Chemical Vapor Reaction Research Articles

Constructing inkjet printed dielectric elastomers with modified silicon carbide nanowire surfaces to enhance electromechanical performance

AbstractDielectric elastomers (DEs), have attracted interest because they can replicate the behavior of muscles. They can change shape when subjected to an electric field. A novel DE is proposed in this study that incorporates silicon carbide (SiC) nanowires into silicone rubber (SR). The nanowires were propagated using polycarbosilane via a chemical vapor reaction (CVR). A boronate polymer was employed to promote compatibility between SR and SiC nanowires which modified the nanowire surfaces, leveraging a strong adhesive quality of the catechol moiety. Electrohydrodynamic (EHD) inkjet printing was then used to form the DEs into various shapes. These DEs had substantial dielectric constants of the order of 4.46. Significantly, one of the DEs achieved the highest actuated area strain of 20.36% in an electric field of 16.5 V/μm, demonstrating excellent driving performance. Furthermore, when used the fabricated DEs showed pronounced long‐term stability, meaning they are capable of finding applications in artificial intelligence, biomimetics, aerospace, and other disciplines.Highlights The SiC nanowires were obtained through a chemical vapor reaction. A boronate polymer with catechol moiety was used to modify the SiC nanowires. DEs were formed various shapes by inkjet printing. DEs achieved very large actuated strains of up to 20.36% at 16.5 V/μm.

Rational Design of Phase-Engineered WS2/WSe2 Heterostructures by Low-Temperature Plasma-Assisted Sulfurization and Selenization toward Enhanced HER Performance.

Efficient hydrogen generation from water splitting underpins chemistry to realize hydrogen economy. The electrocatalytic activity can be effectively modified by two-dimensional (2D) heterostructures, which offer great flexibility. Furthermore, they are useful in enhancing the exposure of the active sites for the hydrogen evolution reaction. Although the 1T-metallic phase of the transition metal dichalcogenides (TMDs) is important for the hydrogen evolution reaction (HER) catalyst, its practical application has not yet been much utilized because of the lack of stability of the 1T phase. Here, we introduce a novel approach to create a 1T-WS2/1T-WSe2 heterostructure using a low-temperature plasma-assisted chemical vapor reaction (PACVR), namely plasma-assisted sulfurization and plasma-assisted selenization processes. This heterostructure exhibits superior electrocatalytic performance due to the presence of the metallic 1T phase and the beneficial synergistic effect at the interface, which is attributed to the transfer of electrons from the underlying WS2 layer to the overlying WSe2 layer. The WS2/WSe2 heterostructure catalyst demonstrates remarkable performance in the HER as evidenced by its small Tafel slope of 57 mV dec-1 and exceptional durability. The usage of plasma helps in replacing the top S atoms with Se atoms, and this ion bombardment also increases the roughness of the thin film, thus adding another factor to enhance the HER performance. This plasma-synthesized low-temperature metallic-phase heterostructure brings out a novel method for the discovery of other catalysts.

Review on preparation technology of carbide resistant ultra-high temperature ceramic fiber

The rapid development of hyper-sonic vehicles has put forward an urgent demand for ultra-high temperature resistance ceramic fibers ceramic matrix composites. The properties of ultrahigh-temperature ceramic matrix composites made of carbon-based ultra-high temperature resistance ceramic fibers are excellent. Therefore, the preparation processes of several commonly used carbide-resistant ultrahigh-temperature ceramic fibers are described in detail. This review compares the advantages and disadvantages of five common methods (Molten-salt synthesis method, Chemical Vapor Reaction Method, Chemical Vapor Deposited method, Sol-Gel Method & Polymer-Derived method) for preparing ceramic fibers, summarizes the preparation methods that should be used in the face of different preparation requirements, and evaluates the improvement and prospect of each method. Among them, the polymer-derived method, as the most difficult and effective preparation method, has been given great hope by material scientists.

