Journal of Physics D: Applied Physics

Dhivakar J, Manoj; Sarathi, Ramanujam; Kornhuber, Stefan

doi: 10.1088/1361-6463/adcbbcpmid: N/A

The present work examines the surface degradation and charge transport mechanism of silicone rubber material with nano-size alumina trihydrate (ATH) and low-melting glass powder (LMGP) fillers, aged in an acid rain solution. The immersion in acid rain forms acid/salt contamination layers on the silicone rubber surfaces. Scanning electron microscope images indicate that the acidic degradation could be minimized by LMGP addition with base silicone rubber. ATH/LMGP filler addition with silicone rubber significantly enhances the contact angle, thermal conductivity and reduces the diffusion coefficient. LMGP filler addition minimizes the formation of Si(–O)4, Si(–O)3, C–O and C=O components following the acid rain immersion. Equivalent circuit modelling of dielectric parameters explains the formation of a quasi-polaron surface polarization interface along with the Maxwell–Wagner interface in the acid rain-aged silicone rubber composites. A significant increase in real and imaginary permittivity is observed with the acid rain-aged silicone rubber samples. The surface potential decay experiment indicates a reduction in trap depth values in acid rain aged samples due to the fast surface potential decay characteristics. The thermal images and T vs F curves indicate that the ATH/LMGP filler addition reduces the local heat accumulated area (LHA). The huge variation in Haralick parameters has observed between the virgin and aged samples. However, considering multiple aging factors, such as ultra violet radiation, thermal cycling, and electrical discharge could accurately determine the overall degradation state of the insulators.

Wang, Jianfei; Li, Zhiqiang; Ma, Liang; Zhao, Yipeng

doi: 10.1088/1361-6463/adcbbapmid: N/A

Janus two-dimensional materials have attracted extensive research attention owing to their intrinsic electric dipole moments and excellent properties. Here, a systematic study on the electronic properties of In2Se2S/WSiGeX4 (X = N, P, As) van der Waals heterostructures (vdWHs) is presented. The results showed that the different interfacial stacking configurations can modulate the net dipole moment strength and band alignment of In2Se2S/WSiGeX4 vdWHs. The In2Se2S/WSiGeP4 vdWHs exhibit type-I band alignment with direct bandgap characteristics when adopting Si(Ge)/Se interfacial contacts, whereas type-II band alignment accompanied by indirect bandgap features emerges in systems with Si(Ge)/S interfacial configurations. Notably, the Si (Ge)/S interface exhibits a higher charge transfer capacity compared to the Si (Ge)/Se interface. Furthermore, the bandgap of heterostructure undergoes significant changes primarily when the interface atoms change from S atom to Se atom. In addition, the bandgap of In2Se2S/WSiGeP4 vdWHs with Ge/Se (S) interface contact exhibits a first increase and then decrease tendency under compressive (tensile) strain, and a directly decrease trend under tensile (compressive) strain. Our results provide immense promise for the development and application of Janus heterostructure, offering a useful guidance for future device designs.

Zhang, Jie; Yuan, Hao; Zhou, Zikai; Liang, Rui; Lu, Ke; Li, Sisi; Yang, Dezheng

doi: 10.1088/1361-6463/adcbb6pmid: N/A

Needle-to-needle discharge plasma in atmospheric pressure air environments has been proven to have applications in different fields depending on its kinds of discharge modes, which in turn lead to the importance of investigating the characteristics and mode transitions of the discharge plasma. In this paper, AC high-voltage is employed to generate a needle-to-needle bare electrodes discharge plasma in the air. The modulation of the discharge mode can be achieved by adjusting key factors such as electrode gap, capacitance and voltage, and can be categorized into four modes: streamer discharge, streamer glow mixed discharge, glow discharge, and arc discharge. The discharge images, waveforms of voltage and discharge current, discharge dynamic evolution processes, and optical emission spectra of the four discharge modes are diagnosed. It is found that, with discharge modes transiting from streamer to arc, both the duration time and gas temperature of discharge increase, while the peak current decreases. Correspondingly, the discharge morphology, current waveform and reactive species generation also undergo significant changes, which are critical for understanding the mode transition.

