Journal of Physics D: Applied Physics

This Roadmap surveys the diversity of different approaches for characterising, modelling and designing metamaterials. It contains articles covering the wide range of physical settings in which metamaterials have been realised, from acoustics and electromagnetics to water waves and mechanical systems. In doing so, we highlight synergies between the many different physical domains and identify commonality between the main challenges. The articles also survey a variety of different strategies and philosophies, from analytic methods such as classical homogenisation to numerical optimisation and data-driven approaches. We highlight how the challenging and many-degree-of-freedom nature of metamaterial design problems call for techniques to be used in partnership, such that physical modelling and intuition can be combined with the computational might of modern optimisation and machine learning to facilitate future breakthroughs in the field.

This review is devoted to the study of ultrafast laser ablation of solids and liquids. The ablation of condensed matter under exposure to subpicosecond laser pulses has a number of peculiar properties which distinguish this process from ablation induced by nanosecond and longer laser pulses. The process of ultrafast ablation includes light absorption by electrons in the skin layer, energy transfer from the skin layer to target interior by nonlinear electronic heat conduction, relaxation of the electron and ion temperatures, ultrafast melting, hydrodynamic expansion of heated matter accompanied by the formation of metastable states and subsequent formation of breaks in condensed matter. In case of ultrashort laser excitation, these processes are temporally separated and can thus be studied separately. As for energy absorption, we consider peculiarities of the case of metal irradiation in contrast to dielectrics and semiconductors. We discuss the energy dissipation processes of electronic thermal wave and lattice heating. Different types of phase transitions after ultrashort laser pulse irradiation as melting, vaporization or transitions to warm dense matter are discussed. Also nonthermal phase transitions, directly caused by the electronic excitation before considerable lattice heating, are considered. The final material removal occurs from the physical point of view as expansion of heated matter; here we discuss approaches of hydrodynamics, as well as molecular dynamic simulations directly following the atomic movements. Hybrid approaches tracing the dynamics of excited electrons, energy dissipation and structural dynamics in a combined simulation are reviewed as well.

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years.

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

The special mechanical properties of nanoparticles allow for novel applications in many fields, e.g., surface engineering, tribology and nanomanufacturing/nanofabrication. In this review, the basic physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first. Then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed. Afterwards, several of the main applications of nanoparticles as a result of their special mechanical properties, including lubricant additives, nanoparticles in nanomanufacturing and nanoparticle reinforced composite coating, are introduced. A brief summary and the future outlook are also given in the final part.

Ultra-fast photoelectric conversion devices are a crucial element in photonics applications and are the subject of intense research and development. In conventional high-speed photo detectors, photoelectric charge generation in semiconductors is rooted in a mechanism that directly outputs current. Owing to the dilemma of the amount of generated charge and high-speed output, it is being faced with fundamental difficult to achieve a higher response. Spin order, rather than charge generation, also exists as a phenomenon that enables ultrafast photoresponses, and magnetic tunnel junction (MTJ) are well-known high-speed electrical detection elements for magnetic states. In this study, we experimentally confirmed the magnetic switching of photoresponsive MTJ using a practical single CoFeB free layer with a high MR ratio of 80% by irradiation with laser light. Furthermore, we experimentally confirmed the operation of the reversible photo detector, and its rise time reached an ultrafast speed of 20 ps. We named it spin photo detector and it has huge potential applications that require ultrafast photo detection.

A comprehensive solution of the electron kinetics in gas discharges, accounting for dependencies in space, velocity and time, is often unfeasible. Therefore, the electron behavior is frequently coupled to fluid models under one of two assumptions: the local-field approximation (LFA), which equates the electron kinetics to the steady-state calculation with the local and instantaneous value of the reduced electric field; or the local-energy approximation (LEA), in which the rate coefficients and the electron power distribution among different collisional channels depend on the local value of the mean electron energy. In this work, we focus on time-locality to assess the impact of the LFA and LEA assumptions on the calculation of the temporal evolution of the electron kinetics in nanosecond discharges. To do so, we consider an accurate Monte Carlo time-dependent formulation as golden standard. We study electron relaxation in different background gases (air, argon, and mixtures of both) at two pressures (10 and 100 Torr). The LEA generally provides more accurate results than the LFA, with increasing differences at lower pressures, where energy relaxation is slower. The greater accuracy of the LEA comes from the temporal effects introduced by the equation for the mean electron energy, which is absent in the LFA. Opting by the LFA in conditions of slow relaxation can lead to serious degradation of the model results, with errors on the production of excited species up to several tens of percent. Hence, in those scenarios, and when a kinetic approach is not possible, the LEA should be adopted instead of the LFA. The comparison is extended to a two-term time-dependent solver based on a quasi-stationary assumption for the first anisotropy. This method provides a good description of the electron kinetics, except at early times ($\lesssim0.2$ ns) at 10 Torr, where the quasi-stationary assumption becomes inaccurate.

