Gas-phase and sample characterizations of multiwall carbon nanotube growth using an atmospheric pressure plasma (original) (raw)
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Diamond and Related Materials, 2004
Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600-3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3-0.6 Pa) systems. CH 4 /H 2 and CH 4 /N 2 were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I-V measurements. The results show that CNTs made by higher plasma pressure system have a higher growth rate (typically 1-3 Am/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lowerfrequency side (or increasing residual tensile stress).
Growth of multiwall carbon nanotubes in an inductively coupled plasma reactor
Journal of Applied Physics, 2002
A high density plasma from a methane-hydrogen mixture is generated in an inductively coupled plasma reactor, and multiwalled carbon nanotubes ͑MWNTs͒ are grown on silicon substrates with multilayered Al/Fe catalysts. The nanotubes are vertically aligned, and the alignment is better than the orientation commonly seen in thermally grown samples. A detailed parametric study varying inductive power, pressure, temperature, gas composition, catalyst thickness, and power to the substrate is undertaken. Transmission electron microscopy and Raman spectroscopy are used to characterize the nanotubes. Emission spectroscopy and a global model are used to characterize the plasma. The power in the lower electrode holding the substrate influences the morphology and results in a transition from MWNTs to nanofibers as the power is increased.
Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis
Thin Solid Films, 2006
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 CH 4 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 CH 4 gas pressure higher than 1.33 kPa leads to an increase of the relative density of the C 2 , C 3 molecules and the clusters, and to a decrease of the C excited atom number density in plasma. The presence of a high amount of sp 2 -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.
2010
The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes (CNTs) by microwave plasma enhanced chemical vapor deposition process has been investigated. Microwave plasma was characterized in-situ using optical emission spectrometer. Morphology of the films was examined by scanning electron microscopy. Structural analysis was carried out by high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDS) and micro-diffraction attachments. It is found that oxide films without H 2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes. The embedded particles were found to be of iron carbide (Fe-C) as confirmed by HRTEM, EDS and micro-diffraction analysis. Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles. Citation: S. K. Srivastava, V. D. Vankar and V. Kumar, "Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes", Nano-Micro Lett. 2, 42-48 (2010).
Advanced Materials Research, 2014
Multi-wall carbon nanotube (MWCNT) structures were grown on cobalt catalyst layer through Plasma Enhanced Chemical Vapor Deposition (PECVD) process. Acetylene (C2H2) and hydrogen (H2) are used as precursors during the PECVD process. The morphology structures of the MWCNTs grown under different PECVD time were investigated and characterized using Scanning Electron Microscope (SEM). The effect of the PECVD time on the MWCNT growth is studied by varying the PECVD time at 45 sec and 600 sec. The morphology structures suggest that the growth rate is proportional to the PECVD time under the similar setting condition of pressure, acetylene flow-rate and temperature.
New continuous gas-phase synthesis of high purity carbon nanotubes by a thermal plasma jet
Carbon, 2004
We have developed a new gas-phase synthesis technique to produce carbon nanotubes (CNTs) with a continuous process and at high temperature, by using a thermal plasma jet. A thermal plasma jet was generated by applying a direct current of 100-300 A, using Ar as the plasma gas with a flow rate of 6ksccm.Thetemperatureofthethermalplasmajetwasveryhigh(6 ksccm. The temperature of the thermal plasma jet was very high (6ksccm.Thetemperatureofthethermalplasmajetwasveryhigh(10 4 K) and the velocity was very fast ($100 m/s). Fe(CO) 5 and CO were used as a catalyst precursor and carbon source, respectively. The yield of CNTs was dramatically increased by attaching a helical extension reactor at the end of the plasma nozzle. High purity ($80%) CNTs were produced with a continuous process by using a thermal plasma jet with helical extension reactor equipment. The number of CNT walls produced was critically affected by the hydrogen gas injected as an auxiliary plasma gas. Without hydrogen gas, singlewalled carbon nanotubes whose diameter was about 1 nm were mostly produced while with hydrogen gas double-walled carbon nanotubes (about 4 nm in diameter) were predominantly produced, with small amount of 3-and 4-walled carbon nanotubes.
Diamond and Related Materials, 2003
The growth behaviour of carbon nanotubes (CNTs), produced by radio-frequency plasma enhanced chemical vapour deposition, is studied here as a function of a CH yAr ratio and Ni catalyst layer thickness. The composition of the plasma mixture was 4 observed as being crucial for the morphology of the nanotubes, indicating a transition from a random to a more uniform orientation, when argon is added to the plasma atmosphere. Scanning tunnelling microscopy shows, as a result of the argon dilution, the formation of a defective structure (i.e. pentagons) at the tip of vertically aligned CNTs while hexagonal atomic arrangement was detected on the sidewall of randomly oriented CNTs deposited by pure methane. The electronic structure of CNTs was then investigated by C 1s' photoemission spectroscopy. The results show a shift of the overall spectral to the higherbinding-energy side, indicating the formation of metallic aligned tubes when argon is added to the plasma atmosphere. Experimental results are applied to develop a coherent picture of the relationship between the deposition parameters and the microstructural features, as well as to check the relationship of the electronic properties predicted for nanotubes with the plasma chemical composition. ᮊ
2007
Carbon nanotubes (CNTs) were synthesized by plasma enhanced chemical vapor deposition from mixture of argon, methane and hydrogen using microwave plasma torch at atmospheric pressure. Nanotubes grew on a complex substrate system consisting of silicon wafer, buffer layer and thin catalytic iron film. As confirmed by scanning electron microscopy (SEM), this deposition technique produces bundles or ropes of nanotubes covered by crust composed of catalytic particles, amorphous carbon and other impurities such as fullerenes or other carbon nanoparticles. Because many scientific and technological applications, as well as characterization techniques require individual nanotubes a great attention has to be paid to the post-deposition processing of the deposit. The nanotube bundle could be separated by ultrasonication of the deposit in organic or inorganic liquid. Most commonly used liquids are water or ethanol. Both liquids proved to be efficient in removing deposited nanotubes from the sub...
Plasma Chemistry and Plasma Processing, 2008
A mixture of acetylene, hydrogen and ammonia (C 2 H 2 /H 2 /NH 3 ) is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor deposition process either without (PE CCVD) or with hot filaments-assistance (PE HF CCVD). A mathematical model based on Chemkin computer package is used for analyzing specific conditions of nanotube synthesis. Simulations are compared with optical emission spectroscopy (OES) measurements. Morphological and structural investigations on the grown carbon nanostructures are also performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that the significant change in the density and the morphology of the CNTs grown in the presence of NH 3 could be mainly explained by the gas phase formation of CN and HCN. Both species display a high etching activity, whereas the species C, CH, CH 2 , CH 2 (S), C 2 and C 2 H are expected to be the most probable carbon nanotube precursors.
Carbon, 2006
High-quality single-walled carbon nanotubes (SWCNTs) have been synthesized from H 2 -CH 4 mixtures on a MgO-supported bimetallic Mo/Co catalyst using microwave plasma-enhanced chemical vapor deposition (PECVD). Reaction parameters including temperature, H 2 :CH 4 ratio, plasma power, and synthesis time have been examined to assess their influence on SWCNT synthesis. Raman spectroscopy and high-resolution field emission scanning electron microscopy reveal that the quality, selectivity, density and predominant diameter of SWCNTs depend on the varied synthesis parameters. Results of this study can be used to optimize SWCNT synthesis conditions and products and to improve understanding of the growth of SWCNTs by PECVD.