KR101313746B1 - Manufacturing method for carbon nanotube - Google Patents

Abstract

The present invention relates to a low temperature mass synthesis method of carbon nanotubes in which carbon nanotubes are directly synthesized in large quantities at low temperature on a metal substrate without the aid of a buffer layer.
In the present invention, iii) surface oxidation of a metal substrate containing any one of nickel, chromium and iron or a plurality of transition metal elements in a heat treatment furnace; Ii) plasma pretreatment of the oxidized metal substrate in a plasma apparatus; And iii) synthesizing the carbon nanotubes by thermochemical vapor deposition using any one or a plurality of carbon source gases of acetylene gas, methane gas, propane gas and ethylene gas in a thermal chemical vapor deposition (CVD) apparatus. A synthetic method is presented.

Description

Low Temperature Bulk Synthesis Method of Carbon Nanotubes {MANUFACTURING METHOD FOR CARBON NANOTUBE}

The present invention relates to a method for mass-synthesizing carbon nanotubes at low temperature, and more particularly, to a method for producing carbon nanotubes on a metal substrate by low-temperature mass synthesis.

Carbon nanotubes are attracting attention as next-generation materials in various fields because of their excellent physical, chemical and electrical properties.

There are various methods for synthesizing carbon nanotubes. One of them is thermochemical vapor deposition (CVD), which has the advantage of synthesizing carbon nanotubes having a large uniform microstructure.

In order to synthesize carbon nanotubes by the CVD method, a catalyst of a transition metal is required, and a high temperature process is inevitably required to decompose a raw material gas containing carbon.

In addition, the catalytic metal heat-treated at a high temperature is nano-particles to serve as a place for the nucleus of carbon nanotubes to generate and grow. As such, the CVD process for synthesizing carbon nanotubes should be performed at high temperature for nanoparticles of catalyst and efficient decomposition of source gas, and is generally synthesized at around 700 ° C to 900 ° C.

On the other hand, glass substrates, which are mainly used as substrates for nanoelectronic devices and field emission display devices (FEDs), have a deformation temperature of about 650 ° C., and are known to have a melting point of about 700 ° C. for aluminum, which is currently used for electric wiring of devices. In order to directly synthesize and apply carbon nanotubes in the field, a low temperature process is essential.

Until now, plasma chemical vapor deposition (PECVD) has been mainly used for low temperature synthesis of carbon nanotubes. However, such a plasma process has a problem that the structure of the carbon nanotubes is damaged by ion irradiation during the process, there is a difficulty in the large area of the plasma process, and the production is limited accordingly.

On the other hand, when synthesizing carbon nanotubes on a synthetic substrate such as a silicon wafer, in order to prevent alloying between the catalyst metal and the substrate material, a complete layer such as a silicon oxide film and an aluminum oxide film is generally deposited.

However, this method works because the characteristics are deteriorated in the field where high conductivity of carbon nanotubes such as a field emission device (FED) is required.

The present invention is to solve the above-described problems, the present invention is to provide a production method for mass-synthesizing carbon nanotubes directly on a metal substrate at low temperature without the aid of a buffer layer.

The low-temperature mass synthesis method of carbon nanotubes according to an embodiment of the present invention includes the steps of: i) surface oxidation of a metal substrate containing any one of nickel, chromium and iron or a plurality of transition metal elements in a heat treatment furnace; Ii) plasma pretreatment of the oxidized metal substrate in a plasma apparatus; And iii) synthesizing the carbon nanotubes by thermochemical vapor deposition using any one or a plurality of carbon source gases of acetylene gas, methane gas, propane gas and ethylene gas in a thermal chemical vapor deposition (CVD) apparatus. It provides a synthetic method to make.

In the low temperature synthesis method of carbon nanotubes according to the present invention, it is preferable to use either Inconel 600 or stainless steel as the metal substrate.

