JP3463091B2 - Method for producing carbon nanotube - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing carbon nanotubes by a CVD method (chemical vapor deposition method) using ECR (electron cyclotron resonance) plasma of a carbon-containing material.

[0002]

2. Description of the Related Art Carbon nanotubes are tubular carbons having a structure in which a graphite sheet having a thickness of several atomic layers is closed in a cylindrical shape. For carbon nanotube synthesis, arc discharge, thermal decomposition method, catalytic thermal CVD method, microwave CVD
The law is often used. In the case of a cold cathode that uses carbon nanotubes as an electron emission source, in order to deposit directly on a predetermined position on the surface of the substrate, a method of adhering and fixing the carbon nanotube on the substrate with a conductive adhesive or a microwave CVD method. A method of directly synthesizing on a substrate by a catalytic thermal CVD method is used. Carbon nanotubes synthesized by the arc discharge method also contain an impurity carbon material, and thus require purification. The thickness and the direction are often random, and it is difficult to align them, and it is difficult to increase the area. Moreover, a very high temperature is required for the synthesis. In order to deposit directly on a predetermined position on the substrate surface, there is a problem that an extra process of adhering and fixing on the substrate with a conductive adhesive is required. In order to solve this problem, attempts have been made to synthesize direction-controlled carbon nanotubes on a substrate. Ago et al. By thermal CVD (ApplPhys.Lett., 77,1,79), Murakami et al.
By (JP 2000-57934, Appl.Phys.Lett., 76,13,177
6) I am doing. In many cases, heating at about 800 to 1000 ° C. is required for the synthesis of carbon nanotubes by the thermal decomposition method or the thermal CVD method, and the uniformity of the direction and diameter of the product may be low due to the temperature gradient in the reaction tank. Many. Although the carbon nanotubes have been orientated by using the microwave CVD method, an electric field is generally required for the orientation, and the synthesis is successful only under the condition that the synthesis pressure is as high as several thousand Pa or more. Was there. Also, it is difficult to make the area where the carbon nanotubes adhere to a practical size, and it is not practical from the viewpoint of industrial use.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
An object of the present invention is to provide a method for efficiently producing high-quality carbon nanotubes without applying an electric field under conditions of a low temperature of about 50 ° C. and a low pressure of 10 ⁻⁴ to 10 ⁻¹ Pa.

[0004]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, 10 ^-4 to 10 ^-1 Pa
Of the carbon-containing material is introduced into the plasma generation chamber in which the microwave is introduced and the microwave is introduced under the pressure of the carbon-containing material to generate electron cyclotron resonance plasma of the carbon-containing material. At the same time, there is provided a method for producing carbon nanotubes, which comprises contacting the plasma with a substrate held at a temperature of 500 to 850 ° C. and vertically depositing the carbon nanotubes on the substrate.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a carbon nanotube (hereinafter simply referred to as CNT) according to the present invention, in order to form a carbon nanotube film by depositing needle-like CNTs on a substrate surface, an ECR ( Electron cyclotron resonance) plasma CVD method is used. This ECR plasma CVD method is a conventional thermal CVD method or plasma CVD method.
Compared with the law, it has the following features. By applying a magnetic field, the plasma density is improved, and synthesis can be performed at a lower temperature. It can be synthesized under a low pressure (1.5 to 2 × 10 ⁻¹ Pa), and has excellent plasma controllability and stability.

In the present invention, a substrate is used for depositing CNT, and various conventionally known substrates can be used as this substrate. As such a substrate, a heat resistant substrate, for example, a quartz substrate, an alumina substrate,
A silicon substrate or the like can be used. In the present invention, the CNT deposition substrate, if necessary, has a CNT deposition aid on its surface in the form of ultrafine particles (particle size 4 nm to 50 n).
It is preferable to attach it in m). The deposition aid causes the CNTs to grow perpendicular to the substrate. As such a CNT deposition aid, various conventionally known transition metals (including alloys) can be used.
Specific examples thereof include metals such as Pd, Fe, Co and Ni and alloys thereof. As a method of attaching the metal to the substrate, a method of attaching it to the substrate by a CVD method, a sputtering method, or the like, or a method of applying a solution containing a metal salt or a metal organic complex to the substrate and then reducing it to a metal Etc. The rate of metal deposited on the substrate is 10 ^-7 to 10 ^-4 g per cm ² , preferably 1
It is about 0 ^-6 to 10 ^-5 g. In the case where the above-mentioned CNT deposition aid is adhered to the substrate or the substrate surface has a rough surface structure or a protrusion structure, those particles, the convex portion or the protrusion portion become the CNT growth start region, and this portion CNTs are deposited on.

