High-Performance Ferroelectric Thin Film Transistors with Large Memory Window Using Epitaxial Yttrium-Doped Hafnium Zirconium Gate Oxide.

Preventing ferroelectric materials from losing their ferroelectricity over a low thickness of several nanometers is crucial in developing multifunctional nanoelectronics. Epitaxially grown 5 at. % yttrium-doped Hf0.5Zr0.5O2 (YHZO) thin films exhibit an atomically smooth surface, an ability to maintain ferroelectricity even at a thickness of 10 nm, and excellent insulating properties, making them suitable for use as gate oxides in ferroelectric thin film transistors (FeTFTs). Through the epitaxial growth of a YHZO/La0.67Sr0.33MnO3 (LSMO)/SrTiO3 (STO) heterostructure, YHZO effectively retains its ferroelectricity and orthorhombic single phase, leading to enhancing electron mobility (∼19.74 cm2 V-1 s-1) and memory window (3.7 V) in the amorphous InGaZnO4 (a-IGZO)/YHZO/LSMO/STO FeTFTs. These FeTFTs demonstrate a consistent memory function with remarkable endurance (∼106 cycles) and retention (∼104 s). Furthermore, they sustain a constant memory window even under ±6 V bias stress for 104 s and exhibit excellent stability even under ±6 V/1 ms pulse cycling for 107 cycles. For comparison, a transistor with the same structure was fabricated using epitaxial nonferroelectric LaAlO3 (LAO) and epitaxial undoped Hf0.5Zr0.5O2 (HZO) as alternatives to YHZO. This study presents a novel approach to exploit the potential of YHZO in FeTFTs, contributing to the development of next-generation logic-in-memory.

Artificial Synapse Based on a δ-FAPbI3/Atomic-Layer-Deposited SnO2 Bilayer Memristor.

Halide perovskite-based resistive switching memory (memristor) has potential in an artificial synapse. However, an abrupt switch behavior observed for a formamidinium lead triiodide (FAPbI3)-based memristor is undesirable for an artificial synapse. Here, we report on the δ-FAPbI3/atomic-layer-deposited (ALD)-SnO2 bilayer memristor for gradual analogue resistive switching. In comparison to a single-layer δ-FAPbI3 memristor, the heterojunction δ-FAPbI3/ALD-SnO2 bilayer effectively reduces the current level in the high-resistance state. The analog resistive switching characteristics of δ-FAPbI3/ALD-SnO2 demonstrate exceptional linearity and potentiation/depression performance, resembling an artificial synapse for neuromorphic computing. The nonlinearity of long-term potentiation and long-term depression is notably decreased from 12.26 to 0.60 and from -8.79 to -3.47, respectively. Moreover, the δ-FAPbI3/ALD-SnO2 bilayer achieves a recognition rate of ≤94.04% based on the modified National Institute of Standards and Technology database (MNIST), establishing its potential in an efficient artificial synapse.

Identifying the Active Sites in MoSi2@MoO3 Heterojunctions for Enhanced Hydrogen Evolution.

Developing Two-dimensional (2D) Mo-based heterogeneous nanomaterials is of great significance for energy conversion, especially in alkaline hydrogen evolution reaction (HER), however, it remains a challenge to identify the active sites at the interface due to the structure complexity. Herein, the real active sites are systematically explored during the HER process in varied Mo-based 2D materials by theoretical computational and magnetron sputtering approaches first to filtrate the candidates, then successfully combined the MoSi2 and MoO3 together through Oxygen doping to construct heterojunctions. Benefiting from the synergistic effects between the MoSi2 and MoO3, the obtained MoSi2@MoO3 exhibits an unprecedented overpotential of 72 mV at a current density of 10 mA cm-2. Density functional theory calculations uncover the different Gibbs free energy of hydrogen adsorption (ΔGH*) values achieved at the interfaces with different sites as adsorption sites. The results can facilitate the optimization of heterojunction electrocatalyst design principles for the Mo-based 2D materials.

Substantially Accelerated Response and Recovery in Pd-Decorated WO3 Nanorods Gasochromic Hydrogen Sensor.

