The 50 most-cited articles in Journal of Applied Physics, 2022

There is a growing concern within the surface science community that the massive increase in the number of XPS articles over the last few decades is accompanied by a decrease in work quality including in many cases meaningless chemical bond assignment. Should this trend continue, it would have disastrous consequences for scientific research. While there are many factors responsible for this situation, the lack of insight of physical principles combined with seeming ease of XPS operation and insufficient training are certainly the major ones. To counter that, we offer a comprehensive tutorial written in the form of a step-by-step guide starting from experimental planning, through sample selection and handling, instrument setup, data acquisition, spectra analysis, and results presentation. Six application examples highlight the broad range of research questions that can be answered by XPS. The topic selection and the discussion level are intended to be accessible for novices yet challenging possible preconceptions of experienced practitioners. The analyses of thin film samples are…

For the first time in history, we are seeing a branching point in computing paradigms with the emergence of quantum processing units (QPUs). Extracting the full potential of computation and realizing quantum algorithms with a super-polynomial speedup will most likely require major advances in quantum error correction technology. Meanwhile, achieving a computational advantage in the near term may be possible by combining multiple QPUs through circuit knitting techniques, improving the quality of solutions through error suppression and mitigation, and focusing on heuristic versions of quantum algorithms with asymptotic speedups. For this to happen, the performance of quantum computing hardware needs to improve and software needs to seamlessly integrate quantum and classical processors together to form a new architecture that we are calling quantum-centric supercomputing. In the long term, we see hardware that exploits qubit connectivity in higher than 2D topologies to realize more efficient quantum error correcting codes, modular architectures for scaling QPUs and parallelizing…

The present Tutorial provides a description of the growth of bulk β-Ga2O3 single crystals by the Czochralski method with a focus on the critical growth aspects. In particular, it details the thermodynamics of Ga2O3 as the key factor for crystal growth along with comprehensive solutions that are essential for crystal size scale-up. Also, free carrier absorption is discussed, as it has a great impact on growth stability. The crystal growth direction and intentional doping, as important factors for crystal growth, are described as well. All of the aspects of the crystal growth are accompanied by resulting crystals, their structural quality, and basic physical properties.

This article focuses on the atomic force microscopy-infrared (AFM-IR) technique and its recent technological developments. Based on the detection of the photothermal sample expansion signal, AFM-IR combines the high spatial resolution of atomic force microscopy with the chemical identification capability of infrared spectroscopy to achieve submicrometric physico-chemical analyses. Since the first publication in 2005, technological improvements have dramatically advanced the capabilities of AFM-IR in terms of spatial and spectral resolution, sensitivity, and fields of applications. The goal of this paper is to provide an overview of these developments and ongoing limitations. We summarize recent progress in AFM-IR implementations based on the major AFM contact, tapping, and peak force tapping modes. Additionally, three new trends are presented, namely, AFM-IR applied to mineral samples, in fluid and a novel, purely surface sensitive AFM-IR configuration, to probe top layers. These trends demonstrate the immense potential of the technique and offer a good insight into the scope of…

The effective operation of certain electronic, medical, industrial, and testing equipment relies on high-quality focusing and imaging capability, which also plays a vital role in the field of wave physics. Therefore, continuously improving the resolution capacity is essential. However, in a homogeneous medium dominated by the diffraction limit, the best resolution for wave focusing and imaging could only reach half the wavelength corresponding to the lowest operating frequency, significantly hindering the relevant application value. The development of phononic crystals (PCs) and acoustic metamaterials (AMMs) has realized sub-wavelength focusing and super-resolution imaging and attracted increasing research attention in physics, mechanics, engineering, and biomedical science. This Tutorial explained the basic principles and traditional methods of acoustic focusing and imaging. Then, the implementation principles and related research progress of sub-wavelength focusing and super-resolution imaging based on artificial acoustic devices, including but not limited to PCs and AMMs, were…

Research of lead-free perovskite solar cells (PSCs) has gained attention with an urgent intent to eliminate toxic lead in perovskite materials. The prime intention of this research is to supplement the current research progress with a comparative analysis of various lead-free PSCs through numerical simulation analysis using solar cell capacitance simulator (SCAPS)-1D software. Lead-based toxicity and instability have been one of the major hurdles in restricting perovskite solar cells from being commercialized. This study caters in substituting the need for toxic lead (Pb)-based PSCs with more efficient Pb-free PSCs. The device simulation is carried out in the n–i–p configuration of FTO/[6,6]-phenyl-C61-butyric acid methyl ester/perovskite layer/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine/Au using six distinct Pb-free perovskites. The impact of various active layers, including hole and electron transport thicknesses and the concentration of doping on solar device performances, has been minutely probed and optimized. CsSnI3 based PSC shows the best power conversion efficiency of…

