JP6228029B2 - Method for producing carbon composite - Google Patents

Description

The present invention relates to a method for manufacturing a carbon composite.

  Patent document 1 is disclosing the conventional carbon composite_body | complex and its manufacturing method. This carbon composite has a sheet-like graphene and a nanostructure having a one-dimensional shape that is bonded and extended to one surface of the graphene, for example, a carbon nanotube. In this carbon composite manufacturing method, first, graphene is formed on the upper surface of a silicon substrate or a glass substrate. Next, a metal catalyst layer is formed on the graphene. Then, a nanostructure is grown on the surface of the graphene opposite to the substrate by a dry method such as chemical vapor deposition or a wet method. In this way, a substantially one-dimensional nanostructure (carbon nanotube) can be formed on graphene. That is, a carbon composite of graphene and a nanostructure (carbon nanotube) can be manufactured.

JP 2011-110694 A

  However, in the carbon composite of Patent Document 1, carbon nanotubes are grown on the surface of graphene formed on the upper surface of a silicon substrate or a glass substrate. According to the knowledge of the present inventors, the carbon nanotubes grown in this way are uneven in chirality. That is, the carbon nanotubes grown in this way have a mixed metal type exhibiting metallic properties and a semiconductor type exhibiting semiconducting properties, and have different diameters.

This invention is made | formed in view of the said conventional situation, Comprising: It is set as the problem which should be solved to provide the manufacturing method of the carbon composite_body | complex which has the several carbon nanotube which shows the same electrical property.

The method for producing a carbon composite of the present invention includes a first step of oxidizing a graphite substrate by immersing it in a strongly acidic solution, and generating sheet-like graphene on the surface of the graphite substrate;
A second step of producing an intermediate in which metal fine particles are present at a high density on the surface of the graphene;
A third step of disposing the intermediate in an atmosphere supplied with alcohol gas at a predetermined pressure, and performing chemical vapor deposition of a plurality of single-walled carbon nanotubes bonded to the surface of the graphene by the metal fine particles acting as a catalyst; It is characterized by having.

  The present invention shows that when single-walled carbon nanotubes are chemically vapor-grown so as to be bonded to the surface of a sheet-like graphene formed on the surface of a graphite substrate, single-walled carbon nanotubes having substantially the same diameter and semiconducting properties can be obtained. They discovered. As a result, a carbon composite having a plurality of single-walled carbon nanotubes having substantially the same diameter and semiconducting properties can be easily produced.

Therefore, a carbon composite having a plurality of carbon nanotubes exhibiting the same electrical characteristics can be manufactured by the carbon composite manufacturing method of the present invention.

It is the schematic which shows the manufacturing method of the carbon composite_body | complex of an Example. It is the image of FESEM which shows the carbon composite of an Example, (a) And (b) supplied alcohol gas with the pressure of 1 * 10 ^<-2 > Pa in the 3rd process in the manufacturing method of a carbon composite. (C) and (d) are obtained by supplying alcohol gas at a pressure of 1 × 10 ⁻⁴ Pa in the third step in the carbon composite production method. It is a FESEM image which shows the carbon composite of the Example which supplied alcohol gas with the pressure of 1 * 10 <^-4> Pa in the 3rd process in the manufacturing method of a carbon composite. The Raman spectrum of the carbon composite of an Example is shown, (a) And (b) supplies alcohol gas with the pressure of 1 * 10 <^-4> Pa in the 3rd process in the manufacturing method of a carbon composite. , (C) and (d) are obtained by supplying alcohol gas at a pressure of 1 × 10 ⁻² Pa in the third step in the carbon composite production method. In the third step of the method for producing a carbon composite, the Raman spectrum measured by changing the wavelength of the excitation laser light was measured for the carbon composite of the example in which alcohol gas was supplied at a pressure of 1 × 10 ⁻⁴ Pa. Show. It is a graph which shows the relationship between the supply pressure of the alcohol gas of the 3rd process in the manufacturing method of a carbon composite, and the diameter of the single-walled carbon nanotube which carried out chemical vapor deposition on the surface of graphene. It is a graph which shows a Kataura plot. It is an HR-TEM image of a carbon composite supplied with alcohol gas at a pressure of 1 × 10 ⁻² Pa in the third step of the carbon composite manufacturing method, and single-walled carbon nanotubes are bonded to the surface of graphene and grow It shows the state. It is a HR-TEM image of the carbon composite which supplied the alcohol gas with the pressure of 1 * 10 <^-4> Pa in the 3rd process in the manufacturing method of a carbon composite, (a) is a single-walled carbon nanotube on the surface of a graphene FIG. 2B shows a state of growing by bonding, and (b) is an additional drawing of the geometric structure of a single-walled carbon nanotube.

