U.S. patent application number 11/158047 was filed with the patent office on 2007-01-25 for method of preparing catalyst for manufacturing carbon nanotubes.
Invention is credited to In-Taek Han, Ha-Jin Kim.
Application Number | 20070020167 11/158047 |
Document ID | / |
Family ID | 35775022 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070020167 |
Kind Code |
A1 |
Han; In-Taek ; et
al. |
January 25, 2007 |
Method of preparing catalyst for manufacturing carbon nanotubes
Abstract
A novel method of forming catalyst particles, on which carbon
nanotubes grow based, on a substrate with increased uniformity, and
a method of synthesizing carbon nanotubes having improved
uniformity are provided. A catalytic metal precursor solution is
applied to a substrate. The applied catalytic metal precursor
solution is freeze-dried, and then reduced to catalytic metal. The
method of forming catalyst particles can minimize agglomeration
and/or recrystallization of catalyst particles when forming the
catalyst particles by freeze-drying the catalyst metal precursor
solution. The catalyst particles formed by the method has a very
uniform particle size and are very uniformly distributed on the
substrate.
Inventors: |
Han; In-Taek; (Seoul,
KR) ; Kim; Ha-Jin; (Suwon-si, KR) |
Correspondence
Address: |
Robert E. Bushnell
Suite 300
1522 K Street, N.W.
Washington
DC
20005
US
|
Family ID: |
35775022 |
Appl. No.: |
11/158047 |
Filed: |
June 22, 2005 |
Current U.S.
Class: |
423/447.3 ;
502/325 |
Current CPC
Class: |
D01F 9/12 20130101; B82Y
30/00 20130101 |
Class at
Publication: |
423/447.3 ;
502/325 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2004 |
KR |
10-2004-0046552 |
Claims
1. A method of preparing catalyst particles for carbon nanotube
manufacture, the method comprising: applying a catalytic metal
precursor solution to a substrate, the catalytic metal precursor
solution comprising a catalytic metal precursor and a solvent;
freeze-drying the catalytic metal precursor solution applied to the
substrate; and reducing the freeze-dried catalytic metal precursor
to catalytic metal.
2. The method of claim 1, wherein the catalytic metal precursor is
an organo-metallic compound.
3. The method of claim 2, wherein the catalytic metal precursor is
an organo-metallic compound containing at least one metal element
selected from the group consisting of Fe, Co, Ni, Y, Mo, Cu, Pt, V,
and Ti.
4. The method of claim 1, wherein the solvent of the catalytic
metal precursor solution is ethanol, ethylene glycol, polyethylene
glycol, polyvinyl alcohol, or a mixture thereof.
5. The method of claim 1, wherein the concentration of the
catalytic metal precursor in the catalytic metal precursor solution
is 10 mM to 200 mM.
6. The method of claim 1, wherein the step of freeze-drying the
catalytic metal precursor solution comprises cooling the catalytic
metal precursor solution applied to the substrate below the
freezing point of the catalytic metal precursor solution and
evaporating the solvent in the catalytic metal precursor solution
under a reduced pressure.
7. The method of claim 6, wherein the step of cooling the catalytic
metal precursor solution comprises using a freezer or liquid
nitrogen.
8. Catalyst particles prepared by the method of claim 1.
9. A method of manufacturing carbon nanotubes, comprising utilizing
the catalyst particles of claim 8.
10. A method of manufacturing carbon nanotubes, the method
comprising: forming catalyst particles on a substrate by applying a
catalytic metal precursor solution comprising a catalytic metal
precursor and a solvent to the substrate, freeze-drying the
catalytic metal precursor solution applied to the substrate, and
reducing the freeze-dried catalytic metal precursor to a catalytic
metal; and growing carbon nanotubes on the catalyst particles by
supplying a carbon source to the catalyst particles.
11. The method of claim 10, wherein the catalytic metal precursor
is an organo-metallic compound, and the solvent is ethanol,
ethylene glycol, polyethylene glycol, polyvinyl alcohol, or a
mixture thereof.
12. The method of claim 10, wherein the catalytic metal precursor
is an organo-metallic compound containing at least one metal
element selected from the group consisting of Fe, Co, Ni, Y, Mo,
Cu, Pt, V, and Ti.
13. The method of claim 10, wherein the concentration of the
catalytic metal precursor in the catalytic metal precursor solution
is 10 mM to 200 mM.
