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It remains a big challenge to synthesize two-dimensional (2D) GaN material for applications in power nanodevices. Traditional synthetic methods require complex equipment and processes and time consuming. Here, we reported a two-step route to prepare polycrystalline 2D GaN film. The amorphous ultrathin Ga2O3 film was first exfoliated from the surface of liquid gallium. In a vapor phase reaction, 2D Ga2O3 film was then converted into 2D GaN film while maintaining the 2D morphology. Raman and high-resolution transmission electron microscope (HRTEM) analysis implies the successful synthesis of wurtzite-type GaN ultrathin film. This simple strategy proposed in this work will provide more opportunities for applications of GaN ultrathin film in many devices. [ABSTRACT FROM AUTHOR]

Efficient thermal management has become one of the most critical issues of electronics because of the high heat flux generated from highly integrated, miniaturized, and increased power. Here we report highly flexible composites with aligned and overlapping interconnected boron nitride nanosheets (BNNSs) assembled in wrinkle structures. Besides high in-plane thermal conductivity of more than 26.58 W m−1 K−1, such structure rendered enhanced through-plane conduction along with increasing pre-stain. As thermal interface materials (TIMs) of both rigid and flexible devices, the composites revealed an outstanding thermal cooling capability outperforming some commercial TIMs. During a record-long bending process of more than 3000 cycles, the maximum temperature fluctuation of the flexible device with 100%-prestrained composite was only within 0.9 °C, less than one-third of that with commercial thermal pad. Moreover, the composite revealed a superior impermeability for flexible seals. Our results illustrate that the composites could be an ideal candidate for the thermal management of emerging flexible electronics. [ABSTRACT FROM AUTHOR]

Liquid-phase exfoliation was employed to synthesize Sr2Nb3O10 perovskite nanosheets with thicknesses down to 1.76 nm. Transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray photoelectron spectrometer (XPS), and other characterization techniques were used to evaluate the atomic structure and chemical composition of the exfoliated nanosheets. A UV photodetector based on individual Sr2Nb3O10 nanosheets was prepared to demonstrate the application of an ultraviolet (UV) photodetector. The UV photodetector exhibited outstanding photocurrent and responsivity with a responsivity of 3 × 105 A·W−1 at 5 V bias under 280 nm illumination, a photocurrent of 60 nA, and an on/off ratio of 3 × 102. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites with nanoparticles dispersed in polymer matrices have attracted extensive attention due to their significantly improved overall performance, in which the nanoparticle-polymer interface plays a key role. Understanding the structures and properties of the interfacial region, however, remains a major challenge for polymer nanocomposites. Here, we directly observe the presence of two interfacial polymer layers around a nanoparticle in polar polymers, i.e., an inner bound polar layer (~10 nm thick) with aligned dipoles and an outer polar layer (over 100 nm thick) with randomly orientated dipoles. Our results reveal that the impacts of the local nanoparticle surface potential and interparticle distance on molecular dipoles induce interfacial polymer layers with different polar molecular conformations from the bulk polymer. The bilayer interfacial features lead to an exceptional enhancement in polarity-related properties of polymer nanocomposites at ultralow nanoparticle loadings. By maximizing the contribution of inner bound polar layer via a nanolamination design, we achieve an ultrahigh dielectric energy storage density of 86 J/cm3, far superior to state-of-the-art polymers and nanocomposites. The nanoparticle-polymer interface plays a key role in nanoparticle-polymer composites but understanding the structures and properties of the interfacial region remains challenging. Here, the authors directly observe the presence of two interfacial polymer layers around a nanoparticle in polar polymers with different polar molecular conformations from the bulk polymer leading to an enhancement in polarity-related properties of polymer nanocomposites [ABSTRACT FROM AUTHOR]

