JP3441923B2 - Manufacturing method of carbon nanotube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide range of functional materials such as electronic devices and microdevices, and structural materials, and particularly to a probe such as an electron emitting material and an STM.
The present invention relates to a method for producing a carbon nanotube that can be effectively used as a functional material such as a fine wire for a micromachine, a fine wire for a quantum effect element, and a biodevice.

[0002]

2. Description of the Related Art Fibrous carbon is generally referred to as carbon fiber, and many types of carbon fiber used as a structural material having a diameter of several μm or more have been studied. . Among them, the mainstream at present is a production method using PAN-based or pitch-based raw materials. The outline of this production method is as follows. Raw materials spun from PAN fiber, isotropic pitch, and mesophase pitch are made infusible and flame-resistant, carbonized at 800 to 1400 ° C.,
This is a method of performing high-temperature treatment at 500 to 3000 ° C. The carbon fiber obtained in this way has excellent mechanical properties such as strength and elasticity and is lightweight, so that it is also used as a composite material for sports goods, heat insulating materials, aerospace-related and automobile-related structural materials, and the like.

[0003] Separately, recently discovered carbon nanotubes are tube-like materials having a diameter of 1 µm or less, and ideally, the surface of a carbon hexagonal mesh is parallel to the tube axis to form a tube. It is formed. In addition, the tubes may be multiplexed. This carbon nanotube is theoretically expected to become metallic or semiconductive depending on the connection of hexagonal networks made of carbon and the thickness of the tube, and is expected as a functional material in the future.

[0004] An outline of a general method for producing these carbon-based fiber materials is as follows. (1) Carbon fiber There are many types of carbon fiber, and it is known that the structure of the fiber to be synthesized varies greatly depending on the synthesis method and its conditions. Selected. Details are described in Michio Inagaki, "New Carbon Materials" (published by Gijudo).

[0005] The three main synthesizing methods will be briefly described below. It is synthesized through three main processes of spinning a precursor, infusibilizing the precursor, and treating at a high temperature using polyacrylonitrile as a PAN-based carbon fiber raw material. In the infusibilizing treatment and the high-temperature treatment, cyclization and dehydrogenation with oxygen, and dehydrocarbonation accompanied by formation of a hexagonal carbon network are performed. It is also known that by applying a drawing operation to the fiber during the process, the carbon hexagonal network is arranged in the axial direction of the fiber, and the properties are remarkably improved. The PAN-based carbon fiber thus obtained includes a general purpose (GP) grade and a high strength (High Tensile Strength, HT) type. Pitch-based carbon fibers Pitch-based carbon fibers are mainly classified into two types: isotropic pitch-based carbon fibers made from isotropic pitch and mesophase-based pitch-based carbon fibers that exhibit optical anisotropy. The production process is similar to the above-mentioned PAN-based carbon fiber, and comprises spinning, infusibilization treatment, and carbonization by high-temperature treatment.

[0006] Mesophase pitch carbon fiber is PAN
Good alignment in the axial direction can be obtained without the need for drawing operation as in the case of carbon fiber, and the texture of the fiber cross section is controlled by pitch viscosity such as radial (radial), random, and coaxial cylindrical (onion). it can. Mesophase pitch carbon fibers are of high modulus (HM) type and are attracting attention as future composite materials. Isotropic pitch-based carbon fibers belong to the GP grade and have been used for heat insulating materials and the like. As a typical example of a vapor growth type carbon fiber, there is a method in which hydrogen is used as a carrier gas, benzene vapor is fed into an electric furnace maintained at about 1050 ° C., and iron fine particles are used as a catalyst to grow on a substrate. Three types of growth processes are considered: nucleation, axial growth of extremely fine fibers, and radial growth phase in which the fibers increase in thickness in the radial direction. The catalyst requires ultrafine iron particles of about 10 nm, and after the fiber is obtained, Fe ₃ C will be present at the tip of the fiber.
Hydrogen gas is also considered to have the effect of reducing iron and suppressing the thermal decomposition of benzene.

The obtained fiber consists of a hollow tube from the center, a flat and thin mesh layer, and a thick outer peripheral portion arranged approximately parallel to the axis and having a mesh of about 1 nm. It is considered that the hollow tube having a flat and thin mesh layer near the center is made of iron catalyst as a core, and the thick outer portion is obtained by thermal decomposition of benzene. Such a tube is also observed when carbon monoxide is pyrolyzed in the gas phase using iron as a catalyst. G.
G. Tibbetss explains in J. Crysi. Growth, 73 (1985) 431 that similar fibers can be obtained using methane gas.

In the vapor phase growth method, a seeding method (Seeding Catalyst Method) in which a catalyst is attached to a substrate, and a flowing catalyst method (Floating Catalyst Metho) in which the catalyst is suspended in a gas phase.
d) there. In the fluidized catalyst method, the diameter of the fiber tends to be small and bent. Ishioka et al. Also found that the use of a mixed gas of hydrogen, carbon dioxide and carbon monoxide as the carrier gas improved the fiber collection rate, and that the use of a mixture of ferrocene and metal acetylacetonate as a catalyst further improved the fiber Carbon, 30 (1992) 859 and Carbon, 30
(1992) 865.

[0009] The fiber obtained by the seeding method develops a graphite-like laminated structure by heat treatment. That is, a network structure develops around 2000 ° C., and 2500 ° C.
The lamination structure of the mesh develops from the vicinity. Graphite-like laminated structures do not develop much with fibers made by the fluid catalytic method. When these fibers are heat-treated at 2800 ° C. or more, polygonization in which the outer walls of the fibers become polygonal occurs.

When these production methods are viewed as a whole, PAN
The system and the pitch system require flame resistance and infusibility in an atmosphere of 150 to 400 ° C. in air, and then require heat treatment for carbonization and graphitization, including vapor phase growth. That is, 1300
A carbonaceous material carbonized by heat treatment near
There is a graphitic material graphitized at around 0 ° C. With this heat treatment, the density tends to increase and the resistivity tends to decrease. By material, generally isotropic pitch system, PAN
System, mesophase pitch system, and vapor phase growth system, the density, tensile strength, and tensile modulus increase, and the resistivity decreases. Average spacing between isotropic carbon fibers is 0.344nm
Even when high-temperature heat treatment is performed to a certain extent, a turbostratic structure remains. However, when a high-temperature heat treatment is performed at 2400 ° C. or higher in the vapor-grown carbon fiber, the average interplanar spacing becomes about 0.336 nm, and an ideal laminated structure can be obtained. This can also be evaluated from the measurement of the magnetoresistance.

