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Deployable solar arrays play an important role in the realization of various spacecraft missions. Taking the flexible spacecraft as an application background, the natural characteristics of...

It has recently been shown that quantum-confined states can appear in epitaxially grown van der Waals material heterobilayers without a rotational misalignment (θ = 0°), associated with flat bands in the Brillouin zone of the moiré pattern formed due to the lattice mismatch of the two layers. Peaks in the local density of states and confinement in a MoS

It has recently been shown that quantum-confined states can appear in epitaxially grown van der Waals material heterobilayers without a rotational misalignment ($\theta=0^\circ$), associated with flat bands in the Brillouin zone of the moir\'e pattern formed due to the lattice mismatch of the two layers. Peaks in the local density of states and confinement in a MoS$_2$/WSe$_2$ system was qualitatively described only considering local stacking arrangements, which cause band edge energies to vary spatially. In this work, we report the presence of large in-plane strain variation across the moir\'e unit cell of a $\theta=0^\circ$ MoS$_2$/WSe$_2$ heterobilayer, and show that inclusion of strain variation and out-of-plane displacement in density functional theory calculations greatly improves their agreement with the experimental data. We further explore the role of twist-angle by showing experimental data for a twisted MoS$_2$/WSe$_2$ heterobilayer structure with twist angle of $\theta=15^\circ$, that exhibits a moir\'e pattern but no confinement., Comment: 13 pages, 6 figures in main text. Supporting information included with 13 pages, 8 figures, and 2 tables

Recently, many neural retrieval models have been proposed and shown competitive results. In particular, interaction-based models have shown superior performance to traditional models in a number of studies. However, the interactions used as the basic matching signals are between single terms or their embeddings. In reality, a term can often match a phrase or even longer segment of text. This paper proposes a Cross-Level Matching Model which enhances the basic matching signals by allowing terms to match hidden representation states within a sentence. A gating mechanism aggregates the learned matching patterns of different matching channels and outputs a global matching score. Our model provides a simple and effective way for word-phrase matching.

International audience; The transparency of two-dimensional (2D) materials to intermolecular interactions of crystalline materials has been an unresolved topic. Here we report that remote atomic interaction through 2D materials is governed by the binding nature, that is, the polarity of atomic bonds, both in the underlying substrates and in 2D material interlayers. Although the potential field from covalent-bonded materials is screened by a monolayer of graphene, that from ionic-bonded materials is strong enough to penetrate through a few layers of graphene. Such field penetration is substantially attenuated by 2D hexagonal boron nitride, which itself has polarization in its atomic bonds. Based on the control of transparency, modulated by the nature of materials as well as interlayer thickness, various types of single-crystalline materials across the periodic table can be epitaxially grown on 2D material-coated substrates. The epitaxial films can subsequently be released as free-standing membranes, which provides unique opportunities for the heterointegration of arbitrary single-crystalline thin films in functional applications.

Advances in ex situ and in situ (operando) characteristic techniques have unraveled unprecedented atomic details in the electrochemical reaction of Li-ion batteries. To bridge the gap between emerging evidences and practical material development, an elaborate understanding on the electrochemical properties of cathode materials on the atomic scale is urgently needed. In this work, we perform comprehensive first-principle calculations within the density functional theory + U framework on the surface stability, morphology, and elastic anisotropy of Ni-rich LiNi1-2yCoyMnyO2 (NCM) (y ≤ 0.1) cathode materials, which are strongly related to the emerging evidence in the degradation of Li-ion batteries. On the basis of the surface stability results, the equilibrium particle morphology is obtained, which is mainly determined by the oxygen chemical potential. Ni-rich NCM particles are terminated mostly by the (012) and (001) surfaces for oxygen-poor conditions, whereas the termination corresponds to the (104) and (001) surfaces for oxygen-rich conditions. Besides, Ni surface segregation predominantly occurs on the (100), (110), and (104) nonpolar surfaces, showing a tendency to form a rocksalt NiO domain on the surface because of severe Li-Ni exchange. The observed elastic anisotropy reveals that an uneven deformation is more likely to be formed in the particles synthesized under poor-oxygen conditions, leading to crack generation and propagation. Our findings provide a deep understanding of the surface properties and degradation of Ni-rich NCM particles, thereby proposing possible solution mechanisms to the factors affecting degradation, such as synthesis conditions, coating, or novel nanostructures.

