JP2007197306A - Manufacturing method of single-wall carbon nanotube, single-wall carbon nanotube, and manufacturing method of electronic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a single-wall carbon nanotube which can be suitably used for easily manufacturing a high quality single-wall carbon nanotube having a controlled structure, containing a single-wall carbon nanotube of a very small diameter, and having a very narrow distribution of the diameter. <P>SOLUTION: In this manufacturing method, the single-wall carbon nanotube is grown by chemical vapor deposition method using an alcohol such as ethanol or a gas obtainable by vaporizing an aqueous alcohol solution as a reaction gas. Reaction is carried out by introducing the gas obtained by evaporating the alcohol or the aqueous alcohol solution by spontaneous vaporization at the outside of the reaction zone of the chemical vapor deposition unit. The alcohol concentration of the aqueous alcohol solution is, for example, not lower than 50% but not higher than 95%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing single-walled carbon nanotubes, a method for producing single-walled carbon nanotubes, and an electronic device, and is suitable for application to various electronic devices using single-walled carbon nanotubes, for example.

  Single-walled carbon nanotubes (SWNTs) have unique electrical, mechanical, electro-optical and electromechanical properties, so that future nano-sizes such as field emission devices, field effect transistors, single electron transistors, molecular sensors, etc. It has been regarded as an attractive structural unit of an electronic device (for example, see Non-Patent Documents 1 to 5). In order to realize such an attractive application, it is inevitably desired to produce high quality single-walled carbon nanotubes with a controlled structure. Many efforts have been made over the past decade to produce single-walled carbon nanotubes, and arc discharge (eg, non-patented) to produce high-quality single-walled carbon nanotubes in high yield and low cost. Various techniques have been developed, including reference 6), laser ablation (for example, see non-patent document 7) and chemical vapor deposition (CVD) (for example, see non-patent documents 8 to 10). Application of single-walled carbon nanotubes (for example, see Non-Patent Document 11) and basic science (for example, see Non-Patent Documents 12 to 16) require new approaches and flexibility in production.

The above CVD method is generally considered to be one effective method for producing high-quality single-walled carbon nanotubes at low cost. For this reason, a lot of research has been conducted to optimize the CVD method by searching for the catalyst composition, support / substrate material, reaction temperature and carbon source gas (for example, Non-Patent Documents 17- 20). Recently, ethanol has been reported to be an ideal carbon source for producing high-quality single-walled carbon nanotubes under reduced pressure conditions by CVD (see, for example, Non-Patent Documents 21 to 23). Also, there is a method for producing single-walled carbon nanotubes under reduced pressure conditions by a CVD method by contacting a mixture of a carbon source comprising an oxygen-containing compound or a compound having oxygen and a carbon-containing compound with a catalyst at a heating temperature. Alcohols or ethers such as ethanol have been proposed as examples of the above carbon source, and mixtures of water and hydrocarbons such as acetylene as examples of the above mixture, and carbons such as NO _x , SO _x and acetylene have been proposed. The mixture with hydrogen etc. are mentioned (for example, refer patent document 1).

