GHz Microwave Irradiation Research Articles

Co-doped BaFe2As2 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 BaFe2As2 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 BaFe2As2 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.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer.

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Microwave‐Responsive Flexible Room‐Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

AbstractThe development of flexible, room‐temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4‐biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg=−27.1 °C), which exhibits a remarkable UV‐light‐dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase‐dependent RTP materials while demonstrating a promising approach toward microwave detection.

Study of 400MHz microwave conduction loss effect for a hydrolysis reaction by thermostable β-Glucosidase HT1.

Microwave irradiation at different frequencies gave molecular selective effects, namely higher frequency microwave effects for waters while lower frequency effects for ions. We already reported that 2.45GHz and 5.80GHz microwave irradiation gave different results for a hydrolysis reaction by thermostable β-Glucosidase HT1. Here, we designed and made a reactor, employed 400MHz microwave irradiation, and studied the effectiveness of 400MHz microwave for HT1 reaction, then 400MHz and 2.45GHz had the ability to accelerate HT1 reaction. In consideration of the general mechanism of enzymatic glycoside hydrolysis, our results would be reasonable if ions are key reaction species because 400MHz microwave activated ions selectively. In addition, the phenomenon that 400MHz microwave would not affect water molecules by dielectric heating might contribute the enzyme stability. This report should support that microwave is not only a tool to heat reactions efficiently but also can bring unique effects for reactions.

Hybrid Nb/Al/Ba0.5K0.5Fe2As2 sandwich Josephson junctions

We fabricated hybrid Josephson junctions between a Ba0.5K0.5Fe2As2 (BKFA) single crystal and the conventional superconductor Nb with normal metal Al as the barrier. An in situ process was used to create clean BKFA/Al/Nb interfaces. Current transport is along the c-axis of BKFA. The current–voltage characteristics are slightly hysteretic at low temperatures. Except for some features indicative of resonant modes the shape of the current–voltage characteristics can be well described by the resistively and capacitvely shunted junction (RCSJ) model, with a product of the Josephson critical current and the normal state resistance of the junction exceeding 180 μV at low temperatures. The temperature dependence of the Josephson current is linear for temperatures down to 2 K. Under 40 GHz microwave irradiation integer Shapiro steps are observed. The power dependence of the Shapiro step-height is in good agreement with RCSJ simulations. Possible relations of our data with the symmetry of the superconducting order parameter of BKFA are discussed.

Nitridation Reaction of Titanium Powders by 2.45 GHz Multimode Microwave Irradiation using a SiC Susceptor in Atmospheric Conditions

A titanium nitride (TiN) coating using microwaves can be accomplished in air, and satisfies the required conditions of an on-demand TiN coating process. However, the coating mechanism using microwaves is not completely clear. In this study, to understand the detailed mechanism of microwave titanium nitridation in air, the quantity of nitrogen and oxygen in reacted TiN powder has been investigated by an inert melting method. Titanium powders were irradiated with microwaves by a multi-mode type 2.45 GHz microwave irradiation apparatus, while also being held at various temperatures for two different dwell times. X-ray diffraction (XRD) results revealed that nitridation of the powder progressed with increasing process temperature, and the nitridation corresponds to the powder color after microwave irradiation. The nitrogen contents of the samples increased with increasing processing temperature and dwell time, unlike oxygen. It is postulated that the reaction of convected air with titanium is a key role to control nitridation in this system.

Development of a Microwave Irradiation Probe for a Cylindrical Applicator

A microwave irradiation probe was newly developed for downsizing microwave applicators and the overall microwave heating apparatus. The key component of the proposed probe is a tapered section composed of polytetrafluoroethylene (PTFE) and alumina. Insertion of the tapered section between the input port and the applicator vessel realizes impedance matching to the microwave power source and reduces the reflected power from the applicator. The proposed microwave probe for a cylindrical applicator was designed using 3D electromagnetic simulations. The permittivity data of two liquid samples—ultrapure water and 2 M NaOH solution—were measured and taken into simulations. The conductivity of the NaOH solution was estimated from the measurement results. The measured reflection ratio of the fabricated applicator was in good accordance with the simulated one. The frequency ranges in which the measured reflection ratio was less than 10% were from 1.45 GHz to 2.7 GHz when using water and from 1.6 GHz to 2.7 GHz when using the NaOH solution as the sample. The heating rate of the applicator was roughly estimated as 63 to 69 K for a 5 min interval during the 2.45 GHz microwave irradiation at the input power of 100 W.

