Anti-parallel β-sheet crystallite as the main component of silk fibroin has attracted much attention due to its superior mechanical properties. In this study, we examine the processes of pulling a peptide chain from ...Anti-parallel β-sheet crystallite as the main component of silk fibroin has attracted much attention due to its superior mechanical properties. In this study, we examine the processes of pulling a peptide chain from β-sheet crystallite using steered molecular dynamics simulations to investigate the rupture behavior of the crystallite. We show that the failure of β-sheet crystallite was accompanied by a propagation of instability of hydrogen-bonds （H-bonds） in the crystallite. In addition, we find that there is an optimum size of the crystallite at which the H-bonds can work cooperatively to achieve the highest shear strength. In addition, we find that the stiffness of loading device and the loading rates have significant effects on the rupture behavior of β-sheet crystallite. The stiff loading device facilitates the rebinding of the Hbond network in the stick-slip motion between the chains, while the soft one suppresses it. Moreover, the rupture force of β-sheet crystallites decreases with loading rate. Particularly, when the loading rate decreases to a critical value, the rupture force of the β-sheet crystallite becomes independent of the loading rates. This study provides atomistic details of rupture behaviors of β-sheet crystallite, and, therefore, sheds valuable light on the underlying mechanism of the superior mechanical properties of silk fibroin.展开更多
Two-dimensional （2D） materials, such as graphene, phosphorene, and transition metal dichalcogenides （e.g., MoS2 and WS2）, have attracted a great deal of attention recently due to their extraordinary structural, me...Two-dimensional （2D） materials, such as graphene, phosphorene, and transition metal dichalcogenides （e.g., MoS2 and WS2）, have attracted a great deal of attention recently due to their extraordinary structural, mechanical, and physical properties. In particular, 2D materials have shown great potential for thermal management and thermoelectric energy generation. In this article, we review the recent advances in the study of thermal properties of 2D materials. We first review some important aspects in thermal conductivity of graphene and discuss the possibility to enhance the ultra-high thermal conductivity of graphene. Next, we discuss thermal conductivity of MoS2 and the new strategy for thermal management of MoS2 device. Subsequently, we discuss the anisotropic thermal properties of phosphorene. Finally, we review the application of 2D materials in thermal devices, including thermal rectifier and thermal modulator.展开更多
Cutting-edge heat spreaders for soft and planar electronics require not only high thermal conductivity and a certain degree of flexibility but also remarkable self-adhesion without thermal interface materials, elastic...Cutting-edge heat spreaders for soft and planar electronics require not only high thermal conductivity and a certain degree of flexibility but also remarkable self-adhesion without thermal interface materials, elasticity, arbitrary elongation along with soft devices, and smart properties involving thermal self-healing, thermochromism and so on. Nacre-like composites with excellent in-plane heat dissipation are ideal as heat spreaders for thin and planar electronics. However, the intrinsically poor viscoelasticity, i.e., adhesion and elasticity, prevents them from simultaneous self-adhesion and arbitrary elongation along with current flexible devices as well as incurring high interfacial thermal impedance. In this paper, we propose a soft thermochromic composite(STC) membrane with a layered structure, considerable stretchability, high in-plane thermal conductivity(~30 Wm^(-1) K^(-1)), low thermal contact resistance(~12 mm^2 KW^(-1), 4–5 times lower than that of silver paste), strong yet sustainable adhesion forces(~4607 Jm^(-2), 2220 Jm^(-2) greater than that of epoxy paste) and self-healing efficiency. As a self-adhesive heat spreader, it implements efficient cooling of various soft electronics with a temperature drop of 20℃ than the polyimide case. In addition to its self-healing function, the chameleon-like behavior of STC facilitates temperature monitoring by the naked eye, hence enabling smart thermal management.展开更多
We propose a multi-field implicit finite element method for analyzing the electromechanical behavior of dielectric elastomers. This method is based on a four-field variational principle, which includes displacement an...We propose a multi-field implicit finite element method for analyzing the electromechanical behavior of dielectric elastomers. This method is based on a four-field variational principle, which includes displacement and electric potential for the electromechanical coupling analysis, and additional independent fields to address the incompressible constraint of the hyperelastic material. Linearization of the variational form and finite element discretization are adopted for the numerical implementation. A general FEM program framework is devel- oped using C＋＋ based on the open-source finite element library deal.II to implement this proposed algorithm. Numerical examples demonstrate the accuracy, convergence properties, mesh-independence properties, and scalability of this method. We also use the method for eigenvalue analysis of a dielectric elastomer actuator subject to electromechanical loadings. Our finite element implementation is available as an online supplementary material.展开更多
Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of...Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of antiperovskite X_(3)NP(X^(2+)=Ca,Mg)upon compression by first-principles calculations.Our results reveal that the system is anisotropic,and the lat-tice constant a of X_(3)NP exhibits the fastest rate of decrease upon compression among the three directions,which is different from the typical Pnma phase of halide and chalcogenide perovskites.Meanwhile,Ca_(3)NP has higher compressibility than Mg_(3)NP due to its small bulk modulus.The electronic and optical properties of Mg_(3)NP show small fluctuations upon compression,but those of Ca_(3)NP are more sensitive to pressure due to its higher compressibility and lower unoccupied 3d orbital energy.For example,the band gap,lattice dielectric constant,and exciton binding energy of Ca_(3)NP decrease rapidly as the pressure increases.In addition,the increase in pressure significantly improves the optical absorption and theoretical conversion effi-ciency of Ca_(3)NP.Finally,the mechanical properties of X_(3)NP are also increased upon compression due to the reduction in bond length,while inducing a brittle-to-ductile transition.Our research provides theoretical guidance and insights for future experi-mental tuning of the physical properties of antiperovskite semiconductors by pressure.展开更多
