Journal of Physics D: Applied Physics

Ugarak, Fehima; Pelisson, Fanny; Raschetti, Marina; Placet, Vincent; Butaud, Pauline; Ouisse, Morvan; Mosset, Alexis; Laude, Vincent

doi: 10.1088/1361-6463/adfb8apmid: N/A

Synthetic and natural fibers with diameters in the range of a few tens of micrometers can be routinely fabricated. Because of the intricate micro-structure of the fibers, however, their elastic properties remain poorly understood. In this study, we employ micro-Brillouin light spectroscopy (micro-BLS) to explore direction-dependent acoustic phonon propagation in amorphous E-glass, synthetic silk, polyamide 11 (PA11), and flax fibers. The technique is non-invasive and non-destructive, and is an alternative to static mechanical tests. The observable frequency shifts of laser light resulting from Brillouin scattering from hypersonic acoustic phonons of the fiber are in a few 10 GHz range. We determine the full elastic tensors and the optical anisotropy, assuming only transversely isotropic symmetry at the optical wavelength scale. The obtained elastic constants are compared with values reported in the literature for similar materials.

Wang, Ao; Zhou, Haimei; Peng, Yiran; Wang, Zhicui; Wan, Wenhui; Liu, Yong; Ge, Yanfeng

doi: 10.1088/1361-6463/adfb8cpmid: N/A

Low-dimensional magnetic semiconductors hold transformative potential for next-generation spintronics. Here, our study employs first principles calculations combined with phonon spectra, Monte Carlo simulations, and nonequilibrium Green’s function methods to investigate the structural stability, magnetism, and spin-dependent transport in one-dimensional ferromagnetic semiconductors CrS3 and CrS2Se. Both materials exhibit dynamic/thermodynamic stability (formation energies: −4.03 eV and −3.85 eV) in a chain structure, displaying intrinsic ferromagnetism with Curie temperatures (TC) of 172 K and 195 K. Under 6% tensile strain, TC rises to 263 K and 295 K, approaching room temperature applicability. Electronic structure reveals indirect bandgaps of 0.46 eV and 0.29 eV (PBE+U), with valence/conduction edges dominated by S(Se)-p and hybridized Cr-d-S(Se)-p states. Spin transport simulations demonstrate near-perfect spin filtration efficiency in parallel magnetization and significant rectification in antiparallel configurations, positioning these materials as promising candidates for multifunctional nanoscale spintronic devices.

Udachin, Viktor; Wegewitz, Lienhard; Zimmermann, Sascha Jan; Gustus, René; Wiche, Henning; Maus-Friedrichs, Wolfgang

doi: 10.1088/1361-6463/adfd6cpmid: N/A

This study explores the application of a dielectric barrier discharge (DBD) plasma jet in an Ar/H2 gas flow for oxide reduction and shielding on E235 steel surfaces. We detail the construction of the non-thermal plasma jet system, including the operational parameters and characterization of reactive species present in the plasma phase using optical emission spectroscopy. Notably, the presence of atomic hydrogen species in the plasma highlights the oxide-reducing capability of this method. Subsequently, analytical techniques such as optical microscopy, field-emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy were employed to evaluate the treatment’s effectiveness. The application of the Ar/H2 plasma jet at 25 °C produced partial deoxidation and cleaning effects on the steel surface, indicating its potential under these conditions. Furthermore, we assessed the plasma jet’s efficiency during rapid thermal processing of steel, where the surface temperature reached approximately 1000 °C within 1 s—a condition relevant to high-temperature metal-joining applications. Our findings revealed that the center of the area directly interacting with the plasma jet was largely protected from oxidation, exhibiting an oxygen concentration of 7 at.% compared to 53 at.% on the untreated surface. The metallic appearance of this central interaction zone was largely preserved, and it measured approximately 2.5 mm2. In contrast, processing with a non-ionized Ar/H2 gas under identical conditions produced a smaller central area of 0.7 mm2 with a higher oxygen concentration of 19 at.%. Importantly, both treatments were conducted using the same setup, ensuring that observed differences resulted from the presence of the plasma jet. These results suggest that the DBD plasma jet process offers improved shielding and oxide reduction over a larger surface area than a non-ionized gas flow. Therefore, this study highlights the potential of Ar/H2 non-thermal plasma jet treatment for enhancing steel surface quality in metal-joining applications.

