Chemical Vapor Deposition Method Research Articles

Polyethyleneglycol-polyhydroxylbutyrate functionalized carbon nanotubes for industrial electroplating wastewater treatment

This study focuses on the production and purification of multi-walled carbon nanotubes (P-CNTs) via a catalytic chemical vapor deposition method and subsequent functionalization with amino polyethylene glycol (NH2-PEG) and its mixture with polyhydroxybutyrate (PHB) through a multi-step purification process to produce NH2-PEG-CNTs and NH2-PEG-PHB-CNTs, respectively. The developed nanoadsorbents were used to treat electroplating wastewater via batch adsorption to sorb potentially toxic metals and emerging pollutants. The nanoadsorbents were characterized before and after treatment with wastewater after thermal regeneration analyzed using HRSEM/EDS/SAED, DLS Nanozetasizer, BET, TGA/DTG, and FTIR. The nanoadsorbents showed a homogeneous distribution of clean and smooth crystalline interwoven tubular/cylindrical shapes and sizes, with broad polydispersed/high aspect ratio, large surface area, mesopores, and functional groups. The batch adsorption study showed simultaneous multi-capturing of toxic metals from industrial electroplating wastewater with a directly proportional relationship between contact time, adsorbent dosage andtemperature, and electrostatic activities via the positive surface charge of the nanoadsorbents (pH > pHzpc). The highest removal of Fe (15.86 %), Ni (79.82 %), Pb (79.82 %), and Cu (84.97 %) were obtained using NH2-PEG-PHB-CNTs. In addition, the ANOVA results show that the adsorption process depends on other parameters such as the concentration of toxic metals in the wastewater, its hydration energy, electronegativity, ionic mobility in the electrostatic activities, pH of the nanoadsorbents, water holding capacity of the polymer-functionalized nanoadsorbents, and synergistic effects of the bi-polymer. Moreover, the nanoadsorbents have a stable morphology after thermal regeneration for reusability purposes, and treated wastewater can be safely reused in the electroplating industry or for other purposes, such as agriculture.

Selective Laser-Assisted Direct Synthesis of MoS2 for Graphene/MoS2 Schottky Junction.

Implementing a heterostructure by vertically stacking two-dimensional semiconductors is necessary for responding to various requirements in the future of semiconductor technology. However, the chemical-vapor deposition method, which is an existing two-dimensional (2D) material-processing method, inevitably causes heat damage to surrounding materials essential for functionality because of its high synthesis temperature. Therefore, the heterojunction of a 2D material that directly synthesized MoS2 on graphene using a laser-based photothermal reaction at room temperature was studied. The key to the photothermal-reaction mechanism is the difference in the photothermal absorption coefficients of the materials. The device in which graphene and MoS2 were vertically stacked using a laser-based photothermal reaction demonstrated its potential application as a photodetector that responds to light and its stability against cycling. The laser-based photothermal-reaction method for 2D materials will be further applied to various fields, such as transparent display electrodes, photodetectors, and solar cells, in the future.

Study of the AlPN/GaN high electron mobility transistors with improved transconductance linearity

In this work, an improved method of metal-organic chemical vapor deposition was utilized to grow high-quality AlPN/GaN heterostructures. The characteristics of AlPN those are essential to achieving high linearity in the resulting devices were then investigated. High linearity AlPN/GaN high electron mobility transistors (HEMTs) with flatter transconductance curves were fabricated, in which the gate voltage swings are 1.85 and 4.35 V at 300 and 400 K when Gm drops 5% from Gm,max. Additionally, the impact of P anti-site defects and surface states on the high linearity of AlPN/GaN HEMTs at different temperatures was discussed. It was found that while both factors benefit linearity at room temperature, only the P anti-site defects have a positive effect on linearity at high temperatures. The results demonstrate the significant advantages of AlPN-based structures in high linearity device applications and provide instructive principles for improving linearity.

