In order to explore the effect of vacancy defects on the structural,electronic,magnetic and optical properties of CoS_(2) and FeS_(2),first-principles calculation method was used to investigate the alloys.The calculat...In order to explore the effect of vacancy defects on the structural,electronic,magnetic and optical properties of CoS_(2) and FeS_(2),first-principles calculation method was used to investigate the alloys.The calculated results of materials without vacancy are consistent with those reported in the literatures,while the results of materials with vacancy defect were different from those of literatures due to the difference vacancy concentration.The Co vacancy defect hardly changes the half-metallic characteristic of CoS_(2).The Fe vacancy defect changes FeS_(2) from semiconductor to half-metal,and the bottom of the spin-down conduction band changes from the p orbital state of S to the d(t_(2g))orbital state of Fe,while the top of the valence band remains the d orbital d(eg)state of Fe.The half-metallic Co vacancy defects of CoS_(2) and Fe vacancy defects of FeS_(2) are expected to be used in spintronic devices.S vacancy defects make both CoS_(2) and FeS_(2) metallic.Both the Co and S vacancy defects lead to the decrease of the magnetic moment of CoS_(2),while both the Fe and S vacancy defects lead to the obvious magnetic property of FeS_(2).Vacancy defects enhance the absorption coefficient of infrared band and long band of visible light obviously,and produce obvious red shift phenomenon,which is expected to be used in photoelectric devices.展开更多
The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics (MD) simula- tions and theoretical analysis based on the Boltzmann equation. Both the MD ...The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics (MD) simula- tions and theoretical analysis based on the Boltzmann equation. Both the MD and theoretical results show that the lattice thermal conductivity dramatically decreases with the increasing of vacancy concentration at 400 and 500 K. In addition, the dependence of vacancy concentration on the thermal conductivity of Ge thin films becomes less sensitive as the temperature increases. Theoretical results also confirm that the major part of the lattice thermal conductivity reduction is associated with the point-defect scattering and phonon-phonon scattering processes.展开更多
Recently,the newly synthesized septuple-atomic layer two-dimensional(2D)material MoSi_(2)N_(4)(MSN)has attracted attention worldwide.Our work delves into the effect of vacancies and external electric fields on the ele...Recently,the newly synthesized septuple-atomic layer two-dimensional(2D)material MoSi_(2)N_(4)(MSN)has attracted attention worldwide.Our work delves into the effect of vacancies and external electric fields on the electronic properties of the MSN/graphene(Gr)heterostructure using first-principles calculation.We find that four types of defective structures,N-in,N-out,Si and Mo vacancy defects of monolayer MSN and MSN/Gr heterostructure are stable in air.Moreover,vacancy defects can effectively modulate the charge transfer at the interface of the MSN/Gr heterostructure as well as the work function of the pristine monolayer MSN and MSN/Gr heterostructure.Finally,the application of an external electric field enables the dynamic switching between n-type and p-type Schottky contacts.Our work may offer the possibility of exceeding the capabilities of conventional Schottky diodes based on MSN/Gr heterostructures.展开更多
Bismuth titanate (Bi_(4)Ti_(3)O_(12),BIT)piezoelectric materials have attracted increasing attention due to their high-temperature applications.However,it is quite challenging to simultaneously achieve outstanding pie...Bismuth titanate (Bi_(4)Ti_(3)O_(12),BIT)piezoelectric materials have attracted increasing attention due to their high-temperature applications.However,it is quite challenging to simultaneously achieve outstanding piezoelectric properties and high Curie temperature in BIT-based systems.In this study,oxygen vacancy defects tailoring strategy was utilized to solve this problem,excellent piezoelectric coefficient(32.1 pC/N),and ultrahigh Curie temperature(659℃)are gotten in Bi_(4)Ti_(3)-x(Mn_(1/3)Nb_(2/3))xO_(12)(BTMN)ceramics,which are among the top values in the BIT-based ceramics.More importantly,the(Mn_(1/3)Nb_(2/3))(4+d)+complex-ion modified Bi_(4)Ti_(3)O_(12)-based ceramics are characterized with excellent piezoelectric stability up to 500℃(d33>30.0 pC/N at 500℃))and significantly reduced conductivity(only~10^(-7)U-1 cm^(-1)at 500℃).Moreover,enhanced ferroelectricity and good dielectric stability were also obtained.The better comprehensive properties can be ascribed to two aspects.First,the concentration of oxygen vacancy defects is obviously reduced,and their distribution is effectively controlled in BITMN ceramics.Second,the introduction of(Mn_(1/3)Nb_(2/3))^((4+δ)+)complex-ion gives rise to the antiphase boundaries and massive ferroelectric domain walls.This works not only reveal the high potential of BITMN ceramics for high-temperature piezoelectric applications but also deepen the understanding of the structure-properties relationship in BIT-based materials.展开更多
Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect ...Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo_(5)Si_(3).Four vacancies(Si_(-Va1),Si_(-Va2),Mo_(-Va1),Mo_(-Va2))and oxygen occupation models(O_(Mo1),O_(Mo2),O_(-Si1),O_(-Si2))are selected for research.It is found that Mo_(-Va2) vacancy has the stronger structural stability in the ground state in comparison with other vacancies.Besides,the deformation resistance and hardness of the parent Mo_(5)Si_(3) are weakened due to the introduction of different vacancy defects and oxygen occupation.The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo_(5)Si_(3).These vacancies and the oxygen atoms occupation change the localized hybridization between Mo-Si and Mo-Mo atoms.The weaker O-Mo bond is a contributing factor for the excellent ductile behavior in the O_(-Si2) model for Mo_(5)Si_(3).展开更多
Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering(SERS)sensing,photoca...Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering(SERS)sensing,photocatalysis,and photovoltaic applications.However,the long-term maintenance and use of photo-induced vacancy defects remain elusive,because of their rapid self-healing upon air exposure.In this study,we demonstrate that photo-induced oxygen vacancy(PIVO)defects can be stabilized by the photoexcitation of metal–organic framework(MOF)materials,which is crucial for SERS analysis.The PIVO defects in MOF materials are stable for at least two weeks in the ambient atmosphere,owing to the combination of steric hindrance and electron delocalization around vacancy defects,which significantly contrasts the short lifetime(within minutes)of PIVO defects in metal-oxide semiconductors.With the formation of stable PIVO defects,a prominent SERS enhancement surpassing that of pristine MOFs is achieved,accompanied with a reduced limit of detection by three orders of magnitude.Moreover,the additional SERS enhancement rendered by PIVO defects can be stably retained and is effective for monitoring various small molecules,such as dopamine and bisphenol A.展开更多
The defect chemistry is successfully modulated on free-standing and binder-free carbon cathodes for highly efficient Li-S redox reactions.Such rationally regulated defect engineering realizes the synchronization of io...The defect chemistry is successfully modulated on free-standing and binder-free carbon cathodes for highly efficient Li-S redox reactions.Such rationally regulated defect engineering realizes the synchronization of ion/electron-conductive and defect-rich networks on the threedimension carbon cathode,leading to its tunable activity for both relieving the shuttle phenomenon and accelerating the sulfur redox reaction kinetics.As expected,the defective carbon cathode harvests a high rate capacity of 1217.8 mAh g^(-1)at 0.2 C and a superior capacity retention of61.7%at 2 C after 500 cycles.Even under the sulfur mass loading of 11.1 mg cm^(-2),the defective cathode still holds a remarkable areal capacity of 8.5 mAh cm^(-2).展开更多
Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic st...Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn3+(d4) into Mn2+(d5).The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn3+(d4) and Mn2+(d5) are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn3+changing into Mn2+will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.展开更多
The Young's modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is d...The Young's modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is demonstrated that the Young's modulus of graphene is largely correlated to the size of vacancy defects perpendicular to the stretching direction. And a linear reduction of Young's modulus with the increasing concentration of monoatomic-vacancy defects (Le., the slope of =0.03) is also observed. The fracture behavior of graphene, including the fracture strength, crack initiation and propagation are then studied by the molecular dynamics simulation, the effective spring model, and the quantized fracture mechanics. The blunting effect of vacancy edges is demonstrated, and the characterized crack tip radius of 4.44 A is observed.展开更多
Based on first-principle calculations, the electronic structures and optical properties of a single-walled (7, 0) SiC nanotube (SiCNT) with a carbon vacancy defect or a silicon vacancy defect are investigated. In ...Based on first-principle calculations, the electronic structures and optical properties of a single-walled (7, 0) SiC nanotube (SiCNT) with a carbon vacancy defect or a silicon vacancy defect are investigated. In the three silicon atoms around the carbon vacancy, two atoms form a stable bond and the other is a dangling bond. A similar structure is found in the nanotube with a silicon vacancy. A carbon vacancy results in a defect level near the top of the valence band, while a silicon vacancy leads to the formation of three defect levels in the band gap of the nanotube. Transitions between defect levels and energy levels near the bottom of the conduction band have a close relationship with the formation of the novel dielectric peaks in the lower energy range of the dielectric function.展开更多
Developing low-cost,efficient,and stable photocatalysts is one of the most promising methods for large-scale solar water splitting.As a metal-free semiconductor material with suitable band gap,graphitic carbon nitride...Developing low-cost,efficient,and stable photocatalysts is one of the most promising methods for large-scale solar water splitting.As a metal-free semiconductor material with suitable band gap,graphitic carbon nitride(g-C_(3)N_(4))has attracted attention in the field of photocatalysis,which is mainly attributed to its fascinating physicochemical and photoelectronic properties.However,several inherent limitations and shortcomings—involving high recombination rate of photocarriers,insufficient reaction kinetics,and optical absorption—impede the practical applicability of g-C_(3)N_(4).As an effective strategy,vacancy defect engineering has been widely used for breaking through the current limitations,considering its ability to optimize the electronic structure and surface morphology of g-C_(3)N_(4) to obtain the desired photocatalytic activity.This review summarizes the recent progress of vacancy defect engineered g-C_(3)N_(4) for solar water splitting.The fundamentals of solar water splitting with g-C_(3)N_(4) are discussed first.We then focus on the fabrication strategies and effect of vacancy generated in g-C_(3)N_(4).The advances of vacancy-modified g-C_(3)N_(4) photocatalysts toward solar water splitting are discussed next.Finally,the current challenges and future opportunities of vacancy-modified g-C_(3)N_(4) are summarized.This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C_(3)N_(4).展开更多
