Nanotechnology – Jin Jang, Suk-jae Chung, cDream Corp
Abstract for “Method for forming carbon nanotubes.”
A high-density plasma is a simple way to purify carbon nanotubes. The plasma chemical vapor deposition method is used to grow carbon nanotubes on a substrate at a plasma density of 1011 cm3 or higher. The process of creating carbon nanotubes includes the following: a layer of carbon nanotubes is grown on a substrate with plasma deposition to a predetermined thickness; plasma etching purifies the carbon nanotube layers; and then the growth and purification of the carbon microtube layer. A halogen-containing gas is used for plasma etching. For example, a carbon trifluoride or gas.
Background for “Method for forming carbon nanotubes.”
“1. “1.
“The invention is a method for forming carbon nanotubes and, more specifically, for the growth and purification carbon nanotubes using plasma.”
“2. “2.
“Carbon is the most important constituent element. It can be combined with oxygen, hydrogen and nitrogen in all organisms, including the human body. It has four distinct crystalline structures, including graphite, fullerene, carbon nanotubes, and diamond. Carbon nanotubes are a helical tubular structure that has a single or multi-wall. This can be obtained by rolling a sheet of multiple hexagons. Each carbon atom is combined with three other carbon atoms to form the sheet. Carbon nanotubes can have a diameter of anywhere from a few nanometers up to several hundred nanometers. Carbon nanotubes can be used as conductors like metals or semiconductors depending on the rolled shape and diameter of the helical tube. Carbon nanotubes have a hollow structure that has a predetermined length, which allows for excellent mechanical, electrical, and chemical properties. They are also used as field emission devices, hydrogen containers, and electrodes for rechargeable batteries.
“Originally, carbon nanotubes were formed by an arc discharge between graphite rods. This was reported in an article titled?Helical microtubules from Graphitic Carbon? (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58) by Sumio lijima. Although this technique is used frequently to make carbon nanotubes it yields only around 15%. For specific device applications, it is necessary to perform a complex purification process.
W. Z. Li and colleagues reported a method to produce carbon nanotubes by thermal decomposition hydrocarbon series gases using chemical vapor deposition. In an article entitled “Large Scale Synthesis Aligned Carbon nanotubes?” (Science, Vol. 274, Dec. 6, 1996, pp. 1701-1703). This technique can only be used with unstable gases such as acetylene and benzene. This technique cannot be used to make carbon nanotubes with methane (CH4) gas.
“The present invention aims to provide a method for forming carbon nanotubes. In this process, carbon nanotubes can be grown with high density using high-density plasma.
“The present invention also aims to provide a method for forming carbon nanotubes. In this process, carbon nanotubes will be purified using graphite or carbon particles using high-density plasma. This allows carbon nanotubes to easily grow with high density.”
“To reach the second goal of the invention, there is a method for forming carbon nanotubes. This involves forming a layer of carbon nanotubes on a substrate with a predetermined thickness using plasma deposition. The carbon nanotube layer is then purified using plasma etching. Next, the growth and purification of carbon nanotube layers are repeated.
“Preferably, the growth of carbon nanotube layers is done by plasma chemical vapor deposition at a high plasma density (1011 cm?3) or greater. A halogen-containing or oxygen-containing gas can be used to purify the carbon nanotube layer.
“According the present invention, high density carbon nanotubes can easily be grown by combining stable CH4 gas and high-density plasma. You can also easily make high-purity carbon nanotubes by repeating the process of growing and purifying carbon nanotubes.
“The present invention will be described in greater detail with the help of the accompanying drawings. These drawings show preferred embodiments. The invention can be expressed in many forms, and should not be taken to mean that it is limited to the ones shown herein. These embodiments are intended to be comprehensive and complete and fully communicate the concept of this invention to all who are skilled in the art.
Referring to FIG. “Referring to FIG. 1, is a substrate that can be used in the formation carbon nanotubes according a preferred embodiment. On a predetermined substrate 11, a silicon thin film 12 is formed, followed by a catalytic metallic layer 13. The substrate 11 is an insulating substrate which can withstand a subsequent plasma process. The present invention uses a glass substrate that allows easy deposition of the thin silicon film 12. Amorphous silicon and polysilicon can be used to form the silicon thin film 12. The catalytic layer 13 can be made of a transitional metal such as nickel, cobalt, iron or an alloy thereof.
