TWI230687B - A method for growing arrays of carbon nanotubes - Google Patents

Abstract

The present invention pertains to a method for growing arrays of carbon nanotubes on a surface of a metal substrate. The method includes selecting a metal substrate having a smooth surface, oxidizing the metal substrate so as to form an oxide layer on the smooth surface of the metal substrate, depositing a catalyst layer on the oxide layer, and exposing the catalyst layer to a carbon source gas, thereby forming the arrays of carbon nanotubes extending from the metal substrate, following the formation of carbon nanotubes a by-product, such as hydrogen gas is produced and reduces the oxide layer.

Description

1230687 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a method for preparing a carbon nanotube, and more particularly to a method for preparing a carbon nanotube array on a common metal substrate. [Previous Technology] Shan M, 1991, Researcher J ij ima of NEC Company of Japan accidentally found nanometers and sigma. See Helical microtubules of graphitic carbon, S. Iijima, Nature, vol. 354, P56 (1991) ^ The excellent characteristics of rice carbon official, its potential application has been widely concerned by people, especially in the field of electronics. Due to the extremely small diameter of carbon nanotubes, which can be as large as ten to a few nanometers, they can emit electrons from their tips under the action of a small electric field, so they can be used as field emission cathodes. In recent years, people have conducted various researches in nanomaterials and their application fields, especially the research on the preparation methods and applications of nanometer carbon tube arrays. Wu Guo Patent No. 6,232,706 discloses a field emission device (Chemical Vapor Deposition) method on a porous stone substrate; = = =; tube array, * including the following steps: · First on the substrate = two layers = ρνη ^ ^ ^ Under the conditions of any temperature, the carbon nanotubes are grown at a temperature of> 1 m, and the result is that the porous silicon-on-substrate 'height is a few hundred microns. The electrode that grows to the vertical or ... whose conductivity = differential and can carry a large current ::: The cathode of a device with good conductivity and high-power traveling wave tubes is also required. 1230687 V. Description of the invention (2) Higher current electrode. In order to make full use of the excellent conductivity of carbon nanotubes, it is necessary to connect them with a good conductor, so metal is still the best choice. Because metal materials have a great influence on the CVD method, metals are likely to form alloys with catalysts, or due to their catalytic effect, they strongly decompose carbon and hydrogen to form carbon deposits, which leads to the inability to grow nano carbon tubes.

Ch. Emmenegger et al. Proposed a method for growing nanometer carbon tube arrays on Shi Xi or metal | Lu substrate, published on Applied Surface

Science 1 6 2- 1 63 (2 0 0 0), 45 2-45 6, the method includes the following steps: 1. Coating the surface of Shi Xi or Ming substrate with Fe (N〇3) 3 film, the thickness is 5 ~ 1 Onm; 2 · Place the substrate in the reaction furnace, and heat it to the carbon nanotube synthesis temperature in a vacuum environment; 3 · Put nitrogen for 5 minutes' flow rate is iQ〇mi / mirl; 4 · Put 2 ral / min Dilute and 98 m] / niin of nitrogen, react at 0.5 to 3 hours at an ambient pressure of 0.5 bar; Result 'Nano carbon tube array grows on the catalyst growth point, the diameter of the nano carbon tube depends on The diameter of the catalyst particles is 5 microns.

The above method can grow a nano-carbon tube array on a metal aluminum substrate. Although the catalyst carrier commonly used in the Ang system is not suitable as a field emission cathode, and 'the method has limited substrate materials, only aluminum and aluminum can be selected. Similar limited metal materials have not been able to solve the aforementioned problem of growing carbon nanotubes on a common metal substrate.

