Showing papers in "Applied Physics Letters in 2021"
TL;DR: It is shown that co-packaged silicon photonics and electronics enable the continued progress of both fields and propel further innovation in both.
Abstract: Silicon photonics is advancing rapidly in performance and capability with multiple fabrication facilities and foundries having advanced passive and active devices, including modulators, photodetectors, and lasers. Integration of photonics with electronics has been key to increasing the speed and aggregate bandwidth of silicon photonics based assemblies, with multiple approaches to achieving transceivers with capacities of 1.6 Tbps and higher. Progress in electronics has been rapid as well, with state-of-the-art chips including switches having many tens of billions of transistors. However, the electronic system performance is often limited by the input/output (I/O) and the power required to drive connections at a speed of tens of Gbps. Fortunately, the convergence of progress in silicon photonics and electronics means that co-packaged silicon photonics and electronics enable the continued progress of both fields and propel further innovation in both.
197 citations
TL;DR: In this article, the authors studied van der Waals heterostructures composed of MoSi2N4 contacted by graphene and NbS2 monolayers using first-principles density functional theory calculations.
Abstract: A two-dimensional (2D) MoSi2N4 monolayer is an emerging class of air-stable 2D semiconductors possessing exceptional electrical and mechanical properties. Despite intensive recent research effort devoted to uncover the material properties of MoSi2N4, the physics of electrical contacts to MoSi2N4 remains largely unexplored thus far. In this work, we study van der Waals heterostructures composed of MoSi2N4 contacted by graphene and NbS2 monolayers using first-principles density functional theory calculations. We show that the MoSi2N4/NbS2 contact exhibits an ultralow Schottky barrier height (SBH), which is beneficial for nanoelectronics applications. For the MoSi2N4/graphene contact, the SBH can be modulated via the interlayer distance or via external electric fields, thus opening up an opportunity for reconfigurable and tunable nanoelectronic devices. Our findings provide insights into the physics of 2D electrical contacts to MoSi2N4 and shall offer a critical first step toward the design of high-performance electrical contacts to MoSi2N4-based 2D nanodevices.
113 citations
TL;DR: An outlook on technological developments required to bring SNSPDs to the next level: a photon-counting, fast time-tagging imaging, and multi-pixel technology that is also compatible with quantum photonic integrated circuits.
Abstract: Two decades after their demonstration, superconducting nanowire single-photon detectors (SNSPDs) have become indispensable tools for quantum photonics as well as for many other photon-starved applications. This invention has not only led to a burgeoning academic field with a wide range of applications but also triggered industrial efforts. Current state-of-the-art SNSPDs combine near-unity detection efficiency over a wide spectral range, low dark counts, short dead times, and picosecond time resolution. The present perspective discusses important milestones and progress of SNSPDs research, emerging applications, and future challenges and gives an outlook on technological developments required to bring SNSPDs to the next level: a photon-counting, fast time-tagging imaging, and multi-pixel technology that is also compatible with quantum photonic integrated circuits.
105 citations
TL;DR: In this paper, a femtosecond-laser-textured super-hydrophilic copper foam surface was used to enhance the vapor generation rate by combining solar-driven thermal and wind effects.
Abstract: Solar-driven vapor generation is a sustainable and environmentally friendly method for water purification Despite recent progress on photothermal steam generation, the rate of vapor generation remains low Here, we enhance the vapor generation rate by combining solar-driven thermal and wind effects on a femtosecond-laser-textured superhydrophilic copper foam surface Significant solar power can be absorbed and transformed into heat on the treated surface This solar power can also be converted into electric power to generate wind to further accelerate steam generation The upper superhydrophilic foam surface facilitates the continuous supply of water A pre-wetted polyurethane sponge minimizes heat loss by preventing direct contact between the heated foam and bulk water The as-prepared evaporator achieved a water evaporation rate of ∼76 kg m−2 h−1 under one sun irradiation (1 kW m−2) at a wind speed of 3 m s−1 This is a promising technology for enhancing water evaporation rates in seawater desalination and wastewater treatment applications
100 citations
TL;DR: In this article, a high performance NiO/β-Ga2O3 pn heterojunction diode with an optimized interface by annealing is presented, which leads to a record high power figure of merit of 0.65 GW/cm2.