Two-dimensional materials have shown great promise for implementation in next-generation devices. However, controlling the film thickness during epitaxial growth remains elusive and must be fully understood before wide scale industrial application. Currently, uncontrolled multilayer growth is frequently observed, and not only does this growth mode contradict theoretical expectations, but it also breaks the inversion symmetry of the bulk crystal. In this work, a multiscale theoretical investigation aided by experimental evidence is carried out to identify the mechanism of such an unconventional, yet widely observed multilayer growth in the epitaxy of layered materials. This work reveals the subtle mechanistic similarities between multilayer concentric growth and spiral growth. Using the combination of experimental demonstration and simulations, this work presents an extended analysis of the driving forces behind this non-ideal growth mode, and the conditions that promote the formation of these defects. Our study shows that multilayer growth can be a result of both chalcogen deficiency and chalcogen excess: the former causes metal clustering as nucleation defects, and the latter generates in-domain step edges facilitating multilayer growth. Based on this fundamental understanding, our findings provide guidelines for the narrow window of growth conditions which enables large-area, layer-by-layer growth.

In this paper, to identify the roof unconfined compressive strength (UCS) in the process of coal mine roadway support in real-time and optimize the real-time drilling speed while drilling, this paper proposes and establishes a drilling test method for assessing the uniaxial compressive strength (UCS) of a roof. This method can be used to optimize the speed of drilling. Moreover, a mathematical model of the power output is developed for a roof-strata identification system with a drilling test system. The results were as follows: (1) the system was able to identify the uniaxial compressive strength of roof rock, (2) the pressure of the drill leg of the pneumatic bolt did not match the output power of the pneumatic motor, the pneumatic motor could not reach the maximum power point, and the insufficient thrust of the pneumatic leg led to failure of the maximum output power of the pneumatic motor, (3) to increase the output power of the air motor and thus improve the drilling speed, we applied a booster valve for the system. The experimental results show that the power of the air motor has a linear relationship with drilling speed. In this way, the speed of the drill can be increased by increasing the motor power.

To achieve efficient degradation of pharmaceutical and personal care products (PPCPs), dual reaction centers ZnO@FePc photo-Fenton catalysts with high-speed electron transmission channel were designed through surface hydroxyl-induced assembly. In ZnO@FePc catalytic system, the photocatalysis center of ZnO and Fenton catalytic center of FePc were formed simultaneously. Concept and process for the control of hydroxyl groups to construct a dual reaction center ZnO@FePc photo-Fenton catalyst were verified ingeniously based on the density functional theory (DFT) analysis and experimental results. A series of catalysts, including ZIF-8 (400 ℃-N2), FePc (400 ℃-N2), ZIF-8 (400 ℃)-FePc (400 ℃) and ZnO@FePc were prepared and characterized by XRD, FTIR, TEM, BET, XPS, PL and DRS, respectively. The ZnO@FePc catalyst showed superior performance for the photo-Fenton degradation of ibuprofen, affording degradation rate larger than 90 % within just 10 min under simulateed sunlight. The excellent performance of ZnO@FePc catalyst is mainly attributed to the synergistic effect between dual reaction centers of ZnO@FePc. This work provides a novel method to construct dual reaction centers ZnO@FePc catalyst with efficient photo-generated electrons transmission link and to strengthen the synergistic effect of dual reaction centers.

Conventional mechanical or chemical exfoliation approach of 2D material synthesis is largely dependent on the inherent structure of the parent material, i.e., whether it is a layered structure or a 3D bulk structure with embedded 2D substructures. A recent experiment demonstrated that unprecedented atomically thin metal oxides without bulk layered structures can be synthesized by using liquid metals. Supported by an experimental realization of atomically thin W layers through the metal atomic layer deposition method, we propose a new type of transition metal (TM)-based 2D materials that can be stabilized at the oxide interfaces with oxide substrates and overlayers. Based on the ab initio density functional theory calculations, we show that most of the TM elements can form unprecedented atomically thin 2D materials by the surface oxygen passivation, which is available from the oxide substrate and the overlayer. The stabilized 2D TM layers show diverse electronic and magnetic properties. Our results suggest a novel way to extend 2D materials study and a possible application of those 2D TM layers embedded in oxides.

