U.S. patent application number 10/886979 was filed with the patent office on 2005-01-20 for carbon nanotube manufacturing method.
Invention is credited to Kurachi, Hiroyuki, Uemura, Sashiro.
Application Number | 20050013762 10/886979 |
Document ID | / |
Family ID | 34055719 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050013762 |
Kind Code |
A1 |
Kurachi, Hiroyuki ; et
al. |
January 20, 2005 |
Carbon nanotube manufacturing method
Abstract
In a carbon nanotube manufacturing method, a substrate made of a
carbon-containing metal material is arranged in a reactor in which
a carbon source gas has been introduced. A plurality of carbon
nanotubes are grown at a first temperature by chemical vapor
deposition. Thereafter, the substrate is heated at a second
temperature lower than the first heating temperature to grow the
plurality of carbon nanotubes longer on the substrate.
Inventors: |
Kurachi, Hiroyuki; (Mie,
JP) ; Uemura, Sashiro; (Mie, JP) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD
SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Family ID: |
34055719 |
Appl. No.: |
10/886979 |
Filed: |
July 7, 2004 |
Current U.S.
Class: |
423/447.3 |
Current CPC
Class: |
D01F 9/1275 20130101;
D01F 9/1271 20130101; D01F 9/1272 20130101; B82Y 30/00 20130101;
D01F 9/1273 20130101; D01F 9/1278 20130101 |
Class at
Publication: |
423/447.3 |
International
Class: |
D01F 009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2003 |
JP |
195325/2003 |
Claims
What is claimed is:
1. A carbon nanotube manufacturing method of arranging a substrate
made of a carbon-containing metal material in a reactor in which a
carbon source gas has been introduced, and growing a plurality of
carbon nanotubes at a first temperature by chemical vapor
deposition, and thereafter heating the substrate at a second
temperature lower than the first heating temperature to grow the
plurality of carbon nanotubes longer on the substrate.
2. A method according to claim 1, wherein at least a surface of the
substrate is made of a metal material containing any one of iron,
nickel, cobalt, and chromium.
3. A method according to claim 1, wherein the first temperature is
750.degree. C. to 1,000.degree. C., and the second temperature is
500.degree. C. to 750.degree. C.
4. A method according to claim 1, wherein the carbon source gas is
one gas selected from the group consisting of carbon monoxide,
acetylene, ethylene, ethane, propylene, propane, and methane gases.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a carbon nanotube
manufacturing method of forming a plurality of carbon nanotubes on
the surface of a substrate.
[0002] A carbon nanotube forms a completely graphitized cylinder
having a diameter of about 40 nm to 50 nm and a length of about 1
.mu.m to 10 .mu.m. Examples of the carbon nanotube include one
having a shape in which a single graphite layer (graphene) is
closed cylindrically and one having a shape in which a plurality of
graphenes are layered telescopically such that the respective
graphenes are closed cylindrically to form a coaxial multilayered
structure.
[0003] The central portions of the cylindrical graphenes are
hollow. The distal end portions of the graphenes may be closed, or
broken and accordingly open.
[0004] It is expected that the carbon nanotube having such a
special shape may be applied to novel electronic materials and
nanotechnology by utilizing its specific electronic physical
properties. For example, the carbon nanotube can be used as an
electronic emitting source for an electron tube. When a strong
electric field is applied to the surface of a solid, the potential
barrier of the surface of the solid which confines electrons in the
solid becomes low and thin. Consequently, the confined electrons
are emitted outside the solid due to the tunnel effect. These
phenomena are called field emission.
[0005] In order to observe field emission, an electric field of as
strong as 10.sup.7 V/cm must be applied to the solid surface. To
realize this, according to one scheme, a metal needle with a sharp
point is used. When an electric field is applied by using such a
needle, the electric field is focused on the sharp point, and a
necessary strong electric field is obtained.
[0006] The carbon nanotube described above has a very sharp point
with a radius of curvature on the nm order, and is chemically
stable and mechanically tough, thus providing physical properties
suitable for the material of a field-emission emitter.