Collagen fibers provide a good example of making strong micro-or mesoscale fibers from nanoscale tropocollagen molecules through a staggered and crosslinked organization in a bottom-up manner.Mimicking the architectur...Collagen fibers provide a good example of making strong micro-or mesoscale fibers from nanoscale tropocollagen molecules through a staggered and crosslinked organization in a bottom-up manner.Mimicking the architectural features of collagen fibers has been shown to be a promising approach to develop carbon nanotube（CNT）fibers of high performance.In the present work,an elastic model is developed to describe the load transfer and failure propagation within the bioinspired CNT bundles,and to establish the relations of the mechanical properties of the bundles with a number of geometrical and physical parameters such as the CNT aspect ratio and longitudinal gap,interface cross-link density,and the functionalizationinduced degradation in CNTs,etc.With the model,the stress distributions along the CNT-CNT interface as well as in every individual CNT are well captured,and the failure propagation along the interface and its effects on the mechanical properties of the CNT bundles are predicted.The work may provide useful guidelines for the design of novel CNT fibers in practice.展开更多
An open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, is used to study a blunt body with the shape of a space crew capsule return vehicle. The rarefied gas has the Knudsen number wi...An open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, is used to study a blunt body with the shape of a space crew capsule return vehicle. The rarefied gas has the Knudsen number with 0.03. The flow with a Mach number 4.35 over the capsule was simulated by DSMC. The distributions of velocity field and temperature around the capsule were calculated. This study may provide some useful information for the reentry of the return vehicle.展开更多
Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface...Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface diffusion of heterogeneous adatoms clusters can be vital for the binary island growth on the surface and can be useful for the formation of alloy-based thin film surface through atomic exchange process. The results of the diffusion process show that at 300 K, the diffusion of small adatoms clusters shows hopping, sliding, and shear motion; whereas for large adatoms clusters（hexamer and above）, the diffusion is negligible. At 500 K, small adatoms clusters, i.e., dimer, show almost all possible diffusion mechanisms including the atomic exchange process; however no such exchange is observed for adatoms clusters greater than dimer. At 700 K, the exchange mechanism dominates for all types of clusters, where Zr adatoms show maximum tendency and Ag adatoms show minimum or no tendency toward the exchange process. Separation and recombination of one or more adatoms are also observed at 500 K and 700 K. The Ag adatoms also occupy pop-up positions over the adatoms clusters for short intervals. At 700 K, the vacancies are also generated in the vicinity of the adatoms cluster,vacancy formation, filling, and shifting can be observed from the results.展开更多
Manmade debris and natural meteoroids, travelling in the Low Earth Orbit at a speed of several kilometers per second, pose a severe safety concern to the spacecraft in service through the HyperVelocity Impact(HVI). To...Manmade debris and natural meteoroids, travelling in the Low Earth Orbit at a speed of several kilometers per second, pose a severe safety concern to the spacecraft in service through the HyperVelocity Impact(HVI). To address this issue, an investigation of shock Acoustic Emission(AE) waves induced by HVI to a downscaled two-layer Whipple shielding structure is performed,to realize a quantitative damage evaluation. Firstly a hybrid numerical model integrating smoothparticle hydrodynamics and finite element is built to obtain the wave response. The projectiles, with various impact velocities and directions, are modelled to impact the shielding structure with different thicknesses. Then experimental validation is carried out with built-in miniaturized piezoelectric sensors to in situ sense the HVI-induced AE waves. A quantitative agreement is obtained between numerical and experimental results, demonstrating the correctness of the hybrid model and facilitating the explanation of obtained AE signals in experiment. Based on the understanding of HVI-induced wave components, assessment of the damage severity, i.e., whether the outer shielding layer is perforated or not, is performed using the energy ratio between the regions of ‘‘high frequency" and ‘‘low frequency" in the acquired AE signals. Lastly, the direct-arrival fundamentalsymmetric wave mode is isolated from each sensing signal to be input into an enhanced delay-andsum algorithm, which visualizes HVI spots accurately and instantaneously with different sensor network configuration. All these works demonstrate the potential of quantitative, in situ, and real time HVI monitoring using miniaturized piezoelectric sensor network.展开更多
Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic beha...Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.展开更多
