Showing papers in "ACS applied electronic materials in 2022"

Dielectric Stability and Energy-Storage Performance of BNT-Based Relaxor Ferroelectrics through Nb5+ and Its Excess Modification

Abstract: The ever-increasing development of compact electronic equipment consumption impels us to design lead-free high-performance dielectric energy-storage materials. Herein, the dielectric and polarization mechanism of BNT-BT-BSTN lead-free relaxors with slim polarization hysteresis loops is investigated through B-site modulation. Substitution by stoichiometric and excessive Nb content is proposed to hinder the oxygen vacancies and reinforce the insulation. Complex impedance spectroscopy shows that all compositions possess n-type dominant conduction behavior. The generation of oxygen vacancies and Ti reduction can be further restricted, caused by the excessive Nb content, leading to the increased dielectric resistivity. Interestingly, simultaneous improvement of energy-storage density (2.07 J/cm3) and efficiency (94.5%) is achieved at a relatively low electric field at the high dopant concentration as a result of the fascinating enhancement in polarization, which may be attributed to the impurity or distorted phase caused by Nb excess. The enhanced stability against dielectric and energy-storage performance is also obtained. All these features guarantee the promising prospects of application for BNT-based dielectrics.

Current Applications and Future Potential of Rare Earth Oxides in Sustainable Nuclear, Radiation, and Energy Devices: A Review

Abstract: To date, rare earth oxides (REOs) have proven to be key components in generating sustainable energy solutions, ensuring environmental safety and economic progress due to their diverse attributes. REOs’ exceptional optical, thermodynamic, and chemical properties have made them indispensable in a variety of sophisticated technologies, including electric vehicle magnets, portable energy devices, fuel cell catalysts, radiation shielding, dosimetry, and many others. Therefore, the successful incorporation of rare earth elements (REEs) into host materials in controlled concentrations offers competitive advantages to fabricate portable energy devices, radiation sensors, and radiation shielding glasses, as well as to improve the performance of existing photovoltaic cells, which is of great interest to both researchers and industry. As the global demand for REEs grows rapidly, it is critical to comprehend the underlying physics as well as the wider consequences of REEs on sustainable energy and nuclear technologies, both in the near and long term. However, despite their relevance, a focused review on the applications, prospects, and challenges of REOs in photovoltaics, nuclear, and energy devices is still unavailable. To this effort, this review succinctly reports recent experimental studies on eight REOs (R2O3, R = Yb, Er, Sm, Eu, Y, Gd, Dy, and Ce) and their specific applications and industrial aspects. While several subdomains are reported, the applications of REOs in next-generation solar cells and photovoltaic devices for promoting zero-emission clean energy and rechargeable batteries for electric vehicles (EVs) are the most pioneering ones. Furthermore, REOs’ chemical stability and compositional versatility allow them to be used in a variety of high-efficiency energy converters, including solid oxide fuel cells (SOFCs). From the perspective of thermodynamic and structural stability, the gamma and neutron absorptivity of REO-doped (such as Dy3+, Eu3+, Sm3+, Nd3+, etc.) glasses shows improved shielding performance in radiation domains. Aside from the applications, the prospects of REOs presented in this article are likely to encourage current and future scholars to pursue a wide range of important studies in the fields of energy and nuclear systems. This review also reports the key challenges (i.e., material degradation, phase transformation, magnetic entropy shift, etc.) associated with REOs in a standalone section. These challenges demand the immediate attention of scientists and engineers for efficient, cost-effective, and environmentally sustainable solutions. At the end, future advancement pathways for REO applications are also suggested.

Research Progress of High-Sensitivity Perovskite Photodetectors: A Review of Photodetectors: Noise, Structure, and Materials

