JP7578281B2 - Method for producing single-walled carbon nanotubes - Google Patents

Description

The present invention relates to a method for producing single-walled carbon nanotubes.

Patent Document 1 discloses a conventional method for producing carbon nanotubes. In this method, Co (cobalt) is deposited on the surface of a single crystal quartz substrate, and then the single crystal quartz substrate is loaded into an electric furnace maintained in a vacuum state at 800°C. Ethanol is then supplied into the electric furnace, allowing carbon nanotubes to grow on the surface of the single crystal quartz substrate.

JP 2011-178631 A

However, the method of Patent Document 1 uses a single crystal quartz substrate and vapor-deposits Co (cobalt) on the surface. For this reason, the method of Patent Document 1 requires the time and effort of preparing the single crystal quartz substrate and using a vapor deposition device when vapor-depositing Co. For this reason, there is a need to establish a method for obtaining carbon nanotubes more easily.

The present invention was made in consideration of the above-mentioned conventional situation, and the problem to be solved is to provide a method for producing carbon nanotubes that can more easily obtain single-walled carbon nanotubes.

The method for producing single-walled carbon nanotubes according to the first aspect of the present invention comprises the steps of:
A first step of cleaning a metal substrate;
A second step of forming either _{an Al2O3} buffer layer or a PDMS buffer layer on the surface of the metal substrate;
a third step of depositing Ir (iridium) on the surface of _{the Al2O3} buffer layer or the PDMS buffer layer;
A fourth step of performing CVD;
The present invention is characterized in that it is provided with:

The method for producing single-walled carbon nanotubes according to the second aspect of the present invention comprises the steps of:
A first step of cleaning a Si substrate;
A second step of coating the front surface side of the Si substrate with an Ir (iridium) ion solution;
a third step of firing the Si substrate;
A fourth step of performing CVD;
The present invention is characterized in that it is provided with:

The method for producing single-walled carbon nanotubes of the first invention involves forming either _{an Al2O3} buffer layer or a PDMS buffer layer on the surface of a metal substrate, and then evaporating Ir (iridium). This method for producing single-walled carbon nanotubes allows carbon nanotubes to grow on a metal substrate, making it easy to obtain carbon nanotubes.

The method for producing single-walled carbon nanotubes of the second invention can easily form Ir particles on the surface of a Si substrate by coating the surface of the Si substrate with an Ir ion solution and then baking it. As a result, this method for producing single-walled carbon nanotubes can form Ir particles on the Si substrate without using a deposition device or the like, making it easy to obtain carbon nanotubes.

1 is a schematic diagram showing a method for producing single-walled carbon nanotubes according to Examples 1 and 2. FIG. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 10 minutes (layer thickness: 30 nm) in the first step of the manufacturing method of Example 1. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 20 minutes (layer thickness: 60 nm) in the first step of the manufacturing method of Example 1. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 30 minutes (layer thickness: 90 nm) in the first step of the manufacturing method of Example 1. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 40 minutes (layer thickness: 120 nm) in the first step of the manufacturing method of Example 1. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 50 minutes (layer thickness: 150 nm) in the first step of the manufacturing method of Example 1. 1 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample in which an Al ₂ O ₃ buffer layer is deposited on a surface of a metal substrate for 60 minutes (layer thickness: 180 nm) in the first step of the manufacturing method of Example 1. These are FE-SEM images of the surface of a metal substrate in a sample in which _{an Al2O3} buffer layer was deposited on the surface of the metal substrate for 30 minutes (layer thickness: 90 nm), and the cross section of the metal substrate was observed in a direction perpendicular to the thickness direction. These are FE-SEM images of the surface of a metal substrate in a sample in which _{an Al2O3} buffer layer was deposited on the surface of the metal substrate for 60 minutes (layer thickness: 180 nm), and the cross section of the metal substrate was observed in a direction perpendicular to the thickness direction. 1 is a graph showing the change in ratio G/D versus thickness of an Al ₂ O ₃ buffer layer deposited on the surface of a metal substrate. 13 is a graph showing a change in the rotation speed of a spin coater in a second step of the manufacturing method of Example 2. 13 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample produced by the production method of Example 2. 13 is an FE-SEM image of the surface of a metal substrate in a sample manufactured using the manufacturing method of Example 2, observed from the plate thickness direction. 1 is a schematic diagram showing a method for producing single-walled carbon nanotubes according to a third embodiment. FIG. 11 is a schematic diagram showing a state in which a Si substrate is pulled up from a 0.01 M iridium acetate ethanol solution in a second step of the manufacturing method of Example 3. 13 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample obtained by lifting the Si substrate from the 0.01 M iridium acetate ethanol solution at a rate of 0.1 mm/sec in the second step of the manufacturing method of Example 3. 13 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample obtained by lifting the Si substrate from the 0.01 M iridium acetate ethanol solution at a rate of 0.2 mm/sec in the second step of the manufacturing method of Example 3. 13 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample obtained by lifting the Si substrate from the 0.01 M iridium acetate ethanol solution at a rate of 0.4 mm/sec in the second step of the manufacturing method of Example 3. 13 is a graph showing a Raman spectrum of single-walled carbon nanotubes in a sample obtained by lifting the Si substrate from the 0.01 M iridium acetate ethanol solution at a rate of 0.6 mm/sec in the second step of the manufacturing method of Example 3. The images are FE-SEM images of the surface of a Si substrate in the thickness direction and the cross section of the Si substrate in a direction perpendicular to the thickness direction in a sample in which the Si substrate was pulled up from a 0.01 M ethanol solution of iridium acetate at a speed of 0.1 mm/sec. 1 is a graph showing the change in the ratio G/D and the ratio G/Si with respect to the rate at which the Si substrate is pulled up from a 0.01 M ethanol solution of iridium acetate.

