Journal of Physics D: Applied Physics

Filipinas, Jae Lord Dexter C; Confesor, Mark Nolan P

doi: 10.1088/1361-6463/adb6b8pmid: N/A

The utilization of mechanical cues in guiding the morphological growth of decentralized organisms has remained unexplored. Here, we present experimental evidence demonstrating the mechanical guidance and durotaxis of a unicellular decentralized organism, Physarum polycephalum. We investigate the spatial-temporal dynamics of its plasmodial nodes as it expands over agar substrates with gradients in stiffness. Our findings reveal directional persistence and strong polarization of the plasmodia towards regions of stiffer substrates, indicating a guided migration response. Notably, as supported by simulations, this guided migration is found to be independent of the absolute gradient of substrate stiffness.

Feng, Lanting; Xu, Weiyi; Luo, Haoyu; Yu, Guodong

doi: 10.1088/1361-6463/adb9fapmid: N/A

In semiconductor technology, bandgap engineering is a cornerstone challenge that continues to evolve. By employing the full and low-energy tight-binding model, we focused on the effects of twist-angle on the bandgaps of twisted bilayer γ-graphyne and graphdiyne. Our results indicated that reducing the twist-angle from 21.79∘ to 0.67∘ can significantly narrow the bandgap by as much as 0.5 eV. Drawing on the concept of hybridization, this reduction in bandgap is elucidated by the average of the interlayer coupling on the valence band maximum state and conduction band minimum state. Our research presents a versatile approach to bandgap modulation in two-dimensional semiconductors.

Bandyopadhyay, Supriyo

doi: 10.1088/1361-6463/adb9f7pmid: N/A

The “straintronic magnetic tunnel junction” (s-MTJ) is a magnetic tunnel junction (MTJ) whose resistance state can be changed continuously or gradually from high to low, or vice versa, with a gate voltage that generates strain in the magnetostrictive soft layer. This unusual feature, not usually available in MTJs that are switched abruptly with spin transfer torque, spin–orbit torque or voltage-controlled-magnetic-anisotropy, enables many analog applications where the typically low tunneling magneto-resistance ratio of MTJs (i.e., the on/off ratio of the switch) and the relatively large switching error rate are not serious impediments unlike in digital logic or memory. More importantly, the transfer characteristic of a s-MTJ (conductance versus gate voltage) always sports a linear region that can be exploited to implement analog arithmetic, vector matrix multiplication and linear synapses in deep learning networks very effectively. In these applications, the s-MTJ is actually superior to the better known memristors and domain wall synapses which do not exhibit the linearity and/or the analog behavior11Invited perspective..

Xiao, Xinyan; Shi, Yuhao; Yang, Lanjun

doi: 10.1088/1361-6463/adb43dpmid: N/A

The aging stability and performance monitoring of zinc oxide (ZnO) surge arresters have attracted considerable attention in the field of electrical engineering. However, the practical performance of existing solutions remains suboptimal. A key factor contributing to this limitation is the lack of sufficient research on the conductive properties of surge arresters and varistors. In time-varying alternating current (AC) fields, ZnO varistors exhibit nonlinear volt-ampere characteristics distinct from those in direct current (DC) fields. Such complex nonlinearity results in challenges in pertinent investigations. In this study, we experimentally investigated the AC response of ZnO varistors under varying voltage amplitudes and frequencies. Subsequently, their dynamic dielectric permittivities were calculated using appropriate models and equations. Moreover, building upon an in-depth exploration of their nonlinear response and dielectric properties, we developed relevant theories (e.g. dielectric relaxation) to analyze influencing factors and underlying mechanisms reasonably. Finally, we linked the relaxation of interfacial charges at the microscopic level with the macroscopic nonlinear characteristics and elaborated on the conduction mechanism in AC fields through the dynamic behavior of nonequilibrium charges in interfacial states. Our findings demonstrate that the dielectric permittivity of ZnO varistors exhibits a voltage dependence in time-varying AC fields, providing valuable insights into their aging stabilities. These insights will provide a foundation for improving the design, performance, and aging stability monitoring of ZnO varistors in surge arresters.

Tomar, Ishu; Sarkar, Abhishek

doi: 10.1088/1361-6463/adb85apmid: N/A

Cathode materials in lithium-ion batteries are prone to delamination under over-voltage and fast charging conditions. This causes loss of active materials, reduction of battery capacity, and cycle life. This work develops a physics-based model to simulate the effect of over and undercharging of different cathode particle sizes in a composite electrode. A chemo-mechanical model is designed to simulate the non-linear volumetric expansion of a range of electrode particle sizes encapsulated in a binder, under different voltage conditions. The cathode fracture is modeled under fast charging conditions due to fatigue loading caused by (de)lithiation of lithium-ions during electrochemical cycling of nickel–manganese–cobalt (NMC) cathode in a half-cell arrangement. Two modes of degradation are considered, i.e. particle surface is free, and particle surface is fixed. Paris’ law is used to model the growth of fatigue cracks. The variation of tangential and radial stress in the particle and film are presented for the charging rate (1C–4C). The results predict crack growth and conditions of failure in the electrode during electrochemical cycling under various charging rates. Finally, an intuitive capacity loss model is developed to predict the cycle life and active material losses due to film delamination and particle fracture.

