Rational design of MXene-based vacancy-confined single-atom catalyst for efficient oxygen evolution reaction

Two-dimensional transition metal carbides(MXenes) have been demonstrated to be promising supports for single-atom catalysts(SACs) to enable efficient oxygen evolution reaction(OER).However,the rational design of MXene-based SACs depends on an experimental trial-and-error approach.A theoretical guidance principle is highly expected for the efficient evaluation of MXene-based SACs.Herein,highthroughput screening was performed through first-principles calculations and machine learning techniques.Ti_(3)C_(2)(OH)_(x),V_(3)C_(2)(OH)_(x),Zr_(3)C_(2)(OH)_(x),Nb_(3)C_(2)(OH)_(x),Hf_(3)C_(2)(OH)_(x),Ta_(3)C_(2)(OH)_(x),and W_(3)C_(2)(OH)_(x) were screened out based on their excellent stability.Zn,Pd,Ag,Cd,Au,and Hg were proposed to be promising single atoms anchored in MXenes based on cohesive energy analysis.Hf_(3)C_(2)(OH)_(x) with a Pd single atom delivers a theoretical overpotential of 81 mV.Both moderate electron-deficient state and high covalency of metal-carbon bonds were critical features for the high OER reactivity.This principle is expected to be a promising approach to the rational design of OER catalysts for metal-air batteries,fuel cells,and other OER-based energy storage devices.

Harvesting Energy Via Water Movement and Surface Ionics in Microfibrous Ceramic Wools

Due to the push for carbon neutrality in various human activities,the development of methods for producing electricity without relying on chemical reaction processes or heat sources has become highly significant.Also,the challenge lies in achieving microwatt-scale outputs due to the inherent conductivity of the materials and diverting electric currents.To address this challenge,our research has concentrated on utilizing nonconductive mediums for water-based low-cost microfibrous ceramic wools in conjunction with a NaCl aqueous solution for power generation.The main source of electricity originates from the directed movement of water molecules and surface ions through densely packed microfibrous ceramic wools due to the effect of dynamic electric double layer.This occurrence bears resemblance to the natural water transpiration in plants,thereby presenting a fresh and straightforward approach for producing electricity in an ecofriendly manner.The generator module demonstrated in this study,measuring 12×6 cm^(2),exhibited a noteworthy open-circuit voltage of 0.35 V,coupled with a short-circuit current of 0.51 mA.Such low-cost ceramic wools are suitable for ubiquitous,permanent energy sources and hold potential for use as self-powered sensors and systems,eliminating the requirement for external energy sources such as sunlight or heat.

In-Situ Characterization of Three-Dimensional Optical Matters by Light Diffraction

Three-dimensional optical matters are created by combining the single beam optical trapping with the conventional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.Three-dimensional optical matters are created by combining the single beam optical trapping with the conven- tional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.

Etching-assisted femtosecond laser microfabrication

Although femtosecond laser microfabrication is one of the most promising three-dimensional（3D） fabrication techniques, it could suffer from low fabrication efficiency for structures with high 3D complexities. By using etching as a main assistant technique, the processing can be speeded up and an improved structure surface quality can be provided. However,the assistance of a single technique cannot satisfy the increasing demands of fabrication and integration of highly functional 3D microstructures. Therefore, a multi-technique-based 3D microfabrication method is required. In this paper, we briefly review the recent development on etching-assisted femtosecond laser microfabrication（EAFLM）. Various processing approaches have been proposed to further strengthen the flexibilities of the EAFLM. With the use of the multi-technique-based microfabrication method, 3D microstructure arrays can be rapidly defined on planar or curved surfaces with high structure qualities.

