Pulsed DC Research Articles

Rapid swimmer using explosive boiling due to electrical discharge in water

A strong micro heat engine that can be used in the untethered state is essential for next-generation microrobotics. Here, we propose a rapid swimmer using explosive boiling due to electrical discharge in water. Specifically, we demonstrate that the water-repellent swimmer that has an aluminum discharge antenna in the rear part can swim with the maximum velocity of ∼14 cm/s on the water surface like a water strider between a pair of parallel electrodes in a shallow water pool by applying direct current high-voltage pulses repeatedly. Moreover, by the video observation with high speed (960 fps), we found that an asymmetrical wave was generated immediately after the discharge, and it propelled the swimmer. Our findings should contribute to next-generation microrobots in the future.

Characterization and Optimization of Plasma Electrolytic Process for Conversion of Molecular Nitrogen to Ammonia in Aqueous Water at Atmospheric Pressure

Ammonia (NH3) is widely used in the chemical and agricultural industries and is of growing interest as a potential energy carrier. Most of the current global NH3 production utilizes the Haber-Bosch process which has a large environmental and physical footprint. For this reason, there have been substantial efforts to develop an alternative process that can be sustainable and distributed. Recently, plasma-based electrolysis reactors have shown promise to convert molecular nitrogen to various forms of fixed nitrogen such as ammonia, nitrate, and nitrite in water at atmospheric pressure. However, selectivity and control over the products has not been adequately demonstrated. In this work, we studied a plasma formed in pure nitrogen gas or mixtures containing nitrogen gas at the surface of liquid water. Various products were characterized in the liquid phase including ammonium ions, nitrate ions, nitrite ions, and hydrogen peroxide as a function of pH, discharge current, and time. In addition, continuous direct current (DC) was compared to pulsed DC voltage plasma operation. We find that the selectivity to different nitrogen products depends on the solution conditions. These results could be used to inform optimization and scale up of similar plasma-liquid systems for sustainable nitrogen fixation.

Vanadium-Doped Ni/YSZ Anode Functional Layers for Solid Oxide Fuel Cells Produced via Magnetron Sputtering

The electrode performance of solid oxide fuel cells (SOFC) strongly depends on its microstructural characteristics, such as the porosity, percolated paths of ionically and electronically conductive phases and in particular, the grain size1. Deploying alternative manufacturing techniques that deposit nanostructured materials results in finer particle sizes and thus, increases the quantity of triple-phase boundaries. For that reason, the magnetron sputtering technique, which offers elemental distribution at the nanoscale, high deposition rates, reproducibility, scalability and excellent uniformity over large-area substrates has been chosen as the deposition method to fabricate anode functional layers (AFLs) for SOFCs.Nanostructured NiO-YSZ thin films have been previously produced by reactive pulsed DC magnetron co-sputtering of metallic targets of zirconium-yttrium and nickel, defining the optimal deposition parameters to create state-of the-art AFLs. Former studies reported limitations of the process control during reactive magnetron sputtering, regarding the film’s composition 1,2. Since the composition strongly relies on the amount of reactive gas, i.e., oxygen, present during deposition, a feedback control system is required to prevent oxygen built-up leading to target poisoning and lower deposition rates.Herein, we present a reactive feedback control system, that manages quantities of oxygen introduced to the sputtering chamber during deposition based on the oxygen partial pressure. This facilitates stable operation conditions, prevents target poisoning, and maintains the coating characteristics, i.e., its microstructure and desired composition when varying process parameters, such as the deposition pressure, target-substrate distance, or the deposition angle.Based on recent studies 3–5, the future of oxide-based anode materials for SOFCs will greatly focus on reducing the Ni catalyst content through alternative non-precious metal doping and increasing the cell performance by tailoring the microstructure of the AFL. This would allow Ni coarsening to be mitigated and maintain the nanostructure over the lifetime of the cell. Therefore, in this study complex transition metal oxides, such as vanadium, tantalum or manganese oxides, were doped into SOFC anodes to study their influence on the structural and morphological properties of magnetron sputtered AFL. The effect of dopant concentration on the properties of Ni-YSZ films in as-deposited, pre-annealed and reduced state was analysed using SEM, EDS, XRD and XPS. To characterise the electrochemical performance of the deposited films, polarisation curves were obtained from SOFC single stack assemblies under hydrogen and air flows for anode and cathode, respectively, at operating temperatures of 750, 800 and 850 ℃.References Lim, Y., Lee, H., Hong, S. & Kim, Y. B. Co-sputtered nanocomposite nickel cermet anode for high-performance low-temperature solid oxide fuel cells. J. Power Sources 412, 160–169 (2019).Ionov, I. V. et al. Reactive co-sputter deposition of nanostructured cermet anodes for solid oxide fuel cells. Jpn. J. Appl. Phys. 57, 30–34 (2018).Atkinson, A. et al. Advanced anodes for high-temperature fuel cells. Nat. Mater. 3, 17–27 (2004).Van Overmeere, Q. & Ramanathan, S. Thin film fuel cells with vanadium oxide anodes: Strain and stoichiometry effects. Electrochim. Acta 150, 83–88 (2014).Garcia-Garcia, F. J., Beltran, A. M., Yubero, F., Gonzalez-Elipe, A. R. & Lambert, R. M. High performance novel gadolinium doped ceria / yttria stabilized zirconia / nickel layered and hybrid thin film anodes for application in solid oxide fuel cells. J. Power Sources 363, 251–259 (2017). Figure 1

