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Semiconductor alloy materials are highly versatile due to their adjustable properties; however, exploring their structural space is a challenging task that affects the control of their properties. Traditional methods rely on ad hoc design based on the understanding of known chemistry and crystallography, which have limitations in computational efficiency and search space. In this work, we present ChecMatE (Chemical Material Explorer), a software package that automatically generates machine learning potentials (MLPs) and uses global search algorithms to screen semiconductor alloy materials. Taking advantage of MLPs, ChecMatE enables a more efficient and cost-effective exploration of the structural space of materials and predicts their energy and relative stability with ab initio accuracy. We demonstrate the efficacy of ChecMatE through a case study of the InxGa1−xN system, where it accelerates structural exploration at reduced costs. Our automatic framework offers a promising solution to the challenging task of exploring the structural space of semiconductor alloy materials. [ABSTRACT FROM AUTHOR]

A two-dimensional symmetric fluid model is established to study the influence of radio frequency (RF) wave driving frequency on the capacitively coupled plasma discharge. The relationship between the driving frequency and electron density is obtained by solving the electron energy balance equation. The calculation results show that the average electron density first increases rapidly with the increase in driving frequency and then gradually tends to saturation at a threshold frequency. A fluid simulation is also carried out, which provides similar results. Physical studies on this phenomenon are conducted, revealing that the essence of this phenomenon is due to the inability of electrons to quickly respond to potential changes within the boundary sheath when the driving frequency of RF exceeds the plasma frequency. In addition, it is also found that increasing gas pressure can enhance the electron density and the type of gas can also affect the electron density. [ABSTRACT FROM AUTHOR]

Unraveling the origin of Helmholtz capacitance is of paramount importance for understanding the interfacial structure and electrostatic potential distribution of electric double layers (EDL). In this work, we combined the methods of ab initio molecular dynamics and classical molecular dynamics and modeled electrified Cu(100)/electrolyte and graphene/electrolyte interfaces for comparison. It was proposed that the Helmholtz capacitance is composed of three parts connected in series: the usual solvent capacitance, water chemisorption induced capacitance, and Pauling repulsion caused gap capacitance. We found the Helmholtz capacitance of graphene is significantly lower than that of Cu(100), which was attributed to two intrinsic factors. One is that graphene has a wider gap layer at interface, and the other is that graphene is less active for water chemisorption. Finally, based on our findings, we provide suggestions for how to increase the EDL capacitance of graphene-based materials in future work, and we also suggest that the new understanding of the potential distribution across the Helmholtz layer may help explain some experimental phenomena of electrocatalysis. [ABSTRACT FROM AUTHOR]

Aqueous rutile TiO2(110) is the most widely studied water–oxide interface, and yet questions about water dissociation are still controversial. Theoretical studies have systematically investigated the influence of the slab thickness on water dissociation energy (Ediss) at 1 monolayer coverage using static density functional theory calculation and found that Ediss exhibits odd–even oscillation with respect to the TiO2 slab thickness. However, less studies have accounted for the full solvation of an aqueous phase using ab initio molecular dynamics due to high computational costs in which only three, four, and five trilayer models of rutile(110)–water interfaces have been simulated. Here, we report Machine Learning accelerated Molecular Dynamics (MLMD) simulations of defect-free rutile(110)–water interfaces, which allows for a systematic study of the slab thickness ranging from 3 to 17 trilayers with much lower costs while keeping ab initio accuracy. Our MLMD simulations show that the dissociation degree of surface water (α) oscillates with the slab thickness and converges to ∼2% as the TiO2 slab becomes thicker. Converting α into dissociation free energy (ΔAdiss) and comparing with dissociation total energy Ediss calculated with a single monolayer of water, we find that the full solvation of the interfaces suppresses surface water from dissociating. It is interesting to note that the machine learning potential trained from the dataset containing exclusively the five trilayer TiO2 model exhibits excellent transferability to other slab thicknesses and further captures the oscillating behavior of surface water dissociation. Detailed analyses indicate that the central plane in odd trilayer slabs modulates the interaction between double trilayers and, thus, the bonding strength between terminal Ti and water, which affects pKa of surface water and water dissociation degree. [ABSTRACT FROM AUTHOR]

It is worth understanding the potentials of zero charge (PZCs) and structures of stepped metal/water interfaces, because for many electrocatalytic reactions, stepped surfaces are more active than atomically flat surfaces. Herein, a series of stepped Pt/water interfaces are modeled at different step densities with ab initio molecular dynamics. It is found that the structures of Pt/water interfaces are significantly influenced by the step density, particularly in regard to the distribution of chemisorbed water. The step sites of metal surfaces are more preferred for water chemisorption than terrace sites, and until the step density is very low, water will chemisorb on the terrace. In addition, it is revealed that the PZCs of stepped Pt/water interfaces are generally smaller than that of Pt(111), and the difference is mainly attributed to the difference in their work function, providing a simple way to estimate the PZCs of stepped metal surfaces. Finally, it is interesting to see that the Volta potential difference is almost the same for Pt/water interfaces with different step densities, although their interface structures and magnitude of charge transfer clearly differ. [ABSTRACT FROM AUTHOR]

Fast evolution of modern society stimulates intense development of new materials with novel functionalities in energy and environmental applications. Due to rapid progress of computer science, computational design of materials with target properties has recently attracted a lot of interest. Accurate and efficient calculation of fundamental thermodynamic properties, including redox potentials, acidity constants, and solvation free energies, is of great importance for selection and design of desirable materials. Free energy calculation based on ab initio molecular dynamics (AIMD) can predict these properties with high accuracy at complex environments, however, they are being impeded by high computational costs. To address this issue, this work develops an automated scheme that combines iterative training of machine learning potentials (MLPs) and free energy calculation and demonstrates that these thermodynamic properties can be computed by ML accelerated MD with ab initio accuracy and a much longer time scale at cheaper costs, improving poor statistics and convergence of numerical integration by AIMD. Our automated scheme lays the foundation for computational chemistry-assisted materials design. [ABSTRACT FROM AUTHOR]