First-principles calculations have been carried out to investigate the adsorption of a hydrogen adatom on 24 metal doped α-Zr (0 0 0 1) surfaces in both a vacuum and an implicit solvation environment. The dopant are the elements in the 4th and 5th periods in the periodic table. Doping elements at the tail of the 4th and 5th periods can significantly reduce the hydrogen pickup in a vacuum environment. A weighted d-band center theory is used to analyze the doping effect. On the other hand, the hydrogen adsorption energies in water are relatively lower for all doped slabs and the surface adsorption of hydrogen adatom is stronger than that in a vacuum environment, especially, for the slabs with doping elements at the tail of the 4th and 5th periods. In the solvation environment, electronegativity difference affects the adsorption. Doping elements Ag, Ga, Ge, Sn, and Sb can reduce the hydrogen pickup in vacuum, while Ag and Cu can reduce the hydrogen pickup of the zirconium alloys in solvent environment.

Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.

In this work, we perform a comprehensive study of five phenomena of LiNi1-2xCoxMnxO2 (NCM) (x = 0–1/3) cathodes at the end of charge (phase reaction, crack propagation, Li-Ni exchange, phase transition, and oxygen evolution), using first-principle calculations within the DFT + U framework. Based on our results, we have located the obstacles toward unity efficiency and revealed that the degradation strongly depends on the Ni concentration and the depth of charge. The threshold capacities for degradation of LiyNi1-2xCoxMnxO2 are 130–140 mA·hg−1 (y

Transition metal (TM) modification is a common strategy for converting an earth-abundant mineral into a cost-effective catalyst for industrial applications. Among a variety of minerals, Al2SiO5, which has three phases, andalusite, sillimanite and kyanite, is emerging as a promising candidate for new catalyst development. In this paper, we use Mn to demonstrate the rationale of 3d TM doping at the Al sites in each of these three phases through first-principles calculations and the cluster expansion method. The results of cluster expansion show that Mn has a strong site preference for the six-coordinated Al octahedral chains in the andalusite and sillimanite phases, while distributing randomly in the kyanite phase. Moreover, Mn can only replace Al in sillimanite and kyanite in low concentrations; however, higher concentrations of Mn can replace Al in andalusite. We found that the concentration sensitivity is due to the Jahn-Teller distortion and 3d orbital splitting. This finding can also explain the low doping concentrations of other 3d TMs (Fe, Cr and V) in Al2SiO5 compounds. Based on the calculated Helmholtz free energy, we constructed a (MnxAl1-x)AlSiO5 temperature-composite phase diagram, which explains the physical mechanisms behind the results for 3d transition metal doping and phase transitions in Al2SiO5. This work could shed light on the related physics, chemistry, and geoscience of (MnxAl1-x)AlSiO5, and more importantly, a design rationale for the engineering of cheap catalysts.

Atomic substitution and doping are two of the most adopted strategies to improve the electrochemical performance of layered cathode materials for Li-ion batteries (LIBs). In this work, we report a comprehensive study on the effects of seven dopants (Al, Ga, Mg, Si, Ti, V, and Zr) on the well-known drawbacks of Ni-rich LiNi1−2yCoyMnyO2 (NCM) (y ≤ 0.1), one of the most promising next-generation cathode materials for LIBs, including phase instability, Li–Ni exchange, Ni segregation, lattice distortion, and oxygen evolution. Our results show that there is not a single dopant that can solve all the problems at the same time and, moreover, while they often improve certain properties, they may have no effect or even worsen others. By comparing different doping sites, we found a strong site preference due to the tradeoff between Mn and Co concentrations. This site preference indicates that a multicomponent-doping strategy should be adopted at both Mn and Co sites. Finally, a rationale for the optimization of the overall electrochemical performance of Ni-rich NCM is proposed, which will ultimately provide practical guidance (Ti or Zr at the Co site and Al at the Mn site) for the design of new Ni-rich layered cathode materials for LIBs.

The mineralization of organic pollutants under visible light is challenging, limiting the practical application of photocatalytic technology in wastewater treatment. To achieve the efficient mineralization of Acid red 3R (AR3R), a series of honeycombed catalysts (TiO

A memristor

Recent deep learning models for information retrieval typically aim to learn features either about the contents of the document and the query, or about the interactions between them. However, the existing literature shows that document ranking depends simultaneously on many factors, including both content and interaction features. The integration of both types of neural features has not been extensively studied. In addition, many studies have also shown that the deep neural features cannot replace completely the traditional features, but are complementary. It is thus reasonable to combine deep neural features with traditional features. In this paper, we propose an integrated end-to-end learning framework based on learning-to-rank (L2R) to learn both neural features and the L2R ranking function simultaneously. The framework also has the flexibility to integrate arbitrary traditional features. Our experiments on public datasets confirm that such an integrated learning strategy is better than separate learning of features and ranking function, and integrating traditional features can further improve the results.