We investigate the microstructures of the pure aluminium foil and filter used on the space solar telescope, irradiated by photons with different doses. The vacancy defect clusters induced by proton irradiation in both...We investigate the microstructures of the pure aluminium foil and filter used on the space solar telescope, irradiated by photons with different doses. The vacancy defect clusters induced by proton irradiation in both samples are characterized by transmission electron microscopy, and the density and the size distribution of vacancy defect clusters are determined. Their transmittances are measured before and after irradiating the samples by protons with energy E = 100 keV and dose φ = 6 × 10^11/mm^2. Our experimental results show that the density and the size of vacancy defect clusters increase with the increase of irradiation doses in the irradiated pure aluminium foils. As irradiation dose increases, vacancies incline to form larger defect clusters. In the irradiated filter, a large number of banded void defects are observed at the agglomerate boundary, which results in the degradation of the optical and mechanical performances of the filter after proton irradiation.展开更多
Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single va...Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single vacancy defect. Our results suggest that because of the single vacancy, the fracture strength of graphene losses about 17.7%. The stress concentration around the vacancy defect leads to the destruction of nearby six-member rings structure, which forms the initial crack. The propagation direction of this crack in defective graphene is at an angle of 60° to the tensile direction initially, but then becomes perpendicular to the tensile direction.展开更多
We study the plasmonic properties of hybrid nanostructures consisting of double vacancy defected graphene(DVDGr)and metallic nanoarrays using the time-dependent density functional theory. It is found that DVDGr with p...We study the plasmonic properties of hybrid nanostructures consisting of double vacancy defected graphene(DVDGr)and metallic nanoarrays using the time-dependent density functional theory. It is found that DVDGr with pure and mixed noble/transition-metal nanoarrays can produce a stronger light absorption due to the coherent resonance of plasmons than graphene nanostructures. Comparing with the mixed Au/Pd nanoarrays, pure Au nanoarrays have stronger plasmonic enhancement. Furthermore, harmonics from the hybrid nanostructures exposed to the combination of lasers ranged from ultraviolet to infrared and a controlling pulse are investigated theoretically. The harmonic plateau can be broadened significantly and the energy of harmonic spectra is dramatically extended by the controlling pulse. Thus, it is possible to tune the width and intensity of harmonic spectrum to achieve broadband absorption of radiation. The methodology described here not only improves the understanding of the surface plasmon effect used in a DVDGr-metal optoelectronic device but also may be applicable to different optical technologies.展开更多
The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals ...The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping valence-changeable ions. The experimental results were discussed and a new reduction process of the photorefractive LN crystal at a relatively low temperature was proposed, and the reduced crystals showed a good effect in practical use.展开更多
The low-efficiency CO_(2) uptake capacity and insufficient photogenerated exciton dissociation of current metal halide perovskite(MHP)nanocrystals with end-capping ligands extremely restrict their application in the f...The low-efficiency CO_(2) uptake capacity and insufficient photogenerated exciton dissociation of current metal halide perovskite(MHP)nanocrystals with end-capping ligands extremely restrict their application in the field of artificial photosynthesis.Herein,we demonstrate that ligand-free CsPbBr_(3) with calliandralike nanostructure(LF-CPB CL)can be synthesized easily through a ligand-free seed-assisted dissolutionrecrystallization growth process,exhibiting significantly enhanced CO_(2) uptake capacity.More specifically,the abundant surface bromine(Br)vacancies in ligand-free MHP materials are demonstrated to be beneficial to photogenerated carrier separation.The electron consumption rate of LF-CPB CL for photocatalytic CO_(2) reduction increases 7 and 20 times over those of traditional ligand-capping CsPbBr_(3)nanocrystal(L-CPB NC)and bulk CsPbBr_(3),respectively.Moreover,the absence of ligand hindrance can facilitate the interfacial electronic coupling between LF-CPB CL and tetra(4-carboxyphenyl)porphyrin iron(Ⅲ)chloride(Fe-TCPP)cocatalyst,bringing forth significantly accelerated interfacial charge separation.The LF-CPB CL/Fe-TCPP exhibits a total electron consumption rate of 145.6μmol g^(-1) h^(-1) for CO_(2)photoreduction coupled with water oxidation which is over 14 times higher than that of L-CPB NC/FeTCPP.展开更多