Abstract: In this Letter, we report a high-performance NiO/β-Ga2O3 pn heterojunction diode with an optimized interface by annealing. The electrical characteristics of the pn diode without annealing (PND) and with annealing (APND) are studied systematically. The APND device has a lower specific on-resistance of 4.1 mΩ cm2, compared to that of the PND, 5.4 mΩ cm2. Moreover, for the APND, a high breakdown voltage of 1630 V with lower leakage current is achieved, which is 730 V higher than that of the PND. The enhanced electrical performance of the APND leads to a record high power figure of merit of 0.65 GW/cm2 in Ga2O3-based pn diodes, which is among the best reported results in Ga2O3 power devices. In addition, the interface trap density of the diode decreases from 1.04 × 1012 to 1.33 × 1011 eV−1 cm−2 after annealing, contributing to much lower hysteresis. Simultaneously, the ideality factor n for the APND is steady at elevated temperatures due to the stable interface. The results of C − V characteristics reveal the bulk defects inside the nickel oxide film grown by sputtering, which are calculated by high- and low-frequency capacitance methods. X-ray photoelectron spectroscopy of NiO illustrates the reasons for the changes in the concentration of holes and defects in the film before and after annealing. This work paves the way for further improving the performance of Ga2O3 diode via interface engineering.
81 citations
TL;DR: The basic concepts of SOT and its relevance for magnetization switching are introduced and several methods to realize deterministic SOT switching in the absence of an external field are focused on.
Abstract: Spintronics, that is, the utilization of electron spin to enrich the functionality of microelectronics, has led to the inception of numerous novel devices, particularly magnetic random-access memory (MRAM). Over the last decade, significant effort has been devoted to magnetization manipulation using spin-orbit torque (SOT), which shows great promise for ultrafast and energy-efficient MRAM. In this Perspective, we summarize the latest progress in the study of SOT and highlight some of the technical challenges facing the development of practical SOT devices. After introducing the basic concepts of SOT and its relevance for magnetization switching, we will focus on several methods to realize deterministic SOT switching in the absence of an external field, which is a requirement for practical SOT devices. Additionally, we summarize the materials used in SOT devices. The final section is devoted to the most important recent advances in the application of SOT devices, including SOT-MRAM, spin logic, spin Hall nano-oscillators, and neuromorphic devices.
79 citations
TL;DR: In this article, the authors highlight key strategies to circumvent these hurdles and hopefully bring this material system to maturity to create far-reaching opportunities for Si-compatible infrared photodetectors, sensors, and emitters for applications in free-space communication, infrared harvesting, biological and chemical sensing, and thermal imaging.
Abstract: (Si)GeSn semiconductors are finally coming of age after a long gestation period. The demonstration of device-quality epi-layers and quantum-engineered heterostructures has meant that tunable all-group IV Si-integrated infrared photonics is now a real possibility. Notwithstanding the recent exciting developments in (Si)GeSn materials and devices, this family of semiconductors is still facing serious limitations that need to be addressed to enable reliable and scalable applications. The main outstanding challenges include the difficulty to grow high-crystalline quality layers and heterostructures at the desired content and lattice strain, preserve the material integrity during growth and throughout device processing steps, and control doping and defect density. Other challenges are related to the lack of optimized device designs and predictive theoretical models to evaluate and simulate the fundamental properties and performance of (Si)GeSn layers and heterostructures. This Perspective highlights key strategies to circumvent these hurdles and hopefully bring this material system to maturity to create far-reaching opportunities for Si-compatible infrared photodetectors, sensors, and emitters for applications in free-space communication, infrared harvesting, biological and chemical sensing, and thermal imaging.
76 citations
TL;DR: A reconfigurable active acoustic metalens is implemented to showcase scanning of the focus along arbitrary trajectories in free space with the help of a previously developed active acoustic metasurface platform.