The wireless charging technology (WPT) is a hot research topic at present. Because of its plug-in-free feature, it is very suitable for patrol robots. In order to reduce the influence of wireless charging coupling mechanism on electromagnetic environment in non-working area, a shielding device was designed and its finite element model (FEM) was established. The feasibility of the method was verified by finite element calculation. The simulation results show that the horizontal active shielding coil can significantly reduce the vertical electromagnetic leakage and eddy current loss of the magnetic coupling mechanism, and the vertical active shielding coil can effectively reduce the horizontal electromagnetic leakage, thereby reducing the radiation loss. It is proved that the active shielding coil can enhance the uniformity of space magnetic field and reduce the electromagnetic interference from the wireless charging system of inspection robot.

Generalized Frequency Division Multiplex (GFDM) is a new multiple subcarrier modulation technology. The problem of inter-carrier interference (ICI) caused by non-orthogonality using GFDM modulation is analyzed in this paper. For fading channel, a new double-band self-interference cancellation algorithm based on channel status information is proposed. Simulation results show that the bit error rate (BER) level of the GFDM system can be controlled to a lower level by the proposed method.

To face the challenge of spectral efficiency for the conventional binary chirp-BOK modulation, an M-ary chirp modulation (MCM) is proposed. Different from the traditional quadrature amplitude modulation technology, M-ary chirp modulation scheme with a constant envelope uses up-chirp and down-chirp as orthogonal components. The expression for its symbol error rate (SER) under AWGN channel is given. MCM has much better performance than MPSK under the multipath fading channels which are selected from COST207 standard.

Due to the relative movement between the transmitter and receiver in wireless communication systems, Doppler shift and time delay are introduced results in the probability of symbol synchronization decreases. Therefore, fast and steady synchronization method is pretty important. In this paper, a new symbol synchronization scheme based on chirp signals has been proposed. The proposed coarse synchronization sequence chosen five chirp signals with same chirp rates which time and bandwidth (TB) product is higher, while the fine synchronization sequence is composed of chirp signals with different chirp rates which TB product is small. The performance of the proposed scheme is evaluated via simulations. The simulation results show that the performance of proposed scheme is superior, and achieves a clearly performance gain with a high estimation accuracy both in timing and frequency offset.

The correlation between lattice oxygen (O) binding energy and O oxidation activity imposes a fundamental limit in developing oxide catalysts, simultaneously meeting the stringent thermal stability and catalytic activity standards for complete oxidation reactions under harsh conditions. Typically, strong O binding indicates a stable surface structure, but low O oxidation activity, and

Resonant wireless charging technology can overcome many shortcomings of traditional charging methods and is favored by universities and research institutions in the world. However, the inevitable leakage flux during transmission may cause electromagnetic interference problems. First of all, this paper designs a set of coils for resonant wireless charging system with the background of wireless charging of slow-moving inspection robots. Secondly, the magnetic field distribution around the coil is analyzed, and some indicators are established to evaluate its shielding performance. Some shielding designs are simulated where the magnetic induction intensity exceeds the standard. Finally, the shielding method is validated by experiments, and some guiding suggestions are put forward for the safe development of wireless charging system.

Furfural is a versatile platform molecule for the synthesis of various chemicals and fuels, and it can be produced by acid-catalyzed dehydration of xylose derived from renewable biomass resources. A series of metal salts and ionic liquids were investigated to obtain the best combination of catalyst and solvent for the conversion of xylose into furfural. A furfural yield of 71.1% was obtained at high xylose loading (20 wt%) from the single-phasic reaction system whereby SnCl4 was used as catalyst and ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIMBr) was used as reaction medium. Moreover, the combined catalyst consisting of 5 mol% SnCl4 and 5 mol% MgCl2 also produced a high furfural yield (68.8%), which was comparable to the furfural yield obtained with 10 mol% SnCl4. The water&ndash, organic solvent biphasic systems could improve the furfural yield compared with the single aqueous phase. Although these organic solvents could form biphasic systems with ionic liquid EMIMBr, the furfural yield decreased remarkably compared with the single EMIMBr phase. Besides, the EMIMBr/SnCl4 system with appropriate water was also efficient to convert xylan and lignocellulosic biomass corn stalk into furfural, obtaining furfural yields as high as 57.3% and 54.5%, respectively.