The primary research of physics is to reveal the underlying law of the physical world. However, for a complex system consisting of multiple components, even if we know every details of each component, we still cannot predict the collective behavior due to the emergence phenomenon. The amorphous networks of mass points hinged by springs belong to such a complex system. Owing to the non-affinity, one of the emergence phenomena of the network, the displacements field of the internal mass points under the external load tends to be chaotic, and there is no well-established theoretical framework to describe these points’ collective behavior analytically. The non-affine mechanical responses of the amorphous networks are very common, whereas the affine response is rare and it occurs only in those lattices with one site per unit cell. The network’s non-affinity prevents us from further investigating the relationship between its intrinsic properties (such as the contact number, local structure, and topological characteristics) and the mechanical behaviors. As a result, it is very complicated and difficult to predict the responses of an amorphous network to an imposed strain. Interestingly, a sort of amorphous network derived from the jammed particles is reported to have almost perfect affine mechanical behavior, in a stark contrast with the general perception. These findings may shed light on uncovering the structural factors that affect the network’s affinity. This article will give a short review of the latest advances in this area. [ABSTRACT FROM AUTHOR]

Wearable electronics with miniaturization and high-power density call for devices with advanced thermal management capabilities, outstanding flexibility, and excellent permeability. However, it is difficult to achieve these goals simultaneously due to the conflict between high thermal conductivity and permeability and flexibility. Here, we report an approach to fabricate flexible, breathable composites with advanced thermal management capability by coating the boron nitride nanosheets (BNNSs) layer with high thermal conductivity on the grids of patterned electrospun thermoplastic polyurethane (TPU) fibrous mats. The composite exhibited a significant enhancement of thermal conductivity and preserved instinctive breathability simultaneously. When the composite was integrated into flexible devices, its saturating operating temperature dropped significantly compared to that of pure Ecoflex packaging. Moreover, the surface temperature fluctuation was less than 0.5 °C during more than 2000 cycles bending-releasing process. Finally, a prototype to fabricate wearable electronics with advanced thermal management capability was proposed. [ABSTRACT FROM AUTHOR]

Electrically tunable surface adhesion is of vital importance for ubiquitous microelectromechanical systems, and is normally symmetric to the applied bias voltage. Here we report the asymmetric bias-tunable surface adhesion of semiconductor nanofilms by taking molybdenum disulfide (MoS2) as a demo with graphene, hexagonal boron nitride, and bulk n-type doped silicon serving as the normal control group. The bias-tunable adhesion force between the Au-coated tip and the Au back electrode supported MoS2 nanofilms was deciphered by combining conductive atomic force microscopic examinations in vacuum and theoretical simulations. The asymmetric bias-tunability is found to be significantly stronger than that of the control group, attributing to the built-in electric field at the Schottky junction between the nanofilm and back electrode. [ABSTRACT FROM AUTHOR]

Manipulation of micro/nano particles has been well studied and demonstrated by optical, electromagnetic, and acoustic approaches, or their combinations. Manipulation of internal structure of droplet/particle is rarely explored and remains challenging due to its complicated nature. Here we demonstrated the manipulation of internal structure of disk-in-sphere endoskeletal droplets using acoustic wave. We developed a model to investigate the physical mechanisms behind this interesting phenomenon. Theoretical analysis of the acoustic interactions indicated that these assembly dynamics arise from a balance of the primary and secondary radiation forces. Additionally, the disk orientation was found to change with acoustic driving frequency, which allowed on-demand, reversible adjustment of the disk orientations with respect to the substrate. This dynamic behavior leads to unique reversible arrangements of the endoskeletal droplets and their internal architecture, which may provide an avenue for directed assembly of novel hierarchical colloidal architectures and intracellular organelles or intra-organoid structures. Endoskeletal droplets are a class of complex colloids containing a solid internal phase cast within a liquid emulsion droplet. Here, authors show acoustic manipulation of solid disks inside liquid droplets whose orientation can be externally controlled with the frequency. [ABSTRACT FROM AUTHOR]