We demonstrate that beam–beam interference can significantly enhance the efficiency of multi-beam traveling-wave devices. Our theoretical analysis explains that a positive coupling of the space-charge field enhances the beam–wave interaction, resulting in increased efficiency in multi-beam devices with beam–beam interference. We validate this mechanism by performing particle-in-cell simulations on 670 GHz grid-loaded rectangular waveguide backward-wave oscillators. Both the multi-beam and single-beam devices exhibit the same dispersion of operating modes and operate under identical conditions. The simulation results indicate that the efficiency of the multi-beam device is up to 1.58 times higher than that of the single-beam device. Additionally, simulations are performed on the same structure at 340 and 1030 GHz, demonstrating efficiency improvements that support the proposed mechanism. These findings present a novel approach for increasing the efficiency of traveling-wave devices. [ABSTRACT FROM AUTHOR]

The characterization and identification of the dynamics of cluster catalysis are crucial to unraveling the origin of catalytic activity. However, the dynamical catalytic effects during the reaction process remain unclear. Herein, we investigate the dynamic coupling effect of elementary reactions with the structural fluctuations of sub-nanometer Au clusters with different sizes using ab initio molecular dynamics and the free energy calculation method. It was found that the adsorption-induced solid-to-liquid phase transitions of the cluster catalysts give rise to abnormal entropy increase, facilitating the proceeding of reaction, and this phase transition catalysis exists in a range of clusters with different sizes. Moreover, clusters with different sizes show different transition temperatures, resulting in a non-trivial size effect. These results unveil the dynamic effect of catalysts and help understand cluster catalysis to design better catalysts rationally. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated the effective enhancement of initiation stability in the combustor of a rotating detonation engine through the use of a pre-detonator. However, when a stable detonation propagates from a small-diameter pre-detonator into a larger-diameter combustor, a brief failure occurs, followed by the re-initiation of the detonation wave. This failure is attributed to detonation diffraction as the wave passes through a sudden expansion section. This study systematically investigates the phenomenon of detonation diffraction and re-initiation through 2D numerical simulations. The effect of the diameter ratio between the pre-detonator and combustor on detonation propagation is examined by adjusting the diameter ratio D/d in the range of 1.1–2.7, where D and d represent the diameters of the larger (corresponding to the combustor) and smaller (corresponding to the pre-detonator) tubes, respectively. Various modes of detonation propagation and the corresponding evolution of the detonation wave are observed. The results reveal that as the detonation wave propagates through the sudden-expansion section, it diffracts at the corner and then rapidly decouples at the boundary. For D/d less than 1.3, the detonation wave can maintain its propagation by adjusting the structure of the cell distribution, referred to as the supercritical mode. As D/d increases, the detonation wave experiences initial failure followed by re-initiation, corresponding to the critical mode. When D/d exceeds 2.6, complete failure of detonation occurs and cannot be re-initiated, resulting in the sub-critical mode. Notably, under the critical mode, the distance LDDT required for re-initiation linearly increases with D/d (LDDT = 41.48(D/d) + 4.30). Additionally, the pressure of the triple point near the wall, formed by the convergence of the reflected shock wave, transmitted wave, and precursor shock wave, determines the possibility of local detonation initiation, which induces re-initiation in the testing tube. It is proposed that when the pressure of the triple point exceeds the theoretical pressure of post-shock (Ppost-shock), a local overdriven detonation occurs. Furthermore, when the convergent point of the transmitted shock wave propagates along the central line and passes through the flame front, local detonation can be induced as well. This study systematically illustrates the details of diffraction and re-initiation when the detonation wave passes through a sudden-expansion section. [ABSTRACT FROM AUTHOR]

Turbulence spreading and its effects on the edge flows and turbulence during sawtooth cycles in the J-TEXT tokamak plasmas are presented. These experiments were performed by Langmuir probe array and electron cyclotron emission. This study aims to understand the rapid transport phenomenon and the role of turbulence in driving flows. Beyond the mixing radius, the turbulence pulse moves faster than the sawtooth heat pulses. The results confirm the existence of turbulence spreading during sawtooth cycles. As the turbulence and heat pulses propagate to the edge, the edge turbulence, radial electric fields, pressures, and geodesic acoustic modes are all enhanced. Hysteresis relationships between the intensities of the turbulence and the radial electric fields are observed. The radial electric field lags behind the turbulence, and its intensity increases/decreases almost linearly with the increase/decrease in the turbulence intensity. The observation suggests that the edge flows are driven dominantly by turbulence during sawtooth cycles. The weakening/enhancement of the edge flows accompanies the increase/decrease in the ion collision rates during sawtooth cycles. [ABSTRACT FROM AUTHOR]

Solid-state electrolyte materials with superior lithium ionic conductivities are vital to the next-generation Li-ion batteries. Molecular dynamics could provide atomic scale information to understand the diffusion process of Li-ion in these superionic conductor materials. Here, we implement the deep potential generator to set up an efficient protocol to automatically generate interatomic potentials for Li10GeP2S12-type solid-state electrolyte materials (Li10GeP2S12, Li10SiP2S12, and Li10SnP2S12). The reliability and accuracy of the fast interatomic potentials are validated. With the potentials, we extend the simulation of the diffusion process to a wide temperature range (300 K–1000 K) and systems with large size (∼1000 atoms). Important technical aspects such as the statistical error and size effect are carefully investigated, and benchmark tests including the effect of density functional, thermal expansion, and configurational disorder are performed. The computed data that consider these factors agree well with the experimental results, and we find that the three structures show different behaviors with respect to configurational disorder. Our work paves the way for further research on computation screening of solid-state electrolyte materials. [ABSTRACT FROM AUTHOR]

