Superspreading Surface with Hierarchical Porous Structure for Highly Efficient Vapor-Liquid Phase Change Heat Dissipation.

Superspreading surfaces with excellent water transport efficiency are highly desirable for addressing thermal failures through the liquid-vapor phase change of water in electronics thermal management applications. However, the trade-off between capillary pressure and viscous resistance in traditional superspreading surfaces with micro/ nanostructures poses a longstanding challenge in the development of superspreading surfaces with high cooling efficiency in confined spaces. Herein, a heat-treated hierarchical porous enhanced superspreading surface (HTHP) for highly efficient electronic cooling is proposed. Compared with the single porous structures in nanograss, nanosheets, and copper foam, HTHP with hierarchical honeycomb pores effectively resolves the trade-off effect by introducing large vertical through-pores to reduce viscous resistance, and connected small pores to provide sufficient capillary pressure synergistically. HTHP exhibits excellent capillary performance in both horizontal spreading and vertical rising. Despite a thickness of only 0.33 mm, the as-prepared ultrathin vapor chamber (UTVC) fabricated to exploit the superior capillary performance of HTHP achieved effective heat dissipation with outstanding thermal conductivity (12 121 Wm-1K-1), and low thermal resistance (0.1 KW-1) at a power of 5 W. This regulation strategy based on hierarchical honeycomb porous structures is expected to promote the development of high-performance superspreading surfaces with a wide range of applications in thermal management.

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.

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.

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.

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.

Tuning friction to a superlubric state via in-plane straining.

Controlling, and in many cases minimizing, friction is a goal that has long been pursued in history. From the classic Amontons-Coulomb law to the recent nanoscale experiments, the steady-state friction is found to be an inherent property of a sliding interface, which typically cannot be altered on demand. In this work, we show that the friction on a graphene sheet can be tuned reversibly by simple mechanical straining. In particular, by applying a tensile strain (up to 0.60%), we are able to achieve a superlubric state (coefficient of friction nearly 0.001) on a suspended graphene. Our atomistic simulations together with atomically resolved friction images reveal that the in-plane strain effectively modulates the flexibility of graphene. Consequently, the local pinning capability of the contact interface is changed, resulting in the unusual strain-dependent frictional behavior. This work demonstrates that the deformability of atomic-scale structures can provide an additional channel of regulating the friction of contact interfaces involving configurationally flexible materials.

[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.

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.

Bending of Multilayer van der Waals Materials.

Out-of-plane deformation patterns, such as buckling, wrinkling, scrolling, and folding, formed by multilayer van der Waals materials have recently seen a surge of interest. One crucial parameter governing these deformations is bending rigidity, on which significant controversy still exists despite extensive research for more than a decade. Here, we report direct measurements of bending rigidity of multilayer graphene, molybdenum disulfide (MoS_{2}), and hexagonal boron nitride (hBN) based on pressurized bubbles. By controlling the sample thickness and bubbling deflection, we observe platelike responses of the multilayers and extract both their Young's modulus and bending rigidity following a nonlinear plate theory. The measured Young's moduli show good agreement with those reported in the literature (E_{graphene}>E_{hBN}>E_{MoS_{2}}), but the bending rigidity follows an opposite trend, D_{graphene}

MicroRNA-138 Suppresses Osteoblastic Differentiation of Valvular Interstitial Cells in Degenerative Calcific Aortic Valve Disease.

The aim of this study was to explore the function of miR-138 in the pathogenesis of degenerative calcific aortic valve disease (DCAVD).Aortic valve calcification tissue and normal tissue from DCAVD patients were collected to detect the expression of miR-138 by qRT-PCR, and immunohistochemical staining was performed to identify the phenotype of valve interstitial cells. QRT-PCR was performed to analyze the expression of miR-138, Runx2, MSX2, and ALP at day 7 after osteogenic differentiation. Alkaline phosphatase activity assay was performed at day 14 after osteogenic differentiation. Alizarin red staining was used to analyze the calcium nodule formation. TargetScan was used to predict potential targets of miR-138. QRT-PCR and Western blotting were performed to analyze the expression of FOXC1 in valve interstitial cells (VICs). The aortic valve calcification was evaluated by quantitative analysis of the velocity in the aortic annulus and transvalvular pressure gradients.In this study, we demonstrated the role of miR-138 in VIC osteogenesis. QRT-PCR results revealed miR-138 was significantly down-regulated in calcified aortic valves compared with non-calcified valves. MiR-138 overexpression inhibited VIC osteogenic differentiation in vitro, while down-regulation of miR-138 enhanced the process. Target prediction analysis and dual-luciferase reporter assay confirmed FOXC1 was a direct target of miR-138. Further research found FOXC1 overexpression promoted VIC osteogenic differentiation. In addition, animal experiments validated indirectly miR-138 could suppress aortic valve calcification.Our findings suggest miR-138 could function as a new inhibitor of VIC osteogenic differentiation, which may act by targeting FOXC1.

