricted transfer technique that allows perfectly transferring the pre-patterned ferromagnetic electrodes onto channel materials without any damage and change on the properties of magnetism, interface, and channel. This technique is found productive for pursuing superior-quality spintronic devices with high controllability and reproducibility. It can also apply to various-kind (organic, inorganic, organic-inorganic hybrid, or carbon-based) and diverse-morphology (smooth, rough, even discontinuous) channel materials. This technique can be very useful for reliable device construction and will facilitate the technological transition of spintronic study.

Two-dimensional ternary pentagonal BCX (X = P, As, and Sb): promising photocatalyst semiconductors for water splitting with strong piezoelectricity.

Seeking high-performance energy conversion materials is one of the most important issues in designing 2D materials. In the framework of density functional theory, we propose a series of ternary monolayers, penta-BCX (X = P, As, and Sb), and systematically investigate their structural stability, mechanical, piezoelectric, and photocatalytic properties. All three materials are semiconductors with a bandgap ranging from 2.56 eV to 3.24 eV, so they could be promising catalysts for the photolysis of water. Penta-BCX exhibits significant piezoelectric properties attributed to their non-centrosymmetric structure and low in-plane Young's modulus, which are expected to efficiently drive photocatalytic water decomposition. Moreover, the bandgap, band edge position, and light absorption of penta-BCX can be modulated by tensile or compressive strain to enhance their photocatalytic performance in the visible light and ultraviolet regions.

Toward Clean 2D Materials and Devices: Recent Progress in Transfer and Cleaning Methods.

Two-dimensional (2D) materials have tremendous potential to revolutionize the field of electronics and photonics. Unlocking such potential, however, is hampered by the presence of contaminants that usually impede the performance of 2D materials in devices. This perspective provides an overview of recent efforts to develop clean 2D materials and devices. It begins by discussing conventional and recently developed wet and dry transfer techniques and their effectiveness in maintaining material "cleanliness". Multi-scale methodologies for assessing the cleanliness of 2D material surfaces and interfaces are then reviewed. Finally, recent advances in passive and active cleaning strategies are presented, including the unique self-cleaning mechanism, thermal annealing, and mechanical treatment that rely on self-cleaning in essence. The crucial role of interface wetting in these methods is emphasized, and it is hoped that this understanding can inspire further extension and innovation of efficient transfer and cleaning of 2D materials for practical applications.

Two new sesquiterpenoids with glycosides from the leaves and stems of Schisandra chinensis (Turcz.) Baill.

Two previously undescribed glycosidic bisnorsesquiterpenoids A - B (1 - 2), together with two known compounds (3 - 4), were isolated from the leaves and stems of Schisandra chinensis. Their structures were elucidated by extensive spectroscopic data (1D, 2D NMR, and HRESIMS). The anti-inflammatory activity, ABTS+ radical scavenging activity, and DPPH radical scavenging activity of compounds 1 - 4 were tested. However, all of these compounds showed only weak anti-inflammatory or antioxidant effects.

Design of aggregation-induced emission-active fluorogen-based nanoparticles for imaging and scavenging Alzheimer's ß-amyloid by photo-oxygenation.

Photo-oxygenation has emerged as an effective modality for scavenging Alzheimer's amyloid-ß (Aß) plaques. However, limitations of the current photo-oxidants, such as low Aß-targeting and single functionality, hinder the scavenging of Aß plaques via photo-oxygenation. Herein, based on an aggregation-induced emission (AIE)-active fluorogen (named TPMD), we designed AIE photo-oxidant nanoparticles (T-LD NPs) for Aß imaging, inhibition, and disaggregation. The T-LD NPs were prepared by the assembly of hydrophobic TPMD with an Aß-targeting peptide (LPPFD, L) conjugated amphiphilic polymer (DSPE-PEG). Such T-LD NPs could specifically label Aß plaques for image-guided therapy. Under laser irradiation, T-LD NPs generated a plethora of reactive oxygen species (ROS), including 1O2, ˙OH, and O2˙-, to oxygenate Aß species, leading to the potent inhibition of Aß fibrillization, and significant alleviation of Aß-mediated neurotoxicity (36% to 10% at 20 µg mL-1). Notably, T-LD NPs could rapidly disaggregate mature Aß fibrils into fractured ß-sheet rich aggregates via photo-oxygenation, resulting in alleviated cytotoxicity. In vivo studies revealed that the photo-activated T-LD NPs scavenged amyloid plaques in the transgenic C. elegans strain CL2006 and extended the lifespan by 4 days. Taken together, this multifunctional T-LD NP integrated Aß-targeting, near-infrared fluorescence imaging, and photo-oxygenation, provides a new strategy for the development of multifunctional AIE photo-oxidants for the treatment of Alzheimer's disease.

