WO2003082738A1

WO2003082738A1 - Method for preparing monolayer carbon nanotube

Info

Publication number: WO2003082738A1
Application number: PCT/JP2003/003884
Authority: WO
Inventors: Sumio Iijima; Masako Yudasaka; Hiroo Hongoh
Original assignee: Japan Science And Technology Agency; Nec Corporation
Priority date: 2002-03-29
Filing date: 2003-03-27
Publication date: 2003-10-09
Also published as: US20050106093A1; JP2003292313A; JP3537811B2

Abstract

A method for preparing a monolayer carbon nanotube, which comprises using the combination of a metal based catalyst exhibiting catalytic function in the formation of graphite and a single crystal substrate exhibiting a certain correspondence with the metal based catalyst with respect to the crystal grain size and the crystal orientation of crystals formed by re-crystallization at a temperature of the following treatment, dispersing the metal based catalyst on the single crystal substrate, and supplying a raw material of carbon to the substrate at a temperature of 500˚C or higher, to thereby grow a monolayer carbon nanotube through a vapor phase thermal decomposition. The method allows the preparation of a monolayer carbon nanotube with controlled diameter without the need for a porous material as a catalyst carrier or fine catalyst particles. Combinations of the above metal based catalyst and a single crystal substrate include that of Fe and a sapphire substrate.

Description

Description Method for producing single-walled carbon nanotubes

The invention of this application relates to a method for producing single-walled carbon nanotubes. More specifically, the invention of this application is directed to the production of single-walled carbon nanotubes that can produce single-walled carbon nanotubes by controlling the diameter without requiring a porous material or catalyst fine particles as a catalyst carrier. It is about the method. Background art

As a method for producing high-quality single-walled carbon nanotubes (SWNTs) with high utility value in various industries, the chemical vapor reaction (CVD) method has been attracting attention. This is because this CVD method is capable of mass production of SWNTs, and has the potential to control the gas phase pyrolysis growth of SWNTs by manipulating the type of catalyst and its particle size. This is because it is a method to have.

Various researchers have been investigating the production of SWNTs by this chemical vapor reaction, and some reports have been made. For example, J. K ing et _{_{al, F e (NO 3) 3}} · 9 Η 2 0, M o (acac) 2, and the substrate was covered with a mixture of alumina nanoparticles under methane gas flow 1 0 0 0 It is reported that SWNTs can be obtained by heating at J. H. Hafner et al. Report that SWNTs grow by flowing CO gas over nanometer-sized metal particles supported on alumina nanoparticles and heat-treating them. In these experiments, salts of Fe and / or Mo were used as metal-based catalysts and alumina nanoparticles were used as their supports. In addition, it has been reported that SWNTs can be produced by using a porous material such as zeolite, silica, or anodized silicon as a carrier for the production of SWNTs by another chemical vapor reaction. .

However, it should be noted that, in the above experiments, when chemical vapor deposition was performed without using such nanoparticles or porous materials as a carrier, regardless of the amount and size of the metal-based catalyst, Instead, SWNTs are not generated, and only multi-walled carbon nanotubes can be obtained.

In other words, in the conventional production of SWNTs by chemical vapor reaction, it was essential to use nanoparticles or porous materials as a carrier for the metal-based catalyst together with the metal-based catalyst. . Considering the mass production of SWNTs, a substrate that has a fine structure comparable to nanoparticles or porous materials and has a large surface area is required as a carrier.

Accordingly, the invention of this application has been made in view of the circumstances described above, and does not require nanoparticles or a porous material as a carrier, and furthermore, manufactures single-walled carbon nanotubes by controlling the diameter. It is an object of the present invention to provide a method for producing a single-walled carbon nanotube that can be used. Disclosure of the invention

Therefore, the invention of this application provides the following inventions to solve the above problems.

That is, first, the invention of this application relates to a metal-based catalyst having a catalytic action in producing graphite, and a single-crystal substrate having a correspondence with the crystal grain size and crystal orientation of the metal-based catalyst. Using a combination, a metal-based catalyst is dispersed in this single-crystal substrate, and a carbon material is supplied in a temperature range of 500 or more to obtain a single-layer carbon. Provided is a method for producing a single-walled carbon nanotube, wherein the nanotube is grown by vapor phase pyrolysis.

