U.S. patent application number 10/252668 was filed with the patent office on 2003-06-12 for carbon nanotubes and method of manufacturing same, electron emission source, and display.
This patent application is currently assigned to International Center for Materials Research. Invention is credited to Hiraoka, Hiroyuki, Itoh, Shigeo, Nawamaki, Kenji, Shiratori, Yosuke, Yamamoto, Masahide.
Application Number | 20030108478 10/252668 |
Document ID | / |
Family ID | 19148777 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030108478 |
Kind Code |
A1 |
Hiraoka, Hiroyuki ; et
al. |
June 12, 2003 |
Carbon nanotubes and method of manufacturing same, electron
emission source, and display
Abstract
The present invention provides carbon nanotubes perpendicularly
and densely deposited over a wide area of a substrate. The carbon
nanotubes are manufactured by supplying alternating-current power
at a specific frequency between an anode and a cathode disposed in
a reactor, and causing plasma to be generated between the anode and
the cathode by introducing mixed gas containing an aliphatic
hydrocarbon having 1-5 carbon atoms and hydrogen or mixed gas
containing an aromatic hydrocarbon and hydrogen. The substrate is
disposed between the anode and the cathode and held at a distance
two times or less of the mean free path of a hydrocarbon cation
from the anode.
Inventors: |
Hiraoka, Hiroyuki;
(Kawasaki-shi, JP) ; Shiratori, Yosuke;
(Kawasaki-shi, JP) ; Yamamoto, Masahide;
(Kusatsu-shi, JP) ; Itoh, Shigeo; (Mobara-shi,
JP) ; Nawamaki, Kenji; (Mobara-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
International Center for Materials
Research
1-1 Minamiwatarida-cho, Kawasaki-ku
Kawasaki-shi
JP
210-0855
Futaba Corporation
629 Oshiba
Mobara-shi
JP
297-8588
|
Family ID: |
19148777 |
Appl. No.: |
10/252668 |
Filed: |
September 24, 2002 |
Current U.S.
Class: |
423/447.2 ;
423/447.3; 427/249.1 |
Current CPC
Class: |
B82Y 40/00 20130101;
Y10S 977/742 20130101; C01B 32/162 20170801; D01F 9/127 20130101;
B82Y 10/00 20130101; H01J 2201/30469 20130101; C23C 16/509
20130101; C23C 16/26 20130101; Y10S 977/844 20130101; Y10S 977/952
20130101; B82Y 30/00 20130101 |
Class at
Publication: |
423/447.2 ;
423/447.3; 427/249.1 |
International
Class: |
D01F 009/12; C23C
016/26 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2001 |
JP |
2001-333529 |
Claims
What is claimed is:
1. Carbon nanotubes perpendicularly and densely deposited on a
substrate, which are obtained by plasma processing in which the
temperature of the substrate is maintained at about 500.degree. C.
or less.
2. A method of manufacturing carbon nanotubes comprising supplying
alternating-current power at a specific frequency between an anode
and a cathode disposed in a reactor, and causing plasma to be
generated between the anode and the cathode by introducing mixed
gas containing an aliphatic hydrocarbon having 1-5 carbon atoms and
hydrogen or mixed gas containing an aromatic hydrocarbon and
hydrogen, thereby allowing carbon nanotubes to be deposited on a
substrate disposed between the anode and the cathode and held at a
distance two times or less of the mean free path of a hydrocarbon
cation from the anode.
3. The method of manufacturing carbon nanotubes according to claim
2, wherein the distance between the anode and the substrate is 20
cm or less.
4. The method of manufacturing carbon nanotubes according to claim
2, wherein the distance between the anode and the substrate is 10
cm or less.
5. The method of manufacturing carbon nanotubes according to claim
2, wherein the specific frequency is 13.56 MHz.
6. The method of manufacturing carbon nanotubes according to claim
2, wherein the aliphatic hydrocarbon having 1-5 carbon atoms is a
saturated aliphatic hydrocarbon having 1-5 carbon atoms or an
unsaturated aliphatic hydrocarbon having 1-5 carbon atoms.
7. The method of manufacturing carbon nanotubes according to claim
2, wherein the aromatic hydrocarbon is benzene, toluene, or
xylene.