Abstract: In recent years, perovskite materials have been widely used in optoelectronic components due to a series of advantages such as a high light absorption coefficient, high carrier mobility, long carrier diffusion length, shallow defect level, and high crystallinity. The photodetector is an important photoelectric device that can convert light radiation signals into electrical signals, so it has significant applications and scientific research value in military, civil, and other fields. Semiconductor materials are an essential part of photodetectors. So far, many semiconductor materials have been used in photodetectors, including silicon, carbon nanotubes, III–V compounds, and quantum dots, and remarkable progress has been made in improving the light detection performance and device structure design. However, photodetectors based on these materials usually require expensive materials, rigorous processes, and complex manufacturing conditions, which hinder their commercial application. Optoelectronic devices based on perovskite materials have the advantages of a simple fabrication process, low cost, and high performance, making them widely considered in optoelectronic applications. This review focuses on the preparation and photoelectric performance of the perovskite photodetector and the effect of noise on the performance of the perovskite detector and how to reduce the detector’s noise to increase the detection rate. In this review, we mainly discuss the following four aspects of work. First, we discuss the various noises of perovskite photodetectors. Then, we explore ways to reduce the noise of perovskite detectors with different structures (photoconductor, photodiode, and phototransistor). We explore corresponding improvement methods for different device structure detectors to reduce noise and improve the detection performance. Next, we discuss the different synthesis methods of all-inorganic perovskites, including solution processing synthesis, vapor-assisted solution synthesis, and chemical vapor deposition. Finally, current challenges of perovskite photodetectors (toxicity, stability, flexibility, and self-powered) are summarized and prospected.

Amorphous InGaZnO (a-IGZO) Synaptic Transistor for Neuromorphic Computing

Abstract: Brain-inspired neuromorphic computing emulates the biological functions of the human brain to achieve highly intensive data processing with low power consumption. In particular, spiking neural networks (SNNs) that consist of artificial synapses can process spatiotemporal information while enabling energy-efficient neuromorphic computations. Artificial synapses are a key element of sophisticated neuromorphic hardware, so a significant amount of research has been conducted to develop various materials and device structures. Of these, we assess amorphous InGaZnO (IGZO)-based synaptic transistors that have exhibited properties suitable for emerging hybrid optoelectronic neuromorphic systems. Here, we describe the fundamental principles of neuromorphic computations, neuron circuits, and synaptic devices according to recent studies. IGZO-based transistors are discussed, from their material properties to various device physics for electronic- and/or photonic-neuromorphic systems with extraordinary biological emulations.

Highly Sensitive and Flexible Capacitive Pressure Sensor Based on a Dual-Structured Nanofiber Membrane as the Dielectric for Attachable Wearable Electronics

Abstract: Wearable devices are an indispensable part of modern life, and flexible capacitive pressure sensors as their luminous subset have assumed a significant role in this day and age owing to ultralow power consumption. In recent years, a fierce debate as well as numerous studies have been conducted to improve the sensitivity of capacitive pressure sensors, but a vital challenge of the mass production of a highly sensitive sensor by a low-cost method still remains. In this paper, to meet industrial demands, we propose a simple method to fabricate sandwich-structured capacitive pressure sensors on an industrial scale and at low cost; as the electrospinning collector, stainless steel screens with regular patterns and structures were utilized to gain the dielectric with both external microstructure and internal pores (dual structure). The prepared pressure sensor is composed of a thermoplastic-urethane electrospun nanofiber film, as a dielectric, in the middle and two conductive woven fabrics on the upper and lower sides as electrodes. Benefiting from the prolific air in the dielectric layer, the designed sensor demonstrates outstanding sensing performance, such as high sensitivity (0.28 kPa–1) in the low-pressure region (0–2 kPa), fast response/relaxation time (65/78 ms), and high-grade durability (1000 cycles). Moreover, the produced pressure sensor is employed for not only detecting human limb movements and object grasping but also detecting pressure distribution in sensor array state, so demonstrating the application potential in attachable wearable electronics.

Review on Organic–Inorganic Two-Dimensional Perovskite-Based Optoelectronic Devices

Abstract: Organic–inorganic two-dimensional (2D) perovskite is an optoelectronic material, with quantum-well structure and improved moisture stabilities, which has been widely used in various optoelectronic devices recently. In this review, the structure and properties of organic–inorganic 2D perovskite materials are first briefly introduced. After that, according to the different photoelectron coupling mechanisms, the recent progress of typical 2D perovskite-based optoelectronic devices is described in detail: including photodetectors, light-emitting diodes, solar cells, and lasers, as well as some optoelectronic devices (e.g., optical memory and optical synapses). We analyzed the influence of structure, manufacturing process, and material selection on device performance and showed promising progress in different applications. Subsequently, we proposed the possible breakthrough development direction of 2D perovskite-based optoelectronic devices in the coming years. This work points out the way for future progress of 2D perovskite-based optoelectronic devices, which is conducive to further improving device performance and inspiring designs of high-performance organic–inorganic 2D perovskite-based optoelectronic devices.