Dresselhaus, M.S.; Dresselhaus, G.; Eklund, P.C.Science of Fullerenes and Carbon Nanotubes; Academic Press: San Diego, 1996 Hafner, J.H.; Cheung, C.-L.; Oosterkamp, T.H.; Lieber, C.M., J.Phys.Chem.B, 2001,105,743 Postma, H.W.Ch.; Teepen, T.; Yao, Z.; Grifoni, M.; Dekker, C., Science 2001,293,76 Javey, A .; Guo, J .; Wang, Q .; Lundstrom, M .; Dai, H., Nature, 2003, 424, 654 Durkop, T .; Getty, S.A .; Cobas, E .; Fuhrer, M.S., Nano Lett. 2004, 4, 35 Journet, C.; Maser, W.K.; Bernier, P.; Loiseau, A.; Lamy de la Chapelle, M.; Lefrant, S.; Deniard, P.; Lee, R.; Fischer, J.E., Nature 1997,388,756 Thess, A.; Lee, R.; Nikolaev, P.; Dai, H.; Petit, P., Robert, J.;. Xu, C.; Lee, YH; Kim, SG; Rinzler, AG; Colbert, DT; Scuseria, GE; Tomanek, D.; Fischer, JE; Smalley, RE, Science 1996,273,483 Ismach, A .; Segev, L .; Wachtel, E .; Joselevich, E., Angew. Chem. Int. Ed. 2004, 43, 6140 Huang, Sh.M.; Cai, X.Y.; Liu, J., J.Am.Chem.Soc.2003,125,5636 Kong, J.; Soh, H.T.; Cassell, A.M.; Quate, C.F.; Dai, H., Nature 1998,395,878 Tanaka, K .; Yamabe, T .; Fukui, K., The Science and Technology of Carbon Nanotubes; Elsevier: Oxford, 1999 Wong, S.; Joselevich, E.; Woolley, A.; Cheung, C.; Lieber, C., Nature 1998,394,52 Fan, S.; Chapline, M.; Franklin, N.; Tombler, T.; Cassell, A.; Dai, H., Science 1999,283,512 Wang, X.B.; Liu, Y.Q.; Zhu, D.B., Chem.Commun.2001,751 Wang, X.B .; Liu, Y.Q .; Zhu, D.B., Adv. Mater. 2002, 14, 165 Wang, X.B.; Liu, Y.Q.; Hu, P.A.; Yu, G.; Xiao, K.; Zhu, D.B., Adv.Mater.2002,14,1557 Song, L.; Ci, L.J.; Zhou, Zh.P.; Xie, S.Sh., Adv.Mater.2004,16,1529 Huang, Sh.M.; Woodson, M.; Smalley, R.; Liu.J., Nano Lett.2004,4,1025 Shi, Z.J.; Okazaki, T.; Shimada, T.; Sugai, T.; Suenaga, K.; Shinohara, H., J.Phys.Chem.B2003,107,2485 Mukhopadhyay, K.; Koshio, A.; Tanaka, N.; Shinohara, H., Jpn.J.Appl.Phys.1998,37,1257 Okamoto.A.; Shinohara, H., Carbon 2000,43,1691 Mukhopadhyay, K.; Koshio, A.; Sugai, T.; Tanaka, N.; Shinohara, H.; Konya, Z., Chem.Phys.Lett., 1999,303,117 Murakami, Y.; Einarsson, E.; Edamura, T.; Maruyama, S., Carbon 2005,43,2664 International Publication No. 03/068676 Pamphlet

However, when manufacturing single-walled carbon nanotubes under reduced pressure conditions by CVD, it is difficult to control the growth parameters of single-walled carbon nanotubes, so high-quality single-walled carbon nanotubes with a controlled structure are manufactured. Difficult to do.
Therefore, the problem to be solved by the present invention is that a high-quality single-walled carbon nanotube having a controlled structure can be easily produced, and the single-walled carbon nanotube having a very small diameter is included, and the distribution of diameters To provide a single-walled carbon nanotube production method capable of easily producing a single-walled carbon nanotube having an extremely narrow width, a single-walled carbon nanotube produced by this method, and a method for producing an electronic device using this method .

In order to solve the above problem, the first invention is:
A method for producing single-walled carbon nanotubes, characterized in that a single-walled carbon nanotube is grown at atmospheric pressure by chemical vapor deposition using a gas obtained by vaporizing alcohol or an aqueous solution of alcohol as a reaction gas It is.
The second invention is
A single-walled carbon nanotube produced by growing single-walled carbon nanotubes at normal pressure by chemical vapor deposition using a gas obtained by vaporizing an alcohol or an aqueous solution of alcohol as a reaction gas. is there.
The third invention is
In the method of manufacturing an electronic device using single-walled carbon nanotubes,
The single-walled carbon nanotube is grown at normal pressure by chemical vapor deposition using a gas obtained by vaporizing an alcohol or an aqueous solution of alcohol as a reaction gas.

  In this invention, typically, the reaction is carried out by introducing a gas obtained by vaporizing alcohol or an aqueous solution of alcohol by natural evaporation or the like outside the reaction part of the chemical vapor deposition apparatus. . The alcohol concentration (volume concentration) of the aqueous solution of alcohol is greater than 0% and less than 100%, and the alcohol concentration is basically not limited as long as it is within this range, but the closer the alcohol concentration is to 75%, the closer to 100%. Single-walled carbon nanotubes with a smaller diameter can be produced, and if the alcohol concentration is 50% or more and 95% or less, preferably 50% or more and 80% or less, single-walled carbon nanotubes with a narrow diameter distribution width are produced. In particular, when the alcohol concentration is 70% or more and 80% or less, single-walled carbon nanotubes having a very narrow diameter distribution range can be produced.

  The growth temperature of the single-walled carbon nanotube is generally 500 ° C. or higher and 1500 ° C. or lower, preferably 650 ° C. or higher and 900 ° C. or lower, more preferably 800 ° C. or higher and 900 ° C. or lower. It is not limited. Single-wall carbon nanotubes are typically grown by contacting a metal catalyst with a gas obtained by vaporizing alcohol or an aqueous solution of alcohol at this growth temperature. As the metal catalyst, various known catalysts conventionally used for the growth of carbon nanotubes can be used.