Although the diameter of the carbon fiber obtained by the above-mentioned production method is several μm or more, when compared among these, the vapor-phase growth method can easily obtain a laminated network structure most parallel to the axis, and the carbon nanotubes It can be said that it is a close material. (2) Regarding carbon nanotubes, a material having a diameter smaller than that of a carbon fiber and having a diameter of 1 μm or less is generally called a carbon nanotube and is distinguished from a carbon fiber, but has no clear boundary. In the present specification, an elongated material having a diameter of several μm or more is referred to as carbon fiber, and a material having a diameter of 1 μm or less and having an elongated shape is referred to as carbon nanotube. In a narrow sense, a material in which the surface of the hexagonal mesh of carbon is substantially parallel to the axis is called a carbon nanotube, and the case where amorphous carbon exists around the carbon nanotube is also included in the carbon nanotube.

At present, two types of carbon nanotube production methods are widely classified. It is a pyrolysis method similar to the vapor growth method of carbon fiber, and a method using thermal plasma. Methods using thermal plasma are further classified into two types: arc discharge method and high frequency induction method. Hereinafter, these methods will be briefly described with representative examples.

1) Pyrolysis method using catalyst This method is almost the same as the vapor growth method of carbon fiber. CE SNYDER et al. Have international disclosure of such a manufacturing method.
O89 / 07163. In this method, a raw material gas for introducing carbon is introduced together with hydrogen into a reaction vessel, and at the same time, ultrafine metal particles are introduced to obtain carbon nanotubes. Here, as a raw material, for example, methane, ethane, propane, butane, hexane, cyclohexane and other saturated hydrocarbons, ethylene, propylene, benzene,
Raw materials containing oxygen such as unsaturated hydrocarbons such as toluene, acetone, methanol, and carbon monoxide are used.
The ratio of the source gas to hydrogen is preferably 1:20 to 20: 1, and the catalyst is Fe alone, or Fe and Mo, Cr, C
A mixture of e or Mn has been recommended, and a method has been proposed for keeping it deposited on fumed alumina. The reaction vessel is in the range of 550 to 850 ° C., and the gas flow rate is preferably about 100 sccm of hydrogen per inch diameter and about 200 sccm of raw material gas containing carbon, and the carbon tube grows in about 30 minutes to 1 hour after introducing fine particles. I do.

The shape of the carbon tube thus obtained has a diameter of about 3.5 to 75 nm and a length of 5 to 75 nm.
Up to 1000 times. The carbon network is parallel to the axis of the tube and less pyrolytic carbon is deposited on the outside of the tube.

2) Arc discharge method The arc discharge method was first discovered by Iijima.
Nature Vol. 354 (1991) p.56-58. The arc discharge method is a simple method of performing a DC arc discharge using a carbon rod electrode in an atmosphere of 100 Torr of argon, and the generated plasma is a thermal plasma. The carbon nanotubes have 5 to 2 parts of the surface of the negative electrode.
It grows with 0 nm carbon fine particles. This carbon tube has a layered structure in which a tubular carbon network of 4 to 30 nm in diameter, about 1 μm in length and 2 to 50 layers is overlapped,
The carbon network structure is spirally formed parallel to the axis. The pitch of the helix is different for each tube and for each layer in the tube. In the case of a multilayer tube, the interlayer distance is 0.34 nm, which is almost equal to the graphite interlayer distance. The tip of the tube is still closed with a carbon network.

Also, TW Ebbesen et al. Set conditions for producing a large amount of carbon nanotubes by the arc discharge method.
ol. 358 (1992) p.220-222. A carbon rod having a diameter of 9 mm for the cathode and a diameter of 6 mm for the anode was placed in the chamber so as to face each other at a distance of 1 mm.
An arc discharge of about 18 V and 100 A is generated in an atmosphere of 0 Torr. If it is less than 500 Torr, the ratio of carbon nanotubes is small, and if it is more than 500 Torr, the total production amount is reduced. At the optimum condition of 500 Torr, the ratio of carbon nanotubes in the product reaches 75%. Even if the input power was changed or the atmosphere was changed to argon, the collection rate of carbon nanotubes decreased. Many nanotubes exist near the center of the formed carbon rod.

3) High-frequency induction plasma method The high-frequency induction plasma method is essentially a method using the same thermal plasma as the arc discharge method. Japanese Patent Application Laid-Open No. Hei 7-61803 discloses a technique used by Tanaka et al. For producing fullerenes and carbon nanotubes. No. 1993. According to this, the container is kept at 100 Torr in an atmosphere such as argon gas.
In this method, an induction plasma is generated in a vessel by a high frequency of several MHz at a pressure of not less than r, carbon powder is fed into the vessel, and the carbon is evaporated and recombined. At this time, the temperature in the plasma is 5,000 to 20,000
K, and such thermal plasma is commonly known as ICP
(Inductively Coupled Plas
ma).

The multilayer tube is generally referred to as a multi-core tube, and the single-layer tube is generally referred to as a single tube.

Briefly summarizing the above, as shown in FIG. 1, the carbon fiber has a shape as shown in FIG. 1 (a) which is parallel to the axis and has not developed a tubular network structure, and 1 (b), there is a tubular structure (consisting of a hexagonal carbon network structure, not shown) parallel to the axis as shown in FIG. 1 (b).
In the arc discharge method, a large amount of carbon having a disordered structure adheres to the periphery thereof, and in the arc discharge method, a tube-like structure (consisting of a hexagonal carbon network structure) parallel to the axis and having a center as shown in FIG. ), And the amount of surrounding amorphous carbon attached is small. FIG. 1D shows a cross-sectional view of a multi-core carbon nanotube.

