Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In this work, we proposed α-TeB and β-TeB monolayers using density functional theory (DFT) combined with the particle swarm-intelligent global structure search method. The high dynamical and thermal stabilities of two TeB structures indicate high feasibility for experimental synthesis. The electronic structure calculations show that the two structures are indirect bandgap semiconductors with bandgaps of 2.3 and 2.1 eV, respectively. The hole mobility of the β-TeB sheet is up to 6.90 × 102 cm2 V-1 s-1. By reconstructing the two structures, we identified two new horizontal and lateral heterostructures, and the lateral heterostructure presents a direct band gap, indicating more probable applications could be further explored for TeB sheets.
The high pressure structure and elastic properties of calcium azide (Ca(N3)2) were investigated using in-situ high-pressure X-ray diffraction and Raman scattering up to 54 GPa and 19 GPa, respectively. The compressibility of Ca(N3)2 changed as the pressure increased, and no phase transition occurred within the pressure from ambient pressure up to 54 GPa. The measured zero-pressure bulk modulus of Ca(N3)2 is higher than that of other alkali metal azides, due to differences in the ionic character of their metal-azide bonds. Using CASTEP, all vibration modes of Ca(N3)2 were accurately identified in the vibrational spectrum at ambient pressure. In the high-pressure vibration study, several external modes(ext.) and internal bending modes(ν2) of azide anions(N3−) softened up to ~7 GPa and then hardened beyond that pressure. This evidence is consistent with the variation observed in the FE-fE data analyzed from the XRD result, where a turning point appears on the curve at 7.1 GPa. The main behaviors under pressure are the alternating compression, rotation, and bending of N3− ions. The bending behavior makes the structure of Ca(N3)2 more stable under pressure.
Semiconductor/metal composite nanomaterials have been used as surface-enhanced Raman scattering (SERS) active substrates and have attracted increasing attention due to their widespread applications in both optical and material fields. Here, we report a facile strategy to prepare highly sensitive SERS substrates with excellent reproducibility and stability based on uniform and well-controlled Ag nanoparticle (NP) decorated Cu2O nanoframes. Our strategy is a unique one-pot procedure. Simply, hollow Cu2O/Ag composite nanoframes (Cu2O/Ag CNFs) with tunable silver content have been successfully designed and constructed by reduction of Ag+ with sodium citrate in a 14 day old Cu2O-containing mother solution, and then a second component (Ag) was directly deposited onto primary nanomaterials (Cu2O nanoframes). There is an optimum amount of Ag NPs. When 0.40 mM AgNO3 is used, the prepared Cu2O/Ag CNFs show significantly improved SERS properties with an enhancement factor of ~105. Furthermore, the enhancement mechanism, reproducibility and stability of Cu2O/Ag CNFs are investigated in detail. The excellent properties of the prepared Cu2O/Ag CNFs suggest that this substrate has a potential application in SERS detection.
Realizable atomization and mixing of high temperature-rise combustors in a wide range of operating conditions is the issue of ensuring the stability of aviation turbine engines, and non-equilibrium plasma has garnered significant attention as a potential active control method to improve engine atomization and ignition. In this work, the "non-equilibrium gliding arc plasma excited atomization" method is proposed. Based on a special designed three-swirl combustor for laser diagnosis of atomization characteristics, experimental studies of atomization characteristics are analyzed in detail. We also construct Rosin-Rammler distribution function models under different excitation conditions. The experiments have been conducted in kerosene-N2 flows in various gas-fuel ratios and nitrogen flow rates. Experimental results are summarized as follows: The coupled mechanisms of gas-fluid ratio and flow rate dominated atomization process within pre-combustion nozzle. Atomization deterioration in the combustion chamber was caused by higher gas-fluid ratios and lower flow rates, resulting in poor spray desperation, narrowed spray cone angle, and large fuel droplet sizes. Gliding arc discharge in kerosene-nitrogen spray had a dynamic self-regulation process related to gas fluid ratios and flow rates. An increase in the nitrogen flow rates, along with a higher concentration of fuel droplets per unit volume and the aggregation of droplet clusters, exacerbated discharge instability and enhanced energy dissipation. Gliding arc plasma discharge induced the coupled electric-thermo-aerodynamic effect, forming a plasma/kerosene interaction zone at the exit of the pre-combustion nozzle. This, in turn, further strengthened the fragmentation, atomization, and mixing of fuel droplets, thereby improving the spatial spray distribution and the droplet size distribution in combustion chambers. Our work substantiates the potential advantages of gliding arc plasma-excited atomization technology for extensive modulation of atomization performance in various operating conditions. It also provides additional evidence for its deployment in advanced combustion chambers of aviation turbine engines.