Role of Contact and Contact Modification on Photo-response in a Charge Transfer Complex Single Nanowire Device

We investigated the feasibility of obtaining large photoresponse in metal-semiconductor-metal(MSM) type single nanowire device where one contact can be blocking type. We showed that suitable modification of the blocking contact by deposition of a capping metal using focused electron beam(FEB) can lead to considerable enhancement of the photoresponse. The work was done in a single Cu:TCNQ nanowire device fabricated by direct growth of nanowires(NW) from pre-patterned Cu electrode which makes the contact ohmic with the other contact made from Au. Analysis of the data shows that the large photoresponse of the devices arises predominantly due to reduction of the barriers at the Au/NW blocking contact on illumination. This is caused by the diffusion of the photo generated carriers from the nanowires to the contact region. When the barrier height is further reduced by treating the contact with FEB deposited Pt, this results in a large enhancement in the device photoresponse.

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor coreshell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence （PL） measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices.

Negative Magnetoresistivity of ErBi and Its Crystal-Field Levels

A theoretical approach is generalized and employed in this work to evaluate the magnetoresistivity of ErBi in external magnetic fields. The calculated results and theoretical analyses show that when an external magnetic field is applied in the z-direction, the magnetoresistivity can be reduced considerably due to the degeneracy lifting of the crystal-field levels. However, when the magnetic field is exerted along the x-axis, the magnetoresistivity will be increased because of the formations of new magnetic states of the Er ion and its transitions within and between these new states.

Magnetic Properties of a Rare-Earth Antiferromagnetic Nanoparticle Investigated with a Quantum Simulation Model

A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell.We study the magnetic properties in the presence and absence of an external magnetic field.Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field;an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction,and turns those in the core(which tries to maintain its original antiferromagnetic structure)towards the orientation in some degree;and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.

Response of colloidal liquids containing magnetic holes of different volume densities to magnetic field characterized by transmission measurement

This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ~150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ~2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ~9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.

Magnetic Orderings and Néel Temperature of TbNi2B2C

We employ a two-ion model to calculate the spontaneous magnetization and susceptibility of TbNi2B2C with the mean-field theory, and derive an analytic formula for the Néel temperature of the material with the perturbation theory. In both the cases, only the four lowest crystal-electric-field （CEF） states are taken into account as base functions. Our theoretical results are consistent with the experimental data, manifesting the strong effects of the low lying CEF states on the magnetic behaviors of the material and the suitability of the theoretical approach proposed here.

Dephasing Measurements in InGaAs/AlInAs Heterostructures: Manifestations of Spin-Orbit and Zeeman Interactions

We have measured weak antilocalization effects, universal conductance fluctuations, and Aharonov-Bohm oscillations in the two-dimensional electron gas formed in InGaAs/AlInAs heterostructures. This system possesses strong spin-orbit coupling and a high Landé factor. Phase-coherence lengths of 2 - 4 μm at 1.5 - 4.2 K are extracted from the magnetoconductance measurements. The analysis of the coherence-sensitive data reveals that the temperature dependence of the decoherence rate complies with the dephasing mechanism originating from electron-electron interactions in all three experiments. Distinct beating patterns superimposed on the Aharonov-Bohm oscillations are observed over a wide range of magnetic fields, up to 0.7 Tesla at the relatively high temperature of 1.5 K. The possibility that these beats are due to the interplay between the Aharonov-Bohm phase and the Berry one, different for electrons of opposite spins in the presence of strong spin-orbit and Zeeman interactions in ring geometries, is carefully investigated. It appears that our data are not explained by this mechanism;rather, a few geometrically-different electronic paths within the ring’s width can account for the oscillations’ modulations.

The Magnetic Properties of TbNi2B2C Investigated with a Two-Sublattice Model

A two-sublattice model for rare-earth emtiferromagnets is employed to study the magnetic properties of TbNi2B2 （2. The theoretical susceptibility and magnetization curves obtained with the model show reasonable agreement with the experimental results.