A preferred embodiment of the present invention will be described.

In the method for producing single-walled carbon nanotubes of the first invention, the thickness of _{the Al2O3} buffer layer can be 30 nm to 200 nm, so that the single-walled carbon nanotubes can be reliably grown on the metal substrate.

In the second step of the method for producing single-walled carbon nanotubes of the second invention, the Si substrate is immersed in an Ir ion solution, and can be pulled out of the Ir ion solution at a speed of 0.1 mm/sec to 0.6 mm/sec with the surface of the Si substrate oriented to intersect with the liquid surface of the Ir ion solution. In this case, particulate Ir can be successfully formed on the Si substrate, and single-walled carbon nanotubes can be reliably grown on the Si substrate.

Next, we will explain Example 1, which embodies the method for producing single-walled carbon nanotubes of the present invention, with reference to the drawings.

Example 1
In the method for producing single-walled carbon nanotubes in Example 1, first, a first step is performed to clean a metal substrate 50 (see FIG. 1(A)). The metal substrate 50 is made of stainless steel and has a flat plate shape. The outer shape of the metal substrate 50 is a square with sides of approximately 10 mm. Stainless steel is easier to obtain than Si. The surface of the metal substrate 50 is the upper surface in FIG. 1(A).

In the first step, the metal substrate 50 is immersed in acetone and cleaned for 5 minutes using an ultrasonic cleaner. The dried metal substrate 50 is then immersed in methanol, cleaned for 5 minutes using an ultrasonic cleaner, and dried. The metal substrate 50 is then immersed in pure water, cleaned for 5 minutes using an ultrasonic cleaner, and dried. This removes foreign matter such as dust adhering to the surface of the metal substrate 50 from the surface of the metal substrate 50. In this manner, the first step is carried out.

Next, after the first step, the second step is performed to form an _Al2O3 buffer layer 51 on the surface of the metal substrate 50 (see FIG _. 1B). In the second step, the _Al2O3 buffer layer 51 is deposited on the surface of the metal substrate 50 using an RF magnetron sputtering device (SVC-700RF II, manufactured by Sanyu Electronics). The _{Al2O3 buffer} layer 51 is deposited on the surface of the metal substrate 50 by about 3 nm every minute of sputtering in the RF magnetron sputtering device. That is, the deposition rate of _{the Al2O3} buffer layer 51 is 3 nm _/ min. In the second step, the thickness of _{the Al2O3} buffer layer 51 deposited on the surface of the metal substrate 50 is 30 nm to 200 nm. In the second step, the time for depositing the _Al2O3 buffer layer 51 on the surface of the metal substrate 50 is 10 minutes (layer thickness 30 nm) to 67 minutes (layer thickness 200 nm). The crystallinity of _{the Al2O3 buffer} layer 51 thus formed on the surface of the metal substrate 50 is _non -crystalline (amorphous).