1230687

5. Description of the invention (3) The method of carbon tube array is really necessary. [Content] The object of the present invention is to provide a method suitable for growing a carbon nanotube on a common metal substrate. Another object of the present invention is to provide a method for manufacturing a field emission cathode. In order to achieve the above object, the method provided by the present invention includes the steps of: providing a metal substrate; oxidizing the metal substrate to form an oxide layer on the surface; A catalyst layer is formed on the surface of the layer; carbon and hydrogen gas is introduced, and a chemical reaction occurs under the action of the catalyst, so that the carbon nanotubes grow from the catalyst and generate reducing gas to reduce the oxide layer. Compared with the prior art, the present invention has the following advantages: the catalyst layer and the metal substrate are separated by an oxide layer, thereby avoiding overreaction of the bimetal substrate to adversely affect the catalyst, and the process of generating carbon nanotubes by the reaction. The generation of IL gas reduces the oxide layer, which can make the nano carbon tube grow directly on the metal substrate, and improve the electrical connection between the nano carbon tube and the metal substrate. [Embodiment] Please refer to the first figure, which is the meaning of the method for preparing a nano carbon tube according to the present invention. The figure includes the following steps: w & Step 1 provides a metal substrate. The support substrate for the metal-based growth of the carbon nanotubes provided in this step. The gold substrate can be a metal used as an alloy sheet, or a metal or human piece can be formed on the surface of the substrate of other materials. There is no special metal or alloy material. The growth temperature of the carbon nanotubes is generally about 700 ° C ~ 100,000. '1, only L' meet 1230687 V. Description of the invention (4) The following conditions can be a) no glare occurs; b) no co-solubility with the substrates of other materials selected; c) selected substrates whose thermal expansion coefficients are more compatible from room temperature to growth temperature; Does not cause swelling or chipping due to hydrogen absorption during growth

If you choose metal or alloy sheet directly, you only need to satisfy & and. π JT Most metal materials can meet the above conditions, such as Ta, Ni, Ag,

Fe Cu, stainless steel and other alloys. The substrate of the other material may be glass silicon or quartz wafer, etc. In order to form a metal or alloy electrode on the surface, a certain flatness is required on the surface. The method for forming the electrode includes electric ore, magnetic control, and the like. In order to obtain an ordered carbon nanotube array, the bottom surface of the metal f may be further polished by mechanical polishing or electrochemical polishing to make the surface have a certain degree of flatness, so as to satisfy the growth of the nano carbon tube array by the ordinary CVD method. It requires 0 step 2 to oxidize the metal substrate to form an oxide layer. The surface of the gold f substrate provided in step 1 is oxidized to form a metal oxide layer, and the thickness of the oxide layer may be less than 1, f. There are many ways to achieve surface oxidation. The simpler method is to heat to a certain temperature in two gases. After a certain time, an oxide layer can be formed on the surface of the metal substrate. Step 3 is to form a catalyst layer on the oxidation substrate. I.e. 1230687 formed in step 2

5. Description of the invention (5) A catalyst layer is formed on the oxide layer on the surface of the metal substrate. Currently, the commonly used catalysts for growing carbon nanotube arrays by CVD are metallic iron, cobalt, nickel, and their oxides. The methods for forming the catalyst layer include electron beam evaporation and other electrochemical methods. The thickness of the catalyst layer only needs to be from 1 nm to 0 nm. Step 4 is an annealing treatment of the catalyst layer. The metal substrate with the metal catalyst layer formed in step 3 is annealed so that the catalyst layer forms nano-sized catalyst particles. If the catalyst is a metal, the metal is oxidized to a metal oxide during the annealing process. The particle size obtained by annealing will determine the diameter of the carbon nanotubes to be grown in the future.

Step 5 is a CVD method for growing a carbon nanotube array and reducing the oxide layer to a metal. A nano-carbon tube array is grown on the metal substrate by a CVD method, and the surface oxide layer of the metal substrate formed in step 2 is reduced to metal. The growth conditions of the CVD method are basically the same as the conditions for growing carbon nanotubes on a porous silicon substrate. 'A carbon source gas, such as ethylene or acetylene, is passed at a certain temperature (for example: 700 ° C ~ 100 0 ° C) Under the reaction, carbon nanotubes grow on the catalyst particles; at the same time as the reaction, the carbon source gas releases hydrogen to reduce the surface oxidation layer of the metal substrate to metal, so that the carbon nanotubes directly contact the metal substrate. The examples illustrate the process of the method of the invention. Please refer to the second figure. In the first embodiment of the present invention, stainless steel 丨 0 is used as the metal substrate. It is a high melting point alloy with a melting point of more than 0.0000t, and does not absorb hydrogen during the reaction for expansion. Or broken, its size can be determined according to specific requirements. The surface of stainless steel 10 must have a certain flatness to meet the needs of growing carbon nanotube arrays (in general, the better the flatness,