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconductive transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+{\delta} (Bi2201) and bilayer Bi2Sr2CaCu2O8+{\delta} (Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tc and doping (p) or pressure (P) at higher pressures. The Tc of under-doped Bi2201 initially increases from 9.6 K at ambient to a peak at ~ 23 K at ~ 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above ~ 40 GPa, Tc rises rapidly without any sign of saturation up to ~ 30 K at ~ 51 GPa. Similarly, the Tc for the slightly overdoped Bi2212 increases after passing a broad valley between 20-36 GPa and reaches ~ 90 K without any sign of saturation at ~ 56 GPa. We have therefore attributed this Tc-resurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3d_(x^2-y^2 ) and the O 2p bands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+{\delta} (Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures., Comment: 13 pages, including 5 figures

In this Letter, we use first-principles simulations to demonstrate the absence of Fermi-level pinning when graphene is in contact with transition metal dichalcogenides (TMDs). We find that formation of either an ohmic or Schottky contact is possible. Then we show that, due to the shallow density of states around its Fermi level, the work function of graphene can be tuned by ion adsorption. Finally we combine work function tuning of graphene and an ideal contact between graphene and TMDs to propose an ionic barristor design that can tune the work function of graphene with a much wider margin than current barristor designs, achieving a dynamic switching among p-type ohmic contact, Schottky contact, and n-type ohmic contact in one device.

Two-dimensional tungsten diselenide (WSe2) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe2-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe2-graphene interface. Electrical transport measurements reveal a lower resistance between WSe2 and fully hydrogenated epitaxial graphene (EG(FH)) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH). Using low-energy electron microscopy and reflectivity on these samples, we extract the work function difference between the WSe2 and graphene and employ a charge transfer model to determine the WSe2 carrier density in both cases. The results indicate that WSe2-EG(FH) displays ohmic behavior at small biases due to a large hole density in the WSe2, whereas WSe2-EG(PH) forms a Schottky barrier junction.

Production of 5-hydroxymethylfurfural (HMF) is a pivotal step in biorefinery. However, the intrinsic HMF production efficiency in traditional catalytic systems are low owing to the side-reactions. Here we report the highly efficient transformation of carbohydrates to HMF via tandem catalysis in heterogeneous catalytic system. The combination of Al and Sn co-modified hydroxyapatite catalyst (Al/Sn-HAP) with ionic liquid exhibit a low activation energy of 68.4 kJ mol-1, affording HMF yields of 70.5 and 46.6% at glucose loading of 10 and 40 wt%, respectively. Compared with other catalysts, Al/Sn-HAP exhibits remarkably higher Lewis acid concentration, specific surface area and pore dimeter with slight Bronsted acid, as are beneficial for glucose isomerization. The efficient conversion of maltose, cellobiose and starch to HMF are achieved via the triple tandem pathway consisted of hydrolysis, isomerization and dehydration with inhibited side-reaction. Besides, the Al/Sn-HAP catalyst after regeneration can be reused without decrease of catalytic performance.

To achieve efficient degradation of dye in wastewater, the core-shell nickel cobalt spinel coated with iron phthalocyanine (NiCo2O4@FePc) catalyst was prepared via a facile template method and investigated as heterogenous catalyst for degradation of dye in Fenton process. The catalysts were systematically characterized by transmission electron microscopy (TEM), N2 adsorption/desorption isotherms, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results indicated that the NiCo2O4@FePc catalyst exhibits core-shell structure with abundant oxygen vacancies and high specific surface area (261.9 m2/g). NiCo2O4@FePc showed much higher catalytic activity for the mineralization of (TOC removal rate > 90%) RhB than nickel cobalt spinel (NiCo2O4), iron phthalocyanine (FePc) and the physical mixture of NiCo2O4 and FePc (NiCo2O4-FePc-M). The radical scavenging experiments and reaction kinetics experiments revealed that the excellent catalytic perormance of NiCo2O4@FePc benefits from the efficient production of •O2− and •OH radical. Moreover, the catalytic performance of NiCo2O4@FePc can be well maintained in the presence of inorganic anions (HCO3− and Cl−), natural organic matter or tap water. Besides, the liquid stability and resubility of NiCo2O4@FePc were demonstrated by filtration and recyling experiment. This work can provide new insight for construction of Fe-based heterogenous catalysts which are promising for the efficient elimination of organic pollutants.