The influence of sputtering parameters on the size distribution of silver (Ag) nanoparticles (NP) synthesized by sputtering onto castor oil and polyethylene glycol (PEG600) was investigated. The sputtered species arriving at the substrate were described in terms of flux and kinetic energy. In both liquids, about 99% of the NPs measured were ⩽5 nm in diameter, with most NPs in the range 1–2 nm and 1–2.5 nm in PEG600 and castor oil, respectively. Overall, larger NPs were obtained in castor oil than in PEG600 (40%–55% and 8%–35% of NPs >2 nm in castor oil and PEG600, respectively). In PEG600, the grey color of the solutions indicated aggregation, already after deposition. The flux variation, ranging from ∼120 to 300 µg·cm⁻²·min⁻¹, did not appear to strongly influence the NP size. Larger proportions of NPs >2 nm seemed primarily triggered by higher kinetic energies, as almost 30% more NPs >2 nm were counted for kinetic energies of 12–18 eV compared to 3–6 eV. The castor oil solutions exhibited an orange color, suggesting no notable aggregation of the NPs. The size distributions were not significantly dependent on flux and kinetic energy, as the proportion of NPs <2 nm varied from 45%–59% for all conditions studied here. This difference in behavior between liquids was attributed to their chemical structures, governing the NP coordination. Hence, limiting the species mobility, the higher coordinating castor oil restricted NP aggregation. While the sputtering parameters influenced the NP size differently depending on the liquid chemistry, their impact on the NP size was overall limited in the deposition parameter range investigated herein.

Working reliably at elevated operating temperatures is a key requirement for semiconductor lasers used in optical communication. InAs/GaAs quantum-dot (QD) lasers have been considered a promising solution due to the discrete energy states of QDs. This work demonstrates temperature-insensitive and low threshold InAs/GaAs QD lasers incorporating co-doping technique, compared with p-type modulation doping. 2 mm long co-doped QD lasers exhibit a low threshold current density of 154 A cm⁻² (210 A cm⁻²) and operate at a high heatsink temperature of 205 °C (160 °C) under the pulsed (continuous-wave) mode, outperforming the p-type doped QD lasers. The results reveal that co-doping effectively enhances both high-temperature stability and threshold reduction in InAs/GaAs QD lasers, surpassing the performance of conventional p-type modulation doping. This approach offers a pathway toward cooling-free operation, making co-doped QD lasers suitable for data and telecommunication applications.

This study delves into the intriguing phenomenon of unidirectional reflectionlessness (UR) in the context of exceptional points (EPs) in a non-Hermitian plasmonic system. Unlike traditional Hermitian systems, non-Hermitian systems provide a distinct domain for the manifestation of UR. Here, we investigate the role of EPs in facilitating UR in terahertz plasmonic metasurfaces. These metasurfaces mimic a non-Hermitian system featuring near-field coupled split ring resonators (SRRs). At EP, we identify backward reflectionlessness occurring at 0.43 THz for one polarization of the incident terahertz probe. Further, we elucidate the intricate interplay between near-field coupling dynamics and the emergence of UR through systematic simulations and experimental validations. Our findings reveal that optimizing inter-SRR near-field coupling can enable precise control over UR, revealing an optimal inter-SRR separation of 2.85 µm (λ/240), where UR is achieved with an asymmetry factor Λ = 1. Conversely, while perfect UR is not observed for the orthogonal probe polarization, the reflection minima are observed for the backward direction as well. These insights underscore the significance of EPs in tailoring the reflection characteristics of planar metasurfaces by embracing the inherent richness of non-Hermitian physics, which can pave the way toward the development of unidirectional devices with enhanced functionality and performance, unlocking unprecedented opportunities for tailoring light–matter interactions.