8. The method of manufacturing carbon nanotubes according to claim
2, wherein a metal, an alloy, a metal complex, or a metal compound
is caused to adhere to the substrate as a catalyst.
9. The method of manufacturing carbon nanotubes according to claim
8, wherein the catalyst is at least one of a metal, an alloy, or a
metal compound of iron, cobalt, nickel, tungsten, platinum,
rhodium, and palladium.
10. The method of manufacturing carbon nanotubes according to claim
2, wherein a magnetic field is applied by disposing a magnet so
that magnetic force occurs in a direction perpendicular to the
substrate.
11. The method of manufacturing carbon nanotubes according to claim
2, wherein the pressure of the mixed gas is 1 to 50 Pa.
12. An electron emission source in which emitters are disposed
between a cathode electrode and a gate electrode and electrons are
emitted from the emitters by applying a voltage between the cathode
electrode and the gate electrode, wherein the emitters comprise the
carbon nanotubes according to claim 1.
13. A display comprising the electron emission source according to
claim 12.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to carbon nanotubes and a
method of manufacturing the same, an electron emission source, and
a display.
[0003] 2. Description of Background Art
[0004] Conventionally, a field electron emission source in which
emitters are disposed between a cathode electrode and a gate
electrode and electrons are emitted from the emitters by applying a
voltage between the cathode electrode and the gate electrode has
been developed.
[0005] The field electron emission source has excellent features
such as low power consumption and long lifetime in comparison with
an electron source which utilizes thermal energy (thermionic
emission source). As a material widely used for the electron
emission source, semiconductors such as silicon (Si), metals such
as tungsten (W) and molybdenum (Mo), a polycrystalline diamond thin
film, and the like are known.
[0006] When an electric field of about 10.sup.9 V/m is applied to
the surface of a metal or a semiconductor, electrons pass through a
barrier using a tunneling effect, whereby the electrons are emitted
under vacuum even at ordinary temperature (field emission
phenomenon). Therefore, the extracting current is determined
depending upon the electric field applied to an emission section
(emitter) from an extracting electrode section (gate electrode) It
is known in the art that a field intensity applied to the emitter
is increased as the tip of the emitter becomes sharper. Therefore,
it is necessary to process the tip of the electron emission section
formed of a semiconductor or a metal into the shape of a sharp
needle.
[0007] In order to enable stable field emission, the operational
atmosphere must be maintained at high vacuum of 133.times.10.sup.-8
Pa or more.
[0008] Carbon nanotubes have attracted attention as a material for
the electron emission source from the above point of view. The
outer diameter and the length of the carbon nanotubes are to
several tens of nanometers and several microns, respectively.
Therefore, the carbon nanotubes have a structure which enables
field emission at a low voltage. Moreover, carbon is chemically
stable and has mechanical strength. Because of this, the carbon
nanotube is an ideal emitter material.
[0009] However, since the carbon nanotubes are manufactured by
using an arc discharge method or laser irradiation to graphite and
used after purification, there have been the following
problems.
[0010] A conventional manufacturing method for the carbon nanotubes
incurs considerable cost. Moreover, yield of the carbon nanotubes
is extremely low due to a high content of impurities. Therefore,
cost of the resulting carbon nanotubes is inevitably increased.
This makes an electron emission source manufactured by using the
carbon nanotubes unprofitable.
[0011] There may be a case where a paste of carbon nanotubes is
printed on a specific electrode as the electron emission source.
However, the carbon nanotubes are aligned parallel to the substrate
after printing due to viscosity of a solvent of the printing paste
or additives. This results in problems such as an insufficient
field emission effect, an increase in extracting voltage, and a
decrease in extracting current.
[0012] As a method of directly depositing the carbon nanotubes on
the substrate, a microwave plasma method and a direct current
plasma method have been proposed. However, it is difficult to
uniformly deposit the carbon nanotubes over a wide area of the
substrate by using these methods. Moreover, the temperature of the
substrate is inevitably increased in order to deposit the carbon
nanotubes in a plasma stream at about 133 Pa. This makes it
difficult to use a substrate having a softening point of about
500.degree. C.
[0013] The present invention has been achieved to solve the above
conventional problems.