Extra-High Mechanical and Phononic Anisotropy in Black Phosphorus Blisters.

Strain is an effective strategy to modulate the electrical, optical, and optoelectronic properties of 2D materials. Conventional circular blisters could generate a biaxial stretching of 2D membranes with notable strain gradients along the hoop direction. However, such a deformation mode cannot be utilized to investigate mechanical responses of in-plane anisotropic 2D materials, for example, black phosphorus (BP), due to its crystallographic orientation dependence. Here, a novel rectangular-shaped bulge device is developed to uniaxially stretch the membrane, and further provide a promising platform to detect orientation-dependent mechanical and optical properties of anisotropic 2D materials. Impressively, the derived anisotropic ratio of Young's modulus of BP flakes is much higher than the values obtained via the nanoindentation method. The extra-high strain-dependent phononic anisotropy in Raman modes along different crystalline orientations is also observed. The designed rectangular budge device expands the uniaxial deformation methods available, allowing to explore the mechanical, and strain-dependent physical properties of other anisotropic 2D materials more broadly.

Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts.

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY2 (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY2 monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m-1. All six XY2 sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H+/H2 and O2/H2O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP2 and SnAs2 could be tuned to improve their photocatalytic performance.

Liquid Phase Edge Epitaxy of Transition-Metal Dichalcogenide Monolayers.

Precise monolayer epitaxy is important for two-dimensional (2D) semiconductors toward future electronics. Here, we report a new self-limited epitaxy approach, liquid phase edge epitaxy (LPEE), for precise-monolayer epitaxy of transition-metal dichalcogenides. In this method, the liquid solution contacts 2D grains only at the edges, which confines the epitaxy only at the grain edges and then precise monolayer epitaxy can be achieved. High-temperature in situ imaging of the epitaxy progress directly supports this edge-contact epitaxy mechanism. Typical transition-metal dichalcogenide monolayers (MX2, M = Mo, W, and Re; X = S or Se) have been obtained by LPEE with a proper choice of molten alkali halide solvents (AL, A = Li, Na, K, and Cs; L = Cl, Br, or I). Furthermore, alloying and magnetic-element doping have also been realized by taking advantage of the liquid phase epitaxy approach. This LPEE method provides a precise and highly versatile approach for 2D monolayer epitaxy and can revolutionize the growth of 2D materials toward electronic applications.

Hydrogel with Robust Adhesion in Various Liquid Environments by Electrostatic-Induced Hydrophilic and Hydrophobic Polymer Chains Migration and Rearrangement.

Hydrogels with wet adhesion are promising interfacial adhesive materials; however, their adhesion in water, oil, or organic solvents remains a major challenge. To address this, a pressure-sensitive P(AAm-co-C18 )/PTA-Fe hydrogel is fabricated, which exhibits robust adhesion to various substrates in both aqueous solutions and oil environments. It is demonstrated that the key to wet adhesion under liquid conditions is the removal of the interfacial liquid, which can be achieved through rational molecular composition regulation. By complexing with hydrophilic polymer networks, phosphotungstic acid (PTA) is introduced into the hydrogel network as a physical cross-linker and anchor point to improve the cohesion strength and drive the migration of polymer chains. The migration and rearrangement of hydrophilic and hydrophobic polymer chains on the hydrogel surface are induced by the electrostatic interactions of Fe3+ , which create a surface with interfacial water- and oil-removing properties. By co-regulating the hydrophilic and hydrophobic polymer chains, the P(AAm-co-C18 )/PTA-Fe hydrogel is able to act as a pressure-sensitive adhesive under water and oils with adhesion strength of 92.6 and 90.0 kPa, respectively. It is anticipated that this regulation strategy for polymer chains will promote the development of wet adhesion hydrogels, which can have a wide range of applications.