Toward Thin Dielectric Films of Polyetherimide Electrodeposited from Aqueous Emulsions of the Polymer

Miniaturized, high power electronic devices are needed for a variety of applications. Although, the miniaturization of these devices is challenging. For instance, high power capacitors need to sustain high electric fields, with typically several hundred volts across micrometric dielectric layers. Among the most promising materials for this application, polyetherimide (PEI) has a number of desired characteristics such as adequate electrical properties, good chemical and mechanical resistance with thermal stability up to 170°C.Spin-coating is the conventional technique used in the microelectronics industry for polymer thin film deposition. However, this technique is not appropriate to form conformal deposits on 3D-structured substrates. To overcome this limitation, we investigate an electrochemical deposition process of PEI in which the electrolyte is an aqueous emulsion formed from organic droplets containing the polymer [1]. In this work, a pulsed voltage below 2 V/ECS, was applied for the deposition of PEI on Cu metal surfaces. The influence of deposition conditions on the thickness and surface smoothness of the deposit was thoroughly investigated, identifying the processing window.PEI aqueous emulsions were synthesized as follows, after the raw material dissolved in a mixture of N-methylpyrrolidone and acetophenone, N-methylpiperazine was added to be grafted on the imide groups of the polymeric chains. The PEI emulsions were subsequently produced by ultrasonic mixing [2] of the reaction crude with an aqueous solution of lactic acid. During mixing, nanoscale droplets were formed and electrostatically charged by protonation of ternary amine groups of N-methylpiperazine.Critical for the application are the droplet size and stability of the emulsion. These properties were modulated upon stoichiometry of both N-methylpiperazine for the degree of modified imide cycles and lactic acid for the degree of protonation of the amine [1,2]. FTIR and NMR were used to screen the quantity of modified imide groups, displaying that the PEI imide function attack by N-methylpiperazine is quantitative. The protonation was indirectly characterized by measuring the zeta potential of the emulsion [3]. As a result, in an optimized sequence, droplets with hydrodynamic diameters below 200 nm were repeatedly formed with zeta potentials greater than 50 mV. For emulsions containing 3.5 wt% PEI with 64 % modified imide groups and 50 % quaternisation, representing 32 % of the imide cycle initial population. The emulsions were stable for at least twenty-one days at 4°C. This is a significant improvement as compared to the stability reported in the literature [1].Deposition tests were conducted in a 3-electrode electrochemical cell, using a 10-time diluted emulsion, at relatively low voltage, below 2 V/ECS with pulsed DC waveform under mild conditions (room temperature, pH between 3 and 5). The pulses allowed the movement of droplets in the emulsion towards the cathode while minimizing H2 evolution. Under these conditions, a PEI coating was obtained with a thickness of a few micrometers within 600 s. The impact of deposition parameters on coverage and uniformity was also studied in detail.The last process step by removing the N-methylpiperazine and the residual solvents consists in recovering the initial unmodified structure of PEI grafted on the substrate. Curing conditions were chosen according to the previous literature [1] under vacuum. The FTIR spectra of the coated substrate were recorded after curing. From the FTIR spectra, the disappearance of the amide (I and II) peaks after curing and a good peak-for-peak correspondence between the spectrum of the cured polymer and the pristine polymer are observed.This work demonstrates that polymer films can be deposited by an electrochemical process under mild conditions, assuming that a stable emulsion of charged polymer droplets can be formed. The process is well suited to coat 3D structured substrates, in contrast with more conventional techniques for polymer deposition. This original electrodeposition process should allow the realization of integrated capacitors on silicon wafers for the next generation of power electronics devices.

