Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation ...Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance.In this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation doses.The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)irradiation.Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film devices.Clear Shapiro steps are observed under 10 GHz microwave irradiation.The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.展开更多
Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform Pd...Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform PdS and PdS_(2)nanofilms(NFs)remains an enormous challenge.In this work,2-inch wafer-scale PdS and PdS_(2) NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique.The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS_(2) NFs.A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations.The electrical transport properties of PdS and PdS_(2) NFs were explored by conductive atomic force microscopy.Our findings have achieved the controllable growth of PdS and PdS_(2) NFs,which may provide a pathway to facilitate PdS and PdS_(2) based applications for next-generation high performance optoelectronic devices.展开更多
Cu2ZnSnS4 (CZTS) thin films were successfully prepared by sulfurization of ion bean sputtered precursors on soda-lime glass substrate. The single phase of stannite-type structure CZTS films were obtained as revealed i...Cu2ZnSnS4 (CZTS) thin films were successfully prepared by sulfurization of ion bean sputtered precursors on soda-lime glass substrate. The single phase of stannite-type structure CZTS films were obtained as revealed in EDS and XRD analysis when the ratios of the constituents of CZTS thin films are close to stoichiometric by optimizing the conditions of precursor preparation and sulfurization. A low sheet resistivity as about 0.156 Ω·cm and a high absorption coefficient as 1×104 cm-1 were achieved in this method by Hall effect measurements and UV-VIS spectrophotometer. The optical band-gap energy of the CZTS sample is about 1.51 eV, which is very close to the optimum value for a solar-cell absorber.展开更多
To obtain thermotolerant mutants of G. oxydans, which can enhance the transformation rate of L-sorbose to 2-Keto-L-gulonate (2-KLG) at 33℃ in a two-step process of vitamin C manufacture, ion beam was used as a muta...To obtain thermotolerant mutants of G. oxydans, which can enhance the transformation rate of L-sorbose to 2-Keto-L-gulonate (2-KLG) at 33℃ in a two-step process of vitamin C manufacture, ion beam was used as a mutation source. Gluconobacter oxydans GO and Bacillus megaterium B0 were used in this study. The original strain Gluconobacter oxydans GO was mutated by the heavy ion implantation facility at the Institute of Plasma Physics, Chinese Academy of Sciences. Several mutants including Gluconobacter oxydans GI13 were isolated and cocultured with Bacillus megaterium B0 at 33℃ in shaking flasks. The average transformation rate of the new mixed strain GI13-B0 in per gram-molecule reached 94.4% after seven passages in shaking flasks, which was increased by 7% when compared with the original mixed strain G0-B0 (Gluconobacter oxydans GO and Bacillus megaterium B0). Moreover, the transformation rate of I13B0 was stable at 94% at temperatures ranging from 25℃ to 33℃, which would be of much value in reducing energy consumption in the manufacture of L-ascorbic acid, especially in the season of summer. To clarify some mechanism of the mutation, the specific activities of L-sorbose dehydrogenase in both GO and GI13 were estimated.展开更多
We report that the corrosion resistance of a Mg-Sn-based alloy with MgzSn precipitates can be considerably improved by surface modification using pulsed electron beam treatment.The alloy subjected to a pulse electron ...We report that the corrosion resistance of a Mg-Sn-based alloy with MgzSn precipitates can be considerably improved by surface modification using pulsed electron beam treatment.The alloy subjected to a pulse electron beam treatment showed a modified surface layer with a thickness of〜12 μm,appearing more resistant to corrosion attack than the bare surface of the alloy.In 0.6 M NaCl solution,the alloys with and without the surface modification exhibited average corrosion rates of 4.3 and 8.1 mm y^-1,respectively.The improved corrosion resistance was attributed to reduced cathodic activation,resulting from the surficial reduction of relatively noble Mg2Sn precipitates.展开更多
Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to t...Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.展开更多