Metal‐free Fabrication of Nitrogen‐doped Vertical Graphene on Graphite Felt Electrodes with Enhanced Reaction Kinetics and Mass Transport for High‐performance Redox Flow Batteries

AbstractGraphite felt is commonly used in redox flow batteries, but the low specific surface area and poor catalytic activity cause unsatisfactory mass transfer and reaction kinetics. Here, nitrogen‐doped vertical graphene is in‐situ grown on graphite felt via a metal‐free chemical vapor deposition method, which exhibits a high specific surface area and remarkable catalytic activity due to abundant exposed high‐density sharp graphene edges and nitrogen doping. Multiphysical simulations reveal that the vertical‐standing nanostructure promotes the accessibility of vanadium ions to electrode/electrolyte interfaces, effectively decreasing the mass transport resistance of active species. Density functional theory calculation evidence shows that nitrogen doping aids in the improvement of catalytic activity via boosting vanadium ions’ adsorption and redox. Consequently, the nitrogen‐doped vertical graphene/graphite felt electrode shows an energy efficiency of 87.1% at 200 mA cm−2, significantly higher than that of pristine (65.9%) and air‐oxidize (73.1%) electrodes, an energy efficiency over 80.2% at 300 mA cm−2 during 1500 cycles, and a high‐peak power density of 1308.56 mW cm−2, which are superior to previously reported carbon nanomaterial decorated electrodes for flow batteries. Significantly, the synthesis process only involves gas‐phase reactions without metal catalysts to avoid hydrogen evolution reactions. This work provides an exciting pathway for developing high‐performance electrodes for flow batteries.

Mechanical properties of a novel tungsten fiber-reinforced tungsten composite prepared through powder extrusion printing and high-pressure high-temperature sintering

Tungsten is one of the most promising candidate materials for plasma-facing materials (PFM) because of its high melting point, superior thermal conductivity, and low sputtering rate. However, its significant brittleness and high ductile-to-brittle transition temperature constrain its broader engineering applications. To address these limitations, we developed a novel tungsten fiber-reinforced tungsten (Wf//W) composite. This composite utilizes commercially available black tungsten wire mesh as the fiber reinforcement phase with a mass ratio of 1 %. The material was synthesized through a combined Powder Extrusion Printing and High-Pressure, High-Temperature sintering process, achieving a relative density exceeding 99 %. Additionally, the composite exhibits a maximum hardness of 589 ± 10 HV, attributable to the presence of high-density dislocations in the matrix. Its compressive strength reaches up to 1530 MPa, and the plastic deformation strain is as high as 15.8 %, both of which are outstanding compared to existing research. These findings offer an alternative route for producing high-density Wf//W materials, in addition to chemical vapor deposition method and powder metallurgy technique.

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.

Low-temperature, ultra-fast, and recyclable self-healing nanocomposites reinforced with non-solvent silylated modified cellulose nanocrystals

Developing polymeric materials with remarkable mechanical properties and fast self-healing performance even at low temperatures is challenging. Herein, the polymeric nanocomposites containing silane-treated cellulose nanocrystals (SCNC) with ultrafast self-healing and exceptional mechanical characteristics were developed even at low temperatures. First, CNC is modified with a cyclic silane coupling agent using an eco-friendly chemical vapor deposition method. The nanocomposite was then fabricated by blending SCNC with matrix prepolymer, prepared from monomers that possess lower critical solution temperature, followed by the inclusion of dibutyltin dilaurate and hexamethylene diisocyanate. The self-healing capability of the novel SCNC/polymer nanocomposites was enhanced remarkably by increasing the content of SCNC (0–3 wt%) and reaching (≥99 %) at temperatures (5 & 25 °C) within <20 min. Moreover, SCNC-3 showed a toughness of (2498 MJ/m3) and SCNC-5 displayed a robust tensile strength of (22.94 ± 0.4 MPa) whereas SCNC-0 exhibited a lower tensile strength (7.4 ± 03 MPa) and toughness of (958 MJ/m3). Additionally, the nanocomposites retain their original mechanical properties after healing at temperatures (5 & 25 °C) owing to the formation of hydrogen bonds via incorporation of the SCNC. These novel SCNC-based self-healable nanocomposites with tunable mechanical properties offer novel insight into preparing damage and temperature-responsive flexible and wearable devices.

