Designing microstructures and unveiling dynamic erosion mechanisms remain important challenges for Ag-based contacts.To simultaneously enhance erosion and compression resistance,an Al Co Cr Fe Ni high-entropy alloy(HE...Designing microstructures and unveiling dynamic erosion mechanisms remain important challenges for Ag-based contacts.To simultaneously enhance erosion and compression resistance,an Al Co Cr Fe Ni high-entropy alloy(HEA)is introduced into Ag-based materials to fabricate novel Ag-HEA contacts with island-and skeletonrestricted microstructures.The arc erosion experimental results reveal that the skeleton-restricted HEA microstructure is the key factor in reducing the hill and crater morphologies of the contact surface,effectively delaying material transfer between the movable and stationary contacts.The molten bridge evolution and compressive deformation behavior of Ag-HEA contacts with various microstructures are investigated using molecular dynamics(MD)simulations.MD results indicate that the constraint of Ag atom diffusion in the molten pool and the involvement of HEA atoms in the molten bridge are the primary mechanisms for improving erosion resistance.The skeleton-restricted HEA microstructure reduces the total energy and structural stability of the molten bridge system and promotes its fracture and disintegration.Moreover,the synergistic effect of the twin and Lomerz–Cottrell lock structures can hinder dislocation glide,generating dispersed and small-area stacking faults in the Ag matrix and mitigating the concentration of shear strains.Thus,the skeleton-restricted HEA microstructure contributes positively to compression resistance.This study presents a novel approach to designing Ag-based contacts.展开更多
The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarizatio...The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.展开更多
Recently,exploration breakthroughs have been made in the Lower Cretaceous sandstone reservoirs in the Doseo Basin,but the identification of reservoir fluid property is difficult due to variable reservoir lithology,com...Recently,exploration breakthroughs have been made in the Lower Cretaceous sandstone reservoirs in the Doseo Basin,but the identification of reservoir fluid property is difficult due to variable reservoir lithology,complex oil-water contact within and faint responses of the oil zone,which causes the lower accuracy of reservoir fluid property identification with conventional mudlogging and wirelogging techniques.Applying the geochemical logging,fluorescent logging,mud logging and cutting logging technology,in combination with formation test data,this paper distinguishes the crude oil types,analyzes the logging response characteristics of oil zone after water washing,and establishes the interpretation charts and parameter standards for reservoir fluid properties.The crude oil can be divided into two types,namely viscous-heavy and thin-light,based on total hydrocarbon content and component concentration tested by mud logging,features of pyrolysis gas chromatogram and fluorescence spectroscopy.The general characteristics of oil layers experienced water washing include the decrease of total hydrocarbon content and component concentration from mud logging,the decrease of S1 and PS values from geochemical logging,the decrease of hydrocarbon abundance and absence of some light components in pyrolysis gas chromatogram,and the decrease of fluorescence area and intensity from fluorescence logging.According to crude oil types,the cross plots of S1 versus peak-baseline ratio,and the cross plots of rock wettability versus fluorescence area ratio are drawn and used to interpret reservoir fluid property.Meanwhile,the standards of reservoir fluid parameter are established combining with the parameters of PS and the parameters in above charts,and comprehensive multiparameter correlation in both vertical and horizontal ways is also performed to interpret reservoir fluid property.The application in the Doseo Basin achieved great success,improving interpretation ability of fluid property in the reservoir with complex oil-water contact,and also provided technical reference for the efficient exploration and development of similar reservoirs.展开更多
The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulti...The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulting in mutual diffusion of atoms at the interface. However, the specific role of diffusing elements in Ohmic contact formation remains unclear.In this work, we investigate the contribution of oxygen atom diffusion to the formation of Ohmic contacts in Ga_(2)O_(3). We prepare a Ti/Au electrode on a single crystal substrate and conduct a series of electrical and structural characterizations.Using density functional theory, we construct a model of the interface and calculate the charge density, partial density of states, planar electrostatic potential energy, and I–V characteristics. Our results demonstrate that the oxygen atom diffusion effectively reduces the interface barrier, leading to low-resistance Ohmic contacts in Ga_(2)O_(3). These findings provide valuable insights into the underlying mechanisms of Ohmic contact formation and highlight the importance of considering the oxygen atom diffusion in the design of Ga_(2)O_(3)-based electronic devices.展开更多
This study aims to develop an analytical model based on the curve beam theory to capture the mechanical response of a multihelix cable considering the internal contact displacements.Accordingly,a double-helix cable su...This study aims to develop an analytical model based on the curve beam theory to capture the mechanical response of a multihelix cable considering the internal contact displacements.Accordingly,a double-helix cable subjected to axial tension and torsion is analyzed,and both the line and point contacts between the neighboring wires and strands are considered via an equivalent homogenized approach.Then,the proposed theoretical model is extended to a hierarchical multihelix cable with mutual contact displacements by constructing a recursive relationship between the high-and low-level multihelix structures.The global tensile stiffness and torsional stiffness of the double-helix cable are successfully evaluated.The results are validated by a finite element(FE)model,and are found to be consistent with the findings of previous studies.It is shown that the contact deformations in multihelix cables significantly affect their equivalent mechanical stiffness,and the contact displacements are remarkably enhanced as the helix angles increase.This study provides insights into the interwire/interstrand mutual contact effects on global and local responses.展开更多
