Search Results (3,063)

During the preparation of silicon carbide (SiC) thin films by chemical vapor deposition (CVD), the Soret effect induced by a large temperature gradient influences the deposition rate and uniformity; its sensitivity to process parameters remains unclear. A computational fluid dynamics model coupling detailed gas-phase and surface reaction kinetics was developed and validated for a cold/warm wall vertical CVD reactor. Comparing simulations with and without the thermal diffusion term reveals the dual role—suppressing deposition rate while degrading film uniformity. The thermal diffusion contributions to deposition rate (TDC_GR) and uniformity (TDC_GU) are introduced as quantitative metrics, and simulations evaluated the effects of inlet–substrate temperature difference (ΔT), reactor pressure (p), substrate rotation speed (ω), and carrier gas flow rate (Q) on the Soret effect, clarifying optimal conditions. Results show ΔT dominates. At ΔT = 1700 K, TDC_GR = −56.39% and TDC_GU = 5.29%. Pressure affected TDC_GR negligibly but significantly reduced TDC_GU by enhancing gas-phase mixing; increasing p from 7500 to 12,500 Pa led to a decrease in TDC_GU from 4.19% to 1.93%. Optimal parameters (ΔT = 1400 K, p = 12,500 Pa, ω = 800 rpm, Q = 50 slm) achieved a deposition rate of 10.71 μm/h and non-uniformity of 0.45%. These findings provide theoretical guidance for precise SiC-CVD process control in cold- or hot-wall vertical reactor architectures. Full article

The morphology of CVD-grown molybdenum disulfide (MoS₂) is sensitive to the local precursor environment, which governs nucleation density, edge stability, and growth kinetics. In this work, we systematically investigate the effect of precursor ratio on the morphological evolution of MoS₂ microstructures synthesized by atmospheric-pressure chemical vapor deposition on SiO₂/Si substrates. By varying the relative amounts of MoO₃ and sulfur precursors, distinct growth regimes were obtained, ranging from compact hexagonal and quasi-circular domains to multilayer hexagonal structures, triangular domains, and dendritic morphologies. At higher MoO₃ loading, growth is dominated by dense nucleation, leading to isolated few-layer hexagonal domains. A moderate reduction in Mo precursor concentration promotes diffusion-assisted growth and secondary nucleation, resulting in multilayer hexagonal structures with aligned or slightly rotated stacked layers. Under sulfur-rich conditions, morphology evolves into triangular domains due to anisotropic edge stabilization, while further increase in sulfur concentration gives rise to branched dendritic structures through kinetically limited, diffusion-dominated growth. Cross-sectional FIB analysis reveals dense vertical stacking and lateral displacement of upper layers in the multilayer hexagonal domains. Raman and photoluminescence measurements confirm strong correlations between morphology, layer thickness, and optical response, with thinner regions exhibiting reduced Raman peak separation, enhanced photoluminescence intensity, and blue-shifted excitonic transitions. The results show that, under fixed APCVD reactor geometry, source positions, temperature profile, carrier-gas flow, and nominal growth duration, the nominal MoO₃ to sulfur source-loading ratio reproducibly correlates with the transition between compact hexagonal, multilayer hexagonal, triangular, and dendritic MoS₂ morphologies on amorphous SiO₂/Si substrates. Because vapor-phase Mo- and S-containing partial pressures were not directly measured, this ratio is treated as a nominal source-inventory descriptor rather than as a direct vapor-phase stoichiometric ratio. The observed trends are interpreted using a qualitative thermodynamic and kinetic framework based on precursor fluence, nucleation density, edge stability, and diffusion-limited growth. Full article

