Chemical Vapor Deposition Of Ethylene Research Articles

Electrical Double-Layer Capacitance of Zeolite-Templated Carbon in Organic Electrolyte

Porous carbon materials have been prepared using chemical vapor deposition of ethylene and acetonitrile on zeolite Y templates with the subsequent removal of the template. The use of zeolite templates enabled tuning of the carbon chemistry, microstructure, and specific surface area while maintaining ordered pores and similar pore-size distribution. Evaluation of the performance of the templated carbons in electrochemical capacitors with tetraethylammonium tetrafluoroborate salt solution in acetonitrile showed a high gravimetric capacitance of up to and a short time constant of up to , indicating fast charge/discharge capability. Nitrogen doping limited the capacitor performance at high current densities without enhancing the energy-storage characteristics at low current densities. Specific capacitance at a constant pore size was found to linearly depend on the surface area, suggesting a potential for further improvements. Carbons produced by zeolite-templating method are promising for use in high-energy, high-power electrochemical capacitors employing organic electrolytes.

Fe-N-C oxygen reduction catalysts supported on vertically aligned carbon nanotubes

Abstract Non-noble metal electrocatalyst (Fe-N-C) for the oxygen reduction reaction (ORR) was sputter deposited onto films of vertically aligned carbon nanotubes (VACNT) and tested by the rotating ring disk electrode (RRDE) technique. The VACNT support was first synthesized at atmospheric pressure on a SiO2/Si wafer substrate in a simple tube furnace by iron-catalyzed chemical vapor deposition of ethylene and ammonia at a temperature of 720 °C. VACNT films, with CNT bundle height of 1.5 μm and CNT diameter of 50 nm, were loaded into a sputtering machine to deposit Fe-N-C materials onto the VACNT as support. Iron and carbon were sputtered in a nitrogen atmosphere in order to deposit an amorphous mixture of Fe-N-C material on the VACNT films. The Fe-N-C material supported on the VACNT films was then annealed in Ar at 800 °C to make the ORR electrocatalyst. The catalyst-coated VACNT was scraped off the SiO2/Si substrate and made into catalyst ink for testing by the RRDE technique. The impact of catalyst loading on the RRDE performance (disk current density and %H2O2) is discussed.

Reinforcement of Polyamide 6 with Nanoparticles

AbstractPolyamide 6 has been reinforced by in situ polymerization of ε‐caprolactam by using either 2 wt % of multiwall carbon nanotubes of two different diameters and length or 2 wt % functionalized nonporous Stöber silica. The carbon nanotubes were synthesized by catalytic chemical vapor deposition of ethylene over two different supports: iron particles supported on MCM41 mesoporous silica and iron‐cobalt particles on CaCO3, in order to produce multiwall carbon nanotubes with average diameter of 32 and 58 nm respectively. The Stöber silica particles with diameters of 85 nm and 150 nm were functionalized with 3‐aminotrimethoxypropyl silane. The thermal stability of nanotubes/Polyamide 6 nanocomposites increases compared to the neat polyamide 6, and this increase is even larger when the functionalized silica nanoparticles are used as a filler. The crystallinity of polyamide is enhanced when carbon nanotubes are functionalized, but it decreases with or without functionalization of the silica particles. The nanotubes increase the temperature of crystallization in the nanocomposites due to the reduction in the mobility of polymer chains.

