Materials Sciences and Applicatio n, 2011, 2, 922-935
doi:10.4236/msa.2011.27123 Published Online July 2011 (http://www.SciRP.org/journal/msa)
Synthesis of Carbon Nano Tubes on Silicon
Substrates Using Alcohol Catalytic Chemical
Vapor Deposition
Mohammad Abu-Abdeen1,2, Abdu Allah Aljaafari1
1Physics Department, College of Science, King Faisal University, Al-Hassa, Kingdom of Saudi Arabia; 2Physics Department, Col-
lege of Science, Cairo University, Giza, Egypt.
Received October 20th, 2010; revised December 13th, 2010; accepted May 21st, 2011.
ABSTRACT
The technique used for synthesizing large quantity carbon nanotubes (CNTs) directly on the surface of silicon sub-
strates has been developed by means of the alcohol catalyst chemical vapor deposition ACCVD method using ethanol.
The proposed method adopts an easy and costless liquid-based dip-coat approach for mounting the catalytic metals on
the substrates. Reasonable quality formation of catalyst preparation was found at 5 min of dipping the substrate into
cobalt acetate solution and withdrawing at speed of 4 cm/min followed by heat treatment at 400˚C. Cobalt acetate
catalyst on silicon substrates were analyzed using an atomic force microscopy (AFM) and scanning electron micros-
copy (SEM). The substrate surface is blackened with a layer of CNTs after the ACCVD at an optimum condition. The
grown CNTs were analyzed using transmission electron microscopy TEM, SEM, XRD, UV/Vis-NIR spectroscopy and
photoacoustic (PA) measurements of thermal parameters. Large quantities of single and multi walled carbon nanotubes
were grown at a growth time of 50 min and growth temperatures of 800˚C and 900˚C. UV-Vis/NIR spectroscopy de-
tected two absorption peaks at 0.78 and 1.35 eV and optical energy gap (Eopt) of 1.16 eV for CNTs grown at 800˚C. The
PA measurements of thermal parameters detected maximum values of thermal diffusivity, effusivity and conductivity for
those grown at 800˚C.
Keywords: CNTs, ACCVD, Dip Coating, Synthesis, Catalysts, Optical, Thermal
1. Introduction
Carbon nanotubes (CNTs) have recently gained great
interest in science and industry due to their highly con-
siderable promises in enabling the future nano-structured
materials with novel properties [1,2]. In this respect,
CNTs with their huge aspect ratio in combination with
high strength and stiffness have become potential rein-
forcing constituents to get common engineering polymers
into multi-functional composites with superior properties
such as conductive polymers with improved mechanical
performance [1,3]. Despite many reported studies in the
literature, the achievement of the desired improvement via
CNTs in final properties of their polymer based compos-
ites has not been successfully realized so far [4-6].
Carbon nano tubes have been drawing increasing at-
tention [7,8] since their discovery [9]. CNTs is divided
into single walled (SWCNTs), double walled (DWCNTs)
and multi walled (MWCNTs). Various synthetic methods
have been developed for the production of CNTs, in-
cluding arcdischarge [10-12], laser ablation [13], pyroly-
sis [14], plasma enhanced [15] and thermal chemical
vapor deposition (CVD) [16]. In the last few years, CVD
has been the preferred method among different methods
because of its potential advantage to produce a large
amount of CNTs growing directly on a desired substrate
with high purity, large yield, and controlled alignment,
whereas the nano tubes must be collected separately in
the other growth techniques. Depending on the final ap-
plication, thermal CVD could be even more desirable than
plasma CVD because thermal CVD processes are more
economical, suitable for large-area, irregular-shaped sub-
strates, and multiple-substrate coatings [17,18]. Addition-
ally, using CVD one can control the diameter [18,19],
length and orientation [19,20] of the nano tubes. Various
CVD methods are now available for SWCNTs synthesis,
including disproportionation of CO [21-23], high pres-
sure catalytic decomposition of carbon monoxide (HiPCO)