Next, after the second step is performed, the third step is performed to deposit Ir20 (iridium) on the surface of _{the Al2O3 buffer} layer 51 (see FIG. 1(C)). Specifically, a pulse arc plasma gun (APS-1 manufactured by Advance Riko) is used to deposit Ir20 acting as a catalyst on the surface of the _Al2O3 buffer layer 51 on the surface of the metal substrate 50. The deposited Ir20 has an average thickness of 0.3 nm in the thickness direction of the _metal substrate 50. The Ir20 becomes particulate and adheres to the surface of the _Al2O3 buffer layer 51. The conditions for depositing Ir20 are a discharge voltage of 100V, five discharges, and a discharge interval of 1 second. In this way, the third step is performed. In this way, Ir20 is deposited on the surface of the _{Al2O3 buffer} layer 51.

Next, after the third step is performed, the fourth step of performing CVD is performed (see FIG. 1(D)). In the fourth step, a hot wall type CVD growth apparatus (Thermo Riko Co., Ltd., soaking heat treatment apparatus) is used to perform CVD (chemical vapor deposition) using ethanol as a carbon source. This hot wall type CVD growth apparatus has a reactor made of quartz. This reactor is configured to be entirely housed in an electric furnace. Since the entire reactor is housed in an electric furnace, a metal substrate 50 up to a size that can fit in the reactor can be introduced. The metal substrate 50 that has been subjected to the third step is introduced into the reactor where CVD is performed. The pressure in the reactor where CVD is performed is set to approximately 1 Pa by exhausting the gas in the reactor. Then, Ar and _H2 are flowed at 100 sccm into the reactor from which the gas has been exhausted to create a reducing atmosphere, and the temperature is raised to a predetermined temperature (approximately 850°C). After reaching a predetermined temperature, the supply of Ar and _H2 into the reactor is stopped, and vaporized ethanol is introduced at 500 sccm to the metal substrate 50 introduced into the reactor, and the metal substrate 50 is exposed to the vapor for 10 minutes. Then, Ir20 acts as a catalyst, and a plurality of single-walled carbon nanotubes 30 bonded to _{the Al2O3} buffer layer 51 on the surface of the metal substrate 50 via Ir20 grow. In this way, the fourth step is performed. Since the reactor is housed in an electric furnace, the ethanol introduced into the reactor is immediately heated. This allows the entire metal substrate 50 to be evenly exposed to the heated gaseous ethanol no matter where the metal substrate 50 is placed in the reactor. For this reason, the hot wall type CVD growth apparatus only needs to be placed so that the surface of the metal substrate 50 is exposed in the reactor, so the metal substrates 50 can be placed so that they are stacked at a predetermined interval, making it possible to introduce more metal substrates 50 into the reactor.

Then, the temperature inside the reactor is lowered to room temperature, and the metal substrate 50 on which multiple single-walled carbon nanotubes 30 have grown is removed from the reactor.

[Evaluation Results of Samples in Example 1]
2 to 7 show Raman spectra of single-walled carbon nanotubes 30 when irradiated with light of four wavelengths, 488 nm, 532 nm, 671 nm, and 785 nm, in samples 1 to 6 produced using the manufacturing method of Example 1 and varying the sputtering time in the second step to six different times: 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes.

As shown in Fig. 2(B), Fig. 3(B), Fig. 4(B), Fig. 5(B), Fig. 6(B), and Fig. 7(B), a sharp G-band spectrum peak appears in the high wavenumber region in each of Sample 1 to Sample 6. As shown in Fig. 2(A), Fig. 3(A), Fig. 4(A), Fig. 5(A), Fig. 6(A), and Fig. 7(A), a plurality of RBM (radial breathing mode) spectrum peaks appear in the vicinity of 170 to 300 cm ^-1 in the low wavenumber region. Note that the peak in the spectrum at 488 nm in Fig. 2(A) is not clear. From the above results, it can be seen that single-walled carbon nanotubes 30 grow in all of Sample 1 to Sample 6. In addition, from the position of the RBM spectrum peak, it can be seen that the diameters of the single-walled carbon nanotubes 30 in Sample 1 to Sample 6 are distributed between approximately 0.8 nm and 1.5 nm.

