MD Simulation of Diffusion Behaviors in Collision Welding Processes of Al-Cu, Al-Al, Cu-Cu

To investigate the effects of material combinations and velocity conditions on atomic diffusion behavior near collision interfaces,this study simulates the atomic diffusion behavior near collision interfaces in Cu-Al,Al-Al and Cu-Cu combinations fabricated through collision welding using molecular dynamic(MD)simulation.The atomic diffusion behaviors are compared between similar metal combinations(Al-Al,Cu-Cu)and dissimilar metal combinations(Al-Cu).By combining the simulation results and classical diffusion theory,the diffusion coefficients for similar and dissimilar metal material combinations under different velocity conditions are obtained.The effects of material combinations and collision velocity on diffusion behaviors are also discussed.The diffusion behaviors of dissimilar material combinations strongly depend on the transverse velocity,whereas those of the similar material combinations are more dependent on the longitudinal velocity.These findings can provide guidance for optimizing welding parameters.

Oxygen Vacancy-induced Electron Density Tuning of Fe_(3)O_(4) for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction(OER)catalysts,there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts.Herein,Fe_(3)O_(4)with oxygen vacancies(Fe_(3)O_(4)-Vac)was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms.The electron density of Fe_(3)O_(4)-Vac around Fe atoms increased compared to that of Fe_(3)O_(4)according to the characterization of synchrotron-based X-ray absorption near-edge structure(XANES),extended X-ray absorption fine structure(EXAFS)spectra,and density functional theory(DFT)calculation.Moreover,the DFT results indicate the enhancement of the desorption of HOO^(*)groups which significantly reduced the OER reaction barrier.Fe_(3)O_(4)-Vac catalyst shows an overpotential of 353 m V,lower than that of Fe OOH(853 m V)and Fe_(3)O_(4)(415 m V)at 10 m A cm^(-2),and a low Tafel slope of 50 m V dec^(-1)in 1 M KOH,which was even better than commercial RuO_(2)at high potential.This modulation approach provides us with valuable insights for exploring efficient and robust water-splitting electrocatalysts.

Investigation of structure and mechanical properties of plasma vapor deposited nanocomposite TiBN films

TiBN coatings have huge potential applications as they have excellent properties with increasing modem industrial requirements.Nanocomposite TiBN coatings were synthesized on cemented carbide,high speed steel and Si substrates by using cathodic arc plasma ion plating from pure TiB2 ceramic targets.The structure and mechanical properties of the TiBN coatings were significantly influenced by the nitrogen partial pressure.Rutherford backscattering spectrometry demonstrates that the nitrogen content of the coating varied from 2.8% to 34.5% and highresolution electron microscopy images reveal that all coatings have the characteristic of nanocrystals embedded in an amorphous matrix.The root-mean-square roughness of the coatings increases from 3.73 to 14.64 nm and the coefficients of friction of the coatings at room temperature vary from 0.54 to 0.73 with increasing nitrogen partial pressure.The microhardness of the coating increases up to 35.7 GPa at 10 sccm N2 flow rate.The smallest wear rate is 2.65 ×10^-15m^3N^-1m^-1 which indicates that TiBN coatings have excellent wear resistance.The adhesion test revealed that the TiBN coatings have good adhesion at low nitrogen partial pressure.

Oxygen vacancies enable the visible light photoactivity of chromium-implanted TiO2 nanowires

Although computational studies have demonstrated that metal ion doping can effectively narrow the bandgap of TiO_(2),the visible-light photoactivity of metal-doped TiO_(2) photoanodes is still far from satisfactory.Herein,we report an effective strategy to activate the visible-light photoactivity of chromiumimplanted TiO_(2) via the incorporation of oxygen vacancies.The chromium-doped TiO_(2) activated by oxygen vacancies(Cr-TiO_(2)-vac)exhibited an incident photon-to-electron conversion efficiency(IPCE)of~6.8%at450 nm,which is one of the best values reported for metal-doped TiO_(2).Moreover,Cr-TiO_(2)-vac showed no obvious photocurrent decay after 100 h under visible-light illumination.

A fast digital timing and analysis system based on real-time dCFD technique for nuclear physics experiments

In this paper a fast digital real-time spectrometer was developed for timing and analysis of nuclear pulse signals.The hardware system design and algorithm implementation with field-programming gate array(FPGA) and digital signal processor(DSP) were introduced.The performance of the digital constant fraction discrimination(dCFD) platform was experimentally tested with Agilent 80 MHz function/arbitrary waveform generator and LaCl 3:Ce 3+ scintillator detector for 22 Na positron annihilation gamma spectroscopy.The amplitude and time information of photon was online obtained.The energy resolution could be 5.525% and the timing resolution 293.75 ps,the system error estimation of dCFD approach was also studied.The results showed that this spectrometer achieved a timing resolution close to that of traditional CFD timing resolution with a more simplified system structure.