“Then, a layer of carbon nanotubes is grown on the catalytical metal layer 13. FIGS. FIGS. 2-6 are sectional views that illustrate the stages of carbon nanotube formation according to the preferred embodiment.
The present embodiment maintains the deposition plasma 18 at a high density (1011 cm?3) or greater, and the carbon-nanotube layer 15 is grown to the desired thickness (between 3 and 300 nm). Deposition time increases the thickness of the carbon-nanotube layer 15. The deposition time can vary from a few seconds up to several hundred seconds. The carbon nanotubes are grown in a plasma deposition mode. This allows for graphitic phase and amorphous carbon particles to form at the ends or sidewalls of carbon nanotubes.
“As described previously, when the amorphous Silicon thin film 12 is formed on the substrate 11, and the catalytic Metal layer 13 are grown on the carbon nanotube layers 15, the catalytical metal diffuses into this amorphous Silicon layer 12, resulting in the metal -induction crystalized Polysilicon layer 14, on which a predetermined amount remains.”
Referring to FIG. 3. After changing the conditions of plasma chemical vapor apparatus to a plasma deposition mode to one that enables plasma etching, the graphitic phase and amorphous carbon particle, which were formed during the growth process of the carbon-nanotube layer 15, are removed to remove the carbon nanotube layers 15, which gives rise to a purified carbon-nanotube layer 17(1). The plasma chemical vapor apparatus must be completely purged before it can be converted to the plasma etching mode. The plasma etching conditions are basically the same as the plasma deposition mode illustrated in FIG. 2. The only difference is the type of plasma source gas.
The plasma source gas used in plasma etching may contain a gas containing F, Cl, Br or an oxygen-containing element. A fluorine-containing gas such as a carbon tetrafluoride gas (CF4) is used in the present invention. Fluorine ions are separated from the carbon tetrafluoride gases to produce a highly volatile carbon fluoride series gaz (CFn) through reaction with carbon ions. The ionized fluorine can react with carbon ions that are decomposed from graphitic phases or amorphous particles. This allows for removal of graphitic particles or amorphous particles with a high selectivity from carbon nanotubes.
Referring to FIG. 4. The plasma etching mode illustrated in FIG. 3. is transformed into the plasma deposit mode. The plasma chemical vapor-deposition apparatus is then purged to remove all fluorine ions. These conditions are the same as those shown in FIG. 3 results in another layer of carbon nanotubes 15 on the purified carbon-nanotube layer 17(1).”
Referring to FIG. Referring to FIG. 5, the plasma deposition mode in FIG. 4. is transformed into the plasma etching mod The plasma chemical vapor deposit apparatus is now completely purge. These conditions are the same as those in FIG. 3 results in another layer of purified carbon nanotube 17(2).”
Referring to FIG. “Referring to FIG. 6, the plasma deposition mode, and the plasma etching methods, which were previously described, are repeated an additional n times. Consider the thickness of final carbon nanotube layer to determine the number of repetitions.
“FIG. 7 is a scan electron microscope (SEM), image of the plane of carbon nanotubes in the preferred embodiment. FIG. FIG. 8 shows a SEM image showing a vertical section under a different magnification for the carbon nanotubes in the preferred embodiment. FIG. 8 Carbon nanotubes are perfectly aligned with a substrate, as shown in FIG.
“FIG. 9 is a transmission electron microscope image (TEM) of carbon nanotubes in the preferred embodiment. FIG. FIG. 9 shows highly tangled filaments. FIG. FIG. 10 shows a magnified TEM view of the carbon nanotubes in the preferred embodiment. FIG. FIG. 10 single-walled carbon nanotubes are twisted together in bundles of very high density.”
“FIG. “FIG. 11” is a graph that comparatively shows field emission properties between carbon nanotubes made in the preferred embodiment and those made by a conventional process. Contrary to the present invention, the conventional method involves continuously growing a layer of carbon nanotubes without having to alternately apply the plasma deposition mode or the plasma etching modes. For a field emission electrode with a 1 cm2 area, the field emission properties were measured. FIG. FIG. 11 shows that purifying carbon nanotubes by removing graphite phase or amorphous carbon particle from the tips or sidewalls of carbon nanotubes allows for high current emission at low electric fields.
The present invention allows for the easy formation of carbon nanotubes using a methane gas, which can be used as a source gas, under high-density plasma conditions. The graphitic phase and amorphous carbon particles that are formed during growth of carbon nanotubes can be easily removed by repeating the plasma-deposition mode or the plasma etching modes. This results in carbon nanotubes with good field emission properties.