Doping Effect of Poly(vinylidene fluoride)on Carbon Nanofibers Deduced by Thermoelectric Analysis of Their Melt Mixed Films

The effect of temperature on the electrical conductivity(σ)and Seebeck coefficient(S)of n-type vapor grown carbon nanofibers(CNFs)and poly(vinylidene fluoride)(PVDF)melt-mixed with 15 wt%of those CNFs is analyzed.At 40°C,the CNFs show stable n-type character(S=-4.8μV·K^(-1))with anσof ca.165 S·m^(-1),while the PVDF/CNF composite film shows anσof ca.9 S·m^(-1)and near-zero S(S=-0.5μV·K^(-1)).This experimental reduction in S is studied by the density functional tight binding(DFTB)method revealing a contact electron transfer from the CNFs to the PVDF in the interface.Moreover,in the temperature range from 40°C to 100°C,theσ(T)of the CNFs and PVDF/CNF film,successfully described by the 3D variable range hopping(VRH)model,is explained as consequence of a thermally activated backscattering mechanism.On the contrary,the S(T)from 40°C to 100°C of the PVDF/CNF film,which satisfactorily matches the model proposed for some multi-walled carbon nanotube(MWCNT)doped mats;however,it does not follow the increase in S(T)found for CNFs.All these findings are presented with the aim of discerning the role of these n-type vapor grown carbon nanofibers on theσand S of their melt-mixed polymer composites.

软磁Ni_(80)Fe_(20)薄膜单元中磁涡旋结构的高分辨磁力显微观察

本文利用高分辨磁力显微技术对Ni80Fe20薄膜单元进行了直接观察,发现在双圆盘"花生形"单元中存在磁涡旋结构,并能够清晰地看到单元中心附近或亮或暗的涡旋核。实验结果表明,在包括针尖卷积效应的情况下,磁涡旋核中心轮廓线的直接测量宽度约为40 nm,这个分辨率远高于迄今为止报道的关于磁涡旋结构的MFM测量结果。

Evidence for Magnetic Fractional Excitations in a Kitaev Quantum-Spin-Liquid Candidate α-RuCl_(3)

It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present the first polarized inelastic neutron scattering study on α-RuCl_(3) single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center,which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence.With polarization analyses,we find that,while the spin-wave excitations around the Γ point vanish above the transition temperature T_(N),the pure magnetic continuous excitations around the Γ point are robust against temperature.Furthermore,by calculating the dynamical spin-spin correlation function using the cluster perturbation theory,we derive magnetic dispersion spectra based on the K-Γ model,which involves with a ferromagnetic Kitaev interaction of −7.2 meV and an off-diagonal interaction of 5.6 meV.We find this model can reproduce not only the spin-wave excitation spectra around the Γ point,but also the non-spin-wave continuous magnetic excitations around the Γ point.These results provide evidence for the existence of fractional excitations around the Γ point originating from the Kitaev QSL state,and further support the validity of the K-Γ model as the effective minimal spin model to describe α-RuCl_(3).

Rotation Stabilises 2D Skyrmions

We present a study of 2D Skyrmions under rotation. The purpose of this study is to establish the result of the rotation on the stability of 2D Skyrmions. Usually the 2D skyrmions are metastable unless the underlying geometry introduces a characteristic length or e.g. magnetic fifield is present in the problem. We have used a previous study of the rotating plane which proves the appearance of curvature as a result of the rotation. The curvature of the rotating disk introduces length and plays here the role of strength of the angular momentum of the field. We have shown that this additional length scale introduced by the curvature stabilises the 2D Skyrnions under

Geant4 application for efficiency simulation of PbF2 based calorimeters

Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter efficiency and measure the particles'energies,momenta and interaction time to detect the particles.This application should become the basis for a new technology of positron emission tomography.Methods To solve the problem,a new C++application based on Geant4 simulation toolkit has been developed.To monitor the response of calorimeters to different types of primary particles,we used different auxiliary Geant4 classes.In addition,we compare the simulation results for the detectors of three different setups,taking into account the detection of both electrons and gamma-quanta,and analyze their efficiency.To evaluate the capability of calorimeters to work under radiation load,we use an experimentally measured transmission function of radiation-damaged PbF_(2).Results Three calorimeter setups exploiting PbF_(2)were simulated with a new C++application based on Geant4.We showed that such type of calorimeter has an energy resolution of 4.1%√E^(e+)[GeV]and good linearity of response for GeV positrons measurements.The efficiency of such structures is found to be approximately 20%for gamma photons’detection.The multilayered structure based on gamma-quanta detection has been proven to be more efficient.It was shown that for the total ionizing dose of 30 krad the Cherenkov light yield decreases by up to two times for 14 cm long PbF_(2)crystals,while for the shorter ones(2.5 and 1.5 cm)this effect is almost negligible.Conclusions We present a new user application in Geant4 for fast simulation of complex structures designed for detection of different high-energy neutral and charged particles.Simulation of calorimeter interaction with 10^(3) of 3 GeV positrons takes 20 min on usual laptop,while for 105511 keV gamma photons it takes 1 min on average.This application allows one to evaluate the efficiency of electromagnetic calorimeters exploiting lead fluoride crystals.Our results pave the way for advanced particle energy measurements,including those used in rapidly developing medical applications such as positron emission tomography,single-photon emission computed tomography etc.