In the method of the present invention, a substrate is placed in a reaction vessel, ECR plasma of a carbon-containing material is generated in the vessel, and the substrate is heated to a temperature of 500 to 850 ° C., preferably 550 to 600 ° C. It is carried out by bringing the ECR plasma formed of a carbon-containing material into contact with the substrate. The reaction time in this case is 10 to 60 minutes, preferably 15 to 30 minutes. The ECR plasma contains 10 ^-4 to 10 ^-1 P in a container filled with a carbon-containing material gas.
a, preferably at a pressure of 10 ^-2 to 10 ^-1 Pa, and can be generated by irradiating the container with microwaves in the presence of a magnetic field. It is sufficient that the microwave has a frequency of 2.45 GHz and the microwave output is about 300 to 1000 W. The magnetic field applied to the microwaves is preferably generated in parallel with the microwave traveling method. The strength of the magnetic field is 7 mT (tesla) or more, preferably 22 mT or more in the central portion of the plasma generating portion in the container. The upper limit value is not particularly limited, but is usually about 50 mT. In the central part of the reaction part, it is 5 mT or more, preferably 20 mT or more, and the upper limit thereof is not particularly limited, but is usually 40 mT.
It is about T.

The carbon-containing material used in the present invention can be in a gaseous state, a liquid state or a solid state at room temperature, but from the viewpoint of handling, it is preferably a gas state at room temperature. A substance that is in a liquid state at room temperature can be turned into a gas by heating and vaporizing the substance. Those that are solid at room temperature can be made into gas by previously decomposing and gasifying. Carbon-containing materials that can be preferably used in the present invention include gaseous hydrocarbons such as methane, ethane, propane and butane;
Examples thereof include liquid hydrocarbons such as benzene, toluene, xylene, hexane, and light oil.

The present invention will now be described in detail with reference to the drawings. FIG. 1 shows a schematic view of one embodiment of a carbon nanotube manufacturing apparatus used for carrying out the method of the present invention. Figure 1
1, 1 is a reaction part, 2 is a plasma generation part, 3 is a diaphragm plate, 4 is a waveguide, 5 is a reaction gas supply pipe, 6 is an exhaust pipe,
7 is a support plate, 8 is a support rod, and 10 is a reaction vessel. 11
-13 shows a magnet coil, S shows a board | substrate. The reaction container 10 is composed of a plasma generating section 2 and a reaction section 1. Further, on the lower inner wall of the plasma generating part 2,
A diaphragm plate 3 is arranged so as to exert a throttling action on the plasma gas flowing from the plasma generating portion 2 into the reaction portion 1. The waveguide 4 is connected to the microwave oscillator, and the exhaust pipe 6
Is connected to a vacuum pump. Magnet coil 11
Nos. 13 to 13 are arranged on the outer circumferences of the reaction unit 1 and the plasma generation unit 2 so that the magnetic fields thereof are parallel to the traveling direction of the microwave introduced into the container via the waveguide 4.

In order to manufacture carbon nanotubes using the apparatus shown in FIG. 1, the pressure inside the reaction vessel is maintained at 10 ⁻⁴ to 10 ⁻¹ Pa via an exhaust pipe, and the carbon nanotubes are arranged on the support plate 7. The substrate temperature is maintained at 500 to 850 ° C. by an electric heating member (not shown) that is installed. Furthermore, the waveguide 4
A microwave is introduced into the container via the magnet and a direct current is passed through the magnet coils 11 to 13 to generate a magnetic field. In this state, a gas of a carbon-containing material such as methane is introduced into the plasma generation part 2 of the reaction container through the reaction gas supply pipe 5. The reaction gas introduced into the plasma generating part 2 is turned into plasma here, and the obtained plasma (ECR plasma) collides with the substrate S and reacts on the substrate surface to cause carbon nanotubes to reach the substrate surface. accumulate.