[0020]

In the above-mentioned conventional method for producing carbon nanotubes, the obtained carbon nanotubes are random in both thickness and direction.
An impurity carbon material is also mixed. When used, the carbon nanotubes obtained by this method must be recovered after synthesis, purified, and formed into a specific shape according to the form to be used. For example, when trying to use it as an electron source, AG Rinzler et al.
69 (1995) As shown in p.1550-1553, take out one carbon fiber and attach one to the electrode to apply electrons from the opposite end of the carbon nanotube that exists at the center of the carbon fiber. Is pulled out by. Walt A. de Heer et al., SCIENCE Vol. 270 (19
95) p.1179-1180 and SCIENCE Vol. 268 (1995) p.845
As shown in -847, after purifying carbon nanotubes produced by arc discharge, an electron source is produced by standing a tube on a substrate using a ceramic filter.

Although carbon nanotubes can be grown directly on a substrate by a thermal decomposition method using a seeding catalyst, it is necessary to set the substrate temperature as high as about 800 ° C. It was not possible to control it, and it was difficult to control the thickness, and amorphous carbon was likely to grow on the peripheral wall of the tube. Also, the bonding between the substrate and the carbon nanotube was weak.

Furthermore, the arc discharge requires a large current and the temperature of the growth portion of the carbon nanotube is extremely high, so that it is impossible to grow the carbon nanotube directly on a substrate such as a quartz or metal substrate. Was. Similarly, even in the high frequency induction plasma method, it was impossible to grow carbon nanotubes directly on the substrate because the temperature in the plasma was as high as several thousand degrees Celsius or more.

As will be understood from the above, it is very difficult to form carbon nanotubes in a desired direction on a substrate made of a wide range of materials. Growth was impossible. An object of the present invention is to solve these problems.

That is, an object of the present invention is to provide a method capable of growing carbon nanotubes on a substrate at a relatively low temperature.

Another object of the present invention is to provide a method for growing carbon nanotubes having uniform properties on a substrate.

It is another object of the present invention to provide a method capable of growing carbon nanotubes with improved orientation on a substrate.

Another object of the present invention is to provide a method capable of growing carbon nanotubes having a specific orientation on a substrate.

Another object of the present invention is to provide a method capable of growing a large number of carbon nanotubes at specific intervals on a substrate.

[0029]

The method for producing carbon nanotubes of the present invention is a method for producing carbon nanotubes by growing carbon nanotubes on a substrate placed in a reaction vessel, wherein carbon nanotube growth is started on the surface. In the state where the substrate in which the region is formed in advance is disposed in the reaction vessel, the substrate is formed of carbon and hydrogen for carbon introduction.
First gas as raw material and less hydrogen or helium
The second gas containing either one of the two gases has a total pressure of 10 ^-2 to 10 ⁴
A Pascal, and the gas partial pressure of the first and the 1-10%
So as to be introduced into the reaction vessel, My in the reaction vessel
The method is characterized in that carbon nanotubes are formed on the substrate by generating plasma by AC glow discharge using a black wave . In this manufacturing method , glow discharge is used for manufacturing carbon nanotubes. This glow discharge is clearly distinguished from arc discharge, and the difference will be described below with reference to FIG. Here, an example of direct current will be described for convenience, but the relationship between glow discharge and arc discharge is the same for alternating current.

FIG. 2 shows the relationship between current and voltage when a DC voltage is applied between the positive and negative electrodes in an appropriate pressure vessel. In the figure, the region A is called a glow discharge region, the region B is called an arc current region, and the region where the voltage in the glow discharge region hardly depends on the current is called a normal glow discharge region. The discharge region and the high current side are called an abnormal glow discharge region. The part between the glow discharge region and the arc discharge region is called a transient state. The glow discharge and arc discharge will be described in more detail below. Glow discharge The glow discharge is a stable low-pressure, low-current discharge having a pressure of several thousand Pascal or less and a discharge current of several tens mA or less. Such a discharge can also be obtained by an AC voltage. In the DC glow discharge, there are an aston dark part (as seen in He, Ne, etc., with high excitation voltage), a cathode glow, a cathode dark part, a negative glow, a Faraday dark part, a positive column that occupies most of them, and finally an anode glow from the cathode side. Most of the applied voltage is concentrated near the cathode. Arc discharge In arc discharge, the voltage is reduced to about one tenth and the current is about four to five orders of magnitude higher than in glow discharge. The cathode is heated as it becomes incandescent, and a large amount of thermoelectrons are emitted therefrom, so that the discharge sustaining voltage is lowered. The arc discharge comprises a cathode bright spot on the cathode side, an anode spot on the anode end, and an arc column in a plasma state therebetween.

The process of obtaining carbon nanotubes by the arc discharge method is considered as follows. That is, carbon evaporates from the carbon electrode heated by the arc discharge and is ionized in the plasma, and the carbon ions C ^{+ and the} like are attracted to the cathode. Since the temperature of the cathode is very high, it is in a state where graphite is likely to occur. However,
It is currently unclear why the shape of the nanotube is easily obtained.

Next, the low pressure low ionization plasma and the high pressure high ionization plasma will be described. The aforementioned glow discharge is a direct current,
Both alternating currents (including high frequencies) are low-pressure, low-ionization plasma. Low-pressure low-ionization plasma is generally plasma generated at a pressure of 10 ⁴ Pa or less, has a low degree of ionization, and contains a large amount of neutral non-ionized gas in addition to electrons and ions in the plasma. Then, it is in a non-equilibrium state in the plasma, and the temperature increases in the order of neutral gas, ions, and electrons. When the substrate is placed in this plasma, the substrate temperature is from several hundred degrees centigrade to about 1000 degrees centigrade at most.

On the other hand, there are two types of high-voltage ionization plasma: arc discharge and high-pressure high-frequency induction plasma. The degree of ionization is high, and electrons and ions are in thermal equilibrium in the plasma. The amount of neutral gas in the plasma is less than that in low-pressure low-ionization plasma. This high-pressure high-ionization plasma is generally generated at a pressure of 10 ⁴ Pascal or more, and the temperature in the plasma reaches several thousand to 20,000 ° C. The high-pressure high-frequency induction plasma is generally generated in a quartz tube installed in a coil in which a current of several tens of amperes is passed at a frequency of several MHz.