The ecological response and distribution characteristics of microorganisms and polycyclic aromatic hydrocarbons in a retired coal gas plant post-thermal remediation site.

Thermal remediation is one of the most common approaches of removing organic pollutants in the retired contamination sites. However, little is known about the performance of bacterial community characteristics after in situ thermal remediation. In this study, the ecological response and spatial distributional characteristics of microorganisms and polycyclic aromatic hydrocarbons (PAHs) were investigated using a high throughput sequencing method in a retired coal gas plant site after in situ thermal remediation in Nanjing, China. Combination of Venn, clustering-correlation heatmap and two - factor correlation network analysis revealed that, microbial communities were obviously affected and classified by soil depths, temperature, and contamination level, respectively. The common and endemic microorganisms of each group were identified. The relative abundances of Thermaerobacter, Calditerricola, Brevibacillus, Ralstonia and Rhodococcus (aerobic bacteria) gradually declined with the increase of soil depth, while those of Bacillus, Fictibacillus, Paenibacillus, Rheinheimera presented opposite tendency. Some thermophilic degradation bacteria of PAHs, including Thermaerobacter, Calditerricola, Bacillus, Rhodococcus, unclassified_p__Firmicutes, Arthrobacter and Deinococcus, were identified and increased in the abundance at heavily polluted sites. Additionally, Proteobacteria, Bacteroidota, Deinococcota, Chloroflexi, Acidobacteriota, and Actinobacteriota showed negative response to the increase of soil depth, temperature and pollution level, while Firmicutes presented a positive response. This implied that Firmicutes has better stress resistance and adaptability to thermal remediation condition. The key environmental factors affecting microorganism composition and distribution were Temperature, Total nitrogen, Oxidation-Reduction Potential, Organic matters, and PAHs concentrations, which explains the dominant driving mechanism of soil depth, temperature, and contamination level on microbial characteristics in thermal remediation site. Our study could contribute to a better understanding of the resilience and adaptation mechanisms of microbial community at the contaminated site after the in situ thermal remediation.

Giant Enhancement and Directional Second Harmonic Emission from Monolayer WS2 on Silicon Substrate via Fabry-Pérot Micro-Cavity.

Two-dimensional transition metal dichalcogenides (TMDs) possess large second-order optical nonlinearity, making them ideal candidates for miniaturized on-chip frequency conversion devices, all-optical interconnection, and optoelectronic integration components. However, limited by subnanometer thickness, the monolayer TMD exhibits low second harmonic generation (SHG) conversion efficiency (<0.1%) and poor directionality, which hinders their practical applications. Herein, we proposed a Fabry-Pérot (F-P) cavity formed by coupling an atomically thin WS2 film with a silicon hole matrix to enhance the SH emission. A maximum enhancement (∼1580 times) is achieved by tuning the excitation wavelength to be resonant with the microcavity modes. The giant enhancement is attributed to the strong electric field enhancement in the F-P cavity and the oscillator strength enhancement of excitons from suspended WS2. Moreover, directional SH emission (divergence angle ∼5°) is obtained benefiting from the resonance of the F-P microcavity. Our research results can provide a practical sketch to develop both high-efficiency and directional nonlinear optical devices for silicon-based on-chip integration optics.

Domino-like stacking order switching in twisted monolayer-multilayer graphene.