In-situ structural evolution of Bi_(2)O_(3) nanoparticle catalysts for CO_(2) electroreduction

Under the complex external reaction conditions,uncovering the true structural evolution of the catalyst is of profound significance for the establishment of relevant structure–activity relationships and the rational design of electrocatalysts.Here,the surface reconstruction of the catalyst was characterized by ex-situ methods and in-situ Raman spectroscopy in CO_(2)electroreduction.The final results showed that the Bi_(2)O_(3) nanoparticles were transformed into Bi/Bi_(2)O_(3) two-dimensional thin-layer nanosheets(NSs).It is considered to be the active phase in the electrocatalytic process.The Bi/Bi_(2)O_(3) NSs showed good catalytic performance with a Faraday efficiency(FE)of 94.8%for formate and a current density of 26 mA cm^(−2) at−1.01 V.While the catalyst maintained a 90%FE in a wide potential range(−0.91 V to−1.21 V)and long-term stability(24 h).Theoretical calculations support the theory that the excellent performance originates from the enhanced bonding state of surface Bi-Bi,which stabilized the adsorption of the key intermediate OCHO^(∗) and thus promoted the production of formate.

Oxygen vacancies and V co-doped Co_(3)O_(4) prepared by ion implantation boosts oxygen evolution catalysis

Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction(OER)performance of electrocatalysts.However,the synergistic interaction of the heteroatom and defect still needs further investigations.Herein,we demonstrated an oxygen vacancy-rich vanadium-doped Co_(3)O_(4)(V-Ov-Co_(3)O_(4)),fabricated by V-ion implantation,could be used for high-efficient OER catalysis.X-ray photoelectron spectra(XPS)and density functional theory(DFT)calculations show that the charge density of Co atom increased,and the reaction barrier of reaction pathway from O∗to HOO∗decreased.V-Ov-Co_(3)O_(4) catalyst shows a low overpotential of 329 mV to maintain current density of 10 mA·cm^(−2),and a small Tafel slope of 74.5 mV·dec^(−1).This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts.

The Evolution of Defects in Deformed Cu-Ni-Si Alloys during Isochronal Annealing Studied by Positron Annihilation

The effect of isochronal annealing on the deformation-induced defects in pure Cu and Cu-Ni-Si alloys is studied by positron annihilation spectroscopy.For the cold-rolled Cu,annealing up to 900℃ causes a gradual recovery of the deformation-induced defects and monotonous decrease of the hardness.This indicates that its hardening is mainly related with defects such as dislocations.However,for the hot-rolled and quenched Cu-Ni-Si alloy,although there is a partial recovery of defects after annealing below 500℃,formation of additional defects is observed after annealing above 500℃.The hardness of Cu-Ni-Si alloy has a maximum value after annealing at 500℃,which suggests that the hardening of Cu-Ni-Si alloy is not due to defects,but primarily due to the precipitation formed during annealing.Further annealing of the Cu-Ni-Si alloy above 500℃ results in over-aging effect and the precipitates lose coherence with the host matrix,which leads to positron trapping by vacancy clusters in the incoherent interface region.

Vacancy-Induced Ferromagnetism in SnO_(2) Nanocrystals:A Positron Annihilation Study

SnO_(2) nanopowders were pressed into pellets and annealed in air from 100 to 1400℃.Both XRD and Raman spectroscopy confirm that all annealed samples were single phase with a tetragonal rutile structure.Annealing induces an increase in the SnO_(2) grain size from 30 to 83 nm.Positron annihilation measurements reveal vacancy defects in the grain boundary region,and the interfacial defects remain stable after annealing below 400℃,then they are gradually recovered with increasing annealing temperature up to 1200℃.Room temperature ferromagnetism was observed for SnO_(2) nanocrystals annealed below 1200℃,and the magnetization decreases continuously with increasing annealing temperature.However,the ferromagnetism disappears at 1200℃ annealing.This shows good coincidence with the recovery of interfacial defects in the nanocrystals,suggesting that the ferromagnetism is probably induced by vacancy defects in the interface region.

An Experimental Study of Mg Aggregation in AA5754 Alloys by Positron Annihilation Spectroscopy

Defects in an AA5754 （Al-3.0%Mg） alloy are investigated by coincidence Doppler broadening spectroscopy and positron lifetime spectroscopy. The results indicate enhancement of positron trapping by Mg atoms in this Al-Mg alloy after quenching treatment at 623K, which may be due to the formation of vacancy-Mg complexes or the aggregation of Mg near the vacancy sites. It is speculated that the aggregation of Mg atoms in the moderate temperature range is responsible for cracking in spot welding of AA5754 alloys.

