Search Results (524)

An Al₂O₃/AlN stack deposited via Atomic Layer Deposition (ALD) methods as a gate insulator for silicon carbide (4H-SiC) has been investigated, focusing on the effects of different Al₂O₃ deposition processes on the nitride layer. In particular, dielectric stacks, consisting of a 10 nm AlN interface (001)-oriented layer directly grown on a 4H–SiC substrate and in 20 nm of additional amorphous Al₂O₃ layers were synthesized in sequential deposition runs by thermal ALD (T-ALD) or plasma-enhanced ALD (PEALD) methods. The evolution of the phenomena occurring at the Al₂O₃/AlN interfaces has been established by in situ ellipsometry measurements. Strong effects of the oxygen plasma because of the O-Al-N bond formation have been clearly observed and corroborated by ex situ structural and electrical characterizations, especially in the case of the plasma-enhanced Al₂O₃ process. In particular, the Al₂O₃/AlN bilayer grown by the Al₂O₃ T-ALD method exhibited good insulating behavior and an 8.7-high dielectric constant was measured. By contrast, the Al₂O₃/AlN bilayer grown by the Al₂O₃ PEALD method demonstrated poor insulating properties. Full article

With the shift in advanced packaging toward 3D integration and flexible electronics, it is becoming critical to produce high-quality silicon nitride films under low thermal budgets. To overcome the limitations of low-temperature deposition, this study compares two gas mixtures—SiH₄/NH₃/N₂ and SiH₄/N₂—in plasma-enhanced chemical vapor deposition of silicon nitride coatings. We systematically evaluated how the NH₃ precursor affects deposition kinetics, chemical bonds, non-uniformity, optical properties, and internal stress at different RF powers and electrode gaps. The test results show that NH₃, with its lower dissociation energy, avoids the high activation barrier associated with pure N₂ plasma, leading to a higher reactive nitrogen flux and a doubled deposition rate. In the SiH₄/NH₃/N₂ system, raising RF power from 300 W to 900 W reduced hydrogen content from 23.58% to 12.25%. This suppression of hydrogen promoted structural densification, shifting the mechanical stress from 173.3 MPa to −989.7 MPa. At a larger electrode gap of 19 mm, NH₃’s better diffusion characteristics offset the electric field sensitivity typical of N₂ systems, reducing large-area film non-uniformity by 28.7% compared to a 13 mm gap. This work offers a practical, mass-production-friendly approach for depositing robust, low-hydrogen, highly uniform silicon nitride films at low temperatures. Full article

The valorization of phosphogypsum (PG), a byproduct of phosphoric acid production, along with waste glass (WG) and silica fume (SF) into value-added materials has attracted growing attention in recent years. The present study aims to synthesize three types of porous geopolymers (GD, GDP, and GDG) using Tunisian clay and locally available mineral wastes, and to investigate their potential as low-cost adsorbents for the removal of methylene blue (MB) dye from aqueous solutions. The physicochemical characteristics of the raw precursors and the resulting porous geopolymers were analyzed using various techniques, including FTIR, XRD, BET, and SEM. Variations in Si/Al, Na/Al, and Ca/Al ratios play a critical role in the geopolymer structure. The high Ca/Al ratio in GDP (porous geopolymer from calcined clay and phosphogypsum) promotes the formation of C-A-S-H, leading to increased macroporosity, which favors adsorption capacity despite the presence of a more heterogeneous morphology. The results indicated that the maximum adsorption capacity (Qmax) for MB dye was obtained for the GDP sample, reaching 68 mg/g. Adsorption experiments revealed the successful removal of MB dye by geopolymers, with the Langmuir isotherm and pseudo-second-order kinetic models adequately describing the adsorption process. The MB uptake by geopolymers was facilitated by weak physicochemical interactions, including electrostatic attraction, hydrogen bonding, and π–π interactions. This study proposes a simple and effective alkali activation strategy that combines different industrial wastes within a single geopolymer system, resulting in improved porosity and adsorption efficiency. Overall, the findings highlight the potential of these waste-derived geopolymers as promising and sustainable adsorbents for wastewater treatment applications. Full article