The rational design of oxygen vacancies and electronic microstructures of electrode materials for energy storage devices still remains a challenge. Herein, we synthesize nickel cobalt-based oxides nanoflower arrays as...The rational design of oxygen vacancies and electronic microstructures of electrode materials for energy storage devices still remains a challenge. Herein, we synthesize nickel cobalt-based oxides nanoflower arrays assembled with nanowires grown on Ni foam via the hydrothermal process followed annealing process in air and argon atmospheres respectively. It is found that the annealing atmosphere has a vital influence on the oxygen vacancies and electronic microstructures of resulting NiCo_(2)O_(4) (NCO-Air) and CoNiO_(2) (NCO-Ar) products, which NCO-Ar has more oxygen vacancies and larger specific surface area of 163.48 m^(2)/g. The density functional theory calculation reveals that more oxygen vacancies can provide more electrons to adsorb –OH free anions resulting in superior electrochemical energy storage performance. Therefore, the assembled asymmetric supercapacitor of NCO-Ar//active carbon delivers an excellent energy density of 112.52 Wh/kg at a power density of 558.73 W/kg and the fabricated NCO-Ar//Zn battery presents the specific capacity of 180.20 mAh/g and energy density of 308.14 Wh/kg. The experimental measurement and theoretical calculation not only provide a facile strategy to construct flower-like mesoporous architectures with massive oxygen vacancies, but also demonstrate that NCO-Ar is an ideal electrode material for the next generation of energy storage devices.展开更多
Vacancy structural defect effects on the lattice thermal conductivity of silicon thin films have been investigated with non-equilibrium molecular dynamics simulation. The lattice thermal conductivities decrease with i...Vacancy structural defect effects on the lattice thermal conductivity of silicon thin films have been investigated with non-equilibrium molecular dynamics simulation. The lattice thermal conductivities decrease with increasing vacancy concentration at all temperatures from 300 to 700 K. Vacancy defects decrease the sample thermal conductivity, and the temperature dependence of thermal conductivity becomes less significant as the temperature increases. The molecular dynamics result is in good agreement with the theoretical analysis values obtained based on the Boltzmann equation. In addition, theoretical analysis indicates that the reduction in the lattice thermal conductivity with vacancy defects can be explained by the enhanced point-defect scattering due to lattice strain.展开更多
Surface vacancy defects,as the bridge between theoretical structural study and the design of heterogenous catalysts,have captured much attention.This work develops a metal-organic framework-engaged replacement-pyrolys...Surface vacancy defects,as the bridge between theoretical structural study and the design of heterogenous catalysts,have captured much attention.This work develops a metal-organic framework-engaged replacement-pyrolysis approach to obtain highly dispersed Ru nanoparticles immobilized on the vacancy-rich Ni-NiO@C hollow microsphere(Ru/Ni-NiO@C).Fine annealing at 400°C introduces nickel and oxygen vacancies on Ru/Ni-NiO@C surface,resulting in an improved electrical conductivity and rapid mass-charge transfer efficiency.Ru/Ni-NiO@C with a hollow micro/nanostructure and interconnected meso-porosity favors the maximal exposure of abundant active sites and elevation of hydrogen oxidation reaction(HOR)activity.Experimental results and density functional theory(DFT)calculations reveal that an electronic effect between Ru and Ni-NiO@C,in conjunction with nickel/oxygen vacancies in the NiO species could synergistically optimize hydrogen binding energy(HBE)and hydroxide binding energy(OHBE).The HBE and OHBE optimizations thus created confer Ru/Ni-NiO@C with a mass activity over 7.75 times higher than commercial Pt/C.Our work may provide a constructive route to make a breakthrough in elevating the hydrogen electrocatalytic performance.展开更多
The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.How...The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.However,these possibilities remain an open question in both theory and experiment.Here,theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects.First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state.Experimentally,ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals,but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals,highlighting the significance played by vacancy defects.Furthermore,the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ion dopants,due to enhancement of the exchange coupling between magnetic polarons.Room-temperature ferromagnetism is also observed in other LHPs,which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs,which is useful for future spintronic devices.展开更多
基金Funded by the Scientific and Technologial Innovation Programs of Higher Education Institutions in Shanxi (No. 2020L0628)the Taiyuan Institute of Technology Scientific Research Initial Funding (No. 2022KJ072)+2 种基金the Program for the (Reserved) Discipline Leaders of Taiyuan Institute of Technologythe Fundamental Research Funds for the Central Universities (Nos. 2017TS004, 2017TS006, and GK201704005)Supported by HZWTECH for providing computational facilities
文摘In order to explore the effect of vacancy defects on the structural,electronic,magnetic and optical properties of CoS_(2) and FeS_(2),first-principles calculation method was used to investigate the alloys.The calculated results of materials without vacancy are consistent with those reported in the literatures,while the results of materials with vacancy defect were different from those of literatures due to the difference vacancy concentration.The Co vacancy defect hardly changes the half-metallic characteristic of CoS_(2).The Fe vacancy defect changes FeS_(2) from semiconductor to half-metal,and the bottom of the spin-down conduction band changes from the p orbital state of S to the d(t_(2g))orbital state of Fe,while the top of the valence band remains the d orbital d(eg)state of Fe.The half-metallic Co vacancy defects of CoS_(2) and Fe vacancy defects of FeS_(2) are expected to be used in spintronic devices.S vacancy defects make both CoS_(2) and FeS_(2) metallic.Both the Co and S vacancy defects lead to the decrease of the magnetic moment of CoS_(2),while both the Fe and S vacancy defects lead to the obvious magnetic property of FeS_(2).Vacancy defects enhance the absorption coefficient of infrared band and long band of visible light obviously,and produce obvious red shift phenomenon,which is expected to be used in photoelectric devices.