  Basically, any alcohol may be used, which may be a monohydric alcohol or a polyhydric alcohol, and may be a saturated alcohol or an unsaturated alcohol. In general, a monohydric alcohol having a small number of carbon atoms is liquid at room temperature, and is arbitrarily mixed with water. Therefore, an aqueous solution having a high alcohol concentration can be easily prepared, which is preferable. Specific examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol (sec-butanol), 2-methyl-1-propanol (isobutanol), 2 -Methyl-2-propanol (tert-butanol), 1-pentanol and the like are exemplified, but not limited thereto.

By adjusting the alcohol concentration of the aqueous alcohol solution and / or the vaporization rate of the aqueous alcohol solution, the diameter and / or diameter distribution of the single-walled carbon nanotubes can be controlled. The vaporization rate of the aqueous alcohol solution can be adjusted, for example, by changing the temperature of the container containing the aqueous alcohol solution.
Preferably, single-walled carbon nanotubes are grown by chemical vapor deposition, and then the product is purified compositionally. This is because the product generally contains amorphous carbon, metal impurities, etc. in addition to the single-walled carbon nanotubes, so that they are removed. This purification is preferably carried out by acid treatment with hydrochloric acid, reflux with nitric acid and air oxidation.

  This single-walled carbon nanotube can be applied to any element as long as it is an element that applies its specific electrical, mechanical, electro-optical or electromechanical characteristics. For example, as an electronic device using this single-walled carbon nanotube, specifically, a field emission device, a field effect transistor (FET) (including a thin film transistor (TFT)), a single electron transistor, a molecular sensor, a solar cell, a photoelectric conversion An element, a light emitting element, a memory, etc. are mentioned.

  In the present invention configured as described above, single-walled carbon nanotubes are grown at atmospheric pressure by chemical vapor deposition, compared to growing single-walled carbon nanotubes under reduced pressure by chemical vapor deposition. Thus, the growth parameters can be easily controlled, and the growth of high-quality single-walled carbon nanotubes having a controlled structure is easy. In addition, by using a gas obtained by vaporizing alcohol or an aqueous solution of alcohol as a reaction gas, it is possible to grow single-walled carbon nanotubes that contain single-walled carbon nanotubes with a very small diameter and a very narrow diameter distribution range. It becomes.

  According to the present invention, a high-quality single-walled carbon nanotube having a controlled structure can be easily manufactured, and the single-walled carbon nanotube includes a very small diameter and has a very narrow diameter distribution width. Carbon nanotubes can be easily produced. A high-performance electronic device can be obtained by using single-walled carbon nanotubes produced by this method.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, a single-walled carbon nanotube is formed at atmospheric pressure by a CVD method using a gas obtained by forming a metal catalyst on a substrate and vaporizing an alcohol (carbon source) or an alcohol aqueous solution as a reaction gas. Synthesize. In this case, the reaction is carried out by introducing a gas obtained by vaporizing alcohol or an aqueous solution of alcohol outside the reaction part (the part of the reaction tube in the furnace) of the CVD apparatus. Thereafter, compositional purification of the single-walled carbon nanotube thus synthesized is performed.

The substrate on which the single-walled carbon nanotube is grown is a substrate made of an inorganic material and / or an organic material, and the material is selected as necessary. As the substrate made of an inorganic material, for example, a silicon substrate (including a substrate on which a SiO ₂ film is formed), a glass substrate, a quartz substrate, or the like is used. As the substrate made of an organic material, for example, a polymer substrate is used. As a substrate made of an inorganic material and an organic material, a combination of these materials is used.

Examples of the metal catalyst formed on the substrate include metals such as Fe, Co, Ni, Mo, Pt, Pd, Rh, Ir, and combinations of two or more of these metals, such as Fe- Co, Ni—Co, Fe—Mo, Co—Mo, and the like can be used, but are not limited thereto. This metal catalyst is typically supported on a predetermined carrier. As this carrier, for example, MgO, silica, alumina, zeolite, zirconia, titania and the like can be used, but are not limited thereto.
The growth temperature is 500 ° C. or higher and 1500 ° C. or lower, preferably 650 ° C. or higher and 900 ° C. or lower, more preferably 800 ° C. or higher and 900 ° C. or lower.

  The alcohol concentration of the aqueous alcohol solution is greater than 0% and less than 100%, preferably 50% to 95%, more preferably 50% to 80%, and even more preferably 70% to 80%. And Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, and 1-pentanol. Can do.