Next, examples embodying the carbon composite manufacturing method of the present invention will be described with reference to the drawings.

<Example>
As shown in FIG. 1, the carbon composite manufacturing method of the example is first oxidized by immersing the graphite substrate 10 in a strongly acidic solution for 1 hour, and the sheet-like graphene 20 is formed on the surface of the graphite substrate 10. The 1st process to produce | generate is performed (refer FIG. 1 (A), (B)). The strongly acidic solution is aqua regia in which 60% by mass of concentrated nitric acid and 35% by mass of concentrated hydrochloric acid are mixed at a volume ratio of 1: 3. Next, the graphite substrate 10 on which the sheet-like graphene 20 is formed on the surface is taken out from the strongly acidic solution, washed with deionized water, acetone and methanol, and dried.

After drying, the graphite substrate 10 is placed in the chamber of the chemical vapor deposition apparatus, and the average film thickness is 0.2 nm using a plasma gun in an ultrahigh vacuum environment of 5 × 10 ⁻⁸ Pa. In this way, the second step of manufacturing the intermediate 1 is performed by depositing platinum particles (hereinafter referred to as “Pt30”), which are metal fine particles, on the surfaces of the graphite substrate 10 and the graphene 20 (see FIG. 1C). .

Next, in order to prevent oxidation of Pt30, H ₂ gas is supplied into the chamber under a pressure of 1 × 10 ⁻³ Pa. Thereafter, the inside of the chamber is heated to 700 ° C. at a temperature raising speed of 15 ° C./min. When the inside of the chamber is heated to 700 ° C., supply of H ₂ gas is stopped, and alcohol gas (ethanol) as a carbon source is chambered at a pressure of 1 × 10 ⁻² Pa or 1 × 10 ⁻⁴ Pa. Supply for 1 hour. Then, Pt30 acts as a catalyst, and a plurality of single-walled carbon nanotubes (hereinafter referred to as “SWNT40”) bonded to the surface of the graphene 20 undergo chemical vapor deposition. In this way, the third step is executed (see FIG. 1D).

  Thereafter, the inside of the chamber is rapidly cooled to room temperature, and a carbon composite composed of the graphite substrate 10, the sheet-like graphene 20 formed on the surface thereof, and a plurality of SWNTs 40 grown on the surface of the graphene 20 is taken out from the chamber. .

  Next, the carbon composite of the Example manufactured with the manufacturing method mentioned above is demonstrated.

In the third step, a field emission type of a carbon composite (hereinafter referred to as “sample 1”) in which an alcohol gas (ethanol) is supplied at a pressure of 1 × 10 ⁻² Pa and a plurality of SWNTs 40 is subjected to chemical vapor deposition. Scanning electron microscope (FESEM) images are shown in FIGS.

In the third step, field emission scanning of a carbon composite (hereinafter referred to as “sample 2”) in which an alcohol gas is supplied at a pressure of 1 × 10 ⁻⁴ Pa and a plurality of SWNTs 40 is subjected to chemical vapor deposition. Images of an electron microscope (FESEM) are shown in FIGS. 2 (c), 2 (d), and 3. FIG. As shown in FIG. 3, each SWNT 40 is bonded to the surface of the graphene 20 and grows in a cobweb shape. Each SWNT 40 is 10 to 150 nm long. The sheet-like graphene 20 has a substantially square shape with a side of about 600 nm. Pt30 is indicated by a fine white dot. Pt30 exists on the surface of the graphene 20 and the graphite substrate 10, but the SWNT 40 grows only from the surface of the graphene 20 and does not grow from the surface of the graphite substrate 10.

