Journal of Physics D: Applied Physics

Isolated metal-coordinated nitrogen embedded carbon (M–N–C) materials are potential alternatives to noble catalysts for oxygen evolution reaction (OER), and the activity of metal centers can be further modulated by adjusting the coordination environment. Recently, experimental studies have shown that the aggregation of metal atoms into small clusters or particles is inevitable during the high temperature pyrolysis, while the influences of metal clusters on the OER activity of single metal atoms in M–N–C are unclear. Herein, taking Ni-based single atom as examples, the interaction characters of NiN₄ doped graphene (NiN₄-graphene) with different Ni clusters were studied. The modulation effects of Ni clusters to the NiN₄-graphene were systematically investigated from the geometric configurations, electronic structures, and the OER activity of the Ni single atom. It was found that the OER performance of NiN₄-graphene can be remarkably improved through the addition of Ni clusters, and the lowest overpotential of 0.43 V is achieved on NiN₄-graphene with the modification of Ni₁₃ cluster, which is smaller than that of 0.69 V on NiN₄-graphene. Electronic properties calculations showed that the charge transfer from Ni clusters to NiN₄-graphene will alter the density of states of Ni single atom near the Fermi level, which promotes the charge transfer from NiN₄-graphene to oxygen containing products and optimizes the adsorption strength of oxygen intermediate to close to the ideal adsorption free energy of 2.46 eV by enhancing the hybridization interaction between the O-p orbitals and the Ni-d_xz, Ni-d_yz orbitals, and finally leading to an enhanced OER activity. The current findings highlight the important role of metal clusters on improving the catalytic performance of M–N–C materials, which benefits for the rational design of M–N–C catalysts with high catalytic activity.

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.

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 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.

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.

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.

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.

Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.

Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO₂ conversion into value-added chemicals and fuels, CH₄ activation into hydrogen, higher hydrocarbons or oxygenates, and NH₃ synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NO_x removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.

Over the past decade, the global cumulative installed photovoltaic (PV) capacity has grown exponentially, reaching 591 GW in 2019. Rapid progress was driven in large part by improvements in solar cell and module efficiencies, reduction in manufacturing costs and the realization of levelized costs of electricity that are now generally less than other energy sources and approaching similar costs with storage included. Given this success, it is a particularly fitting time to assess the state of the photovoltaics field and the technology milestones that must be achieved to maximize future impact and forward momentum. This roadmap outlines the critical areas of development in all of the major PV conversion technologies, advances needed to enable terawatt-scale PV installation, and cross-cutting topics on reliability, characterization, and applications. Each perspective provides a status update, summarizes the limiting immediate and long-term technical challenges and highlights breakthroughs that are needed to address them. In total, this roadmap is intended to guide researchers, funding agencies and industry in identifying the areas of development that will have the most impact on PV technology in the upcoming years.

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹² to 3.76 × 10¹⁴ cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According to in-situ Raman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

Recently, the optical vortex (OV) has gained increasing interest since the potential for applications of the orbital angular momentum (OAM) carried by optical vortex beams. However, generation is currently limited single static circular intensity profile, greatly constraining the breadth of achievable spatiotemporal dynamics. Here, we propose a novel phase distribution to generate a dynamic propagation OV with a customized topological charge (TC ⩾ 10) based on Fibonacci series annular subzone (FSAS) by tailoring the local phase gradient along the azimuthal direction. We describe the generation of the FSAS vortex phase. The Fibonacci vortex beam (FVB) have customization TC, multi-singularity intensity distributions. Furthermore, such optical fields exhibit the spatial dynamic rotation and self-focusing have yielded fascinating phenomena. The simulation results are agreed with the experimental results, which provide an important basis for the generation of OV with spatial dynamic propagation. These results contribute to the advanced complex light manipulation with spatial dynamic propagation and pave the way to achieve a new laser with the structured light based on modified phase control.