  According to this embodiment, since single-walled carbon nanotubes are grown at normal pressure by a CVD method using a gas obtained by vaporizing an alcohol or an aqueous solution of alcohol as a reaction gas, a high-quality product having a controlled structure is obtained. Single-walled carbon nanotubes can be easily produced. In addition, it is possible to easily produce single-walled carbon nanotubes including single-walled carbon nanotubes having a very small diameter of, for example, 0.6 to 1.8 nm and having a very narrow diameter distribution width of, for example, 0.6 to 0.7 nm. it can.

<Example 1>
(1) Preparation of catalyst Fe-Co was prepared as a catalyst by a conventional chemical impregnation method. Specifically, first, metal nitrate is dissolved by dissolving iron nitrate (Fe (NO ₃ ) ₃ 9H ₂ O) and cobalt nitrate (Co (NO ₃ ) ₃ 9H ₂ O) in ethanol (typically 40 ml). A solution was prepared. Next, magnesium oxide (MgO) obtained by decomposition of the magnesium carbonate salt was added to this solution as a carrier. The resulting mixture was then sonicated for 3 hours for homogenization. After removing ethanol from this mixture by a rotary evaporator, the obtained material was dried at 115 ° C. overnight. This material was then powdered. The total catalyst amount in the MgO support was fixed at 10 wt%, and the transition metal molar ratio was Fe / Co = 1: 2.

(2) Atmospheric pressure CVD
FIG. 1 shows a CVD apparatus designed by the present inventors for producing single-walled carbon nanotubes at normal pressure. As shown in FIG. 1, a quartz tube 11 that is a reaction tube is placed in a furnace 12. Both ends of the quartz tube 11 protrude outside the furnace 12. The temperature of the furnace 12 is measured by a thermocouple 13 and controlled by a temperature control device 14. A container 16 containing ethanol or an aqueous ethanol solution 15 was placed inside one end of the quartz tube 11 outside the furnace 12. The concentration of ethanol or ethanol aqueous solution 15 was 100 to 50%. About 1 g of a catalyst 18 made of MgO carrying Fe / Co fine particles as catalyst metal fine particles was placed on the quartz boat 17 and inserted into the quartz tube 11 at the center of the furnace 12. Then, while the ethanol or ethanol and water gas evaporated from the ethanol or the ethanol aqueous solution 15 in the container 16 is transported by an Ar / H ₂ mixed gas flow (Ar: 250 ml / min, H ₂ : 20 ml / min), the normal pressure Single-walled carbon nanotubes were produced by CVD at a reaction time of 850 ° C., typically 30 minutes. The vaporization rate of the ethanol or the ethanol aqueous solution 15 is controlled by moving the container 16 by fixing the iron piece 19 on the bottom surface of the container 16 and moving the magnet 20 provided outside the quartz tube 11 along the quartz tube 11. Thus, the distance to the furnace 12 was changed, and the temperature change of the ethanol or ethanol aqueous solution 15 due to the radiant heat from the heated quartz tube 11 was controlled.

(3) Purification A compositional purification process was applied to a sample immediately after production by the atmospheric pressure CVD method. First, the catalyst (both MgO support and fine metal particles) was removed by acid treatment using concentrated hydrochloric acid (HCl). Typically, the freshly prepared sample was placed in 50 ml of 6N concentrated hydrochloric acid with sonication for 30 minutes. Next, in order to remove amorphous carbon, residual metal fine particles and MgO support, the sample treated with HCl was refluxed in a 4N nitric acid (HNO ₃ ) solution at 120 ° C. for 12 hours. The obtained sample was filtered and washed with distilled water until the color of the filtrate became transparent. In the final stage of the purification process, the sample was heated in air at 470 ° C. for 30 minutes and then treated again with 6N concentrated hydrochloric acid to remove residual impurities. After rinsing the sample and drying at 120 ° C., a grayish black and thin mat was finally obtained.

(4) Characterization Using a scanning electron microscope (SEM, Hitachi S-4300, 15 kV), a high-resolution transmission electron microscope (HRTEM, Philips CM200, 200 kV) and Raman spectroscopy (632.8 nm, Renishaw 1000). The samples were characterized. The contents of the metal catalyst fine particles and the MgO carrier (metal impurities) were measured using a thermogravimetric analyzer (TGA, 951 TGA manufactured by DuPont Instruments). After removing moisture from the sample at 105 ° C. in dry air, the sample was heated to 1000 ° C. at a rate of 5 ° C./min while flowing dry air at 100 ml / min. The residual weight refers to the metal impurity content in the sample.