基金supported by the Program for Changjiang Scholars and Innovative Research Team in the Universities of the Ministry of Education of China (No. IRT0520)
文摘The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics (MD) simula- tions and theoretical analysis based on the Boltzmann equation. Both the MD and theoretical results show that the lattice thermal conductivity dramatically decreases with the increasing of vacancy concentration at 400 and 500 K. In addition, the dependence of vacancy concentration on the thermal conductivity of Ge thin films becomes less sensitive as the temperature increases. Theoretical results also confirm that the major part of the lattice thermal conductivity reduction is associated with the point-defect scattering and phonon-phonon scattering processes.
基金Project supported by the Industry and Education Combination Innovation Platform of Intelligent Manufacturing and Graduate Joint Training Base at Guizhou University(Grant No.2020-520000-83-01-324061)the National Natural Science Foundation of China(Grant No.61264004)the High-level Creative Talent Training Program in Guizhou Province of China(Grant No.[2015]4015).
文摘Recently,the newly synthesized septuple-atomic layer two-dimensional(2D)material MoSi_(2)N_(4)(MSN)has attracted attention worldwide.Our work delves into the effect of vacancies and external electric fields on the electronic properties of the MSN/graphene(Gr)heterostructure using first-principles calculation.We find that four types of defective structures,N-in,N-out,Si and Mo vacancy defects of monolayer MSN and MSN/Gr heterostructure are stable in air.Moreover,vacancy defects can effectively modulate the charge transfer at the interface of the MSN/Gr heterostructure as well as the work function of the pristine monolayer MSN and MSN/Gr heterostructure.Finally,the application of an external electric field enables the dynamic switching between n-type and p-type Schottky contacts.Our work may offer the possibility of exceeding the capabilities of conventional Schottky diodes based on MSN/Gr heterostructures.
基金supported by the National Natural Science Foundation of China,China(Grant No.51932010)by the National Natural Science Foundation of Shanghai,China(Grant No.19ZR1464600).
文摘Bismuth titanate (Bi_(4)Ti_(3)O_(12),BIT)piezoelectric materials have attracted increasing attention due to their high-temperature applications.However,it is quite challenging to simultaneously achieve outstanding piezoelectric properties and high Curie temperature in BIT-based systems.In this study,oxygen vacancy defects tailoring strategy was utilized to solve this problem,excellent piezoelectric coefficient(32.1 pC/N),and ultrahigh Curie temperature(659℃)are gotten in Bi_(4)Ti_(3)-x(Mn_(1/3)Nb_(2/3))xO_(12)(BTMN)ceramics,which are among the top values in the BIT-based ceramics.More importantly,the(Mn_(1/3)Nb_(2/3))(4+d)+complex-ion modified Bi_(4)Ti_(3)O_(12)-based ceramics are characterized with excellent piezoelectric stability up to 500℃(d33>30.0 pC/N at 500℃))and significantly reduced conductivity(only~10^(-7)U-1 cm^(-1)at 500℃).Moreover,enhanced ferroelectricity and good dielectric stability were also obtained.The better comprehensive properties can be ascribed to two aspects.First,the concentration of oxygen vacancy defects is obviously reduced,and their distribution is effectively controlled in BITMN ceramics.Second,the introduction of(Mn_(1/3)Nb_(2/3))^((4+δ)+)complex-ion gives rise to the antiphase boundaries and massive ferroelectric domain walls.This works not only reveal the high potential of BITMN ceramics for high-temperature piezoelectric applications but also deepen the understanding of the structure-properties relationship in BIT-based materials.
基金supported by grants from the Province Nature Science Foundation of Liaoning Province(Grant No.2019JH/30100019)。
文摘Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials.By means of first-principles calculations,in this paper,we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo_(5)Si_(3).Four vacancies(Si_(-Va1),Si_(-Va2),Mo_(-Va1),Mo_(-Va2))and oxygen occupation models(O_(Mo1),O_(Mo2),O_(-Si1),O_(-Si2))are selected for research.It is found that Mo_(-Va2) vacancy has the stronger structural stability in the ground state in comparison with other vacancies.Besides,the deformation resistance and hardness of the parent Mo_(5)Si_(3) are weakened due to the introduction of different vacancy defects and oxygen occupation.The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo_(5)Si_(3).These vacancies and the oxygen atoms occupation change the localized hybridization between Mo-Si and Mo-Mo atoms.The weaker O-Mo bond is a contributing factor for the excellent ductile behavior in the O_(-Si2) model for Mo_(5)Si_(3).