Next, the surface of the metal substrate 50 in Sample 3 and Sample 6 was observed in the thickness direction, and the cross section of the metal substrate 50 was observed in the direction perpendicular to the thickness direction using an FE-SEM. The results are shown in Figures 8 and 9. As shown in Figure 8, in Sample 3 and Sample 6, the single-walled carbon nanotubes 30 are vertically oriented and grown relative to the metal substrate 50, and are highly dense. Note that Figure 8 (B) shows the state in which the single-walled carbon nanotubes 30 grown vertically oriented relative to the metal substrate 50 are tilted in the direction along the surface of the metal substrate 50. The length of the single-walled carbon nanotubes 30 in Sample 3 and Sample 6 was approximately 4 μm to 7 μm. The length of the single-walled carbon nanotubes 30 in Sample 3 and Sample 6 was roughly the same. Although not shown, it was also confirmed that the single-walled carbon nanotubes 30 were grown in the sample in which the sputtering time in the second step was 67 minutes (layer thickness 200 nm).

Next, Figure 10 shows the ratio G/D of the magnitude of the G-band spectrum peak to the magnitude of the D-band spectrum peak caused by defects (hereinafter also referred to as the ratio G/D) for each of samples 1 to 6.

The ratio G/D is an index of the crystallinity of the grown single-walled carbon nanotube 30, and is the value obtained by dividing the peak value of the G-band spectrum by the peak value of the D-band spectrum. The peak of the D-band spectrum becomes larger as the number of point defects and the like that occur in the single-walled carbon nanotube 30 increases. In other words, as the peak value of the D-band spectrum increases, the ratio G/D decreases, indicating that the crystallinity of the single-walled carbon nanotube 30 becomes less good. And as the peak value of the D-band spectrum decreases, the ratio G/D increases, indicating that the crystallinity of the single-walled carbon nanotube 30 becomes more good.

The ratio G/D was approximately 1.1 to 2.3 in sample 1, approximately 2.4 to 4.5 in sample 2, approximately 2.0 to 4.0 in sample 3, approximately 2.5 to 4.5 in sample 4, approximately 1.7 to 2.6 in sample 5, and approximately 1.8 to 3.3 in sample 6. In addition, samples in which the sputtering time in the second step was 7 minutes or less (layer thickness 20 nm or less) had a ratio G/D of 1 or less, indicating that the crystallinity of the single-walled carbon nanotubes 30 was not good.

From the results of the FE-SEM observation and the results of the ratio G/D, it was found that single-walled carbon nanotubes 30 with good crystallinity can be grown by setting the thickness of _{the Al2O3} buffer layer 51 to 30 nm (sputtering time 10 minutes) to 200 nm (sputtering time 67 minutes). The sputtering time in the second step is preferably 60 nm (sputtering time 20 minutes) to 180 nm (sputtering time 60 minutes), and more preferably 60 nm (sputtering time 20 minutes) to 120 nm (sputtering time 40 minutes).

Next, we will explain the effects of the above example.

This method for producing single-walled carbon nanotubes includes a first step of cleaning a metal substrate 50, a second step of forming an _{Al2O3 buffer} layer 51 on the surface of the metal substrate 50, a third step of depositing Ir (iridium) 20 on the surface of _{the Al2O3} buffer layer 51, and a fourth step of performing CVD. According to this configuration, in this method for producing single-walled carbon nanotubes, _{the Al2O3} buffer layer 51 is formed on the surface of the metal substrate 50, and then Ir (iridium) 20 is deposited. As a result, this method for producing single-walled carbon nanotubes can grow single-walled carbon nanotubes 30 on the metal substrate 50, and therefore single-walled carbon nanotubes 30 can be obtained easily.

In this method for producing single-walled carbon nanotubes, the thickness of the Al ₂ O ₃ buffer layer 51 is 30 nm to 200 nm. In this case, the single-walled carbon nanotubes 30 can be reliably grown on the metal substrate 50.