(5) Results and Discussion FIG. 2 shows a Raman spectrum of a sample immediately after production using 100% ethanol concentration, FIG. 3 shows a Raman spectrum after refluxing this sample with nitric acid, and FIG. 4 shows a final result. The Raman spectrum of the sample after simple purification is shown. From FIG. 2, radial-breathing, which is one of the characteristic Raman scattering modes of single-walled carbon nanotubes, in the low frequency region of 130 to 350 cm ⁻¹ .
The mode (RBM) is clearly observed. The frequency of the RBM mode is inversely proportional to the diameter of the single-walled carbon nanotube, and the relationship can be expressed as ω = 223.75 / d + 6.5 (for example, Lyu, SC; Liu, BC; Lee, TJ; Liu, ZY; Yang, CW; Park, CY; See Lee, CJ, Chem. Commun. 2003, 734). Where ω is the RBM frequency in cm ⁻¹ , and d is the diameter of the single-walled carbon nanotube in nm, taking into account the bundle effect. An RBM frequency of 130-350 cm ^-1 corresponds to a diameter of 0.6-1.8 nm. Shoulder peak of 1552 cm ^-1 appearing on the left side of the main peak of 1586 cm ^-1 (G band) is derived from the division of E _{2 g} mode graphite. This shoulder peak is also one of the characteristic Raman scattering modes of single-walled carbon nanotubes (for example, A. Kasuya, Y. Sasaki, Y. Saito, K. Tohji, Y. Nishina, Phys. Rev. Lett. .1997,78,4434). In addition to these characteristic peaks, a defect-induced mode, the so-called D band, appears at 1320 cm ⁻¹ , indicating that the sample contains defective carbon such as amorphous carbon. The intensity ratio of the G band to the D band (G / D ratio) was 2.8. The G / D ratio is a good measure of the purity of single-walled carbon nanotubes, and this ratio increases with increasing single-walled carbon nanotube purity of the sample (eg, H. Kataura, Y. Kumazawa, Y. Maniwa, Y. (See Ohtsuka, R. Sen, S. Suzuki, Y. Akiba, Carbon 2000, 38, 1691).

  Fibrous products are observed in the scanning electron microscope (SEM) image of the sample immediately after manufacture (FIG. 5a), which is considered as a bundle of single-walled carbon nanotubes containing impurities such as amorphous carbon and fine metal particles. It is done. Thermogravimetric analysis showed that the metal impurity content of the sample immediately after manufacture was 54 wt%.

FIGS. 5b, c, d show SEM images of the sample, FIG. 5b shows after HCl treatment, FIG. 5c shows after HNO ₃ reflux, and FIG. 5d shows the final purified sample. For purification, we used samples prepared at 100% ethanol concentration. A number of bundles containing large amounts of amorphous carbon were observed after HCl treatment (FIG. 5b). The HCl treatment reduced the metal impurity content from 54% to 18%. In order to remove amorphous carbon and residual metal impurities, the HCl-treated sample was refluxed at 120 ° C. for 12 hours in an HNO ₃ solution. The refluxed sample mainly consisted of bundles with a large diameter (FIG. 5c), and the content of metal impurities was reduced to 8%. The Raman spectroscopic result of the refluxed sample showed a D band with significant intensity (FIG. 3). The inventors believe that this D-band is derived from amorphous carbon pieces that are produced during reflux in HNO ₃ and cover a bundle of single-walled carbon nanotubes. In order to completely remove residual impurities, the refluxed sample was subjected to heat treatment at 470 ° C. and HCl treatment in air. The SEM image of the final purified sample shows almost no impurities (FIG. 5d).

  FIG. 6 shows a transmission electron microscope (TEM) image of the final purified sample, where (a) is a low magnification and (b) is a high magnification. This sample basically consists of a bundle of single-walled carbon nanotubes with almost no impurities. The Raman spectrum of the final purified sample shows a negligible D band (FIG. 4), indicating that most of the amorphous carbon was removed during the final purification process. The G / D ratio increased from 2.8 to over 100 due to our compositional purification.

In order to confirm the purity of the single-walled carbon nanotube of the sample, thermogravimetric analysis measurement was performed. The results are shown in FIGS. 7 shows the measurement result of the sample immediately after production, FIG. 8 shows the measurement result of the sample after HCl treatment, FIG. 9 shows the measurement result of the sample after refluxing HNO ₃ , and FIG. 10 shows the measurement result of the final purified sample. As shown in FIG. 10, the residual weight of the final purified sample was 2 wt% or less. In the weight change rate (−dW / dT) profile, only one peak with a maximum value around 585 ° C. was obtained, which means that the sample contains one combustible component. This maximum temperature is consistent with the reported combustion temperature of single-walled carbon nanotubes, suggesting that the final purified sample consists of 98% pure single-walled carbon nanotubes. This suggestion is supported by TEM observation (FIG. 6).

