Search

The structure and electronic and spintronic properties of two-dimensional (2D) ternary compounds ABC (A = Sb, Bi; B = Se, Te; C = Br; I) monolayers are investigated using the first-principles method. The ABC monolayers possess typical Janus structures with a considerable potential gradient normal to the surface, inducing intrinsic Rashba spin splitting (RSS) at the conduction band minimum near the

Combined with first-principles calculations and semiclassical Boltzmann transport theory, Janus {\alpha}-STe2 and {\alpha}-SeTe2 monolayers are investigated systematically. Janus {\alpha}-STe2 and {\alpha}-SeTe2 monolayers are indirect semiconductors with band gaps of 1.20 and 0.96 eV. It is found they possess ultrahigh figure of merit (ZT) values of 3.9 and 4.4 at 500 K, much higher than that of the pristine {\alpha}-Te monolayer (2.8). The higher ZT originates from Janus structures reduce lattice thermal conductivities remarkably compared with pristine {\alpha}-Te monolayer. The much higher phonon anharmonicity in Janus monolayers leads to significant lower lattice thermal conductivity. It is also found electronic thermal conductivity can play an important role in thermoelectric efficiency for the materials with quite low lattice thermal conductivity. This work suggests the potential applications of Janus {\alpha}-STe2 and {\alpha}-SeTe2 monolayers as thermoelectric materials and highlights Janus structure as an effective way to enhance thermoelectric performance.

We summarize the strategies for improving the waterproofness of Mn4+-doped fluoride phosphors, including organic coating, inorganic heterogeneous/homogeneous coating, surface deactivation, preparation of single crystal phosphor, and other methods.

A hydrogen processing strategy is developed to enable bulk LaNi5 to attain high activity and long‐term stability toward the electrocatalytic oxygen evolution reaction (OER). By a combination of in situ Raman and quasi in situ X‐ray absorption (XAS) spectra, secondary‐electron‐excited scanning transmission electron microscopy (STEM) patterns as well as the Rietveld method and density functional theory (DFT) calculations, it is discovered that hydrogen‐induced lattice distortion, grain refinement, and particle cracks dictate the effective reconstruction of the LaNi5 surface into a porous hetero‐nanoarchitecture composed of uniformly confined active γ‐NiOOH nanocrystals by La(OH)3 layer in the alkaline OER process. This significantly optimizes the charge transfer, structural integrity, active‐site exposure, and adsorption energy toward the reaction intermediates. Benefiting from these merits, the overpotential (322 mV) at 100 mA cm−2 for the hydrogen‐processed OER catalyst deposited on nickel foam is reduced by 104 mV as compared to the original phase. Notably, it exhibits remarkable stability for 10 days at an industrial‐grade current density of more than 560 mA cm−2 in alkaline media.

Defect engineering is an important strategy to regulate electronic structure of electrocatalysts for electrochemical N2 fixation, aiming at improving the electron state density and enhancing the adsorption and activation of inert N2. In this paper, a high-temperature strategy to anneal the natural molybdenite under Ar atmosphere was developed, and the as-obtained molybdenite with S vacancies boosted a high activity for N2 reduction reaction. In 0.1 M HCl, the catalyst annealed at 800 °C exhibits a high Faradic efficiency of 17.9% and a NH3 yield of 23.38 μg h−1 mg-1cat. at −0.35 V versus reversible hydrogen electrode, two times higher than that of the pristine molybdenite. The facile one-step annealing method introduces the defects (e.g., S vacancies) in the surface of the natural molybdenite particles to prepare catalysts for generating ammonia by reducing nitrogen at room temperature under ordinary pressure, promoting the development of low-carbon economic prospect.

Due to the low solubility of BaF2, the BaTiF6:Mn4+ phosphor for whitelight-emitting diodes application has been generally synthesized by the hydrothermal route, during which process the valence of the manganese dopant is difficult to be controlled as tetravalent. In this paper, a new synthesis method that proceeded at room temperature was reported. This method uses BaTiOF4 as the precursor and allows for the control of the phase transformation rate from BaTiOF4 to BaTiF6 in the K2MnF6/HF acid solution. Benefitting from that, we successfully prepared red-emitting BaTiF6:Mn4+ elongated crystals with a single-crystal nature up to a record-breaking length of 200-300 μm. The effects of the crystallinity of the BaTiOF4 precursor on its phase transformation rate into BaTiF6 and on the optimal Mn4+ doping concentration were studied. The BaTiF6:Mn4+ single-crystal phosphor exhibits relatively excellent hydrolysis-resistant behavior after being immersed in water for 3 h, at which condition the commercial K2SiF6:Mn4+ has become brown. This study may inspire the room-temperature preparation of other hydrolysis-resistant alkali earth fluorotitanate or fluorosilicate phosphors with stable tetravalent manganese doping.

