Journal of Physics D: Applied Physics

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.

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.

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.

Over the past 3 decades, phononic crystals experienced revolutionary development for understanding and utilizing mechanical waves by exploring interaction between mechanical waves and structures. With the significant advances in manufacture technologies from nanoscale to macroscale, phononic crystals attract researchers from diverse disciplines to study abundant directions such as bandgaps, dispersion engineering, novel modes, reconfigurable control, efficient design algorithms and so on. The aim of this roadmap is to present the current state of the art, an overview of properties, functions and applications of phononic crystals, opinions on the challenges and opportunities. The various perspectives cover wide topics on basic property, homogenization, machine learning assisted design, topological, non-Hermitian, nonreciprocal, nanoscale, chiral, nonlocal, active, spatiotemporal, hyperuniform properties of phononic crystals, and applications in underwater acoustics, seismic wave protection, vibration and noise control, thermal transport, sensing, acoustic tweezers, written by over 40 renown experts. It is also intended to guide researchers, funding agencies and industry in identifying new prospects for phononic crystals in the upcoming years.

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.

Sun, wind and tides have huge potential in providing us electricity in an environmental-friendly way. However, its intermittency and non-dispatchability are major reasons preventing full-scale adoption of renewable energy generation. Energy storage will enable this adoption by enabling a constant and high-quality electricity supply from these systems. But which storage technology should be considered is one of important issues. Nowadays, great effort has been focused on various kinds of batteries to store energy, lithium-related batteries, sodium-related batteries, zinc-related batteries, aluminum-related batteries and so on. Some cathodes can be used for these batteries, such as sulfur, oxygen, layered compounds. In addition, the construction of these batteries can be changed into flexible, flow or solid-state types. There are many challenges in electrode materials, electrolytes and construction of these batteries and research related to the battery systems for energy storage is extremely active. With the myriad of technologies and their associated technological challenges, we were motivated to assemble this 2020 battery technology roadmap.

We present a method for a precise determination of magnetic anisotropy and anisotropy of quadratic magneto-optical (MO) response of thin films of ferromagnetic and ferrimagnetic materials. The method is based on measurements of a MO response for light close to the normal incidence on the sample with a fixed position. The measurement is performed for a set of orientations of an external magnetic field and a series of incident light linear polarizations beyond the standard s and p orientations. Based on the symmetry of the signal, we are able to separate the part of MO response that is even with respect to magnetization and, in turn, to exclude all non-magnetic contributions which come from imperfections of the experimental setup or from the sample itself. It is, therefore, possible to study the sample placed inside a cryostat: the polarization changes due to cryostat windows and possible strain-induced optical anisotropy of the sample are removed by the applied data processing. Thanks to this, we can perform measurements on low or elevated temperatures (from 15 to 800 K in our case), making it possible to study the behavior of magnetic materials in different magnetic phases and/or close to phase transitions. The applicability of this experimental technique was tested by measuring the low-temperature response of two samples of ferromagnetic semiconductor (Ga,Mn)As with a different Mn content at several wavelengths, which enabled us to deduce the magnetic and quadratic MO anisotropies in this material. In particular, we observed that the anisotropy of quadratic MO coefficients in (Ga,Mn)As is much weaker than that reported previously for other magnetic material systems.

CO₂ has recently emerged as a leading candidate in the search for a more environmentally friendly alternative to SF₆. In high voltage circuit breakers, where the gas serves dual roles as both gaseous insulation and switching medium, commercially available solutions use CO₂ either alone or as the primary component of a mixture. In order for breakers to reach the level of performance necessary to support growing energy demands, a thorough understanding of the transient arc properties of CO₂ during the current interruption process is urgently needed. In support of these efforts, an experimental puffer circuit breaker has been developed to study thermal interruption in these gases with a high degree of control, under conditions otherwise comparable to a commercial breaker exposed to short-line fault-like current and voltage stresses. This test setup was used together with a suite of optical diagnostics including high-speed imaging and optical emission spectroscopy, with the main goal of measuring the temporal evolution of a CO₂ arc's radial temperature profile in the stagnation region near the instant of current interruption. To achieve this goal, a novel diagnostic technique—intensified video optical emission spectroscopy—has been applied for detailed analysis of plasma properties. This advanced technique allows for evaluation of time-dependent temperature decay with microsecond resolution through current zero, which is not possible with other emission spectroscopy methods. This method has allowed for the time-evolution of the decaying arc's temperature profile to be characterized for the first time throughout the decisive period surrounding current zero, under conditions relevant for thermal current interruption in commercial high voltage circuit breakers. Results showing temporal evolution can be obtained within one shot, and thus be separated from effects of nozzle aging. Results showed little temperature variation more than 50 µs before current zero, with changes in current mainly found to affect the arc cross-section. Fast temperature decay was limited to a period within 20 µs of current zero, when maximum temperatures were found to drop from 12 000 K to 7000 K, with a stable temperature near 6000 K measurable up to 40 µs after current interruption. The results also revealed the influence of nozzle erosion on the arc temperature profile, showing that fresh nozzles provide stronger cooling, resulting in a higher temperature, more constricted arc.