Silicone rubber is an important external insulating material for composite bushings, composite insulators, and other power equipment. During long-term service, it is inevitably exposed to coupled environmental and electrical stresses, such as elevated temperature, moisture ingress, strong electric fields, and partial discharge, which may lead to hydrophobicity loss, surface chalking, crack propagation, and particle shedding. To reveal the microscopic degradation mechanism of silicone rubber under complex operating conditions, a molecular model of methyl vinyl silicone rubber was constructed using Materials Studio. A stable silicone rubber molecular structure was obtained through crosslinking, geometry optimization, and ensemble relaxation. Subsequently, a reactive molecular dynamics simulation system under coupled temperature–humidity–electric field conditions was established using LAMMPS and the ReaxFF reactive force field. Different temperature gradients, electric field intensities, and aging–recovery stages were designed to investigate the degradation behavior of silicone rubber. The evolution of the maximum carbon content, maximum silicon content, carbon-containing decomposition products, and typical small-molecule products, including H₂, H₂O, CH₄, C₂H₂, C₂H₄, and C₂H₆, was statistically analyzed. In addition, atomic trajectory tracking was performed to clarify the processes of methyl group detachment, Si-O bond cleavage, water molecule participation, and molecular chain reconstruction. The results show that high temperature mainly promotes methyl group detachment from side chains and fracture of the siloxane main chain, while a strong electric field accelerates the decomposition process and induces the transformation of long siloxane chains into shorter chains. Water molecules can react with broken siloxane chains to form hydroxyl-containing structures, making the structural degradation partially irreversible. The degradation process of silicone rubber under coupled temperature–humidity–electric field stress can be summarized as side-chain detachment, main-chain scission, water-assisted reactions, free-radical recombination, and local molecular aggregation. This study provides a molecular-level theoretical basis for aging mechanism analysis, condition assessment, and lifetime prediction of composite external insulating materials. Full article

Zeolite morphology strongly determines its performance. Herein, Silicalite-1 was synthesized in a low-template system (TPA⁺/Si = 0.007) via a synergistic strategy using potassium bisulfate and seed suspension. The seeds supply abundant structural units to reduce nucleation barrier and accelerate crystallization, while KHSO₄ facilitates silicate polycondensation and suppresses non-MFI impurities. Sulfate ions selectively adsorb on specific crystal facets via hydrogen bonding and induce preferential crystal growth along the c-axis. The c-axis size of Silicalite-1 can be precisely regulated by adjusting dosages of seeds and KHSO₄. Well-defined plate-like crystals were obtained under the conditions of K⁺/Si = 0.25, a seed content of 2.42 wt%, and hydrothermal treatment at 180 °C for 8 h. Scale-up synthesis in a 2 L autoclave verifies its industrial potential. The product exhibits excellent adsorption capacity and cyclic stability toward methylene blue. This work provides a low-cost and green route for morphology-controlled synthesis of MFI-type zeolites. Full article

Pyrrolidinyl-substituted silacyclopentane (CH₂)₄Si(Pyr)₂ and α-amino isobutyric acid (H₂Aib) react with the release of one equivalent pyrrolidine (HPyr) and the formation of the pentacoordinate silicon bis-chelate (Aib)Si(CH₂)₄(HPyr), which features the di-anion of the amino acid as an (O,N)-chelator and one equivalent of pyrrolidine as an additional lone-pair donor. Crystallographic analyses of the chloroform solvate (Aib)Si(CH₂)₄(HPyr)·(CHCl₃), which undergoes a phase transition at 200 K, and a solvent-free modification (Aib)Si(CH₂)₄(HPyr), which features two crystallographically independent molecules of the complex, revealed that the N atom of the HPyr ligand, as well as the carboxylate of Aib, occupy the axial positions in the trigonal bipyramidal Si coordination sphere; the Si–C bonds of the silacyclopentane rest on equatorial sites. For the isolated molecule in a solvent environment, computational analyses revealed that the energy difference between this configuration and the related isomer with an equatorial HPyr and equatorial–axial positioning of the silacyclopentane motif is marginal. In DMSO solution, the adduct (Aib)Si(CH₂)₄(HPyr) decomposed, forming the hexacoordinate Si complex (HAib)₂Si(CH₂)₄ as one of the decomposition products. In a deliberate manner, this compound was accessible from the diethylamino-substituted silacyclopentane (CH₂)₄Si(NEt₂)₂ and H₂Aib with the liberation of diethylamine. (HAib)₂Si(CH₂)₄ features two mono-anions of the α-amino acid as (O,N)-chelators, their carboxylate O atoms are trans-disposed to silacyclopentane, and their NH₂ groups are mutually trans. Full article

