Carbon Nanotubes Grown on the Surface of Cathode Deposit by Arc Discharge

Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH₄ gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH₄ gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH₄ gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm.     

Multi-walled carbon nanotubes grow under low pressure hydrogen,air, and argon ambient by arc discharge plasma

Multi-walled carbon nanotubes (MWCNTs) were grown on cathode deposit by arc discharge plasma under H₂, Ar, and air ambient environment. The influence of ambient gas pressure on the structure and physical properties of carbon nanotube were compared. Herein, we highlight the influence of ambient environment and pressure to grow high quality carbon nanotubes. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction were used for structural characterization and yield determination. The result revealed that background gas and pressure were crucial factor for growing highly crystalline and highly graphitic with I_D/I_G ratio 0.237 obtained for MWCNTs' synthesized in H₂ environment with extreme low defects.     

Preparation of high yield multi-walled carbon nanotubes by microwave plasma chemical vapor deposition at low temperature

Vertically-aligned carbon nanotubes(CNTs) with multi-walled structure were successfully grown on a Fe-deposited Si substrate at low temperature below 330°C by using the microwave plasma chemical vapor deposition of methane and carbon dioxide gas mixture. This is apparently different from the conventional reaction in gas mixtures of hydrogen and methane, hydrogen and acetylene, and hydrogen and benzene ... etc. High quality carbon nanotubes were grown at lower temperature with CO₂ and CH₄ gas mixture than those used by the previous. After deposition, the microstructure morphology of carbon nanotubes was observed with scanning electron microscope and high-resolution transmission electron microscope. The characteristics of carbon nanotubes were analyzed by laser Raman spectroscopy. The results showed the variation of the flow rate ratio of CH₄/CO₂ from 28.5 sccm/30 sccm to 30/30 sccm and the DC bias voltage from –150 V to –200 V, at 300 W microwave power, 1.3–2.0 kPa range of total gas pressure, and substrate temperatures between 300°C and 350°C. Vertically aligned carbon nanotubes with the diameter of about 15 nm and multi-walled structure were illustrated by SEM and HRTEM. However, the highest yield of carbon nanotubes of about 50% was obtained at low temperature below 330°C by MPCVD for the CH₄/CO₂ gas mixture with properly controlled parameters.     

Adsorption Properties of Multi‐wall Carbon Nanotubes

Abstract

Preparation of multi‐wall carbon nanotubes by means of arc‐discharge in He atmosphere was worked out and optimized. Electron micrographs show that electrode deposit consists of crossed multi‐wall carbon nanotubes. For study of adsorption properties of multi‐wall carbon nanotubes, the thermodynamic characteristics of adsorption of different classes organic compounds at small coverage were determined by gas chromatography and compared with those for graphitized carbon black and molecular crystals of fullerene C₆₀ (fullerite). The comparison of adsorption data for organic compounds with different functional groups on multi‐wall carbon nanotubes, on graphitized carbon black and fullerene C₆₀ shows the similarity of adsorption properties of multi‐wall carbon nanotubes and graphitized carbon black and the differences in molecular interaction of adsorbed molecules with crystal C₆₀.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

ABSTRACT

A high yield (～32?wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800–1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis

The role of carbon atoms in a dc plasma-enhanced chemical vapor deposition for carbon nanotubes (CNTs) synthesis was investigated. It was observed that at 1.33 kPa pressure of CH₄ gas in plasma, a high value of the ratio between the intensities of the graphite peak (G peak) and the disorder peak (D peak) in the Raman spectrum corresponds to the maximum value of the excited C number density in the vicinity of the Si substrate. It was found that a CH₄ gas pressure higher than 1.33 kPa leads to an increase of the relative density of the C₂, C₃ molecules and the clusters, and to a decrease of the C excited atom number density in plasma. The presence of a high amount of sp²-graphite in the composition of CNTs observed in Raman spectrum was also confirmed by the measurement of the IR-active G peak at 1584 cm^- 1 in the transmission spectrum.     

