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-dxz, Ni-dyz 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.
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Runchuan Shi et al 2024 J. Phys. D: Appl. Phys. 57 205301
Alfred Leitenstorfer et al 2023 J. Phys. D: Appl. Phys. 56 223001
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.
I Adamovich et al 2022 J. Phys. D: Appl. Phys. 55 373001
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.
Dan Guo et al 2014 J. Phys. D: Appl. Phys. 47 013001
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.
H Amano et al 2018 J. Phys. D: Appl. Phys. 51 163001
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.
Manuel Le Gallo and Abu Sebastian 2020 J. Phys. D: Appl. Phys. 53 213002
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.
I Adamovich et al 2017 J. Phys. D: Appl. Phys. 50 323001
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.
Jianmin Ma et al 2021 J. Phys. D: Appl. Phys. 54 183001
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.
Alexey Kimel et al 2022 J. Phys. D: Appl. Phys. 55 463003
Magneto-optical (MO) effects, viz. magnetically induced changes in light intensity or polarization upon reflection from or transmission through a magnetic sample, were discovered over a century and a half ago. Initially they played a crucially relevant role in unveiling the fundamentals of electromagnetism and quantum mechanics. A more broad-based relevance and wide-spread use of MO methods, however, remained quite limited until the 1960s due to a lack of suitable, reliable and easy-to-operate light sources. The advent of Laser technology and the availability of other novel light sources led to an enormous expansion of MO measurement techniques and applications that continues to this day (see section 1). The here-assembled roadmap article is intended to provide a meaningful survey over many of the most relevant recent developments, advances, and emerging research directions in a rather condensed form, so that readers can easily access a significant overview about this very dynamic research field. While light source technology and other experimental developments were crucial in the establishment of today's magneto-optics, progress also relies on an ever-increasing theoretical understanding of MO effects from a quantum mechanical perspective (see section 2), as well as using electromagnetic theory and modelling approaches (see section 3) to enable quantitatively reliable predictions for ever more complex materials, metamaterials, and device geometries. The latest advances in established MO methodologies and especially the utilization of the MO Kerr effect (MOKE) are presented in sections 4 (MOKE spectroscopy), 5 (higher order MOKE effects), 6 (MOKE microscopy), 8 (high sensitivity MOKE), 9 (generalized MO ellipsometry), and 20 (Cotton–Mouton effect in two-dimensional materials). In addition, MO effects are now being investigated and utilized in spectral ranges, to which they originally seemed completely foreign, as those of synchrotron radiation x-rays (see section 14 on three-dimensional magnetic characterization and section 16 on light beams carrying orbital angular momentum) and, very recently, the terahertz (THz) regime (see section 18 on THz MOKE and section 19 on THz ellipsometry for electron paramagnetic resonance detection). Magneto-optics also demonstrates its strength in a unique way when combined with femtosecond laser pulses (see section 10 on ultrafast MOKE and section 15 on magneto-optics using x-ray free electron lasers), facilitating the very active field of time-resolved MO spectroscopy that enables investigations of phenomena like spin relaxation of non-equilibrium photoexcited carriers, transient modifications of ferromagnetic order, and photo-induced dynamic phase transitions, to name a few. Recent progress in nanoscience and nanotechnology, which is intimately linked to the achieved impressive ability to reliably fabricate materials and functional structures at the nanoscale, now enables the exploitation of strongly enhanced MO effects induced by light–matter interaction at the nanoscale (see section 12 on magnetoplasmonics and section 13 on MO metasurfaces). MO effects are also at the very heart of powerful magnetic characterization techniques like Brillouin light scattering and time-resolved pump-probe measurements for the study of spin waves (see section 7), their interactions with acoustic waves (see section 11), and ultra-sensitive magnetic field sensing applications based on nitrogen-vacancy centres in diamond (see section 17). Despite our best attempt to represent the field of magneto-optics accurately and do justice to all its novel developments and its diversity, the research area is so extensive and active that there remains great latitude in deciding what to include in an article of this sort, which in turn means that some areas might not be adequately represented here. However, we feel that the 20 sections that form this 2022 magneto-optics roadmap article, each written by experts in the field and addressing a specific subject on only two pages, provide an accurate snapshot of where this research field stands today. Correspondingly, it should act as a valuable reference point and guideline for emerging research directions in modern magneto-optics, as well as illustrate the directions this research field might take in the foreseeable future.