We present an experimental method to obtain neutral beam injection (NBI) power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission effi...We present an experimental method to obtain neutral beam injection (NBI) power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code (TSC) show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.展开更多
HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed diwrtor were simulated by the current filament code and t...HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed diwrtor were simulated by the current filament code and they were in agreement with the diagnostic results in the divertor. Supersonic molecular beam injection (SMBI) system was first installed and tested on the HL-2A tokamak in 2004. In the present experiment low pressure SMBI fuelling on the HL-2A closed divertor was carried out. The experimental results indicate that the divertor was operated in the 'linear regime' and during the period of SMB pulse injection into the HL-2A plasma the power density eonvected at the target plate surfaces was 0.4 times of that before or after the beam injection. It is a useful fuelling method for decreasing the heat load on the neutralizer plates of the divertor.展开更多
As a kind of mutagen, ion beam irradiation can create abundant biological mutations. A population of about 2000 lines was generated by irradiating dry wheat seeds of XiaoYan 81 with low-energy nitrogen ion beams. The ...As a kind of mutagen, ion beam irradiation can create abundant biological mutations. A population of about 2000 lines was generated by irradiating dry wheat seeds of XiaoYan 81 with low-energy nitrogen ion beams. The traits of the plant, such as height, spike type, fertility, stem color and awn length, were investigated. The mutation rate in terms of the plant height in M2 was 2.9%. Eighteen deletion mutants of TaGA2ox1 were obtained. Associate analysis showed that TaGA2ox1 was closely related to the plant height. Most of the TaGA2ox1-deleted mutants were higher than the control, suggesting that the biological function of TaGA2ox1 is similar to its homologues in other plants. These results demonstrate that ion beam irradiation is an efficient tool in the construction of a mutant library for wheat.展开更多
This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure. Taking the deposited ene...This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure. Taking the deposited energy of ion beams in TBCs as the source term in the thermal conduction equation, the distribution of temperature in TBCs was simulated. Then, based on the distribution, the evolution of thermal stress was calculated by the finite element method. The results show that tensile radial stress formed at the valley of TBC surfaces after irradiation by HIPIB. Therefore, if cracks happen, they must be at valleys instead of peaks. As for the stress waves, no matter whether through peak or valley position, tensile and compressive stresses are present alternately inside TBCs along the depth direction, and the strength of stress decreases with time.展开更多
PdTe2, a member of layered transition metal dichalcogenides (TMDs), has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions. It provides a promising platform ...PdTe2, a member of layered transition metal dichalcogenides (TMDs), has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions. It provides a promising platform to explore the inter- play between superconducting quasiparticles and Dirac fermions. Moreover, PdTe2 has also been used as a substrate for monolayer antimonene growth. Here in this paper, we report the epitaxial growth of high quality PdTe2 films on bilayer graphene/SiC(0001) by molecular beam epitaxy (MBE). Atomically thin films are characterized by scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and Raman spec- troscopy. The band structure of 6-layer PdTe2 film is measured by angle-resolved photoemission spectroscopy (ARPES). Moreover, our air exposure experiments show excellent chemical stability of epitaxial PdTe2 film. High-quality PdTe2 films provide opportunities to build antimonene/PdTe2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.展开更多
