Possible tactics to improve the growth of single-walled carbon nanotubes by chemical vapor deposition

Centre for Nanoscale Science and Technology (CNST), College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China
Carbon (Impact Factor: 6.2). 12/2002; 40(14):2693-2698. DOI: 10.1016/S0008-6223(02)00175-6


The growth time, growth mode and the method of preparing the supported catalysts play an important role in the growth of single-walled nanotubes (SWNTs). Their effects on the chemical vapor deposition (CVD) growth of SWNTs with MgO-supported catalysts were investigated in this study. It is shown that the growth rate of SWNTs was large during the initial few minutes of growth, however the quality of the tubes was low owing to the formation of many defects. Long term growth may favor the formation of tubes with high quality and high yield, but the introduction of other forms of carbon (impurities) is also unavoidable. There was a balance between the increase in yield and quality and sacrifice of the purity during growth of SWNTs. MgO-supported catalysts prepared by the co-precipitation method were found to be more effective for the synthesis of SWNTs than those prepared by the widely used impregnation method. The size and dispersion state of the catalyst were found to be crucial in enhancing the growth of SWNTs. In addition, growth on the surface of SWNTs over nanosized catalyst films was shown to be more favorable for the synthesis of tube products with higher quality, yield and purity.

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    • "In particular the A 1g mode zone of CNT–Fe1%–Co1%-800-30, which is presented in the inset of Fig. 2b, exhibits two sharp peaks at 232 cm À1 and 273 cm À1 . The RBM of CNTs corresponds to the coherent vibration of the C atoms in the radial direction and it is characteristic of SWCNTs [8] [42] [43], DWCNTs [40] [44] [45] or a combination of those two [24] synthesized by CCVD and other methods. The RBM position is strongly depended on the CNT diameter and therefore, it can be used to estimate the value of the synthesized tube's diameter. "
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    ABSTRACT: Fe–Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA–TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe–Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe–Co loadings resulted to the formation of multi-wall CNTs.
    Full-text · Article · Oct 2010 · Carbon
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    • "However, we normally synthesis CNT bundles tens to hundreds of microns long in electronics packaging, making this requirement difficult to meet. But improvements can be made by optimization of the growth process [72] [73], post growth annealing at high temperature [74] or by microwave [75]. "
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    ABSTRACT: Carbon nanotubes (CNTs), owing to their fabulous electrical, mechanical and thermal properties, are getting more and more applied into the electronics packaging technology. In this paper, applications of CNTs in electronics packaging field are reviewed, which can be divided into two parts: interconnections and thermal management solutions. Examples such as flip chip bumps, through silicon vias (TSVs), CNT based thermal interface materials (TIMs) and micro coolers are introduced, including a new CNT interconnect method, which is using indium (In) to transfer the CNT bumps from original substrates at low temperature to target substrates. The resistivity of one bump after transfer is around 6.54×10-5 Ω • m, which is one order of magnitude lower than previous results. At the end of this paper, challenges on using CNTs in electronics packaging at an engineering scale are discussed.
    Full-text · Conference Paper · Sep 2010
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    • "DWCNTs would find application in field emission devices [1] and super-tough fibers [2] [3] [4]. In the chemical vapor deposition (CVD) process to prepare DWCNTs, active components are usually deposited on porous supports, such as Al 2 O 3 , MgO, SiO 2 , etc. [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18], which is one of the most important processes due to easy mass production at low cost. Major focus has been put on keeping a high specific surface area (SSA, Brunauer–Emmett–Teller (BET)) and dispersing the metal nanoparticles (NPs) on the catalyst to control the nucleation [10] [13], so as to control the purity and yield of DWCNTs. "
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    ABSTRACT: Double-walled carbon nanotubes (DWCNTs) were prepared from methane using a Fe/MgO porous catalyst. A series of catalyst powders with different pore size distributions were obtained by compression at pressures of 0–233 MPa. These were used to decompose methane and synthesize DWCNTs which differed in activity, purity, yield and degree of perfection. Characterization by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermo-gravimetric analysis, N2 adsorption measurement (Brunauer–Emmett–Teller (BET)) and Hg penetration provided direct evidence that a compact catalyst structure is not good for the nucleation and growth of DWCNTs, e.g., a catalyst with a compact structure that did not have pores larger than 30–50 nm mostly produced multi-walled carbon nanotubes. The confined growth and buckling model of DWCNTs inside the porous catalysts are proposed to explain the growth behavior. These results suggest that a porous catalyst for DWCNT synthesis should have a large pore size distribution or loose stacked structure, which provides new guidelines for catalyst design.
    Full-text · Article · Nov 2008 · Carbon
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