Elemental mercury has been used in the production of bleach since at least 1892 and continues to be utilized in some manufacturing processes today. This case study examines a former bleach manufacturing facility in the western United States, where elemental mercury was utilized as an electrical conductor in the chlor-alkali process to produce chlorine and sodium hydroxide, essential constituents in bleach formulation. The operational practices implemented at the facility led to the discharge of elemental mercury into both soil and groundwater. Subsequent investigations identified the presence of mercury in indoor air at levels surpassing the screening thresholds established by the California Environmental Protection Agency (CalEPA) Department of Toxic Substances Control (DTSC) and the United States Environmental Protection Agency (USEPA) for commercial exposure scenarios. Additionally, these concentrations exceeded the California Office of Environmental Health Hazard Assessment (OEHHA) acute 1 h reference exposure level (REL). The origins of mercury in indoor air have been identified as vapor intrusion associated with subsurface sources, along with a potential secondary indoor air source associated with mercury deposition and adsorption in building materials through the years. In the context of interim vapor intrusion mitigation, air purifiers and fans were deployed to enhance air exchange rates, while a comprehensive assessment led to the identification and sealing of 52 preferential pathways. Even with these interim vapor intrusion mitigation systems in place, elevated concentrations of elemental mercury are still present in the building and may represent the presence of a secondary indoor air source from accumulation of elemental mercury in building materials. Full article

Graphene grown by chemical vapor deposition (CVD) on polycrystalline Cu/Si and transferred onto SiO₂/Si substrates was subjected to low-energy nitrogen ion implantation (350 eV) at fluences ranging from 10¹² to 10¹⁶ cm⁻² and subsequently investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Extensive Raman mapping performed prior to implantation indicates that the transferred samples consist predominantly of single-layer graphene (SLG), along with small domains of folded graphene (FG) that resemble bilayer graphene (BLG) with effectively random twist angles. At relatively low fluences, nitrogen ion implantation does not induce significant structural modifications in SLG, but leads to only a slight increase in doping compared to unimplanted samples. In contrast, at high ion fluences, SLG undergoes amorphization accompanied by severe damage of the substrate, as evidenced by the presence of an intense photoluminescence signal attributed to implantation-induced defects in the SiO₂ layer. Data analysis indicates that, for fluences 10¹³ and 10¹⁴, the implantation-induced defects in SLG are predominantly vacancy-like, with a smaller contribution from sp³-type defects, whereas FG domains appear less sensitive to defect accumulation. Full article

Functional coatings have evolved from their early role as passive barriers against corrosion and wear into engineered interfaces that actively mediate the interaction between a bulk material and its environment. This review traces the evolution of coating technologies from traditional macroscopic protective layers to nanoscale and multifunctional systems, and finally to smart and stimuli-responsive architectures. Advanced deposition and surface modification techniques are examined, including atomic layer deposition, physical vapor deposition, electrochemical and sol–gel approaches. The discussion is structured around two complementary application domains: extreme energy environments, focusing on coatings developed for advanced nuclear systems, and modern medical implants, including bioactive and antimicrobial surfaces and drug-delivery interfaces. The review highlights that, despite the differences between reactor and biomedical environments, both sectors share a common set of design principles and challenges, including interfacial adhesion, mechanical durability, the dual role of nanostructuring, and the trade-off between architectural complexity and operational reliability. Long-term stability, scalability, and standardized validation remain key barriers to deployment, while data-driven design and the deliberate integration of multiple functions emerge as the principal directions for future development. Full article

Graphene and its derivatives have attracted sustained research interest as adsorbent materials for environmental applications, driven by their large surface area, chemically tunable surface, and compatibility with a wide range of functional modifications. This review covers recent developments in the use of graphene-based materials for water, air, and soil remediation, focusing primarily on work published over the last five years. A concise overview of graphene, its derivatives, and other carbon nanostructures, such as carbon nanotubes and fullerenes, is also provided. The main graphene derivatives are briefly described (graphene oxide, reduced graphene oxide, graphene nanoribbons, and graphene quantum dots) together with a comparative overview of the principal synthesis methods, from mechanical exfoliation and chemical vapor deposition to liquid-phase exfoliation, oxidation/reduction, and flash Joule heating. The discussion then turns to how surface functionalization and composite formation affect adsorption performance in practice. In water treatment, the results are most developed: functionalized composites have reached adsorption capacities of 484.3 mg g⁻¹ for organic dyes and 157.23 mg g⁻¹ for Cr(VI). Air purification is a smaller but growing area, with plasma-treated graphene aerogels achieving CO₂ capture capacities of 3.3 mmol g⁻¹ and retaining performance over 40 cycles. Soil remediation remains the least explored compartment, though arsenic immobilization efficiencies of up to 99.3% have been reported. Remaining challenges around scalability, behavior in real environmental matrices, and long-term ecotoxicological impact are identified and discussed. Full article

