Chemical Vapor Deposition Of Carbon Research Articles

The Soret effect in laser chemical vapor-deposited carbon fibers

The Soret effect in laser chemical vapor-deposited carbon fibers

Cryo‐TEM Study of High‐Performance Iron Difluoride Cathode Enabled by Low Temperature CVD Carbon Coating

AbstractMetal fluorides (MFs) are regarded as high‐capacity conversion cathode materials for next‐generation lithium‐ion batteries with high energy density. However, these cathodes suffer from poor electronic conductivity, sluggish reaction kinetics, and deleterious cathode solid electrolyte interface (CEI) formation, which may cause rapid cell degradation upon cycling. Herein, a low temperature chemical vapor deposition (CVD) carbon coating technology is successfully achieved to coat MFs‐FeF2 with a thin amorphous carbon layer, which promotes the formation of a stable CEI with improved electronic and ionic transport property. Consequently, a discharge capacity higher than 450 mAh g−1 of the CVD coated FeF2 is achieved with a capacity retention at about 75% after 2500 cycles in a saturated electrolyte. Moreover, an unprecedented cycling performance with the discharge capacity of 350 mAh g−1 after 500 cycles in a super diluted electrolyte is also achieved. Advanced cryo‐electron microscopy reveals that the carbon coating significantly suppresses the undesirable CEI formation and promotes the formation of a thin CEI with excellent chemo‐mechanical property. This work provides a feasible technology to stabilize the important interface on MFs and offers a new strategy to accelerate the commercial adoption of such cathodes.

Mechanisms for Chemical Vapor Deposition Carbon Nanotube Growth by Surface Modification of 316L Stainless Steel.

Mechanisms for Chemical Vapor Deposition Carbon Nanotube Growth by Surface Modification of 316L Stainless Steel.

Carbon‐Coated Porous Hollow Silicon Microspheres for High‐Capacity and Durable Lithium Storage

AbstractSilicon‐based materials are promising lithium‐ion battery (LIB) anodes owing to their natural abundance and high capacity. However, their practical application is restricted by the poor electrical conductivity and large volume expansion. Herein, we successfully construct carbon coated porous hollow silicon microspheres (Si‐40@C) as LIB anode materials, which are derived from the acid etching of commercial AlSi alloy with subsequent chemical vapor deposition carbon coating. The porous hollow structure of Si‐40@C buffers the volume variation and promotes the transportation of Li+; the carbon coating enhances the overall conductivity as well as structural stability. The as‐prepared Si‐40@C porous hollow microspheres deliver a high reversible capacity (2029 mAh g−1 at 0.2 A g−1), good cyclability (1668 mAh g−1 after 100 cycles at 0.2 A g−1), and an ideal rate capability (1200 mAh g−1 at 10 A g−1).

Few-layered-graphene/zirconia composites: Single-step powder synthesis, spark plasma sintering, microstructure and properties

The chemical vapor deposition of carbon is performed onto a commercial yttria-stabilized zirconia (3YSZ) powder bed. This produces few-layered-graphene (FLG) film uniformly covering the 3YSZ grains, without the manipulation of any pre-existing nanocarbon in the form of graphene platelets. The powders are then consolidated by spark plasma sintering, producing specimens where FLG is located along the grain boundaries of the 3YSZ matrix, which is below 0.3 μm in grain size. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The pure 3YSZ exhibits higher toughness and fracture strength compared to composites, but the trend is that their toughness increases upon the increase in carbon content. Crack-deflection and crack-bridging are observed. The composites are electrically conducting with a percolation threshold between 1.48 and 1.98 vol.% of carbon, reflecting the continuous nature of the FLG film over very long distances.