The development of hydrogen (H2) gas sensors is essential for the safe and efficient adoption of H2 gas as a clean, renewable energy source in the challenges against climate change, given its flammability and associated safety risks. Among various H2 sensors, gasochromic sensors have attracted great interest due to their highly intuitive and low power operation, but slow kinetics, especially slow recovery rate limited its further practical application. This study introduces Pd-decorated amorphous WO3 nanorods (Pd-WO3 NRs) as an innovative gasochromic H2 sensor, demonstrating rapid and highly reversible color changes for H2 detection. In specific, the amorphous nanostructure exhibits notable porosity, enabling rapid detection and recovery by facilitating effective H2 gas interaction and efficient diffusion of hydrogen ions (H+) dissociated from the Pd nanoparticles (Pd NPs). The optimized Pd-WO3 NRs sensor achieves an impressive response time of 14 s and a recovery time of 1 s to 5% H2. The impressively fast recovery time of 1 s is observed under a wide range of H2 concentrations (0.2-5%), making this study a fundamental solution to the challenged slow recovery of gasochromic H2 sensors.

Data-centric artificial olfactory system based on the eigengraph.

Recent studies of electronic nose system tend to waste significant amount of important data in odor identification. Until now, the sensitivity-oriented data composition has made it difficult to discover meaningful data to apply artificial intelligence in terms of in-depth analysis for odor attributes specifying the identities of gas molecules, ultimately resulting in hindering the advancement of the artificial olfactory technology. Here, we realize a data-centric approach to implement standardized artificial olfactory systems inspired by human olfactory mechanisms by formally defining and utilizing the concept of Eigengraph in electrochemisty. The implicit odor attributes of the eigengraphs were mathematically substantialized as the Fourier transform-based Mel-Frequency Cepstral Coefficient feature vectors. Their effectiveness and applicability in deep learning processes for gas classification have been clearly demonstrated through experiments on complex mixed gases and automobile exhaust gases. We suggest that our findings can be widely applied as source technologies to develop standardized artificial olfactory systems.

MAPbBr3 Halide Perovskite-Based Resistive Random-Access Memories Using Electron Transport Layers for Long Endurance Cycles and Retention Time.

Recent studies have focused on exploring the potential of resistive random-access memory (ReRAM) utilizing halide perovskites as novel data storage devices. This interest stems from its notable attributes, including a high ON/OFF ratio, low operating voltages, and exceptional mechanical properties. Nevertheless, there have been reports indicating that memory systems utilizing halide perovskites encounter certain obstacles pertaining to their stability and dependability, mostly assessed through endurance and retention time. Moreover, the presence of these problems can potentially restrict their practical applicability. This study explores a resistive switching memory device utilizing MAPbBr3 perovskite, which demonstrates bipolar switching characteristics. The device fabrication procedure involves a low-temperature, all-solution process. For the purpose of enhancing the device's reliability, the utilization of TPBI(2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) as an electron transfer material on the MAPbBr3 switching layer was implemented for the first time. The formation and rupture of Ag filaments in the MAPbBr3 perovskite switching layer are attributed to reduction-oxidation reactions. The TPBI is involved in the regulation of filaments during the SET and RESET processes. Hence, it can be shown that the MAPbBr3 device incorporating TPBI exhibited about 1000 endurance cycles when subjected to continuous voltage pulses. Moreover, the device consistently maintained ON/OFF ratios above 107. In contrast, the original MAPbBr3 device without TPBI demonstrated a significantly lower endurance with only 90 cycles observed. In addition, the MAPbBr3 device integrated with TPBI exhibited a retention time exceeding 3 × 103 s. The findings of this research provide compelling evidence to support the notion that electron transfer materials have promise for the development of halide perovskite memory systems owing to their favorable attributes of dependability and stability.

Rapid assays of SARS-CoV-2 virus and noble biosensors by nanomaterials.

The COVID-19 outbreak caused by SARS-CoV-2 in late 2019 has spread rapidly across the world to form a global epidemic of respiratory infectious diseases. Increased investigations on diagnostic tools are currently implemented to assist rapid identification of the virus because mass and rapid diagnosis might be the best way to prevent the outbreak of the virus. This critical review discusses the detection principles, fabrication techniques, and applications on the rapid detection of SARS-CoV-2 with three categories: rapid nuclear acid augmentation test, rapid immunoassay test and biosensors. Special efforts were put on enhancement of nanomaterials on biosensors for rapid, sensitive, and low-cost diagnostics of SARS-CoV-2 virus. Future developments are suggested regarding potential candidates in hospitals, clinics and laboratories for control and prevention of large-scale epidemic.

Recent Advances in Wide Bandgap Perovskite Solar Cells: Focus on Lead-Free Materials for Tandem Structures.