In the first manufacturing method of the present invention, the former AC glow discharge is used. In the arc discharge method, it is almost impossible to use a substrate other than the electrode rod. Further, in a high-pressure high-frequency induction plasma, it is almost impossible to install a substrate in the plasma because of the high temperature. In the first method of the present invention, ions such as carbon and hydrocarbon are formed in a low-pressure low-ionization gas plasma, and the ions are accelerated and supplied by a sheath voltage generated between the plasma and the substrate, and growth is started. The carbon nanotubes are grown on the surface of the substrate by the effect of the current induced in the carbon nanotubes themselves.

[0035]

[0036]

[0037]

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the manufacturing method of the present invention, carbon nanotubes are grown using a growth starting region or a growth nucleus provided on the surface of a substrate as a starting point. As the carbon nanotube growth start region or growth nucleus, for example, by changing the physical shape or chemical composition of the other portion, or the like, by providing a region capable of providing a portion where carbon nanotube growth is easier to start than other portions or What is necessary is just what was formed as a core part.

As a method of forming the carbon nanotube growth start region by changing the chemical composition, for example, a method of forming a portion having a composition capable of functioning as a carbon nanotube growth start region or a growth nucleus on a substrate can be mentioned. As a preferable method of forming the growth start region or the growth nucleus of the carbon nanotube by changing the physical shape, for example, a method of providing a projection structure capable of concentrating a voltage or the like can be preferably mentioned. By providing the carbon nanotube growth start region on the substrate in this manner, it is possible to suppress the growth of the amorphous carbon or graphite-like structure and to effectively promote the growth of the carbon nanotube.

As the carbon nanotube growth start region or growth nucleus having a changed chemical composition, those capable of forming a portion capable of inducing the start of carbon nanotube growth more effectively can be used. For example, a metal or a low-resistance semiconductor can be used. It can be mentioned as a suitable one. These metals or low-resistance semiconductors include Fe, Ti, V,
Cr, Mn, Co, Ni, Cu, Nb, Mo, Pd,
Transition metals such as W and Pt, lanthanoid elements and SiC
And the like. Among these, Fe, C, which are metal catalysts capable of promoting the dehydrogenation of hydrocarbons,
Alloys such as o, Ni and invar containing them are more preferred.

As a method of forming a carbon nanotube growth start region or a growth nucleus made of these materials on a substrate, for example, a method of fixing ultrafine particles made of these materials on a substrate, or a method of forming these on the surface of the substrate, A method of forming a portion made of a material can be used.

As a method of immobilizing the ultrafine particles on the substrate, a method of spraying the ultrafine particles onto the surface of the substrate can be used.

The ultrafine particles made of these materials are:
For example, it can be obtained by a general method called a gas evaporation method. That is, the method is a method in which a metal is heated and evaporated using a crucible or the like in an inert gas such as argon of about 10 ⁴ pascals, and grows into ultrafine particles in the gas. The generated ultrafine particles can be sprayed directly on the substrate placed in another chamber using a differential pressure, or the ultrafine particles can be collected once and then dispersed and applied to the substrate or sprayed. It is. In addition to such a method, for example, it is also possible to obtain ultrafine particles by forming an ultrathin film on a substrate and then performing heat aggregation.

As a further controlled method, an SEM (Scanning Electron Micro) in which some gas such as oil exists.
By irradiating the substrate with an electron beam using a scope (scanning electron microscope) or the like, it is possible to grow carbon ultrafine particles on that portion. In this case, it is possible to grow a metal other than carbon by changing the gas to a specific raw material such as an organic metal.

It is to be noted that "ultrafine particles" are generally recognized as follows. That is, small particles are called “fine particles”, and smaller ones are called “ultra fine particles”. It is widely practiced to call a “cluster” smaller than “ultrafine particles” and having a few hundred atoms or less. However, each boundary is not strict and changes depending on what kind of property is focused on. Also, “fine particles” and “ultra fine particles” may be collectively referred to as “fine particles”.

"Experimental Physics Course 14 Surface / Particle"
(Edited by Kinoshita Yoshio, Kyoritsu Shuppan published September 9, 1986) describes as follows.

"In the present case, the fine particles have a diameter of about 2 to 3 μm to about 10 nm, and especially the fine particles have a diameter of about 10 nm to 2 to 10 nm.
It means up to about 3 nm. The two are collectively simply written as fine particles, so they are not strictly accurate, but are approximate. When the number of atoms constituting a particle is two to several tens to several hundreds, it is called a cluster. (See p. 195, lines 22-26).

In addition, the definition of "ultra fine particles" in the New Technology Development Corporation "Hayashi / Ultra Fine Particle Project" has the following lower limit of the particle size, and is as follows.

In the "Ultrafine Particle Project" of the Creative Science and Technology Promotion System (1981 to 1986), a particle having a particle size (diameter) in the range of about 1 to 100 nm is called an "ultrafine particle" (utlra fain particle). I was in. then one of the ultra-fine particles are ultra-fine particles if you look at about 100 to 10 it comes to ^eight much of atom aggregate of. atoms measure of is a large - huge particle. "(" ultra-fine particles, Creative Science and Technology "Hayashi tax, Ryoji Ueda, Akira Tazaki, Mita Publishing 1988
(See page 2, lines 1 to 4 of the year) "A smaller particle than an ultrafine particle, that is, a single particle composed of several to several hundred atoms is usually called a cluster." Eyes).

[0050] Based on the above general terms,
In the present specification, “ultrafine particles” refers to fine particles having a particle size in the range of 1 nm to several μm, and the particle size of the ultrafine particles for the growth start region of the carbon nanotube can be determined by the method of the present invention. The degree is not particularly limited as long as the degree is about.

Further, as a method without using ultrafine particles,
A method of forming a surface portion made of the above-described material at a desired position by a lithography technique using drawing of visible light, ultraviolet light, X-ray, electron beam, or the like can be given.

On the other hand, as a method of forming a projection structure which can be used as a growth start region or a growth nucleus on the surface of a substrate by changing a physical shape, a FE is used.
(Field Emission: field emission) The manufacturing method used for the electron source and the manufacturing method used for manufacturing the tip of STM (Scanning Tunneling Microscope: scanning tunnel microscope) are mentioned. For this purpose, metal is obliquely deposited from the top of the resist hole with a reverse taper, and the spint method is used to lift off the hole part. An etching method that removes or a mask is attached to a part of the substrate other than the part that will become a hole, anisotropic etching is performed, a hole is opened, a mold is formed, and a metal film is formed on the mold to remove the mold part. And so on.