Phase-change memory (PCM) is an emerging non-volatile memory technology that has recently been commercialized as storage-class memory in a computer system. PCM is also being explored for non-von Neumann computing such as in-memory computing and neuromorphic computing. Although the device physics related to the operation of PCM have been widely studied since its discovery in the 1960s, there are still several open questions relating to their electrical, thermal, and structural dynamics. In this article, we provide an overview of the current understanding of the main PCM device physics that underlie the read and write operations. We present both experimental characterization of the various properties investigated in nanoscale PCM devices as well as physics-based modeling efforts. Finally, we provide an outlook on some remaining open questions and possible future research directions.

The organic-inorganic hybrid MAPbI₃ perovskite material has remarkable optoelectronic properties for excellent device performance. However, the poor long-term stability of MAPbI₃ perovskite in light, heat, and humid environments is a major obstacle to commercialization. Degradation of MAPbI₃ and an impairment in non-radiative charge recombination, a major impediment to increasing the stability and efficiency of photovoltaic devices, are made possible by the trap state and surface imperfections between the perovskite and electron transport layer interfaces. Here, the surface defect was healed by 2-amino benzothiazole (2-ABT) (Lewis's base) by activating the heteroatoms of S and N and the amine functional group for defect passivation. In the context of defect passivation, a systematic investigation is conducted on the formation of hydrogen bonds between N–H–I or the coordination between uncoordinated Pb²⁺ and heteroatoms of S and N. The investigations have been done into the optoelectronic properties, chemical interaction, structure, crystal orientation, morphology, and photovoltaic performance characteristics of MAPbI₃ in association with 2-amino benzothiazole surface integration. A high photovoltaic efficiency of 21.5% with improved open circuit voltage (V_oc) and fill factor was demonstrated with the optimum concentration of passivating material (2 mg ml⁻¹ IPA) than the pristine MAPbI₃ PCE of 19.4%. As demonstrated by stability studies, the 2-ABT integrated device outscored the pristine MAPbI₃ device, retaining 87% of its PCE after 500 h.

Experimental evidence indicates that significant exchange coupling may exist between magnetic nanoparticles (MNPs) in dense MNP aggregates such as nanoflower clusters. Here, we examine the role of inter-particle exchange interactions in determining the magnetic properties of MNP clusters, in particular their athermal hysteresis in a low-frequency alternating field. We consider mechanically fixed close-packed clusters where each particle is modeled as a single macrospin coupled to the others by both dipolar interactions and nearest-neighbor exchange. Upon simulating the quasi-static hysteresis curves, we compute the loop area, remanent moment and coercive field, and we classify each curve by its shape. Computing curve types across parameter space reveals how their shape is determined by the interplay between exchange coupling, dipolar interactions, and uniaxial anisotropy. Strong exchange coupling produces fully saturated loops with coherent moment rotation. Moderate exchange and anisotropy result in magnetically soft clusters with high susceptibility. Finally, for complex clusters, weak to moderate exchange and strong anisotropy may produce highly irregular curves with several abrupt changes in magnetization. Our analysis demonstrates that exchange coupling between MNPs significantly increases the cluster energy product, thereby contributing to explain the exceptional heating power of nanoflowers.

This study evaluates the erosion resistance and thermal stability of Cu/W–La₂O₃ composite electrodes exposed to plasma arc conditions in ambient air. Through comparative analysis with pure copper and W–La₂O₃ electrodes, it was found that the Cu/W–La₂O₃ composites exhibit superior erosion resistance, with a notably advantageous negative erosion rate due to a self-formed oxide layer that mitigates surface degradation. Detailed microstructural characterization revealed that this oxide layer, primarily consisting of copper tungstates and lanthanum tungstates, enhances electrode durability by reducing oxidation rates and improving heat dissipation. This adaptive surface layer also contributes to a more stable arc, effectively minimizing material loss, particularly at higher current intensities where pure copper electrodes experience rapid thermal and oxidative degradation. The findings suggest that Cu/W–La₂O₃ composites, with their negative erosion rates, offer significant benefits for air plasma torches, making them promising candidates for applications demanding high-performance and long-lasting electrodes in oxidizing environments.

