Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method
The carbon nanostructure composed of an array of vertically aligned carbon nanotubes (CNTs) and a planar graphite layer (PGL) located at the top of the array has been obtained by the injection chemical vapor deposition method, realized using high temperature catalytic pyrolysis of xylene-ferrocen...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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nasplib_isofts_kiev_ua-123456789-1182102025-06-03T16:26:26Z Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method Labunov, V.A. Shulitski, B.G. Prudnikava, A.L. Shaman, Y.P. Basaev, A.S. The carbon nanostructure composed of an array of vertically aligned carbon nanotubes (CNTs) and a planar graphite layer (PGL) located at the top of the array has been obtained by the injection chemical vapor deposition method, realized using high temperature catalytic pyrolysis of xylene-ferrocene mixture. The carbon nature of the planar layer was identified using Auger electron spectroscopy. Scanning electron microscopy analysis enabled to ascertain peculiarities of CNT-PGL nanostructure morphology, in particular, the internal layer-built structure of PGL and its links with the underlying CNT array. The mechanism of CNT-PGL nanostructure formation was considered. The authors acknowledge the BelMicroSystems R&D Center, Minsk for giving us an opportunity to perform SEM investigations, and the Institute of Heat and Mass Transfer, Minsk, in particular Prof. S.A. Filatov, for EDX measurements. 2010 Article Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method/ V.A. Labunov, B.G. Shulitski, A.L. Prudnikava, Y.P. Shaman, A.S. Basaev // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 2. — С. 137-141. — Бібліогр.: 10 назв. — англ. 1560-8034 PACS 61.46.-w, 61.46.Fg, 61.48.De https://nasplib.isofts.kiev.ua/handle/123456789/118210 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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English |
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The carbon nanostructure composed of an array of vertically aligned carbon
nanotubes (CNTs) and a planar graphite layer (PGL) located at the top of the array has
been obtained by the injection chemical vapor deposition method, realized using high
temperature catalytic pyrolysis of xylene-ferrocene mixture. The carbon nature of the
planar layer was identified using Auger electron spectroscopy. Scanning electron
microscopy analysis enabled to ascertain peculiarities of CNT-PGL nanostructure
morphology, in particular, the internal layer-built structure of PGL and its links with the
underlying CNT array. The mechanism of CNT-PGL nanostructure formation was
considered. |
| format |
Article |
| author |
Labunov, V.A. Shulitski, B.G. Prudnikava, A.L. Shaman, Y.P. Basaev, A.S. |
| spellingShingle |
Labunov, V.A. Shulitski, B.G. Prudnikava, A.L. Shaman, Y.P. Basaev, A.S. Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Labunov, V.A. Shulitski, B.G. Prudnikava, A.L. Shaman, Y.P. Basaev, A.S. |
| author_sort |
Labunov, V.A. |
| title |
Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method |
| title_short |
Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method |
| title_full |
Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method |
| title_fullStr |
Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method |
| title_full_unstemmed |
Composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection CVD method |
| title_sort |
composite nanostructure of vertically aligned carbon nanotube array and planar graphite layer obtained by the injection cvd method |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2010 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118210 |
| citation_txt |
Composite nanostructure of vertically aligned carbon nanotube
array and planar graphite layer obtained
by the injection CVD method/ V.A. Labunov, B.G. Shulitski, A.L. Prudnikava, Y.P. Shaman, A.S. Basaev // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 2. — С. 137-141. — Бібліогр.: 10 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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| first_indexed |
2025-11-24T10:13:55Z |
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2025-11-24T10:13:55Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 2. P. 137-141.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
137
PACS 61.46.-w, 61.46.Fg, 61.48.De
Composite nanostructure of vertically aligned carbon nanotube
array and planar graphite layer obtained
by the injection CVD method
V.A. Labunov1, B.G. Shulitski1, A.L. Prudnikava1, Y.P. Shaman1, A.S. Basaev2
1The Belarusian State University of Informatics and Radioelectronics,
Laboratory of Integrated Micro- and Nanosystems,
Minsk, 220013 Belarus, Phone/Fax: +375 17 202-10-05
2Technological Center, Moscow State Institute of Electronic Technology,
Moscow, K-498, 103498 Russia, Phone: +7(095) 532-8906; fax: +7(095) 913-2192
Abstract. The carbon nanostructure composed of an array of vertically aligned carbon
nanotubes (CNTs) and a planar graphite layer (PGL) located at the top of the array has
been obtained by the injection chemical vapor deposition method, realized using high
temperature catalytic pyrolysis of xylene-ferrocene mixture. The carbon nature of the
planar layer was identified using Auger electron spectroscopy. Scanning electron
microscopy analysis enabled to ascertain peculiarities of CNT-PGL nanostructure
morphology, in particular, the internal layer-built structure of PGL and its links with the
underlying CNT array. The mechanism of CNT-PGL nanostructure formation was
considered.