Molecule self-assembly on the surface of alumina ceramic and its influence on the surface flashover characteristics of the alumina ceramic insulators were studied in this paper. First, octadecyltrichlorosilane was assembled on the surface of alumina ceramic insulators in the toluene solution. Then, 393 K thermal treatment of 2 h was conducted on the specimens to promote the growth of the molecule membrane. Quality detection of the prepared molecule membrane by Energy Dispersive x-ray Analysis and water contact angle test showed that the molecules were linked to the alumina surface and the arrangement of the molecules on the surface was regular and tight. Gas release characteristic suggested that the formation of the molecule membrane made the gas release rate of the treated alumina decrease. The flashover voltage test on the home-made, short-pulsed, high-voltage vacuum platform indicated that the flashover voltages of the treated insulators increased by over 200% compared with the original alumina insulators. These results indicated that a layer of regular molecule membrane was formed on the surface of alumina through molecule self-assembly, which could improve the surface voltage withstand strength of the treated insulators. [ABSTRACT FROM AUTHOR]

Photocatalysis induced by sunlight is one of the most promising approaches to environmental protection, solar energy conversion, and sustainable production of fuels. The computational modeling of photocatalysis is a rapidly expanding field that requires to adapt and to further develop the available theoretical tools. The coupled transfer of protons and electrons is an important reaction during photocatalysis. In this work, we present the first step of our methodology development in which we apply the existing kinetic theory of such coupled transfer to a model system, namely, methanol photodissociation on the rutile TiO2(110) surface, with the help of high-level first-principles calculations. Moreover, we adapt the Stuchebrukhov–Hammes-Schiffer kinetic theory, where we use the Georgievskii–Stuchebrukhova vibronic coupling to calculate the rate constant of the proton coupled electron transfer reaction for a particular pathway. In particular, we propose a modified expression to calculate the rate constant, which enforces the near-resonance condition for the vibrational wave function during proton tunneling. [ABSTRACT FROM AUTHOR]

Molecular dynamic simulation is used to simulate the corrosion process of Fe or Ni in liquid Cs by Large-scale Atomic/Molecular Massively Parallel Simulator. The embedded-atom method potential is used to describe the interaction of Fe–Fe, Ni–Ni, and Cs–Cs, and Morse two-body potential is used to describe the Fe–Cs and Ni–Cs atomic interaction. Temperature is considered as a critical condition in this work. Results indicate that corrosion is easy to occur in the systems. The increase in temperature can help the process of Cs corrosion. Compared to the Ni–Cs system, the Fe–Cs system has a higher atomic concentration function. The radial distribution function shows that Cs atoms are dissolved into the substrates, but the Fe and Ni substrates are still crystalline structures. Moreover, Cs in Fe or Ni is still a liquid phase. [ABSTRACT FROM AUTHOR]

A separated vortex ring is the main aerodynamic feature of the dandelion seed which enables its flight. However, recent research on simply modeled dandelion seeds with a pappus angle of 180° (flat porous disk) shows that the vortex ring is not entirely separated from the pappus. This significantly differs from what is observed in a real dandelion seed and would prevent us from fully understanding its flight mechanism. In this work, the two key structural features of the pappus that are considered in the work of others, i.e., the circular disk-like geometry and the porosity, were expected to be insufficient to form an entirely separated vortex ring. Therefore, refined numerical simulations were conducted on model pappi with different pappus angles, which are more similar to real dandelion seeds than flat porous disks. A stable and entirely separated vortex ring and a small vortex ring above the central disk were observed. The lower pappus angle increases the radial pressure gradient toward the central axis between the root of the filaments. When the net effect of this pressure gradient is large enough to overcome the effect of the pressure gradient away from the central axis below the pappus, the streamlines near the root of the filaments deflect to the central axis and the vortex ring is lifted and separates entirely. It is concluded that an appropriate pappus angle is another key feature for forming an entirely separated vortex ring. This more in-depth flow mechanism is of considerable reference value for future research. [ABSTRACT FROM AUTHOR]

A solid-state electrolyte with high ionic conductivity and improved safety is a strong competitor in the race for the development of next-generation solid-state lithium batteries, which have stepped into the limelight of materials research. Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with satisfied ionic conductivity (∼10−4 S cm−1) at room temperature, high stability in the ambient atmosphere, and a facile sintering nature shows a promising potential for applications in solid-state lithium batteries. However, the current synthesis methods like solid-state strategy and liquid phase route all require harsh conditions, such as long thermal treatments, expensive raw materials, and complex operation. In this study, we propose a co-precipitation method for synthesizing the LAGP solid electrolyte with low-cost and nontoxic GeO2 as the germanium source. Process optimization in the pH value and water bath temperature was employed as a strategy to eliminate the remnants of GeO2, and the pure LAGP phase is acquired. Moreover, the co-precipitation method can also reduce the sintering temperature of LAGP to 750 °C so that uniform nano-LAGP grains (∼150 nm) can be obtained. During the subsequent processing, denser LAGP pellets are fabricated and exhibit a high ionic conductivity of 5.87 × 10−4 S cm−1 at 30 °C; the Li/Li symmetrical batteries periodically cycle at room temperature for above 310 h with a constant current density of 0.05 mA cm−2. [ABSTRACT FROM AUTHOR]