Improved creep resistance of AZ91 magnesium alloy after the micro arc oxidation process

AZ91 Mg alloy has a wide range of applications in the automotive industry, although its use is restricted to powertrain applications due to its low creep resistance. In this study, the effect of the micro arc oxidation (MAO) coating on the creep resistance of an AZ91 Mg alloy was investigated to take advantage of the coating layer with high thermal insulation properties. In this context, the MAO process was applied to AZ91 Mg alloy using a bipolar pulsed DC power supply. The creep tests were conducted at different temperatures (150–200 °C) and stresses (25–90 MPa) for the bare and coated samples, and the minimum creep rates were determined. It has been shown that the MAO coating reduces the creep rate of the bare alloy by 35%–84% depending on the temperature and the stress due to the stress-reducing effect and thermal barrier properties of the MAO coating. Based on the calculated creep activation energy and stress exponents, creep mechanisms were proposed for the bare and coated alloys. Effective activation energy was also calculated and lattice diffusion-controlled dislocation climb was determined to be the effective creep mechanism for both samples at lower stresses, while pipe diffusion-controlled dislocation climb was effective at higher stresses.

Control and optimization algorithm for lattice power grids with multiple input/output operation for improved versatility

With the proliferation of alternative energy sources, power grids are increasingly dominated by grid-tied power converters. With this development comes the requirement of grid-forming, but current architectures exclude high-voltage applications through serial connectivity. Lattice power grids allow for the generation of both higher voltages and currents than their individual modules by marrying the advantages of serial and parallel connectivity, which include reduced switching and conduction losses, sensorless voltage balancing, and multiport operation. We use graph theory to model lattice power grids and formalize lattice generation processes for square, triangular, and hexagonal lattice grids. This article proposes depth-first-search based algorithms for the control and efficient operation of lattice power grids, achieving voltage and current objectives while minimizing switching losses. Furthermore, we build upon previous algorithms by harnessing multiple input/output operation. The algorithm allows for sequential operation (in which loads are added one by one), simultaneous operation (in which several loads are added at the same time), and combined sequential-simultaneous operation. These methods were applied to a variety of lattice structures, and simulations of dc analysis and pulse train generation were performed. These modeled results validate the proposed algorithms and improve versatility in the operation of lattice power grids in both grid-connected and standalone applications. The potential of applying this method in transcranial magnetic stimulation (TMS) is discussed.