Design of Wireless Multiple Gases Complementary Architecture Sensors Based on SnSe2 and PtSe2 Layered Films and Oscillating Circuits

AbstractOwing to the increasing demand for monitoring harmful toxic gases using small‐sized low‐power‐consumption gas sensors, a room‐temperature wireless complimentary gas sensor incorporating layered materials is proposed and demonstrated. The compact design allows the sensing module to be installed under all conditions and facilitates multiple detections of toxic gas. Highly chemical‐resistance‐sensitive materials based on n‐type SnSe2 and p‐type PtSe2 layered materials prepared by the plasma‐assisted chemical vapor reaction (PACVR) method at low temperatures are integrated with an oscillation circuit and antenna fabricated by a 28‐nm CMOS high‐k metal gate logic process to achieve dense, low‐powered, and wireless characteristics. By pairing n‐ and p‐type layered semiconductors, the gas sensors feature less influence from the surroundings, such as temperature and humidity, and enhance sensitivity to the target gas simultaneously. The wireless sensing detection method enables a sensor to make signal reception more convenient. Furthermore, a wireless gas sensor with self‐converging calibration using the advantage of a floating‐gate (FG) transistor to control the charge quantity by shifting the threshold voltage (Vth) of each transistor via the channel hot electron injection effect, which helps to reduce the impact of process variations, minimizing readout errors, is proposed.

Encapsulation of Titanium Disulfide into MOF-Derived N,S-Doped Carbon Nanotablets Toward Suppressed Shuttle Effect and Enhanced Sodium Storage Performance.

Titanium disulfide (TiS2) is a promising anode material for sodium-ion batteries due to its high theoretical capacity, but it suffers from severe volume variation and shuttle effect of the intermediate polysulfides. To overcome the drawbacks, herein the successful fabrication of TiS2@N,S-codoped C (denoted as TiS2@NSC) through a chemical vapor reaction between Ti-based metal-organic framework (NH2-MIL-125) and carbon disulfide (CS2) is demonstrated. The C─N bonds enhance the electronic/ionic conductivity of the TiS2@NSC electrode, while the C─S bonds provide extra sodium storage capacity, and both polar bonds synergistically suppress the shuttle effect of polysulfides. Consequently, the TiS2@NSC electrode demonstrates outstanding cycling stability and rate performance, delivering reversible capacities of 418/392mAhg-1 after 1000 cycles at 2/5Ag-1. Ex situ X-ray photoelectron spectroscopy and transmission electron microscope analyses reveal that TiS2 undergoes an intercalation-conversion ion storage mechanism with the generation of metallic Ti in a deeper sodiation state, and the pristine hexagonal TiS2 is electrochemically transformed into cubic rock-salt TiS2 as a reversible phase with enhanced reaction kinetics upon sodiation/desodiation cycling. The strategy to encapsulate TiS2 in N,S-codoped porous carbon matrices efficiently realizes superior conductivity and physical/chemical confinement of the soluble polysulfides, which can be generally applied for the rational design of advanced electrodes.

Improving the oxidation resistance of carbon fibers via B4C coating by modified boron oxide chemical vapor deposition

Carbon fiber is one of the engineering materials frequently used in high-temperature applications despite its very poor oxidation resistance. To enhance the oxidation resistance of C fibers and improve the service temperature, boron carbide coatings were prepared by the modified reactive boron oxide chemical vapor deposition (BOCVD) method. For the coating process, a tube furnace system was utilized. Experiments were performed at 1100–1400 °C for up to 6 h under a flowing Ar atmosphere. Coatings were analyzed by SEM, Raman, XRD, and XPS analysis. B4C coatings were found to be in nodular form around 30–50 nm. Oxidation tests performed in flowing air up to 1500 °C by DTA-TG analysis and oxidation mechanisms were explained in details. We revealed that the base oxidation resistance increased up to 180 °C with no net mass gain or loss.

