Severe polysulfide shuttling and sluggish sulfur redox kinetics significantly decrease sulfur utilization and cycling stability in lithium-sulfur batteries(LSBs).Herein,we develop a hollow CoO/CoP-Box core-shell heter...Severe polysulfide shuttling and sluggish sulfur redox kinetics significantly decrease sulfur utilization and cycling stability in lithium-sulfur batteries(LSBs).Herein,we develop a hollow CoO/CoP-Box core-shell heterostructure as a model and multifunctional catalyst modified on separators to induce interfacial charge modulation and expose more active sites for promoting the adsorption and catalytic conversion ability of sulfur species.Theoretical and experimental findings verify that the in-situ formed core-shell hetero-interface induces the formation of P-Co-O binding and charge redistribution to activate surface O active sites for binding lithium polysulfides(LiPSs)via strong Li-O bonding,thus strongly adsorbing with Li PSs.Meanwhile,the strong Li-O bonding weakens the competing Li-S bonding in LiPSs or Li2S adsorbed on CoO/CoP-Box surface,plus the hollow heterostructure provides abundant active sites and fast electron/Li+transfer,so reducing Li2S nucleation/dissolution activation energy.As expected,LSBs with CoO/CoP-Box modified separator and traditional sulfur/carbon black cathode display a large initial capacity of 1240 mA h g^(-1)and a long cycling stability with 300 cycles(~60.1%capacity retention)at 0.5C.Impressively,the thick sulfur cathode(sulfur loading:5.2 mg cm^(-2))displays a high initial areal capacity of 6.9 mA h cm^(-2).This work verifies a deep mechanism understanding and an effective strategy to induce interfacial charge modulation and enhance active sites for designing efficient dual-directional Li-S catalysts via engineering hollow core-shell hetero-structure.展开更多
We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to prcsent the two-dimensional electronic band structure of graphene. Using the...We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to prcsent the two-dimensional electronic band structure of graphene. Using the LandauerButticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.展开更多
We trace the conceptual basis of the Multi-Band Approach (MBA) and recall the reasons for its wide following for composite superconductors (SCs). Attention is then drawn to a feature that MBA ignores: the possibility ...We trace the conceptual basis of the Multi-Band Approach (MBA) and recall the reasons for its wide following for composite superconductors (SCs). Attention is then drawn to a feature that MBA ignores: the possibility that electrons in such an SC may also be bound via simultaneous exchanges of quanta with more than one ion-species—a lacuna which is addressed by the Generalized BCS Equations (GBCSEs). Based on several papers, we give a concise account of how this approach: 1) despite employing a single band, meets the criteria satisfied by MBA because a) GBCSEs are derived from a temperature-incorporated Bethe-Salpeter Equation the kernel of which is taken to be a “superpropagator” for a composite SC-each ion-species of which is distinguished by its own Debye temperature and interaction parameter and b) the band overlapping the Fermi surface is allowed to be of variable width. GBCSEs so-obtained reduce to the usual equations for the Tc and Δ of an elemental SC in the limit superpropagator → 1-phonon propagator;2) accommodates moving Cooper pairs and thereby extends the scope of the original BCS theory which restricts the Hamiltonian at the outset to terms that correspond to pairs having zero centre-of-mass momentum. One can now derive an equation for the critical current density (j0) of a composite SC at T = 0 in terms of the Debye temperatures of its ions and their interaction parameters— parameters that also determine its Tc and Δs;3) transforms the problem of optimizing j0 of a composite SC, and hence its Tc, into a problem of chemical engineering;4) provides a common canopy for most composite SCs, including those that are usually regarded as outside the purview of the BCS theory and have therefore been called “exceptional”, e.g., the heavy-fermion SCs;5) incorporates s±-wave superconductivity as an in-built feature and can therefore deal with the iron-based SCs, and 6) leads to presumably verifiable predictions for the values of some relevant parameters, e.g., the effective mass of electrons, for the SCs for which it has been employed.展开更多