Density functional theory calculations have been employed for the theoretical studies of the geometric structures and electronic characteristics of PdGe_n (n = 1−11) clusters. An analysis of the second- order energy differences indicates that PdGe₇ and PdGe₁₀ clusters possess superior thermodynamic stability. PdGe₁₀ displays the highest chemical stability and the lowest chemical activity, due to its largest energy gap value (E_g). Vertical ionization potential and vertical electron affinity exhibit the decreasing and increasing trends, respectively, with the increase of the number n of Ge atoms. PdGe₁₀ presents the highest electronegativity among these clusters. The analysis on the adsorption properties of PdGe_n (n = 7,10) clusters for gas molecules (e.g. CO, NO, NO₂, NH₃, SO₂ and H₂S) yields the adsorption structures, adsorption energies, Mulliken charge transfer and the changes in the electronic properties. All the listed gas molecules chemically adsorb onto PdGe₇. PdGe₁₀ has a better adsorption performance for NO₂, while its adsorption ability for CO is poorer. The potentiality of PdGe_n (n = 7, 10) clusters as gas sensors is also evaluated and reveals that NO adsorption significantly affects the electronic properties, especially conductivity, of the systems. PdGe₁₀ has an appropriate NO adsorption capacity and significant charge transfer, with the adsorption energy of −0.278 eV and the recovery time of about 10⁻⁹s, indicating its fast response and hence good potentiality as the NO sensor. In contrast, PdGe₇ has a higher adsorption capability towards NO with a lower adsorption energy of −1.16 eV, leading to the difficulty in desorption and a longer recovery time of over 12 h.

We propose a lamina-shaped metamaterial absorber based on the coherently coupled weak resonances of high-order Helmholtz resonators in this work. Such an ultra-thin lamina metamaterial can achieve broadband tunable absorption (maximal absorption >0.9), which exhibits near-perfect ventilation performance (ventilated area ratio >0.8, ratio of wind velocity >0.95). Benefiting from coherently coupled weak resonances between units with different structure parameters, the lamina metamaterial presents a broadband absorption (506–659 Hz with 2 × 3 units and 480–679 Hz with 2 × 4 units). The ultra-thin and simple structure shape of this sound absorption metamaterial lamina leads to not only an efficient ventilation performance but also high potential value in various scenarios of ventilated sound absorption, especially in ventilation tubes with high noise.

To improve the performance of energy storage devices, research into anode materials is essential. This study explores the potential of two-dimensional (2D) materials, particularly silicon carbide (Si₂C), to enhance the efficacy of lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (KIBs). Our first-principles calculations indicate that Si₂C achieves storage capacities of 174.7 mAh g⁻¹ for LIBs, 436.8 mAh g⁻¹ for SIBs, and 349.4 mAh g⁻¹ for KIBs. The exceptional performance of Si₂C comes from its high conductivity, large surface area, high capacitance, synergistic atomic radius and electronegativity effects. Furthermore, this study delves into the diffusion kinetics of Li/Na/K-ions in Si₂C, revealing extremely low energy barriers and uncovering the fundamental principles behind its superior electrochemical performance. This research emphasizes Si₂C's potential in energy storage, highlighting its capacity and diffusion advantages for Li/Na/K-ion batteries.

Sensing devices for rapid analytics are important societal requirements, with wide applications in environmental diagnostics, food testing, and disease screening. Nanomaterials present excellent opportunities in sensing applications owing to their superior structural strength, and their electronic, magnetic, and optoelectronic properties. Among the various mechanisms of gas sensing, including chemiresistive sensors, electrochemical sensors, and acoustic sensors, another promising area in this field involves plasmonic sensors. The advantage of nanomaterial-plasmonic sensors lies in the vast opportunities for tuning the sensor performance by optimizing the nanomaterial structure, thereby producing highly selective and sensitive sensors. Recently, several novel plasmonic sensors have been reported, with various configurations such as nanoarray resonator-, ring resonator-, and fibre-based plasmonic sensors. Going beyond noble metals, some promising nanomaterials for developing plasmonic gas sensor devices include two-dimensional materials, viz. graphene, transition metal dichalcogenides, black phosphorus, blue phosphorus, and MXenes. Their properties can be tuned by creating hybrid structures with layers of nanomaterials and metals, and the introduction of dopants or defects. Such strategies can be employed to improve the device performance in terms of its dynamic range, selectivity, and stability of the response signal. In this review, we have presented the fundamental properties of plasmons that facilitate its application in sensor devices, the mechanism of sensing, and have reviewed recent literature on nanomaterial-based plasmonic gas sensors. This review briefly describes the status quo of the field and prospects.

The number of vision sensors continues to increase with the rapid development of intelligent systems. The effective transmitting and processing of the sensing data become difficult due to the sensing, computing and memory units being physically separated. In-sensor computing architecture inspired by biological visual systems with efficient information processing has attracted increasing attention for overcoming these performance limitations. Bipolar cells in the retina can generate ON/OFF information processing channels to amplify marginal information. The synaptic structure is plastic and can enhance the output information that is repeated many times. In recent years, numerous new material and device strategies to implement in-sensor computing by mimicking the functions of bipolar cells and synapses have been reported: ON/OFF optical responses have been realized on two-dimensional materials by band-modulation and tunneling; synaptic responses, such as short-term plasticity and long-term plasticity, have been realized by phase transition and carrier regulating. In this review, we will summarize the biological vision processes, analyse the physical mechanisms behind the in-sensor computational vision sensors (ICVSs), and then overview the emerging physical artificial neural networks implemented with ICVSs. After that, we will discuss ICVS design based on biological mechanisms beyond ON/OFF bipolar-cell-response and synaptic response.