Abstract: Acoustic metasurfaces have enabled unprecedented control over acoustic waves, offering opportunities in areas such as holographic rendering, sound absorption, and acoustic communication Despite the steady progress made in this field, most acoustic metasurface designs are passive in that they only provide static functionalities Here, a reconfigurable active acoustic metalens is implemented to showcase scanning of the focus along arbitrary trajectories in free space with the help of a previously developed active acoustic metasurface platform Each unit cell of the metasurface contains a cavity, whose size can be tuned continuously by a dynamic control system to adjust the phase of the reflected wave While this work focuses on beam focusing, it could hold great promise for a wide range of applications including acoustic levitation and tweezers
69 citations
TL;DR: In this article, the biaxial strain and external electric field are used for bandgap engineering of bilayer MoSi2N4 and WSi2Ns4 and it is found that strain can lead to indirect bandgap to direct bandgap transition and electric field can result in semiconductor to metal transition.
Abstract: With exceptional electrical and mechanical properties and at the same time air-stability, layered MoSi2N4 has recently drawn great attention. However, band structure engineering via strain and electric field, which is vital for practical applications, has not yet been explored. In this work, we show that the biaxial strain and external electric field are effective ways for the bandgap engineering of bilayer MoSi2N4 and WSi2N4. It is found that strain can lead to indirect bandgap to direct bandgap transition. On the other hand, electric field can result in semiconductor to metal transition. Our study provides insights into the band structure engineering of bilayer MoSi2N4 and WSi2N4 and would pave the way for its future nanoelectronics and optoelectronics applications.
64 citations
TL;DR: In this paper, the authors focus on temporal multilayer structures, and propose the synthesis of higher-order transfer functions by modeling the wave propagation through a generalized temporal multi-layer structure, consisting of a cascade over time of different media.
Abstract: Temporal metamaterials are artificial materials whose electromagnetic properties change over time. In analogy with spatial media and metamaterials, where their properties change smoothly or abruptly over space, temporal metamaterials can exhibit a smooth variation over time, realizing a temporal non-homogeneous medium, or a stepwise transition, and the temporal version of dielectric slabs or multilayer structures. In this Letter, we focus our attention on temporal multilayer structures, and we propose the synthesis of higher-order transfer functions by modeling the wave propagation through a generalized temporal multilayer structure, consisting of a cascade over time of different media. The tailoring of the scattering response of the temporal structure as a function of frequency is presented, deriving the corresponding scattering coefficients for a properly designed set of medium properties, i.e., permittivity and permeability, and application time, in analogy with what is typically done in optical and electromagnetic spatial multilayered structures. This allows us to design novel electromagnetic and optical devices with higher-order transfer functions by exploiting the temporal dimension instead of the spatial one.
63 citations
TL;DR: In this article, a tunable phononic crystal plate with Y-shaped prisms is designed to support valley transport of elastic waves, based on the analogy of the quantum valley Hall effect.
Abstract: Topological insulators have attracted intensive attention due to their robust properties of path defect immunity, with diverse applications in electromagnetic, acoustic, and elastic systems. The recent development of elastic topological insulators (ETIs), based on artificially structured phononic crystals, has injected new momentum into the manipulation of elastic waves. Earlier ETIs with unreconfigurable geometry and narrow frequency bandgaps hinder the exploration and design of adaptable devices. In this work, a tunable phononic crystal plate with Y-shaped prisms is designed to support valley transport of elastic waves, based on the analogy of the quantum valley Hall effect. By rotating the prisms to reconstruct the configuration, the mirror symmetry is broken to open a new bandgap. Based on this characteristic, we design an interface between two ETIs with different symmetry-broken geometries, which supports topologically protected edge states. We further design a reconfigurable device for elastic wave channel switching and beam splitting and demonstrate it both numerically and experimentally. In addition, in order to meet the requirement of the wide frequency range, the genetic algorithm is adopted to optimize the geometry so as to achieve the broadband valley transportation of elastic waves. The results obtained in this paper can promote the practical applications of tunable broadband elastic wave transmission.
TL;DR: In this paper, the authors clarify some commonly held misconceptions about chalcogenide phase change materials and offer a perspective on new research frontiers in the field of PCM.
Abstract: Uniquely furnishing giant and nonvolatile modulation of optical properties and chalcogenide phase change materials (PCMs) have emerged as a promising material to transform integrated photonics and free-space optics alike. The surge of interest in these materials warrants a thorough understanding of their characteristics specifically in the context of photonic applications. This article seeks to clarify some commonly held misconceptions about PCMs and offer a perspective on new research frontiers in the field.
TL;DR: In this paper, the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN4 using first-principles calculations were investigated.