Ag nanoparticles were in-situ grown on the surface of MXene nanosheets to prepare thermally conductive hetero-structured MXene@Ag fillers.With polyvinyl alcohol(PVA)as the polymer matrix,thermally conductive MXene@Ag/...Ag nanoparticles were in-situ grown on the surface of MXene nanosheets to prepare thermally conductive hetero-structured MXene@Ag fillers.With polyvinyl alcohol(PVA)as the polymer matrix,thermally conductive MXene@Ag/PVA composite films were fabricated by the processes of solution blending,pouring,evaporative self-assembly.With the same mass fraction,MXene@Ag-III(MXene/Ag,2:1,w/w)presents more significant improvement in thermal conductivity coefficient(λ)than MXene@Ag,single MXene,Ag,simply blending MXene/Ag.MXene@Ag-III/PVA composite films show dual functions of excellent thermal conductivity and electromagnetic interference(EMI)shielding.When the mass fraction of MXene@Ag-III is 60 wt.%,the in-planeλ(λ_(∥)),through-planeλ(λ_(⊥)),EMI shielding effectiveness(EMI SE)are 3.72 and 0.41 W/(m∙K),32 dB,which are increased by 3.1,1.3,105.7 times than those of pure PVA film(0.91 and 0.18 W/(m∙K),0.3 dB),respectively.The 60 wt.%MXene@Ag-III/PVA composite film also has satisfying mechanical and thermal properties,with Young’s modulus,glass transition temperature,heat resistance index of 3.8 GPa,58.5 and 175.3℃,respectively.展开更多
Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&elec...Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression.BNN-30@BNNS-Ⅲ(fBNN-30/fBNNS,1/2,wt/wt)fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites.When the mass fraction of BNN-30@BNNS-Ⅲwas 15 wt%,λvalue of the BNN-30@BNNS-Ⅲ/E-44 composites was up to0.61 W m^(-1)K^(-1),increased by 2.8 times compared with pure E-44(λ=0.22 W m^(-1)K^(-1)),also higher than that of the 15 wt%BNN-30/E-44(0.56 W m^(-1)K^(-1)),15 wt%BNNS/E-44(0.42 W m^(-1)K^(-1)),and 15 wt%(BNN-30/BNNS)/E-44(direct blending BNN-30/BNNS hybrid fillers,1/2,wt/wt,0.49 W m^(-1)K^(-1))composites.Theλin-plane(λ//)andλcross-plane(λ_(⊥))of 15 wt%BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites significantly reached 2.75 W m^(-1)K^(-1)and 1.32 W m^(-1)K^(-1),186.5%and 187.0%higher than those of Si-GFs/E-44 laminated composites(λ//=0.96 W m^(-1)K^(-1)andλ_(⊥)=0.46 W m^(-1)K^(-1)).Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites.Under the condition of point heat source,the introduction of BNN-30@BNNS-Ⅲfillers were conducive to accelerating heat flow trans fe r.BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties(cross-plane withstanding voltage,breakdown strength,surface&volume resistivity of 51.3 kV,23.8 kV mm^(-1),3.7×10^(14)Ω&3.4×10^(14)Ω·cm,favorable mechanical properties(flexural strength of 401.0 MPa and ILSS of 22.3 MPa),excellent dielectric properties(εof 4.92 and tanδof 0.008)and terrific thermal properties(T_(g )of 167.3℃and T_(HRI) of 199.2℃).展开更多
A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to anal...A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (~ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 106 S/m2), susceptance (10.4 × 107 S/m2), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (〉 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.展开更多
To obtain a high-performance heterogeneous photo-catalyst, herein, the hetero-structured Zn In_(2)S_(4)-Ni O@MOF(ZNM) nano-sheets are designed and prepared by partial pyrolysis of nickel-based MOFs(NiMOF) combined wit...To obtain a high-performance heterogeneous photo-catalyst, herein, the hetero-structured Zn In_(2)S_(4)-Ni O@MOF(ZNM) nano-sheets are designed and prepared by partial pyrolysis of nickel-based MOFs(NiMOF) combined with the low-temperature solvo-thermal method. The results indicate that the NiO nanoparticles, produced by partial pyrolysis of the Ni-MOF, have a high density of the surface active sites with limited aggregation, which act as a co-catalyst to capture photo-induced charge carriers. In addition, the morphology and structure of Ni-MOF nano-sheets were preserved in ZNM, which is beneficial to the reduction of the conduction barrier for the photo generated electron-hole pairs. With the synergetic advantages of co-catalyst and unique two-dimensional hetero-structure, ZNM nano-sheets exhibited significantly improved activity for photo-catalytic hydrogen production.展开更多
The impact of Ca and Si nano-scale structures on parameters and density of states of single-crystalline CaF2(111) was studied. It was shown that at low concentration of ions of Ar+ (D ≤ 5 × 1015 cm-2) one witnes...The impact of Ca and Si nano-scale structures on parameters and density of states of single-crystalline CaF2(111) was studied. It was shown that at low concentration of ions of Ar+ (D ≤ 5 × 1015 cm-2) one witnesses formation of nanoscale phases on CaF2 surface. It was revealed that these phases lead to narrowing of the forbidden band Еg between the phases by 4 - 4.5 eV. At higher concentrations (D ≈ 6 × 1016 cm-2) the surface completely is covered by Ca atoms. It was shown that deposition of θ = 10 thick Si single layer on CaF2 surface manifests island picture. The concentration of Ca and Si nano-scale phases on the surface of CaF2 and the band gap of the phases were investigated as a function of (hν) of passing light. Nano-scale phases and nano-scale films of Ca were obtained by using the technique of bombardment with ions of Ar+ of CaF2 surface. Formation of nano-scale phases were accompanied by change in the composition and structure of CaF2 zones located between the phases. These changes led to narrowing of the forbidden band of CaF2 down to 7.5 - 8 eV. The concentration of Ca and Si nano-scale phases on the surface of CaF2 and the band gap of the phases were investigated as a function of (hν) of passing light.展开更多