Keywords: carbon nanotubes, graphite, graphene, chemical vapor deposition, ferrocene,
xylene.
Manuscript received 14.01.10; accepted for publication 25.03.10; published online 30.04.10.
The unique electrophysical, chemical and mechanical
properties of carbon nanotubes (CNTs) predetermine a
variety of the areas of their application [1]. These areas
can be considerably extended due to composite
nanostructures and branch architecture creation on the
CNT basis, especially in a combination with different
allotropic forms of carbon.
Presently, some of these composite nanostructures
have been created, for example, CNTs filled with
fullerenes, the so-called “peapods” [2], and
nanostructures composed of an array of vertically
aligned CNTs and a planar graphite layer located at the
top of the array [3]. The composite nanostructure
obtained by Kondo et al. [3] was grown using high
temperature catalytic pyrolysis of acetylene at the low
pressure (1000 Pa) by using localized bimetallic catalyst
Co/TiN preliminary deposited on Si/SiO2 substrate.
This investigation is aimed at creation of the
composite nanostructure like to that in ref. 3, but using
the injection CVD method as the most simple and
controllable one.
The composite carbon nanostructure was
synthesized by the injection CVD method (with the
injected catalyst) using a feeding solution of ferrocene
([Fe(C5H5)2], Aldrich) in fluid hydrocarbon (p-xylene
[С8Н10], Aldrich) which was injected into the reaction
zone of the tubular silica reactor of 10 mm in diameter.
Argon was used as a gas-carrier with the constant flow
(100 cm3·min-1) through the reactor. The synthesis
process was carried out at the temperature 850 ºC for
60 min under atmospheric pressure by using 1.0 wt.%
feeding solution. Wafers of n-type silicon covered with
100-nm thermally grown SiO2 were used as substrates.
Under the mentioned above conditions, the
composite nanostructure consisting of the array of
vertically aligned CNTs and a self-organized planar
layer located at the top of the array was obtained
(Fig. 1).
The SEM image of the obtained composite
nanostructure (Fig. 1a) is presented in a convenient
aspect angle for its analysis. The cleavage of
nanostructure was done in a way that permits to observe
not only the planar layer and CNT array but the substrate
surface open after deleting a part of the composite
nanostructure.
From Fig. 1a, one can conclude that the composite
nanostructure has a height of ~2.3 µm, it is very firm
(not destroyed during the mechanical cleavage), and
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 2. P. 137-141.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
138
CNT array has good adhesion both to the upper planar
layer and to the substrate. Using the Auger electron
spectroscopy (AES) method (Fig. 1b), it was established
that the only element of the planar layer is carbon with
the negligible amount of Fe. It means that we obtained
CNT-planar graphite layer (PGL) nanostructure, which
we designate as “CNT-PGL nanostructure”.
In Fig. 2, the SEM images of CNT-PGL
nanostructure for various aspect angles and
magnifications are presented. In Fig. 2a, it is seen that
PGL represents the layer-built structure, which was
designated in ref. 3 as a “graphene multi-layer”. One
should note that the surface of this layer is very rough in
a nanoscale. The thickness of PGL is close to ~25 nm.
Fig. 2b demonstrates the incorporation of separate CNTs
into PGL through the catalyst nanoclusters, which
ensures strong adhesion of CNTs to PGL. Data of Fig. 2
give important information to understand the mechanism
of CNT-PGL nanostructure formation.