[0007] When the carbon nanotube having the characteristic feature
as described above is to be used for, e.g., an electronic emitting
source in an electron tube such as an FED (Field Emission Display),
carbon nanotubes must be formed on a substrate having a large
area.
[0008] Carbon nanotube manufacturing methods include electric
discharge in which two carbon electrodes are separated from each
other by about 1 mm to 2 mm in helium gas and DC arc discharge is
caused, laser vapor deposition, and the like.
[0009] With these manufacturing methods, however, the diameter and
length of the carbon nanotube are difficult to adjust, and the
yield of the carbon nanotube as the target cannot be increased very
much. A large amount of amorphous carbon products other than carbon
nanotubes are produced simultaneously. Thus, a refining process is
required, making the manufacture cumbersome.
[0010] In order to solve these problems, a method of preparing a
catalyst metal layer on a substrate, and heating the substrate and
supplying a carbon source gas onto the catalyst metal layer, thus
growing a large amount of carbon nanotubes from the catalyst metal
layer by chemical vapor deposition (CVD) is proposed (see Japanese
Patent Laid-Open No. 2001-048512). With the carbon nanotube
manufacture in accordance with chemical vapor deposition (CVD), the
length and diameter of the carbon nanotube to be formed can be
controlled in accordance with the type of the catalyst metal, the
duration of growth, and the type of the substrate.
[0011] When the carbon nanotube is used as the electronic emitting
source, if a thinner carbon nanotube is used, electrons can be
emitted with a lower voltage. For example, when the carbon nanotube
is used as an electronic emitting source for an FED, if a thinner
carbon nanotube is used, driving with a lower voltage is enabled.
This is preferable in terms of power consumption saving.
[0012] When the carbon nanotube is formed by chemical vapor
deposition (CVD), a plurality of carbon nanotubes can be formed
close to each other on a substrate. When the substrate temperature
is set as high as 800.degree. C. to 1,000.degree. C., a thin carbon
nanotube having a diameter of about 10 nm can be formed.
[0013] When the carbon nanotube is grown at a high temperature, a
thin carbon nanotube with a diameter of about 10 nm can be
obtained. This is suitable as an electronic emitting source for
low-voltage driving. However, the growing speed of the carbon
nanotube per unit time is low. To obtain a carbon nanotube having a
desired length, much time is needed.
[0014] When the carbon nanotube is grown at a high temperature,
part of a layer including a plurality of carbon nanotubes formed on
the substrate may separate from the substrate, or cracking may
occur, to form steps on the surface of the layer. Therefore, it is
difficult to form a carbon nanotube layer uniformly.
[0015] In this manner, when the height of the layer including the
carbon nanotubes formed on the substrate varies locally, local
field concentration occurs on the highest (longest) carbon
nanotube, thus causing field emission locally. Local field emission
leads to destruction of the carbon nanotubes. Depending on the
case, a chain of destruction of a large number of carbon nanotubes
is caused. When destruction of the carbon nanotubes serving as an
electronic emitting source occurs, stable field emission cannot be
obtained.
SUMMARY OF THE INVENTION
[0016] It is, therefore, the principal object of the present
invention to provide a method of manufacturing a carbon nanotube
which is thinner than in the prior art and with which a uniform
electronic emitting source can be obtained.
[0017] It is another object of the present invention to provide a
carbon nanotube manufacturing method with which a plurality of
carbon nanotubes which are thinner than in the prior art can be
manufactured quickly.
[0018] It is further object of the present invention to provide a
method of manufacturing a carbon nanotube which can form a layer
including a plurality of thinner carbon nanotubes uniformly on a
substrate.
