Construction of all-organic low dielectric polyimide hybrids via synergistic effect between covalent organic framework and cross-linking structure

Polyimide(PI)is a promising electronic packaging material,but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer.Herein,a series of allorganic PI hybrid films were successfully prepared by introducing the covalent organic framework(COF),which could induce the formation of the cross-linking structure in the PI matrix.Due to the synergistic effects of the COF fillers and the cross-linking structure,the PI/COF hybrid film containing 2 wt%COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss(tanδ)of 0.0077 at 1 MHz.It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI.Besides,the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume(FFV).The molecular dynamics simulation results are well consistent with the dielectric properties data.Furthermore,the PI/COF hybrid film with 5 wt%COF showed a significant enhancement in breakdown strength,which increased to 412.8 kV/mm as compared with pure PI.In addition,the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient(CTE).It also exhibited excellent thermal,hydrophobicity,and mechanical performance.The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.

A compact and closed-loop spin-exchange relaxation-free atomic magnetometer for wearable magnetoencephalography

Atomic magnetometers operated in the spin-exchange relaxation-free(SERF)regime are the promising sensor to replace superconducting quantum interference devices(SQUIDs)in the biomagnetism field.The SERF magnetometer with compact size and good performance is crucial to the new generation of wearable magnetoencephalography(MEG)system.In this paper,we developed a compact and closed-loop SERF magnetometer with the dimensions of 15.0×22.0×30.0 mm^(3)based on a single-beam configuration.The bandwidth of the magnetometer was extended to 675 Hz while the sensitivity was maintained at 22 f T/Hz^(1/2).A nearly 3-fold enhancement of the bandwidth was obtained in comparison with the open-loop control.The implementation of the closed-loop control also greatly improved the dynamic range,enabling the magnetometer to be robust against the disturbance of the ambient field.Moreover,the magnetometer was successfully applied for the detection of humanα-rhythm and auditory evoked fields(AEFs),which demonstrated the potential to be extended to multi-channel MEG measurements for future neuroscience studies.

Piezoresistive design for electronic skin: from fundamental to emerging applications

There is growing recognition that the developments in piezoresistive devices from personal healthcare to artificial intelli-gence,will emerge as de novo translational success in electronic skin.Here,we review the updates with regard to piezoresistive sensors including basic fundamentals,design and fabrication,and device performance.We also discuss the prosperous advances in piezoresistive sensor application,which offer perspectives for future electronic skin.

Sub-10 nm fabrication:methods and applications

Reliable fabrication of micro/nanostructures with sub-10 nm features is of great significance for advancing nanoscience and nanotechnology.While the capability of current complementary metal-oxide semiconductor(CMOS)chip manufacturing can produce structures on the sub-10 nm scale,many emerging applications,such as nano-optics,biosensing,and quantum devices,also require ultrasmall features down to single digital nanometers.In these emerging applications,CMOS-based manufacturing methods are currently not feasible or appropriate due to the considerations of usage cost,material compatibility,and exotic features.Therefore,several specific methods have been developed in the past decades for different applications.In this review,we attempt to give a systematic summary on sub-10 nm fabrication methods and their related applications.In the first and second parts,we give a brief introduction of the background of this research topic and explain why sub-10 nm fabrication is interesting from both scientific and technological perspectives.In the third part,we comprehensively summarize the fabrication methods and classify them into three main approaches,including lithographic,mechanics-enabled,and post-trimming processes.The fourth part discusses the applications of these processes in quantum devices,nano-optics,and high-performance sensing.Finally,a perspective is given to discuss the challenges and opportunities associated with this research topic.

Vertical Tire Forces Estimation of Multi-Axle Trucks Based on an Adaptive Treble Extend Kalman Filter

Vertical tire forces are essential for vehicle modelling and dynamic control.However,an evaluation of the vertical tire forces on a multi-axle truck is difficult to accomplish.The current methods require a large amount of experimental data and many sensors owing to the wide variation of the parameters and the over-constraint.To simplify the design process and reduce the demand of the sensors,this paper presents a practical approach to estimating the vertical tire forces of a multi-axle truck for dynamic control.The estimation system is based on a novel vertical force model and a proposed adaptive treble extend Kalman filter(ATEKF).To adapt to the widely varying parameters,a sliding mode update is designed to make the ATEKF adaptive,and together with the use of an initial setting update and a vertical tire force adjustment,the overall system becomes more robust.In particular,the model aims to eliminate the effects of the over-constraint and the uneven weight distribution.The results show that the ATEKF method achieves an excellent performance in a vertical force evaluation,and its performance is better than that of the treble extend Kalman filter.

