In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’d...In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.展开更多
The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron co...The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron composition contrast observation was introduced and discussed. By using multilayer P+Si1-xGex/pSi heterojunction internal photoemission infrared detector as an example, the applications of secondary electron composition contrast imaging in microstructure studies on heterojunction semiconducting materials and devices were stated. The characteristics of the image were compared with the ordinary transmission electron diffraction contrast image. The prospects of applications of the imaging method in heterojunction semiconductor devices and multilayer materials are also discussed.展开更多
The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic s...The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic structure precisely. The threading dislocations are reduced. We also optimize the growth and annealing parameters of the InGaAs quantum well (QW). The 1.3-μm GaAs based metamorphic InGaAs QW is completed. A 1.3-μm GaAs based metamorphic laser is reported.展开更多
Organic magnetic semiconductors have aroused much attention for spintronic applications. However, it remains challenging to achieve organic semiconductors with strong room-temperature ferromagnetism. Here, we report a...Organic magnetic semiconductors have aroused much attention for spintronic applications. However, it remains challenging to achieve organic semiconductors with strong room-temperature ferromagnetism. Here, we report a two-dimensional (2D) tetragonal organic-inorganic ferrimagnetic (FIM) semiconductor of Fe_(14)Se_(16)(peha)_(0.7) (peha = pentaethylenehexamine) with excellent thermal stability and a Curie temperature (T_(C)) higher than 519 K. Magnetic and Mössbauer measurements reveal a long-range magnetic ordering in single crystalline Fe_(14)Se_(16)(peha)0.7 nanosheets. The saturation magnetization and coercivity are 5.9 emu g^(−1) and 0.42 kOe at 5 K, which slightly reduces to 4.6 emu g^(−1) and ∼0 Oe at 300 K. A direct optical bandgap of 2.22 eV is obtained by tuning electronic structure of β-Fe3Se4 host layers through spacer layers consisting of Fe^(3+) and peha. Electrical and Seebeck coefficient data indicate that the n-type semiconductor follows the thermally-activated conduction mechanism (lnρ ∝ T^(−1)) in a range of 130–300 K with an activation energy (Ea) of 62.69 meV. Thermal conductivity is 2.5 W m^(−1) K^(−1) at 300 K, while the Wiedemann–Franz law is strongly violated according to electrical-thermal transport data due to weak incorporation of organic spacer layers and host layers. This study sets the stage for exploiting new room-temperature organic magnetic semiconductor systems for spintronic materials.展开更多
Two-dimensional nanostructures shed new light on the enhancement of the thermoelectric figure of merit due to the potential decoupling of electronic and phononic transport coefficients.In contrast to the gapless chara...Two-dimensional nanostructures shed new light on the enhancement of the thermoelectric figure of merit due to the potential decoupling of electronic and phononic transport coefficients.In contrast to the gapless character of graphene-like silicene,a recently reported silicon allotropy with a honeycomb-kagome lattice is a semiconductor.Here,based on first-principles calculations,we set out to investigate the thermoelectric transport performance of this semiconducting silicene.Since the mean free path of a large number of phonons in this structure is less than the Ioffe–Regel limit,we employ the quantum Boltzmann transport equation(BTE)method to obtain an accurate prediction of lattice thermal conductivity.Importantly,we unexpectedly find much lower lattice thermal conductivity compared to that of graphene-like silicene,i.e.,about 1.73W·m^(−1)·K^(−1)at room temperature.Meanwhile,the electronic transport coefficient is calculated within the strictly electron–phonon coupling calculation and a full solution of the electron BTE.The optimal thermoelectric figure of merit ZT reaches 3.2 in N-doped silicene at 700K with an optimized low carrier concentration of 8×10^(10)cm^(−2),which is a recorded value among two-dimensional materials.Our work paved the way for applications of silicon-based two-dimensional materials in on-chip thermoelectric cooling and clean energy.展开更多
Over the past half-century,significant efforts have been dedicated to the photocatalytic H_(2)production from H_(2)O under UV–visible light irradiation.These endeavors have yielded remarkable results,with efficiency ...Over the past half-century,significant efforts have been dedicated to the photocatalytic H_(2)production from H_(2)O under UV–visible light irradiation.These endeavors have yielded remarkable results,with efficiency levels now approaching near 100%apparent quantum yields,notably utilizing inorganic semiconducting materials such as modified Al-doped SrTiO_(3)photocatalysts.Meanwhile,advancements in organic polymer semiconducting materials,exemplified by g-C_(3)N_(4),have led to substantial improvements in the efficiency of photocatalytic overall water splitting for H_(2)evolution reaction.These improvements,achieved through chemical engineering methods and molecular-level modifications,have resulted in an apparent quantum yield of 69%at 405 nm,accompanied by significant red-shifting of optical absorption to 1400 nm.These developments are presented in chronological order over the past half-century,underscoring the ongoing quest for innovative breakthroughs to enable largescale practical applications of solar hydrogen production.Key considerations in this pursuit include efficiency,stability,cost-effectiveness,and the independent evolution of H_(2)and O_(2).展开更多
