Temperature Chemical Vapor Deposition Research Articles

Multi-interfaced FeCoNi@C/carbon cloth composites for eliminating electromagnetic wave pollution

To tackle the increasing electromagnetic pollution, new and efficient electromagnetic wave absorption (EWA) and shielding (EWS) materials are urgently needed. Multi-component synergism and complex microstructure design are effective measures to improve the EWA and EWS properties. However, how to implement the above designs still faces huge challenges. Herein, multi-interface carbon-coated FeCoNi nanoneedles grown on carbon cloth (FeCoNi@C/CC) were synthesized by a combination of hydrothermal process and chemical vapor deposition (CVD) technology with the concept of “green synthesis”. Using acetylene as the carbon source and atmosphere, the FeCoNi ternary hydroxide can be transformed into a multiple magnetic component (Fe3O4, Ni, and Co metals) by simple annealing. Simultaneously, a uniform carbon layer is formed on the surface, resulting in a composite system with a variety of heterogeneous interfaces and loss mechanisms. Additionally, the dielectric and magnetic loss capacities can be effectively adjusted by changing the temperature of CVD. The optimized FeCoNi@C/CC as filler exhibits remarkable EWA performance with a minimum reflection loss of −69.3 ​dB at a thickness of 1.82 ​mm and a maximum effective absorption bandwidth of 6.80 ​GHz. Moreover, the composites as an integrated component also show a fascinating electromagnetic interference shielding efficiency of 42.2 ​dB. This work provides a guide for the structural design of high-performance electromagnetic protection materials with multi-heterogeneous interfaces.

Improving the capacitive performance of wood-derived carbon monolith by anchoring heteroatom-doped carbon nanotubes in the vessels via in situ chemical vapor deposition

Wood, with high carbon contents and abundant vertically oriented channels, has unique advantages in preparing high mass-loading carbon-based freestanding supercapacitor electrodes. However, there is considerable room for enhancing the capacitive performance of wood-derived carbon electrodes. A one-step chemical vapor deposition (CVD) method mediated by dicyandiamide using iron-based nanoparticles as catalysts was proposed to enhance the utilization of vertical channels in wood-based carbon electrodes and improve their pore structure and chemical composition. This approach aimed to fabricate composite electrodes with enhanced mass loading, interwoven conductive carbon nanotube networks, well-developed hierarchical porous structure, and abundant nitrogen/oxygen-containing functional groups. The effect of CVD temperature on the physical/chemical properties and capacitance performance of the composite material was investigated. Consequently, the optimal electrode (CW/NCNTs-800) attained a competitive initial specific capacitance of 5762 mF cm−2 at 5 mA cm−2 and demonstrated a satisfactory rate performance with the specific capacitance of 3520 mF cm−2 at 300 mA cm−2. In addition, the durable electrode demonstrated commendable cycle stability, maintaining a capacitance retention of 93 % through 30,000 cycles at 30 mA cm−2. This study on wood-derived high mass-loading supercapacitor electrodes can provide a novel perspective on the application of high-performance energy storage devices.

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.

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.

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.

Effect of sulfur and phosphorous doping on the growth rate of CVD diamond (111)

The purpose with the present study has been to theoretically investigate the effect of P (or S) doping on the chemical vapor deposition (CVD) growth rate of diamond. Density functional theory (DFT) calculations under periodic boundary conditions were then used for the investigation of the highly symmetric H-terminated diamond (111) surface. It was shown that both the thermodynamics and kinetics of P (or S) substitutional doping during diamond (111) growth were severely affected by the dopants (as compared with the non-doped situation).As a result of the thermodynamic calculations, except for P doping in C layer 1, the thermodynamic driving force for the diamond (111) growth was found to be largely improved by positioning P within the upper surface region of the H-terminated diamond (111) surface, while the opposite was true for S-doping. The P doping had a local vertical influence on the H abstraction energies, which was not the situation for the S doping. Also, both P and S doping showed a local lateral influence on the H abstraction energies, which was more pronounced for P doping.As a result of the kinetic calculations, the vertical and lateral P doping showed no local effect on the H abstraction energy barriers. In fact, these energy barriers became zero for P positioned in C layer 2 and downwards and were also zero for longer distances from the H adsorbate. On the other hand, the vertical S doping showed a local effect on the calculated barrier energies, but no lateral effect. The calculated energy barriers were zero for all surface H adsorbates on the H-terminated diamond (111) surface when S was positioned in the 4th atomic C layer. The different results for P doping versus S doping could be explained by the fact that S contains one electron extra and that P has a larger electronegativity value.Consequently, the results showed that P positioned in the upper diamond (111) surface lattice caused an enhancement in the diamond growth rate. The exception was the position in C atomic layer 1, for which both P doping and S doping had no effect on the diamond growth rate. On the other hand, a growth rate improvement was only found for S positioned in the 4th C layer. Due to the much higher (i.e., more positive) theoretical incorporation energies of S dopants versus P dopants in the diamond lattice, it has here been concluded that P doping is more effective than S doping in increasing the growth rate of the H-terminated diamond (111). Especially when considering that the H adsorbates are very mobile on this diamond surface, which has been shown by ab initio MD simulations at experimental CVD temperatures. These observations correlate well with experimental results.