To investigate the influence of particle size on the erosion damage behavior and failure mechanisms of thermal barrier coatings (TBCs) in a simulated aero-engine erosion environment, erosion tests were conducted using Al₂O₃ particles of different sizes (65 μm, 120 μm, and 175 μm) under a nominal gas-flow condition of Mach 0.4 at 1150 °C with custom-built multi-factor coupled erosion test equipment. TBCs were prepared using electron beam physical vapor deposition (EB-PVD). By combining macroscopic/microscopic morphology, composition, white-light interferometry, and Raman residual stress testing, the damage evolution and failure behavior of TBCs under different particle size conditions were analyzed. The results indicate that particle size has a significant effect on the erosion behavior of thermal barrier coatings. Under erosion conditions involving 65, 120, and 175 μm particles, the erosion rates were 10.83, 4.19, and 2.05 g/kg, with corresponding coating lifetimes of approximately 3, 12, and 22 h. As particle size increases, the erosion rate decreases and the coating lifetime increases. Under small 65 μm particles, the coating exhibits high-frequency continuous micro-cutting. The ceramic layer rapidly thins, leading to localized penetration. Under erosion by 120 μm particles, the coating exhibits a composite damage mechanism involving cutting, compaction, and brittle fracture. Under large-particle impacts of 175 μm, the damage mechanism is dominated by localized brittle fracture and spalling induced by high-energy impacts. Although the single-impact energy of large-particle impacts is higher, the lower particle number density results in a discrete distribution of damage zones, leading to a lower material removal rate. The Raman test results further indicate that, after 2 h of erosion, the differences in residual stress in the TGO layer were relatively small across different particle size conditions, suggesting that the early degradation process of the coating is primarily controlled by the mechanical removal of the ceramic surface layer rather than by the evolution of TGO stress. No statistically significant difference in TGO residual stress was observed among different particle sizes after 2 h of erosion (p > 0.05). Not only is the erosion life of EB-PVD YSZ TBCs is influenced by the impact energy of individual particles, but more importantly, it is also closely related to particle number density, impact frequency, and the spatial distribution of damage. Full article

Hydrogen is a clean energy carrier essential for carbon neutrality, but its invisible and odorless nature poses significant safety risks, particularly during low-concentration leaks. Although metal oxide semiconductor (MOS) sensors offer fast response and high sensitivity, their ability to detect ppb-level hydrogen remains limited. In this work, we present a high-performance hydrogen gas sensor based on nickel-doped tin dioxide (Ni-SnO₂) nanorods, directly grown on planar electrodes via aerosol-assisted chemical vapor deposition (AACVD). By optimizing the Ni doping ratio and nanorod morphology, the 3 wt% Ni-SnO₂ sensor achieves a low detection limit of 100 ppb for H₂, demonstrating promising potential for low-concentration hydrogen detection. Moreover, the sensor exhibits outstanding selectivity, with a response to 100 ppm H₂ nearly six times higher than that to the next most responsive interfering gas (NH₃). Comprehensive XPS and Raman analyses reveal that Ni doping introduces abundant oxygen vacancies and lattice defects, which are the key origins of the enhanced sensing performance. Notably, the 3 wt% Ni-SnO₂ sensor strikes an optimal balance between lattice defects and structural stability, delivering both high sensitivity and good moisture resistance with minimal baseline drift over weeks of operation. This work establishes a facile and scalable AACVD strategy for engineering defect-rich SnO₂ nanostructures, enabling sub-ppm hydrogen detection with high selectivity and long-term stability—addressing a critical gap in practical hydrogen safety monitoring. Full article