In the low temperature synthesis method of carbon nanotubes according to the present invention, i) the surface oxidation treatment step of the metal substrate is preferably heated to 500 ° C. to 750 ° C. under an air atmosphere and then maintained for 5 minutes to 30 minutes for oxidation treatment.

In addition, in the low temperature synthesis method of carbon nanotubes, the plasma pretreatment step of ii) the metal substrate may be performed in an inert gas atmosphere to raise the temperature of the reaction chamber to 500 ° C. to 600 ° C. and to maintain the temperature for 5 to 20 minutes. It is preferable to supply a plasma to generate a plasma and to maintain the conditions for generating such plasma for 20 to 60 minutes.

As the inert gas used in this plasma pretreatment step, argon gas is preferably used.

In the plasma pretreatment step, the vacuum degree of the reaction chamber is preferably 0.1 Torr to 30 Torr.

In the low temperature synthesis method of the carbon nanotubes of the present invention, iii) thermochemical vapor deposition supplies a gas mixed with an inert gas and hydrogen gas into the reaction chamber of the thermochemical vapor deposition apparatus, and supplies power to the thermochemical vapor deposition apparatus. After the temperature of the metal substrate reaches 350 ℃ ~ 750 ℃ it is preferably maintained for 5 minutes to 30 minutes, and then supplying the carbon source gas into the reaction chamber to synthesize the carbon nanotubes.

In the thermochemical vapor deposition, the carbon nanotubes may be synthesized while supplying the carbon source gas and maintaining the temperature of the metal substrate for 20 to 60 minutes.

In the thermochemical vapor deposition, it is preferable to synthesize the carbon nanotubes in a state where the temperature of the metal substrate is 450 ° C. or less.

According to the embodiments of the present invention, when synthesizing carbon nanotubes through a thermochemical vapor deposition method after a pretreatment process in which a metal substrate is mixed with an oxidative heat treatment and a plasma treatment, there is a technical effect of synthesizing the carbon nanotubes even at a low temperature.

In addition, when synthesizing carbon nanonueves by the thermal chemical vapor deposition method after such a pretreatment can significantly improve the synthesis yield of carbon nanotubes.

In the case of synthesizing carbon nanotubes by the thermal chemical vapor deposition method after such pretreatment, carbon nanotubes having good physical properties can be synthesized by applying metals containing catalyst metals without the process of depositing a separate metal catalyst.

In addition, when synthesizing carbon nanotubes by the thermal chemical vapor deposition method after such a pretreatment, the metal substrate to be used can be reused without a separate catalyst deposition process, so that mass production is possible, and thus it is excellent in terms of economic efficiency.

When the carbon nanotubes are synthesized by the thermal chemical vapor deposition after the pretreatment, the oxide buffer layer is not deposited on the substrate. Therefore, the interface between the grown carbon nanotubes and the metal substrate has a technical effect of improving electrical conductivity and mechanical adhesive strength. .

In addition, when controlling the plasma applied voltage in the plasma pretreatment process, there is a technical effect that can control the carbon nanotube yield.

1 is a schematic diagram of a heat treatment furnace for an oxidation pretreatment process according to an embodiment of the present invention.
2 is a schematic diagram of a plasma processing apparatus for a plasma pretreatment process according to an embodiment of the present invention.
3 is a process diagram for synthesizing carbon nanotubes on a metal substrate by thermochemical vapor deposition after pretreatment according to an embodiment of the present invention.
Figure 4 is a graph measuring the height of the carbon nanotubes changed according to the temperature of each thermal chemical vapor deposition for the carbon nanotubes synthesized according to the Examples and Comparative Examples of the present invention.
5 is a real picture of the carbon nanotubes synthesized according to the Examples and Comparative Examples of the present invention.
Figure 6 is a graph showing the Raman spectrum analysis results for the carbon nanotubes synthesized according to an embodiment of the present invention.
FIG. 7 is a scanning electron micrograph of a carbon nanotube synthesized at 375 ° C. according to one embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

An embodiment of the present invention relates to a method for synthesizing carbon nanotubes by thermochemical vapor deposition.