Effects of bionic mechanical stimulation on the properties of engineered cartilage tissue

Tissue-engineered cartilage(TEC)remains a potential alternative for the repair of articular cartilage defects.However,there has been a significant different between the properties of TEC and those of natural cartilage.Studies have shown that mechanical stimulation such as compressive load can help regulate matrix remodelling in TEC,thus affecting its biomechanical properties.However,the influences of shear induced from the tissue fluid phase have not been well studied and may play an important role in tissue regeneration especially when integrated with the compressive load.Therefore,the aim of this study was to quantitatively investigate the effects of combined loading mechanisms on TEC in vitro.A bespoke biosimulator was built to incorporate the coupled motion of compression,friction and shear.The specimens,encapsulating freshly isolated rabbit chondrocytes in a hydrogel,were cultured within the biosimulator under various mechanical stimulations for 4 weeks,and the tissue activity,matrix contents and the mechanical properties were examined.Study groups were categorized according to different mechanical stimulation combinations,including strain(5-20%at 5%intervals)and frequency(0.25 Hz,0.5 Hz,1 Hz),and the effects on tissue behaviour were investigated.During the dynamic culture process,a combined load was applied to simulate the combined effects of compression,friction and shear on articular cartilage during human movement.The results indicated that a larger strain and higher frequency were more favourable for the specimen in terms of the cell proliferation and extracellular matrix synthesis.Moreover,the combined mechanical stimulation was more beneficial to matrix remodelling than the single loading motion.However,the contribution of the combined mechanical stimulation to the engineered cartilaginous tissue matrix was not sufficient to impede biodegradation of the tissue with culture time.

Study on Preparation and Ns-Laser Damage of HfO₂Single Layers

The effects of the main parameters of argon flux, oxygen flux and beam voltage on the surface morphology, transmittance spectrum and laser damage of the HfO2 single layers prepared by ion beam sputtering are studied. The HfO2 amorphous single layers have porous surface morphologies. Different processes will cause differences in coatings absorption and surface morphology, which in turn will cause changes in the spectral transmittance curve. The ion beam sputtering HfO2 single layers have high content of argon (4.5% - 8%). The laser damage of HfO2 single layers is related to argon inclusions and non-stoichiometric defects. The changes of argon flux and beam voltage have a greater impact on argon content and O/Hf ratio. When the argon content in the coatings is lower and the O/Hf ratio is higher, the laser damage thresholds of the HfO2 single layers are higher.

Laser powder bed fusion of NiTiFe shape memory alloy via premixed powder:microstructural evolution,mechanical and functional properties

High-cost pre-alloyed powder is the bottleneck problem that limits the widespread application of additivemanufactured shape memory alloys.In this work,the lowcost ternary NiTiFe shape memory alloy is fabricated by laser powder bed fusion(LPBF)technique via mechanically mixed pre-alloy NiTi powder and varying contents pure Fe powder(1,2,3 wt%).All NiTiFe alloys show a relative density of up to 99.8%by optimizing the LPBF processing parameters.Owing to the heterogeneous nucleation effect of micron-sized Fe particles,both grain refinement and texture weakening are generated in the NiTiFe alloys,accompanied by the reduction of dislocation density.For the room-temperature mechanical properties,the NiTi-3Fe alloy shows the highest microhardness of HV370,but the fracture strength and elongation reduce to1701 MPa and 23%simultaneously.The evolution of mechanical properties is attributed to the high internal defects,low dislocation density and the incoherent oxide.Moreover,the NiTi-3Fe alloy shows the quasi-linear superelasticity behavior;the superelastic recoverable strain of NiTi-1Fe and NiTi-2Fe decreased with the increase in Fe content.This study provided a new-fangled insight for the development of multi-component NiTi-based shape memory alloys by additive manufacturing.