Chemically assisted 2.45 GHz microwave irradiation for the simultaneous removal of mercury and organics from contaminated marine sediments

This work aims to investigate the simultaneous mercury (Hg) and polycyclic aromatic hydrocarbons (PAHs) removal from seabed sediments by means of 2.45 GHz microwave irradiation with chemical enhancers. Decontamination kinetics were assessed applying Tween® 80, methylglycinediacetic acid (MGDA) and citric acid as enhancers. Results clearly showed that sediment dielectric features allowed a large conversion of microwaves (MW) irradiated energy into temperature increase (405 °C within 7 min). The combined use of Tween® 80 and MGDA in a 650 W MW irradiation treatment brought a final residual Hg concentration of 2.2 mg kg−1, whereas Tween® 80 and citric acid allowed a residual concentration less than 1 mg kg−1 (R = ~ 99%). Lower residual concentration was found also for total PAHs (< 1 mg kg−1) already after 1-min irradiation. Modelling revealed for all treatments that exponential decay has a very good fit with experimental points. For the unenhanced MW treatment, the decay rate (k) was 0.259. When Tween® 80 and acid citric were contextually used, they brought an almost doubled k value of 0.493. The co-presence of PAHs decreased the Hg removal kinetic only without citric acid addiction. A simultaneous and very rapid Hg and PAHs total removal is very difficult to be achieved by other cleanup techniques, which operate in a selective way. Desorption parameters calculated are useful for Hg-PAH co-contamination removal kinetics prediction and for scaling-up studies that, at the moment, are essential to meet the great challenge of applying MW at the full scale.

Kinetics of microwave synthesis of AlN by carbothermal‐reduction‐nitridation at low temperature

AbstractAluminum nitride (AlN) was synthesized at 1000‐1400°C from a mixture of alumina and carbon powders using 2.45 GHz microwaves in a N2 atmosphere. High nitridation ratios (&gt;0.90) were obtained in the temperature range 1200‐1400°C. The apparent activation energy of the carbothermal reduction and nitridation (CRN) reaction using 2.45 GHz microwave irradiation was calculated from the nitridation ratio. The value obtained, 79.9 kJ/mol, is 11% of the energy reported for conventional synthesis using α‐Al2O3 as the raw material. This result indicates that 2.45 GHz microwave irradiation could promote the kinetics of the CRN reaction, and AlN could be effectively synthesized at low temperature.

Dissipation effects in superconducting heterostructures with tungsten nanorods as weak links

Thin-film hybrid heterostructures formed by superconducting molybdenum-rhenium-alloy films with a critical temperature of about 9 K and nanoscale silicon-based semiconducting interlayers with metallic tungsten nanorods have been fabricated and studied. Current-voltage characteristics of the junctions were measured at 4.2 K and under influence of 11 GHz microwave irradiation. The evidence of a quasi-one-dimensional transport through the tungsten weak links disrupted by phase-slip centers was revealed in MoRe/doped Si/MoRe trilayers under irradiation by a high-frequency field. Also, measured current-voltage characteristics of five-layer MoRe/doped Si/MoRe/doped Si/MoRe devices exhibit a strong influence of a dissipation state in the MoRe interlayer. Namely, the switching from a superconducting state with low dissipation to a finite-conductance regime can be initiated by the emergence of an extra phase-slip center in the MoRe interlayer. Possible physical mechanisms of the two findings are discussed.

