Search Results (133)

This study evaluated potentially toxic element (PTEs) contamination (As, Cd, Co, Cr, Cu, Ni, Pb, and Zn) in soil and grapevine leaves across 36 sites in a historical vineyard near Iași, Romania, transitioning toward residential development. Soil samples were analyzed using energy-dispersive X-ray fluorescence (ED-XRF), while leaf tissues collected during the véraison stage (mid-August) underwent microwave-assisted acid digestion followed by inductively coupled plasma mass spectrometry (ICP-MS). Soil analyses revealed that average concentrations of Cr, Ni, and Pb exceeded national normal legal thresholds, while Cu and As surpassed alert permissible limits. Contamination factor ($CF$) and Geoaccumulation Index ($I_{geo}$) metrics confirmed significant anthropogenic Cu enrichment from historical viticultural treatments. Soil-to-leaf transfer factors ($TF$) approached or exceeded 1 for Cu and Zn, though grapevine was not identified as a hyperaccumulator. Spearman correlation modeling demonstrated a statistical decoupling between soil concentrations and foliar tissue levels for Cu ($r_s=-0.21$) and Zn ($r_s=0.075$), confirming that canopy accumulation is governed by historical agrochemical spraying and atmospheric deposition rather than root-driven uptake. Conversely, Pb ($r_s=0.43$) exhibited a moderate direct soil-to-leaf pathway. The potential ecological risk ($PER$) index indicated moderate-to-considerable cumulative risk, primarily driven by Cu ($E_{Cu}=68.64$) and Cd ($E_{Cd}=59.17$). Human health risk assessments established direct ingestion as the primary exposure pathway, with current non-carcinogenic hazards remaining within tolerable limits ($HI<1$). However, the proposed residential conversion increases exposure risks for vulnerable cohorts, underscoring the necessity of systematic soil screening and remediation prior to land redevelopment. Full article

Graphene was directly synthesized on monocrystalline Si(100) at 500 °C by microwave plasma-enhanced chemical vapor deposition using an increased CH₄/H₂ gas flow ratio. Raman analysis revealed spectral features and intensity ratios consistent with the growth of hydrogenated graphene and revealed changes in defect structure, graphene layer number, and self-doping. Atomic force microscopy measurements showed that the surface morphology and local conductivity strongly depended on the growth conditions. The electrical and photoelectrical characteristics of graphene/Si junctions were correlated with the Raman parameters and surface morphology. For the hydrogenated graphene samples synthesized at 500 °C, the photocurrent, short-circuit current, and open-circuit voltage were found to be competitive with those of pristine graphene reference samples grown at 700 °C. The results demonstrate the potential of low-temperature direct PECVD synthesis for graphene/Si optoelectronic devices. Full article

A two-step growth process was developed to fabricate a 3-inch homogeneously {100}-textured free-standing diamond wafer by microwave plasma enhanced chemical vapor deposition (MPCVD). The sequential growth process is based on a change in the growth parameter α, which is given by the growth rates on {100} and {111} facets, α = $\sqrt{3}$·(V₁₀₀/V₁₁₁). Initial growth was executed with nitrogen addition, yielding an α value close to 3 for evolutionary selection of the (100) face, followed by cessation of nitrogen addition to yield a lower α value. A homogeneously grown {100}-textured diamond over an area of ca. 175 cm² with a thickness ≥ 0.8 mm was obtained after 196 h growth. The diamond growth rate was 4.0–5.5 µm/h, which is four times higher than the conventional growth of oriented diamond. This was substantiated by optical microscopy, Raman spectroscopy, and XRD analysis. The large crystal size of 210 ± 60 µm has been assigned to the second growth step, where growth is preferentially in the <111> direction. The homogeneous {100} texture and the large crystal size are conducive to achieving high thermal conductivity, as the in-plane thermal conductivity of the polycrystalline diamond wafer was increased from ca. 850 W/(mK) to 1125 W/(mK). Full article