Thermal shock behavior and oxidation resistance of novel SiC nanowires+Si/Yb2Si2O7-Si/Yb2Si2O7 environmental barrier coatings

The objective of this work is to design environmental barrier coatings with new structure to improve the thermal shock and oxidation resistance. A novel tri-layer SiC nanowires+Si/Yb2Si2O7-Si/Yb2Si2O7 coating was designed and fabricated on the surface of C/SiC composites by chemical vapor reaction route and combination of the method of atmospheric plasma spraying. All coated samples were subjected to thermal shock test at 1300 ℃. Results indicated that the interfacial bond among the layers in the coating system and C/SiC composites was still intact without delamination crack. The Si in the Yb2Si2O7-Si layer consumed the oxygen diffused into coating and then reacted with Yb2SiO5 to form Yb2Si2O7, which could decrease the release of tensile stress caused by thermal mismatch. The study also investigates the Yb2Si2O7 formation in the Yb2SiO5-Si system, and finds that the Yb2Si2O7 formation was controlled by the diffusion of Yb3+ and Si4+ ions through the Yb2Si2O7 layer.

Chemical vapor reaction synthesis and photoelectronic properties of CuS and Cu3SbS4 thin films

Chemical vapor reaction is a simple and efficient experimental means of preparing metal sulphide films. Through systematically studying the effect of vulcanisation temperature on the growth of copper sulfide (CuS) thin film. The copper antimony sulfide (Cu3SbS4) thin film was obtained by further vulcanized Sb/Cu mental film. The structure and optical properties of the as-prepared films were characterized by x-ray diffraction, Raman and photoluminescence spectra. The hexagonal structure of CuS film was confirmed and Cu3SbS4 grew preferentially along the (112) crystal plane. The surface grains of CuS and Cu3SbS4 films were finally condensed into spheres. The content of S and the resistance of the films increase with the increase in temperature, but the bandgap of the films will be decreased. The bandgap of Cu2−xS films prepared at 195 °C−350 °C is in the range of 2.2–2.5 eV and that of Cu3SbS4 thin films prepared at 350 °C is 1.77 eV, and has good absorption in the visible light range. In addition, The Hall effect measurement indicated CuS and Cu3SbS4 films have p-type semiconducting behavior. The carrier concentration and mobility are 2.45 × 1021 cm−3 and 1.28 cm2 Vs−1 for CuS, and 4.30 × 1017 cm−3 and 185.93 cm2 Vs−1 for Cu3SbS4, respectively. The I-T tests show that the CuS and Cu3SbS4 thin films have photoconductive properties.

Oxidation resistance improvement of carbon fiber nonwoven fabrics through SiC coating technology

The oxidation resistance of carbon fiber (CF) was enhanced by SiC coating layer. A hybrid sol–gel approach and chemical vapor reaction (CVR) were utilized to produce coating layer. SiO2 was applied to the CF surface, after which SiOx and SiH4 vapor were added via CVR method to intensify SiC formation and bonding. Interfacial bonding was further reinforced by the addition of graphene oxide (GO) prior to heat treatment. Three different samples were generated, and the gas liberated upon conversion to SiC was evaluated to determine relationships with microstructure. The amount of gas released differed depending on the chemical used in the sol–gel, and the mechanism of SiC formation under different conditions was also distinct. The results of a flame test indicated approximately 20% improvement in oxidation resistance compared to CF. The proposed SiC coating can circumvent the restricted process method that necessitates specialized equipment to manufacture high-quality CF with improved oxidation resistance.

Morphological and microstructural evolutions of chemical vapor reaction-fabricated SiC under argon ion irradiation

Chemical vapor reaction (CVR) fabricated-SiC samples were irradiated with 300 keV Ar2+ ions in the fluence range of 5 × 1015 –1 × 1017 ions·cm−2. Raman spectrum and grazing incidence X-ray diffraction analysis display amorphization and lattice expansion of the irradiated CVR-SiC. Transmission electron microscope observations show that small black spots with an average diameter of 1.5 nm are formed at a low fluence of 5 × 1015 ions·cm−2. Moreover, large argon bubbles with an average diameter of 15.1 nm are formed at a high fluence of 1 × 1017 ions·cm−2, and the Ar concentration threshold for bubble formation is 8.83 at.%. The influence of implantation amorphization and Ar atom migration in CVR-SiC on the formation of Ar bubbles is discussed. The results provide a basis for understanding the noble-gas-induced irradiation behavior of CVR-SiC for preventing irradiation damages in future nuclear applications.