Liu, Wenlong; Tang, Yidan; Liu, Chaoming; Hu, Zheng; Bai, Yun; Tian, Xiaoli; Li, Xuan; Hao, Jilong; Xiao, Yiping; Huo, Mingxue; Liu, Xinyu

doi: 10.1088/1361-6463/adfb89pmid: N/A

Gong, Ruiling; Guo, Hui; An, Junyang; Peng, Yanghu; Qiao, Guang; Sun, Na; Shao, Pengfei; Ye, Jiandong; Zhou, Yugang; Lu, Hai; Zhang, Rong; Zheng, Youdou; Chen, Dunjun

doi:

Wang, Ruixue; Kong, Xianghao; Jiang, Peiqi; Li, Sisi; Yan, An; Li, Chun; Yang, Dezheng; Ning, Wenjun

doi: 10.1088/1361-6463/adfae6pmid: N/A

Atmospheric-pressure low-temperature plasma is a powerful tool for surface modification to introduce functional groups of membrane. The transmission path and distribution pattern of reactive species inside the fiber membrane determined the uniformity and effectiveness of surface modification. This study systematically investigated the spatial distribution characteristics of reactive species within the fiber membrane through a combination of experimental diagnosis and multi-physics field simulation. Studies showed that plasma exhibited multi-branch discharge characteristics when penetrating multi-layer fiber membrane, with reactive species forming a non-uniform distribution in the fiber channels and exhibiting obvious channel selectivity. Further analysis showed that charged particles had strong penetration capabilities, while excited particles decayed significantly between fiber layers and had limited penetration depth in multi-layer structures. In addition, the fiber arrangement structure had a significant impact on the reactive species flux and distribution uniformity. Different misaligned superimposed structural fiber models broke the continuity of longitudinal channels, inducing reactive species to achieve different coating effects in lateral expansion. This study revealed the migration and distribution patterns of active species in multilayer fiber membrane, providing a theoretical basis for optimizing fiber membrane structure design and improving modification efficiency.

Yin, Zhi-Xiang; Chen, Xiao-Jie; Chen, Hao; Yin, Sheng-Feng; Zhang, Dan; Tang, Xin-Gui; Sun, Qi-Jun

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

Recently, heterojunction-based optoelectronic artificial synaptic devices present a promising avenue for the advancement of neuromorphic computing. However, the sophisticated fabrication procedures have impeded their future applications. In this work, a low-cost solution process is employed to fabricate the poly(ethylenedioxythiophene):poly(styrylsulfonate) (PEDOT:PSS)/indium zinc oxide (IZO) heterojunction-based optoelectronic artificial synapses. The device demonstrates the ability to simulate a variety of optoelectronic synaptic behaviors and successfully implement the transition between short/long-term memory states under diverse light pulse stimulation. Additionally, in comparison to single-layer IZO based optoelectronic artificial synapses, the PEDOT:PSS/IZO heterojunction-based device exhibits superior optoelectronic synaptic characteristics. This enhancement is primarily attributed to the PEDOT:PSS/IZO heterojunction, which effectively promotes the separation and transport of photogenerated carriers. The findings of this study highlight the significant potential of the fabricated optoelectronic artificial synapses for application in the area of neuromorphic computing.