To accelerate the transition to sustainable energy, efficient methods for CO₂-free hydrogen production and carbon utilization are needed. This study presents a new, sustainable approach for the simultaneous production of hydrogen, valuable hydrocarbons, and functional carbon materials by converting methane in low-pressure microwave plasma. Compared to traditional methane reforming methods (such as steam reforming), our plasma-based process operates at low temperatures, eliminates direct CO₂ emissions, and enables the conversion of methane into three valuable products: (1) environmentally friendly hydrogen for fuel cells and energy storage systems, (2) a range of valuable organic products (C₂H₂, C₂H₄, C₂H₆), and (3) functional carbon films with self-improving catalytic properties. Optical emission spectroscopy (OES) and the Langmuir double probe method were used for plasma diagnostics, revealing an increase in the concentration of active species (CH, Hα, C₂) and electron temperature upon argon addition. The structure, morphology, and impurity composition of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Gas-phase byproducts were analyzed using gas chromatography–mass spectrometry (GC-MS). Argon addition at an Ar/CH₄ ratio of 1 leads to the formation of carbon films with a more ordered structure, as confirmed by XRD data, and improved surface morphology. It was established that argon, by effectively participating in the excitation and dissociation processes of methane molecules through energy transfer from metastable states and increased electron temperature, optimizes plasma–chemical reactions, promoting the deposition of higher-quality carbon coatings. Full article

Per- and polyfluoroalkyl substances (PFASs) in fluorinated firefighting wastewater (FFW), which are difficult to remediate using conventional technologies, represent a critical environmental hazard due to the extreme persistence and bioaccumulation potential of soil–groundwater systems. Niobium-supported boron-doped diamond (BDD) anodes were synthesized by microwave plasma chemical vapor deposition, and their performance in the electrochemical advanced oxidation processes (EAOPs) of FFW were systematically investigated. Under optimized conditions (100 mM Na₂SO₄ electrolyte with 100 mM peroxymonosulfate (PMS), current density of 33.3 mA/cm², pH = 6), the BDD anode achieved near-complete mineralization, with 92.5% total organic carbon (TOC) removal and significant defluorination (77.5% F⁻ release) within 240 min in simulated FFW-contaminated groundwater. For FFW-contaminated soil remediation, 90.2% TOC removal and 41.6% defluorination were achieved after 720 min under optimal treatment (water-to-soil ratio of 20:1). Quenching experiments and electron paramagnetic resonance (EPR) tests revealed that hydroxyl radicals (·OH) and singlet oxygen (¹O₂) were the predominant reactive species. Liquid chromatography–mass spectrometry/mass spectrometry (LC-MS/MS) analysis indicated that PFASs were removed by shortened carbon chains, ultimately mineralizing to CO₂ and F⁻. Toxicity assessment using Vibrio fischeri luminescence demonstrated a reduction in toxicity (from 99.8% to 20.9%), confirming the effective detoxification of BDD-based EAOPs. This work establishes BDD-based EAOPs as a promising technology for eliminating PFASs in groundwater and soil, offering theoretical insights into EAOPs and engineering solutions for PFAS remediation. Full article