Example 2
Next, a second embodiment of the method for producing single-walled carbon nanotubes according to the present invention will be described with reference to the drawings. The method for producing single-walled carbon nanotubes in the second embodiment is different from the first embodiment in that a PDMS buffer layer 52 is formed on the surface of a metal substrate 50 in the second step. The same components as those in the first embodiment are given the same reference numerals, and the description of the structure, action and effect will be omitted.

In the method for producing single-walled carbon nanotubes in Example 2, the first step is carried out as in Example 1, and then the second step is carried out to produce a PDMS buffer layer 52 on the surface of the metal substrate 50 (see FIG. 1(B)). The material of the PDMS buffer layer 52 is PDMS (polydimethylsiloxane). In the second step, the PDMS buffer layer 52 is produced by applying PDMS to the surface of the metal substrate 50 using a spin coater (Opticast MS-A100 manufactured by Mikasa). By using a spin coater, PDMS can be applied uniformly and thinly to the surface of the metal substrate 50 even when the outer shape of the metal substrate 50 is small.

The rotation speed of the spin coater when applying PDMS to the surface of the metal substrate 50 will be described. After the metal substrate 50 is set on the spin coater and PDMS is applied to the surface of the metal substrate 50, the spin coater starts rotating. As shown in FIG. 11, the rotation speed of the spin coater gradually increases when the rotation starts, and reaches 4000 rpm 5 seconds after the rotation starts. Thereafter, the spin coater maintains the rotation speed at 4000 rpm. Then, 65 seconds after the rotation starts, the spin coater reduces the rotation speed from 4000 rpm to 1000 rpm, and then maintains the rotation speed at 1000 rpm. Then, 125 seconds after the rotation starts, the spin coater reduces the rotation speed from 1000 rpm to 0 rpm and stops the rotation. After applying PDMS to the surface of the metal substrate 50, it is dried for 2 hours. Then, the metal substrate 50 to which PDMS has been applied is baked at 800° C. for 1 hour. By baking the metal substrate 50 in this manner, the PDMS is converted into _SiO2 , forming the PDMS buffer layer 52. In this manner, the second step is performed. The crystallinity of the PDMS buffer layer 52 thus formed on the surface of the metal substrate 50 is non-crystalline (amorphous).

Next, after the second step is performed, the third step is performed in which Ir20 (iridium) is evaporated onto the surface of the PDMS buffer layer 52, as in Example 1 (see FIG. 1(C)). Next, after the third step is performed, the fourth step is performed in which CVD is performed, as in Example 1 (see FIG. 1(D)). Specifically, the metal substrate 50 that has been subjected to the third step is introduced into a reactor in which CVD is performed. The conditions in the reactor are the same as those in Example 1. Then, Ir20 acts as a catalyst, and multiple single-walled carbon nanotubes 30 bonded to the PDMS buffer layer 52 on the surface of the metal substrate 50 via Ir20 grow. In this way, the fourth step is performed. After that, the temperature in the reactor is lowered to room temperature, and the metal substrate 50 on which multiple single-walled carbon nanotubes 30 have grown is taken out of the reactor.

[Evaluation results of samples in Example 2]
12 shows the Raman spectrum of the single-walled carbon nanotubes 30 when irradiated with light of four wavelengths, 488 nm, 532 nm, 671 nm, and 785 nm, in the sample 7 produced by the manufacturing method of the embodiment 2. As shown in FIG. 12B, a sharp G-band spectrum peak appears in the high wavenumber region. As shown in FIG. 12A, a plurality of RBM (radial breathing mode) spectrum peaks appear in the low wavenumber region, around 170 to 300 cm ⁻¹ . This shows that the single-walled carbon nanotubes 30 have grown in the sample 7. Also, from the position of the RBM spectrum peak, it can be seen that the diameter of the single-walled carbon nanotubes 30 in the sample 7 is distributed between approximately 0.8 nm and 1.5 nm.

Next, FIG. 13 shows the results of observing the surface of the metal substrate 50 in sample 7 from the plate thickness direction using an FE-SEM. As shown in FIG. 13, in sample 7, the single-walled carbon nanotubes 30 extend in a direction parallel to the surface of the metal substrate 50 and are entangled with each other to form a mesh-like structure. Although the growth direction is not fixed and is irregular, they grow in large quantities on the surface of the metal substrate 50.