Two-Dimensional (2D) Materials-Inserted Conductive Bridge Random Access Memory: Controllable Injection of Cations in Vertical Stacking Alignment of MoSe2 Layers Prepared by Plasma-Assisted Chemical Vapor Reaction

Two-Dimensional (2D) Materials-Inserted Conductive Bridge Random Access Memory: Controllable Injection of Cations in Vertical Stacking Alignment of MoSe₂ Layers Prepared by Plasma-Assisted Chemical Vapor Reaction

Bifunctional SiC/Si 3N 4 aerogel for highly efficient electromagnetic wave absorption and thermal insulation

SiC ceramics are attractive electromagnetic (EM) absorption materials for the application in harsh environment because of their low density, good dielectric tunable performance, and chemical stability. However, the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching. Herein, we report ultralight SiC/Si₃N₄ composite aerogels (~15 mg·cm⁻³) consisting of numerous interweaving SiC nanowires and Si₃N₄ nanoribbons. Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method. The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss (RL, −48.6 dB) and a wide effective absorption band (EAB, 7.4 GHz) at a thickness of 2 mm, attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure. In addition, the aerogel exhibits high thermal stability in air until 1000 ℃ and excellent thermal insulation performance (0.030 W·m⁻¹·K⁻¹). These superior performances make the SiC/Si₃N₄ composite aerogel promising to become a new generation of absorption material served under extreme conditions.

Embedded Integration of Sb2Se3 Film by Low-Temperature Plasma-Assisted Chemical Vapor Reaction with Polycrystalline Si Transistor for High-Performance Flexible Visible-to-Near-Infrared Photodetector.

Flexible optoelectronics have garnered considerable interest for applications such as optical communication, motion capture, biosignal detection, and night vision. Transition-metal dichalcogenides are widely used as flexible photodetectors owing to their outstanding electrical and optical properties and high flexibility. Herein, a two-dimensional (2D) Sb2Se3 film-based one transistor-one resistor (1T1R) flexible photodetector with high photosensing current and detection ranges from visible to near-infrared was developed. The flexible 1T1R was fabricated using an efficient field-effect transistor platform with the 2D Sb2Se3 film directly deposited on the sensing region using a low-temperature plasma-assisted chemical vapor reaction. The photodetector could achieve a maximum Iphoto/Idark of 15,000 under white light with a power density of 26 mW/cm2, in which the photodetector showed quick rising and falling response times of 0.16 and 0.28 s, respectively. The 2D Sb2Se3 film exhibits broadband absorption in the visible and IR regions, yielding an excellent photoresponse under laser illumination with different wavelengths. To investigate the flexibility and stability of the 1T1R photodetector, the photoresponses were measured under different bending cycles and curvatures, which maintained its functions and exhibited high stability under convex and concave bending at a curvature radius of 20 mm.

Study on explosive emission characteristics of the silicon carbide modified graphite cathodes with varied morphologies

Explosive emission cathodes are extensively used in high power microwave sources. Growing requirements are highlighted in the performance of the explosive emission cathode with the development of the high power microwave technology. In order to improve the emission properties of the graphite cathode, modifications using SiC particles or whiskers are carried out by the in situ chemical vapor reaction method. The experiments demonstrate that SiC whiskers accelerate the explosive emission turn-on speed of the graphite cathode for large field enhancement factors and improve the emission uniformity due to the surface flashover plasma generation mechanism. SiC particles increase the emission capability of the graphite cathode, possibly corresponding to the dielectric properties of SiC particles. These results suggest that the SiC whiskers modified graphite cathode is suitable for applications under low magnetic field and large emission area conditions, while the SiC particles modified graphite cathode has a brighter application prospect in the long-time stable operation.

