Search Results (15)

In this study, plasma-activated water (PAW) was generated using a large-volume (5 L) plasma reactor with a quasi-stationary, water-cathode glow-type discharge in atmospheric pressure air. Tap water was activated up to 75 min. PAW exhibited high concentrations of long-lived reactive nitrogen species (RNSs), reaching 8 mM, which is between 4 and 26 times higher than those reported in previous studies. The reactor reached an RNS synthesis efficiency of 61 nmol/J and an RNS production rate of 526 μmol/min, both among the highest reported. PAW was evaluated on tomato and bell pepper. Seedling emergence was determined in a nutrient-free substrate. To assess plant growth, seedlings were transplanted into pots filled with either nitrogen-free or nutrient-rich substrate. PAW-irrigation significantly promoted seedling emergence and leaf expansion, especially in tomato plants. The plant growth-stimulating effects of PAW were more pronounced in nitrogen-free substrate: fresh weight of tomato and bell pepper increased up to 13.1-fold and 2.6-fold, respectively. In contrast, the effect on the nutrient-rich substrate was negligible. Tomato plants grown in the nitrogen-free substrate and irrigated with 75-min PAW reached a dry weight comparable to those grown in nutrient-rich substrate. PAW irrigation did not induce oxidative stress, as confirmed by malondialdehyde (MDA) levels and antioxidant enzyme activity. Full article

Flexible polymer-based piezoelectric nanogenerators (PENGs) have gained significant interest due to their ability to deliver clean and sustainable energy for self-powered electronics and wearable devices. Recently, the incorporation of fillers into the ferroelectric polymer matrix has been used to improve the relatively low piezoelectric properties of polymer-based PENGs. In this study, we investigated the effect of various nanofillers such as titania (TiO₂), zinc oxide (ZnO), reduced graphene oxide (rGO), and lead zirconate titanate (PZT) on the PENG performance of the nanocomposite thin films containing the nanofillers in poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) matrix. The nanocomposite films were prepared by depositing molecularly thin films of P(VDF-TrFE) and nanofiller nanoparticles (NPs) spread at the air/water interface onto the indium tin oxide-coated polyethylene terephthalate (ITO-PET) substrate, and they were characterized by measuring their microstructures, crystallinity, β-phase contents, and piezoelectric coefficients (d₃₃) using SEM, FT-IR, XRD, and quasi-static meter, respectively. Multiple PENGs incorporating various nanofillers within the polymer matrix were developed by assembling thin film-coated substrates into a sandwich-like structure. Their piezoelectric properties, such as open-circuit output voltage (V_OC) and short-circuit current (I_SC), were analyzed. As a result, the PENG containing 4 wt% PZT, which was named P-PZT-4, showed the best performance of V_OC of 68.5 V with the d₃₃ value of 78.2 pC/N and β-phase content of 97%. The order of the maximum V_OC values for the PENGs of nanocomposite thin films containing various nanofillers was PZT (68.5 V) > rGO (64.0 V) > ZnO (50.9 V) > TiO₂ (48.1 V). When the best optimum PENG was integrated into a simple circuit comprising rectifiers and a capacitor, it demonstrated an excellent two-dimensional power density of 20.6 μW/cm² and an energy storage capacity of 531.4 μJ within 3 min. This piezoelectric performance of PENG with the optimized nanofiller type and content was found to be superior when it was compared with those in the literature. This PENG comprising nanocomposite thin film with optimized nanofiller type and content shows a potential application for a power source for low-powered electronics such as wearable devices. Full article

