Device Applications Research Articles

When the Study of the Post-Synthetic Modification Method on a 1D Spin Crossover Coordination Polymer Highlights its Catalytic Activity.

We are interested in studying the catalytic activity of the spin crossover (SCO) complex ([Fe(NH2trz)3](NO3)2). In this work, we demonstrate that, by adapting the experimental conditions, we can switch from a quantitative post-synthetic modification (PSM) reaction to the use of this complex as a catalyst for the formation of imine from 4-amino-1,2,4-triazole. During the catalytic reaction, the iron complex undergoes two different PSM reactions: the first is the action of the aldehyde on the NH2 groups present on the complex, whereas the second PSM reaction occurs between the imine complex and aminotriazole, leading back to the starting complex. These two PSM reactions are at least partially involved in the catalytic mechanism. Furthermore, the combination of these two PSM reactions enables us to modulate the particle size and shape of the final amine complex without altering its excellent SCO properties. This result is of interest in the field of heterogeneous catalysis, where particle size has a strong influence on the catalytic activity, and for the proper integration in devices for different applications.

Flexible Near-Infrared Plasmon-Polaritons in Epitaxial Scandium Nitride Enabled by van der Waals Heteroepitaxy.

Van der Waals heteroepitaxy refers to the growth of strain- and misfit-dislocation-free epitaxial films on layered substrates or vice versa. Such heteroepitaxial technique can be utilized in developing flexible near-infrared transition metal nitride plasmonic materials to broaden their photonic and bioplasmonic applications, such as antifogging, smart windows, and bioimaging. Here, we show the first conclusive experimental demonstration of the van der Waals heteroepitaxy-enabled flexible semiconducting scandium nitride (ScN) thin films exhibiting near-infrared, low-loss epsilon-near-zero, and surface plasmon-polariton resonances. Deposited on fluorophlogopite-mica substrates with molecular beam epitaxy, polaritonic ScN heterostructures mark the first semiconducting nitride to exhibit plasmon resonance at the 1100-1250 nm spectral range, inside the biological transmission window. Interestingly, optical properties of such ScN exhibit remarkable stability even after bending more than 100 times. Creating low-cost and high-quality flexible yet refractory plasmonic ScN heterostructures for the near-infrared spectral range will advance flexible optics and bioplasmonic devices for practical applications.

Improvement of Thermal Stability of Charges in Polylactic Acid Electret Films for Biodegradable Electromechanical Sensors.

Eco-friendly sensors fabricated from biocompatible and biodegradable materials are promising candidates for wearable and implantable electronics due to their environmental sustainability and biosafety. This article reports a fully biodegradable electromechanical sensor (FBES) utilizing a sandwich structure with macro ripple structured polylactic acid (PLA) electret films acting as sensitive layers and molybdenum (Mo) sheets serving as electrodes for a wearable device application. The stability of the space charge stored within the PLA film has been enhanced by introducing an internal cellular structure and improving the polarization process. A macro ripple structure of the PLA layer with higher deformation is a great guarantee for boosting the pressure sensitivity. The results indicate that inserting cell microstructures and optimizing the polarization process significantly improve the charge storage stability of PLA films by nearly 55%. This enhancement is attributed to several factors, including the extended charge drift path of the charges in cellular films, a synergy effect of surface charges, and "macroscopic" dipole charges distributed in the cells. The fabricated sensor achieves a high sensitivity of 1000 pC/kPa, a wide pressure detection range of 0.03-62.4 kPa, and satisfactory stability. Such sensors are not only sensitive to body movements but also to subtle physiological signals, satisfying the diverse needs of wearable healthcare. Importantly, all the composition materials of the sensor can be completely degraded after their service, aligning with the environmentally friendly principles of green development.

Pressure induced tunable physical properties of cubic KHgF3 fluoro-perovskite: A first principle study

The structural, electronic, optical, mechanical, and thermodynamic properties of KHgF3 perovskite under various hydrostatic pressures are examined in this study in the frameworkof Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) Perdew-Burke-Ernzerhof (PBE) exchange–correlation function. Tunable physical properties have been observed in KHgF3 as pressure is incrementally applied. The investigated compound displays mechanical instability beyond the pressure range of 0 to –10 GPa, as confirmed by the elastic constant analysis. Under ambient pressure, the lattice constants of KHgF3 closely align with theoretically calculated values, affirming the accuracy of this investigation. In addition, the bandgap of KHgF3 narrows with increasing pressure, facilitating easier electron transition from the valence band to the conduction band. The study reveals that when subjected to different hydrostatic pressures, fluctuations are observed in the peaks of the conductivity spectrum, loss spectrum, and absorption spectrum, particularly shifting towards higher photon energies, as analyzed through the optical properties. Moreover, KHgF3 exhibits ductile behavior at 0 GPa pressure, and this ductility rises with pressure. Thermodynamic analysis reveals a decrease in Debye temperature with increasing pressure, while the melting temperature rises correspondingly. The findings of this investigation also imply that KHgF3 can be a good candidate for optoelectronic device application under different hydrostatic pressures.