14. The method of claim 10, wherein the step of freeze-drying the
catalytic metal precursor solution comprises cooling the catalytic
metal precursor solution applied to the substrate below the
freezing point of the catalytic metal precursor solution and
evaporating the solvent in the catalytic metal precursor solution
under a reduced pressure.
15. The method of claim 10, wherein the step of cooling the
catalytic metal precursor solution comprises using a freezer or
liquid nitrogen.
16. The method of 10, wherein the step of growing the carbon
nanotubes comprises placing the substrate on which the catalyst
particles are formed in a reaction chamber, supplying carbon
precursor gas into the reaction chamber, and decomposing the carbon
precursor gas in the reaction chamber to supply carbon to the
catalyst particles.
17. The method of 16, wherein the internal temperature of the
reaction chamber is in the range of about 450 to 1100.degree.
C.
18. The method of claim 10, wherein the reduction of the
freeze-dried catalytic metal precursor to a catalytic metal
comprises heating the freeze-dried catalytic metal precursor in an
oxidation atmosphere to oxidize the catalytic metal precursor, and
reducing the oxidized catalytic metal precursor to the catalyst
metal by heat-treatment or plasma-treatment.
19. A method of manufacturing carbon nanotubes, the method
comprising: applying a catalytic metal precursor solution to the
substrate, the catalytic metal precursor solution comprising a
catalytic metal precursor dissolved in a solvent; cooling the
catalytic metal precursor solution applied to the substrate below
the freezing point of the catalytic metal precursor solution;
evaporating the solvent in the catalytic metal precursor solution
to form catalytic metal precursor particles; converting the
catalytic metal precursor particles to a catalyst particles; and
growing carbon nanotubes on the catalyst particles.
20. The method of claim 19, wherein the step of converting the
catalytic metal precursor particles to the catalyst particles
comprises heating the catalytic metal precursor particles in an
oxidation atmosphere to oxidize the catalytic metal precursor
particles, and reducing the oxidized catalytic metal precursor
particles to the catalyst particles by heat-treatment or
plasma-treatment.
Description
CLAIM OF PRIORITY
[0001] This application claims the priority of Korean Patent
Application No. 10-2004-0046552, filed on Jun. 22, 2004, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of preparing a
catalyst for manufacturing carbon nanotubes and a method of
manufacturing carbon nanotubes using the same.
[0004] 2. Description of the Related Art
[0005] A carbon nanotube has a cylindrical structure having a
diameter of several nano-meter and a very large aspect ratio of
about 10 to 1,000. In the carbon nanotube, carbon atoms are
generally arranged in a hexagonal honeycomb pattern. One carbon
atom bonds to three adjacent carbon atoms. The carbon nanotube may
be a conductor or a semiconductor according to its structure. As a
conductor, the carbon nanotube has high electroconductivity. Also,
the carbon nanotube has superior mechanical strength, Young's
modulus of tera level, and high heat conductivity. The carbon
nanotube having these properties can be advantageously used in
various technical fields, such as an emitter of FED, a cathode
material for a secondary battery, a catalyst support of a fuel
cell, a high strength composite, and the like.
[0006] Examples of a method of preparing the carbon nanotube
include arc discharge, laser deposition, plasma enhanced chemical
vapor deposition (PECVD), chemical vapor deposition, vapor phase
growth, electrolysis, and the like. The vapor phase growth is
suitable for preparing the carbon nanotube in bulk form since it
synthesizes the carbon nanotube in a vapor phase by directly
supplying a reaction gas and a catalytic metal into a reactor
without using a substrate. The arc discharge and the laser
deposition have relatively low yields of carbon nanotubes. When
using the arc discharge and the laser deposition, It is difficult
to control the diameter and the length of the carbon nanotube.
Further, in the arc discharge and the laser deposition, clusters of
amorphous carbon besides the carbon nanotubes are produced in a
large amount, and thus a complicated purifying process must be
performed.
[0007] Chemical vapor deposition (CVD) methods, such as thermal
chemical vapor deposition, low pressure chemical vapor deposition
and PECVD are generally used to form carbon nanotubes on a
substrate. In the PECVD, the carbon nanotubes can be synthesized at
low temperatures by activating gas with a plasma. In the PECVD, it
is relatively easy to control the diameter, the length, the
density, etc. of the carbon nanotube.
[0008] In the case of chemical vapor deposition (CVD) methods,
catalyst particles, on which carbon nanotubes grow based, are first
dispersed on a substrate in order to obtain a uniform density of
the carbon nanotubes formed on the substrate.
[0009] For example, Korean Patent Laid-Open Publication No.