A simple scheme of the proposed mechanism is
presented in Fig. 3. This mechanism is based on the
analysis of CNT growth mechanisms. Despite some
peculiarities, in general the mechanisms of CNT growth
are considered as the multistage ones [4-8].
In the first stage, after the feeding solution of (p-
xylene in the mixture with ferrocene) is injected into the
reaction zone, the thermal homogeneous gas-phase
decomposition of ferrocene under the temperature of
around 500 ºC is going on. As a result, Fe is deposited
onto Si/SiO2 substrate surface creating a layer of Fe
catalyst nanoclusters (Fig. 3a(1)).
(a)
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0
0
1
2
3
4
5
6
7
8
9
1 0
FeAr
C
Kinetic Energy (eV)
A
rb
itr
ar
y
U
ni
ts
(b)
Fig. 1. Composite nanostructure consisting of an array of
vertically aligned CNTs and a planar layer on top: (a) SEM
image, (b) Auger spectrum of the planar layer surface.
(a)
(b)
Fig. 2. CNT-PGL nanostructure at different aspect angles and
magnifications (SEM): (a) top view of the planar graphite
layer; (b) view of CNT-PGL junction.
In the second stage, Fe nanoclusters decompose
carbon source (hydrocarbons), creating carbon atoms
and dissolve them up to a certain limit. Dissolved carbon
atoms activate Fe in nanoclusters and under the
temperature close to 800 C form fluid-like Fe carbide
(Fig. 3a(2)). Let’s designate this process as
“carbidization cycle”.
In the third stage, due to the metastable character of
fluid-like Fe carbide, the process reversed to the carbide
formation leads to the carbide decomposition by
segregating a part of the dissolved carbon (Fig. 3a(3)).
The segregated carbon atoms diffuse to the catalyst
surface and extrusion of one of the carbon allotropic
forms of different dimensionalities from the catalyst
surface starts (“carbonization cycle”). This stage is
designated as the nucleation one. CNT growth in the
nucleation stage has various interpretations by different
investigators. According to refs. 4 and 5, carbon
extrusion leads to the fullerene hemisphere formation,
which nucleates the CNT growth. This mechanism is
based on the in-situ TEM observations [5].
The main idea of ref. 7 is that this extrusion of
carbon leads to the direct growth of CNTs on the catalyst
surface. The gas-phase precursor, Cgas, is deposited on
the open sides of the catalyst surface being converted to
an activated surface-bound form, C*, which dissolves
into the Fe carbide nanocluster maintaining it in a fluid-
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 2. P. 137-141.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
139
Сgas
graphene
"b
a
se
"
"t
ip
"
(а)
(b)
Fe Fe/С
Carbidization cycle
Carbonization cycle
"t
ip
g
ro
w
th
"
"b
as
e
g
ro
w
th
"
(c)
FexCy
Сgas
Cgas
1 2 3
1 2 3
С С С
1 2 3
Fig. 3. Scheme of the CNT-PGL nanostructure formation:
(a) Fe catalyst nanoclusters formation on the substrate
surface, (b) graphene layer formation on the surface of Fe
catalyst nanoclusters, (c) PGL and CNT array growth with
lifted up PGL by the growing CNT array.
like phase with the oversaturated concentration of
carbon. Under the concentration gradient, C* diffuses
through the catalyst nanoclusters and directly
incorporates into the growing CNT. In ref. 7, a very
important aspect of CNT growth is considered. It is
shown that C* can form on the catalyst nanocluster
surface the amorphous graphite patches which can grow
up and fully cover surface, what will lead to deactivation
of the catalyst and termination of CNT growth. In a
general case, it will lead to termination of any carbon
allotropic form growth. Let’s designate this process as
“graphitization cycle” of CNT growth.
In ref. 8, it is undoubtedly declared that the islands
of graphene layer are formed on the catalyst surface as a
result of carbon extrusion (Fig. 3b(1)). This gives rise to
a carbon-concentration gradient in the catalyst allowing
more carbon source to be decomposed and segregated.