Oxidation resistance and thermal cycling properties of the SiCnws–SiC coating on the C/SiC composites

AbstractSiC coatings reinforced with SiC nanowires were prepared on carbon/silicon carbide (C/SiC) composites through chemical vapor reaction route and chemical vapor deposition (CVD). The SiC nanowires were introduced to mainly improve the interface bonding properties of the coating and C/SiC composites. The microstructure, phase composition, thermal cycling, and bonding strength of the SiCnws–SiC coating were investigated. After nine thermal cycles, the weight loss of the SiCnws–SiC‐coated C/SiC composites was only 4.6 wt.%. Tensile test results show that the tensile strength of the SiCnws–SiC‐coated C/SiC composites was more than 4.5–4.6 MPa. The introduction of SiC nanowires effectively improved interface bonding strength, thus enhancing the thermal cycling and mechanical properties of the coating.

Hydrophobic Cellulose Acetate Aerogels for Thermal Insulation.

As naturally derived material, cellulose aerogels have excellent thermal insulation properties due to their unique high porosity and three-dimensional mesoporous structure. However, its hydrophilic properties limit its application in the field of building insulation. Here, we propose a method to prepare high hydrophobicity by adopting the sol-gel method and chemical vapor reaction strategy using cellulose acetate type II as raw material and 2,4-toluene diisocyanate as the cross-linking agent. Thermal properties of cellulose acetate aerogels (CAAs) were measured, where pyridine was the catalyst, acetone was the solvent, and perfluorodecyltriethoxysilane (PFDS), hexamethyldisilazane (HMDS), and methyltriethoxysilane (MTES) were used as hydrophobic agents (by process hydrophobic test). Compared with MTES-modified cellulose acetate aerogels (M-CAAs) and HMDS (H-CAAs)-modified cellulose acetate aerogels, PFDS-modified (P-CAAs) cellulose acetate aerogels are the most hydrophobic. By implementing hydrophobic modification of PFDS both inside and outside the structure of cellulose acetate aerogels, the water contact angle can reach up to 136°, strongly demonstrating the potential of PFDS as a hydrophobic agent. The results show that the thermal conductivity and compressive strength of cellulose acetate aerogel with the best hydrophobic properties are 0.035 W m−1 K−1 at normal pressure and 0.39 MPa at 3% strain, respectively. This work shows that the highly hydrophobic cellulose acetate aerogel has potential as a waterproof material in the field of building thermal-insulation materials.

(Best Student Presentation Award) Ppb-Level Detection on Formaldehyde By Phase-Engineered 2D-WSe2 Layers Grown By Plasma-Assisted Chemical Vapor Reaction

Layered transition metal dichalcogenides (TMDs) have attracted increasing attention for semiconducting applications owing to their distinctive properties, such as high surface-to-volume ratio, good electronic transport and phase-engineered. However, most of the methods for fabricating thermodynamic metastable phase have so far been induced by conventional CVD process. The high synthesis temperature may cause damages to the substrate and also the processing time is extended. In this concept, here, we incorporated a plasma function into a typical selenization process, which is then applied to metal oxides, namely, a plasma-assisted chemical vapor reduction (PACVR) process, to overcome the disadvantage of CVD process since the presence of high-energy Se ions under plasma treatment lower the energy barrier for a reaction and facilitate the formation of TMDCs at lower temperature. In this work, we developed a facile method to achieve phase control and report a ppb-level detection gas sensor on formaldehyde. Tunable phase synthesis of WSe2 can be achieved by varying conditions such as temperature, carrier gas flow rate and plasma power in a low-temperature PACVR system. Through the detailed investigation of chemical bonding in WSe2 by Raman and XPS, it was found that 100% 2H phase and hybrids of 1T’ and 2H phases can be achieved, and the ratio of 1T’/2H is tunable, relying on substrate temperatures under plasma treatment. By investigating the sensing behavior towards HCHO gas, the performance is highly associated to the ratio of 1T’/2H. The responsivity of 33 % can be achieved with the ratio of the hybrids around 0.46 in WSe2. The phase-engineered 2D-WSe2 layers grown by plasma-assisted chemical vapor reaction with tunable performance can be applied to detect other VOCs efficiently. Figure 1

