Microscopic evidence for Mn-induced long range magnetic ordering in MAX phase compounds

Zero and low field nuclear magnetic resonance measurements have been performed on MAX phase samples (Cr_1-x Mn _x )₂AC with A = Ge and Ga in order to obtain local microscopic information on the nature of magnetism in this system. Our results unambiguously provide evidence for the existence of long-range magnetic order in (Cr_0.96Mn_0.04)₂GeC and for (Cr_0.93Mn_0.07)₂GaC, but not for (Cr_0.97Mn_0.03)₂GaC. We point to a possible dependence of long range magnetic order in these MAX phase compounds on the A atom.

Theoretical investigation of the scanning tunneling microscopy of Majorana bound states in topological superconductor vortices

Scanning tunneling microscopy (STM) is an indispensable tool in detecting Majorana bound states (MBSs) in vortices of topological superconductors. By reducing the computational complexity via non-uniform grids, we systematically study the tunnel coupling as well as the temperature dependence of the differential conductance of MBSs in two dimensional devices. Numerical results show that the conductance peak approaches the quantized value 2e ²/h in strong coupling limit at low temperatures which are characteristic features of MBSs. More interestingly, a conductance local minimum in the spatially scanning is observed when the STM tip is placed at the vortex center. The dip structure can be enhanced with increased temperature or enlarged vortex size. We ascribe this observation to the sensitivity of the Andreev reflection processes of carriers at the vortex center where the thermal energy could be comparable to the vanishing pair potential. We also investigate the STM of two-vortex systems where the hybridization of the vortices can lead to oscillatory behavior of the state energy. With small inter-vortex distances, the original MBSs in vortices can merge into topologically trivial states and the conductance peak can be significantly suppressed.

Wettability-Controlled Directional Actuating Strategy Based on Bilayer Photonic Crystals

Although the water-triggered bending behavior of bilayer films has been a wide concerned, there are few reports on wettability-controlled directional actuators with visible color changes. Using photonic crystals as carriers, bilayer directional bending structural color actuators were prepared based on the hydrophilic difference. Top inverse opal with strong hydrophilicity can promote water penetration and strengthen the effect of swelling. While, bottom inverse opal with weak hydrophilicity can inhibit water penetration and weaken the effect of swelling. When the bilayer structure is immersed in water, its wettability differences will produce different optical responses for visualization and will bring different swelling performances, resulting in directional bending. Infiltration differences are visualized as structural color red shifts or transparency. The mechanism of the design involves optical diffractions in the fabricated periodic nanostructures, differences in the surface wettability and swelling rate, uses the infiltration and capillary evaporation of water to realize the spectral diversity of reflectance, and the enhancement of bending by gradient infiltration. This work deeply analyzes the improvement of the photonic crystal structure on the optical and bending performance of the wettability-controlled actuator, provides a basic model for the design of bionic components, and opens an idea for the combination of bilayer photonic crystals and actuators.

Exploring the Efficient Na/K Storage Mechanism and Vacancy Defect-Boosted Li+ Diffusion Based on VSe2/MoSe2 Heterostructure Engineering

As typical 2D materials, VSe₂ and MoSe₂ both play a complementary role in Li/Na/K storage. Therefore, we designed and optimized the VSe₂/MoSe₂ heterostructure to gain highly efficient Li/Na/K-ion batteries. Most importantly, achieving fast Li/Na/K-ion diffusion kinetics in the interlayer of VSe₂/MoSe₂ is a key point. First of all, first-principles calculations were carried out to systematically investigate the packing structure, mechanical properties, band structure, and Li/Na/K storage mechanism. Our calculated results suggest that a large interlayer spacing (3.80 Å), robust structure, and metallic character pave the way for achieving excellent charge-discharge performance for the VSe₂/MoSe₂ heterostructure. Moreover, V and Mo ions both suffer a very mild redox reaction even if Li/Na/K ions fill the interlayer space. These structures were all further verified to show thermal stability (300 K) by means of the AIMD method. By analyzing the Li/Na/K diffusion behavior and the effect of vacancy defect on the structural stability and energy barrier for Li interlayer diffusion, it is found that the VSe₂/MoSe₂ heterostructure exhibits very low-energy barriers for Na/K interlayer diffusion (0.21 eV for Na and 0.11 eV for K). Compared with the VSe₂/MoSe₂ heterostructure, the V_0.92Se_1.84/MoSe₂ heterostructure not only can still maintain a stable structure and metallic character but also has much lower energy barrier for Li interlayer diffusion (0.07 vs 0.48 eV). These discoveries also break new ground to eliminate the obstacles preventing Li⁺ diffusion in the interlayer of other heterostructure materials. Besides, both VSe₂/MoSe₂ and V_0.92Se_1.84/MoSe₂ heterostructures have low average open-circuit voltage (OCV) values during Li/Na/K interlayer diffusion (1.07 V for V_0.92Se_1.84/MoSe₂ vs Li⁺, 0.86 V for VSe₂/MoSe₂ vs Na⁺, and 0.54 V for VSe₂/MoSe₂ vs K⁺), such low OCV values are beneficial for anode materials with excellent electrochemical properties. The above findings offer a new route to design anode materials for Li/Na/K-ion batteries.

Direct-Write of Nanoscale Domains with Tunable Metamagnetic Order in FeRh Thin Films

We have directly written nanoscale patterns of magnetic ordering in FeRh films using focused helium-ion beam irradiation. By varying the dose, we pattern arrays with metamagnetic transition temperatures that range from the as-grown film temperature to below room temperature. We employ transmission electron microscopy, X-ray diffraction, and temperature-dependent transport measurements to characterize the as-grown film, and magneto-optic Kerr effect imaging to quantify the He⁺ irradiation-induced changes to the magnetic order. Moreover, we demonstrate temperature-dependent optical microscopy and conductive atomic force microscopy as indirect probes of the metamagnetic transition that are sensitive to the differences in dielectric properties and electrical conductivity, respectively, of FeRh in the antiferromagnetic (AF) and ferromagnetic (FM) states. Using density functional theory, we quantify strain- and defect-induced changes in spin-flip energy to understand their influence on the metamagnetic transition temperature. This work holds promise for in-plane AF-FM spintronic devices, by reducing the need for multiple patterning steps or different materials, and potentially eliminating interfacial polarization losses due to cross material interfacial spin scattering.

Metal-Organic Framework-Encapsulated CoCu Nanoparticles for the Selective Transfer Hydrogenation of Nitrobenzaldehydes: Engineering Active Armor by the Half-Way Injection Method

A novel armor-type composite of metal-organic framework (MOF)-encapsulated CoCu nanoparticles with a Fe₃ O₄ core (Fe₃ O₄ @SiO₂ -NH₂ -CoCu@UiO-66) has been designed and synthesized by the half-way injection method, which successfully serves as an efficient and recyclable catalyst for the selective transfer hydrogenation. In this half-way injection approach, the pre-synthetic Fe₃ O₄ @SiO₂ -NH₂ -CoCu was injected into the UiO-66 precursor solution halfway through the MOF budding period. The formed MOF armor could play a role of providing significant additional catalytic sites besides CoCu nanoparticles, protecting CoCu nanoparticles, and improving the catalyst stability, thus facilitating the selective transfer hydrogenation of nitrobenzaldehydes into corresponding nitrobenzyl alcohols in high selectivity (99 %) and conversion (99 %) rather than nitro group reduction products. Notably, this method achieves the precise assembly of a MOF-encapsulated composite, and the ingenious combination of MOF and nanoparticles exhibits excellent catalytic performance in the selective hydrogen transfer reaction, implementing a "1+1>2" strategy in catalysis.