Also, the invention of this application is a method for producing single-walled carbon nanotubes, which comprises using a single-crystal substrate coated with a metal-based catalyst thin film in the above-mentioned invention. The method for producing single-walled carbon nanotubes, characterized in that the thickness of the catalyst thin film is 0.1 to 10 nm or less.Fourth, the metal-based catalyst is composed of iron group, platinum group, rare earth metal, A method for producing a single-walled carbon nanotube characterized by being a transition metal or a mixture of two or more of any of these metal compounds. the method for manufacturing a single layer forces one carbon nanotube that wherein a stable material above at 0, the sixth, the single crystal substrate, Safuai § (a 1 ₂ 0 _3), silicon (S i) , to characterized in that either S i 〇 _2, S i C, M g O Seventh, a method for producing single-walled carbon nanotubes, characterized by using hydroxyapatite instead of a single-crystal substrate, and eighthly, a metal-based catalyst A method for producing a single-layer carbon nanotube, characterized in that a single-wall carbon nanotube having a diameter controlled by a combination of a substrate and a single-crystal substrate and a crystal plane thereof is grown by vapor phase pyrolysis. The single-walled carbon nanotubes are characterized in that the combination of the metal-based catalyst and the single-crystal substrate and its crystal plane is any one of A, R, and C planes of Fe and sapphire. The first method is a method for producing a single-walled carbon nanotube, wherein the carbon raw material is a carbon-containing substance that is a gas at 500 or more. Is the carbon Fee, provide methane, ethylene, Fuenatoren, a process for producing single-walled carbon nanotubes, wherein either benzene. BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows the SEM of the deposit grown at 800 on the (a) A-plane, (b) R-plane, and (c) C-plane of sapphire coated with a 2 nm thick Fe thin film. It is the photograph which illustrated the image.

Figure 2 shows the SEM of the deposit grown at 800 on the (a) A-plane, (b) R-plane, and (c) C-plane of sapphire coated with a 5 nm thick Fe thin film. It is the photograph which illustrated the image.

FIG. 3 is a photograph illustrating a TEM image of a deposit grown on (a) A (2 nm), (b) R (2 nm), and (c) C (5 nm).

Fig. 4 shows the Raman scattering spectrum of the single-walled carbon nanotubes manufactured in the example, in the range of (a) to 500 cm- ¹ and (b) in the range of 1200 to 180 cm- ¹ . FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The invention of this application has the features as described above, and embodiments thereof will be described below.

First, the method for producing single-walled carbon nanotubes provided by the invention of the present application has a correspondence relationship between a metal-based catalyst having a catalytic action in producing graphite, and the crystal grain size and crystal orientation of the metal-based catalyst. Using a combination with a single-crystal substrate, a metal-based catalyst is dispersed in the single-crystal substrate, and a carbon material is supplied in a temperature range of 500 or more, so that single-walled carbon nanotubes are grown by gas phase thermal decomposition. It is characterized by

In the invention of the present application, as the metal-based catalyst, various metals having a catalytic action in the production of graphite, that is, in the gas phase pyrolysis growth of single-walled carbon nanotubes can be used. Specifically, for example, iron group such as Ni, Fe, Co, etc., platinum group such as Pd, Pt, Rh, rare earth metal such as La, Y, or Mo, Mn, etc. A transition metal or one of these metal compounds, if

Four

(Replacement paper 0 ^ IJ26) Alternatively, a mixture of two or more of these can be used.

As the single crystal substrate, it is possible to use one made of stable each class of materials in the above process temperature 5 0 0, for example, Safuai § (A 1 ₂ 0 _3), silicon (S i), S i 0 ₂ , S i C, M g O and the like can be exemplified. These need not be porous structures or nanoparticles as in the past, but may be, for example, planar ones. In the invention of this application, columnar crystals such as hydroxyapatite can be used instead of these single crystal substrates.