Rapid electric field–induced second harmonic generation measurements are performed using a laser optical loop approach, which facilitates the use of each single laser shot several times. From a single laser shot, E-FISH signals at multiple points in the time domain are generated and recorded as a single waveform. It is also demonstrated experimentally that the polarization-sensitive nature of E-FISH allows to tailor the E-FISH response sensitivity within the pulse train traveling in the optical loop to optimize the measured signal waveform for a given electric field profile while avoiding the saturation of the detector and extending the dynamics range of the measurements.

This Roadmap surveys the diversity of different approaches for characterising, modelling and designing metamaterials. It contains articles covering the wide range of physical settings in which metamaterials have been realised, from acoustics and electromagnetics to water waves and mechanical systems. In doing so, we highlight synergies between the many different physical domains and identify commonality between the main challenges. The articles also survey a variety of different strategies and philosophies, from analytic methods such as classical homogenisation to numerical optimisation and data-driven approaches. We highlight how the challenging and many-degree-of-freedom nature of metamaterial design problems call for techniques to be used in partnership, such that physical modelling and intuition can be combined with the computational might of modern optimisation and machine learning to facilitate future breakthroughs in the field.

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.

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.

This Roadmap surveys the diversity of different approaches for characterising, modelling and designing metamaterials. It contains articles covering the wide range of physical settings in which metamaterials have been realised, from acoustics and electromagnetics to water waves and mechanical systems. In doing so, we highlight synergies between the many different physical domains and identify commonality between the main challenges. The articles also survey a variety of different strategies and philosophies, from analytic methods such as classical homogenisation to numerical optimisation and data-driven approaches. We highlight how the challenging and many-degree-of-freedom nature of metamaterial design problems call for techniques to be used in partnership, such that physical modelling and intuition can be combined with the computational might of modern optimisation and machine learning to facilitate future breakthroughs in the field.

Plasmonic metamaterials and all-dielectric metamaterials, based on metallic or dielectric nanostructures, can concentrate light into subwavelength regions and manipulate light at nanometre length scales through the collective oscillation of free electrons in a metal (plasmon resonances) or from the oscillation of polarization charges and the circular displacement current that are excited inside dielectric material (Mie resonances). However, the plasmonic nanostructures undergo large Joule losses and inevitable thermal heating. The all-dielectric metamaterials may overcome the critical issue of heat dissipation and could bridge the gap between fundamental nanoscience and devices. The dielectric resonance elements can be excited by electric and magnetic Mie resonances, and these Mie-type resonance modes can couple or interfere with each other or with other optical modes. Specially, while the radiation of the electric dipole and toroidal dipole modes are similar and in opposite phases, the total scattering cancelation in the far field is reduced to zero, i.e. non-radiating anapole dark state is generated. By manipulating of interaction of multipolar resonances in structured materials, the new field of all-dielectric resonant meta-optics has achieved rapid development. Here, we review the recent development of anapole dark state in dielectric metamaterials, including excitation, probing, coupling, and manipulation. We further discuss the potential applications of anapole state in nanophotonics. This review provides new insights into anapole physics, discussing its excitation, probing, coupling, manipulation, and potential applications in dielectric metamaterials, as well as hybrid and metal structures. We highlight the unique advantages of dielectric platforms, particularly their low-loss characteristics, and explore how these properties enable advanced control of light at the nanoscale.

Surface-sensitive optical microscopies are able to study light-matter interactions occurring in the near-field area on a metallic surface and have been widely applied in the fields of biomedicine, material science, nanophotonics, surface chemistry, etc. As one of such microscopies, surface plasmon resonance holographic microscopy (SPRHM) has been proved to be a powerful tool for exploring samples of interest in the near field. Basically, SPRHM combines digital holography, which can measure complex amplitudes of object waves, with the surface plasmon resonance (SPR) sensing technique, which possesses high sensitivity with tiny changes of physical parameters in the near field. SPRHM provides SPR intensity and phase images simultaneously to visualize extremely weak interacting phenomena in a wide-field and label-free manner with high detection sensitivity. Up to now, SPRHM has demonstrated its capabilities in investigating cell-substrate interactions, mapping thickness distribution of thin films, measuring complex refractive index of 2D materials, etc. In this review, we outline the development trace of SPRHM, elucidate its principle and implementation methods, introduce the experimental setups which feature the common-path hologram recording structures, and summarize its applications. Furthermore, important issues regarding the dynamic range and spatial resolution of SPRHM are discussed in detail and the research perspective is given.