Acceleration of Water Electrolysis by Accumulation of Microwave Energy at a Pt Disk Electrode

The current density of water reduction using a commercial Pt disk electrode was enhanced under 2.45 GHz microwave irradiation. The transitional alternation of temperature distribution was explained with a heat-transfer simulation using COMSOL Multiphysics based on the finite element method. Results show that most of the microwave energy was converted into thermal energy at the vicinity of the Pt electrode. A local high-temperature region enhancing the water-reduction reaction was hence formed.

Synthesis of Ti4O7 Nanoparticles by Carbothermal Reduction Using Microwave Rapid Heating

The polymer electrolyte fuel cell (PEFC) is an attractive power generation method from the perspective of environmental protection. Carbon is usually used as a catalyst support in PEFC, but it is oxidized under high electrical potential conditions. Ti4O7 is expected as a new catalyst support because of its high electrical conductivity and chemical resistivity. Though Ti4O7 as a catalyst support must have a high specific surface area for a high performance, it is difficult to synthesize nanostructured Ti4O7. In this research, Ti4O7 nanoparticles with a size of about 60 nm were synthesized by carbothermal reduction of TiO2 nanoparticles with polyvinylpyrrolidone (carbon source) using 2.45 GHz microwave irradiation. The experiment condition was at 950 °C for 30 min and the samples synthesized by conventional heating showed a grain growth. The findings of this study suggest that microwave processing can drastically reduce the total processing time for the synthesis of nanostructured Ti4O7.

Finite Element Modelling of CNT-Filled Magnesium Alloy Matrix Composites under Microwave Irradiation

Finite element modelling of a magnesium alloy matrix filled with a 2% volume fraction of carbon nanotubes (CNT) under 2.45 GHz microwave (MW) irradiation is reported. The effective dielectric and permeability data of the simulated compact are evaluated using the effective medium approximation. Subsequently, these values are used to solve Maxwell’s electromagnetic equations followed by the heat conduction equation, thus both the field distribution in the oven cavity and the predicted heating of the model compact are obtained. At an applied power of 1 kW and a 9-minute simulation time, the results show poor coupling between the monolithic metal compact and the MW, resulting in a maximum temperature of ~163 °C. It is in good agreement with earlier studies and theory in which metals did not couple very well with MWs at room temperatures. The model also predicts the temperature in the 2% CNT-filled alloy compact to be 13 °C higher than in the monolithic compact after a similar simulated microwave irradiation duration. Furthermore, the effect of susceptor-assisted microwave heating is investigated by introducing a susceptor kiln into the model. Simulation results predict the temperature of the compact to rise to about 600 °C after 9 minutes, highlighting the importance of susceptor-assisted sintering. The model developed is significant in providing important details for predicting the response of metal compacts and their composites to MW heating as well as further improving the development of MW technology for the production of materials with enhanced properties.

Low‐Temperature Synthesis of Aluminum Nitride from Transition Alumina by Microwave Processing

Aluminum nitride (AlN) was synthesized by carbothermal reduction and nitridation method from a mixture of various transition alumina powders and carbon black using 2.45 GHz microwave irradiation in N2 atmosphere. We achieved the synthesis of AlN at 1300–1400°C using 2.45 GHz microwave irradiation for 60 min. Our results suggest that θ‐Al2O3 is more easily nitrided than γ‐, δ‐, and α‐Al2O3. On the other hand, nitridation ratio of samples synthesized in a conventional furnace under nitrogen atmosphere were zero or very low. These results show that 2.45 GHz microwave irradiation enhanced the reduction and nitridation reaction of alumina.

Synthesis of homologous compounds Fe2O3(ZnO)m (m=6, 8, 34) by various selective microwave heating conditions

Homologous compounds, Fe2O3(ZnO)m, with a modulated natural superlattice structure, were synthesized within 10min at 1200°C in a simple solid-state reaction under 2.45 and 28GHz microwave irradiation. Transmission electron microscopy and energy dispersive X-ray spectroscopy results revealed that m decreased with increasing the synthesis temperature and microwave frequency. In the Zn–Fe–O system, γ-Fe2O3 was heated in H and E-field and ZnO was heated in E-field under 2.45GHz microwave irradiation. However, α, γ-Fe2O3 and calcined ZnO were heated under 28GHz microwave irradiation. This selective microwave heating resulted in the different diffusion conditions than conventional heating; therefore, homologous compounds with low m values were rapidly synthesized at low temperature.