[0014] Accordingly, an object of the present invention is to
provide carbon nanotubes which are perpendicularly deposited on a
substrate and manufactured without excessively increasing the
temperature of the substrate.
[0015] Another object of the present invention is to provide a
method of manufacturing carbon nanotubes which are uniformly
deposited over a wide area, have a regular crystal structure, and
are aligned perpendicularly to a substrate, even if the temperature
of the substrate is 500.degree. C. or less.
[0016] Still another object of the present invention is to provide
an electron emission source excelling in electron emission
characteristics obtained by using the carbon nanotubes.
[0017] Yet another object of the present invention is to provide a
display using the electron emission source.
SUMMARY OF THE INVENTION
[0018] In order to achieve the above objects, the present invention
provides carbon nanotubes perpendicularly and densely deposited on
a substrate, which are obtained by plasma processing in which the
temperature of the substrate is maintained at about 500.degree. C.
or less. Since the carbon nanotubes according to the present
invention are perpendicularly and densely deposited on the
substrate, the carbon nanotubes exhibits an excellent field
emission effect. Moreover, since the carbon nanotubes are
manufactured by plasma processing in which the temperature of the
substrate is maintained at about 500.degree. C. or less, a
substrate having a low softening point such as a glass substrate
can be used.
[0019] The present invention also provides a method of
manufacturing carbon nanotubes comprising supplying
alternating-current power at a specific frequency between an anode
and a cathode disposed in a reactor, and causing plasma to be
generated between the anode and the cathode by introducing mixed
gas containing an aliphatic hydrocarbon having 1-5 carbon atoms and
hydrogen or mixed gas containing an aromatic hydrocarbon and
hydrogen, thereby allowing carbon nanotubes to be deposited on a
substrate disposed between the anode and the cathode and held at a
distance two times or less of the mean free path of a hydrocarbon
cation from the anode.
[0020] In the method of manufacturing carbon nanotubes according to
the present invention, the distance between the anode and the
substrate is preferably 20 cm or less, and still more preferably 10
cm or less.
[0021] In the method of manufacturing carbon nanotubes according to
the present invention, the specific frequency is preferably 13.56
MHz.
[0022] In the method of manufacturing carbon nanotubes according to
the present invention, the aliphatic hydrocarbon having 1-5 carbon
atoms may be a saturated aliphatic hydrocarbon having 1-5 carbon
atoms or an unsaturated aliphatic hydrocarbon having 1-5 carbon
atoms. The aromatic hydrocarbon may be benzene, toluene, or
xylene.
[0023] In the method of manufacturing carbon nanotubes according to
the present invention, a metal, an alloy, a metal complex, or a
metal compound is preferably caused to adhere to the substrate as a
catalyst. The catalyst is preferably at least one of a metal, an
alloy, or a metal compound of iron, cobalt, nickel, tungsten,
platinum, rhodium, and palladium.
[0024] In the method of manufacturing carbon nanotubes according to
the present invention, a magnetic field is preferably applied by
disposing a magnet so that magnetic force occurs in a direction
perpendicular to the substrate.
[0025] In the method of manufacturing carbon nanotubes according to
the present invention, the pressure of the mixed gas is preferably
1 to 50 Pa.
[0026] The present invention also provides an electron emission
source in which emitters are disposed between a cathode electrode
and a gate electrode and electrons are emitted from the emitters by
applying a voltage between the cathode electrode and the gate
electrode, wherein the emitters comprise the above carbon
nanotubes. According to the present invention, a field emission
source excelling in electron emission characteristics can be
provided by forming the emitters using the above carbon
nanotubes.
[0027] The present invention further provides a display comprising
the above electron emission source. An excellent flat display can
be manufactured by using the field emission source of the present
invention as an electron emission source of a field emission
display.
[0028] Other objects, features, and advantages of the present
invention will hereinafter become more readily apparent from the
following description.
BRIEF DESCRIPTION OF THE DRAWING
[0029] FIG. 1 is a view showing an apparatus for manufacturing
carbon nanotubes used in an embodiment of the present
invention.
[0030] FIG. 2 is an SEM photograph showing carbon nanotubes
manufactured in Example 1 of the present invention.