$ 9 pages 1230687 V. Description of the invention (6) The orderliness of the obtained carbon nanotubes is as follows: 1) Mechanical and optical methods, electrochemical and optical methods have emerged: the surface flatness can pass the machine. As shown in the next three pictures, 'stainless steel 10 is added to the air to 5 0 C, the emulsification reaction is scattered, and after a flood-..., a metal oxide layer 12 is formed: strictly over the surface of the stainless steel 10 The shape is related to the time of the lice reaction. The longer the shield, the thicker the thickness, and the metal oxide f may be, preferably, 〇, 〇nm. The degree of the layer 2 is less than 1 micron, that is, as shown in the fourth figure, a -layer catalyst layer 14 is formed on the metal oxide layer 12 by the electron beam evaporation method, said catalyst layer! 4 Generally, it is metallic iron, cobalt, nickel or its oxides, etc. The thickness of the catalyst layer 14 is approximately 10 Å. Thus, the catalyst layer 14 and the stainless steel 10 are connected by the metal oxide layer 12, so that the catalyst layer 14 and the stainless steel 10 are spaced apart. Preferably, the catalyst layer 14 is left in the air and annealed at 300 ° C for a period of time, so that the catalyst layer 14 is oxidized and shrunk into nano-sized catalyst particles. Finally, the carbon source gas ethylene was passed in, and a carbon nanotube array 16 was grown on the catalyst layer 14 by the CVD method. 'Because the catalyst layer 14 passed through the stainless steel 10 and the metal oxide layer 12 was spaced apart,' this occurred. The absence of surface i 〇 during the reaction will not affect the catalytic effect of the catalyst, and nano carbon tubes can be grown smoothly. The ethylene cracking reaction generates nano-carbon tubes 16 while releasing hydrogen gas. The hydrogen reacts with the metal oxide layer 12 on the surface of the stainless steel 10, and finally reduces the metal oxide layer 12 to a metal. Qian Gang 10 contacts, as shown in the fifth figure. In the second embodiment of the present invention, a silicon substrate is first provided, and the surface of the silicon substrate is polished to make it have a certain flatness;

1230687 V. Description of the invention (7) A metal or alloy layer is formed on the surface of the sheet by electroplating as a metal substrate; the metal substrate is then formed on the metal substrate through steps 2, 3, 4, and 5 described above. Nano carbon tubes. The above silicon substrate can also be replaced by other non-metal materials such as glass and quartz. The method for preparing a nano carbon tube provided by the present invention may use ordinary metals or alloys as the metal substrate, and is not limited to the aforementioned ones. In addition, the method of oxidizing the metal substrate to form a catalyst layer is not limited to those listed in the examples. In addition, the carbon source gas and catalyst used for growing the carbon nanotubes are not limited to those described above, and any carbon source gas and catalyst known to those skilled in the art can be used. In summary, the present invention has indeed met the requirements for an invention patent, and a patent application was filed in accordance with the law. However, the above is only a preferred embodiment of the present invention, and it cannot be used to limit the scope of patent application in this case. Any equivalent modifications or changes made by those familiar with the technology of the case with the aid of the spirit of the present invention should be covered by the scope of the following patent applications.