Ion beam-induced luminescence(IBIL) experiments were performed to investigate the in situ luminescence of GaN/Al_(2)O_(3) at varying ion energies,which allowed for the measurement of defects at different depths within...Ion beam-induced luminescence(IBIL) experiments were performed to investigate the in situ luminescence of GaN/Al_(2)O_(3) at varying ion energies,which allowed for the measurement of defects at different depths within the material.The energies of H^(+)were set to 500 keV,640 keV and 2 MeV,the Bragg peaks of which correspond to the GaN film,GaN/Al_(2)O_(3) heterojunction and Al_(2)O_(3) substrate,respectively.A photoluminescence measurement at 250 K was also performed for comparison,during which only near band edge(NBE) and yellow band luminescence in the GaN film were observed.The evolution of the luminescence of the NBE and yellow band in the GaN film was discussed,and both exhibited a decrease with the fluence of H^(+).Additionally,the luminescence of F centers,induced by oxygen vacancies,and Cr^(3+),resulting from the ^(2)E →^(4)A_(2) radiative transition in Al_(2)O_(3),were measured using 2 MeV H^(+).The luminescence intensity of F centers increases gradually with the fluence of H^(+).The luminescence evolution of Cr^(3+)is consistent with a yellow band center,attributed to its weak intensity,and it is situated within the emission band of the yellow band in the GaN film.Our results show that IBIL measurement can effectively detect the luminescence behavior of multilayer films by adjusting the ion energy.Luminescence measurement can be excited by various techniques,but IBIL can satisfy in situ luminescence measurement,and multilayer structural materials of tens of micrometers can be measured through IBIL by adjusting the energy of the inducing ions.The evolution of defects at different layers with ion fluence can be obtained.展开更多
Under electron beam irradiation, the in-situ formation of 2H-SiC dentritic nanocrystals from amorphous silicon carbide at room temperature was observed. The homogenous transition mainly occurs at the thin edge and on ...Under electron beam irradiation, the in-situ formation of 2H-SiC dentritic nanocrystals from amorphous silicon carbide at room temperature was observed. The homogenous transition mainly occurs at the thin edge and on the surface of specimen where the energy obtained from electron beam irradiation is high enough to cause the amorphous crystallizing into 2H-SiC.展开更多
An Electron Cyclotron Resonance Heating (ECRH) launcher for four-beam injection has been installed on the HL-2A tokamak and used in plasma heating experiments. By the launcher, four EC wave beams can be injected int...An Electron Cyclotron Resonance Heating (ECRH) launcher for four-beam injection has been installed on the HL-2A tokamak and used in plasma heating experiments. By the launcher, four EC wave beams can be injected into the tokamak through a φ350 mm port, which are generated from 2 sets of 68 GHz/1 s and 2 sets of 68 GHz/1.5 s gyrotron tubes manufactured by GYCOM, with maximum output power of 500 kW for each. In this paper, the properties of the EC beam in the launcher and plasma are presented: at the centre of the cross section of the tokamak, the beam radius is 31.7 mm; thermal analysis of a 3D model indicates that the peak temperature increase would be only 30 o C at the mirror surface for a 500 kW/1 s pulse; ray-tracing calculation predicts satisfactory power deposition. In the plasma experiment, six beams including four beams from this launcher and two from another launcher have been injected simultaneously. Besides, obtaining ELM-y H-mode discharges, the ECRH system shows reliability and stability of the launcher functions.展开更多
Nanocomposite Cr C/hydrogenated amorphous carbon(nc-CrC/a-C:H) coatings were deposited by a hybrid beams system comprised of a hollow cathode ion source and a cathodic arc ion-plating unit with varying H_2 flow rates....Nanocomposite Cr C/hydrogenated amorphous carbon(nc-CrC/a-C:H) coatings were deposited by a hybrid beams system comprised of a hollow cathode ion source and a cathodic arc ion-plating unit with varying H_2 flow rates. The influences of H_2 flow rates on the morphologies, microstructures, and properties of the coatings were systematically studied. The morphologies and microstructures of the coatings were characterized by SEM, AFM, XPS, Raman spectroscopy, GIXRD, and HRTEM. The mechanical and tribological properties were measured by a nano-indenter, scratch tester, and ball-ondisk tribometer. The wear tracks were evaluated using 3D profilometer, optical microscope, and EDS analysis. It has been found that a moderate H_2 flow rate can effectively smooth the surface, enlarge the fraction of a sp^3 bond, and improve the properties. The coating exhibits the highest hardness and elastic modulus at the H_2 flow rate of 40 sccm. A superior combination of adhesion strength,friction coefficient, and wear resistance can be achieved at the H_2 flow rate of 80 sccm.展开更多