Ferroelastic Nanodomain-mediated Mechanical Switching of Ferroelectricity in Thick Epitaxial Films

Mechanical switching of ferroelectric polarization, typically realized via a scanning probe, holds promise in (multi)ferroic device applications. Whereas strain gradient-associated flexoelectricity has been regarded to be accountable for mechanical switching in ultrathin (<10 nm) films, such mechanism can hardly be extended to thicker materials due to intrinsic short operating lengths of flexoelectricity. Here, we demonstrate robust mechanical switching in ∼100 nm thick Pb(Zr_0.2Ti_0.8)O₃ epitaxial films with a characteristic microstructure consisting of nanosized ferroelastic domains. Through a combination of multiscale structural characterizations, piezoresponse force microscopy, and phase-field simulations, we reveal that the ferroelastic nanodomains effectively mediate the 180° switching nucleation in a dynamical manner during tip scanning. Coupled with microstructure engineering, this newly revealed mechanism could boost the utility of mechanical switching through extended material systems. Our results also provide insight into competing polarization switching pathways in complex ferroelectric materials, essential for understanding their electromechanical response.

Combined coarse-grained molecular dynamics and finite-element study of light-activated deformation of photoresponsive polymers

The azobenzene-containing crosslinked liquid crystalline polymer is a potential candidate for a stimuli-responsive soft robot, as it provides contactless actuation without the implementation of any separate component. For facilitating practical applications of this novel material, complicated and predefined motions have been realized by tailoring the chemical structure of the polymer network. However, conventional multiscale mechanical analysis, which utilizes the all-atom molecular dynamics to represent a microscopic model, is unsuitable for handling diverse material design parameters due to excessive computational costs. Hence, a multiscale optomechanical simulation framework, which combines the coarse-grained molecular dynamics (CG MD) and the finite-element (FE) method, is developed in this study. The CG MD simulation satisfactorily reproduces the light-induced phase transition and photosoftening effect on the mechanical properties. In particular, using the mesoscale analysis, the presented methodology can treat diverse morphology parameters (liquid crystal phase, spacer length, and crosslinking density) to observe the associated photodeformations. The photostrain and elastic modulus profiles in terms of photoisomerization ratio are implemented into the continuum-scale governing equation, which is based on the neoclassical elasticity theory. To efficiently reflect the light-induced large rotations of liquid crystal mesogens and the corresponding geometric nonlinearity, a corotational formulation is employed in the FE shell model. We examine the mesostructural-morphology-dependent photobending deformations of the nematic and smectic photoresponsive polymers (PRPs). In addition, the mesoscopic-texture-mediated unique 3D deformations are investigated by modeling the topological defects. This study offers insight into the engineering of PRP materials for designing the mechanical motions of smart actuators.

Bending Setups for Reliability Investigation of Flexible Electronics

Flexible electronics is a rapidly growing technology for a multitude of applications. Wearables and flexible displays are some application examples. Various technologies and processes are used to produce flexible electronics. An important aspect to be considered when developing these systems is their reliability, especially with regard to repeated bending. In this paper, the frequently used methods for investigating the bending reliability of flexible electronics are presented. This is done to provide an overview of the types of tests that can be performed to investigate the bending reliability. Furthermore, it is shown which devices are developed and optimized to gain more knowledge about the behavior of flexible systems under bending. Both static and dynamic bending test methods are presented.

Cellulose-Based Hybrid Structural Material for Radiative Cooling

Structural materials with excellent mechanical properties are vitally important for architectural application. However, the traditional structural materials with complex manufacturing processes cannot effectively regulate heat flow, causing a large impact on global energy consumption. Here, we processed a high-performance and inexpensive cooling structural material by bottom-up assembling delignified biomass cellulose fiber and inorganic microspheres into a 3D network bulk followed by a hot-pressing process; we constructed a cooling lignocellulosic bulk that exhibits strong mechanical strength more than eight times that of the pure wood fiber bulk and greater specific strength than the majority of structural materials. The cellulose acts as a photonic solar reflector and thermal emitter, enabling a material that can accomplish 24-h continuous cooling with an average dT of 6 and 8 °C during day and night, respectively. Combined with excellent fire-retardant and outdoor antibacterial performance, it will pave the way for the design of high-performance cooling structural materials.

Quantifying the Dynamics of Protein Self-Organization Using Deep Learning Analysis of Atomic Force Microscopy Data

The dynamics of protein self-assembly on the inorganic surface and the resultant geometric patterns are visualized using high-speed atomic force microscopy. The time dynamics of the classical macroscopic descriptors such as 2D fast Fourier transforms, correlation, and pair distribution functions are explored using the unsupervised linear unmixing, demonstrating the presence of static ordered and dynamic disordered phases and establishing their time dynamics. The deep learning (DL)-based workflow is developed to analyze detailed particle dynamics and explore the evolution of local geometries. Finally, we use a combination of DL feature extraction and mixture modeling to define particle neighborhoods free of physics constraints, allowing for a separation of possible classes of particle behavior and identification of the associated transitions. Overall, this work establishes the workflow for the analysis of the self-organization processes in complex systems from observational data and provides insight into the fundamental mechanisms.

The required acoustic parameters simplification of invisibility cloaks and concentrators using the impedance-tunable coordinate transformation

Transformation acoustics, as an unconventional theory, provides a powerful tool to design various kinds of acoustic devices with excellent functionalities. However, the required ideal parameters, which are prescribed by the method, are both complex and hard to implement-even using acoustic metamaterials. Furthermore, simplified parameter materials are generally favored in transformation-acoustic design due to its easier realization with artificial structures. In this letter, we propose a coordinate transformation methodology for achieving simplified parameters by tuning the impedance distribution in the geometric limit, where the transformation media parameters can be derived by setting tunable impedance functions in the original space and a combination of suitable linear or nonlinear coordinate transformation. Based on this approach, both two-dimensional acoustic cloak and concentrators are designed with different sets of simplified parameters. Numerical simulations indicate good performance of these devices with minimized scattering at higher frequencies. The proposed method provides more opportunities to realize the designed acoustic devices experimentally, and can also be used for other transformation-acoustic designs including 3D cases.