Miniaturized circularly polarized wearable array antenna for medical device applications

Antenna miniaturization is essential for healthcare applications, and numerous studies have tackled the challenge of presenting miniaturized, reliable designs while maintaining performance. This paper presents a small circularly polarized (CP) sequential wearable array antenna with overall dimensions of only 110 mm × 95 mm × 1.8 mm. It comprises four novel designs of circular-shaped elements arranged sequentially in an array configuration measured only 24 mm×24 mm×1 mm. It is fed by a separate cascade feeding network incorporating a single rat-race and two branch-line couplers. The antenna is designed for medical device applications within the 2.4 GHz Industrial Scientific Medical (ISM) frequency band. The proposed design is fabricated and experimentally tested, demonstrating wide impedance bandwidths of 21.24% (2.2–2.72 GHz) and an Axial Ratio (AR) bandwidth (AR < 3 dB) covering the entire 2.4 GHz ISM frequency band. At 2.43 GHz, the antenna achieves a gain of -14.9 dBi. Both simulation and experimental results confirm excellent performance in impedance matching, gain pattern, and circular polarization, making it promising for wearable wireless communication in medical applications. The link margin was calculated, and the specific absorption rate of the antenna was analyzed, the result revealing that it aligns with the safety limits of IEEE C95.1-1999 standards.

Intraband Exciton Dynamics of n-Doped Silver Selenide Quantum Dots.

AgxSe (x > 2) colloidal quantum dots (CQDs) have recently emerged as a promising environmentally friendly material contender for mid- and long-wave infrared optoelectronics, leveraging their intraband transition (1Se-1Pe). However, multicarrier interactions in CQDs, particularly Auger recombination, have profound implications on the optoelectronic properties of the materials and their potential in device applications. Understanding the intraband excited-state dynamics in n-doped AgxSe is therefore essential for the assessment and successful implementation of this material platform in devices. We, herein, investigate the carrier dynamics of AgxSe in both solution and thin-film states using a femtosecond mid-infrared transient absorption spectrometer. Our observations reveal that the multicarrier Auger process depends on the degree of doping in AgxSe CQDs and accelerates when the Fermi energy (EF) level approaches the 1Pe state. The calculated intraband Auger coefficients (CA) are measured to be on the order of ∼10-28 cm6 s-1, significantly larger compared to analogous n-doped HgS/Se CQDs.

Impact of Pre-Silica-Coating on the Luminescence Properties of Silica-Coated Indium Phosphide Nanoparticles

This study examined the impact of silica-coating on the luminescence characteristics of indium phosphide (InP) nanoparticles. Silica-coated InP nanoparticles were prepared using three different techniques. The first method utilized tetraethoxysilane (TEOS) as the silica source, resulting in the encapsulation of multiple InP nanoparticles within silica spheres. This approach caused a red-shift in the luminescence peak wavelength of the InP colloidal solution post-TEOS coating, compared to the original InP colloidal solution. Conversely, the second method employed tetramethoxysilane (TMOS), resulting in the formation of irregularly shaped silica-coatings on multiple InP nanoparticles, which reduced the red-shift in the luminescence peak wavelength of the silica-coated InP colloidal solution. The third method involved pre-coating InP nanoparticles with TMOS, followed by thickening the silica shells using TEOS. This technique successfully encapsulated multiple InP nanoparticles within silica spheres, maintaining the luminescence peak wavelength of the InP colloid solution post-coating with TMOS and TEOS nearly identical to that of the original solution. This method merged the advantageous outcomes of the first two methods. Additionally, silica spheres containing InP nanoparticles synthesized using both TMOS and TEOS exhibited the highest luminescence intensity. In summary, this study introduces a novel approach in nanoparticle engineering, enhancing the functional properties of InP nanoparticles and expanding their potential applications in optoelectronic devices.