Gregory M Wilson et al 2020 J. Phys. D: Appl. Phys. 53 493001
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.
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Gang Wu et al 2024 J. Phys. D: Appl. Phys. 57 293001
The two-dimensional (2D) materials are regarded as the ideal solid lubricants at micro- and nano-scale. Besides the experiments and analytical models, the atomistic simulations are important tools to investigate the frictional properties of 2D materials. This review will focus the recent atomistic simulation studies on frictional properties 2D materials with a particular emphasis on the density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Starting from the proper calculation of long range dispersion forces, the correlations between the physical characteristics (e.g. electronic charge redistribution, interfacial commensurability, chemical modification, moiré superlattice, layer effect, atomic contact quality, defect, external fields, humidity and temperature) and frictional properties of 2D materials are reviewed for both the interlayer and surface sliding. Meanwhile, recent MD simulations about the phononic energy dissipation in friction of 2D materials are summarized. At last, some shortcomings in current simulation techniques are summarized and it is suggested that the atomistic simulations combined with machine learning will be a more powerful strategy to investigate the frictional properties of 2D materials.
Jogendra Kumar and K Mukherjee 2024 J. Phys. D: Appl. Phys. 57 295304
The magnetocaloric effect in the cryogenic temperature regime has gained enormous attention due to its application in the field of cryogenic refrigeration technology, which is required for quantum computing, space sciences and basic research activities. In this context, Gd- and Dy-based frustrated systems are considered as promising cryogenic magnetocaloric materials. Hence, in this paper the magnetic and magnetocaloric properties of GdTaO4, GdNbO4 and DyNbO4 are comprehensively investigated. Structural analysis suggests that these compounds crystallize in a monoclinic structure, wherein magnetic ions form an elongated diamond geometry. Analysis of magnetization, heat capacity and field-dependent magnetic entropy changes confirms the presence of short-range magnetic correlations in these compounds. Additionally, a remarkably large magnetic entropy change and relative cooling power are noted. The mechanical efficiency is found to be comparable to (or even better than) those reported for good magnetic refrigerants. Our study suggests that GdTaO4, GdNbO4 and DyNbO4 can be regarded as promising cryogenic magnetic refrigerant materials.
Ji Xu et al 2024 J. Phys. D: Appl. Phys. 57 295104
Photonic nanojets (PNJs) and photonic hooks (PHs) are two significant effects in Mesotronics. However, it is difficult to analyze and control the two phenomena generated by diffraction-based structures, such as rectangles and right-angled trapezoids, using diffraction theory. This work focuses on the modulation of incident fields by edge diffraction and the reconstruction of energy distribution, and proposes a model based on energy flows and energy reconstruction, called the 'energy-based model', to analyze the formation of PNJs and PHs through such structures. This model reveals that the morphology of PNJ and PH originates from the contributions of different regions of the incident energy, especially the crucial influence of edge diffraction, and successfully clarifies the modulation mechanism of the near-field and far-field regions of PNJ, as well as the tailoring mechanism of the two arms of PH. On the one hand, the model provides reasonable and intuitive explanations for the control of energy flow paths resulting from edge diffraction in rectangles and their variants with different parameters on the generation of PNJs and PHs. On the other hand, it also serves as a basis for reverse design. By adjusting energy flow and energy reconstruction through alterations in incident conditions or structural shapes, PHJs and PHs can be tailored easily and flexibly. The model is also been validated to be applicable in explaining many reported works. The results indicate that the 'energy-based model', which describes the energy flow paths resulting from edge diffraction, offers intuitive, convenient, and predictive advantages in analyzing the morphological variations of PNJs and PHs generated by diffraction-based structures, such as rectangles, trapezoids, and their variants. This provides a valuable reference for relevant research on Mesotronics.