Initial Rotor Position Estimation of SynRM Based on Pulsating Voltage Injection Combined With Finite Position Set Algorithm

Initial rotor position estimation is the basis of stable starting without reverse rotation; also initial position estimation directly affects the maximum starting torque. DC pulse voltage injection is one of the common methods for estimating the initial rotor position, which has low implementation complexity. However, the conventional DC voltage pulse injection methods, which works through injecting three DC voltage pulses, has low accuracy and slow response in estimating initial position. A rotor initial position estimation method based on pulsating voltage injection combined with an iteration algorithm is proposed in this paper. This method works by injecting only one DC voltage pulse to the motor and measuring the peak values of currents and fluxes of the motor; afterwards these values should be applied to an iterative algorithm. The iteration algorithm in the proposed method leads to increment of the accuracy of initial position estimation, and reduction of the number of injected dc pulses in comparison with the conventional methods. The performance of the proposed method is verified experimentally on a synchronous reluctance motor (SynRM). Also, a comparison between the two conventional methods and the proposed method is provided by this SynRM drive experimental setup.

Dual Outputs Switch Mode Power Supply (DOSMPS) Utilizing Forward Converter Topology

Experimental works of dual, 5 volt DC outputs switch mode power supply (DOSMPS) is presented in this paper. To design, construct and evaluate the DOSMPS using forward converter topology are the objectives of this article. In this work, a 556 timer was picked as the pulse width modulator. The 556 timer was picked because it is widely used, cheap and capable of producing stable dual pulse width modulations. Since, this work targeted dual DC outputs, two forward converter circuits were built. However, switching frequencies at two transistors were controlled by only one 556 timer. The complete circuit of the DOSMPS consist of full bridge rectifier, smoothing capacitor, two high frequency transformers and two forward converter circuits. At the first stage of this work, the DOSMPS circuit was designed using Proteus software. Later, the complete DOSMPS circuit was constructed on two breadbroads after all of the electronic components and devices were available. Important parameters such as the input and output voltages and duty cycles were measured using digital oscilloscope and multimeter. Results from these measurements have shown that the designed circuit can convert single-phase 24 Vrms 50 Hz AC voltage input into dual and stable 5±0.1 V DC outputs. Also from this work, it was observed that, pulsed DC voltages with peak value of 2 V and frequency less than 20 kHz are sufficient in controlling the switching frequencies of both BJT transistors. This allows the regulation of the output voltage within the desired range. Analysis carried out after the measurements has shown close correlation between the theoretical and experimental results, where the calculated and measured switching frequencies had only deviated by 1.1%.

Flow Structures and Charge Behaviors of Electroconvective Silicone Flows Induced by a Surface Dielectric Barrier Injection Actuator Subjected to Bipolar Pulsed DC Signals

Surface dielectric barrier injection (SDBI) actuators have received increasing interest due to the presence of dielectric barriers, which can greatly improve the applied voltage. The success of SDBI actuators in driving silicone oil makes silicone flow a very promising application in the field of microfluidics. However, polarity-dependent flows that are different from conventional cases are observed experimentally under bi-polar pulsed DC signals. To interpret this specific phenomenon, a new model of electrohydrodynamic (EHD) wall jet considering both electrochemical injection and the initial presence of an electrical double layer (EDL) at the dielectric solid/liquid interface is developed for the first time based on the finite element method. The results show that the flow field in the simulation is consistent with the experimental bidirectional flow field. The silicone vortex movement is accompanied by charge injection, migration and accumulation in the near-wall region. Through studies of the effect of signal parameters on flow behavior, including voltage amplitude, duty cycle, frequency and waveform, a square wave signal with a frequency of 0.2 Hz proves to be the most efficient in generating a high-velocity silicone flow.

Characterization of fish assemblages in eleven multi-use reservoirs from North Carolina, USA

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas ­fisheries research has historically focused on assessing fish ­populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.