Abstract: Motivated by the recent experimental realization of a two-dimensional (2D) BeN4 monolayer, in this study we investigate the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN4 using first-principles calculations. The calculated phonon band dispersion reveals the dynamical stability of a free-standing BeN4 layer, while the cohesive energy indicates the energetic feasibility of the material. Electronic band dispersions show that monolayer BeN4 is a semi-metal whose conduction and valence bands touch each other at the Σ point. Our results reveal that increasing the layer number from single to six-layers tunes the electronic nature of BeN4. While monolayer and bilayer structures display a semi-metallic behavior, structures thicker than that of three-layers exhibit a metallic nature. Moreover, the optical parameters calculated for monolayer and bilayer structures reveal that the bilayer can absorb visible light in the ultraviolet and visible regions better than the monolayer structure. Our study investigates the electronic properties of Dirac-semimetal BeN4 that can be an important candidate for applications in nanoelectronic and optoelectronic.
TL;DR: In this article, a three-layer staggered quantum well (QW) was used to improve the energy efficiency of InGaN-based yellow light-emitting diodes (LEDs) with high brightness.
Abstract: High-efficiency InGaN-based yellow light-emitting diodes (LEDs) with high brightness are desirable for future high-resolution displays and lighting products. Here, we demonstrate efficient InGaN-based yellow (∼570 nm) LEDs with optimized three-layer staggered quantum wells (QWs) that are grown on patterned sapphire substrates. Numerical simulations show that the electron–hole wavefunction overlap of staggered InGaN QWs with high In content exhibits a 1.7-fold improvement over that of square InGaN QWs. At the same injection current, LEDs with staggered QWs exhibit lower forward voltages and narrower full widths at half maximum than LEDs with square QWs. The light output power and external quantum efficiency of a staggered QW LED are 10.2 mW and 30.8%, respectively, at 15 mA. We combine atomic probe tomography (APT), time-resolved photoluminescence (TRPL), and transmission electron microscopy (TEM) with energy-dispersive x-ray (EDX) mapping spectroscopy to shed light on the origin of enhanced device performance. APT results confirm the staggered In profile of our designed staggered QWs structure, and TRPL results reveal decreased defect-state carrier trapping in staggered QWs. Furthermore, TEM with EDX mapping spectroscopy supports the viewpoint that staggered QWs exhibit uniform elemental distribution and improved crystal quality. Together, these factors above contribute to enhanced LED performance. Our study shows that staggered InGaN QWs provide a promising strategy for the development of LEDs that are efficient in the long-wavelength region.
TL;DR: In this paper, the authors demonstrate the use of a Rydberg atom-based sensor for determining the angle of arrival of an incident radio frequency (RF) wave or signal.
Abstract: In this work, we demonstrate the use of a Rydberg atom-based sensor for determining the angle of arrival of an incident radio frequency (RF) wave or signal. The technique uses electromagnetically induced transparency in Rydberg atomic vapor in conjunction with a heterodyne Rydberg atom-based mixer. The Rydberg atom mixer measures the phase of the incident RF wave at two different locations inside an atomic vapor cell. The phase difference at these two locations is related to the direction of arrival of the incident RF wave. To demonstrate this approach, we measure phase differences of an incident 19.18 GHz wave at two locations inside a vapor cell filled with cesium atoms for various incident angles. Comparisons of these measurements with both the full-wave simulation and the plane wave theoretical model show that these atom-based sub-wavelength phase measurements can be used to determine the angle of arrival of an RF field.
TL;DR: In this article, a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron mobility transistor (HEMT) configuration was demonstrated.
Abstract: In this work, we demonstrate a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron mobility transistor (HEMT) configuration. When the device is biased at off state, the peak photoresponsivity (R) of 3.6 × 107 A/W under 265 nm illumination and 1.0 × 106 A/W under 365 nm illumination can be obtained. Those two R values are one of the highest among the reported UVPTs at the same detection wavelength under off-state conditions. In addition, we investigate the gate-bias (VGS) dependent photoresponse of the fabricated device with the assistance of band structure analysis. It was found that a more negative VGS can significantly reduce the rise/decay time for 265 nm detection, especially under weak illumination. This can be attributed to a largely enhanced electric field in the absorptive AlGaN barrier that pushes the photo-generated carriers rapidly into the GaN channel. In contrast, the VGS has little impact on the switching time for 365 nm photodetection, since the GaN channel has a larger absorption depth and the entire UVPT simply acts as a photoconductive-type device. In short, the proposed AlGaN/GaN HEMT structure with the superior photodetection performance paves the way for the development of next generation UVPTs.