Active Basal Plane Catalytic Activity via Interfacial Engineering for a Finely Tunable Conducting Polymer/MoS2 Hydrogen Evolution Reaction Multilayer Structure

The fixation of the catalyst interface is an important consideration for the design of practical applications. However, the electronic structure of MoS₂ is sensitive to its embedding environment, and the catalytic performance of MoS₂ catalysts may be altered significantly by the type of binding agents and interfacial structure. Interfacial engineering is an effective method for designing efficient catalysts, arising from the close contact between different components, which facilitates charge transfer and strong electronic interactions. Here, we have developed a layer-by-layer (LbL) strategy for the preparation of interfacial MoS₂-based catalyst structures with two types of conducting polymers on various substrates. We demonstrate how the assembled partners in the LbL structure can significantly impact the electronic structures in MoS₂. As the number of bilayers grows, using polypyrrole as a binder remarkably increases the catalytic efficacy as compared to using polyaniline. On the one hand, the ratio of S₂^2- (or S^2-), which is related to the remaining active hydrogen evolution reaction (HER) species, is further increased. On the other hand, density functional theory calculations indicate that the interfacial charge transport from the conducting polymers to MoS₂ may boost the HER activity of the interfacial structure of the conducting polymer/MoS₂ by decreasing the adsorption free energy of the intermediate H* at the S sites in the basal plane of MoS₂. The optimized catalytic efficacy of the (conducting polymer/MoS₂)_n assembly peaks is obtained with 16 assembly cycles. In preparing interfacial catalytic structures, the LbL-based strategy exhibits several key advantages, including the flexibility of choosing assembly partners, the ability to fine-tune the structures with precision at the nanometer scale, and planar homogeneity at the centimeter scale. We expect that this LbL-based catalyst immobilization strategy will contribute to the fundamental understanding of the scalability and control of highly efficient electrocatalysts at the interface for practical applications.

Building Better Li Metal Anodes in Liquid Electrolyte: Challenges and Progress

Li metal has been widely recognized as a promising anode candidate for high-energy-density batteries. However, the inherent limitations of Li metal, that is, the low Coulombic efficiency and dendrite issues, make it still far from practical applications. In short, the low Coulombic efficiency shortens the cycle life of Li metal batteries, while the dendrite issue raises safety concerns. Thanks to the great efforts of the research community, prolific fundamental understanding as well as approaches for mitigating Li metal anode safety have been extensively explored. In this Review, Li electrochemical deposition behaviors have been systematically summarized, and recent progress in electrode design and electrolyte system optimization is reviewed. Finally, we discuss the future directions, opportunities, and challenges of Li metal anodes.

Modeling the ternary chalcogenide Na2MoSe4 from first-principles

In the ongoing pursuit of inorganic compounds suitable for solid-state devices, transition metal chalcogenides have received heightened attention due to their physical and chemical properties. Recently, alkali-ion transition metal chalcogenides have been explored as promising candidates to be applied in optoelectronics, photovoltaics and energy storage devices. In this work, we present a theoretical study of sodium molybdenum selenide (Na₂MoSe₄). First-principles computations were performed on a set of hypothetical crystal structures to determine the ground state and electronic properties of Na₂MoSe₄. We find that the equilibrium structure of Na₂MoSe₄ is a simple orthorhombic (oP) lattice, with space group Pnma, as evidenced by thermodynamics. Finally, meta-GGA computations were performed to model the band structure of oP Na₂MoSe₄ at a predictive level. We employ the Tran-Blaha modified Becke-Johnson potential to demonstrate that oP Na₂MoSe₄ has a direct bandgap at the Γ point that is suitable for optoelectronics. Our results provide a foundation for future studies concerned with the modeling of inorganic and hybrid organic-inorganic materials chemically analogous to Na₂MoSe₄.

Superfast Growth Dynamics of High-Quality Silicon Nanowires on Polymer Films via Self-Selected Laser-Droplet-Heating

Growing high quality silicon nanowires (SiNWs) at elevated temperature on cooler polymer films seems to be contradictive but highly desirable for building high performance flexible and wearable electronics. In this work, we demonstrate a superfast (v_nw > 3.5 μm·s^-1) growth of high quality SiNWs on polymer/glass substrates, powered by self-selected laser at 808 nm heating of indium catalyst droplets that absorb amorphous Si layer to produce SiNWs. Because of the tiny heat capacity of the nanodroplets, the SiNW growth can be quickly heated up and frozen via rapid laser ON/OFF switching, enabling a deterministic diameter modulation in the ultralong SiNWs. Finally, prototype field effect transistors are also fabricated upon the laser-droplet-heating grown SiNWs with a high I_on/I_off ratio of >10⁴ and reasonable subthreshold swing of 386 mV·dec^-1, opening a generic new route to integrate high-quality NW channels directly upon large area and lightweight polymer substrates for developing high-performance flexible electronics.

High-Performance Bamboo Steel Derived from Natural Bamboo

It is highly desirable to develop green and renewable structural materials from biomaterials to replace synthetic materials involved from civil engineering to aerospace industries. Herein, we put forward a facile but effective top-down strategy to convert natural bamboo into bamboo steel. The fabrication process of bamboo steel involves the removal of lignin and hemicellulose, freeze-drying followed by epoxy infiltration, and densification combined with in situ solidification. The prepared bamboo steel is a super-strong composite material with a high specific tensile strength (302 MPa g^-1 cm³), which is higher than that (227 MPa g^-1 cm³) of conventional high specific strength steel. The bamboo steel demonstrates a high tensile strength of 407.6 MPa, a record flexural strength of 513.8 MPa, and a high toughness of 14.08 MJ/m³, which is improved by 360, 290, and 380% over those of natural bamboo, respectively. Particularly, the mechanical properties of the bamboo steel are the highest among the biofiber-reinforced polymer composites reported previously. The well-preserved bamboo scaffolds assure the integrity of bamboo fibers, while the densification under high pressure results in a high-fiber volume fraction with an improved hydrogen bonding among the adjacent bamboo fibers, and the epoxy resin impregnated enhances the stress transfer because of its chemical crosslinking with cellulose molecules. These endow the bamboo steel with superior mechanical performance. Furthermore, the bamboo steel demonstrates an excellent thermal insulating capability with a low thermal conductivity (about 0.29 W/mK). In addition, the bamboo steel shows a low coefficient of thermal expansion (about 6.3 × 10^-6 K^-1) and a very high-dimensional stability to moisture attack. The strategy of fabricating high-performance bamboo steel with green and abundant natural bamboo as raw materials is highly attractive for the sustainable development of structural engineering materials.

A Hierarchical Anodic Aluminum Oxide Template

Anodic aluminum oxide (AAO) templates are widely used for the development of various functional nanomaterials due to their highly ordered and tunable porous structures. Here, we report a new hierarchical AAO (hAAO) template with the hexagonally ordered unit cells and the radially distributed nanochannels. It is formed by integrating the self-assembled polystyrene microsphere template into the AAO fabrication process and rationalized in terms of mechanical stress and electric-field-induced oxide dissolution. The back side of the hAAO template resembles a moth-eye-like nanoarray, which shows good hydrophobicity. A variety of radial nanopillar arrays and moth-eye-like nanoarrays are fabricated by a series of materials and synthesis techniques employing the hAAO template. These unique nanoarrays demonstrate many physicochemical properties that are distinct from those obtained from the conventional AAO template.