The two-dimensional(2D)material-based thermal switch is attracting attention due to its novel applications,such as energy conversion and thermal management,in nanoscale devices.In this paper,we observed that the rever...The two-dimensional(2D)material-based thermal switch is attracting attention due to its novel applications,such as energy conversion and thermal management,in nanoscale devices.In this paper,we observed that the reversible 2H–1T′phase transition in MoTe_(2)is associated with about a fourfold/tenfold change in thermal conductivity along the X/Y direction by using first-principles calculations.This phenomenon can be profoundly understood by comparing the Mo–Te bonding strength between the two phases.The 2H-MoTe_(2)has one stronger bonding type,while 1T′-MoTe_(2)has three weaker types of bonds,suggesting bonding inhomogeneity in 1T′-MoTe_(2).Meanwhile,the bonding inhomogeneity can induce more scattering of vibration modes.The weaker bonding indicates a softer structure,resulting in lower phonon group velocity,a shorter phonon relaxation lifetime and larger Gr¨uneisen constants.The impact caused by the 2H to 1T′phase transition in MoTe_(2)hinders the propagation of phonons,thereby reducing thermal conductivity.Our study describes the possibility for the provision of the MoTe_(2)-based controllable and reversible thermal switch device.展开更多
The ultrafast growth of large-area,high-quality WSe2 domains with a compact triangular morphology has recently been achieved on a gold substrate via chemical vapor deposition.However,the underlying mechanism responsib...The ultrafast growth of large-area,high-quality WSe2 domains with a compact triangular morphology has recently been achieved on a gold substrate via chemical vapor deposition.However,the underlying mechanism responsible for ultrafast growth remains elusive.Here,we first analyze growth processes and identify two possible pathways that might achieve ultrafast growth:Path 1,fast edge attachment and ultrafast edge diffusion;Path 2,fast kink nucleation and ultrafast kink propagation.We perform kinetic Monte Carlo simulations and first-principles calculations to assess the viability of these two paths,finding that Path 1 is not viable due to the high edge diffusion barrier calculated from first-principles calculations.Remarkably,Path 2 reproduces all the experimental growth features(domain morphology,domain orientation,and growth rate),and the associated energetic data are consistent with first-principles calculations.The present work unveils the underlying mechanism for the ultrafast growth of WSe2,and may provide a new route for the ultrafast growth of other two-dimensional materials.展开更多
Herein we computationally explore the modulation of the release kinetics of an encapsulated vip molecule from the cucurbit[7]uril(CB7)cavity by ligands binding to the host portal.We uncovered a correlation between t...Herein we computationally explore the modulation of the release kinetics of an encapsulated vip molecule from the cucurbit[7]uril(CB7)cavity by ligands binding to the host portal.We uncovered a correlation between the ligand-binding affinity with CB7 and the vip residence time,allowing us to rapidly predict the release kinetics through straightforward energy minimization calculations.These high-throughput predictions in turn enable a Monte-Carlo Tree Search(MCTS)to de novo design a series of cap-shaped ligand molecules with large binding affinities and boosting vip residence times by up to 7 orders of magnitude.Notably,halogenated aromatic compounds emerge as top-ranking ligands.Detailed modeling suggests the presence of halogen-bonding between the ligands and the CB7 portal.Meanwhile,the binding of top-ranked ligands is supported by^(1)H NMR and 2D DOSY-NMR.Our findings open up possibilities in gating of molecular transport through a nanoscale cavity with potential applications in nanopore technology and controlled drug release.展开更多
High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechani...High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al_(1.2)CrFeCoNi(comprising a body-centered cubic phase) and Al_(0.3)CrFeCoNi(comprising a face-centered cubic phase) single-crystal micropillars with three orientations([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al_(1.2)CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast,Al_(0.3)CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al_(1.2)CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al_(0.3)CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization(involving dislocation tangles, and formation of dislocation cell structures and sub-grains)plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress(and work hardening rate)with increasing temperature in the Al_(1.2)CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al_(0.3)CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al_(1.2)CrFeCoNi and Al_(0.3)CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.展开更多
Inelastic quantum mechanical tunneling of electrons across plasmonic tunnel junctions can lead to surface plasmon polariton(SPP)and photon emission.So far,the optical properties of such junctions have been controlled ...Inelastic quantum mechanical tunneling of electrons across plasmonic tunnel junctions can lead to surface plasmon polariton(SPP)and photon emission.So far,the optical properties of such junctions have been controlled by changing the shape,or the type of the material,of the electrodes,primarily with the aim to improve SPP or photon emission efficiencies.Here we show that by tuning the tunneling barrier itself,the efficiency of the inelastic tunneling rates can be improved by a factor of 3.We exploit the anisotropic nature of hexagonal boron nitride(hBN)as the tunneling barrier material in Au//hBN//graphene tunnel junctions where the Au electrode also serves as a plasmonic strip waveguide.As this junction constitutes an optically transparent hBN–graphene heterostructure on a glass substrate,it forms an open plasmonic system where the SPPs are directly coupled to the dedicated strip waveguide and photons outcouple to the far field.We experimentally and analytically show that the photon emission rate per tunneling electron is significantly improved(~×3)in Au//hBN//graphene tunnel junction due to the enhancement in the local density of optical states(LDOS)arising from the hBN anisotropy.With the dedicated strip waveguide,SPP outcoupling efficiency is quantified and is found to be∼80%stronger than the radiative outcoupling in Au//hBN//graphene due to the high LDOS of the SPP decay channel associated with the inelastic tunneling.The new insights elucidated here deepen our understanding of plasmonic tunnel junctions beyond the isotropic models with enhanced LDOS.展开更多