In future fusion reactors, the confinement of α-particles is a crucial issue. The perfect omnigenity may be difficult to achieve in the quasi-isodynamic and quasi-symmetric stellarators when a multi-objective optimization is considered. Non-axisymmetric field can result in collisionless particles' transport via localized trapping by ripples. Specific loss channels have been revealed to essentially exist in quasi-axisymmetric stellarators [Yang et al., Europhys. Lett. 129, 35001 (2020)] and W7-X [J. M. Faustin et al., Nucl. Fusion 56, 092006 (2016)]. It indicates a drastic loss of collisionless ions through these channels. This paper is devoted to investigate the effects of axisymmetry-breaking magnetic fields on collisionless α-particle transport in the CFQS (Chinese First Quasi-axisymmetric Stellarator) -like reactor configuration. A semi-analytic representation of radial and poloidal drifts in Boozer coordinates is given, by which we found an effective route to mitigate α-particle losses, i.e., adjusting the location of the quasi-axisymmetric radial position. Such a route enables the enhancement of the poloidal drift and decrease of radial drift in peripheral regions of the identified loss channels. The particles launched inside the quasi-axisymmetric radial surface can be well confined because localized particles that may fall in loss channels can transit into blocked particles near the quasi-axisymmetric surface, escaping from loss channels, which is beneficial for the improvement of the particle confinement. Moreover, this paper may provide a set of proxy functions for suppression of energetic particle losses to optimize stellarator configurations. [ABSTRACT FROM AUTHOR]

Due to the presence of capacitance in the transmission line, the current collected by the retarding field analyzer (RFA) becomes asymmetrical (i.e., hysteresis) during voltage scanning, and it further affects the measurement of the ion temperature (Ti). In this article, we first analyze the hysteresis of the RFA's I–V characteristics measured in the edge plasma of the J-TEXT tokamak, and we found that the ion temperature fitted from the falling side of the collector current is about 14% higher than that fitted from the rising side. An analytic model is built and verified by experimental results. Based on the model, the influence of the capacitance of transmission lines and the frequency of the scanning voltage on the hysteresis is investigated. It is found that the hysteresis becomes more remarkable with increasing capacitance or scanning frequency. Besides, the impact of the capacitance and the scanning frequency on the Ti measurement is also studied, which indicates that Ti is overestimated due to the hysteresis. The temperature error is linearly dependent on the capacitance and the scanning frequency. Furthermore, the analytical results are expected to be used in the prediction of scanning frequency for RFA applications. [ABSTRACT FROM AUTHOR]

The toroidal flow damping has been investigated in the edge plasma of J-TEXT tokamaks with an electrode biasing (EB). The estimated viscosity of the toroidal flow after the bias turning off is about 67 times of the classical viscosity and four times of the neo-classical viscosity, which infers that the flow damping is anomalous in the transition phase. In the equilibrium phase, the torque densities driven by the EB, the momentum transport, and the neo-classical toroidal viscosity (NTV) under different bias conditions are calculated, which show that the NTV torques are comparable with the other terms. According to the angular momentum balance equation, the remnant damping torque densities and the effective damping coefficients have been obtained. Considering that the remnant damping is mainly contributed by the neutral particle damping, this investigation provides a method to estimate the neutral particle density ( n H ), which gives that the n H in the edge plasma of J-TEXT is in the range of 1–4 (×1017 m−3). [ABSTRACT FROM AUTHOR]

We present a compact 3D printed x-ray emission spectrometer based on the von Hamos geometry that represents a significant upgrade to the existing von Hamos geometry-based miniature x-ray emission spectrometer (miniXES) [Mattern et al., Rev. Sci. Instrum. 83(2), 023901 (2012)]. The upgrades include the incorporation of a higher pixel density 500K detector for improved energy resolution and an enlarged sample area to accommodate a wider range of sample formats. The versatile spectrometer houses removable crystal holders that can be easily exchanged, as well as movable alignment eyelets that give flexibility in Bragg angle selection. Designed for ease of manufacture, all the components, except for the apertures, can be 3D printed and readily assembled. We describe its implementation in measurements of resonant and non-resonant Cu Kα and Kβ x-ray emission and report the theoretical and measured energy resolution and collected solid angle of the emission. [ABSTRACT FROM AUTHOR]

In structurally ordered magnetic thin films, the Curie temperature (TC) of ferromagnetic films depends on the exchange integral of the short range ordered neighboring atoms. The exchange integral may be adjusted by controlling the elemental substitutional concentration at the lattice site of interest. We show how to control the TC in high anisotropy L10 Fe50 Pt50 magnetic thin films by substituting Rh into the Pt site. Rh substitution in L10 FePt modified the local atomic environment and the corresponding electronic properties, while retaining the ordered L10 phase. The analysis of extended x-ray Absorption Fine Structure spectra shows that Rh uniformly substitutes for Pt in L10 FePt. A model of antiferromagnetic defects caused by controlled Rh substitution of the Pt site, reducing the TC, is proposed to interpret this phenomenon and its validity is further examined by ab initio density functional calculations. [ABSTRACT FROM AUTHOR]