2001-0049398 discloses a method of forming a plurality of catalyst
particles by forming a catalytic metal film on a substrate and
etching the catalytic metal film with an etching gas.
[0010] In addition, Chemical Physics Letter, vol. 377 p. 49, 2003
discloses a method of forming catalyst particles on a substrate by
applying a catalytic metal precursor solution to the substrate, and
then drying and heat-treating the applied catalytic metal precursor
solution. However, in this case, recrystallization and
agglomeration of the catalytic metals occur during the drying and
heat-treatment processes so that uniformity of the catalyst
particles formed on the substrate is deteriorated. Due to the
deterioration in the uniformity of the catalyst particles formed on
the substrate, the uniformity of the diameter and production
density of the carbon nanotubes grown on the basis of the catalytic
particles are both deteriorated.
[0011] The uniformity of the catalyst particles formed on the
substrate can be evaluated by measuring the uniformity of the
particle sizes of the catalyst particles and the uniformity of the
production density of the catalyst particles. The uniformity of the
catalyst particles formed by the conventional methods is not
sufficient. Thus, a novel method of forming catalyst particles in
order to improve the uniformity of the catalyst particles formed on
a substrate is needed.
SUMMARY OF THE INVENTION
[0012] It is therefore an object of the present invention to
provide a novel method of forming catalyst particles.
[0013] It is a further object of the present invention to provide a
novel method of forming catalyst particles with increased
uniformity, on which carbon nanotubes grow based, on a
substrate.
[0014] It is also an object of the present invention to provide a
method of synthesizing carbon nanotubes with improved
uniformity.
[0015] According to an aspect of the present invention, there is
provided a method of forming catalyst particles, the method
including: applying a catalytic metal precursor solution to a
substrate, the catalytic metal precursor solution comprising a
catalytic metal precursor and a solvent; freeze-drying the
catalytic metal precursor solution applied to the substrate; and
reducing the freeze-dried catalytic metal precursor to a catalytic
metal.
[0016] It is preferred that the catalytic metal precursor solution
is freeze-dried by cooling the catalytic metal precursor solution
applied to the substrate below the freezing point of the catalytic
metal precursor solution and evaporating the solvent in the
catalytic metal precursor solution under a reduced pressure.
[0017] The method of forming catalyst particles can minimize the
agglomeration and/or recrystallization of the catalytic metal
particles when forming the catalytic metal particles by
freeze-drying the catalytic metal precursor solution. Therefore,
the catalytic metal particles formed by the method of the present
invention have particle sizes with very high uniformity and are
very uniformly distributed on the substrate.
[0018] According to another aspect of the present invention, there
is provided a method of manufacturing carbon nanotubes, the method
including: forming catalyst particles, on which carbon nanotubes
grow based, on a substrate by applying a catalytic metal precursor
solution to the substrate, freeze-drying the catalytic metal
precursor solution applied to the substrate, and reducing the
freeze-dried catalytic metal precursor to a catalytic metal; and
growing carbon nanotubes on the catalyst particles by supplying a
carbon source to the catalyst particles.
[0019] According to another aspect of the present invention, there
is provided a method of manufacturing carbon nanotubes, the method
including: applying a catalytic metal precursor solution to the
substrate; cooling the catalytic metal precursor solution applied
to the substrate below the freezing point of the catalytic metal
precursor solution; evaporating the solvent in the catalytic metal
precursor solution under a reduced pressure to form catalytic metal
precursor particles; converting the catalytic metal precursor
particles to a catalyst particles; and growing carbon nanotubes on
the catalyst particles.
[0020] It is preferred that the catalytic metal precursor particles
is converted into the catalyst particles by heating the catalytic
metal precursor particles in an oxidation atmosphere to oxidize the
catalytic metal precursor particles and reducing the oxidized
catalytic metal precursor particles to the catalyst particles by
heat-treatment or plasma-treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] A more complete appreciation of the present invention, and
many of the above and other features and advantages of the present
invention, will be readily apparent as the same becomes better
understood by reference to the following detailed description when
considered in conjunction with the accompanying drawings in which
like reference symbols indicate the same or similar components,
wherein:
[0022] FIG. 1 is an optical microscopic image illustrating catalyst
particles for manufacturing carbon nanotubes, prepared according to
an Example of the present invention;
[0023] FIG. 2 is an electron microscopic image illustrating a side
view of carbon nanotubes prepared according to an Example of the
present invention;
[0024] FIG. 3 is an electron microscopic image illustrating a top
view of carbon nanotubes prepared according to an Example of the
present invention;
[0025] FIG. 4 is an optical microscopic image illustrating catalyst
particles for manufacturing carbon nanotubes, prepared according to
a Comparative Example;
[0026] FIG. 5 is an enlarged view of a part of FIG. 4; and
[0027] FIG. 6 is an electron microscopic image illustrating a state
of carbon nanotubes prepared according to a Comparative
Example.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Hereinafter, a method of forming catalyst particles, on
which carbon nanotubes grow based, on a substrate according to an
embodiment of the present invention will be described in
detail.