The mineralization of organic pollutants under visible light is challenging, limiting the practical application of photocatalytic technology in wastewater treatment. To achieve the efficient mineralization of Acid red 3R (AR3R), a series of honeycombed catalysts (TiO2, C-TiO2-X, Au@TiO2 and Au@C-TiO2-X) were prepared via a facile in situ synthetic method and characterized by XRD, TEM, BET, XPS and DRS, respectively. The introduction of C and Au species promote the simultaneous generation of •O2− and •OH over Au@C-TiO2-X under visible light radiation. The Au@C-TiO2-X catalyst showed superior performance for the deep mineralization of AR3R, affording a TOC removal rate larger than 90 % within 240 min under visible light (> 420 nm). The photocatalytic degradation mechanism of AR3R is proposed according to UV–vis and in situ DRIFTS analysis. The superior photocatalytic activity of Au@C-TiO2-X is attributed to the synergistic effect of •O2− and •OH owing to C doping and Au deposition.

Biological Event Extraction is an important task towards the goal of extracting biomedical knowledge from the scientific publications by capturing biomedical entities and their complex relations from the texts. As a crucial step in event extraction, event trigger identification, assigning words with suitable trigger category, has recently attracted substantial attention. As triggers are scattered in large corpus, traditional linguistic parsers are hard to generate syntactic features from them. Thereby, trigger sparsity problem restricts the model's learning process and becomes one of the main hinder in trigger identification. In this paper, we employ Noise Contrastive Estimation with Multi-Layer Perceptron model for solving triggers’ sparsity problem. Meanwhile, in the light of recent advance in word distributed representation, word-embedding feature generated by language model is utilized for semantic and syntactic information extraction. Finally, experimental study on commonly used MLEE dataset against baseline methods has demonstrated its promising result.

Quantum Hall effect (QHE) is a macroscopic manifestation of quantized states that only occurs in confined two-dimensional electron gas (2DEG) systems. Experimentally, QHE is hosted in high-mobility 2DEG with large external magnetic field at low temperature. Two-dimensional van der Waals materials, such as graphene and black phosphorus, are considered interesting material systems to study quantum transport because they could unveil unique host material properties due to the easy accessibility of monolayer or few-layer thin films at the 2D quantum limit. For the first time, we report direct observation of QHE in a novel low-dimensional material system, tellurene. High-quality 2D tellurene thin films were acquired from recently reported hydrothermal method with high hole mobility of nearly 3000 cm2/(V s) at low temperatures, which allows the observation of well-developed Shubnikov-de Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau levels in SdH oscillations and QHE was revealed. Quantum oscillations were investigated under different gate biases, tilted magnetic fields, and various temperatures, and the results manifest the inherent information on the electronic structure of Te. Anomalies in both temperature-dependent oscillation amplitudes and transport characteristics were observed that are ascribed to the interplay between the Zeeman effect and spin-orbit coupling, as depicted by the density functional theory calculations.

Advances in ex situ and in situ (operando) characteristic techniques have unraveled unprecedented atomic details in the electrochemical reaction of Li-ion batteries. To bridge the gap between emerging evidences and practical material development, an elaborate understanding on the electrochemical properties of cathode materials on the atomic scale is urgently needed. In this work, we perform comprehensive first-principle calculations within the density functional theory + U framework on the surface stability, morphology, and elastic anisotropy of Ni-rich LiNi

Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe2) via metal–organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe2/sapphire exhibit ambipolar behavior with excellent on/off ratios (∼107), high current density (1–10 μA·μm–1), and good field-effect transistor mobility (∼30 cm2·V–1·s–1) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D inte...

Using the Bardeen tunneling method with first-principles wave functions, computations are made of the tunneling current in graphene/hexagonal-boron-nitride/graphene (G/h-BN/G) vertical structures. Detailed comparison with prior experimental results is made, focusing on the magnitude of the achievable tunnel current. With inclusion of the effects of translational and rotational misalignment of the graphene and the h-BN, predicted currents are found to be about 15× larger than experimental values. A reduction in this discrepancy, to a factor of 2.5×, is achieved by utilizing a realistic size for the band gap of the h-BN, hence affecting the exponential decay constant for the tunneling.

To overcome the limitation of conventional fixed charge potential methods for the study of Li-ion battery cathode materials, a dynamic charge potential method, charge-transfer modified embedded atom method (CT-MEAM), has been developed and applied to the Li-Co-O ternary system. The accuracy of the potential has been tested and validated by reproducing a variety of structural and electrochemical properties of LiCoO2. A detailed analysis on the local charge distribution confirmed the capability of this potential for dynamic charge modeling. The transferability of the potential is also demonstrated by its reliability in describing Li-rich Li2CoO2 and Li-deficient LiCo2O4 compounds, including their phase stability, equilibrium volume, charge states and cathode voltages. These results demonstrate that the CT-MEAM dynamic charge potential could help to overcome the challenge of modeling complex ternary transition metal oxides. This work can promote molecular dynamics studies of Li ion cathode materials and other important transition metal oxides systems that involve complex electrochemical and catalytic reactions.