What is unique in the invention of this application is the combination of the metal catalyst and the single crystal substrate. In the invention of this application, the metal-based catalyst and the single-crystal substrate have a certain relationship, and are formed by a solid-phase reaction such as precipitation and recrystallization of the metal-based catalyst at a processing temperature of 500 ^ or more. A combination with a single crystal substrate that has an effect on the crystal grain size of the recrystallized grains and the correspondence of the crystal orientation between adjacent unrecrystallized grains can be used. More specifically, for example, when the single crystal substrate is at a processing temperature of 500 or more, the crystal grain size of the metal-based catalyst is controlled in a range of about 0.1 to 10 nm, or Further, it is desirable that the relationship is such that the crystal plane of the metal-based catalyst has an effect of orienting the crystal plane with respect to the single crystal substrate. In the invention of the present application, as a combination of such a metal-based catalyst and a single crystal substrate, a combination of Fe and sapphire can be exemplified as a preferable combination.

There is no particular limitation on the dispersion of the metal-based catalyst on the single-crystal substrate.For example, the dispersion can be realized by uniformly dispersing the fine particles of the metal-based catalyst or by coating the single-crystal substrate with a metal-based catalyst thin film. . In particular, the latter method is preferred because it is simple in the actual manufacturing process. Various methods can be used for these dispersion methods. Specifically, for example, a vacuum deposition method, a sputtering method, etc. A wet process such as a lye process, a solution dripping method, a spray coat method, or a spin coat method can be used.

The amount of the metal-based catalyst dispersed in the single-crystal substrate is not particularly limited, and may be arbitrary. For example, on a single crystal substrate

It only needs to be about one atomic layer thick and dispersed partially or entirely. If it is desired to obtain single-walled carbon nanotubes in a relatively high yield, it depends on the combination of the metal-based catalyst and the single-crystal substrate. It can be used as a guideline to adjust the film thickness in the range of 0.1 to 10 nm or less. If the thickness is too large, a portion not interacting with the single crystal substrate is locally formed on the surface of the metal-based catalyst thin film, and the metal-based catalyst particles may not be controlled. Absent.

The temperature of the single crystal substrate in which the metal-based catalyst is dispersed is set to 500 or more, and then a carbon raw material is supplied.

The heating of the single crystal substrate to a temperature of 500 or more can be performed in an inert atmosphere. As the carbon raw material, various carbon-containing substances which are gaseous at a temperature of 500 or more can be used. More specifically, for example, methane (CH ₄ ), ethylene (C ₂ H ₄ ), carbon monoxide (CO), etc. are gaseous at room temperature, and solid or liquid at room temperature, such as phenathrene or benzene. In this case, it is possible to exemplify a material which is a gas at a temperature of 500 or more by heating. Thus, single-walled carbon nanotubes can be grown by vapor phase pyrolysis on the surface of the single-crystal substrate.

By making the combination of a metal-based catalyst and a single-crystal substrate appropriate, it is possible to produce single-walled carbon nanotubes without making the single-crystal substrate into a porous structure or particle shape as in the past. There is a monkey.

Further, in the invention of this application, the metal catalyst and the single crystal substrate As a result of conducting a more detailed study focusing on the interaction between the metal catalyst and the single-crystal substrate, the interaction between the metal-based catalyst and the single-crystal substrate It has been found that the crystal plane of the substrate can also be taken into consideration, and furthermore, the diameter of the single-walled carbon nanotube generated by the combination can be controlled to a specific diameter. The ability to control the diameter in the vapor phase pyrolysis growth of single-walled carbon nanotubes has not been known at all, and is realized for the first time by the inventors of the present application. In other words, the method for producing single-walled carbon nanotubes provided by the invention of the present application is a method of producing single-walled carbon nanotubes whose diameter is controlled by a combination of a metal-based catalyst, a single-crystal substrate and its crystal plane. It is characterized by being thermally decomposed and grown.