Constructing controllable thermal conduction networks is the key to efficiently improve thermal conductivities of polymer composites.In this work,graphite oxide(GO)and functionalized carbon nanotubes(f-CNTs)are combin...Constructing controllable thermal conduction networks is the key to efficiently improve thermal conductivities of polymer composites.In this work,graphite oxide(GO)and functionalized carbon nanotubes(f-CNTs)are combined to prepare“Line-Plane”-like hetero-structured thermally conductive GO@f-CNTs fillers,which are then performed to construct controllable 3D GO@f-CNTs thermal conduction networks via selfsacrificing template method based on oxalic acid.Subsequently,thermally conductive GO@f-CNTs/polydimethylsiloxane(PDMS)composites are fabricated via casting method.When the size of oxalic acid is 0.24 mm and the volume fraction of GO@f-CNTs is 60 vol%,GO@f-CNTs/PDMS composites present the optimal thermal conductivity coefficient(λ,4.00 W·m^(-1)·K^(-1)),about 20 times that of theλof neat PDMS(0.20 W·m^(-1)·K^(-1)),also much higher than theλ(2.44 W·m^(-1)·K^(-1))of GO/f-CNTs/PDMS composites with the same amount of randomly dispersed fillers.Meanwhile,the obtained GO@f-CNTs/PDMS composites have excellent thermal stability,whoseλdeviation is only about 3%after 500 thermal cycles(20-200℃).展开更多
Ta_(3)N_(5)/CdS core–shell S-scheme heterojunction nanofibers are fabricated by in situ growing CdS nanodots on Ta_(3)N_(5) nanofib-ers via a simple wet-chemical method.These Ta_(3)N_(5)/CdS nanofibers not only affor...Ta_(3)N_(5)/CdS core–shell S-scheme heterojunction nanofibers are fabricated by in situ growing CdS nanodots on Ta_(3)N_(5) nanofib-ers via a simple wet-chemical method.These Ta_(3)N_(5)/CdS nanofibers not only affords superior photocatalytic tetracycline degradation and mineralization performance,but also cause an efficient photocatalytic Cr(VI)reduction performance.The creation of favorable core–shell fiber-shaped S-scheme hetero-structure with tightly contacted interface and the maximum interface contact area promises the effective photo-carrier disintegration and the optimal photo-redox capacity synchronously,thus leading to the preeminent photo-redox ability.Some critical environmental factors on the photo-behavior of Ta_(3)N_(5)/CdS are also evaluated in view of the complexity of the authentic aquatic environment.The degradation products of tetracycline were confirmed by HPLC–MS analyses.Furthermore,the effective decline in eco-toxicity of TC intermediates is confirmed by QSAR calculation.This work provides cutting-edge guidelines for the design of high-performance Ta_(3)N_(5)-based S-scheme heterojunction nanofibers for environment restoration.展开更多
Hetero-structure induced high performance catalyst for oxygen evolution reaction(OER)in the water splitting reaction has received increased attention.Herein,we demonstrated a novel catalyst system of NiSe_(2)-CoSe_(2)...Hetero-structure induced high performance catalyst for oxygen evolution reaction(OER)in the water splitting reaction has received increased attention.Herein,we demonstrated a novel catalyst system of NiSe_(2)-CoSe_(2) consisting of nanorods and nanoparticles for the efficient OER in the alkaline electrolyte.This catalyst system can be easily fabricated via a low-temperature selenization of the solvothermal synthesized NiCo(OH)x precursor and the unique morphology of hybrid nanorods and nanoparticles was found by the electron microscopy analysis.The high valence state of the metal species was indicated by X-ray photoelectron spectroscopy study and a strong electronic effect was found in the NiSe_(2)-CoSe_(2) catalyst system compared to their counterparts.As a result,NiSe_(2)-CoSe_(2) exhibited high catalytic performance with a low overpotential of 250 mV to reach 10 mA·cm^(-2) for OER in the alkaline solution.Furthermore,high catalytic stability and catalytic kinetics were also observed.The superior performance can be attributed to the high valence states of Ni and Co and their strong synergetic coupling effect between the nanorods and nanoparticles,which could accelerate the charge transfer and offer abundant electrocatalytic active sites.The current work offers an efficient hetero-structure catalyst system for OER,and the results are helpful for the catalysis understanding.展开更多