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.

This paper presents a design strategy for highly compact filters based on ${\lambda _g}/4$ effective localized surface plasmons (ELSPs). Leveraging the robustness of ELSPs to their cross-sectional shapes, the proposed design facilitates easier integration into printed circuit boards (PCBs). However, challenges such as dielectric material stacking and excessive lateral dimensions remain. By employing ${\text{ }}{\lambda _g}/4$ ELSPs, the longitudinal size of the ELSPs-based filters is significantly reduced. Furthermore, embedding the ELSPs directly into the PCB effectively solves the stability problems associated with dielectric material and PCB stacking in conventional dielectric resonator filters, while minimizing the overall filter size. To demonstrate this approach, third-order, fourth-order, and fifth-order ELSPs-based filters were fabricated on a single-layer PCB, achieving center frequencies of 3.6 GHz with fractional bandwidths of 9.3%, 5.1%, and 7.7%, respectively. Experimental results show excellent agreement with simulations. This work provides an ultra-compact filtering solution for next-generation microwave and radio-frequency devices, particularly for applications in 5G and satellite communications.

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.

Carbon fiber reinforced polymer composites (CFRPs) are widely used in aerospace, transportation, and defense industries due to their excellent properties such as lightweight, high specific strength and stiffness, superior thermal stability, and corrosion resistance. However, the smooth and chemically inert surface of carbon fiber (CF) results in poor interfacial adhesion between the fiber and matrix, thereby impacting the mechanical performance of CFRPs. To address this issue, nanomaterials have been introduced to the fiber surface, leveraging their exceptional mechanical properties and large specific surface area to enhance the interfacial properties of CFRPs. Compared to conventional modification methods like sizing, plasma treatment, and oxidation treatment, nanomaterials provide a superior approach by creating a robust transition layer at the interface. This layer can enhance mechanical interlocking, balance the modulus of the CF with that of the matrix, and effectively disperse interfacial stress, thus improving load transfer from the matrix to the fiber. This review examines recent advances in CF surface modification using nanomaterials and discusses the mechanisms behind interfacial enhancement. It also explores the potential future directions for research in this field, aiming to promote nanomaterial applications for advancing the use of higher-performance CFRPs from lab to industry.

Metabolic heterogeneity within tumors is a key driver of drug resistance, as distinct subpopulations adapt to the tumor microenvironment by exploiting specific metabolic pathways. This diversity enables certain subpopulations to evade therapeutic intervention, thereby leading to therapy failure and cancer relapse. Metabolic reprogramming exacerbates resistance by enabling cancer cells to modulate their metabolic pathways to counteract therapeutic pressures, promoting the survival of resistant subpopulations. Traditional metabolic analyses generally measure average metabolite levels across cell populations, while Raman metabolic imaging offers a more precise, subcellular perspective, enabling non-destructive and real-time monitoring of dynamic metabolic processes related to drug resistance. Our review highlights advancements in Raman spectroscopy and microscopy, and explores their applications in cancer drug resistance research. We focus on their role in revealing intratumoral metabolic heterogeneity, monitoring metabolic reprogramming in drug-resistant cells, and enabling rapid cancer drug sensitivity evaluation.

Graphene is an atomically thin material composed of a single layer of carbon atoms arranged in a hexagonal lattice, which exhibits unique electrical, thermal, and mechanical properties. The intentional introduction of foreign atoms into the structure of graphene by doping is a powerful approach for modifying these properties, making graphene suitable for a range of advanced applications. Among the various synthesis techniques, chemical vapor deposition (CVD) is particularly effective for doping because it allows precise control over the growth conditions and dopant incorporation, outperforming other synthesis strategies in terms of scalability, uniformity, and clean growth. This review examines how solid, liquid, and gaseous precursor types play crucial roles in CVD doping, directly affecting the growth dynamics, doping efficiency, and material quality. By analyzing the mechanisms associated with each precursor form, this review highlights how these strategies address the challenges of achieving consistent and high-quality doped graphene. This discussion provides valuable insight into advancing CVD techniques for producing doped graphene with enhanced properties for cutting-edge applications.