Effect of Side-Chain Modification on the Active Layer Morphology and Photovoltaic Performance of Liquid Crystalline Molecular Materials

Controlling the nanoscale morphology of the photoactive layer by fine-tuning the molecular structure of semiconducting organic materials is one of the most effective ways to improve the power conversion efficiency of organic solar cells. In this contribution, we investigate the photovoltaic performance of benzodithiophene (BDT)-based p-type small molecules with three different side chains, namely alkyl-thio (BTR-TE), dialkylthienyl (BTR), and trialkylsilyl (BTR-TIPS) moieties substituted on the BDT core, when used alongside a nonfullerene acceptor. The side-chain changes on the BDT core are shown to have a profound effect on energy levels, charge generation, recombination, morphology, and photovoltaic performance of solid-state molecules. Compared with BTR and BTR-TIPS, BTR-TE-based single-junction binary blend solar cells show the best power conversion efficiency (PCE) of 13.2% due to improved morphology and charge transport with suppressed recombination. In addition, we also achieved relatively good performances for ternary blend solar cells with a PCE of 16.1% using BTR-TE as a third component. Our results show that side-chain modification has a significant effect on modulating active layer morphology, and in particular that thioether side-chain modification is an effective way to achieve optimum morphology and performance for organic photovoltaic (OPV) devices.

Designing a Rare DNA-Like Double Helical Microfiber Superstructure via Self-Assembly of In Situ Carbon Fiber-Encapsulated WO3-x Nanorods as an Advanced Supercapacitor Material

Double helical DNA structure is one of the most beautiful and fascinating nanoarchitecture nature has produced. Mimicking nature's design by the tailored synthesis of semiconductor nanomaterials such as WO₃ into a DNA-like double helical superstructure could impart special properties, such as enhanced stability, electrical conductivity, information storage, signal processing, and catalysis, owing to the synergistic interaction across helices. However, double helical WO₃ synthesis is extremely challenging and has never been reported earlier. This investigation presents the first-ever report on a facile synthesis route for designing a DNA-like double helical WO_3-x/C microfiber superstructure via self-assembly of in situ carbon fiber-encapsulated WO_3-x nanorods. This innovative design strategy is completely template-free and does not require predesigned helical templates or hydro/solvothermal treatment. Detailed spectroscopic material characterization and electrochemical studies confirmed that the double helical structure with carbon fiber-WO_3-x heterostructures enabled effective induction and distribution of oxygen vacancies along with W⁵⁺/W⁶⁺ redox surface states. Furthermore, faster electrode-electrolyte interfacial kinetics, improved electrical conductivity, and cycling stability has been observed in the carbon fiber-WO_3-x heterostructures which resulted in a high area specific capacitance of 401 mF cm^-2 at 2 mA cm^-2 with excellent capacitance retention of >94% for more than 5000 cycles. Additionally, the carbon fiber-WO_3-x heterostructures demonstrated promising performance when fabricated in a solid-state asymmetric supercapacitor device with the power density of 498 W kg^-1 at an energy density of 15.4 W h kg^-1. Therefore, the rare DNA-like double helical WO_3-x/C superstructure synthesized in this study could open new doorways toward in situ, facile fabrication of double helical superstructures for energy and environmental applications.

Why In2O3 Can Make 0.7 nm Atomic Layer Thin Transistors

In this work, we demonstrate enhancement-mode field-effect transistors by an atomic-layer-deposited (ALD) amorphous In₂O₃ channel with thickness down to 0.7 nm. Thickness is found to be critical on the materials and electron transport of In₂O₃. Controllable thickness of In₂O₃ at atomic scale enables the design of sufficient 2D carrier density in the In₂O₃ channel integrated with the conventional dielectric. The threshold voltage and channel carrier density are found to be considerably tuned by channel thickness. Such a phenomenon is understood by the trap neutral level (TNL) model, where the Fermi-level tends to align deeply inside the conduction band of In₂O₃ and can be modulated to the bandgap in atomic layer thin In₂O₃ due to the quantum confinement effect, which is confirmed by density function theory (DFT) calculation. The demonstration of enhancement-mode amorphous In₂O₃ transistors suggests In₂O₃ is a competitive channel material for back-end-of-line (BEOL) compatible transistors and monolithic 3D integration applications.

In Situ Quantification of Interactions between Charged Nanorods in a Predefined Potential Energy Landscape

Quantitative understanding of nanoscale interactions is a prerequisite for harnessing the remarkable collective properties of nanoparticle systems. Here, we report the combined use of liquid-phase transmission electron microscopy and electron beam lithography to elucidate the interactions between charged nanorods in a predefined potential energy landscape. In situ site-selective lift-off of surface-functionalized lithographed gold nanorods is achieved by patterning them with adhesion layer materials that undergo etching at different rates. Analysis of the subsequent nanorod motion, which is two-dimensionally confined as a result of the particle-substrate attraction, allows quantification of interparticle interactions in a lithographically engineered environment. For lithographed nanorods patterned with the same adhesion layer material, their self-assembly behavior following lift-off is tuned by changing their starting spatial arrangement. Our approach facilitates investigation of interparticle interactions in designed nanoparticle systems and affords fundamental insights into the role of the potential energy landscape in determining the kinetic pathway for nanoparticle self-assembly.

Multiple-Stimuli-Responsive and Cellulose Conductive Ionic Hydrogel for Smart Wearable Devices and Thermal Actuators

Stimulus-responsive hydrogels, such as conductive hydrogels and thermoresponsive hydrogels, have been explored extensively and are considered promising candidates for smart materials such as wearable devices and artificial muscles. However, most of the existing studies on stimulus-responsive hydrogels have mainly focused on their single stimulus-responsive property and have not explored multistimulus-responsive or multifunction properties. Although some works involved multifunctionality, the prepared hydrogels were incompatible. In this work, a multistimulus-responsive and multifunctional hydrogel system (carboxymethyl cellulose/poly acrylic-acrylamide) with good elasticity, superior flexibility, and stable conductivity was prepared. The prepared hydrogel not only showed excellent human motion detection and physiological signal response but also possessed the ability to respond to environmental temperature changes. By integrating a conductive hydrogel with a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel to form a bilayer hydrogel, the prepared bilayer also functioned as two kinds of actuators owing to the different degrees of swelling and shrinking under different thermal stimuli. Furthermore, the different thermochromic properties of each layer in the bilayer hydrogel endowed the hydrogel with a thermoresponsive "smart" feature, the ability to display and conceal information. Therefore, the prepared hydrogel system has excellent prospects as a smart material in different applications, such as ionic skin, smart info-window, and soft robotics.

Difluoroboron β-diketonate polylactic acid oxygen nanosensors for intracellular neuronal imaging

Critical for metabolism, oxygen plays an essential role in maintaining the structure and function of neurons. Oxygen sensing is important in common neurological disorders such as strokes, seizures, or neonatal hypoxic-ischemic injuries, which result from an imbalance between metabolic demand and oxygen supply. Phosphorescence quenching by oxygen provides a non-invasive optical method to measure oxygen levels within cells and tissues. Difluoroboron β-diketonates are a family of luminophores with high quantum yields and tunable fluorescence and phosphorescence when embedded in certain rigid matrices such as poly (lactic acid) (PLA). Boron nanoparticles (BNPs) can be fabricated from dye-PLA materials for oxygen mapping in a variety of biological milieu. These dual-emissive nanoparticles have oxygen-insensitive fluorescence, oxygen-sensitive phosphorescence, and rigid matrix all in one, enabling real-time ratiometric oxygen sensing at micron-level spatial and millisecond-level temporal resolution. In this study, BNPs are applied in mouse brain slices to investigate oxygen distributions and neuronal activity. The optical properties and physical stability of BNPs in a biologically relevant buffer were stable. Primary neuronal cultures were labeled by BNPs and the mitochondria membrane probe MitoTracker Red FM. BNPs were taken up by neuronal cell bodies, at dendrites, and at synapses, and the localization of BNPs was consistent with that of MitoTracker Red FM. The brain slices were stained with the BNPs, and the BNPs did not significantly affect the electrophysiological properties of neurons. Oxygen maps were generated in living brain slices where oxygen is found to be mostly consumed by mitochondria near synapses. Finally, the BNPs exhibited excellent response when the conditions varied from normoxic to hypoxic and when the neuronal activity was increased by increasing K+ concentration. This work demonstrates the capability of BNPs as a non-invasive tool in oxygen sensing and could provide fundamental insight into neuronal mechanisms and excitability research.