“While the preferred embodiments of this invention have been shown and described, it will be apparent to those skilled in art that many modifications in form and details can be made without departing from its spirit and scope as defined in the appended claims.”
Summary for “Method for forming carbon nanotubes.”
“1. “1.
“The invention is a method for forming carbon nanotubes and, more specifically, for the growth and purification carbon nanotubes using plasma.”
“2. “2.
“Carbon is the most important constituent element. It can be combined with oxygen, hydrogen and nitrogen in all organisms, including the human body. It has four distinct crystalline structures, including graphite, fullerene, carbon nanotubes, and diamond. Carbon nanotubes are a helical tubular structure that has a single or multi-wall. This can be obtained by rolling a sheet of multiple hexagons. Each carbon atom is combined with three other carbon atoms to form the sheet. Carbon nanotubes can have a diameter of anywhere from a few nanometers up to several hundred nanometers. Carbon nanotubes can be used as conductors like metals or semiconductors depending on the rolled shape and diameter of the helical tube. Carbon nanotubes have a hollow structure that has a predetermined length, which allows for excellent mechanical, electrical, and chemical properties. They are also used as field emission devices, hydrogen containers, and electrodes for rechargeable batteries.
“Originally, carbon nanotubes were formed by an arc discharge between graphite rods. This was reported in an article titled?Helical microtubules from Graphitic Carbon? (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58) by Sumio lijima. Although this technique is used frequently to make carbon nanotubes it yields only around 15%. For specific device applications, it is necessary to perform a complex purification process.
W. Z. Li and colleagues reported a method to produce carbon nanotubes by thermal decomposition hydrocarbon series gases using chemical vapor deposition. In an article entitled “Large Scale Synthesis Aligned Carbon nanotubes?” (Science, Vol. 274, Dec. 6, 1996, pp. 1701-1703). This technique can only be used with unstable gases such as acetylene and benzene. This technique cannot be used to make carbon nanotubes with methane (CH4) gas.
“The present invention aims to provide a method for forming carbon nanotubes. In this process, carbon nanotubes can be grown with high density using high-density plasma.
“The present invention also aims to provide a method for forming carbon nanotubes. In this process, carbon nanotubes will be purified using graphite or carbon particles using high-density plasma. This allows carbon nanotubes to easily grow with high density.”
“To reach the second goal of the invention, there is a method for forming carbon nanotubes. This involves forming a layer of carbon nanotubes on a substrate with a predetermined thickness using plasma deposition. The carbon nanotube layer is then purified using plasma etching. Next, the growth and purification of carbon nanotube layers are repeated.
“Preferably, the growth of carbon nanotube layers is done by plasma chemical vapor deposition at a high plasma density (1011 cm?3) or greater. A halogen-containing or oxygen-containing gas can be used to purify the carbon nanotube layer.
“According the present invention, high density carbon nanotubes can easily be grown by combining stable CH4 gas and high-density plasma. You can also easily make high-purity carbon nanotubes by repeating the process of growing and purifying carbon nanotubes.
“The present invention will be described in greater detail with the help of the accompanying drawings. These drawings show preferred embodiments. The invention can be expressed in many forms, and should not be taken to mean that it is limited to the ones shown herein. These embodiments are intended to be comprehensive and complete and fully communicate the concept of this invention to all who are skilled in the art.
Referring to FIG. “Referring to FIG. 1, is a substrate that can be used in the formation carbon nanotubes according a preferred embodiment. On a predetermined substrate 11, a silicon thin film 12 is formed, followed by a catalytic metallic layer 13. The substrate 11 is an insulating substrate which can withstand a subsequent plasma process. The present invention uses a glass substrate that allows easy deposition of the thin silicon film 12. Amorphous silicon and polysilicon can be used to form the silicon thin film 12. The catalytic layer 13 can be made of a transitional metal such as nickel, cobalt, iron or an alloy thereof.
“Then, a layer of carbon nanotubes is grown on the catalytical metal layer 13. FIGS. FIGS. 2-6 are sectional views that illustrate the stages of carbon nanotube formation according to the preferred embodiment.