Page 11 1230687 Brief description of the diagram The first diagram is a flowchart of a method for preparing a nano carbon tube according to the present invention. The second figure is a schematic view of a substrate used in the method for preparing a carbon nanotube of the present invention. The third figure is a schematic diagram of forming an oxide layer on the surface of the substrate used. The fourth diagram is a schematic diagram of forming a catalyst layer on an oxide layer. The fifth figure is a schematic view of a nano carbon tube array obtained by using the method for preparing a nano carbon tube according to the present invention. [Description of Symbols of Main Components] Stainless Steel Catalyst Layer 10 14 Metal Oxide Layer Nano Carbon Tube Array 12 16

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Claims (1)

1230687 6. Scope of patent application 1. A method for preparing a nano carbon tube, comprising the steps of: providing a metal substrate; oxidizing the metal substrate to form an oxide layer on its surface; forming a catalyst layer on the surface of the oxide layer; passing in carbon The hydrogen gas undergoes a chemical reaction under the action of the catalyst, so that the carbon nanotubes grow from the catalyst layer, and a reducing gas is generated to reduce the oxide layer. 2. The method for preparing a nano carbon tube according to item 1 of the scope of patent application, wherein the metal substrate includes Ta, Ni, Ag, Fe, Cu. 3. The method for preparing a nano carbon tube according to item 1 of the scope of patent application, wherein the metal substrate comprises a metal alloy. 4. The method for preparing a nano carbon tube as described in item 3 of the scope of patent application, wherein the alloy includes stainless steel. 5. The method for preparing a nano carbon tube as described in item 1 of the scope of patent application, wherein the thickness of the oxide layer is 100 nm. 6. The method for preparing a nano carbon tube according to item 1 of the scope of patent application, wherein the catalyst layer comprises a metal catalyst or an oxide thereof. 7. The method for preparing a nano carbon tube according to item 6 of the scope of patent application, wherein the metal catalyst includes iron, starting, nickel, or an alloy thereof. 8. The method for preparing a nano carbon tube according to item 1 of the scope of patent application, wherein the thickness of the catalyst layer is 1 to 10 nanometers. 9. The method for preparing a nano carbon tube according to item 1 of the scope of the patent application, wherein the reducing gas is hydrogen. 10. —A method for preparing a carbon nanotube field emission cathode, comprising the steps of: Page 13 1230687 6. The scope of the patent application provides a cathode substrate; forming a metal electrode on the surface of the cathode substrate; oxidizing the metal electrode to form an oxide layer on the surface; forming a catalyst layer on the surface of the oxide layer; passing in a hydrocarbon gas A chemical reaction occurs under the action of the catalyst, so that the carbon nanotubes grow from the catalyst layer, and a reducing gas is generated to reduce the oxide layer. 1 1 · The method for preparing a nano-carbon tube field emission cathode as described in item 10 of the patent application scope, wherein the cathode substrate includes glass, silicon or quartz. 1 2 · The method for preparing a nano-carbon tube field emission cathode as described in item No. 丨 0, wherein the metal electrode includes Ta, Ni, Ag, Fe, Cu ° '1 3 The method for preparing a nano-carbon tube field emission cathode according to item 〇, wherein the metal electrode includes a metal alloy. 1 4. The method for preparing a field emission cathode of a nano carbon tube according to item 3 of the scope of the patent application, wherein the alloy is covered with no steel. 15 · The method for preparing a nanometer carbon tube field emission cathode as described in item No. 0 of the patent application range, wherein the oxide layer has a friction of 1 to 1,000 nanometers. 16 · The method for preparing a nano-carbon tube field emission cathode as described in item No. 0 of the patent application, wherein the catalyst layer comprises a metal catalyst or an oxide thereof. 17. A method for preparing a nano-carbon tube field emission cathode as described in the patent application, wherein the metal catalyst includes iron, cobalt, nickel, or an alloy thereof. 1230687 6. Scope of patent application 1 8. The method for preparing a nanometer carbon tube field emission cathode as described in item 10 of the scope of patent application, wherein the thickness of the catalyst layer is 10 nanometers. 19. The method for preparing a nano-carbon tube field emission cathode according to item 10 of the scope of the patent application, wherein the reducing gas is hydrogen. Page 15