Photonic structures with optical resonances beyond a single controllable mode are strongly desired for enhancing light±matter interactions and bringing about advanced photonic devices. However, the realization of...Photonic structures with optical resonances beyond a single controllable mode are strongly desired for enhancing light±matter interactions and bringing about advanced photonic devices. However, the realization of effective multimodal photonic structures has been restricted by the limited tunable range of mode manipulation, the spatial dispersions of electric fields or the polarization-dependent excitations. To overcome these limitations, we create a dualmode metasurface by integrating the plasmonic surface lattice resonance and the gap plasmonic modes;this metasurface offers a widely tunable spectral range, good overlap in the spatial distribution of electric fields, and polarization independence of excitation light. To show that such dual-mode metasurfaces are versatile platforms for enhancing light±matter interactions, we experimentally demonstrate a significant enhancement of second-harmonic generation using our design, with a conversion efficiency of 1±3 orders of magnitude larger than those previously obtained in plasmonic systems. These results may inspire new designs for functional multimodal photonic structures.展开更多
In this paper, the authors study further properties and applications of weighted homology and persistent homology. The Mayer-Vietoris sequence and generalized Bockstein spectral sequence for weighted homology are intr...In this paper, the authors study further properties and applications of weighted homology and persistent homology. The Mayer-Vietoris sequence and generalized Bockstein spectral sequence for weighted homology are introduced. For applications, the authors show an algorithm to construct a filtration of weighted simplicial complexes from a weighted network. They also prove a theorem to calculate the mod p^(2) weighted persistent homology provided with some information on the mod p weighted persistent homology.展开更多
The elastic conductor is crucial in wearable electronics and soft robotics.The ideal intrinsic elastic bulk conductors show uniform three-dimensional conductive networks and stable resistance during large stretch.A ch...The elastic conductor is crucial in wearable electronics and soft robotics.The ideal intrinsic elastic bulk conductors show uniform three-dimensional conductive networks and stable resistance during large stretch.A challenge is that the variation of resistance is high under deformation due to disconnection of conductive pathway for bulk elastic conductors.Our strategy is to introduce buckled structure into the conductive network,by self-assembly of a carbon nanotube layer on the interconnecting micropore surface of a prestrained foam,followed by strain relaxation.Both unfolding of buckles and flattening of micropores contributed to the stability of the resistance under deformation(2.0%resistance variation under 70%strain).Microstructural analysis and finite element analysis illustrated different patterns of two-dimensional buckling structures could be obtained due to the imperfections in the conductive layer.Applications as all-directional interconnects,stretchable electromagnetic interference shielding and electrothermal tumor ablation were demonstrated.展开更多
Thermal conductivity of two-dimensional(2D)materials has gained prominence due to the attractive applications in thermal management and thermoelectric devices.In this work,we present a new member of bilayer 2D boron a...Thermal conductivity of two-dimensional(2D)materials has gained prominence due to the attractive applications in thermal management and thermoelectric devices.In this work,we present a new member of bilayer 2D boron allotropes,denoted as bilayerβ12 borophene,and study the thermal transport properties by solving phonon Boltzmann transport equation based on density functional theory.Based on quantitative chemical bonding analysis,we identify large degrees of covalent bonding of the interlayer interaction.In comparison to its monolayer counterpart,the bilayer exhibits much higher in-plane thermal conductivity despite the lower phonon group velocity and buckling structure,inferring a new physical mechanism.The thermal conductivity(κ)of bilayerβ_(12)borophene at 300 K is 140.5(86.3)W·m^(-1)·K^(-1)along armchair(zigzag)direction,andκ_(armchair)is about 52.7%higher than that of monolayerβ12 borophene.The abnormal enhancement is attributed to the suppressed phonon scattering possibility and elongation of phonon lifetime.More interesting,after forming bilayerβ12 borophene through interlayer covalent bonding,the dominated phonon branch to thermal conductivity changes to transverse acoustic phonons from out-of-plane flexural acoustic(ZA)phonons in the monolayer borophene.Our study elucidates the rich thermal transport characteristics in bilayer covalently bonded 2D materials,and injects fresh insights into the phonon engineering of 2D borophene relevant for emergent thermal management applications.展开更多
基金supported by the National Science Foundation of China (Grants 11025208, 11372042, 11221202, and 11202026)the support from CSIRO-Intelligent Processing TCP+1 种基金CAFHS’ Capability Development FundCSIRO-Advanced Materials TCP
文摘Anti-parallel β-sheet crystallite as the main component of silk fibroin has attracted much attention due to its superior mechanical properties. In this study, we examine the processes of pulling a peptide chain from β-sheet crystallite using steered molecular dynamics simulations to investigate the rupture behavior of the crystallite. We show that the failure of β-sheet crystallite was accompanied by a propagation of instability of hydrogen-bonds （H-bonds） in the crystallite. In addition, we find that there is an optimum size of the crystallite at which the H-bonds can work cooperatively to achieve the highest shear strength. In addition, we find that the stiffness of loading device and the loading rates have significant effects on the rupture behavior of β-sheet crystallite. The stiff loading device facilitates the rebinding of the Hbond network in the stick-slip motion between the chains, while the soft one suppresses it. Moreover, the rupture force of β-sheet crystallites decreases with loading rate. Particularly, when the loading rate decreases to a critical value, the rupture force of the β-sheet crystallite becomes independent of the loading rates. This study provides atomistic details of rupture behaviors of β-sheet crystallite, and, therefore, sheds valuable light on the underlying mechanism of the superior mechanical properties of silk fibroin.