基金supports from the National Key Research and Development Program of China(No.2020YFB1505703)This work was supported by the National Natural Science Foundation of China(Nos.52172299,22175198,51772319,51772320,and 51972331)+3 种基金Z.G.Z would like to acknowledge the support from the External Cooperation Program of the Chinese Academy of Sciences(No.121E32KYSB20190008)Six Talent Peaks Project of Jiangsu Province(No.XCL-170)S.C would like to acknowledge the support from the Youth Innovation Promotion Association,CAS(No.2018356)the Outstanding Youth Fund of Jiangxi(No.20192BCBL23027).
文摘Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering(SERS)sensing,photocatalysis,and photovoltaic applications.However,the long-term maintenance and use of photo-induced vacancy defects remain elusive,because of their rapid self-healing upon air exposure.In this study,we demonstrate that photo-induced oxygen vacancy(PIVO)defects can be stabilized by the photoexcitation of metal–organic framework(MOF)materials,which is crucial for SERS analysis.The PIVO defects in MOF materials are stable for at least two weeks in the ambient atmosphere,owing to the combination of steric hindrance and electron delocalization around vacancy defects,which significantly contrasts the short lifetime(within minutes)of PIVO defects in metal-oxide semiconductors.With the formation of stable PIVO defects,a prominent SERS enhancement surpassing that of pristine MOFs is achieved,accompanied with a reduced limit of detection by three orders of magnitude.Moreover,the additional SERS enhancement rendered by PIVO defects can be stably retained and is effective for monitoring various small molecules,such as dopamine and bisphenol A.
基金supported by the National Natural Science Foundation of China(52172239)Project of State Key Laboratory of Environment-Friendly Energy Materials+2 种基金Southwest University of Science and Technology(Grant Nos.21fksy24 and 18ZD320304)Chongqing Talents:Exceptional Young Talents Project(Grant No.CQYC201905041)Natural Science Foundation of Chongqing China(Grant No.cstc2021jcyj-jqX0031)。
文摘The defect chemistry is successfully modulated on free-standing and binder-free carbon cathodes for highly efficient Li-S redox reactions.Such rationally regulated defect engineering realizes the synchronization of ion/electron-conductive and defect-rich networks on the threedimension carbon cathode,leading to its tunable activity for both relieving the shuttle phenomenon and accelerating the sulfur redox reaction kinetics.As expected,the defective carbon cathode harvests a high rate capacity of 1217.8 mAh g^(-1)at 0.2 C and a superior capacity retention of61.7%at 2 C after 500 cycles.Even under the sulfur mass loading of 11.1 mg cm^(-2),the defective cathode still holds a remarkable areal capacity of 8.5 mAh cm^(-2).
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61204008,11075176,and 11505211)the National Key Basic Research Special Foundation of China(Grant No.2013CB328705)
文摘Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn3+(d4) into Mn2+(d5).The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn3+(d4) and Mn2+(d5) are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn3+changing into Mn2+will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.
文摘The Young's modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is demonstrated that the Young's modulus of graphene is largely correlated to the size of vacancy defects perpendicular to the stretching direction. And a linear reduction of Young's modulus with the increasing concentration of monoatomic-vacancy defects (Le., the slope of =0.03) is also observed. The fracture behavior of graphene, including the fracture strength, crack initiation and propagation are then studied by the molecular dynamics simulation, the effective spring model, and the quantized fracture mechanics. The blunting effect of vacancy edges is demonstrated, and the characterized crack tip radius of 4.44 A is observed.
基金Project supported by the China Postdoctoral Science Foundation(No.201104619)the Fund of Shaanxi Provincial Educational Department (No.2010JK775)
文摘Based on first-principle calculations, the electronic structures and optical properties of a single-walled (7, 0) SiC nanotube (SiCNT) with a carbon vacancy defect or a silicon vacancy defect are investigated. In the three silicon atoms around the carbon vacancy, two atoms form a stable bond and the other is a dangling bond. A similar structure is found in the nanotube with a silicon vacancy. A carbon vacancy results in a defect level near the top of the valence band, while a silicon vacancy leads to the formation of three defect levels in the band gap of the nanotube. Transitions between defect levels and energy levels near the bottom of the conduction band have a close relationship with the formation of the novel dielectric peaks in the lower energy range of the dielectric function.
基金This work is supported mainly by the National Key Research and Development Program of China(Grant No.2018YFE0204000)the National Natural Science Foundation of China(Grant Nos.21975245,U20A20206,51972300,12004094,and 32101004)+4 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB43000000)the Science and Technology Research and Development Program of Handan(Grant No.21422111246)Prof.Y.Huang.also acknowledges the support from the Doctoral Special Fund Project of Hebei University of Engineering.Prof.K.Liu.appreciates the support from Youth Innovation Promotion Association,the Chinese Academy of Sciences(Grant No.2020114)the Beijing Nova Program(Grant No.2020117)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515110578).