[0019] In order to achieve the above objects, according to the
present invention, there is provided a carbon nanotube
manufacturing method comprising arranging a substrate made of a
carbon-containing metal material in a reactor in which a carbon
source gas has been introduced, and growing a plurality of carbon
nanotubes at a first temperature by chemical vapor deposition, and
thereafter heating the substrate at a second temperature lower than
the first heating temperature to grow the plurality of carbon
nanotubes longer on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A to 1C are sectional views showing the steps in a
carbon nanotube manufacturing method according to an embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The embodiment of the present invention will be described
with reference to the accompanying drawings.
[0022] FIGS. 1A to 1C show a carbon nanotube manufacturing method
according to an embodiment of the present invention. First, as
shown in FIG. 1A, a substrate 101 made of stainless steel such as a
426-alloy is prepared.
[0023] Subsequently, as shown in FIG. 1B, the substrate 101 is
placed in a reactor 104 formed of, e.g., a quartz pipe. While a
carbon source gas and hydrogen gas (carrier gas) are supplied from
one side of the reactor 104, the substrate 101 is heated by a
heater 105. FIGS. 1B and 1C schematically show the section of the
reactor 104.
[0024] In the chemical vapor deposition growth process using the
reactor 104 described above, carbon monoxide gas may be used as the
carbon source gas, and its flow rate may be set to about 500 sccm.
The flow rate of the carrier gas may be set to 1,000 sccm. As the
carbon source gas, one of C1 to C3 hydrocarbon gases such as
acetylene, ethylene, ethane, propylene, propane, and methane gases
can be used. In the above process, as the substrate 101, one made
of stainless steel is used. However, the present invention is not
limited to this. It suffices as far as the surface of the substrate
where carbon nanotubes are to be formed is made of a material
containing a metal from which carbon nanotubes grow by chemical
vapor deposition. The metal is any one of, e.g., iron, nickel,
cobalt, and chromium, or an alloy of them.
[0025] According to this embodiment, the heating temperature for
the substrate 101 is set as high as at about 800.degree. C. to
900.degree. C., and chemical vapor deposition is performed for 10
min. Then, as shown in FIG. 1B, a plurality of carbon nanotubes 102
each having a diameter of about 10 nm grow on the surface of the
substrate 101. The carbon nanotubes 102 grow to have a length of
about 1 .mu.m. In this case, for example, the plurality of carbon
nanotubes 102 extend upright closely on the surface of the
substrate 101.
[0026] After the above chemical vapor deposition is performed,
subsequently, the heating temperature of the heater 105 is
decreased to heat the substrate 101 at a low temperature of about
650.degree. C. Chemical vapor deposition is performed for 20
min.
[0027] Then, the carbon nanotubes 102 that have grown on the
surface of the substrate 101 grow longer. As shown in FIG. 1C, a
plurality of carbon nanotubes 103 are formed uniformly to have a
length of about 13 .mu.m. As a result, a carbon nanotube layer
having a uniform thickness is formed on the substrate 101. In the
carbon nanotube layer, for example, a plurality of carbon nanotube
fibers are entangled with each other to be fluffy. The
high-temperature treatment may be performed within the range of
750.degree. C. to 1,000.degree. C. If the temperature is less than
the lower limit of the above range, CNTs cannot be formed; if the
temperature exceeds 1,000.degree. C., it is not preferable because
problems may occur in heat resistance of the substrate and quartz
pipe. The low-temperature treatment as the second step may be
performed within the range of 500.degree. C. to 750.degree. C. When
the temperature was lower than 750.degree. C., preferably near
650.degree. C., CNTs can grow from the metal substrate quickly.
[0028] As has been described above, according to the present
invention, the substrate is heated at the first temperature, and a
plurality of carbon nanotubes are grown on the surface of the
substrate by chemical vapor deposition. Subsequently, the substrate
is heated at the second temperature lower than the first
temperature, so that the plurality of carbon nanotubes grow longer.
As a result, according to the present invention, the thin, about
10-nm diameter carbon nanotubes which have grown in the early stage
grow longer in the second stage with a faster growing speed after
the temperature is decreased. Therefore, a layer including a
plurality of carbon nanotubes which are thinner than in the prior
art can be uniformly formed on the substrate.
* * * * *