Using particle swarm optimization(PSO)methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D)monolayer of silicide diphosphorus compound:SiP_(2),which exhibits good stability as examined...Using particle swarm optimization(PSO)methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D)monolayer of silicide diphosphorus compound:SiP_(2),which exhibits good stability as examined via cohesive energy,mechanical criteria,molecular dynamics simulation and all positive phonon spectrum,respectively.The SiP_(2)monolayer is an indirect semiconductor with the band gap as 1.8484 eV(PBE)or 2.681 eV(HSE06),which makes it more advantageous for high-frequencyresponse optoelectronic materials.Moreover,the monolayer is a relatively hard auxetic material with negative Possion’s ratios,and also possesses a ultrahigh carrier mobility(1.069×10^(5)cm^(2)V^(-1)s^(-1))which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers.Furthermore,the effects of strains on band structures and optical properties of SiP_(2)monolayer have been studied,as well as CO_(2)molecules can be strongly chemically adsorbed on the SiP_(2)monolayer.A semiconductor-to-metal transition for-9.5%strain ratio case and a huge optical absorption capacity on the order of 10^(6)cm^(-1)in visible region present.These theoretical findings endow SiP_(2)Monolayer to be a novel 2 D material holding great promises for applications in highperformance electronics,optoelectronics,mechanics and CO_(2)capturing material.展开更多
Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.B...Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.展开更多
The seminal 1972 demonstration of photocatalytic water splitting marked the advent of a revolutionary low-carbon energy technology capable of harnessing solar radiation for direct hydrogen production through aqueous d...The seminal 1972 demonstration of photocatalytic water splitting marked the advent of a revolutionary low-carbon energy technology capable of harnessing solar radiation for direct hydrogen production through aqueous dissociation [1]. Half a century after this groundbreaking discovery, titanium dioxide(TiO_(2)) continues to occupy a central position in photocatalysis research. This semiconducting material demonstrates a unique combination of advantageous characteristics: outstanding photocatalytic activity, remarkably prolonged charge carrier lifetime, and exceptional photochemical stability against corrosion [2–6].展开更多
文摘In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.
文摘The principle, imaging condition and experimental method for obtaining high resolution composition contrast in secondary electron image were described. A new technique of specimen preparation for secondary electron composition contrast observation was introduced and discussed. By using multilayer P+Si1-xGex/pSi heterojunction internal photoemission infrared detector as an example, the applications of secondary electron composition contrast imaging in microstructure studies on heterojunction semiconducting materials and devices were stated. The characteristics of the image were compared with the ordinary transmission electron diffraction contrast image. The prospects of applications of the imaging method in heterojunction semiconductor devices and multilayer materials are also discussed.
基金supported by the National Natural Science Foundation of China (Nos.90921015 and 10734060)the National Basic Research Program of China (No.2010CB327601)
文摘The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic structure precisely. The threading dislocations are reduced. We also optimize the growth and annealing parameters of the InGaAs quantum well (QW). The 1.3-μm GaAs based metamorphic InGaAs QW is completed. A 1.3-μm GaAs based metamorphic laser is reported.
基金supported by the National Natural Science Foundation of China(Nos.52371203,51971221 and 52031014).
文摘Organic magnetic semiconductors have aroused much attention for spintronic applications. However, it remains challenging to achieve organic semiconductors with strong room-temperature ferromagnetism. Here, we report a two-dimensional (2D) tetragonal organic-inorganic ferrimagnetic (FIM) semiconductor of Fe_(14)Se_(16)(peha)_(0.7) (peha = pentaethylenehexamine) with excellent thermal stability and a Curie temperature (T_(C)) higher than 519 K. Magnetic and Mössbauer measurements reveal a long-range magnetic ordering in single crystalline Fe_(14)Se_(16)(peha)0.7 nanosheets. The saturation magnetization and coercivity are 5.9 emu g^(−1) and 0.42 kOe at 5 K, which slightly reduces to 4.6 emu g^(−1) and ∼0 Oe at 300 K. A direct optical bandgap of 2.22 eV is obtained by tuning electronic structure of β-Fe3Se4 host layers through spacer layers consisting of Fe^(3+) and peha. Electrical and Seebeck coefficient data indicate that the n-type semiconductor follows the thermally-activated conduction mechanism (lnρ ∝ T^(−1)) in a range of 130–300 K with an activation energy (Ea) of 62.69 meV. Thermal conductivity is 2.5 W m^(−1) K^(−1) at 300 K, while the Wiedemann–Franz law is strongly violated according to electrical-thermal transport data due to weak incorporation of organic spacer layers and host layers. This study sets the stage for exploiting new room-temperature organic magnetic semiconductor systems for spintronic materials.
