Search Results (173)

Metamaterial absorbers in terahertz (THz) based bands have garnered significant attention for their potential applications in military stealth, terahertz imaging, and other fields. Nevertheless, the limited bandwidth, low absorption rate, and heavy weight greatly reduce the further development and wide application of terahertz absorbers. To solve these problems, we propose a polystyrene (PS)-based ultra-broadband metamaterial absorber integrated with a polyethylene terephthalate (PET) double-sided adhesive layer and a patterned indium tin oxide (ITO) film through the simulation method, which operates in the THz band. The electromagnetic wave absorption properties and underlying physical absorption mechanisms of the proposed metamaterial absorbers are comprehensively modeled and rigorously numerically simulated. The research demonstrates the metamaterial absorber can achieve absorption performance of over 90% for fully polarized incident waves in the ultra-wideband range of 1.2–10 THz, especially achieving perfect absorption characteristics of over 99.9% near 1.8–1.9 THz and 5.8–6.2 THz. The proposed absorber has a lightweight physical property of 0.7 kg/m² and polarization-insensitive characteristic, and it achieves a broad-angle that allows a range of incidence angles up to 60°. The simulation research results of this article provide theoretical support for the design of terahertz absorbers with ultra-wideband absorption characteristics. Full article

Films of a Ni/Al-layered double hydroxide intercalated with reduced graphene oxide were deposited, by means of a simple and rapid electrochemical synthesis, on Pt electrodes previously submitted to a special cleaning procedure. The aim of the research was to determine whether the better electrocatalytic properties of the Ni(III)/Ni(II) couple, due to the presence of the carbon nanomaterial, as compared to the Ni/Al-LDH alone, could allow glucose detection at physiological pHs, as normally LDHs work as redox mediators in basic solutions. Chronoamperometric experiments were carried out by applying a potential of 1.0 V vs. SCE to the electrode soaked in solutions buffered at pHs from 5.0 to 9.0 to which glucose was continuously added. The steady-state currents increased as the pH solution increased, but at pH = 7.0 the modified electrode exhibited a fast and rather sensitive response, which was linear up to 10.0 mM glucose, with a sensitivity of 0.56 A M⁻¹ cm⁻² and a limit of detection of 0.05 mM. Our results suggest the potential application of Ni/Al-LDH(ERGO) composite for the non-enzymatic detection of glucose or other oxidizable analytes under biological conditions. Full article

In this paper, nanoscale graphene film electrodes were prepared using laser-induced technology, and an in situ electrochemical cell was constructed. The normalized peak areas at 2.82 ppm for the samples without the in situ electrochemical cell and with an in situ electrochemical cell are 4.02 and 4.41, respectively. Tests showed that this in situ electrochemical cell has minimal interference from the nuclear magnetic resonance (NMR) magnetic field, allowing for high-resolution in situ spectra. Using this in situ electrochemical cell and employing in situ electrochemistry combined with NMR techniques, we investigated the oxidation reaction of 0.01 M procarbazine (PCZ) in real-time. We elucidated the following oxidation mechanism for procarbazine: the oxidation of PCZ first generates azo-procarbazine, which then undergoes a double bond shift to hydrazo-procarbazine. hydrazo-procarbazine undergoes hydrolysis to yield benzaldehyde-procarbazine, and then finally oxidizes to produce N-isopropylterephthalic acid. This confirms that the combination of in situ electrochemistry and nuclear magnetic resonance technology provides chemists with an effective tool for in situ studying the reaction mechanisms of drug molecules. Full article

B₄C is beneficial for forming a glassy film that is effective at impeding oxygen diffusion and improving the oxidation resistance of coatings at high temperature. The effect of B₄C content on the oxidation resistance of a B₄C-SiO₂–Albite/Al₂O₃ (BSA/AO) double-layer coating by the slurry brushing method at 900 °C was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and differential scanning calorimetry (DSC) with thermogravimetric analysis (TGA) in this work. It is indicated that the composite coating with 20 wt% B₄C exhibits excellent oxidation resistance at high temperature, which shows a mass loss of only 0.11% for the coated carbon block after being exposed to 900 °C for 196 h. This is attributed to the in situ formation of a thin, dense glass layer with good self-healing ability at the interface of the B₄C-SiO₂–Albite/Al₂O₃ composite coating within 1 h and the persistence and stability of the dense glass layer during exposure. The mechanism is discussed in detail. Full article