Dual Threshold and Memory Switching Induced By Conducting Filament Morphology in Ag/WSe2 Based ECM Cell

In recent years, two-dimensional (2D) materials-based RRAMs have gained high importance because of their thermal and mechanical stability, and better potentiation-depression controllability. 2D materials based conductive bridge random access memory (CBRAM) has been considered as promising approach for neuromorphic and image processing technology [1]. Despite much progress in CMOS technology, the growth and deposition technology of 2D materials for semiconductor integrated circuit are much complex and is generally available at wafer scale [2]. In addition, high growth temperature for high quality of 2D materials complicates direct wafer growth and makes transfer process desirable. At the device level, challenges are linked to controlled and uniform growth of 2D material for high density electronic structure.Recently, discreet 2D based memristor have been used in crossbar structure as synapse for neuromorphic computing. However, the plasma-assisted chemical vapor reaction (PACVR) based memristor for neuromorphic application are rarely demonstrated. Here, we report the co-integration of plasma-assisted chemical vapor reaction (PACVR) with silicon CMOS technology to provide brain-inspired computing device. PACVR offers compatibility with temperature limited 3D integration process and also provides much better thickness control over a large area. Furthermore, it an easy platform for direct and controlled synthesis of TMDs compared to conventional CVD approach. The PACVR grown WSe2 layer (~2 nm) on silicon substrate is realized, which exhibits both threshold and bipolar switching. The threshold and bipolar switching emulate integrate-fire neuron function and is obtained by modulating the compliance current in the device. The dynamics of the switching is closely related to the diffusive dynamics of the active metal (Ag or Cu) which can be controlled by device current. As a result, the WSe2/Si memristor shows synaptic behavior for neuromorphic system with learning accuracy of 96%.

Ti3SiC2-SiC multilayer thin films deposited by high temperature reactive chemical vapor deposition

Ti3SiC2-SiC multilayer film coatings synthesis was investigated with the high temperature reactive chemical vapor deposition technique. The method consists of a reaction between SiC (as the substrate and interlayers) and H2-TiClx gaseous mixture. Cross-section morphologies and phases were studies by scanning electron microscopy (SEM), X-ray diffraction (XRD) and automated crystal orientation mapping in transmission electron microscopy (ACOM-TEM). Thermodynamic calculations were carried out to select more appropriate gas composition for reactor conditions and understand the chemistries of reaction between layers in the different steps. Nano and Vickers micro-indentation mechanical tests determined hardness and elastic modulus of the Ti3SiC2 and Ti5Si3Cx surfaces samples. Oxidation tests and emissivity measurements allowed the evaluation of Ti3SiC2-SiC coatings as materials for high temperature applications. The multilayered systems kept their mechanical integrity and showed low degradation after 25 h of thermal cycles at 900 °C in air. The measurement of the optical properties also revealed an increase of the absorptivity after the oxidation of Ti3SiC2 surface sample.

Effect of PyC Inner Coating on Preparation of 3C-SiC Coating on Quartz Glass by Chemical Vapor Reaction

The cubic polycrystal of SiC (3C-SiC) coating on the quartz glass (QG) surface was successfully prepared via a two-step chemical vapor deposition (CVD) by introducing a thin PyC coating as a buffer layer. Through combining the intake system of CVD PyC and CVD SiC, the SiC/PyC composite coating can be in-situ prepared on the QG without halfway in-and-out chamber. The results showed that the SiC/PyC composite coating possesses highly uniform, dense, and continuous features, while the pure SiC coating exhibits many cracks, implying that the internal stress between the SiC coating and the QG can be relieved by adding the PyC buffer coating. The average hardness of the SiC/PyC/QG is measured to be 46.8 GPa, and its calculated modulus is 416.3 GPa by using a nanoindentation technique. Compared to the pure QG, the friction coefficient of the SiC/PyC/QG is slightly increased to 1.47 vs. 1.45. Moreover, the SiC/PyC/QG displays the excellent anti-acid corrosion in the 5%HF and 5%HCl mixed solution with the weight loss of about 33% lower than the pure QG after 8 h acid test at 80°C.