Zhang, Liwei; Li, Haolin; Liu, Wenxuan; Fu, Yuliang; Zhang, Siyuan; Yang, Jinyuan; Pu, Yanxu; Liu, Haoyan; Zhang, Guanjun; Sun, Anbang

doi: 10.1088/1361-6463/adfbf8pmid: N/A

Ion thrusters are widely used in satellite operations due to their high specific impulse, efficiency, and precise thrust control. However, unexpected electrical breakdowns in ion optics severely limit the performance and reliability of ion thrusters. To investigate the initiation mechanisms of such breakdowns, a two-step 2D particle-in-cell/Monte Carlo collision simulation model is developed, integrating ion beam extraction with inter-grid breakdown processes. The accuracy of the model is validated by comparison with the experimental data. Simulation results reveal that the breakdown initiation evolves through three distinct stages: the formation of a neutral gas region, the development of cathode plasma, and a rapid surge in gap current. The point at which ion and electron densities near micro-protrusions become equal is identified as a key indicator of the breakdown onset, triggering the final breakdown stage. Breakdown initiation is strongly influenced by the electric field, background gas pressure, and micro-protrusion geometry, while the influence of short-term ion beam extraction is negligible due to its limited effect on the inter-grid field and metal evaporation. Strategies such as increasing the gap voltage while widening the gap spacing and minimizing high-energy particle impacts are shown to effectively enhance thruster performance and suppress breakdown risk. These findings provide valuable insights for optimizing ion optics design and improving the operational reliability of electric propulsion systems.

Stelmashuk, Vitaliy; Schmidt, Jiri; Kolacek, Karel; Frolov, Alexandr

doi: 10.1088/1361-6463/adfce4pmid: N/A

This study investigates the detailed generation mechanism of ball plasmoids formed by millisecond-scale atmospheric discharges in contact with water. Using high-speed filming with a higher frame rate and shorter exposure time than in previous studies, we focus on capturing and analyzing the rapid processes that occur at the beginning of plasmoid formation. Particular attention is given to the initiation phase, in which an electrical breakdown within a cathode ceramic cup containing conductive liquid triggers a shockwave and the subsequent injection of the liquid. This critical initial event results in the formation of a mixture of water vapor and droplets, which is weakly ionized by the breakdown and provides the primary material for plasmoid development. We also demonstrate that the electrical arc formed after the breakdown evolves into a plasma jet that supplies plasma to the forming plasmoid. We then explore the mechanism by which plasma is formed and transported into the developing plasmoid. The post-breakdown electrical arc transitions into a plasma jet that dynamically accelerates and channels plasma upwards into the plasmoid region. This jet transports ionized matter and facilitates ionization through interactions with entrained vapor and droplets, establishing a continuous supply of plasma to the plasmoid. We obtained optical emission spectra from different parts of the surface discharge at different times. The presence of the Balmer series is characteristic of the jet, which weakens as the current decreases, allowing the atomic sodium doublet line to become dominant in the plasmoid spectra.

Li, Longfei; Huang, Qiuming; Osada, Minoru; Zhao, Jicong; Li, Yun

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

The rapid development of the Internet of Things is driving advances in neuromorphic photonic computing systems that leverage light for highly efficient and parallel information processing. Note that to achieve neuromorphic computing with artificial optical synapses, tunable synaptic plasticity and photo-memory functions enabled by direct optical modulation are essential. In this study, we design an organic optical synaptic device with a two-dimensional (2D) metal oxide nanosheet as the charge storage layer, demonstrating bimodal synaptic plasticity and multilevel photo-memory. The precise layer-by-layer liquid deposition technology enables direct integration of 2D Cs2.7W11O351.3− nanosheet films with controllable thickness into the device for charge storage. Through interfacial band engineering, a type-II heterojunction is established between the organic semiconductor channel and the inorganic nanosheet, enabling gate-voltage-free photogenerated charge transfer and storage. Under optical modulation, the device exhibits tunable synaptic behaviors ranging from short- to long-term plasticity and a multilevel photo-memory capability with a retention time of 103 s. Then, we confirm the potential of the synaptic device for highly efficient neuromorphic computing, demonstrating a recognition capability with a high accuracy of 97.8%. Therefore, our device sheds new light on the development of optical computing systems.