The binary H-O system almost exclusively exists in the form of water ice with stoichiometry of ${\mathrm{H}}_{2}\mathrm{O}$ in a wide range of pressure (\ensuremath{\sim}5 TPa) that is one of the most abundant substances in the solar system. Hydrogen peroxide (${\mathrm{H}}_{2}{\mathrm{O}}_{2}$) is only metastable at ambient condition. We herein report a stable ${\mathrm{H}}_{2}{\mathrm{O}}_{2}$ phase at high pressure identified by first-principles calculations in combination with a swarm-intelligence structure search. The predicted ${\mathrm{H}}_{2}{\mathrm{O}}_{2}$ compound is formed by stacking of an intriguing planar ${\mathrm{H}}_{2}{\mathrm{O}}_{2}$ molecule different from the metastable three-dimensional isomer at ambient condition. The planarity of hydrogen peroxide molecules is expected to be caused by the steric repulsion between molecules at high pressure, which is responsible for the stability of the crystal. The phase is energetically stable in the pressure range of \ensuremath{\sim}423--600 GPa. It is thus a low-pressure phase of binary H-O system with H:O stoichiometry other than 2:1 and promises to be accessible in static compression experiment.
The forms of boron atoms are many and varied in the structure of transition metal borides (TMBs). The form of boron atoms determines the structure, morphology, and properties of borides. Herein, transition metal monoborides (CrB and WB) with different arrangement of one-dimensional (1D) boron chains were synthesized under high pressures and high temperatures. The 1D boron chains between the interlayers of CrB are parallel to one another, while the 1D boron chains between the interlayers of WB are perpendicular to one another. The morphologies of CrB and WB also show large differences due to the difference in 1D boron chain arrangement. As electrocatalysts for hydrogen evolution reactions (HERs), CrB and WB show good catalysis activity and durability. WB has the smallest overpotential (210 mV) and Tafel slope (90.09 mV dec−1), which is mainly attributed to the intercrossing boron chains improving the electrical properties of WB, as well as the 5d electrons of W being more chemically active. The TOF value of WB is 1.35 s−1, proving that WB has a higher intrinsic catalytic activity during HERs. This work provides a data reference for the development of high-efficiency electrocatalysts.
Abstract The search for new inorganic electrides has attracted significant attention due to their potential applications in transparent conductors, battery electrodes, electron emitters, as well as catalysts for chemical synthesis. However, only a few inorganic electrides have been successfully synthesized thus far, limiting the variety of electride examples. Here, we show the stabilization of inorganic electrides in the Ti-rich Ti–O system through first-principles calculations in conjunction with swarm-intelligence-based CALYPSO method for structure prediction. Besides the known Ti-rich stoichiometries of Ti 2 O, Ti 3 O, and Ti 6 O, two hitherto unknown Ti 4 O and Ti 5 O stoichiometries are predicted to be thermodynamically stable at certain pressure conditions. We found that these Ti-rich Ti–O compounds are primarily zero-dimensional electrides with excess electrons confined in the atom-sized lattice voids or between the cationic layers playing the role as anions. The underlying mechanism behind the stabilization of electrides has been rationalized in terms of the excess electrons provided by Ti atoms and their accommodation of excess electrons by multiple cavities and layered atomic packings. The present results provide a viable direction for searching for practical electrides in the technically important Ti–O system.
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