Chemical Vapor Deposition Process Research Articles

Molten glass-mediated conditional CVD growth of MoS2 monolayers and effect of surface treatment on their optical properties

In the rapidly developing field of optoelectronics, the utilization of transition-metal dichalcogenides with adjustable band gaps holds great promise. MoS2, in particular, has garnered considerable attention owing to its versatility. However, a persistent challenge is to establish a simple, reliable and scalable method for large-scale synthesis of continuous monolayer films. In this study, we report the growth of continuous large-area monolayer MoS2 films using a glass-assisted chemical vapor deposition (CVD) process. High-quality monolayer films were achieved by precisely controlling carrier gas flow and sulfur vaporization with a customized CVD system. Additionally, we explored the impact of chemical treatment using lithium bistrifluoromethylsulfonylamine (Li-TFSI) salt on the optical properties of monolayer MoS2 crystals. To investigate the evolution of excitonic characteristics, we conditionally grew monolayer MoS2 flakes by controlling sulfur evaporation. We reported two scenarios on MoS2 films and flakes based on substrate-related strain and defect density. Our findings revealed that high-quality monolayer MoS2 films exhibited lower treatment efficiency due to substrate-induced surface strain. whereas defective monolayer MoS2 flakes demonstrated a higher treatment sensitivity due to the p-doping effect. The Li-TFSI-induced changes in exciton density were elucidated through photoluminescence, Raman, and x-ray photoelectron spectroscopy results. Furthermore, we demonstrated treatment-related healing in flakes under variable laser excitation power. The advancements highlighted in our study carry significant implications for the scalable fabrication of diverse optoelectronic devices, potentially paving the way for widespread real-world applications.

Catalytic strategies for uniform monolayer MoSe2 growth in CVD processes

To facilitate the widespread utilization of devices based on two-dimensional transition metal dichalcogenide (TMDC) materials, addressing the challenge of producing large-area and uniform monolayers is crucial. In this study, we investigated the efficacy of various catalysts in promoting the growth of monolayer MoSe2 through chemical vapor deposition (CVD) as a potential solution to improve surface coverage and uniformity while maintaining the monolayer structure. Five distinct water-soluble catalysts (sodium chloride (NaCl), zinc chloride (ZnCl2), potassium hydroxide (KOH), potassium chloride (KCl), potassium oxalate (K2C2O4)) were employed in conjunction with a glass substrate for the CVD-based growth of monolayer MoSe2. We applied these catalyst solutions as thin layers onto SiO2/Si substrates to observe their specific catalytic effects on monolayer MoSe2 formation. MoSe2 was selected as the target material due to its promising characteristics within the TMDC family, particularly its high mobility. Our findings revealed that NaCl, ZnCl2, KCl, and K2C2O4 catalysts enhanced monolayer growth in the 2H phase on SiO2/Si substrates, while the glass substrate resulted in a hybrid 1T/2H MoSe2 structure, albeit with the highest surface coverage. Furthermore, the use of a catalyst allowed us to bypass the laborious transfer step by enabling direct growth of the MoSe2 flakes on the Si/SiO2 substrate, eliminating the risk of flake damage arising from the transfer process. Among the catalyst solutions, NaCl yielded the most homogeneous MoSe2 monolayer growth with relatively high coverage.

Assessing the impact of sargassum algae biodiesel blends on energy conversion in a modified single-cylinder diesel engine with a silica-incorporated diamond-like coated piston

ABSTRACT As coal and oil reserves deplete, the world is shifting to alternative fuels and renewable energy. Researchers are exploring a cleaner alternative to fossil fuels for powering automobiles. In this investigation, biodiesel was synthesized from brown marine algae (Sargassum algae) using transesterification process. Silica-incorporated diamond-like coating (DLC) was done on the engine piston by using the chemical vapor deposition (CVD) process with flow rate of 7sccm of C2H2. Three different coating thicknesses, such as 50,100, and 150 µm, were employed on the CI engine piston. Mechanical properties such as hardness, wear, and microstructure analysis were investigated. Analysis of mechanical characteristics reveals that pistons with a 100 μm coating have enhanced characteristics compared to those with other pistons. Using a 100 μm silicon coated piston on a single-cylinder Kirloskar engine, four blends (B10, B20, B30, and B40) were compared to neat diesel. At maximum engine load conditions, the B40 blends produced 42 ppm of HC whereas neat diesel with 19 ppm which is 57% higher than diesel and CO emission concentration increased by 4.9% than diesel. Similarly, brake-specific fuel consumption was observed at maximum load conditions for diesel with 0.18 kg/kWh and 0.20 kg/kWh for B10D90 which is 9.54% higher than diesel. As a result, it is critical to recognize the importance of sargassum’s potential for producing sustainable energy toward green globalization.