The reciprocity principle governs the symmetry in transmission of electromagnetic and acoustic waves, as well as the diffusion of heat between two points in space, with important consequences for thermal management and energy harvesting. There has been significant recent interest in materials with time-modulated properties, which have been shown to efficiently break reciprocity for light, sound, and even charge diffusion. However, time modulation may not be a plausible approach to break thermal reciprocity, in contrast to the usual perception. We establish a theoretical framework to accurately describe the behavior of diffusive processes under time modulation, and prove that thermal reciprocity in dynamic materials is generally preserved by the continuity equation, unless some external bias or special material is considered. We then experimentally demonstrate reciprocal heat transfer in a time-modulated device. Our findings correct previous misconceptions regarding reciprocity breaking for thermal diffusion, revealing the generality of symmetry constraints in heat transfer, and clarifying its differences from other transport processes in what concerns the principles of reciprocity and microscopic reversibility. The use of time modulation to break reciprocity is well understood for light, sound or charge diffusion, but it's unclear whether it can work for thermal diffusion. Here, the authors answer in the negative by analysing diffusive processes under time modulation, and giving numerical and experimental evidence. [ABSTRACT FROM AUTHOR]

Dry eye disease (DED), a multifactorial ocular surface disease, is estimated to affect up to 34% of individuals over 50 years old. Although numerous animal models, including rodents and rabbits, have been developed to mimic the pathophysiologic mechanisms involved in dry eye, there is a lack of non-human primate (NHP) models, critical for translational drug studies. Here, we developed a novel desiccating stress-induced dry eye disease model using Rhesus macaque monkeys. The monkeys were housed in a controlled environment room for 21 to 36 days under humidity, temperature, and airflow regulation. Following desiccating stress, NHPs demonstrated clinical symptoms similar to those of humans, as shown by increased corneal fluorescein staining (CFS) and decreased tear-film breakup time (TFBUT). Moreover, corticosteroid treatment significantly reduced CFS scoring, restored TFBUT, and prevented upregulation of tear proinflammatory cytokines as observed in dry eye patients following steroid treatment. The close resemblance of clinical symptoms and treatment responses to those of human DED patients provides great translational value to the NHP model, which could serve as a clinically relevant animal model to study the efficacy of new potential treatments for DED. [ABSTRACT FROM AUTHOR]

We investigate the energy transport in simple networks consisting of one-dimensional nonlinear chain with self-coupled loop. The impacts of the loop length and coupling strength on the heat flux and spatiotemporal correlation functions of energy–momentum fluctuations are discussed via Langevin thermostats generated by spatiotemporal noise. For thermostats at different temperatures, the spatiotemporal ones can weaken the total heat flux of the system in comparison with the normal Langevin ones. The total heat flux will increase when the dispersal kernel or the loop length or the coupling strength increases, while the heat flux in the loop does not change as the dispersal kernel or the loop length increases, and decrease as the coupling strength increases. Then the underlying mechanism of heat flux can be well explained by the phonon spectra and Fourier's law. For the thermostats at the same temperatures, it is shown that the peak of the propagating front for the trunk (PT) and the peak of the propagating front from the coupling position to the outer trunk (PC) do not change almost for the normal Langevin and spatiotemporal thermostats. The PT decreases and PC increases when the loop length or coupling strength increases. Our results may contribute to further understanding of thermal information appearing in coupled nanotubes, polymer chains and biological networks. Heat flux J vs the coupling strength k. The red circle, blue triangle and green five-pointed star refer to the total heat flux, heat flux in the self-coupled loop and shortcut, respectively. The length of the FPU- β lattice N = 500 , coupling at i = 151 , j = 350 . [ABSTRACT FROM AUTHOR]