Copper oxide memristor as artificial synapses emulating Hebbian symmetric and asymmetric learning behavior for neuromorphic computing beyond von Neumann architecture

Beyond von Neumann’s architecture, artificial neural network-based neuromorphic computing in a simple two-terminal resistive switching device is considered the future potential technology for simultaneous data processing and storage. These are also compatible with low-power consumption nanoelectronic devices and, thus, suitable for applications such as image recognition toward solving complex pattern recognition problems. Herein, motivated by the human biological brain, we successfully synthesized low-cost RRAM devices using the thermal oxidation of Cu, i.e., CuO as the active material together with Cu as the top electrode and FTO as the bottom contact for a two-terminal resistive switching device, and investigated characteristics for neuromorphic computing. Cu/CuO/FTO-based devices showed excellent bipolar analog RRAM characteristics with 150 repeatable cycles, retention for 11 000 s, and DC pulse endurance for 5000 cycles. Moreover, devices exhibit a remarkable mimicking ability, demonstrating spike time-dependent plasticity (STDP), pulse-paired facilitation (PPF), synaptic weight, and learning and forgetting characteristics, substantiating the recognition ability. Furthermore, the artificial neural network synaptic membrane exhibits excellent long-term (LTP) and short-term (STP) potentiation for six consecutive cycles. Thus, the present work on Cu/CuO/FTO-based devices provides a detailed understanding of CuO active material-based resistive switching with a potential for neuromorphic computing beyond the von Neumann architecture.

Chemical Composition, Structure, and Physical Properties of AlN Films Produced via Pulsed DC Reactive Magnetron Sputtering

The chemical composition, structure, and physical properties of aluminum nitride (AlN) films obtained using pulsed DC reactive magnetron sputtering in asymmetric bipolar mode have been studied. X-ray diffraction and electron diffraction confirmed the composition of c–axis textured hexagonal AlN films required for piezoelectric applications. The surface of the films obtained is quite smooth; the arithmetic average roughness does not exceed 2 nm. Transmission electron microscopy has shown the presence of a transition layer at the film–substrate interface. Transmission electron microscopy and X-ray photoelectron spectroscopy depth profile analysis have shown that the films have an oxidized surface layer which has an influence on the optical model of the films derived from ellipsometric data. However, it does not significantly influence the films’ piezoresponse. Piezoelectric force microscopy indicated a piezoelectric effect in the films that is uniform over their surface.

Characterization of Structural, Optical, Corrosion, and Mechanical Properties of HfO2 Thin Films Deposited Using Pulsed DC Magnetron Sputtering.

Various properties of HfO2, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO2 thin films deposited with different conditions of reactive magnetron sputtering process is presented. Four thin films were sputtered in processes that varied in plasma ignition method (continuous or sequential) and target-substrate distance. The structural characteristics of the HfO2 thin films were examined using Raman spectroscopy and X-ray diffraction measurements. Furthermore, the optoelectronic properties were determined based on transmittance and current-voltage characteristics. The mechanical properties of the HfO2 thin films were determined using nanoindentation and scratch test. In turn, the corrosion properties were determined by analyzing the voltametric curves. The transparent HfO2 thin films deposited in the continuous process are characterized by better corrosion resistance than the same layer formed in the sequential process, regardless of the target-substrate distance (8 cm or 12 cm). Furthermore, these samples are also characterized by the highest value of Young's modulus and scratch resistance. The combination of good corrosion and scratch resistance could contribute to the new application of HfO2 as a corrosion protective material.

Production of high-density metastable argon atoms with periodic fast pulsed DC discharge.