Objective:Based on the theory of“Knowledge,Attitude,Practice,”health education was carried out for close contact with tuberculosis(TB)at a university in Beijing,and its impact on the students’awareness of TB was st...Objective:Based on the theory of“Knowledge,Attitude,Practice,”health education was carried out for close contact with tuberculosis(TB)at a university in Beijing,and its impact on the students’awareness of TB was studied.This study could provide a reference for effective health education interventions among close contacts of TB in undergraduates.Methods:102 undergraduates who had close contact with one confirmed case of pulmonary TB in April 2021 at a university were randomly divided into a control group and an intervention group.The intervention group was given the“Knowledge,Attitude,Practice”health education intervention by professionally trained doctors,and were asked to complete a self-designed TB-related questionnaire before and after the intervention.Both groups performed the Tuberculin Skin Test(TST)and chest X-ray(CR)examination.Results:The rate of the TST test was 18.6%,and CR examination showed 0 cases of pulmonary TB.The survey results showed that the TB awareness rate(96.1%,49/51)in the intervention group was significantly higher than that of the control group(51.0%,26/51),and the differences in awareness rate between the two groups were statistically significant(P<0.05).Regarding the attitude/skills toward TB,the prevalence rate of tuberculosis-related attitude/behavior in the intervention group(94.1%,47/51)was significantly higher than that of the control group(60.8%,31/51),and the differences between the two groups were statistically significant(P<0.05).Conclusion:Both self-controlled and parallel-controlled studies showed that the health education intervention of“Knowledge,Attitude,Practice”improved the awareness of TB among close contacts of TB in undergraduates.展开更多
Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the i...Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the investigation into the tunneling current indicates that the tunneling effect is of great importance under reverse biases.The Schottky barrier diode current due to Schottky effect is in agreement with the theoretical one.The barrier lowering is found a profound effect on the current transport at the metal semiconductor interface.展开更多
N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffracti...N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffraction （XRD） analysis after metallization annealing. An amorphous C film at the Ni2 Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer （XEDS）. The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing. Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2 Si and amorphous C film are replaced by new metal films. The sheet resistance Rsh of the implanted layers decreases from 975 to 438f2/D, because carbon vacancies （Vc） appeared during annealing,which act as donors for electrons in SiC.展开更多
The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the in...The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the interface performances of the engineering structures.In this paper,a contact model is established,which is suitable for tensile and bending deformed contact surfaces.Four contact forms of asperities are proposed,and their distribution characteristics are analyzed.This model reveals the mechanism of friction generation from the perspective of the force balance of asperity.The results show the contact behaviors of the deformed contact surface are significantly different from that of the plane contact,which is mainly reflected in the change in the number of contact asperities and the real contact area.This study suggests that the real contact area of the interface can be altered by applying tensile and bending strains,thereby regulating its contact mechanics and conductive behavior.展开更多
All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid...All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.展开更多
Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si...Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si-faced p-type 4H-SiC epilayer. The polysilicon is deposited using low-pressure chemical vapor deposition （LPCVD） and doped by phosphorous ions implantation followed by diffusion to obtain a sheet resistance of 22Ω/□. The specific contact resistance pc of n^＋ polysilicon contact to n-type 4H-SiC as low as 3.82 × 10^-5Ω· cm^2 is achieved. The result for sheet resistance Rsh of the phosphorous ion implanted layers in SiC is about 4.9kΩ/□. The mechanisms for n^＋ polysilicon ohmic contact to n-type SiC are discussed.展开更多
Magnesium and its alloys have gained relevance for their light-weight combined with a high value of strength-to-weight ratio,which makes them useful in fields such as aerospace,automotive as well as biomedical enginee...Magnesium and its alloys have gained relevance for their light-weight combined with a high value of strength-to-weight ratio,which makes them useful in fields such as aerospace,automotive as well as biomedical engineering.Unfortunately,the poor corrosion resistance of Mg-alloys limits their wide acceptance.Advanced composite coatings which are self-healing,superhydrophobic anti corrosive,and wear resistant are new synthetic materials for abating these challenges.The superimposed superhydrophobic surfaces help in minimizing their water contact,thus slowing down the electrochemical reactions on the surface of the alloys,while their self-healing characteristics autonomously aid in the repair of any induced micro-crack,defect or damage towards ensuring the metal's long-term protection.In addition,the integration of wear-resistant materials further improves the durability of coatings under mechanical stress.The most recent research efforts have been directed towards the preparation of multifunctional composites,with an emphasis on nanomaterials,functional polymers,and state-of-the-art fabrication techniques in order to take advantage of their synergistic effects.Some of the methods that have so far exhibited promising potentials in fabricating these materials include the sol-gel method,layer-by-layer assembly,and plasma treatments.However,most of the fabricated products are still faced with significant challenges ranging from long-term stability to homogeneous adhesion of the coatings and their scalability for industrial applications.This review discusses the recent progress and the relationship between corrosion inhibition and self-healing efficiencies of wear resistant polymer nanocomposite coatings.Some challenges related to optimizing coating performance were also discussed.In addition,future directions ranging from the consideration of bioinspired designs,novel hybrid nanocomposite materials,and environmentally sustainable solutions integrated with smart protective coatings were also proposed as new wave technologies that can potentially revolutionize the corrosion protection offered by Mg alloys while opening up prospects for improved performance and sustainability.展开更多
The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,an...The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.展开更多
Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was appli...Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.展开更多