Chemical Vapor Deposition of Hollow Graphitic Spheres for Improved Electrochemical Durability

The wet-chemical synthesis of hollow graphitic spheres, a highly defined model catalyst support for electrocatalytic processes, is laborious and not scalable, which hampers potential applications. Here, we present insights into the chemical vapor deposition (CVD) of ferrocene as a simple, scalable method to synthesize hollow graphitic spheres (HGScvd). During the CVD process, iron and carbon are embedded in the pores of a mesoporous silica template. In a subsequent annealing step, iron facilitates the synthesis of highly ordered graphite structures. We found that the applied temperature treatment allows for controlling of the degree of graphitization and the textural properties of HGScvd. Further, we demonstrate that platinum loaded on HGScvd is significantly more stable during electrochemical degradation protocols than catalysts based on commercial high surface area carbons. The established CVD process allows the scalable synthesis of highly defined HGS and therefore removes one obstacle for a broader application.

Initial competing chemical pathways during floating catalyst chemical vapor deposition carbon nanotube growth

Ferrocene (Fc) is an effective precursor for the direct synthesis of high quality single-walled carbon nanotubes (SWCNTs) via floating catalyst chemical vapor deposition (FCCVD). However, the formation mechanism of the Fe floating catalyst and the SWNCT growth precursors, such as carbon chains, during Fc decomposition are not well understood. Here, we report first principles nonequilibrium quantum chemical molecular dynamics simulations that investigate the decomposition of Fc during FCCVD. We examine the influence of additional growth precursors including ethylene, methane, CO, and CO2 on the Fc decomposition mechanism and show that the dissociation of these species into C2Hx radicals and C atoms provides the key growth agents for the nucleation of carbon chains from Fc-derived species such as cyclopentadienyl rings. Without an additional growth precursor, Fc decomposes via the spontaneous cleavage of Fe–C and C–H bonds, thereby enabling Fe atoms to cluster and form the floating catalyst. On the basis of these simulations, we detail the two competing chemical pathways present during the initial stages of FCCVD: Fe catalyst nanoparticle growth and carbon chain growth. The latter is accelerated in the presence of the additional growth precursors, with the identity of the precursor determining the nature of the balance between these competing pathways.

Graphitic Nanocup Architectures for Advanced Nanotechnology Applications.

The synthesis of controllable hollow graphitic architectures can engender revolutionary changes in nanotechnology. Here, we present the synthesis, processing, and possible applications of low aspect ratio hollow graphitic nanoscale architectures that can be precisely engineered into morphologies of (1) continuous carbon nanocups, (2) branched carbon nanocups, and (3) carbon nanotubes–carbon nanocups hybrid films. These complex graphitic nanocup-architectures could be fabricated by using a highly designed short anodized alumina oxide nanochannels, followed by a thermal chemical vapor deposition of carbon. The highly porous film of nanocups is mechanically flexible, highly conductive, and optically transparent, making the film attractive for various applications such as multifunctional and high-performance electrodes for energy storage devices, nanoscale containers for nanogram quantities of materials, and nanometrology.

Effects of CVD Carbon on the Erosion Behavior of 5D Carbon-Carbon Composite in a Solid Rocket Motor

An experimental study was conducted to study the effects of chemical vapor deposition (CVD) carbon content on the erosion behavior of 5 direction (5D) carbon-carbon (C/C) composite in a solid rocket motor (SRM). A small SRM, which can compare the erosion performance of two samples under the same working conditions, was designed and tested. The erosion of the carbon-carbon composite ablative morphology at macroscale and microscale was obtained and analyzed. Results show that the average erosion rates of 1# and 2# samples are 0.35 mm/s and 0.45 mm/s, respectively, which means the erosion rate of the sample with high CVD carbon content is 22.2% times lower than the one with low CVD carbon content. During SRM operation, the fibers within fiber bundles and carbon rods are in a dispersive and integral state, respectively, thus carbon rods have a better anti-ablation capability, followed by fiber bundles and matrix in turn. As a result, a carbon rod will be positioned higher than the matrix and fiber bundles around. Furthermore, the ablation of fibers within fiber bundles and carbon rods, although they have significant differences in the ablation process, can both be described as a single fiber ablation. The oxidizing species react with the matrix, then with the CVD carbon and the fiber within a fiber bundle in turn, while they react with the matrix, the CVD carbon and the fiber within a carbon rod simultaneously. This shows that the increase in CVD carbon content will improve the ablation performance of C/C composite by protecting the fibers within the fiber bundles. The present study provides a fundamental understanding of the effect of CVD carbon on the ablation performance of C/C composite, serving as a reference for further design and optimizations of C/C composite.