FIG. 3 shows a typical structure of the carbon nanotube growth start region obtained by the above method. FIG.
3A to 3C are schematic cross-sectional views showing a state in which a carbon nanotube growth start region 2 is formed on a substrate 1. FIG. 3A shows a case in which the carbon nanotube growth start region 2 is formed using ultrafine particles. FIG. 3B shows a case where a thin film of metal or the like patterned into a predetermined dot shape using lithography technology is used, and FIG. 3C shows a case where a protrusion structure (when the apex is sharp) is used. Are respectively shown.

Examples of the substrate that can be used in the method of the present invention include various metal substrates, Si wafers, quartz, glass, and ceramics. In the production method of the present invention, carbon nanotubes can be grown directly on the substrate. Can be greatly expanded.

In the production method of the present invention , the growth method of cambon nanotubes is performed by generating plasma as a raw material by AC glow discharge. Less than,
A representative example of this method will be described.

In the production method of the present invention , after a carbon nanotube growth start region is formed in advance on the surface of the substrate by the above-described method , the region is placed at a predetermined position in a reaction vessel whose internal pressure can be adjusted.

When the arrangement of the substrates is completed, the inside of the reaction vessel is evacuated to a reduced pressure of about 10 ^-6 Pa, and then a gas containing a raw material for introducing carbon is continuously introduced into the reaction vessel. The introduction rate can be appropriately selected according to the desired structure and growth rate of the carbon nanotubes.For example, the pressure in the reaction vessel is adjusted by adjusting the introduction system of the source gas and the exhaust system of the reaction vessel. It is preferable to introduce the raw material gas into the reaction vessel so as to be in the range of 10 ^-2 to 10 ⁴ Pascal.

As a raw material for introducing carbon into the reaction vessel, a compound containing carbon that can be introduced into the reaction vessel in a gas state can be used. For example, methane, ethane, propane, butane, pentane, hexane, ethylene, acetylene, benzene,
Examples thereof include hydrocarbons such as toluene and cyclohexane, benzonitrile containing other elements, acetone, ethyl alcohol, methyl alcohol, and carbon monoxide.
Among these, the preferred raw materials are slightly different depending on the type of the substrate, the composition of the ultrafine particles and the like, the growth temperature and the pressure,
The raw material composed of carbon and hydrogen may be less likely to contain impurities. Although it is possible to use only these raw materials, it is preferable to use a mixture of hydrogen and helium. These mixing ratios can be selected according to a desired growth rate or the like.

While the state of introduction of the raw material gas into the reaction vessel is maintained, an AC glow discharge is generated to generate plasma, and the growth of the carbon nanotube is started from the carbon nanotube growth start region provided in advance on the substrate surface. Let it start. As the AC glow discharge, a high frequency (RF) or a microwave is preferably used. In this case, the substrate may also serve as an electrode, and of course, may be configured to be installed in the plasma separately from the electrode.

In some cases, carbon nanotubes tend to grow in the direction of the current induced in the plasma. Using this positively, microwave was used as a power source, plasma was generated in a microwave cavity, and the directionality was controlled by growing carbon nanotubes in the direction of current induction in the cavity. Growth can take place. As the cavity resonator that can be used at this time, for example, a coaxial resonator, a semi-coaxial resonator, a circular cavity resonator, a square cavity resonator, a donut-shaped cavity resonator, a concave cavity resonator, or the like can be used. The direction of the induced current depends on the shape of the cavity resonator and the mode set during use, etc.
It can be selected according to the desired growth direction.

For example, in the TE ₀₁₁ mode of the circular cavity resonator, the current is in a direction along the circumference around the axis of the cylinder as shown in FIG.
_{In the 111} mode, the current flows in a direction perpendicular to the axis of the cylinder as shown in FIG. The base may be placed in the space of the circular cavity resonator or may be placed along the wall. The causal relationship between the direction of current induction and the growth direction of the carbon nanotube is not clear, but it is important that ions such as C ⁺ are involved in the growth, the electrical conductivity in the axial direction of the carbon nanotube is large, There may be multiple causes such as the electric field being easily concentrated.

The substrate temperature is, for example, 400 to 900.
The temperature can be selected from the range of ° C.
It may be set according to the gas pressure, the composition of the growth start region, and the like.

FIG. 5 shows an example of an apparatus using microwaves as an AC glow discharge. 11 is a circular cavity resonator as a reaction vessel, 12 is a quartz microwave introduction window, and 1 is a base. 14 is a substrate holder that does not or hardly absorbs macro waves, 15 is a microwave oscillator,
16 is an isolator, 17 is a matching and detector. Reference numeral 18 denotes a gas introduction system, and 19 denotes an exhaust system including a rotary pump and a turbo pump. In addition, although not shown, a waveguide, a substrate temperature monitor, a vacuum gauge and its monitor, a pressure adjusting valve, a gas flow meter, and the like are provided. Further, the matching can be adjusted by screws in the circular cavity resonator.

In this device, first, the base holder 1
After the substrate 1 is placed on the reaction vessel 4, the inside of the reaction vessel 11 is set to a predetermined pressure.
For example, exhaust to about ^10-6 Pascal. Thereafter, a source gas (for example, ethylene) and a gas for dilution or growth promotion (for example, helium, hydrogen gas, or the like) are introduced into the reaction vessel as necessary. At the stage where the pressure of each gas in the reaction vessel 11 after the introduction is adjusted to a predetermined value, a microwave is oscillated. At this time, the pressure in the reaction vessel 11 is, for example, 10
It can be selected from ^-2 to 10 ⁴ Pascal range.
In addition, the pressure in the reaction vessel can be adjusted by the flow rate of the gas and the exhaust amount of the exhaust system. Here, the matching is adjusted to generate plasma in the reaction vessel 11, and the carbon nanotubes are grown for a predetermined time. Then, the oscillation of the microwaves is terminated to stop the plasma, the gas supply is cut off, the chamber is evacuated, the nitrogen leaks, and the substrate 1 is taken out to the atmosphere.