High performance microwave absorption(MA)materials especially those with tunable frequency are highly desirable for telecommunication industries and military camouflage in the information era.Herein,we constructed hie...High performance microwave absorption(MA)materials especially those with tunable frequency are highly desirable for telecommunication industries and military camouflage in the information era.Herein,we constructed hierarchical heterostructures based on VB-group laminated vanadium disulfide(VS_(2))nanosheets embedded with cobalt tetroxide(Co_(3)O_(4))nanoparticles.The highly dispersed Co_(3)O_(4)nanoparticles generate strong electromagnetic coupling networks that could enhance the loss properties of MA materials.Moreover,the interconnected VS_(2)layered network results in dipolar/interfacial polarization,multiple reflection and scattering favorable for the enhanced MA performance.Impressively,the maximum reflection loss of the VS_(2)/Co_(3)O_(4)hybrids containing 10%Co_(3)O_(4)can reach 57.96 dB at a thin thickness of 1.57 mm,and the bandwidth with an RL value less than-10 dB is as large as 3.5 GHz.The effective MA band could be adjusted in a range of 15.1 GHz(2.9-18 GHz)from S to Ku bands by the increase in thickness from 1.2 mm to 5.5 mm.The results show that the synergistic effect of multiple loss mechanisms and good impedance matching could be the reasons for strong MA capability in nearly all frequency bands,and thus,the high-performance and lightweight MA materials could be developed by the VS_(2)/Co_(3)O_(4)hybrids.展开更多
Li-and Mn-rich(LMR)cathode materials have received tremendous attention due to the highly reversible specific capacity(>250 m Ah·g^(-1)).In the analysis of its crystal structure,the two-phase composite model g...Li-and Mn-rich(LMR)cathode materials have received tremendous attention due to the highly reversible specific capacity(>250 m Ah·g^(-1)).In the analysis of its crystal structure,the two-phase composite model gains increasing acceptance,and the phase transition behaviors in LMR cathode materials have been extensively studied.Herein,the structure controversy of LMR cathode materials,and the mechanisms of phase transition are summarized.Particularly,the causes of initiating or accelerating the phase transition of LMR cathode materials have been summarized into three main driving forces,i.e.,the electrochemical driving force,the component driving force and the thermodynamic driving force.Additionally,the applications of phase transition behavior in improving the electrochemical performance of LMR cathode materials,including the construction of spinel surface coating and spinel/layered hetero-structure are discussed.展开更多
We compared several different band-to-band tunneling (BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si-Ge hetero-junctions. It was shown that in Si...We compared several different band-to-band tunneling (BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si-Ge hetero-junctions. It was shown that in Si homo-junctions, different models could achieve similar results. However, in the Si-Ge hetero-junctions, there were significant differences among these models at high reverse biases (over 2 V). Compared to the nonlocal model, the local models in Sentaurus underrated the BTBT rate distinctly, and the Monte Carlo method was shown to give a better approximation. Additionally, it was found that in the Si region near the interface of the Si-Ge hetero-junctions, the direct tunneling rates increased largely due to the interaction of the band structures of Si and Ge.展开更多
The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding(1) the development of high-quality epitaxy techniques,(2...The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding(1) the development of high-quality epitaxy techniques,(2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and(3) the design, realization,and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an isovalent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO.Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.展开更多
基金supported by the National Natural Science Foundation of China(51972066)the Natural Science Foundation of Guangdong Province of China(2021A1515011718)the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme 2017。