Primc, Gregor; Spasić, Kosta; Zaplotnik, Rok; Puač, Nevena; Malović, Gordana; Mozetič, Miran; Petrović, Zoran Lj

doi: 10.1088/1361-6463/adb591pmid: N/A

The spatial profile of atomic oxygen in a cylindrical afterglow chamber with a height of 41 cm and an inner diameter of 30 cm was measured. The source of oxygen atoms was a remote microwave plasma operating at a discharge power of about 250 W. The gas flowed through a quartz-glass tube with inner and outer diameters of 3.8 and 6.0 mm, respectively. The exhaust of the quartz tube widened to cones of various geometries. The spatial distribution of atomic oxygen was determined for cones with an outer diameter of up to 40 mm. The tube with the widest cone (Tube 3) provided the largest O-atom density of 6 × 1020 m−3 in the upper part of the afterglow chamber away from the main gas stream in the pressure range from 50–200 Pa, while the tube (Tube 1) with the narrowest cone enabled an O-atom density of up to 2 × 1020 m−3. The differences in measured oxygen density for three tubes at positions ‘up’ and ‘down’ decreased with increasing pressure and were below the detection limit at pressures above 350 Pa. In the case of the ‘middle’ position, Tube 2 with an outer diameter of 19.3 mm exhibited a sharper decrease in oxygen density compared to Tube 1 and Tube 3. The O-atom density in the middle of the afterglow chamber increased with the increase in the percentage of pump valve opening at the lowest probed constant pressure of 40 Pa, but it stayed constant for the opening of the pump valve above 70%. For constant pressures above 100 Pa the O-atom density decreases with the larger pump valve opening. The pressure is kept constant by the corresponding increase in oxygen gas flow while increasing the percentage of the pump valve opening. The spatial profiles are explained by the effects of gas flow and diffusion.

Tiwari, P; Atkar, S A; Sharma, P; Datta, A; Singha, A D; Roy-Chowdhury, M; Sarkar, T; Thota, S

doi: 10.1088/1361-6463/adb417pmid: N/A

Efficient control of the structural, magnetic and electrical properties of Rare-earth (RE) based perovskites (ABO3) is crucial for advanced spintronic applications and can be achieved by means of site-specific substitution. In this comprehensive study, we explore the role of (Nd)A-site and (Mn)B-site co-substitution on the physical properties of pristine LaCoO3 perovskite. The resulting compound La0.5Nd0.5Co0.5Mn0.5O3 (LNCMO) with an orthorhombic (Pbnm) crystal structure (a =5.4811(4) Å, b = 5.5074(4) Å and c =7.7491(5) Å) exhibits a significantly reduced Jahn-Teller distortion (JT) compared to pristine LaCoO3 with a monoclinic (I2/a) structure. The ac-magnetic susceptibility χ(T, f, Hdc) measurements and wait time dependence of the isothermal magnetization M(t) provide clear evidence for the re-entrant spin-glass-like behavior with freezing temperature TSG =133 K below the ferrimagnetic Curie temperature (TFiM ∼137.4 K). Additionally, the asymmetric response of magnetic relaxation in the system to positive and negative temperature cycling well below the freezing temperature has been explained by means of the hierarchical model. Furthermore, a giant coercivity (HC ∼14 kOe) and remanence (MR ∼ 6440 emu mol−1 ) with weak loop-asymmetry indicates the presence of large magnetic anisotropy in LNCMO, evidenced by a high magneto-crystalline anisotropy field (HK ∼80 kOe) and anisotropy constant (K1 ∼ 1.45 × 107 erg cm−3). The unique electronic structure of trivalent Nd (5f 3) and mixed valent Mn (3d4/3d3) with spin-orbit coupling energies 4 eV and 11.43 eV/10.51 eV, respectively and competing exchange interaction (∼0.67 meV) between Mn and Co cations in different pathways results in enhanced magnetic-order parameters. Moreover, the co-substitution results to a pseudo-first order like state close to the spin-state transition H* of Co (S = 0 → 2) which has been verified by the modified Arrott plot analysis yielding critical exponents β = 0.67, γ = 1.44 and δ = 3.13. A field-induced metamagnetic transition HT emerges in the range 30 K ⩽T⩽ 130 K which has been mapped along with other parameters resulting in a H-T phase diagram which clearly distinguishes various magnetic phases and sharp crossover between the different states providing a clear and vivid picture of the overall magnetic structure of LNCMO.