This study explores the direct growth of boron-doped diamond films on biocompatible silicon nitride (Si₃N₄) ceramic substrates using hot-filament chemical vapor deposition (HFCVD), with a view toward their use in implantable electrochemical biosensors. The focus of this work is the establishment of process–structure–property relationships relevant to biosensor performance, including microstructure, surface chemistry, wettability, and electrical behaviour. The effects of key deposition parameters, namely methane concentration, deposition pressure, and sample holder configuration, were analysed in relation to film microstructure, crystallographic orientation, surface chemistry, wettability, and electrical performance. Under low CH₄/H₂ ratios, microcrystalline diamond films with a pronounced (111) preferential orientation were obtained, enabling improved boron incorporation and electrical resistivity values within the range required for biosensor operation (≈1–10 kΩ). Surface analyses revealed partially hydrogen-terminated diamond layers enriched with oxygen-containing functional groups (C–O and C–O–C), which enhance surface wettability and are suitable for enzyme immobilization. Among the studied conditions, films deposited at 150 mbar and low methane flow displayed the most balanced combination of electrical conductivity, surface wettability, and microstructural stability. Overall, the results highlight the potential of boron-doped CVD diamond grown directly on Si₃N₄ as a robust and biocompatible material platform for future implantable biosensors, particularly for glucose monitoring applications. Full article

This study presents a comprehensive evaluation of sorbent injection to mitigate sodium emissions in a 250 MW_e cyclone-fired boiler using lignite coal. Using historical boiler operational data, a computational fluid dynamics (CFD) model was validated and simulations were subsequently conducted to identify optimum sorbent injection locations for maximizing dispersion within the boiler cross-section and limiting sorbent temperatures to avoid deactivation. Data from the literature were used to guide sorbent injection rates and target sorbent particle sizes. Subsequent field demonstrations with the injection of a commercially available sorbent achieved a 60–80% reduction in the gas phase sodium, which was visually corroborated by reduced deposition on heat exchanger probes placed inside the boiler as well as by data on ash composition as a function of size. Furthermore, a diffusion-kinetic model, incorporating alkali vapor (NaOH) capture and subsequent sorbent deactivation, was developed and integrated into the CFD simulations as a post-processing tool and tested against the field demonstration data. Additional bench-scale testing was conducted with a range of sorbents as part of tool development for selecting from locally available sorbent sources. These bench-scale tests indicated a definite shift in the aerosol particle size distribution (PSD) toward a coarser range and depletion in the ultra-fine sizes, confirming the capture of vapor phase sodium species by the sorbents. Notably, in these tests, the sorbents remained effective even when they became molten, suggesting the potential for more convenient and cost-effective injection strategies. Full article

The interaction of biomaterial surface with cells is a pivotal factor in tissue engineering and three-dimensional (3D) modeling. This paper presents an approach to modifying polystyrene surface by plasma-enhanced chemical vapor deposition of thin plasma-polymerized hexamethyldisiloxane (pp-HMDSO) films to enhance biocompatibility and stimulate the formation of 3D cellular structures. The coatings were characterized by SEM, EDS, XPS, FTIR, AFM, contact angle measurements, and surface free energy (SFE) analysis. A hydrophobic surface initiates 3D structure formation by ensuring uniform cell repulsion and stimulating intercellular interactions. Biological evaluation was performed on U-87 MG (glioblastoma) and HMC3 (microglia) cell lines. For U-87 MG, the pp-HMDSO layer proved critical: cell death and atypical adhesion occurred on untreated plastic, whereas stable spheroids formed on the modified surface. HMC3 cells formed small spheroids even on unmodified surfaces, but on pp-HMDSO coatings, the process was more intense and the structures more uniform due to surface hydrophobicity. These results demonstrate the potential of plasma-polymerized HMDSO films as a scalable platform for creating biomaterials with controlled properties for 3D culturing. Full article

Transition metal oxides constitute an important materials platform for chromic phenomena because their optical response is strongly coupled to the changes in electronic structure, phase state, carrier concentration, and defect chemistry. This review discusses selected transition metal oxide thin films, with emphasis on VO₂ and other vanadium oxides, WO₃, NiO, and TiO₂. The review summarizes the structural and electronic characteristics of these representative oxide systems and highlights the role of phase composition, crystal structure, oxygen non-stoichiometry, and defect chemistry in determining their optical response. The main thin film preparation routes, including pulsed laser deposition, magnetron sputtering, sol–gel and aerosol spray methods, atomic layer deposition, chemical vapor deposition, electrochemical routes, and molecular beam epitaxy, are reviewed with respect their influence on obtained thin films. Particular attention is given to applications in thermochromic VO₂-and electrochromic WO₃/NiO-based smart windows, and transition metal oxide-based gasochromic hydrogen sensors. Key challenges related to transition temperature tuning, luminous transmittance, solar modulation, optical contrast, cycling stability, ion transport and large-area integration are also discussed. Overall this review provides a comparative overview of selected transition metal oxide thin films by connecting material chemistry and physics, thin film preparation technology and functionality. Full article