T Tansel and O Aydin 2024 J. Phys. D: Appl. Phys. 57 295103
Infrared (IR) detectors play crucial roles in various applications. A significant milestone in advancing the next-generation low-cost silicon technology is the enhancement of hyperdoped black silicon (b-Si) photodetectors, particularly within the IR wavelength range. In this study, highly selenium (Se)-doped b-Si photodetectors. Through the optimization of laser parameters and the application of SiO2 passivation, significant enhancements were achieved in responsivity (R), external quantum efficiency, and specific detectivity (D*) within the long-wave IR range, culminating in a D* of 1.3 × 1012 Jones at 9.5 μm. Additionally, the Se: b-Si photodetectors maintain a D* of approximately 1.3 × 1011 Jones at critical optical telecommunications wavelengths of 1.3 μm and 1.5 μm. These results significantly contribute to the advancement of IR photodetector technology and provide a foundation for the development of highly efficient, low-cost, and broadband IR detectors for Si photonic applications.
Shuai Xu(徐帅) et al 2024 J. Phys. D: Appl. Phys. 57 295001
The integration of two-dimensional materials into spintronics represents a frontier in the development of novel computational devices. In this work, by utilizing ab initio many-body theory, we investigate the spin dynamics within the Co-doped γ-graphyne structure, with a particular emphasis on the role of cobalt atoms as magnetic centers. The result reveals that each cobalt atom on the γ-graphyne hosts states with enough spin-density localization to facilitate both local spin flips and global spin transfers. The spin-dynamic processes in our study are characterized by ultrafast time scales and high fidelities, demonstrating efficient spin control in the system. Building upon these spin-dynamic processes, we theoretically construct a spin-based Reset-Set latch, thus demonstrating the feasibility of sophisticated logic operations in our system. Such spin-based devices exhibit the advantages of nano-spintronics over conventional-electronic approaches, offering lower energy consumption, faster operational speeds, and greater potential for miniaturization. The results highlight the efficacy of γ-graphyne nanoflakes doped with cobalt atoms as spin-information processing units, signifying a pivotal advancement in the incorporation of graphyne-based materials into sophisticated spintronic devices. This research paves the way for their application in areas such as data storage, quantum computing, and the development of complex logic-processing architectures.
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Gang Wu et al 2024 J. Phys. D: Appl. Phys. 57 293001
The two-dimensional (2D) materials are regarded as the ideal solid lubricants at micro- and nano-scale. Besides the experiments and analytical models, the atomistic simulations are important tools to investigate the frictional properties of 2D materials. This review will focus the recent atomistic simulation studies on frictional properties 2D materials with a particular emphasis on the density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Starting from the proper calculation of long range dispersion forces, the correlations between the physical characteristics (e.g. electronic charge redistribution, interfacial commensurability, chemical modification, moiré superlattice, layer effect, atomic contact quality, defect, external fields, humidity and temperature) and frictional properties of 2D materials are reviewed for both the interlayer and surface sliding. Meanwhile, recent MD simulations about the phononic energy dissipation in friction of 2D materials are summarized. At last, some shortcomings in current simulation techniques are summarized and it is suggested that the atomistic simulations combined with machine learning will be a more powerful strategy to investigate the frictional properties of 2D materials.
Antara Vaidyanathan et al 2024 J. Phys. D: Appl. Phys. 57 263002
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.
Hang Xu et al 2024 J. Phys. D: Appl. Phys. 57 263001
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.
Lujing Wang et al 2024 J. Phys. D: Appl. Phys. 57 253001
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.
Sung Hyuk Park et al 2024 J. Phys. D: Appl. Phys. 57 253002
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.