Linear alkylbenzene (LAB) is the main raw material used to make biodegradable detergents, and its production process is based on aromatic alkylation. HY zeolites that have undergone controlled dealumination and desilication have led industrial standards amongst solid acid catalysts because of their controllable acidity and hierarchical pore structure. Coke formation in such systems can assume a dual role, which is dependent on its condition. Though the over-deposition is known to cause deactivation by blocking the micropores, Bronsted acid-site masking, and diffusion collapse, the low-level deposition could also be done to increase the monoalkylate selectivity by the pore mouth catalysis, steric modulation, and selective suppression of secondary alkylation pathways. The critical review is done on the structural-kinetic interaction that determines the coke evolution in HY-based catalysts. In order to moderate the acid-site density and enhance hydrothermal stability, dealumination (Si/Al optimization of about 2.5 to 30–100) occurs, but to reduce deep-pore coke formation, desilication (interconnected mesopores) is created. The bimodal porosity and regulated acidity are found to be synergistic, as hierarchical HY zeolites produced through successive cycles of steam and alkaline treatments not only show LAB selectivity in excess of 90% but also exhibit much longer catalyst lifetimes. Quantitative research on the beneficial coke regime revealed that it was composed of about 36 wt% hydrogen-rich species, which were localized at the pore mouths, hence enhancing monoalkylation selectivity by 15–40%. Beyond a critical transition window (e.g., 8–12 wt.%), coke formation to condensed polyaromatic and graphitic products leads to fast deactivated coke formation, which is due to percolation limits and transport-controlled kinetics. More advanced techniques of characterization of the coke, e.g., temperature-programmed oxidation (TPO), ²⁷Al MAAS NMR, and UV-Raman spectroscopy, indicate how the coke is changed to highly structured graphitic deposits of high oxidation activation energy. Activity recovery of 85–98% is obtained in regeneration processes, including controlled oxidative calcination, microwave-based and plasma-based processes, and thermal management protocols, and it would be determined by the chemistry of the coke, its spatial distribution, and the regeneration protocols. This paper has developed a mechanistic coke control system by cross-tuning the acidity and development of an effective pore network, which led to a sustainable aromatic alkylation reaction with minimal activity loss, high selectivity, and long life. Full article

This study investigates the deposition of amorphous silicon carbon nitride (a-SiCN) films using a microwave sheath–voltage combination plasma (MVP) source under duty-cycle-controlled deposition conditions. Duty ratios of 10, 30, 50, and 70% resulted in substrate temperatures of 180, 600, 980, and 1040 °C, respectively. The deposition rate reached a maximum of approximately 208 μm/h at a duty ratio of 30%. The atomic ratios of C, N, and Si remained nearly constant for duty ratios from 30% to 70%. X-ray diffraction confirmed that all films were amorphous. Raman spectra revealed features characteristic of amorphous carbon (a-C) for duty ratios of 30% or higher, suggesting the incorporation of a-C-like structures into the a-SiCN matrix. The film hardness increased as the duty-cycle-controlled deposition conditions shifted from 10% to 50% (180 to 980 °C), reaching a maximum of 22.65 ± 6.78 GPa at a duty ratio of 50%, and then decreased at 70% (1040 °C). These variations in hardness are suggested to be associated with coupled changes in hydrogen incorporation, C–N bonding, and the evolution of sp²-rich carbon clustering (graphite-like short-range ordering) under elevated temperature and ion-bombardment conditions. Full article

Diamond is becoming an increasingly popular substrate material in the semiconductor industry due to its high thermal conductivity and wide forbidden band characteristics. With the development of high-power electronic devices, the demand for large-area single-crystal diamond films is also dramatically increasing. Microwave plasma chemical vapor deposition (MPCVD) technology is the dominant method for producing high-quality diamond films due to its advantages of high controllability, fast deposition rate, and low contamination. Despite the excellent performance of MPCVD reactors in various aspects, the question of how to increase the plasma size while improving its homogeneity remains a challenge for device design and optimization. This paper proposes a method to expand the geometrical sizes of the TM₀₁-mode MPCVD reactor while maintaining the mode’s axisymmetric homogeneity. The size-enlarged TM₀₁-mode MPCVD reactor was first designed and optimized with electromagnetic simulations. A multiphysics model that accounted for the microwave field, hydrogen gas discharge, and energy conservation was proposed to evaluate the performance of the MPCVD reactor afterwards. The results demonstrate that the size-enlarged MPCVD reactor can generate a plasma sphere with a diameter of 4 inches while still maintaining TM₀₁-mode single-mode transmission, either with or without plasma. Its outstanding robustness and adaptability underlie excellent potential for large-area diamond thin-film deposition. Full article