[0029] The method of forming catalyst particles includes: applying
a catalytic metal precursor solution to a substrate; freeze-drying
the catalytic metal precursor solution applied to the substrate;
and reducing the freeze-dried catalytic metal precursor to
catalytic metal.
[0030] The catalytic metal precursor solution includes a catalytic
metal precursor and a solvent for dissolving the catalytic metal
precursor.
[0031] The catalytic metal precursor may be any material that can
be converted to metal particles, on which carbon nanotubes can grow
based. An example of the catalytic metal precursor includes an
organo-metallic compound. The organo-metallic compound can contain
at least one metal element selected from the group consisting of
Fe, Co, Ni, Y, Mo, Cu, Pt, V, and Ti. Examples of the
organo-metallic compound include iron acetate, iron oxalate, cobalt
acetate, nickel acetate, ferrocene, or a mixture thereof.
[0032] The solvent may be any liquid material that can dissolve the
catalytic metal precursor. Examples of the solvent include ethanol,
ethylene glycol, polyethylene glycol, polyvinyl alcohol, and a
mixture thereof.
[0033] The concentration of the catalytic metal precursor in the
catalytic metal precursor solution is not particularly limited. If
the concentration of the catalytic metal precursor in the catalytic
metal precursor solution is too low, the carbon nanotubes may not
be generated in a subsequent process of manufacturing. If the
concentration of the catalytic metal precursor in the catalytic
metal precursor solution is too high, the diameter of the carbon
nanotubes generated in a subsequent process of manufacturing may be
increased or the crystallinity of the carbon nanotubes generated or
carbon nanofibers may be reduced. The concentration of the
catalytic metal precursor in the catalytic metal precursor solution
can preferably be about 10 mM to 200 mM.
[0034] The substrate may be composed of any material, to which
catalyst particles can be attached, for example, a metal with a
high melting point, such as Mo, Cr, and W, silicon, glass, plastic,
quartz, and the like.
[0035] The method of applying the catalytic metal precursor
solution to the substrate may be any method capable of uniformly
coating the solution on the surface of the substrate. Examples of
the method include dip coating, evaporation coating, screen
printing, spin coating, and the like. These methods can also be
used in a combination.
[0036] The catalytic metal precursor solution can be applied to the
entire surface of the substrate or on only a part of the surface of
the substrate.
[0037] The catalytic metal precursor solution applied to the
substrate is freeze-dried. The freeze-drying process includes
cooling the catalytic metal precursor solution applied to the
substrate below the freezing point of the catalytic metal precursor
solution and evaporating the solvent in the catalytic metal
precursor solution under a reduced pressure.
[0038] The freezing point of the catalytic metal precursor solution
may vary depending on a composition of the catalytic metal
precursor solution. That is, the freezing point of the catalytic
metal precursor solution can be determined by the type of the
catalytic metal precursor, the type of the solvent, the
concentration of the catalytic metal precursor, and the like. The
freezing point of the catalytic metal precursor solution can be
easily determined by those skilled in the art through
thermodynamical calculation and the method of trial and error. The
freezing point of the catalytic metal precursor solution can also
be selected by adjusting the composition of the catalytic metal
precursor solution.
[0039] The process of cooling the catalytic metal precursor
solution applied to the substrate below the freezing point of the
catalyst solution can be performed using a cooling method suitable
for the freezing point of the catalytic metal precursor solution.
For example, a freezer, liquid nitrogen, etc. can be used. When
using liquid nitrogen, the catalytic metal precursor solution
applied to the substrate can be cooled to below the freezing point
of the catalytic metal precursor solution by dipping the substrate
with the catalytic metal precursor solution applied thereto in
liquid nitrogen.