Whether in the form of zinc blende, wurtzite, or a composite structure of the two, silicon carbide (SiC) crystals possess a pair of polar crystal faces along the stacking direction of Si–C bilayers, namely the Si-face and the C-face. These two faces have different atomic structures and surface properties, resulting in anisotropic and surface polarity (SP)-dependent effects on growth and mechanical processing of SiC materials and electrical performance of SiC-based devices. Although much effort has been spent on the studies of the SiC polarity and SP-dependent effects, no systematic review of these studies has been reported. Herein, we aim to comprehensively outline the main aspects of the polarity-dependent effects of SiC, starting from the origin of polarity and culminating in a discussion on how SP affects device performance. Along the way, we will cover several methods for identifying SP and SP-dependent effects on crystal growth, mechanical processing and heteroepitaxy. The particular significance of this study lies in providing a clear research framework and overview that serves as a reference for future research and applications.

In the early stages of introducing the term superatom to describe atomic clusters exhibiting chemical properties similar to periodic table elements, the electronic structures of these clusters were understood through simplified calculations based on the jellium model with spherical potential. Against this backdrop, a superatomic physical image based on the sequence of electronic energy levels predicted by the model was formed. In this work, the analysis of the development of superatoms first indicates that, due to their non-ideal spherical structures, density functional theory calculations that take into account realistic atomic potential without relying on the simplified jellium sphere model can yield more reliable results. Although the electronic structure of some single-element atomic clusters under this calculation may agree with the results of jellium model, their orbitals with the same angular momentum actually split. Moreover, in more complex multi-element systems, the sequence may change further. Nevertheless, these systems still maintain well-defined electronic shell structures, allowing them to be classified as superatoms. This work also verifies these findings through calculations of specific stereoscopic, planar and compressed superatoms. Thus, superatoms intrinsically surpass the results from the jellium model approximation, the realistic atomic potential provides more detailed insights into their electronic structures. This finding will contribute to both fundamental and applied research of superatoms.

In this article, a degradation mechanism based on electric field reconstruction was proposed to evaluate the impact of heavy ion irradiation on the gate oxide of 1200V SiC MOSFETs with planar gate structure. Experimental tests were firstly conducted by starting with a low VDS, which was gradually increased in steps of 20V, using 181Ta heavy ion species with an energy of 1483MeV. Notably, the real-time monitoring data showed observable changes in the increasing rate of gate leakage current (IGSS) in the high VDS region (i.e., when VDS exceeded 320V in this experiment). For mechanism analysis of such experimental phenomena, TCAD simulations were carried out. Simulation results revealed that the gate oxide degradation was influenced by the coupling of two mechanisms, with ion strikes generating two electric field peaks corresponding to different physical processes. The first peak was attributed to conventional hole accumulation in the JFET region, while the second peak resulted from electric field reconstruction caused by the activation of the parasitic bipolar junction transistor (BJT). It was found that the second electric field peak which continued to rise as VDS increased plays a dominant role in gate oxide degradation under high VDS conditions, resulting in a change in the increasing rate of IGSS. Furthermore, simulation results showed that the second electric field was less influenced by the ion strike position or the width of the JFET region, indicating that the electric field reconstruction could be triggered in almost any location within the active area and the traditional radiation hardness technique of optimizing JFET structures was ineffective.

In this article, we investigate parity-time (PT) symmetry in a non-Hermitian terahertz (THz) metasurface comprising orthogonally placed metallic resonators exhibiting toroidal behaviour. The metals with different conductivity are diagonally placed in close proximity. The PT symmetry nature is observed when toroidal resonators are displaced diagonally owing to strong near-field coupling between resonators. This is observed through the appearance of exceptional point (EP) when resonators are displaced to a certain distance leading to optimal coupling. Beyond EP, the proposed metasurface design undergoes a sudden change from unbroken to broken phase resulting in transformation from PT symmetric to PT asymmetric state. These observations are also apparent from the measurements of eigenvalues, phase spectra and eigenstates at different displacement values of one toroidal resonator with respect to other. We suggest coupled mode theory to validate the numerically obtained transmission results. Further Poincaré sphere and circular transmission components are reported to understand the emergence of exceptional point and hence the PT symmetry in toroidal metasurface. The study reported here enhances the fundamental understanding on PT symmetry and its emergence in terahertz metasurface via toroidal excitations which can pave the way to innovative applications such as enhanced sensing, phase and polarization modulation etc.