Cesium Doping for Performance Improvement of Lead(II)-acetate-Based Perovskite Solar Cells

Lead(II)-acetate (Pb(Ac)2) is a promising lead source for the preparation of organolead trihalide perovskite materials, which avoids the use of inconvenient anti-solvent treatment. In this study, we investigated the effect of cesium doping on the performance of Pb(Ac)2-based perovskite solar cells (PSCs). We demonstrate that the quality of the CH3NH3PbI3 perovskite film was improved with increased crystallinity and reduced pinholes by doping the perovskite with 5 mol% cesium. As a result, the power conversion efficiency (PCE) of the PSCs was improved from 14.1% to 15.57% (on average), which was mainly induced by the significant enhancements in short-circuit current density and fill factor. A PCE of 18.02% was achieved for the champion device of cesium-doped Pb(Ac)2-based PSCs with negligible hysteresis and a stable output. Our results indicate that cesium doping is an effective approach for improving the performance of Pb(Ac)2-based PSCs.

Doping-Free All PtSe2 Transistor via Thickness-Modulated Phase Transition

Achieving a high-quality metal contact on two-dimensional (2D) semiconductors still remains a major challenge due to the strong Fermi level pinning and the absence of an effective doping method. Here, we demonstrate high performance "all-PtSe₂" field-effect transistors (FETs) completely free from those issues, enabled by the vertical integration of a metallic thick PtSe₂ source/drain onto the semiconducting ultrathin PtSe₂ channel. Owing to its inherent thickness-dependent semiconductor-to-metal phase transition, the transferred metallic PtSe₂ transforms the underlying semiconducting PtSe₂ into metal at the junction. Therefore, a fully metallized source/drain and semiconducting channel could be realized within the same PtSe₂ platform. The ultrathin PtSe₂ FETs with PtSe₂ vdW contact exhibits excellent gate tunability, superior mobility, and high ON current accompanied by one order lower contact resistance compared to conventional Ti/Au contact FETs. Our work provides a new device paradigm with a low resistance PtSe₂ vdW contact which can overcome a fundamental bottleneck in 2D nanoelectronics.

Valve-based consecutive bioprinting method for multimaterial tissue-like constructs with controllable interfaces

Bioprinting is a promising technology focusing on tissue manufacturing, whose vital problem is the precise assembly of multiple materials. As the primary solution, the extrusion-based multi-printhead bioprinting (MPB) method could cause material interface defects and inefficient motion time during multimaterial switching. We present a valve-based consecutive bioprinting (VCB) method to resolve these problems, containing an integrated precise switching printhead and a well-matched voxelated digital model. The rotary valve isolates the bio-inks' elastic potential energy in the cartridge from precision interface assembling based on the Maxwell viscoelastic model. We study the coordinated control approach of the valve rotation and pressure adjustment to actualize the seamless switching, leading to a controllable multimaterial interface, including boundary and suture. Furthermore, we compare the VCB method and MPB method, quantitatively and comprehensively, indicating that the VCB method obtained greater mechanical strength (increased by 44.37%) and higher printing efficiency (increased by 29.48%). As an exemplar, we fabricate a muscle-like tissue with vascular tree and suture interface encapsulating C2C12 and human dermal fibroblasts (HDFB) cells, then placed in complete medium with continuous perfusion for five days. Our study suggests that the VCB method is sufficient to fabricate heterogeneous tissues with complex multimaterial interfaces.

Robust tunable plasmon induced transparency in coupled-resonance finite array of metasurface nanostructure

Robust and dynamically polarization-controlled tunable plasmon induced transparency (PIT) resonance in designed finite-array nanostructures metasurface is demonstrated, where sharp resonance is guaranteed by design and protected against large geometrical imperfections even for micro-zone sub-array. By employing the explicit analysis of near-field characteristic in the reciprocal-space based on the momentum matching, and the far-field radiation features with point-scattering approach in real-space sparked from Huygens’s principles, the physics of interference resonance for plane-wave optical transmission and reflection of the metasurface is theoretically and thoroughly investigated. The distinctive polarization-selective and Q-tunable PIT shows robust features to performance degradations in traditional PIT system caused by inadvertent fabrication flaws or geometry asymmetry-variations, which paves way for the development of reconfigurable and flexible metasurface and, additionally, opens new avenues in robust and multifunctional controllable nanophotonics device design and applications.

Alkalide-Assisted Direct Electron Injection for the Noninvasive n-Type Doping of Graphene

Although the doping of graphene grown by chemical vapor deposition is crucial in graphene-based electronics, noninvasive methods of n-type doping have not been widely investigated in comparison with p-type doping methods. We developed a convenient and robust method for the noninvasive n-type doping of graphene, wherein electrons are directly injected from sodium anions into the graphene. This method involves immersing the graphene in solutions of [K(15-crown-5)₂]Na prepared by dissolving a sodium-potassium (NaK) alloy in a 15-crown-5 solution. The n-type doping of the graphene was confirmed by downshifted G and 2D bands in Raman spectra and by the Dirac point shifting to a negative voltage. The electron-injected graphene showed no sign of structural damage, exhibited higher carrier mobilities than that of pristine graphene, and remained n-doped for over a month of storage in air. In addition, we demonstrated that electron injection enhances noncovalent interactions between graphene and metallomacrocycle molecules without requiring a linker, as used in previous studies, suggesting several potential applications of the method in modifying graphene with various functionalities.

Nanorolls Decorated with Nanotubes as a Novel Type of Nanostructures: Fast Anodic Oxidation of Amorphous Fe-Cr-B Alloy in Hydrophobic Ionic Liquid

The formation of oxide nanorolls decorated with nanotubes during anodic oxidation of amorphous Fe70Cr15B15 alloy in hydrophobic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (IL) was revealed. The unusual architecture was observed for the first time on the surface of amorphous alloy. The generation of the novel type of nanostructure by electrochemical oxidation of the amorphous Fe70Cr15B15 alloy occurs only in hydrophobic ionic liquid and in the presence of the natural oxide film at the surface. Anodization of the oxide-free metal surface of the amorphous Fe70Cr15B15 alloy to be achieved by the treatment of the electrode with benzoic acid was found to result in no formation of both nanorolls and nanotubes. Electrochemical behavior of the amorphous Fe70Cr15B15 alloy in ionic liquid was proved to depend strongly on the state of the electrode surface before oxidation. The influence of the state of the surface of amorphous Fe70Cr15B15 alloy leading to the nanostructure formation was studied by means of preliminary partial etching with benzoic acid of various concentrations.