More specifically, for example, the combination of Fe and sapphire, which is a combination of the above-described preferred metal-based catalyst and single crystal substrate, is further combined with any combination of Fe and sapphire with the A-plane, R-plane, or C-plane. This can be taken into account, and the single-walled carbon nanotubes controlled to have different diameters for each of these combinations can be grown by gas phase pyrolysis. For example, due to the combination of Fe and sapphire A-plane, R-plane, or C-plane, the diameter of the growing single-layer bonano tube is 1.43 nm, 1.30 ηm for A-plane, 1.20 nm, 1.45 nm, 1.24 nm, 1.18 nm for R-plane, 1.49 nm, 1.31 nm, 1.18 nm for C-plane It will be controlled to a specific value.

Further, in the invention of this application, the yield of single-walled carbon nanotubes can be increased by controlling the thickness of the metal-based catalyst thin film for each crystal plane of the single-crystal substrate. More specifically, for example,

For the combination of Fe and sapphire A-plane, R-plane, or C-plane, the yield of single-walled carbon nanotubes is within the above range for the A-plane and R-plane. The thinner the inside, the higher The thickness of the C-plane can be increased by increasing the thickness of the Fe thin film.

On the other hand, it is known that single-walled carbon nanotubes have various symmetry (chirality). The chirality of the single-walled carbon nanotube can be expressed by the chirality index (m, n), and has a strong correlation with the diameter of the single-walled carbon nanotube. This suggests that the method of the present invention can control not only the diameter of the single-walled carbon nanotube but also the power irritation.

According to the invention of this application described above, it has been shown that the interaction between the metal-based catalyst and the single-crystal substrate material plays an important role in the vapor-phase pyrolysis growth of single-walled carbon nanotubes. By using a dispersed single crystal substrate, single-walled carbon nanotubes can be grown by gas phase pyrolysis. In addition, by appropriately selecting the combination of the metal-based catalyst, the single-crystal substrate, and the crystal plane, a single-walled carbon nanotube having a controlled diameter can be produced. Further, the yield of single-walled carbon nanotubes can be increased by adjusting the crystal plane of the single-crystal substrate and the thickness of the catalyst thin film.

Hereinafter, embodiments will be described with reference to the accompanying drawings, and embodiments of the present invention will be described in further detail. Example

An attempt was made to produce SWNTs using a 2-inch inner diameter tube furnace and methane gas as a carbon source. A-plane, R-plane and C-plane of sapphire were used as single-crystal substrates. On the single crystal substrate, such that F e film thickness. 2 to 5 nm as a metal catalyst, and an electron beam deposition under a vacuum of ^{~ 4 X 1 0- 6 T orr} .

After introducing these substrates into a tube furnace, After reaching a predetermined temperature of 600: 800 "C, methane (9.999%) as a carbon raw material was introduced at a flow rate of 0.61 / min. The introduction of methane was performed for 5 minutes, and then the argon was introduced again, and the tube furnace was cooled until it reached room temperature.

The heat-treated substrate was examined in detail by scanning electron microscope (SEM) observation, Raman spectroscopy, and transmission electron microscope (TEM) observation. The sample for SEM observation was covered with a Pd-Pt thin film of about 2 nm in thickness for clearer observation. The Raman spectrum was obtained by measurement using 488 nm light (30 mW) from an Ar laser with a focused spot size of ~ 1 m. Samples for TEM observation were prepared by collecting sediments from a sapphire substrate, dispersing them in ethanol, dropping them on TEM grids, and drying.

K SEM observation>

Figures 1 (a), (b), and (c) show the S of the deposit grown at 800 on the A, R, and C planes of sapphire coated with a 2-nm-thick Fe thin film. EM images are shown. It was clearly observed that the amount of tubular sediment deposited on the A-side was greater than that on the R-side. The amount of tubular sediment on the C-plane was found to be the least of the three.

Figures 2 (a), (b), and (c) show deposits grown at 800 on the A, R, and C planes of sapphire coated with a 5-nm thick Fe thin film. The SEM image of each was shown. It was confirmed that tubular deposits similar to the above were formed on all three surfaces. These capillaries are either thick and short (20-50 nm in diameter, about 1 mm in length) or thin and long (less than 3 nm in diameter, more than 2 mm in length). I found it.