Atomic reconstruction has been widely observed in two-dimensional van der Waals structures with small twist angles1-7. This unusual behaviour leads to many novel phenomena, including strong electronic correlation, spontaneous ferromagnetism and topologically protected states1,5,8-14. Nevertheless, atomic reconstruction typically occurs spontaneously, exhibiting only one single stable state. Using conductive atomic force microscopy, here we show that, for small-angle twisted monolayer-multilayer graphene, there exist two metastable reconstruction states with distinct stacking orders and strain soliton structures. More importantly, we demonstrate that these two reconstruction states can be reversibly switched, and the switching can propagate spontaneously in an unusual domino-like fashion. Assisted by lattice-resolved conductive atomic force microscopy imaging and atomistic simulations, the detailed structure of the strain soliton networks has been identified and the associated propagation mechanism is attributed to the strong mechanical coupling among solitons. The fine structure of the bistable states is critical for understanding the unique properties of van der Waals structures with tiny twists, and the switching mechanism offers a viable means for manipulating their stacking states.

[A new norsesquiterpenoid from Schisandra chinensis].

This study investigated the chemical components from the leaves and stems of Schisandra chinensis. Three norsesquiterpenoids were isolated from S. chinensis by various column chromatographies(silica gel, Sephadex LH-20, and MCI), reversed-phase medium-pressure preparative, and semi-preparative high-performance liquid chromatography(HPLC). Their structures were identified based on physicochemical properties, mass spectrometry(MS), nuclear magnetic resonance(NMR), ultraviolet(UV), and electro-nic circular dichroism(ECD) as(3R,4R,5R,6S,7E)-3,4,5,6-tetrahydroxy-7-megastigmen-9-one(1),(3S,5R,6R,7E)-3,5,6-trihydroxy-7-megastigmen-9-one(2), and(3S,4R,9R)-3,4,9-trihydroxymegastigman-5-ene(3). Compound 1 was a new compound, and its absolute configuration was determined by ECD. Compounds 2 and 3 were isolated from the Schisandra plant for the first time.

Four sesquiterpenoids from the vegetable raw material Schisandra chinensis (Turcz.) Baill.: leaves and stems.

Four sesquiterpenoids A-D (1-4) were isolated from the ethanol extracts of the leaves and stems from Schisandra chinensis. Their structures and absolute configurations were elucidated by a combination of NMR, MS and ECD. Compounds 1-4 (10 µM) exhibited moderate hepatoprotective activities against APAP-induced LO2 cell damage with increasing cell viability by 18%, 17%, 16%, and 19% compared to the model group (bicyclol, 26%) at 10 µM, respectively. All the compounds displayed no cytotoxic activity against five human cell lines, which also suggested the safety of leaves and stems of S. chinensis as an edible vegetable in a degree.

Elastocapillary cleaning of twisted bilayer graphene interfaces.

Although layered van der Waals (vdW) materials involve vast interface areas that are often subject to contamination, vdW interactions between layers may squeeze interfacial contaminants into nanopockets. More intriguingly, those nanopockets could spontaneously coalesce into larger ones, which are easier to be squeezed out the atomic channels. Such unusual phenomena have been thought of as an Ostwald ripening process that is driven by the capillarity of the confined liquid. The underlying mechanism, however, is unclear as the crucial role played by the sheet's elasticity has not been previously appreciated. Here, we demonstrate the coalescence of separated nanopockets and propose a cleaning mechanism in which both elastic and capillary forces are at play. We elucidate this mechanism in terms of control of the nanopocket morphology and the coalescence of nanopockets via a mechanical stretch. Besides, we demonstrate that bilayer graphene interfaces excel in self-renewal phenomena.

Probing the interactions of GlcNH2 with boric acid via NMR spectroscopy.

The essential role of boronic esters in controlling both the direction and selectivity of chemical reactions as well as their significant function in catalytic activity have been demonstrated for industrially important processes. The specific interaction analyses of the monosaccharide GlcNH2 with boric acid are of interest since monosaccharides serve as model systems for the more sophisticated carbohydrate molecules. The interaction of GlcNH2 with boric acid was systematically investigated by numerous NMR techniques. A 1 : 1 chelate boron complex coordinated at the cis-1,2 position of GlcNH2 was identified as the major species in DMSO-d6 solution via1H and 13C INEPT DOSY NMR spectroscopy. This specific boron nitrogen coordination mechanism was further supported by the 1H-15N HSQC spectra. Variations in the spin-lattice relaxation times (T1) of the 13C1 nucleus also provided quantitative data regarding this non-covalent interactions. This is an application of 1H, 13C INEPT DOSY, 1H-15N HSQC, and relaxation methods to study such aggregations in solutions. These methods have potential applications in the characterization of reactive intermediates in biomass conversions.

