Method of forming carbon nanotubes

Details Method of forming carbon nanotubes Method of forming carbon nanotubes

2000-04-21

2001-12-18

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S094000, C117S095000, C117S103000, C117S929000, C423S44500R

Reexamination Certificate

active

06331209

ABSTRACT:

This disclosure is based on Korean Patent Applications Nos. 99-14306 and 00-19559 filed on Apr. 21, 1999 and Apr. 14, 2000, respectively, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming carbon nanotubes, and more particularly, to the growth and purification of carbon nanotubes using plasma.
2. Description of the Related Art
Carbon, the most important constituent element, which is combined with oxygen, hydrogen, nitrogen and the like, of all organisms including the human body, has four unique crystalline structures including diamond, graphite, fullerene and carbon nanotubes. In particular, carbon nanotubes refer to a helical tubular structure grown with a single wall or multi-wall, which can be obtained by rolling up a sheet formed of a plurality of hexagons, the sheet formed by combining each carbon atom thereof with three neighboring carbon atoms. The carbon nanotubes have a diameter in the order of a few nanometers to a few hundred nanometers. Carbon nanotubes can function as either a conductor, like metals, or a semiconductor, according to the rolled shape and the diameter of the helical tubes. Also, its hollow structure with a predetermined length allows for good mechanical, electrical and chemical properties, so that carbon nanotubes are known to be a material for field emission devices, hydrogen containers and electrodes of rechargeable batteries.
Originally, carbon nanotubes produced by an arc discharge between two graphite rods was discovered and reported in an article entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58) by Sumio lijima. This technique is commonly used to produce carbon nanotubes, however, yield of pure carbon nanotubes with respect to the end product is only about 15%. Thus, a complicated purification process must be carried out for particular device applications.
Another conventional approach to produce carbon nanotubes, which was described in an article entitled “Epitaxial Carbon Nanotube Film Self-organized by Sublimation Decomposition of Silicon Carbide” (AppI. Phys. Lett. Vol. 71, pp. 2620, 1977), by Michiko Kusunoki, is to produce carbon nanotubes at high temperatures by irradiating a laser onto graphite or silicon carbide. In this case, the carbon nanotubes are produced from graphite at about 1200° C. or more and from silicon carbide at about 1600 to 1700° C. However, this method also requires multiple stages of purification which increases the cost. In addition, this method has difficulties in large-device applications.
A method of producing carbon nanotubes through a thermal decomposition of hydrocarbon series gases by chemical vapor deposition (CVD) was reported by W. Z. Li et al. in an article entitled “Large-Scale Synthesis of Aligned Carbon Nanotubes” (Science, Vol. 274, Dec. 6, 1996, pp. 1701-1703). This technique is applicable only with a gas that is unstable, such as acetylene or benzene. For example, a methane (CH
4
) gas cannot be used to produce carbon nanotubes by this technique.
SUMMARY OF THE INVENTION
It is an objective of the present invention is to provide a method of forming carbon nanotubes, in which carbon nanotubes are grown with a high density using a high-density plasma.
It is another objective of the present invention to provide a method of forming carbon nanotubes, in which carbon nanotubes are purified by removing graphite or carbon particles using a high-density plasma, so that carbon nanotubes can be easily grown with a high density.
To achieve the first objective of the present invention, there is provided a method of forming carbon nanotubes, in which a carbon nanotubes layer is grown on a substrate using a plasma chemical vapor deposition method at a high density of10
11
cm
−3
or more. Preferably, the substrate is an amorphous silicon or polysilicon substrate on which a catalytic metal layer is formed. In the growth of the carbon nanotube layer, a hydrocarbon series gas may be used as a plasma source gas, the temperature of the substrate may be in the range of 600 to 900° C., and the pressure may be in the range of 10 to 1000 mTorr.
To achieve the second objective of the present invention, there is provided a method of forming carbon nanotubes, comprising growing a carbon nanotube layer on a substrate to have a predetermined thickness by plasma deposition. Next, the carbon nanotube layer is purified by plasma etching. Then the growth and the purification of the carbon nanotube layer are repeated.
Preferably, growing the carbon nanotube layer is carried out by a plasma chemical vapor deposition method at a high plasma density of10
11
cm
−3
or more. In purifying the carbon nanotube layer, a halogen-containing gas or an oxygen containing gas may be used as a plasma source gas for etching.
According to the present invention, high-density carbon nanotubes can be grown by decomposing a stable CH
4
gas with high-density plasma. Also, high-purity carbon nanotubes can be formed easily by repeating the growth and purification of carbon nanotubes.


REFERENCES:
patent: 5698175 (1997-12-01), Hiura et al.
patent: 5916642 (1999-06-01), Chang
patent: 6062931 (2000-05-01), Chuang et al.
patent: 6097138 (2000-08-01), Nakamoto
patent: 6156256 (1999-06-01), Kennel
patent: 6159538 (2000-12-01), Rodriguez et al.
patent: 5-133048 (1993-05-01), None
patent: 8-12310 (1996-01-01), None
C. Journet et al., “Large-scale production of single-walled carbon nanotubes by the electric-arc technique,” Nature, vol. 388, Aug. 21, 1977, pp. 756-758.
D.S. Bethune et al., “Cobalt-catalysed growth of carbon nanotubes with single-atomic-layer walls,” Nature, vol. 363, Jun. 17, 1993, pp. 605-607.
A. Thess et al., “Crystalline Ropes of Metallic Carbon Nanotubes,” Science, vol. 273, Jul. 26, 1996, pp. 483-487.
R. Andrews et al., “Continuous production of aligned carbon nanotubes: a step closer to commercial realization,” Chemical Physics Letters, Apr. 16, 1999, pp. 467-474.
W.Z. Li et al., “Large-scale Synthesis of Aligned Carbon Nanotubes,” Science, vol. 274, Dec. 6, 1996, pp. 1701-1703.
Kingsuk Mukhopadhyay et al., “A Simple and Novel Way to Synthesize Aligned Nanotube Bundles at Low Temperature,” Japan J. Appl. Phys., vol. 37, Part 2, No. 10B, Oct. 15, 1998, pp. L1257-L1259.
Z.F. Ren et al., “Synthesis of Large Arrays of Well-Aligned Carbn Nanotubes on Glass,” Science, vol. 282, Nov. 6, 1998, pp. 1105-1107.
M. Kusunoki et al., “Epitaxial carbon nanotube film self-organized by sublimation decomposition of silicon carbide,” Appl. Phys. Lett., vol. 71, No. 18, Nov. 3, 1977, pp. 2620-2622.
S. Iijima, “Helical microtubules of graphitic carbon,” Nature, vol. 354, Nov. 7, 1991, pp. 56-58.
S. Kanemaru et al., “Active Matrix of Si Field Emitters Driven by Built-in MOSFETS,” IDW '97, pp. 735-738, 1997.
H. Gamo et al., “Actively-Controllable Field Emitter Arrays with Built-in Thin Film Transistors on Glass For Active-Matrix FED Applications,” IDW '98, pp. 667-670, 1998.

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