TL;DR: Machine-learning approaches, the versatility of metamaterials, and more advanced interface circuits should receive more attention from researchers, since these cutting-edge techniques may have the potential to address the multi-physics modeling problem of FIV energy harvesters and significantly improve the operation performance.
Abstract: Flow-induced vibration (FIV) energy harvesting has attracted extensive research interest in the past two decades. Remarkable research achievements and contributions from different aspects are briefly overviewed. Example applications of FIV energy harvesting techniques in the development of Internet of Things are mentioned. The challenges and difficulties in this field are summarized from two sides. First, the multi-physics coupling problem in FIV energy harvesting still cannot be well handled. There is a lack of system-level theoretical modeling that can accurately account for fluid–structure interaction, the electromechanical coupling, and complicated interface circuits. Second, the robustness of FIV energy harvesters needs to be further improved to adapt to the uncertainties in practical scenarios. To be more specific, the cut-in wind speed is expected to be further reduced and the power output to be increased. Finally, Perspectives on the future development in this direction are discussed. Machine-learning approaches, the versatility of metamaterials, and more advanced interface circuits should receive more attention from researchers, since these cutting-edge techniques may have the potential to address the multi-physics modeling problem of FIV energy harvesters and significantly improve the operation performance. In addition, in-depth collaborations between researchers from different disciplines are anticipated to promote the FIV energy harvesting technology to step out of the lab and into real applications.
TL;DR: In this paper, a β-Ga2O3 HJBS diode with p-type NiOx was shown to achieve a low specific on-resistance (Ron,sp) of 1.94 mΩ cm2 with a breakdown voltage 1.34
Abstract: In this paper, we show that high-performance β-Ga2O3 hetero-junction barrier Schottky (HJBS) diodes with various β-Ga2O3 periodic fin widths of 1.5/3/5 μm are demonstrated with the incorporation of p-type NiOx. The β-Ga2O3 HJBS diode achieves a low specific on-resistance (Ron,sp) of 1.94 mΩ cm2 with a breakdown voltage of 1.34 kV at a β-Ga2O3 periodic fin width of 3 μm, translating to a direct-current Baliga's power figure of merit (PFOM) of 0.93 GW/cm2. In addition, we find that by shrinking the β-Ga2O3 width, the reverse leakage current is minimized due to the enhanced sidewall depletion effect from p-type NiOx. β-Ga2O3 HJBS diodes with p-type NiOx turn out to be an effective route for Ga2O3 power device technology by considering the high PFOM while maintaining a suppressed reverse leakage current.
TL;DR: In this article, high performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms.
Abstract: In this Letter, high-performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga2O3 p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of EC-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (Ron,sp) of 7.7 mΩ·cm2 are achieved, yielding a high Baliga's figure-of-merit (FOM, BV2/Ron,sp) of 0.46 GW/cm2. The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga2O3 bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga2O3 power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga2O3.
TL;DR: In this article, the authors demonstrate the demonstration of ferroelectricity in ScxAl1-xN grown by molecular beam epitaxy on GaN templates, which is nearly lattice-matched with GaN, exhibiting a coercive field of ∼ 4.2 MV/cm at 10 kHz and a remnant polarization of ∼ 135 μC/cm2.
Abstract: We report on the demonstration of ferroelectricity in ScxAl1-xN grown by molecular beam epitaxy on GaN templates. Distinct polarization switching is unambiguously observed for ScxAl1-xN films with Sc contents in the range of 0.14–0.36. Sc0.20Al0.80N, which is nearly lattice-matched with GaN, exhibiting a coercive field of ∼ 4.2 MV/cm at 10 kHz and a remnant polarization of ∼135 μC/cm2. After electrical poling, Sc0.20Al0.80N presents a polarization retention time beyond 105 s. No obvious fatigue behavior can be found with up to 3 × 105 switching cycles. The work reported here is more than a technical achievement. The realization of ferroelectric single-crystalline III–V semiconductors by molecular beam epitaxy promises a thickness scaling into the nanometer regime and makes it possible to integrate high-performance ferroelectric functionality with well-established semiconductor platforms for a broad range of electronic, optoelectronic, and photonic device applications.