Transition metal (TM) modification is a common strategy for converting an earth-abundant mineral into a cost-effective catalyst for industrial applications. Among a variety of minerals, Al

Chemical and physical adsorption of a H 2 O molecule on a Zr (0 0 0 1) surface is studied by first principle calculations. A surface zirconium atom is substituted by a metal element atom in the 4th and 5th period of the periodic table to investigate the doping effect on the water adsorption. Doping elements Ge, Sn, Sb, Zn, Ga, Ru, Rh, Pd, Ag, Cr, Mn, Fe, Co, Ni, Cu, Nb, and Mo can increase the oxidation resistance. This strategy can be used to design high oxidation resistance cladding material for light water reactor.

The atomic layer deposition (ALD) of high-k dielectrics could build an efficient barrier against moisture and O2 adsorption. Such a barrier is highly needed for MoTe2 and WTe2 transition metal dichalcogenides because of the poor structural stability and the fast oxidization in ambient air. In situ x-ray photoelectron spectroscopy and ex situ atomic force microscopy and scanning transmission electron microscopy were employed to report a comparative study between the growth of Al2O3 on MoTe2 and WTe2 by means of traditional thermal ALD and plasma-enhanced ALD (PEALD). Similar to what has been observed on other 2D materials such as MoS2 and Graphene, the thermal ALD results in an islanding growth of Al2O3 on MoTe2 due to the dearth of dangling bonds, whereas, a uniform coverage of Al2O3 on WTe2 is observed and likely contributed to the high concentration of intrinsic structural defects. The PEALD behavior is consistent between MoTe2 and WTe2 providing a conformal and linear growth rate (∼0.08 nm/cycle), which correlates with the creation of Te-O and metal-O nucleation sites. However, a thin layer of interfacial Mo or W oxides gradually forms, resulting from the plasma-induced damage in the topmost (1-2) layers. Attempts to enhance the Al2O3/MoTe2 interfacial quality by physically evaporating an Al2O3 seed layer are investigated as well. However, the evaporated Al2O3 process causes thermal damage on MoTe2, necessitating a more 'gentle' ALD technique for the surface passivation.

The authors investigate the thermodynamic and electronic properties of few- and monolayer MoS2 using density functional theory. They calculate the formation energies of S vacancies and the doping effect of C and O under various chemical environments which are commonly observed during MoS2 deposition. The results show that in the oxidizing condition, O readily gets incorporated into the MoS2 layer and assists in C doping. They analyze the bandgap and density of states of MoS2 at different concentrations of defect. They find that the bandgap decreases as the defect concentration increases, wherein the ordering of S vacancies has a more significant influence than that of the other two defects. The S vacancy and C dopants generate deep acceptor gap states within the bandgap of MoS2, while O dopant states are delocalized. They also observe that the carbon dopants form penetrative dimers, which lead to shallow acceptor states. This work contributes to the understanding of defect/impurity incorporation during deposition and prediction of electronic behavior of deposited low-quality MoS2 materials.The authors investigate the thermodynamic and electronic properties of few- and monolayer MoS2 using density functional theory. They calculate the formation energies of S vacancies and the doping effect of C and O under various chemical environments which are commonly observed during MoS2 deposition. The results show that in the oxidizing condition, O readily gets incorporated into the MoS2 layer and assists in C doping. They analyze the bandgap and density of states of MoS2 at different concentrations of defect. They find that the bandgap decreases as the defect concentration increases, wherein the ordering of S vacancies has a more significant influence than that of the other two defects. The S vacancy and C dopants generate deep acceptor gap states within the bandgap of MoS2, while O dopant states are delocalized. They also observe that the carbon dopants form penetrative dimers, which lead to shallow acceptor states. This work contributes to the understanding of defect/impurity incorporation during de...

