JP2006188382A - Method for producing carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form carbon nanotubes while dispensing with a step of applying a catalyst. <P>SOLUTION: A plasma generation coil 2 connected to a high-frequency power source 3 is placed in a vacuum chamber 1. A wire 4 containing a metal catalyzing the formation of carbon nanotubes is supportably passed into the coil 2. The wire 4 is heated by passing an electric current therethrough. A negative bias voltage is applied from a bias power source 8. A raw material gas is fed to form a plasma 9. A film of carbon nanotubes is then formed on the wire 4 by the catalysis of the metal contained in the wire 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Carbon nanotubes are materials that are expected to have many applications such as displays, lamps, nanodevices, and electron guns.

As a method for producing this carbon nanotube, a substrate on which a catalyst has been formed in advance is placed in an apparatus and heated, and a source gas is supplied to thermally decompose the source gas, and carbon is grown using the catalyst on the substrate as a seed. There is a vapor phase growth method (for example, Patent Document 1).
JP 2002-180252 A

  However, in this vapor phase growth method, in order to grow carbon nanotubes, there is a problem that a step of forming a catalyst in advance on a base material such as a substrate is required.

  An object of the present invention is to make it possible to produce carbon nanotubes without previously forming a catalyst on a substrate.

  The present invention is configured as follows in order to achieve the above-described object.

  That is, the present invention is a method for forming a carbon nanotube on a base material by converting the raw material gas introduced into the vacuum chamber into a plasma, and heating the base material and applying a bias voltage to the base material It is.

  Here, the base material refers to an object on which the carbon nanotube is formed, and its shape is not limited, and includes, for example, a substrate, a wire, and the like. This base material is preferably made of a catalyst metal that serves as a catalyst for the formation of carbon nanotubes, for example, a material containing Fe, Ni, Co, etc., such as stainless steel. Furthermore, it is preferable that this base material is heated by energization.

  The bias voltage is preferably a negative DC bias voltage. The negative bias voltage is preferably a voltage whose absolute value is greater than 100V.

  In addition, it is preferable that a plasma generating coil to be supplied with a high frequency power source is provided in the vacuum chamber, and the base material is disposed in the plasma generating coil.

  According to the present invention, carbon nanotubes can be formed without requiring a step of previously applying a catalyst metal to a substrate as in the prior art. This is considered as follows. That is, since a bias voltage is applied to the base material and the surface of the base material is sputtered, the catalyst metal fine particles ejected from the surface of the base material are removed by using the base material containing the catalytic metal. It is considered that carbon nanotubes are formed by using the fine particles of the catalyst metal adhering to the surface of the catalyst metal as a seed.

  According to the present invention, carbon nanotubes can be produced without requiring a step of applying a catalyst in advance.

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

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a manufacturing apparatus to which a manufacturing method according to an embodiment of the present invention is applied.

  The manufacturing apparatus includes a vacuum chamber 1, and a plasma generating coil 2 is installed in the vacuum chamber 1. The plasma generating coil 2 is made of, for example, Cu, Ni, stainless steel, carbon or the like, and is connected to the high frequency power source 3. The high frequency power supply 3 supplies high frequency power of 13.56 MHz, for example.

  In this plasma generating coil 2, a base material for forming carbon nanotubes, in this embodiment, for example, a wire 4 having a diameter of 1 mm is inserted and disposed. The wire 4 preferably contains a metal that serves as a catalyst for the formation of carbon nanotubes, and is made of, for example, stainless steel, Fe, Ni, or the like.

  In addition, a heating power source 5 is connected to the wire 4 and is heated by energization to, for example, about 700 ° C. to 800 ° C. The wire 4 is not limited to a linear shape, and may be a coil shape or a wave shape, or may be a twisted piece of a plurality of wires.

The vacuum chamber 1 is provided with a gas introduction part 6 and a gas exhaust part 7, and a raw material gas such as a hydrocarbon gas and a carrier gas such as CH ₄ / H ₂ , CH ₄ / Ar from the gas introduction part 6. , CH ₄ / O ₂ is introduced, and the treated gas is exhausted from the gas exhaust unit 7.

  The gas pressure (total pressure) is preferably about 10 Pa to 1000 pa.

  In this embodiment, a bias power supply 8 is connected to the wire 4, and a negative DC bias voltage is applied to the wire 4.

  In the manufacturing apparatus of this embodiment, the wire for forming the carbon nanotubes is provided in the plasma generating coil 2 in the vacuum chamber 1 without passing through a step of previously forming a catalytic metal as in the prior art. 4 is inserted and supported.

  Next, while energizing and heating the wire 4, a negative bias voltage is applied, and further, high-frequency power is supplied to the plasma generating coil 2, and the flow rate of the raw material gas and the like from the gas introduction unit 6 is controlled. While introducing.

  In the plasma generating coil 2, plasma 9 is generated, the source gas is excited, and carbon nanotubes are formed on the wire 4.

  That is, in this embodiment, carbon nanotubes can be formed on the wire 4 without forming a catalyst metal in advance.

