查看更多>>摘要：Superlubricity,a novel lubricity mode ascribing to moiré superlattice(MSL),has attracted attention in ultra-precise manufacture,microelectronic devices,and national defense areas.Based on incommensu-rate MSL,nearly zero friction can be achieved by eliminating sliding lock-in and offsetting lateral force in principle,and the theoretical foundations are still under extensive investigation.Here,the effects of MSL-induced lattice distortion on π bond and tribological performance in twist MoS2/graphene and MoS2/BN heterointerfaces were studied by first-principles calculations comprehensively.Various contributions of 2pz orbital electron polarization among AA-,AB-,and AC-stacking symmetry areas in different MSL were reflected by band structures to explain the sensitivity of π bond to MSL.The π bond perpendicular to the atomic plane depended closely on interfacial distortion,which can not only influence the local dis-tribution of intralayer bond strength but also determine the interlayer charge redistribution.Meanwhile,the interfacial potential energy was changed with the interlayer interaction fluctuation caused by twist angle and atomic stacking modes.Through evaluating the energy barriers and lateral force,MoS2/BN with a twist angle of 20.79° exhibited superlubricity.Moreover,the connection among sliding energy barriers,twist angles,and specific electronic structures has been bridged paving a path to reveal the superlubricity mechanism of two-dimensional materials with π bond.
查看更多>>摘要：Bacterial adhesion is a critical process in many fields,such as implant infections,microbiologically influ-enced corrosion and bioelectricity generation in microbial fuel cells.During bacterial adhesion,the con-tact area between the attached bacteria and the patterned surface plays an important role.In this study,different surface topographies and treatments were employed to simulate three circumstances with dif-ferent contact areas.A nanostripe structure with a period of 576.9 nm and a height of 203.5 nm was fabricated on pure titanium by femtosecond laser ablation.Bacteria in liquid attached to the peaks of the nanostripe structure and were stretched on the two adjacent nanostripes.Compared with the polished surface,the contact area between bacteria and the nanostripe surface was reduced to 50％,resulting in a reduction(about 50％)in the coverage rate of attached bacteria.In addition,the nanostripe surface was a hydrophobic surface with a water contact angle(WCA)of 112.1°,and the surface potential of the nanos-tripe surface was higher than that of the polished surface.However,the surface potential and wettability of the nanostripe surface played a minor role in the bacterial adhesion due to the reduced contact area.Upon drying,the attached bacteria on the nanostripe surface sank into the valley region and the contact area was about 40％larger than that on the polished surface.The lateral strength of bacterial adhe-sion on nanostripe surfaces was higher than that on polished surfaces,due to the larger contact area.Upon applying a lateral force of 10.0 nN,the percentage of bacteria remaining on the nanostripe sur-face(31.1％)was higher than that on the polished surface(11.9％).Hence,the bacterial adhesion on the nanopatterned surface was mainly determined by the contact area.The in-depth exploration of the rela-tion between bacterial adhesion on the nanopatterned surface and the contact area enables the rational surface designs of biomaterials to regulate bacterial adhesion.
查看更多>>摘要：Solid solutions of Na0.5Bi0.5TiO3(NBT)and BiNi0.5Ti0.5O3(BNiT)were prepared by a solid-state reaction route,and their electrical properties investigated by a combination of impedance spectroscopy and elec-tromotive force measurements to explore the possibility of developing mixed ionic-electronic conduc-tors based on NBT.Phase analysis showed that BNiT has a large solid solution limit in NBT(60 mol％based on X-ray diffraction),and the room temperature crystal structure changes from rhombohedral to pseudo-cubic with increasing BNiT content.Neutron diffraction revealed the coexistence of rhombohe-dral and tetragonal phases when the BNiT content ≥ 40 mol％.Electrically,incorporation of BNiT induces p-type electronic conduction into NBT by hopping of holes between Ni2+(NiNix)and Ni3+(NiNi),and there-fore changes the electrical conduction mechanism systematically from predominant oxide-ion conduction to mixed ionic-electronic conduction and then to predominant p-type electronic conduction.The total conductivity of the solid solutions showed a"V-shape"variation with increasing BNiT content.Possi-ble mechanisms for the phase evolution and the conductivity-composition relationships are discussed.Achieving high levels of ionic and electronic conductivity simultaneously in NBT by introducing elements with variable oxidation states remains challenging due to the competition between an enhanced elec-tronic component and a suppressed ionic component.Low levels of BNiT incorporation are,however,beneficial to reducing the dielectric loss of NBT for dielectric applications.