Aqueous zinc-ion batteries (AZIBs) have emerged as competitive alternatives for energy storage systems. By comparison with traditional cathode materials, the unique combination advantages of improved specific capacity, high electrical conductivity and tunable structures exhibited by chalcogenides contribute to receiving increasing attention. However, it should be noted that chalcogenides still show unsatisfactory electrochemical performance in aqueous batteries, because of their inferior chemical stability and sensitivity to pH value in aqueous media. Consequently, the application of chalcogenides in AZIBs still requires further investigation and optimization. This review offers a systematic summary of recent advancements in the rational design strategies employed to develop advanced cathode materials derived from chalcogenides. Furthermore, the review comprehensively presents the applications of various transition metal dichalcogenides, as well as sulfur (S), selenium (Se), tellurium (Te), and their corresponding solid solutions, in AZIBs. Lastly, the challenges currently confronting chalcogenides research are deliberated upon, followed by a perspective outlining future directions for practical applications of AZIBs.

Ferroelectric tunnel junctions (FTJs) have been the subject of ongoing research interest due to its fast operation based on the spontaneous polarization direction of ultrathin ferroelectrics and its simple two-terminal structure. Due to the advantages of FTJs, such as non-destructive readout, fast operation speed, low energy consumption, and high-density integration, they have recently been considered a promising candidate for non-volatile next-generation memory. These characteristics are essential to meet the increasing demand for high-performance memory in modern computing systems. In this review, we explore the basic principles and structures of FTJs and clarify the elements necessary for the successful fabrication and operation of FTJs. Then, we focus on the recent progress in perovskite oxide, fluorite, 2-dimensional van der Waals, and polymer-based FTJs and discuss ferroelectric materials expected to be available for FTJs use in the future. We highlight various functional device applications, including non-volatile memories, crossbar arrays, and synapses, utilizing the advantageous properties of ferroelectrics. Lastly, we address the challenges that FTJ devices currently face and propose a direction for moving forward.

Microplastics (MPs) are plastic residues with a size <5 mm, which are often further broken into micro/nano size particles in the environment. Owing to their minute scale, widespread distribution, and substantial toxicity potential, MPs has emerged as a critical environmental concern. Therefore, accurate characterization of these particles becomes a formidable yet imperative challenge in environmental science. In this review, a comprehensive overview on current MP characterization techniques, including microscopy/electron microscopy, spectroscopy, and mass spectrometry, have been summarized and discussed. We assess their applicability, strengths, limitations, as well as recent advancements. We also highlight the features offered by different techniques and the particles size range for which each technique is suitable. Furthermore, the combination of different characterization techniques and some novel techniques that can be used in MP characterization are also mentioned. This work offers a reference for MP characterization, which will facilitate the detection of MP in the environment.

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹² to 3.76 × 10¹⁴ cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According to in-situ Raman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

In the recent past, significant research efforts have been put forth to fabricate cost-effective substrates for surface-enhanced Raman scattering (SERS) applications. Here we propose semiconducting TiO₂ multi-leg nanotubes and Au nanoparticle-coated TiO₂ multi-leg nanotubes (TiO₂ MLNTs and Au/TiO₂ MLNTs) as SERS substrates. The unique multi-leg architecture of TiO₂ nanotubes demonstrated enhanced light-harvesting properties facilitated by an induced photonic absorption edge. Remarkable high SERS sensitivity is observed towards the detection of Methylene blue (MB), up to nM concentration (E.F. ~10⁴) using TiO₂ MLNTs. The same is attributed to the resonantly matched photonic absorption edge of TiO₂ MLNTs with the wavelength of incident laser probe light. On the other hand, the Au nanoparticle coating further leveraged the light absorption ability of TiO₂ MLNTs with the aid of localized surface plasmon resonance mode (LSPRs). As such, Au/TiO₂ MLNTs showed excellent enhancement in SERS sensitivity (E.F. ~10⁵, for nM of MB) facilitated by the synergy between the plasmonic modes of Au and the photonic absorption mode of TiO₂ MLNTs. UV-Vis diffuse reflectance and Raman spectroscopy measurements are highlighted to elucidate the light absorption and SERS sensitivity of the TiO₂ and Au/TiO₂ MLNTs.