Investigation of Material Properties Based on 3D Graphite Morphology for Compacted Graphite Iron

The strength and thermal conductivity of compacted graphite iron(CGI)are crucial performance indicators in its engineering application.The presence of graphite in CGI significantly influences the two properties.In the previous studies,graphite in CGI was often described using two-dimensional(2D)morphology.In this study,the three-dimensional(3D)size,shape,and distribution of graphite in CGI were analyzed using X-ray tomography.Based on this,a new method is introduced to calculate the 3D vermicularity and compare it with the 2D vermicularity in terms of tensile properties and thermal conductivity.The results demonstrate that vermicular graphite exhibits greater connectivity in 3D observation compared to 2D observation.Therefore,the calculation method of 3D vermicularity is determined by considering the surface area and volume of the connected graphite.Then a linear relationship between 3 and 2D vermicularity has been observed.By comparing the correlation coefficient,it has been found that the 3D vermicularity offers a more accurate method to establish the relationship among graphite morphology,thermal conductivity and tensile property of CGI.

Liquid Crystal Based Label-Free Optical Sensors forBiochemical Application

Biochemical sensors have important applications in biology,chemistry,and medicine.Nevertheless,many biochemical sensors are hampered by intricate techniques,cumbersome procedures,and the need for labeling.In the past two decades,it has been discovered that liquid crystals can be used to achieve the optical amplification of biological interactions.By modifying recognition molecules,a variety of label-free biochemical sensors can be created.Consequently,biochemical sensors based on the amplification of liquid crystals have become one of the most promising sensors.This paper describes in detail the optical sensing principle of liquid crystals,sensing devices,and optical detection technologies.Meanwhile,the latest research findings are elucidated.Finally,the challenges and future research directions are discussed.

Comparative Study of Intrachain versus Interchain Cross-linking on the Mechanical,Thermal and Dielectric Properties of Low-k Polyimide

Polyimide(PI)is widely used in high-frequency communication technology due to its exceptional comprehensive properties.However,traditional PI has a relatively elevated dielectric constant and dielectric loss.Herein,the different cross-linked structures were introduced in PI matrix and conducted a detailed discussion on the influence of cross-linking agent content and cross-linking structure type on the overall performance of PI films.In comparison to the dielectric constant of 2.9 of neat PI,PI with an interchain cross-linking structure containing 2 wt%1,3,5-tris(4-aminophenyl)benzene(TAPB)(interchain-PI-2)exhibited the reduced dielectric constant of 2.55 at 1 MHz.The PI films with intrachain crosslinking structure containing 2 wt%TAPB(intrachain-PI-2)exhibited the lowest dielectric constant of 2.35 and the minimum dielectric loss of0.0075 at 1 MHz.It was due to the more entanglement junctions of intrachain-PI resulting in decreased carrier transport.The thermal expansion coefficients of both interchain-PI and intrachain-PI films were effectively reduced.Moreover,in contrast to interchain-PI films,the intrachain-PI films maintained colorlessness and transparency as the cross-linking agent content increased.This work compared the effects of two different cross-linked structures on the performance of PI films and provided a feasible way to obtain low-k PI films with excellent comprehensive performance for 5G applications.

Special issue on a 90-year journey towards light from the intramolecular universe

Over the past nearly 90 years,scientists have gradually revealed the mysteries of intramolecular motion and chemical bonds through continuous research and innovation.In 1928,Irish scientist E.Synge proposed a method to overcome the limit of classical optical resolution,which laid the foundation for the subsequent development of scanning near-field optical microscopes.Near-field optical microscopy continues to push optical resolution to new records,well beyond the diffraction limit of traditional optical microscopy.