Optically pumped metastable rare gas laser (OPRGL), as a potential high-energy laser has attracted much attention. During extensive research on OPRGL, the realization of volume discharge with high-metastable density has always been a priority and is essential to the efficient lasing of OPRGL. A large-volume plasma of He/Ar with high metastable density at atmospheric pressure can be generated by applying peaking capacitors near the electrodes. In this article, 0.8 cm3 of He/Ar plasma at a pressure of 900 mBar, with a peak value of metastable argon density higher than 1014 cm-3 was realized. The metastable density was measured by absorption spectroscopy based on the absorption bandwidths acquired at a pressure range of 400-900 mbar where a probe beam at a weak line with wavelength 772.38 nm was applied. Furthermore, the high metastable density was verified by the laterally-observed laser-induced fluorescence, as well as the laser oscillation of 100 mW under a longitudinal pumping with a short gain length of 8 mm.

Investigation and Band Gap Analysis of Pulsed Dc Magnetron Sputtered Diamond‐Like Carbon to Enhance Contact‐Electrification and Durability of Triboelectric Nanogenerators

AbstractThis work details the triboelectric characteristics of diamond‐like carbon (DLC) film where a proportioned sp3:sp2 bond ratio is engineered through a patented pulsed DC magnetron sputtering process to achieve a durable commercial energy harvesting material. A triboelectric nanogenerator (TENG) is fabricated by creating the triboelectric interface between DLC and PTFE. The presence and synchronization of σ – σ and σ – π bonds between DLC‐PFTE contact surface amplify the electronic cloud overlap between their atoms leading to an enhancement of the triboelectric surface charge density. The inherent hardness and reduced friction achieved through DLC and PTFE respectively prevent the mass transfer, and consequent power loss upon consecutive mechanical contact and achieves a stable electric power output of 141 mW m−2. The DLC durability achieved with PTFE in TENG demonstrates its significant potential as low frequency (1 – 10 Hz) energy harvesting devices and self‐/low‐power electronic devices and sensors. The paper uniquely contributes to a better understanding of the triboelectrification mechanism by insightfully detailing the band‐to‐band transition of electrons between the PTFE and DLC tribo‐interface, as well as discussing gap and frequency limitation of the tribo‐pair on the triboelectric charge yield, storage, transfer, and on the friction layer electric field.

Polyvinyl-alcohol, chitosan and graphene-oxide composed conductive hydrogel for electrically controlled fluorescein sodium transdermal release

Accurate and controlled release of drug molecules is crucial for transdermal drug delivery. Electricity, as an adjustable parameter, offers the potential for precise and controllable drug delivery. However, challenges exist in selecting the appropriate drug carrier, electrical parameters, and release model to achieve controlled electronic drug release. To overcome these challenges, this study designed a functional hydrogel using polyvinyl alcohol, chitosan, and graphene oxide as components that can conduct electricity, and constructed a drug transdermal release model using fluorescein sodium salt with proper electrical parameters. The results demonstrated that the hydrogel system exhibited low cytotoxicity, good conductivity, and desirable drug delivery characteristics. The study also integrated the effects of drug release and tissue repair promotion under electrical stimulation. Cell growth was enhanced under low voltage direct current pulses, promoting cell migration and the release of VEGF and FGF. Furthermore, the permeability of fluorescein sodium salt in the hydrogel increased with direct current stimulation. These findings suggest that the carbohydrate polymers hydrogel could serve as a drug carrier for controlled release, and electrical stimulation offers new possibilities for functional drug delivery and transdermal therapy.

Nitrogen Oxidation in a Multi-Pin Plasma System in the Presence and Absence of a Plasma/Liquid Interface