This method for producing single-walled carbon nanotubes includes a first step of cleaning the metal substrate 50, a second step of forming a PDMS buffer layer 52 on the surface of the metal substrate 50, a third step of depositing Ir (iridium) 20 on the surface of the PDMS buffer layer 52, and a fourth step of performing CVD. According to this configuration, this method for producing single-walled carbon nanotubes produces a PDMS buffer layer 52 on the surface of the metal substrate 50, and then deposits Ir (iridium) 20. As a result, this method for producing single-walled carbon nanotubes can grow single-walled carbon nanotubes 30 on the metal substrate 50, so that single-walled carbon nanotubes 30 can be obtained easily.

Example 3
Next, a third embodiment of the method for producing single-walled carbon nanotubes according to the present invention will be described with reference to the drawings. The method for producing single-walled carbon nanotubes in the third embodiment differs from the first and second embodiments in that a Si substrate 110 is used instead of the metal substrate 50, that an Ir (iridium) ion solution is coated on the surface of the Si substrate in the second step, and that the Si substrate 110 is baked in the third step. The same components as those in the first and second embodiments are denoted by the same reference numerals, and the description of the structure, action, and effect will be omitted.

In the method for producing single-walled carbon nanotubes in Example 3, first, the first step of cleaning the Si (silicon) substrate 110 is performed (see FIG. 14(A)). The Si substrate 110 is made of Si and has a flat plate shape. The outer shape of the Si substrate 110 is a rectangle of approximately 20 mm x 10 mm. The surface of the Si substrate 110 (the upper surface in FIG. 14(A)) is a (111) surface. In the first step, the Si substrate 110 is immersed in acetone and cleaned for 5 minutes using an ultrasonic cleaner. The dried Si substrate 110 is then immersed in methanol, cleaned for 5 minutes using an ultrasonic cleaner, and dried. Thereafter, the Si substrate 110 is immersed in pure water, cleaned for 5 minutes using an ultrasonic cleaner, and dried. This removes foreign matter such as dust adhering to the surface of the Si substrate 110 from the surface of the metal substrate 50. In this way, the first step is performed.

Next, after the first step is performed, a thermal oxidation step is performed in which the Si substrate 110 is heat-treated to thermally oxidize the surface of the Si substrate 110 (see FIG. 14B). In the thermal oxidation step, a _SiO2 layer 110A of a predetermined thickness is formed on the surface of the Si substrate 110 by thermal oxidation. In the thermal oxidation step, the Si substrate 110 is introduced into a tubular furnace whose temperature inside the furnace is set to 1000° C. for 14 minutes. At that time, _H2O (water) is bubbled using _N2 as a carrier gas to perform steam oxidation. In this manner, the thermal oxidation step is performed.

Next, after the thermal oxidation process, the second process is carried out in which an Ir ion solution is coated on the surface side of the Si substrate 110 (see FIG. 14(C)). Specifically, the Si substrate 110 is first immersed in a 0.01 M iridium acetate ethanol solution 140, which is an Ir ion solution (see FIG. 15). Then, the Si substrate 110 immersed in the 0.01 M iridium acetate ethanol solution 140 is pulled out of the solution.

At this time, the Si substrate 110 is held in a position in which the surface of the Si substrate 110 intersects with the liquid surface S of the 0.01M iridium acetate ethanol solution 140 (in a state in which the plate thickness direction is horizontal) as shown in FIG. 15, and is pulled up and taken out from the solution at a speed of 0.1 mm/sec to 0.6 mm/sec. The angle at which the surface of the Si substrate 110 intersects with the liquid surface S of the 0.01M iridium acetate ethanol solution 140 is approximately 90°. The surface of the SiO ₂ layer 110A of the Si substrate 110 taken out of the 0.01M iridium acetate ethanol solution 140 is in a state of being coated with the 0.01M iridium acetate ethanol solution 140. The Si substrate 110 taken out of the 0.01M iridium acetate ethanol solution 140 is dried for a predetermined time. In this manner, the second process is carried out. The thickness of the coated 0.01 M iridium acetate ethanol solution 140 is approximately 100 nm.