Temperature significantly impacts responsivity, detectivity, and stability of photodetectors, which are crucial for converting optical signals to electrical signals in applications like optical communication and imaging. WS₂, a transition metal dichalcogenide with tunable band gaps and high carrier mobility, shows promise in optoelectronics. However, previous studies on WS₂ nanotube-based photodetectors primarily focused on room temperature conditions and traditional synthesis methods, which have limitations in morphology control and reproducibility. In contrast, this study explores the temperature-dependent performance of WS₂ nanotube-based photodetectors synthesized via a gold nanoparticle-catalyzed chemical vapor deposition process. This method allows for better control over the nanotube morphology and size. The optoelectronic properties, including responsivity and detectivity, were evaluated across a temperature range of 50–300 K. Results show that the photodetectors exhibit enhanced on-off ratios and reduced dark currents at lower temperatures, improving signal-to-noise ratios. The devices also demonstrated excellent stability over multiple cycles, as well as consistent performance under varying optical power densities. These findings highlight the potential of WS₂ nanotube photodetectors for applications in extreme temperature environments, such as space communication and low-temperature optical imaging systems, where devices must operate under harsh environmental conditions.

The phase-field (PF) method is commonly used for modeling phase transitions in materials. The evolution of electrical trees in dielectric materials represents a typical phase transition process. However, in the case of dielectric nanocomposites, the interfacial region plays a crucial role in overall performance but has been largely overlooked in PF modeling. In this study, we propose a corrected PF model by incorporating an interfacial layer. Specifically, in the nano-Al2O3/epoxy resin (ER) composite, an interfacial layer that considers interfacial molecular configuration and barrier height is applied on the surface of nanoparticles. The evolution of the electrical tree is investigated across different filler contents. Furthermore, corresponding ER composites are prepared and tested to assess their insulating properties. Experimental results align well with simulation models, showing higher dielectric strength in the 0.1 vol% sample. The localized distortion of the electric field stands out as a key factor driving the evolution of electrical trees, a phenomenon that our synergistically modified PF model accurately captures. This work offers a more precise and dependable approach to modeling the evolution of electrical trees, thereby enhancing theoretical guidance for predicting the dielectric strength of nanocomposites.

Hollow cathodes are widely used as neutralizers in electric propulsion. Currently, with the trend of satellite miniaturization and diversification of space missions, alternative neutralization technology based on new materials and alternative propellants has become a hot topic. This study compared the discharge characteristics and performance of different cathode materials LaB6 and 304 stainless steel in a direct-current (DC) glow discharge hollow cathode (GDHC). Numerical and experimental investigations were conducted on the inner discharge region and outer plume region of the GDHC to analyze the plasma behavior, respectively. Experimental results show that the LaB6 configuration (adding a LaB6 insert into the 304 configuration) can effectively reduce the discharge power cost and improve the gas utilization factor. An anode current of 213.6 mA was achieved at 2 sccm of argon in the LaB6 configuration, corresponding to a discharge power cost of 182 W/A and a gas utilization factor of 1.5. The LaB6 configuration exhibits a higher discharge current, resulting in a higher plume plasma density. The simulation results show that the electron density and ion density in the cathode fall (CF) region near the LaB6 insert increase significantly, thereby improving the electron and ion conductivity, and effectively reducing the cathode fall voltage. Comparison reveals that the performance of the GDHC (LaB6) is comparable to RF cathodes and microwave cathodes with argon propellent.

Electrified transportations are playing more important role during the sustainable development of society, while much more complex environment, such as gas discharge in high altitude, should be considered for the outdoor high voltage insulation safety. The ambient air pressure and temperature are both recognized as significant factors in the streamer dynamics. Herein we established a 2D fluid plasma chemical model with a 5 mm rod-plate gap to explore streamer propagation in air at 50kPa, 233-353K. Under sub-atmospheric pressure, temperature increases from 233 K to 353 K accelerate charged particle movement, enhancing streamer velocity and radius. Meanwhile, temperature affects the ionization process. Rising temperature increases electron density in the streamer channel but reduces electric field strength at the streamer head. This study systematically investigates how electron transport coefficients, mean electron energy, space charge and effective ionization coefficients influence streamer discharge. It is observed that, in contrast to atmospheric pressure, the evolution of space charge shows an inverse trend, showing reduced space charge with rising temperature. These findings enhance understanding of sub-atmospheric streamer behavior and establish theoretical foundations for evaluating high-altitude high-voltage system insulation.