In our day-to-day lives, we are regularly exposed to a wide spectrum of dangerous gases. Their origins vary, ranging from industrial activities to objects found within our very homes. Naturally, there is an interest in developing cost-efficient and durable devices that can successfully track these gases within our environment. One such candidate is represented by chemoresistive gas sensors based on metal oxides. This is due to their simple architecture and the possibility of scaling down their size, making them valid contenders for future advancements in portable gas sensors. This review focuses on chemoresistive gas sensors that have been obtained through different Physical Vapor Deposition (PVD) methods, which are easily scalable for potential technological transfer towards commercialization or are already exploited at the industrial level, and how varying different deposition parameters impacts the structure of the active material, thus modifying the gas sensing properties of the device. In this review, we report results obtained for different metal oxides: WO₃, ZnO, CeO₂, TiO₂, NiO, and SnO₂. The main findings of these studies revealed that the sensor’s response was highly impacted by oxygen deficiencies within the deposited material, the specific surface area, and the thickness of the film. Moreover, this study also delves into different strategies of functionalization that result in improved gas sensing properties. Thus, we herein report how tailoring functional properties modifies the gas sensing performance of different metal oxides. Full article

Laser directed energy deposition (LDED) is a promising metal additive manufacturing process, but printed parts’ quality highly depends on spatter formation and melt pool stability. In this work, a high-speed camera is employed to capture and record the complex interaction between the laser, fed powders, and fusion region under various LDED process conditions. A deep learning algorithm, the YOLOv7 model, is trained to automatically detect and track the location and motion of the melt pool and spatter particles. The well-trained YOLOv7 model achieves a precision of 0.94 and is then applied to extract information on spatter count, spatter size, and melt pool geometry. We find that an elevated laser power intensifies spatter formation due to augmented vapor recoil pressure, while a high scanning speed promotes spatter ejection through Plateau–Rayleigh capillary instability. A low powder feed rate further exacerbates spatter formation owing to high metal evaporation and hydrodynamic instability within the small melt pool. In addition, this work introduces a novel melt pool stability index for real-time process assessment based on the melt pool length change rate. A stable melt pool with a high stability index generates less spatter. Otherwise, more spatters are detected. These findings advance the mechanistic understanding of spatter dynamics in LDED, introduce a novel quantitative metric for real-time melt pool stability assessment, and establish a direct correlation between the detected spatter amount and the melt pool stability. This work provides a practical framework for spatter mitigation, melt pool stability enhancement, and in-process control in advanced manufacturing. Full article

Carbon nanotube (CNT) films prepared via floating catalyst chemical vapor deposition generally suffer from residual iron impurities, structural defects, and weak inter-tube interfaces, which severely limit their mechanical performance. Here, we propose a post-treatment approach, which is dominated by Joule heating, to substantially improve the mechanical properties of CNT films. Acid washing after Joule heating effectively removes iron catalyst and amorphous carbon, increasing the specific strength from 0.64 N/tex to 2.96 N/tex. Pre-stretching induces alignment of the CNTs along the stretching direction, further raising the specific strength to 5.57 N/tex. Subsequent Joule heating not only raises graphitization degree and repairs lattice defects but also transforms the weak van der Waals contacts between tubes into continuous carbon networks, leading to network densification and locking of the aligned structure. The final specific strength reaches 7.04 N/tex and true tensile strength 8.05 GPa, surpassing previous representative carbon materials. The purification mechanism of Joule heating depends on the initial iron content of the film: for high-iron films, iron melts, migrates and forms Fe/Fe₃C@C core–shell particles, which can be converted into hollow carbon shells via acid etching; for low-iron films, iron is removed via atomic diffusion and evaporation. This work provides a fast, controllable and synergistic technical route for the preparation of high-performance CNT macrostructures. Full article