Next, after the second step is performed, the third step of baking the Si substrate 110 is performed (see FIG. 14(D)). Specifically, the dried Si substrate 110 is placed on a hot plate (Corning PC-400D) with the SiO ₂ layer 110A facing up, and baked at 250° C. for 15 minutes. As a result, the Ir ions in the 0.01M iridium acetate ethanol solution 140 coated on the surface of the SiO ₂ layer 110A aggregate to form particulate Ir 120. Since the thickness of the 0.01M iridium acetate ethanol solution 140 coated in the second step is approximately 100 nm, the particle size of Ir 120 is considered to be approximately 0.5 nm to 1.5 nm. In this manner, the third step is performed.

Next, after the third step is performed, the fourth step of performing CVD is performed (see FIG. 14(E)). Specifically, the Si substrate 110 that has been subjected to the third step is introduced into a reactor in which CVD is performed. The conditions in the reactor are the same as those in Example 1. Then, the Ir 120 acts as a catalyst, and a plurality of single-walled carbon nanotubes 130 bonded to the SiO ₂ layer 110A on the surface of the Si substrate 110 via the Ir 120 are grown. In this way, the fourth step is performed. After that, the temperature in the reactor is lowered to room temperature, and the Si substrate 110 on which the plurality of single-walled carbon nanotubes 130 have grown is taken out of the reactor.

[Evaluation results of samples in Example 3]
Figures 16 to 19 show Raman spectra of single-walled carbon nanotubes 130 in samples 8 to 11 produced by using the manufacturing method of Example 3 and changing the pulling speed of Si substrate 110 immersed in 0.01 M iridium acetate ethanol solution 140 in the second step to four different speeds, 0.1 mm/sec, 0.2 mm/sec, 0.4 mm/sec, and 0.6 mm/sec, when irradiated with light of four different wavelengths, 488 nm, 532 nm, 671 nm, and 785 nm.

As shown in Figures 16(B), 17(B), 18(B), and 19(B), a sharp G-band spectrum peak appears in the high wavenumber region in each of Samples 8 to 11. And as shown in Figures 16(A), 17(A), 18(A), and 19(A), multiple RBM (radial breathing mode) spectrum peaks appear in the low wavenumber region around 170 to 300 cm ^-1 . From this, it can be seen that single-walled carbon nanotubes 130 grow in each of Samples 8 to 11. Also, from the position of the RBM spectrum peak, it can be seen that the diameters of the single-walled carbon nanotubes 130 in Samples 8 to 11 are distributed between approximately 0.8 nm and 1.5 nm.

Next, FIG. 20 shows the results of observing the surface of the Si substrate 110 in sample 8 in the thickness direction and the cross section of the Si substrate 110 in a direction perpendicular to the thickness direction using an FE-SEM. As shown in FIG. 20(A), it can be seen that in sample 8, the single-walled carbon nanotubes 130 grow aligned perpendicular to the Si substrate 110 and have a high density. The length of the single-walled carbon nanotubes 130 in sample 8 was approximately 200 nm (see FIG. 20(B)).

Next, Figure 21 shows the ratio G/D for each of samples 8 to 11, and the ratio G/Si of the magnitude of the G-band spectrum peak to the magnitude of the spectrum peak originating from the Si substrate 110 (hereinafter also referred to as the ratio G/Si).

Here, the ratio G/Si is an index of the yield of single-walled carbon nanotubes 130, and is a value obtained by dividing the peak value of the G-band spectrum by the peak value derived from the Si substrate 110. Here, the peak derived from the Si substrate 110 is a peak that appears near 520 cm ⁻¹ in the Raman spectrum (not shown).

As shown in FIG. 21(A), the ratio G/D was approximately 1.7 to 4.4 in sample 8, approximately 1.4 to 3.6 in sample 9, approximately 1.3 to 3.2 in sample 10, and approximately 1.2 to 2.7 in sample 11. As shown in FIG. 21(B), the ratio G/Si was approximately 0.06 to 0.28 in sample 8, approximately 0.07 to 0.16 in sample 9, approximately 0.04 to 0.12 in sample 10, and approximately 0.02 to 0.12 in sample 11.