Magnetic imaging of thermally switchable antiferromagnetic/ferromagnetic modulated thin films

Nanoscale magnetic patterning can lead to the formation of a variety of spin textures, depending on the intrinsic properties of the material and the microstructure. Here we report on the spin textures formed in laterally patterned antiferromagnetic (AF)/ferromagnetic (FM) thin film stripes with a period of 200 nm (100 nm FM/100 nm AF). We make use of the AF to FM phase transition in FeRh thin films at ∼100 °C, thereby creating a nanoscale pattern that is thermally switchable between AF/FM stripes and uniformly FM. A combination of spin-resolved photoemission electron microscopy, magnetic force microscopy, and magnetometry measurements allow direct nanoscale observations of the stray magnetic fields emergent from the nanopattern as well as the underlying magnetisation. Our measurements reveal pinning centres resistant to temperature cycling that govern the modulated spin-texture as well as a sub-texture consisting of grain-driven nanoscale magnetisation structure directed out of the film plane. The nanoscale magnetic structure is thus strongly influenced by the film microstructure. Signatures of exchange bias are not observed, most likely due to the small contact area between the AF and FM regions, combined with the fact that the interfaces between the damaged and undamaged regions are likely to be highly diffuse owing to the lateral scattering of incoming ions. These results show that temperature controllable spin textures can be created in FeRh thin films which could find application in domain wall, microwave, or magnonic devices.

Atomic Fabrication of 2D Materials Using Electron Beams Inside an Electron Microscope.

Two-dimensional (2D) materials have garnered increasing attention due to their unusual properties and significant potential applications in electronic devices. However, the performance of these devices is closely related to the atomic structure of the material, which can be influenced through manipulation and fabrication at the atomic scale. Transmission electron microscopes (TEMs) and scanning TEMs (STEMs) provide an attractive platform for investigating atomic fabrication due to their ability to trigger and monitor structural evolution at the atomic scale using electron beams. Furthermore, the accuracy and consistency of atomic fabrication can be enhanced with an automated approach. In this paper, we briefly introduce the effect of electron beam irradiation and then discuss the atomic structure evolution that it can induced. Subsequently, the use of electron beams for achieving desired structures and patterns in a controllable manner is reviewed. Finally, the challenges and opportunities of atomic fabrication on 2D materials inside an electron microscope are discussed.

The impact of proton ion irradiation on Se70Te20In10 thin films: Linear and non-linear optical properties for photonic applications

The examination of the linear and non-linear optical features was conducted on amorphous ternary Se70Te20 In10 thin films, which were exposed to proton irradiation energy of 3 MeV at varying fluences of 5×1013, 5×1014, 5×1015 and 5×1016 ions/cm2. The bulk sample was produced using the melt quenching method, and subsequently, thin films were obtained through electron beam evaporation. Calculations of linear and non-linear optical parameters were carried out based on transmittance and reflectance data acquired from UV–Vis–NIR spectroscopy spanning 300–2500 nm. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) confirmed an amorphous phase in the films. The optical parameters showed strong dependency on the proton radiation fluence. In addition, the existence of minima or maxima for a number of parameters at a fluence of 5×1014 ions/cm2 showed that this was the optimum fluence. The linear and non-linear properties showed that the sample have potential applications in photonic devices.

Vacuum Filtration-Coated Silver Electrodes Coupled with Stacked Conductive Multi-Walled Carbon Nanotubes/Mulberry Paper Sensing Layers for a Highly Sensitive and Wide-Range Flexible Pressure Sensor

Flexible pressure sensors based on paper have attracted considerable attention owing to their good performance, low cost, and environmental friendliness. However, effectively expanding the detection range of paper-based sensors with high sensitivities is still a challenge. Herein, we present a paper-based resistive pressure sensor with a sandwich structure consisting of two electrodes and three sensing layers. The silver nanowires were dispersed deposited on a filter paper substrate using the vacuum filtration coating method to prepare the electrode. And the sensing layer was fabricated by coating carbon nanotubes onto a mulberry paper substrate. Waterborne polyurethane was introduced in the process of preparing the sensing layers to enhance the strength of the interface between the carbon nanotubes and the mulberry paper substrate. Therefore, the designed sensor exhibits a good sensing performance by virtue of the rational structure design and proper material selection. Specifically, the rough surfaces of the sensing layers, porous conductive network of silver nanowires on the electrodes, and the multilayer stacked structure of the sensor collaboratively increase the change in the surface contact area under a pressure load, which improves the sensitivity and extends the sensing range simultaneously. Consequently, the designed sensor exhibits a high sensitivity (up to 6.26 kPa−1), wide measurement range (1000 kPa), low detection limit (~1 Pa), and excellent stability (1000 cycles). All these advantages guarantee that the sensor has potential for applications in smart wearable devices and the Internet of Things.