The structure of chemical vapor deposited graphene substrates for graphene-enhanced Raman spectroscopy

Defects and nanocrystalline grain structures play a critical role in graphene-enhanced Raman spectroscopy (GERS). In this study, we selected three types of few-layer, polycrystalline graphene films produced by chemical vapor deposition (CVD), and we tested them as GERS substrates. The graphene structure was controlled by decreasing the CVD temperature, thus obtaining (i) polycrystalline with negligible defect density, (ii) polycrystalline with high defect density, (iii) nanocrystalline. We applied rhodamine 6G as a probe molecule to investigate the Raman enhancement. Our results show that nanocrystalline graphene is the most sensitive GERS substrate, indicating that the GERS effect is primarily connected to the nanocrystalline structure, rather than to the presence of defects.

Dimethoxydimethylsilane-derived silica membranes prepared by chemical vapor deposition at 973 K exhibiting improved thermal/hydrothermal stability

With the aim of developing thermally/hydrothermally stable silica membranes for H2 separation, dimethoxydimethylsilane-derived silica membranes were prepared via chemical vapor deposition (CVD) at various temperatures. This process employed a substrate having an intermediate layer with a gallium-loaded γ-alumina coating that had been calcined at 1073 K. The data demonstrate that this intermediate layer was itself thermally stable at 1073 K and hydrothermally stable at 973 K. A systematic evaluation of membrane performances under thermal/hydrothermal conditions confirmed that membranes prepared at 973 K were more stable than those fabricated at 873 K under dry conditions. In addition, the loss in H2 permeance under hydrothermal conditions was lower in the case that the CVD temperature was 973 K. Hence, to ensure stability, the temperature at which such membranes are employed should be lower than the CVD processing temperature.

Large-scale synthesis of 3D ordered microporous carbon at low temperature using cobalt ions exchanged zeolite Y as a template

Zeolite-templated carbons (ZTCs) have a unique three-dimensional (3D) ordered microporous structure and an extra-large surface area, and have excellent properties in adsorption and energy storage. Unfortunately, the lack of efficient synthesis strategies and the difficulty of doing this on a large-scale have seriously limited their development. We have developed a large-scale simple production route using a relatively low synthesis temperature and direct acetylene chemical vapor deposition (CVD) using Co ion-exchanged zeolite Y (CoY) as the template. The Co2+ confined in the zeolite acts as Lewis acid sites to catalyze the pyrolysis of acetylene through the d-π coordination effect, making carbon deposition occur selectively inside the zeolite at 400 °C rather than on the external surface. By systematically investigating the CVD temperature and time, the optimum conditions of 8 h deposition at 400 °C produces an excellent 3D ordered-microporous structure and outstanding structure parameters (3 000 m2 g−1, 1.33 cm3 g−1). Its CO2 adsorption capacity and selectivity are 2.78 mmol g−1 (25 °C, 100 kPa) and 98, respectively. This simple CVD process allows the synthesis of high-quality ZTCs on a large scale at a low cost.