An important technical task is to develop methods for recording the phase transitions of water to ice. At present, many sensors based on various types of acoustic waves are suggested for solving this challenge. This paper focuses on the theoretical and experimental study of the effect of water-to-ice phase transition on the properties of Lamb and quasi shear horizontal (QSH) acoustic waves of a higher order propagating in different directions in piezoelectric plates with strong anisotropy. Y-cut LiNbO₃, 128Y-cut LiNbO₃, and 36Y-cut LiTaO₃ plates with a thickness of 500 μm and 350 μm were used as piezoelectric substrates. It was shown that the amplitude of the waves under study can decrease, increase, or remain relatively stable due to the water-to-ice phase transition, depending on the propagation direction and mode order. The greatest decrease in amplitude (42.1 dB) due to glaciation occurred for Lamb waves with a frequency of 40.53 MHz and propagating in the YX+30° LiNbO₃ plate. The smallest change in the amplitude (0.9 dB) due to glaciation was observed for QSH waves at 56.5 MHz propagating in the YX+60° LiNbO₃ plate. Additionally, it was also found that, in the YX+30° LiNbO₃ plate, the water-to-ice transition results in the complete absorption of all acoustic waves within the specified frequency range (10–60 MHz), with the exception of one. The phase velocities, electromechanical coupling coefficients, elastic polarizations, and attenuation of the waves under study were calculated. The structures “air–piezoelectric plate–air”, “air–piezoelectric plate–liquid”, and “air–piezoelectric plate–ice” were considered. The results obtained can be used to develop methods for detecting ice formation and measuring its parameters. Full article

This paper proposes a unique configuration for an all-optical D Flip Flop (D-FF) utilizing a quasi-square ring resonator (RR) and T-Splitter, as well as NOT and OR logic gates within a 2-dimensional square lattice photonic crystal (PC) structure. The components realizing the all-optical D-FF comprise of optical waveguides in a 2D square lattice PC of 45 × 23 silicon (Si) rods in a silica (SiO₂) substrate. The utilization of these specific materials has facilitated the fabrication process of the design, diverging from alternative approaches that employ an air substrate, a method inherently unattainable in fabrication. The configuration underwent examination and simulation utilizing both plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methodologies. The simulation outcomes demonstrate that the designed waveguides and RR effectively execute the operational principles of the D-FF by guiding light as intended. The suggested configuration holds promise as a logic block within all-optical arithmetic logic units (ALUs) designed for digital computing optical circuits. The design underwent optimization for operation within the C-band spectrum, particularly at 1550 nm. The outcomes reveal a distinct differentiation between logic states ‘1’ and ‘0’, enhancing robust decision-making on the receiver side and minimizing logic errors in the photonic decision circuit. The D-FF displays a contrast ratio (CR) of 4.77 dB, a stabilization time of 0.66 psec, and a footprint of 21 μm × 12 μm. Full article

In this paper, we propose a stacked dual-patch antenna with 3D printed thick quasi-air substrates and a cavity wall for wideband applications. To achieve the theoretical maximum bandwidth of the patch antenna, the quality factor of the system needs to be minimized. To achieve this, the area of the conductive radiator should be enlarged, while the permittivity of the substrate within the patch must be reduced close to 1. To realize a patch antenna with this maximum bandwidth, the stacked dual-patch configuration is employed to obtain an extended conductive radiator area. In addition, square-pipe resin frames manufactured using a 3D printing method are applied to the proposed antenna to implement a quasi-air substrate structure that has a low permittivity value close to 1. The proposed stacked dual-patch antenna with a quasi-air substrate has a broad bandwidth of 20.7%. The results demonstrate that by using the proposed antenna structure, broadband characteristics close to the fundamental bandwidth limit of the patch antenna can be achieved. Full article

In this study, we have employed a film deposition technique based on convective forces acting at the triple air–solution–substrate contact line to tune the rate of solvent evaporation and, thus, to exert control over the morphology of the resulting mixed lead halide perovskite CH₃NH₃PbI_3-xCl_x films. By varying the speed of film deposition while processing at two different temperatures, perovskite crystals of various shapes and dimensions were generated upon the crystallization of the initial perovskite precursor ink. More precisely, longer than half a millimeter 3D needle-like perovskite crystals exhibiting sharp edges co-existing with large cross-like 3D perovskite crystals could only be obtained upon the slow deposition of films at a low sample processing temperature of 17 °C, i.e., under conditions of low solvent evaporation rate. On the contrary, the utilization of higher film deposition speeds and/or processing temperatures led to smaller 3D needle-like or quasi-2D rectangular perovskite crystals that often appeared interconnected and coalesced. Moreover, as it was revealed by the photoluminescence measurements, the emission intensity of perovskite crystals was larger and dominated by a shorter wavelength peak, as compared to the uncrystallized material that emitted much less light, but at a longer wavelength. Full article