Carbon nanotube synthesis according to an embodiment of the present invention is first oxidized pretreatment of the metal substrate and then plasma pretreatment, followed by synthesis of carbon nanotubes by thermochemical vapor deposition (CVD).

To this end, first, a process of oxidizing and pretreating a metal substrate will be described.

1 is a schematic diagram of a heat treatment furnace for an oxidation pretreatment process according to an embodiment of the present invention.

The oxidation pretreatment process of the metal substrate according to the present embodiment is performed in a heat treatment furnace. Referring to FIG. 1, the heat treatment furnace is disposed in a state where the reaction tube 10 penetrates into the resistance heat treatment furnace 30, and the reaction tube is preferably a thermally stable tube such as quartz. One end of the reaction tube 10 is sealed to form an inlet for gas inflow, and a flow meter 31 is installed between the inlet and the reaction tube 10 to control the gas supplied into the reaction tube 10. A vacuum pump 33 is disposed at the other end of the reaction tube 10 to seal the other side of the reaction tube 10 and to control the degree of vacuum in the reaction tube 10 by using the vacuum bump 33. The heat treatment gas is discharged through the outside of the bump 33.

The substrate support 20 is disposed in the reaction tube 10, and the metal substrate 21 is disposed on the substrate support 20.

As the metal substrate 21 used in the present embodiment, a plate-like metal containing a transition metal catalyst such as nickel, chromium or iron may be used. Preferably, Inconel 600 or stainless steel 316L is used. Here, when Inconel or stainless steel is used as a substrate, a transition metal such as nickel, chromium, or iron in the steel acts as a catalyst for growing carbon nanotubes, so a separate catalyst deposition process is not necessary in this embodiment.

Such metal substrates can be subjected to conventional surface treatments prior to oxidation pretreatment. That is, the surface may be polished, or the metal substrate may be ultrasonically cleaned, washed sequentially or separately with acetone or methanol, and then dried.

The metal substrate is oxidized and heat-treated using the heat treatment furnace described above. In the oxidative heat treatment, the substrate support 20 is first charged into the reaction tube 10 and the metal substrate 21 is disposed on the substrate support 20. In this state, the vacuum bump 33 is operated while the heat treatment furnace 30 is heated, and the flow meter 31 is controlled to inject air into the reaction tube 10. The heat treatment furnace 30 is heated to 500 ° C. to 750 ° C., and the metal substrate is oxidized while maintaining this temperature section for 5 to 30 minutes.

The following describes a process of plasma pretreatment of an oxide pretreated metal substrate.

2 is a schematic diagram of a plasma processing apparatus for a plasma pretreatment process according to an embodiment of the present invention.

Plasma pretreatment of the metal substrate according to the present embodiment is performed in a plasma apparatus. Referring to FIG. 2, in the plasma apparatus, a gas injection unit 41 for supplying an atmosphere gas into the reaction chamber 40 is disposed on a part of a side wall of the reaction chamber 40, and a reaction gas is disposed on the injection unit 41 side. Flow meter (not shown) for controlling the is installed. In addition, a gas exhaust part 43 for discharging the atmosphere gas reacted in the reaction chamber 40 is disposed on a part of the other side wall of the reaction chamber 40, and a vacuum bump 45 is connected to the exhaust part 43. To control the degree of vacuum in the reaction chamber 40.

The upper electrode 50 is provided above the reaction chamber 40, and the lower electrode 51 is provided below. The lower electrode 51 is also used as a substrate support, and an oxide pretreated metal substrate 21 is disposed on the lower electrode 51. In addition, a resistance heating element 53 capable of heating the lower electrode may be disposed below the lower electrode 51. The resistance heating element 53 may be configured in the form of a coil.

DC reaction power or RF power may be applied to the reaction chamber 40.

When the DC power is applied, the upper electrode 50 becomes a ground electrode, and a plasma is formed between the upper electrode 50 and the lower electrode 510 by applying a DC voltage to the lower electrode 51.