Neuromorphic devices, with their distinct advantages in energy efficiency and parallel processing, are pivotal in advancing artificial intelligence applications. Among these devices, memristive transistors have attracted significant attention due to their superior stability and operation flexibility compared to two-terminal memristors. However, the lack of a robust model that accurately captures their complex electrical behavior has hindered further exploration of their potential. In this work, we introduce the GEneral Memristive transistor (GEM) model to address this challenge. The GEM model incorporates time-dependent differential equation, a voltage-controlled moving window function, and a nonlinear current output function, enabling precise representation of both switching and output characteristics in memristive transistors. Compared to previous models, the GEM model demonstrates a 300% improvement in modeling the switching behavior, while effectively capturing the inherent nonlinearities and physical limits of these devices. This advancement significantly enhances the realistic simulation of memristive transistors, thereby facilitating further exploration and application development.&#xD;

Ion-induced condensation has attracted increasing attention in the field of atmospheric precipitation. Supersaturation plays an important role in promoting vapour condensation. This study explores the interaction between supersaturated vapour and corona discharge by examining the characteristics of negative corona discharge in a steam jet and its effect on the condensation of supersaturated steam. Experiments were conducted using two steam jets with different degrees of supersaturation. The voltage–current curve of the corona discharge and the distribution characteristics of the droplet size and concentration along the central axis of the steam jet were evaluated. The results showed that the steam jet suppressed the corona discharge, while the corona discharge enhanced condensation within the jet. The concentration of condensed droplets in steam jets with higher supersaturation was more strongly influenced by corona discharge than in jets with lower supersaturation. Calculations indicated that the attachment coefficient in supersaturated water vapour was higher than in air, contributing to the suppression of the corona discharge within the steam jet. Ions introduced by the corona discharge reduced the Gibbs free energy required for droplet condensation in the steam jet, with a greater reduction in highly supersaturaed steam jets. These findings provide insights into the mechanisms through which corona discharge influences steam jet condensation, suggesting potential applications in optimizing charged steam jets.

Nitrogen activation by the clean solar energy is a promising way to break through the bottlenecks of industrial ammonia production with harsh conditions. However, limited interfacial charge transfer of photocatalysts is a rate-determining factor of photocatalytic nitrogen reduction reaction. Herein, C-In2O3@CuInS2 with carbon support synthesized from the calcination of MIL-68 (In) under argon and sequential solvothermal method, which significantly enhanced the catalyst activity with the optimal performance of 33.38 μmol·g-1·h-1 compared to C-In2O3 (Trace) and CuInS2 (9.494 μmol·g-1·h-1). Crucially, the experimental results showed photocatalyst with carbon support can greatly improve the separation and migration of photocarriers by making comparison of ammonia yield and electrochemical testing of C-In2O3@CuInS2 and In2O3@CuInS2. The work lays the foundation for constructing heterojunctions for photocatalytic nitrogen fixation from the perspective of enhancing photogenerated carrier migration rate.

Rapid electric field–induced second harmonic generation measurements are performed using a laser optical loop approach, which facilitates the use of each single laser shot several times. From a single laser shot, E-FISH signals at multiple points in the time domain are generated and recorded as a single waveform. It is also demonstrated experimentally that the polarization-sensitive nature of E-FISH allows to tailor the E-FISH response sensitivity within the pulse train traveling in the optical loop to optimize the measured signal waveform for a given electric field profile while avoiding the saturation of the detector and extending the dynamics range of the measurements.

This Roadmap surveys the diversity of different approaches for characterising, modelling and designing metamaterials. It contains articles covering the wide range of physical settings in which metamaterials have been realised, from acoustics and electromagnetics to water waves and mechanical systems. In doing so, we highlight synergies between the many different physical domains and identify commonality between the main challenges. The articles also survey a variety of different strategies and philosophies, from analytic methods such as classical homogenisation to numerical optimisation and data-driven approaches. We highlight how the challenging and many-degree-of-freedom nature of metamaterial design problems call for techniques to be used in partnership, such that physical modelling and intuition can be combined with the computational might of modern optimisation and machine learning to facilitate future breakthroughs in the field.