4A and 4B and FIGS. 5A and 5B show the results of Raman spectrum measurement of Sample 2 using excitation laser light having a wavelength of 785 nm. A spectrum called a radial bridging mode (RBM) appears in the vicinity of the frequency (Raman shift) indicated on the horizontal axis at 237 cm ⁻¹ . The frequency ω (cm ⁻¹ ) where the peak of the RBM spectrum is located is hereinafter referred to as “RBM Raman shift value”. The RBM Raman shift value ω (cm ⁻¹ ) is inversely proportional to the SWNT diameter D. That is, the diameter D (nm) of the SWNT 40 can be expressed by Equation 1.

Diameter D (nm) = 248 / RBM Raman shift value ω (cm ⁻¹ ) Equation 1

  Therefore, the diameter of each SWNT 40 of sample 2 can be calculated as 1.05 nm.

  Further, as shown in FIGS. 5A and 5B, even if the Raman spectrum is measured by changing the wavelength of the excitation laser beam, the spectrum of the RBM does not appear with the excitation laser beam having a wavelength other than 785 nm. For this reason, each SWNT 40 of sample 2 can be considered to have a single chirality.

Further, as shown in FIG. 5B, Sample 2 has a spectrum called G-band that appears in common with graphite materials at a frequency of around 1590 cm ⁻¹ . Furthermore, a spectrum called D-band caused by a defect appears at a frequency near 1350 cm ⁻¹ . If the nanotube has a point defect or the like, the D-band spectrum becomes strong, so the relative intensity with the G-band spectrum is a measure of the amount of defects.

Next, FIGS. 4C and 4D show the results of Raman spectrum measurement of Sample 1 using excitation laser light having a wavelength of 633 nm. An RBM spectrum appears in the vicinity of a frequency (Raman shift) indicated on the horizontal axis of 284 cm ⁻¹ . For this reason, the diameter of SWNT40 of sample 1 can be calculated as 0.84 nm.

Sample 1 shows a G-band spectrum at a frequency of around 1590 cm ⁻¹ , but does not show a D-band spectrum at a frequency of around 1350 cm ⁻¹ . The SWNT 40 of sample 1 is also considered to have a single chirality because the RBM spectrum does not appear with excitation laser light having a wavelength other than 633 nm.

  It is considered that there is a correlation between the supply pressure of alcohol gas when chemical vapor deposition of SWNT 40 is performed in the third step and the diameter of SWNT 40 chemical vapor grown on the surface of graphene 20 as shown in FIG.

  Next, FIG. 7 shows a Kataura plot showing the relationship between the RBM Raman shift value (the diameter of SWNT 40 calculated from the Raman shift value) obtained by Raman spectrum measurement and the energy of the excitation laser beam. In this Kataura plot, black dots indicate semiconductor-type carbon nanotubes, and white dots indicate metal-type carbon nanotubes.

The energy of the excitation laser beam having a wavelength of 785 nm is 1.58 eV. Moreover, the RBM Raman shift value at the time of performing a Raman spectrum measurement with respect to the sample 2 using the excitation laser beam with a wavelength of 785 nm is 237 cm < ^-1 > (the diameter of SWNT40 is 1.05 nm). When these values are applied to the Kataura plot, it is considered that SWNTs existing in a portion surrounded by a circle A are observed as shown in FIG. Since the SWNT surrounded by the circle A is indicated by a black dot, it can be seen that the SWNT 40 of the sample 2 is a semiconductor type.