Structure‐Dependent Electrical Properties of Carbon Nanotube Fibers

Spun carbon nanotube (CNT) fibers have great potential for conducting and sensing applications owing to their unique, tunable electrical properties. Here we report the electron transport properties of neat, well-aligned CNT fibers spun from arrays of millimeter-long CNTs. The conductivity of asspun CNT fibers is around 595.2 S cm at room temperature, and its variation with temperature shows a semiconductive behavior from 300 to 75.4 K. The electron transport was found to follow a three-dimensional (3D) hopping mechanism. Importantly, it was found that chemical treatments may significantly affect the conductivities of as-spun fibers. Oxidizing the CNT fibers in air or HNO3 increased the conductivities, while covalent bonding of Au nanoparticles to the CNT fibers remarkably improved conductivity and changed conduction behavior. Conversely, annealing CNT fibers in Ar+ 6% H2 at 800 °C or under the CNT array growth conditions at 750 °C led to a dramatic decrease in conductivity. Owing to their conjugated and highly anisotropic 1D structures, carbon nanotubes (CNTs) are a fascinating new class of electronic materials from both theoretical and applied standpoints. The excellent conductivities of CNTs and their ability to carry very high current density, along with their high thermal conductivity, chemical stability, and mechanical strength, make CNTs uniquely promising for a broad range of applications, including building blocks for nanoscale electronic devices, microsensors for bio-agents and chemicals, and power cables for space shuttles. The electrical resistivity q of individual CNTs has been measured under ballistic conductions to be as low as 10 X cm for single-walled and 3× 10 X cm for multiwalled CNTs, respectively, indicating that CNTs may be better conductors than metals such as copper at room temperature. However, in most cases, due to the presence of various defects or impurities formed during the CNT growth, the conductivities of individual CNTs are often much lower than those under ballistic conduction with nanotubes free of defects. The electron transport in CNT assemblies is different from that in individual nanotubes. It has been reported that singlewalled carbon nanotube (SWNT) fibers, either synthesized directly by vertical floating chemical vapor deposition (CVD) methods or extruded from a super-acid suspension, exhibit room-temperature resistivities in the range of 1 × 10 to 7 × 10 X cm, which is nearly 100 times higher than the resistivities of single nanotubes. The resistivities of multiwalled carbon nanotube (MWNT) fibers are typically one or two orders of magnitude higher than that of SWNT fibers. Such large differences between single nanotubes and fiber assemblies may arise from a high impurity content (such as amorphous carbon and catalytic particles) in the fibers, which may profoundly affect electron transport by causing significant scattering, and contact resistances between nanotubes. Therefore, two approaches can be used to improve the electrical conductivity of CNT fibers: 1) minimize the contact resistances between nanotubes by improving the alignment of CNTs and by increasing the lengths of individual tubes; 2) improve the conductivity of individual CNTs by post-synthesis treatments. Itwas the objective of the study reported here to use these two approaches to produce CNT fibers with high conductivity and to study the fundamental conduction mechanisms of the CNT fibers. Thin and clean CNT fibers (typically 3 lm in diameter) were spun from arrays of well-aligned, millimeter-long CNTs, which were synthesized using ethylene CVD on a Fe catalyst film. By measuring the resistance of CNT fibers at temperatures from 300 K to 75.4 K, we investigated the electronic properties of as-spun fibers and their possible conducting mechanisms. It was also found that the conductivity of CNT fibers could be tuned through mild post-treatments. The spun CNT fibers were post-treated with five different procedures: 1) Annealing in air at 480 °C for half an hour in an attempt to clean off the amorphous carbon, whose oxidation temperature is often around 400 °C. 2) Oxidizing in dilute 5 M HNO3 solution at 40 °C to cause a weak chemical C O M M U N IC A TI O N

Selective Matching of Catalyst Element and Carbon Source in Single-Walled Carbon Nanotube Synthesis on Silicon Substrates

We have studied the compatibility of various catalysts for ethylene and ethanol chemical vapor deposition (CVD) syntheses of single-walled carbon nanotubes (SWNTs) on Si substrates. A strong selectivity between the catalyst elemental species and carbon source was found; SWNT yield for Fe (Co) catalysts was much higher for ethylene (ethanol) CVD than for ethanol (ethylene) CVD. This strong and completely opposite selectivity implies significantly different SWNT growth mechanisms for ethanol and ethylene CVD on Si substrates.