In order to explore the mechanism of improving the surface wettability of low-energy polytetrafluoroethylene(PTFE)by new extended surfactants,five kinds of extended anionic surfactants with different numbers of oxypro...In order to explore the mechanism of improving the surface wettability of low-energy polytetrafluoroethylene(PTFE)by new extended surfactants,five kinds of extended anionic surfactants with different numbers of oxypropylene(PO)and oxyethylene(EO),octadecyl-(PO)_(m)-(EO)_(n)-sodium carboxylate(C_(18)PO_(m)EO_(n)C,m=5,10,15,n=5,10,15),were studied.The surface tension and contact angle of C_(18)PO_(m)EO_(n)C solution with different concentrations were measured,and the adhesion tension,PTFE-water interfacial tension,and adhesion work were calculated.It was found that the extended surfactant molecules adsorb on the surface of the solution and the PTFE-liquid interface simultaneously when the concentration is lower than the critical micelle concentration(cmc),and there was a linear relationship between surface tension and adhesion tension.The adsorption amount of C_(18)PO_(m)EO_(n)C at the PTFE-water interface was significantly lower than that on the surface of the solution.As the concentration increases above cmc,semi-micelle aggregates on the surface of PTFE are formed by C_(18)PO_(m)EO_(n)C molecules through hydrophobic interaction,and the hydrophilic group faces the solution to modify the surface of PTFE with high efficiency.展开更多
[Background and purposes]Proton exchange membrane fuel cells(PEMFCs),which convert hydrogen energy directly into electrical energy and water,have received overwhelming attention,owing to their potential to significant...[Background and purposes]Proton exchange membrane fuel cells(PEMFCs),which convert hydrogen energy directly into electrical energy and water,have received overwhelming attention,owing to their potential to significantly reduce energy consumption,pollution emissions and reliance on fossil fuels.Bipolar plates are the major part and key component of PEMFCs stack,which provide mechanical strength,collect and conduct current segregate oxidants and reduce agents.They contribute 70-80%weight and 20-30%cost of a whole stack,while significantly affecting the power density.There are three types plates,including metal bipolar plate,graphite bipolar plate and composite bipolar plate.Stainless steel bipolar plates,as one of metal bipolar plate,exhibit promising manufacturability,competitive cost and durability among various metal materials.However,stainless steel would be corroded in the harsh acid(pH 2-5)and humid PEMFCs environment,whereas the leached ions will contaminate the membrane.In addition,the passivated film formed on the surface will increase the interfacial contact resistance(ICR).In order to improve the corrosion resistance and electrical conductivity of steel bipolar plates,surface coatings are essential.Metal nitride coatings,metal carbide coatings,polymer coatings and carbon-based coatings have been introduced in recent years.Carbon-based coatings,mainly including a-C(amorphous Carbon),Ta-C(Tetrahedral amorphous carbon)and DLC(diamond-like carbon),have attracted considerable attention from both academia and industry,owing to their superior performance,such as chemical inertness,mechanical hardness and electrical conductivity.However,Ta-C films as protective coating of PEMFCs have been rarely reported,due to the difficulty in production for industrial application.In this paper,multi-layer Ta-C composite films were produced by using customized industrial-scale vacuum equipment to address those issues.[Methods]Multiple layered Ta-C coatings were prepared by using PIS624 equipment,which assembled filtered cathodic arc evaporation,ion beam and magnetron sputtering into one equipment,while SS304 and silicon specimens were used as substrate for testing and analysis.Adhesion layer and intermediate layer were deposited by using magnetron sputtering at deposition temperature of 150℃and pressure of 3×10^(−1) Pa,while the sputtering current was set to be 5 A and bias power to be 300 V.The Ta-C layer was coated at arc current of 80-100 A,bias voltage of 1500 V and gas flow of 75 sccm.A scanning electron microscope(CIQTEK SEM3200)was used to characterize surface morphology,coating structure and cross-section profile of the coatings.Raman spectrometer(LabRam HR Evolution,HORIBA JOBIN YVON)was used to identify the bonding valence states.Electrochemical tests were performed by using an electrochemical work station(CHI760,Shanghai Chenhua Instrument Co.,Ltd.),with the traditional three electrode system,where saturated Ag/AgCl and platinum mesh were used as the reference electrode and counter electrode,respectively.All samples were mounted in plastic tube and sealed with epoxy resin,with an exposure area of 2.25 cm^(2),serving as the working electrode.Electrochemical measurements were carried out in simulated PEMFCs cathode environment in 0.5 mol·L^(−1) H_(2)SO_(4)+5 ppm F−solution,at operating temperature of 70℃.As the cathode environment was harsher than the anode environment,all the samples are stabilized at the open-circuit potential(OCP)for approximately 30 min before the EIS measurements.ICR between bipolar plates and GDL was a key parameter affecting performance of the PEMFCs stack.The test sample sandwiched between 2 pieces of carbon paper(simulate gas diffusion layer,GDL)was placed between 2 gold-plated copper electrodes at a compaction pressure of 1.4 MPa,which was considered to be the conventional compaction pressure in the PEMFCs.Under the same conditions,the resistance of a single carbon paper was measured as well.The ICR was calculated according to the formula ICR=1/2(R2−R1)×S,where S was the contact area between GDL and coated stainless steel BPPs.All data of ICR were measured three times for averaging.[Results]The coatings deposited by filtered cathodic arc technology were compact and smooth,which reduced coating porosity and favorable to corrosion resistance.The coating thickness of adhesion and intermediate layers were 180 nm,while the protective Ta-C coating thickness was about 300 nm,forming multiple coating to provide stronger protection for metal bipolar plates.Cr,Ti,Nb and Ta coatings were selected as adhesion layers for comparison.According to electrochemical test,Ta and Nb coatings have higher corrosion resistance.However,Ta and Nb materials would be costly when they are used for mass production.Relatively,Cr and Ti materials were cost effective.Hence,a comprehensive assessment was indispensable to decide the materials to be selected as adhesion layer.Ta-TiN and Ti-TiN combined adhesion and intermediate layer exhibited stronger corrosion resistance,with the corrosion current to be less than 10^(−6) A·cm^(−2).Ta-C protective coating deposited by using filtered cathodic arc technology indicated displayed higher corrosion resistance,with the average corrosion density to be about 1.26×10^(−7) A·cm^(−2).Ta-C coating also shown larger contact angle,with the highest hydrophobicity,which was one of the important advantages for Ta-C,in terms of corrosion resistance.According to Raman spectroscopy,the I(D)/I(G)=549.8/1126.7=0.487,with the estimated fraction of sp^(3) bonding to be in the range of 5154%.The intermediate layer TiN has higher conductivity than the CrN layer.Considering cost,corrosion performance and ICR result,the Ti-TiN layer combination is recommended for industrial scale application.[Conclusions]Multiple layer coating structure of Ta-C film had stronger corrosion resistance;with more than 50%sp^(3) content,while it also had larger water contact angle and higher corrosion resistance than DLC film.The filtered arcing deposition technology was able to make the film to be more consistent and stable than normal arcing technology in terms of the preparation of Ta-C.The coating displayed corrosion density of 1.26×10^(−7) A·cm^(−2) and ICR of less than 5 mΩ·cm^(2),far beyond technical target of 2025 DOE(US Department of Energy).This indicated that the mass-production scale coating technology for PEMFC bipolar plates is highly possible.展开更多
