Co-doped BaFe_(2)As_(2) Josephson junction fabricated with a focused helium ion beam

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.

Experiment and simulation on degradation and burnout mechanisms of SiC MOSFET under heavy ion irradiation

Experiments and simulation studies on 283 MeV I ion induced single event effects of silicon carbide(SiC) metal–oxide–semiconductor field-effect transistors(MOSFETs) were carried out. When the cumulative irradiation fluence of the SiC MOSFET reached 5×10^(6)ion·cm^(-2), the drain–gate channel current increased under 200 V drain voltage, the drain–gate channel current and the drain–source channel current increased under 350 V drain voltage. The device occurred single event burnout under 800 V drain voltage, resulting in a complete loss of breakdown voltage. Combined with emission microscope, scanning electron microscope and focused ion beam analysis, the device with increased drain–gate channel current and drain–source channel current was found to have drain–gate channel current leakage point and local source metal melt, and the device with single event burnout was found to have local melting of its gate, source, epitaxial layer and substrate. Combining with Monte Carlo simulation and TCAD electrothermal simulation, it was found that the initial area of single event burnout might occur at the source–gate corner or the substrate–epitaxial interface, electric field and current density both affected the lattice temperature peak. The excessive lattice temperature during the irradiation process appeared at the local source contact, which led to the drain–source channel damage. And the excessive electric field appeared in the gate oxide layer, resulting in drain–gate channel damage.

High-Temperature Superconducting YBa_(2)Cu_(3)O_(7-δ)Josephson Junction Fabricated with a Focused Helium Ion Beam

As a newly developed method for fabricating Josephson junctions,a focused helium ion beam has the advantage of producing reliable and reproducible junctions.We fabricated Josephson junctions with a focused helium ion beam on our 50 nm YBa_(2)Cu_(3)O_(7-δ)(YBCO)thin films.We focused on the junction with irradiation doses ranging from 100 to 300 ions/nm and demonstrated that the junction barrier can be modulated by the ion dose and that within this dose range,the junctions behave like superconductor–normal conductor–superconductor junctions.The measurements of the I–V characteristics,Fraunhofer diffraction pattern,and Shapiro steps of the junctions clearly show AC and DC Josephson effects.Our findings demonstrate high reproducibility of junction fabrication using a focused helium ion beam and suggest that commercial devices based on this nanotechnology could operate at liquid nitrogen temperatures.

Supported Atomically Dispersed Pd Catalyzed Direct Alkoxylation and Allylic Alkylation

A new approach to allylic alkylation is realized using an atomically dispersed palladium catalyst(Pd1/TiO2-EG).Unlike conventional methods that require derivation of substrates and utilization of additives,this method allows for direct allylic alkylation from allylic alcohols,producing H2O as the sole by-product.The catalyst's high efficiency is attributed to the local hydrogen bonding at the or-ganic-inorganic interface(Pd-EG interface),facilitating hydroxyl group activation forη3π-allyl complex formation.The system demonstrates successful direct C—O and C—C coupling reactions with high selectivity,requiring no additives.This study highlights the potential of supported atomically dispersed catalysts for greener and more efficient catalysis,meanwhile,offers unique insights into the distinct behavior of atomically dispersed catalysts in comparison to homogeneous or nanoparticle-based catalysts.

Unsteady aerodynamic characteristics of a horizontal wind turbine under yaw and dynamic yawing

Horizontal axis wind turbine(HAWT)often works under yaw due to the stochastic variation of wind direction.Yaw also can be used as one of control methods for load reduction and wake redirection of HAWT.Thus,the aerodynamic performance under yaw is very important to the design of HAWT.For further insight into the highly unsteady characteristics aerodynamics of HAWT under yaw,this paper investigates the unsteady variations of the aerodynamic performance of a small wind turbine under static yawed and yawing process with sliding grid method,as well as the there-dimensional effect on the unsteady characteristics,using unsteady Reynolds-averaged Navier-Stokes(URANS)simulations.The simulation results are validated with experimental data and blade element momentum(BEM)results.The comparisons show that the CFD results have better agreement with the experimental data than both BEM results.The wind turbine power decreases according to a cosine law with the increase of yaw angle.The torque under yaw shows lower frequency fluctuations than the non-yawed condition due to velocity component of rotation and the influence of spinner.Dynamic yawing causes larger fluctuate than static yaw,and the reason is analyzed.The aerodynamic fluctuation becomes more prominent in the retreating side than that in the advancing side for dynamic yawing case.Variations of effective angle of attack and aerodynamic forces along the blade span are analyzed.The biggest loading position moves from middle span to outer span with the increase of yaw angle.Three-dimensional stall effect presents load fluctuations at the inner board of blade,and becomes stronger with the increase of yaw angle.

Fenton-like degradation of Methylene Blue using paper mill sludge-derived magnetically separable heterogeneous catalyst:Characterization and mechanism

For the paper industry, the disposal and management of the yielded sludge are a considerable challenge. In our work, the paper mill sludge-derived magnetically separable heterogeneous catalyst（PMS-Fe-380） was prepared easily through a facile synthesis method. The morphology and structure of PMS-Fe-380 were fully characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmet–Teller analysis. The catalytic activity of PMS-Fe-380 was evaluated by degradation of Methylene Blue（MB）. The reusability and stability of PMS-Fe-380 were evaluated in five repeated runs, which suggested that PMS-Fe-380 manifested excellent stability of catalytic activity. Moreover,leaching tests indicated that the leached iron is negligible（〈0.5 mg/L）. This study provides an alternative environmentally friendly reuse method for paper mill sludge and a novel catalyst PMS-Fe-380 that can be considered as a promising heterogeneous Fenton-like catalyst.