基金Project supported by the Science and Engineering Research Council,Singapore(Grant No.152-70-00017)the Agency for Science,Technology and Research(A*STAR)Singapore
文摘Two-dimensional （2D） materials, such as graphene, phosphorene, and transition metal dichalcogenides （e.g., MoS2 and WS2）, have attracted a great deal of attention recently due to their extraordinary structural, mechanical, and physical properties. In particular, 2D materials have shown great potential for thermal management and thermoelectric energy generation. In this article, we review the recent advances in the study of thermal properties of 2D materials. We first review some important aspects in thermal conductivity of graphene and discuss the possibility to enhance the ultra-high thermal conductivity of graphene. Next, we discuss thermal conductivity of MoS2 and the new strategy for thermal management of MoS2 device. Subsequently, we discuss the anisotropic thermal properties of phosphorene. Finally, we review the application of 2D materials in thermal devices, including thermal rectifier and thermal modulator.
基金the financial support from the National Science Foundation of China (NSFC) (No.52103178)Science and Technology Project of Sichuan Province (No. 2023NSFSC0997)+2 种基金Sixth Two-hundred Talent B plan of Sichuan Universitysupport by the Australian Research Council Discovery Program (DP190103290)Australian Research Council Future Fellowships (FT200100730, FT210100804)。
文摘Cutting-edge heat spreaders for soft and planar electronics require not only high thermal conductivity and a certain degree of flexibility but also remarkable self-adhesion without thermal interface materials, elasticity, arbitrary elongation along with soft devices, and smart properties involving thermal self-healing, thermochromism and so on. Nacre-like composites with excellent in-plane heat dissipation are ideal as heat spreaders for thin and planar electronics. However, the intrinsically poor viscoelasticity, i.e., adhesion and elasticity, prevents them from simultaneous self-adhesion and arbitrary elongation along with current flexible devices as well as incurring high interfacial thermal impedance. In this paper, we propose a soft thermochromic composite(STC) membrane with a layered structure, considerable stretchability, high in-plane thermal conductivity(~30 Wm^(-1) K^(-1)), low thermal contact resistance(~12 mm^2 KW^(-1), 4–5 times lower than that of silver paste), strong yet sustainable adhesion forces(~4607 Jm^(-2), 2220 Jm^(-2) greater than that of epoxy paste) and self-healing efficiency. As a self-adhesive heat spreader, it implements efficient cooling of various soft electronics with a temperature drop of 20℃ than the polyimide case. In addition to its self-healing function, the chameleon-like behavior of STC facilitates temperature monitoring by the naked eye, hence enabling smart thermal management.
基金the support under A*STAR SERC grant (132-183-0025)
文摘We propose a multi-field implicit finite element method for analyzing the electromechanical behavior of dielectric elastomers. This method is based on a four-field variational principle, which includes displacement and electric potential for the electromechanical coupling analysis, and additional independent fields to address the incompressible constraint of the hyperelastic material. Linearization of the variational form and finite element discretization are adopted for the numerical implementation. A general FEM program framework is devel- oped using C＋＋ based on the open-source finite element library deal.II to implement this proposed algorithm. Numerical examples demonstrate the accuracy, convergence properties, mesh-independence properties, and scalability of this method. We also use the method for eigenvalue analysis of a dielectric elastomer actuator subject to electromechanical loadings. Our finite element implementation is available as an online supplementary material.
基金supported by the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJQN202100626)the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJQN202200619)+3 种基金supported by Beijing Institute of Technology Research Fund Program for Young Scholars (Grant No. XSQD-202222008)the support from the National Natural Science Foundation of China (Grant No. 12204081)the Natural Science Foundation of Chongqing (Grant No. 2022NSCQ-MSX2540)supported by TianHe Qingsuo Project-spec ial fund project
文摘Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of antiperovskite X_(3)NP(X^(2+)=Ca,Mg)upon compression by first-principles calculations.Our results reveal that the system is anisotropic,and the lat-tice constant a of X_(3)NP exhibits the fastest rate of decrease upon compression among the three directions,which is different from the typical Pnma phase of halide and chalcogenide perovskites.Meanwhile,Ca_(3)NP has higher compressibility than Mg_(3)NP due to its small bulk modulus.The electronic and optical properties of Mg_(3)NP show small fluctuations upon compression,but those of Ca_(3)NP are more sensitive to pressure due to its higher compressibility and lower unoccupied 3d orbital energy.For example,the band gap,lattice dielectric constant,and exciton binding energy of Ca_(3)NP decrease rapidly as the pressure increases.In addition,the increase in pressure significantly improves the optical absorption and theoretical conversion effi-ciency of Ca_(3)NP.Finally,the mechanical properties of X_(3)NP are also increased upon compression due to the reduction in bond length,while inducing a brittle-to-ductile transition.Our research provides theoretical guidance and insights for future experi-mental tuning of the physical properties of antiperovskite semiconductors by pressure.