In the present paper,the electron beam irradiation was used to improve gas sensing properties of ZnGa_2O_4 gas sensors.The effects of electron beam irradiation on the performance of ZnGa_2O_4 gas sensors were reported...In the present paper,the electron beam irradiation was used to improve gas sensing properties of ZnGa_2O_4 gas sensors.The effects of electron beam irradiation on the performance of ZnGa_2O_4 gas sensors were reported.Results show that the sensitivity of ZnGa_2O_4 gas sensors to various gases increased after electron beam irradiation,and the optimal working temperature decreased.The effect of irradiation dose and the reaction mechanism were discussed.展开更多
Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investi...Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.展开更多
Epitaxial growth and structural characteristics of metastableβ-In2Se3 thin films on H-terminated Si(111)substrates are studied.The In2Se3 thin films grown below theβ-to-αphase transition temperature(453 K)are chara...Epitaxial growth and structural characteristics of metastableβ-In2Se3 thin films on H-terminated Si(111)substrates are studied.The In2Se3 thin films grown below theβ-to-αphase transition temperature(453 K)are characterized to be strainedβ-In2Se3 mixed with significantγ-In2Se3 phases.The pure-phased single-crystallineβ-In2Se3 can be reproducibly achieved by in situ annealing the as-deposited poly-crystalline In2Se3 within the phase equilibrium temperature window ofβ-In2Se3.It is suggeted that the observedγ-to-βphase transition triggered by quite a low annealing temperature should be a rather lowered phase transition barrier of the epitaxy-stabilized In2Se3 thin-film system at a state far from thermodynamic equilibrium.展开更多
Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered Mn...Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.展开更多
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2020YFF01014706 and 2017YFC0601901)the National Natural Science Foundation of China (Grant Nos.61571019 and 52177026)。
文摘Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance.In this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation doses.The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)irradiation.Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film devices.Clear Shapiro steps are observed under 10 GHz microwave irradiation.The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.
基金supported by National Natural Science Foundation of China (No.11974301)Key Research and Development Program of Hunan Province (No.2022GK2007)+2 种基金Key Project from Department Education of Hunan Province (No.22A0123)Scientific Research Fund of Hunan Provincial Education Department (No.21B0136)National college students innovation and entrepreneurship training program (No.S202310530016)。
文摘Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform PdS and PdS_(2)nanofilms(NFs)remains an enormous challenge.In this work,2-inch wafer-scale PdS and PdS_(2) NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique.The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS_(2) NFs.A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations.The electrical transport properties of PdS and PdS_(2) NFs were explored by conductive atomic force microscopy.Our findings have achieved the controllable growth of PdS and PdS_(2) NFs,which may provide a pathway to facilitate PdS and PdS_(2) based applications for next-generation high performance optoelectronic devices.
基金This work was financially supported by the National Natural Science Foundation (No.10574106), the Science & Technology Plan of Guangdong Province (No.2003C105005) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Chinese State Education Ministry (No.(2004)176).
文摘Cu2ZnSnS4 (CZTS) thin films were successfully prepared by sulfurization of ion bean sputtered precursors on soda-lime glass substrate. The single phase of stannite-type structure CZTS films were obtained as revealed in EDS and XRD analysis when the ratios of the constituents of CZTS thin films are close to stoichiometric by optimizing the conditions of precursor preparation and sulfurization. A low sheet resistivity as about 0.156 Ω·cm and a high absorption coefficient as 1×104 cm-1 were achieved in this method by Hall effect measurements and UV-VIS spectrophotometer. The optical band-gap energy of the CZTS sample is about 1.51 eV, which is very close to the optimum value for a solar-cell absorber.