In recent years, the impressive photovoltaic performance of halide perovskites has been commonly attributed to their defect tolerance. This attribution is seemingly intuitive and has been widely promoted in the field, though it has not been rigorously assessed. In this Perspective, we critically discuss the proposition of defect tolerance in halide perovskites based on first-principles calculations. We show that halide perovskites actually do suffer from defect-assisted nonradiative recombination, i.e., they are not defect tolerant. The nonradiative recombination rates in halide perovskites are comparable to or even greater than those in more conventional semiconductors. We note that to obtain accurate defect properties in halide perovskites, the level of theory and computational details are highly important, which was previously not sufficiently recognized. A distinctive feature of halide perovskites is that they can be grown with moderate defect densities using low-cost deposition techniques. But, similar to the case of conventional semiconductors, defect engineering is still key…

Majorana bound states are quasiparticle excitations localized at the boundaries of a topologically nontrivial superconductor. They are zero-energy, charge-neutral, particle–hole symmetric, and spatially-separated end modes which are topologically protected by the particle–hole symmetry of the superconducting state. Due to their topological nature, they are robust against local perturbations and, in an ideal environment, free from decoherence. Furthermore, unlike ordinary fermions and bosons, the adiabatic exchange of Majorana modes is noncommutative, i.e., the outcome of exchanging two or more Majorana modes depends on the order in which exchanges are performed. These properties make them ideal candidates for the realization of topological quantum computers. In this tutorial, I will present a pedagogical review of 1D topological superconductors and Majorana modes in quantum nanowires. I will give an overview of the Kitaev model and the more realistic Oreg–Lutchyn model, discuss the experimental signatures of Majorana modes, and highlight their relevance in the field of topological…

The development of terahertz integrated circuits is vital for realizing sixth-generation (6G) wireless communication, high-speed on-chip interconnects, high-resolution imaging, on-chip biosensors, and fingerprint chemical detection. Nonetheless, the existing terahertz on-chip devices suffer from reflection, and scattering losses at sharp bends or defects. Recently discovered topological phases of light endow the photonics devices with extraordinary properties, such as reflectionless propagation and robustness against impurities or defects, which is vital for terahertz integrated devices. Leveraging the robustness of topological edge states combined with a low-loss silicon platform is poised to offer a remarkable performance of the terahertz devices providing a breakthrough in the field of terahertz integrated circuits and high-speed interconnects. In this Perspective, we present a brief outlook of various terahertz functional devices enabled by a photonic topological insulator that will pave the path for augmentation of complementary metal oxide semiconductor compatible terahertz…

The photothermal phenomenon involves material photon heating in the form of continuous waves, modulated waves, or pulses. The resulting temperature rise carries very rich information about the material's structures and thermophysical properties. This review is constructed to cover some of the extended ideas of the photothermal phenomenon for measuring a material's thermophysical properties and interface thermal conductance/resistance. For frequency-domain photothermal phenomena, the photoacoustic (PA) and photothermal radiation (PT) techniques provide great ways to measure coatings and suspended samples, which can also be measured using the laser flash and time-domain thermoreflectance (TDTR) techniques. Thermal probing based on electrical thermal sensing is successfully implemented in the transient photo-electro-thermal (TPET) and pulsed laser-assisted thermal relaxation (PLTR) techniques, which significantly extend the capability of laser flash technique to micro/nanoscale 1D structures. The energy transport state-resolved Raman (ET-Raman) is distinct from traditional techniques…

The technological and societal impacts of electronic devices based on Ge, Si, and compound semiconductors like GaAs have been profound, fueling the decades long quest in identifying ever-larger bandgap semiconductors to untap new applications and possibilities. Specifically, an increase in the bandgap leads to shorter wavelength emission and an increased breakdown electric field, which has direct consequences for solid-state lighting like light-emitting diodes (LEDs) and laser diodes (LDs) from the visible (blue-green, blue, and violet) and beyond (UV and deep-UV) spectral range and for radically improved power devices supported by a higher intrinsic breakdown strength. Wide bandgap (WBG) semiconductors represent the frontier of materials that satisfy these criteria and include group IV, III–V, and II–VI material families like SiC (3.2 eV), GaN (3.4 eV), and ZnO (3.4 eV), respectively. With even larger bandgaps exceeding 4 eV, ultrawide bandgap (UWBG) semiconductors include diamond, III-nitrides incorporating Al and B (e.g., AlN, BN, and AlGaN), and sesquioxides like Ga2O3 and…

The aim of this Tutorial is to help new researchers understand how to perform molecular dynamics (MD) simulations of the shock response of materials and to provide a brief discussion of how MD can provide important insights into issues in the shock physics of crystalline and amorphous materials. Two distinct approaches for generating shock waves are reviewed. Non-equilibrium MD simulations generate a shock front, usually moving along one axis of the sample, with the processes associated with shock wave propagation monitored throughout the simulation. Equilibrium MD simulations characterize the equilibrated state of a shocked material behind the shock wave front, without explicit consideration of the dynamics of wave propagation. Ultimately, using either method, and by using analysis techniques capable of extracting thermodynamic information and identifying defects, MD simulations can provide a powerful mechanistic understanding of shock that complements shock experiments.