Polar unsaturated ferromagnetic thin films are promising for low-power and high-speed nonvolatile resistive and optical memories. Here we measure the magnetooptical (MO) response of polar unsaturated Co₉₀Fe₁₀ and Co₄₀Fe₄₀B₂₀ thin films in the spectral range from 400 nm to 1000 nm using vector magnetooptical generalized ellipsometry (VMOGE) in an out-of-plane applied magnetic field of ±0.4 T where magnetization of the ferromagnetic (FM) thin film is not saturated. Using Magneto- Optical Simulation software (MagOpS®), we extract the complex MO coupling constant (Q) of the polar unsaturated FM thin films from difference spectra of VMOGE data recorded in polar configuration at Hz = +0.4 T and at Hz = −0.4 T. Presented approach opens a path to determine Q of both polar saturated and polar unsaturated FM thin films for simulating the MO properties of application-relevant optical memory multilayer structures.

A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1MHz is employed to create&#xD;atmospheric pressure pulsed plasma in pure CO₂ gas. The short bursts contain up to four nanosecond pulses. The CO₂ conversion and corresponding energy efficiency are measured ex-situ with Fourier-transform infrared absorption spectroscopy. Trends in the absorption line profile of in-situ quantum cascade laser infrared absorption spectroscopy indicate an elevated vibrational temperature of CO₂ with an increasing number of pulses per burst. The key result of this paper is that the dissociation energy efficiency is higher when operating the plasma in burst mode. Furthermore, a larger number of pulses in a burst is associated with a further increase of the dissociation efficiency. The highest efficiency measured is (17.7 ± 0.3)% for single pulses spaced 2 ms apart, and (20.0±0.3)% for bursts of three pulses, with an in-burst frequency of 1MHz and bursts spaced 4 ms apart.

Surface acoustic waves, the microcosmic cousins of seismic waves, can be generated and precisely controlled on a microscopic scale by applying a periodic electrical signal to a piezoelectric substrate. Harnessing and exploring their interactions with two-dimensional van derWaals systems opens new frontiers in materials science and engineering. As part of a special issue on these guided elastic waves&#xD;for hybrid nano- and quantum technologies, our review highlights work focusing on acousticallyinduced transport phenomena at low temperatures that arise from the interaction between the SAW in a piezoelectric substrate and a van der Waals material on its surface. A main focus is on technological methods to control the carrier concentration in transport and strain-related effects that can act on the carrier motion as an effective magnetic field.

The development of real-time control strategies for key discharge parameters, such as densities, fluxes, and energy distributions, is of fundamental interest to many plasma sources. Over the last decade, multi-harmonic 'tailored' voltage waveforms have been successfully employed to achieve enhanced control of key parameters in a wide range of radio-frequency (RF) plasma sources through application of the electrical asymmetry effect (EAE). More recently, the analogous magnetic asymmetry effect (MAE) has been numerically and experimentally demonstrated to achieve a notable degree of control in parallel plate RF plasma sources. The MAE is achieved via selectively magnetising the charged species adjacent to one electrode, altering the charge flux to the surface and enforcing a DC self-bias to maintain quasineutrality. This study addresses the degree of control achieved by the MAE in a non-planar geometry via 2D fluid/kinetic simulations of a magnetised RF capacitively coupled plasma (RF-CCP) source employing two different magnetic topologies. The simultaneous application of the EAE and MAE is then presented for the same geometry, demonstrating a degree of non-linear behaviour dependant upon the applied magnetic topology. Control of the DC self-bias voltage ηDC is demonstrated for a single 600 Vpp, 13.56 MHz discharge in both 'convergent' (maximum on-axis field strength) and 'divergent' (minimum on-axis field strength) magnetic topolgies. MAE induced modulations of ηDC = 0.13 Vpp and ηDC = 0.03 Vpp are achieved for each magnetic topology, respectively, for magnetic field strengths between 50 - 1000 G. Simultaneous application of an EAE and MAE is achieved through a multi-harmonic 'peak'-type tailored voltage waveform employing varying harmonic phase offsets between 0◦ ≤ θ ≤ 360◦ . The degree to which the DC self-bias voltage is modulated by the applied EAE is mediated by the orientation and magnitude of the applied magnetic field. The EAE induced DC self-bias modulations exhibit non-linear behaviour in response to a superimposed MAE, such that the resulting DC self-bias differs from an additive combination of the two effects alone Simultaneous application of the electrical and magnetic asymmetry effects offers the possibility of further decoupling ion and electron dynamics in RF plasma sources, and represents an improvement over each approach in isolation.