In addition, when the RF power is applied, a high frequency voltage is applied to the upper electrode 50 from the RF power to form a plasma in the space between the upper electrode 50 and the lower electrode 51.

The plasma substrate is subjected to plasma pretreatment using the plasma apparatus described above.

Plasma pretreatment first arranges the metal substrate 21 subjected to oxidation pretreatment on the lower electrode 51 in the reaction chamber 40. In this state, the vacuum bump 45 is operated to control the degree of vacuum in the reaction chamber 40. In addition, the flow meter of the gas injection unit 41 is controlled to supply the reaction gas into the reaction chamber 40. At this time, the reactive gas to be supplied is preferably an inert gas, more preferably argon (Ar) gas.

In this state, when the plasma power supply is operated to supply a voltage to the substrate, plasma is generated from the atmospheric gas. At this time, the conditions of the reaction chamber are first raised to a temperature of 500 ~ 600 ℃ inside the reaction chamber 40 and maintained for 5 to 20 minutes, then supplying power to generate a plasma and 20 Hold for minutes to 60 minutes. At this time, the vacuum degree of the vacuum chamber 40 is preferably maintained at 0.1 Torr to 30 Torr. After the plasma treatment is completed, the power is turned off to cool the reaction chamber 40.

The following describes a process of synthesizing carbon nanotubes on a plasma-treated metal substrate in a thermochemical vapor deposition (CVD) apparatus.

The thermochemical vapor deposition (CVD) apparatus used in the embodiment of the present invention is the same as the thermochemical vapor deposition apparatus commonly used, so the description of this apparatus is omitted.

In the thermochemical vapor deposition according to the embodiment of the present invention, a plasma-treated metal substrate is first charged into a thermochemical vapor deposition apparatus, and then a thermochemical vapor deposition process is performed.

As the carbon source gas used for synthesizing the carbon nanotubes in the embodiment of the present invention, acetylene gas, methane gas, propane gas or ethylene gas may be used, and an inert gas or hydrogen gas may be mixed with the carbon source gas. .

In the case of the present invention, the mixing ratio of the gas at the temperature raising and holding (holding) of the deposition apparatus is Ar: H ₂ = 900: 100 sccm, the mixing ratio of the gases in the deposition apparatus when synthesizing carbon nanotubes is Ar: H ₂ : C It is preferred that ₂ H ₂ = 500: 500: 50 sccm.

Thermochemical vapor deposition first supplies a gas in which an inert gas and hydrogen gas are mixed as an atmosphere gas to the deposition apparatus, and gradually increases the temperature by operating a heat source to the deposition apparatus while the atmosphere gas is supplied. Then, when the temperature of the plasma-treated metal substrate reaches 350 ℃ ~ 750 ℃ it is maintained for about 5 to 30 minutes.

Next, a carbon source gas is supplied into the deposition apparatus to synthesize carbon nanotubes. At this time, the temperature in the deposition apparatus is maintained while the carbon source gas is supplied, and the holding time is preferably 20 minutes to 60 minutes.

In this case, the thermal chemical vapor deposition is preferably synthesized carbon nanotubes in the state that the temperature of the metal substrate is 450 ℃ or less.

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Examples>

Inconel 600 was used as a substrate to synthesize carbon nanotubes. The Inconel 600 in the state of lamination was polished with abrasive paper and then put in an ultrasonic cleaning bath and washed with acetone for 10 minutes, and then washed with methanol for 10 minutes.

It was then charged into a dryer to dry the substrate.

The specimen size of Inconel 600 was 3 cm x 3 cm x 0.8 cm.

The metal substrate thus prepared was disposed above the substrate support 20 in the reaction tube 10 described in the heat treatment furnace of FIG. In this state, the vacuum bump 33 was operated while the heat treatment furnace 30 was heated, and the flow meter 31 was controlled to inject air into the reaction tube 10.

At this time, the metal substrate 21 in the reaction tube was heated to 725 ° C., and then the metal substrate was oxidized while being kept at this temperature section for 10 minutes.