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition923
[24,25] and the recently introduced alcohol catalytic
chemical vapor deposition (ACCVD) [26-32]. In the
ACCVD method developed by Maruyama et al [26], bi-
metallic Fe–Co nano-particles impregnated into zeolite
supports are used as the catalysts and alcohol vapor is
used as the carbon source to obtain SWCNTs with high
purity at 800˚C. The high purity is attributed to OH radi-
cals associated with alcohols, which effectively removes
the amorphous carbon during growth. This method is
economical and offers advantages such as low synthesis
temperature, simplicity and high yield as determined by a
thermal gravimetric analyzer (TGA) [28]. The ACCVD
method was also used to synthesize SWCNTs on sub-
strates such as quartz, silicon [28,30] and meso porous
silica [29]. Dip coating was utilized for loading catalyst
particles onto the substrates, and either randomly [28]
or vertically aligned [30,31] SWCNTs were obtained.
The vertically aligned SWCNTs were obtained by util-
izing a good background vacuum and low leak condi-
tions. In addition to the work of Maruyama et al., alco-
hol vapor has also been shown to be an effective carbon
source for synthesis of SWCNTs by other groups [33-
35].
In this work, we will report on the growth of CNTs
using the ACCVD method. We will perform a parametric
study of various factors influencing both the preparation
of catalyst and the growth of carbon nanotubes. Specifi-
cally, we will investigate the effect of the time of immer-
sion of Si substrates in cobalt acetate solution as well as
the temperature of heat treatment for the prepared cata-
lysts. The effect of growth temperature on the character-
istics of grown CNTs will also be investigated. Analysis
of the prepared CNTs will be done using SEM, TEM,
UV-Vis/NIR spectroscopy. Thermal parameters of the
grown CNTs will also be studied.
2. Experimental Details
2.1. Preparation of Catalyst
Metal acetate solution was prepared first by dissolving
cobalt acetate (CH3COOH)2Co-4H2O (99.999%, Sigma-
Aldrich) into ethanol (typically 42 mg of cobalt acetate in
10 ml of ethanol) so that the concentration of each metal-
lic species was 0.01 wt% with stirring for 10 min fol-
lowed by sonication for 2 h at room temperature. The
choice of Co catalyst because of its better performance
over the others, at least, in the tested range of metallic
concentrations and CVD conditions [29].
For a substrate, we employed p-type Si wafer with
(100) surface polished at one surface (University Wafers,
USA) and a thickness of 0.5 mm. The substrate was cut
into a strip of about 10 × 25 mm2. The substrate was
cleaned by consecutive acetone sonication for 5 min,
washed with DI water and blown with dry nitrogen.
The dip coating method was applied to substrates. The
substrate was held by a small clip with a stabilizing
weight and a nylon fishing line. The substrate piece was
then submerged vertically into a prepared metallic ace-
tate solution for different times (typically 5 and 10 min),
leaving upper 5 mm of it above the solution level to pre-
vent the clip from contacting the solution. This piece was
then drawn up from the solution at a constant speed of 4
cm/min. The surface of the substrate was rapidly dried at
several millimeters above the liquid contact level as soon
as it was removed from the solution. Right after this
process, the piece was placed in a furnace and main-
tained at 400˚C or 500˚C for 5 or 10 min.
2.2. Growth of Carbon Nano Tubes
CNTs were grown via the alcohol catalytic chemical va-
por deposition (ACCVD) technique using a 50 cm long
ceramic tube furnace and diameter of 12 cm as shown
schematically in Figure 1. The reasons behind the choice
of this method are low coast one and produces a large
quantity of CNTs [36]. The growth process followed the
following procedure. Cobalt acetate supported catalyst
was placed into alumina combustion boat; whereas a 10˚
inclined graphite stage was used to support the substrates
and the group was then placed at the center of the tube
furnace. The tube was evacuated to 150 mTorr, and sam-
ples were heated to the desired reaction temperature un-
der 250 sccm of flowing argon. Once the growth tem-
perature was reached (depending on the growth tem-
perature), samples were held at that temperature for 5
min. The argon was then shut off and the tube was
evacuated before the introduction of alcohol vapor. The
alcohol vapor (ethanol) was then transferred into the tube
furnace to achieve a pressure of 5 - 10 Torr. The alcohol
flow rate in the growth chamber was controlled by con-
trolling the alcohol bath temperature. After growth, the
alcohol vapor was evacuated, argon was introduced again
and the reaction tube was cooled to room temperature.
CNTs growth time was kept constant at 50 min unless
otherwise stated.
2.3. Characterization of Catalysts and Carbon
Nano Tubes
2.3.1. AFM, SEM, TEM and XRD
Surface analysis was performed using a Pico scan
Agilent AFM contact mode in order to confirm the pres-
ence of nano particles catalysis that distributed above the
Si substrate surface.
SEM studies were performed on a JSM-6380 high
resolution scanning electron microscope operated at 20
kV in KSU, Saudi Arabia. Furthermore, nanotubes
grown in powder form were sonicated in methanol and
placed onto holey/lacey carbon coated copper grids for