文摘Severe polysulfide shuttling and sluggish sulfur redox kinetics significantly decrease sulfur utilization and cycling stability in lithium-sulfur batteries(LSBs).Herein,we develop a hollow CoO/CoP-Box core-shell heterostructure as a model and multifunctional catalyst modified on separators to induce interfacial charge modulation and expose more active sites for promoting the adsorption and catalytic conversion ability of sulfur species.Theoretical and experimental findings verify that the in-situ formed core-shell hetero-interface induces the formation of P-Co-O binding and charge redistribution to activate surface O active sites for binding lithium polysulfides(LiPSs)via strong Li-O bonding,thus strongly adsorbing with Li PSs.Meanwhile,the strong Li-O bonding weakens the competing Li-S bonding in LiPSs or Li2S adsorbed on CoO/CoP-Box surface,plus the hollow heterostructure provides abundant active sites and fast electron/Li+transfer,so reducing Li2S nucleation/dissolution activation energy.As expected,LSBs with CoO/CoP-Box modified separator and traditional sulfur/carbon black cathode display a large initial capacity of 1240 mA h g^(-1)and a long cycling stability with 300 cycles(~60.1%capacity retention)at 0.5C.Impressively,the thick sulfur cathode(sulfur loading:5.2 mg cm^(-2))displays a high initial areal capacity of 6.9 mA h cm^(-2).This work verifies a deep mechanism understanding and an effective strategy to induce interfacial charge modulation and enhance active sites for designing efficient dual-directional Li-S catalysts via engineering hollow core-shell hetero-structure.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60621061)the National Basic Research Program of China (Grant Nos. 2006CB921305 and 2009CB929103)
文摘We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to prcsent the two-dimensional electronic band structure of graphene. Using the LandauerButticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.
文摘We trace the conceptual basis of the Multi-Band Approach (MBA) and recall the reasons for its wide following for composite superconductors (SCs). Attention is then drawn to a feature that MBA ignores: the possibility that electrons in such an SC may also be bound via simultaneous exchanges of quanta with more than one ion-species—a lacuna which is addressed by the Generalized BCS Equations (GBCSEs). Based on several papers, we give a concise account of how this approach: 1) despite employing a single band, meets the criteria satisfied by MBA because a) GBCSEs are derived from a temperature-incorporated Bethe-Salpeter Equation the kernel of which is taken to be a “superpropagator” for a composite SC-each ion-species of which is distinguished by its own Debye temperature and interaction parameter and b) the band overlapping the Fermi surface is allowed to be of variable width. GBCSEs so-obtained reduce to the usual equations for the Tc and Δ of an elemental SC in the limit superpropagator → 1-phonon propagator;2) accommodates moving Cooper pairs and thereby extends the scope of the original BCS theory which restricts the Hamiltonian at the outset to terms that correspond to pairs having zero centre-of-mass momentum. One can now derive an equation for the critical current density (j0) of a composite SC at T = 0 in terms of the Debye temperatures of its ions and their interaction parameters— parameters that also determine its Tc and Δs;3) transforms the problem of optimizing j0 of a composite SC, and hence its Tc, into a problem of chemical engineering;4) provides a common canopy for most composite SCs, including those that are usually regarded as outside the purview of the BCS theory and have therefore been called “exceptional”, e.g., the heavy-fermion SCs;5) incorporates s±-wave superconductivity as an in-built feature and can therefore deal with the iron-based SCs, and 6) leads to presumably verifiable predictions for the values of some relevant parameters, e.g., the effective mass of electrons, for the SCs for which it has been employed.
基金the National Natural Science Foundation of China(Nos.U21A2093 and 51973173)the Technological Base Scientific Research Projects(Highly Thermally Conductive Nonmetal Materials)+1 种基金the Fundamental Research Funds for the Central Universities,the Undergraduate Innovation&Business Program in Northwestern Polytechnical University(Nos.S202210699381 and S202210699172)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2022073).
文摘Ag nanoparticles were in-situ grown on the surface of MXene nanosheets to prepare thermally conductive hetero-structured MXene@Ag fillers.With polyvinyl alcohol(PVA)as the polymer matrix,thermally conductive MXene@Ag/PVA composite films were fabricated by the processes of solution blending,pouring,evaporative self-assembly.With the same mass fraction,MXene@Ag-III(MXene/Ag,2:1,w/w)presents more significant improvement in thermal conductivity coefficient(λ)than MXene@Ag,single MXene,Ag,simply blending MXene/Ag.MXene@Ag-III/PVA composite films show dual functions of excellent thermal conductivity and electromagnetic interference(EMI)shielding.When the mass fraction of MXene@Ag-III is 60 wt.%,the in-planeλ(λ_(∥)),through-planeλ(λ_(⊥)),EMI shielding effectiveness(EMI SE)are 3.72 and 0.41 W/(m∙K),32 dB,which are increased by 3.1,1.3,105.7 times than those of pure PVA film(0.91 and 0.18 W/(m∙K),0.3 dB),respectively.The 60 wt.%MXene@Ag-III/PVA composite film also has satisfying mechanical and thermal properties,with Young’s modulus,glass transition temperature,heat resistance index of 3.8 GPa,58.5 and 175.3℃,respectively.