Carbon nanostructures supported on Co/serpentinite for sulfentrazone removal

The presence of environmental contaminants is a major problem today. In this context, it is necessary to develop new sustainable materials to be used to remediate these contaminants. In this work, the serpentinite rock was impregnated with cobalt, 5%, 10% and 20% and used as a support for the synthesis of carbon nanostructures by CVD (chemical vapour deposition) process, at 900°C. This temperature was chosen due to the high thermal stability of the carbon source. The materials were characterized by X-ray diffraction, Raman spectroscopy, thermal analysis, scanning and transmission microscopy. As expect the main phases formed were forsterite, Mg2SiO4, graphitic carbon and metallic cobalt. All the synthesis showed the formation of carbon structures as multiwalled carbon nanostructures over cobalt cores. The carbon structures showed good thermal stability, between 470 and 600°C. The higher the cobalt content, the higher the yield of the carbon structures synthesis, i.e. 14%, 23% and 37% for Serp5, Serp10 and Serp20, respectively. The produced materials were used to removal of the environmental contaminant sulfentrazone. After CVD process, the removal of sulfentrazone increase to 17.3%, 18.4% and 25.2% for Serp5, Serp10 and Serp20, respectively, showing an increase in sulfentrazone removal with the increase in carbon content. In addition, the percentage of sulfentrazone removal by Serp20 was greater at acidic pH values, decreasing from 41.7% to 12.7% with an increase from 2 to 10 in pH. The removal capacity obtained experimentally at a sulfentrazone concentration of 50 mg L−1 was equal to 14.9 mg g−1. According to literature and data obtained in this work, it was observed that the removal of contaminants from the aqueous medium occurred through two mechanisms: reduction of the organic compound by Co nanoparticles and adsorption carried out by carbon nanostructures.

Direct Selective Epitaxy of 2D Sb2Te3 onto Monolayer WS2 for Vertical p-n Heterojunction Photodetectors.

Two-dimensional transition metal dichalcogenides (2D-TMDs) possess appropriate bandgaps and interact via van der Waals (vdW) forces between layers, effectively overcoming lattice compatibility challenges inherent in traditional heterojunctions. This property facilitates the creation of heterojunctions with customizable bandgap alignments. However, the prevailing method for creating heterojunctions with 2D-TMDs relies on the low-efficiency technique of mechanical exfoliation. Sb2Te3, recognized as a notable p-type semiconductor, emerges as a versatile component for constructing diverse vertical p-n heterostructures with 2D-TMDs. This study presents the successful large-scale deposition of 2D Sb2Te3 onto inert mica substrates, providing valuable insights into the integration of Sb2Te3 with 2D-TMDs to form heterostructures. Building upon this initial advancement, a precise epitaxial growth method for Sb2Te3 on pre-existing WS2 surfaces on SiO2/Si substrates is achieved through a two-step chemical vapor deposition process, resulting in the formation of Sb2Te3/WS2 heterojunctions. Finally, the development of 2D Sb2Te3/WS2 optoelectronic devices is accomplished, showing rapid response times, with a rise/decay time of 305 μs/503 μs, respectively.

Shear Field-Controlled Synthesis of Nitrogen-Doped Carbon Nanochains Forest with High-Density sp3 Defects for Efficient CO2 Electroreduction Reaction.

