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.

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.

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.

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.

Wire arc additive manufacturing (WAAM) is a metal additive manufacturing (AM) process attracting interest from the automotive, defence, aerospace, architecture/engineering/construction and other industries because of its ability to manufacture large metal parts cost-effectively. Nevertheless, problems such as part defects and process efficiency remain, and consequently, efforts to improve WAAM are continuing. The WAAM process involves physical phenomena that include fluid flow, heat transfer, phase changes including melting, solidification and vaporization, multi-phase interactions, and deformations resulting from residual stresses—so obtaining a complete understanding is challenging. While numerical modelling is widely used to understand and assist with developing processes, modelling of AM processes such as WAAM is sophisticated because of their multi-physics and multiscale nature. This review addresses the existing and likely future roles of numerical modelling in advancing WAAM technology. Consideration is given to the known problems with WAAM, the different types of numerical modelling, including computational fluid dynamics, the finite element method, and smoothed particle hydrodynamics, and their potential to address persistent issues. Additionally, this review seeks to provide an understanding of the physics associated with the WAAM process, examines the trends in the development of WAAM technology, and recommends possible future directions. These include the combination of different physics-based modelling approaches to overcome their individual shortcomings, and the inclusion of modelling as part of a digital twin of the WAAM process.

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.

Atmospheric pressure plasma jets operated in an ambient environment are known to generate a rich mixture of reactive oxygen species and reactive nitrogen species, collectively referred to as RONS. At the cellular level, RONS have been linked to well-established signaling pathways that are important in tackling disease. However, there are still major gaps in our knowledge of which RONS (speciation, dose, and depth) are delivered by plasma into tissue; and following on from this, how we can control the plasma to deliver RONS effectively and safely into tissue. The purpose of this topical review is to highlight the research achievements that have helped improve our understanding of the physical and chemical mechanisms underpinning the plasma jet production of RONS and how to control their delivery into biological systems. The review also identifies new research ideas to address gaps in our knowledge (of RONS generation and delivery) to tailor the next generation of plasma jets to deliver RONS into human tissue with the precision needed to realize the full clinical potential of the technology. Completing these gaps in our knowledge is vital for the future development of medical plasma technologies; and will improve the possibility of developing optimal plasma technologies and protocols tailored specifically for the requirements of each patient.

Characterisation plays a vital role in both the academic and industrial worlds, providing a feedback loop between the design and optimisation of device performance. The rapid development of hardware and software has pushed characterisation techniques to new extremes, while their combination has provided new insight in cross-disciplinary fields, where multi-physics and multi-scale measurements are needed. In the Special Issue of the Journal of Physics D: Applied Physics, entitled 'Advanced Characterisations of Materials, Devices and Applications', we have compiled a comprehensive collection of 29 articles, showcasing the latest advancements in various fields, such as semiconductor materials and devices, plasmonics and nanophotonics, and two-dimensional materials and devices, among others. In this editorial, we concisely summarise the key research highlights of these studies.

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.

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.

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

Atmospheric pressure plasma jets operated in an ambient environment are known to generate a rich mixture of reactive oxygen species and reactive nitrogen species, collectively referred to as RONS. At the cellular level, RONS have been linked to well-established signaling pathways that are important in tackling disease. However, there are still major gaps in our knowledge of which RONS (speciation, dose, and depth) are delivered by plasma into tissue; and following on from this, how we can control the plasma to deliver RONS effectively and safely into tissue. The purpose of this topical review is to highlight the research achievements that have helped improve our understanding of the physical and chemical mechanisms underpinning the plasma jet production of RONS and how to control their delivery into biological systems. The review also identifies new research ideas to address gaps in our knowledge (of RONS generation and delivery) to tailor the next generation of plasma jets to deliver RONS into human tissue with the precision needed to realize the full clinical potential of the technology. Completing these gaps in our knowledge is vital for the future development of medical plasma technologies; and will improve the possibility of developing optimal plasma technologies and protocols tailored specifically for the requirements of each patient.

As an inherent and important property of light, polarization could provide information beyond light intensity and spectrum. However, traditional polarization detectors require bulky polarization optics and accurate heterogeneous integration, which limits their miniaturization. Conversely, recently developed miniaturized near-field polarization photodetectors can efficiently achieve detection with the advantages of being filterless, cost-effective, and portable. These attributes play a significant role in various fields, including astronomy, quantum optics, and medical diagnosis. In this paper, we review the progress of miniaturized near-field polarization photodetectors, including polarization photodetectors based on the nanowire, two-dimensional materials, chiral materials, and metasurface. Furthermore, this review analyzes the detection mechanisms of these photodetectors and provides a comprehensive summary of their operational wavelengths, photo responsivities, and polarization sensitivities, including polarization ratio for linear polarization and asymmetric ratio for circular polarization. Finally, the applications of near-field polarization photodetector are reviewed to highlight its potential in broad aspects of applications.