Efficiency of 2.45 and 5.80 GHz microwave irradiation for a hydrolysis reaction by thermostable β-Glucosidase HT1.

Microwave irradiation at different frequencies gave unique results for the hydrolyses of glycosyl bonds by β-Glucosidase HT1. With the observed relative complex permittivity data for the reaction buffer, 2.45 GHz microwave radiation affected both waters and ions, while 5.80 GHz only affected waters. We, here, propose that would be one of the unique "microwave nonthermal effects".

Synthesis of aluminium nitride under 2.45 GHz microwave irradiation

Aluminium nitride (AlN) is a functional ceramic which has several properties, and it is applied to substrate materials and fillers for packaging materials of electronic devices. Microwave heating has characteristics such as internal heating, rapid heating and selective heating, so it is useful for synthesis of ceramics. In this work, spherical AlN particles were synthesised by carbothermal reduction and nitridation of Al2O3 under 2.45 GHz microwave irradiation. The mixture of spherical Al2O3 particles and carbon was used as the starting materials. Carbon absorbed microwaves selectively, and the starting materials were heated rapidly in flowing nitrogen gas. Al2O3 was converted to AlN in a short time; and finally, polycrystalline spherical AlN particles were successfully formed. They retained particle diameters of spherical Al2O3 particles used as the starting material.

Crystallization Behavior of Ibuprofen under Microwave Irradiation

The batch cooling crystallization of the organic compound, ibuprofen, was carried out under 2.45 GHz microwave irradiation. n-Hexane containing a small amount of acetone (5 mol%) and Fluorinert™, which did not absorb microwave, were selected as the solvent and coolant circulating through the jacket of crystallizer, respectively. The ibuprofen-hexane solution was cooled from 40 to −1°C under microwave irradiation and no irradiation. When the solution was not irradiated to the solution, ibuprofen crystals appeared at 35°C. On the other hand, when irradiation with 300 W microwave was carried out, nucleation did not occur even when the solution temperature reached to −1°C. At that time, the supersaturation ratio was 9.5. Thus, crystal nucleation of ibuprofen was inhibited by the microwave irradiation. The effect of microwave irradiation continued for at least 100 min after the irradiation was stopped at −1°C. By adding a small amount of crystals to the highly supersaturated solution, small crystals with a narrow size distribution were produced.

Rapid Microwave Annealing of Amorphous Lead Zirconate Titanate Thin Films Deposited by Sol‐Gel Method on LaNiO3/SiO2/Si Substrates

The heating behavior of LaNiO3 (LNO) films on SiO2/Si substrate heated by 2.45 GHz microwave irradiation in the microwave magnetic field was first investigated, and then amorphous Pb(Zr0.52Ti0.48)O3 (PZT) thin films were deposited on LNO‐coated SiO2/Si substrates by a sol‐gel method and crystallized in the microwave magnetic field. The crystalline phases and microstructures as well as the electrical properties of the PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT films with a highly (100)‐preferred orientation can be obtained by microwave annealing at 700°C for only 180 s of total processing time, and have good electrical properties. The results demonstrated that conductive metal oxide LNO as a bottom electrode layer is an advantage for the crystallization of PZT thin films by microwave irradiation in the microwave magnetic field.

SNS Junctions for AC Josephson Voltage Standards

Abstract We developed and fabricated series arrays of overdamped SNS Josephson junctions for AC Josephson voltage standards (S: superconductor, N: normal conductor). The junctions are based on NbxSi1-x barriers allowing nearly independent tuning of critical current density and characteristic voltage by varying niobium content and thickness of the barrier. We optimised the junction barrier deposition for the co-sputtered NbxSi1-x so that we are able to fabricate Josephson junction series arrays with up to 69,632 junctions for output voltages up to 10 V under 70 GHz microwave irradiation. The width of the constant-voltage steps at 10 V exceeds 1 mA for a typical critical current of about 3 mA.