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 924
Figure 1. Schematic presentation of the apparatus used in
the growth of CNT.
TEM (Model 1011 JEM at 100 KV KSU, Saudi Arabia)
observations to confirm both their existence and morpho-
logy.
The phase purity of the samples is examined using
X-ray diffractometer with Cu-K radiation, 40 mA and
45 KV.
2.3.2. Optical Measurements
The absorption spectra of the prepared CNTs were
measured using a scanning double beam UV-Vis/NIR
spectrophotometer (Shimadzu, Model 1601) in the wave-
length range 190 - 3000 nm at room temperature. The
absorbance “A” was calculated according to the Beer-
Lambert Law equation:
10
1
log
o
A
I



(1)
where, I is the transmission intensity through the sample
and Io is the intensity through the air gap as a reference.
The absorption spectra are presented as the absorbance
versus wave length (nm) and energy (eV). The absorp-
tion coefficient α of the samples composite was calcu-
lated from the optical absorption spectrum using the rela-
tion:
( )2.303
A
d
  (2)
where d is the sample thickness in cm and A is the ab-
sorbance [37-39].
2.3.3. Photoacoustic Measurements (PA)
A schematic diagram of the PA experimental set-up is
presented in Figure 2. The PA measurements were car-
ried out by Gas-microphone detection method. A xenon
arc lamp was used as the light source. A monochromatic
light beam at a fixed wavelength was obtained by passing
the light through a monochromator. The light was modu-
lated with a mechanical chopper and focused on the sur-
face of a sample placed inside a sealed PA cell. The light
absorbed by the sample is converted into heat by nonra-
Figure 2. Schematic presentation of the Photoacoustic ex-
perimental set-up.
diative relaxation processes and results in pressure fluc-
tuations in the air inside the cell. The amplitude of the
detected signal (by the microphone enclosed in the PA
cell) as a function of modulation frequency is recorded
using a dual channel digital lock-in amplifier (SR830).
Sample holder was filled of samples (in the powder
form), then entered into the PA chamber. The overall
thickness of the sample is determined by the holder depth.
For thermal effusivity measurements, the reference sam-
ple was Si wafer of known effusivity (1.5 Ws1/2/cm2K).
3. Results and Discussions
3.1. Optimization of Catalyst Composition
Catalysts were prepared at different conditions to achieve
the smallest available dimensions of particles on the sub-
strate. The morphology of the substrate surface is very
important to understand the particles (dispersed phase)
distribution because it is the most important aspect which
governs the growth of CNTs. SEM analysis of the sub-
strates allows for the observation of a peculiar experi-
mental feature. Figures 3(a) and (b) show the SEM mi-
crographs of two substrates immersed in cobalt acetate
solution for 10 min and then transferred to a box furnace
and heated in air to 500˚C and 400˚C, respectively. The
dispersed morphology could be witnessed by the figures.
The cobalt particles are homogeneous and uniformly
distributed over the surface of the substrates. The parti-
cles formed have approximately a spherical shape. The
average minimum diameters of these particles for both
conditions are 68 and 38 nm for catalysts heated at 500
and 400˚C respectively. On the other hand, particles
formed on substrates with 5 min immersion in cobalt
acetate, withdrawn at 4 cm/min and heated at 400˚C have
average minimum diameter of 9 nm as shown in Figure
3(c). The resolution of the used SEM is not high enough