Self-Powered X-ray Detection and Imaging using Cs2AgBiCl6 Lead-Free Double Perovskite Single Crystal

Abstract: Despite the high performance of lead-halide perovskite-based X-ray detectors, the toxicity and instability of lead require the development of lead-free perovskites for X-ray detection applications. Here, we demonstrate lead-free and environmentally friendly, all-inorganic millimeter-sized Cs2AgBiCl6 double perovskite single crystal (SC) for X-ray detection and imaging. The high dark resistivity (3.1 × 1010 Ω cm), high carrier mobility-lifetime product (5.36 × 10–4 cm2 V–1), and lower trap density (1.18 × 109 cm–3) in these double perovskite SCs render them a potential material for X-ray detection. The fabricated vertical structured X-ray detector exhibits a sensitivity of 325.78 μC Gy air–1 cm–2 and a limit of detection of 241 nGy s–1. Additionally, the Cs2AgBiCl6 SCs exhibit self-powered X-ray detection at zero bias with a sensitivity of 7 μC Gy air–1 cm–2. Moreover, the fabricated perovskite X-ray detector exhibits a stable and robust performance under continuous X-ray irradiation and long-term ambient storage. Further, we demonstrated the imaging capability of the Cs2AgBiCl6 X-ray detector using a metal test object and obtained a distortion-free image. Our findings demonstrate that the Cs2AgBiCl6 single crystal-based X-ray detectors have great potential as practical X-ray detectors and imaging for medical radiography.

Enhanced Electrohydrodynamics for Electrospinning a Highly Sensitive Flexible Fiber-Based Piezoelectric Sensor

Abstract: The single-jet mode in an electrohydrodynamic (EHD) system is the most desirable mode for generating uniform droplets and fibers and has many applications in numerous fields. Several studies have been carried out to enhance the performance of the EHD process focusing on this mode. In this paper, we introduce the use of a chamfered nozzle in an EHD system to greatly extend the single-jet mode’s voltage range, and generally, to enhance the EHD process in terms of control capability and product quality. We carried out simulations and experiments to compare the performance of a chamfered nozzle and conventional flat-end nozzle. Both theoretical analysis and experiments demonstrate that the chamfered nozzle in an EHD system reduces the critical voltage, broadens the voltage range for the single-jet mode, and enhances homogeneity in particle and fiber generation. Furthermore, the chamfered nozzle’s advantages were demonstrated in fabricating highly uniform poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) fibers for piezoelectric sensor development. Owing to the fibers’ excellent quality, the sensor shows high sensitivity that can detect and differentiate between the drops of a metal bead, a water droplet, and an oil droplet. The use of a chamfered nozzle with its advantages shows potential for development of better EHD-based devices.

Accordion-like-Ti3C2 MXene-Based Gas Sensors with Sub-ppm Level Detection of Acetone at Room Temperature

Abstract: Compared to traditional-metal oxide-based gas sensors (MOS), the progress of high-performance room-temperature (RT) gas-sensing materials has captivated a lot of interest in recent years. MXenes, two-dimensional (2D) transition-metal carbides/nitrides, have recently been discovered and gained tremendous consideration for gas sensing applications due to their superior chemical and physical properties. Herein, we successfully synthesized accordion-like Ti3C2Tx MXene multilayers by a selective HF-etching method at 60 °C to be used as a chemiresistive sensor for acetone vapor. The fabricated sensor successfully detected acetone vapor at the parts per billion (ppb) level and showed a p-type sensing behavior. The limit of detection (LOD) of acetone vapor was about 250 ppb with a fast response time of 53 s. The sensor exhibited good repeatability, high selectivity toward acetone among other test gases, and excellent stability even after 4 months. The sensing mechanism was proposed in terms of the interaction between the charge carriers of accordion-like Ti3C2Tx, multiple hydrogen bonding between different functional groups on the MXene surface, and acetone vapor species. The prepared sensor also showed high sensitivity toward acetone vapor at RT (23 °C); hence, it lends itself high potential as a breath sensor for diabetic patients.