A Review of Perovskite-based Lithium-Ion Battery Materials

Lithium-ion batteries (Li-ion batteries or LIBs) have garnered significant interest as a promising technology in the energy industry and electronic devices for the past few decades owing to their superior energy and power density profiles, small size, long cycle life, low self-discharge rate, no memory effect, long-lasting power properties, and environmental friendly. The ongoing advancement of electrode and electrolyte materials has contributed significantly to enhancing and spreading the application of lithium-ion battery technology. Among the non-precious metal-based materials, perovskites have emerged as attention over the last decade, holding a prominent position in materials and energy. Due to their unique physical and chemical properties, these materials have garnered particular interest for their potential application in electrochemical energy devices. Perovskite oxides have piqued the interest of researchers as potential catalysts in Li-O₂ batteries due to their remarkable electrochemical stability, high electronic and ionic conductivity, and the ability to modify their properties through doping and element substitution. The purpose of this article is to provide an overview of recent developments in the application of perovskites as lithium-ion battery materials, including the exploration of novel compositions and structures, optimization of fabrication methods, and a deeper understanding of the fundamental mechanisms that can unveil the potential of perovskite materials.

Topological traveling-wave radiation based on chiral edge states in photonic Chern insulators.

Topological chiral edge states in photonic Chern insulators, which exhibit the one-way propagation property with reflection-free behavior and excellent robustness against perturbations, have become an important frontier in topological photonics. Currently, there have been many studies on its robust propagation behavior, but few studies have focused on its radiation properties. In developing functional photonic devices (e.g., topological antennas) for real-world applications, studying traveling-wave radiation characteristics based on chiral edge states deserves more attention. In this Letter, we propose a topological traveling-wave radiation system based on chiral edge states in photonic Chern insulators that show a steerable beam and reflection-free property. By introducing the perturbation controlled by magnetic fields, we demonstrate that exploiting a certain strength of perturbation can flexibly manipulate the radiation beam. In particular, the proposed dual-channel topological traveling-wave radiation system can not only improve the gain but also overcome the issue of impedance matching. The proposed configurations provide a novel way to manipulate topological-wave radiation and have potential applications for designing topological traveling-wave antennas with a reflection-free property.

Field-free spin–orbit torque magnetization switching in Pt/CoTb devices grown on flexible substrates for neuromorphic computing

Flexible spintronic devices based on spin–orbit torque (SOT)-induced perpendicular magnetization switching (PMS) have attracted increasing attention due to their high storage intensity and good programming capability. However, to achieve deterministic PMS, an in-plane auxiliary magnetic field is required, which greatly limits its application. Here, we show that “robust” magnetic field-free SOT-driven PMS is realized in the oblique sputtered Pt/CoTb multilayers grown on a flexible polyimide substrate. “Robust” means the magnetic field-free SOT switching is highly repeatable and stable after 100 bending cycles under various bending conditions. Additionally, the fabricated flexible multilayers exhibit nearly linear and nonvolatile multistate plasticity as synapses and a nonlinear sigmoid activation function when acting as neurons. We construct a fully connected neural network for handwritten digit recognition, achieving an over 96.27% recognition rate. Our findings may spur further investigations on the SOT-based flexible spintronic devices for wearable artificial intelligence applications.

Scalable fabrication of vertically arranged Bi2Se3 crossbar arrays for memristive device applications

Despite the unique advantages of the memristive switching devices based on two-dimensional (2D) transition metal dichalcogenides, scalable growth technologies of such 2D materials and wafer-level fabrication remain challenging. In this work, we present the gold-assisted large-area physical vapor deposition (PVD) growth of Bi2Se3 features for the scalable fabrication of 2D-material-based crossbar arrays of memristor devices. This work indicates that gold layers, prepatterned by photolithography processes, can catalyze PVD growth of few-layer Bi2Se3 with 100-folds larger crystal grain size in comparison with that grown on bare Si/SiO2 substrates. We also present a fluid-guided growth strategy to improve growth selectivity of Bi2Se3 on Au layers. Through the experimental and computational analyses, we identify two key processing parameters, i.e., the distance between Bi2Se3 powder and the target substrate and the distance between the leading edges of the substrate and the substrate holder with a hollow interior, which plays a critical role in realizing large-scale growth. By optimizing these growth parameters, we have successfully demonstrated cm-scale highly-selective Bi2Se3 growth on crossbar-arrayed structures with an in-lab yield of 86%. The whole process is etch- and plasma-free, substantially minimizing the damage to the crystal structure and also preventing the formation of rough 2D-material surfaces. Furthermore, we also preliminarily demonstrated memristive devices, which exhibit reproducible resistance switching characteristics (over 50 cycles) and a retention time of up to 106 s. This work provides a useful guideline for the scalable fabrication of vertically arranged crossbar arrays of 2D-material-based memristive devices, which is critical to the implementation of such devices for practical neuromorphic applications.