[0031] FIG. 3 is a characteristic chart of a field
intensity-current density curve of the carbon nanotubes
manufactured in Example 1 of the present invention
[0032] FIG. 4 is an SEM photograph showing carbon nanotubes
manufactured in Example 2 of the present invention.
[0033] FIG. 5 is an SEM photograph showing carbon nanotubes
manufactured in Example 3 of the present invention.
[0034] FIG. 6 is an SEM photograph showing carbon nanotubes
manufactured in Example 6 of the present invention.
[0035] FIG. 7 is an SEM photograph showing carbon nanotubes
manufactured in Example 7 of the present invention.
[0036] FIG. 8 shows an SEM photograph showing carbon nanotubes
grown on a substrate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0037] Carbon nanotubes and a method of manufacturing the same, an
electron emission source, and a display according to an embodiment
of the present invention are described below.
[0038] The carbon nanotubes according to the present invention are
perpendicularly and densely deposited on a substrate. The carbon
nanotubes are manufactured by supplying alternating-current power
at a specific constant frequency between two electrodes (anode and
cathode) disposed in a reactor, and causing plasma to be generated
between the anode and the cathode by introducing mixed gas
containing an aliphatic hydrocarbon having 1-5 carbon atoms
(C.sub.1-C.sub.5) and hydrogen or mixed gas containing an aromatic
hydrocarbon and hydrogen, thereby allowing carbon nanotubes to be
deposited on a substrate disposed between the anode and the cathode
and held at a distance two times or less of the mean free path of a
hydrocarbon cation from the anode.
[0039] Specifically, the carbon nanotubes are directly deposited
over a wide area of the substrate at specific positions with high
resolution at a comparatively low temperature of 500.degree. C. or
less by applying electric power at a specific frequency between the
anode and the cathode and introducing a C.sub.1-C.sub.5 aliphatic
hydrocarbon and hydrogen or an aromatic hydrocarbon and hydrogen so
as to be reacted in plasma.
[0040] In this case, the carbon nanotubes can be uniformly
deposited for a short period of time by causing a metal, an alloy,
a metal complex, or a metal compound to adhere to the substrate as
a catalyst in the area in which the carbon nanotubes are deposited.
Moreover, the carbon nanotubes can be directly deposited at desired
positions with high resolution.
[0041] Plasma density can be increased and alignment of the carbon
nanotubes in the direction perpendicular to the substrate can be
promoted by applying a magnetic field at a specific strength by
disposing a magnet so that magnetic force occurs in the direction
perpendicular to the substrate. The resulting carbon nanotubes have
a regular crystal structure and adhere to the substrate while being
aligned perpendicularly to the substrate.
[0042] In the present embodiment, it is important to dispose the
anode and the substrate at a distance two times or less of the mean
free path of a hydrocarbon cation. If the distance between the
anode and the substrate exceeds two times the mean free path of a
hydrocarbon cation, the growth rate of the carbon nanotubes is
decreased. In more detail, the distance between the anode and the
substrate is 20 cm or less, and preferably 10 cm or less taking
into consideration the pressure, bias voltage, and the like under
usual formation conditions for carbon nanotubes.
[0043] This enables occurrence of collision between hydrocarbon
cations to be minimized by causing plasma to be generated in a
state in which the concentration of hydrocarbon molecules is as low
as possible, whereby the carbon nanotubes can be efficiently and
rapidly produced. Moreover, the carbon nanotubes can be grown
perpendicularly to the substrate.
[0044] Density of plasma generated in the reactor is decreased by
decreasing the concentration of hydrocarbon molecules,
specifically, by setting the pressure of the mixed gas at 1-50 Pa,
and preferably 1-20 Pa. This prevents an increase in the
temperature of the substrate. Therefore, the temperature of the
substrate can be maintained at 500.degree. C. or less. This enables
utilization of a low-melting-point glass substrate such as soft
glass as the substrate.
[0045] For example, a case of using acetylene as a hydrocarbon
under conditions employed in Example 1 is described below.
[0046] In the case of single gas, the mean free path .lambda. of a
molecule is shown by the following equation.