Carbon dioxide-based copolymers such as polypropylene carbonate (PPC) can offer the double environmental benefit of capturing CO₂ and replacing oil-based raw materials in the plastics industry with renewable ones. However, their production at an industrial level is still limited by the range of applications in which their physicochemical properties are competitive and ideally surpass those of fossil-based polymeric commodities. This work introduces PPC materials with high-stretch and self-healing properties that were prepared by copolymerization of CO₂ and propylene oxide using tailored Zn glutarate catalysts. The PPC materials were analyzed in terms of composition, molecular weight, thermal and mechanical behavior, particularly focusing on their tensile properties, strain recovery, creep response, and self-healing ability. All the prepared PPC materials showed good ductility and self-healing properties. The most promising ones achieved excellent and fast recovery of extremely high elongations (>700%), still reaching remarkable values (>600%) after proper self-healing. These high-stretch and self-healing PPC materials are completely amorphous, present good optical transparency, and can be processed using techniques normally used for other thermoplastics. Therefore, they are promising for a variety of applications, including shrink films and self-healing packaging, thus providing new, valuable perspectives for the industrialization of these CO₂-based polymers. Full article

In this work, we report on the fabrication of a novel Organic Double-Layer Supercapacitor (ODLSC) using recycled palm as the substrate and electrodes based on halogenated indium and copper phthalocyanines. The electrodes were characterized using Reflectance, the Kulbeka–Munk function, and Fluorescence. Finally, their electrical behavior was evaluated, and the results were compared with those obtained for a more conventional supercapacitor fabricated on polyethylene terephthalate substrate and using indium tin oxide film for electrodes. Based on the experimental measurements of the fabricated ODLSC, the parameter identification of the classical equivalent circuit model was carried out using the Least Squares of Orthogonal Distances (LSOD) algorithm. The results indicated that the palm supercapacitor exhibited behavior more like that of traditional supercapacitors, as the root square mean error (RMSE) values in the model approximation of the experimental data were in the order of ${10}^{-7}$. Furthermore, the models obtained allowed a determination of the device’s Electrical Impedance Spectroscopy (EIS), revealing that the Palm SC-T1 exhibited capacitive behavior. In contrast, the manufactured Palm SC-T2, PET SC-T1, and PET SC-T2 devices exhibited inductive behavior. All the materials used in this work, such as the substrates, electrodes, separator membranes, and electrolytes, have a high potential to be used in organic supercapacitors. Full article

Polyvinyl alcohol (PVA) is used in various fields; however, its highly flammable property greatly limits its application. In order to improve the flame-retardant properties of PVA, one method is by adding flame retardants directly, while another method is through grafting, cross-linking and hydrogen bonding. A flame retardant, 9, 10-dihydro-9, 10-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-vinyltrimethoxysilane (VTES), was synthesized through the addition reaction of a P–H bond on the DOPO and unsaturated carbon–carbon double bonds on the VTES. Then, the DOPO-VTES and zirconium phosphate (α-ZrP) were blended with PVA to cast a film, in which DOPO-VTES was grafted onto the PVA by cross-linking the hydroxyl group in the molecular structure of DOPO-VTES with the hydroxyl group in PVA; α-ZrP was used as a cooperative agent of DOPO-VTES. The cone calorimetry test (CCT) showed a significant reduction in both the heat release rate (HRR) and total heat release rate (THR) for the flame-retardant PVA films compared to pure PVA. Additionally, thermogravimetric analysis (TGA) revealed a higher residual char content in the flame-retardant PVA films than in pure PVA. These findings suggested that the combination of DOPO-VTES and α-ZrP could improve the flame retardancy of PVA. The cooperative flame-retardant mode of action at play was possibly that DOPO in the DOPO-VTES acted as a mainly gas-phase flame retardant, which yielded a PO radical; VTES in the DOPO-VTES produced silicon dioxide (SiO₂), which acted as a thermal insulator; and α-ZrP catalyzed the carbonization of the PVA. By combining DOPO-VTES with α-ZrP, a continuous dense carbon layer was formed, which effectively inhibited oxygen and heat exchange, resulting in a flame-retardant effect. It is expected that flame-retardant films for PVA have a broad development prospect and potential in the fields of packaging materials, electronic appliances, and lithium-ion battery separators. Full article