3D Nanoarchitectured Hexagonal Boron Nitride with Integrated Single Photon Emitters

AbstractTwo‐dimensional (2D) hexagonal boron nitride (hBN) is one of the most promising candidates to host solid‐state single photon emitters (SPEs) for various quantum technologies. However, the 2D nature with an atomic‐scale thickness leads to inevitable challenges in spectral variability caused by substrate disturbance, lattice strain heterogeneity, and defect variation. Here, three‐dimensional (3D) nanoarchitectured hBN is reported with integrated SPEs from native defects generated during high‐temperature chemical vapor deposition (CVD). The 3D hBN has a quasi‐periodic gyroid minimal surface structure and is composed of a continuous 2D hBN sheet with built‐in convex and concave curvatures that promote the formation of optically active and thermally robust native defects. The free‐standing feature of the gyroid hBN with a nearly zero mean curvature can effectively eliminate the substrate disturbance and minimize lattice strain heterogeneity. As a result, naturally occurring defects with a narrow SPE spectral distribution can be created and activated as color centers in the 3D hBN, and the density of the SPEs can be tailored by CVD temperature.

Continuous Growth of Carbon Nanotubes on Carbon Fiber Surface by Chemical Vapor Deposition Catalyzed by Cobalt with Thiourea

The continuous preparation of carbon nanotubes (CNTs)/carbon fiber (CF) multiscale reinforcements was realized via one-step chemical vapor deposition (CVD) method. In order to alleviate the damage of CF caused by catalyst etching at high temperature, catalytic promoter was adopted to improve the activity of the catalyst, thus reducing the CVD temperature. By adjusting the cobalt-based catalyst system, the effects of thiourea concentration on the morphology, microstructure and tensile strength of CNTs/CF samples were systematically investigated. It was found that the length and quantity of CNTs were added as the thiourea concentration increased, and the graphitization degree of the sample increased at first because of the well-grown CNTs, and then decreased due to the formation of amorphous carbon. Moreover, the tensile strength of CNTs/CF multiscale reinforcements was improved, which derived from the enhanced defect repair function of synthesized CNTs. Remarkably, CNTs/CF-0.02 exhibited a high single-filament tensile strength value (up to 4.51 GPa), which was about 6.6% higher than that of Desized cf Besides, the crystal structure and composition of reduced catalysts were analyzed, confirming the successful sulfur doping into cobalt particles. Therefore, the work offers a facile, economical, and efficient route for manufacturing CNTs/CF multi-scale reinforcements at comparatively low temperature.

Fabrication of multilayer Graphene-coated Copper nanoparticles for application as a thermal interface material

A process to fabricate a thermal interface material (TIM) was developed to coat graphene, which is chemically stable and thermally conductive, on the surface of copper nanoparticles (CNPs) to prevent their oxidation while promoting heat dissipation. The CNPs were synthesized using the polyol method to convert polyvinylpyrrolidone (PVP) into multilayer graphene (MLG) via chemical vapor deposition (CVD). For optimization, CVD temperature, the amount of additional PVP solution, and PVP molecular weight (MW) in polyol process were varied. The results showed that thermal properties degraded with increasing residual PVP, and an increasing ID/IG ratio confirmed improved MLG quality. The optimal MLG coating conditions were found to be a CVD temperature of 880℃, 50 wt% additional PVP solution and using K30 PVP in polyol process (MW: 45,000). These conditions provided the highest thermal conductivity of 19.66 W/m∙K. Thermogravimetric analysis established that oxidation began at 150℃, which is higher than the upper temperature limit of electronic components. Therefore, MLG-coated CNPs would be suitable as TIM.

Controlled Growth of Organosilane Micropatterns on Hydrophilic and Hydrophobic Surfaces Templated by Vacuum Ultraviolet Photolithography.