Structural symmetry plays a crucial role in the electronic band structure and properties of two-dimensional materials. In contrast to graphene, monolayer transition metal dichalcogenides exhibit intrinsic in-plane asymmetry with suitable direct bandgaps and distinctive optical properties. Efforts have been devoted to breaking their out-of-plane mirror symmetry by applying external electric fields, vertical stacking, or functionalization. The successful fabrication of Janus transition metal dichalcogenides offers a synthetic strategy to breaking the vertical mirror symmetry, leading to a variety of novel properties, such as vertical piezoelectricity, Rashba spin splitting, and excellent exciton properties. Here, we discuss the universal fabrication approaches and unique properties of Janus transition metal dichalcogenides and further present a brief perspective on their potential applications and challenges.

This Perspective seeks to understand and assess why ultrawide bandgap (UWBG) semiconductor-based deep-UV photodetectors have not yet found any noticeable presence in real-world applications despite riding on more than two decades of extensive materials and devices’ research. Keeping the discussion confined to photodetectors based on epitaxial AlGaN and Ga2O3, a broad assessment of the device performance in terms of its various parameters is done vis-à-vis the dependence on the material quality. We introduce a new comprehensive figure of merit (CFOM) to benchmark photodetectors by accounting for their three most critical performance parameters, i.e., gain, noise, and bandwidth. We infer from CFOM that purely from the point of view of device performance, AlGaN detectors do not have any serious shortcoming that is holding them back from entering the market. We try to identify the gaps that exist in the research landscape of AlGaN and Ga2O3 solar-blind photodetectors and also argue that merely improving the material/structural quality and device performance would not help in making this…

The evolution of the Griffiths phase (GP) with a ferromagnetic metal (FMM) cluster above the Curie temperature (TC) and its effect on the magnetic properties, electrical transport, magnetoresistance (MR), and magnetocaloric effect (MCE) is studied comprehensively, using bulk compounds of La1−xBaxMnO3 (0.15 ≤ x ≤ 0.25) with different lattice distortions but with the same structural symmetry and space group. These La1−xBaxMnO3 samples show ferromagnetic transition at TC increasing from 229 K for x = 0.15–300 K for x = 0.25, in addition to the presence of GP with FMM clusters in the paramagnetic (PM) region, which have been confirmed by the combination of magnetization (susceptibility) measurements, the GP theory, and electron paramagnetic resonance technology. With increasing the Ba2+ ion doping, GP temperature (TG) and TC of La1−xBaxMnO3 are increased, and the GP regime is strengthened. The GP ratio in the PM region reached 27.7% for the sample with x = 0.20. The resistivity decreases and the FMM phase increases with increasing x from 0.15 to 0.25, which can be explained by the…

Non-Hermitian Hamiltonians provide an alternative perspective on the dynamics of quantum and classical systems coupled non-conservatively to an environment. Once primarily an interest of mathematical physicists, the theory of non-Hermitian Hamiltonians has solidified and expanded to describe various physically observable phenomena in optical, photonic, and condensed matter systems. Self-consistent descriptions of quantum mechanics based on non-Hermitian Hamiltonians have been developed and continue to be refined. In particular, non-Hermitian frameworks to describe magnonic and hybrid magnonic systems have gained popularity and utility in recent years with new insights into the magnon topology, transport properties, and phase transitions coming into view. Magnonic systems are in many ways a natural platform in which to realize non-Hermitian physics because they are always coupled to a surrounding environment and exhibit lossy dynamics. In this Perspective, we review recent progress in non-Hermitian frameworks to describe magnonic and hybrid magnonic systems, such as cavity magnonic…

Thermoreflectance-based techniques, such as pump–probe thermoreflectance (pump–probe TR) and thermoreflectance thermal imaging (TTI), have emerged as the powerful and versatile tools for the characterization of wide bandgap (WBG) and ultrawide bandgap (UWBG) semiconductor thermal transport properties and device temperatures, respectively. This Review begins with the basic principles and standard implementations of pump–probe TR and TTI techniques, illustrating that when analyzing WBG and UWBG materials or devices with pump–probe TR or TTI, a metal thin-film layer is often required. Due to the transparency of the semiconductor layers to light sources with sub-bandgap energies, these measurements directly on semiconductors with bandgaps larger than 3 eV remain challenging. This Review then summarizes the general applications of pump–probe TR and TTI techniques for characterizing WBG and UWBG materials and devices where thin metals are utilized, followed by introducing more advanced approaches to conventional pump–probe TR and TTI methods, which achieve the direct characterizations of…

Fe-based amorphous/nanocrystalline alloys exhibit excellent soft magnetic properties, including high saturation magnetic flux density (Bs), high permeability, low coercivity (Hc), and low magnetostriction. They are utilized in distribution transformers, transformers, reactors, and other devices. As green, energy-saving, and environmentally friendly materials, their application fields have more possibilities. In this paper, the development history, composition design principle, heat treatment process, magnetic properties, and annealing brittleness of Fe-based amorphous/nanocrystalline alloys are introduced.