Nonlocal Probing of Amplitude Mode Dynamics in Charge-Density-Wave Phase of EuTe4

Amplitude mode is collective excitation emerging from frozen lattice distortions below the charge-density-wave(CDW)transition temperature TCDW and relates to the order parameter.Generally,the amplitude mode is non-polar(symmetry-even)and does not interact with incoming infrared photons.However,if the amplitude mode is polar(symmetry-odd),it can potentially couple with incoming photons,thus forming a coupled phonon-polariton quasiparticle that can travel with light-like speed beyond the optically excited region.Here,we present the amplitude mode dynamics far beyond the optically excited depth of ∼150 nm in the CDW phase of ∼10-μm-thick single-crystal EuTe4 using time-resolved x-ray diffraction.The observed oscillations of the CDW peak,triggered by photoexcitation,occur at the amplitude mode frequency ωAM.However,the underdamped oscillations and their propagation beyond the optically excited depth are at odds with the observation of the overdamped nature of the amplitude mode measured using meV-resolution inelastic x-ray scattering and polarized Raman scattering.The ωAM is found to decrease with increasing fluence owing to a rise in the sample temperature,which is independently confirmed using polarized Raman scattering and ab-initio molecular dynamics simulations.We rationalize the above observations by explicitly calculating two coupled quasiparticles—phonon-polariton and exciton-polariton.Our data and simulations cannot conclusively confirm or rule out the one but point toward the likely origin from propagating phonon-polariton.The observed non-local behavior of amplitude mode thus provides an opportunity to engineer material properties at a substantially faster time scale with optical pulses.

Can ChatGPT be used to generate scientific hypotheses?

We investigate whether large language models can perform the creative hypothesis generation that human researchers regularly do.While the error rate is high,generative AI seems to be able to effectively structure vast amounts of scientific knowledge and provide interesting and testable hypotheses.The future scientific enterprise may include synergistic efforts with a swarm of“hypothesis machines”,challenged by automated experimentation and adversarial peer reviews.

探索Bi_(2)SeO_(5)的高介电性能:从块体到双层和单层

Bi_(2)SeO_(5)是一种具有优异电绝缘性能的范德华(vdW)层状介电材料,引起了极大关注.然而,目前关于Bi_(2)SeO_(5)的研究主要停留在实验层面,仍然缺乏对其原子级薄膜的介电性能的相关理论认识.本文通过第一性原理计算确定了Bi_(2)SeO_(5)的介电性能,发现其块体、双层和单层均具有超高平均介电常数(εr>20).研究表明,单层Bi_(2)SeO_(5)与双层Bi_(2)O_(2)Se之间的导带和价带能量偏移量均大于1 eV,表明单层Bi_(2)SeO_(5)依然可作为原子薄Bi_(2)O_(2)Se的良好介电层.此外,不同于h-BN或其他2D vdW绝缘体,Bi_(2)SeO_(5)的εr由其离子部分主导,且随着厚度的减小几乎保持不变.计算发现,单层Bi_(2)SeO_(5)的等效氧化层厚度可薄至0.3 n m,且单层Bi_(2)SeO_(5)在拉伸或压缩应变达到6%时均能保持高介电常数,这极大地促进了它与各种二维半导体的集成.本工作证明单层Bi_(2)SeO_(5)可以作为高性能二维电子器件良好的封装和介电层.