.lambda.=kT/(.pi.P.sigma..sup.2{square root}2) (1)
[0047] wherein k=Boltzmann constant (1.38066.times.10.sup.-23
JK.sup.-1) T=temperature of surface of substrate (absolute
temperature K) .sigma.=collision diameter (nm) of molecule, and
P=partial pressure (Pa) of. gas in reactor (chamber).
[0048] The concentration of acetylene is very low in the plasma
formation conditions employed in Example 1, since acetylene is
diluted with hydrogen and is at low pressure. Therefore, the mean
free path of an acetylene molecule in the actual plasma formation
conditions can be roughly calculated by using the equation (1).
[0049] Specifically, collision between acetylene molecules is
ignored in comparison with collision between acetylene and
hydrogen, since the concentration of acetylene gas is low. The
collision diameter .sigma. of molecules in the equation (1) is
considered to be the sum of the collision diameters of acetylene
and hydrogen.
[0050] The collision diameters of acetylene and hydrogen are
respectively about 0.24 nm and about 0.14 nm. Therefore, the
collision diameter .sigma. is 0.38 nm.
[0051] The mean free path .lambda. of acetylene at a substrate
temperature of 400.degree. C. (measured value) and a pressure of
acetylene-hydrogen mixed gas of 10 Pa calculated according to the
equation (1) is about 0.15 cm.
[0052] Since acetylene is ionized in the plasma conditions and a
bias voltage of -50 V is applied between the anode and the cathode,
an acetylene cation has an energy of 50 eV. The kinetic energy of
acetylene is 0.1 eV (3kT/2 at 400.degree. C.=0.1 eV). Therefore, an
acetylene cation has an energy 500 times the energy of the
acetylene molecule (50 eV/0.1 eV) (.degree.500 times (about 22
times) in speed).
[0053] Therefore, the mean free path of an acetylene cation is 0.15
cm.times.22=3.3 cm at a mixed gas pressure of 10 Pa.
[0054] It is preferable that the number of collisions between an
acetylene cation and other molecules before the acetylene cation
reaches the substrate be as small as possible from the viewpoint of
formation of the carbon nanotubes. If these considerations are
applied to hydrocarbons used in the present embodiment other than
acetylene, the mean free path of a hydrocarbon cation is estimated
to be about 5 to 15 cm.
[0055] Therefore, the target is attained by holding the substrate
at a distance of 20 cm or less, and preferably 10 cm or less from
the anode.
[0056] Since this value relates to the pressure P, specifically,
the internal pressure of the mixed gas as shown in the equation
(1), it is important to maintain the pressure P as small as
possible (increase the degree of decompression).
[0057] The C.sub.1-C.sub.5 aliphatic hydrocarbon used in the
present embodiment includes a saturated aliphatic hydrocarbon and
an unsaturated aliphatic hydrocarbon. These hydrocarbons may be
used either individually or in combination of two or more. As
examples of C.sub.1-C.sub.5 aliphatic hydrocarbons, methane,
ethane, propane, n-butane, i-butane, n-pentane, i-pentane, and the
like can be given. Since the collision diameter of a methane cation
is 0.2 nm, the mean free path .lambda. of a methane cation is 8.0
cm at 5 Pa. This does not significantly affect the distance between
the anode and the substrate.
[0058] C.sub.1-C.sub.5 unsaturated aliphatic hydrocarbons have a
double bond and/or a triple bond. As examples of C.sub.1-C.sub.5
unsaturated aliphatic hydrocarbons, a monoolefin, diolefin,
conjugated diolefin, acetylene, and the like may be used.
[0059] As the monoolefin, ethylene, propylene, butene-1, butene-2,
isobutylene, pentene-1, pentene-2, and the like may be used. As the
diolefin, penta-1,4-diene may be used. As the conjugated diolefin,
butadiene, isoprene, and the like may be used. As the acetylene,
acetylene, propyne-1, butyne-1, and the like may be used.
[0060] As aromatic hydrocarbons, benzene, toluene, xylene, and the
like may be used.
[0061] As C.sub.1-C.sub.5 aliphatic hydrocarbons, methane, ethane,
ethylene, butadiene, acetylene, and the like are particularly
preferable.
[0062] As aromatic hydrocarbons, benzene and toluene are
particularly preferable.