In this report, micropatterns of (3-aminopropyl)trimethoxysilane (APTMS) were developed on hydrophilic and hydrophobic surfaces after patterning using 172 nm vacuum ultraviolet (VUV) photolithography. Self-assembled monolayers (SAMs) formed on Si substrates through UV hydrosilylation of 1-hexadecene (HD) and 10-undecenoic acid (UDA) were used as hydrophilic and hydrophobic surfaces, respectively. For templating the HD- and UDA-SAMs, the VUV light was exposed to HD- and UDA-SAMs from the slits of photomasks in atmospheric and evacuated environments, respectively. Various oxygenated groups were generated at the exposed domains of HD-SAM, while the COOH groups were trimmed from the irradiated domains of UDA-SAM. The APTMS molecules were immobilized on the domains that were terminated by oxygenated groups after chemical vapor deposition (CVD). The thicknesses of the developed APTMS micropatterns increased significantly by raising the CVD temperature and in the presence of ambient air in the CVD Teflon container as well. The increase in thicknesses was ascribed to the formation of APTMS multilayers, which were mediated by H3N+ ions. Also, the developed APTMS micropatterns on the UDA-SAM patterned by VUV light irradiation in a high-vacuum environment (HV-VUV) were thicker than those on the VUV/(O) patterned HD-SAM due to the presence of inactive oxygenated groups at the surface of VUV/(O)-terminated domains of HD-SAM such as COO-C and C-O-C groups. The presence of water or ambient air facilitated the silane coupling between the silyl groups with the oxygenated and amino groups The combination of VUV photolithography and the CVD method with control of the conditions would enable us to control the thicknesses and shapes of the developed APTMS micropatterns. These findings illustrate the applicability of VUV photolithography for templating hydrophobic and hydrophobic surfaces toward the development of organosilane architectures, which can be feasible for several applications.

Impact of C-CVD synthesis conditions on the hydraulic and electronic properties of SiC/CNTs nanocomposite microfiltration membranes

In this study, commercial SiC ceramic microfiltration membranes were coated with carbon nanotubes (CNTs) using chemical vapor deposition (CVD) to obtain a conductive and hydrophobic membrane material. In order to have better control of the surface and electronic properties of the developed material, two adjacent fractional factorial designs (25-2) were implemented to quantify CNTs synthesis parameters influence. The design of experiments revealed that the quantity of the synthesized CNTs was mainly controlled by CVD temperature, duration and iron catalyst concentration. The structure of the CNTs layer was mainly controlled by CVD temperature within the investigated parameter range (650–850 °C). It was demonstrated that pure water permeability was anti-correlated with CNTs synthesis yield due to an increase in membranes' hydrophobicity and potential pore blockage. The membrane coated with the largest amount of CNTs was obtained at 850 °C for a duration of at least 1 h and showed relatively low electrical resistance and good microwave absorption. Finally, such tunable nanocomposite material has the potential to further improve the filtration performances and membranes widespread application.

Radially grown carbon nanomaterials on hollow glass microspheres and their application in composite foams with excellent electromagnetic interference shielding

AbstractIn the current study, we investigated the effect of processing temperature in chemical vapor deposition (CVD) on the formation of carbon nanomaterials over the hollow glass microsphere. The surface morphology and structural information of the carbon nanomaterials (CNM)‐coated hollow glass microsphere (HGM) were analyzed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then, the 5‐CH [CNF‐coated HGM (Synthesizing temperature in CVD being 500 °C)], 6‐CH [MWCNT‐coated HGM (Synthesizing temperature in CVD being 600 °C)], and 7‐CH [MWCNT‐coated HGM (Synthesizing temperature in CVD being 700 °C)] were individually used as fillers in the epoxy composite foam. Thorough characterization of mechanical and thermo‐mechanical behavior suggests that compression stress, compression modulus, and storage modulus of 6‐CH‐based composite foam are higher than the 5‐CH‐ and 7‐CH‐based composite foam with the contribution of 10%, 15%, and 20%, respectively. The electromagnetic interference (EMI) shielding effectiveness over the frequency of 8–12 GHz increased from 15 dB for without HGM to 21 dB, 25 dB, and 23 dB for 5‐CH, 6‐CH‐, and 7‐CH‐based composite foam, respectively. It is also noticed that, 6‐CH‐based composite foams presented the highest EMI‐SE compared to 5‐CH‐ and 7‐CH‐based composite foams. Enhanced mechanical, thermo‐mechanical, and shielding properties of 6‐CH‐based composite foams are due to improved morphology and quality of CNT grown at 600°C.