Li Storage Performance for the Composite Structure Of Graphene and Boron Fullerene

We study the stability and performance of Li absorption on the composite structure （B80 C72） of boron fullerene and graphene by first-principles calculations. Our results show that the Li storage capacity of the composite structure is estimated to be at least Li54B80C72, which is steady with improved dispersibility and electronic conductivity. The composite structure could have the potential application as the anode material of Li-ion batteries with high Li storage capacity and great mechanical property.

Chemical Quenching of Positronium in CuO/Al2O3 Catalysts

CuO/Al2O3 catalysts were prepared by mixing CuO and environment of the catalysts are characterized by positron v-AI203 nanopowders. Microstrueture and chemical annihilation spectroscopy. The positron annihilation lifetime measurements reveal two long lifetime components 73 and τ4, which correspond to ortho-positronium （o- Ps） annihilating in mierovoids and large pores, respectively. With increasing CuO content from 0 to 40 wt%, both 3-4 and its intensity I4 show significant decrease, which indicates quenching effect of o-Ps. The para-positronium （p-Ps） intensities derived from multi-Gaussian fitting of the coincidence Doppler broadening spectra also decreases gradually with increasing CuO content. This excludes the possibility of spin-conversion of positronium. Therefore, the chemicM quenching by CuO is probably responsible for the decrease of o-Ps lifetime. Variation in the o-Ps annihilation rate A4 （1/T4） as a function of CuO content can be well fitted by a straight line, and the slope of the fitting line is （1.83 ± 0.05） × 10^7 s-1.

Recent progress of radiation response in nanostructured tungsten for nuclear application

Engineering materials for nuclear reactors exposed to high-dose irradiation breed various radiation damage,leading to performance degradation of materials,which seriously limits the application of materials in the future advanced nuclear reactors.Tungsten-based materials applied in future nuclear reactors have to withstand not only the attack of high-energy neutron and plasma,but also the repeated impact of steady-state or even transient thermal load.Researches in the past decades have proved that tailored nanostructure have advantage in annihilating radiation defects.With the rapid development of nanostructured tungsten,probing radiation application of nanostructured tungsten is of great significance in promoting the development of novel radiation-resistant materials.Herein,the development status of three kinds of nanostructured tungsten namely nanocrystalline,nanofilm and nanoporous tungsten designed for radiation tolerance and the performance enhancement mechanism of diverse nanostructure in irradiation environment is reviewed.Finally,future perspectives and technical challenges are discussed,to inspire more creative designs of novel nanostructured tungsten for radiation tolerance.

Atomistic simulation of{0001}<1210>crack propagation with Nb precipitates inα-Zr

The fracture characteristics of Zr alloys significantly impact the performance of fuel cladding tubes in pressurized water reactors of nuclear power plants.In this study,molecular dynamics(MD)simulations were performed to investigate the{0001}(1210)crack propagation inα-Zr.The influence of temperature and Nb precipitates on the crack propagation was investigated.A total of 469tensile simulations were conducted.An innovative approach to study the interaction between crack propagation and second-phase particles in the crystals was adopted,which could effectively capture the interaction of secondphase particles with dislocations and twins generated during crack propagation.In the simulation,{1126}<1121>and{1012}<1011>twins were observed during crack propagation with Nb precipitates in the matrix.The simulation results revealed that the Nb precipitates further resisted crack propagation,especially those with a radius of approximately 2 nm.In addition,the Nb precipitates in the extension direction of the{1026}<1121>twin exhibited higher resistance to crack propagation than those at other locations.

Recent progress about 2D metal dichalcogenides: Synthesis and application in photodetectors

In recent years, two-dimensional (2D) layered metal dichalcogenides (MDCs) have received enormous attention on account of their excellent optoelectronic properties. Especially, various MDCs can be constructed into vertical/lateral heterostructures with many novel optical and electrical properties, exhibiting great potential for the application in photodetectors. Therefore, the batch production of 2D MDCs and their heterostructures is crucial for the practical application. Recently, the vapour phase methods have been proved to be dependable for growing large-scale MDCs and related heterostructures with high quality. In this paper, we summarize the latest progress about the synthesis of 2D MDCs and their heterostructures by vapour phase methods. Particular focus is paid to the control of influence factors during the vapour phase growth process. Furthermore, the application of MDCs and their heterostructures in photodetectors with outstanding performance is also outlined. Finally, the challenges and prospects for the future application are presented.