Defect engineering and nitrogen doping being effective strategies for modulating the surface chemical state of the carbon matrix have been widely explored to promote the catalytic activity in the territory of electrochemical energy storage and conversion devices. However, the controllable synthesis of carbon material with high-density specific defects and high nitrogen doping is still full of challenges. Here, we first synthesize one-dimensional necklace-like nitrogen-doped carbon nanochains (N-CNCs) with abundant defects on carbon fiber paper (CFP) by chemical vapor deposition (CVD) method. The resultant nanostructures are a bunch of interconnected carbon spheres with a hollow structure at the internode and present the complete one-dimensional nanochain configuration. Specifically, the N-CNCs with a corrugated surface possesses high content of sp3 defects (31.2%) and nitrogen (23.6 at %). Combining finite element analysis and experimental results, it reveals that the robust shear field generated by etching gas releasing from thermal decomposition of melamine in situ modulates the CVD process via changing the size and force environment of the metal catalyst droplets for formation of N-CNCs. Benefiting from the high ratio of sp3/sp2 and nitrogen doped on the surface, the N-CNCs@CFP displays a superior electrocatalytic performance for CO2RR, delivering CO Faradaic efficiency of 95.9% and a current density of 23.2 mA cm-2 at -0.86 V vs RHE. This work provides promising synthesis strategy and some inspirations for construction of ultradense and specific defects coupling with nitrogen doping sites into carbon materials to achieve high-efficiency electrocatalysis applications.

First principles investigation of ammonia borane decomposition for understanding h-BN growth on the copper surface

Ammonia borane (AB) is a highly promising precursor for the large-scale growth hexagonal boron nitride (h-BN) via chemical vapor deposition (CVD) methods. However, the unclear decomposition mechanism of precursor molecules on the Cu surface poses a great challenge for understanding the CVD growth process of h-BN. In this work, we addressed this issue by conducting first-principles calculations to investigate the decomposition mechanism of AB on the Cu surface. Our calculations revealed that AB preferentially decomposed into ammonia and borane. Further analysis demonstrates that borane exhibits a higher dehydrogenation rate than ammonia, suggesting a single atom self-assembly growth mode of h-BN under B-rich conditions. Our calculations revealed the formation of BNHx-related byproducts during h-BN growth using AB as a precursor, resulting from the intricate decomposition of AB on the Cu surface under CVD conditions. Our findings have significant implications for comprehending and controlling the growth of h-BN in CVD process.

Broad band modulation of two-dimensional Mo1-x W x S2 by variational compositions

Precisely tuning bandgap enables tailored design of materials, which is of crucial importance for optoelectronic devices. Towards this end, ternary Mo1-x W x S2 monolayers with continually variational transition metal compositions are synthesized by precisely control of the precursors and growth temperatures in the chemical vapor deposition process, and thus to manipulate the bandgap of the monolayers. Energy dispersive x-ray spectroscopy demonstrates that the composition of the ternary Mo1-x W x S2 monolayers can be effectively modulated by the precursors and synthesizing temperatures. Frequency and intensity of the Raman and photoluminescent peaks of the Mo1-x W x S2 monolayers are continually modulated by the variational Mo and W compositions. The maximum of 0.148 eV bandgap modulation is achieved by modulating the transition metal compositions, which is highly consistent to the calculated 0.158 eV by first-principles theory. Photodetectors based on the Mo1-x W x S2 monolayers are fabricated and U-shape of photoresponse characteristics are demonstrated as x change from 0 to 1 under the same measurement conditions. The estimated photocurrent, photoresponsivity and external quantum efficiency show that the minimum values appear at the composition of x = 0.5, while the maximum values appear at x = 1. The results illustrate an excellent level of control on the band structure of two-dimensional ternary Mo1-x W x S2 by precisely control of the transition metal compositions.

Chemical vapor deposition-grown single-layer graphene-supported nanostructured Co3O4 composite as binder-free electrode for asymmetric supercapacitor and electrochemical detection of caffeic acid

In this study, we developed a monolayer graphene/nanostructured cobalt oxide (MLG/Co3O4) composite for asymmetric supercapacitor and electrochemical sensor applications. The MLG was grown by chemical vapor deposition process and the Co3O4 nanostructures were electrodeposited on the MLG surface. Scanning electron microscopy proved that there were flower-like nanostructured Co3O4 densely electrodeposited on the MLG surface. At a current density of 3 mA cm−2, the MLG/Co3O4 composite produced an areal capacitance of 3.73 F cm−2. After 10,000 cycles, the composite electrode still had 93.6 % of its initial capacitance at 5 mA cm−2. The asymmetric system displayed an areal capacitance of 929 mF cm−2 at 4 mA cm−2 with good cycle stability. The asymmetric electrode produced a specific energy of 51 μWh cm−2 and a specific power of 11.1 mW cm−2. Cyclic voltammetric measurements demonstrated that the composite showed redox peaks at 0.48 eV and 0.09 eV toward the determination of CA. With a sensitivity of 0.13 µA/µM/cm2 and a limit of detection of 0.009 µM, the composite showed CA concentrations, ranging from 0.5 to 480 M. The composite displayed excellent selectivity and the current produced for the interfering compounds was exceedingly low. Using the composite electrode, the spiked CA in red wine and green tea samples recovered remarkably effectively.