A Protocol for Digitalized Collection of Traditional Chinese Medicine(TCM)Pulse Information Using Bionic Pulse Diagnosis Equipment

Pulse diagnosis equipment used in Traditional Chinese Medicine(TCM)has long been developed for collecting pulse information and in TCM research.However,it is still difficult to implement pulse taking automatically or efficiently in clinical practice.Here,we present a digital protocol for TCM pulse information collection based on bionic pulse diagnosis equipment,which ensures high efficiency,reliability and data integrity of pulse diagnosis information.A four-degree-of-freedom pulse taking platform together with a wrist bracket can satisfy the spatial positioning and angle requirements for individually adaptive pulse acquisition.Three-dimensional reconstruction of a wrist surface and an image localization model are combined to provide coordinates of the acquisition position and detection direction automatically.Three series elastic joints can not only simulate the TCM pulse taking method that“Three fingers in a straight line,the middle finger determining the‘Guan’location and finger pulp pressing on the radial artery,”but also simultaneously carry out the force-controlled multi-gradient pressing process.In terms of pulse information integrity,this proposed protocol can generate rich pulse information,including basic individual information,pulse localization distribution,multi-gradient dynamic pulse force time series,and objective pulse parameters,which can help establish the fundamental data sets that are required as the pulse phenotype for subsequent comprehensive analysis of pulse diagnosis.The implementation of this scheme is beneficial to promote the standardization of the digitalized collection of pulse information,the effectiveness of detecting abnormal health status,and the promotion of the fundamental and clinical research of TCM,such as TCM pulse phenomics.

Effect of near-field optical angular momentum on molecular junctions

The role of molecular junctions in nanoelectronics is most often associated with electronic transport;however,their precise characterisation hinders their widespread development.The interaction of light with molecular junctions is a supplementary factor for the development of molecular switches,but it has rarely been addressed.The influence of light interaction with molecular junctions on the response of molecules in the near field was demonstrated by properly characterising the optical angular momentum at the junctions.Consequently,the molecular switching dynamics were observed in the Raman signatures of the conducting molecules.The illumination geometry and voltage applied to the junction were changed to demonstrate numerically and experimentally how the Raman intensity can be turned ON and OFF with a difference of nearly five orders of magnitude.These molecular-scale operations result from the combined interaction of a current-induced electronic rearrangement in the molecular junction and a plasmonically enhanced electromagnetic field near the tip of the junction.This study of the effect of optical angular momentum on the near field of the molecular junction shows significant potential for the development of molecular electronics.

Fluorescence microscope light source based on integrated LED

An LED-integrated excitation cube(LEC)was designed to address the limitations of conventional fluorescence lamps.The LEC has a decentralized structure,high optical power density,and efficient illumination.The optical efficiency of LECs is 1–2 orders of magnitude higher than that of mercury lamps,enabling high-quality fluorescence imaging with spectral coverage from UV to red.LECs can be easily installed on commercial fluorescence microscopes by replacing conventional fluorescence filter cubes,and a built-in LEC driver can identify the types of LEDs in different spectral bands to adopt optimal operating conditions.

A sandwich-like structure hybrid coating of cold galvanizing coating/polydopamine on hot-dip galvanized steel with enhanced adhesion and corrosion resistance

This study aims to enhance the adhesion strength and anti-corrosion performance of the cold galvanizing coating(CGC)applied on the hot-dip galvanized steel(HDG).Polydopamine(PDA)is deposited on the HDG surface with different time ranges and as an interlayer between CGC and HDG through covalent immobilization.The surface morphology and the covalent interaction between PDA/HDG are exhibited by scanning electron microscope(SEM),atomic force microscopy(AFM)and X-ray photoelectron spectroscopy(XPS).The pull-off adhesion tests before and after neutral slat spry tests show an enhanced dry adhesion strength and less adhesion loss of the hybrid CGC/PDA coated HDG compared with the direct CGC coated HDG.In addition,open circuit potential(OCP)reveals that the corrosion protection performance of the hybrid CGC/PDA coated HDG increases by 200%(up to 201 d)and the corrosion density icorrattaining about 4.45×10^(-7)A/cm^(2).Electrochemical impedance spectroscopy(EIS)measurements and X-ray diffraction(XRD)analysis confirm that the precipitate of the stable chelation formed by PDA and Zn^(2+)between CGC and HDG substrate can also improve the corrosion protection performance.Such a strategy of strengthening adhesion and forming the chelate compound at the HDG surface promises a new route to corrosion protection of CGC on HDG.