Interface-Governed Deformation of Nanobubbles and Nanotents Formed by Two-Dimensional Materials.

Nanoblisters such as nanobubbles and nanotents formed by two-dimensional (2D) materials have been extensively exploited for strain engineering purposes as they can produce self-sustained, nonuniform in-plane strains through out-of-plane deformation. However, deterministic measure and control of strain fields in these systems are challenging because of the atomic thinness and unconventional interface behaviors of 2D materials. Here, we experimentally characterize a simple and unified power law for the profiles of a variety of nanobubbles and nanotents formed by 2D materials such as graphene and MoS_{2} layers. Using membrane theory, we analytically unveil what sets the in-plane strains of these blisters regarding their shape and interface characteristics. Our analytical solutions are validated by Raman spectroscopy measured strain distributions in bulged graphene bubbles supported by strong and weak shear interfaces. We advocate that both the strain magnitudes and distributions can be tuned by 2D material-substrate interface adhesion and friction properties.

An Environmentally-Adaptive Positioning Method Based on Integration of GPS/DTMB/FM.

The Global Positioning System (GPS) yields good precision and availability in open outdoor environment. However, the errors of GPS may suffer degradation in some complex environments, such as forests and urban canyons. To solve this problem, a new positioning method is designed integrating GPS, Digital Terrestrial Multimedia Broadcast (DTMB) and frequency-modulated (FM) radio signal. In this method, the DTMB transmitter acts as a pseudo-satellite to assist GPS positioning. Furthermore, the FM fingerprint positioning is used to correct the positioning bias. An adaptive selection scheme is proposed to provide an optimal integration mode of the sensors. Field experiments in complex environment were carried out for evaluation. Comparing to the GPS-only and GPS + DTMB approach, positioning accuracy was improved by at least 68.21 % and 21.27 % with the proposed method, respectively.

Measuring Interlayer Shear Stress in Bilayer Graphene.

Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial shear interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling shear deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer shear zone outside the bubble edge and extract an interlayer shear stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial shear stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial shear responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer shear properties of the emerging 2D materials for potential applications in multilayer systems.

Liquid crystalline behavior of graphene oxide in the formation and deformation of tough nanocomposite hydrogels.

In this paper, we report the formation and transformation of graphene oxide (GO) liquid crystalline (LC) structures in the synthesis and deformation of tough GO nanocomposite hydrogels. GO aqueous dispersions form a nematic LC phase, while the addition of poly(N-vinylpyrrolidone) (PVP) and acrylamide (AAm), which are capable of forming hydrogen bonding with GO nanosheets, shifts the isotropic/nematic transition to a lower volume fraction of GO and enhances the formation of nematic droplets. During the gelation process, a phase separation of the polymers and GO nanosheets is accompanied by the directional assembly of GO nanosheets, forming large LC tactoids with a radial GO configuration. The shape of the large tactoids evolves from a sphere to a toroid as the tactoids increase in size. Interestingly, during cyclic uniaxial tensile deformation a reversible LC transition is observed in the very tough hydrogels. The isolated birefringent domains and the LC domains in the tactoids in the gels are highly oriented under a high tensile strain.

Serum albumin-embedding copper nanoclusters inhibit Alzheimer's ß-amyloid fibrillogenesis and neuroinflammation.

Increasing evidence suggests that the accumulations of reactive oxygen species (ROS), ß-amyloid (Aß), and neuroinflammation are crucial pathological hallmarks for the onset of Alzheimer's disease (AD), yet there are few effective treatment strategies. Therefore, design of nanomaterials capable of simultaneously elimination of ROS and inhibition of Aß aggregation and neuroinflammation is urgently needed for AD treatment. Herein, we designed human serum albumin (HSA)-embedded ultrasmall copper nanoclusters (CuNCs@HSA) via an HSA-mediated fabrication strategy. The as-prepared CuNCs@HSA exhibited outstanding multiple enzyme-like properties, including superoxide dismutase (>5000 U/mg), catalase, and glutathione peroxidase activities as well as hydroxyl radicals scavenging ability. Besides, CuNCs@HSA prominently inhibited Aß fibrillization, and its inhibitory potency was 2.5-fold higher than native HSA. Moreover, CuNCs@HSA could significantly increase the viability of Aß-treated cells from 60 % to over 96 % at 40 µg/mL and mitigate Aß-induced oxidative stresses. The secretion of neuroinflammatory cytokines by lipopolysaccharide-induced BV-2 cells, including tumor necrosis factor-α and interleukin-6, was alleviated by CuNCs@HSA. In vivo studies manifested that CuNCs@HSA effectively suppressed the formation of plaques in transgenic C. elegans, reduced ROS levels, and extended C. elegans lifespan by 5 d. This work, using HSA as a template to mediate the fabrication of copper nanoclusters with robust ROS scavenging capability, exhibited promising potentials in inhibiting Aß aggregation and neuroinflammation for AD treatment.