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 925
(a)
(b)
(c)
Figure 4. Three dimensional images of catalysts prepared at
(a) 500˚C after immersion in cobalt acetate solution for 10
min, (b) 400˚C after immersion in cobalt acetate solution
for 10 min and (c) 400˚C after immersion in cobalt acetate
solution for 5 min.
these features is about 96 nm. In case of Figures 4(b)
and 4(c) these features have heights of 106 and 13 nm,
respectively. Fine detailed particles are, also present in
Figure 4(c). Figures 6 and 7 show the section analysis of
these substrates. Figure 6 detects maximum heights
(z-direction) of 108, 35.5, and 4 nm for the particles
formed on substrates thermally treated at 500˚C with
immersion time 10 min, 500˚C with immersion time 10
min and 400˚C with immersion time of 5 min, respec-
tively. The average length (y-direction) of these particles
are found to equal 114, 42, and 4.5 nm for same sub-
strates as shown in Figure 7.
Figure 3. SEM micrographs for catalysts (a) immersed in
cobalt acetate solution for 10 min and heated to 500˚C and
(b) immersed in cobalt acetate solution for 10 min and
heated to 400˚C. and (c) immersed in cobalt acetate solution
for 5 min and heated to 400˚C.
to show the detailed features of the surfaces, accordingly
AFM is used to follow up more details.
Figures 4 and 5 illustrate the AFM three and two di-
mensional topography of catalysts prepared at tempera-
tures 500˚C, 400˚C after immersion in cobalt acetate so-
lution for 10 min and 400˚C after immersion in the solu-
tion for 5 min only. These scans are acquired at 2 μm
except for figures 4(c) and 5(c), which acquired at 0.5 m.
The scans are done in air at 25˚C and scan rate of 1 Hz. It
appears from Figures 4(a-c) that the surfaces are rough
with two different types of small and large dispersed par-
ticles. Additionally, narrow features are present along the
edges of the large particles of Figure 4(a). The height of
Statistical parameters of the particles dispersed on
these different substrates prepared at different conditions
are listed in Table 1. It is clear that the minimum parti-
cles parameters appear for substrates immersed in cobalt
acetate solution for 5 min and then heated in air up to
400˚C.
3.2. Growth of Carbon Nano Tubes
In ACCVD method for growing CNTs there are many
factors affect the growth namely, growth time, carbon

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 926
Figure 5. Two dimensional images of catalysts prepared at (a) 500˚C after immersion in cobalt acetate solution for 10 min, (b)
400˚C after immersion in cobalt acetate solution for 10 min and (c) 400˚C after immersion in cobalt acetate solution for 5
min.
(a) (b) (c)
Figure 6. 051 (z-direction) of the particles formed prepared at (a) 500˚C after immersion in cobalt acetate solution for 10 min,
(b) 400˚C after immersion in cobalt acetate solution for 10 min and (c) 400˚C after immersion in cobalt acetate solution for 5
min.
(a) (b) (c)
Figure 7. Lengths distribution (y-direction) of the particles formed prepared at (a) 500˚C after immersion in cobalt acetate
solution for 10 min, (b) 400˚C after immersion in cobalt acetate solution for 10 min and (c) 400˚C after immersion in cobalt
acetate solution for 5 min.