The recent energy crisis revealed that there is a strong need to replace hydrocarbon-fueled industrial nitrogen fixation processes by alternative, more sustainable methods. In light of this, plasma-based nitrogen fixation remains one of the most promising options, considering both theoretical and experimental aspects. Lately, plasma interacting with water has received considerable attention in nitrogen fixation applications as it can trigger a unique gas- and liquid-phase chemistry. Within this context, a critical exploration of plasma-assisted nitrogen fixation with or without water presence is of great interest with an emphasis on energy costs, particularly in plasma reactors which have potential for large-scale industrial application. In this work, the presence of water in a multi-pin plasma system on nitrogen oxidation is experimentally investigated by comparing two pulsed negative DC voltage plasmas in metal–metal and metal–liquid electrode configurations. The plasma setups are designed to create similar plasma properties, including plasma power and discharge regime in both configurations. The system energy cost is calculated, considering nitrogen-containing species generated in gas and liquid phases as measured by a gas analyzer, nitrate sensor, and a colorimetry method. The energy cost profile as a function of specific energy input showed a strong dependency on the plasma operational frequency and the gas flow rate, as a result of different plasma operation regimes and initiated reverse processes. More importantly, the presence of the plasma/liquid interface increased the energy cost up to 14 ± 8%. Overall, the results showed that the presence of water in the reaction zone has a negative impact on the nitrogen fixation process.

Non-thermal to thermal electric field effects induced by DC and current pulses in pure and doped VO2 single crystals

Pure VO2, GexV1−xO2 (x < 0.2), and AlxV1−xO2 (x ≤ 0.02) exhibit above room temperature the well-known insulator-metal-transition (IMT) (at TIMT ≅ 340 K). In addition, AlxV1−xO2 exhibits an insulator-insulator-transition (IIT) at TIIT < TIMT. Both transitions can be induced either by external or by Joule heating. Both leave prominent marks on the I–V characteristics of the investigated samples, IIT at low currents and IMT at high currents. Reported herein is a comparative study of the I–V characteristics of needle-like pure and doped VO2 single crystals obtained with pulsed currents of various durations and with DC, in an attempt to separate thermal from non-thermal electric field effects. Identification of the Poole–Frenkel effect (a non-thermal electric field effect) in the I–V characteristics of the doped crystals may play an important role in a long-standing debate on the mechanism of IMT. Such an identification was obtained in this investigation for several Ge- and Al-doped VO2 crystals, so far only in narrow ranges of electric fields (<2000 V/cm) and pulse durations (≤1 ms) above which the non-linear conductivity of the crystals is dominated by Joule heating.

ВЗАЄМОУЗГОДЖЕННЯ ПАРАМЕТРІВ ДЖЕРЕЛА ЖИВЛЕННЯ ТА РОБОЧОЇ КАМЕРИ ДЛЯ ОБРОБКИ ВОДИ ІМПУЛЬСНИМ БАР'ЄРНИМ РОЗРЯДОМ

To determine the mutually agreed parameters of the output link of the generator of short (~100 ns) pulses with a working chamber, in which water is treated in the droplet-film state by a pulsed barrier discharge, an approximate mathematical model was developed that describes the transient processes in the circuit. The reliability of the model is confirmed by experimental data. The optimal parameters of the capacitance of the dielectric barrier and magnetic keys were calculated, according to which the efficiency of energy transfer to the working chamber reaches 62%. It is shown that it largely depends on the ratio of the barrier capacity of the working chamber to the output capacity of the pulse generator, the optimal value of which is ≈2.6. The selection of the value of the dissipation inductance of the magnetic key, through which the discharge of the barrier capacity occurs after the end of the direct current pulse, is justified. It was established that the consistency of the parameters of the output link of the pulse generator and the working chamber makes it possible to significantly reduce the thermal load on the fast-acting opening diode in the output link of the pulse generator. References 15, Figures 8.

Enhanced emission from hBN in sputtered microcavities.

In this observational study, we embed few-layer hexagonal boron nitride (hBN) inside a planar Fabry-Perot cavity fabricated using a pulsed DC magnetron sputtering system and show that the hBN retains its inherent visible range, defect-based luminescent properties following relatively energetic deposition processing. The observed surface-normal emission enhancement factor of ∼40 is in good agreement with theoretical predictions. We also found that embedded hBN subjected to a rapid thermal annealing treatment exhibits a cracking effect where the edges of the material glow distinctly brighter than adjacent regions. Our results might inform future efforts involving monolithic integration of hBN active layers.