查看更多>>摘要：Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,SiBCN ceramic matrix composites with excellent high-temperature wave-transparent perfor-mance were prepared through PDC method.Three hyperbranched polyborosilazanes(PBSZs)were pre-pared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups.The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precur-sor and the pyrolysis temperature.The lower the methyl number and pyrolysis temperature,the lower the dielectric constant of the polymer-derived SiBCN ceramics,which is favorable for electromagnetic wave(EMW)transmittance.The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000 ℃ was 90.56％at room temperature.More excitingly,the excellent wave-transparent performance was also maintained in the temperature range of 100-800 ℃.At the test temperature of 800 ℃,SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13％and 88.96％,respectively.This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.
查看更多>>摘要：A novel Si-Al alloyed press hardening steel(PHS)with the ferrite(α)-austenite(y)-martensite(α')triplex microstructure was developed to have marginal oxidization after the hot forming in air,and the resultant ultimate tensile strength(UTS)of 1620 MPa and total elongation(TE)of 14％were achieved simultane-ously at reduced density.Both performances are superior to the existing PHSs.Particularly,the baking at 170 ℃ leads to remarkable increases in both strength and ductility together with the transition of tensile fracture from the brittle interfacial cracking to the ductile one.This is because austenite and ferrite were hardened due to the segregation of C atoms into geometry necessary dislocations(GNDs)but marten-site softened due to the loss of supersaturated C atoms during the baking.Atomic probe tomography examination reveals that some C atoms segregated to the α/α'interfaces during the baking for increased cohesive energy of the phase interface,thus hindering the interfacial cracking.In addition,the employed Al/Si alloying affords stronger oxidization resistance than both Al/Cr and Si/Cr because they are more rapidly oxidized than Cr to form the dense Al2O3/SiO2 layers for earlier protection.
查看更多>>摘要：Rechargeable zinc-ion micro-batteries(ZIMBs)are promising candidates for powering various microelec-tronic devices,although they typically exhibit low areal energy of～0.1 mWh cm-2.In this study,we reported the design and assembly of zinc micro-batteries through an ink extrusion-based printing ap-proach.In the process,a three-axis printer was adopted,allowing for the fabrication of microelectrodes with large areal loading and diverse morphologies.Vanadium oxide anchored with carbon nanotubes was employed as the cathode material,zinc powder was used as the anode material,and a polyacrylamide gel containing ethylene glycol was selected as the electrolyte.The printed micro-batteries demonstrate an areal capacity of 0.51 mAh cm-2 and an energy density of 0.37 mWh cm-2 at a charge-discharge cur-rent of 0.2 mA,outperforming state-of-the-art zinc counterparts.This work provides a simple yet efficient solution to the development of high-energy micro-batteries.
查看更多>>摘要：The development of high-performance neuromorphic phototransistors is of paramount importance for image perception and depth memory learning.Here,based on metal-oxide heterojunction architecture,artificial synaptic phototransistors with synaptic plasticity have been achieved,demonstrating an arti-ficial synapse that integrates central and optic nerve functions.Thanks to the sensitive light-detection properties,the optical power consumption of such photonic artificial synapses can be as low as 22 pico-joules,which is extremely competitive compared with other pure metal oxide photoelectric synapses ever reported.What is more,owing to its good short-term(STP)and tunable amplitude-frequency character-istics,the as-constructed device can function as a biomimetic high-pass filter for picture edge detection.Dual-mode synaptic modulation has been performed,combining photonic pulse with gate voltage stim-ulus.After photoelectric-synergistic modulation,the high synaptic weights enable the device to simulate complex neural learning rules for neuromorphic applications,including gesture recognition,image per-ception in the visual system,and classically conditioned reflexes.These results suggest that the current oxide-based heterojunction architecture displays potential application in future multifunction neuromor-phic devices and systems.