High-throughput thermodynamic study of SiC high-temperature chemical vapor deposition from TMS-H2

A systematic study on the tetramethylsilane-hydorgen (TMS-H2) system by high-throughput thermodynamic method is conducted with a large experimental condition range (500 ∼ 2700 K, 0 ∼ 75 kPa, and H2:TMS ratio of 0.1 to 10000) towards the deposition of pure single-crystal SiC by high-temperature chemical vapor deposition (HTCVD) method. The temperature, pressure and H2:TMS ratio dependence phase diagrams are calculated to describe the deposition condition of single-phase “gas + SiC” region. Due to the etching effect of hydrogen on graphite, the increasing temperature and pressure could suppress the formation of graphite and favor the growth of SiC in the H2:TMS ratio above 1000, however, excessive H2:TMS ratio could reduce the TMS consumption efficiency. TMS consumption efficiency maps focusing on the gas + SiC region based on the phase diagrams have been carried out to balance the deposition parameters, SiC mole fraction and TMS consumption efficiency. When H2:TMS ratio > 1000, an accepted window for preparing single-phase SiC with a high TMS consumption efficiency (>90%) is provided, and this window could expand furtherly with increasing the ratio. TMS consumption efficiency maps offer the theoretic basis and guidance for improving the quality and cost of industrial production of single-crystal SiC by HTCVD method.

A new method for evaluation of nanotube growth kinetics in aerosol CVD

Aerosol chemical vapor deposition (CVD) – a particular case of floating catalyst CVD method with an extreme dilution of catalyst – has been demonstrated to be one of the most advanced one-stage and continuous techniques for the production of single-walled carbon nanotubes (SWCNTs) for various applications in electronics, optics, energy storage, etc. Nevertheless, rational scaling of the aerosol CVD reactor is often limited by a fundamental problem of tracking the growth kinetics, in particular, the nanotube growth rate and the catalyst deactivation rate. We propose a robust method for the assessment of nanotube growth kinetics (growth rate and catalyst lifetime) based on the analysis of the SWCNT film equivalent sheet resistance (R90) versus residence time (τ) dependencies. We have demonstrated identical trends of R90-vs-τ and length-vs-τ curves at different concentrations of CO2 used as a promoter in the Boudouard reaction- (CO-) based synthesis. As a result, we have revealed the mechanisms behind the CO2 effect on the catalyst deactivation rate not reported before. In particular, we observed an increase in CO2 concentration to provide a faster growth rate but an earlier catalyst deactivation. We believe this work might be useful for researchers from both academia and industry and facilitate more active development of aerosol CVD methods for the production of new materials.

Research status and prospect of electrode materials for lithium-ion battery

The lithium-ion battery has become one of the most widely used green energy sources, and the materials used in its electrodes have become a research hotspot. There are many different types of electrode materials, and negative electrode materials have developed to a higher level of perfection and maturity than positive electrode materials. Enhancing the electrochemical capabilities of positive electrode materials is therefore crucial. In addition to exploring and choosing the preparation or modification methods of various materials, this study describes the positive and negative electrode materials of lithium-ion batteries. Among the negative electrode materials, Li4Ti5O12 is beneficial to maintain the stability of the battery structure, and the chemical vapor deposition method is the best way to prepare nitrogen-doped graphene materials. Doping and coating modifications for positive electrode materials can offer a smoother mobile route for lithium ions, which can enhance the cathode materials cycling performance. This papers study, summary, and outlook on electrode materials for lithium-ion batteries can aid those researchers in developing a more thorough understanding of electrode materials. Also, it can be advantageous for the growth of associated follow-up research projects and the expansion of the lithium battery market.

Magnetic proximity effect in the two-dimensional ε-Fe2O3/NbSe2 heterojunction

Two-dimensional (2D) magnet/superconductor heterostructures can promote the design of artificial materials for exploring 2D physics and device applications by exotic proximity effects. However, plagued by the low Curie temperature and instability in air, it is hard to realize practical applications for the reported layered magnetic materials at present. In this paper, we developed a space-confined chemical vapor deposition method to synthesize ultrathin air-stable ε-Fe2O3 nanosheets with Curie temperature above 350 K. The ε-Fe2O3/NbSe2 heterojunction was constructed to study the magnetic proximity effect on the superconductivity of the NbSe2 multilayer. The electrical transport results show that the subtle proximity effect can modulate the interfacial spin–orbit interaction while undegrading the superconducting critical parameters. Our work paves the way to construct 2D heterojunctions with ultrathin nonlayered materials and layered van der Waals (vdW) materials for exploring new physical phenomena.