Preliminary study of light yield dependence on LAB liquid scintillator composition

Liquid scintillator （LS） will be adopted as the detector material in JUNO （Jiangmen Underground Neutrino Observatory）. The energy resolution requirement of JUNO is 3%, which has never previously been reached. To achieve this energy resolution, the light yield of liquid scintillator is an important factor. PPO （the fluor） and bis-MSB （the wavelength shifter） are the two main materials dissolved in LAB. To study the influence of these two materials on the transmission of scintillation photons in LS, 25 and 12 cm-long quartz vessels were used in a light yield experiment. LS samples with different concentration of PPO and bis-MSB were tested. At these lengths, the light yield growth is not obvious when the concentration of PPO is higher than 4 g/L. The influence from bis-MSB becomes insignificant when its concentration is higher than 8 mg/L. This result could provide some useful suggestions for the JUNO LS.

Highly improved resistive switching performances of the self-doped Pt/HfO_2:Cu/Cu devices by atomic layer deposition

Metal-oxide electrochemical metallization (ECM) memory is a promising candidate for the next generation nonvolatile memory.But this memory suffers from large dispersion of resistive switching parameters due to the intrinsic randomness of the conductive filament. In this work, we have proposed a self-doping approach to improve the resistive switching characteristics. The fabricated Pt/HfO_2:Cu/Cu device shows outstanding nonvolatile memory properties, including high uniformity, good endurance, long retention and fast switching speed. The results demonstrate that the self-doping approach is an effective method to improve the metal-oxide ECM memory performances and the self-doped Pt/HfO_2:Cu/Cu device has high potentiality for the nonvolatile memory applications in the future.

胶体球自组装制备周期性结构在光学应用方面的研究进展

胶体晶体是由单分散胶体颗粒周期性有序排列而成的一类新型自组装材料,在许多领域都具有非常广泛的应用.基于胶体晶体自组装的微纳结构具有从几十纳米到几微米可调控的固有周期性,这赋予了它们独特的光学性质.本文主要介绍了近年来胶体球自组装技术制备周期性图案及其在光学应用方面的研究进展,具体包括:(a)胶体晶体的可控自组装;(b)通过自组装所获得的胶体球充当掩模板,构造更多新颖的功能纳米结构;(c)图案化纳米结构在等离激元、抗反射、光子晶体、光催化、电子器件等光学领域的新特性及应用前景.最后,对此领域当前的挑战和未来的前景进行了展望.本文旨在通过胶体自组装技术设计更巧妙的周期结构和探索更广泛的应用.

Recent progress in the fabrication of SERS substrates based on the arrays of polystyrene nanospheres

Micro/nanostructures have broad applications in diverse application fields, such as surface enhanced Raman spectroscopy (SERS), photocatalysis, field emission, photonic crystals, microfluidic devices, electrochemical devices, etc. Using polystyrene (PS) spheres formed monolayer colloidal crystal templates as masks, scaffolds, or molds with different materials growth techniques, many different periodic nanostructured arrays can be obtained with the building units varied from nanoparticles, nanopores, nanorings, nanorods, to nanoshells. Significant progresses have been made on the synthesis of micro/nanostructures with efficient SERS response. In this review, we mainly focus on the various PS template-based fabrication techniques in realizing micro/nanostructured arrays and the SERS applications.

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

Graphene-plasmonic hybrid platforms have attracted an enormous amount of interest in surface-enhanced Raman scattering(SERS);however,the mechanism of employing graphene is still ambiguous,so clarification about the complex interaction among molecules,graphene,and plasmon processes is urgently needed.We report that the number of graphene layers controlled the plasmon-driven,surface-catalyzed reaction that converts para-aminothiophenol(PATP)-to-p,p'-dimercaptoazobenzene(DMAB)on chemically inert,graphene-coated,silver bowtie nanoantenna arrays.The catalytic reaction was monitored by SERS,which revealed that the catalytic reaction occurred on the chemical inertness monolayer graphene(1G)-coated silver nanostructures.The introduction of 1G enhances the plasmon-driven surface-catalyzed reaction of the conversion of PATP-to-p,p'-DMAB.The chemical reaction is suppressed by bilayer graphene.In the process of the catalytic reaction,the electron transfer from the PATP molecule to 1G-coated silver nanostructures.Subsequently,the transferred electrons on the graphene recombine with the hot-hole produced by the localized surface plasmon resonance of silver nanostructures.Then,a couple of PATP molecules lost electrons are catalyzed into the p,p'-DMAB molecule on the graphene surface.The experimental results were further supported by the finite-difference time-domain method and quantum chemical calculations.