As one of the representative transparent conducting oxides, perovskite-typed La-doped BaSnO₃ (LBSO) films could be integrated with other perovskite materials to create all-perovskite oxide devices exhibiting exotic physical properties. To overcome the intricate trade-off between conductivity and transmittance in LBSO-based devices, understanding the structural modulating mechanisms of transmittance is definitely crucial. In this paper, the influences of the prevailing Ruddlesden–Popper faults (RP faults) on the transmittance of LBSO films were systematically illuminated, whose density were regulated by the oxygen partial pressures during film growth. High-angle annular dark field (HAADF) STEM and X-ray diffraction (XRD) were employed to characterize the microstructures of the films growing under various oxygen partial pressures and annealing under different oxygen partial pressures. A decrease in RP fault density was observed in the films grown and annealed at high oxygen partial pressures, which displayed improved visible light transmittance. Atomic-scale energy-dispersive spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) analyses revealed the different electronic structure at RP faults compared with the bulk material, including the double concentration of La and increased M5/M4 white line ratio, which is modulative by the oxygen deficiency in LBSO film. It is revealed that the RP defaults in LBSO films annealed at low oxygen pressures displayed larger changes in electronic structure compared with the counterparts with low oxygen deficiency. This work suggests that the oxygen deficiency in LSBO films plays a crucial role in changing the density of RP faults and their electronic structures, thereby regulating the transmittance of LBSO films, which would provide guidance for fabricating high-performance LBSO films. Full article

Stainless steels are used in the aeronautical industry for their corrosion resistance and good mechanical performance. The chemical treatment used to improve corrosion resistance is passivation, forming a compact, continuous, adherent chromium oxide film. This research aimed to investigate the effect of citric acid at different concentrations (citric acid; citric acid + oxalic acid, citric acid + hydrogen peroxide, and citric acid + hydrogen peroxide + ethanol) on AM 350 stainless steel passivated for 90 and 120 min at 25 and 50 °C and immersed in 5% by weight sodium chloride (NaCl) solutions. The electrochemical technique used was electrochemical impedance spectroscopy (EIS) based on ASTM-G106. The EIS (equivalent circuit) results indicate that there are one and two constant phase elements (CPE), which indicate the presence of various factors on the stainless steel surface, such as roughness and the formation of porous and passive layers, respectively. A double-layer system was employed for some samples. However, when the ethanol was added to the passivation bath, the behavior changed to a one-time constant system. The AM 350 passivated in citric and oxalic acid presented the higher corrosion resistance with values of 6 × 10⁵ Ω·cm². Full article

The in situ electrochemical behaviors of Ti-39Nb-6Zr alloy were investigated in 2.3 ppm Li⁺ and 1500 ppm B³⁺ solution at 300 °C and 14 MPa. The activation energy is 12.84 kJ/mol, and the oxidation of titanium is controlled by oxygen ions diffusion in the liquid phases. The morphology, phase structure, and composition of the oxide film after 700 h exposure time in 300 °C and 14 MPa solution were characterized. The oxide film mainly included anatase TiO₂ phases, ZrO₂, Nb₂O₅, and a slight B₂O₃. The morphology of the film is shown by many nanocrystalline grains and the thickness is about 5 μm. The passivation film on the alloy substrate transforms from a single-layer film structure to a double-layer film structure. The impedance of the passivation decreases with the increase in temperature, which is related to the enhanced ion conductivity of the passivation film at high temperatures. The impedance of the dense layer inside the passivation film is much greater than that of the loose layer outside, and the dense layer inside plays a crucial role in the corrosion resistance of the Ti-39Nb-6Zr alloy. During the insulation process, the impedance of the dense layer inside the passivation film first increases and then slowly decreases, and the corrosion resistance of the passivation film first increases and decreases. Full article

Hole-doped manganese oxides exhibit a gigantic negative magnetoresistance, referred to as colossal magnetoresistance (CMR), owing to the interplay between double-exchange (DE) ferromagnetic metal and charge-ordered antiferromagnetic insulator/semiconductor phases. Magnetoresistive manganites display a sharp resistivity drop at the metal–insulator transition temperature (T^MI). CMR effects in perovskite manganites, specifically La_0.67Ca_0.33MnO₃ (La-Ca-Mn-O or LCMO), have been extensively investigated. This review paper provides a comprehensive introduction to the crystallographic structure, as well as the electronic and magnetic properties, of LCMO films. Furthermore, we delve into a detailed discussion of the effects of epitaxial strain induced by different substrates on LCMO films. Additionally, we review the early findings and diverse applications of LCMO thin films. Finally, we outline potential challenges and prospects for achieving superior LCMO film properties. Full article

WO₃/Ag/TiO₂ composite photoelectrodes were formed via the high-temperature calcination of a WO₃ film, followed by the sputtering of a very thin silver film and deposition of an overlayer of commercial TiO₂ nanoparticles. These synthetic photoanodes were characterized in view of the oxidation of a model organic compound glucose combined with the generation of hydrogen at a platinum cathode. During prolonged photoelectrolysis under simulated solar light, these photoanodes demonstrated high and stable photocurrents of ca. 4 mA cm⁻² due, on one hand, to the occurrence of the so-called photocurrent doubling and, on the other hand, to the plasmonic effect of Ag nanoparticles. The post-photoelectrolysis analyses of the electrolyte demonstrated the formation of high-value final glucose photo-reforming products, principally gluconic acid, erythrose and formic acid. Full article