As the critical weak link in grouting reinforcement systems, the interfacial adhesion between cementitious grout and rock minerals is highly susceptible to performance degradation under high-temperature and water-rich conditions. In this paper, molecular dynamics simulations were performed across a temperature range of 293 K to 368 K to systematically investigate the effects of high-temperature and water-rich environments on the mechanical response, bonding structure, and dynamic behavior of the grout–rock interface. All simulations were performed using the LAMMPS package with the ClayFF force field. Two interface models, including a CSH/SiO₂ direct-contact model and a CSH/H₂O/SiO₂ water-containing model, were constructed and subjected to uniaxial tensile tests. Key findings are as follows: (i) The tensile strength and interaction energy of the CSH/SiO₂ interface exhibit distinct thermal degradation characteristics. The tensile strength decreases by 32.57%, and the interaction energy by 15.78% when the temperature rises from 293 K to 368 K. High temperatures induce expansion of the interface transition zone from 2.74 Å to 4.60 Å and loosening of the interface structure. (ii) High temperatures intensify atomic diffusion at the interface. The number and stability of Ca-O bonds and hydrogen bonds formed between CSH and SiO₂ are reduced, leading to a decline in interfacial adhesion. (iii) The presence of an interfacial water layer significantly impairs the tensile strength and interaction energy of the interface. Compared with the direct-contact interface, the interaction energy is reduced by 38% at 293 K, and the tensile strength decreases by 73.58%. Water molecules in the solution compete for bonding sites of hydrogen bonds and Ca-O bonds at the interface, weakening the direct interaction between CSH and SiO₂ and transforming it into an indirect interaction mediated by water molecules. Full article

Optical fiber sensors deployed in harsh industrial fields, e.g., high-temperature wet-oxygen, face severe challenges in signal attenuation and mechanical degradation. While amorphous silicon oxycarbide (a-SiOC) coatings offer a promising solution due to their adjustable thermo-mechanical properties, balancing their structural density with environmental stability remains a critical technical bottleneck. In this study, a-SiOC coatings were deposited on optical fibers using hexamethyldisilane (HMDS) and trace oxygen via radio-frequency capacitively coupled plasma-enhanced chemical vapor deposition (PECVD). A systematic investigation was conducted to determine the impact of deposition temperature (70–420 °C) on the precursor dissociation kinetics, microstructural evolution, and corrosion resistance of the coatings. An elevation in temperature promotes the elimination of organic terminal groups (–CH₃, –H) and enhances surface diffusion, driving the coating from a loose, carbon-rich “polymer-like” structure (dominated by Si–C bonds) to a dense, inorganic “silica-like” skeleton (dominated by Si–O–Si bonds). High-temperature corrosion tests in a wet-oxygen environment (500–900 °C) demonstrate that the failure mechanism is highly dependent on deposition temperature. Coatings deposited at low temperatures suffer catastrophic cracking due to pronounced oxidative shrinkage and the release of volatile species, whereas coatings deposited at 420 °C exhibit microcracking caused by severe carbon phase separation and stress concentration within the rigid inorganic network. In the present system, 350 °C is identified as the optimal deposition temperature, as it achieves the best balance of network densification and structural flexibility, while exhibiting the best mechanical performance. Full article

In this paper, we report on the effect of combining porous silicon with aluminum microparticles (PS/Al-µPs) on the optical and electronic properties of multicrystalline silicon (mc-Si). An aluminum film was deposited on the mc-Si surface, annealed at 750 °C for 20 min, and partially remained on the surface after CP₄ treatment. The surface was subsequently treated with a stain-etching solution (HF/HNO₃/H₂O) to form a porous silicon (PS) layer. The resulting mc-Si with PS/Al-µPs modification led to a marked improvement in the optoelectronic performance of the treated mc-Si. Surface reflectance was reduced from 34.6% to 9.1% across 400–800 nm wavelength range, corresponding to a 74% decrease. Minority carrier lifetime increased from 2 µs in untreated samples to 1 ms after Al-µPs passivation and remained elevated at 285 µs following stain etching. Additionally, the effective surface recombination velocity dropped from 50 cm·s⁻¹ to 0.35 cm·s⁻¹ and a reduction in [Fe] after treatment confirms the effectiveness of the PS-Al-µPs gettering process. FTIR analysis confirmed the formation of Si–H and Al–O bonds, highlighting effective surface passivation and suppression of recombination losses. Full article