On the other hand, when the AC glow discharge is carried out at a high frequency, the electrode for generating the high frequency should be one which can generate a desired AC glow discharge and does not hinder the growth of carbon nanotubes. It can be used without any particular restrictions. At this time, the material and structure of the substrate can be selected and used so that at least the surface of the substrate on which the carbon nanotube growth start region is arranged becomes an electrode. The distance between the electrodes depends on the gas used, the pressure, and the like. In order to align the growth direction of carbon nanotubes in a specific direction, the average electric field intensity applied between the electrodes is 5
It is effective that it is 0 V / cm or more. The upper limit of the average electric field strength can be set according to the electrode structure, gas type, gas pressure, and the like, but can be, for example, about 10 kV / cm.

Although the causal relationship between the direction of the electric field and the growth direction of the carbon nanotubes is not clear as described above, even when a high frequency is used, the fact that ions such as C ⁺ are involved in the growth, and There may be multiple causes such as a high electrical conductivity in the axial direction and a tendency for the electric field to concentrate at the tip of the tube.

FIG. 6 shows an example of an apparatus for growing carbon nanotubes using high frequency. In FIG.
Is a reaction vessel, 22 is a counter electrode, and 1 is a substrate. Reference numeral 24 denotes a substrate holder having a built-in heater for heating the substrate 1.
It has a structure necessary for the base 1 itself to function as an electrode. An RF power supply 25 for generating glow discharge is integrated with the matching box. 26 is a gas introduction system, 2
Reference numeral 7 denotes an exhaust system including a rotary pump and a turbo pump. Further, although not shown, a temperature monitor of the substrate,
A vacuum gauge and its monitor, a pressure regulating valve, a gas flow meter, etc. are installed. Further, the distance between the electrodes may be several mm to 100 mm depending on the type and pressure of the gas to be introduced and the input power.
It can be variably adjusted up to mm. The counter electrode 22 and the base holder 24 are made of, for example, carbon in order to avoid mixing of impurities due to sputtering.

The production of carbon nanotubes in this apparatus can be performed, for example, as follows. First, the substrate 1 is set in the substrate holder 24 in the reaction container 21 and the inside of the reaction container 21 is evacuated to a predetermined pressure (for example, to 10 ⁻⁶ Pascal) by the exhaust system 27. Heat and introduce a source gas (eg, acetylene) and, if necessary, hydrogen or an inert gas (eg, helium). The total pressure in the reaction vessel 21 and the partial pressure of the raw material gas after the start of gas introduction are selected according to a desired reaction rate and the like, but the total pressure can be, for example, 500 Pascal. The pressure in the reaction vessel can be adjusted by the flow rate of the gas and the amount of exhaust in the exhaust line.

When a predetermined pressure is stably obtained in the reaction vessel 21, RF power is applied between the electrodes to generate plasma, thereby forming carbon nanotubes on the substrate 1. After maintaining this state for a predetermined time, the application of the voltage is stopped to stop the plasma, the gas supply is cut off, the inside of the reaction vessel 21 is evacuated, the temperature of the substrate 1 is brought to room temperature, and nitrogen is leaked to remove the substrate 1. Remove to atmosphere.

According to the method of the present invention described above, the number n
It has a diameter of m to submicron and a length of several tens nm to several tens.
A carbon nanotube having a length of μm can be obtained. In addition, since one side of the tube, that is, the substrate side is already bonded to the substrate, it is particularly convenient for an application in which only one side of a nanotube such as a probe such as a field electron emission or an STM or a vibrator of a micromachine is joined. Of course, the present invention can be applied to both-side joining and joining of a plurality of electrodes.
Further, it can also be used as a modification of the surface of a substrate such as a surface treatment, for example, a surface inactivation treatment or a high strength treatment.

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The present invention will be further described with reference to the following examples.
Describe in detail. Example 1 First, on a predetermined surface of a quartz substrate, FeNi having a diameter of about 20 nm was used.
Alloy (Fe_0.5Ni_0.5) Several ultra-fine particles per 1 μm square
The heat treatment is performed so that a dispersion state of
On the holder 14 of the device having the structure shown in FIG.
It is installed at a predetermined position, and the inside of the reaction^-6Pascal
And exhausted by the exhaust system 19. Next, the substrate temperature is set to 50
0 ° C, ethylene gas, helium gas and hydrogen gas
Is introduced from the gas introduction system 18 and the total pressure of these gases is increased.
10 Pascal, ethylene partial pressure 1 Pascal, hydrogen partial pressure
The pressure was 10 Pascal. In this state the microwave oscillator
Oscillates microwaves (200W) from the
Generate plasma in the reaction vessel 11 by adjusting
Hold for a while. Then, the microwave oscillation ends and the
After stopping the gas supply and shutting off the gas supply,
Pull out and release the substrate into the atmosphere after nitrogen leak
Was. The surface of the quartz substrate taken out is treated with an FE-SEM (Field
Emission-Scanning Electron Miciroscope: Field emission scan
Observation with a scanning electron microscope) revealed that the substrate
In the center of the vessel, the ultra-fine particle dispersion surface is perpendicular to the current induction direction.
When installed in the directionFIG.Number of diameters as shown in (a)
10 to several 100 nm carbon nanotubes on the substrate surface
With one side of the tube bonded to
And the ultra-fine particle dispersion of the substrate in the cavity resonator
When the surface is set in the direction parallel to the current induction direction,FIG.
As shown in (b), carbon nanotubes are placed on the substrate.
It was growing almost parallel. In addition, the quartz of the substrate
Dry amorphous carbon deposition was observed, but carbon
The amount was small compared to the growth of nanotubes.