Sp3-Defect and pore engineered carbon framework for high energy density supercapacitors

Carbon based supercapacitor suffers from low energy density due to inefficient electrical double-layer storage mechanism. Herein, sp3-defect engineered sp2 carbon framework with hierarchical porous architecture (HCF) is developed via a one-step chemical vapor deposition (CVD) method for high energy density supercapacitor. Theoretical calculations are performed firstly and results reveal that the sp3-defects in host sp2 carbon sheets promote the sodium-ion storage performance attributed to the reduced energy barrier of sodium-ion adsorption and increased density of states around Fermi level. The HCF is extensively characterized and the results show that the density of sp3-defects and hierarchical micro-meso-macropore size of HCF can be well tuned by regulating the CVD temperature. Owing to reasonably engineered sp3-defects (~32.8 at%), well-defined multiscale pore architectures and wide interlayer in HCF, extra pseudocapacitive sodium-ion storage sites are obtained and therefore a capacitance up to 558.8 F/g is achieved. The resultant HCF based symmetric supercapacitor device gives a high energy density of 38.76 Wh/kg at a power density of 375.04 W/kg and still retains 30.00 Wh/kg at a high power density of 5970.15 W/kg. This work provides a facile strategy to explore the intrinsic defect in carbon electrode materials for high performance energy storage systems.

Rotational stability of twisted bilayer graphene

Moir\'e superlattices form in twisted graphene bilayers due to periodic regions of commensurability, but truncation of the moir\'e patterns affects the rotational stability of finite-sized sheets. Here, we report the stepwise untwisting of nanometer-sized bilayer graphene flakes at elevated temperatures, each step corresponding to a potential energy barrier formed by changes to the commensurability between the moir\'e superlattice and flake size with twist angle. The number of locally stable energy states and their barrier energies scale with the flake size, allowing twisted graphene flakes of several tens of nanometers to remain thermally stable even at chemical vapor deposition temperatures.

Optimizing synthetic diamond samples for quantum sensing technologies by tuning the growth temperature

Control of the crystalline orientation of nitrogen-vacancy (NV) defects in diamond is here demonstrated by tuning the temperature of chemical vapor deposition (CVD) growth on a (113)-oriented diamond substrate. We show that preferential alignment of NV defects along the [111] axis is improved when the CVD growth temperature is decreased, leading to 79% preferential orientation at 800∘C, as compared to only 47.5% at 1000∘C. This effect is then combined with temperature-dependent incorporation of NV defects during the CVD growth to obtain preferential alignment over dense ensembles of NV defects spatially localized in thin diamond layers. These results demonstrate that growth temperature can be exploited as an additional degree of freedom to engineer optimized diamond samples for quantum sensing applications.

Tunable growth of carbon nanotubes forests on nickel foam as structured support for palladium catalyst toward polystyrene hydrogenation

Heterogeneous catalytic hydrogenation of polystyrene (PS) over classical porous catalysts to polycyclohexylethylene (PCHE) with added commercial values is severely limited by pore diffusion of polymer coils due to the large molecule size and high solution viscosity. To improve accessibility of PS to active sites and eliminate catalyst separation, a structured catalyst, Pd supported on CNTs decorated nickel foam (Pd/[email protected]) was prepared and displayed an excellent hydrogenation activity. The high performance could be contributed to the non-porous and wide-open structure of CNTs layer and strong π–π interaction between CNTs surface and PS molecules which facilitates the diffusion and adsorption of PS coils respectively. The average diameter and graphitization degree of CNTs could be tuned by adjusting the chemical vapor deposition (CVD) temperature and consequently its surface area and interaction with PS molecules. CVD temperature was optimized to obtain Pd/[email protected] with highly dispersed Pd nanoparticles and enhanced adsorption capacity of PS. It shows great industrial potential for structured Pd/[email protected] catalyst with outstanding catalytic activity and stability.

On the reactivity of carbon formed from CO CVD over Ni(1 1 1)/TiO2

The formation and reactivity of carbon on the supported nickel catalyst is a key issue for the low temperature activity and stability with methanation, reforming and other reactions. In this work, Ni(1 1 1)/TiO2 was prepared and applied as the catalyst to deposit carbon using low temperature chemical vapor deposition (CVD) of carbon monoxide. It was found that the CVD temperature could significantly affect the formation of carbon. With the CVD temperature decreasing, the disorder of the carbon increased, while the degree of graphitization was reduced. As a result, graphene-like films can be obtained at low CVD temperatures (from 300 to 350 °C). Such carbon films show a significantly improved reactivity with hydrogen and carbon dioxide. This explains the excellent low temperature activity and stability for CO2 or CO methanation over Ni catalysts with Ni(1 1 1).