In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumu...In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumulation of identical line contacts with half-width given by the truncated area divided by the contact patch number at varying heights.Based on the contact stiffness of two-dimensional flat punch,the total stiffness of rough surface is estimated,and then the normal load is calculated by an incremental method.For various rough surfaces,the approximately linear load-area relationships predicted by the proposed model agree well with the results of finite element simulations.It is found that the real average contact pressure depends significantly on profile properties.展开更多
Semiconducting transition-metal dichalcogenides(TMDs)have garnered significant interest due to their unique structures and properties,positioning them as promising candidates for novel electronic and optoelectronic de...Semiconducting transition-metal dichalcogenides(TMDs)have garnered significant interest due to their unique structures and properties,positioning them as promising candidates for novel electronic and optoelectronic devices.However,the performance of TMDs-based devices is hampered by the suboptimal quality of metal electrodes contacting the atomically thin TMDs layers.Understanding the mechanisms that influence contact quality is crucial for advancing TMDs devices.In this study,we investigated the conductive properties of tungsten selenide(WSe_(2))-based devices with different film thicknesses.Using the transmission line method,a negative correlation between contact resistance and film thickness in multi-electrode devices was revealed.Additionally,repeatability tests conducted at varied temperatures indicated enhanced device stability with increasing film thickness.Theoretical analysis,supported by thermionic emission theory and thermal simulations,suggests that the degradation in electrical properties is primarily due to the thermal effect at the contact interface.Furthermore,we found that van der Waals contacts could mitigate the thermal effect through a metal transfer method.Our findings elucidate the critical role of contact resistance in the electronic performance of 2D material-based field-effect transistors(FETs),which further expands their potential in the next generation of electronic and optoelectronic devices.展开更多
When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two...When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two layers of soil with different properties, pore water flows slowly along the pore channels, demonstrating laminar flow phenomenon. To predict the thermal contact resistance and flow contact resistance at the interface, this paper constructs general imperfect thermal contact model and general imperfect flow contact model, respectively. Utilizing a thermo-hydro- mechanical coupling model, the thermal consolidation behavior of multilayered saturated soil under two-dimensional conditions is investigated. Fourier and Laplace transformations are applied to decouple the governing equations, yielding expressions for the temperature increment, pore water pressure, and displacement in multilayered saturated soil. The inverse Fourier-Laplace transformation is then used to obtain numerical solutions, which are compared with degeneration solutions to validate the computational accuracy. The differences in the thermal consolidation process under various thermal contact and flow contact resistance models are discussed. Furthermore, the impact of parameters such as the thermal resistance coefficient, partition thermal contact coefficient, flow contact resistance coefficient, and partition flow contact coefficient on thermal consolidation are investigated. Results indicate that thermal contact resistance creates a relative thermal gradient at the interface, leading to increased pore water pressure and reduced displacement nearby. In contrast, flow contact resistance generates a relative pore pressure gradient at the interface, resulting in increased displacement within the saturated soil with minimal effect on temperature increment distribution.展开更多
During the grinding train operation process,the grinding force between the grinding wheel and the rail is critical in ensuring the grinding quality and efficiency.The coupling vibration among the frame,the grinding wh...During the grinding train operation process,the grinding force between the grinding wheel and the rail is critical in ensuring the grinding quality and efficiency.The coupling vibration among the frame,the grinding wheels,and the wheelsets will seriously affect the stability of the grinding force.In this paper,the coupled mechanical model of the grinding wheel/rail is established based on the contact mechanics theory,which is embedded as a submodel into the dynamic model of the multi-rigid buggy.The interaction among the frame,the grinding wheels and the wheelsets is analysed by setting the convex irregularity on the rail.The grinding effect is evaluated in combination with the subway’s long wave corrugation grinding conditions.The results show that when the grinding buggy passes the convex irregularity,the vibration excited by the wheelset system has a significant impact on the dynamic behavior of the grinding wheels.The vibration of the grinding wheel is mainly transmitted between the grinding wheel and the frame,less affecting the wheelset.For the long wave corrugation of the subway,the grinding effect of the grinding wheel has a certain correlation with the phase angle of the wheelset through the corrugation.The research results provide an important reference for the setting of the grinding pattern.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52007137 and 51807069)China Postdoctoral Science Foundation(No.2021M702566)+3 种基金Xi’an Science and Technology Plan Project(No.22GXFW0028)the Scientific Research Program Funded by Shaanxi Provincial Education Department(No.23JK0461)the NaturalScience Foundation of Shaanxi Province(No.2023-YBGY-171)Graduate Students’Innovation Foundation of Xi’an Polytechnic University(No.chx2023031).