This work presents an in vivo stem-mounted sensor for Nicotiana tabacum plants and an in situ cell suspension sensor for Solanum lycopersicum cells. Stem-mounted sensors are mechanically stable and less sensitive to plant and air movements than the previously demonstrated leaf-mounted sensors. Interdigitated-electrode-arrays with a dual working electrode configuration were used with an auxiliary electrode and an Ag/AgCl quasi-reference electrode. Signal amplification by redox cycling is demonstrated for a plant-based sensor responding to enzyme expression induced by different cues in the plants. Functional biosensing is demonstrated, first for constitutive enzyme expression and later, for heat-shock-induced enzyme expression in plants. In the cell suspension with redox cycling, positive detection of the enzyme β-glucuronidase (GUS) was observed within a few minutes after applying the substrate (pNPG, 4-Nitrophenyl β-D-glucopyranoside), following redox reactions of the product (p-nitrophenol (pNP)). It is assumed that the initial reaction is the irreversible reduction of pNP to p-hydroxylaminophenol. Next, it can be either oxidized to p-nitrosophenol or dehydrated and oxidized to aminophenol. Both last reactions are reversible and can be used for redox cycling. The dual-electrode redox-cycling electrochemical signal was an order of magnitude larger than that of conventional single-working electrode transducers. A simple model for the gain is presented, predicting that an even larger gain is possible for sub-micron electrodes. In summary, this work demonstrates, for the first time, a redox cycling-based in vivo plant sensor, where diffusion-based amplification occurs inside a tobacco plant’s tissue. The technique can be applied to other plants as well as to medical and environmental monitoring systems. Full article

This study presents a mass-production process for conductive carbon membrane-type sponge electrodes derived from recyclable cellulose biowaste. It includes an all-in-one hydrogel fabrication process for mass production, which significantly shortens the complex and expensive process for the conventional process of catalytic electrodes based on conductive supporting substrates such as the gas diffusion layer (GDL). The presence of pre-adsorbed melamine powder in the all-in-one hydrogel induces internal diffusion of the gaseous reactant for the uniform growth of carbon nanotubes (CNTs) onto the sponge-like porous carbon aerogel with a relatively thick and tortuous pore structure, thereby providing the electrochemical properties and mechanical strength simultaneously required for the air electrodes of rechargeable and quasi solid-state zinc-air batteries. Full article

Ammonia sensors with high sensitivity, reproducible response, and low cost are of paramount importance for medicine, i.e., being a biomarker to diagnose lung and renal conditions, and agriculture, given that fertilizer application and livestock manure account for more than 80% of NH₃ emissions. Thus, in this work, we report the fabrication of ultra-sensitive ammonia sensors by a rapid, efficient, and solvent-free laser-based procedure, i.e., laser-induced forward transfer (LIFT). LIFT has been used to transfer carbon nanowalls (CNWs) onto flexible polyimide substrates pre-patterned with metallic electrodes. The feasibility of LIFT is validated by the excellent performance of the laser-printed CNW-based sensors in detecting different concentrations of NH₃ in the air, at room temperature. The sensors prepared by LIFT show reversible responses to ammonia when exposed to 20 ppm, whilst at higher NH₃ concentrations, the responses are quasi-dosimetric. Furthermore, the laser-printed CNW-based sensors have a detection limit as low as 89 ppb and a response time below 10 min for a 20 ppm exposure. In addition, the laser-printed CNW-based sensors are very robust and can withstand more than 200 bending cycles without loss of performance. This work paves the way for the application and integration of laser-based techniques in device fabrication, overcoming the challenges associated with solvent-assisted chemical functionalization. Full article

In this work, we present and analyze a design of an absorber–waveguide system combining a highly sensitive waveguide array concept with a resonant selective absorber. The waveguide part is composed of an array of coupled strip waveguides and is therefore called a coupled strip array (CSA). The CSA is then coupled to the end of a slab Tamm plasmon (STP-) resonator, which is composed of a quasicrystal-like reflector formed by the patterning of a silicon slab and an interfacing tungsten slab. The concept describes an emitter–waveguide or waveguide–detector system featuring selective plasmon-enhanced resonant absorption or emission. These are crucial properties for corresponding optical on-chip integrated devices in context with evanescent field absorption sensing in fluids or gases, for example. Thus, the concept comprises a valuable and more cost-effective alternative to quantum cascade lasers. We designed the lateral dimensions of the STP resonator via a simple quasi-crystal approach and achieved strong narrowband resonances (emittance and Q-factors up to 85% and 88, respectively) for different silicon thicknesses and substrate materials (air and silicon oxide). Moreover, we analyze and discuss the sensitivity of the complete emitter–waveguide system in dependence on the slab thickness. This reveals the crucial correlation between the expected sensitivity assigned to the absorber–waveguide system and field confinement within the silicon. Full article