External photo-stimuli on heterojunctions commonly induce an electric potential gradient across the interface therein, such as photovoltaic effect, giving rise to various present-day technical devices. In contrast, in-plane potential gradient along the interface has been rarely observed. Here we show that scanning a light beam can induce a persistent in-plane photoelectric voltage along, instead of across, silicon-water interfaces. It is attributed to the following movement of a charge packet in the vicinity of the silicon surface, whose formation is driven by the light-induced potential change across the capacitive interface and a high permittivity of water with large polarity. Other polar liquids and hydrogel on silicon also allow the generation of the in-plane photovoltage, which is, however, negligible for nonpolar liquids. Based on the finding, a portable silicon-hydrogel array has been constructed for detecting the shadow path of a moving Cubaris. Our study opens a window for silicon-based photoelectronics through introducing semiconductor-water interfaces. Common photovoltaic effect is across the interface of heterojunctions. Here, the authors find that scanning a light beam can induce a persistent in-plane photoelectric voltage along silicon-water interfaces, due to the following movement of a charge packet in the vicinity of the silicon surface. [ABSTRACT FROM AUTHOR]

Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined, especially when the dielectric hexagonal boron nitride (BN) is involved. Here, we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN, BN-molybdenum disulfide, and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory. The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107 ± 0.062 and 0.999 ± 0.053 times that at BN-BN interface, respectively, while increase to 1.195 ± 0.076 and 1.085 ± 0.075 a.u. after exposure of the tip to radiation in scanning electron microscopy, with data repeatability higher than 86%. The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method, whereas the effect of radiation comes from the introduced charges in the tip, indicating the crucial roles of both dispersion and electrostatic interactions in construction, manipulation and device application of two-dimensional heterostructures. [ABSTRACT FROM AUTHOR]

For a nonperiodic system, a bamboo SiGe nanowire with axially degraded components, it is impossible to obtain its phonon dispersion relations through lattice dynamic or the first principle calculation. Therefore, we present a simple and available method to solve this problem. At first, the SiGe nanowire with axially degraded component is divided into several sections according to its component distribution like bamboos' sections formed in the growth process. For each section with a given x value, we constructed a pseudo-cell to calculate its phonon dispersion relations. Thermal conductances of junctions and of each section are then calculated by the phonon mismatch model and the phonon transmission probability with diffusive and ballistic portions. The dependences of thermal conductivity on the length of each section and the gradient of degraded component between sections are presented. We studied thermal conductivity dependence on temperature, length and diameter of the SiGe nanowire with axially degraded component. And we found κ ~ l , in which the exponent 0.8 is ascribed to the competition between phonons ballistic and diffusive transport. Furthermore, thermal conductivities along axial (100), (110), and (111) directions are discussed in detail. The method provides a simple and available tool to study thermal conductivity of a non-period system, such as a quasiperiodic superlattice or a nanowire with axially degraded component. [ABSTRACT FROM AUTHOR]

We study phonon Hall effect (PHE) for ionic crystals in the presence of static magnetic field. Using Green-Kubo formula, we present an exact calculation of thermal conductivity tensor by considering both positive and negative frequency phonons. Numerical results are shown for some lattices such as hexagonal lattices, triangular lattices, and square lattices. We find that the PHE occurs on the nonmagnetic ionic crystal NaCl, although the magnitude is very small which is due to the tiny charge-to-mass ratio of the ions. The off-diagonal thermal conductivity is finite for nonzero magnetic field and changes sign for high value of magnetic field at high temperature. We also found that the off-diagonal thermal conductivity diverges as ±1/ T at low temperature. [ABSTRACT FROM AUTHOR]

The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk length-scales, engineering the thermal conductivity at micro- and nano-scale dimensions is considerably more challenging. In this work, we show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The underlying mechanism is understood through molecular dynamics simulations and quantitative phonon-defect scattering rate analysis, where the behaviour of thermal conductivity with dose is attributed to the accumulation and agglomeration of scattering centres at lower doses. Beyond a threshold dose, a crystalline-amorphous transition was observed. [ABSTRACT FROM AUTHOR]