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 927
Table 1. Statistical parameters for catalysts prepared at different conditions.
Parameter Substrate prepared at 10 min and
heated to 500˚C
Substrate prepared at 10 min
and heated to 400˚C
Substrate prepared at 5 min and
heated to 400˚C
Average value (nm) 27.38 8.40 2.24
Maximum (nm) 92.59 110.8 12.53
Median (nm) 26.43 5.8 1.98
Ra (nm) 6.08 4.8 0.64
Rms (nm) 8.82 9.0 1.04
source and growth temperature [36]. The change in al-
cohol flow rate does not affect the properties of grown
CNTs [36]. In this work, the growth time is fixed at 50
min and the carbon source used is ethanol and its flow
rate is fixed by fixing the temperature of the hot plate
used to heat it. The growth temperature is changed at
400˚C, 500˚C, 700˚C, 800˚C and 900˚C. SEM images of
the nano tubes grown on cobalt acetate substrate at these
temperatures are shown in Figures 8(a)–(e). At tem-
peratures 400˚C and 500˚C, carbon appears to be a nano
Figure 8. SEM images of CNT grown on cobalt acetate catalyst on Si substrate at (a) 400˚C, (b) 500˚C, (c) 700˚C, (d) 800˚C
and (e) 900˚C.

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 928
powder of particle size ranging from 20 to 58.5 nm, re-
spectively. At a higher temperature of 700˚C, multiwalled
carbon nano tubes with outer diameters ranging from ap-
proximately 12 to 37 nm appear beside the carbon nano
powder as shown in Figure 9(a). On the other hand, the
grown nanotubes at ˚C at same growth time appear to be
mainly bundles of single walled carbon nanotubes with an
average diameter of 1.6 nm as shown in Figure 9(b). At a
growth temperature of 900˚C the majority of grown
nanotubes are multiwalled besides a little of single walled
carbon nanotubes bundles as shown in Figure 9(c).
3.3. XRD Analysis
Figure 10 shows the XRD pattern for as prepared CNTs
at temperatures (a) 800˚C and (b) 900˚C, respectively.
The patterns confirm that the powders prepared by using
ACCVD are CNTs with (002), (101), and (004) orienta-
tions [40-42]. The positions of these orientations are
slightly shifted. The values of 2 for these planes at
800˚C are 26.097˚, 44.783˚ and 52.013˚, respectively,
while they become 26.364˚, 44.654˚ and 52.135˚, respec-
tively, when the growth temperature equal 900˚C. The
d-spacing of these planes are 3.425, 2.024 and 1.757 Ao,
respectively for CNTs formed at 800˚C while for those
prepared at 900˚C the d-spacing values are 3.381, 2.029
and 1.753 Ao respectively. The XRD of SWCNTs is
characterized by a small relative intensity of the peak
located at 2 equal 26.097˚ [31].
Figure 9. TEM images of CNTs grown on cobalt acetate catalyst on Si substrate at (a) 700˚C, (b) 800˚C, (c) 900˚C.

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition929
(a)
(b)
Figure 10. XRD patterns for CNTs grown at (a) 800˚C and (b) 900˚C.
3.4. Uv-Vis/NIR Spectroscopy
Jeong, M. S. and Byeon, C. C. [43] reported that the ab-
sorption spectrum of SWCNTs mainly consists of three
absorption peaks. The first one is at around 0.8 eV (S11)
and the second is at around 1.2 eV (S22) while the third
one (M11) is at around 1.75 eV. The first two peaks cor-
responding to absorption characteristics of semiconduct-
ing SWCNTs. The third peak corresponds to the valence
band conduction band transition of metallic SWCNT.
Besides, Kim, D.Y. et al. [38], show that the optical ab-
sorbance increases with increasing average CNTs length.
However, one of the power full analyses used to recog-
nize both the existence and quality of SWCNTs is UV-
visible and NIR spectra [43-45].
In the present work, UV-visible and NIR spectra for
CNTs prepared at 700˚C and 800˚C were measured in the
spectrum range 200 - 3000 nm. Figure 11 shows the
UV-visible absorbance spectra for the prepared CNTs at
temperatures 700˚C and 800˚C, respectively. Figure 12
shows the absorption spectra as a function of photon en-
ergy at NIR region. From Figure 12(a), one can clearly
observe the characteristic peaks (peak I and peak II) for
CNT at around 0.78 eV and 1.35 eV [44] when the
preparation temperature is 800˚C. Such results indicate
that the prepared CNTs are mostly single walled type at
least at preparation temperature of 800˚C. Furthermore,
the increase of the absorbance in Figure 12 when the