基金support and funding from Guangdong Basic and Applied Basic Research Foundation(2019B1515120093)National Natural Science Foundation of China(51773169 and 51973173)+3 种基金Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(2019JC11)Open Fund from Henan University of Science and Technology(2020-RSC02)Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX202055)financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars。
文摘Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression.BNN-30@BNNS-Ⅲ(fBNN-30/fBNNS,1/2,wt/wt)fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites.When the mass fraction of BNN-30@BNNS-Ⅲwas 15 wt%,λvalue of the BNN-30@BNNS-Ⅲ/E-44 composites was up to0.61 W m^(-1)K^(-1),increased by 2.8 times compared with pure E-44(λ=0.22 W m^(-1)K^(-1)),also higher than that of the 15 wt%BNN-30/E-44(0.56 W m^(-1)K^(-1)),15 wt%BNNS/E-44(0.42 W m^(-1)K^(-1)),and 15 wt%(BNN-30/BNNS)/E-44(direct blending BNN-30/BNNS hybrid fillers,1/2,wt/wt,0.49 W m^(-1)K^(-1))composites.Theλin-plane(λ//)andλcross-plane(λ_(⊥))of 15 wt%BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites significantly reached 2.75 W m^(-1)K^(-1)and 1.32 W m^(-1)K^(-1),186.5%and 187.0%higher than those of Si-GFs/E-44 laminated composites(λ//=0.96 W m^(-1)K^(-1)andλ_(⊥)=0.46 W m^(-1)K^(-1)).Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites.Under the condition of point heat source,the introduction of BNN-30@BNNS-Ⅲfillers were conducive to accelerating heat flow trans fe r.BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties(cross-plane withstanding voltage,breakdown strength,surface&volume resistivity of 51.3 kV,23.8 kV mm^(-1),3.7×10^(14)Ω&3.4×10^(14)Ω·cm,favorable mechanical properties(flexural strength of 401.0 MPa and ILSS of 22.3 MPa),excellent dielectric properties(εof 4.92 and tanδof 0.008)and terrific thermal properties(T_(g )of 167.3℃and T_(HRI) of 199.2℃).
文摘A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (~ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 106 S/m2), susceptance (10.4 × 107 S/m2), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (〉 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.
基金support of National Science Foundation of China (Nos.91963207 and 12075174)。
文摘To obtain a high-performance heterogeneous photo-catalyst, herein, the hetero-structured Zn In_(2)S_(4)-Ni O@MOF(ZNM) nano-sheets are designed and prepared by partial pyrolysis of nickel-based MOFs(NiMOF) combined with the low-temperature solvo-thermal method. The results indicate that the NiO nanoparticles, produced by partial pyrolysis of the Ni-MOF, have a high density of the surface active sites with limited aggregation, which act as a co-catalyst to capture photo-induced charge carriers. In addition, the morphology and structure of Ni-MOF nano-sheets were preserved in ZNM, which is beneficial to the reduction of the conduction barrier for the photo generated electron-hole pairs. With the synergetic advantages of co-catalyst and unique two-dimensional hetero-structure, ZNM nano-sheets exhibited significantly improved activity for photo-catalytic hydrogen production.
文摘The impact of Ca and Si nano-scale structures on parameters and density of states of single-crystalline CaF2(111) was studied. It was shown that at low concentration of ions of Ar+ (D ≤ 5 × 1015 cm-2) one witnesses formation of nanoscale phases on CaF2 surface. It was revealed that these phases lead to narrowing of the forbidden band Еg between the phases by 4 - 4.5 eV. At higher concentrations (D ≈ 6 × 1016 cm-2) the surface completely is covered by Ca atoms. It was shown that deposition of θ = 10 thick Si single layer on CaF2 surface manifests island picture. The concentration of Ca and Si nano-scale phases on the surface of CaF2 and the band gap of the phases were investigated as a function of (hν) of passing light. Nano-scale phases and nano-scale films of Ca were obtained by using the technique of bombardment with ions of Ar+ of CaF2 surface. Formation of nano-scale phases were accompanied by change in the composition and structure of CaF2 zones located between the phases. These changes led to narrowing of the forbidden band of CaF2 down to 7.5 - 8 eV. The concentration of Ca and Si nano-scale phases on the surface of CaF2 and the band gap of the phases were investigated as a function of (hν) of passing light.