One-step synthesis of few-layered-graphene/alumina powders for strong and tough composites with high electrical conductivity

The chemical vapor deposition of carbon onto a commercial α-Al2O3 powder bed produces a pristine film of few-layered-graphene (FLG) uniformly covering the α-Al2O3 grains. This obviates both the manipulation of nanocarbons, lengthy mixing steps and the risk of damaging any pre-existing graphene platelets. The powders are consolidated to 99 % by SPS, producing samples where a FLG film is located along the grain boundaries of the submicron α-Al2O3. Compared to the pure α-Al2O3, the composites are moderately stronger and similarly tough and hard due to crack-deflection and crack-bridging and they are electrically conducting with a percolation threshold below 0.74 vol.% of carbon. The high conductivity values reflect the high quality of the thin FLG film and its continuous nature over very long distances. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy.

Ultrasensitive Detection of Dopamine with Carbon Nanopipets.

Carbon fiber micro- and nanoelectrodes have been extensively used to measure dopamine and other neurotransmitters in biological systems. Although the radii of some reported probes were ≪1 μm, the lengths of the exposed carbon were typically on the micrometer scale, thus limiting the spatial resolution of electroanalytical measurements. Recent attempts to determine neurotransmitters in single cells and vesicles have provided additional impetus for decreasing the probe dimensions. Here, we report two types of dopamine sensors based on carbon nanopipets (CNP) prepared by chemical vapor deposition of carbon into prepulled quartz capillaries. These include 10-200 nm radius CNPs with a cavity near the orifice and CNPs with an open path in the middle, in which the volume of sampled solution can be controlled by the applied pressure. Because of the relatively large surface area of carbon exposed to solution inside the pipet, both types of sensors yielded well-shaped voltammograms of dopamine down to ca. 1 nM concentrations, and the unprecedented voltammetric response to 100 pM dopamine was obtained with open CNPs. TEM tomography and numerical simulations were used to model CNP responses. The effect of dopamine adsorption on the CNP detection limit is discussed along with the possibilities of measuring other physiologically important analytes (e.g., serotonin) and eliminating anionic and electrochemically irreversible interferences (e.g., ascorbic acid).

Formation of Carbon-Nanotube Layers on Bulk Nickel: The Effect of Surface Topography Defects

The initial stages of the chemical vapor deposition of carbon onto nickel substrates subjected to different mechanical abrasion treatments are studied by optical, scanning electron, and atomic force microscopies, as well as X-ray diffraction and profilometry. We find that the local accelerated deposition of carbon layers with a highly disordered structure, which occurs at the initial stages of the process, is the underlying cause of nonuniformity in carbon nanotube layers synthesized directly onto a metal surface. Enhanced deposition rates are observed at surface topography defects, including microcavities with a large surface-to-volume ratio. Open microvoids in the subsurface layer left behind by mechanical abrasion treatment also act as foci of the accelerated formation of carbon layers. The cause of this enhanced growth lies in the specific chemistry of the extended pyrolysis of hydrocarbons trapped in microvoids. A high carbon deposition rate results in the formation of carbon-containing materials with a highly disordered structure within such defects. Microscopic asperities and microprotrusions formed as a result of mechanical abrasion are sites of intensive hydrocarbon-induced dusting of the metal. Numerous microslits originate from these defects due to corrosion scattering, which in turn facilitate the emergence of sites for accelerated formation in limited volumes of carbon with a disordered structure.