Carbon nanostructures for high-frequency line-filtering supercapacitors

Supercapacitors (SCs) are considered one of the front-runner energy storage devices for future electronic and automobile device applications. Even though their high-power densities, fast charge/discharge, and long cycling stabilities make them promising for future applications, their charge-discharge takes place below 1 Hz, a major issue for using them as capacitors for line filtering applications. Therefore, developing ultrafast electrochemical supercapacitors with alternating current (AC) line filtering functions has gained research attention to replace conventional aluminum electrolytic capacitors (AEC). Most available SCs possess resistive features rather than capacitive at 120 Hz because of the electrode geometry and configurations, which is a bottleneck in the research of line-filtering SCs. Addressing this challenge could be possible by developing novel electrode materials using hybrid nanostructures to meet the critical requirements for line filtering functions. This mini-review focuses on the advancement and challenges of carbon nanostructure-based electrode materials for AC line filtering applications and the future directions of this growing research area.

A comparative analysis of optical and electrical properties of pure CuO and Zn doped CuO nanoparticles for optoelectronic device applications

A comparative analysis of optical and electrical properties of pure CuO and Zn doped CuO nanoparticles for optoelectronic device applications

Manipulating formation of different InGaAs/GaAs nanostructures via tailoring As4 flux

This research provides a flexible approach to manipulate formation of InGaAs nanostructures on the GaAs (100) surface by varying arsenic (As4) beam equivalent pressure (BEP). By selecting the As4/(In+Ga) BEP ratio to be 4, 8, 20, 50 and 100, we were able to obtain different quantum structures from quantum well (QW) to quantum dots (QDs), then to spatially ordered quantum dot chains (QD-chains), and finally to quantum wires (QWRs), respectively. This transformation of nanostructures was explained by anisotropic surface diffusion coupled with the strain relieving Stranski–Krastanov growth mode, while the anisotropy was modulated by increasing As4 flux and subsequently enhanced by multilayer-stacking growth with a suitable spacer thickness. Photoluminescence characteristics show correlation to the nanostructure morphology for each sample. In particular, the formation of QD-chains and QWRs results in anisotropic features that offer potential device applications.

Black Jamun Fruit Peel Extract Modified Gum Acacia Biopolymer Suitable for Energy Device Applications via Charge Transfer Enhancement

The visible light absorption capabilities, along with its electrical characteristics, of a low-cost, plant-based, biopolymer, gum acacia, have been chemically modified by tailoring its defect concentrations via pH modification, where the acid solvent of fruit (peel) extracts of jamun was used to influence the chemical structure by reactive modification. Ultraviolet-visible and photoluminescence spectroscopy of the gum acacia biopolymer treated with the extracted anthocyanin from jamun peel showed a prominent, characteristic red shift in the visible spectrum range. Impedance spectroscopy analysis showed the occurrence of localized ionic conduction. The bulk conductivity of the modified specimens increased due to the profound release of conducting ions in the water-swollen network. The reactively modified biopolymer could be used in multiple fields of material science, specifically in energy device applications, viz., photovoltaics (PV), by utilizing its cost effectiveness and photolytic effectiveness. 2nd, as a polymer electrolyte and dye-sensitised solar cells (DSSCs) material by utilizing its capacity of gel formation. In our research described in this article, the underlying charge transfer mechanism for such responses was examined after crosslinking in the organic dyes extracted from the peel of jamun fruit with gum acacia.

Optoelectronic Reconfigurable Logic Gates Based on Two-Dimensional Vertical Field-Effect Transistors.

Optoelectronic reconfigurable logic gates are promising candidates to meet the multifunctional and energy-efficient requirements of integrated circuits. However, complex device architectures need more power and hinder multifunctional device applications. Here, we design vertical field-effect transistors (VFET) based on the two-dimensional (2D) graphene/MoS2/WSe2/graphene van der Waals heterojunction forming ohmic and Schottky contact. The modulation of the Schottky barrier via gate bias enables the device to switch between positive and negative photocurrents, which can effectively achieve optoelectronic reconfigurable logic gates (XNOR, NOR, NAND, AND, OR, and Inhibit) in a single device. Particularly, the transistor number is reduced by 75% for ("XNOR", "NOR", "NAND") and 83% for ("AND", "OR") gates compared to traditional logic circuits. This work provides a promising route for using a single device to realize optoelectronic reconfigurable logic gates, which can advance the development of high-speed, high-throughput, and intricate data processing in future optical computing applications.