Lead halide perovskites have been revolutionary in the last decade in many optoelectronic sectors. Their bismuth-based counterparts have been considered a good alternative thanks to their composition of earth-abundant elements, good chemical stability, and low toxicity. Moreover, their electronic structure is in a quasi-zero-dimensional (0D) configuration, and they have recently been explored for use beyond optoelectronics. A significant limitation in applying thin-film technology is represented by the difficulty of synthesizing compact layers with easily scalable methods. Here, the engineering of a two-step synthesis in an air of methylammonium bismuth iodide compact thin films is reported. The critical steps of the process have been highlighted so that the procedure can be adapted to different substrates and application areas. Full article

Spinel ZnGa₂O₄ films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGa₂O₄ films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGa₂O₄ films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGa₂O₄ film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGa₂O₄ film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGa₂O₄ film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGa₂O₄ film exhibits a higher photo/dark current ratio of ~10⁴ order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGa₂O₄ films have significant potential in deep-ultraviolet applications. Full article

A new cost-efficient, low-loss Ka-band diplexer designed in inverted microstrip gap waveguide technology is presented in this paper. Gap waveguide allows to propagate quasi-TEM modes in the air between two metal plates without the need for contact between them by using periodic metasurfaces. The diplexer is realized by using a bed of nails as AMC (Artificial Magnetic Conductor), first modeled with a PMC (Perfect Magnetic Conductor) surface for design simplification, and two fifth order end-coupled passband filters (BPFs) along with a power divider. The experimental verification confirms that the two channels centered at 24 GHz and 28 GHz with 1 GHz of bandwidth show measured insertion losses of 1.5 dB and 2 dB and 60 dB of isolation between them. A slight shift in frequency is observed in the measurements that can be easily explained by the variation in the permittivity of the substrate. Full article

The Langmuir–Blodgett technique, in which a layer of nanoparticles is spread at the water/air interface and further transferred onto a solid support, is a versatile approach for the preparation of SERS substrates with a controllable arrangement of hotspots. In a previous work, we demonstrated that fine-tuning the lateral packing and subsequent seed growth of 10 nm gold nanoparticles led to a quasi-resonant enhanced in the SERS signal of a test analyte. Here, we explore further enhancements by modifying the size and shape of the spread gold nanoparticles in order to take advantage of the inherent interparticle repulsion mechanisms present at the interface. We show that the size of the used nanoparticles is also a determinant factor, which cannot be compensated by the subsequent electroless growth. We also show that, although the seeded growth leads to rough hotspots, the sensitivity can be optimized by self-assembling urchin-shaped nanoparticles, with a roughness that is fine-tuned a priori. Our results suggest an intriguing correlation between surface homogeneity and SERS signal enhancement, indicating that regular substrates will have the optimal performance. Full article

In this study, two new quasi-three-dimensional Surface Enhanced Raman Scattering (SERS) substrates, namely porous Ag and Ag-NiO nanofibrous mats, were prepared using a simple, electrospinning-calcination, two-step synthetic process. AgNO₃/polyvinyl pyrrolidone (PVP) and AgNO₃/Ni(NO₃)₂/PVP composites serving as precursors were electrospun to form corresponding precursory nanofibers. Porous Ag and Ag-NiO nanofibers were successfully obtained after a 3-h calcination at 500 °C under air atmosphere, and analyzed using various material characterization techniques. Synthesized, quasi-three-dimensional porous Ag and Ag-NiO nanofibrous mats were applied as SERS substrates, to measure the model compound Rhodamine 6G (R6G), and investigate the corresponding signal enhancement. Furthermore, porous Ag and Ag-NiO nanofibrous mats were employed as SERS substrates for melamine and methyl parathion respectively. Sensitive detection of melamine and methyl parathion was achieved, indicating their feasibility as an active SERS sensing platform, and potential for food safety and environmental monitoring. All the results suggest that the electrospinning-calcination, two-step method offers a new, low cost, high performance solution in the preparation of SERS substrates. Full article