Gortschakow, Sergey; Uhrlandt, Dirk; Kloc, Petr; Aubrecht, Vladimir; Coufal, Oldrich; De Holanda Sousa, Renan; Robin-Jouan, Philippe

doi: 10.1088/1361-6463/adb858pmid: N/A

Ten years after its invention, g3— the mixture of C4F7N, CO2 and O2— remains the most promising candidate for the substitution of SF6 as an insulating and switching gas. The extension and optimization of g3 applications at a high-voltage level, especially in circuit breakers, requires knowledge of the properties and dynamics of arc discharges in this gas. The features of the arc plasma can be obtained from appropriate magneto-hydrodynamic simulations. To predict the arc behaviour, a consistent set of thermo-physical and radiation properties is necessary. The corresponding database is calculated for the case of local thermodynamic equilibrium and covers the temperature range 250–40 000 K, the pressure range 0.01–150 bar and various contents of C4F7N, O2 and Teflon (nozzle material). This contribution presents examples of plasma composition, thermo-physical and radiation properties for g3 mixtures. The feasibility of the new database is demonstrated on an example of simulation results for a g3-filled high-voltage circuit breaker. Predicted arc voltage and pressure build-up in selected volumes are compared with available experimental data. Furthermore, to explore the differences in switching behaviour between g3 and SF6, simulations for these two gases at the same operation conditions were performed. The space- and time-dependent temperature and pressure profiles are presented and discussed.

Pathak, Ram Mohan; Jayanarasimhan, Ananthanarasimhan; Rao, Lakshminarayana

doi: 10.1088/1361-6463/adb43cpmid: N/A

Tar, a by-product of gasification, is a complex mixture of high molecular weight hydrocarbons that can cause significant damage to downstream equipment and reduce the efficiency of gas utilization. Effective tar destruction is therefore essential for producing clean syngas. Non-thermal plasmas (NTP’s) technology offers a promising solution for gas cleaning by effectively destroying tar. This review explores various plasma sources and experimental approaches for using NTP’s in tar destruction. It evaluates the performance of different plasma sources on the destruction of toluene and naphthalene, the most prevalent tar compounds in gasifier product gas, and discusses the chemical mechanisms and modeling approaches involved in their destruction. The most common modeling approach includes reaction kinetics, demonstrating how chemical reactions occur and behave in the NTP’s system. This approach, known as the plasma global model, simplifies plasma modeling by focusing on reaction rates to predict the production and loss of species without needing to model plasma’s bulk properties. The works that investigated plasma-catalysis for tar destruction were considered. A comparison of literature works reveals that the best performance for naphthalene destruction is achieved by corona plasma and reverse vortex flow gliding arc reactors, with the destruction efficiency (ηd) of 99% and 99.8% at concentrations of 5 g m−3 and 10.3 g m−3, respectively. For toluene, the gliding arc discharge and rotating gliding arc combined with the catalyst demonstrate the highest efficiency, achieving 99% and 99.9% destruction at 22.9 g m−3 and 4 g m−3, respectively. The synergy between plasma and catalysts offers key benefits, including higher energy efficiency, faster reactions, and lower operating temperatures compared to traditional thermal methods. The review suggests that NTP’s technology shows strong potential for removing biomass tar from gasification. It could be a promising solution for biomass tar cracking and upgrading product gas in real gasification applications. Several pilot and small-scale plasma plants have been developed, but the technology is still emerging and faces various technical and economic challenges.

Wang, Siyao; Zhao, Jingxiang

doi: 10.1088/1361-6463/adba72pmid: N/A

As a clean and sustainable energy source, hydrogen is expected to play a crucial role in addressing excessive carbon dioxide emissions and the depletion of fossil fuels. Herein, by means of density functional theory computations, we have systematically investigated the effects of interface engineering in a series of graphene/g-C3N4 (G/g-C3N4) with heteroatom doping (X-G/g-C3N4 and G/X-g-C3N4, X = B, N, Si, P and S) on hydrogen evolution reaction (HER) catalytic performance. Our results reveal that these X-doped G/g-C3N4 interfaces exhibit excellent stability, enhanced metallic features, terrific mechanic properties, and exceptional magnetic properties. Remarkably, through precise regulation of the positioning of Si or P heteroatom, X-G/g-C3N4 interfaces demonstrate outstanding excellent catalytic performance, characterized by hydrogen adsorption free energy (ΔGH*) values approaching zero, which can be ascribed to its appropriately positioned p-band centers near the Fermi level. This work provides valuable insights for the rational design of HER catalysts aimed at sustainable high-purity H2 production.