Emergent Phenomena in Magnetic Two-Dimensional Materials and van der Waals Heterostructures

Abstract: Two-dimensional (2D) materials and their van der Waals (vdW) heterostructures provide powerful platforms for exploring fascinating physical phenomena and implementing intriguing applications. The recent discovery of 2D magnetic materials opens up many exciting topics in the research of 2D materials. 2D magnetic materials not only exhibit diverse properties on their own, which can be effectively controlled via external stimuli, but also can serve as a part of vdW heterostructures, creating a variety of unprecedented properties and functionalities. The field of 2D magnetism has grown rapidly in the past few years. In this review, we summarize the recent progress on the emergent phenomena in this active field. We review the well-established understanding of typical 2D magnetic materials and the vdW heterostructures and introduce the manipulations of their magnetic properties. In addition, we discuss the interplay between magnetism and topology in some recently discovered 2D materials. Moreover, we also address the valley relevant physics and the topological spin textures in 2D magnetic materials. Finally, we highlight some future interests in this promising field.

Recent Studies on the Humidity Sensor: A Mini Review

Abstract: For the time being, a number of humidity measurement instruments made of a variety of different materials and operating on a number of different principles are accessible. There are numerous ways that may be utilized to categorize them. I begin by discussing the most commonly used designs for flexible humidity sensors. Following that, the section on humidity-sensitive materials, the sensing mechanism, the major properties of humidity sensors, and the influence of temperature on humidity sensors are discussed. The study concludes with a review of current research in this area, as well as the challenges that exist. The majority of the studies included in this review were published between 2020 and 2022. These remarks are expected to serve as an overview to humidity measurement for researchers and graduate students who are new to the field or who are already working in it and would like to learn more about the issue.

Highly Sensitive Band Alignment of the Graphene/MoSi2N4 Heterojunction via an External Electric Field

Abstract: The combination of graphene (GR) and monolayer MoSi2N4 has attracted much attention; however, the comprehension of its electrical contact modulation is still not fully explored. Herein, the influence of the interlayer spacing and external electric field on the interfacial characteristic and electronic structure of the GR/MoSi2N4 heterojunction was systematically investigated using first-principles calculations. It is found that a stable van der Waals heterojunction forms when GR incorporates on the MoSi2N4 sheets. The results indicate that both the type and height of the Schottky barrier could be tuned by altering the interlayer spacing between GR and MoSi2N4 sheets or applying a vertical external electric field on the GR/MoSi2N4 heterojunction. Noteworthily, the Schottky barrier height markedly changes about 0.2–0.3 eV with the increase of external electric field per 0.1 V·Å–1. It is confirmed that the change of energy bands is caused by the charge redistribution with the interlayer spacing and external electric field. These findings will provide rational evidence for the design of next-generation field-effect transistors.

Broadband NIR Garnet Phosphors with Improved Thermal Stability via Energy Transfer

Abstract: Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have attracted more and more attention because of their many potential optical applications. However, high-performance broadband NIR phosphors are still rare. Here, we demonstrated that Cr3+-to-Yb3+ energy transfer (ET) is an effective strategy to boost the properties of NIR luminescence materials in Ca2LaZr2Ga2.8Al0.2O12: Cr3+,Yb3+ (CZGG: Cr3+, Yb3+). In addition to the enrichment of short-wave NIR emission in 900–1100 nm, the overall thermal stability of CZGG: Cr3+, Yb3+ can be improved by leveraging high-efficiency ET from Cr3+ to Yb3+, ascribed to the fast ET from Cr3+ to its nearest Yb3+ as well as the superior thermal stability of Yb3+. Additionally, an NIR pc-LED device was packaged via combining CZGG: Cr3+, Yb3+ with a blue LED chip to demonstrate its possible application in compact nonvisible light sources.