Over the past decade, a combination of crystal structure prediction techniques and experimental synthetic work has thoroughly explored the phase diagrams of binary hydrides under pressure. The fruitfulness of this dual approach is demonstrated in the recent identification of several superconducting hydrides with Tcs approaching room temperature. We start with an overview of the computational procedures for predicting stable structures and estimating their propensity for superconductivity. A survey of phases with high Tc reveals some common structural features that appear conducive to the strong coupling of the electronic structure with atomic vibrations that leads to superconductivity. We discuss the stability and superconducting properties of phases containing two of these—molecular H2 units mixed with atomic H and hydrogenic clathrate-like cages—as well as more unique motifs. Finally, we argue that ternary hydride phases, whose exploration is still in its infancy, are a promising route to achieve simultaneous superconductivity at high temperatures and stability at low pressures.…

Routes to semi-stable phases of Ga2O3 are the subject of extended discussions based on the review of growth methods, growth conditions, and precursors in works that report semi-stable phases other than the thermally stable β phase. The focus here is on mist chemical vapor deposition because it has produced single-phase Ga2O3 of α, γ, and ε (or κ) in terms of the substrate materials, and features of this growth method for phase control are emphasized. Recent reports of phase control by other growth technology give a deeper understanding of how to determine and control the phases, increasing the opportunities to fully utilize the novel and unique properties of Ga2O3.

In order to harness the capabilities of terahertz waves, various metasurface-based functional devices have been developed recently. However, due to the limited usage of systematic optimization methodologies, many existing designs leave room for further bandwidth and efficiency improvement. This article provides an overview on the bandwidth limiting factors associated with metasurfaces and gives a tutorial on a semi-analytical approach to broadband design. The broadband approach incorporates network analysis and genetic algorithm to determine the frequency-independent optimal circuit parameters for multi-layer transmissive metasurfaces, so that targeted complex transmission coefficients can be achieved over a wide bandwidth. The broadband design approach is enabling the configuration and optimization of diverse metasurfaces for wavefront and polarization control of terahertz waves, including quarter- and half-waveplates.

Developing advanced electrode materials for supercapacitors (SCs) has received incredible attention. The suitable electrode for high capacitance and energy density are significant challenges for SCs. This work reports an efficient hydrothermal synthesis of MoS2 nanosheets on carbon cloth (MoS2@CC). The large surface area of the binder-free MoS2@CC electrode provides rich active sites and an improved electrolyte ion diffusion rate. The MoS2@CC electrode exhibits good electrochemical performance by delivering a high specific capacitance of 947 F g−1 at the current density of 1.0 A g−1 and retains an excellent capacitance of 96.5% over 10 000 cycles. The high performance of the MoS2@CC electrode can be clarified through density functional theory (DFT) calculations. The DFT outcomes reveal that the electrode possesses favorable Li-ion intercalation and adsorption properties. The calculated adsorption energy of −0.352 eV at the hollow site shows the high stability of the system. The low energy barrier of path 1 (0.83 eV) easily facilitates Li-ions in the electrode material, which is…

Since the beginning of the applications of non-destructive testing/evaluation (NDT/NDE) techniques, efforts have been made consistently to improve their detection sensitivity and resolution. In the present paper, factors governing lateral resolution in three major NDT techniques, viz., ultrasonic testing (UT), x-ray radiographic testing (XRT), and eddy current testing (ECT) are presented. Furthermore, a review of recent advances in these NDT techniques to reach the theoretically achievable resolution limit or even surpassing the same using alternate approaches is also discussed. For example, resolution in UT is theoretically limited to half the wavelength by the Rayleigh limit; however, subwavelength resolutions have been achieved through the applications of near field methods by capturing the evanescent field. On the other hand, the resolution achieved in XRT is primarily limited to half the source/focal spot size, which is many orders of magnitude larger than the wavelength. Over the years, the reduction in the focal spot from macro-focus to micro-focus and now to nano-focus has…

We use a multi-scale modeling to study the time-dependent dielectric breakdown of an amorphous (a-) HfO2 insulator in a metal–oxide–metal capacitor. We focus on the role played by electron injection in the creation of oxygen vacancies, which eventually form the percolation path responsible for dielectric breakdown. In this scenario, the electron transport through the dielectric occurs by multi-phonon trap assisted tunnelling (MPTAT) between O vacancies. Energy parameters characterizing the creation of oxygen vacancies and the MPTAT process are calculated using density functional theory employing a hybrid density functional. The results demonstrate that the formation of neutral O vacancies facilitated by electron injection into the oxide represents a crucial step in the degradation process dominating the kinetics at common breakdown fields. We further show the importance of the so-called “energetic correlation” effect, where pre-existing O vacancies locally increase the generation rate of additional vacancies accelerating the oxide degradation process. This model gives realistic…