Ab initio investigation of topological phase transitions induced by pressure in trilayer van der Waals structures: the example of h-BN/SnTe/h-BN

The combination of two-dimensional crystals through the formation of van der Waals bilayers, trilayers, and heterostructures has been considered a promising route to design new materials due to the possibility of tuning their properties through the control of the number of layers, alloying pressure, strain, and other tuning mechanisms. Here, we report a density functional theory study on the interlayer phonon coupling and electronic structure of the trilayer h-BN/SnTe/h-BN, and the effects of pressure on the encapsulation of this trilayer system. Our findings demonstrated the establishment of a type I junction in the system, with a trivial bandgap of 0.55 eV, which is 10 % lower than the free-standing SnTe one. The almost inert h-BN capping layers allow a topological phase transition at a pressure of 13.5 GPa, in which the system evolves from a trivial insulator to a topological insulator. In addition, with further increase of the pressure up to 35 GPa, the non-trivial energy bandgap increases up to 0.30 eV. This behavior is especially relevant to allow experimental access to topological properties of materials, since large non-trivial energy bandgaps are required.

Mechanical Reshaping of Inorganic Nanostructures with Weak Nanoscale Forces

Inorganic nanomaterials are often depicted as rigid structures whose shape is permanent. However, forces that are ordinarily considered weak can exert sufficient stress at the nanoscale to drive mechanical deformation. Here, we leverage van der Waals (VdW) interactions to mechanically reshape inorganic nanostructures from planar to curvilinear. Modified plate deformation theory shows that high-aspect-ratio two-dimensional particles can be plastically deformed via VdW forces. Informed by this finding, silver nanoplates were deformed over spherical iron oxide template particles, resulting in distinctive bend contour patterns in bright-field (BF) transmission electron microscopy (TEM) images. High-resolution TEM images of deformed areas reveal the presence of highly strained bonds in the material. Finally, we show that the distance between two nearby template particles allows for the engineering of several distinct curvilinear morphologies. This work challenges the traditional view of nanoparticles as static objects and introduces methods for postsynthetic mechanical shape control.

Temperature-Dependent Charge Carrier Transfer in Colloidal Quantum Dot/Graphene Infrared Photodetectors

Colloidal PbS quantum dot (QD)/graphene hybrid photodetectors are emerging QD technologies for affordable infrared light detectors. By interfacing the QDs with graphene, the photosignal of these detectors is amplified, leading to high responsivity values. While these detectors have been mainly operated at room temperature, low-temperature operation is required for extending their spectral sensitivity beyond a wavelength of 3 μm. Here, we unveil the temperature-dependent response of PbS QD/graphene phototransistors by performing steady-state and time-dependent measurements over a large temperature range of 80-300 K. We find that the temperature dependence of photoinduced charge carrier transfer from the QD layer to graphene is (i) not impeded by freeze-out of the (Schottky-like) potential barrier at low temperatures, (ii) tremendously sensitive to QD surface states (surface oxidation), and (iii) minimally affected by the ligand exposure time and QD layer thickness. Moreover, the specific detectivity of our detectors increases with cooling, with a maximum measured specific detectivity of at least 10¹⁰ Jones at a wavelength of 1280 nm and a temperature of 80 K, which is an order of magnitude larger compared to the corresponding room temperature value. The temperature- and gate voltage-dependent characterization presented here constitutes an important step in expanding our knowledge of charge transfer at interfaces of low-dimensional materials and toward the realization of next-generation optoelectronic devices.

Role of Postdeposition Thermal Annealing on Intracrystallite and Intercrystallite Structuring and Charge Transport in Poly(3-hexylthiophene)

The performance of electronic devices comprising conjugated polymers as the active layer depends not only on the intrinsic characteristics of the materials but also on the details of the extrinsic processing conditions. In this study, we examine the effect of postdeposition thermal treatments on the microstructure of poly(3-hexylthiophene) (P3HT) thin films and its impact on their electrical properties. Unsurprisingly, we find thermal annealing of P3HT thin films to generally increase their crystallinity and crystallite coherence length while retaining the same crystal structure. Despite such favorable structural improvements of the polymer active layers, however, thermal annealing at high temperatures can lead to a net reduction in the mobility of transistors, implicating structural changes in the intercrystallite amorphous regions of these semicrystalline active layers take place on annealing, and the simplistic picture that crystallinity governs charge transport is not always valid. Our results instead suggest tie-chain pullout, which occurs during crystal growth and perfection upon thermal annealing to govern charge transport, particularly in low-molecular-weight systems in which the tie-chain fraction is low. By demonstrating the interplay between intracrystallite and intercrystallite structuring in determining the macroscopic charge transport, we shed light on how structural evolution and charge-transport properties of nominally the same polymer can vary depending on the details of processing.

High-Performance Vertical Organic Phototransistors Enhanced by Ferroelectrics

Organic phototransistors with high sensitivity and responsivity to light irradiance have great potential applications in national defense, meteorology, industrial manufacturing, and medical security. However, undesired dark current and photoresponsivity limit their practical applications. Here, a novel vertical organic phototransistor combined with ferroelectric materials is developed. The device structure has nanometer channel length, which can effectively separate photogenerated carriers and reduce the probability of carrier recombination and defect scattering, thus improving the device performance of phototransistors. Moreover, by inserting the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) ferroelectric layer, the Schottky barrier at the interface between the semiconductor and source can be adjusted by the polarization of the external electric field, which can effectively reduce the dark current of the phototransistor to further improve the device performance. Therefore, our phototransistors exhibit a high photoresponsivity of more than 5.7 × 10⁵A/W, an outstanding detectivity of 1.15 × 10¹⁸ Jones, and an excellent photosensitivity of 5 × 10⁷ under 760 nm light illumination, which are better than those of conventional lateral organic phototransistors. This work provides a new approach for the development of high-performance phototransistors, which opens a new pathway for organic phototransistors in practical application.

Engineering Giant Rabi Splitting via Strong Coupling between Localized and Propagating Plasmon Modes on Metal Surface Lattices: Observation of √N Scaling Rule

We present a strong coupling system realized by coupling the localized surface plasmon mode in individual silver nanogrooves and propagating surface plasmon modes launched by periodic nanogroove arrays with varied periodicities on a continuous silver medium. When the propagating modes are in resonance with the localized mode, we observe a √N scaling of Rabi splitting energy, where N is the number of propagating modes coupled to the localized mode. Here, we confirm a giant Rabi splitting on the order of 450-660 meV (N = 2) in the visible spectral range, and the corresponding coupling strength is 160-235 meV. In some of the strong coupling cases studied by us, the coupling strength is about 10% of the mode energy, reaching the ultrastrong coupling regime.