Wang, Jian; Xing, Zexi; Zhu, Jianzhao; Li, Hongjian; Han, Zhiyun; Ren, Hanwen; Li, Qingmin

doi: 10.1088/1361-6463/adcbb5pmid: N/A

Copper–aluminum electrical contact components in the operation process will be subjected to mechanical friction and current ablation of the joint role. These components often operate under extreme conditions characterized by high current, elevated temperatures, and significant stress coupling. As a result, the interface sliding electrical contact state is severely compromised, which can lead to a degradation of the service performance of the alloy material. In this paper, copper–aluminum current-carrying friction experiments were conducted in different devices to study the microstructure morphology and material transfer strength of the worn surface. The adhesion-diffusion process and interfacial degradation behavior were also analyzed from micro-evolution and energy transfer. It was found that under low-speed friction, the worn surface was dominated by grooves and abrasive chips. Conversely, under high-speed friction conditions, the aluminum material was thermally softened, resulting in its deposition on the copper surface. The analysis indicates that an increase in interface temperature will facilitate the upward thermal excitation and diffusion of copper atoms. This process along with the melting of aluminum atoms leads to the formation of columnar grain structures within the metal. These structures are firmly adhered to the copper substrate, resulting in increased static contact resistance and reduced contact stability. The study elucidates the degradation mechanisms of the copper–aluminum interface state under electrical interaction, which is valuable for informing the design and enhancing the performance of the armature rail surface.

Li, Longfei; Jia, Hongyin; Jiang, Anlin; Wu, Long; Cui, Pengcheng; Wu, Xiaojun

doi: 10.1088/1361-6463/adc46apmid: N/A

The nanosecond pulsed surface dielectric barrier discharge for gasdynamic control in high-temperature non-equilibrium flows is modeled using the multi-species Navier–Stokes equations coupled with self-consistent drift-diffusion equations, encompassing 16 species and 36 reactions. A ‘plasma-to-fluid’ loose coupling strategy is employed, with corresponding spatial and temporal discretization applied. The simulation focuses on a proposed annular dielectric barrier discharge actuator configuration integrated into the outer surface of a simplified semi-sphere experimental model. A nanosecond voltage pulse with a peak voltage of 14 kV and a width of 35 ns is applied to the actuator to control the high-temperature non-equilibrium flow at a Mach number of 15.3. The energy characteristics, temperature distributions and species variations are analyzed, and the pressure perturbation and gasdynamic force evolution are also illustrated. Results indicate that the dominant dissociation and compound reactions produce atomic species and consume molecular and charged species, driven by the rapid temperature rise induced by the discharge. Due to the generation and propagation of the compression wave perturbations, the gasdynamic drag is observed to peak at a 20.5% increase, and an average rise of 3.7% within 200 ns, demonstrating potential applications in gasdynamic deceleration for re-entry vehicles.

Tsai, Ping Chieh; Zhao, Chunyu; Tan, Swee Tiam; Demir, Hilmi Volkan

doi: 10.1088/1361-6463/adc8b4pmid: N/A

We propose and demonstrate the InGaN-based light-emitting diodes (LEDs) with thyristor function for the first time by incorporating an Mg-doped p-GaN layer between the n-GaN layer and InGaN/GaN multiple-quantum-well active layer. Utilizing the thyristor-like structure, a distinctive negative differential resistance (NDR) appears on the I–V characteristics of InGaN-based LEDs. This unique bi-switching characteristics of the thyristor will enable a fast switching of the LEDs and thus reducing the complexity of the driving circuit design, making it a potential switching devices in the field of optical communications. In this work, the Mg doping concentration and thickness of the additionally added p-GaN layer were found to have a significant impact on the NDR. The formation of NDR becomes more and more obvious with the increase of Mg doping and thickness. In our structure, the Mg doping flow rate of about 0.583–1.057 μmol min−1 and the thickness of about 300–400 nm yield the best NDR properties. The brightness of LEDs decreases monotonically with the increasing Mg doping flow rate. Moreover, when the Mg doping concentration is insufficient, two NDR regions will appear in the I–V characteristics as the thickness increases. When the thickness is set to 300 nm and the Mg doping flow rates are 0.583, 0.802, and 1.057 μmol min−1, the optical output powers of the LEDs are measured to be 13.1, 12.8, and 14.3 mW at the driving current of 201 mA while the output powers at 4.61 mA are 0.46, 0.52, and 0.54 mW. The forward voltages at 201 mA are 3.71, 3.75, and 3.95 V for the Mg doping flow rates of 0.583, 0.802, and 1.057 μmol min−1, respectively. The characteristics of the thyristor-like InGaN LEDs need to be further optimized to reduce the operating current.