Atmospheric plasma jets enable the precise generation and transport of reactive oxygen and nitrogen species (RONS) to a designated target, making them particularly valuable for applications in plasma medicine. In these contexts, it is crucial to understand their generation mechanisms in the plasma and interactions with the surrounding atmosphere during transport. This is studied for the hydroxyl (OH) radical in the COST reference microplasma jet (COST-Jet) operated with helium (He) feed gas. Using laser-induced fluorescence (LIF) spectroscopy, the radical's absolute density in the jet's effluent is resolved in all three dimensions. By separately controlling the humidity levels in the feed gas and ambient air atmosphere, the plasma and post-plasma generation of OH is explored. When water vapor is added to the feed gas, comparably high and homogeneously distributed OH densities (∼1 × 10¹⁴ cm⁻³) occur at the jet's nozzle showing a rapid radial and axial decay down the effluent. In contrast, OH production from ambient moisture alone is observed only at the interface between the He effluent and the surrounding air, resulting in densities roughly one order of magnitude lower. Higher relative humidities in the surrounding air cause the OH density peak to shift closer to the nozzle in every direction, as moisture penetrates deeper into the effluent.

Memristor-based analog in-memory learning (AIML) has emerged as a promising approach to improve energy efficiency in deep neural network training. However, non-idealities in memristive devices, such as nonlinearity, asymmetry, and cycle-to-cycle and device-to-device variations, pose significant challenges. These issues lead to increased energy consumption, reduced write precision, and compromised in-situ learning performance. To address these problems, we propose a mixed-precision training strategy that combines gradient accumulation with single pulse blind write method. We analyze the failure mechanisms of in-situ learning without these techniques and systematically investigate how various non-idealities affect AIML performance. We demonstrate that, by using our GA-Single Pulse strategy, high accuracy (95.36%) can be achieved even under significant non-idealities, including device conductance states being limited to 10 pulses for potentiation as well as 5 pulses for depression, the asymmetry of conductance state constrained to a factor of 2, the nonlinearity in LTP/LTD curve reaching up to 5, C2C variation as high as 50%, and device-to-device variation extending up to 40% for learning handwritten digits in MNIST handwritten digit dataset, outperforms all previous reports. The results suggest that the idealities of memristive devices may not be as critical as previously assumed for AIML's practical deployment.

The modeling of deposition rates in thermal laser epitaxy (TLE) is essential for the accurate prediction of the evaporation process and for improved dynamic process control. We demonstrate excellent agreement between experimental data and a model based on a finite element simulation that describes the temperature distribution of an elemental source when irradiated with continuous wave laser radiation. The simulation strongly depends on the thermophysical constants of the material, thermal conductivity, specific heat capacity, density, reflectivity and thermal emissivity, data of which is lacking for many elements. Effective values for the parameters may be determined with precision by means of an unambiguous reference provided by the melting point of the material, which is directly observed during the experiments. TLE may therefore be used to study the high temperature thermophysical and optical properties of the elements.

Hexagonal boron nitride (h-BN) has emerged as a critical thermal management material in electrical insulation systems due to its superior thermal conductivity and dielectric properties. Nevertheless, suboptimal filler-matrix interfacial compatibility hinders both thermal conductivity enhancement and dielectric performance in composites. This study introduces an innovative plasma bubble treatment strategy, utilizing the discharge within bubbles to simultaneously achieve h-BN exfoliation and surface hydroxylation. By producing plasma in a 3% H₂O₂ solution with Ar/O₂ mixed gas, hydroxyl groups are successfully grafted onto h-BN surfaces. This surface modification improves the silane grafting efficiency with KH560, resulting in improved filler dispersion within the epoxy resin (EP) and the introduction of deep charge traps in interfacial regions. Under 9.77 W discharge power, composites containing 20 wt% h-BN treated for 10 min exhibits optimal performance characteristics. The modified composite attains a 327% thermal conductivity of pure EP while showing superior dielectric properties with a 12.4% increase in breakdown strength relative to untreated composite. These findings present an effective surface engineering approach for developing high-performance polymer composites for electrical insulation applications.