A tandem solar cell, which is composed of a wide bandgap (WBG) top sub-cell and a narrow bandgap (NBG) bottom subcell, harnesses maximum photons in the wide spectral range, resulting in higher efficiency than single-junction solar cells. WBG (>1.6 eV) perovskites are currently being studied a lot based on lead mixed-halide perovskites, and the power conversion efficiency of lead mixed-halide WBG perovskite solar cells (PSCs) reaches 21.1%. Despite the excellent device performance of lead WBG PSCs, their commercialization is hampered by their Pb toxicity and low stability. Hence, lead-free, less toxic WBG perovskite absorbers are needed for constructing lead-free perovskite tandem solar cells. In this review, various strategies for achieving high-efficiency WBG lead-free PSCs are discussed, drawing inspiration from prior research on WBG lead-based PSCs. The existing issues of WBG perovskites such as VOC loss are discussed, and toxicity issues associated with lead-based perovskites are also addressed. Subsequently, the natures of lead-free WBG perovskites are reviewed, and recently emerged strategies to enhance device performance are proposed. Finally, their applications in lead-free all perovskite tandem solar cells are introduced. This review presents helpful guidelines for eco-friendly and high-efficiency lead-free all perovskite tandem solar cells.

Halide Perovskites-Based Diffusive Memristors for Artificial Mechano-Nociceptive System.

Numerous efforts for emulating organ systems comprised of multiple functional units have driven substantial advancements in bio-realistic electronics and systems. The resistance change behavior observed in diffusive memristors shares similarities with the potential change in biological neurons. Here, the diffusive threshold switching phenomenon in Ag-incorporated organometallic halide perovskites is utilized to demonstrate the functions of afferent neurons. Halide perovskites-based diffusive memristors show a low threshold voltage of ≈0.2 V with little variation, attributed to the facile migration of Ag ions uniformly dispersed within the halide matrix. Based on the reversible and reliable volatile threshold switching, the memristors successfully demonstrate fundamental nociceptive functions including threshold firing, relaxation, and sensitization. Furthermore, to replicate the biological mechano-nociceptive phenomenon at a system level, an artificial mechano-nociceptive system is built by integrating a diffusive memristor with a force-sensing resistor. The presented system is capable of detecting and discerning the detrimental impact caused by a heavy steel ball, effectively exhibiting the corresponding sensitization response. By further extending the single nociceptive system into a 5 × 5 array, successful stereoscopic nociception of uneven impulses is achieved in the artificial skin system through array-scale sensitization. These results represent significant progress in the field of bio-inspired electronics and systems.

Nanoelectronics Using Metal-Insulator Transition.

Metal-insulator transition (MIT) coupled with an ultrafast, significant, and reversible resistive change in Mott insulators has attracted tremendous interest for investigation into next-generation electronic and optoelectronic devices, as well as a fundamental understanding of condensed matter systems. Although the mechanism of MIT in Mott insulators is still controversial, great efforts have been made to understand and modulate MIT behavior for various electronic and optoelectronic applications. In this review, recent progress in the field of nanoelectronics utilizing MIT is highlighted. A brief introduction to the physics of MIT and its underlying mechanisms is begun. After discussing the MIT behaviors of various Mott insulators, recent advances in the design and fabrication of nanoelectronics devices based on MIT, including memories, gas sensors, photodetectors, logic circuits, and artificial neural networks are described. Finally, an outlook on the development and future applications of nanoelectronics utilizing MIT is provided. This review can serve as an overview and a comprehensive understanding of the design of MIT-based nanoelectronics for future electronic and optoelectronic devices.

Strain Engineering in Perovskites: Mutual Insight on Oxides and Halides.

Perovskite materials have garnered significant attention over the past decades due to their applications, not only in electronic materials, such as dielectrics, piezoelectrics, ferroelectrics, and superconductors but also in optoelectronic devices like solar cells and light emitting diodes. This interest arises from their versatile combinations and physiochemical tunability. While strain engineering is a recognized powerful tool for tailoring material properties, its collaborative impact on both oxides and halides remains understudied. Herein, strain engineering in perovskites for energy conversion devices, providing mutual insight into both oxides and halides is discussed. The various experimental methods are presented for applying strain by using thermal mismatch, lattice mismatch, defects, doping, light illumination, and flexible substrates. In addition, the main factors that are influenced by strain, categorized as structure (e.g., symmetry breaking, octahedral distortion), bandgap, chemical reactivity, and defect formation energy are described. After that, recent progress in strain engineering for perovskite oxides and halides for energy conversion devices is introduced. Promising methods for enhancing the performance of energy conversion devices using perovskites through strain engineering are suggested.

Enhancing Performance of Ultraviolet C Photodetectors Through Single-Domain Epitaxy of Monoclinic ß-Ga2 O3 Films and Tailored Anti-Reflection Coating.