文摘Designing microstructures and unveiling dynamic erosion mechanisms remain important challenges for Ag-based contacts.To simultaneously enhance erosion and compression resistance,an Al Co Cr Fe Ni high-entropy alloy(HEA)is introduced into Ag-based materials to fabricate novel Ag-HEA contacts with island-and skeletonrestricted microstructures.The arc erosion experimental results reveal that the skeleton-restricted HEA microstructure is the key factor in reducing the hill and crater morphologies of the contact surface,effectively delaying material transfer between the movable and stationary contacts.The molten bridge evolution and compressive deformation behavior of Ag-HEA contacts with various microstructures are investigated using molecular dynamics(MD)simulations.MD results indicate that the constraint of Ag atom diffusion in the molten pool and the involvement of HEA atoms in the molten bridge are the primary mechanisms for improving erosion resistance.The skeleton-restricted HEA microstructure reduces the total energy and structural stability of the molten bridge system and promotes its fracture and disintegration.Moreover,the synergistic effect of the twin and Lomerz–Cottrell lock structures can hinder dislocation glide,generating dispersed and small-area stacking faults in the Ag matrix and mitigating the concentration of shear strains.Thus,the skeleton-restricted HEA microstructure contributes positively to compression resistance.This study presents a novel approach to designing Ag-based contacts.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFB3608601).
文摘The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.
基金funded by a project entitled exploration field evaluation and target optimization of key basins in Chad and Niger(No.2019D-4308)initiated by the scientific research and technology development project of china national petroleum corporation.
文摘Recently,exploration breakthroughs have been made in the Lower Cretaceous sandstone reservoirs in the Doseo Basin,but the identification of reservoir fluid property is difficult due to variable reservoir lithology,complex oil-water contact within and faint responses of the oil zone,which causes the lower accuracy of reservoir fluid property identification with conventional mudlogging and wirelogging techniques.Applying the geochemical logging,fluorescent logging,mud logging and cutting logging technology,in combination with formation test data,this paper distinguishes the crude oil types,analyzes the logging response characteristics of oil zone after water washing,and establishes the interpretation charts and parameter standards for reservoir fluid properties.The crude oil can be divided into two types,namely viscous-heavy and thin-light,based on total hydrocarbon content and component concentration tested by mud logging,features of pyrolysis gas chromatogram and fluorescence spectroscopy.The general characteristics of oil layers experienced water washing include the decrease of total hydrocarbon content and component concentration from mud logging,the decrease of S1 and PS values from geochemical logging,the decrease of hydrocarbon abundance and absence of some light components in pyrolysis gas chromatogram,and the decrease of fluorescence area and intensity from fluorescence logging.According to crude oil types,the cross plots of S1 versus peak-baseline ratio,and the cross plots of rock wettability versus fluorescence area ratio are drawn and used to interpret reservoir fluid property.Meanwhile,the standards of reservoir fluid parameter are established combining with the parameters of PS and the parameters in above charts,and comprehensive multiparameter correlation in both vertical and horizontal ways is also performed to interpret reservoir fluid property.The application in the Doseo Basin achieved great success,improving interpretation ability of fluid property in the reservoir with complex oil-water contact,and also provided technical reference for the efficient exploration and development of similar reservoirs.
基金Projects supported by the National Natural Science Foundation of China (Grant Nos.61874084,61974119,and U21A20501)。
文摘The formation of low-resistance Ohmic contacts in Ga_(2)O_(3) is crucial for high-performance electronic devices. Conventionally, a titanium/gold(Ti/Au) electrode is rapidly annealed to achieve Ohmic contacts, resulting in mutual diffusion of atoms at the interface. However, the specific role of diffusing elements in Ohmic contact formation remains unclear.In this work, we investigate the contribution of oxygen atom diffusion to the formation of Ohmic contacts in Ga_(2)O_(3). We prepare a Ti/Au electrode on a single crystal substrate and conduct a series of electrical and structural characterizations.Using density functional theory, we construct a model of the interface and calculate the charge density, partial density of states, planar electrostatic potential energy, and I–V characteristics. Our results demonstrate that the oxygen atom diffusion effectively reduces the interface barrier, leading to low-resistance Ohmic contacts in Ga_(2)O_(3). These findings provide valuable insights into the underlying mechanisms of Ohmic contact formation and highlight the importance of considering the oxygen atom diffusion in the design of Ga_(2)O_(3)-based electronic devices.
基金Project supported by the National Natural Science Foundation of China(Nos.11932008 and 12102380)the Natural Science Foundation of Jiangsu Province of China(No.BK20180894)。
文摘This study aims to develop an analytical model based on the curve beam theory to capture the mechanical response of a multihelix cable considering the internal contact displacements.Accordingly,a double-helix cable subjected to axial tension and torsion is analyzed,and both the line and point contacts between the neighboring wires and strands are considered via an equivalent homogenized approach.Then,the proposed theoretical model is extended to a hierarchical multihelix cable with mutual contact displacements by constructing a recursive relationship between the high-and low-level multihelix structures.The global tensile stiffness and torsional stiffness of the double-helix cable are successfully evaluated.The results are validated by a finite element(FE)model,and are found to be consistent with the findings of previous studies.It is shown that the contact deformations in multihelix cables significantly affect their equivalent mechanical stiffness,and the contact displacements are remarkably enhanced as the helix angles increase.This study provides insights into the interwire/interstrand mutual contact effects on global and local responses.
文摘Objective:Based on the theory of“Knowledge,Attitude,Practice,”health education was carried out for close contact with tuberculosis(TB)at a university in Beijing,and its impact on the students’awareness of TB was studied.This study could provide a reference for effective health education interventions among close contacts of TB in undergraduates.Methods:102 undergraduates who had close contact with one confirmed case of pulmonary TB in April 2021 at a university were randomly divided into a control group and an intervention group.The intervention group was given the“Knowledge,Attitude,Practice”health education intervention by professionally trained doctors,and were asked to complete a self-designed TB-related questionnaire before and after the intervention.Both groups performed the Tuberculin Skin Test(TST)and chest X-ray(CR)examination.Results:The rate of the TST test was 18.6%,and CR examination showed 0 cases of pulmonary TB.The survey results showed that the TB awareness rate(96.1%,49/51)in the intervention group was significantly higher than that of the control group(51.0%,26/51),and the differences in awareness rate between the two groups were statistically significant(P<0.05).Regarding the attitude/skills toward TB,the prevalence rate of tuberculosis-related attitude/behavior in the intervention group(94.1%,47/51)was significantly higher than that of the control group(60.8%,31/51),and the differences between the two groups were statistically significant(P<0.05).Conclusion:Both self-controlled and parallel-controlled studies showed that the health education intervention of“Knowledge,Attitude,Practice”improved the awareness of TB among close contacts of TB in undergraduates.