Then, the oxidized metal substrate was charged into the reaction chamber 40 of the plasma apparatus and subjected to plasma pretreatment.

In the plasma pretreatment, the vacuum bump 45 was first operated to control the degree of vacuum in the reaction chamber 40 to 0.5 torr. In addition, argon (Ar) gas was supplied into the reaction chamber 40 by controlling the flow meter of the gas injection part 41. At this time, the conditions of the reaction chamber were first raised to a temperature of 525 ° C. in the reaction chamber 40 and maintained for 10 minutes. Then, a voltage was applied to the substrate to generate plasma, and the conditions for generating such plasma were maintained for 30 minutes. .

The cooled plasma treated metal substrate was then loaded into a CVD apparatus and grown with carbon nanotubes with varying temperature conditions.

Thermochemical vapor deposition was first supplied to the vapor deposition apparatus gas mixture of argon gas and hydrogen gas as the atmosphere gas, and the temperature was gradually raised by operating the heat source to the vapor deposition apparatus while the atmosphere gas is supplied.

In this case, the mixing ratio of argon gas and hydrogen gas was Ar: H ₂ = 900: 100 sccm.

Then, when the temperature of the plasma-treated metal substrate reached 375 ℃ ~ 725 ℃ was maintained for about 10 minutes. Herein, carbon nanotubes were grown under different temperature conditions by setting the temperature of the metal substrate to 375 ° C., 400 ° C., 425 ° C., 475 ° C., 525 ° C., 625 ° C., and 725 ° C., respectively.

As described above, carbon nanotubes are synthesized by supplying acetylene (Acethylene: C ₂ H ₂ ) gas as a carbon source gas into the deposition apparatus while the metal substrate is heated. At this time, the temperature in the vapor deposition apparatus was maintained while the acetylene gas was supplied, and the holding time was 30 minutes.

In synthesizing carbon nanotubes, the ratio of argon gas, hydrogen gas and acetylene gas in the deposition apparatus was Ar: H ₂ : C ₂ H ₂ = 500: 500: 50 sccm.

3 shows a process diagram for synthesizing the carbon nanotubes of the metal substrate described above by thermochemical vapor deposition.

<Comparative Example>

In the comparative example, only the thermochemical vapor deposition was performed without performing the oxidation pretreatment and the plasma pretreatment using the same metal substrate used in the above-described embodiment. The thermochemical vapor deposition conditions in the comparative example are the same as in the examples.

The carbon nanotubes synthesized according to the above-described examples and comparative examples were measured for the carbon nanotubes changed according to the temperature of each thermochemical vapor deposition.

The growth results of the carbon nanotubes thus measured are shown in FIG. 4.

Referring to Figure 4 the height of the carbon nanotubes synthesized according to an embodiment of the present invention is the height of the carbon nanotubes grown at 375 ℃ grows with increasing temperature as the temperature increases the carbon nanotubes grown under the conditions of 525 ℃ The height is highest and then gradually decreases, indicating that carbon nanotubes are grown even at 725 ° C.

On the other hand, it was found that carbon nanotubes hardly grew when the metal substrate was not subjected to oxidation pretreatment and plasma pretreatment as in the comparative example.

Figure 4 shows the results of the experiment as it is, according to the embodiment of the present invention was able to synthesize carbon nanotubes without performing a process of depositing a separate metal catalyst, the height of the synthesized carbon nanotubes is also very It was found that the synthesis yield was also significantly improved. In addition, it was confirmed that carbon nanotubes were synthesized even at a low synthesis temperature of 375 ° C., and thus, carbon nanotubes could be synthesized even at low temperature when the oxidation and plasma pretreatment were performed as in the present embodiment.

In addition, since the carbon nanotubes synthesized according to the present embodiment do not use a buffer layer such as an oxide film on the metal substrate, it was confirmed that the electrical conductivity and mechanical adhesive strength at the interface between the synthesized carbon nanotubes and the metal substrate were good.