Improved photostability of mixed-cation perovskite microplatelets fabricated by a chemical vapor deposition method

Promising performances have been demonstrated for photovoltaic and light-emitting devices based on perovskite absorbers. However, to further fulfill this promise, the photo-instability that has long been observed in them must be overcome. In this work, ordinary CsPbBr3 and mixed cation FAxCs1−xPbBr3 perovskite microplates are synthesized by a chemical vapor deposition method. Under continuous intensive ultraviolet (UV) irradiation of 100 W/cm2, the photoluminescence (PL) of pristine CsPbBr3 quickly quenches within 10 minutes due to the vacancy assisted ion migration. Whereas, the PL of mixed cation FAxCs1−xPbBr3 perovskite maintains 80% of its original intensity after similar UV irradiation for 25 minutes. The narrower PL bandwidth, higher PL quantum yield, and longer PL lifetime reveal the reduced defect traps in the FAxCs1−xPbBr3. Therefore, the improved photostability of the mixed cation FAxCs1−xPbBr3 perovskite benefits from the suppressed ion migration due to the reduced density of halide vacancy. This work provides a promising approach to prepare photostable perovskites, which will promote their applications in optoelectronic devices.

Uniform Co9S8 nanosheets on carbon nanotube arrays grown on Ni mesh as free-standing electrodes for asymmetric supercapacitors

A free-standing 3D core/shell composite material CNTs@Co9S8 on nickel mesh has been prepared by a simple two-step method. Carbon nanotubes (CNTs) grown vertically on the surface of nickel mesh by chemical vapor deposition (CVD) method act as conductive skeleton. Then Co9S8 nanosheets uniformly aligned on the surface of the CNTs by solvothermal method are interconnected to form a honeycomb structure. Owing to the close contact of the CNTs@Co9S8 hybrid with the nickel mesh and the hierarchical 3D porous structure, the prepared Ni@CNTs@Co9S8 electrodes exhibit low resistance and excellent charge storage capability with a specific capacitance of 1305.4 F g−1 at 1 A g−1. The composite delivers an excellent rate capability with 84.3 % capacitance retention at 10 A g−1. An asymmetric supercapacitor composed of Ni@CNTs@Co9S8 and nitrogen-doped carbon nanotubes (NCNTs) shows an energy density of 23.8 Wh kg−1 and a high power density of 8007.4 W kg−1. The specific capacitance of the ASC device remained 87.31 % after 10,000 charge-discharge cycles and two tandem ASCs can power two red LED diodes for at least 7 min, suggesting the potential application of the obtained free-standing electrode for supercapacitors.

Deposition of thin TiO2 films on fluorophlogopite particle surface by CVD in fluidized bed reactor to prepare silver pearlescent pigments

Two critical parameters: Glossiness and chromaticity space of pearlescent pigments were evaluated based on crystallinity and grain size. Both the roughness and the vertical distance evolution along the surface of deposited TiO2 film are affected by the crystallinity. The optimal crystallinity of TiO2 was deposited at the temperature of 350 °C. The TiCl4 concentration effectively changed the grain size. However, the high flow rate of fluidizing gas and optimal gas–solid ratio (<0.11 m3/(kg h)) restricted the change of TiCl4 concentrations in fluidized bed reactor. In this case, the grain size of the deposited TiO2 film was about 55 nm. Depending on the grain size, the color of pearlescent pigments was adjusted by controlling the film thickness based on TiO2 concentration. Finally, the silver pearlescent pigment with high glossiness was prepared by chemical vapor deposition method in a fluidized bed reactor.

Light blocking and phase modulation based on thermo-plasmonic hotspots in WS2 monolayer

Here we demonstrate light blocking and phase modulation in nano-plasmonic donate shape rings based on the thermo-plasmonic effect in these structures. For this purpose, we use a laser writing system to fabricate nanohole arrays and cover them with plasmonic gold thin film via a sputtering machine. The chemical vapor deposition method is also used to produce a WS2 layer, which is suitable for light blocking and phase modulation due to the nonlinearity of this two-dimensional material. After theoretically and experimentally evaluating the plasmonic donate-shaped substrate, we use the ellipsometric method to characterize the optical modes of the samples and record the switching manner and light-blocking phenomena under the probe laser excitation set to 980 nm. Our results show phase modulation based on the thermo-plasmonic effect of nano gap in donated double rings and light blocking by thermal expansion of the WS2 layer, which can open new insight into plasmon and two-dimensional material-based devices.