Optimizing the chemical vapor deposition process of 4H–SiC epitaxial layer growth with machine-learning-assisted multiphysics simulations

This work addresses a novel technique for selecting the best process parameters for the 4H–SiC epitaxial layer in a horizontal hot-wall chemical vapor reactor using a transient multi-physical (thermal-fluid-chemical) simulation model and combined with a machine-learning model. An experiment was performed to validate the feasibility of the numerical model. Secondly, a single-factor analysis was conducted to investigate the effects of process parameters, including the deposition temperature, inlet-flow volume, rotational speed of the susceptor, and cavity pressure, on the quality of the 4H–SiC epitaxial layer. Finally, a machine learning algorithm, the ant colony optimization-back propagation neural network (ACO–BPNN), was employed to develop the input/output model and optimize process parameters for obtaining a high-quality epitaxial layer and reducing the optimization cycle and costs. Notably, the optimized process was validated by real experiments, where the error between calculation and experiment is 4.03 % for deposition rate and 0.49 % for coefficient of variation, respectively. The results highlight the model as reliable and lay the foundation for the CVD growth of the 4H–SiC epitaxial layer.

Unique ping-pong daisy-like catalysts: Efficient overall hydrolysis catalysis driven by vanadium-doped Fe2P and Co3(PO4)2 nanosheet composites

Balancing catalytic activity and durability remains a challenge in the development of high performance, inexpensive and durable electrocatalysts. In this study, fully hydrolyzed composite catalyst V–Fe2P@Co3(PO4)2/NF with ping-pong daisy-like morphology was synthesized using conventional hydrothermal and chemical vapor deposition (CVD) processes. In alkaline electrolyte, V–Fe2P@Co3(PO4)2/NF showed excellent electrochemical performance, achieving a current density of 10 mA cm−2 when the driving overpotentials for the hydrogen production reaction (HER) and oxidation reaction (OER) were 56 mV and 178 mV, respectively. Meanwhile, V–Fe2P@Co3(PO4)2/NF demonstrated good durability in terms of both HER and OER stability. Furthermore, the driving voltage required for the electrolyser assembled with V–Fe2P@Co3(PO4)2/NF as the electrode is lower than that of the RuO2/NF||Pt/C/NF electrode, both of which have driving voltages of 1.503 and 1.562 V (10 mA cm−2), respectively. Meanwhile, it achieves a Faraday efficiency of 95%. This study offers a feasible solution towards synthesizing and applying bifunctional water decomposition electrocatalysts.

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Achieving excellent physico-mechanical properties of Cu matrix composites by incorporating a low content of a three-dimensional graphene network

In-depth investigation of the distribution form of the reinforcement and associated mechanisms has great significance for fabricating highly strengthened and conductive Cu matrix composites. The three-dimensional graphene (3DG) network can withstand more strain due to its large specific surface area, and provides interlinked high-speed conductive paths within the composites. In this study, we propose a feasible method to fabricate 3DG-reinforced Cu matrix composites; here, the Cu foam serves as the initial substrate during the chemical vapour deposition (CVD) process and as the matrix of the composites. Through constructing an ideal 3DG network, the graphene content is approximately 0.28 vol%, and a remarkable 230 % improvement in the ultimate tensile strength (418 MPa) with a high electrical conductivity (97.02 %IACS) is obtained in the composite. The continuous high-quality 3DG network is conducive for achieving excellent physico-mechanical properties of the composites, and the enhanced efficiency is superior. A new concept of fabricating Cu matrix composites was proposed for future research.