文摘Developing low-cost,efficient,and stable photocatalysts is one of the most promising methods for large-scale solar water splitting.As a metal-free semiconductor material with suitable band gap,graphitic carbon nitride(g-C_(3)N_(4))has attracted attention in the field of photocatalysis,which is mainly attributed to its fascinating physicochemical and photoelectronic properties.However,several inherent limitations and shortcomings—involving high recombination rate of photocarriers,insufficient reaction kinetics,and optical absorption—impede the practical applicability of g-C_(3)N_(4).As an effective strategy,vacancy defect engineering has been widely used for breaking through the current limitations,considering its ability to optimize the electronic structure and surface morphology of g-C_(3)N_(4) to obtain the desired photocatalytic activity.This review summarizes the recent progress of vacancy defect engineered g-C_(3)N_(4) for solar water splitting.The fundamentals of solar water splitting with g-C_(3)N_(4) are discussed first.We then focus on the fabrication strategies and effect of vacancy generated in g-C_(3)N_(4).The advances of vacancy-modified g-C_(3)N_(4) photocatalysts toward solar water splitting are discussed next.Finally,the current challenges and future opportunities of vacancy-modified g-C_(3)N_(4) are summarized.This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C_(3)N_(4).
基金Project supported by the National Natural Science Foundation of China (Grant No. 50671042)the Program for Innovative Research Team of Jangsu University and the Program for Exellent Talents of Jangsu University (Grant No. 07JDG032)
文摘We investigate the microstructures of the pure aluminium foil and filter used on the space solar telescope, irradiated by photons with different doses. The vacancy defect clusters induced by proton irradiation in both samples are characterized by transmission electron microscopy, and the density and the size distribution of vacancy defect clusters are determined. Their transmittances are measured before and after irradiating the samples by protons with energy E = 100 keV and dose φ = 6 × 10^11/mm^2. Our experimental results show that the density and the size of vacancy defect clusters increase with the increase of irradiation doses in the irradiated pure aluminium foils. As irradiation dose increases, vacancies incline to form larger defect clusters. In the irradiated filter, a large number of banded void defects are observed at the agglomerate boundary, which results in the degradation of the optical and mechanical performances of the filter after proton irradiation.
基金supported by the Open Research Fund Program(2042014kf0002)of Wuhan Universitythe National Natural Science Foundation of China(11372230)the Open Research Fund Program(HBKLWJ-2014F02)of Key Laboratory of Hubei Province for Water Jet Theory&Technology
文摘Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single vacancy defect. Our results suggest that because of the single vacancy, the fracture strength of graphene losses about 17.7%. The stress concentration around the vacancy defect leads to the destruction of nearby six-member rings structure, which forms the initial crack. The propagation direction of this crack in defective graphene is at an angle of 60° to the tensile direction initially, but then becomes perpendicular to the tensile direction.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0303600)the National Natural Science Foundation of China(Grant Nos.11974253 and 11774248)。
文摘We study the plasmonic properties of hybrid nanostructures consisting of double vacancy defected graphene(DVDGr)and metallic nanoarrays using the time-dependent density functional theory. It is found that DVDGr with pure and mixed noble/transition-metal nanoarrays can produce a stronger light absorption due to the coherent resonance of plasmons than graphene nanostructures. Comparing with the mixed Au/Pd nanoarrays, pure Au nanoarrays have stronger plasmonic enhancement. Furthermore, harmonics from the hybrid nanostructures exposed to the combination of lasers ranged from ultraviolet to infrared and a controlling pulse are investigated theoretically. The harmonic plateau can be broadened significantly and the energy of harmonic spectra is dramatically extended by the controlling pulse. Thus, it is possible to tune the width and intensity of harmonic spectrum to achieve broadband absorption of radiation. The methodology described here not only improves the understanding of the surface plasmon effect used in a DVDGr-metal optoelectronic device but also may be applicable to different optical technologies.
文摘The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping valence-changeable ions. The experimental results were discussed and a new reduction process of the photorefractive LN crystal at a relatively low temperature was proposed, and the reduced crystals showed a good effect in practical use.
基金financially supported by the Natural Science Foundation of Tianjin City(17JCJQJC43800)the National Key R&D Program of China(2017YFA0700104)+1 种基金the National Science Foundation of China(21931007,U21A20286)Jiangsu Funding Program for Excellent Postdoctoral Talent and the 111 Project of China(D17003)。
文摘The low-efficiency CO_(2) uptake capacity and insufficient photogenerated exciton dissociation of current metal halide perovskite(MHP)nanocrystals with end-capping ligands extremely restrict their application in the field of artificial photosynthesis.Herein,we demonstrate that ligand-free CsPbBr_(3) with calliandralike nanostructure(LF-CPB CL)can be synthesized easily through a ligand-free seed-assisted dissolutionrecrystallization growth process,exhibiting significantly enhanced CO_(2) uptake capacity.More specifically,the abundant surface bromine(Br)vacancies in ligand-free MHP materials are demonstrated to be beneficial to photogenerated carrier separation.The electron consumption rate of LF-CPB CL for photocatalytic CO_(2) reduction increases 7 and 20 times over those of traditional ligand-capping CsPbBr_(3)nanocrystal(L-CPB NC)and bulk CsPbBr_(3),respectively.Moreover,the absence of ligand hindrance can facilitate the interfacial electronic coupling between LF-CPB CL and tetra(4-carboxyphenyl)porphyrin iron(Ⅲ)chloride(Fe-TCPP)cocatalyst,bringing forth significantly accelerated interfacial charge separation.The LF-CPB CL/Fe-TCPP exhibits a total electron consumption rate of 145.6μmol g^(-1) h^(-1) for CO_(2)photoreduction coupled with water oxidation which is over 14 times higher than that of L-CPB NC/FeTCPP.