Background/Objectives: Root perforation treatment is essential for restoring the tightness of the root system, preventing periradicular inflammation and tooth loss. The present study aimed to evaluate the biocompatibility of Ketac™ Molar EasyMix as well as conduct a thorough morphological and structural characterization of the material, considering its potential use in managing root perforations. Methods: Morpho-structural characterization was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FT–IR), and X-ray diffraction (XRD). Biocompatibility tests were performed on osteosarcoma cell line (ATCC—G 292 CRL-1423), monitoring metabolic activity and cell viability (MTT, n = 3), as well as the inflammatory response (nitric oxide—NO, n = 6), after 24 and 48 h of incubation. The control group consisted of cells unexposed to the material. Results: Microstructurally, the material exhibits a heterogeneous structure, along with pores and cracks. The specific bonds of the material, including both organic acid (COO⁻, O-H) and the glass components (Si-O-Al, Ca-O, C-F), were identified by FT-IR, while the crystalline phase composed of calcium fluorolanthanate was determined by XRD. Moreover, in vitro metabolic activity and viability test (MTT) showed a decrease of ~28% (p = 0.029) and ~30% (p = 0.150) after 24 and 48 h for samples incubated with Ketac™ Molar EasyMix. The statistically significantly increased levels of NO (p = 0.002, p = 0.004) suggest that the cells are trying to adapt to the environment that they have been exposed to. Conclusions: Within the limitations of the present study, under the tested conditions, our results suggest that Ketac™ Molar EasyMix maintained cell viability close to the 70% threshold defined by ISO 10993-5:2009, indicating a borderline biological response, a feature that may be influenced by the composition and behavior of the material. Full article

The crystallinity of cubic silicon carbide (3C-SiC) epilayers is improved through the use of a novel wafer bonding and regrowth technique resulting in a reduction in planar defects. The process involves the epitaxial growth of a 3–6 µm thick 3C-SiC seed on silicon (Si), which is polished and bonded to a new handle wafer before the original substrate and defective interface region of the 3C-SiC epilayer are removed. Further epitaxial growth on this Bonded Switchback template results in higher quality 3C-SiC epilayers through the reduction in crystal mosaicity, stacking fault defects, and elimination of interface voids. The process could be applied to 3C-SiC grown on both on- and off-axis substrates, and the form of the new handle has no impact on the growth process, enabling this technology to be applied to sapphire or hexagonal 4H-SiC substrates. The use of such substrates would overcome the thermal budget limitations of Si substrates for 3C-SiC heteroepitaxy and ion implantation. Bonded Switchback can improve material quality for applications in power electronics, as well as see the heterogeneous integration of 3C-SiC into other device structures, potentially leading to a new range of hybrid 3C-SiC/Si devices without the high density of defects observed at the interface between these two materials. Full article

Silicomanganese slag (SiMnS), a Mn-bearing by-product from silicomanganese alloy production, is often stockpiled in large quantities and may pose environmental concerns due to potential metal leaching. This study develops an OPC-rich hybrid SiMnS–steel slag–fly ash–OPC-activated composite binder, referred to as SMSAB, in which OPC accounts for 55% of the solid precursor mass. Different alkali contents and sodium silicate moduli were investigated, and the optimised paste was characterised in terms of mechanical strength, reaction products, pore structure, carbon-footprint and heavy-metal leaching. The best performance was obtained at an alkali content of 4% and a sodium silicate modulus of 1.0, giving 28-day compressive and flexural strengths of 65.13 MPa and 3.37 MPa, respectively. XRD, SEM-EDS, FTIR and MIP results showed that the main reaction products were C-(A)-S-H, N-A-S-H and C-N-A-S-H gels, which refined the pore structure and produced a dense matrix. The reduction in Mn leaching may be associated with physical encapsulation, possible charge-balancing interactions within gel structures, changes in Mn-related bonding environments and the presence of Mn-bearing phases. Leaching concentrations of Zn, Mn, Cr, Cu and Ni satisfied the Grade III groundwater limits used in China. The calculated carbon intensity of SMSAB was 3.97 kg·(m³·MPa)⁻¹, indicating a favourable strength-to-emission balance compared with the reference systems considered. It should be noted that the present work examines paste specimens only; aggregate skeleton, traffic loading, freeze–thaw cycling and wet–dry/moisture cycling were not included. Therefore, the results demonstrate binder-level potential rather than direct qualification of SMSAB as a pavement base or subbase material. Full article