Passive immunotherapy with monoclonal antibodies (mAbs) is an efficacious treatment for Ebola virus (EBOV) infections in animal models and humans. Understanding what constitutes a protective response is critical for the development of novel therapeutic strategies. We generated an EBOV-glycoprotein-pseudotyped Human immunodeficiency virus to develop sensitive neutralizing and antibody-dependent cellular cytotoxicity (ADCC) assays as well as a bioluminescent-imaging-based mouse infection model that does not require biosafety level 4 containment. The in vivo treatment efficiencies of three novel anti-EBOV mAbs at 12 h post-infection correlated with their in vitro anti-EBOV ADCC activities, without neutralizing activity. When they were treated with these mAbs, natural killer cell (NK)-deficient mice had lower viral clearance than WT mice, indicating that the anti-EBOV mechanism of the ADCC activity of these mAbs is predominantly mediated by NK cells. One potent anti-EBOV mAb (M318) displayed unprecedented neutralizing and ADCC activities (neutralization IC50, 0.018 μg/ml; ADCC EC50, 0.095 μg/ml). These results have important implications for the efficacy of antiviral drugs and vaccines as well as for pathogenicity studies of EBOV. [ABSTRACT FROM AUTHOR]

The article focuses on an example of a one-way acoustic mirror developed by Jian-Chun Cheng and his colleagues from Nanjing University. It states that the mirror features an acoustic diode consists of two segment, a phonic crystal and a nonlinear acoustic medium. It mentions that the phonic crystal serves as acoustic filter due to the ability of its bandgap to prevent acoustic waves. It adds that the proposed diode only functions for a single frequency or a narrow band of frequencies.

Due to the increasing concern of using smallpox virus as biological weapons for terrorist attack, there is renewed interest in studying the pathogenesis of human smallpox and development of new therapies. Animal models are highly demanded for efficacy and safety examination of new vaccines and therapeutic drugs. Here, we demonstrated that both wild type and immunodeficient rats infected with an engineered vaccinia virus carrying Firefly luciferase reporter gene (rTV-Fluc) could recapitulate infectious and clinical features of human smallpox. Vaccinia viral infection in wild type Sprague-Dawley (SD) rats displayed a diffusible pattern in various organs, including liver, head and limbs. The intensity of bioluminescence generated from rTV-Fluc correlated well with viral loads in tissues. Moreover, neutralizing antibodies had a protective effect against virus reinfection. The recombination activating gene 2 (Rag2) knockout rats generated by transcription activator-like effector nucleases (TALENs) technology were further used to examine the infectivity of the rTV-Fluc in immunodeficient populations. Here we demonstrated that Rag2-/- rats were more susceptible to rTV-Fluc than SD rats with a slower virus clearance rate. Therefore, the rTV-Fluc/SD rats and rTV-Fluc/Rag2-/- rats are suitable visualization models, which recapitulate wild type or immunodeficient populations respectively, for testing human smallpox vaccine and antiviral drugs. [ABSTRACT FROM AUTHOR]

The ability to design the control of heat flow has innumerable benefits in the design of electronic systems such as thermoelectric energy harvesters, solid-state lighting, and thermal imagers, where the thermal design plays a key role in performance and device reliability. In this work, we employ one identical sensu-unit with facile natural composition to experimentally realize a new class of thermal metamaterials for controlling thermal conduction (e.g., thermal concentrator, focusing/resolving, uniform heating), only resorting to positioning and locating the same unit element of sensu-shape structure. The thermal metamaterial unit and the proper arrangement of multiple identical units are capable of transferring, redistributing and managing thermal energy in a versatile fashion. It is also shown that our sensu-shape unit elements can be used in manipulating dc currents without any change in the layout for the thermal counterpart. These could markedly enhance the capabilities in thermal sensing, thermal imaging, thermal-energy storage, thermal packaging, thermal therapy, and more domains beyond. [ABSTRACT FROM AUTHOR]