The utilization of clean hydrogen energy is becoming more feasible for the sustainable development of this society. Considering the safety issues in the hydrogen production, storage, and utilization, a sensitive hydrogen sensor for reliable detection is essential and highly important. Though various gas sensor devices are developed based on tin oxide, tungsten trioxide, or other oxides, the relatively high working temperature, unsatisfactory response time, and detection limitation still affect the extensive applications. In the current study, an amorphous tungsten trioxide (a-WO

Hot electron shows the merits of activating reactants and reducing the activation energy barrier (Ea) of a reaction through electron donation. However, a comprehensive understanding on the intrinsic driving force of electron-donating effect is lacking, let alone the precise manipulation of electron donation processes. Herein, the essential and promotional role of hot electron energy on electron-donating effect was elucidated using molecular oxygen activation (MOA) as a model reaction. Through providing an available electron source to the conventional photo-thermal conversion system, the high energy carried by hot electrons was liberated and greatly enhanced the electron donation towards the LUMO (π*) orbit of O2. The energy was also transferred to O2 and elevated the potential energy surface (PES) of MOA, which was reflected by the enhanced formation of superoxide oxygen anions. As predicted, the Ea of MOA decreased by 45.3% and exhibited a substantial light dependence, demonstrating that MOA became energy-efficient due to improved exploitation and conversion of photon energies.

A single-crystalline defect-less phosphor is desired for efficient luminescence of the therein doped optical activators. In this paper, microsized MgAl2O4:Mn4+ single-crystal phosphors with bright red luminescence were grown in molten LiCl salt at 950 °C, for application in blue LED pumped white lighting. By comparing the phosphor formation from various Mg2+- and Al3+-bearing sources, both the template-formation and the dissolution-diffusion processes were evidenced to account for the formation of the microsized MgAl2O4:Mn4+ crystallites. Using nano γ-Al2O3 as the Al3+-bearing precursor, the uniform MgAl2O4:Mn4+ microcrystallites with a {111} planes-exposed tetragonal bipyramid morphology were obtained. The photoluminescence property was studied at various temperatures, and Mg ↔ Al anti-site disorder induced luminescence broadening was discussed. The Mn4+ 2Eg → 4A2g transition in MgAl2O4 shows a quite short luminescence wavelength peaking at 651 nm and ultrabroadband emission extending to 850 nm. The luminescence is relatively robust against thermal effect with relatively high thermal quenching temperature of 400 K and activation energy of 0.23 eV. Employing the red-emitting MgAl2O4:Mn4+ crystallites, blue LED pumped white lighting prototypes were fabricated which simulate the solar-like spectrum and show neutral to warm white.

Developing efficient catalysts for the oxygen evolution reaction (OER) is critical to supplying renewable and clean energy. In heterogeneous catalysis, a strategy with a second active site has been developed to improve OER catalytic performance. Here we propose the design of dual-active sites consisting of two adjacent TMN4(OH) (TM = Cr/Mn/Fe/Co/Ni/Cu) sites confined to a nanotube and use first-principles calculations to investigate their OER mechanisms. It was found that the OER pathway including the chemical step of O2 generation from direct O–O coupling (*O + *O → 2* + O2, ΔG5) can be carried out on the TMN4(OH) dual-active sites. It associates with a newly linear OER activity trend function, with ΔG5 as the descriptor. Importantly, the potential-independent process should occur under mild conditions, which limits ΔG5 to be relatively negative. This law of thermodynamic feasibility gives an optimal overpotential (0.18 V) for the FeN4(OH) dual-active sites. Besides, the ΔG5 descriptor is only related to the binding energy of *O, implying a facile route to achieve optimal activity. Our proposed dual-active-sites catalysis provides new insights into the fundamental understanding of OER mechanisms and theoretical guidelines for the accelerated discovery of efficient OER catalysts.

Mexican-hat-like band dispersion is extremely critical to the realization of hole-doping-induced magnetism in monolayer metal monochalcogenides. However, it is absent from transition-metal dichalcogenides (TMDCs), i.e., WSe2. Herein, using first-principles calculations, we show that Mexican-hat-like band dispersion can be achieved by applying interlayer strain (e) in the WSe2/SnS2 van der Waals (vdW) heterostructure when e exceeds 15%. This is because in the strain-induced distorted trigonal prismatic crystal field, at the valence band edge, the W_dz2 orbitals shift upward around the Γ point, while the double-degenerate W_dxy/dx2-y2 orbitals shift downward at the K point, resulting in Mexican-hat-like band dispersion near the Γ point when the energy level of the Γ point surpasses that of the K point. On account of the appearance of the Mexican-hat-like band edge (MHBE), hole-doping in the strained WSe2/SnS2 heterostructure induces magnetization readily from the nonmagnetized phase. Our findings may provide a new strategy for the realization of magnetized TMDC-based vdW heterostructures.