[0063] Use of C.sub.1-C.sub.5 aliphatic hydrocarbon or aromatic
hydrocarbon enables the carbon nanotubes to be manufactured at a
low temperature and a high formation rate.
[0064] As a catalyst, a metal, an alloy, or a metal compound of
iron, cobalt, nickel, tungsten, platinum, rhodium, and palladium,
and the like may be used. Of these, a metal, an alloy, or a metal
compound of iron, cobalt, or nickel is particularly preferable.
These catalysts may be used either individually or in combination
of two or more. These catalysts may be caused to adhere to the
substrate by deposition, printing, coating, an ink-jet method, or
the like. In particular, it is preferable to use nanoparticles of
these catalysts when using printing, coating, an ink-jet method, or
the like.
[0065] The frequency of an alternating-current power supply used to
generate plasma may be a constant frequency of 13.56 MHz. However,
the frequency is not limited to 13.56 MHz.
[0066] It is preferable to dispose a magnet so that magnetic force
occurs in the direction perpendicular to the substrate in order to
increase plasma density and promote alignment of the carbon
nanotubes in the direction perpendicular to the substrate. In more
detail, the magnet is disposed on the top and/or bottom or the side
of the substrate. There are no specific limitations to the magnetic
field. The magnetic field is preferably about 100-10,000 G.
[0067] In order to ensure that magnetic force uniformly occurs in
the direction perpendicular to a large substrate, a fixed permanent
magnet may be disposed so that a magnetic field is applied between
the cathode and the anode. The magnetic field may be caused to
occur uniformly between the cathode and the anode by rotating the
permanent magnet.
[0068] A conventional formation temperature for the carbon
nanotubes is about 550.degree. C. at a gas pressure of 133-1330 Pa
in the case of using a direct current plasma method or a microwave
plasma method. Therefore, soft glass cannot be used as the
substrate at such a high temperature. In the present embodiment,
the carbon nanotubes can be perpendicularly deposited over a wide
area of the substrate with high resolution even at a low
temperature of 500.degree. C. or less. Moreover, the resulting
carbon nanotubes have a regular crystal structure. Therefore, the
carbon nanotubes can be easily deposited on a substrate having a
low melting point.
[0069] FIG. 1 is a view showing an example of an apparatus for
manufacturing the carbon nanotubes used in the present embodiment.
The apparatus shown FIG. 1 was used in each example described
later. In FIG. 1, 101 indicates a reactor (chamber), 102 indicates
an anode, 103 indicates a stainless steel ring, 104 indicates a
sample base made of stainless steel, 105 indicates a substrate, 106
indicates a Teflon ring, 107 indicates a cathode, 108 indicates a
permanent magnet, and 109 indicates an alternating-current power
supply at a frequency of 13.56 MHz. The alternating-current power
supply 109 causes plasma to be generated between the anode 102 and
the cathode 107. The permanent magnet 108 produces a magnetic field
for causing high-density plasma to be generated near the substrate
105. Source gas is supplied from a tube 110, passes through the
reactor 101, and is guided to a vacuum pump (not shown) through a
tube 111.
[0070] In the case of producing the carbon nanotubes in the reactor
101, alternating-current power at a constant frequency (13.56 MHz
in the present embodiment) is supplied between the two electrodes
(anode 102 and cathode 107) from the alternating-current power
supply 109. The inside of the reactor 101 is maintained at a
specific pressure by discharging mixed gas containing an aliphatic
hydrocarbon having 1-5 carbon atoms (C.sub.1-C.sub.5) and hydrogen
or an aromatic hydrocarbon and hydrogen from the tube 111 through
the tube 110 and the reactor 101. Plasma is generated between the
anode 101 and the cathode 107 in this state, whereby the carbon
nanotubes are formed on the substrate 105. The substrate 105 is
disposed between the anode 102 and the cathode 107 and held at a
distance of 10 cm or less from the anode 102.
[0071] Reaction gases are introduced into the reactor 101 from the
tube 110 as source gas. The reaction gases are reacted in plasma
and deposited on the substrate 105 placed on the sample base 104.