Discrimination of Xylene Isomers by Precisely Tuning the Interlayer Spacing of Reduced Graphene Oxide Membrane.

Separating xylene isomers is a challenging task due to their similar physical and chemical properties. In this study, we developed a molecular sieve incorporating a reduced graphene oxide (rGO) membrane for the precise differentiation of xylene isomers. We fabricated GO membranes using a vacuum filtration technique followed by thermal-induced reduction to produce rGO membranes with precisely controllable interlayer spacing. Notably, we could finely tune the interlayer spacing of the rGO membrane from 8.0 to 5.0 Å by simply varying the thermal reduction temperature. We investigated the reverse osmosis separation ability of the rGO membranes for xylene isomers and found that the rGO membrane with an interlayer spacing of 6.1 Å showed a high single component permeance of 0.17 and 0.04 L m-2 h-1 bar-1 for para- and ortho-xylene, respectively, exhibiting clear permselectivity. The separation factor reached 3.4 and 2.8 when 90:10 and 50:50 feed mixtures were used, respectively, with permeance 1 order of magnitude higher than that of current state-of-the-art reverse osmosis membranes. Additionally, the membrane showed negligible permeance and selectivity decay even after continuous operation for more than 5 days, suggesting commendable membrane resistance to solvent swelling and operating pressure.

Bioinspired Slippery Surfaces for Liquid Manipulation from Tiny Droplet to Bulk Fluid.

Slippery surfaces, which originate in nature with special wettability, have attracted considerable attention in both fundamental research and practical applications in a variety of fields due to their unique characteristics of superlow liquid friction and adhesion. Although research on bioinspired slippery surfaces is still in its infancy, it is a rapidly growing and enormously promising field. Herein, a systematic review of recent progress in bioinspired slippery surfaces, beginning with a brief introduction of several typical creatures with slippery property in nature, is presented. Subsequently,this review gives a detailed discussion on the basic concepts of the wetting, friction, and drag from micro- and macro-aspects and focuses on the underlying slippery mechanism. Next, the state-of-the-art developments in three categories of slippery surfaces of air-trapped, liquid-infused, and liquid-like slippery surfaces, including materials, design principles, and preparation methods, are summarized and the emerging applications are highlighted. Finally, the current challenges and future prospects of various slippery surfaces are addressed.

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.

High mechanical performance of layered graphene oxide/poly(vinyl alcohol) nanocomposite films.

The design and fabrication of strong, lightweight, and damage-resistant composite materials are major topics of studies on composites. Biomimetics, a developing multidisciplinary field, is now leading the fabrication of novel materials with remarkable mechanical properties. Graphene oxide (GO), a graphene derivative, possesses good mechanical properties, a high aspect ratio, and good solubility in aqueous solutions, indicating great potential in nanocomposite fields. In this work, bioinspired layered GO/poly(vinyl alcohol) (PVA) nanocomposite films with remarkable mechanical performances are prepared by an environmental friendly, bottom-up assembly methodology. The structural analysis shows alternate piles of inorganic GO platelets and organic PVA binder. Tensile tests indicate that the borate-treated GO/PVA nanocomposite films display 360 MPa of strength, which is twofold to threefold higher than that of biological materials (e.g., nacre). Toughness of GO/PVA nanocomposites is also enhanced fourfold compared with nacre. To reveal the toughening function of the intercalated polymer in the nanocomposites, the influence of polymer with varied molecular weights (Mws) on the fracture mode of the nanocomposites is systematically investigated through quasi-static tensile and creep tests. The PVA molecules with a higher Mw can connect more neighboring GO platelets through inter- and intra-linkages than those with a lower Mw, resulting in efficient stress transfer along the GO plane direction. Thus, tensile strength and toughness are improved. This work illustrates the functions of bonding types between inorganic-organic phases and intercalated polymers with different Mws on the mechanical properties of the layered nanocomposites, including stiffness, strength, and toughness.