Electron-beam-induced deposition of carbon films on Si(1 0 0) using chemisorbed ethylene as a precursor molecule

We studied the electron-beam-induced deposition of carbon on Si(1 0 0) at room temperature. Ethylene molecules dosed from the background were adsorbed on the surface and decomposed by an electron-beam. The chemical properties and structure of the resulting carbon film, as well as its evolution with the dose of ethylene and annealing temperature after dosing, were investigated by Auger electron spectroscopy (AES) (line-shape analysis), by X-ray photoelectron spectroscopy (XPS) and by temperature-programmed desorption (TPD). Additionally, the amorphous-like hydrogenated carbon structure obtained after electron-beam-induced deposition (EBID) converted completely into SiC upon annealing to ∼1150 K as evidenced by the shift of the Si(2p) plasmon loss peak and the C(1s) peak. We also show that C–H bonds in ethylene are cracked by electron bombardment and that some of the hydrogen atoms produced from cracking are captured. The EBID of carbon was also compared with the chemical vapor deposition of ethylene on Si(1 0 0) in the absence of an electron-beam and a more stable carbon structure can be formed by EBID. It is postulated that EBID deposition produces an amorphous hydrogenated film which contains a high fraction of multiple carbon-carbon bonds, compared to films made by thermal decomposition of the ethylene precursor. This leads to a higher conversion temperature to SiC.

Plasma etching carbon nanotube arrays and the field emission properties

We study the morphologies and the field emission properties of carbon nanotube (CNT) arrays grown on silicon substrate before and after Ar and O 2 plasmas etching. The CNT arrays are synthesized by chemical vapor deposition of ethylene and argon gases in the presence of iron catalysts. Plasma etching is carried out in a DC magnetron-sputtering apparatus. After the treatment, a novel structure of needle-shaped bundles on the surface of CNT arrays is obtained, whose morphologies will be quite different under varied conditions. Enhanced field emission properties are observed after proper treatment.

Interaction-mediated growth of carbon nanotubes on acicular silica-coated α-Fe catalyst by chemical vapor deposition

Multi-walled carbon nanotubes (MWNTs) with 20 nm outer diameter were prepared by chemical vapor deposition of ethylene using ultrafine surface-modified acicular α-Fe catalyst particles. The growth mechanism of MWNTs on the larger catalyst particles are attributed to the interaction between the Fe nanoparticles with the surface-modified silica layer. This interaction-mediated growth mechanism is illustrated by studying the electronic, atomic and crystal properties of surface-modified catalysts and MWNTs products by characterization with X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), thermal gravimetric analysis (TGA) and Raman spectra.

Dense arrays of well-aligned carbon nanotubes completely filled with single crystalline titanium carbide wires on titanium substrates

We report the synthesis of dense and uniform arrays of well-aligned carbon nanotubes on titanium substrates over large areas, in which all the tubes are simultaneously and completely filled with single crystals of titanium carbide. The carbon nanotubes were synthesized by thermal chemical vapor deposition of ethylene on iron-coated substrates, while the titanium carbide was simultaneously formed inside the nanotubes through a simultaneous solid state reaction. We propose a base dissolution and precipitation mechanism for the growth of titanium carbide filled carbon nanotubes. The same method can be used to fabricate oriented nanotube arrays filled with other carbides on a variety of substrates over large scale. Such well-aligned and densely packed uniform carbon nanotubes, completely filled with nanowires on conducting substrates, will have great potential in many applications.

X-ray photoelectron spectroscopy study of Si-C film growth by chemical vapor deposition of ethylene on Si(100)

The growth of a thin film of SiC grown by chemical vapor deposition (CVD) of ethylene on Si(100) at 970 K was studied by x-ray photoelectron spectroscopy (XPS). The growth of the film was observed through the behavior of the Si(2p) and C(1s) core levels and their plasmon losses. A 1.2-eV (towards higher binding energy) shift is observed for the Si(2p) binding energy between silicon in Si(100) and silicon in SiC. The plasmon loss energies measured as a function of film thickness below the C(1s) emission indicate that the C/Si ratio of the Si-C film throughout the CVD process is fairly constant.