Sulfur hexafluoride (SF6) is commonly used in gas insulated switchgears (GIS) as an insulating medium. When local overheating or partial discharge occurs in GIS, SF6 may be decomposed into various products including CO. In this paper, based on the photoacoustic (PA) effect of gas molecules, the infrared absorption line at 6380.318 cm−1 was chosen as the target line. An infrared laser with a center wavelength of 1567 nm was chosen as the light source, and a cantilever enhanced PA detector was used as the sensor; then, the experimental platform was constructed. The influence of the temperature and pressure on the infrared absorption coefficient of CO was analyzed. The relationship of the PA signal and the CO concentration under the background of SF6 and N2 were obtained. The results show that the temperature has a great influence on the CO absorption coefficient while the influence of pressure is negligible, and the temperature influential coefficient is about 5.0 × 10−6 cm−1/°C. The detection system has the highest signal-to-noise ratio when the frequency of the chopper is 40 Hz. Under N2 and SF6 background gases, there is a good linear relationship between CO concentration and pure PA signals. The minimum detection limit of CO in the background of N2 is 3.63 ppm, while it is 9.88 ppm in SF6. The different kinds of the background gases can influence the PA signals. The PA signals decrease with the increase of the temperature of the gas cell, and they also decrease with the increase of the pressure. [ABSTRACT FROM AUTHOR]

We demonstrated the controllable acquisition of optical gated spectra from a chirped supercontinuum (SC) pulse based on ultrafast transient lens (TrL) effect. Comparing with CS2, the gated spectra had much narrower spectral bandwidths using tellurite glass (Te glass) as the nonlinear medium due to its ultrafast nonlinear response. Experimental results showed that the chirp structure of the SC pulse measured by TrL method was quite accordant with that measured by femtosecond optical Kerr gate method. [ABSTRACT FROM AUTHOR]

We present a stoichiometry-dependent structural phase transition in SrRuO3 film on SrTiO3 substrate. The oxygen stoichiometry in the films was varied by changing the oxygen partial pressure P(O2) during the deposition process. For SrRuO3 films with P(O2) ≥ 60 mTorr, they exhibited a pseudo-orthorhombic structure with in-plane uniaxial magnetic anisotropy. On the other hand for films with P(O2) ≤ 45 mTorr, the tetragonal SrRuO3 phase with a perpendicular uniaxial magnetic anisotropy was stabilized at room temperature. The big difference in the magnetic anisotropy of these two SrRuO3 phases was shown to be closely linked to their respective RuO6 octahedral rotation patterns: the RuO6 octahedra rotate differently along the two orthogonal in-plane directions in the pseudo-orthorhombic phase, whereas in the tetragonal phase only octahedral rotations around z-axis are present and the octahedral tilts along the in-plane axes are diminished. First-principles calculations show that such a suppression of the RuO6 octahedra tilting in the tetragonal phase arises from the oxygen vacancies at the octahedral apex (along z-axis). This work demonstrates that the stoichiometry plays an important role in determining the octahedral rotations and tilts in the perovskite materials, which may induce new phases with distinctively different structural symmetry and physical property. [ABSTRACT FROM AUTHOR]

The fabrication method of grooves on the surface of alumina and their influence on the surface flashover characteristics of the alumina insulator were studied in this paper. To prepare grooves with a regular surface structure, the UV laser was applied to carve grooves on the surface of alumina ceramic, and dilute hydrochloric acid was used to corrode and remove the residual materials produced in the laser carving process. By adjusting the laser parameters, periodic grooves were prepared on the surface of a cylindrical alumina insulator with a groove depth of 60 µm and a groove width of approximately 50 µm on the laser spinning carving platform. Then, alumina insulators with different periods were prepared, and their vacuum surface flashover voltages were tested on a short pulsed high-voltage test platform. The test results indicated that the flashover voltages of the alumina insulators with laser carved periodic grooves were increased over 200%, and the improvement did not change much with the groove periods. A further study of the groove parameters showed that several grooves fabricated on the cathode end of the insulators were able to improve the flashover voltage of the alumina insulator to the voltage-withstand level of the fully grooved insulators. [ABSTRACT FROM AUTHOR]

A series of reverberating shock experiments on the precompressed hydrogen-deuterium (H-D) mixture were performed by using a two-stage light gas gun, and an elaborately designed diagnostic configuration was presented to probe the multishock states of dense fluid H-D mixtures. The particular diagnostics allowed multiple physical parameters, including the equation of state (EOS), refractive index, reflectivity, molecular polarizability, and energy gap, of H-D mixtures under double-shock compression to be simultaneously determined in a single shot. The multiple parameters obtained provide a comprehensive evaluation for existing theoretical models from multiple perspectives. It is found that, compared with the semilocal Perdew–Burke–Ernzerhof xc functional, the EOS data predicted by a nonlocal van der Waals exchange-correlation (xc) functional (vdW-DF1) are in much better agreement with the experimental results. Furthermore, the commonly used Gladstone–Dale relation is not appropriate for describing the refractive index in high-pressure-temperature regions, and the refractive index and reflectivity can be well reproduced by the Heyd–Scuseria–Ernzerhof hybrid xc functional. These observations may provide insights into future theoretical developments and a better understanding of material properties under extreme pressure-temperature conditions. [ABSTRACT FROM AUTHOR]

The simple working principles and versatility of the hydrothermal diamond-anvil cell (HDAC) make it highly useful for synchrotron x-ray studies of aqueous and fluid samples at high pressure-temperature (P-T) conditions. However, safety concerns need to be overcome in order to use the HDAC for synchrotron studies of aqueous radioactive samples at high temperatures and pressures. For accomplishment of such hydrothermal experiments of radioactive materials at synchrotron beamlines, the samples are required to be enclosed in a containment system employing three independent layers of airtight sealing at some synchrotron facilities while enabling access to the sample using several experimental probes, including incoming and outgoing x-rays. In this article, we report the design and implementation of a complete radiological safety enclosure system for an HDAC specialized for high P-T x-ray absorption spectroscopy (XAS) measurements of aqueous solutions containing the actinides at synchrotron beamlines. The enclosure system was successfully tested for XAS experiments using the HDAC with aqueous samples containing depleted uranium at temperatures ranging from 25 to 500 °C and pressures ranging from vapor pressure to 350 MPa. [ABSTRACT FROM AUTHOR]