From the calculation results of the ratio G/D and the ratio G/Si, it was found that the single-walled carbon nanotubes 30 grow well when the speed at which the Si substrate 110 immersed in the 0.01 M iridium acetate ethanol solution 140 in the second step is pulled up is between 0.1 mm/sec and 0.6 mm/sec. Furthermore, it was found that the crystallinity of the single-walled carbon nanotubes 130 becomes better and the growth amount of the single-walled carbon nanotubes 130 increases as the speed at which the Si substrate 110 immersed in the 0.01 M iridium acetate ethanol solution 140 in the second step is pulled up decreases.

This method for manufacturing single-walled carbon nanotubes includes a first step of cleaning the Si substrate 110, a second step of coating the surface side of the Si substrate 110 with a 0.01 M iridium acetate ethanol solution 140, a third step of baking the Si substrate 110, and a fourth step of performing CVD. With this configuration, particles of Ir120 can be easily formed on the surface of the Si substrate 110 by coating the surface of the Si substrate 110 with the 0.01 M iridium acetate ethanol solution 140 and then baking it. As a result, this method for manufacturing single-walled carbon nanotubes can form particles of Ir120 on the Si substrate 110 without using a deposition device or the like, so that single-walled carbon nanotubes 130 can be easily obtained.

In the second step of the method for producing single-walled carbon nanotubes, the Si substrate 110 is immersed in a 0.01 M iridium acetate ethanol solution 140, and is pulled up from the 0.01 M iridium acetate ethanol solution 140 at a speed of 0.1 mm/sec to 0.6 mm/sec with the surface of the Si substrate 110 oriented to intersect with the liquid surface S of the 0.01 M iridium acetate ethanol solution 140. With this configuration, particulate Ir 120 can be successfully formed on the Si substrate 110, and single-walled carbon nanotubes 130 can be reliably grown on the Si substrate 110.

The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments are also included within the technical scope of the present invention.
(1) In the first and second embodiments, stainless steel is used for the metal substrate. However, the present invention is not limited to this, and other metals such as tungsten, molybdenum, cobalt, and nickel alloys may be used for the metal substrate.
(2) In the above embodiment, the inside of the reactor was heated to 850° C. when the single-walled carbon nanotubes were grown by CVD (chemical vapor deposition). However, the heating temperature may be changed as appropriate.
(3) In the above embodiment, ethanol is supplied into the reactor as a carbon source when growing single-walled carbon nanotubes by CVD (chemical vapor deposition). However, a carbon source other than ethanol may be supplied.
(4) In the third embodiment, the surface of the Si substrate is a (111) surface. However, the surface of the Si substrate may be changed to another crystal surface such as a (100) surface or a (110) surface.
(5) In the third embodiment, a 0.01 M iridium acetate ethanol solution is used as the Ir ion solution. However, the present invention is not limited to this, and a solution in which Ir ions are dissolved in water may be used as the Ir ion solution.
(6) In Example 3, the Si substrate is immersed in the 0.01 M iridium acetate ethanol solution. Alternatively, the Si substrate may be coated with the 0.01 M iridium acetate ethanol solution using a spin coater. Alternatively, the Si substrate may be coated with the 0.01 M iridium acetate ethanol solution using a bar coating method.
(7) In Example 3, the angle at which the surface of the Si substrate and the liquid surface of the 0.01 M iridium acetate ethanol solution intersect is approximately 90°. Specifically, the angle at which the surface of the Si substrate and the liquid surface of the 0.01 M iridium acetate ethanol solution intersect may be 90° or may be an angle slightly different from 90°.

20,120...Ir (iridium)
30, 130... Single-walled carbon nanotubes 50... Metal substrate 51... _{Al2O3 buffer} layer 52... PDMS buffer layer 110... Si substrate 140... 0.01M iridium acetate ethanol solution (Ir (iridium) ion solution)
S...Ir (iridium) ion solution surface

Claims (2)

A first step of cleaning a metal substrate;
A second step of forming _{an Al2O3} buffer layer on the surface of the metal substrate by sputtering ;
A third step of depositing Ir (iridium) on the surface of _{the Al2O3} buffer layer;
A fourth step of performing CVD;
A method for producing single-walled carbon nanotubes, comprising: 2. The method for producing single-walled carbon nanotubes according to claim 1, wherein the thickness of _{the Al2O3} buffer layer is 30 nm to 200 nm.

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