查看更多>>摘要：Owing to the ppb-level detection standard toward the toxic and harmful gas,the detection of trace gases has become an important subject in the field of indoor environment management.However,the traditional resistive gas sensors hardly meet the requirement due to the weak signal generated by trace gas molecules that are difficult to capture.Herein,a visible-light-assisted Pd/TiO2 gas sensor is proposed to endow the effective detection of trace formaldehyde(HCHO)gas without heating temper-ature.Benefiting from the enhanced photocatalytic prop-erties of TiO2 by Pd decoration,the visible-light-assisted Pd/TiO2 gas sensor can detect the HCHO gas as low as 80 × 10-9 at room temperature.The successful preparation of nanoscale TiO2 sensing layer is facilitated by the ultra-thin carbon nanotube interdigital electrode in the gas sen-sor,which avoids the discontinuity of the sensing layer caused by the excessive thickness of the traditional metal electrode.In addition,the whole preparation process of the Pd/TiO2 gas sensor with carbon nanotube electrodes is compatible with mainstream CMOS fabrication technol-ogy,which is expected to realize the batch fabrication and micro-integrated application of gas sensors.It is expected that our work can provide a new strategy for the batch preparation of high-performance trace HCHO gas sensors and their future applications in portable electronic devices such as smartphones.
查看更多>>摘要：Formaldehyde is a common atmospheric pol-lutant produced in industrial production and daily life.However,the traditional semiconductor formaldehyde gas sensor cannot work at room temperature,which limits its practical application.Therefore,developing high-perfor-mance gas sensors for rapidly and accurately detecting formaldehyde at room temperature is an important topic.In this study,Ti3C2Tx/SnO2 heterostructures were con-structed,which could selectively detect formaldehyde at room temperature with a response value of 29.16％(10 × 10-6).In addition,the sensor shows a remarkable theoretical detection limit of 5.09 × 10-9 and good long-term stability.Density functional theory(DFT)simulations reveal that SnO2 nanospheres provide the majority of adsorption sites that strongly interact with formaldehyde.Meanwhile,Ti3C2Tx acting as a conductive layer facilitates the transfer of charge carriers so that they show a sensing response to formaldehyde at room temperature.Moreover,the formation of p-n heterostructures between SnO2 and Ti3C2Tx boosts the Schottky barrier at the interface,which is the critical factor in enhancing the sensing properties by turning the Schottky barrier upon introducing formalde-hyde gas.This perspective is expected to provide instruc-tive guidance for utilizing MXene/metal oxide nanocomposites to improve the gas sensing performance at room temperature.
查看更多>>摘要：The use of electrochemical-metallization-based volatile threshold switching selectors in cross-point arrays has been widely explored owing to their high on-off ratios and simple structure.However,these devices are unsuit-able for cross-point architectures because of the difficulty in controlling the random filament formation that results in large fluctuations in the threshold voltage during operation.In this study,we investigated the unidirectional threshold transition characteristics associated with an Ag/GST/HfOx/Pt-based bilayer selector and demonstrated the occurrence of a low leakage current(＜1 × 10-11 A)and low distri-bution of the threshold voltage(△0.11 V).The bilayer structure could control the filament formation in the intermediate state through the insertion of an HfOx tun-neling barrier.By stacking a bilayer selector with NiOx-based resistive random-access memory,the leakage and programming currents of the device could be significantly decreased.For the crossbar array configuration,we per-formed equivalent circuit analysis of a one-selector one-resistor(1S1R)devices and estimated the optimal array size to demonstrate the applicability of the proposed structure.The maximum acceptable crossbar array size of the 1S1R device with the Ag/GST/HfOx/Pt/Ti/NiOx/Pt structure was 5.29 × 1014(N2,N=2.3 × 107).