The present embodiment maintains the deposition plasma 18 at a high density (1011 cm?3) or greater, and the carbon-nanotube layer 15 is grown to the desired thickness (between 3 and 300 nm). Deposition time increases the thickness of the carbon-nanotube layer 15. The deposition time can vary from a few seconds up to several hundred seconds. The carbon nanotubes are grown in a plasma deposition mode. This allows for graphitic phase and amorphous carbon particles to form at the ends or sidewalls of carbon nanotubes.
“As described previously, when the amorphous Silicon thin film 12 is formed on the substrate 11, and the catalytic Metal layer 13 are grown on the carbon nanotube layers 15, the catalytical metal diffuses into this amorphous Silicon layer 12, resulting in the metal -induction crystalized Polysilicon layer 14, on which a predetermined amount remains.”
Referring to FIG. 3. After changing the conditions of plasma chemical vapor apparatus to a plasma deposition mode to one that enables plasma etching, the graphitic phase and amorphous carbon particle, which were formed during the growth process of the carbon-nanotube layer 15, are removed to remove the carbon nanotube layers 15, which gives rise to a purified carbon-nanotube layer 17(1). The plasma chemical vapor apparatus must be completely purged before it can be converted to the plasma etching mode. The plasma etching conditions are basically the same as the plasma deposition mode illustrated in FIG. 2. The only difference is the type of plasma source gas.
The plasma source gas used in plasma etching may contain a gas containing F, Cl, Br or an oxygen-containing element. A fluorine-containing gas such as a carbon tetrafluoride gas (CF4) is used in the present invention. Fluorine ions are separated from the carbon tetrafluoride gases to produce a highly volatile carbon fluoride series gaz (CFn) through reaction with carbon ions. The ionized fluorine can react with carbon ions that are decomposed from graphitic phases or amorphous particles. This allows for removal of graphitic particles or amorphous particles with a high selectivity from carbon nanotubes.
Referring to FIG. 4. The plasma etching mode illustrated in FIG. 3. is transformed into the plasma deposit mode. The plasma chemical vapor-deposition apparatus is then purged to remove all fluorine ions. These conditions are the same as those shown in FIG. 3 results in another layer of carbon nanotubes 15 on the purified carbon-nanotube layer 17(1).”
Referring to FIG. Referring to FIG. 5, the plasma deposition mode in FIG. 4. is transformed into the plasma etching mod The plasma chemical vapor deposit apparatus is now completely purge. These conditions are the same as those in FIG. 3 results in another layer of purified carbon nanotube 17(2).”
Referring to FIG. “Referring to FIG. 6, the plasma deposition mode, and the plasma etching methods, which were previously described, are repeated an additional n times. Consider the thickness of final carbon nanotube layer to determine the number of repetitions.
“FIG. 7 is a scan electron microscope (SEM), image of the plane of carbon nanotubes in the preferred embodiment. FIG. FIG. 8 shows a SEM image showing a vertical section under a different magnification for the carbon nanotubes in the preferred embodiment. FIG. 8 Carbon nanotubes are perfectly aligned with a substrate, as shown in FIG.
“FIG. 9 is a transmission electron microscope image (TEM) of carbon nanotubes in the preferred embodiment. FIG. FIG. 9 shows highly tangled filaments. FIG. FIG. 10 shows a magnified TEM view of the carbon nanotubes in the preferred embodiment. FIG. FIG. 10 single-walled carbon nanotubes are twisted together in bundles of very high density.”
“FIG. “FIG. 11” is a graph that comparatively shows field emission properties between carbon nanotubes made in the preferred embodiment and those made by a conventional process. Contrary to the present invention, the conventional method involves continuously growing a layer of carbon nanotubes without having to alternately apply the plasma deposition mode or the plasma etching modes. For a field emission electrode with a 1 cm2 area, the field emission properties were measured. FIG. FIG. 11 shows that purifying carbon nanotubes by removing graphite phase or amorphous carbon particle from the tips or sidewalls of carbon nanotubes allows for high current emission at low electric fields.
The present invention allows for the easy formation of carbon nanotubes using a methane gas, which can be used as a source gas, under high-density plasma conditions. The graphitic phase and amorphous carbon particles that are formed during growth of carbon nanotubes can be easily removed by repeating the plasma-deposition mode or the plasma etching modes. This results in carbon nanotubes with good field emission properties.
“While the preferred embodiments of this invention have been shown and described, it will be apparent to those skilled in art that many modifications in form and details can be made without departing from its spirit and scope as defined in the appended claims.”
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