Self-Driven Reactive Oxygen Species Generation via Interfacial Oxygen Vacancies on Carbon-Coated TiO2-x with Versatile Applications

The effective activation and utilization of O₂ have always been the focus of scientists because of its wide applications in catalysis, organic synthesis, life and medical science. Here, a novel method for activating O₂ spontaneously via interfacial oxygen vacancies on carbon-coated TiO_2-x to generate reactive oxygen species (ROS) with versatile applications is reported. The interfacial oxygen vacancies can be stabilized by the carbon layer and hold its intrinsic properties for spontaneous oxygen activation without light irradiation, while common surface oxygen vacancies on TiO_2-x are always consumed by the capture of H₂O to form the surface hydroxyls. Thus, O₂ absorbed at the interface of carbon and TiO_2-x can be directly activated into singlet oxygen (¹O₂) or superoxide radicals (·O₂^-), confirmed both experimentally and theoretically. These reactive oxygen species exhibit excellent performance in oxidation reactions and inhibition of MCF-7 cancer cells, providing new insight into the effective utilization of O₂ via oxygen vacancies on metal oxides.

Non-Isothermal Decomposition as Efficient and Simple Synthesis Method of NiO/C Nanoparticles for Asymmetric Supercapacitors

A series of NiO/C nanocomposites with NiO concentrations ranging from 10 to 90 wt% was synthesized using a simple and efficient two-step method based on non-isothermal decomposition of Nickel(II) bis(acetylacetonate). X-ray diffraction (XRD) measurements of these NiO/C nanocomposites demonstrate the presence of β-NiO. NiO/C nanocomposites are composed of spherical particles distributed over the carbon support surface. The average diameter of nickel oxide spheres increases with the NiO content and are estimated as 36, 50 and 205 nm for nanocomposites with 10, 50 and 80 wt% NiO concentrations, respectively. In turn, each NiO sphere contains several nickel oxide nanoparticles, whose average sizes are 7–8 nm. According to the tests performed using a three-electrode cell, specific capacitance (SC) of NiO/C nanocomposites increases from 200 to 400 F/g as the NiO content achieves a maximum of 60 wt% concentration, after which the SC decreases. The study of the NiO/C composite showing the highest SC in three- and two-electrode cells reveals that its SC remains almost unchanged while increasing the current density, and the sample demonstrates excellent cycling stability properties. Finally, NiO/C (60% NiO) composites are shown to be promising materials for charging quartz clocks with a power rating of 1.5 V (30 min).

Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe1-xSex through Isoelectronic Substitution

In this paper, we report a series of x polycrystalline AgCuTe_1-xSe samples with high thermoelectric performance. X-ray photoelectron spectroscopy data suggest the observation of Ag⁺, Cu⁺, Te^2-, and Se^2- states of Ag, Cu, Te, and Se. Meanwhile, the carrier concentration of the obtained p-type samples changes from 9.12 × 10¹⁸ to 0.86 × 10¹⁸ cm^-3 as their carrier mobility varies from 698.55 to 410.12 cm²·V^-1·s^-1 at 300 K. Compared with undoped AgCuTe, an ultralow thermal conductivity is realized in AgCuTe_1-xSe_x due to the enhanced phonon scattering. Ultimately, a maximum figure of merit (ZT) of ∼1.45 at 573 K and a high average ZT above 1.0 at temperatures ranging from room temperature to 773 K can be achieved in AgCuTe_0.9Se_0.1, which increases by 186% compared to that of the undoped AgCuTe (0.82 at 573 K). This work provides a viable insight toward understanding the effect of the Se atom on the lattice structure and thermoelectric properties of AgCuTe and other transition-metal dichalcogenides.

Two-Dimensional Giant Tunable Rashba Semiconductors with Two-Atom-Thick Buckled Honeycomb Structure

Spin field-effect transistors (SFETs) based on the Rashba effect could manipulate the spin of electrons electrically, while seeking desirable Rashba semiconductors with large Rashba constant and strong electric-field response, to preserve spin coherence remains a key challenge. Herein, we propose a series of 2D Rashba semiconductors with two-atom-thick buckled honeycomb structure (BHS) according to high-throughput first-principles density functional theory calculations. BHS semiconductors show large Rashba constants that are favorable to be integrated into nanodevices superior to conventional bulk materials, and they can be fabricated by mechanical exfoliation or chemical vapor deposition. In particular, 2D AlBi monolayer has the largest Rashba constant (2.77 eVÅ) of all 2D Rashba materials. Furthermore, 2D BiSb monolayer is a promising candidate for SFETs due to its large Rashba constant (1.94 eVÅ) and strong electric field response (0.92 eŲ). Our designed 2D-BiSb-SFET shows shorter spin channel length (42 nm with strain) than conventional SFETs (2-5 μm).

High-Performance Two-Dimensional Perovskite Ca2Nb3O10 UV Photodetectors

We first report two-dimensional (2D) perovskite Ca₂Nb₃O₁₀ ultraviolet photodetectors (UV PDs), which are prepared via a facile calcination-exfoliation method. The 2D Ca₂Nb₃O₁₀ PDs demonstrate high performance at 3 V at 280 nm, high responsivity (14.94 A W^-1), high detectivity (8.7 × 10¹³ Jones), high spectral selectivity (R₂₈₀/R₄₀₀ = 8.84 × 10³), fast speed (0.08/5.6 ms), and long-term stability, exceeding those of most reported UV PDs. Furthermore, the Ca₂Nb₃O₁₀ PDs integrated with poly(ethylene terephthalate) (PET) show excellent flexibility and have high linear dynamic range (96 dB). Our work provides a general strategy for searching new UV PDs based on numerous layered niobates. The Ca₂Nb₃O₁₀ nanosheets may be one of the optimum semiconductor materials for next-generation high-performance UV PDs.

Tailoring Superconductivity in Large-Area Single-Layer NbSe2 via Self-Assembled Molecular Adlayers

Two-dimensional transition metal dichalcogenides (TMDs) represent an ideal testbench for the search of materials by design, because their optoelectronic properties can be manipulated through surface engineering and molecular functionalization. However, the impact of molecules on intrinsic physical properties of TMDs, such as superconductivity, remains largely unexplored. In this work, the critical temperature (T_C) of large-area NbSe₂ monolayers is manipulated, employing ultrathin molecular adlayers. Spectroscopic evidence indicates that aligned molecular dipoles within the self-assembled layers act as a fixed gate terminal, collectively generating a macroscopic electrostatic field on NbSe₂. This results in an ∼55% increase and a 70% decrease in T_C depending on the electric field polarity, which is controlled via molecular selection. The reported functionalization, which improves the air stability of NbSe₂, is efficient, practical, up-scalable, and suited to functionalize large-area TMDs. Our results indicate the potential of hybrid 2D materials as a novel platform for tunable superconductivity.

Nonmonotonic Temperature-Dependent Dissipation at Nonequilibrium in Atomically Thin Clean-Limit Superconductors

Resistance in superconductors arises from the motion of vortices driven by flowing supercurrents or external electromagnetic fields and may be strongly affected by thermal or quantum fluctuations. The common expectation is that as the temperature is lowered, vortex motion is suppressed, leading to a decreased resistance. We show experimentally that in clean-limit atomically thin 2H-NbSe₂ the resistance below the superconducting transition temperature may be nonmonotonic, passing through a minimum before increasing again as the temperature is decreased further. The effect is most pronounced in monolayer devices and cannot be understood in terms of known mechanisms. We propose a qualitative two-fluid vortex model in which thermal fluctuations of pinned vortices control the mobility of the free vortices. The findings provide a new perspective on fundamental questions of vortex mobility and dissipation in superconductors.