In addition, when sapphire coated with a 2-nm-thick Fe thin film was subjected to a heat treatment at 600, tubular deposits were formed on the A and R surfaces. Although little had grown, small but thicker tubules (approximately 30-50 nm in diameter) were observed growing on the C-plane. The structures of these capillaries were examined by TEM observation and Raman spectra.

Figure 3 (a) shows a TEM image of the deposit grown on a sapphire surface (hereinafter referred to as A (2 nm)) coated with a 2 nm-thick Fe thin film. This A (2 nm) was found to contain SWNT s and a very small amount of amorphous carbon (hereinafter a-C). From the TEM image of the deposit grown on the sapphire R surface (hereinafter referred to as R (2 nm)) coated with a 2 nm-thick Fe thin film shown in Fig. 3 (b), R (2 nm) Is composed of SWNTs and a—C. From the TEM image of the deposit grown on the sapphire C-plane (hereinafter referred to as C (5 nm)) coated with a 5 nm-thick Fe thin film shown in Fig. 3 (c), the C (5 nm) It was confirmed that the amount of a—C was the highest and that SWNT s was hardly found. Although not shown in Fig. 3 (c), it was confirmed that some double-walled carbon nanotubes grew on C (5 nm).

From TEM observation, it was found that the diameter of SWNTs bunched on the A-plane, R-plane, and C-plane was approximately 1.0 to: 0.7 nm.

Figures 4 (a) and 4 (b) show the Raman scattering spectra of the deposits formed on the A, R, and C planes of sapphire covered with the 2-nm, 3-nm, and 5-nm-thick Fe thin films. . For all samples, peaks were observed at about 1592 cm- ¹ and 1570 cm- ¹ and 1 to 4 narrow peaks were observed in the range of ¹⁰⁰ to 230 cm- ¹ . These peaks are characteristic of SWNTs and indicate the presence of SWNTs in sediments. About 1 5 9 2 cm—1 5 7 0 c ^m-1 peak corresponds to the tangential mode, 1 0 0~ 2 3 0 cm one ^first peak between is equivalent to the Raman breathing mode (RBM) of SWNT s.

And, for example, SWNT s formed on the R (2 nm) plane has a strong RBM peak at 167 cm- ¹ indicating SWNT Ts with a diameter of 1.4 nm. Although there is a weak peak at 203 cm- ¹ indicating that it is a SWNT s of 1.2 nm, these peaks are not so prominent for a sample covered with a thicker Fe thin film. It turns out there is no. Thus, from the tangential mode and the peak intensity of the RBM, as the thickness of the Fe thin film increases from 2 nm to 5 nm, the amount of SWNTs generated for the A-plane and R-plane decreases. I understand. On the other hand, in the case of the C-plane, the SWNT amount was found to increase as the thickness of the Fe thin film increased from 2 nm to 5 nm.

In addition, the peak positions and RBM intensities of these SWNTs were different in individual sediments. However, a more careful examination of more than 10 different sites for each sediment revealed the following trends: In other words, the width of the RBM peak was as narrow as approximately 7 to 12 cm- ¹ , the number of peaks was 1 to 4, and the peak position was found to depend on the sapphire surface. More specifically, for example, for the A (2 nm) plane, the R (2 nm) plane, and the C (2 nm) plane, the average of the Raman spectra obtained from 10 locations is averaged, and the RBM peak is calculated. Table 1 shows the diameters of the SWNTs obtained. RBM peak (cm- ¹ )

Sample

SWNT diameter ( _nm )

170 188 203

A (2nm)

1.43 1.30 1.20

168 194 207

R (2nm)

1.45 1.24 1.18

164 186 206

C (2nm)

1.49 1.31 1.18 Thus, by selecting the crystal plane of the sapphire substrate,

It was demonstrated that the diameter of S WNT s can be controlled to a specific value. <(Comparative Example 1)

When using the silicon single crystal surface instead of the sapphire (or S i 0 ₂ surface that is thermally grown on silicon) in the above embodiment, regardless of the thickness of the F e film, 8 0 0 (: 0 3

WN T s could not be generated.

(Comparative Example 2)

When the sapphire substrate was covered with a Ni thin film instead of the Fe thin film in the above-described embodiment, and thereafter the same operation was performed, SWNTs was not generated.