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Toyama et al
We demonstrate a high-throughput experimental characterization of anomalous Nernst conductivity (αxyA) of L10-ordered CoPt using Co1–xPtx composition-spread thin films on MgO(100) substrates. The compositional dependence of the anomalous Nernst effect (ANE), anomalous Hall effect (AHE) and Seebeck effect is systematically measured. As increasing the Pt concentration, the crystal structure in the composition-spread film grown at 500 °C changes from fcc Co, A1-disordered CoPt, L10-ordered CoPt, A1-CoPt to fcc Pt. The largest αxyA of 2.52 A m–1 K–1 is obtained in L10-CoPt for Pt-rich composition of x = 70%, which is larger than that for an additionally fabricated nearly stoichiometric L10-Co48Pt52 reference uniform film. The contribution from direct conversion of a temperature gradient to a transverse charge current through αxyA is dominant to the total anomalous Nernst coefficient compared to the AHE-related contribution. From a scaling analysis of the AHE, the intrinsic contribution is found to be dominant for x = 70%. A theoretical calculation for αxyA of L10-Co50Pt50 agrees with the experimental αxyA value for the nearly stoichiometric reference film by considering on-site Coulomb interaction for Co atoms. We also point out the possible electron doping effect by the addition of Pt in L10-CoPt, which could explain the larger αxyA for the off-stoichiometric Pt-rich composition than that for the nearly stoichiometric one. Our experimental and theoretical results suggest the potential of L10-CoPt with a large αxyA originating from the intrinsic mechanism for future thermoelectric applications.
Hui et al
Understanding the unique properties of perovskite materials is crucial in advancing solar energy technologies. Factors like heat of formation and bandgap significantly influence the light absorption capability and stability of perovskite solar cells. However, it is time-consuming and labor-intensive to obtain the properties of perovskites using traditional experimental or high-throughput computational methods. As a prospective method, machine learning can find regularities in the given training data and give accurate prediction results. In this article, we use deep learning models based on attention mechanisms and elemental features to predict the heat of formation and bandgap of perovskite materials. Random Forest and Gradient Boosted Regression Tree models have also been used for interpretable predictions of properties. The compositionally restricted attention-based network was improved by introducing a densely connected network and optimizing the network structure to increase data processing capabilities. The experiment results show that the mean absolute errors of the heat of formation and bandgap on the test sets are decreased by 5.77% and 3.37% respectively. The optimized model also shows better performance when used for classification tasks. In addition, we use the Gradient Boosting Regression Tree model and the Shapley Additive Explanations tool to conduct an interpretable analysis, explaining the impact of different features on the predictions of the properties.
Huang et al
We report on an obvious performance enhancement of separated absorption charger-layer multiplication (SACM) Ge/Si avalanche photodetector with the sidewalls passivated by low temperature remote oxygen plasma (ROP) treatment. The dangling bonds on the Ge surface can be efficiently passivated by the formation of ideal Ge/GeO2 interface. With ROP passivation, the leakage current of device shows a (3~4)-fold decrease at 300 K, resulting in a dark current (Idark) of 3.5×10-6 A at 90% avalanche voltage (Vbr) and 3.4×10-7 A at punch-through voltage (Vpuhch-through) for the 26-μm-diameter device. At 200 K, more than 10-fold decrease is demonstrated, and the passivation mechanism is revealed. Moreover, a multiplication gain of 94 is obtained under 1550 nm illumination. The device with ROP passivation shows an improved gain bandwidth product (GBP) of 190 GHz. The enhanced high frequency response of the device with ROP passivation can be ascribed to the relief of the retarding effect caused by the interface state on the sidewalls. An opening eye diagram at 28 Gbps without using any trans-impedance amplifier (TIA) is demonstrated, indicating a reliable device transmission performance.