Vacancy engineering is deemed as one of the powerful protocols to tune the catalytic activity of electrocatalysts. Herein, Se vacancy with charge polarization is created in the NiSe2 structure NiSe2 VSe via a sequential phase conversion strategy. By a combined analysis of the Rietveld method, transient photovoltage spectra TPV , in situ Raman and density functional theory DFT calculation, it is unequivocally discovered that the presence of charge polarized Se vacancy is beneficial for stabilizing the structure, decreasing the electron transfer kinetics, as well as optimizing the free adsorption energy of reaction intermediate during two electron oxygen reduction reaction 2e amp; 8722; ORR . Benefiting from these merits, the as prepared NiSe2 VSe delivered the highest selectivity of 96 toward H2O2 in alkaline media, together with a selectivity higher than 90 over the wide potential range from 0.25 to 0.55 V, ranking it in the top level among the previously reported transition metal based electrocatalysts. Most notably, it also displayed admirable stability with only a slight selectivity decay after 5000 cycles of accelerated degradation test ADT

Due to the low solubility of BaF

Charge doping is an effective way to induce metal-insulate transition (MIT) in correlated materials for many important utilizations, which is however practically limited by problem of low stability. In this study, we have achieved pronounced phase modulation and stabilized the metallic state of monoclinic vanadium dioxide (VO2) at room temperature, via a novel electron-proton co-doping mechanism driven by surface absorption of self-assembled L-ascorbic acid (AA) molecules. The ionized AA- species in solution donate effective electrons to the adsorbed VO2 surface, which then electrostatically attract surrounding protons to penetrate, and eventually results in stable hydrogen-doped metallic VO2. The variations of phase and electronic structures as well as the electron occupancy of V-3d/O-2p hybrid orbitals were examined by synchrotron characterizations and first-principle theoretical simulations, which explain the formation of stable metallic state. Importantly, the adsorbed molecules protect hydrogen dopants from escaping out of lattice and thereby stabilize the metallic phase for VO2. Such an electron-proton co-doping mechanism driven by suitable molecules absorption would open a new door for engineering properties of correlated oxide materials., 25 pages, 5 figures

Polypyrrole (PPy) used as popular coatings can improve the electrochemical performance of electrodes greatly; however, uniform coatings of PPy on nanostructures is a challenging task in a solution system. Substitution for liquid phase polymerization reaction, herein a developed evaporation method is reported to make pyrrole vapor in situ polymerization on CuO arrays for the uniform PPy coatings. With the help of this uniform PPy coatings, the unique structure of arrayed CuO film can well maintain the stability of mechanical structures and has rapid transmission of lithium ions and electrons during charge/discharge processes, hence harvesting a high lithium storage. Electrochemical tests indicate that PPy can not only enhance the specific capacities of CuO anodes greatly but also improve the cyclic stability at a high-current density. The specific capacity of the CuO@PPy integrated anode can be up to 561 mAh g−1 at 1 C after 100 cycles, which is increased by almost 33% than that of the pure CuO anode.

Graphene hydrogenation is an attractive approach to functionalize graphene. However, the hydrogenating treatment could only be achieved under harsh conditions due to the weak hydrogen affinity of graphene. It has also made the direct writing of electronic circuits on graphene by hydrogenation very difficult. Here we propose a metal-enhanced approach to hydrogenate graphene with atomic pattern that enables to produce hydrogenation pattern on demand. First-principles calculations reveal that certain metals (Cu, Ag, Al) attached to graphene can significantly lower the energy barrier for hydrogen binding process, while the hydrogen binding energy itself is much enhanced. Such metal-promoted hydrogenation is spatially localized, which paves the way to precisely write pre-designed hydrogenation patterns on graphene with well-controlled metallic clusters and tips.