基金supported by the Scientific and Technological Research of the Chongqing Municipal Education Commission(Grant No.KJZD-K202100602)the funding from the Institute for Advanced Sciences of Chongqing University of Posts and Telecommunications(Grant No.E011A2022326)partially supported by the RIE2020 Advanced Manufacturing and Engineering(AME)Programmatic(Grant No.A1898b0043 for G.Z.)。
文摘Two-dimensional nanostructures shed new light on the enhancement of the thermoelectric figure of merit due to the potential decoupling of electronic and phononic transport coefficients.In contrast to the gapless character of graphene-like silicene,a recently reported silicon allotropy with a honeycomb-kagome lattice is a semiconductor.Here,based on first-principles calculations,we set out to investigate the thermoelectric transport performance of this semiconducting silicene.Since the mean free path of a large number of phonons in this structure is less than the Ioffe–Regel limit,we employ the quantum Boltzmann transport equation(BTE)method to obtain an accurate prediction of lattice thermal conductivity.Importantly,we unexpectedly find much lower lattice thermal conductivity compared to that of graphene-like silicene,i.e.,about 1.73W·m^(−1)·K^(−1)at room temperature.Meanwhile,the electronic transport coefficient is calculated within the strictly electron–phonon coupling calculation and a full solution of the electron BTE.The optimal thermoelectric figure of merit ZT reaches 3.2 in N-doped silicene at 700K with an optimized low carrier concentration of 8×10^(10)cm^(−2),which is a recorded value among two-dimensional materials.Our work paved the way for applications of silicon-based two-dimensional materials in on-chip thermoelectric cooling and clean energy.
文摘Over the past half-century,significant efforts have been dedicated to the photocatalytic H_(2)production from H_(2)O under UV–visible light irradiation.These endeavors have yielded remarkable results,with efficiency levels now approaching near 100%apparent quantum yields,notably utilizing inorganic semiconducting materials such as modified Al-doped SrTiO_(3)photocatalysts.Meanwhile,advancements in organic polymer semiconducting materials,exemplified by g-C_(3)N_(4),have led to substantial improvements in the efficiency of photocatalytic overall water splitting for H_(2)evolution reaction.These improvements,achieved through chemical engineering methods and molecular-level modifications,have resulted in an apparent quantum yield of 69%at 405 nm,accompanied by significant red-shifting of optical absorption to 1400 nm.These developments are presented in chronological order over the past half-century,underscoring the ongoing quest for innovative breakthroughs to enable largescale practical applications of solar hydrogen production.Key considerations in this pursuit include efficiency,stability,cost-effectiveness,and the independent evolution of H_(2)and O_(2).
基金funded by the Scientific Research Fund of Hunan Provincial Education Department of China(No.16A081)the Natural Science Foundation of China(Nos.21603109,11304128)+2 种基金the Henan Joint Fund of the National Natural Science Foundation of China(No.U1404216)the Science and Technology Program of Henan Department of Science and Technology,China(No.182102310609)the Construct Program of Applied Characteristic Discipline in Hunan University of Science and Engineering(Mathematics,Electronic Science and Technology)。
文摘Using particle swarm optimization(PSO)methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D)monolayer of silicide diphosphorus compound:SiP_(2),which exhibits good stability as examined via cohesive energy,mechanical criteria,molecular dynamics simulation and all positive phonon spectrum,respectively.The SiP_(2)monolayer is an indirect semiconductor with the band gap as 1.8484 eV(PBE)or 2.681 eV(HSE06),which makes it more advantageous for high-frequencyresponse optoelectronic materials.Moreover,the monolayer is a relatively hard auxetic material with negative Possion’s ratios,and also possesses a ultrahigh carrier mobility(1.069×10^(5)cm^(2)V^(-1)s^(-1))which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers.Furthermore,the effects of strains on band structures and optical properties of SiP_(2)monolayer have been studied,as well as CO_(2)molecules can be strongly chemically adsorbed on the SiP_(2)monolayer.A semiconductor-to-metal transition for-9.5%strain ratio case and a huge optical absorption capacity on the order of 10^(6)cm^(-1)in visible region present.These theoretical findings endow SiP_(2)Monolayer to be a novel 2 D material holding great promises for applications in highperformance electronics,optoelectronics,mechanics and CO_(2)capturing material.
基金supported by the National Key Research and Development Program of China(Grant Nos.2024YFA1408400,2023YFA1406100,2023YFA1607400,2022YFA1403800,and 2022YFA1403203)the National Natural Science Foundation of China(Grant Nos.12474055,12404067,12025408,52025026,and U23A6003)+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33000000)the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2024PG0003)the Outstanding Member of Youth Promotion Association of Chinese Academy of Sciences(Grant No.Y2022004)supported by the CAC station of Synergetic Extreme Condition User Facility(SECUF,https://cstr.cn/31123.02.SECUF)。
文摘Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.
文摘The seminal 1972 demonstration of photocatalytic water splitting marked the advent of a revolutionary low-carbon energy technology capable of harnessing solar radiation for direct hydrogen production through aqueous dissociation [1]. Half a century after this groundbreaking discovery, titanium dioxide(TiO_(2)) continues to occupy a central position in photocatalysis research. This semiconducting material demonstrates a unique combination of advantageous characteristics: outstanding photocatalytic activity, remarkably prolonged charge carrier lifetime, and exceptional photochemical stability against corrosion [2–6].