Light microscopy is one of the most powerful techniques for nondestructive real-time imaging of specimens at a resolution beyond the reach of human eyes. However, the spatial resolution of any conventional microscope is fundamentally limited by the diffraction of light waves at the lens aperture. Microsphere-assisted microscopy (MAM) has emerged in the past decade as an interestingly simple yet efficient method to improve imaging resolution. In MAM, a micrometer-scale dielectric sphere is placed in the immediate vicinity of the specimen to enhance the imaging resolution and magnification. MAM is highly versatile and can be combined with various systems including wide-field, confocal, and fluorescent microscopes to name a few. The exact resolution enhancement mechanism in MAM is not yet clearly understood and is under intense investigation; however, fundamentally, it can be linked to the increase in the system's effective numerical aperture and evanescence wave collection, and possibly to contributions from photonic nanojet effect, resonance, and coherent effects. Various claims have…

Despite several decades long research on moving contact line dynamics due to its remarkable role in interfacial science and technological fields, there is still a significant lack of comprehensive knowledge about the true nature of the contact line. The moving contact line is much more complex than just a geometric flow condition. Given the role of moving contact line physics in numerous emerging advanced technologies including bioprinting, tissue engineering, pharmaceutical industry, smart functional coatings, flexible electronics, and healthcare, it is needed for scientific community to direct their focus in advancement on better understanding of interfacial science and physics of moving contact line. Therefore, this review primarily concentrates on the current physical theories which describe the moving contact line dynamics. Moreover, numerous potential and ongoing applications of moving contact line dynamics linked to the interfacial science are thoroughly discussed. Finally, this review presents the future perspectives related to the current challenges in moving contact line…

Aluminum nitride (AlN) is an insulator that has shown little promise to be converted to a semiconductor via impurity doping. Some of the historic challenges for successfully doping AlN include a reconfigurable defect formation known as a DX center and subsequent compensation that causes an increase in dopant activation energy resulting in very few carriers of electricity, electrons, or holes, rendering doping inefficient. Using crystal synthesis methods that generate less compensating impurities and less lattice expansion, thus impeding the reconfiguration of dopants, and using new dopants, we demonstrate: (a) well behaved bulk semiconducting functionality in AlN, the largest direct bandgap semiconductor known with (b) substantial bulk p-type conduction (holes = 3.1 × 1018 cm−3, as recently reported in our prior work), (c) dramatic improvement in n-type bulk conduction (electrons = 6 × 1018 cm−3, nearly 6000 times the prior state-of-the-art), and (d) a PN AlN diode with a nearly ideal turn-on voltage of ∼6 V for a 6.1 eV bandgap semiconductor. A wide variety of AlN-based…

In recent years, there has been significant fundamental research into surface phonon polaritons, owing to their ability to compress light to extremely small dimensions, low losses, and the ability to support anisotropic propagation. In this Perspective, after briefly reviewing the present state of mid-infrared optoelectronics, we will assess the potential of surface phonon polariton-based nanophotonics for infrared (3–100 μm) light sources, detectors, and modulators. These will operate in the Reststrahlen region where conventional semiconductor light sources become ineffective. Drawing on the results from the past few years, we will sketch some promising paths to create such devices and we will evaluate their practical advantages and disadvantages when compared to other approaches to infrared optoelectronics.

MXenes combine distinctive properties, including high electrical conductivity, high thermal conductivity, and efficient absorption of electromagnetic waves, which allow them to be utilized in various applications such as electrical energy storage, sensors, and functional composites. This study aims to grow thin and large area Mo2C flakes in a controlled manner by using chemical vapor deposition, avoiding surface functionalization, and limited lateral dimensions. Herein, we investigate the effects of CH4 flow, the precursor/catalyst (Mo/Cu) ratio, and flow rates of carrier gas on the growth of two-dimensional Mo2C structures. This study examines the effects of the precursor/catalyst (Mo/Cu) ratio and flow rates of carrier gas on the growth of Mo2C structures. Our results show that when the flow rates of CH4, catalyst/precursor (Cu/Mo) ratio, and carrier gas (N2/H2) ratio are varied, we can control both thickness (from 7 to 145 nm) and coverage of the substrate surface (from 11% to 68%) of the Mo2C flakes. Therefore, this study reveals that it is possible to realize centimeter-scale…