The influence of the inhomogeneities of single-walled carbon nanotube (SWCNT) film/Si
Schottky barriers on their parameters was studied by measuring the current-voltage characteristics
over a wide temperature range, from 20 K to 315 K. Data were analyzed both within the thermionic
emission theory and its modification employing the Gaussian distribution of the Schottky barrier
height. The entire temperature range was divided into three sub-ranges for an adequate description
of the experimental data. It was also necessary to consider the decrease in the effective area of the
heterojunction, caused by the morphology features of the SWCNT film, and the increasing role of
additional factors of current transport through the barrier, in addition to thermionic emission, with
decreasing temperature.

Experimental evidence indicates that significant exchange coupling may exist between magnetic nanoparticles (MNPs) in dense MNP aggregates such as nanoflower clusters. Here, we examine the role of inter-particle exchange interactions in determining the magnetic properties of MNP clusters, in particular their athermal hysteresis in a low-frequency alternating field. We consider mechanically fixed close-packed clusters where each particle is modeled as a single macrospin coupled to the others by both dipolar interactions and nearest-neighbor exchange. Upon simulating the quasi-static hysteresis curves, we compute the loop area, remanent moment and coercive field, and we classify each curve by its shape. Computing curve types across parameter space reveals how their shape is determined by the interplay between exchange coupling, dipolar interactions, and uniaxial anisotropy. Strong exchange coupling produces fully saturated loops with coherent moment rotation. Moderate exchange and anisotropy result in magnetically soft clusters with high susceptibility. Finally, for complex clusters, weak to moderate exchange and strong anisotropy may produce highly irregular curves with several abrupt changes in magnetization. Our analysis demonstrates that exchange coupling between MNPs significantly increases the cluster energy product, thereby contributing to explain the exceptional heating power of nanoflowers.

This study evaluates the erosion resistance and thermal stability of Cu/W–La₂O₃ composite electrodes exposed to plasma arc conditions in ambient air. Through comparative analysis with pure copper and W–La₂O₃ electrodes, it was found that the Cu/W–La₂O₃ composites exhibit superior erosion resistance, with a notably advantageous negative erosion rate due to a self-formed oxide layer that mitigates surface degradation. Detailed microstructural characterization revealed that this oxide layer, primarily consisting of copper tungstates and lanthanum tungstates, enhances electrode durability by reducing oxidation rates and improving heat dissipation. This adaptive surface layer also contributes to a more stable arc, effectively minimizing material loss, particularly at higher current intensities where pure copper electrodes experience rapid thermal and oxidative degradation. The findings suggest that Cu/W–La₂O₃ composites, with their negative erosion rates, offer significant benefits for air plasma torches, making them promising candidates for applications demanding high-performance and long-lasting electrodes in oxidizing environments.

Metal-oxide interactions are pivotal for the functionality of supported-metal catalysts. In this work, x-ray photoelectron spectroscopy and scanning tunneling microscopy (STM) are employed to study the interface reaction between Ti metal and crystalline Cu₂O/Pt(111) films. Already at room-temperature, deposited Ti spontaneously oxidizes to predominately +4 and +2 charge states at low and high coverage, respectively. The electron transfer is accompanied by oxygen migration towards the Ti ad-layer, whereby Cu₂O gradually reduces to Cu and Ti converts to TiO₂. The process gets reinforced by heating the system to 450 K. The local nature of the interface reaction is derived from STM conductance spectroscopy. At low Ti load, electron transfer out of the ad-layer leads to a downward bending of the Cu₂O electronic bands. With increasing coverage, the band bending ceases and formation of a Cu_xO/TiO_x hetero-junction is revealed in the spectra. The signature of metallic ad-particles is only detected at high Ti load, when electron tunneling into Ti deposits bound to the oxide spacer leads to Coulomb-charging effects. The observed strength of the redox reaction at the Ti/Cu₂O interface impressively demonstrates the high reductive power of titanium.

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.

Cold atmospheric plasma (CAP) and plasma-activated water (PAW) have emerged as promising tools with potential applications in the agricultural sector. The reactive oxygen and nitrogen species (RONS) present in CAPs and PAWs have been reported to promote seed germination, enhance plant growth, and improve stress tolerance. The objective of this study is to investigate the effects of PAW on selected maize hybrids, focusing on its application methods, including kernels priming, short cultivation, and foliar application. The application of PAW for kernel priming significantly enhanced growth, with improvements noticed in root and shoot length, leaf area, fresh weight, water uptake, and accelerated lignification. Additionally, an increase in carotenoid and phenolic concentrations was observed in the leaves. When PAW was applied during cultivation, minimal improvements were observed compared to cultivation with tap water (TW). Further, foliar application of PAW was observed to increase carotenoid content in the leaves, enhancing antioxidant capacity. This application also yielded the most notable outcomes in terms of growth parameters and carotenoid concentrations. On the other hand, it did not affect the activity of guaiacol-peroxidase (G-POX), nor did it influence the concentration of phenolics and chlorophylls. These findings collectively suggest that PAW may be beneficial for enhancing antioxidant capacity in maize, potentially improving resilience under abiotic stress. Further research into the optimization of PAW composition and timing of its application could maximise these benefits, contributing to more sustainable crop production.