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on ß-Ga2 O3 films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic ß-Ga2 O3 films on a hexagonal sapphire substrate. Unlike 3D ß-Ga2 O3 films with twin domains, 2D ß-Ga2 O3 films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of ß-Ga2 O3 films and the application of ARC for the development of high-performance UVC PDs.

Reduction of Structural Defects in the GaSb Buffer Layer on (001) GaP/Si for High Performance InGaSb/GaSb Quantum Well Light-Emitting Diodes.

Monolithic integration of GaSb-based optoelectronic devices on Si is a promising approach for achieving a low-cost, compact, and scalable infrared photonics platform. While tremendous efforts have been put into reducing dislocation densities by using various defect filter layers, exploring other types of extended crystal defects that can exist on GaSb/Si buffers has largely been neglected. Here, we show that GaSb growth on Si generates a high density of micro-twin (MT) defects as well as threading dislocations (TDs) to accommodate the extremely large misfit between GaSb and Si. We found that a 250 nm AlSb single insertion layer is more effective than AlSb/GaSb strained superlattices in reducing both types of defects, resulting in a 4× and 13× reduction in TD density and MT density, respectively, compared with a reference sample with no defect filter layer. InGaSb quantum well light-emitting diodes were grown on the GaSb/Si templates, and the effect of TD density and MT density on their performance was studied. This work shows the importance of using appropriate defect filter layers for high performance GaSb-based optoelectronic devices on standard on-axis (001) Si via direct epitaxial growth.

Dual-frequency piezoelectric micromachined ultrasound transducer based on polarization switching in ferroelectric thin films.

Due to its additional frequency response, dual-frequency ultrasound has advantages over conventional ultrasound, which operates at a specific frequency band. Moreover, a tunable frequency from a single transducer enables sonographers to achieve ultrasound images with a large detection area and high resolution. This facilitates the availability of more advanced techniques that simultaneously require low- and high-frequency ultrasounds, such as harmonic imaging and image-guided therapy. In this study, we present a novel method for dual-frequency ultrasound generation from a ferroelectric piezoelectric micromachined ultrasound transducer (PMUT). Uniformly designed transducer arrays can be used for both deep low-resolution imaging and shallow high-resolution imaging. To switch the ultrasound frequency, the only requirement is to tune a DC bias to control the polarization state of the ferroelectric film. Flextensional vibration of the PMUT membrane strongly depends on the polarization state, producing low- and high-frequency ultrasounds from a single excitation frequency. This strategy for dual-frequency ultrasounds meets the requirement for either multielectrode configurations or heterodesigned elements, which are integrated into an array. Consequently, this technique significantly reduces the design complexity of transducer arrays and their associated driving circuits.

Selective Cell-Cell Adhesion Regulation via Cyclic Mechanical Deformation Induced by Ultrafast Nanovibrations.

The adoption of dynamic mechanomodulation to regulate cellular behavior is an alternative to the use of chemical drugs, allowing spatiotemporal control. However, cell-selective targeting of mechanical stimuli is challenging due to the lack of strategies with which to convert macroscopic mechanical movements to different cellular responses. Here, we designed a nanoscale vibrating surface that controls cell behavior via selective repetitive cell deformation based on a poroelastic cell model. The vibrating indentations induce repetitive water redistribution in the cells with water redistribution rates faster than the vibrating rate; however, in the opposite case, cells perceive the vibrations as a one-time stimulus. The selective regulation of cell-cell adhesion through adjusting the frequency of nanovibration was demonstrated by suppression of cadherin expression in smooth muscle cells (fast water redistribution rate) with no change in vascular endothelial cells (slow water redistribution rate). This technique may provide a new strategy for cell-type-specific mechanical stimulation.

g-C3N4-Co3O4 Z-Scheme Junction with Green-Synthesized ZnO Photocatalyst for Efficient Degradation of Methylene Blue in Aqueous Solution.