Electromagnetic (EM) composites have stimulated tremendous fundamental and practical interests owing to their flexible electromagnetic properties and extensive potential engineering applications. Hence, it is necessary to systematically understand the physical mechanisms and design principles controlling EM composites. In this Tutorial, we first provide an overview of the basic theory of electromagnetism about electromagnetic constitutive parameters that can represent the electromagnetic properties of materials. We show how this corpus allows a consistent construction of effective medium theories and allows for numerical simulation of EM composites to deal with structure–property relationships. We then discuss the influence of spatial dispersion of shaped inclusions in the material medium on the EM properties of composites, which has not been systematically illustrated in the context of this interdisciplinary topic. Next, artificial composites or metamaterials with peculiar properties not readily available in nature are highlighted with particular emphasis on the control of the EM…

This article reports lattice deformation and phase transition of AlScN thin films in the whole composition. AlScN films were deposited on Pt/Ta/SiO2/Si substrates by direct current magnetron reactive sputtering with Al and Sc targets. At Sc concentration up to 30%, AlScN has a wurtzite structure with piezoelectricity. Transition from a wurtzite phase to a two-phase mixture happens between 30% and 35% Sc concentration, and transition from a two-phase mixture to a cubic phase happens between 38% and 43% Sc concentration. The wurtzite structure gradually deforms with the decrease in lattice constant c from 16% to 35% Sc concentration. Lattice constant c at 38% Sc in the two-phase mixture region is larger than that of 35% Sc concentration. These increases mean that distortion of c axis for the wurtzite structure over 35% Sc concentration in the two-phase mixture region is considered to be released and/or eased due to the appearance of the cubic phase, and that Sc concentration of the wurtzite phase to be smaller and that of the cubic phase larger than the film composition measured by…

Significant progress has been achieved with silicon carbide (SiC) high power electronics and quantum technologies, both drawing upon the unique properties of this material. In this Perspective, we briefly review some of the main defect characterization techniques that have enabled breakthroughs in these fields. We consider how key data have been collected, interpreted, and used to enhance the application of SiC. Although these fields largely rely on separate techniques, they have similar aims for the material quality and we identify ways in which the electronics and quantum technology fields can further interact for mutual benefit.

Electrical percolation in two-phase materials involves a very singular behavior, manifested as a huge change in the electrical conductivity, for a given volume or mass fraction of the phase with higher conductivity. In contrast, in the case of heat transfer, in two-phase composite systems, analogous percolative phenomena are far more elusive and have been rather difficult to observe in various physical systems. In this Perspective, we present a critical analysis of experimental results and the application of theoretical models aimed to study the effects of percolation phenomena on the thermal and electrical properties of two-phase materials. Our attention will be focused on composites made of high conductivity particles in a polymeric matrix. The effect of several factors, such as the geometrical and physical characteristics of fillers and their connectivity with the matrix, the proportion between the conductivity of filler and the matrix, as well as the crucial role of interfacial thermal resistance, is considered. In particular, the differences between the thermal and electrical…

With the advancement and up-gradation of wireless technology, people worldwide are surrounded by microwaves, however, with the brighter side comes the darker side too. These microwave/electromagnetic wireless signals interfere with the environment/mankind and are referred to as electromagnetic interference (EMI)/electromagnetic or microwave pollution. Microwave/electromagnetic absorbers are used to mitigate this EMI or electromagnetic pollution. Researchers have been working on microwave absorbents of different kinds to save humans, their gadgets, electronically printed cards, etc. to create a healthy and radiation-free environment. Recently, there is an advancement in different forms of ferrite absorbers. This review presents a description of what are ferrite-based microwave absorbers, the preparation method of absorbers, the working principle, and detailed insights involving necessary models and mechanisms regarding microwave absorption. It also encapsulates the description of how the ferrite composition, morphology, doping, reflection loss peaks, and matrix account for optimizing…

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the…

Metal-trihalide perovskite quantum dots combine the unique semiconducting properties of bulk perovskites with the controllable exciton dynamics benefiting from the quantum confinement effect. Composition- and size-adjustable electronic and optical properties of perovskites convert into a variety of applications. Here, we start from a brief introduction to perovskite quantum dots, followed by a detailed description of the synthesis methods and surface modification/passivation strategies of these nano-sized particles. Then, we review the applications of perovskite quantum dots including light-emitting diodes, photovoltaics, catalysis, sensing, bioimaging, and lasers. Finally, we develop outlooks for promising futures toward the commercial application of perovskite quantum dots.