We report on the key design factors for the development of Type-II 'W'-lasers for O-band (1260–1360 nm) applications. We investigate the effects of InGaAs and GaAsSb quantum well composition and thicknesses on the emission wavelength and recombination efficiency as well as of (Al, Ga) As barriers on optimum electrical and optical confinement. Photoluminescence (PL) tests structures and full device structures were fabricated and characterised. 1.25 µm emitting lasers were demonstrated with a threshold current density and J_th values of 480 ± 10 A cm⁻² at 290 K, whereas 1.3 µm lasers showed an increased J_th value of 5.5–7 kA cm⁻² at 290 K. The PL test structures exhibited a similar trend with decreasing intensity with increasing wavelength. Gain measurements of the 1.3 µm device demonstrate reasonably low optical losses of 10–15 ${\text{c}}{{\text{m}}^{ - 1}}$ and a threshold modal gain of ≈25 ${\text{c}}{{\text{m}}^{ - 1}}$.

This paper computationally investigates partial discharges (PDs) in the form of self-sustained gas discharges. It presents two methods for predictive modeling: (1) a new low-fidelity algorithm for the PD inception voltage is introduced. The method is volume-resolved and describes both the strength of the self-sustained Townsend mechanism as well as the conventional streamer (or bulk) mechanism. It also intrinsically computes the inception region, i.e. the region where a first electron also leads to a discharge. (2) We apply a high-fidelity plasma model based on kinetic Monte Carlo, which self-consistently resolves the plasma dynamics during the PD process. The two models are complementary in the sense that the low-fidelity model provides the when and where the PD occurs, while the high-fidelity model resolves the PD process itself, starting from the first electron. Prediction and quantification of the PD processes is provided for four application cases: (1) protrusion-plane gaps, (2) spherical voids, (3) twisted wire pairs, and (4) triple junctions. Validation of the low-fidelity method is done through comparison with published experiments (where available), as well as virtual verification through comparison with the high-fidelity plasma model.

The adhesion/friction interplay continues to be an enigma when soft matter is involved. By utilizing a simple two-stage (loading and then unloading) mixed-type (normal and tangential) indentation testing of a transparent layer of adhesive rubber-like gel material, the normal and tangential contact forces acting on a rigid spherical probe are monitored along with the in situ variation of the apparent contact area between the probe and the layer surface. Whereas the force/area relations for the oblique loading and normal unloading do almost coincide, as seen with the naked eye, the postpredictive analysis reveals a drastic difference in variation of the apparent work of adhesion in the concord to fluctuations of the friction force. Each of the interface slips such exposed starts with simultaneous minimum and maximum values of the normal and tangential force sensors, respectively, and proceeds with a non-monotonic variation of the contact area, indicating adhesive reattachment. The occurrence of sliding instabilities upon unloading is supported by the on-the-spot observations of the contact area.

The capability of characterizing low-bandgap two-dimensional (2D) materials is crucial for a wide range of applications from fundamental science to commercial implementation. Current techniques rely heavily on expensive characterization equipment and thus hinder focused research on low-bandgap materials, compared to their counterparts in the visible range of the electromagnetic spectrum. This work demonstrates a cost-efficient and easily rebuildable optical setup to probe low-bandgap 2D materials using photocurrent spectroscopy. The heart of the setup consists of a supercontinuum laser in combination with a diffraction grating to create a tunable light source working from 500 to 2000 nm, allowing to access bandgaps in the short-wave infrared (IR), far from what is possible using standard silicon detector technology. Apart from a complete technical guide to facilitate reproduction of the system, two popular narrow-gap materials (MoTe₂ and black phosphorus) have been studied to extract bandgaps and excitonic features of these materials. The results highlight the simple, yet powerful approach of utilizing photocurrent spectroscopy in the IR and thus expanding the analysis toolbox for narrow-gap 2D semiconductor research.

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.