  In this Example 1, the diameter and chirality of the single-walled carbon nanotube are determined by the production reaction in the catalyst. Therefore, the present inventors have hypothesized that the structure of single-walled carbon nanotubes can be controlled by the ethanol supply rate. To test this hypothesis, single-walled carbon nanotubes were produced with different ethanol concentrations. Table 1 summarizes the ethanol concentrations tested and the results obtained. The diameter distribution was estimated from the RBM frequency in the Raman spectrum. FIG. 11 is a graph showing the results in Table 1.

  As shown in FIG. 11, the ethanol concentration clearly affects the distribution of the diameter of the single-walled carbon nanotubes. In general, if the ethanol concentration is high, the ethanol vapor concentration will be correspondingly high, resulting in many more types of carbon deposition based on the gas-liquid-solid (VLS) growth process of carbon nanotubes. On the other hand, if the ethanol concentration is low, the ethanol vapor concentration is accordingly reduced, and the type of carbon adhesion type is reduced. This trend can be seen in FIG.

  The production of high-quality single-walled carbon nanotubes is highly dependent on the experimental setup such as the shape of the reaction part of the CVD apparatus. In conventional ethanol CVD, single-walled carbon nanotubes are produced under reduced pressure in order to prevent evaporation of evaporated ethanol. Under reduced pressure, it is difficult to control growth parameters such as ethanol concentration compared to under normal pressure. In the CVD apparatus shown in FIG. 1, a container 16 in which ethanol or an aqueous ethanol solution 15 is placed inside one end of a quartz tube 11 outside the furnace 12 is installed. For this reason, the ethanol concentration and the vaporization rate are adjusted. This makes it possible to produce high-quality single-walled carbon nanotubes with a controlled diameter distribution under normal pressure.

  As described above, high-quality single-walled carbon nanotubes can be produced from ethanol or an aqueous ethanol solution at normal pressure using a CVD apparatus uniquely designed by the present inventors. The quality and diameter distribution of single-walled carbon nanotubes are controlled by adjusting the ethanol concentration and vaporization rate. A compositional purification method combining HCl treatment, reflux of nitric acid and air oxidation yielded single-walled carbon nanotubes of 98% purity.

<Example 2>
As in Example 1, single-walled carbon nanotubes were produced by atmospheric pressure CVD using Fe-Co / MgO catalyst and various monohydric alcohols (concentration 100%). As the monohydric alcohol, ethanol, 1-propanol, 1-butanol and 1-pentanol were used. Typical SEM images of single-walled carbon nanotubes just prepared with these ethanol, 1-propanol, 1-butanol and 1-pentanol are shown in FIGS. 12a, b, c and d, and the Raman spectrum is shown in FIG. 13a. , B, c and d (the data from which the upper curve was obtained, the lower curve shows the peak fitted by spectral analysis), a three-dimensional comparative plot of the low-frequency Raman spectrum in FIG. Images are shown in FIGS. 15a, b, c and d (scale bar represents 8 nm), and the G band region of the Raman spectrum is shown in FIG. 12a, b, c and d that a large amount of single-walled carbon nanotubes are produced. FIGS. 13a, b, c and d and FIG. 14 also show the presence of single-walled carbon nanotubes. Moreover, it can confirm that a single-walled carbon nanotube exists from FIG. 15a, b, c, and d.

13a, b, c and d, in order of ethanol, 1-propanol, 1-butanol and 1-pentanol, in other words, as the ratio of the mass of OH groups to the mass of these molecules decreases relatively. It can be seen that the purity of the single-walled carbon nanotubes immediately after the production is clearly reduced. As a result of detailed comparison with the revised Kataura plot (see Strano, MSJAm. Chem. Soc. 2003, 125, 16148), the Raman peaks near 140 to 180 cm ⁻¹ and 200 to 280 cm ⁻¹ are respectively metallic. It can be concluded that they are derived from typical single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes. From FIGS. 13a, b, c and d, the proportion of metallic single-walled carbon nanotubes tends to increase in the order of ethanol, 1-propanol, 1-butanol and 1-pentanol, in contrast to semiconducting single-walled carbon nanotubes. is there. Further, the increase in the proportion of the metallic single-walled carbon nanotube is apparent from the analysis of the G band shown in FIG. It is well known that the tangential mode (1500 to 1600 cm ⁻¹ ) shows a mode of characteristic behavior of metallic single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes. Semiconducting single-walled carbon nanotubes have a narrow Lorentzian in this region, whereas metallic single-walled carbon nanotubes are characterized by a high-frequency Lorentzian coupled with a broad, low-energy Breit-Wigner-Fano tail. The Fano component in metallic single-walled carbon nanotubes is essentially due to the coupling of discrete phonons with the electron continuum, resulting in greater downshifting and broadening of this feature as the tube diameter decreases. This again shows the increase in metallic single-walled carbon nanotubes in FIG.