The energy of the excitation laser beam having a wavelength of 633 nm is 1.96 eV. The sample 1 has an RBM Raman shift value of 284 cm ⁻¹ (the diameter of SWNT 40 is 0.84 nm) when Raman spectrum measurement is performed using excitation laser light having a wavelength of 633 nm. When these values are applied to the Kataura plot, it is considered that SWNTs existing in a portion surrounded by a circle B were observed as shown in FIG. Since the SWNT surrounded by the circle B is indicated by a black dot, it can be seen that the SWNT 40 of the sample 1 is also a semiconductor type.

  Next, the results of observing Samples 1 and 2 with a high-resolution transmission electron microscope (HR-TEM) will be described.

  In Sample 1, as shown in FIG. 8, SWNTs 40 are grown from graphene 20 around Pt30. The SWNT 40 has a diameter of 0.84 nm. In Sample 2, as shown in FIGS. 9A and 9B, SWNTs 40 are grown from graphene 20 around Pt30. The SWNT 40 has a chiral index of (10, 5) and a diameter of 1.05 nm. The graphene 20 is indicated by a dotted line in FIG.

  As described above, the samples 1 and 2 are a sheet-like graphene 20 and a plurality of SWNTs 40 (single-walled carbon nanotubes) that are bonded to one surface of the graphene 20 and have a semiconductor property with substantially the same diameter. ) And a continuous graphite substrate on the other surface of the graphene 20. In this carbon composite, each SWNT 40 has a single chirality, and each SWNT 40 has substantially the same band gap. For this reason, this carbon composite can be applied to an electronic device or the like as it is by utilizing the characteristics of these SWNT40.

  Moreover, the graphene 20 can be peeled from the graphite substrate 10 to form a carbon composite made of the graphene 20 and the SWNT 40. Thus, even if it is a carbon composite which consists of graphene 20 and SWNT40, it can apply to an electronic device etc. as it is, making use of the characteristic of SWNT40.

  Therefore, the carbon composite manufactured by the carbon composite manufacturing method of the example can have a plurality of carbon tubes exhibiting the same electrical characteristics. Further, the SWNT 40 can be separated from the graphene 20 to make only the SWNT 40. In this way, SWNTs 40 having the same electrical characteristics can be mass-produced.

The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the examples, aqua regia was used as a strongly acidic solution for oxidizing a graphite substrate, but concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide solution, and a mixture of these acids may be used.
(2) In the examples, in order to generate sheet-like graphene on the surface of the graphite substrate, oxidation was performed by immersion in aqua regia for 1 hour, but the immersion time may be changed as appropriate.
(3) In the examples, Pt was present on the surface of graphene to serve as a catalyst for SWNT growth, but other metal fine particles such as Co may be present on the surface of graphene as a catalyst.
(4) In the example, Pt was vapor-deposited on the surface of graphene so that the average film thickness was 0.2 nm in the second step of the carbon composite manufacturing method. You may vapor-deposit on the surface of a graphene so that it may become a thickness of 0.25 nm.
(5) In the example, when chemical vapor deposition of SWNT is performed, the inside of the chamber is heated to 700 ° C., but the heating temperature may be changed as appropriate.
(6) In the example, when chemical vapor deposition of SWNTs was performed, ethanol was supplied into the chamber for 1 hour, but the ethanol supply time may be appropriately changed.
(7) Although ethanol was supplied to the chamber as a carbon source in the examples, a carbon source other than ethanol may be supplied.

1 ... Intermediate 10 ... Graphite substrate (graphite)
20 ... graphene 30 ... Pt (platinum particles) (metal fine particles)
40 ... SWNT (Single-walled carbon nanotube)

Claims (1)

A first step of oxidizing the graphite substrate by immersing it in a strongly acidic solution and generating sheet-like graphene on the surface of the graphite substrate;
A second step of producing an intermediate in which metal fine particles are present at a high density on the surface of the graphene;
A third step of disposing the intermediate in an atmosphere supplied with alcohol gas at a predetermined pressure, and performing chemical vapor deposition of a plurality of single-walled carbon nanotubes bonded to the surface of the graphene by the metal fine particles acting as a catalyst; And a method for producing a carbon composite.