基金supported by the National Major Technologies R&D Program of China during the 10th Five-Year Plan Period (No. 2001BA302B)
文摘To obtain thermotolerant mutants of G. oxydans, which can enhance the transformation rate of L-sorbose to 2-Keto-L-gulonate (2-KLG) at 33℃ in a two-step process of vitamin C manufacture, ion beam was used as a mutation source. Gluconobacter oxydans GO and Bacillus megaterium B0 were used in this study. The original strain Gluconobacter oxydans GO was mutated by the heavy ion implantation facility at the Institute of Plasma Physics, Chinese Academy of Sciences. Several mutants including Gluconobacter oxydans GI13 were isolated and cocultured with Bacillus megaterium B0 at 33℃ in shaking flasks. The average transformation rate of the new mixed strain GI13-B0 in per gram-molecule reached 94.4% after seven passages in shaking flasks, which was increased by 7% when compared with the original mixed strain G0-B0 (Gluconobacter oxydans GO and Bacillus megaterium B0). Moreover, the transformation rate of I13B0 was stable at 94% at temperatures ranging from 25℃ to 33℃, which would be of much value in reducing energy consumption in the manufacture of L-ascorbic acid, especially in the season of summer. To clarify some mechanism of the mutation, the specific activities of L-sorbose dehydrogenase in both GO and GI13 were estimated.
基金This work was supported by the National Research Foundation of Korea(NRF)grant funded by the Korea govemment(MSIT)(No.2019R1A2C1003905).
文摘We report that the corrosion resistance of a Mg-Sn-based alloy with MgzSn precipitates can be considerably improved by surface modification using pulsed electron beam treatment.The alloy subjected to a pulse electron beam treatment showed a modified surface layer with a thickness of〜12 μm,appearing more resistant to corrosion attack than the bare surface of the alloy.In 0.6 M NaCl solution,the alloys with and without the surface modification exhibited average corrosion rates of 4.3 and 8.1 mm y^-1,respectively.The improved corrosion resistance was attributed to reduced cathodic activation,resulting from the surficial reduction of relatively noble Mg2Sn precipitates.
文摘Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.
文摘We present an experimental method to obtain neutral beam injection (NBI) power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code (TSC) show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.
基金Project supported by the National Science Foundation of China (Grant Nos 19775011, 10075016 and 10475024).The authors wish to thank the HL-2A team members for their hard work.
文摘HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed diwrtor were simulated by the current filament code and they were in agreement with the diagnostic results in the divertor. Supersonic molecular beam injection (SMBI) system was first installed and tested on the HL-2A tokamak in 2004. In the present experiment low pressure SMBI fuelling on the HL-2A closed divertor was carried out. The experimental results indicate that the divertor was operated in the 'linear regime' and during the period of SMB pulse injection into the HL-2A plasma the power density eonvected at the target plate surfaces was 0.4 times of that before or after the beam injection. It is a useful fuelling method for decreasing the heat load on the neutralizer plates of the divertor.
基金supported by National Natural Science Foundation of China (No.30800204)Chinese Ministry of Agriculture supported by the Open Project of the Chinese Academy of Sciences
文摘As a kind of mutagen, ion beam irradiation can create abundant biological mutations. A population of about 2000 lines was generated by irradiating dry wheat seeds of XiaoYan 81 with low-energy nitrogen ion beams. The traits of the plant, such as height, spike type, fertility, stem color and awn length, were investigated. The mutation rate in terms of the plant height in M2 was 2.9%. Eighteen deletion mutants of TaGA2ox1 were obtained. Associate analysis showed that TaGA2ox1 was closely related to the plant height. Most of the TaGA2ox1-deleted mutants were higher than the control, suggesting that the biological function of TaGA2ox1 is similar to its homologues in other plants. These results demonstrate that ion beam irradiation is an efficient tool in the construction of a mutant library for wheat.