基金support from IHPC,A*STARpartially supported by the China Postdoctoral Science Foundation(Grant No.2014M562055)
文摘Collagen fibers provide a good example of making strong micro-or mesoscale fibers from nanoscale tropocollagen molecules through a staggered and crosslinked organization in a bottom-up manner.Mimicking the architectural features of collagen fibers has been shown to be a promising approach to develop carbon nanotube（CNT）fibers of high performance.In the present work,an elastic model is developed to describe the load transfer and failure propagation within the bioinspired CNT bundles,and to establish the relations of the mechanical properties of the bundles with a number of geometrical and physical parameters such as the CNT aspect ratio and longitudinal gap,interface cross-link density,and the functionalizationinduced degradation in CNTs,etc.With the model,the stress distributions along the CNT-CNT interface as well as in every individual CNT are well captured,and the failure propagation along the interface and its effects on the mechanical properties of the CNT bundles are predicted.The work may provide useful guidelines for the design of novel CNT fibers in practice.
文摘An open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, is used to study a blunt body with the shape of a space crew capsule return vehicle. The rarefied gas has the Knudsen number with 0.03. The flow with a Mach number 4.35 over the capsule was simulated by DSMC. The distributions of velocity field and temperature around the capsule were calculated. This study may provide some useful information for the reentry of the return vehicle.
文摘Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface diffusion of heterogeneous adatoms clusters can be vital for the binary island growth on the surface and can be useful for the formation of alloy-based thin film surface through atomic exchange process. The results of the diffusion process show that at 300 K, the diffusion of small adatoms clusters shows hopping, sliding, and shear motion; whereas for large adatoms clusters（hexamer and above）, the diffusion is negligible. At 500 K, small adatoms clusters, i.e., dimer, show almost all possible diffusion mechanisms including the atomic exchange process; however no such exchange is observed for adatoms clusters greater than dimer. At 700 K, the exchange mechanism dominates for all types of clusters, where Zr adatoms show maximum tendency and Ag adatoms show minimum or no tendency toward the exchange process. Separation and recombination of one or more adatoms are also observed at 500 K and 700 K. The Ag adatoms also occupy pop-up positions over the adatoms clusters for short intervals. At 700 K, the vacancies are also generated in the vicinity of the adatoms cluster,vacancy formation, filling, and shifting can be observed from the results.
基金the Hong Kong Research Grants Council via a General Research Fund(Nos.15201416 and 15212417)the National Natural Science Foundation of China(No.51635008)
文摘Manmade debris and natural meteoroids, travelling in the Low Earth Orbit at a speed of several kilometers per second, pose a severe safety concern to the spacecraft in service through the HyperVelocity Impact(HVI). To address this issue, an investigation of shock Acoustic Emission(AE) waves induced by HVI to a downscaled two-layer Whipple shielding structure is performed,to realize a quantitative damage evaluation. Firstly a hybrid numerical model integrating smoothparticle hydrodynamics and finite element is built to obtain the wave response. The projectiles, with various impact velocities and directions, are modelled to impact the shielding structure with different thicknesses. Then experimental validation is carried out with built-in miniaturized piezoelectric sensors to in situ sense the HVI-induced AE waves. A quantitative agreement is obtained between numerical and experimental results, demonstrating the correctness of the hybrid model and facilitating the explanation of obtained AE signals in experiment. Based on the understanding of HVI-induced wave components, assessment of the damage severity, i.e., whether the outer shielding layer is perforated or not, is performed using the energy ratio between the regions of ‘‘high frequency" and ‘‘low frequency" in the acquired AE signals. Lastly, the direct-arrival fundamentalsymmetric wave mode is isolated from each sensing signal to be input into an enhanced delay-andsum algorithm, which visualizes HVI spots accurately and instantaneously with different sensor network configuration. All these works demonstrate the potential of quantitative, in situ, and real time HVI monitoring using miniaturized piezoelectric sensor network.
基金the support from National Natural Science Foundation of China(Grant No.11872139)Nian Zhou appreciates the supportfrom Guizhou Provincial Departmentof Education(Grant No.KY[2021]255).
文摘Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.
基金the China Scholarship Council(Grant No.202107000030)RIE2020 Advanced Manufacturing and Engineering(AME)Programmatic(Grant No.A1898b0043)A*STAR Aerospace Programme(Grant No.M2115a0092)。
文摘The two-dimensional(2D)material-based thermal switch is attracting attention due to its novel applications,such as energy conversion and thermal management,in nanoscale devices.In this paper,we observed that the reversible 2H–1T′phase transition in MoTe_(2)is associated with about a fourfold/tenfold change in thermal conductivity along the X/Y direction by using first-principles calculations.This phenomenon can be profoundly understood by comparing the Mo–Te bonding strength between the two phases.The 2H-MoTe_(2)has one stronger bonding type,while 1T′-MoTe_(2)has three weaker types of bonds,suggesting bonding inhomogeneity in 1T′-MoTe_(2).Meanwhile,the bonding inhomogeneity can induce more scattering of vibration modes.The weaker bonding indicates a softer structure,resulting in lower phonon group velocity,a shorter phonon relaxation lifetime and larger Gr¨uneisen constants.The impact caused by the 2H to 1T′phase transition in MoTe_(2)hinders the propagation of phonons,thereby reducing thermal conductivity.Our study describes the possibility for the provision of the MoTe_(2)-based controllable and reversible thermal switch device.
基金The authors gratefully acknowledge the support from the Science and Engineering Research Council through grant(152-70-00017)use of computing resources at the A*STAR Computational Resource Centre and National Supercomputer Centre,Singapore.J.Gao also thanks the Start-Up grant of DUT(3005-852069).