(Comparative Example 3)

A silicon wafer provided with a mixture of F e (NO 3) ₃ · Η ₂₀ and alumina nanoparticles (no Mo (acac) ₂ ) was prepared as a substrate, and the same heat treatment as in the above example was performed. Was performed, and SWNTs were generated. The Raman spectrum obtained for this SWNTs is also shown in FIG. This Raman spectrum has a broad RBM peak in the range of 120 to 200 cm- ¹ and a wide range of SWNT s diameters of 2.0 to 1.2 nm. You.

Therefore, although the alumina nanoparticles are metal-based catalyst support is the same A 1 ₂ 〇 ₃ and sapphire, alumina, because nanoparticles has internal various crystal faces and amorphous characteristics from the shape of its However, it was found that SWNTs could be grown, but their diameter could not be controlled, resulting in wide distribution.

From the above, in the conventional production of SWNTs by vapor phase pyrolysis growth, porous materials and nanoparticles are used as essential catalyst carriers. However, according to the invention of this application, the SWNT s can be obtained even on a smooth crystal substrate by appropriately selecting the substrate crystal, its crystal plane, the metal-based catalyst, its film thickness and the growth temperature. Was shown to be possible. It can also be concluded that these requirements affect the diffusion coefficient of the catalyst metal and the associated grain size and orientation of the catalyst metal, resulting in SWNTs growing to a specific diameter. .

Of course, the present invention is not limited to the above-described example, and it goes without saying that various aspects can be applied to the details. Industrial applicability

As described in detail above, the present invention relates to a method for producing a single-walled carbon nanotube. More specifically, the invention of this application relates to a method for producing a single-walled carbon nanotube capable of producing a single-walled carbon nanotube by controlling the diameter without using a porous material or catalyst fine particles. Provided.

Claims

The scope of the claims

1. A combination of a metal-based catalyst having a catalytic action in producing graphite and a single-crystal substrate having a correspondence relationship with the crystal grain size and crystal orientation of the metal-based catalyst is used. A method for producing single-walled carbon nanotubes, comprising dispersing a catalyst and supplying a carbon raw material in a temperature range of 500 or more to grow the single-walled carbon nanotubes by gas phase pyrolysis.

2. The method for producing single-walled carbon nanotubes according to claim 1, wherein a single-crystal substrate coated with a metal-based catalyst thin film is used.

3. The method for producing single-walled carbon nanotubes according to claim 1 or 2, wherein the thickness of the metal-based catalyst thin film is 0.1 to 10 nm or less.

4. The metal-based catalyst according to any one of claims 1 to 3, wherein the metal-based catalyst is an iron group, a platinum group, a rare earth metal, a transition metal, or a mixture of any one or more of these metal compounds. A method for producing a single-walled carbon nanotube.

5. The method for producing a single-walled carbon nanotube according to any one of claims 1 to 4, wherein the single-crystal substrate is a material which is stable at 500 or more.

6. Single crystal substrate, sapphire (A 1 ₂ O _3), silicon (S i), S i 〇 _2, S i C, single of claim 5, wherein a is any one of M g O A method for producing a monolayer nanotube.

7. The method for producing single-walled carbon nanotubes according to claim 1, wherein octyl hydroxyapatite is used instead of the single-crystal substrate.

8. The gas-phase thermal decomposition growth of a single-walled carbon nanotube having a controlled diameter by a combination of a metal-based catalyst, a single-crystal substrate, and a crystal plane thereof, according to any one of claims 1 to 7, Of producing single-walled carbon nanotubes.

9. The combination of a metal-based catalyst, a single-crystal substrate, and a crystal plane thereof, wherein the combination of Fe and sapphire is any one of A-plane, R-plane, and C-plane. A method for producing bon nanotubes.

10. The method for producing single-walled carbon nanotubes according to any one of claims 1 to 9, wherein the carbon raw material is a carbon-containing substance which is a gas at 500 or more.

11. The method for producing a single-walled carbon nanotube according to claim 10, wherein the carbon raw material is any one of methane, ethylene, phenanthrene, and benzene.