基金Project supported by the National Natural Science Foundation of China (Grant No 50575037)the Doctoral Foundation of Dalian University of China (Grant No SBQ200810)
文摘This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure. Taking the deposited energy of ion beams in TBCs as the source term in the thermal conduction equation, the distribution of temperature in TBCs was simulated. Then, based on the distribution, the evolution of thermal stress was calculated by the finite element method. The results show that tensile radial stress formed at the valley of TBC surfaces after irradiation by HIPIB. Therefore, if cracks happen, they must be at valleys instead of peaks. As for the stress waves, no matter whether through peak or valley position, tensile and compressive stresses are present alternately inside TBCs along the depth direction, and the strength of stress decreases with time.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61390501,61622116,and 61471337)the Science Fund from the Chinese Academy of Sciences(CAS)(Grant Nos.XDPB0601 and XDPB0801)the CAS Pioneer Hundred Talents Program,and the Beijing Nova Program(Grant No.Z181100006218023)
文摘PdTe2, a member of layered transition metal dichalcogenides (TMDs), has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions. It provides a promising platform to explore the inter- play between superconducting quasiparticles and Dirac fermions. Moreover, PdTe2 has also been used as a substrate for monolayer antimonene growth. Here in this paper, we report the epitaxial growth of high quality PdTe2 films on bilayer graphene/SiC(0001) by molecular beam epitaxy (MBE). Atomically thin films are characterized by scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and Raman spec- troscopy. The band structure of 6-layer PdTe2 film is measured by angle-resolved photoemission spectroscopy (ARPES). Moreover, our air exposure experiments show excellent chemical stability of epitaxial PdTe2 film. High-quality PdTe2 films provide opportunities to build antimonene/PdTe2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.
文摘Ion beam-induced luminescence(IBIL) experiments were performed to investigate the in situ luminescence of GaN/Al_(2)O_(3) at varying ion energies,which allowed for the measurement of defects at different depths within the material.The energies of H^(+)were set to 500 keV,640 keV and 2 MeV,the Bragg peaks of which correspond to the GaN film,GaN/Al_(2)O_(3) heterojunction and Al_(2)O_(3) substrate,respectively.A photoluminescence measurement at 250 K was also performed for comparison,during which only near band edge(NBE) and yellow band luminescence in the GaN film were observed.The evolution of the luminescence of the NBE and yellow band in the GaN film was discussed,and both exhibited a decrease with the fluence of H^(+).Additionally,the luminescence of F centers,induced by oxygen vacancies,and Cr^(3+),resulting from the ^(2)E →^(4)A_(2) radiative transition in Al_(2)O_(3),were measured using 2 MeV H^(+).The luminescence intensity of F centers increases gradually with the fluence of H^(+).The luminescence evolution of Cr^(3+)is consistent with a yellow band center,attributed to its weak intensity,and it is situated within the emission band of the yellow band in the GaN film.Our results show that IBIL measurement can effectively detect the luminescence behavior of multilayer films by adjusting the ion energy.Luminescence measurement can be excited by various techniques,but IBIL can satisfy in situ luminescence measurement,and multilayer structural materials of tens of micrometers can be measured through IBIL by adjusting the energy of the inducing ions.The evolution of defects at different layers with ion fluence can be obtained.
基金Project supproted by the National Natural Science Foundation of China (60025409 and 50472068) and National "863" High Technology Plan (2001AA311080) and Program for New Century Excellent Talents in Shangdong University
文摘Under electron beam irradiation, the in-situ formation of 2H-SiC dentritic nanocrystals from amorphous silicon carbide at room temperature was observed. The homogenous transition mainly occurs at the thin edge and on the surface of specimen where the energy obtained from electron beam irradiation is high enough to cause the amorphous crystallizing into 2H-SiC.