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 930
Figure 11. UV-Vis absorption spectra of the prepared CNTs
at 700˚C and 800oC.
(a)
(b)
Figure 12. NIR absorption spectra of the prepared CNTs at
700˚C and 800˚C.
preparation temperature is 800˚C reveals that the CNTs
lengths are increased and as a result their aspect ratios
are also increased [38]. From the above results, one can
say that the optimum temperature for SWCNTs prepara-
tion with high aspect ratio is 800˚C.
Chen D et al. [45] reported that semiconducting
SWCNTs has a direct band-gap and the value of the op-
tical energy gap is located in the range from 0.5 eV up to
above 1.2 eV. In the present work we use Mott, Davis,
and Tauc formula [46]:

,
() 0
opt opt
opt
r
hEh E
hhE
 
 





(3)
where  is the absorption coefficient,
  is the fre-
quency of light,
 is a constant equals to (4πσ0/ncΔE), σ0
is the extrapolated DC conductivity, ΔE is the energy gap
tail (or energy which is interpreted as the width of the tail
of localized states in the forbidden band gap), n is the
refractive index, Eopt is the optical energy gap and r is an
index. The value of r determines the type of electronic
transition causing the optical absorption; it can take val-
ues 1/2, 3/2, 2, and 3 for direct-allowed, direct-forbidden,
indirect-allowed, and indirect-forbidden transitions, re-
spectively. It was found that the transition type is direct
with r =0.5 for both CNTs prepared at 700˚C (Figure
13(a)) and 800˚C (Figure 13(b)). The value of the opti-
cal energy gap is about 1.16 eV. This result is in a good
agreement with those reported by Chen, D. et al. [45].
From the above analysis, we can say that the prepared
CNTs are mainly semiconducting SWCNTs and the as
pect ratio is clearly improved when the preparation tem-
perature elevated up to 800 C.
3.5. Photoacoustic (PA) Measurements of
Thermal Parameters
For thermal properties measurements of the samples at
room temperature, the variation of the PA signal is ob-
served at different chopping frequencies. This depth pro-
filing was used for the measurement of the thermal diffu-
sivity using the characteristic frequency (fc) for each of
the samples.
The main idea of PA technique is that the sample is
placed in a closed chamber filled with a gas such as air
and illuminated with monochromatic radiation of any
desired wavelength, with intensity modulated at some
suitable acoustic frequency; the non-radiative decay of
the absorbed radiation results in a periodic heat diffused
from the sample to the air adjacent to the sample surface.
This temperature variation produces a pressure fluctua-
tion in the air within the cell which is detected as an
acoustic signal by a sensitive microphone attached to the
chamber. Accordingly, the PA signal contains informa-