Author(s): Pan, Y; Folsch, S; Lin, YC; Jariwala, B; Robinson, JA; Nie, Y; Cho, K; Feenstra, RM | Abstract: Scanning tunneling microscopy (STM) at 5 K is used to study WSe2 layers grown on epitaxial graphene which is formed on Si-terminated SiC(0 0 0 1). Specifically, a partial hydrogenation process is applied to intercalate hydrogen at the SiC-graphene interface, yielding areas of quasi-free-standing bilayer graphene coexisting with bare monolayer graphene. We find that an abrupt and structurally perfect homojunction (band-edge offset ∼0.25 eV) is formed when WSe2 overgrows a lateral junction between adjacent monolayer and quasi-free-standing bilayer areas in the graphene. The band structure modulation in the WSe2 overlayer arises from the varying work function (electrostatic potential) of the graphene beneath. Scanning tunneling spectroscopy measurements reveal that this effect can be also utilized to create WSe2 quantum dots that confine either valence or conduction band states, in agreement with first-principles band structure calculations.

Theoretical predictions are made for the current-voltage characteristics of two-dimensional heterojunction interlayer tunneling field-effect transistors (Thin-TFETs), focusing on the magnitude of the current that is achievable in such devices. A theory based on the Bardeen tunneling method is employed, using wavefunctions from first-principles density-functional theory. This method permits convenient incorporation of differing materials into the source and drain electrodes, i.e. with different crystal structures, lattice constants, and/or band structures. Large variations in the tunnel currents are found, depending on the particular two-dimensional materials used for the source and drain electrodes. Tunneling between states derived from the center (Gamma-point) of the Brillouin zone (BZ) is found, in general, to lead to larger current than for zone-edge (e.g. K-point) states. Differences, as large as an order of magnitude, between the present results and various prior predictions are discussed. Predicted values for the tunneling currents, including subthreshold swing, are compared with benchmark values for low-power digital applications. Contact resistance is considered and its effect on the tunneling currents is demonstrated., 20 pages, 9 figures

Metal-insulator transitions in low-dimensional materials under ambient conditions are rare and worth pursuing due to their intriguing physics and rich device applications. Monolayer MoTe2 and WTe2 are distinguished from other TMDs by the existence of an exceptional semimetallic distorted octahedral structure (T') with a quite small energy difference from the semiconducting H phase. In the process of transition metal alloying, an equal stability point of the H and the T' phase is observed in the formation energy diagram of monolayer WxMo1-xTe2. This thermodynamically driven phase transition enables a controlled synthesis of the desired phase (H or T') of monolayer WxMo1-xTe2 using a growth method such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). Furthermore, charge mediation, as a more feasible method, is found to make the T' phase more stable than the H phase and induce a phase transition from the H phase (semiconducting) to the T' phase (semimetallic) in monolayer WxMo1-xTe2 alloy. This suggests that a dynamic metal-insulator phase transition can be induced, which can be exploited for rich phase transition applications in two-dimensional nanoelectronics.

Machine learning algorithms depend heavily on the data representation, which dominates its success in experiment accuracy. Autoencoder model structure is proposed to learn from data a good representation with the least possible amount of distortion. Furthermore, it has been proven that boosting sparsity when learning representation can significantly improve performance on classification tasks and also make the feature vector easy to interpret. One straightforward approach for autoencoder to obtain sparse representation is to impose sparse penalty on its overall cost function. Nevertheless, few comparative analysis has been conducted to evaluate which sparse penalty term works better. In this paper, we adopt L1 norm, L2 norm, Student-t penalties, which are rarely deployed to penalise the hidden unit outputs, and commonly used penalty KL-divergence in the literature. Then, we present a detailed analysis to evaluate which penalty achieves better result in terms of reconstruction error, sparseness of representation and classification performance on test datasets. Experimental study on MNIST, CIFAR-10, SVHN, OPTDIGITS and NORB datasets reveals that all these penalties achieve sparse representation and outperforms representations learned by pure autoencoder on classification performance and sparseness of feature vectors. Moreover, we hope this topics and the practices would provide insights for future research.

Molecular events normally have significant meanings since they describe important biological interactions or alternations such as binding of a protein. As a crucial step of biological event extraction, event trigger identification has attracted much attention and many methods have been proposed. Traditionally those methods can be categorised into rule-based approach and machine learning approach and machine learning-based approaches have demonstrated its potential and outperformed rule-based approaches in many situations. However, machine learning-based approaches still face several challenges among which a notable one is how to model semantic and syntactic information of different words and incorporate it into the prediction model. There exist many ways to model semantic and syntactic information, among which word embedding is an effective one. Therefore, in order to address this challenge, in this study, a word embedding assisted neural network prediction model is proposed to conduct event trigger identification. The experimental study on commonly used dataset has shown its potential. It is believed that this study could offer researchers insights into semantic-aware solutions for event trigger identification.

The limited grain size (