This letter reports the structural, dielectric, ferroelectric, and magnetic properties of Fe substituted nonstoichiometric STO ceramics. X-ray diffraction and Scanning electron microscope reveal the microstructure of the samples. The room temperature multiferroicity of the Fe-doped Ti-rich STO ceramics is successfully realized by M-H hysteresis loop, P-E hysteresis loop and magnetodielectric measurement. The origins of ferroelectricity may be related to the lattice distortions and antisite-like defects with net local dipoles. The ferromagnetism are mainly contributed by the competitions among the double exchange interactions, super-exchange interactions and the non-linear ferromagnetic exchange coupling. In addition, the ordered spin arrangement of the ferromagnetism is formed by the exchange interaction of Fe atom using first principle simulations.

Tuning the interlayer twist angle provides a new degree of freedom to exploit the potentially excellent properties of two dimensional layered materials. Here we investigate the structural and electronic properties of twisted bilayer SiC under a series of twist angles using first principle calculations. The interplay of interlayer van der Waals interactions and intralayer strain induces dramatic in-plane and out-of-plane displacements. The expansion or contraction of specific stacking domains can be interpreted as the result of the energy minimization rule. By means of order parameter analysis, the triangular or hexagonal strain soliton networks are found to separate adjacent stacking domains. The unique overlapped zigzag atom lines in strain solitons provide a unique characteristic for experimental imaging. The top valence band and bottom conduction band evolve into flat bands with the smallest band width of 4 meV, indicating a potential Mott-insulator phase. The moire-potential-modulated localization pattern of states in the flat band, which is dependent sensitively on the structure relaxation, controls the flat band width. The moire-pattern-induced structural and electronic properties of twisted bilayer SiC are promising for application in nanoscale electronic and optical devices.

A single-crystalline defect-less phosphor is desired for efficient luminescence of the therein doped optical activators. In this paper, microsized MgAl

Mexican-hat-like band dispersion is extremely critical to the realization of hole-doping-induced magnetism in monolayer metal monochalcogenides. However, it is absent from transition-metal dichalcogenides (TMDCs), i.e., WSe2. Herein, using first-principles calculations, we show that Mexican-hat-like band dispersion can be achieved by applying interlayer strain (ε) in the WSe2/SnS2 van der Waals (vdW) heterostructure when ε exceeds 15%. This is because in the strain-induced distorted trigonal prismatic crystal field, at the valence band edge, the W_dz2 orbitals shift upward around the Γ point, while the double-degenerate W_dxy/dx2-y2 orbitals shift downward at the K point, resulting in Mexican-hat-like band dispersion near the Γ point when the energy level of the Γ point surpasses that of the K point. On account of the appearance of the Mexican-hat-like band edge (MHBE), hole-doping in the strained WSe2/SnS2 heterostructure induces magnetization readily from the nonmagnetized phase. Our findings may provide a new strategy for the realization of magnetized TMDC-based vdW heterostructures.

Hydrogen doping of metal oxide semiconductors is promising for manipulation of their properties toward various applications. Yet it is quite challenging because it requires harsh reaction conditions and expensive metal catalysts. Meanwhile, acids as a cheap source of protons have long been unappreciated. Here, we develop a sophisticated acid-metal treatment for tunable hydrogenation of metal oxides at ambient conditions. Using first-principles simulations, we first show that, with proper work function difference between the metal and metal oxide, H-diffusion into negatively charged metal oxide can be well controlled, resulting in tunable H-doping of metal oxides with quasi-metal characteristics. This has been verified by proof-of-concept experiments that achieved the controllable hydrogenation of WO3 using Cu and hydrochloric acid at ambient conditions. Further, H-doping of other metal oxides (TiO2/Nb2O5/MoO3) has been achieved by metal-acid treatment and induced a change in properties. Our work provides a promising way to tailor metal oxides via tunable H-doping.

Optimizing physical or chemical properties via electronic phase transitions is important for developing high-performance semiconductor materials. Using first-principles calculations, we established hydrogen doping (H-doping) as an alternative strategy for modulating phase transitions in metal oxide semiconductors. We found that H-doping can induce an insulator-to-metal phase transition in rutile TiO2 or wurtzite ZnO, a metal-to-insulator phase transition in rutile VO2, and sequential insulator-metal-insulator phase transitions in SnO2. H-doping not only creates defect-induced states inside the original bandgap but also induces new occupancy patterns in conduction band edge states. A linear relationship between occupation of the conduction band edge and H-doping concentration was found, offering the possibility of precisely tuning the material's free-carrier concentration, electrical conductance, and photoabsorption ability. We envision that this work will provide a promising way to tune electrical phase transitions in metal oxides.