3D-Printed Bioinspired Cassie-Baxter Wettability for Controllable Microdroplet Manipulation

It is a great challenge to fabricate a surface with Cassie-Baxter wettability that can be continuously adjusted from hydrophilicity to superhydrophobicity by changing of geometric parameters. In this paper, we propose and demonstrate a bioinspired surface fabricated by using a projection micro-stereolithography (PμSL) based 3D printing technique to address the challenge. Independent of materials, the bioinspired textured surface has a maximum contact angle (CA) of 171°, which is even higher than that of the omniphobic springtail skin we try to imitate. Most significantly, we are able to control the CA of the bioinspired surface in the range of 55-171° and the adhesion force from 71 to 99 μN continuously by only changing the geometric parameters of the bioinspired microstructures. The underlying mechanisms of the CA control of our bioinspired surface are also revealed by using a multi-phase lattice Boltzmann model. Furthermore, we demonstrate potential applications in droplet-based microreactors, nonloss water transportation, and coalescence of water droplets by employing our 3D-printed bioinspired structures with their remarkable precise Cassie-Baxter wettability control and petal effects. The present results potentially pave a new way for designing next generation functional surfaces for microdroplet manipulation, droplet-based biodetection, antifouling surfaces, and cell culture.

Density functional study of gallium clusters on graphene: electronic doping and diffusion

Motivated by experimental results on transport properties of graphene covered by gallium atoms, the density functional theory study of clustering of gallium atoms on graphene (up to a size of 8 atoms) is presented. The paper explains a rapid initial increase of graphene electron doping by individual Ga atoms with Ga coverage, which is continually reduced to zero, when bigger multiple-atom clusters have been formed. According to density functional theory calculations with and without the van der Waals correction, gallium atoms start to form a three-dimensional cluster from five and three atoms, respectively. The results also explain an easy diffusion of Ga atoms while forming clusters caused by a small diffusion barrier of 0.11 eV. Moreover, the calculations show this barrier can be additionally reduced by the application of an external electric field, which was simulated by the ionization of graphene. This effect offers a unique possibility to control the cluster size in experiments only by applying a gate-voltage to the graphene in a field-effect transistor geometry and thereby without growth temperature assistance.

Sub-nanometric Manganous Oxide Clusters in Nitrogen Doped Mesoporous Carbon Nanosheets for High-Performance Lithium-Sulfur Batteries

The greatest challenge for lithium-sulfur (Li-S) batteries application is the development of cathode hosts to address the low conductivity, huge volume change, and shuttling effect of sulfur or lithium polysulfides (LiPs). Herein, we demonstrate a composite host to circumvent these problems by confining sub-nanometric manganous oxide clusters (MOCs) in nitrogen doped mesoporous carbon nanosheets. The atomic structure of MOCs is well-characterized and optimized via the extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations. Benefiting from the unique design, the assembled Li-S battery displays remarkable electrochemical performances including a high reversible capacity (990 mAh g^-1 after 100 cycles at 0.2 A g^-1) and a superior cycle life (60% retention over 250 cycles at 2 A g^-1). Both the experimental results and DFT calculations demonstrate that the well-dispersed MOCs could significantly promote the chemisorption of LiPs, thus greatly improving the capacity and rate performance.

3D Nanomagnetism in Low Density Interconnected Nanowire Networks

Free-standing, interconnected metallic nanowire networks with densities as low as 40 mg/cm³ have been achieved over centimeter-scale areas, using electrodeposition into polycarbonate membranes that have been ion-tracked at multiple angles. Networks of interconnected magnetic nanowires further provide an exciting platform to explore 3-dimensional nanomagnetism, where their structure, topology, and frustration may be used as additional degrees of freedom to tailor the materials properties. New magnetization reversal mechanisms in cobalt networks are captured by the first-order reversal curve method, which demonstrate the evolution from strong demagnetizing dipolar interactions to intersection-mediated domain wall pinning and propagation, and eventually to shape-anisotropy dominated magnetization reversal. These findings open up new possibilities for 3-dimensional integrated magnetic devices for memory, complex computation, and neuromorphics.

Kerr Metasurface Enabled by Metallic Quantum Wells

Optical metasurfaces have emerged as promising candidates for multifunctional devices. Dynamically reconfigurable metasurfaces have been introduced by employing phase-change materials or by applying voltage, heat, or strain. While existing metasurfaces exhibit appealing properties, they do not express any significant nonlinear effects due to the negligible nonlinear responses from the typical materials used to build the metasurface. In this work, we propose and experimentally demonstrate one kind of Kerr metasurface that shows strong intensity-dependent responses. The Kerr metasurface is composed of a top layer of gold antennas, a dielectric spacer, and a ground layer of metallic quantum wells (MQWs). Because of the large Kerr nonlinearity supported by the MQWs, the effective optical properties of the MQWs can change from metallic to dielectric with increasing of the input intensity, leading to dramatic modifications of the metasurface responses. This opens up new routes for potential applications in the field of nonlinear optics.

Tunable Substrate Functionalities Direct Stem Cell Fate toward Electrophysiologically Distinguishable Neuron-like and Glial-like Cells

Engineering cellular microenvironment on a functional platform using various biophysical cues to modulate stem cell fate has been the central theme in regenerative engineering. Among the various biophysical cues to direct stem cell differentiation, the critical role of physiologically relevant electric field (EF) stimulation was established in the recent past. The present study is the first to report the strategy to switch EF-mediated differentiation of human mesenchymal stem cells (hMSCs) between neuronal and glial pathways, using tailored functional properties of the biomaterial substrate. We have examined the combinatorial effect of substrate functionalities (conductivity, electroactivity, and topography) on the EF-mediated stem cell differentiation on polyvinylidene-difluoride (PVDF) nanocomposites in vitro, without any biochemical inducers. The functionalities of PVDF have been tailored using conducting nanofiller (multiwall-carbon nanotube, MWNT) and piezoceramic (BaTiO₃, BT) by an optimized processing approach (melt mixing-compression molding-rolling). The DC conductivity of PVDF nanocomposites was tuned from ∼10^-11 to ∼10^-4 S/cm and the dielectric constant from ∼10 to ∼300. The phenotypical changes and genotypical expression of hMSCs revealed the signatures of early differentiation toward neuronal pathway on rolled-PVDF/MWNT and late differentiation toward glial lineage on rolled-PVDF/BT/MWNT. Moreover, we were able to distinguish the physiological properties of differentiated neuron-like and glial-like cells using membrane depolarization and mechanical stimulation. The excitability of the EF-stimulated hMSCs was also determined using whole-cell patch-clamp recordings. Mechanistically, the roles of intracellular reactive oxygen species (ROS), Ca²⁺ oscillations, and synaptic and gap junction proteins in directing the cellular fate have been established. Therefore, the present work critically unveils complex yet synergistic interaction of substrate functional properties to direct EF-mediated differentiation toward neuron-like and glial-like cells, with distinguishable electrophysiological responses.