A simple wet chemical ultrasonic-assisted synthesis method was employed to prepare visible light-driven g-C3N4-ZnO-Co3O4 (GZC) heterojunction photocatalysts. X-ray diffraction (XRD), scanning electromicroscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), ultraviolet (UV), and electrochemical impedance spectroscopy (EIS) are used to characterize the prepared catalysts. XRD confirms the homogenous phase formation of g-C3N4, ZnO, and Co3O4, and the heterogeneous phase for the composites. The synthesized ZnO and Co3O4 by using cellulose as a template show a rod-like morphology. The specific surface area of the catalytic samples increases due to the cellulose template. The measurements of the energy band gap of a g-C3N4-ZnO-Co3O4 composite showed red-shifted optical absorption to the visible range. The photoluminescence (PL) intensity decreases due to the formation of heterojunction. The PL quenching and EIS result shows that the reduction of the recombination rate and interfacial resistance result in charge carrier kinetic improvement in the catalyst. The photocatalytic performance in the degradation of MB dye of the GZC-3 composite was about 8.2-, 3.3-, and 2.5-fold more than that of the g-C3N4, g-C3N4-ZnO, and g-C3N4-Co3O4 samples. The Mott-Schottky plots of the flat band edge position of g-C3N4, ZnO, Co3O4, and Z-scheme g-C3N4-ZnO-Co3O4 photocatalysts may be created. Based on the stability experiment, GZC-3 shows greater photocatalytic activity after four recycling cycles. As a result, the GZC composite is environmentally friendly and efficient photocatalyst and has the potential to consider in the treatment of dye-contaminated wastewater.

An electrochemically fabricated cobalt iron oxyhydroxide bifunctional electrode for an anion exchange membrane water electrolyzer.

For an anion exchange membrane water electrolyzer (AEMWE), exploring bifunctional electrodes with low cost and high efficiency is a crucial task for future renewable energy systems. Herein, we report a simple method to fabricate cobalt iron oxyhydroxide (CozFe1-zOxHy) bifunctional electrodes for AEMWEs. The bifunctional electrodes were prepared via one-pot electrodeposition on Ti paper (TP). By adjusting the electrodeposition conditions, the morphology and composition of CozFe1-zOxHy/TP could be controlled. The Co65Fe35OxHy/TP electrode demonstrated the highest activity for overall water electrolysis owing to the maximized synergy effect between Co and Fe. The bifunctional activities of Co65Fe35OxHy/TP were well retained at -50 and 50 mA cm-2 for 12 h. Co65Fe35OxHy/TP, which shows the highest bifunctional activity, was employed in an AEMWE single cell as the anode and cathode. The AEMWE single cell employing Co65Fe35OxHy/TP showed a current density of 0.605 A cm-2 at a cell voltage of 2.0 Vcell. The calculated energy efficiency of the single cell is 55.7% at 2.0 A cm-2, which is comparable with those of the state-of-the-art AEMWE single cells with bifunctional electrodes. Furthermore, the cell voltage of the single cell with Co65Fe35OxHy/TP showed negligible degradation for 50 h at 0.6 A cm-2.

Recent Advances in Water-Splitting Electrocatalysts Based on Electrodeposition.

Green hydrogen is being considered as a next-generation sustainable energy source. It is created electrochemically by water splitting with renewable electricity such as wind, geothermal, solar, and hydropower. The development of electrocatalysts is crucial for the practical production of green hydrogen in order to achieve highly efficient water-splitting systems. Due to its advantages of being environmentally friendly, economically advantageous, and scalable for practical application, electrodeposition is widely used to prepare electrocatalysts. There are still some restrictions on the ability to create highly effective electrocatalysts using electrodeposition owing to the extremely complicated variables required to deposit uniform and large numbers of catalytic active sites. In this review article, we focus on recent advancements in the field of electrodeposition for water splitting, as well as a number of strategies to address current issues. The highly catalytic electrodeposited catalyst systems, including nanostructured layered double hydroxides (LDHs), single-atom catalysts (SACs), high-entropy alloys (HEAs), and core-shell structures, are intensively discussed. Lastly, we offer solutions to current problems and the potential of electrodeposition in upcoming water-splitting electrocatalysts.

Multicomponent Metal Oxide- and Metal Hydroxide-Based Electrocatalysts for Alkaline Water Splitting.

Developing cost-effective, highly catalytic active, and stable electrocatalysts in alkaline electrolytes is important for the development of highly efficient anion-exchange membrane water electrolysis (AEMWE). To this end, metal oxides/hydroxides have attracted wide research interest for efficient electrocatalysts in water splitting owing to their abundance and tunable electronic properties. It is very challenging to achieve an efficient overall catalytic performance based on single metal oxide/hydroxide-based electrocatalysts due to low charge mobilities and limited stability. This review is mainly focused on the advanced strategies to synthesize the multicomponent metal oxide/hydroxide-based materials that include nanostructure engineering, heterointerface engineering, single-atom catalysts, and chemical modification. The state of the art of metal oxide/hydroxide-based heterostructures with various architectures is extensively discussed. Finally, this review provides the fundamental challenges and perspectives regarding the potential future direction of multicomponent metal oxide/hydroxide-based electrocatalysts.