查看更多>>摘要：Double-exchange(DE)interaction plays an important role in electrocatalytic oxygen evolution reaction(OER).However,precise achievement of DE interaction often requires foreign dopants or vacancy engineering,leading to destabilization of the catalysts and deterioration of performance.By contrast,the utilization of environ-mentally friendly,contactless,and continuously adjustable magnetic fields to study the OER process is profitable to avoid aforementioned interference factors and further elucidate the direct relationship 0.5between DE interaction and OER activity.Here,by using cobalt hydroxide carbonate(Co(OH)(CO3)·xH2O,CoHC)nanos-tructures as a proof-of-concept study,external magnetic fields are carefully implemented to verify the role of DE interaction during water oxidation reaction.Detailed stud-ies reveal that external magnetic fields effectively enhance the reaction rate of the catalyst,the overpotential decreases from 386 to 355 mV(100 mA·cm-2),while Tafel slopes drastically decline from 93 to 67 mV.dec-1(1.0 T).Moreover,magnetic field increment exhibits robust dura-bility.Through in situ Raman and impedance measure-ments under external field,it can be found that magnetic field promotes the electron migration between Co2+and Co3+in the CoHC catalysts with the assistance of DE interactions,thus boosting the OER efficiency.
查看更多>>摘要：Extremely small-sized iron oxide nanoparticles(IONPs)are of great interest in magnetic resonance imaging(MRI)due to their biosafety as an alternative to clinical gadolinium(Ⅲ)complexes-based contrast agents.Espe-cially when the particle size is less than 10 nm,it has strong diffusion ability and deep penetration distance in tumor tis-sue.Substitution doping can significantly enhance the T1 contrast effect of nanoparticles by regulating the surface exposed atoms.However,the nucleation and growth pro-cesses of multi-component synthesis systems are complex and difficult to be accurately controlled,leading to great challenges in the synthesis of ultra-small-sized nanoparticles with different components and sizes.Here,extremely small-sized superparamagnetic gadolinium-doped iron oxide nanoparticles(GdIONPs,GdxFe3-xO4 NPs)with adjustable doping amount and controllable size in the range of 3.5-7.5 nm were synthesized by thermal decomposition.Then,as-synthesized GdIONPs were surface modified with a highly water-soluble and biocompatible carboxyl-poly-ethylene glycol-phosphoric acid ligand with high binding affinity.Gd0.65Fe2.35O4 NPs exhibited very high r1 relaxivity of 10.6 mmol-1·L·s-1 in terms of all metal concentrations and 49.0 mmol-1·L·s-1 in terms of gadolinium alone,respectively,3 and 14 times higher than clinical T1 contrast agents(Gd-DTPA).GdIONPs can continuously obtain high resolution images of blood vessels,and can be used as an efficient and multifunctional contrast agent for MR T1 imaging.This stable and efficient doping strategy provides an easy and effective method to individually optimize the magnetic properties of complex oxides and their relaxation effects for a variety of biomedical applications.
查看更多>>摘要：Traditional theoretical and empirical calculation methods can guide the design of β-and metastable β-alloys for bio-titanium.However,it is still difficult to obtain novel near-β-Ti alloys with low modulus.This study developed a method that combines machine learning with calculation of phase diagrams(CALPHAD)to facilitate the design of near-β-Ti alloys.An elastic modulus database of Ti-Nb-Zr-Mo-Ta-Sn system was constructed first,and then three features(the electron to atom ratio,mean absolute devia-tion of atom mass,and mean electronegativity)were selected as the key factors of modulus by performing a three-step feature selection.With these features,a highly accurate model was built for predicting the modulus of near-β-Ti alloys.To further ensure the accuracy of mod-ulus prediction,machine learning with the elastic constants calculated was leveraged by CALPHAD database.The root mean square error of the well-trained model can be as low as 6.75 GPa.Guided by the prediction of machine learning and CALPHAD,three novel near-β-Ti alloys with elastic modulus below 50 GPa were successfully designed in this study.The best candidate alloy(Ti-26Nb-4Zr-4Sn-1Mo-Ta)exhibits an ultra-low modulus(36.6 GPa)after cold rolling with a thickness reduction of 20％.Our method can greatly save time and resources in the development of novel Ti alloys,and experimental verifications have demonstrated the reliability of this method.