Black soldier fly (BSF) melanin is a new supply of the brown-black pigment eumelanin. Given that eumelanin is a model bioelectronic material for applications such as medical devices and sensors, understanding BSF melanin's electrical properties is important to confirm its viability as an advanced material. Presented here is a systematic, hydration dependent alternating current study of BSF melanin utilising both H₂O and D₂O vapours. There is a clear difference between the vapours, enabling a thorough analysis including Nyquist plots with model circuit analysis, broad band dielectric spectroscopic modelling as well as applying the Trukhan model to understand free ion concentration and mobility changes as a function of hydration. We find that BSF melanin behaves similarly to previous reports on synthetic systems, and the analysis here sheds additional light on potential charge transport changes. Significantly, a key finding is that there are two different mobility mechanisms for ion transport depending on hydration.

An extensive study on the green auroral emission characterization is presented based on a single dielectric barrier discharge geometry argon plasma jet driven by a kHz sine voltage. The plasma was generated by using 99.999% pure argon and the observed 557.7 nm green line resulted from the excited O(¹S) state. An optical emission spectroscopy method using line ratios of argon was used to obtain the electron density and electron temperature under different conditions in the downstream region. The characteristics of discharge and green emission with variations in interelectrode distance, applied voltage (power) and flow rate are discussed. The spatially diffuse distribution of O(¹S), owing to its long lifetime, is shown by the short exposure imaging. Two discharge regimes are presented, accompanied by two distinct branches of the green emission intensity, with a clear conclusion that the 557.7 nm emission is favored in the low electron temperature environment. In this work, the intense and diffuse green plume only forms when the downstream electron density is approximately lower than 1 × 10¹⁴ cm⁻³ and the electron temperature is lower than 1.1 eV. By charging the two electrodes in two opposite ways, it is shown that the green emission from oxygen is favored in the case where the electric field and the electron drift are not continuous.

The aims of this study encompass the characterization of process parameters and the antimicrobial potential during operation of a novel non-thermal plasma (NTP) source in a duct system containing a particulate matter (PM) filter thus mimicking the interior of an air purifier. Simulating conditions of a long-term operation scenario, in which bacterial aerosols in indoor environments accumulate on PM filters, the filter surfaces were artificially inoculated with Escherichia coli (E. coli) and exposed to an air stream enriched with reactive species. Electrical power consumption, key plasma parameters, volume flow and air flow velocity, reactive gas species concentrations as well as inactivation rates of E. coli were assessed. The NTP operated at a gas temperature close to ambient air temperature and featured a mean electron energy of 9.4 eV and an electron density of 110¹⁹ m⁻³. Ozone was found to be the dominating reactive gas species with concentrations of approx. 10 ppm in close vicinity to the PM filters. An inactivation rate of 99.96 % could be observed after exposure of the PM filters to the gas stream for 15 min. This inactivation efficiency appears very competitive in combating realistic bacterial aerosol concentrations in indoor environments.

Experimentally it is shown that without any oxygen manipulation for TiO₂, a strong room temperature ferromagnetism could be expected only in ultra-thin films, with the ideal thickness below 100 nm. Both bulks and nano-powders of TiO₂ are diamagnetic, indicating that the surface and its nano-sublayers play very important roles in tailoring the magnetic properties in this type of compound. To shed a new light on the defect-related magnetism in the typical case of anatase TiO₂ surfaces, we have performed a series of quantum-mechanical calculations for TiO₂ slabs containing Ti or O vacancies in different distances from the (001) surface. The lowest formation energies were obtained for the Ti vacancies in the first sub-surface layer and the O vacancies within the surface. The computed magnetic states reflect complicated structural relaxations of atoms influenced by both the surface and vacant atomic positions. O atoms cannot contribute much to magnetic moment when Ti vacancies are isolated and far from the surface. Ti vacancies in TiO₂ are only metastable. The formation energy of Ti interstitials is lower than for Ti vacancies since high-temperature annealing, especially with a lot of O₂ available that would fill up O-related defects, and as a result, eliminate most of Ti vacancies. Lower temperatures, less O₂, and shorter exposure times may enable not only partial elimination of Ti vacancies but also can facilitate their diffusion into different states of aggregations. In the ferromagnetic films (i.e. thin films below 100 nm), it looks like that the O atoms are located closer to the Ti vacancies.