Example 2 Ni, Fe, Co, FeNi (F
e _0.5 Ni _0.5 ), NiCo (Ni _0.5 Co _0.5 ), ultrafine particles made of any one of Au and Ag are 1 μm
What was dispersed several to several tens at the corner was prepared as a substrate. Next, using these substrates individually, carbon nanotubes were produced by the apparatus shown in FIG. That is,
The substrate to which the ultrafine particles were previously applied was placed on the holder 14 of the apparatus shown in FIG. After evacuation of the reaction vessel 11 to 10 ⁻⁶ Pa, the holder 14 was heated to 600 ° C., and a mixed gas of benzene, which is a raw material gas, mixed with helium and hydrogen was introduced. The total pressure after the introduction was 10 Pascal, the partial pressure of benzene was 0.1 Pascal, and the partial pressure of hydrogen was 1 Pascal. Then, a microwave (200 W) was oscillated from the microwave oscillator 15 to adjust the matching to generate plasma in the reaction vessel 11 and held for 60 minutes. Then, the oscillation of the microwave was terminated to stop the plasma, the gas supply was cut off, and the vacuum was evacuated by the exhaust system 19, and after the nitrogen leak, the substrate was taken out into the atmosphere.
When the surface of the quartz substrate taken out was observed by FE-SEM, it was found that the ultrafine particles of Ni, Fe, Co, FeNi and NiCo had a diameter of several tens to several hundreds nm as shown in FIG. Carbon nanotubes grew slightly vertically from the substrate surface. At this time, a slight amount of amorphous carbon was deposited on the quartz substrate, but the amount was slightly smaller than the growth of carbon nanotubes. On the other hand, when the fine particles made of Au or the fine particles made of Ag were used, some deposition of amorphous carbon was observed, but almost no growth of carbon nanotubes was observed.

Embodiment 3 Next, a description will be given of an embodiment in which a growth portion of a carbon nanotube is formed by using a lithography technique or the like.

First, the following three types of substrates were prepared. (1) Ti was thinly formed (film thickness: 20 nm) on a quartz substrate, and Pt was then formed by a sputtering method (film thickness: 40 nm). Further, a Ni film having a thickness of 10 nm is formed thereon, and this Ni thin film layer is formed into a dot shape of about 50 nm to 10 μm square (interval of each dot: 10 times the dot diameter) by an electron beam lithography method and a general exposure method. Degree). (2) A slight carbon source (CH ₄ or oil) is formed on the surface of the quartz substrate on which the Pt thin film (thickness: 40 nm) is formed.
By applying an electron beam to a part of the substrate in an SEM under a certain atmosphere, carbon dots of several tens of nm square (interval of each dot: about 10 times the dot diameter) were formed. (3) A Ni film having a thickness of about 10 nm was formed on a quartz substrate, and the Ni film was heated to 1000 ° C. in a vacuum to coagulate the Ni film to change it into ultrafine particles.

The substrates thus obtained were individually placed in the holder 24 of the apparatus shown in FIG. 6, and the inside of the reaction vessel 21 was evacuated to 10 ^-6 Pascal by the exhaust system 27, and then the holder 24 was heated to 300 ° C. Helium and hydrogen were introduced from a gas introduction system 26 in addition to acetylene as a raw material gas. The gas pressure in the reaction vessel 21 is set to a total pressure of 50 Pascal,
Acetylene partial pressure of 5 Pascal, Helium partial pressure of 40
The pressure was adjusted to Pascal, and an FR power (300 W) was applied between the substrate 1 and the counter electrode 22 to generate plasma, and the plasma was maintained for 30 minutes. The distance between the electrodes was adjusted to 20 mm. After the completion of the reaction, the application of voltage was stopped, the plasma was stopped, the gas supply was cut off, the chamber was evacuated, and the substrate was cooled to room temperature.

The surface of the quartz substrate taken out was subjected to FE-SEM
As a result, the diameter of each of the three types of substrates was 10 to 100, as shown in FIG.
nm carbon nanotubes had grown slightly vertically from the substrate. At this time, a slight amount of amorphous carbon was deposited on the other portion of the substrate, but the amount was small compared to the growth of carbon nanotubes.

Embodiment 4 Next, a description will be given of an embodiment in which a needle-shaped growth portion is formed by using a lithography technique or the like.

First, a thin film of Ti (film thickness: 20 nm) was formed on a quartz substrate, and a film of Pt was formed (film thickness: 40 nm) by sputtering. Then, a resist (trade name: RD20)
00; Hitachi Chemical Co., Ltd., and a hole having a reverse taper of several μm in diameter was formed by a usual lithography method for patterning a metal thin film. From above, a Co film was formed by the oblique incidence method, and then the resist was removed to form a conical Co-projection structure as shown in FIG. 3C on the substrate surface.

This substrate was set as the substrate 1 in the holder 24 of the apparatus shown in FIG. 6, and the inside of the reaction vessel 21 was evacuated to 10 ⁻⁶ Pascal by the exhaust system 27.
C., and benzene and hydrogen as raw material gases were introduced from a gas introduction system 26. The gas pressure in the reaction vessel 21 was adjusted so that the total pressure was 5 Pascal and the partial pressure of benzene was 0.5 Pascal, and an FR power (300 W) was applied between the substrate 1 and the counter electrode 22 to generate plasma. Generated and held for 60 minutes. The distance between the electrodes was adjusted to 20 mm. After the completion of the reaction, the application of voltage was stopped, the plasma was stopped, the gas supply was cut off, the chamber was evacuated, and the substrate was cooled to room temperature.

The surface of the quartz substrate taken out was subjected to FE-SEM
As a result, carbon nanotubes having a diameter of several hundred nm as shown in FIG. 12A were grown almost perpendicularly from the substrate. At this time, a slight amount of amorphous carbon was found to be deposited on the substrate Pt film, but the amount was small compared to the growth of carbon nanotubes.

Example 5 Next, carbon nanotubes were produced using the same apparatus shown in FIG.

In the same manner as in the first embodiment, FeNi
Are dispersed in a 1 μm square in the order of several to several tens, and placed on the holder 14 of the apparatus shown in FIG. After evacuation of the reaction vessel to 10 ^-6 Pa, the raw material gas A and the other gas B were introduced. The total pressure after introduction is 1
And 0 ^over 2-10 ⁴ Pa, 1 the partial pressure of gas A is the total pressure
-10%. The types of gas A and gas B and their combinations are as shown in Table 1 below.

[0102]

[Table 1] When the specified pressure is reached, microwave (200W)
Was oscillated, the matching was adjusted, and plasma was generated in the reaction vessel 11 and held for 30 minutes. The substrate temperature was set at 600 ° C. Then, the oscillation of the microwave was terminated to stop the plasma, the gas supply was cut off, and the vacuum was evacuated by the exhaust system 19, and after the nitrogen leak, the substrate was taken out into the atmosphere. The surface of the quartz substrate taken out was observed by FE-SEM. As a result, FIG.
(A) Carbon nanotubes having a diameter of several tens to several hundreds of nm as shown in FIG. In 5 to 10, the carbon nanotubes were fine and a fine network structure parallel to the axis was obtained, and the amount of amorphous carbon deposited on the quartz substrate was small.

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According to the production method of the present invention, carbon nanotubes can be formed directly on a substrate at a relatively low substrate temperature, and the range of choice of the material of the substrate can be expanded. Further, it is possible to produce carbon nanotubes having uniform characteristics and improved growth directionality.

[0121]

Further, according to the present invention, it is possible to provide a carbon nanotube which does not require a purification treatment. Furthermore,
The carbon nanotube obtained by the present invention is provided in a state where one end thereof is bonded to a substrate, and can be formed of a material capable of functioning as an electrode of the substrate, and thus can be used as it is as an electronic functional material.

[Brief description of the drawings]

1A and 1B are diagrams schematically showing the structures of carbon fibers and carbon nanotubes, wherein FIG. 1A is a cross-sectional view of an isotropic carbon fiber in a fiber axis direction, FIG. Sectional view in the fiber axis direction of the carbon fiber obtained by the vapor phase growth method, (c) is a sectional view in the fiber axis direction of the carbon nanotube, and (d) is a cross section in the direction perpendicular to the fiber axis of the multi-core carbon nanotube. FIG.

FIG. 2 is a correlation diagram of current and voltage in glow discharge and arc discharge.

3A and 3B are diagrams illustrating a structure of a growth start region of a carbon nanotube formed on a substrate surface, wherein FIG. 3A is a diagram illustrating a growth start region obtained by dispersing ultrafine particles on the surface, and FIG. FIG. 3C shows a growth start region formed by the region, (c).
FIG. 3 is a diagram showing a growth start region composed of needle-like protrusions.

4A and 4B are schematic diagrams of a current induction direction of a microwave circular cavity resonator, wherein FIG. 4A is a cross-sectional view of a T ₀₁₁ mode, and FIG.
Is a sectional view of the _T111 mode.

FIG. 5 is a diagram showing an example of an apparatus for producing carbon nanotubes using microwaves.

FIG. 6 is a diagram illustrating an example of a carbon nanotube manufacturing apparatus using RF.

FIGS. 7A and 7B are schematic diagrams of carbon nanotubes grown on a substrate, wherein FIG. 7A shows a growth state in a direction perpendicular to the substrate surface, and FIG. It is a figure showing a growth state.

[Explanation of symbols]

1 Substrate (substrate) 1b Substrate surface 2 Growth nucleus 4 Carbon nanotube 11 Reaction vessel 12 Microwave introduction window 14 Substrate holder 15 Microwave oscillator 16 Isolator 17 Matching and detector 18 Gas introduction system 19 Exhaust system 21 Reaction vessel 22 Counter electrode 24 Substrate holder 25 RF power supply (integrated with matching box) 26 Gas introduction system 27 Exhaust system

Continuation of front page (56) References JP-A-8-13254 (JP, A) JP-A-7-11520 (JP, A) JP-A-8-100328 (JP, A) JP-A-10-265208 (JP) , A) JP-A-10-203810 (JP, A) MASAKO YUDASAKA, et al, Specific condition for Nicatalyzed carbon nanobutapartment biochemical delivery. Phys. Lett, October 23, 1995, Vol. 67, No. 17, p. 2477-2479 Japan Society of Applied Physics, Thin Film and Surface Physics Subcommittee, Handbook for Thin Film Preparation, Kyoritsu Publishing Co., Ltd., March 25, 1991, p. 277-280W. Z. Li, et al, Large-Scale Synthesis of Aligned Carbon Nanotubes, SCIENCE, December 6, 1996, Vol. 274, pp. 1701-1703 Masako Yuda, Rie Kikuchi, Preparation of Graphite Thin Film and Carbon Nanotube by CVD Method, Surface Science, Japan, 1996, Vol. 17, No. 4, p. 208-213 Yasuyuki Takarada et al., Synthesis of Carbon Nanotubes by Microwave Plasma CVD, Proceedings of the Chemical Engineering Society of Japan, Kanto Chapter, July 16, 1997, Vol. 1997, No. Gunma, p. 42 (58) Fields surveyed (Int. Cl. ⁷ , DB name) C01B 31/02 D01F 9/127 C23C 16/26

Claims (7)

(57) [Claims] 1. A method for producing carbon nanotubes by growing carbon nanotubes on a substrate placed in a reaction vessel, wherein a substrate having a carbon nanotube growth start region formed on the surface in advance is placed in the reaction vessel. In a state, there is a first gas and hydrogen which are raw materials composed of carbon and hydrogen for carbon introduction.
Its second gas had comprising at least one of helium
A total pressure of 10 ^-2 to 10 ⁴ Pa, and the first moth
Forming carbon nanotubes on the substrate by introducing plasma into the reaction vessel so that the partial pressure becomes 1 to 10%, and generating plasma by AC glow discharge using microwaves in the reaction vessel. A method for producing carbon nanotubes. 2. A carbon Nanochi according carbon nanotube growth starting area of the substrate, to claim 1 where the physical shape or chemical composition formed by changing the other parts
Method of manufacturing tube . 3. The carbon nanotube growth start area is:
The method for producing a carbon nanotube according to claim 1 or 2 , wherein the method is a metal ultrafine particle. 4. A carbon nanotube growth start region,
Claims: It contains any metal of Fe, Co and Ni.
4. The method for producing a carbon nanotube according to 2 or 3 . 5. The carbon nanotube growth start region is:
The method for producing a carbon nanotube according to claim 2 , wherein the method comprises a projection structure. 6. The projection structure according to claim 6, wherein the projection structure is a needle-like structure.
6. The method for producing a carbon nanotube according to item 5 . 7. An apparatus for carrying out the method for producing carbon nanotubes according to claim 1 , comprising the reaction vessel and a pressure regulating valve.