Temperature sensors play important roles in wide-spreading human activities. The non-contact method of using temperature sensors offers significant advantages but faces challenges in detection precision. In this work, a double-layer asymmetric terahertz (THz) metamaterial combined with phase transition oxide was proposed to realize non-contact temperature sensor with high sensitivity. The metamaterial exhibited band-stop filtering effects in the simulated transmission spectra. Temperature changes induced a reversible phase transition in VO₂, resulting in altered conductivity. The numerical results indicated that the S21 parameter increases from −44.33 dB to −4.78 dB at a frequency of 1.22 THz as the conductivity of the VO₂ film increases from 10 to 5000 S/m, achieving a modulation depth of 89%. In addition, the 86 nm thick VO₂ film underwent a phase transition in the temperature range of 54.93 °C to 66.93 °C, achieving a sensitivity of 1.82 dB/°C for temperature sensing. This work provided great insights into the development of metamaterials based on high-precision temperature measurement. Full article

The main goal of this research was to create biocompatible hydrogels using gelatin and a double cross-linking technique involving both covalent and ionic bonds to immobilize propolis. The covalent bonds were formed through Schiff base cross-links between protein-free amino groups (NH₂) from the lysine residue and aldehyde groups (CHO) produced by oxidizing sodium alginate with NaIO₄, while the ionic bonds were achieved using Mg²⁺ ions. Hydrogel films were obtained by varying the molar ratios of –CHO/–NH₂ under different pH conditions (3.5 and 5.5). The presence of aldehyde groups in the oxidized sodium alginate (OSA) was confirmed using FTIR and NMR spectroscopy. The oxidation degree was monitored over 48 h, and the influence of temperature was examined. Results showed that higher –CHO/–NH₂ molar ratios led to increased conversion index values of NH₂ groups, and a decrease in swelling degree values was observed in mediums with pH values of 5.5 and 7.4. The encapsulation and release efficiency of propolis decreased with an increase in the hydrogel cross-linking degree. UV irradiation enhanced the antioxidant activity of both free and encapsulated propolis. These findings offer valuable insights for the biomedical and pharmaceutical fields into designing biocompatible hydrogels for propolis immobilization, with potential for controlled release. Full article

A novel double-impurity doping process for silicon (Si) surfaces was developed, utilizing nanosecond-laser melting of an 11 nm thick gold (Au) top film and a Si wafer substrate in a laser plasma-activated liquid nitrogen (LN) environment. Scanning electron microscopy revealed a fluence- and exposure-independent surface micro-spike topography, while energy-dispersive X-ray spectroscopy identified minor Au (~0.05 at. %) and major N (~1–2 at. %) dopants localized within a 0.5 μm thick surface layer and the slight surface post-oxidation of the micro-relief (oxygen (O), ~1.5–2.5 at. %). X-ray photoelectron spectroscopy was used to identify the bound surface (SiN_x) and bulk doping chemical states of the introduced nitrogen (~10 at. %) and the metallic (<0.01 at. %) and cluster (<0.1 at. %) forms of the gold dopant, and it was used to evaluate their depth distributions, which were strongly affected by the competition between gold dopants due to their marginal local concentrations and the other more abundant dopants (N, O). In this study, 532 nm Raman microspectroscopy indicated a slight reduction in the crystalline order revealed in the second-order Si phonon band; the tensile stresses or nanoscale dimensions of the resolidified Si nano-crystallites envisioned by the main Si optical–phonon peak; a negligible a-Si abundance; and a low-wavenumber peak of the Si₃N₄ structure. In contrast, Fourier transform infrared (FT-IR) reflectance and transmittance studies exhibited only broad structureless absorption bands in the range of 600–5500 cm⁻¹ related to dopant absorption and light trapping in the surface micro-relief. The room-temperature electrical characteristics of the laser double-doped Si layer—a high carrier mobility of 1050 cm²/Vs and background carrier sheet concentration of ~2 × 10¹⁰ cm⁻² (bulk concentration ~10¹⁴–10¹⁵ cm⁻³)—are superior to previously reported parameters of similar nitrogen-implanted/annealed Si samples. This novel facile double-element laser-doping procedure paves the way to local maskless on-demand introductions of multiple intra-gap intermediate donor and acceptor bands in Si, providing related multi-wavelength IR photoconductivity for optoelectronic applications. Full article