查看更多>>摘要：Fretting damage is common in the high-strength titanium alloy fastener widely used in the aeronautic industry,leading to the failure of fastening fit or the initiation of crack.The titanium alloy fasteners often have typical preferred orientation characteristics(i.e.,texture),and this is one of the important factors affecting its performance.However,the investigations on the mechanism of β rolling-texture intensity on fretting damage resistance and subsurface deformation are less addressed.Hence,fretting wear tests were carried out on samples with different rolling texture intensities.The results demonstrate that the samples with quite low(A-10％sample)and quite high(D-70％sample)rolling-texture intensity both exhibit excellent fretting wear resistance,but their mechanisms are completely different.Uniformly dis-persed grain orientation renders the A-10％sample with good recovery ability and a positive friction effect during wear.Low stress only concentrating at grain boundaries(GBs)weakens cracks'initiation and propagation.The unique orientation-layered structure(OLS)leads to excellent recovery ability and a positive friction effect.Crack propagation is inhibited and only propagates along the OLS boundary with-out a connected trend.However,samples with moderate rolling texture intensity exhibit severe wear.Dislocations are restricted in local areas,so the poor recovery ability makes them have a negative friction effect.Crack propagation driving force continuously increases.Appropriate rolling texture intensity can reduce wear by three times.This study can provide information on the principle for designing fretting damage-resistant alloys.
查看更多>>摘要：The control of undesired electromagnetic radiation in S-and C-band spectra requires novel mi-crowave absorbing materials(MAMs)having high microwave attenuation capability together with op-timal impedance matching.CNTs are conformally coated onto the surface of one-dimensional FeCo-based magnetic microchains via electrostatic self-assembly,and then the magnetic inclusions are collectively oriented in matrices by applying an external magnetic field.The proper incorporation of CNTs with mag-netic microchains demonstrates a feasible pathway for effectively absorbing microwaves in the S and C band.MAMs consisting of oriented microchains have anisotropic complex permittivity,of which the real part ranges from 6.1 to 30.4 at 2 GHz.When the electric field is parallel to microchains,the 5-mm-thick MAM has an effective absorbing bandwidth(EAB)in the range of 2.3 to 2.9 GHz,and reduces the radar cross section to be lower than-15.9 dB m2 from the vertical to the glancing incidence.When the mag-netic field is parallel to microchains,the MAM adsorbs C-band microwaves with an EAB of 1.5 GHz,and achieves maximal reflection loss of-46.4 dB.The collective orientation of shape-anisotropic magnetic materials,in addition to the composition and microstructure,is a new variable for the design of effective MAMs.
查看更多>>摘要：The conception of epoxy thermosets with both reprocessability and flame retardancy delineates a new horizon in polymer science,offering a material solution that is not only superior in fire safety but is also environment friendly.Herein,a flame-retardant epoxy vitrimer(EV)was prepared using partially bio-based IADPPO(diphenylphosphine oxide itaconic anhydride)and citric acid as curing reagents via a solvent-free process.Their incorporation created covalent adaptable networks(CANs)in the matrix which promote reprocessability and recyclability.The EV exhibits excellent thermal stability with high initial decomposition temperature(T.5wt％～308 ℃)and high glass transition temperature(Tg～107 ℃),similar to the blank EV(115 ℃).The flame retardancy,mechanical properties,transesterification-based repro-cessability,and flame-retardant mechanism were investigated.The EV containing 3 wt％phosphorus(EV IADPPO 3P)achieved UL-94 V0 classification with a limiting oxygen index(LOI)of 27％,while the virgin sample Blank EV(without phosphorus)burned completely.Additionally,increased flexural strength of 79％was observed for EV IADPPO 3P compared to Blank EV.Furthermore,the flame-retardant EV showed high malleability and reparability that could be thermomechanically reprocessed without sacrificing the thermal,mechanical,and flame-retardant properties.Thus,the newly developed epoxy vitrimer is not only fire-safe but fulfills the sustainability goals of today's society.
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