文摘Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the investigation into the tunneling current indicates that the tunneling effect is of great importance under reverse biases.The Schottky barrier diode current due to Schottky effect is in agreement with the theoretical one.The barrier lowering is found a profound effect on the current transport at the metal semiconductor interface.
文摘N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffraction （XRD） analysis after metallization annealing. An amorphous C film at the Ni2 Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer （XEDS）. The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing. Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2 Si and amorphous C film are replaced by new metal films. The sheet resistance Rsh of the implanted layers decreases from 975 to 438f2/D, because carbon vacancies （Vc） appeared during annealing,which act as donors for electrons in SiC.
基金This work are supported by the Natural Science Foundation of China General Program(Grant No.12272157)the Natural Science Foundation of China Major Program(Grant No.12327901)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2023-ey05)the 111 Project(Grant No.B14044).
文摘The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the interface performances of the engineering structures.In this paper,a contact model is established,which is suitable for tensile and bending deformed contact surfaces.Four contact forms of asperities are proposed,and their distribution characteristics are analyzed.This model reveals the mechanism of friction generation from the perspective of the force balance of asperity.The results show the contact behaviors of the deformed contact surface are significantly different from that of the plane contact,which is mainly reflected in the change in the number of contact asperities and the real contact area.This study suggests that the real contact area of the interface can be altered by applying tensile and bending strains,thereby regulating its contact mechanics and conductive behavior.
基金supported by the Beijing Natural Science Foundation(Z200011,L233004)the National Key Research and Development Program(2021YFB2500300)+3 种基金the National Natural Science Foundation of China(52394170,52394171,22109011,22393900,and 22108151)the Tsinghua-Jiangyin Innovation Special Fund(TJISF)(2022JYTH0101)the S&T Program of Hebei(22344402D)the Tsinghua University Initiative Scientific Research Program.
文摘All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.
文摘Polysilicon ohmic contacts to n-type 4H-SiC have been fabricated. TLM （transfer length method） test patterns with polysilicon structure are formed on n-wells created by phosphorus ion （P^＋） implantation into a Si-faced p-type 4H-SiC epilayer. The polysilicon is deposited using low-pressure chemical vapor deposition （LPCVD） and doped by phosphorous ions implantation followed by diffusion to obtain a sheet resistance of 22Ω/□. The specific contact resistance pc of n^＋ polysilicon contact to n-type 4H-SiC as low as 3.82 × 10^-5Ω· cm^2 is achieved. The result for sheet resistance Rsh of the phosphorous ion implanted layers in SiC is about 4.9kΩ/□. The mechanisms for n^＋ polysilicon ohmic contact to n-type SiC are discussed.
文摘Magnesium and its alloys have gained relevance for their light-weight combined with a high value of strength-to-weight ratio,which makes them useful in fields such as aerospace,automotive as well as biomedical engineering.Unfortunately,the poor corrosion resistance of Mg-alloys limits their wide acceptance.Advanced composite coatings which are self-healing,superhydrophobic anti corrosive,and wear resistant are new synthetic materials for abating these challenges.The superimposed superhydrophobic surfaces help in minimizing their water contact,thus slowing down the electrochemical reactions on the surface of the alloys,while their self-healing characteristics autonomously aid in the repair of any induced micro-crack,defect or damage towards ensuring the metal's long-term protection.In addition,the integration of wear-resistant materials further improves the durability of coatings under mechanical stress.The most recent research efforts have been directed towards the preparation of multifunctional composites,with an emphasis on nanomaterials,functional polymers,and state-of-the-art fabrication techniques in order to take advantage of their synergistic effects.Some of the methods that have so far exhibited promising potentials in fabricating these materials include the sol-gel method,layer-by-layer assembly,and plasma treatments.However,most of the fabricated products are still faced with significant challenges ranging from long-term stability to homogeneous adhesion of the coatings and their scalability for industrial applications.This review discusses the recent progress and the relationship between corrosion inhibition and self-healing efficiencies of wear resistant polymer nanocomposite coatings.Some challenges related to optimizing coating performance were also discussed.In addition,future directions ranging from the consideration of bioinspired designs,novel hybrid nanocomposite materials,and environmentally sustainable solutions integrated with smart protective coatings were also proposed as new wave technologies that can potentially revolutionize the corrosion protection offered by Mg alloys while opening up prospects for improved performance and sustainability.
基金supported by the Natural Science Foundation of Heilongjiang Province(No.ZD2021E006)the National Natural Science Foundation of China(Nos.52174075 and 52074110).
文摘The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.
基金The financial supports by the Chinese Academy of Sciences(Nos.XDC04030300 and XDB0510303)CAS-HK Joint Laboratory of Nanomaterials and MechanicsShenyang National Laboratory for Materials Science are acknowledged.
文摘Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.