  This is because, since a negative bias voltage is applied to the wire 4, the surface of the wire 4 is sputtered, and the catalyst metal fine particles contained in the sputtered wire 4 have a relatively high gas pressure. Therefore, it is considered that carbon nanotubes grow by being attracted to the wire 4 side and attached to the surface of the wire 4 and using this as a catalyst.

  Next, the state of the formed film and its electron emission characteristics were evaluated when the film forming conditions, particularly the bias voltage was changed.

  As shown in FIG. 2, the electron emission characteristics are as follows: a wire 4 on which a carbon nanotube is formed is disposed between the anode 10 and the anode 10 in a vacuum, and a DC voltage is applied using the wire 4 as a cathode. The measurement was performed by applying and measuring the emission current at 5 V / μm.

  Table 1 shows the film formation conditions, electron emission characteristics, and evaluation results of the film state by SEM images.

In Table 1, the input is the high frequency power supplied to the plasma generating coil 2, the voltage and current are the voltage and current for energization heating of the wire 4, the time is the film formation time, and the temperature is The wire temperature, the pressure represents the total pressure of CH ₄ and H ₂ , and the electron emission characteristic represents the emission current measured as described above.

  SEM images corresponding to the respective conditions are shown in FIGS. In each figure, (b) is a partially enlarged view of (a).

  Condition No. in which no bias voltage is applied In 1, a small growth of carbon nanowall (CNW) was observed, but no electron emission current at 5 V / μm was observed.

  Condition No. 2-5, as the absolute value of the negative bias voltage is increased, the growth of the carbon nanowall (CNW) increases, and further, the graphite grows, and the electron emission current at 5 V / μm increases. An increase was observed.

  Furthermore, condition no. As shown in FIGS. 6 to 8, when the bias voltage is −160 V, the growth of carbon nanotubes (CNT) is recognized, and the condition NO. 7 and 8, an electron emission current at 5 V / μm was observed.

  The absolute value of the negative bias voltage is preferably a value exceeding 100.

  Thus, by performing plasma CVD while applying a negative bias voltage to the wire 4, carbon nanotubes can be formed on a wire or substrate on which no catalyst has been previously formed.

  When the base material such as the wire 4 or the substrate for forming the carbon nanotube is long and protrudes from the plasma generation region of the plasma generating coil 2, the base material such as the wire 4 or the substrate is attached to the plasma generating coil. The plasma generating coil 2 may be moved relative to the base material to form the carbon nanotubes over the entire length of the base material.

  In addition, as shown in FIG. 11, when the base material such as the wire 4 or the substrate is longer than the plasma generating coil 2, the plurality of plasma generating coils 2 are arranged in the longitudinal direction of the base material such as the wire 4. The plasma may be formed on the entire substrate so that the plasma generated in each of the plasma generating coils 2 overlaps with each other.

  Further, as shown in FIG. 12, the winding diameter of the central portion 2a in the longitudinal direction of the plasma generating coil 2 is increased and the winding diameter of both end portions 2b is decreased so that the plasma is efficiently confined in the central portion. The film formation rate may be increased.

(Other embodiments)
The present invention is applied to the capacitively coupled plasma CVD apparatus shown in FIG. 13 or the inductively coupled plasma CVD apparatus shown in FIG. 14, and applies a negative bias voltage to the substrate 11 such as a substrate or a wire. Heating may be performed indirectly by the heater 12 or the like.

  As another embodiment of the present invention, the bias voltage may be applied only at the initial stage of carbon nanotube film formation.

  The present invention is useful for the production of carbon nanotubes used in various applications.

It is a schematic block diagram of the apparatus which enforces the manufacturing method of the carbon nanotube which concerns on embodiment of this invention. It is a figure for demonstrating the evaluation method of an electron emission characteristic. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a SEM image which shows the state of the film | membrane from which film-forming conditions differ. It is a figure which shows the modification of the coil for plasma generation of FIG. It is a figure which shows the other modification of the coil for plasma generation of FIG. It is a figure which shows the other example of the apparatus of FIG. FIG. 6 shows yet another example of the apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Coil for plasma generation 3 High frequency power supply 4 Wire (base material)
5 Power supply for heating 8 Bias power supply

Claims (6)

A method of forming a carbon nanotube on a base material by converting a raw material gas introduced into a vacuum chamber into plasma,
A method for producing a carbon nanotube, comprising heating the base material and applying a bias voltage to the base material.   The method of manufacturing a carbon nanotube according to claim 1, wherein the bias voltage is a negative DC bias voltage.   The method for producing carbon nanotubes according to claim 1 or 2, wherein the base material contains a catalytic metal serving as a catalyst for forming carbon nanotubes.   The manufacturing method of the carbon nanotube of any one of Claims 1-3 in which the said base material is electrically heated.   The method for producing carbon nanotubes according to claim 4, wherein the base material is a stainless steel wire.   The plasma generating coil to which a high-frequency power is supplied is provided in the vacuum chamber, and the base material is disposed in the plasma generating coil. A method for producing carbon nanotubes.