Under DC voltage, space charge inevitably accumulates within the spacer, thereby influencing the dissipation of surface charges. In this study, a charge measurement platform for epoxy resin spacers is constructed. The temporal variation of the surface charge distribution under space charges is compared. The results indicate that homopolar space charges enhance the surface charge dissipation. This is because about 95% of the total dissipation charge depends on the recombination of surface charges with heteropolar charged particles in the air. The homopolar space charge inside the spacer augments the normal electric field intensity in the gas side, facilitating the surface charge dissipation. It is inferred that the effect of the space charge inside the spacer should be considered when measuring the surface charge after disconnecting the operation voltage. This study provides important theoretical support for revealing the decay characteristic of surface charge on the spacer.

Separation is a crucial step in the analysis of living microparticles. In particular, the selective microseparation of phytoplankton by size and shape remains an open problem, even though these criteria are essential for their gender and/or species identification. However, microseparation devices necessitate physical membranes which complicate their fabrication, reduce the sample flow rate and can cause unwanted particle clogging. Recent advances in microfabrication such as High Precision Capillary Printing allow to rapidly build electrode patterns over wide areas. In this study, we introduce a new concept of membrane-less dielectrophoretic (DEP) microseparation suitable for large scale microfabrication processes. The proposed design involves two pairs of interdigitated electrodes at the top and the bottom of a microfluidic channel. We use finite-element calculations to analyse how the DEP force field throughout the channel, as well as the resulting trajectories of particles depend on the geometry of the system, on the physical properties of the particles and suspending medium and on the imposed voltage and flow rates. We numerically show that in the negative DEP regime, particles are focused in the channel mid-planes and that virtual pillars array leads either to their trapping at specific stagnation points, or to their focusing along specific lines, depending on their dielectrophoretic mobility. Simulations allow to understand how particles can be captured and to quantify the particle separation conditions by introducing a critical dielectrophoretic mobility. We further illustrate the principle of membrane-less dielectrophoretic microseparation using the proposed setup, by considering the separation of a binary mixture of polystyrene particles with different diameters, and validate it experimentally.

Amorphous oxide thin films are crucial materials for micro- and nanoelectronics device fabrication and have frequently been employed as a component of device stacks (e.g., gate dielectrics), as well as hard masks for lithography and protective layers for ion etching. In this work, we report thin films of a-SiOx deposited on Si substrates using reactive magnetron sputtering techniques. By adjusting the oxygen content and silicon magnetron power during the deposition process we found that it is possible to obtain films with a density up to 7% lower and up to 25% higher compared to the bulk counterpart (ρ = 2.20 g/cm3). Through first-principles density functional theory (DFT) simulations, we investigated the formation of native point defects in amorphous silicon dioxide (a-SiO2). Radial distribution function (RDF) analysis of defective a-SiO2 revealed substantial changes in the structural properties due to defect formation. We thus provide an atomistic explanation and understanding for the significant variation in mass density and correlate it with the different point defect formations that occur under varying deposition conditions.

This article introduces a new type of graphene-based perfect absorber that features tunability across four wave peaks and high sensitivity, consisting of Ag-SiO2-graphene. By controlling the Fermi level and relaxation time of graphene, the tunability of the absorber is achieved, and by changing the refractive index of SiO2, the selectivity of the resonant wavelength is realized. The results show that the absorber achieves absorption rates of 96.55%, 98.71%, 99.37%, and 99.96% at four wavelengths: 2092.24 nm, 2180.67 nm, 2230.08 nm, and 2336.17 nm, respectively, with an average absorption rate of 98.54%. Through simulations of electric field distribution intensity and verification of whether it meets the impedance matching theory, the physical mechanism behind the high absorption rate of the four peaks is explored. The absorber's polarization insensitivity and tilt insensitivity are investigated through different polarized light and tilted incident angles. It is found that the absorber is insensitive to polarized light and has excellent insensitivity within a tilt angle range of 0° to 65°. The sensitivities of the four peaks are 501.54 nm/RIU, 565.76 nm/RIU, 605.47 nm/RIU, and 582.70 nm/RIU, respectively. Finally, the practical application of the absorber in detecting aqueous solutions of 10%, 20%, 25% glucose solutions, and 30%, 50% sugar solutions is simulated, and the results show that the absorber has good sensing performance. This paper's absorber features four-peak perfect absorption and excellent tilt insensitivity, good refractive index sensitivity, and holds great potential applications in detectors and optical communication systems.