[0040] After the catalytic metal precursor solution applied to the
substrate freezes, the substrate is subjected to a reduced pressure
in order to allow the solvent in the frozen catalytic metal
precursor solution to evaporate. For example, the substrate with
the frozen catalytic metal precursor solution applied thereto is
placed in a vacuum chamber, and then the pressure of the inside of
the vacuum chamber is reduced.
[0041] The reduced pressure should be sufficient to allow the
solvent in the frozen catalytic metal precursor solution to
evaporate. Hereinafter, the reduced pressure sufficient to allow
the solvent in the frozen catalytic metal precursor solution to
evaporate is abbreviated to "evaporation pressure". The evaporation
pressure can vary depending on a composition the used catalytic
metal precursor solution. That is, the evaporation pressure can be
determined by the type of the catalytic metal precursor, the type
of the solvent, the concentration of the catalytic metal precursor,
freezing point, and the like. The evaporation pressure of the
catalytic metal precursor solution can be easily determined by
those skilled in the art through thermodynamical calculation and
the method of trial and error. The evaporation pressure of the
catalytic metal precursor solution can also be selected by
adjusting the composition of the catalytic metal precursor
solution, freezing point, and the like.
[0042] The solvent in the frozen catalytic metal precursor solution
is removed through the evaporation. As a result, catalytic metal
precursor components are formed in a particle form on the
substrate. It is noted that the catalytic metal precursor particles
formed according to the present method have particle size with high
uniformity and a uniform distribution on the substrate.
[0043] Subsequently, the catalytic metal precursor particles formed
on the substrate are reduced to catalytic metal particles. The
process of reducing the catalytic metal precursor particles to
catalytic metal particles can be performed, for example, as
follows. First, the catalytic metal precursor is converted into an
oxide through heat-treatment in an oxidation atmosphere, and then
the oxide is heat-treated or plasma treated in a reduction
atmosphere to be reduced to a metal. The process of reducing the
catalytic metal precursor can be performed by various methods known
in the art, and thus, the detailed description thereof will be
omitted herein.
[0044] FIG. 1 is an electron microscopic image of catalytic metal
particles prepared according to an Example of the present
invention. Referring to FIG. 1, the catalytic metal particles are
uniformly distributed on the substrate and the particle sizes
thereof are relatively uniform.
[0045] A method of manufacturing carbon nanotubes according to an
embodiment of the present invention will now be described in more
detail.
[0046] The method of manufacturing carbon nanotubes includes
forming catalyst particles, on which carbon nanotubes grow based,
on a substrate by applying a catalytic metal precursor solution to
the substrate, freeze-drying the catalytic metal precursor solution
applied to the substrate, and reducing the freeze-dried catalytic
metal precursor to catalytic metal; and growing carbon nanotubes on
the catalyst particles by supplying a carbon source to the catalyst
particles.
[0047] The process of forming catalyst particles on the substrate
is performed in the same manner as described in the method of
forming catalyst particles.
[0048] The process of growing carbon nanotubes on the catalyst
particles by supplying the carbon source to the catalyst particles
may be performed by various methods useful for the manufacture of
carbon nanotubes.
[0049] For example, the process of growing carbon nanotubes on the
catalyst particles includes placing the substrate on which the
catalyst particles are formed in a reaction chamber, supplying
carbon precursor gas into the reaction chamber, and decomposing the
carbon precursor gas in the reaction chamber to supply carbon to
the catalyst particles.
[0050] The process of growing the carbon nanotubes can be performed
by low pressure chemical vapor deposition, thermal chemical vapor
deposition, PECVD, or a combination thereof.
[0051] Examples of the carbon precursor gas include carbon
containing compounds such as acetylene, methane, propane, ethylene,
carbon monoxide, carbon dioxide, alcohol, and benzene.
[0052] If the internal temperature of the reaction chamber is too
low, the crystallinity of the generated carbon nanotubes may be
diminished. If the internal temperature of the reaction chamber is
too high, the carbon nanotubes may not be formed. In view of this,
the internal temperature of the reaction chamber may preferably be
in the range of about 450 to 1100.degree. C.
[0053] Other conditions in the process of growing carbon nanotubes
may typically be those suitable for the growth of carbon nanotubes
and be easily selected by those skilled in the art according to
specific application purposes. Thus, detailed description of other
conditions will be omitted herein.
[0054] Since in the method of manufacturing carbon nanotubes of the
present embodiment, carbon nanotubes grow based on catalyst
particles that have a uniform particle size and are uniformly
distributed on the substrate, the uniformity of the resulting
carbon nanotubes is also highly improved. The uniformity of carbon
nanotubes is evaluated by the uniformity of the lengths and
diameters of the carbon nanotubes. The lengths and diameters of
carbon nanotubes can be measured by an electron microscope and a
transmittance electron microscope, respectively.