Simple control of the pore structures and gas separation performances of carbon hollow fiber membranes by chemical vapor deposition of propylene

In this study, we investigated the effects of one-step chemical vapor deposition (CVD) of propylene on the pore structures and gas separation performances of carbon hollow fiber membranes derived from sulfonated poly(phenylene oxide) (SPPO). The CVD is performed by feeding a 5–100% of propylene gas at the carbonization peak temperature. The obtained CVD carbon membranes had higher carbon concentrations and were hydrophobic. Their water permeances were considerably lower than those of uncoated membranes in pervaporation experiments. The gas permeances of the CVD membranes also decreased but the ideal selectivities greatly improved, especially for H2/CH4 from 130 to 1625 with the membrane prepared by pyrolysis at 650 °C for 60 min in combination with CVD of 100% propylene for 5 min. We found that the gas separation performance could be easily controlled by changing the propylene volume fraction and CVD time. The highest H2/CH4 selectivity of 29,940 was obtained for a membrane pyrolyzed at 700 °C for 20 min with CVD using 10% propylene for 20 min.

Evaluation of a method for micro-defect sealing in ZSM-5 zeolite membranes by chemical vapor deposition of carbon

This work presents a systematic study on closing micro-defects in zeolite membranes using chemical vapor deposition of carbon. For chemical vapor deposition (CVD), different carbon sources, dwell times and temperatures were applied. The zeolite membranes used in this study were fabricated by hydrothermal syntheses on the inner surface of porous ceramic substrates in single channel geometry. The quality of the membranes was characterized by permporometry, single gas permeation measurements and microstructural techniques (e.g. electron microscopy).For proof of concept, γ-Al2O3 ultrafiltration membranes with 2 nm pore diameter without any zeolite layer were coated with carbon by CVD using n-hexane and ethyne. Especially a treatment with ethyne lead to a narrowing of the pore size of the ultrafiltration membrane and reduced the number of micro defects. Subsequently, the method was applied to close intercrystalline defects in zeolite ZSM-5 membranes. Compared to pure ZSM-5 membranes, CVD treated membranes exhibited lower permeances and enhanced ideal permselectivity for H2/SF6 and He/SF6. Though the method has to be further improved, those first results emphasize the potential of this general method for closing defects in different zeolite membranes.

Chemical Vapor Deposition Carbon Film as a Capping Layer in 4H-SiC Based MOSFETs.

Radio-frequency plasma enhanced CVD (RF-PECVD) carbon films were grown directly on 4-inch 4H-SiC substrates as a capping layer for MOSFET device applications. An approximately 50-nm-thick CVD carbon capping layer was found to reduce the surface roughness, as determined by atomic force microscopy (AFM). The secondary ion mass spectroscopy (SIMS) depth profile results revealed that carbon capping layer can suppress the dopant out-diffusion on the implanted surface after annealing even at high temperature (1700 °C) for 30 min. The calculated subthreshold swing (S) values of devices with CVD carbon capping layer and photo-resist process (base) measured at room temperature were 460 ± 50 (mV/dec) and 770 ± 70 (mV/dec), respectively. The lower value of 'S' for the device with carbon capping layer was related to the very low density of interface traps at the SiC-SiO2 interface. These results show the potential of CVD carbon as a capping layer for SiC MOSFET device applications.

Numerical simulation of carrier gas effects on flow field, species concentration and deposition rate in the chemical vapor deposition of carbon

A 2D numerical model was established for simulating the chemical vapor deposition (CVD) of carbon in a vertical reactor. A full multi-component diffusion model was proposed to describe the diffusion of the gas species. The effects of Ar, N2or H2 carrier gases on the flow field, species concentration and deposition rate of pyrocarbon were investigated using C3H6 as the carbon source. Results show that H2 improves the stability of the gas flow. The concentration distributions of CH4, C2H2, C2H4 and C6H6 are uniform in H2. The pyrocarbon deposition rate is lowered, but the uniformity of deposition is improved when H2 is used as the carrier gas compared with N2 or Ar. The simulation results agree well with the experimental ones.