TL;DR: In this paper, the state-of-the-art set of GaAs-based quantum dots is presented as a benchmark to discuss the challenges toward the realization of practical quantum networks.
Abstract: The generation and long-haul transmission of highly entangled photon pairs is a cornerstone of emerging photonic quantum technologies with key applications such as quantum key distribution and distributed quantum computing. However, a natural limit for the maximum transmission distance is inevitably set by attenuation in the medium. A network of quantum repeaters containing multiple sources of entangled photons would allow overcoming this limit. For this purpose, the requirements on the source's brightness and the photon pairs' degree of entanglement and indistinguishability are stringent. Despite the impressive progress made so far, a definitive scalable photon source fulfilling such requirements is still being sought after. Semiconductor quantum dots excel in this context as sub-Poissonian sources of polarization entangled photon pairs. In this work, we present the state-of-the-art set by GaAs based quantum dots and use them as a benchmark to discuss the challenges toward the realization of practical quantum networks.
TL;DR: In this paper, the authors present challenges and future directions related to the up-scaling of nanowire devices and detector systems toward widespread applications in demanding real-world settings.
Abstract: Superconducting nanowires have emerged as a powerful tool for detecting single photons in the visible and near-infrared range with excellent device performance metrics. We outline challenges and future directions related to the up-scaling of nanowire devices and detector systems toward widespread applications in demanding real-world settings. Progress on achieving superconducting single-photon detectors with a large active area and an increasing number of pixels is reviewed, comparing the recent literature in terms of the reported key detector parameters. Furthermore, we summarize currently available readout and multiplexing schemes for multi-pixel detector arrays and discuss implications of the recently discovered microwire-based detector geometries.
TL;DR: In this paper, the authors summarize the current progress of 18-electron half-Heusler thermoelectric materials and focus on the discovery and challenge of the cation-deficient 19-electRON half-heusler compounds with the vacancy-related short-range order.
Abstract: Semiconducting half-Heusler compounds with the valence electron count of 18 have been identified as a class of promising high-temperature thermoelectric materials. Recently, nominal 19-electron half-Heusler compounds, traditionally regarded as metals, have gained reacquaintance and popularity due to their unexpected high thermoelectric performance and fascinating defective structure. In this Perspective, we summarize the current progress of 18-electron half-Heusler thermoelectric materials and focus on the discovery and challenge of the cation-deficient 19-electron half-Heusler compounds with the vacancy-related short-range order. Further outlook on the discovery of promising half-Heusler thermoelectrics and the insightful understanding of the defect-tailored thermoelectric properties are offered.
TL;DR: The transverse thermoelectric effect refers to the conversion of a temperature gradient into a transverse charge current, or vice versa, which appears in a conductor under a magnetic field or in a magnetic material with spontaneous magnetization as discussed by the authors.
Abstract: The transverse thermoelectric effect refers to the conversion of a temperature gradient into a transverse charge current, or vice versa, which appears in a conductor under a magnetic field or in a magnetic material with spontaneous magnetization. Among such phenomena, the anomalous Nernst effect in magnetic materials has been receiving increasing attention from the viewpoints of fundamental physics and thermoelectric applications owing to the rapid development of spin caloritronics and topological materials science. In this research trend, a conceptually different transverse thermoelectric conversion phenomenon appearing in thermoelectric/magnetic hybrid materials has been demonstrated, enabling the generation of a large transverse thermopower. Here, we review the recent progress in fundamental and applied studies on the transverse thermoelectric generation using magnetic materials. We anticipate that this perspective will further stimulate research activities on the transverse thermoelectric generation and lead to the development of next-generation thermal energy harvesting and heat-flux sensing technologies.
TL;DR: In this paper, the authors provide a perspective on the recent progress, challenges, and prospects of curvilinear magnetism with a special focus on novel physical effects caused by tailoring curvature and topology of conventional magnetic materials.