In such a way, the area of the graphene layer is growing
up on the catalyst surface (Fig. 3b(2)). This process will
continue until all surface of the carbide nanocluster is
covered with two-dimensional graphene nuclii
(Fig. 3b(3)). We consider the latter approach as the most
realistic one, because graphene, as a product of carbon
extrusion, is the most energetically favorable carbon
allotropic form to be created [9].
A stable graphene layer on the catalyst surface can
be obtained, if it has perfect structure, i.e. contains only
hexagonal ones (honeycomb lattice). The combination in
the graphene layer of the hexagonal cells with the
“imperfect” ones (penta-, hepta-, dodecagonal cells)
makes it unstable, and it becomes a basic building block
for graphitic materials of all other dimensionalities. It
can be wrapped up into 0D fullerenes (buckyballs),
rolled into 1D nanotubes or stacked into 3D graphite or
soot [10].
The existence of the carbonization or graphitization
cycles can be determined by several reasons. In
particular, when the rate of carbon supply to the catalyst
surface exceeds the rate of its diffusion (outflow)
through the catalyst, more probably graphitization of the
catalyst surface occurs. In the case of too slow rate of
carbon supply to the catalyst surface, carbonization of
catalyst surface would preferably occur, because the
carbon extrusion products have enough time to form the
most energetically favorable carbon allotropic form –
graphene.
Both rates depend on the numerous factors, such as
the rate of hydrocarbon decomposition and partial
pressure of its products, which in turn can be regulated
by the temperature in the reaction zone, the rate of
feeding solution injection, etc. Thus, regulating these
parameters one may create conditions for carbonization
or graphitization of the catalyst nanoclusters.
We use the considered mechanism of CNT growth
as a basis for the developing the mechanism of CNT-
PGL nanostructure formation.
In ref. 3, the probable mechanism of CNT–planar
“graphene multi-layer” nanostructure formation was
briefly considered. The main feature of this mechanism
is that after the planar layer formation (it is not
considered in what a way) the CNT array is synthesized
simply by the tip-growth mechanism [6].
Our vision of the mechanism of CNT-PGL
nanostructure formation is different. Since the feeding
solution is continuously supplied into the reaction zone
during the CNT-PGL nanostructure formation, Cgas and
Fe atoms are continuously generated and take part in the
growth process. In our opinion, the processes of PGL
and CNT arrays formation are going on simultaneously.
Under the realized conditions of CNT-PGL
nanostructure formation, the graphene layer grown at the
nucleation stage on the catalyst surface is transformed by
some reasons into the planar graphite layer
(“graphitization cycle”) at the upper surface of catalyst
and into CNTs at the interface between catalyst and
substrate surface.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 2. P. 137-141.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
140
While in the case of CNT growth the graphitization
process leads to the catalyst deactivation and CNT
growth termination, in the case of CNT-PGL
nanostructure formation the graphitization process leads
to the PGL creation.
PGL grows in the following way (Fig. 3c). In the
course of CVD process realization, the carbon atoms from
the gas phase precipitate on the substrate, successively
creating by the epitaxial growth the layers of the
“graphene multi-layer” nanostructure (PGL), which
covers the substrate surface with the catalyst nanoclusters
on it. In this case, the PGL thickness grows up during the
synthesis process. Fe atoms also precipitate onto the
surfaces of the growing graphene layers creating Fe
nanoclusters, which are encapsulated between these layers
(not shown in Fig. 3). This assumption is confirmed by
Fig. 2a where the PGL surface is presented, which is very
rough in a nanoscale. Evidently, the graphene layers of
PGL replicate the underlying Fe nanoclusters. AES in
Fig. 1b confirms the existence of small amount of Fe in
the CNT-PGL nanostructure.
All the time during PGL growth, carbon atoms
from the gas phase diffuse through growing PGL to the
catalyst facilitating CNT growth (Fig. 3c).
Iron atoms can diffuse through graphite layers only
at temperatures above 1600 ºC [10], what is much higher
than our CVD condition (850 ºC), therefore participation
of iron from the gas phase in CNT growth is excluded.