Materials research studies are dealing with a large number of images, which can now be facilitated via image-based machine learning techniques. In this article, we review recent progress of machine learning-driven image recognition and analysis for the materials and chemical domains. First, the image-based machine learning that facilitates the property prediction of chemicals or materials is discussed. Second, the analysis of nanoscale images including those from a scanning electron microscope and a transmission electron microscope is discussed, which is followed by the discussion about the identification of molecular structures via image recognition. Subsequently, the image-based machine learning works to identify and classify various practical materials such as metal, ceramics, and polymers are provided, and the image recognition for a range of real-scenario device applications such as solar cells is provided in detail. Finally, suggestions and future outlook for image-based machine learning for classification and prediction tasks in the materials and chemical science are…

Metalenses comprised of artificial subwavelength structures known as meta-atoms have demonstrated abilities beyond conventional bulky optical components by modulating the phase, amplitude, and polarization of light in an ultrathin planar form factor. In this Tutorial, we present the fundamental principles and practical design procedures to exploit the abilities of metalenses, including achromaticity, high numerical aperture, and tunability. The fundamental principles include both plasmonic and dielectric meta-atoms, which require different physics to describe their light–matter interactions. In the phase modulation section, we compare the methods of physically implementing phase via meta-atoms including both the propagation and geometric phase methods. Next, we cover the recent progress of nanofabrication procedures from the perspective of the metalenses using materials such as titanium dioxide, gallium nitride, and hydrogenated amorphous silicon. We further compare the various fabrication methods with regard to the resolution, size, cost, and optical properties of fabricated…

More than a decade of active electrocaloric (EC) material research has produced several EC materials that exhibit a giant electrocaloric effect (ECE) at high electric fields, which is assured by direct measurement. These EC materials have enabled the demonstration of EC cooling devices, which exhibit temperature lifts of more than 10 K. These research and development efforts have revealed the critical importance of electrical breakdown, which is common in all electric and dielectric materials and devices under high voltages and electric fields. In general, the electric field for reliable device operation of dielectrics has to be less than 25% of the typical electric breakdown strength. To realize EC cooling devices with competitive performance requires advanced EC materials that generate large ECE (ΔT > 5 K) under these low electric fields. Double-bond (DB) defect modified P(VDF-TrFE-CFE) relaxor polymers, as reported recently, generate large ECE under low electric fields without any fatigue effects even after 1 × 106 field cycles. These relaxor ferroelectrics promise to meet the…

The role of structural and dynamical disorder in semiconductors is a topic of fundamental relevance because of its contribution to the spectral line shape of the photoluminescence, and it plays a major role in ruling the carrier transport properties at the band edge. In this regard, a class of semiconductors, i.e., halide perovskites, deeply investigated in the last decade, shows a peculiar degree of disorder, which has only been recently under investigation. The interest to study disorder in halide perovskites is related to the large set of innovative applications of this class of materials, spanning from energy harvesting to high brilliance incoherent and coherent light emitters. In this perspective, we show that quantitative information on the disorder in halide perovskites can be extracted by deep analysis of the photoluminescence in different experimental conditions. Our study, conducted on a large set of samples of a metal halide perovskite, CsPbBr3, prepared with various synthesis/deposition methods, clarifies the relative weight of the static and dynamic contributions. A…

A multi-scale approach to electrospray ion source modeling has been developed. The evolution of a single-emitter electrospray plume in a pure ionic regime is simulated with a combination of electrohydrodynamic fluids and n-body particle modeling. Simulations are performed for the ionic liquid, EMI-BF4, firing in a positive pure-ion mode. The metastable nature of ion clusters is captured using an ion fragmentation model informed by molecular dynamics simulations and experimental data. Results are generated for three operating points (120, 324, and 440 nA) and are used to predict performance relevant properties, such as the divergence angle and the extractor surface impingement rate. Comparisons to experimental data recorded at similar operating points are provided.

The recent discovery of “giant” electrostrictors has re-ignited the interest in electrostriction, an electromechanical coupling existing in all dielectrics but overshadowed by its linear counterpart: piezoelectricity. In this Review, after a reminder of “classical” electrostriction, we propose a definition of “giant” electrostriction based on two empirical relations (“Newnham” relation and the one we posit). From this definition, we review previous reports on “giant” electrostrictors to assess their nature. Focusing on the ones satisfying our definition, we compare their performances and characteristics. We also identify some of the hurdles to overcome before their adoption in the wide range of electromechanical applications, despite their fundamental and applicative interests.

High room temperature n-type mobility, exceeding 300 cm2/Vs, was demonstrated in Si-doped AlN. Dislocations and CN−1 were identified as the main compensators for AlN grown on sapphire and AlN single crystalline substrates, respectively, limiting the lower doping limit and mobility. Once the dislocation density was reduced by the growth on AlN wafers, C-related compensation could be reduced by controlling the process supersaturation and Fermi level during growth. While the growth on sapphire substrates supported only high doping ([Si] > 5 × 1018 cm−3) and low mobility (∼20 cm2/Vs), growth on AlN with proper compensation management enabled controlled doping at two orders of magnitude lower dopant concentrations. This work is of crucial technological importance because it enables the growth of drift layers for AlN-based power devices.