Pressure and discharge current dependence of production rate of single-walled carbon nanotubes by the bipolar pulsed arc-discharge method

Bipolar pulsed arc-discharge method has been studied for the efficient production of high quality single-walled carbon nanotubes (SWNTs). Gas pressure and discharge current dependence of this method has been carried out to obtain the optimum production condition. The experimental results show no cathode deposition, and almost all the sublimated carbon becomes soot containing SWNTs. The production rate increases with increasing gas pressure and discharge current. The high production rate with high quality SWNTs is obtained around the conditions of helium gas pressure, p (He) = 50 – 70 kPa and discharge current, I_d ? 55 A. The morphology of the SWNTs is measured by a TEM and the quality is analyzed by a Raman spectrometer.     

由二种烟煤制备碳纳米管的探索性研究

以一种中国烟煤和一种新西兰烟煤为原料,采用电孤等离子体法制备碳纳米管。碳纳米管及其副产物富勒烯烟灰的表征采用扫描电镜（SEM）和红外光谱（FT－IR）等技术。结果表明：电弧放电时的缓冲气体压力对碳纳米管的产率影响很大;在一定的缓冲气压下电极间电流和电极间距各存在一最佳值。在He气压力为0.0665MPa、工作电流为40A条件下进行电弧放电,阴极上棒状沉积物的内芯中碳纳米管含量高达75％以上。基于实验结果,讨论了以煤为原料用电弧等离子体法制备碳纳米管过程中的工艺参数对碳纳米管生长的影响。     

Nano-crystalline CVD diamond films deposited on cemented carbide using high current extended DC arc plasma process

Nano-crystalline diamond (NCD) films have been grown on cemented carbide substrates by high current extended DC arc plasma process using Ar/H₂/CH₄ gas mixture at low gas pressure. The plain view and cross section of films are characterized with scanning electron microscopy. A uniform and smooth surface morphology of NCD thin films is observed. Raman spectroscopy has been used to investigate purity of the NCD films. Experimental results on the synthesis and characterization of the NCD films on cemented carbide substrates are discussed in this article.     

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Abstract

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH₄ molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH₄ molecule is preferentially adsorbed onto the CNT with a binding energy of ?2.84 kcal mol^?1. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of ?3.00 and ?1.44 kcal mol^?1 per adsorbed CH₄ molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.     

Synthesis of graphene flakes using a non-thermal plasma based on magnetically stabilized gliding arc discharge

Abstract

The use of non-thermal plasma at atmospheric pressure has emerged as a technique for the substrate-free, gas-phase synthesis of graphene nanoflakes (GNFs). In this paper, a non-thermal plasma based on magnetically stabilized gliding arc discharge (MSGAD) was employed to prepare GNFs. The effects of the carbon-containing precursor, plasma gas, and arc current on the GNFs synthesis were investigated. The technique produced GNFs with sizes of 50–200?nm and 1–20 layers, spherical carbon nanoparticles with 10–40?nm diameters, and graphitic particles. The results showed that the formation of GNFs depended on the selection of proper process parameters, such as precursors with a high H/C ratio, an Ar-N₂ plasma gas, a low arc current, a low precursor flow rate, and a suitable plasma gas flow rate. Correlations between the process parameters and the product morphology indicated that abundant H atoms and fewer polycyclic aromatic hydrocarbons were favorable for the formation of GNFs.     

Infrared transmission properties of germanium carbon thin films deposited by reactive RF magnetron sputtering

Germanium carbon (GeC) thin films were prepared on ZnS substrates by reactive RF magnetron sputtering in Ar and CH₄ mixtures with a Ge disc as the target. H content in the films was studied as a function of the deposition parameters and low H content GeC film was obtained. RF power had a little effect on IR absorptions, hence had a little effect on H content. IR absorption of the GeC film increased a little with the increase in partial pressure of CH₄ as well as total pressure of gas mixture. Increase in substrate temperature decomposed CH₄ and CH_x in the GeC film into C and H and H was desorbed from the film, lowering the IR absorption. However, high substrate temperature prevented CH₄ or CH_x from adsorbing onto the substrate, which decreased C content in the GeC film and increased the film's refractive index. Higher annealing temperature of the GeC film reduced H content, but high annealing temperature (500 °C) caused the graphitization of the GeC film and destroyed its continuity.     