Abstract: By exploring geometry-governed magnetic interactions, curvilinear magnetism offers a number of intriguing effects in curved magnetic wires and curved magnetic films. Recent advances in experimental techniques change the status of curvilinear magnetism, allowing the exploitation of 3D curved nanomagnets in emerging devices with numerous applications. Here, we provide our Perspective on the recent progress, challenges, and prospects of curvilinear magnetism with a special focus on novel physical effects caused by tailoring curvature and topology of conventional magnetic materials.
TL;DR: In this paper, the optical, structural, mechanical, and electronic properties of the C6N7 monolayer were investigated by employing the density functional theory (DFT) method.
Abstract: The fabrication of the C6N7 monolayer [Zhao et al., Sci. Bull. 66, 1764 (2021)] motivated us to discover the optical, structural, mechanical, and electronic properties of the C6N7 monolayer by employing the density functional theory (DFT) method. We find that the shear modulus and Young's modulus of the C6N7 monolayer are smaller than the relevant values of graphene. However, Poisson's ratio is more significant than that of graphene. Applying the PBE (HSE06) functional bandgap of the C6N7 monolayer is 1.2 (1.97) eV, and the electronic dispersion is almost isotropic around the Γ point. C6N7 is more active in the ultraviolet region as compared to the visible light region. This study provides outstanding results, highlighting the bright viewpoints for the applications of the C6N7 monolayer in electronic and optical systems.
TL;DR: The metasurface not only promises a reduction in the size and complexity of optical components but also brings new functionalities, which will help in the development of flat optical components.
Abstract: Flat optical components based on metasurfaces will appear in our daily life in the near future. Our discussion focuses on metasurface-based components consisting of sub-wavelength spaced dielectric nanostructures in the optical region. After an introduction to the underlying technology, the advantages of metasurfaces are highlighted and the efforts in the development of metasurface components is discussed. The metasurface not only promises a reduction in the size and complexity of optical components but also brings new functionalities. Examples of achromatic optical components, a full-Stokes metasurface camera, and a metasurface depth sensor with superior performance are highlighted. Finally, future trends and opportunities are discussed.
TL;DR: In this paper, the authors investigated the electronic properties and thermoelectric performance of triangulene π-dimer junctions with the twist angle from 0° to 60° by using first-principles calculations in combination with a non-equilibrium Green's function method.
Abstract: In this work, we investigate the electronic properties and thermoelectric performance of triangulene π-dimer junctions with the twist angle from 0° to 60° by using first-principles calculations in combination with a non-equilibrium Green's function method. It is found that the triangulene π-dimer can be transformed between nonmagnetic state and antiferromagnetic or ferromagnetic state by varying the twist angle. The reason is that the relative rotation between the monomers weakens the overlap of two single occupied molecular orbital. More importantly, our theoretical analysis shows that the ferromagnetic states of the triangulene π-dimer junctions at the twist angle of 20°, 30°, and 60° have outstanding thermoelectric performance. The corresponding ZT value is as high as around 6, which is mainly contributed from the spin splitting nature. This work is instructive to improve the thermoelectric properties of π-stacking molecular junctions or organic polymers.
TL;DR: The progress that has been made and the remaining challenges for applying terahertz imaging to skin cancer detection are discussed.
Abstract: It was first suggested that terahertz imaging has the potential to detect skin cancer twenty years ago. Since then, THz instrumentation has improved significantly: real time broadband THz imaging is now possible and robust protocols for measuring living subjects have been developed. Here, we discuss the progress that has been made as well as highlight the remaining challenges for applying THz imaging to skin cancer detection.
TL;DR: In this paper, the temperature dependence of ferroelectric switching in Al0.84Sc 0.16N, Al 0.93B 0.07N, and AlN thin films was investigated.
Abstract: This manuscript reports the temperature dependence of ferroelectric switching in Al0.84Sc0.16N, Al0.93B0.07N, and AlN thin films. Polarization reversal is demonstrated in all compositions and is strongly temperature dependent. Between room temperature and 300 °C, the coercive field drops by almost 50% in all samples, while there was very small temperature dependence of the remanent polarization value. Over this same temperature range, the relative permittivity increased between 5% and 10%. Polarization reversal was confirmed by piezoelectric coefficient analysis and chemical etching. Applying intrinsic/homogeneous switching models produces nonphysical fits, while models based on thermal activation suggest that switching is regulated by a distribution of pinning sites or nucleation barriers with an average activation energy near 28 meV.