Carbon-nanotube-grafted glass-fiber-reinforced composites: Synthesis and mechanical properties

Glass fibers (GFs) are commonly used as reinforcements for advanced polymer composites. To improve the interfacial shear properties and mechanical properties of GF-reinforced composites (GFRPs), carbon nanotubes (CNTs) are directly grafted onto GFs using chemical vapor deposition (CVD). However, this process requires high temperatures, which causes thermal degradation of GFs, deteriorating their mechanical properties. In this study, a low-temperature CNT-grafting process was investigated using a bimetallic catalyst introduced onto a GF fiber surface via precursor solutions. The mechanical properties of the CNT-grafted GFs fabricated at different CVD temperatures were evaluated; they consistently showed low tensile strengths at temperatures above 400 °C. Subsequently, various CNT-grafted GFRPs were manufactured, and their mechanical properties were characterized. Interestingly, the flexural strengths of the composites increased with maintained tensile strength, despite a deterioration of the CNT-grafted GF reinforcements due to the CVD process. This could be attributed to the improved interfacial shear strength (IFSS) of the CNT-grafted GFs at the fiber level, and the enhanced compressive strength and interlaminar shear strength (ILSS) of CNT-grafted GFRPs at the composite level. Considering the properties of GF through CVD processes, particularly in relation to temperature, and factors such as IFSS, ILSS, tensile, compressive and flexural properties of composite materials, grafting CNTs on GF via a CVD system demonstrated its highest optimality at 450 °C.

Functional Polymer Thin Films for Establishing an Effective Electrode Interface in Sulfide‐Based Solid‐State Batteries

AbstractSulfide solid electrolytes (SSEs) have garnered significant attention for their high ionic conductivity in the development of all‐solid‐state batteries (ASSBs). However, SSEs face challenges due to poor chemical and electrochemical stability, leading to SE decomposition at the anode, which in turn increases internal resistance and reduces cycle performance. Herein, to address this issue, thin polymer layers are applied to prevent direct contact between the SSE and anode using the initiated chemical vapor deposition process. This method facilitates the uniform coating of eight types of polymers with polar functionalities on indium (In) anodes. Half‐cell tests and X‐ray photoelectron spectroscopy analysis reveals that poly(acrylic acid) and poly((perfluorohexyl)ethyl acrylate), containing ─COOH and C─F bonds respectively, effectively stabilized the In/SSE interface. In full cells assembled with polymer‐coated In and LiNi0.8Co0.1Mn0.1O2 (NCM811), capacity retention show remarkable improvement, achieving 64.8% for In@pAA and 50.7% for In@pC6FA after 100 cycles, compared to 29.0% for bare In. This study provides insights into the interaction between polar bonds in polymers and SSEs, potentially bridging a significant knowledge gap resulting from the significant lack of research investigating the relationship between polymers, one of the primary materials commonly used in ASSBs.

Intrinsically Photopatternable High‐k Polymer Dielectric for Flexible Electronics

AbstractThe development of flexible and stretchable devices is crucial for realizing future electronics. In particular, for dielectric layer, conventional inorganic materials are limited by their brittle nature, while organic materials suffer from a low dielectric constant. Here, a novel intrinsically photopatternable high‐k Parylene‐based thin film (Parylene‐OH) is fabricated via a chemical vapor deposition process based on the Gorham method, which provides pin‐hole free, conformal polymeric film on any type of surface. Parylene‐OH can be photo‐patterned by UV crosslinking without further lithography processes and dielectric constant of Parylene‐OH increases from 6.05 to 7.53 after crosslinking, without degrading other parameters, making it comparable to conventional high‐k dielectric, Al2O3. Flexible In─Ga─Zn─O (IGZO) thin‐film transistors (TFTs) with patterned dielectric layers can withstand higher strain owing to the localized pattern of each unit. A CMOS inverter integrated with n‐type IGZO and p‐type Te TFTs is successfully fabricated. Parylene‐OH can be used in the future of state‐of‐the‐art flexible electronic devices.

Synthesis and growth mechanism of silicon-based nanostructures from polysiloxane via CVD process