The density functional theory based molecular dynamics (DFTMD) method for the computation of redox free energies presented in previous publications and the more recent modification for computation of acidity constants are reviewed. The method uses a half reaction scheme based on reversible insertion/removal of electrons and protons. The proton insertion is assisted by restraining potentials acting as chaperones. The procedure for relating the calculated deprotonation free energies to Bro\nsted acidities (pKa) and the oxidation free energies to electrode potentials with respect to the normal hydrogen electrode is discussed in some detail. The method is validated in an application to the reduction of aqueous 1,4-benzoquinone. The conversion of hydroquinone to quinone can take place via a number of alternative pathways consisting of combinations of acid dissociations, oxidations, or dehydrogenations. The free energy changes of all elementary steps (ten in total) are computed. The accuracy of the calculations is assessed by comparing the energies of different pathways for the same reaction (Hess’s law) and by comparison to experiment. This two-sided test enables us to separate the errors related with the restrictions on length and time scales accessible to DFTMD from the errors introduced by the DFT approximation. It is found that the DFT approximation is the main source of error for oxidation free energies. [ABSTRACT FROM AUTHOR]

The samples of LuBa3B9O18 and YBa3B9O18 have been prepared by the solid-state reaction technique at high temperature and their luminescent properties were investigated for both under x-ray and vuv excitation. It is believed that the lattice defects have played an important role on the luminescent performances of the two compounds and the thermoluminescence measurement confirmed the existence of lattice defects in them. The corresponding thermoactivation energy E is estimated to be about 0.36 eV for YBa3B9O18 and 0.24 eV LuBa3B9O18, respectively, by the total glow peak method. The electronic structure of YBa3B9O18 was calculated using the CASTEP code. The results showed that it is an insulator with a band gap of 5.3 eV. The calculated total and partial densities of states indicate that the top of valence bands is mainly built upon O 2p states and the low of conduction bands mostly originate from B 2s and 2p states. Considering the luminescent properties and electronic band structures of the two compounds, the potential applications of them are discussed. [ABSTRACT FROM AUTHOR]

Various structural possibilities for AlnBm (n=1–7, m=1–2) neutral isomers were investigated using B3LYP/6-311G(d) and CCSD(T)/6-311G(d) methods. Our calculations predicted the existence of a number of previously unknown isomers. The B atom favors to locate over/inside of all clusters in this series. All structures of the AlnB (n=2–7) may be derived from capping/putting a B atom over/inside the Aln cluster. All AlnB2 (n=1–5) may be understood as two substitutions of Al atoms by B atoms in the Aln+2 molecule. The strong B–B bond is a dominant factor in the building-up principle of mixed AlnB2 neutral clusters. The second difference in energy showed that the AlnBm clusters with even n+m are more stable than those with odd n+m. Our results and analyses revealed that the mixed Al–B clusters exhibit aromatic behaviors. [ABSTRACT FROM AUTHOR]

Elastic behaviors of single polymer chains adsorbed on the attractive surface are first investigated using Monte Carlo simulation method based on the bond fluctuation model. We investigate the chain size and shape of adsorbed chains, such as mean-square radius of gyration 〈S2〉, mean-square bond length 〈b2〉, shape factors 〈sfi〉 and 〈δ*〉, and the orientation of chain segments P2〈cos θ〉, to illuminate how the shape of polymer chains changes during the process of tensile elongation. There are some special behaviors of the chain size and shape at the beginning of elongation, especially for strong attraction interaction. For example, mean fraction of adsorbed segments decreases abruptly in the region of small elongation ratio and then decreases slowly with increasing elongation ratio. In fact, the chain size and shape also changes abruptly for small elongation ratio with strong attraction interaction. Some thermodynamics properties are also investigated here. Average Helmholtz free energy increases fast for elongation ratio λ<1.15, especially with strong attraction, and increases slowly for λ>1.15. Similar behaviors are obtained for average energy per bond. Elastic force (f ) and energy contribution to force (fU) are also studied, and we find that elastic force decreases abruptly for λ<1.15, and there is a minimum of elastic force for strong attraction interaction, then increases very slowly with increasing elongation ratio. However, there are different behaviors for weak attraction interaction. For energy contribution to force (fU), there is a maximum value for strong attraction interaction in the region of λ<1.15. Some comparisons with the atomic force microscopy experiments are also made. These investigations may provide some insights into the elastic behaviors of adsorbed polymer chains. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Mn K edge X-ray absorption near edge structures (XANES) of Pr0.67Sr0.33MnO3 film (100 nm) on (001) LaAlO3 substrate was measured at different temperatures to probe the MnO6 octahedron distortion and corresponding electronic structure. The absorption of high temperature paramagnetic-insulator phase differed from that of the low temperature ferromagnetic-metal phase. The temperature-dependent absorption intensity of Mn K edge XANES was correlated with the relaxation of distorted MnO6 octahedron, which changed the crystal field acting on the Mn site and the related electronic structure and properties. At low temperature, the splitting of Mn majority eg orbitals decreased and the density of states above the Fermi level increased in the relaxed MnO6 octahedron, as reflected by a wider separation between two sub-peaks in the pre-edge XANES spectra. [ABSTRACT FROM AUTHOR]