Gas-liquid detonation synthesis of CNTs@Fe/Fe3C composites and their application as electrode materials for double-layer capacitors

Abstract

The carbon nanotubes doping with Fe and Fe₃C nanocrystal (CNTs@Fe/Fe₃C) are successfully synthesized by the gas-liquid detonation (GLD) decomposition of CH₄, O₂, C₁₀H₁₀Fe and C₁₀H₈. The composition and structural properties of the as-obtained composites were investigated by XRD, TEM, XPS and Raman spectroscopy. The obtained composites were also applied to the electric double-layer capacitor. The results showed that the specific capacitance of CNTs@Fe/Fe₃C can reach 125?F·g^?1 at the current density of 100?mA·g^?1 and after 10000 cycles the capacitance retention is 93.1% at a current density of 2?A·g^?1.     

Synthesis of high quality single-walled carbon nanotubes by arc discharge method in large scale

Single-walled carbon nanotubes (SWNTs) were synthesized by a novel method. The dc arc discharge in H₂-Ar gas atmosphere with Fe₃O₄ as catalyst was used. The morphology and structures of the as-prepared SWNTs were characterized by SEM, HRTEM and Raman spectroscopy techniques. The results indicated that this new catalyst could be used to produce SWNTs with high purity and yield in large scale. The purity and yield of the SWNTs synthesized from these new catalysts were affected by the mixture buffer gas. Based on the overall ease and low-cost advantages of these new catalysts, these results suggest a potential opportunity for cost-effective and commercial production of SWNTs.     

Growth of single and double walled carbon nanotubes over Co/V/MgO catalysts

High quality single walled carbon nanotubes (SWCNTs) and double walled carbon nanotubes (DWCNTs) were synthesized on Co/V/MgO catalysts by catalytic decomposition of CH₄ in H₂. Raman spectroscopy data revealed that the diameters of as-prepared SWCNTs are 1.28 and 0.73 nm. The diameter value of DWCNTs from Raman analysis also showed a narrow diameter distribution. Using field emission transmission electron microscopy (TEM), it was found that the diameter of carbon nanotubes can be controlled mainly by adjusting the molar ratio of Co–V versus the MgO support. The structure properties of catalysts were examined by X-ray diffraction (XRD). The formation of C₇V₈ may play an important role in preserving carbon in the catalyst particle and favoring the dissociation balance of CH₄.     

Influence of gas pressure on low-temperature preparation and film properties of nanocrystalline 3C-SiC thin films by HW-CVD using SiH4/CH4/H2 system

We investigated an influence of gas pressure on low-temperature preparation of nanocrystalline cubic silicon carbide (nc-3C-SiC) films by hot-wire chemical vapour deposition (HW-CVD) using SiH₄/CH₄/H₂ system. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra revealed that the films prepared below 1.5 Torr were Si-nanocrystallite-embedded hydrogenated amorphous SiC. On the other hand, nc-3C-SiC films were successfully prepared at gas pressure above 2 Torr. The high gas pressure plays two important roles in low-temperature preparation of nc-3C-SiC films: (1) leading to sufficient decomposition of CH₄ molecules through a gas phase reaction and an increase in the incorporation of carbon atoms into film and (2) promoting a creation of H radicals on the heated filament, allowing the sufficient coverage of growing film surface and a selective etching of amorphous network structure and/or crystalline-Si phase. It was found that total gas pressure is a key parameter for low-temperature preparation of nc-3C-SiC films.     