The source gas has a composition in which 0.5-20 vol of a
C.sub.1-C.sub.5 aliphatic hydrocarbon or aromatic hydrocarbon is
mixed with 100 vol of hydrogen, for example. The flow rate is
10-100 sccm/s, for example. However, the flow rate may differ
depending on the size of the reactor. The output of the
alternating-current power supply 109 is 50-1000 W, for example. The
pressure inside the reactor 101 is preferably 1-50 Pa. -5 to -500 V
is preferably applied to the cathode 107 as a bias potential with
respect to the anode 102.
[0072] The growth rate of the carbon nanotubes is decreased if an
insulation substance such as glass is used as the substrate 105.
However, the growth rate of the carbon nanotubes is increased by
maintaining a catalyst layer on the surface of the substrate and
the cathode at the same voltage. Since the catalyst layer on the
surface of the substrate and the cathode are at the same potential,
electrons are smoothly supplied to the surface of the catalyst.
This prevents occurrence of charge-up on the surface of the
substrate due to a cation, whereby environment which enables a
cation to easily attack is maintained. Therefore, the growth rate
of the carbon nanotubes is increased. In this case, it is necessary
to maintain the catalyst layer on the surface of the substrate and
the cathode in an electrically conducting state by winding a
conductor such as aluminum foil on the periphery of the substrate,
for example.
[0073] When a voltage was applied to carbon nanotubes deposited on
an appropriate substrate under vacuum, it was confirmed that
current flowed through the carbon nanotubes. Multi-walled carbon
nanotubes manufactured by using the method of the present
embodiment are deposited on the substrate in a state in which the
carbon nanotubes are aligned perpendicularly to the substrate.
Therefore, the carbon nanotubes are extremely suitably used as
emitters for an electron emission source.
[0074] As described above, according to the present embodiment,
carbon nanotubes perpendicularly and densely deposited on a
substrate can be efficiently manufactured. The carbon nanotubes are
uniformly deposited over a wide area of the substrate with high
resolution.
[0075] According to the present embodiment, a method of
manufacturing carbon nanotubes having characteristics in which
deposited carbon nanotubes have a regular crystal structure, are
uniformly deposited over a area, and are aligned perpendicularly to
the substrate, even if the temperature of the substrate is
500.degree. C. or less, can be provided.
[0076] According to the present embodiment, a field emission source
excelling in electron emission characteristics, in which emitters
are disposed between a cathode conductor and a gate electrode and
electrons are emitted from the emitters by applying a voltage
between the cathode conductor and the gate electrode, can be
provided by forming the emitters using the carbon nanotubes
manufactured by the above method.
[0077] An excellent flat display can be manufactured by using the
field emission source thus obtained as an electron emission source
of a field emission display. FIG. 8 shows an SEM photograph showing
carbon nanotubes grown on a substrate of a display by using the
above method.
EXAMPLES
[0078] The present invention is described below in more detail by
examples. However, these examples should not be construed as
limiting the present invention.
Example 1
[0079] Carbon nanotubes were deposited under conditions given below
by using the manufacturing apparatus shown in FIG. 1. Acetylene was
used as an unsaturated hydrocarbon.
[0080] Flow rate of hydrogen gas (sccm/s): 23.0
[0081] Flow rate of acetylene gas (sccm/s): 0.4
[0082] RF (frequency) power (W): 360
[0083] Pressure inside reactor (Pa): 10
[0084] Bias potential (V): -50
[0085] The distance between the anode 102 and the substrate 105 was
8 cm. As the substrate 105, a substrate obtained by depositing
chromium on soda-lime glass and further depositing nickel on
chromium was used. Carbon nanotubes were deposited for 60 minutes.
FIG. 2 shows an SEM photograph of the resulting carbon nanotubes.
As shown in FIG. 2, the carbon nanotubes were perpendicularly and
densely deposited on the substrate 105.
[0086] FIG. 3 is a characteristic chart showing results for a field
intensity-current density curve measured using the substrate 105 on
which the carbon nanotubes were deposited. The maximum current
density was 1.4 mA/cm.sup.2.
Example 2
[0087] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, a substrate obtained by causing iron, which
functions as a catalyst during formation of carbon nanotubes, to
adhere to a copper substrate was used as the substrate 105.