文摘The ultrafast growth of large-area,high-quality WSe2 domains with a compact triangular morphology has recently been achieved on a gold substrate via chemical vapor deposition.However,the underlying mechanism responsible for ultrafast growth remains elusive.Here,we first analyze growth processes and identify two possible pathways that might achieve ultrafast growth:Path 1,fast edge attachment and ultrafast edge diffusion;Path 2,fast kink nucleation and ultrafast kink propagation.We perform kinetic Monte Carlo simulations and first-principles calculations to assess the viability of these two paths,finding that Path 1 is not viable due to the high edge diffusion barrier calculated from first-principles calculations.Remarkably,Path 2 reproduces all the experimental growth features(domain morphology,domain orientation,and growth rate),and the associated energetic data are consistent with first-principles calculations.The present work unveils the underlying mechanism for the ultrafast growth of WSe2,and may provide a new route for the ultrafast growth of other two-dimensional materials.
基金H.L.and T.-C.L.are grateful to the studentship funded by the A*STAR-UCL Research Attachment Programme through the EPSRC Centre for Doctoral Training in Molecular Modelling and Materials Science(Grant EP/L015862/1)T.-C.L.is grateful to the Research Project Grant(Grant RPG-2016-393)funded by the Leverhulme Trust+1 种基金We acknowledge the use of the UCL Myriad High Performance Computing Facility(Myriad@UCL),and associated support services,in the completion of this workThis work is partially supported financially by the Agency for Science,Technology and Research(A^(*)STAR)under grant AMDM A1898b0043,and A^(*)STAR SERC CRF Award.
文摘Herein we computationally explore the modulation of the release kinetics of an encapsulated vip molecule from the cucurbit[7]uril(CB7)cavity by ligands binding to the host portal.We uncovered a correlation between the ligand-binding affinity with CB7 and the vip residence time,allowing us to rapidly predict the release kinetics through straightforward energy minimization calculations.These high-throughput predictions in turn enable a Monte-Carlo Tree Search(MCTS)to de novo design a series of cap-shaped ligand molecules with large binding affinities and boosting vip residence times by up to 7 orders of magnitude.Notably,halogenated aromatic compounds emerge as top-ranking ligands.Detailed modeling suggests the presence of halogen-bonding between the ligands and the CB7 portal.Meanwhile,the binding of top-ranked ligands is supported by^(1)H NMR and 2D DOSY-NMR.Our findings open up possibilities in gating of molecular transport through a nanoscale cavity with potential applications in nanopore technology and controlled drug release.
基金financial support from the National Natural Science Foundation of China (Grant Nos. 11522218, 11720101002)the Beijing Natural Science Foundation (Grant No. Z180014)+1 种基金the National Science and Technology Major Project (Grant No. 2017-VI-0003-0073)financial support from the National Science Foundation (Grant No. DMR-1709318)。
文摘High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al_(1.2)CrFeCoNi(comprising a body-centered cubic phase) and Al_(0.3)CrFeCoNi(comprising a face-centered cubic phase) single-crystal micropillars with three orientations([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al_(1.2)CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast,Al_(0.3)CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al_(1.2)CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al_(0.3)CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization(involving dislocation tangles, and formation of dislocation cell structures and sub-grains)plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress(and work hardening rate)with increasing temperature in the Al_(1.2)CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al_(0.3)CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al_(1.2)CrFeCoNi and Al_(0.3)CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.
基金The authors acknowledge the National Research Foundation(NRF)for supporting this research under the Prime Minister’s Office,Singapore,under its Medium Sized Centre Programme and the Competitive Research Programme(CRP)(NRF-CRP17-2017-08).
文摘Inelastic quantum mechanical tunneling of electrons across plasmonic tunnel junctions can lead to surface plasmon polariton(SPP)and photon emission.So far,the optical properties of such junctions have been controlled by changing the shape,or the type of the material,of the electrodes,primarily with the aim to improve SPP or photon emission efficiencies.Here we show that by tuning the tunneling barrier itself,the efficiency of the inelastic tunneling rates can be improved by a factor of 3.We exploit the anisotropic nature of hexagonal boron nitride(hBN)as the tunneling barrier material in Au//hBN//graphene tunnel junctions where the Au electrode also serves as a plasmonic strip waveguide.As this junction constitutes an optically transparent hBN–graphene heterostructure on a glass substrate,it forms an open plasmonic system where the SPPs are directly coupled to the dedicated strip waveguide and photons outcouple to the far field.We experimentally and analytically show that the photon emission rate per tunneling electron is significantly improved(~×3)in Au//hBN//graphene tunnel junction due to the enhancement in the local density of optical states(LDOS)arising from the hBN anisotropy.With the dedicated strip waveguide,SPP outcoupling efficiency is quantified and is found to be∼80%stronger than the radiative outcoupling in Au//hBN//graphene due to the high LDOS of the SPP decay channel associated with the inelastic tunneling.The new insights elucidated here deepen our understanding of plasmonic tunnel junctions beyond the isotropic models with enhanced LDOS.