基金financially supported by the National Natural Science Foundation of China(No.51973173)Technological Base Scientific Research Projects(Highly Thermally Conductive Nonmetal Materials)+3 种基金Natural Science Foundation of Chongqing,China(No.2023NSCQ-MSX2547)Shaanxi Province Key Research and Development Plan Project(No.2023-YBGY-461)Fundamental Research Funds for the Central Universities,the Innovation Capability Support Program of Shaanxi(No.2024RS-CXTD-57)financially supported by Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars。
文摘Constructing controllable thermal conduction networks is the key to efficiently improve thermal conductivities of polymer composites.In this work,graphite oxide(GO)and functionalized carbon nanotubes(f-CNTs)are combined to prepare“Line-Plane”-like hetero-structured thermally conductive GO@f-CNTs fillers,which are then performed to construct controllable 3D GO@f-CNTs thermal conduction networks via selfsacrificing template method based on oxalic acid.Subsequently,thermally conductive GO@f-CNTs/polydimethylsiloxane(PDMS)composites are fabricated via casting method.When the size of oxalic acid is 0.24 mm and the volume fraction of GO@f-CNTs is 60 vol%,GO@f-CNTs/PDMS composites present the optimal thermal conductivity coefficient(λ,4.00 W·m^(-1)·K^(-1)),about 20 times that of theλof neat PDMS(0.20 W·m^(-1)·K^(-1)),also much higher than theλ(2.44 W·m^(-1)·K^(-1))of GO/f-CNTs/PDMS composites with the same amount of randomly dispersed fillers.Meanwhile,the obtained GO@f-CNTs/PDMS composites have excellent thermal stability,whoseλdeviation is only about 3%after 500 thermal cycles(20-200℃).
基金supported by the Natural Science Foundation of Zhejiang Province(LY20E080014)the Science and Technology Project of Zhoushan(2022C41011,2020C21009)the National Natural Science Foundation of China(51708504).
文摘Ta_(3)N_(5)/CdS core–shell S-scheme heterojunction nanofibers are fabricated by in situ growing CdS nanodots on Ta_(3)N_(5) nanofib-ers via a simple wet-chemical method.These Ta_(3)N_(5)/CdS nanofibers not only affords superior photocatalytic tetracycline degradation and mineralization performance,but also cause an efficient photocatalytic Cr(VI)reduction performance.The creation of favorable core–shell fiber-shaped S-scheme hetero-structure with tightly contacted interface and the maximum interface contact area promises the effective photo-carrier disintegration and the optimal photo-redox capacity synchronously,thus leading to the preeminent photo-redox ability.Some critical environmental factors on the photo-behavior of Ta_(3)N_(5)/CdS are also evaluated in view of the complexity of the authentic aquatic environment.The degradation products of tetracycline were confirmed by HPLC–MS analyses.Furthermore,the effective decline in eco-toxicity of TC intermediates is confirmed by QSAR calculation.This work provides cutting-edge guidelines for the design of high-performance Ta_(3)N_(5)-based S-scheme heterojunction nanofibers for environment restoration.
基金The work is supported by the National Natural Science Foundation of China(21972124)the Priority Academic Program Development of Jiangsu Higher Education Institution.the support of the Six Talent Peaks Project of Jiangsu Province(XCL-070-2018)。
文摘Hetero-structure induced high performance catalyst for oxygen evolution reaction(OER)in the water splitting reaction has received increased attention.Herein,we demonstrated a novel catalyst system of NiSe_(2)-CoSe_(2) consisting of nanorods and nanoparticles for the efficient OER in the alkaline electrolyte.This catalyst system can be easily fabricated via a low-temperature selenization of the solvothermal synthesized NiCo(OH)x precursor and the unique morphology of hybrid nanorods and nanoparticles was found by the electron microscopy analysis.The high valence state of the metal species was indicated by X-ray photoelectron spectroscopy study and a strong electronic effect was found in the NiSe_(2)-CoSe_(2) catalyst system compared to their counterparts.As a result,NiSe_(2)-CoSe_(2) exhibited high catalytic performance with a low overpotential of 250 mV to reach 10 mA·cm^(-2) for OER in the alkaline solution.Furthermore,high catalytic stability and catalytic kinetics were also observed.The superior performance can be attributed to the high valence states of Ni and Co and their strong synergetic coupling effect between the nanorods and nanoparticles,which could accelerate the charge transfer and offer abundant electrocatalytic active sites.The current work offers an efficient hetero-structure catalyst system for OER,and the results are helpful for the catalysis understanding.