The work is concerned with the deposition of ceramic layers of various morphologies, containing silicon and nitrogen, from a polysiloxane precursor in the chemical vapor deposition (CVD) process. The experiments involved the saturation of nitrogen as a gaseous carrier with polysiloxane molecules in the CVD reaction. Saturated nitrogen was supplied to the reaction zone and depending on the synthesis temperature (1000–1800 °C) and the concentration of resin in gas phase, various nanocrystalline and amorphous deposits were obtained on graphite foil, including polygranulated SiOC powders, fibrous layers composed of nanofibers (NFs) containing silicon and nitrogen, nanochains and composite fibrous components. The morphology, structure and chemical composition of the deposits formed in the CVD reaction changed with increasing temperature. Above 1300 °C, oxygen in the silicon oxycarbide deposits was gradually replaced by nitrogen, creating SiN bonds. The dominant phase in the deposits obtained in the temperature range of 1700–1800 °C were two-phase silicon oxynitride NFs. The core of these NFs consisted of a polycrystalline structure surrounded by an amorphous shell. These structures grew preferentially in the [111] direction through heterogeneous nucleation in the vapor-solid process (VS). The changes in deposits morphology were influenced by the CVD temperature and the resin content in the gas carrier. The activation energy of the crystallization process of silicon oxynitride nanofibers was approximately 96 kJ/mol.

Study of field distribution characteristics in CVD reactors and enhanced growth of SWNCT

The low efficiency of growing single-walled carbon nanotubes (SWCNT) poses a barrier to their application in high-performance electronic devices. However, it is difficult to control the uniform growth of SWCNT in a floating catalytic reactor due to the complex parameter control. Therefore, it is essential to enhance the growth of SWCNT in the floating catalyst chemical vapor deposition (FCCVD) process. In the present work, the influence of the reactive flow field on the growth of SWCNT, which is often neglected, is revealed. To address this issue, this work combines experiments and simulations to obtain the characteristics of the field distribution within the reactor and the trend of the products. The results of the flow field analysis indicate that thermal buoyancy is the cause of SWCNT growth limitation in FCCVD. By weakening the thermal buoyancy, a homogeneous reaction field is obtained; vortices in the flow field are reduced or even disappear; the temperature field is more homogeneous, and, importantly, the crystallinity of SWCNT is enhanced (IG/ID up to 20-fold). In addition, the decomposition process of the carbon source is also enhanced, thus suppressing the generation of by-products. Based on the results of the small tube experiments, both the increase in temperature and the decrease in residence time increased the IG/ID. Furthermore, the distributions of the maximum and minimum diameters in SWCNT imply variations in the growth modes of SWCNT at different temperatures.

Area-Selective Chemical Vapor Deposition of Gold by Electron Beam Seeding.

Chemical vapor deposition (CVD) is an established method for producing high-purity thin films, but it typically necessitates the pre- and post-processing using a mask to produce structures. This study presents a novel maskless patterning technique that enables area-selective CVD of gold. A focused electron beam is used to decompose the metal-organic precursor Au(acac)Me2 locally, thereby creating an autocatalytically active seed layer for subsequent CVD with the same precursor. The procedure can be included in the same CVD process without the need for clean room lithographic processing. Moreover, it operates at low temperatures of 80°C, over 200K lower than standard CVD temperatures for this precursor, reducing thermal load on the specimen. Given that electron beam seeding operates on any even moderately conductive surface, the process does not constrain device design. This is demonstrated by the example of vertical nanostructures with high aspect ratios of ≈40:1 and more. Written using a focused electron beam and the same precursor, these nanopillars exhibit catalytically active nuclei on their surface. Furthermore, by using the onset of the autocatalytic CVD growth, for the first time the local temperature increase caused by the writing of nanostructures with an electron beam can be preciselydetermined.

Numerical investigation on the effect of gas-phase dynamics on graphene growth in chemical vapor deposition

Chemical vapor deposition (CVD) is a crucial technique to prepare high-quality graphene because of its controllability. In the research, we perform a systematic computational fluid dynamics numerical investigation on the effect of gas-phase reaction dynamics on the graphene growth in a horizontal tube CVD reactor. The research results indicate that the gas-phase chemical reactions in the CVD reactor are in a nonequilibrium state, as evidenced by the comparison of species mole fraction distributions during the CVD process and under chemical equilibrium conditions. The effect of gas-phase reaction dynamics on the deposition rate of graphene under different conditions is studied, and our research shows that the main causes of change in graphene growth rates under different conditions are gas-phase reaction dynamics and active species transport. The results of numerical simulation agree well with the experimental phenomena. The research results also indicate that, for methane, the main limiting factor of graphene growth is the surface kinetic reaction rate. Conversely, for active species, the main limiting factor of graphene growth is species transport. Our research suggests that the growth rate of graphene can be regulated from the perspective of the gas reaction mechanism. This method has theoretical guiding significance and can be extended to the preparation of large-area graphene.