In image super-resolution task, the existing convolutional neural network methods proceed to increase the number of network layers and filters to achieve better performance. Nevertheless, such approaches not only lead to a dramatic increase in network parameters, but also restrict the practical application of super-resolution methods. In order to address this problem, we propose a lightweight model called Channel Rearrangement Multi-Branch Network (CRMBN) for super-resolution of single images. Specifically, we design a channel rearrangement algorithm based on the total variation of the feature maps. It is inspired by the fact that the feature maps with high total variation contain more high-frequency details, which are valuable for super-resolution reconstruction. Therefore, for the super-resolution networks, the more feature maps with high total variation, the better performance of reconstruction. The rearranged channels are divided into two groups, one with high total variation and the other with the opposite. In order to reduce the parameters while mining for more details, we send the features with low total variation to the deep network. Finally, high total variation features and deep features are fused to reconstruct high-resolution image. The experimental results show that compared with other lightweight models, the proposed method can offer a favorable improvement in terms of PSNR and SSIM.

論説(Article)

The use of electric-field to manipulate the transport properties of correlated oxides is promising for achieving nano-functional electronic devices. As a typical correlated oxide material, vanadium dioxide (VO2) displays a special metal-insulator transition (MIT) at about 340 K. In this work, we select a water-free electrolyte gel, Li+/propylene carbonate, to achieve a non-volatile and reversible Li-doping and phase modulation in nano-VO2 crystal film under gating voltages. Synchrotron characterizations indicate the originally insulating VO2 undergoes an effective structure change and an increased V 3d-O 2p hybrid t2g-orbital occupancy, which is responsible for the metallic state formation as proved by first-principle calculation. The field-driving Li-doping shows pronounced facet dependence, indicating the existence of energetically favored channels for Li-ions diffusion along V-V chains as proved by dynamic stimulation. Our current findings will supply opportunities for the electric-field control of atomic sieve, correlated ionitronics and synaptic transistor.

Here we demonstrate that the performance of TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced through oxygen vacancy doping. The ion irradiation is a simple method to introduce oxygen vacancies on the surface and into the interior of TiO2 for making oxygen-deficient titania (TiO2-x). The TiO2-x thin films exhibit obvious increase in the performance of photoelectrochemical water splitting under light irradiation. The photoconversion efficiency η of the TiO2-x photoanode is 0.5-fold higher than that of the pristine TiO2 photoanode, which benefits from the introducing of oxygen vacancies produced by ion irradiation. While the irradiation-induced titanium vacancies act as trapping centers for charge carriers and decrease the photoelectrochemical performance of the samples. Positron annihilation spectroscopy (PAS) was used to study the type of the formed vacancies. Combining experimental with theoretical study, this study demonstrates that ion irradiation technique combing with thermal annealing could be an effective way to enhance the performance of photoanode for water splitting.

The construction of an efficient and sensitive platform for HgII analysis is of great importance because of the potential hazards of HgII to human safety and environmental stability. Herein, we propose a new strategy for HgII sensing based on the synergistic effect of fluorescent MoO3–x quantum dots (QDs) and HgII on cobalt porphyrin formation, in which the accelerated reaction rate far exceeds the simple sum of the contributions from the individuals. A first-principles theoretical study reveals the synergistic mechanism of cobalt(II) porphyrin generation, with mercury(II) porphyrin and CoII being docked together on the MoO3–x QD platform. The synergistic reaction results in a distinct and rapid evolution of the optical properties of porphyrins and MoO3–x QDs, facilitating kinetic HgII sensing and intracellular HgII imaging. Compared with the traditional “substitution reaction” method in the presence of an individual accelerator, the present strategy can markedly shorten the analysis time, largely improve...

The stabilization of semiconductor against photocorrosion has become one of the most essential targets in photoelectrochemical water splitting. Herein, a research of three mixing enhancement strategies of WO3/BiVO4 heterojunction, W doping, and oxygen vacancy formation can be made to incorporate into such a nanostructure during the preparation of BiVO4 in terms of PEC performance improvement. The WO3 layer not only facilitated the electron transfer, but importantly, was used as a diffusion source for W doping which brought oxygen vacancies on the bulk material. Moreover, the introduction of different W doping profiles,- bottom, middle, and top, all electrodes exhibited a photo-activation character with the improved photocurrent and the negative shift of onset potential. The bottom W doping led to the most notable enhancement in charge separation efficiency on BiVO4 electrode, which yielded the close photocurrent densities of ∼4.4 mA cm−2 at 1.23 VRHE under front and back 1 sun illumination. More importantly, the cocatalyst-free W:BiVO4-Ov photoanode present a favorable stability during 25 h test applied at 1.0 VRHE. By experimental and theoretical arguments, it demonstrated that the multiple collaborative strategies shed light on designing efficient and stable photoelectrodes for solar energy conversion.