Hysteresis,structural and composition characteristics of deposited thin films by reactively sputtered titanium target in Ar/CH4/N2 gas mixture

Abstract

Hysteresis, crystal structure and chemical composition of thin films deposited through reactive sputtering of titanium metal target in Ar/CH₄/N₂ gas mixture have been investigated. The transition from metallic to compound sputtering mode was clearly seen as the reactive gases (CH₄ and N₂) flowrate concentration first increased and subsequently decreased. Abrupt cathode current drop from 273 mA to reach a minimum value of 195 mA was observed upon addition of nitrogen gas from 0 to 10% flowrate concentration to the Ar/CH₄ gas mixture. This was also accompanied by an abrupt change in reactive gas partial pressure. Exploration of the deposition rate and film thickness showed that it decreased from 4·5 to 1·5 nm min^?1 and from 140 to 40 nm as the N₂ flowrate concentration increased from 1·5 to 7·5% at 5·5%CH₄ flowrate concentration respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses of the deposited films confirmed the formation of titanium carbide and carbonitride phases as the methane and nitrogen gas concentrations in the sputtering gas were increased.     

Comparison of Structure and Conductivity of Multiwall Carbon Nanotubes Obtained over Ni and Ni/Fe Catalysts

Abstract

Multiwall carbon nanotubes (MWNT) were produced by pyrolysis of acetonitrile (CH₃CN) on metallic particles of Ni and Ni/Fe at 850°C. The special program for statistical treatment of electron micrograph images was developed. Research of diameter distribution of MWNT grown over different catalysts was carried out. Two kinds of carbon nanotubes with different diameter and microstructure are formed on Ni catalyst. The MWNT with smaller diameter and cylindrical packing of layers were found to have the higher conductivity.     

Multi-phase structured silicon carbon nitride thin films prepared by hot-wire chemical vapour deposition

In this work, Silicon Carbon Nitride (Si-C-N) thin films were deposited by Hot Wire Chemical Vapour Deposition (HWCVD) technique from a gas mixture of silane (SiH₄), methane (CH₄) and nitrogen (N₂). Six sets of Si-C-N thin films were produced and studied. The component gas flow rate ratio (SiH₄:CH₄:N₂) was kept constant for all film samples. The total gas flow-rate (SiH₄ + CH₄ + N₂) was changed for each set of films resulting in different total gas pressure which represented the deposition pressure for each of these films ranging from 40 to 100 Pa. The effects of deposition pressure on the chemical bonding, elemental composition and optical properties of the Si-C-N were studied using Fourier transform infrared (FTIR) spectroscopy, Auger Electron Spectroscopy (AES) and optical transmission spectroscopy respectively. This work shows that the films are silicon rich and multi-phase in structure showing significant presence of hydrogenated amorphous silicon (a-Si:H) phase, amorphous silicon carbide (a-SiC), and amorphous silicon nitride (a-SiN) phases with Si-C being the most dominant. Below 85 Pa, carbon content is low, and the films are more a-Si:H like. At 85 Pa and above, the films become more Si-C like as carbon content is much higher and carbon incorporation influences the optical properties of the films. The properties clearly indicated that the films underwent a transition between two dominant phases and were dependent on pressure.     

Carbon occupancy of interstitial sites in vanadium carbide films deposited by direct current reactive magnetron sputtering

Vanadium carbide thin films were deposited on Si substrates by direct current reactive magnetron sputtering from a V target in Ar/CH₄ plasma, varying the Ar/CH₄ partial pressure ratio and substrate temperature. The films were characterized by glancing angle X-ray diffraction and Rutherford backscattering spectrometry. Well defined crystalline structures were obtained for CH₄ content higher than 13%. The increase of substrate temperature during deposition diminishes the film thickness slightly while diminishing substantially the C/V atomic ratio. The intensity ratio of the Bragg peaks (111)/(200) decreases for increasing substrate temperature. This result is discussed in terms of a proposed mechanism for interstitial diffusion of carbon atoms in vanadium carbide thin films with fcc-like crystalline structure and the temperature dependence of carbon occupancy of tetrahedral or octahedral interstitial sites.