This study investigates the synergistic effects of co-doping with ultralow-concentration nitrogen and trace carbon dioxide on the growth of polycrystalline diamond films via microwave plasma chemical vapor deposition (MPCVD). The films were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence spectroscopy. Results indicate that trace nitrogen effectively promotes <111> oriented growth and enhances the deposition rate, whereas excessive nitrogen leads to the formation of defects such as pores and microcracks. The introduction of CO₂ suppresses the formation of nitrogen-vacancy-related defects through a selective etching mechanism. Under co-doping conditions, diamond films with high growth rates, strong <111> texture, and superior thermal conductivity (up to 1863.94 W·m⁻¹·K⁻¹) were successfully synthesized, demonstrating significant potential for thermal management applications in high-power integrated circuits. Full article

Nanocrystalline diamond (NCD) films were synthesized by microwave plasma chemical vapor deposition (MPCVD) from a CH₄/Ar mixture on seedless p-type Si(111) substrates at 100–400 °C. Crystallinity was evaluated by X-ray diffraction (Cu Kα); bonding by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS); morphology and thickness by scanning electron microscopy (SEM); defect states by thermoluminescence (TL). SEM shows continuous films with uniform thickness. XRD displays a broad (111) reflection near 2θ = 44°. Raman and XPS reveal temperature-dependent bonding: between 300 and 400 °C, the sp³ fraction increases relative to sp². TL glow curves show peaks at 157 °C and 270 °C, indicating electron-trap centers. These results demonstrate hydrogen-free and seedless NCD growth at low substrate temperatures, supporting potential electronic and dosimetry applications requiring a low thermal load. Full article

The development of advanced semiconductor-based catalysts for the rapid degradation of emerging pharmaceutical pollutants in water remains a critical challenge in environmental science. In this study, we present the synthesis, characterization, and catalytic performance of zinc oxide (ZnO) microtetrapods decorated with plasmonic Ag nanoparticles. These microtetrapods have been designed to enhance piezo-, photo-, and piezo-photocatalytic degradation of metronidazole (MNZ), a persistent antibiotic contaminant. ZnO microtetrapods were synthesized by high-temperature pyrolysis and using atmospheric-pressure microwave nitrogen plasma, followed by photochemical deposition of Ag nanoparticles at various precursor concentrations (0–1 mmol AgNO₃). The structural integrity of the samples was confirmed through X-ray diffraction (XRD) analysis, while the morphology was examined using scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). Additionally, spectroscopic analysis, including Raman, electron paramagnetic resonance (EPR), and photoluminescence (PL) spectroscopy, was conducted to verify the successful formation of heterostructures with adjustable surface loading of Ag. It has been shown that ZnO microtetrapods decorated with plasmonic Ag nanoparticles exhibit Raman-active properties. A systematic evaluation under photocatalytic, piezocatalytic, and combined piezo-photocatalytic conditions revealed a pronounced volcano-type dependence of catalytic activity on Ag content, with the 0.75 mmol composition exhibiting optimal performance. In the presence of both light irradiation and ultrasonication, the optimized Ag/ZnO composite exhibited 93% degradation of MNZ within a span of 5 min, accompanied by an apparent rate constant of 0.56 min⁻¹. This value stands as a significant improvement, surpassing the degradation rate of pristine ZnO by over 24-fold. The collective identification of defect modulation, plasmon-induced charge separation, and piezoelectric polarization as the predominant mechanisms driving enhanced reactive oxygen species (ROS) generation is a significant advancement in the field. These findings underscore the synergistic interplay between plasmonic and piezoelectric effects in oxide-based heterostructures and present a promising strategy for the efficient removal of recalcitrant water pollutants using multi-field activated catalysis. Full article

This study deals with diamond films grown via the microwave plasma-enhanced chemical vapor deposition technique (MWPECVD) on molybdenum (Mo) substrates of different roughness. This work is motivated by the necessity of overcoming the poor adhesion of diamond films on smooth Mo substrates, to ensure their effective application as cathodes for aerospace propulsion. The deposition process was monitored in situ using pyrometric interferometry (PI), thus enabling the real-time monitoring of both the rate and the temperature of deposition. The characterization of the obtained diamond films was performed using different techniques, such as Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The poor adhesion of diamond films on Mo substrates was solved by roughening their surface, which promotes residual stress reduction in the diamond films. In this work, the PI technique was also exploited to support the prediction of the adhesion and stability of diamond films before their exposure in air through the monitoring of the deposition temperature. This represents a novel point of our work that has never been discussed in other research papers, as pyrometric interferometry is generally mainly used to assess the rate and the temperature of deposition. Full article