Reported articles (Maruyama, S .; Kojima, R .; Miyauchi, Y .; Chiashi, S .; Kohno, M., Chem. Phys. Lett., 2002, 360, 229, Hata, K; Futaba, DN; Mizuno , K.; Namai, T.; Yumura, M.; Iijima, S.
, Science 2004, 306, 1362 and Zhang, GY; Mann, D .; Zhang, L .; Javey, A .; Li, YM; Yenilmez, E., Wang, Q .; McVittie, JP; Nishi, Y .; Gibbons, J .; Dai, HJ, Proc. Natl. Acad. Sci. USA, 2005, 102, 16141) and our experimental results show that the increase in metallic single-walled carbon nanotubes is from monohydric alcohols. This is due to the role of selective etching of OH radicals. OH radicals from monohydric alcohol selectively etch metallic single-walled carbon nanotubes relative to semiconducting single-walled carbon nanotubes. The relative abundance ratio of semiconducting single-walled carbon nanotubes and metallic single-walled carbon nanotubes does not necessarily follow the 2: 1 ratio expected for a random chirality distribution.

Consider the entire manufacturing process of single-walled carbon nanotubes in two stages. In the first stage, the growth of single-walled carbon nanotubes is dominant, whereas the etching effect of OH radicals is considered to be secondary (see FIG. 17). OH radicals released by thermal decomposition (C _n H _{2n + 1} OH → nC · + (2n + 1) H · + OH · (n = 2 to 5)) of monohydric alcohol molecules on the catalyst are single-walled carbon nanotubes However, the etching amount for the entire single-walled carbon nanotube is small. The growth rate of carbon nanotubes decreases with time, which has been reported to be due to catalyst poisons and is evidence of the formation of carbon shells near the catalyst particles, which have been thought to poison the catalyst. Yes. Therefore, in the second stage (subsequent catalyst poison), carbon atoms generated by thermal decomposition of 1-pentanol produce the most amorphous carbon, but the amount of amorphous carbon produced in the order of 1-propanol, 1-butanol and ethanol. The main reason why selective etching with OH radicals in the order of ethanol, 1-propanol, 1-butanol, and 1-pentanol is difficult, and this leads to changes in the electronic properties and purity of single-walled carbon nanotubes immediately after production. It is. The presence of amorphous carbon is hated during the production of single-walled carbon nanotubes, but protects the single-walled carbon nanotubes immediately after production. Furthermore, for the purpose of confirming the change in the electronic properties of single-walled carbon nanotubes caused by selective etching of OH radicals rather than the molecular structure, isobutanol and tert-butyl are used as carbon sources for comparison with 1-butanol. Alcohol was selected. As a result, basically, the produced single-walled carbon nanotubes did not differ in terms of purity or electronic properties (FIGS. 18 and 19).

  As described above, the growth of single-walled carbon nanotubes with controlled chirality is enabled by the selective etching effect of OH radicals from monohydric alcohol. Both the purity and electronic properties of single-walled carbon nanotubes as prepared are independent of the molecular structure of these alcohols and are based on the ratio of the mass of OH groups to the mass of alcohol molecules. The results of this Example 2 highlight the effect of OH radicals on the growth and structure of single-walled carbon nanotubes and further studies are underway to elucidate the special etching process.

Although one embodiment and example of the present invention have been specifically described above, the present invention is not limited to the above-described embodiment and example, and various modifications based on the technical idea of the present invention are possible. It is.
For example, the configuration, numerical values, materials, raw materials, processes, and the like of the CVD apparatus mentioned in the above-described embodiments and examples are merely examples, and if necessary, the configuration of the CVD apparatus, numerical values, materials, raw materials, A process or the like may be used.