This paper investigates the delay synchronization between two temporal Boolean networks base on semi-tensor product method, which improve complete synchronization. Necessary and sufficient conditions for delay synchronization are drawn base on algebraic expression of temporal Boolean networks. A example is presented to show the effectiveness of theoretical analysis. [ABSTRACT FROM AUTHOR]

A new synchronization method is investigated for node of complex networks consists of complex chaotic system. When complex networks realize synchronization, different component of complex state variable synchronize up to different scaling complex function by a designed complex feedback controller. This paper change synchronization scaling function from real field to complex field for synchronization in node of complex networks with complex chaotic system. Synchronization in constant delay and time-varying coupling delay complex networks are investigated, respectively. Numerical simulations are provided to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The elastic behavior of a single chain transporting through complex channel which can be seen as the combination of three different channels (left channel, middle channel, and right channel, respectively) is investigated using the new pruned-enriched Rosenbluth method with importance sampling. The elastic force during the translocation process is calculated. At the entrance into the middle channel, there is the first plateau in the curve of the elastic force f (f > 0) versus x, here x represents the position of the first monomer along the x-axis direction. When the first monomer moves to a certain position, a second plateau is observed with the elastic force f < 0, which represents spontaneous translocation. The free energy difference between the subchain in the right channel and the subchain in the left channel may drive the translocation. The influence of chain length and width of the left and right channels on the translocation process are also investigated. From the simulation results, more detailed explanations for the reason why the component translocation time is not the same for different channels can be presented. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) are two main x-ray techniques in synchrotron radiation facilities. In this Note, we present an experimental setup capable of performing simultaneous XRD and XAS measurements by the application of a pixel-array area detector. For XRD, the momentum transfer in specular diffraction was measured by scanning the X-ray energy with fixed incoming and outgoing x-ray angles. By selecting a small fixed region of the detector to collect the XRD signal, the rest of the area was available for collecting the x-ray fluorescence for XAS measurements. The simultaneous measurement of XRD and X-ray absorption near edge structure for Pr0.67Sr0.33MnO3 film was demonstrated as a proof of principle for future time-resolved pump-probe measurements. A static sample makes it easy to maintain an accurate overlap of the X-ray spot and laser pump beam. [ABSTRACT FROM AUTHOR]

Epitaxial SrRuO3 films were grown under different oxygen partial pressures inducing different amounts of oxygen vacancies. In spite of microstructural disorders, a considerable improvement in the conductivity was observed at ambient temperature with increasing the oxygen vacancies. The oxygen vacancies are responsible for the conductivity improvement by enhancing the orbital overlap between Ru dz2 and O pz orbitals. The finding indicates that the oxygen vacancy plays an important role in determining the transport properties of perovskite oxides, by modifying their electronic structures. [ABSTRACT FROM AUTHOR]

In an attempt to overcome the technical challenges in the conventional solution-processed near infrared (NIR) photodetectors, we have used NaYF4:Yb, Er upconversion fluorescence nanocrystals to replace the semiconductor quantum dots in conjugated polymers. Under NIR excitation, the NaYF4:Yb, Er nanocrystals emit visible light in the solution-processed NIR photodetectors. The emitted visible light is simultaneously absorbed by the host conjugated polymer to generate photocurrent, which indicates that our approach is applicable to fabricate NIR photodetectors while avoiding the major technical challenges associated with semiconductor quantum dot based NIR photodetectors. [ABSTRACT FROM AUTHOR]

Compared with conventional plasma-enhanced chemical vapor deposition, laser-assisted plasma-enhanced chemical vapor deposition (LAPECVD) can be used to deposit crystalline SiGe films on Si substrates at low temperature. In the LAPECVD system, a CO2 laser with a wavelength of 10.6 μm was utilized to assist the pyrolytical decomposition of SiH4 and GeH4 reactant gases. The resultant Si0.78Ge0.22 films were obtained and verified through the use of the Auger electron spectroscopy measurement. As the diffraction pattern of a glancing incident angle X-ray diffraction measurement had indicated, several significant diffraction peaks corresponding to a diamond-cubic structure at (111), (220), and (311) were clearly observed. Crystalline SiGe films were also identified by the electron diffraction pattern of high-resolution transmission electron microscopy images. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles of CoFe are used as dopants to enhance the quantum efficiency of electroluminance in a single layer organic light emitting device (OLED). The enhancement of quantum efficiency increases with both increasing density of CoFe nanoparticles and external magnetic field. For a given OLED with 0.1 wt % doping, the enhancement of the quantum efficiency reaches ∼27% and ∼32% without and with a magnetic field, respectively. The origin of these improvements could be attributed to the simultaneous increases of the portion of excitons among total charge carriers and the fraction of singlets among the total excitons [ABSTRACT FROM AUTHOR]

The sample of Eu2+-doped Ba3BP3O12 was prepared by a solid-state reaction at high temperature and was showed to be an excellent scintillator when excited with hard x ray s. The phosphor showed a broad emission band in the wavelength range of 400–650 nm and a comparable light yield with that of Bi4Ge3O12 powders. Its room temperature fluorescence decay curve exhibited a two-exponent shape with decay time of 20.0±1.4 ns (98.97%) and 522±9 ns (1.03%), respectively. Considering the suitable emission wavelength range, large light yield, short decay time, moderate density, moderately low melting point, and nonhygroscopic property of Ba3BP3O12:Eu2+, one has reason to assume that this compound might find an application as a new scintillation material. [ABSTRACT FROM AUTHOR]