[0088] Iron was caused to adhere to the copper substrate as
follows. Specifically, after applying isopropyl alcohol containing
5% ferric (II) nitrate (Fe(NO.sub.3).sub.3.multidot.9H.sub.2O) to
the copper substrate, ferric (II) nitrate was reduced to iron by
hydrogen plasma processing (processing conditions: pressure; 8 Pa,
output of alternating-current power supply 109; 400 W, bias
potential; -40 to -70V, processing time; 10 min.).
[0089] FIG. 4 shows an SEM photograph of the resulting carbon
nanotubes. As shown in FIG. 4, the carbon nanotubes were
perpendicularly and densely deposited on the substrate 105. A
current-voltage curve was measured by using this substrate. As a
result, the maximum current density was 0.7 mA/cm.sup.2.
Example 3
[0090] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, a substrate obtained by causing cobalt, which
functions as a catalyst during formation of carbon nanotubes, to
adhere to a copper substrate was used as the substrate 105.
[0091] Cobalt was caused to adhere to the copper substrate as
follows. Specifically, after applying isopropyl alcohol containing
5% cobalt (II) nitrate (Co(NO.sub.3).sub.2.multidot.6H.sub.2O) to
the copper substrate, cobalt (II) nitrate was reduced to cobalt by
hydrogen plasma processing (processing conditions: pressure; 8 Pa,
output of alternating-current power supply 109; 400 W, bias
potential;-40 to -70V, processing time; 10 min.).
[0092] FIG. 5 shows an SEM photograph of the resulting carbon
nanotubes. As shown in FIG. 5, the carbon nanotubes were
perpendicularly and densely deposited on the substrate 105. A
current-voltage curve was measured by using this substrate. As a
result, the maximum current density was 0.6 mA/cm.sup.2.
Example 4
[0093] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, a substrate obtained by depositing chromium on
soda-lime glass, depositing copper on chromium, and further
depositing nickel on copper was used as the substrate 105.
[0094] The deposition state of carbon nanotubes was the same as
that shown in FIG. 2. A current-voltage curve was measured by using
the substrate 105. As a result, the maximum current density was 1.8
mA/cm.sup.2. Therefore, emission characteristics were improved in
comparison with Examples 1-3.
Example 5
[0095] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, ethylene gas was used instead of acetylene gas.
The deposition state of carbon nanotubes was the same as that shown
in FIG. 2.
Example 6
[0096] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, methane gas was used instead of acetylene gas.
The experimental conditions were as follows.
[0097] Flow rate of hydrogen gas (sccm/s): 20
[0098] Flow rate of methane gas (sccm/s): 0.4
[0099] Output power (W) of AC power supply 109: 400
[0100] Pressure inside chamber (Pa): 12
[0101] Deposition time (min): 120
[0102] FIG. 6 shows an SEM photograph of carbon nanotubes obtained
in Example 6. As shown in FIG. 6, the carbon nanotubes were
perpendicularly and densely deposited on the substrate 105.
Example 7
[0103] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, benzene was used instead of acetylene gas. FIG.
7 shows an SEM photograph of the resulting carbon nanotubes. As
shown in FIG. 7, the carbon nanotubes were perpendicularly and
densely deposited on the substrate 105.
Example 8
[0104] An experiment was conducted under the same conditions
(distance between the anode and the substrate and the like) as in
Example 1. However, the flow rate of hydrogen gas was set at 20
sccm/s and the flow rate of acetylene gas was set at 0.8 sccm/s. An
SEM photograph of the resulting carbon nanotubes was the same as in
Example 1.
[0105] As described above, according to the present invention,
carbon nanotubes perpendicularly and densely deposited on a
substrate can be provided without excessively increasing the
temperature of the substrate.
[0106] Moreover, a method of manufacturing carbon nanotubes which
are uniformly deposited over a wide area, have a regular crystal
structure, and are aligned perpendicularly to a substrate can be
provided, even if the temperature of the substrate is 500.degree.
C. or less.
[0107] Furthermore, an electron emission source excelling in
electron emission characteristics obtained by using the carbon
nanotubes and a display using the electron emission source can be
provided. An excellent flat display can be manufactured by using
the field emission source as an electron emission source of a field
emission display.
[0108] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that, within the scope of the
appended claims, the invention may be practiced otherwise than as
specifically described herein.
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