文摘In order to explore the mechanism of improving the surface wettability of low-energy polytetrafluoroethylene(PTFE)by new extended surfactants,five kinds of extended anionic surfactants with different numbers of oxypropylene(PO)and oxyethylene(EO),octadecyl-(PO)_(m)-(EO)_(n)-sodium carboxylate(C_(18)PO_(m)EO_(n)C,m=5,10,15,n=5,10,15),were studied.The surface tension and contact angle of C_(18)PO_(m)EO_(n)C solution with different concentrations were measured,and the adhesion tension,PTFE-water interfacial tension,and adhesion work were calculated.It was found that the extended surfactant molecules adsorb on the surface of the solution and the PTFE-liquid interface simultaneously when the concentration is lower than the critical micelle concentration(cmc),and there was a linear relationship between surface tension and adhesion tension.The adsorption amount of C_(18)PO_(m)EO_(n)C at the PTFE-water interface was significantly lower than that on the surface of the solution.As the concentration increases above cmc,semi-micelle aggregates on the surface of PTFE are formed by C_(18)PO_(m)EO_(n)C molecules through hydrophobic interaction,and the hydrophilic group faces the solution to modify the surface of PTFE with high efficiency.
基金Major Science and technology projects of Anhui Province (202103a05020003)。
文摘[Background and purposes]Proton exchange membrane fuel cells(PEMFCs),which convert hydrogen energy directly into electrical energy and water,have received overwhelming attention,owing to their potential to significantly reduce energy consumption,pollution emissions and reliance on fossil fuels.Bipolar plates are the major part and key component of PEMFCs stack,which provide mechanical strength,collect and conduct current segregate oxidants and reduce agents.They contribute 70-80%weight and 20-30%cost of a whole stack,while significantly affecting the power density.There are three types plates,including metal bipolar plate,graphite bipolar plate and composite bipolar plate.Stainless steel bipolar plates,as one of metal bipolar plate,exhibit promising manufacturability,competitive cost and durability among various metal materials.However,stainless steel would be corroded in the harsh acid(pH 2-5)and humid PEMFCs environment,whereas the leached ions will contaminate the membrane.In addition,the passivated film formed on the surface will increase the interfacial contact resistance(ICR).In order to improve the corrosion resistance and electrical conductivity of steel bipolar plates,surface coatings are essential.Metal nitride coatings,metal carbide coatings,polymer coatings and carbon-based coatings have been introduced in recent years.Carbon-based coatings,mainly including a-C(amorphous Carbon),Ta-C(Tetrahedral amorphous carbon)and DLC(diamond-like carbon),have attracted considerable attention from both academia and industry,owing to their superior performance,such as chemical inertness,mechanical hardness and electrical conductivity.However,Ta-C films as protective coating of PEMFCs have been rarely reported,due to the difficulty in production for industrial application.In this paper,multi-layer Ta-C composite films were produced by using customized industrial-scale vacuum equipment to address those issues.[Methods]Multiple layered Ta-C coatings were prepared by using PIS624 equipment,which assembled filtered cathodic arc evaporation,ion beam and magnetron sputtering into one equipment,while SS304 and silicon specimens were used as substrate for testing and analysis.Adhesion layer and intermediate layer were deposited by using magnetron sputtering at deposition temperature of 150℃and pressure of 3×10^(−1) Pa,while the sputtering current was set to be 5 A and bias power to be 300 V.The Ta-C layer was coated at arc current of 80-100 A,bias voltage of 1500 V and gas flow of 75 sccm.A scanning electron microscope(CIQTEK SEM3200)was used to characterize surface morphology,coating structure and cross-section profile of the coatings.Raman spectrometer(LabRam HR Evolution,HORIBA JOBIN YVON)was used to identify the bonding valence states.Electrochemical tests were performed by using an electrochemical work station(CHI760,Shanghai Chenhua Instrument Co.,Ltd.),with the traditional three electrode system,where saturated Ag/AgCl and platinum mesh were used as the reference electrode and counter electrode,respectively.All samples were mounted in plastic tube and sealed with epoxy resin,with an exposure area of 2.25 cm^(2),serving as the working electrode.Electrochemical measurements were carried out in simulated PEMFCs cathode environment in 0.5 mol·L^(−1) H_(2)SO_(4)+5 ppm F−solution,at operating temperature of 70℃.As the cathode environment was harsher than the anode environment,all the samples are stabilized at the open-circuit potential(OCP)for approximately 30 min before the EIS measurements.ICR between bipolar plates and GDL was a key parameter affecting performance of the PEMFCs stack.The test sample sandwiched between 2 pieces of carbon paper(simulate gas diffusion layer,GDL)was placed between 2 gold-plated copper electrodes at a compaction pressure of 1.4 MPa,which was considered to be the conventional compaction pressure in the PEMFCs.Under the same conditions,the resistance of a single carbon paper was measured as well.The ICR was calculated according to the formula ICR=1/2(R2−R1)×S,where S was the contact area between GDL and coated stainless steel BPPs.All data of ICR were measured three times for averaging.[Results]The coatings deposited by filtered cathodic arc technology were compact and smooth,which reduced coating porosity and favorable to corrosion resistance.The coating thickness of adhesion and intermediate layers were 180 nm,while the protective Ta-C coating thickness was about 300 nm,forming multiple coating to provide stronger protection for metal bipolar plates.Cr,Ti,Nb and Ta coatings were selected as adhesion layers for comparison.According to electrochemical test,Ta and Nb coatings have higher corrosion resistance.However,Ta and Nb materials would be costly when they are used for mass production.Relatively,Cr and Ti materials were cost effective.Hence,a comprehensive assessment was indispensable to decide the materials to be selected as adhesion layer.Ta-TiN and Ti-TiN combined adhesion and intermediate layer exhibited stronger corrosion resistance,with the corrosion current to be less than 10^(−6) A·cm^(−2).Ta-C protective coating deposited by using filtered cathodic arc technology indicated displayed higher corrosion resistance,with the average corrosion density to be about 1.26×10^(−7) A·cm^(−2).Ta-C coating also shown larger contact angle,with the highest hydrophobicity,which was one of the important advantages for Ta-C,in terms of corrosion resistance.According to Raman spectroscopy,the I(D)/I(G)=549.8/1126.7=0.487,with the estimated fraction of sp^(3) bonding to be in the range of 5154%.The intermediate layer TiN has higher conductivity than the CrN layer.Considering cost,corrosion performance and ICR result,the Ti-TiN layer combination is recommended for industrial scale application.[Conclusions]Multiple layer coating structure of Ta-C film had stronger corrosion resistance;with more than 50%sp^(3) content,while it also had larger water contact angle and higher corrosion resistance than DLC film.The filtered arcing deposition technology was able to make the film to be more consistent and stable than normal arcing technology in terms of the preparation of Ta-C.The coating displayed corrosion density of 1.26×10^(−7) A·cm^(−2) and ICR of less than 5 mΩ·cm^(2),far beyond technical target of 2025 DOE(US Department of Energy).This indicated that the mass-production scale coating technology for PEMFC bipolar plates is highly possible.