Optimizing Comprehensive Performance of Aggregation-Induced Emission Nanoparticles through Molecular Packing Modulation for Multimodal Image-Guided Synergistic Phototherapy.

Fluorescent nanoparticles (NPs) with aggregation-induced emission (AIE) characteristics hold remarkable potential for image-guided phototherapy. The molecular packing is the key point for optimizing the performance of AIE luminogens (AIEgens) in the aggregated or solid state. However, so far, the packing mode of AIEgens in NPs is still vague, causing some challenges for understanding the relationship between the photophysical property and packing mode, as well as further optimizing the performance of NPs for biomedical applications. In this contribution, by simply controlling the length of alkoxy chains in the donor-acceptor conjugated OPTPA, a packing balance between the twisted molecular structure and effective π-conjugation is actualized. Subsequently, the possibility of amorphous-crystalline transition of AIEgens in the polymer-encapsulated NPs is presented for the first time, and the comprehensive performance of NPs is further optimized. Both in vitro and in vivo experiments indicate that crystalline AIEgen-based NPs are remarkably effective in trimodal imaging-guided synergistic phototherapy.

One-for-All Phototheranostic Agent Based on Aggregation-Induced Emission Characteristics for Multimodal Imaging-Guided Synergistic Photodynamic/Photothermal Cancer Therapy.

Phototheranostics represents a promising direction for modern precision medicine, which has recently received considerable attention for cancer research. The ingenious integration of all phototheranostic modalities in a single molecule with precise spatial colocalization is a tremendously challenging task, which mainly arises from the complexity of molecular design and energy dissipation. Reports on a single molecular one-for-all theranostic agent are still very rare. Herein, we designed two novel aggregation-induced emission (AIE)-active fluorogens (AIEgens, named DPMD and TPMD) with a cross-shaped donor-acceptor structure via a facile synthetic method and constructed versatile nanoparticles (NPs) by encapsulating AIEgen with an amphiphilic polymer. The AIEgen TPMD with a twisted structure, high donor-acceptor (D-A) strength, small singlet-triplet energy gap, and abundant intramolecular rotators and vibrators was selected as an ideal candidate for balancing and utilizing the radiative and nonradiative energy dissipations. Notably, TPMD NPs simultaneously possess adequate near-infrared (NIR) fluorescence emission at 821 nm for fluorescence imaging, effective reactive oxygen species generation for photodynamic therapy (PDT), and outstanding photothermal effect for photoacoustic imaging, photothermal imaging, and photothermal therapy (PTT), which demonstrates the superior potential of AIE NPs in multimodal imaging-guided synergistic PDT/PTT therapy.

Out-of-Plane Deformations Determined Mechanics of Vanadium Disulfide (VS2) Sheets.

The rapid development of two-dimensional (2D) materials has significantly broadened the scope of 2D science in both fundamental scientific interests and emerging technological applications, wherein the mechanical properties play an indispensably key role. Nevertheless, particularly challenging is the ultrathin nature of 2D materials that makes their manipulations and characterizations considerably difficult. Herein, thanks to the excellent flexibility of vanadium disulfide (VS2) sheets, their susceptibility to out-of-plane deformation is exploited to realize the controllable loading and enable the accurate measurements of mechanical properties. In particular, the Young's modulus is estimated to be 44.4 ± 3.5 GPa, approaching the lower limit for 2D transition metal dichalcogenides (TMDs). We further report the first measurement of thickness-dependent bending rigidity of VS2, which deviates from the prediction of the classical continuum mechanics theory. Additionally, a deeper understanding of the mechanics within two dimensions also facilitates the modulation of strain-coupled physics at the nanoscale. Our Raman measurements showed the Grüneisen parameters for VS2 were determined for the first time to be γE2g1 ≈ 0.83 and γA1g ≈ 0.32.