Progress in the preparation of high-quality wafer-scale monolayer and multilayer MS2 (M = Mo; W) films by CVD

MS2 (M = Mo; W), with natural atomic thickness, are typical two-dimensional (2D) semiconductor materials, which have excellent electronic/optoelectronic properties and mechanical flexible properties. With the development of semiconductor device miniaturization, much attention has been brought to MS2, especially in large-scale integrated circuits, ultra-sensitive photodetectors, and flexible electronic devices. Here, we present the recent research progress on the controllable synthesis of high-quality, wafer-scale, uniform monolayer and multilayer MS2 films by chemical vapor deposition methods, focusing on the most concerning grain orientation control and defect modulation in whole wafer, besides the pursuit of more larger wafer size in MS2 films’ preparation. We also discuss some critical issues in the process of MS2 films growth and give a brief outlook in the controllable preparation of high-quality MS2 films for device application later on.

Thermal Contact Resistance of the Copper–Copper Pair with Graphene Thermal Interface in Magnetic Fields up to 10 T

Abstract—&#x0D; The thermal contact resistance of a detachable connection in copper-copper contact pair with a thermal interface from layers of graphene synthesized by the method of a low pressure chemical vapor deposi-tion on the contact surface was studied. Obtaining the value of the thermal contact resistance of a detachable contact pair copper–graphene–copper by the method of transient heat flow, at a temperature of 15–150 K under the influence of an external magnetic field up to 10 T.

Bypassing Formation of Oxide Intermediate via Chemical Vapor Deposition for the Synthesis of an Mn-N-C Catalyst with Improved ORR Activity.

A significant barrier to the commercialization of proton exchange membrane fuel cells (PEMFCs) is the high cost of the platinum-based oxygen reduction reaction (ORR) cathode electrocatalysts. One viable solution is to replace platinum with a platinum-group metal (PGM) free catalyst with comparable activity and durability. However, PGM-free catalyst development is burdened by a lack of understanding of the active site formation mechanism during the requisite high-temperature synthesis step, thus making rational catalyst design challenging. Herein we demonstrate in-temperature X-ray absorption spectroscopy (XAS) to unravel the mechanism of site evolution during pyrolysis for a manganese-based catalyst. We show the transformation from an initial state of manganese oxides (MnOx) at room temperature, to the emergence of manganese-nitrogen (MnN4) site beginning at 750 °C, with its continued evolution up to the maximum temperature of 1000 °C. The competition between the MnOx and MnN4 is identified as the primary factor governing the formation of MnN4 sites during pyrolysis. This knowledge led us to use a chemical vapor deposition (CVD) method to produce MnN4 sites to bypass the evolution route involving the MnOx intermediates. The Mn-N-C catalyst synthesized via CVD shows improved ORR activity over the Mn-N-C synthesized via traditional synthesis by the pyrolysis of a mixture of Mn, N, and C precursors.

Carbon nanotubes/carbon nanofibers@carbon fiber construction of 3D network hierarchical structures toward multiple synergistic losses for electromagnetic wave absorption

Exploring carbon materials is promising for innovative electromagnetic wave (EMW) absorption materials, nevertheless challenged by balancing efficient EMW absorption and continuous large-scale fabrication. In this work, CNTs/CNFs@CF with inimitable 3D network hierarchical structures are fabricated as EMW absorbers via the chemical vapor deposition method. Through detailed characterization of its morphology, structure, composition, and magnetic properties, the material obtained optimal electromagnetism parameters and showed exceptional EMW absorption performance. Herein, the minimum reflection loss (RLmin) was −66.00 dB at 1.00 mm and the maximum effective absorption bandwidth of 4.48 GHz was obtained at 1.29 mm. In addition, good mechanical properties with a single-filament tensile strength of 4.99 GPa were achieved, thereby expanding the range of applications. Undoubtedly, CNTs/CNFs@CF realizes the synergy of multiple synergistic loss mechanisms and impedance matching for EMW absorption. In summary, this implies a good prospect for the continuous large-scale preparation of ultrathin and efficient EMW absorbers.

High-performance silicon/graphite anode prepared by CVD using SiCl4 as precursor for Li-ion batteries

Graphite/silicon composite anode shows increased capacity but suffering from the volume expansion of Si during cycling. Herein, we reported a facile chemical vapor deposition (CVD) method using silicon tetrachloride (SiCl4) as precursor to deposit silicon into graphite to prepare composite as anode for Li-ion batteries. Si can be deposit as the nano-sized particles in the open spaces of graphite, and closely attached on the graphite flakes. Such architecture effectively increased the contact between Si and graphite, and provided semi-enveloping confinement for Si volume change. Typically, the composite anode with 10% Si could maintain above 600 mAh/g for 100 cycles.