Zn2SnO4 Thin Film Based Nonvolatile Positive Optoelectronic Memory for Neuromorphic Computing

Abstract: An optoelectronic synaptic device based on the ITO/Zn2SnO4(ZTO)/ITO structure is fabricated which integrates the electronic memory and optical sensing properties along with synaptic functions. The fabricated device shows over 80% optical transparency for the entire visible region (400–800 nm). Post-oxide annealing treatment is performed in a nitrogen environment at 200 °C. Significant improvements in bipolar resistive switching properties of the device with low SET voltage (+0.93 V) and long DC endurance cycles (∼12000) are observed in the annealed device. The linearity of such memristive synapse is improved for 350 training epochs with a total number of 175000 pulses. The spike time dependent plasticity learning rule for the annealed device is demonstrated through the electric field. The optical sensing capabilities of this device including photonic potentiation (responsivity: 0.52 μA/W), photonic paired pulse facilitation by adjusting time interval between two identical light pulses, learning experience behavior, and multilevel memory feature by the repetition of optical pulse for ∼103 s are demonstrated under the blue light (wavelength “λ” = 405 nm) illumination at 50 mW/cm2. Photonic potentiation and electric depression behavior of the device mimic its nonvolatile synaptic plasticity. The linear fitting of I–V curve illustrates the dominance of Schottky emission and Poole–Frenkel conduction mechanisms at high and low resistance states, respectively. The electric response of the device is explained by the oxygen vacancy based filamentary model. The trapping and detrapping of electrons during the adsorption and desorption processes of atmospheric oxygen molecules on the ITO surface are responsible for the photoconduction phenomenon. To train the Hopfield neural network (HNN) model for image processing of 28 × 28 pixels, the normalized experimental data of long-term potentiation/depression are employed to mimic the learning behavior of the human brain. The convergence of electronic data storage and optical sensor has high potential which provides a path toward the future smart invisible optoelectronics for artificial intelligence.

Toward 100% Spin–Orbit Torque Efficiency with High Spin–Orbital Hall Conductivity Pt–Cr Alloys

Abstract: 5d transition metal Pt is the canonical spin Hall material for efficient generation of spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures. However, for a long while with tremendous engineering endeavors, the damping-like SOT efficiencies (${\xi}_{DL}$) of Pt and Pt alloys have still been limited to ${\xi}_{DL}$<0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin-orbital Hall conductivity (${\sigma}_{SH}{\sim}6.5{\times}10^{5}({\hbar}/2e){\Omega}^{-1}{\cdot} m^{-1}$) can be developed. Especially for the Cr-doped case, an extremely high ${\xi}_{DL}{\sim}0.9$ in a Pt$_{0.69}$Cr$_{0.31}$/Co device can be achieved with a moderate Pt$_{0.69}$Cr$_{0.31}$ resistivity of ${\rho}_{xx}{\sim}133 {\mu}{\Omega}{\cdot}cm$. A low critical SOT-driven switching current density of $J_{c}{\sim}3.2{\times}10^{6} A{\cdot}cm^{-2}$ is also demonstrated. The damping constant (${\alpha}$) of Pt$_{0.69}$Cr$_{0.31}$/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high ${\sigma}_{SH}$, giant ${\xi}_{DL}$, moderate ${\rho}_{xx}$, and reduced ${\alpha}$ of such a Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.

Highly Efficient Invisible TaO_<i>x</i>/ZTO Bilayer Memristor for Neuromorphic Computing and Image Sensing

Abstract: In today’s new era, multifunctional devices are most prominent due to their compact design, reduction in operating cost, and reduced need of being limited to single functional devices. The electronic synapses and electro-optic functions of the device are such a cornerstone for neuromorphic computing and image sensing applications. In this work, we fabricate a ZTO-based invisible memristor for simulating the human brain for neuromorphic computing and image sensing applications. Long-term potentiation and depression─at least 790─repetitive cycles are observed which ensures the synaptic strength. The first-principles density functional theory calculations give insights into the device’s microscopic charge density distribution and switching mechanism. The experimental potentiation and depression data are used to train the Hopfield neural network (HNN) for image recognition of 28 × 28 pixels comprising 784 synapses. The HNN can be successfully trained to identify the input image with a training accuracy of more than 96% in 17 iterations. Furthermore, the device shows excellent highly stable electrical set and optical reset endurance for at least 1500 cycles without degradation, good retention (104 s) at 90 °C, and high transparency (∼85%). This work not only enables us to use our device in artificial intelligence but also provides a significant advantage in the field of image sensing.