Martín Valderrama et al
We have experimentally studied the relationship in between non-collinear magnetization states in ferromagnetic (FM) multilayers and their resulting magneto-optical (MO) properties. Hereby, we observe that the phase of the complex-valued MO parameters are especially sensitive towards non-collinear magnetization states and enable their unambiguous detection. For the purpose of our experimental study, we designed, fabricated and characterized a set of epitaxial FM/NM/FM multilayers with in-plane uniaxial anisotropy, in which the non-magnetic (NM) interlayer thickness t was varied, so that tunable FM interlayer exchange coupling strength in between the two FM layers could be achieved. Furthermore, the two FM layers were made from different alloys, so that they exhibit different levels of magnetocrystalline anisotropy, which enables a collinear to non-collinear magnetization state transition upon applying a magnetic field H away from the in-plane easy axis for samples with sufficiently large t. Utilizing generalized magneto-optical ellipsometry, we determined the full reflection matrix R as a function of H and we observed that the phases of the complex-valued MO coefficients in R change with H in multilayers that have sufficiently weak interlayer coupling strength, i.e. large t, which can only happen if non-collinear magnetization states of varying non-collinearity occur in those samples. For samples with small t, corresponding to strongly exchange coupled FM layers, this effect is absent, consistent with the existence of collinear magnetization states in those multilayers for all H values.
Rahaman et al
Ferromagnetic resonance and magneto-optic Kerr effect (MOKE) techniques are employed to unravel the nature of 'in-plane' (IP) magnetic anisotropy and magnetization reversal (MR) processes in magnetron-sputtered 100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films, deposited (and subsequently annealed) at different substrate temperatures (Ts) ranging from 200°C to 550°C. By varying TS, the CFTS films are produced with different amounts of anti-site (AS) atomic disorder. Irrespective of the degree of AS disorder, the IP uniaxial magnetic anisotropy (UMA) is prevalent in all the CFTS films. The TS450 and TS500 films, deposited at TS = 450 oC and 500 oC, stand out as they have (i) the least AS disorder, (ii) lowest value (α = 0.0055) of the Gilbert damping constant, (iii) high saturation magnetization (≅ 770 ) at 300 K, (iv) UMA
at300 K, (v) spin-wave stiffness (0 ≅ 175Å2 and, as in other CFTS films,the electron-magnon interaction is primarily responsible for the thermal renormalization of.Furthermore, in the TS450 and TS500 films, MOKE hysteresis loops at various angles ()
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Dongho Lee et al 2024 J. Phys. D: Appl. Phys.
Utilizing alternative propellants has been recognized as a strategy to reduce the total cost of propellants in electric propulsion-based missions. The aim of this study is to quantify the Hall effect thruster (HET) performance and operating characteristics using a Kr-Ar mixture to enable mission designers to evaluate the impact on mission and spacecraft design. We present the performance and plume plasma properties of the P5 5 kW-class HET operated with a Kr-Ar mixture with Ar volumetric flow rate fractions from 0 to 100%. The thruster is characterized at discharge power levels of 2.6 kW and 4.1 kW at constant discharge current and voltage over the range of Ar fractions. Despite higher ionization energy and lower mass of Ar, the thruster exhibited a similar level of thrust within 2% when comparing the pure Kr and 26%-Ar mixture cases. The derived ion energy distribution functions and analytical modeling suggest that the characteristic length for the ionization region is extended as the Ar fraction increases. The increased residence time of Kr at the extended ionization region and background energetic electrons from the ionized Ar neutrals are considered to cause this enhanced ionization of the injected Kr neutrals, leading to a 6% higher Kr ion density at the 26%-Ar case even at the 16% reduced injected neutral density than in the pure Kr case. The enhanced Kr ionization and generated Ar ions in the 26%-Ar case consequently led to a comparable thrust with that of the pure Kr case. The study indicates that mixing Ar with approximately 26% volumetrically with Kr can provide a similar or even higher thrust performance at the same discharge power. This will be particularly advantageous for various space missions that require high impulses by reducing the total cost of the propellant.
Lin Li et al 2024 J. Phys. D: Appl. Phys.
We present a detailed method for accumulating Ca+ ions controllably in a linear Paul trap. The ions are generated by pulsed laser ablation and dynamically loaded into the ion trap by switching the trapping potential on and off. The loaded ions are precooled by buffer gas and then laser-cooled to form Coulomb crystals for verifying quantity. The number of ions is controlled by manipulating the trapping potential of the ion trap, partial pressure of buffer gas and turn-on time of the entrance end cap voltage. With single-pulse laser ablation, the number of trapped ions ranges from tens to ten thousand. The kinetic energy of loaded ions can be selected via the optimal turn-on time of the entrance end cap. Using multiple-pulse laser ablation, the number is further increased and reaches about 4×10^4. The dynamic loading method has wide application for accumulating low-yielding ions via laser ablation in the ion trap.