This study presents a highly effective method for depositing diamond-like carbon (DLC) films onto pipe substrates using a scanning deposition by plasma enhanced chemical vapor deposition. A microwave–sheath voltage combination plasma was employed to generate local high-density plasma along a rotating pipe. While conventional contact-mode deposition using a metal contactor suffers from arcing and surface damage due to unstable sliding contact during rotation, a non-contact deposition using a metal antenna was developed to overcome these limitations. Electromagnetic field simulations were conducted to evaluate microwave power absorption in various antenna geometries, showing that the flat-plate antenna demonstrated the most effective power coupling. Subsequent scanning deposition experiments to a rotating pipe using flat-plate antennas of different lengths revealed that the 100 mm configuration achieved the highest deposition volume rate (exceeding that of the contact-mode) while avoiding arcing. Optical emission observations during deposition confirmed the formation of high-density plasma surrounding the flat-plate antenna and Raman spectroscopy of the deposited film showed typical spectra of DLC films. The deposition rates of DLC-coated pipe showed no significant variation with respect to rotational angle, suggesting that rotation during deposition contributes to achieving uniform film thickness along the circumferential direction of the pipe. Full article

Diamond, as an exceptional material with many superior properties, requires a single crystal in a reasonably large size for practical industrial applications. However, achieving large-area single-crystal diamond (SCD) growth without the formation of polycrystalline rims remains challenging. Microwave plasma chemical vapor deposition (MPCVD) using a gas mixture of 10% CH₄-H₂ was used for the homoepitaxial growth of (001) SCD. The effect of nitrogen gas addition in the range of 0–2000 ppm on lateral growth was investigated. Deposition with 180 ppm N₂ over a growth duration of 20 h to reach a thickness of 0.95 mm resulted in significantly enhanced lateral growth without the appearance of a polycrystalline diamond (PCD) rim for the grown diamond, and the total top surface area of SCD increased by an area gain of 1.6 relative to the substrate. The corresponding vertical and lateral growth rates were 47.3 µm/h and 52.5 µm/h, respectively. Characterization by Raman spectroscopy and atomic force microscopy (AFM) revealed uniform structural integrity across the whole surface from the laterally grown regions to the center, including the entire expanded area, in terms of surface morphology and crystalline quality. Moreover, measurements of the etch pit densities (EPDs) showed a substantial reduction in the laterally grown regions, approximately an order of magnitude lower than those in the central region. The high quality of the homoepitaxial diamond layer was further verified with (004) X-ray rocking curve analysis, showing a narrow full width at half maximum (FWHM) of 11 arcsec. Full article

The development of high-speed computers and electronic memories, high-frequency communication networks, electroluminescent and photovoltaic devices, flexible displays, and more requires new materials with unique properties, such as a low dielectric constant, an adjustable refractive index, high hardness, thermal resistance, and processability. SiOC coatings possess a number of desirable properties required by modern technologies, including good heat and UV resistance, transparency, high electrical insulation, flexibility, and solubility in commonly used organic solvents. Chemical vapor deposition (CVD) is a very useful and convenient method to produce this type of layer. In this article we present the results of studies on SiOC coatings obtained from tetramethylcyclotetrasiloxane in a remote hydrogen plasma CVD process. The elemental composition (XPS, EDS) and chemical structure (FTIR and NMR spectroscopy-¹³C, ²⁹Si) of the obtained coatings were investigated. Photoluminescence analyses and ellipsometric and thermogravimetric measurements were also performed. The surface morphology was characterized using AFM and SEM. The obtained results allowed us to propose a mechanism for the initiation and growth of the SiOC layer. Full article