There are some options of CNT growth under the
CNT-PGL nanostructure formation. If the adhesion of the
catalyst to PGL is stronger than to the substrate, the CNT
growth starts at the catalyst-substrate interface towards the
substrate (Fig. 3c(1)). The growing CNTs detach and lift
up the catalyst nanoclusters and PGL from the substrate
surface. As a result, the catalyst moves upwards in the
direction opposite to the direction of CNT growth, what
represents classical tip-growth mechanism [6]. If the
adhesion of catalyst to the substrate is stronger than to
PGL, the CNT growth starts at the catalyst-PGL interface
towards PGL. The growing CNTs lift up PGL and detach
catalyst from PGL. Catalyst remains at the substrate
during the CNT growth (Fig. 3c(2)), what represents the
classical base-growth mechanism [6]. There might be an
intermediate situation as additional one to the case of
Fig. 3c(1) when CNT growth happens at the both sides of
catalyst starting at catalyst-substrate interfaces and
continues on the catalyst-PGL interfaces. In this case, the
CNT growth goes on by combination of the base- and tip-
growth mechanisms (Fig. 3c(3)), and catalyst might
happen to locate somewhere in the CNT array between
PGL and substrate.
Fig. 4 confirms the proposed mechanism of CNT
growth under the CNT-PGL nanostructure formation.
There is easily recognized situation that CNTs grow both
from PGL and from substrate, and it looks like they are
meeting each other just in the middle of the distance
between PGL and substrate. It is important to note that
the density of the CNT array growing from the substrate
looks higher than source growing from PGL.
1.5 µm
Fig. 4. View of the CNT array located between PGL and
substrate.
Additional evidence that CNTs grow from PGL can
be taken from Fig. 2b. On the contrary, Fig. 1a
demonstrates that CNTs grow from substrate, because on
the open side of the substrate surface one can observe
the rests of the broken-down during the cleavage process
CNTs that are very likely located at the catalyst
nanoclusters.
The process of CNT growth continues until it
terminates by some reasons. The growth cessation may
be caused either by graphitization of the catalyst
nanocluster surface or by limitations imposed by
diffusion of carbon atoms to the catalyst clusters through
PGL. At the beginning of the CNT-PGL nanostructure
formation, when PGL thickness is small and the
diffusion length of carbon atoms is larger than the PGL
thickness, graphitization might be responsible for the
cessation. As the PGL thickness is growing, the gas-
diffusion controlled mode can prevail at the certain
crucial thickness, and growth cessation would be caused
by the limitations imposed by diffusion of carbon atoms
through PGL. The proposed mechanism of the CNT-
PGL nanostructure formation is different from the
mechanism proposed in ref. 3 for the same type of
composite nanostructure. Our mechanism describing the
growth of the planar “graphene multi-layer” combines
both the base- and tip-growth mechanisms in different
manifestations. We propose to designate this mechanism
as the “combined CNT-PGL growth” mechanism.
In summary, for the first time the carbon
nanostructures composed of an array of vertically
aligned CNTs and a planar graphite layer (PGL) located
at the top of the array (CNT-PGL nanostructures) have
been synthesized by the injection CVD method. The
mechanism of CNT-PGL nanostructures formation by
injection CVD method is proposed, which is based on
the analysis of all the stages of CNT growth
mechanisms. From different interpretations of CNT
growth mechanism, the most appropriate ones was
chosen, according to which CNT growth goes on
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 2. P. 137-141.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
141
through the stages of metal carbide formation
(carbidization cycle) and its decomposition with the
following graphene layer creation at the catalyst surface
(carbonization cycle). CNT-PGL nanostructure
formation goes on by the transformation of the graphene
layer into PGL at the upper surface of catalyst and into
CNTs at the interface between catalyst and substrate
surface. The proposed mechanism is designated as
“combined CNT-PGL growth” mechanism. The
obtained CNT-PGL nanostructure is expected to have
unique electro-physical properties and therefore is likely
to find many applications in electronics.
Acknowledgements
The authors acknowledge the BelMicroSystems R&D
Center, Minsk for giving us an opportunity to perform
SEM investigations, and the Institute of Heat and Mass
Transfer, Minsk, in particular Prof. S.A. Filatov, for
EDX measurements.
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