查看更多>>摘要：Initially defined high entropy alloys(HEAs)usually exhibit a single-phase solid-solution structure.However,two and/or more types of phases in HEAs pos-sibly induce the desired microstructure features,which contribute to improving the wear properties of HEAs.Here,we prepare a series of(AlCoCrFeNi)100-xHfx(x=0,2,4 and 6;at％)HEAs and concern their phase compositions,microstructures and wear properties.Hf leads to the for-mation of(Ni,Co)2Hf-type Laves phase and tailors the microstructure from a body-centered cubic(BCC)single-phase structure to a hypoeutectic structure.An increased hardness from～HV 512.3 to～HV 734.1 is due to solid-solution strengthening,grain refinement strengthen-ing and precipitated phase strengthening.And a few oxides(Al2O3+Cr2O3)caused by the wear heating contribute to an 85.5％decrease in wear rate of the HEA system from 6.71 × 10-5 to 0.97 × 10-5 m3·N-1·m-1.In addition,Hf addition changes the wear mechanism from abrasive wear,mild oxidative wear and adhesive wear to oxidative wear and adhesive wear.
查看更多>>摘要：Impact,tensile,and fatigue tests were performed in In783 alloy serving 4000,23,000 and 48,000 h.The microstructure was then analysed by optical microscopy(OM),scanning electron microscopy(SEM),and trans-mission electron microscopy(TEM)to probe the relation-ship between microstructure and properties.The results show that a new Ni5Al3 phase is found,which grows gradually in β phase with serving time increasing,destroying the martensitic structure of the β phase,and degenerating the toughness of the β phase(approximately 13.88％reduction).Therefore,the degradation of the βphase results in a sharp dropping of the resistance to stress accelerated grain boundary oxygen(SAGBO)during serving;thus,the intergranular fracture morphology degree increases with duration of service(almost 40％increase from the fractured surface).In addition,the strength of alloy will be gradually enhanced when the γ'phase becomes relatively bulky with serving time increasing due to considerable distortion of the dislocations as a result of the spacing of individual particles,in which any movement of the dislocation will have to overcome a larger number of obstacles per unit length.
查看更多>>摘要：Design of heat treatments is related to the key technology for development of nickel-based single crystal superalloys(Ni-SXs).Based on the full understanding of the solidification characteristics,this work applies opti-mization design of heat treatments for a second-generation Ni-SX.Microstructure evolution and creep properties are compared in the material under conventional/standard(Std.)and optimized(Opt.)treatments.For the Std.sample,strong dendritic segregations determine inconsistent microstructure evolution in the dendritic(D)and inter-dendritic region(ID),while the latter serves as weak area to have the prior microcrack initiation,damaging overall performance of the alloy.The Opt.treatment applies higher homogenization temperature,leading to overall reduced segregations,while not inducing incipient melting.A lower temperature of first-step ageing is used to lower the size of γ'particles.These help to form the more uniform microstructure in dendritic and interdendritic region and relieve the inconsistent microstructure evolution.The bal-anced local strength makes ID no longer as the weak area,thus restricting microcrack initiation.Great improvement of high temperature and low stress property is obtained by this progress,leading to the pronounced increase of creep rupture life under 1100 ℃/140 MPa.
查看更多>>摘要：Dielectric and energy storage properties of PbO-SrO-Na2O-Nb2O5-SiO2(PSNNS)thin films with anneal-ing temperature from 700 to 850 ℃ were investigated by measuring their capacitance-electric filed curve and hys-teresis loops.The results show that the highest dielectric constant and energy density are 81.2 and 17.0 J·cm-3,respectively,which is obtained in the sample with annealing temperature of 800 ℃.Annealed from 700 to 800 ℃,the dielectric constant and energy storage perfor-mance of PSNNS films are continuously improved.How-ever,with annealing temperature up to 850 ℃,their dielectric constant decreases,which might be related with the removal of interfacial defects as a function of annealing temperature.Defect is one of the causes of space charge phenomenon,resulting in the increase in dielectric con-stant.Moreover,the microstructure analysis by X-ray diffraction(XRD)and transmission electron microscope(TEM)indicates that the change of crystallization phase and interfacial polarization takes responsibility to the results.
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