A comprehensive experimental investigation into the switching behavior of CO2-based SF6 alternative gas mixtures under short-line fault-like conditions has been performed at ETH Zurich. The first part of this study presented a validation of the experimental methodology, and showed the dependence of the interruption limit in these mixtures on the blow pressure and arc length at current zero. The second part presented here will explore how modifications to the flow conditions through nozzle shape parameters can influence the interruption performance, and extend conclusions drawn in Part I regarding the insensitivity of the interruption performance to arc length. Measurements using different nozzle expansion angles show that this insensitivity applies more broadly to all conditions downstream of the nozzle throat, including the location of the shock in the diverging region of the nozzle. The influence of nozzle erosion was also investigated, where it was found in a severely eroded nozzle that the hot-dielectric performance deteriorated while the thermal performance remained similar when the same pu = 10.8 bar blow pressure was maintained. The experimental results further demonstrate that lu, the length of a nozzle's upstream acceleration zone, is a key parameter that should be limited in order to reduce hot-dielectric failures. The investigation was aided by a one-dimensional arc model introduced herein, that was used to inform nozzle design choices and better understand experimental results. The modeling results reveal that extending lu reduces flow acceleration, limiting the convective cooling in the stagnation zone, potentially offering a physical explanation for the experimentally observed decline in hot-dielectric performance with increasing values of lu.

A comprehensive experimental investigation into the short-line fault (SLF) switching behavior of CO2-based SF6 alternative gas mixtures has been performed at ETH Zurich. An initial investigation into mixture composition sensitivity showed similar thermal interruption performance among all CO2-based mixtures, but also revealed that under SLF-like conditions, those mixtures that do not contain fluorinated additives may suffer hot-dielectric failures that reduce their overall interruption limit. The first part of the parameter study presented here is focused on relating the results of experimental investigations into the parameter dependence of current interruption in CO2-based mixtures, particularly the dependence on blow pressure and arc length at current zero. A detailed examination of these dependencies was made possible by the high level of control, reproducibility, and number of tests afforded by an experimental puffer circuit breaker. The experimental approach and statistical methodology for evaluating a very large dataset of such interruption tests is introduced and rigorously validated in order to establish the uncertainties sufficiently for clear conclusions to be drawn. Part II will go on to examine how modifications to the flow conditions through nozzle shape parameters can influence the interruption performance, and will more closely examine the findings of the study with the aid of a 1-D arc model.

Nanosecond discharges are characterized by a shift in energy branching toward the excitation of electronic levels and dissociation, making them particularly attractive for plasma chemistry. Understanding the spatio-temporal structure of these discharges is especially important. This paper presents a detailed 2D-axisymmetric numerical analysis of a nanosecond discharge propagating in a long tube and in pure nitrogen. The modeling is conducted using a self-consistent plasma fluid solver under the local mean energy approximation, including photoionization. The discharge develops at moderate pressures, 1–10 Torr, in the form of a fast ionization wave (FIW). Simulations are performed for both negative and positive polarities of the voltage pulse applied to the high-voltage electrode. The computational results are validated against available experimental data, including FIW velocity within the studied pressure range, electron density, longitudinal electric field, and the radial distribution of N₂(C$^3\Pi_u$) emission on a nanosecond timescale.

Contact Glow Discharge Electrolysis (CGDE) denotes a plasma inside a vapor layer surrounding a gas-evolving electrode immersed in an aqueous electrolyte and operated at high voltages.&#xD; We used a high-speed camera to image the formation of the vapor layer as well as its dynamic behavior during continuous CGDE on a Au wire cathode.&#xD; The plasma ignites with a spark within a large bubble at the tip, which expands along the wire to the top, leaving a stable glow within the vapor layer behind.&#xD; Using an in-house developed open-source Python-based software we deduced, from a thorough statistical analysis of images taken during continuous CGDE, a vapor layer thickness between 0.1 and 0.4 mm. &#xD; Furthermore, we provide information on the dynamic behavior of individual discharges through the vapor layer from a series of images. The discharges are confined within the vapor layer and, thus, the extent of the discharges is similar to the vapor layer thickness. &#xD; We find that the discharges have approximately the shape of oblate spheroids, which appear either as circles or ellipses in the camera images, depending on the orientation of the discharge with respect to the camera.&#xD; We discuss the relevance of our results for the fundamental understanding of atomic scale surface structural changes and products formed in the solution in the presence of the plasma.