基金supported by International S&T Cooperation Program of China (No.S2011GR0412)
文摘An Electron Cyclotron Resonance Heating (ECRH) launcher for four-beam injection has been installed on the HL-2A tokamak and used in plasma heating experiments. By the launcher, four EC wave beams can be injected into the tokamak through a φ350 mm port, which are generated from 2 sets of 68 GHz/1 s and 2 sets of 68 GHz/1.5 s gyrotron tubes manufactured by GYCOM, with maximum output power of 500 kW for each. In this paper, the properties of the EC beam in the launcher and plasma are presented: at the centre of the cross section of the tokamak, the beam radius is 31.7 mm; thermal analysis of a 3D model indicates that the peak temperature increase would be only 30 o C at the mirror surface for a 500 kW/1 s pulse; ray-tracing calculation predicts satisfactory power deposition. In the plasma experiment, six beams including four beams from this launcher and two from another launcher have been injected simultaneously. Besides, obtaining ELM-y H-mode discharges, the ECRH system shows reliability and stability of the launcher functions.
基金supported by the National Natural Science Foundation of China(Nos.11275141 and 11175133)the International Cooperation Program of the Ministry of Science and Technology of China(No.2015DFR00720)+2 种基金the Center for Electron Microscopy of Wuhan Universitythe Center of Nanosci. and Nanotech,Research of Wuhan Universitythe Analysis and Test Center of Wuhan University
文摘Nanocomposite Cr C/hydrogenated amorphous carbon(nc-CrC/a-C:H) coatings were deposited by a hybrid beams system comprised of a hollow cathode ion source and a cathodic arc ion-plating unit with varying H_2 flow rates. The influences of H_2 flow rates on the morphologies, microstructures, and properties of the coatings were systematically studied. The morphologies and microstructures of the coatings were characterized by SEM, AFM, XPS, Raman spectroscopy, GIXRD, and HRTEM. The mechanical and tribological properties were measured by a nano-indenter, scratch tester, and ball-ondisk tribometer. The wear tracks were evaluated using 3D profilometer, optical microscope, and EDS analysis. It has been found that a moderate H_2 flow rate can effectively smooth the surface, enlarge the fraction of a sp^3 bond, and improve the properties. The coating exhibits the highest hardness and elastic modulus at the H_2 flow rate of 40 sccm. A superior combination of adhesion strength,friction coefficient, and wear resistance can be achieved at the H_2 flow rate of 80 sccm.
文摘In the present paper,the electron beam irradiation was used to improve gas sensing properties of ZnGa_2O_4 gas sensors.The effects of electron beam irradiation on the performance of ZnGa_2O_4 gas sensors were reported.Results show that the sensitivity of ZnGa_2O_4 gas sensors to various gases increased after electron beam irradiation,and the optimal working temperature decreased.The effect of irradiation dose and the reaction mechanism were discussed.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0301004 and 2015CB921001)the National Natural Science Foundation of China(Grant Nos.11334006,11725418,and 11674188)
文摘Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0306102 and 2018YFA0306703)the National Natural Science Foundation of China(Grant Nos.61474014 and U1601208)the Sichuan Science and Technology Program,China(Grant Nos.2019YJ0202 and 20GJHZ0229).
文摘Epitaxial growth and structural characteristics of metastableβ-In2Se3 thin films on H-terminated Si(111)substrates are studied.The In2Se3 thin films grown below theβ-to-αphase transition temperature(453 K)are characterized to be strainedβ-In2Se3 mixed with significantγ-In2Se3 phases.The pure-phased single-crystallineβ-In2Se3 can be reproducibly achieved by in situ annealing the as-deposited poly-crystalline In2Se3 within the phase equilibrium temperature window ofβ-In2Se3.It is suggeted that the observedγ-to-βphase transition triggered by quite a low annealing temperature should be a rather lowered phase transition barrier of the epitaxy-stabilized In2Se3 thin-film system at a state far from thermodynamic equilibrium.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11604366,11634007,21872099,and 22072102)the National Natural Science Foundation of Jiangsu Province,China(Grant No.BK 20160397)support from the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017370)。
文摘Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.