Dense (1-y)BiFe1-x(Mg0.5Ti0.5)xO3 - yBaTiO3 (BFMT-BT, y = 0.29, x = 0-0.12) ceramics with a pseudocubic perovskite crystal structure exhibit remarkably high-temperature stable piezoelectric properties. In particular, x = 0.03 BFMT-BT ceramics, with a Curie temperature, Tc, of ∼425 °C, show a stable piezoelectric coefficient, d33, of ∼155 pC/N up to a depolarization temperature, Td, of ∼400 °C. This Td is higher than Tc for Pb(Zr,Ti)O3, therefore suggesting BFMT-BT ceramics to be promising high-temperature Pb-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

Aqueous rutile TiO 2 (110) is the most widely studied water-oxide interface, and yet questions about water dissociation are still controversial. Theoretical studies have systematically investigated the influence of the slab thickness on water dissociation energy (E diss ) at 1 monolayer coverage using static density functional theory calculation and found that E diss exhibits odd-even oscillation with respect to the TiO 2 slab thickness. However, less studies have accounted for the full solvation of an aqueous phase using ab initio molecular dynamics due to high computational costs in which only three, four, and five trilayer models of rutile(110)-water interfaces have been simulated. Here, we report Machine Learning accelerated Molecular Dynamics (MLMD) simulations of defect-free rutile(110)-water interfaces, which allows for a systematic study of the slab thickness ranging from 3 to 17 trilayers with much lower costs while keeping ab initio accuracy. Our MLMD simulations show that the dissociation degree of surface water (α) oscillates with the slab thickness and converges to ∼2% as the TiO 2 slab becomes thicker. Converting α into dissociation free energy (ΔA diss ) and comparing with dissociation total energy E diss calculated with a single monolayer of water, we find that the full solvation of the interfaces suppresses surface water from dissociating. It is interesting to note that the machine learning potential trained from the dataset containing exclusively the five trilayer TiO 2 model exhibits excellent transferability to other slab thicknesses and further captures the oscillating behavior of surface water dissociation. Detailed analyses indicate that the central plane in odd trilayer slabs modulates the interaction between double trilayers and, thus, the bonding strength between terminal Ti and water, which affects pKa of surface water and water dissociation degree.

Solid-state electrolyte materials with superior lithium ionic conductivities are vital to the next-generation Li-ion batteries. Molecular dynamics could provide atomic scale information to understand the diffusion process of Li-ion in these superionic conductor materials. Here, we implement the deep potential generator to set up an efficient protocol to automatically generate interatomic potentials for Li 10 GeP 2 S 12 -type solid-state electrolyte materials (Li 10 GeP 2 S 12 , Li 10 SiP 2 S 12 , and Li 10 SnP 2 S 12 ). The reliability and accuracy of the fast interatomic potentials are validated. With the potentials, we extend the simulation of the diffusion process to a wide temperature range (300 K-1000 K) and systems with large size (∼1000 atoms). Important technical aspects such as the statistical error and size effect are carefully investigated, and benchmark tests including the effect of density functional, thermal expansion, and configurational disorder are performed. The computed data that consider these factors agree well with the experimental results, and we find that the three structures show different behaviors with respect to configurational disorder. Our work paves the way for further research on computation screening of solid-state electrolyte materials.

X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) are two main x-ray techniques in synchrotron radiation facilities. In this Note, we present an experimental setup capable of performing simultaneous XRD and XAS measurements by the application of a pixel-array area detector. For XRD, the momentum transfer in specular diffraction was measured by scanning the X-ray energy with fixed incoming and outgoing x-ray angles. By selecting a small fixed region of the detector to collect the XRD signal, the rest of the area was available for collecting the x-ray fluorescence for XAS measurements. The simultaneous measurement of XRD and X-ray absorption near edge structure for Pr0.67Sr0.33MnO3 film was demonstrated as a proof of principle for future time-resolved pump-probe measurements. A static sample makes it easy to maintain an accurate overlap of the X-ray spot and laser pump beam.

The density functional theory based molecular dynamics (DFTMD) method for the computation of redox free energies presented in previous publications and the more recent modification for computation of acidity constants are reviewed. The method uses a half reaction scheme based on reversible insertion/removal of electrons and protons. The proton insertion is assisted by restraining potentials acting as chaperones. The procedure for relating the calculated deprotonation free energies to Brønsted acidities (pK(a)) and the oxidation free energies to electrode potentials with respect to the normal hydrogen electrode is discussed in some detail. The method is validated in an application to the reduction of aqueous 1,4-benzoquinone. The conversion of hydroquinone to quinone can take place via a number of alternative pathways consisting of combinations of acid dissociations, oxidations, or dehydrogenations. The free energy changes of all elementary steps (ten in total) are computed. The accuracy of the calculations is assessed by comparing the energies of different pathways for the same reaction (Hess's law) and by comparison to experiment. This two-sided test enables us to separate the errors related with the restrictions on length and time scales accessible to DFTMD from the errors introduced by the DFT approximation. It is found that the DFT approximation is the main source of error for oxidation free energies.

Various structural possibilities for Al(n)B(m) (n=1-7, m=1-2) neutral isomers were investigated using B3LYP6-311G(d) and CCSD(T)6-311G(d) methods. Our calculations predicted the existence of a number of previously unknown isomers. The B atom favors to locate over/inside of all clusters in this series. All structures of the Al(n)B (n=2-7) may be derived from capping/putting a B atom over/inside the Al(n) cluster. All Al(n)B(2) (n=1-5) may be understood as two substitutions of Al atoms by B atoms in the Al(n+2) molecule. The strong B-B bond is a dominant factor in the building-up principle of mixed Al(n)B(2) neutral clusters. The second difference in energy showed that the Al(n)B(m) clusters with even n+m are more stable than those with odd n+m. Our results and analyses revealed that the mixed Al-B clusters exhibit aromatic behaviors.