Carbon 40 (2002) 2693–2698
P ossible tactics to improve the growth of single-walled carbon
nanotubes by chemical vapor deposition
Hao Yan, Qingwen Li, Jin Zhang , Zhongfan Liu
Centre for Nanoscale Science and Technology (CNST), College of Chemistry and Molecular Engineering, Peking University,
Beijing 100871, PR China
Received 5 April 2002; accepted 17 May 2002
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
2002 Elsevier Science Ltd. All rights reserved.
Keywords: A. Carbon nanotubes; B. Chemical vapor deposition; C. Raman spectroscopy
1 . Introduction
of the tube products. When a gaseous hydrocarbon flows
over a metal catalyst at high temperature, many forms of
carbon deposits can be produced, such as carbon fiber,
amorphous carbon, multi-walled carbon nanotubes, single-
walled carbon nanotubes, etc. . The forms of carbon
materials are found to be closely dependent upon the types
of carbon source, the properties of the support materials
and the catalytic metals. In general, the successful growth
of SWNTs may be mainly attributed to the formation of
well-dispersed metal nanoparticles, which can be achieved
by choosing suitable support materials. During the CVD
growth of SWNTs, the role of the support materials is not
only to load the metal species, but importantly to prevent
metal particles from aggregating into large clusters, other-
wise MWNTs or other kinds of carbon materials may be
formed. Therefore, many attempts have been made to
prepare supported catalysts for the optimal growth of
SWNTs. For instance, Liu was successful in greatly
improving the yield of SWNTs by using an alumina
aerogel-supported Fe/Mo catalyst ; Dai synthesized
SWNTs by preparing silica/alumina-supported Fe, Co or
Since their discovery in 1991 , carbon nanotubes
have attracted much attention due to their unique prop-
erties [2–4]. At present they can be used as SPM tips ,
to fabricate field-emission devices , synthesize high-
(SWNTs) are especially intriguing, as they have an atomi-
cally well-defined structure, providing an ideal model of
low-dimensional nanostructures. The scaleable synthesis of
SWNTs with high yield and quality is therefore of great
importance for both theoretical research and practical use.
Chemical vapor deposition (CVD) appears to be a
promising method to achieve this , as it is advantageous
compared with other methods such as arc-discharge or
laser-ablation with its low cost, simple apparatus and
multiple adjustable parameters to control the fine structures
*Corresponding author. Tel.: 186-10-6275-2555; fax: 186-
E-mail address: firstname.lastname@example.org (J. Zhang).
0008-6223/02/$ – see front matter
2002 Elsevier Science Ltd. All rights reserved.
H. Yan et al. / Carbon 40 (2002) 2693–2698
particles may ensure sufficient contact with hydrocarbon
molecules, while vertical floating of the catalytic particles
and hexane enable the growth of SWNTs along a preferred
direction and assembles them into long arrays. In sum-
mary, SWNT products of the desired quality and properties
may be obtained by suitable utilization of the catalytic
activities of catalyst particles, growth time and growth
Post Doctoral fellowship granted from the China Education
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4 . Conclusions
We carried out a series of experiments to improve the
CVD synthesis of SWNTs, and found that growth time,
preparation of the catalysts and growth mode greatly affect
SWNT growth. The quality and purity of as-prepared
SWNT products varied with growth time. There was an
optimum time at which we could obtain SWNT products
with acceptable quality and productivity. We further opti-
mized the preparation of the catalyst by changing from a
conventional chemical impregnation method to a novel
co-precipitation method. The catalyst thus obtained was
found to be highly active for SWNT growth with a carbon
yield of up to 40% without further optimization. This high
performance of the catalyst was attributed to reduced
particle size and the excellent dispersion of Fe species over
the MgO support. Finally, we prepared a catalyst-coated
Si(111) surface by a sol–gel method which was found to
be even more effective for SWNT growth and the SWNTs
deposited on it formed a dense film.
JE. ChemPhys Lett
We are grateful for financial support from the National
Natural Science Foundation of China (NSFC 6989022,
59910161982, 29973001, 30000044), the Ministry of
Science and Technology of China (2001CB6105) and a