Direct welding of fused silica to pure titanium (Ti) foil using conventional methods faces significant challenges, such as poor interfacial wettability, insufficient joint strength, and the need for interlayers or surface pretreatments. Existing femtosecond (fs) laser welding techniques for these materials often require high-energy millijoule (mJ)-level pulses or alloy interlayers. Moreover, reports on direct microjoule (μJ)-level fs laser welding of Ti foil to fused silica remain scarce. This study successfully demonstrates a direct welding process for pure Ti foil and fused silica using μJ-level fs laser pulses under ambient conditions, achieving joints with a maximum shear strength of 9.19 MPa. Microstructural analysis revealed an elemental interdiffusion region at the weld interface, supported by mechanical interlocking effects. X-ray photoelectron spectroscopy (XPS) confirmed the occurrence of interfacial chemical reactions, forming titanium silicide (TiSi₂) and titanium oxide (TiO₂). Additionally, a 24 h water immersion test of a square sealed cavity revealed outstanding hermeticity, with no water ingress. This work provides a simple, efficient, and robust solution for high-strength, additive-free bonding of fused silica to Ti foil under low-energy processing conditions. Full article

While both Urbach tails and dangling bonds are known to be present in a-Si films, the current literature lacks parametrization that simultaneously accounts for both types of defects using only transmittance spectra, reflectance spectra, or spectroscopic ellipsometry. To address this issue, we performed parametrizations of three magnetron-sputtered a-Si thin films deposited on glass substrates at different low pressures of argon gas, using only their measured UV–Vis–NIR transmittance spectra T(λ = [300, 2500] nm) and different dispersion models. We preprocessed T(λ) by suppressing both general and bandpass noise to yield the spectrum T_d(λ). The films were parametrized from T_d(λ) using two versions of the Tauc–Lorentz–Urbach dispersion model and the universal dispersion model (UDM) of Franta. The most accurate parametrization was achieved employing UDM including Urbach tail and three subgap oscillators. JDOS and the dielectric function ε(E) were computed by this UDM, and it was concluded that these three oscillators correspond to electron transitions via two bands of dangling bonds. The respective DOS is similar to the DOS previously reported for a-Si:H, but not to a-Si, indicating a relatively low density of dangling bonds in our a-Si films. Record low parametrization errors are achieved, which confirms the accuracy of these results. Full article

Environmental fires pose a serious threat to energy security, ecosystems and public safety, whilst traditional halogenated flame retardants suffer from limitations such as high environmental residue risks and insufficient flame-retardant efficacy. In this study, sodium alginate (SA) was utilised as the matrix, with the incorporation of ammonium polyphosphate (APP) and phytic acid (PA), in conjunction with SiO₂-APTES surface modification, to prepare nitrogen–phosphorus synergistic bio-based flame-retardant gels. The present study systematically investigated the influence of the N/P molar ratio on the gelation kinetics, rheological behaviour, microstructure and flame-retardant performance of the gel. The study revealed a nitrogen–phosphorus coupled gas–solid two-phase synergistic flame-retardant mechanism. The results indicate that at an N/P ratio of 1/4, the gel forms a stable dual-network structure comprising ionic cross-links and Si–O–P covalent bonds. In the gas phase, the thermal decomposition of APP releases inert NH₃, which dilutes oxygen and quenches gas-phase radicals (·OH, ·H). In the condensed phase, the phosphate groups of PA-catalysed SA form Si–O–P covalent bonds with SiO₂ under the mediation of APTES, creating a dense, insulating char layer. In comparison with the control group (N/P = 0/0), the optimal gel sample (N/P = 1/4) demonstrated a 33% increase in shear stress, a 10% reduction in the peak heat release rate (HRR), a 75% decrease in total smoke production (TSP), and a 150% increase in char layer thickness after combustion, while maintaining adequate mechanical strength, thermal stability, and environmental friendliness. This work provides novel insights and strategies for the development of green, highly efficient flame-retardant materials for environmental fire prevention and control. Full article