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.

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.

Planar laser-induced fluorescence (LIF) was employed to measure the absolute density of hydroxyl radicals (OH) in the effluent of the COST Reference Microplasma Jet for two feed gas mixtures: He/H₂O and He/O₂. Experiments were conducted with the effluent propagating into air and N₂ environments. For the He/H₂O case, measurements were also performed with the effluent impinging on a solid target at varying distances from the jet nozzle. Calibration of the OH-LIF signal from the COST-Jet was achieved by comparing it to a reference signal generated by the photofragmentation of H₂O₂. Results demonstrated that OH densities were sustained longer when the effluent propagates in a nitrogen environment compared to air, particularly with water added to the feed gas. The broader OH distribution in N₂ suggests slower consumption due to the absence of oxygen, which accelerates OH depletion in air via reactions involving O₂ and HO₂. Even when water was not added to the feed, as in the He/O₂ case, appreciable OH densities were observed, due to gas impurities and reactive species interactions with atmospheric humidity, forming reaction fronts that delineate the gas flow. Two-dimensional fluid dynamics simulations elucidated the influence of atmospheric gas entrainment and solid targets on the OH distribution. Experimental trends were further compared with a zero-dimensional chemistry model to explore OH production and consumption mechanisms in air and nitrogen environments.

Metal-oxide interactions are pivotal for the functionality of supported-metal catalysts. In this work, X-ray photoelectron spectroscopy (XPS) 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 when 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 comes to an end and formation of a CuxO/TiOx hetero-junction is revealed in the spectra. The signature of metallic ad-particles is only detected at high Ti load, when electron tunneling into single Ti deposits located on an 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.

This study investigates the removal of per- and polyfluoroalkyl substances (PFAS) using a hyperbolic vortex plasma discharge under various plasma-atmospheric conditions demonstrating varied degradation times for PFAS of different chain lengths. Experiments with spiked long-chain perfluorooctane sulfonic acid in deionized (DI) water show that bipolar 'flashover' plasma polarity achieves more effective degradation compared to monopolar positive or negative polarity. For a spiked PFAS matrix of varying chain lengths in DI water, results indicate that the production of reactive species in the gas phase by plasma discharge, and their subsequent dissolution in water through the water vortex, enables the degradation of short-chain perfluorobutanoic acid in the bulk liquid. In contrast, the degradation of long-chain PFAS primarily occurs at the gas-water interface, likely due to direct interactions between the plasma and the PFAS molecules. The addition of the Hyamine 1622 surfactant during treatment significantly enhances the degradation of both short- and long-chain PFAS in DI water, groundwater, and industrial effluent. The results of groundwater treatment indicate that the presence of high concentrations of other substances, particularly anions, slows down the degradation of PFAS, especially short-chain PFAS with carboxylic acid groups. Depending on the conditions and the type of PFAS, degradation can be achieved up to 99% after 75 min of treatment, with typical energy input around 7.2 kJ L⁻¹ or 2 kWh m⁻³.

Understanding axonal growth and pathfinding during cortical folding is crucial to unravel the mechanisms underlying brain disorders that disturb connectivity during human brain development. However, this topic remains incompletely understood. Here, we propose and evaluate a diffusion-based continuum model to understand how axons grow and navigate in the folding brain. To do so, a bilayer growth model simulating the brain was devised with a thin gray matter (GM) overlying a thick white matter (WM). The stochastic model of axonal growth was linked with the stress and deformation fields of the folding bilayer system. Results showed that the modulus ratio of the GM to the WM and the axonal growth rate are two critical parameters that influence axon pathfinding in the folding brain. The model demonstrated strong predictive capability in identifying axonal termination points and offered a potential explanation for why axons settle more in gyri (ridges) than sulci (valleys). Importantly, the findings suggest that alterations in the mechanical properties of the folding system impact underlying connectivity patterns. This mechanical insight enhances our understanding of brain connectivity development during the fetal stage and provides new perspectives on brain disorders associated with cortical folding abnormalities and disrupted connectivity.

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 minimising material loss, particularly at higher current intensities where pure copper electrodes experienced 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 oxidising environments.