基金supported by the National Natural Science Foundation of China(51772160 and 51977009)China Postdoctoral Science Foundation(Grant No.2020M682029)Regional Joint Fund for Basic Research and Applied Basic Research of Guangdong Province(No.2020SA001515110905)。
文摘High performance microwave absorption(MA)materials especially those with tunable frequency are highly desirable for telecommunication industries and military camouflage in the information era.Herein,we constructed hierarchical heterostructures based on VB-group laminated vanadium disulfide(VS_(2))nanosheets embedded with cobalt tetroxide(Co_(3)O_(4))nanoparticles.The highly dispersed Co_(3)O_(4)nanoparticles generate strong electromagnetic coupling networks that could enhance the loss properties of MA materials.Moreover,the interconnected VS_(2)layered network results in dipolar/interfacial polarization,multiple reflection and scattering favorable for the enhanced MA performance.Impressively,the maximum reflection loss of the VS_(2)/Co_(3)O_(4)hybrids containing 10%Co_(3)O_(4)can reach 57.96 dB at a thin thickness of 1.57 mm,and the bandwidth with an RL value less than-10 dB is as large as 3.5 GHz.The effective MA band could be adjusted in a range of 15.1 GHz(2.9-18 GHz)from S to Ku bands by the increase in thickness from 1.2 mm to 5.5 mm.The results show that the synergistic effect of multiple loss mechanisms and good impedance matching could be the reasons for strong MA capability in nearly all frequency bands,and thus,the high-performance and lightweight MA materials could be developed by the VS_(2)/Co_(3)O_(4)hybrids.
基金the Natural Science Foundation of Fujian Province of China(Nos.2019J06003 and 2020J05014)the National Natural Science Foundation of China(Nos.51931006 and 51871188)+4 种基金the National Key R&D Program of China(No.2016YFA0202602)Guangdong Basic and Applied Basic Research Foundation(Nos.2021A1515010139 and 2019A1515011070)the Science and Technology Planning Projects of Fujian Province,China(No.2020H0005)the Fundamental Research Funds for the Central Universities of China(Nos.20720200068 and 20720190013)the“Double-First Class”Foundation of Materials Intelligent Manufacturing Discipline of Xiamen University。
文摘Li-and Mn-rich(LMR)cathode materials have received tremendous attention due to the highly reversible specific capacity(>250 m Ah·g^(-1)).In the analysis of its crystal structure,the two-phase composite model gains increasing acceptance,and the phase transition behaviors in LMR cathode materials have been extensively studied.Herein,the structure controversy of LMR cathode materials,and the mechanisms of phase transition are summarized.Particularly,the causes of initiating or accelerating the phase transition of LMR cathode materials have been summarized into three main driving forces,i.e.,the electrochemical driving force,the component driving force and the thermodynamic driving force.Additionally,the applications of phase transition behavior in improving the electrochemical performance of LMR cathode materials,including the construction of spinel surface coating and spinel/layered hetero-structure are discussed.
文摘We compared several different band-to-band tunneling (BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si-Ge hetero-junctions. It was shown that in Si homo-junctions, different models could achieve similar results. However, in the Si-Ge hetero-junctions, there were significant differences among these models at high reverse biases (over 2 V). Compared to the nonlocal model, the local models in Sentaurus underrated the BTBT rate distinctly, and the Monte Carlo method was shown to give a better approximation. Additionally, it was found that in the Si region near the interface of the Si-Ge hetero-junctions, the direct tunneling rates increased largely due to the interaction of the band structures of Si and Ge.
基金Project supported by the National Natural Science Foundation of China(Nos.61025020,61274058,61322403,61504057,61574075)the Natural Science Foundation of Jiangsu Province(Nos.BK2011437,BK20130013,BK20150585)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Fundamental Research Funds for the Central Universities
文摘The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding(1) the development of high-quality epitaxy techniques,(2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and(3) the design, realization,and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an isovalent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO.Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.