基金supported by the National Natural Science Foundation of China(Grant Nos.12372100,12302126,and 12302141)the China Postdoctoral Science Foundation(Grant No.2023M732799)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.xzy012024020)Sihe Wang also thanks the support from the China Scholarship Council(CSC).
文摘In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumulation of identical line contacts with half-width given by the truncated area divided by the contact patch number at varying heights.Based on the contact stiffness of two-dimensional flat punch,the total stiffness of rough surface is estimated,and then the normal load is calculated by an incremental method.For various rough surfaces,the approximately linear load-area relationships predicted by the proposed model agree well with the results of finite element simulations.It is found that the real average contact pressure depends significantly on profile properties.
基金supported by the Science and Technology Innovation Council of Shenzhen(No.KQTD20170810105439418)the National Key R&D Project from Minister of Science and Technology,China(No.2021YFB3200304)+2 种基金National Natural Science Foundation of China(Nos.6237129,52125205,U20A20166,61805015 and 61804011)the Natural Science Foundation of Beijing Municipality(No.Z180011)the Fundamental Research Funds for the Central Universities.
文摘Semiconducting transition-metal dichalcogenides(TMDs)have garnered significant interest due to their unique structures and properties,positioning them as promising candidates for novel electronic and optoelectronic devices.However,the performance of TMDs-based devices is hampered by the suboptimal quality of metal electrodes contacting the atomically thin TMDs layers.Understanding the mechanisms that influence contact quality is crucial for advancing TMDs devices.In this study,we investigated the conductive properties of tungsten selenide(WSe_(2))-based devices with different film thicknesses.Using the transmission line method,a negative correlation between contact resistance and film thickness in multi-electrode devices was revealed.Additionally,repeatability tests conducted at varied temperatures indicated enhanced device stability with increasing film thickness.Theoretical analysis,supported by thermionic emission theory and thermal simulations,suggests that the degradation in electrical properties is primarily due to the thermal effect at the contact interface.Furthermore,we found that van der Waals contacts could mitigate the thermal effect through a metal transfer method.Our findings elucidate the critical role of contact resistance in the electronic performance of 2D material-based field-effect transistors(FETs),which further expands their potential in the next generation of electronic and optoelectronic devices.
基金Projects(52108347, 52179112, 52178371) supported by the National Natural Science Foundation of ChinaProjects(2020C01147, 2023C01165) supported by the Primary Research and Development Plan of Zhejiang Province,ChinaProject(LQ22E080010) supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,China。
文摘When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two layers of soil with different properties, pore water flows slowly along the pore channels, demonstrating laminar flow phenomenon. To predict the thermal contact resistance and flow contact resistance at the interface, this paper constructs general imperfect thermal contact model and general imperfect flow contact model, respectively. Utilizing a thermo-hydro- mechanical coupling model, the thermal consolidation behavior of multilayered saturated soil under two-dimensional conditions is investigated. Fourier and Laplace transformations are applied to decouple the governing equations, yielding expressions for the temperature increment, pore water pressure, and displacement in multilayered saturated soil. The inverse Fourier-Laplace transformation is then used to obtain numerical solutions, which are compared with degeneration solutions to validate the computational accuracy. The differences in the thermal consolidation process under various thermal contact and flow contact resistance models are discussed. Furthermore, the impact of parameters such as the thermal resistance coefficient, partition thermal contact coefficient, flow contact resistance coefficient, and partition flow contact coefficient on thermal consolidation are investigated. Results indicate that thermal contact resistance creates a relative thermal gradient at the interface, leading to increased pore water pressure and reduced displacement nearby. In contrast, flow contact resistance generates a relative pore pressure gradient at the interface, resulting in increased displacement within the saturated soil with minimal effect on temperature increment distribution.
基金Supported by National Natural Science Foundation of China(Grant No.52475137)Sichuan Provincial Science and Technology Program(Grant No.2024YFHZ0280)Sichuan Provincial Nature and Science Foundation Innovation Research Group Project(Grant No.2023NSFSC1975).
文摘During the grinding train operation process,the grinding force between the grinding wheel and the rail is critical in ensuring the grinding quality and efficiency.The coupling vibration among the frame,the grinding wheels,and the wheelsets will seriously affect the stability of the grinding force.In this paper,the coupled mechanical model of the grinding wheel/rail is established based on the contact mechanics theory,which is embedded as a submodel into the dynamic model of the multi-rigid buggy.The interaction among the frame,the grinding wheels and the wheelsets is analysed by setting the convex irregularity on the rail.The grinding effect is evaluated in combination with the subway’s long wave corrugation grinding conditions.The results show that when the grinding buggy passes the convex irregularity,the vibration excited by the wheelset system has a significant impact on the dynamic behavior of the grinding wheels.The vibration of the grinding wheel is mainly transmitted between the grinding wheel and the frame,less affecting the wheelset.For the long wave corrugation of the subway,the grinding effect of the grinding wheel has a certain correlation with the phase angle of the wheelset through the corrugation.The research results provide an important reference for the setting of the grinding pattern.