[0011]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 Carbon nanotubes were manufactured using the apparatus shown in FIG. The main operating conditions in this case are shown below. (1) Reaction part 1 (i) Diameter: 35 cm (ii) Height: 30 cm (2) Plasma generation part 2 (i) Diameter: 15 cm (ii) Length: 30 cm (iii) Pressure: 1.8 × 10 ^{− 1} Pa (3) Substrate S (i) A substrate having Ni, Pd, and CoFe metals deposited on an n-type Si substrate having a low electric resistance by vacuum vapor deposition was used. (Ii) Temperature: 600 ° C (4) Microwave (i) Frequency: 2.45 GHz (ii) Output: 800 W (5) Magnet coil (i) Current: 40 A direct current (ii) Magnetic field strength (a) Plasma Center part of generating part 2: about 34 mT or more (b) Center part of reaction part 1: 22 mT or more (6) Reaction gas (i) Mixed gas of 91% methane gas (CH ₄ ) and 9% carrier gas (Ar) Use (ii) CH ₄ flow rate: 2.2 × 10 ⁻⁴ mol / min (7) Plasma (i) Diameter: 15 cm (ii) Length: 30 cm (8) Reaction time: 30 minutes As the reaction time, The time during which the substrate and plasma were in continuous contact was adopted. (9) Produced carbon nanotube (i) Average diameter: 50 to 80 nm, average length: 15 to 15
20 μm needle-shaped tube (ii) Property: vertically deposited on the substrate (iii) 10 ⁹ to ¹⁰ 10 needle-like carbon nanotubes per 1 cm ^{2 of the} substrate

[0013]

According to the present invention, under a low temperature of 850 ° C. or lower and a low pressure condition of 10 ⁻⁴ to 10 ⁻¹ Pa, the average diameter of vertically protruding particles on the substrate can be increased without applying an electric field. 50-80 nm, the average length of which is 0.1-20 μm
It is possible to efficiently produce high quality acicular carbon nanotubes.

[Brief description of drawings]

FIG. 1 shows a schematic view of one embodiment of a carbon nanotube manufacturing apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

1 Reaction part 2 Plasma generator 3 diaphragm 4 microwave waveguide 5 Reaction gas supply pipe 6 exhaust pipe 7 Substrate support plate 8 support rods 10 reaction vessels 11-13 Magnet coil S substrate

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takefumi Ishikura 1-5-20 Kaigan, Minato-ku, Tokyo Inside Tokyo Gas Co., Ltd. (72) Inventor Morio Yumura 1-1, Higashi, Tsukuba-shi, Ibaraki Industrial Technology Institute Institute of Materials Science and Technology (72) Inventor Shuzo Fujiwara, 1-1, Higashi, Tsukuba, Ibaraki Industrial Technology Institute, Institute of Materials and Engineering (72) Inventor, Yoshinori Koga, 1-1, Higashi, Tsukuba, Ibaraki (56) Reference JP 2001-192829 (JP, A) JP 2001-295047 (JP, A) JP 11-11917 (JP, A) S.S. H. TSAI et al, Synthesis of characterization of the a ligneed hydrogenated amorphous carbon carbon nanotube by elect ron, Thin Solid May, 6000, May 1st 2000, 2000. 11-15 (58) Fields investigated (Int.Cl. ⁷ , DB name) C01B 31/02 C23C 16/00-15/56 JISST file (JOIS) INSPEC (DIALOG)

Claims (7)

(57) [Claims] ^1. A pressure of 10 ^-4 to 10 ^-1 Pa is maintained,
And a microwave is introduced, and a gas of a carbon-containing material is introduced into a plasma generation chamber in which a magnetic field is applied to the microwave to generate an electron cyclotron resonance plasma of the carbon-containing material. 500
A method for producing carbon nanotubes, which comprises bringing the carbon nanotubes into contact with a substrate held at a temperature of 850 ° C. and vertically depositing the carbon nanotubes on the substrate. 2. The carbon nanotubes have an average diameter of 40.
The method for producing a carbon nanotube according to claim 1, wherein the carbon nanotube has a thickness of ˜80 nm. 3. The method for producing carbon nanotubes according to claim 1, wherein the substrate has a carbon nanotube deposition aid attached to the surface thereof. 4. The method for producing carbon nanotubes according to claim 3, wherein the auxiliary agent is ultrafine particles of a transition metal. 5. The method for producing carbon nanotubes according to claim 3, wherein the auxiliary agent is at least one metal selected from the metals selected from the group consisting of Pd, Fe, Co and Ni. . 6. The method for producing carbon nanotubes according to claim 1, wherein a hydrocarbon gas is used as the carbon-containing material. 7. The method for producing carbon nanotubes according to claim 6, wherein methane is used as the hydrocarbon gas.