Anthony Ouali et al 2024 J. Phys. D: Appl. Phys.
The plasma-water interface is a complex medium characterized by interesting physical and chemical phenomena useful for many applications such as water processing or material synthesis. In this context, optimizing the transport of reactive species from plasma to water is crucial, and it may be achieved by increasing the surface-to-volume ratio of the processed object. Herein, we study the characteristics of a streamer produced by nanosecond discharge in air gap with a droplet of deionized water. The discharge is characterized experimentally by electrical measurements as well as by 1-ns-intergated ICCD images. To report plasma properties that are not accessible through experiment, such as the spatio-temporal evolution of electron density, electric field, and space charge density, a 2D fluid model is developed and adapted to the experimental geometry. Due to the fast propagation of the ionization front, the droplet is considered as a solid dielectric. The model solves Poisson's equation as well as the drift-diffusion equation for electrons, positive ions, and negative ions. The utilized transport coefficients are tabulated as a function of the reduced electric field. Helmholtz equations are also included in the model to account for photoionization. The electron impact ionization source obtained from the model is compared to experimental 1-ns-integrated ICCD images, and a good agreement is observed. Finally, the model is used to investigate the influence of droplet dielectric permittivity and wetting angle (the angle between a liquid surface and a solid surface) on the properties of the discharge. Overall, the data reported herein demonstrate that the model can be used to investigate plasma properties under different conditions.
Kinga Kutasi et al 2024 J. Phys. D: Appl. Phys.
A surface-wave microwave discharge is applied to deposit reactive oxygen and nitrogen species (RONS) into the liquid subsequently used as a medium for laser ablation of a Zn metallic target. It is shown that during laser ablation in plasma-treated liquids the H2O2 concentration decreases, while in deionized water (DIW) significant H2O2 is produced. Meanwhile, the pH - initially adjusted by applying reductive metals - increases in the acidic liquids and decreases in the alkaline ones. During months of storage the pH of colloids stabilize around pH 6, which insures the long-term stability of RONS. It is demonstrated that in DIW metallic Zn NPs are created, which gradually oxidize during storage, while in the plasma-treated liquids ZnO NPs are produced with the mean size of 17 nm. In the alkaline plasma-treated liquid the NPs form large aggregates, which slows the dissolution of NPs. In the acidic and neutral solutions besides NPs nanosheets are also formed, which during storage evolve into nanosheet networks as a result of the dissolution of NPs. The band gap of the colloidal ZnO is found to decrease with the formation of aggregates and nanosheet networks. The ZnO NPs ablated in plasma-treated liquids exhibit a high-intensity visible emission covering the green-to-red spectral region. The photoluminescence spectra is dominated by the orange-red emission - previously not detected in the case of laser-ablated ZnO NPs and attributed to the interstitial Zn and oxygen sites - and the yellow emission, which can be attributed to the OH groups on the surface. It is shown that during months of storage, due to the dissolution of NPs and formation of nanosheets, the intensity of the visible emission decreases and shifts to the blue-green spectral region.
Md Abu Jafar Rasel et al 2024 J. Phys. D: Appl. Phys. 57 295102
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.
Ondrej Sefl et al 2024 J. Phys. D: Appl. Phys.
The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina, are employed as the dielectric coating (insulation) of test samples. Each material's dielectric properties change differently with relative humidity—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating's thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity).Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the unsealed alumina material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the relative humidity of the surrounding air is varied between 10% to 80 %.
S Harini et al 2024 J. Phys. D: Appl. Phys.
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.
Rajkumar Patra et al 2024 J. Phys. D: Appl. Phys.
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.
Antoine Post et al 2024 J. Phys. D: Appl. Phys.
A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1MHz is employed to create
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.
Pai Zhao et al 2024 J. Phys. D: Appl. Phys.
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
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.