基金This work was supported by the Natural Science Foundation of China(51962032,61704114,and 51764049)the Youth Innovative Talents Cultivation Fund,Shihezi University(KX01480109)the Opening Project of The Research Center for Material Chemical Engineering Technology of Xinjiang Bingtuan(2017BTRC007).
文摘The rational design of oxygen vacancies and electronic microstructures of electrode materials for energy storage devices still remains a challenge. Herein, we synthesize nickel cobalt-based oxides nanoflower arrays assembled with nanowires grown on Ni foam via the hydrothermal process followed annealing process in air and argon atmospheres respectively. It is found that the annealing atmosphere has a vital influence on the oxygen vacancies and electronic microstructures of resulting NiCo_(2)O_(4) (NCO-Air) and CoNiO_(2) (NCO-Ar) products, which NCO-Ar has more oxygen vacancies and larger specific surface area of 163.48 m^(2)/g. The density functional theory calculation reveals that more oxygen vacancies can provide more electrons to adsorb –OH free anions resulting in superior electrochemical energy storage performance. Therefore, the assembled asymmetric supercapacitor of NCO-Ar//active carbon delivers an excellent energy density of 112.52 Wh/kg at a power density of 558.73 W/kg and the fabricated NCO-Ar//Zn battery presents the specific capacity of 180.20 mAh/g and energy density of 308.14 Wh/kg. The experimental measurement and theoretical calculation not only provide a facile strategy to construct flower-like mesoporous architectures with massive oxygen vacancies, but also demonstrate that NCO-Ar is an ideal electrode material for the next generation of energy storage devices.
基金Project supported by the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (No.IRT0520).
文摘Vacancy structural defect effects on the lattice thermal conductivity of silicon thin films have been investigated with non-equilibrium molecular dynamics simulation. The lattice thermal conductivities decrease with increasing vacancy concentration at all temperatures from 300 to 700 K. Vacancy defects decrease the sample thermal conductivity, and the temperature dependence of thermal conductivity becomes less significant as the temperature increases. The molecular dynamics result is in good agreement with the theoretical analysis values obtained based on the Boltzmann equation. In addition, theoretical analysis indicates that the reduction in the lattice thermal conductivity with vacancy defects can be explained by the enhanced point-defect scattering due to lattice strain.
基金supported by the National Natural Science Foundation of China(21965005)the Natural Science Foundation of Guangxi Province(2018GXNSFAA294077,2021GXNSFAA076001)+1 种基金the Project of High-Level Talents of Guangxi(F-KA18015)the Guangxi Technology Base and Talent Subject(GUIKEAD18126001,GUIKE AD20297039)。
文摘Surface vacancy defects,as the bridge between theoretical structural study and the design of heterogenous catalysts,have captured much attention.This work develops a metal-organic framework-engaged replacement-pyrolysis approach to obtain highly dispersed Ru nanoparticles immobilized on the vacancy-rich Ni-NiO@C hollow microsphere(Ru/Ni-NiO@C).Fine annealing at 400°C introduces nickel and oxygen vacancies on Ru/Ni-NiO@C surface,resulting in an improved electrical conductivity and rapid mass-charge transfer efficiency.Ru/Ni-NiO@C with a hollow micro/nanostructure and interconnected meso-porosity favors the maximal exposure of abundant active sites and elevation of hydrogen oxidation reaction(HOR)activity.Experimental results and density functional theory(DFT)calculations reveal that an electronic effect between Ru and Ni-NiO@C,in conjunction with nickel/oxygen vacancies in the NiO species could synergistically optimize hydrogen binding energy(HBE)and hydroxide binding energy(OHBE).The HBE and OHBE optimizations thus created confer Ru/Ni-NiO@C with a mass activity over 7.75 times higher than commercial Pt/C.Our work may provide a constructive route to make a breakthrough in elevating the hydrogen electrocatalytic performance.
基金This work was financially supported by NSFC(61725402)the Natural Science Foundation of Jiangsu Province(BK20190475).
文摘The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.However,these possibilities remain an open question in both theory and experiment.Here,theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects.First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state.Experimentally,ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals,but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals,highlighting the significance played by vacancy defects.Furthermore,the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ion dopants,due to enhancement of the exchange coupling between magnetic polarons.Room-temperature ferromagnetism is also observed in other LHPs,which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs,which is useful for future spintronic devices.