High-Performance and Lightweight Thermal Management Devices by 3D Printing and Assembly of Continuous Carbon Nanotube Sheets.

Free-standing carbon nanotube films or buckypaper can provide a significant platform to develop practical applications of nanocarbon materials. For this research, buckypaper with high thermal conductivity (20 W/m K) and large surface area (350 m2/g) was mass produced in-house to investigate for use in lightweight thermal management devices. Floating catalyst chemical vapor deposition carbon nanotube sheets were also studied in this work. We introduced two manufacturing techniques to use the sheets for heat dissipation: (1) printing conductive composite ink on the sheets to make lightweight thermal devices, such as heat sinks and (2) assembling the sheets directly into 3D structures that were mounted on the back of heat-generating devices. These manufacturing techniques resulted in extremely lightweight, high-performance heat dissipation devices compared with other heat sink materials.

Mechanical enhancement effect of the interlayer hybrid CNT film/carbon fiber/epoxy composite

Floating catalyst chemical vapor deposition carbon nanotube (CNT) film was intercalated into carbon fiber (CF) prepregs to fabricate hybrid composites. The effect of CNT film thickness was studied by using a 25 μm thick film and an ultrathin 2 μm film respectively. The results showed that the ultrathin CNT film interlayer had dramatically improved the compression strength of hybrid composite by 34% compared with CF/epoxy control composite owing to the altered failure modes. The damping ratio of ultrathin CNT film hybridized composite was substantially increased by two orders of magnitude, due to the energy dissipation of numerous nanoscale interconnections and interfaces. Moreover, the interlaminar properties and water resistance of the hybrid composites were all improved. Since a small amount of CNT film can significantly enhance the mechanical properties of CF/epoxy composite, this type of hybrid composite has potential application in multifunctional lightweight structures.

A Double Core-shell Structure Silicon Carbon Composite Anode Material for a Lithium Ion Battery

Silicon with high theoretical specific capacity is a promising anode material, but the poor electronic conductivity and excessive volume expansion hinder its practical application. In order to solve this problem, a novel double core-shell structure composite Si/G/C-CVD coated by pitch pyrolysis and CVD (Chemical Vapor Deposition) carbon has been prepared. In the Si/G/C-CVD composite, nano-silicon particles and pitch particles are embedded on the surface of graphite particles, then the second carbon layer via CVD is added. The double carbon layer can protect nano-silicon particles from direct exposure to the electrolyte and enhance the electrochemistry performance during the lithium intercalation/extraction process. The as-prepared Si/G/C-CVD composite demonstrates superior electrochemical performance, with enhanced specific reversible capacity (688.44 mAh g−1 at 100 mA g− 1), excellent rate performance (261.66 mAh g−1 even at the specific current of 1.6A g− 1) and good cycle performance with little fading (91% after 155 cycles).

Chemical Vapor-Deposited Carbon Nanotubes as Electrode Material for Supercapacitor Applications

ABSTRACTWe report the capacitance of entangled carbon nanotubes (CNTs) synthesized on flexible carbon fabric via water-assisted chemical vapor deposition. The CNTs were grown at atmospheric pressure with iron (Fe) as the catalyst, ethylene (C2H4) and 5%/95% H2/Ar as precursor gasses, and aluminum oxide as a buffer/barrier layer. The effect of the catalyst thickness (5 and 10 nm) on the specific capacitance was studied. The capacitance behavior of CNTs was evaluated by cyclic voltammetry measurements via a three-electrode system. The highest specific capacitance, approximately 56 F/g, was obtained for electrodes with 5nm Fe thickness. A nearly rectangular shaped cyclic voltammogram was exhibited for the CNTs grown on the carbon fabric. A specific power density of 0.012 KW/Kg and specific energy density 0.15 Wh/Kg were calculated from the galvanic charge/discharge (CD) curves. In addition, electrochemical impedance spectroscopy (EIS) revealed a characteristic supercapacitive behavior with a low equivalent series resistance of 7 Ωcm2.