Nano- and micro-electromechanical systems (N/MEMSs) are traditionally based on electrostatic or piezoelectric coupling, which couples electrical and mechanical energy through acoustic resonator structures. Most recently, N/MEMS devices based on magnetoelectrics are gaining much attention. Unlike electrostatic or piezoelectric N/MEMS that rely on an AC electric field or voltage excitation, magnetoelecric N/MEMS rely on the electromechanical resonance of a magnetostrictive/piezoelectric bilayer heterostructure exhibiting a strong strain-mediated magnetoelectric coupling under the excitation of a magnetic field and/or electric field. As a consequence, magnetoelectric N/MEMS enable unprecedented new applications, ranging from magnetoelectric sensors, ultra-compact magnetoelectric antennas, etc. This Tutorial will first outline the fundamental principles of piezoelectric materials, resonator design, specifically different acoustic modes, and piezoelectric-based N/MEMS applications, i.e., radio frequency front end filters and infrared radiation sensors. We will then provide an overview of…

The thermal properties of two-dimensional (2D) materials, such as MoS2, are known to be affected by interactions with their environment, but this has primarily been studied only with SiO2 substrates. Here, we compare the thermal conductivity (TC) and thermal boundary conductance (TBC) of monolayer MoS2 on amorphous (a-) and crystalline (c-) SiO2, AlN, Al2O3, and h-BN monolayers using molecular dynamics. The room temperature, in-plane TC of MoS2 is ∼38 Wm−1 K−1 on amorphous substrates and up to ∼68 Wm−1 K−1 on crystalline substrates, with most of the difference due to substrate interactions with long-wavelength MoS2 phonons (<2 THz). An h-BN monolayer used as a buffer between MoS2 and the substrate causes the MoS2 TC to increase by up to 50%. Length-dependent calculations reveal TC size effects below ∼2 μm and show that the MoS2 TC is not substrate- but size-limited below ∼100 nm. We also find that the TBC of MoS2 with c-Al2O3 is over twice that with c-AlN despite a similar MoS2 TC on both, indicating that the TC and TBC could be tuned independently. Finally, we compare the thermal…

In the power industry, sulfur hexafluoride (SF6) as an insulating gas is widely used in gas-insulated switchgears (GISs). Owing to the latent inner insulation defects of GIS, various SF6 gas decompositions are generated in the process of partial superheating and partial discharge (PD). The decomposition components and concentrations are different under different PD types. A number of gas sensors were reported for the detection of these decompositions. Photoacoustic spectroscopy (PAS) gas sensors have been developed for many applications owing to their high sensitivity and selectivity, such as gas pollutant detection, industrial process control, and non-invasive medical diagnosis. Due to the SF6 physical constants being different from that of nitrogen (N2) or air, the sensor structure should be redesigned. A detailed review of four different types of PAS-based gas sensors is discussed and compared.

Acoustic vortices provide a single-beam approach to manipulate objects with sizes from nanometers to millimeters, gaining increasing interest in recent years. The helical beam renders them good ability to trap particles in three dimensions stably. At the same time, the orbital angular momentum of acoustic vortices can be used to realize object rotation and data transmission. In this review, we summarize the generation and characterization of acoustic vortices. Furthermore, we present the application of acoustic vortices in particle manipulation, object rotation, acoustic communication, and especially in the biomedical field. Finally, perspectives on the future directions for acoustic vortex research are discussed.

The magnetic properties, critical behavior, and magnetocaloric effect of perovskite NdMnO3 are studied. The Nd ordering is induced by the Mn ferromagnetic component with antiferromagnetic coupling with each other and then magnetization reversal occurs due to Mn moments reorientation induced by the ordering Nd moments, which explains the phenomenon of negative magnetization at low temperatures. The critical behavior of NdMnO3 is studied using Kouvel–Fisher and self-consistent methods. The results show that the Kouvel–Fisher method is reliable and critical exponents are coming out as β = 0.462 for TC = 11.15 K, γ = 1.041 for TC = 11.42 K, δ = 3.252 by critical isotherm analysis. Magnetic exchange distance may decay as J(r)≈r−4.563, that is, somewhere between the three-dimensional Heisenberg model and the mean field model. Remarkably, three temperature transitions and the corresponding three extremum values including positive and negative entropy change are observed in NdMnO3, which is different from previous reports on NdMnO3. A positive entropy change as 3.82 J/kg K at 10–15 K for…

This work discusses the potential of combining non-thermal plasmas and conducting membranes for in situ resource utilization (ISRU) on Mars. By converting different molecules directly from the Martian atmosphere, plasmas can create the necessary feed-stock and base chemicals for processing fuels, breathing oxygen, building materials, and fertilizers. Different plasma sources operate according to different principles and are associated with distinct dominant physicochemical mechanisms. This diversity allows exploring different energy transfer pathways leading to CO2 dissociation, including direct electron-impact processes, plasma chemistry mediated by vibrationally and electronically excited states, and thermally driven dissociation. The coupling of plasmas with membranes is still a technology under development, but a synergistic effect between plasma decomposition and oxygen permeation across conducting membranes is anticipated. The emerging technology is versatile, scalable, and has the potential to deliver high rates of production of molecules per kilogram of instrumentation sent…