基金supported by the National Key R&D Program of China (2016YFA0301300)the National Natural Science Foundation of China (11974437 and 91750207)+6 种基金the Key-Area Research and Development Program of Guangdong Province (2018B030329001)Guangdong Special Support Program (2017TQ04C487)Guangdong Natural Science Funds for Distinguished Young Scholars (2017B030306007)Guangdong Natural Science Funds (2020A0505140004)Pearl River S&T Nova Program of Guangzhou (201806010033)the Open Fund of IPOC (BUPT) (IPOC2019A003)the Fundamental Research Funds for the Central Universities (20lgzd30)。
文摘Photonic structures with optical resonances beyond a single controllable mode are strongly desired for enhancing light±matter interactions and bringing about advanced photonic devices. However, the realization of effective multimodal photonic structures has been restricted by the limited tunable range of mode manipulation, the spatial dispersions of electric fields or the polarization-dependent excitations. To overcome these limitations, we create a dualmode metasurface by integrating the plasmonic surface lattice resonance and the gap plasmonic modes;this metasurface offers a widely tunable spectral range, good overlap in the spatial distribution of electric fields, and polarization independence of excitation light. To show that such dual-mode metasurfaces are versatile platforms for enhancing light±matter interactions, we experimentally demonstrate a significant enhancement of second-harmonic generation using our design, with a conversion efficiency of 1±3 orders of magnitude larger than those previously obtained in plasmonic systems. These results may inspire new designs for functional multimodal photonic structures.
基金This work was supported by the Singapore Ministry of Education Research Grant(AcRF Tier 1 WBS No.R-146-000-222-112)the Postdoctoral International Exchange Program of China 2019 Project from the Office of China Postdoctoral Council+4 种基金China Postdoctoral Science Foundationthe President’s Graduate Fellowship of National University of Singaporethe Natural Science Foundation of China(Nos.11971144,12001310)High-Level Scientific Research Foundation of Hebei ProvinceChina Postdoctoral Science Foundation(No.2019-2021)。
文摘In this paper, the authors study further properties and applications of weighted homology and persistent homology. The Mayer-Vietoris sequence and generalized Bockstein spectral sequence for weighted homology are introduced. For applications, the authors show an algorithm to construct a filtration of weighted simplicial complexes from a weighted network. They also prove a theorem to calculate the mod p^(2) weighted persistent homology provided with some information on the mod p weighted persistent homology.
基金supported by the National Key Research and Development Program of China(2017YFB0307000)the National Natural Science Foundation of China(51973093,U1533122 and 51773094)+5 种基金the Natural Science Foundation of Tianjin(18JCZDJC36800)the Science Foundation for Distinguished Young Scholars of Tianjin(18JCJQJC46600)the Fundamental Research Funds for the Central Universities(63171219)the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University(LK1704)the National Special Support Plan for High-level Talents people(C041800902)the Eugene McDermott Graduate Fellows Program。
文摘The elastic conductor is crucial in wearable electronics and soft robotics.The ideal intrinsic elastic bulk conductors show uniform three-dimensional conductive networks and stable resistance during large stretch.A challenge is that the variation of resistance is high under deformation due to disconnection of conductive pathway for bulk elastic conductors.Our strategy is to introduce buckled structure into the conductive network,by self-assembly of a carbon nanotube layer on the interconnecting micropore surface of a prestrained foam,followed by strain relaxation.Both unfolding of buckles and flattening of micropores contributed to the stability of the resistance under deformation(2.0%resistance variation under 70%strain).Microstructural analysis and finite element analysis illustrated different patterns of two-dimensional buckling structures could be obtained due to the imperfections in the conductive layer.Applications as all-directional interconnects,stretchable electromagnetic interference shielding and electrothermal tumor ablation were demonstrated.
基金We gratefully acknowledge funding supporting from the National Natural Science Foundation of China(No.11804040)the Scientific and Technological Research of Chongqing Municipal Education Commission(No.KJZD-K202100602)G.Z.is supported in part by RIE2020 Advanced Manufacturing and Engineering Programmatic(No.A1898b0043).
文摘Thermal conductivity of two-dimensional(2D)materials has gained prominence due to the attractive applications in thermal management and thermoelectric devices.In this work,we present a new member of bilayer 2D boron allotropes,denoted as bilayerβ12 borophene,and study the thermal transport properties by solving phonon Boltzmann transport equation based on density functional theory.Based on quantitative chemical bonding analysis,we identify large degrees of covalent bonding of the interlayer interaction.In comparison to its monolayer counterpart,the bilayer exhibits much higher in-plane thermal conductivity despite the lower phonon group velocity and buckling structure,inferring a new physical mechanism.The thermal conductivity(κ)of bilayerβ_(12)borophene at 300 K is 140.5(86.3)W·m^(-1)·K^(-1)along armchair(zigzag)direction,andκ_(armchair)is about 52.7%higher than that of monolayerβ12 borophene.The abnormal enhancement is attributed to the suppressed phonon scattering possibility and elongation of phonon lifetime.More interesting,after forming bilayerβ12 borophene through interlayer covalent bonding,the dominated phonon branch to thermal conductivity changes to transverse acoustic phonons from out-of-plane flexural acoustic(ZA)phonons in the monolayer borophene.Our study elucidates the rich thermal transport characteristics in bilayer covalently bonded 2D materials,and injects fresh insights into the phonon engineering of 2D borophene relevant for emergent thermal management applications.