Davies, Bryn; Szyniszewski, Stefan; Dias, Marcelo A; de Waal, Leo; Kisil, Anastasia; P Smyshlyaev, Valery; Cooper, Shane; Kamotski, Ilia V; Touboul, Marie; Craster, Richard V; Capers, James R; Horsley, Simon A R; Hewson, Robert W; Santer, Matthew; Murphy, Ryan; Thillaithevan, Dilaksan; Berry, Simon J; Conduit, Gareth J; Earnshaw, Jacob; Syrotiuk, Nicholas;

Liu, Shu-Zhong; Liu, Rong; Li, Le-Yi; Meng, Fan-Yi; Xu, Shanshan; Ding, Chang

doi: 10.1088/1361-6463/adcbb7pmid: N/A

This paper presents the design and implementation of an ultra-wideband ferrite circulator. The main transmission line of the circulator adopts the form of Y junction and quarter-wavelength impedance converter. To extend the lower-frequency operating bandwidth, the design adopts double-Y and single-stub (DYSS) matching technology. DYSS is equivalent to parallel LC resonance and plays the role of reactance compensation. In addition, the composite ferrite (CF) technology is introduced innovatively which broadens the high-frequency working bandwidth effectively. CF effectively improves the magnetic vector distribution in the center of the circulator. Considering the actual magnetization state of ferrite, non-uniform simulation of ferrite is also carried out in this paper. The results of non-uniform simulation are more consistent with the test results. In the operating frequency range of 2.3 GHz–6.5 GHz, the insertion loss is controlled within 0.7 dB, and the return loss and isolation are better than 15 dB. In particular, the circulator has a compact size of 0.37λ0 × 0.37λ0 (λ0 is the free-space wavelength at 4.4 GHz) and an impressive relative bandwidth of 95%, which is rare among its counterparts. This design approach provides a reference for the miniaturization and broadband design of microstrip circulators.

Tan, Shengxia; Chai, Yi-Feng; Wang, Binglin; Guo, Shengwei; Jiang, Ru; Zhu, ZhongHua; Huang, Gui-Fang; Huang, Wei-Qing

doi: 10.1088/1361-6463/adccd3pmid: N/A

Simultaneously achieving high charge separation efficiency and structural stability in solar-driven photocatalysts remains a critical challenge. Here, we report a Z-scheme g-C3N4/ZnS heterojunction synthesized via hydrothermal deposition, which enhances redox capabilities through efficient charge carrier transfer/separation to improve photocatalytic activity and stability. The direct interfacial chemical bonds between g-C3N4 and ZnS enable unidirectional electron transfer and minimized recombination losses. The optimized heterojunction achieves 95.75% degradation of methylene blue under visible light within 2 h—6.38-fold and 4.76-fold higher than pristine g-C3N4 and ZnS, respectively. Mechanistic studies reveal superoxide radicals (•O2−) as the dominant active species, synergistically supported by hydroxyl radicals (•OH) and holes. Remarkably, the heterojunction composite retains 75.12% efficiency after four cycles, demonstrating exceptional stability attributed to its robust interfacial structure and suppressed ZnS oxidation. This work advances Z-scheme photocatalysts with dual redox capabilities toward scalable environmental remediation.

Wang, Zhaoxiang; Jiang, Guisheng; Zheng, Yijun; Ma, Hongliang; Liu, Yu; Zhu, Ziren; Yang, Yinhui; Huang, Zefan; Wang, Heng; Chen, Lin; Tan, Rongqing

doi: 10.1088/1361-6463/adc69bpmid: N/A

This study establishes a two-dimensional fluid theoretical model for a two-electrode spark gap switch, linking the behavior of microscopic particles with the macroscopic discharge phase through multiscale dynamic coupling. It further investigates the temporal characteristics of the switch’s conductive process and streamer evolution from the perspective of microscopic particles. Using the finite element analysis method, the study investigates the effects of factors such as gas pressure, operating voltage, electrode spacing, and electrode curvature on the time characteristics of key discharge stages, including electron directed motion, electron avalanche formation, discharge channel (streamer) evolution, and full switch conduction. Based on the model’s significant advantage in comprehensively considering the internal microscopic particle behavior, the study quantifies the differential control of discharge stages by electrode geometry (curvature radius of 0.5–2.5 cm, spacing of 0.8–1.2 cm) and achieves precise breakdown delay prediction within the pressure range of 0.6–1.4 atm and voltage range of 16–24 kV. This provides a reliable theoretical basis for the design and delay prediction of high-voltage switches, making an important contribution to the advancement of the high-voltage switch field.