Hierarchical pomegranate-structure design enables stress management for volume release of Si anode

Si is a promising anode material for lithium-ion batteries owing to its high theoretical capacity.How-ever,large stress during(de)lithiation induces severe structural pulverization,electrical contact failure,and unstable solid-electrolyte interface,which hampers the practical application of Si anode.Herein,a Si-based anode with a hierarchical pomegranate-structure(HPS-Si)was designed to modulate the stress variation,and a sub-micronized Si-based sphere was assembled by the nano-sized Si nanospheres with sub-nanometer-sized multi-phase modification of the covalently linked SiO_(2-x),SiC,and carbon.The sub-micronized HPS-Si stacked with Si nanospheres can avoid agglomerates during cycling due to the high surface energy of nanomaterials.Meanwhile,the reasonable pore structure from SiO_(2) reduction owing to density difference is enough to accommodate the limited volume expansion.The Si spheres with a size of about 50 nm can prevent self-cracking.SiO_(2-x),and SiC as flexible and rigid layers,have been syner-gistically used to reduce the surface stress of conductive carbon layers to avoid cracking.The covalent bonding immensely strengthens the link of the modification with Si nanospheres,thus resisting stress effects.Consequently,a full cell comprising an HPS-Si anode and a LiCoO_(2) cathode achieved an energy density of 415 Wh kg^(-1) with a capacity retention ratio of 87.9%after 300 cycles based on the active ma-terials.It is anticipated that the hierarchical pomegranate-structure design can provide inspiring insights for further studies of the practical application of silicon anode.

Si/C particles on graphene sheet as stable anode for lithium-ion batteries

Silicon is considered as one of the most promising anodes for Li-ion batteries(LIBs), but it is limited for commercial applications by the critical issue of large volume expansion during the lithiation. In this work, the structure of silicon/carbon(Si/C) particles on graphene sheets(Si/C–G) was obtained to solve the issue by using the void space of Si/C particles and graphene. Si/C–G material was from Si/PDA-GO that silicon particles was coated by polydopamine(PDA) and reacted with oxide graphene(GO). The Si/C–G material have good cycling performance as the stability of the structure during the lithiation/dislithiation.The Si/C–G anode materials exhibited high reversible capacity of 1910.5 mA h g^(-1) and 1196.1 mA h g^(-1) after 700 cycles at 357.9 m A g^(-1), and have good rate property of 507.2 mA h g^(-1) at high current density,showing significantly improved commercial viability of silicon electrodes in high-energy-density LIBs.

Strong interface contact between NaYF_(4):Yb,Er and CdS promoting photocatalytic hydrogen evolution of NaYF_(4):Yb,Er/CdS composites

To acquire efficient photocatalysts,it is necessary to make effective use of visible light/Near Infrared(NIR)light,which takes up a large percentage of sunlight.Integrating upconversion materials with visible light active photocatalysts has attracted much attention in this regard.The interface contact between upcon-version material and photocatalyst has potential influence on the properties and thus the performance of the system.In this work,NaYF_(4):Yb,Er/CdS composites of the upconversion material NaYF_(4):Yb,Er nanorods and CdS nanoparticles were synthesized by ion adsorption/precipitation process and were then annealed in an argon atmosphere at different temperatures to modulate the microstructures.The annealing pro-cess endows the crystal transformation of cubic CdS with low crystallinity to hexagonal CdS with high crystallinity and,importantly,good interface contact between NaYF_(4):Yb,Er and CdS.Consequently,the hy-drogen evolution activity greatly increases from 171 to 2539μmol h^(−1) g^(−1) under the light irradiation ofλ>400 nm,and from 0 to 19μmol h^(−1) g^(−1) under the light irradiation ofλ>600 nm.This work might provide a useful reference for the rational design of promising photocatalyst involving upconversion ma-terials.

Bioinspired tungsten-copper composites with Bouligand-type architectures mimicking fish scales

The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials;nevertheless,it is challenging to reproduce in metals.Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers.These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization.The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures.In particular,under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening,stretching,interfacial sliding with the matrix,and the cooperative kinking deformation of fiber grids,representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness.This study may serve to promote the development of new high-performance tungsten-copper composites for applications,e.g.,as electrical contacts or heat sinks,and offer a viable approach for constructing bioinspired architectures in metallic materials.