[0055] Further, the vertical orientation characteristic of carbon
nanotubes manufactured by the method of the present embodiment is
very good. This can be confirmed from an electron microscopic image
of FIG. 2. FIG. 2 is an image showing a side view of carbon
nanotubes prepared in an Example of the present invention.
Referring to FIG. 2, the carbon nanotubes prepared according to the
method of the present embodiment are vertically oriented without
being entangled with one another.
[0056] FIG. 3 is an image showing a top view of carbon nanotubes
prepared in an Example of the present invention. Referring to FIG.
3, the production density of carbon nanotubes prepared according to
the method of the present embodiment is uniform.
EXAMPLE
[0057] A 40 mM iron acetate solution was prepared using ethanol and
ethylene glycol as a solvent. 20 mL of ethanol and 20 mL of
ethylene glycol were added to 0.1 g of iron acetate powder to
obtain a solution having a proper viscosity. A silicon substrate
with a diameter of 20.32 cm was dipped in the obtained solution.
The coated substrate was cooled immediately with liquid nitrogen
and then transferred into a vacuum chamber. Then, a vacuum less
than 0.1 mmHg was applied to the chamber in order to evaporate the
solvent. To minimize an amount of the remained solvent, the
substrate was further heated at 100.degree. C.
[0058] The freeze-dried substrate was heat-treated at 300.degree.
C. for 10 minutes in order to oxidize the iron acetate. Then, the
substrate was subjected to a reduction treatment with hydrogen at
600.degree. C.
[0059] As a result, the iron particles were uniformly formed on the
substrate. FIG. 1 is an electron microscopic image of iron
particles formed on the silicon substrate according to the present
Example. Referring to FIG. 1, the iron particles are uniformly
distributed on the substrate and the particle sizes thereof are
relatively uniform.
[0060] The substrate having iron particles formed thereon was
placed in a reaction chamber for chemical vapor deposition (CVD),
an internal temperature of which is 600.degree. C., and then a
mixed gas of carbon monoxide and hydrogen (weight ratio 1:2) was
supplied to the reaction chamber for 20 minutes to synthesize
carbon nanotubes based on the iron particles.
[0061] FIG. 2 is an image showing a side view of carbon nanotubes
prepared in the present Example. As is apparent from FIG. 2, the
carbon nanotubes prepared in the present Example are vertically
oriented without being entangled with one another. FIG. 3 is an
image showing a top view of carbon nanotubes prepared in the
present Example. It can be seen from FIG. 3 that the production
density of carbon nanotubes prepared in the present Example is
uniform.
[0062] To evaluate the uniformity of the formed carbon nanotubes,
the measurements of the lengths and the diameters of the carbon
nanotubes using an electron microscope and a transmittance electron
microscope, respectively, were performed on the respective parts of
the substrate, which were equally divided into 9 parts. As a
result, it is confirmed that carbon nanotubes on the substrate
equally divided into 9 parts has a uniformity within .+-.5%.
Comparitive Example
[0063] Carbon nanotubes were synthesized in the same manner as in
the above Example, except that the iron acetate solution applied to
the substrate was not freeze-dried but naturally dried.
[0064] FIG. 4 is an optical microscopic image showing iron
particles prepared in Comparative Example. FIG. 5 is an enlarged
view of a part of FIG. 4. As seen from FIGS. 4 and 5, iron
particles prepared in Comparative Example have no uniformity.
[0065] FIG. 6 is an electron microscopic image showing a form of
carbon nanotube clusters synthesized in Comparative Example.
Referring to FIG. 6, the carbon nanotubes synthesized in
Comparative Example are partially lumped on the substrate, are
entangled with one another, and not vertically oriented.
[0066] The method of forming catalyst particles according to an
embodiment of the present invention can minimize the agglomeration
and/or recrystallization of the catalyst particles when forming the
catalyst particles by freeze-drying the catalyst metal precursor
solution. The catalyst particles formed by the method of the
present embodiment have a very uniform particle size and a very
uniform distribution on the substrate.
[0067] In the method of manufacturing carbon nanotubes according to
another embodiment of the present invention, the carbon nanotubes
grow based on the catalyst particles having a uniform particle size
and a uniform distribution on the substrate, and thus, the
synthesized carbon nanotubes have highly improved uniformity.
[0068] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *