JP4706852B2 - Method for producing carbon nanotube - Google Patents

Description

  The present invention relates to a method for producing carbon nanotubes, and more particularly to a method for producing carbon nanotubes capable of growing a carbon nanotube film having a high density and a vertical orientation on a substrate surface.

  Carbon nanotubes (CNT) have a three-dimensional structure in which graphene sheets corresponding to one layer of graphite (sheets in which carbon atoms are arranged in a hexagonal network) are rolled into a cylindrical shape. The CNT includes a single-walled CNT made of one cylindrical graphene sheet and a multi-walled CNT in which a plurality of cylindrical graphene sheets are concentrically overlapped. In addition, the tip of the synthesized unprocessed CNT usually has a structure closed with a hemispherical graphite layer called “cap”.

  CNTs have a diameter on the order of nm and a length on the order of μm to cm, have an extremely large aspect ratio, and have a feature that the radius of curvature of the tip is as small as several nm to several tens of nm. CNT is mechanically tough, has excellent chemical and thermal stability, and is characterized by being both a metal and a semiconductor depending on the helical structure of the cylindrical portion. Therefore, CNTs are electronic wiring materials for light-emitting devices, heat dissipation materials, fiber materials, electron emission sources for flat panel displays, transistor materials, electron emission sources (point light sources) for electron microscopes, or probes for SPM. Application to such as is expected.

To synthesize CNT,
(1) An arc method in which arc discharge is performed between carbon rods in a gas atmosphere such as Ar or hydrogen, and CNTs are deposited on the cathode;
(2) A laser evaporation method in which a strong pulsed light such as a YAG laser is applied to the surface of the graphite mixed with the catalyst, the generated carbon smoke is heated in an electric furnace, and the CNT is recovered downstream of the reaction tube.
(3) a chemical vapor deposition method in which a carbon compound (for example, methane, acetylene, benzene, etc.) is thermally decomposed on catalytic metal fine particles,
Etc. are known.

  The CNTs obtained by the synthesis methods (1) and (2) are both in a state of being intertwined in a completely random direction. Moreover, it may contain a large amount of carbon nanocapsules, amorphous particles, and the like. On the other hand, in order to maximize the ultimate anisotropy of CNTs, it is desirable to orient a large number of CNTs on the substrate surface. In addition, when applying CNTs to electronic wiring materials, heat dissipation materials, fiber materials, etc., in order to obtain high current density, high thermal conductivity, high strength, etc., it is desirable to generate CNTs at a high density on the substrate surface. The chemical vapor deposition method (3) is suitable for this purpose. Furthermore, since the characteristics of CNT depend on the degree of spiral, it is desirable that the degree of spiral of CNT can be arbitrarily controlled during CNT synthesis. For this reason, various proposals have been made in the past regarding methods for aligning and growing CNTs on a substrate surface with high density, catalyst particles used in the synthesis of CNTs, CNT diameter control, CNT replication technology, and the like.

For example, Patent Document 1 discloses that a cationic surfactant (didecyldimethylammonium bromide) is dissolved in toluene, cobalt chloride hexahydrate is dissolved therein, sodium borohydride is added thereto, and cobalt chloride is added. A method for producing a catalyst for synthesizing carbon nanotubes which is reduced to obtain cobalt fine particles is disclosed. In the same document,
(1) Cobalt particles having an average particle size of about 4 nm can be obtained by such a method,
(2) A catalyst solution in which the cobalt particles are dispersed in toluene is dropped on a silicon substrate and brought into contact with a hydrogen sulfide / hydrogen mixed gas to generate cobalt sulfide particles on the surface of the substrate. By placing the acetylene / N ₂ mixed gas in a reaction tube at 900 ° C. for 1 hour, CNTs having a diameter of 20 to 50 nm and a length of 0.5 to 5 μm can be obtained, and
(3) As a catalyst for CNT synthesis, a metal of group 5 to 8 such as Ni, Co, Mo, Fe, Cu, V, and Pd can be used.
Is described.

Patent Document 2 discloses a method for producing a catalyst in which an iron zirconium alloy thin film having a film thickness of 1 to 100 nm or a cobalt vanadium alloy thin film having a film thickness of 2.5 nm is formed on a glass substrate surface and heated. . In the same document,
(1) When the substrate on which the thin film is formed is heated, crystalline metal fine particles functioning as a catalyst are generated inside the thin film,
(2) When the substrate on which the thin film is formed is heated and brought into contact with a reactive carbon gas, CNT can be grown on the surface of the substrate, and
(3) When a group 4 element or group 5 element is added to iron or cobalt, the heating temperature (growth furnace temperature) of the substrate can be lowered,
Is described.

Further, Non-Patent Document 1 discloses a Ti—Co particle that is produced by laser ablating a Ti—Co alloy target and then classified using a differential type electrostatic classifier (Differential Mobility Analyzer, DMA). A manufacturing method is disclosed. In the same document,
(1) By such a method, Ti—Co fine particles having an average particle diameter of 5.8 nm and a standard deviation of 1.09 nm can be obtained, and
(2) The fine particles are supported on the surface of the Si substrate, and when CNTs are grown using a thermal CVD method, CNTs having an average diameter of 5.7 nm and a standard deviation of 1.13 nm can be obtained.
Is described.

In Non-Patent Document 2, a 20 nm thick TiN thin film (buffer layer for suppressing the formation of Co silicide) is formed on the surface of a Si substrate, and Co particles generated by pulsed arc plasma are carried on the surface. A method for producing such a catalyst is disclosed. In the same document,
(1) By such a method, Co nanoparticles having a diameter of 2 to 3 nm can be obtained, and
(2) When a TiN / Si substrate supporting Co nanoparticles is used, CNTs having an outer diameter of 3 to 6.6 nm can be grown.
Is described.
Non-Patent Document 3 describes that CNTs having a diameter corresponding to the diameter of nanoparticles are synthesized using nanoparticles having a uniform particle diameter synthesized in advance in a liquid phase as a catalyst.

Furthermore, when synthesizing CNTs by chemical vapor deposition, amorphous carbon may usually adhere between the entangled CNTs or on the wall surfaces or cap surfaces of the CNTs. Amorphous carbon becomes an impurity that deactivates the catalytic activity during growth and adversely affects the properties of CNT. Therefore, a method for removing amorphous carbon during synthesis has also been proposed.
For example, in Non-Patent Document 4, water (0-2.0 ml) is added to a solution of ferrocene (0.6 g) dissolved in xylene (5 ml) as a C source, and this solution is continuously added to a tubular furnace. A method for producing carbon nanotubes is disclosed in which carbon nanotubes are supplied and grown on the surface of a quartz substrate. In the same document,
(1) When CNT is synthesized in an atmosphere containing water, amorphous carbon covering the tube wall can be efficiently removed,
(2) When water is not added to the solution, the CNT is linear, whereas when water is added to the solution, the CNT bends and its surface becomes non-smooth, resulting in a “bamboo” structure,
(3) When CNT is synthesized under an atmosphere containing water, the graphite layer constituting the side surface of the CNT is broken and is no longer a continuous graphite sheet, and (4) CNT increases as the amount of water added to the solution increases. The growth rate of
Is described.

In Non-Patent Document 5, an Al ₂ O ₃ (10 nm) / Fe (1 nm) sputtered film is formed on the Si substrate surface as a catalyst, ethylene flow rate: 10 to 150 cm ³ STP / min, water concentration 20 to 500 ppm. Discloses a method for synthesizing CNTs in which CNTs are grown on a substrate surface under conditions of a temperature of 750 ° C. × 10 min. In the same document,
(1) The activity and life of the catalyst are improved by adding water during CVD synthesis, and
(2) By such a method, it is possible to synthesize single-walled CNTs with high density and vertically aligned millimeter height (maximum: 2.5 mm thickness),
Is described.

In Non-Patent Document 6, an Al ₂ O ₃ (10 nm) / Fe (1 nm) film is formed on a Si substrate having a 600 nm SiO ₂ film, and CVD synthesis is performed at 750 ° C. using ethylene as a carbon source. A method for producing single-walled CNTs is disclosed. In the same document,
(1) Up to a water concentration of 100 ppm, the maximum height of CNT increases with an increase in water concentration, and when the water concentration exceeds 140 ppm, the maximum height of CNT decreases with an increase in water concentration, and
(2) The point where the film thickness becomes maximum when the water / ethylene ratio of the discharge part of the reaction tube is 1/1000,
Is described.

Further, Non-Patent Document 7 discloses that an Fe film having a thickness of 0.1 to 0.2 nm is formed on the SiO ₂ / Si substrate surface by electron beam evaporation, and this is annealed in oxygen at 550 ° C., and further in hydrogen. Was heated at 720 ° C. to produce Fe clusters of ˜1.3 nm on SiO ₂ and mixed gas of methane (66%), hydrogen (12%), oxygen (1%) and argon (21%) A method for producing CNTs is disclosed in which CNTs are produced on the surface of a substrate by CVD. In the same document,
(1) By this method, a vertically aligned single-walled CNT having a thickness of about 10 μm can be obtained in 10 minutes, and
(2) If oxygen is not added, vertically aligned single-walled CNTs cannot be obtained,
Is described.

Japanese Patent No. 3438041 JP 2004-267926 A S. Sato et al., Chemical Physics Letters 402 (2005) 149-154 M.Hiramasu et al., Japanese Journal of Applied Physics, 44 (2005) L693-695 Journal of Physical Chemistry, B105 (2001) 11424-11431 A. Cal et al., Journal of Materials Research, 16 (2001) 3107-3110 K. Hata et al., Science, 306 (2004) 1362-1364 D.N.Futaba et al., Physical Review Letters, 95 (2005) 056104 G. Zhang et al., Proceedings of the National Academy of Science of the United States of America, 102 (2005) 16141-16145

It is known that Fe, Co, Ni, and the like belonging to groups 8 to 10 of the periodic table and alloys thereof have high catalytic ability for growing CNT. Therefore, if fine particles made of these metals or alloys are densely arranged on the substrate surface and the CNT synthesis conditions are optimized, high-density CNTs can be grown on the substrate surface.
In the usual CNT growth method by chemical vapor deposition, a catalyst metal thin film or a catalyst metal precursor is formed on the substrate surface, and then subjected to heat treatment or plasma treatment to produce fine particles, which are used as a catalyst to produce CNTs. Grow. However, it is extremely difficult to control the particle diameter, number density, and the like of these fine particles, and accordingly, it is difficult to control the diameter of the CNT.
In Non-Patent Document 3 and the like, CNTs having a diameter corresponding to the diameter of the nanoparticles are synthesized using nanoparticles having a uniform particle diameter synthesized in advance in a liquid phase as a catalyst. However, the catalytic activity of the liquid phase synthetic nanoparticles reported so far is extremely low, and only low-density CNTs grown randomly on the substrate are obtained.
On the other hand, the Ti—Co binary alloy fine particles produced by the gas phase method disclosed in Non-Patent Document 1 have high catalytic activity of the fine particles, and the diameters of the fine particles and the CNTs substantially correspond to each other. Excellent growth and diameter controllability. However, the method of generating fine particles by laser ablation and electrostatically classifying the particles is inefficient as a method of obtaining particles with a uniform particle size, and it is difficult to obtain a uniform particle with a small particle size.
Furthermore, since the conventional catalyst has low catalytic activity, amorphous carbon is likely to deposit around the catalyst. Therefore, there is a problem of reducing the number of catalyst fine particles that act effectively. Amorphous carbon has also been a cause of reducing the activity and life of the catalyst and reducing the growth rate of CNTs.

The problem to be solved by the present invention is to provide a method for producing carbon nanotubes having high density, vertical alignment and excellent diameter controllability.
In addition, another problem to be solved by the present invention is to provide a method for producing a carbon nanotube capable of suppressing a decrease in catalyst activity and life due to the deposition of amorphous carbon around the catalyst. It is in.

In order to solve the above-described problems, the carbon nanotube production method according to the present invention is summarized as having the following configuration.
(1) The method for producing the carbon nanotube is as follows:
Mosquitoes over catalyst dispersion liquid in which carbon nanotubes synthesis catalyst dispersed was coated on a substrate surface, a catalyst supporting step of supporting the carbon nanotube synthesizing catalyst to the substrate surface,
Bei example a growth step of growing the carbon nanotubes on the substrate surface which was supported prior Symbol carbon nanotube synthesis catalyst,
Before Symbol carbon nanotube synthesis catalyst comprises Group 8 elements, and one or more first element selected from Group 9 element and Group 10 element, and one or more second elements selected from Group 4 elements and Group 5 element e Bei microparticles, and a protective layer consisting of one or more organic material selected from organic acids and organic amines covering the external surface of the fine particles,
Before Symbol growth step, over the catalyst for the carbon nanotube synthesis was carried on the substrate surface, flowing at least a carbon-containing compound gas and an oxygen-containing compound gas, growing carbon nanotubes on the substrate surface by chemical vapor deposition also of the is to be.
(2) The oxygen-containing compound gas is water vapor.
(3) The carbon-containing compound gas is acetylene.
(4) The molar ratio (y / x) of the water vapor (y) to the acetylene (x) is 0.0002 or more and 0.02 or less at the introduction portion of the reaction tube.

  When the first raw material, the second raw material, the alcohol, and the organic acid and / or organic amine are mixed at a predetermined ratio and heated at a predetermined temperature, the first raw material, the second element, and the surroundings are formed of fine particles containing the first element and the second element. Catalyst fine particles coated with a protective layer are obtained. The protective layer has an action of preventing aggregation between fine particles during synthesis of the catalyst fine particles. Therefore, fine particles having a relatively small average particle diameter and a small standard deviation can be obtained by such a method. The fine particles thus obtained are dispersed in a suitable dispersion medium, and the dispersion is applied to a suitable substrate surface and dried, whereby the catalyst fine particles can be densely supported on the substrate surface. Furthermore, when synthesizing CNTs by CVD using this, if oxygen-containing compound gas is flowed over the catalyst in addition to the carbon-containing compound gas, amorphous carbon deposited around the catalyst is selectively oxidized and removed. Can do. Therefore, it is possible to synthesize high-density, vertically-oriented CNTs having substantially the same diameter and standard deviation as the catalyst at a high growth rate.

Hereinafter, an embodiment of the present invention will be described in detail.
First, the CNT synthesis catalyst used in the method according to the present invention will be described. In the present invention, the CNT synthesis catalyst includes fine particles containing a first element and a second element, and a protective layer that covers the periphery of the fine particles.
“First element” means one or more elements selected from group 8 elements (Fe, Ru, Os), group 9 elements (Co, Rh, Ir) and group 10 elements (Ni, Pd, Pt) (main catalyst) Element). The “second element” refers to one or more elements (promoter elements) selected from Group 4 elements (Ti, Zr, Hf) and Group 5 elements (V, Nb, Ta). The fine particles may contain only the first element and the second element, or may contain other elements in addition to the first element and the second element. Examples of other elements include other metal / nonmetal elements and elements derived from starting materials (for example, oxygen).
When a plurality of first elements are included in the catalyst, the ratio thereof can be arbitrarily selected. Similarly, when a plurality of second elements are contained in the catalyst, their ratio can be arbitrarily selected. When the catalyst contains an element other than the first element and the second element, the number of elements that adversely affect the catalytic activity of the fine particles is preferably small. Since oxygen is removed to some extent by exposure to a reducing (non-oxidizing) atmosphere when synthesizing CNTs, it may be contained in the catalyst.
Among these, group 4 elements (particularly Ti) are particularly suitable as the second element because they have a greater effect of increasing the growth rate of CNTs than other elements. In addition, Group 5 elements (particularly V) are particularly suitable as the second element because they are superior in diameter controllability of the synthesized CNTs compared to other elements.

The ratio of the first element and the second element contained in the catalyst affects the catalyst activity. The first element has a relatively high catalytic activity for growing CNTs by itself when fine particles are formed from the thin film by heat treatment or plasma treatment, but is synthesized by a liquid phase method. In this case, the catalyst activity becomes extremely small. However, the addition of the second element to this can dramatically improve the catalyst activity even in the liquid phase method. In order to obtain such an effect, the content of the second element (= number of atoms of the second element × 100 / (number of atoms of the first element + number of atoms of the second element)) is preferably 2 at% or more. .
On the other hand, when the content of the second element is excessive, the catalyst activity is lowered. Accordingly, the content of the second element is preferably 50 at% or less.
The optimal content of the second element varies depending on the types of the first element and the second element. For example, in the case of Fe—Ti binary alloy or Fe—Ti—O-based oxide, the Ti content is preferably 2 to 50 at%, more preferably 4 to 40 at%, still more preferably 10 to 35 at%, further preferably Is 15 to 30 at%.
Further, for example, in the case of an Fe-V binary alloy or an Fe-VO-based oxide, the V content is preferably 2 to 50 at%, more preferably 4 to 35 at%, and further preferably 5 to 30 at%. is there.
Further, for example, in the case of Fe—Ti—V ternary alloy or Fe—Ti—V—O-based oxide (Ti / V atomic ratio = 1), the content of (Ti + V) is preferably 2 to 50 at%. More preferably, it is 5-45 at%, More preferably, it is 7-35 at%, More preferably, it is 11-27 at%.

The diameter and standard deviation of the catalyst fine particles influence the outer diameter and standard deviation of the synthesized CNT. In general, the smaller the catalyst particle diameter, the smaller the outer diameter of the CNT. Further, the smaller the standard deviation of the diameter of the catalyst fine particles, the smaller the standard deviation of the outer diameter. Furthermore, the CNT having an outer diameter almost equal to the diameter of the catalyst fine particles can be synthesized such that the aggregation of the catalyst fine particles is less likely to occur during the synthesis of the CNT.
When the production method according to the present invention described later is used, catalyst fine particles having a diameter of 1 to 15 nm can be synthesized. Further, when the production conditions are optimized, catalyst fine particles having a diameter of 3 to 5 nm can be synthesized. Furthermore, when the production method described later is used, catalyst fine particles having a standard deviation of the diameter of 1 nm or less can be synthesized without classification. Furthermore, when the conditions are optimized, catalyst fine particles having a standard deviation of the diameter of 0.5 nm or less can be synthesized, and the particles can be further finely classified by fractional precipitation by adjusting the polarity of the dispersion solvent.

The protective layer mainly has an action of suppressing the aggregation of the fine particles when synthesizing the fine particles, making the particle diameter uniform, and an action of suppressing the aggregation of the fine particles when dispersed in a dispersion described later. The protective layer is made of one or more organic substances selected from organic acids and organic amines. These organic substances are a kind of surfactant having a hydrophobic group and a hydrophilic group in one molecule. By covering the surface of the fine particles with these, aggregation of fine particles during synthesis or dispersion can be suppressed. .
Specific examples of the organic acid include RCOOH, RSOH, and RPOH. Specific examples of the organic amine include RNH ₂ , R ₂ NH, and R ₃ N. R represents an alkyl chain (C _n H _{2n + 1} —, n is a natural number).
The protective layer may be composed of one kind of organic substance, or may be composed of two or more kinds of organic substances. In particular, when two or more organic substances are used as the protective layer, there is an advantage that the particle diameter of the fine particles is stabilized and uniformized.

Next, the catalyst dispersion used in the method according to the present invention will be described.
The catalyst dispersion is composed of the carbon nanotube synthesis catalyst described above dispersed in a dispersion solvent.
The dispersion solvent may be any solvent that can uniformly disperse the catalyst fine particles. Examples of such a dispersion solvent include organic solvents having low polarity such as hexane, toluene, and chloroform.
The catalyst fine particle concentration in the catalyst dispersion can be arbitrarily selected according to the purpose. In general, the lower the concentration of the catalyst fine particles, the easier it is to disperse the fine particles uniformly. However, if the concentration of the catalyst fine particles is too low, it becomes difficult to densely arrange the catalyst fine particles on the substrate surface. Therefore, the concentration of the catalyst fine particles is preferably 0.001 wt% or more.
On the other hand, if the concentration of the catalyst fine particles becomes too high, it becomes difficult to form a monomolecular film of particles on the substrate surface. Accordingly, the concentration of the catalyst fine particles is preferably 1.0 wt% or less.
The optimum concentration of catalyst fine particles depends on other manufacturing conditions such as the substrate pulling speed, and therefore it is preferable to select the optimum concentration in consideration of these.

Next, a method for producing a carbon nanotube synthesis catalyst will be described.
The method for producing a catalyst for carbon nanotube synthesis includes a dissolution / mixing step and a heating step.
The dissolution step is a step of dissolving and mixing the first raw material, the second raw material, the alcohol, and the organic substance in an organic solvent.
The “first raw material” is a compound containing one or more first elements of any of group 8 elements, group 9 elements, and group 10 elements, and is soluble in an organic solvent. As the first raw material, one kind of compound that satisfies such conditions may be used, or two or more kinds of compounds may be used in combination.
Specifically, as the first raw material,
(1) An organic complex in which an organic substance is coordinated to an ion of a first element,
(2) There is an organic acid salt of the first element.
Specific examples of the organic complex containing the first element include Fe (III) acetylacetonate, Fe (II) acetylacetonate, Co (II) acetylacetonate, Co (III) acetylacetonate, Ni (II ) Acetylacetonate, platinum (II) acetylacetonate, and the like.
Specific examples of the organic acid salt containing the first element include iron acetate (II), iron oxalate (II), iron oxalate (III), cobalt acetate (II), cobalt acetate (III), There are nickel acetate (II), palladium acetate (II), palladium nitrate hydrate (II), palladium nitrate (II) and the like.

The “second raw material” refers to a compound containing at least one second element selected from group 4 elements and group 5 elements and soluble in an organic solvent. As the second raw material, one kind of compound that satisfies such conditions may be used, or two or more kinds of compounds may be used in combination.
Specifically, as the second raw material,
(1) An organic complex in which an organic group is coordinated to an ion or MO ion of the second element (M),
(2) Organic salt of the second element,
and so on.
Specific examples of the organic complex containing the second element include VO acetylacetonate, TiO acetylacetonate, Zr trifluoroacetylacetonate, Hf trifluoroacetylacetonate, Ti diisopropoxide bistetramethylheptanedionate. and so on.
Specific examples of the organic acid salt containing the second element include titanium oxalate, titanium sulfate, vanadium oxide sulfate, vanadium sulfate, zirconium acetate, and hafnium sulfate.

Alcohol is a reducing agent for reducing the first raw material and the second raw material to bring the metal ions or MO ions into a nonionic state in the organic solvent. As the reducing agent, one kind of alcohol may be used, or two or more kinds may be used in combination.
Specific examples of the alcohol that can be used as the reducing agent include 1,2-hexadecanediol, 1,2-octadecanediol, and 1,2-tetradecanediol.
The “organic substance” is composed of an organic acid or an organic amine as described above. As the organic substance, one kind of organic acid or organic amine may be used, or two or more kinds may be used in combination.
Specific examples of the organic acid include oleic acid, caproic acid, lauric acid, butyric acid, and linoleic acid.
Specific examples of the organic amine include oleylamine, hexylamine, and laurylamine.
The organic solvent should just be what can melt | dissolve the 1st raw material mentioned above, the 2nd raw material, alcohol, and organic substance. Further, since the solution is heated to a predetermined temperature as described later, it is preferable to use a solvent having a boiling point of 200 ° C. or higher. Specific examples of the organic solvent include octyl ether and phenyl ether. These organic solvents may be used alone or in combination of two or more.

The ratio of the first raw material and the second raw material is selected as an optimum ratio according to the composition of the catalyst fine particles to be produced. When the method according to the present invention is used, catalyst fine particles substantially matching the charged composition can be obtained.
Further, the concentrations of the first raw material and the second raw material in the solution are selected to be optimum depending on the diameter, standard deviation, etc. of the catalyst fine particles to be produced. In general, when a dilute solution is used, uniform catalyst fine particles having a uniform particle diameter can be obtained. The amount of the solvent added to the first raw material and the second raw material is usually about 10 to 50 mL with respect to 1 mmol of the first raw material and the second raw material, although it depends on the types of the first raw material and the second raw material.
A reducing agent is for giving an electron to the ion of 1st element or 2nd element contained in a solution, or MO ion as mentioned above, and making it a nonionic state. When metal ions or MO ions are reduced, they gather together to form fine particles. The amount of the reducing agent added depends on the types of the first raw material, the second raw material, and other raw materials, but is usually 1 to 1 of the number of moles of ions of the first element or the second element or MO ions contained in the solution. It is about 20 times.
Organic acids or organic amines are believed to bind to ions of first or second elements or MO ions in solution. When a reducing agent is further added to the solution, metal ions or MO ions are reduced and aggregated into fine particles, and at the same time, the periphery of the fine particles is covered with an organic acid or organic amine. The amount of the organic acid or organic amine added depends on the types of the first raw material, the second raw material, and other raw materials, but is usually the number of moles of ions of the first element or the second element or MO ions contained in the solution. About 1 to 10 times.

The heating step is a step of heating the uniform solution obtained in the dissolution / mixing step at 180 ° C. to 300 ° C. in an inert atmosphere. Catalyst fine particles coated with a protective layer are generated in the solution by heating.
The solution is heated under an inert atmosphere (for example, under a nitrogen atmosphere or an argon atmosphere) in order to prevent oxidation of fine particles generated in the solution.
As the heating temperature, an optimum temperature is selected according to the type of raw material used and the target diameter. Generally, when the heating temperature is too low, the reaction between the raw materials becomes insufficient. In order to advance the reaction between the raw materials efficiently, the heating temperature is preferably 180 ° C. or higher.
On the other hand, if the heating temperature is too high, the aggregation of the fine particles proceeds and the diameter of the particles becomes inhomogeneous. Therefore, the heating temperature is preferably 300 ° C. or lower.
After the completion of the reaction, the fine particles and the solvent are separated using means such as centrifugation, and dispersed again in a suitable dispersion solvent, a catalyst dispersion for CNT synthesis is obtained.

Next, the manufacturing method of the carbon nanotube which concerns on this invention is demonstrated.
The carbon nanotube manufacturing method according to the first embodiment of the present invention includes a catalyst supporting step and a growth step.

The catalyst supporting step is a step of applying the catalyst dispersion described above to the substrate surface and supporting the carbon nanotube synthesis catalyst on the substrate surface.
The material of the substrate is not particularly limited, and an optimum material is selected according to the composition of the CNT synthesis catalyst, the growth conditions in the growth process described later, the use of the CNT, and the like. Specific examples of the material of the substrate include Si, Si with thermal oxide film, sapphire, magnesia, Si substrate on which various metals, oxides, and nitrides are deposited, and mesoporous material.

When a mesoporous material is used as the substrate, only the substrate surface may be a mesoporous material, or the entire substrate may be a mesoporous material.
Specifically, the substrate having only the surface made of mesoporous silica is
(1) Add appropriate amounts of water, ethanol, surfactant, and acid to silicon alkoxide to form a sol,
(2) A mesoporous silica film containing a surfactant is formed on the surface of the substrate by applying it to the surface of a suitable substrate (for example, Si substrate) and polycondensing it,
(3) removing the surfactant from the mesoporous silica film by oxidation or solvent extraction;
Can be obtained.
Further, the substrate made entirely of mesoporous silica is specifically
(1) An appropriate amount of water, ethanol, or surfactant is added to silicon alkoxide (for example, tetraalkoxysilane) to hydrolyze the silica raw material under basic conditions.
(2) separating the powdered product from the solution;
(3) The surfactant contained in the powder is removed by oxidation or solvent extraction,
(4) The powder is formed into a plate shape and sintered.
Can be obtained.
When a metal alkoxide containing a specific metal element is used as a starting material instead of silicon alkoxide, a mesoporous material made of a material other than silica (for example, titania, zirconia, alumina, etc.) can be obtained.

To apply the catalyst dispersion on the substrate surface,
(1) A method in which the catalyst dispersion is applied to the substrate surface by spraying, brushing, etc.
(2) A method of spin-coating the catalyst dispersion on the substrate surface,
(3) dipping the substrate into the catalyst dispersion and lifting the substrate at a predetermined pulling speed;
and so on. Any method may be used in the present invention.
In particular, the dipping method can uniformly apply the catalyst dispersion to the substrate surface, and if the concentration of the fine particles in the catalyst dispersion and the pulling speed of the substrate are optimized, the fine particles are uniformly and densely applied to the substrate surface. Since it can carry | support, it is suitable as a coating method.
When the substrate surface to be used is hydrophilic, it is preferable to subject the substrate surface to a hydrophobic treatment with a silane coupling agent or the like before applying the catalyst dispersion. By applying a hydrophobic treatment in advance, the fine particles can be uniformly supported.
After the catalyst dispersion is applied to the substrate surface, the substrate is dried, and the dispersion solvent contained in the catalyst dispersion is removed. At least after the step, the catalyst fine particles are oxidized to form metal oxide fine particles. The protective layer covering the surface of the catalyst fine particles may be removed by heat treatment or plasma treatment in an oxidizing atmosphere prior to the growth process, or the CNT synthesis can be performed without removing the protective layer. It may be used. In the present invention, as described later, since an appropriate amount of oxygen-containing compound gas is used during the synthesis of CNTs, it is not always necessary to remove the protective layer prior to the growth of CNTs.

The growth step is a step of growing carbon nanotubes on the surface of the substrate carrying the CNT synthesis catalyst.
Specifically, the growth of CNTs is performed by supplying a carbon-containing compound gas to the surface of the substrate carrying the catalyst and thermally decomposing the carbon-containing compound gas (so-called “chemical vapor deposition method”). When the carbon-containing compound gas is thermally decomposed on the substrate surface, CNTs grow using the catalyst supported on the substrate surface as a seed. Moreover, in this invention, oxygen-containing compound gas is supplied simultaneously with flowing carbon-containing compound gas.

As carbon-containing compounds,
(1) hydrocarbons such as methane, acetylene, ethane, propane, propylene, benzene, toluene, xylene,
(2) Hydroxy compounds such as methanol and ethanol in which H of the hydrocarbon is substituted with a hydroxy group (OH),
(3) carbon monoxide,
Etc. are suitable. Any one of these carbon-containing compounds may be used, or two or more thereof may be used in combination.
Among these, hydrocarbons and hydroxy compounds are particularly suitable as carbon-containing compounds because they can efficiently generate CNTs and are easy to handle.

Examples of the oxygen-containing compound gas include water vapor, oxygen, carbon monoxide, and alcohol. In particular, since water vapor has a relatively weak oxidizing power, it is easy to selectively remove only amorphous carbon harmful to CNT growth. In addition, water vapor is suitable as an oxygen-containing compound gas used when synthesizing CNTs, since it is easy to measure and control the amount added to the reaction gas.
The amount of the oxygen-containing compound gas added affects the CNT growth rate. In general, the smaller the amount of oxygen-containing compound gas added, the lower the growth rate of CNTs. In order to obtain a relatively high growth rate, the molar ratio (y / x) of the oxygen-containing compound gas (y) to the carbon-containing compound gas (x) is preferably 0.0002 or more at the introduction portion of the reaction tube. . The molar ratio (y / x) is more preferably 0.0007 or more, further preferably 0.002 or more, and further preferably 0.003 or more.
On the other hand, when the amount of the oxygen-containing compound gas added is excessive, the CNT oxidation proceeds, so that the CNT growth rate decreases. Accordingly, the molar ratio (y / x) is preferably 0.02 or less at the introduction portion of the reaction tube. The molar ratio (y / x) is more preferably 0.014 or less, further preferably 0.01 or less, and further preferably 0.008 or less.

  In addition, when supplying a carbon-containing compound gas and an oxygen-containing compound gas to the substrate surface, an appropriate carrier gas is used. Specifically, hydrogen, ammonia, nitrogen, argon, helium, or a mixed gas thereof is suitable as the carrier gas. The ratio of the carbon-containing compound gas and oxygen-containing compound gas to the carrier gas, the total gas flow rate, etc. should be optimized according to the type of carbon-containing compound and oxygen-containing compound, the size of the reaction tube, the thermal decomposition method, etc. select.

For the method of pyrolyzing the carbon-containing compound gas,
(1) Thermal chemical vapor deposition in which a substrate is placed in a reaction vessel, the substrate is heated to a predetermined temperature using a heater, infrared rays, laser, etc., and a carbon-containing compound gas is introduced into the reaction vessel together with an appropriate carrier gas. (Thermal CVD) method,
(2) A substrate is placed in a reaction vessel, and the substrate is heated to a predetermined temperature by generating plasma in the reaction vessel using, for example, a microwave oscillator, and a carbon-containing compound gas is appropriately placed in the reaction vessel. Plasma vapor deposition (plasma CVD) method introduced with carrier gas,
(3) A hot filament gas in which a substrate is placed in a reaction vessel, the substrate is heated to a predetermined temperature using a hot filament placed near the substrate surface, and a carbon-containing compound gas is introduced into the reaction vessel together with an appropriate carrier gas. Phase growth (hot filament thermal CVD) method,
(4) A combination of the various methods described above,
and so on. Any method may be used in the present invention.

In the synthesis of CNTs, first, the substrate is put in a reaction vessel and the pressure is reduced to a predetermined pressure (for example, 10 ⁻⁵ Torr (1.3 × 10 ⁻³ Pa or less)). Next, the substrate is heated up to the synthesis temperature using a heating device. When the substrate reaches the synthesis temperature, the carrier gas, the carbon-containing compound gas, and the oxygen-containing compound gas are allowed to flow for several minutes to several hours while adjusting the pressure at a predetermined flow rate ratio using the reaction gas supply device. Thereby, CNT grows on the substrate surface.
The synthesis temperature of CNT should just be more than the temperature which can thermally decompose carbon containing compound gas. The synthesis temperature of CNT is usually 500 to 1000 ° C.
The flow rate ratio, flow rate, and the like of the carbon-containing compound gas, the oxygen-containing compound gas, and the carrier gas are selected according to the types of the carbon-containing compound gas and the oxygen-containing compound gas, the heating method, and the like.

Next, the effect | action of the manufacturing method of the carbon nanotube which concerns on this invention is demonstrated.
It is known that all Group 8-10 elements such as Fe have a strong catalytic action for growing CNTs. The outer diameter of the CNT is almost determined by the diameter of the catalyst fine particle at the time when the CNT starts growing. Therefore, in order to synthesize CNTs having a predetermined outer diameter and uniform outer diameter, it is necessary to control the diameter and standard deviation of the catalyst fine particles. For example, in a method in which a metal thin film is formed on the substrate surface and this is heat-treated, there is a limit in controlling the diameter and standard deviation of the catalyst fine particles.
On the other hand, as described in Non-Patent Document 3, there is a CNT growth method in which fine particles having a uniform diameter are prepared in advance using these metals, and this is used as a catalyst. However, only very low activity can be obtained with this method.

On the other hand, it is known that when a Group 4 element or a Group 5 element is added to Group 8 to 10 elements such as Fe, Co, and Ni, the catalytic activity is improved (for example, Patent Document 2, Non-Patent Document 1). reference). The catalytic activity is improved by adding a group 4 element or a group 5 element to the group 8-10 element. The group 4 element such as Ti and the group 5 element such as V all have a strong affinity for carbon, It is considered that heat is generated when the carbide is formed.
As disclosed in Patent Document 1, if alloy fine particles containing a group 4 element are prepared by laser ablation of an alloy target and classified by a differential electrostatic classifier, catalyst fine particles having a relatively narrow particle size distribution can be obtained. However, this method is inefficient.

On the other hand, when the first raw material, the second raw material, the alcohol, and the organic acid and / or organic amine are mixed at a predetermined ratio and heated at a predetermined temperature, the first element and the second element are included, and the surroundings. Catalyst fine particles coated with a protective layer can be obtained. The protective layer has an action of preventing aggregation between fine particles during synthesis of the catalyst fine particles. Therefore, fine particles having a relatively small average particle diameter and a smaller standard deviation can be obtained by such a method. Moreover, since it is not necessary to classify the fine particles after synthesis, the cost of the catalyst fine particles can be reduced.
In addition, the protective layer acts to suppress aggregation of fine particles when the synthesized fine particles are dispersed in the dispersion, and as a spacer to arrange fine particles densely when the fine particles are arranged on the substrate surface. There is also. For this reason, the synthesized fine particles are dispersed in an appropriate dispersion medium to form a catalyst dispersion liquid, and when this catalyst dispersion liquid is applied to the substrate surface and dried, the catalyst fine particles having the same particle diameter are closely supported on the substrate surface. Can be made.

Furthermore, when CNT is synthesized using this, the growth activity of the CNT is improved, and the growth of the CNT starts before the fine particles aggregate. Therefore, a high-density CNT having a diameter almost equal to the catalyst fine particle diameter can be obtained. In particular, when a group 4 element (especially Ti) is used as the second element, CNTs having a long length can be grown at a high density in a relatively short time. In addition, when a Group 5 element (particularly V) is used as the second element, CNTs having an outer diameter substantially matching the catalyst fine particle diameter can be obtained.
Further, when a mesoporous material is used as a substrate when growing CNTs, catalyst fine particles can be densely arranged on the surface of the substrate, and aggregation of the catalyst fine particles during CNT growth is further suppressed. Diameter controllability is further improved.
Furthermore, when growing a CNT, if a mixed gas containing at least a carbon-containing compound gas and an oxygen-containing compound gas is used, the growth rate of the CNT is further improved. This is presumably because amorphous carbon deposited around the catalyst and on the CNT side wall is removed by introducing an appropriate amount of oxygen-containing compound gas having an appropriate oxidizing power into the reaction system.

(Reference Example 1)
[1. Preparation of catalyst dispersion]
Inactive Fe acetylacetonate (first raw material), VO acetylacetonate (second raw material), 1,2-hexadecanediol (reducing agent), oleic acid and oleylamine (protective layer), and octyl ether (solvent) The mixture was mixed at a predetermined ratio in a gas atmosphere and reacted at 250 ° C. or 290 ° C. for 30 minutes. Octyl ether was 20 ml, and the amount of each raw material added was Fe acetylacetonate: VO acetylacetonate: reducing agent: oleic acid: oleylamine = 0.9 mmol: 0.1 mmol: 7 mmol: 3 mmol: 3 mmol.
After completion of the reaction, the mixture was cooled to room temperature, and catalyst fine particles were obtained by centrifugation. This was added to hexane to prepare a catalyst dispersion.

[2. Evaluation of catalyst dispersion]
The obtained catalyst dispersion was dropped on a TEM grid and dried, and then TEM observation of the fine particles was performed. FIG. 1A and FIG. 1B show TEM photographs of catalyst fine particles (hereinafter referred to as “Fe—VO fine particles”) using Fe acetylacetonate and VO acetylacetonate as starting materials. FIG. 1A shows a lattice image taken with just focus on Fe—V—O fine particles synthesized under the condition of 250 ° C. × 30 minutes. FIG. 1A shows that uniform catalyst fine particles having an average particle diameter of 3.1 nm are obtained. FIG. 1B is a photograph of Fe-VO fine particles synthesized under conditions of 290 ° C. × 30 minutes by under focus. From FIG. 1 (b), it can be seen that uniform catalyst fine particles having an average particle diameter of 4.5 nm and having a periphery coated with a protective layer are obtained.

[3. Synthesis and evaluation of CNT]
As the substrate, a Si substrate having a mesoporous silica film formed on its surface (hereinafter simply referred to as “mesoporous silica substrate”) and a Si substrate with a thermal oxide film were used. The mesoporous silica substrate was produced by a known method (for example, see J. Phys. Chem. B 2000, 104, 12095-12097). That is, a surfactant was added to a sol solution that was aged by adding water and an acid to tetraethoxysilane, and this was applied to the surface of the Si substrate and baked in the air to obtain a mesoporous silica substrate. Next, the mesoporous silica substrate was subjected to a hydrophobic treatment with a silane coupling agent. Similarly, the Si substrate with a thermal oxide film was also subjected to a hydrophobic treatment.
Each of these substrates was dipped in a catalyst dispersion, and the substrates were pulled at a constant pulling rate (0.5 mm / sec) and dried. After drying, the protective layer was removed by plasma treatment. Next, this substrate was placed in a reaction vessel, and CNTs were generated by a thermal CVD method. In the thermal CVD, acetylene was used as the carbon-containing compound gas, the acetylene flow rate was 10 sccm (cc / min), the hydrogen (reducing gas) flow rate was 45 sccm (cc / min), the reaction temperature was 700 ° C., and the reaction time was 10 min.

FIG. 2A is a SEM photograph of a cross section of a CNT film synthesized using a mesoporous silica substrate supporting a Fe—V—O catalyst (V / (Fe + V): 10 at%, reaction temperature: 250 ° C.). Show. FIG. 2B shows a TEM photograph of CNT collected from the substrate surface. From FIG. 2, it can be seen that CNTs having a substantially constant outer diameter are grown vertically and densely with respect to the substrate. Although not shown, it was found that the amount of CNT grown was larger when the mesoporous silica substrate was used than when the thermal oxide film-attached Si substrate was used.
Next, the outer diameter of the CNT collected from the mesoporous silica substrate surface was measured by TEM observation, and the standard deviation was obtained. Similarly, the diameter of the catalyst fine particles in the catalyst dispersion was measured by TEM observation, and the standard deviation was obtained. FIG. 3A and FIG. 3B show histograms of Fe—V—O catalyst fine particles and CNT synthesized using the same, respectively. From FIG. 3, it can be seen that the diameter of the catalyst fine particles and the diameter of the CNT are substantially the same, and the standard deviation is also substantially the same.

(Reference Example 2, Comparative Example 1)
[1. Preparation of catalyst dispersion]
A catalyst dispersion was prepared using VO acetylacetonate and / or TiO acetylacetonate as the second raw material. The following four types of catalyst dispersions were prepared. Other manufacturing conditions were the same as those in Reference Example 1.
(A) One containing only Fe acetylacetonate (hereinafter referred to as “Fe—O fine particles (Comparative Example 1)”).
(B) The ratio of Fe acetylacetonate to VO acetylacetonate is 98: 2 to 50:50 (Fe-VO fine particles).
(B) The ratio of Fe acetylacetonate to TiO acetylacetonate is 98: 2 to 50:50 (hereinafter referred to as “Fe—Ti—O fine particles”).
(C) The ratio of Fe acetylacetonate to (VO acetylacetonate + TiO acetylacetonate) is 98: 2 to 50:50, and the ratio of VOacetylacetonate to TiO acetylacetonate is 1: 1. (Hereinafter referred to as "Fe-Ti-VO fine particles").

[2. Evaluation of catalyst dispersion]
The obtained catalyst dispersion was subjected to ICP emission analysis, and the composition ratio of Fe and V or Fe and Ti in the fine particles was measured. FIG. 4A shows the relationship between the charged composition of the Fe—V—O fine particles and the chemical analysis composition. FIG. 4B shows the relationship between the charged composition of the Fe—Ti—O fine particles and the chemical analysis composition. As can be seen from FIG. 4, catalyst fine particles having a chemical analysis composition almost identical to the charged composition are obtained. Although not shown, similar results were obtained for Fe-Ti-VO fine particles.

[3. Synthesis and evaluation of CNT]
[1. CNTs were synthesized using the catalyst dispersion obtained in the above. The substrate and CNT synthesis conditions used were the same as in Reference Example 1.
FIG. 5 shows a relationship between the catalyst composition and the CNT film thickness, and an SEM photograph of a cross section of the CNT film synthesized using Fe—O fine particles and Fe—Ti—O fine particles (Fe-10 to 40 at% Ti). . When Fe—O fine particles were used, the number of CNTs generated was extremely small, and CNTs were generated so as to crawl the substrate surface. On the other hand, when Fe—Ti—O fine particles were used, CNTs were generated perpendicular to the substrate and with high density. The film thickness of the CNT after a lapse of a certain time depends on the Ti content, and the film thickness became the thickest at 20 to 25 at% Ti.
The same applies to the case of using Fe—V—O fine particles and Fe—Ti—V—O fine particles, and CNTs were formed at a high density perpendicular to the substrate in any composition. The film thickness of the CNT after a certain period of time depends on the amount of V and Ti. In the case of Fe-VO fine particles, it is about 10 at% V. In the case of Fe-Ti-VO fine particles Was about 15 at% (Ti + V).

FIG. 6 shows the relationship between the diameter of the catalyst fine particles (Fe—V—O fine particles, Fe—Ti—O fine particles, and Fe—Ti—V—O fine particles) and the outer diameter of the CNT synthesized using them. . FIG. 6 also shows the diameter of the catalyst synthesized in advance by other researchers and the outer diameter of the CNT synthesized using the catalyst. The sources are as follows.
(1) S. Sato et al., Chemical Physics Letters 402 (2005) 149-154 (Non-Patent Document 1)
(2) M.Hiramasu et al., Japanese Journal of Applied Physics, vol.44, No.22, 2005, pp.L693-695 (non-patent document 2)
(3) Kobayashi et al., Thin Solid Films, 464 (2004) 286-289
(4) Cheung et al., J. Phys. Chem. B, 106 (2002), 2429-2433
(5) Choi et al., J. Phys. Chem. B, 106 (2002) 12361-12365
(6) Fu et al., J. Phys. Chem. B, 108 (2004) 6124-6129
(7) Li et al., J. Phys. Chem. B, 105 (2002) 2429-2433
(8) Sato et al., Chem. Phys. Lett., 382 (2003) 361-366
(9) Hiramasu et al., Jpn.J.Appl.Phys., 44 (2005) 1150-1154

In FIG. 6, the black marks indicate that CNTs are grown at low density and randomly, and a film in which CNTs are vertically aligned is not obtained. In many cases, there is almost no correspondence between the diameter of the catalyst fine particles and the outer diameter of the CNT.
On the other hand, the CNT obtained by Sato et al. Had a high density and was oriented substantially perpendicular to the substrate. Further, the diameter of the fine particles and the outer diameter of the CNT corresponded to approximately 1: 1. However, these fine particles have a relatively large average particle diameter, a standard deviation of more than 1 nm, and are classified using a differential electrostatic classifier. Have difficulty. Similarly, the CNTs obtained by Hiramasu et al. Had a high density and were oriented substantially perpendicular to the substrate. However, since the fine particles aggregate during the CNT synthesis, there is no 1: 1 correspondence between the diameter of the fine particles and the outer diameter of the CNT.
On the other hand, when the catalyst dispersion liquid according to the present invention is used, high-density and vertically aligned CNTs are obtained, and the diameter of the fine particles and the outer diameter of the CNTs are the same regardless of which catalyst is used. There was a 1: 1 correspondence between them. Furthermore, the outer diameter of CNT was in the range of 3 to 5 nm, and the standard deviation of the outer diameter was 1 nm or less.

(Example 1, Comparative Example 2)
[1. Preparation of catalyst dispersion]
An inert gas atmosphere containing Fe acetylacetonate (first raw material), TiO acetylacetonate (second raw material), 1,2-hexadecanethiol (reducing agent), oleic acid and oleylamine (protective layer), and octyl ether (solvent) The mixture was mixed at a predetermined ratio below and reacted at 210 to 290 ° C. for 1 to 30 minutes. Octyl ether was 20 ml, and the amount of each raw material added was Fe acetylacetonate: TiO acetylacetonate: reducing agent: oleic acid: oleylamine = 0.8 mmol: 0.2 mmol: 7 mmol: 3 mmol: 3 mmol.
After completion of the reaction, the mixture was cooled to room temperature, impurities were removed using a centrifuge, and fine particles coated with a protective layer were obtained. This was redispersed in hexane at an appropriate concentration (absorbance: 0.5) to obtain a catalyst dispersion.

[2. Synthesis of CNT]
A mesoporous silica substrate subjected to a hydrophobization treatment (silylation treatment) [1. The monomolecular film of fine particles was formed on the substrate in a self-organized manner by immersing in the catalyst dispersion prepared in [1] and pulling it up to the atmosphere at a constant speed (pickup speed: 0.5 mm / sec). Thereafter, the protective layer covering the surface of the fine particles was removed by plasma treatment (10 minutes). Next, the substrate carrying the catalyst was placed in a CNT growth apparatus, and the pressure in the growth apparatus was reduced to 1 × 10 ⁻⁴ Pa or less. When water vapor is not introduced into the system (Comparative Example 2), the flow rate ratio of hydrogen: argon: acetylene is continuously fixed at 16 sccm: 24 sccm: 10 sccm, growth temperature: 700 to 900 ° C., atmospheric pressure: 267 Pa, growth time : A CNT film was formed on the substrate in 10 minutes.
On the other hand, when water vapor was introduced into the system (Example 1), only a desired amount of water vapor was introduced into the system using a water vapor introducing device (not shown), and a growth experiment was conducted. When controlling the amount of water vapor using a water vapor introduction device, a trace amount of water vapor sensors are placed in the introduction and discharge parts of the reaction tube, and control is performed so that the amount of water vapor in the system is constant during growth. It was.

[3. Evaluation of CNT]
FIG. 7 shows the relationship between the water / acetylene ratio and the growth height together with a substrate cross-sectional photograph. FIG. 7 shows that the growth height of the CNT film becomes about twice or more that when water vapor is not introduced when the molar ratio of acetylene gas and water vapor is in the range of 0.0002 to 0.02.
Next, the crystallinity of the obtained CNT film was evaluated by Raman scattering spectroscopy (evaluated by an average value of G / D ratios at three arbitrary measurement points). FIG. 8 shows the Raman spectra of CNTs without water vapor and when water vapor is introduced (water / acetylene ratio = 5/1000).
Further, CNTs were peeled from the substrate, ultrasonically dispersed in an organic solvent, developed on a grid for a transmission electron microscope, and the microstructure was evaluated using a transmission electron microscope (evaluation number: 70 for each). FIG. 9 shows TEM photographs of CNTs without water vapor and when water vapor was introduced (water / acetylene ratio = 5/1000).

  Table 1 below summarizes the evaluation results. Since water vapor acts as a weak oxidant during CNT growth, there was concern about a decrease in CNT crystallinity, but it was found that the same level of crystallinity was maintained as compared to the case where water vapor was not introduced ( (Refer FIG. 8, FIG. 9). Moreover, the production | generation ratio of 3 or less CNT was 74% when water vapor | steam was introduce | transduced, and 64% when not introduce | transduced. From the above results, it has been clarified that when the water vapor amount is appropriate, a vertically aligned CNT film having a uniform diameter can be grown while maintaining a high growth rate.

(Example 2)
A CNT film was grown in the same manner as in Example 1 except that the protective layer covering the surface of the fine particles was not removed in advance. The water / acetylene ratio was 5/1000. As a result, a vertically aligned CNT film having a thickness of 100 μm equivalent to that obtained when the plasma treatment was performed was obtained.

(Example 3)
A CNT film was grown in the same manner as in Example 1 except that the protective layer covering the surface of the fine particles was previously removed by UV ozone treatment (30 seconds). The water / acetylene ratio was 5/1000. As a result, a vertically aligned CNT film having a thickness of 94 μm equivalent to that obtained when the plasma treatment was performed was obtained.

(Comparative Example 3)
Except that TiO acetylacetonate was not used, [1. ], A catalyst dispersion containing only Fe-O fine particles was prepared. Using the catalyst dispersion obtained, [2. ], A CNT film was grown. The water / acetylene ratio was 5/1000. As a result, a vertically aligned CNT film was not obtained.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.
For example, in the above embodiment, acetylene was used as the carbon-containing compound gas. However, in consideration of the crystallinity, growth rate, growth temperature, etc. of the obtained CNT, carbonization of known ethylene, methane, etc. as the CNT growth gas Hydrogen gas, alcohol, or the like may be used.
The steam introduction method is
(1) A method of introducing water maintained at a constant temperature into a reaction furnace by bubbling with a carrier gas such as Ar,
(2) A method of adding water to a known carbon-containing compound and introducing it into the reactor directly or together with a carrier gas,
(3) A method of spraying water directly into the reactor,
Etc. can be used.

  The carbon nanotube production method according to the present invention includes a semiconductor wiring material, a heat dissipation material, a fiber material, an electron emission source (point light source) used for an electron microscope, a scanning tunnel microscope, an atomic force microscope, a magnetic force microscope, It can be used as a method for producing CNT used in a probe used in a scanning probe microscope such as a scanning near-field optical microscope.

FIG. 1A is an electron micrograph (lattice image by just focus) of Fe—V—O fine particles synthesized under conditions of 250 ° C. × 30 minutes, and FIG. 1B is 290 ° C. × 30. It is an electron micrograph (under focus) of the Fe-VO fine particle synthesize | combined on the conditions for minutes. FIG. 2A is an SEM photograph of a cross section of a CNT film synthesized using Fe—V—O fine particles (reaction temperature: 250 ° C.), and FIG. 2B is shown in FIG. It is a TEM photograph of CNT collected from the substrate surface. FIG. 3A is a particle size histogram of Fe—V—O fine particles (reaction temperature: 250 ° C.), and FIG. 3B is a graph showing mesoporous silica substrate carrying the Fe—V—O fine particles. It is the outer diameter histogram of the produced | generated CNT. 4A shows the relationship between the charged composition of the Fe—V—O fine particles and the chemical component composition, and FIG. 4B shows the relationship between the charged composition of the Fe—Ti—O fine particles and the chemical component composition. is there. It is a figure which shows the relationship between the composition of a catalyst fine particle and a CNT film thickness, and the SEM photograph of the cross section of the CNT film | membrane synthesized using the Fe-O fine particle and the Fe-Ti-O fine particle. It is a figure which shows the relationship between the diameter of a catalyst fine particle, and the outer diameter of CNT synthesized using this. It is a figure which shows the relationship between water / acetylene ratio and the growth height of CNT. It is a Raman spectrum of CNT when there is no water vapor and with water vapor (water / acetylene ratio = 5/1000). It is a TEM photograph of CNT when there is no water vapor and with water vapor (water / acetylene ratio = 5/1000).

Claims (2)

The manufacturing method of the carbon nanotube provided with the following structures.
(1) The method for producing the carbon nanotube is as follows:
Applying a catalyst dispersion liquid in which a catalyst for carbon nanotube synthesis is dispersed on the surface of the substrate, and a catalyst supporting step of supporting the catalyst for carbon nanotube synthesis on the surface of the substrate;
A growth step of growing carbon nanotubes on the surface of the substrate carrying the carbon nanotube synthesis catalyst,
The carbon nanotube synthesis catalyst includes fine particles containing one or more first elements selected from Group 8 elements, Group 9 elements and Group 10 elements, and one or more second elements selected from Group 4 elements and Group 5 elements. And a protective layer made of one or more organic substances selected from organic acids and organic amines covering the periphery of the fine particles,
In the growth step, at least a carbon-containing compound gas and an oxygen-containing compound gas are flowed over the carbon nanotube synthesis catalyst supported on the substrate surface, and carbon nanotubes are grown on the substrate surface by chemical vapor deposition. Is .
(2) The oxygen-containing compound gas is water vapor.
(3) The carbon-containing compound gas is acetylene.
(4) The molar ratio (y / x) of the water vapor (y) to the acetylene (x) is 0.0002 or more and 0.02 or less at the introduction portion of the reaction tube.   2. The method for producing carbon nanotubes according to claim 1, wherein y / x is 0.002 or more and 0.02 or less in the introduction portion of the reaction tube.

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