In FIG. 5, the carbon nanotubes synthesized according to the comparative example are shown on the left side, and a real picture of the carbon nanotubes synthesized according to the example is shown on the right side.

Referring to FIG. 5, the comparative example without oxidation and plasma pretreatment showed very low yield of carbon nanotubes, whereas the embodiment with oxidation and plasma pretreatment showed very high yield of carbon nanotubes. Could.

In order to analyze crystallinity of the carbon nanotubes synthesized according to the example shown on the right side of FIG. 5, Raman spectra were analyzed and the results are shown in FIG. 6.

Referring to Figure 6, in the case of carbon nanotubes synthesized according to each temperature of the embodiment within the temperature range of the embodiment regardless of the temperature change (375 ℃, 400 ℃, 425 ℃, 475 ℃, 525 ℃, 625 ℃, 725 ℃ In the C), carbon nanotubes were synthesized, and all of the synthesized carbon nanotubes had good crystallinity.

7 shows a scanning electron micrograph of the carbon nanotubes synthesized at 375 ° C. which is one of the examples.

Referring to FIG. 7, carbon nanotubes were well synthesized even at a low temperature of 375 ° C., and thus, carbon nanotubes synthesized at low temperature had good crystallinity.

As mentioned above, preferred embodiments of the present invention have been described, but the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

10: reaction tube 20: substrate support
21: metal substrate 30: heat treatment furnace
31: flow meter 33: vacuum pump
40: reaction chamber 41: gas injection unit
43: gas exhaust 45: vacuum pump
50: upper electrode 51: lower electrode
53: resistance heating element

Claims (9)

Surface oxidation of a metal substrate containing any one of nickel, chromium and iron or a plurality of transition metal elements in a heat treatment furnace;
Plasma pretreatment of the oxidized metal substrate in a plasma apparatus; And
Synthesizing the carbon nanotubes by thermochemical vapor deposition using any one or a plurality of carbon source gases of acetylene gas, methane gas, propane gas, and ethylene gas in a thermal chemical vapor deposition (CVD) apparatus of the plasma pretreated metal substrate; Including,
The surface oxidation treatment step of the metal substrate is heated to 500 ℃ ~ 750 ℃ under an air atmosphere and then maintained for 5 to 30 minutes to oxidize,
In the plasma pretreatment step of the metal substrate, the inside of the reaction chamber is heated to a temperature of 500 ° C. to 600 ° C. under an inert gas atmosphere and maintained therefor for 5 to 20 minutes, and then the plasma apparatus is supplied with power to generate plasma. Keep the condition occurring for 20 to 60 minutes,
The inert gas is a low temperature mass synthesis method of carbon nanotubes are argon gas. The method of claim 1,
The metal substrate is a low temperature mass synthesis method of carbon nanotubes of either Inconel 600 or stainless steel. delete delete delete The method of claim 1,
The plasma pretreatment step is a low-temperature mass synthesis method of carbon nanotubes in which the vacuum degree of the reaction chamber is 0.1 Torr to 30 Torr. The method of claim 1,
The thermochemical vapor deposition supplies a gas in which an inert gas and hydrogen gas are mixed into the reaction chamber of the thermochemical vapor deposition apparatus, and supplies power to the thermochemical vapor deposition apparatus so that the temperature of the metal substrate reaches 350 ° C to 750 ° C. And then maintaining for 5 to 30 minutes, and then supplying the carbon source gas into the reaction chamber to synthesize carbon nanotubes. The method of claim 7, wherein
The thermochemical vapor deposition is a low-temperature mass synthesis method of carbon nanotubes to synthesize the carbon nanotubes while supplying the carbon source gas and maintaining the temperature of the metal substrate for 20 to 60 minutes. 9. The method of claim 8,
The thermochemical vapor deposition is a low-temperature mass synthesis method of carbon nanotubes for synthesizing the carbon nanotubes in a state where the temperature of the metal substrate is 450 ℃ or less.

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