It is sectional drawing which shows the structure of the CVD apparatus used in Example 1 of this invention. It is a basic diagram which shows the Raman spectrum of the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. It is a basic diagram which shows the Raman spectrum after performing reflux with nitric acid with respect to the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. It is a basic diagram which shows the Raman spectrum after the final refinement | purification of the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. In the photograph substituted for drawing which shows the SEM image of the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention, the sample after HCl processing, the sample after HNO ₃ reflux, and the sample after final purification is there. It is a drawing substitute photograph which shows the TEM image of the sample finally performed to refinement | purification with respect to the sample immediately after manufacturing using 100% ethanol density | concentration in Example 1 of this invention. It is a basic diagram which shows the result of the thermogravimetric analysis measurement of the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. It is a basic diagram which shows the result of the thermogravimetric analysis measurement of the sample which performed to the HCl process with respect to the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. Is a schematic diagram showing the results of thermogravimetric analysis measurement of the sample went to reflux by HNO ₃ to the sample immediately after prepared with 100% ethanol concentration in the first embodiment of the present invention. It is a basic diagram which shows the result of the thermogravimetric analysis measurement of the sample finally performed to refinement | purification with respect to the sample immediately after manufacturing using 100% ethanol concentration in Example 1 of this invention. It is a basic diagram which shows the measurement result of the distribution of the diameter of the single-walled carbon nanotube which grew by changing ethanol concentration in Example 1 of this invention. It is a drawing substitute photograph which shows the SEM image of the sample immediately after manufacturing using various monohydric alcohol in Example 2 of this invention. It is a basic diagram which shows the Raman spectrum of the sample immediately after manufacturing using various monohydric alcohol in Example 2 of this invention. It is a basic diagram which shows the three-dimensional comparison plot of the low frequency Raman spectrum of the sample immediately after manufacturing using various monohydric alcohol in Example 2 of this invention. It is a drawing substitute photograph which shows the TEM image of the sample immediately after manufacturing using various monohydric alcohol in Example 2 of this invention. It is a basic diagram which shows the G band area | region of the Raman spectrum of the sample immediately after manufacturing using various monohydric alcohol in Example 2 of this invention. It is a basic diagram for demonstrating the reaction mechanism at the time of manufacturing a sample using various monohydric alcohol in Example 2 of this invention. In Example 2 of the present invention, Raman of a sample immediately after production using 1-butanol, isobutanol and tert-butyl alcohol was used for the purpose of confirming the change in electronic properties of single-walled carbon nanotubes caused by selective etching of OH radicals. It is a basic diagram which shows a spectrum. In Example 2 of the present invention, for the purpose of confirming the change in the electronic properties of single-walled carbon nanotubes caused by the selective etching of OH radicals, it was confirmed that the sample immediately after being produced using 1-butanol, isobutanol and tert-butyl alcohol It is a basic diagram which shows the three-dimensional comparison plot of a frequency Raman spectrum.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Quartz tube, 12 ... Furnace, 13 ... Thermocouple, 14 ... Temperature controller, 15 ... Ethanol or ethanol aqueous solution, 16 ... Container, 17 ... Quartz boat, 18 ... Catalyst, 19 ... Iron piece, 20 ... Magnet

Claims (12)

  A method for producing single-walled carbon nanotubes, characterized in that a single-walled carbon nanotube is grown at atmospheric pressure by chemical vapor deposition using a gas obtained by vaporizing alcohol or an aqueous solution of alcohol as a reaction gas .   The single-walled carbon nanotube according to claim 1, wherein a gas obtained by vaporizing the alcohol or an aqueous solution of the alcohol is introduced into the reaction part outside the reaction part of the chemical vapor deposition apparatus. Production method.   2. The method for producing single-walled carbon nanotubes according to claim 1, wherein the alcohol concentration of the aqueous alcohol solution is greater than 0% and less than 100%.   The method for producing single-walled carbon nanotubes according to claim 1, wherein the alcohol concentration of the alcohol aqueous solution is 50% or more and 95% or less.   2. The method for producing single-walled carbon nanotubes according to claim 1, wherein the alcohol concentration of the aqueous alcohol solution is 50% or more and 80% or less.   2. The method for producing single-walled carbon nanotubes according to claim 1, wherein the single-walled carbon nanotubes are grown at a growth temperature of 500 ° C. or higher and 1500 ° C. or lower.   The method for producing single-walled carbon nanotubes according to claim 1, wherein the single-walled carbon nanotubes are grown at a growth temperature of 650 ° C or higher and 900 ° C or lower.   The method for producing single-walled carbon nanotubes according to claim 1, wherein the alcohol is a monohydric alcohol.   2. The diameter and / or the distribution of diameters of the single-walled carbon nanotubes are controlled by adjusting an alcohol concentration of the aqueous alcohol solution and / or a vaporization rate of the aqueous alcohol solution. Of producing single-walled carbon nanotubes.   2. The method for producing a single-walled carbon nanotube according to claim 1, wherein after the single-walled carbon nanotube is grown, purification is performed by acid treatment using hydrochloric acid, reflux using nitric acid and air oxidation. .   A single-walled carbon nanotube produced by growing single-walled carbon nanotubes at normal pressure by chemical vapor deposition using a gas obtained by vaporizing an alcohol or an aqueous solution of alcohol as a reaction gas. In the method of manufacturing an electronic device using single-walled carbon nanotubes,
A method for producing an electronic device, characterized in that an alcohol or a gas obtained by vaporizing an alcohol aqueous solution is used as a reaction gas, and the single-walled carbon nanotubes are grown at normal pressure by a chemical vapor deposition method.

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