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition931
(a)
(b)
Figure 13. (h)2 as a function of light energy for CNTs
prepared at 700˚C and 800˚C.
tion about the optical absorption within the sample in
addition to the way with which the heat is diffused
through the sample.
It has been proved that the pressure variations depend
on the relationship among three “length” parameters of
the sample: the sample thickness ℓ, the optical absorption
length
 B  and the thermal diffusion length  . The pres-
sure variations at the front surface of an optically opaque
material (ℓ >
 B) can be written as the product of two
terms, one depends on f and the other independent of f.
When f > fc the variations of the frequency dependent
term is independent of thermal diffusivity (
 ) and when f
< fc the variations in PA signal depends on that can be
calculated from [47]
2
c
f
  (4)
Here the characteristic frequency fc is defined as the
frequency at which the sample goes from thermally thick
(  < ℓ) to thermally thin (  > ℓ) region [47]. At this fre-
quency, a distinct change in the slope of log (frequency)
versus log (amplitude) plot occurs and knowing ℓ we can
calculate. The PA amplitude as a function of the fre-
quency (log-log plot) is shown in Figure 14. It is easily
observed that there is a distinct change in slope, at a fre-
quency fc where crossover takes place and thermal diffu-
sivity is calculated and listed in Table 2.
In the case of front surface illumination configuration
optically opaque and thermally thick samples, the PA
signal is given by
*
e
A
q
f
 (5)
where A* is constant and e is the thermal effusivity. Us-
ing Si as a standard material of known effusivity, the
constant A* can be determined and applied to calculate
the unknown effusivity of the sample. The plots of PA
amplitude versus the inverse of chopping frequency for
CNTs grown at 700˚C, 800˚C and 900˚C and their refer-
ences are given in Figure 15. The calculated values of
the thermal effusivity are listed in Table 2.
Thermal conductivity can be calculated using the rela-
tion ke

 and the calculated values are presented in
Table 2 with a maximum value of 170.4 (W/mK) is re-
corded for CNTs grown at 800˚C.
In comparison with the literature, Hone et al. [48]
measured the thermal conductivity of crystalline ropes of
SWNT’s and obtained a value of 35 W/mK at room tem-
perature. One year later, the former authors reported a
value of 200 W/mK for magnetically aligned SWNT film
[49] which is in agreement with our prepared CNTs at
800˚C. However, experimental measurements of thermal
conductivity of SWCNTs made by Dong Zhan et al. [50]
indicated that aligned bundles of theses CNTs show a
value of 250 W/mK and only 2.3 W/m K for sintered
samples.
4. Conclusions
The preparation of catalyst using dip coating a silicon
substrate into a diluted solution of cobalt acetate is stud-
ied as a function of time of dipping the substrate inside
the solution and different heat treatment temperatures.
The optimum time and temperature for preparing cata-
lysts with nano particles with diameters ranging from 5
to 10 nm are 5 min and 400˚C.
The growth of CNTs using the ACCVD method is per-
formed as a function of growth temperature and at con-
stant growth time, alcohol flow rate, catalyst concentra-
tion and carbon source. Carbon nanopowder is observed
at preparation temperatures of 400˚C and 500˚C. Mixture
of multiwalled carbon nanotubes and carbon nanopowder
is achieved at a growth temperature of 700˚C. Bundles of
single walled carbon nanotubes with a little multwalled

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 932
(a)
(a)
(b)
(b)
(c)
Figure 15. PA signal versus 1/f for CNTs prepared at dif-
ferent temperatures.
ones are grown at 800˚C. A majority of multiwalled
nanotubes and little bundles of single walled CNTs are
grown at temperature of 900˚C. CNTs grown at tem-
perature of 800˚C are in the range of semiconducting
(c)
Figure 14．PA amplitude as a function of ln(f) for CNTs
prepared at different temperatures.

Synthesis of Carbon Nano Tubes on Silicon Substrates Using Alcohol Catalytic Chemical Vapor Deposition 933
Table 2. Thermal diffusivity, effusivity and conductivity of prepared CNTs at different temperatures.
Synthesis temperature (˚C) Diffusivity (cm2/s) Effusivity (Ws1/2 /cm2K) Thermal conductivity (W/mK)
700 1 0.48 48
800 1.72 1.3 170.4
900 1.2 1.083 118.6
single walled carbon nanotubes with an optical energy
gap of 1.16 eV and also, have maximum thermal conduc-
tivity of 170.4 (W/mK).
Besides, the features of the used technique lie in its
easy, costless, and versatile nature in addition to its easi-
ness to mount a small amount of catalytic metals by us-
ing diluted metal acetate solution. This method can be
applied toward solids of various geometries without ne-
cessitating deposition/sputtering devices.
5. Acknowledgements
The authors acknowledge the King Abdelaziz City for
Science and Technology (KACST), Saudi Arabia for
funding and providing the facilities required for this in-
vestigation.
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