JP2011190172A - Method for manufacturing one-dimensional carbon nanostructure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for synthesizing individual carbon nanotubes at preselected position on a substrate to manufacture carbon nanotubes and carbon nanostructures using chemical vapor deposition. <P>SOLUTION: In the method, an organometallic layer is deposited on a substrate which has a deposition mask. When the mask is removed, the portion of an organometallic precursor deposited on the mask is also removed. The remaining portion of the organometallic layer is oxidized to obtain a metal growth catalyst on the substrate which can be used for synthesis of carbon nanostructures. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing carbon nanotubes and carbon nanostructures using chemical vapor deposition.

  Carbon nanotubes are hexagonal networks made of carbon atoms and have a seamless tube shape with both ends closed by hemispheric fullerenes. As the first carbon nanotube, a multi-layered coaxial tube or multi-walled carbon nanotube obtained by vapor deposition of carbon during arc discharge was reported in 1991 by Sumio Iijima. At this time, carbon nanotubes of up to seven layers were reported. In 1993, the Iijima group and the IBM team led by Donald Bethune can independently create single-wall nanotubes by evaporating carbon in an arc generator with transition metals such as iron and cobalt. (See Iijima et al., Nature 363: 603 (1993); Bethune et al., Nature 363: 605 (1993) and US Pat. No. 5,424,054). This synthesis yielded a small amount of heterogeneous nanotubes mixed with a large amount of smoke and metal particles.

  Currently, there are mainly three methods for synthesizing single-walled and multi-walled carbon nanotubes. Arc discharge of carbon soot (Journet et al., Nature 388: 756 (1997)), laser cutting of carbon (Thess et al., Science 273: 483 (1996)), and chemical vapor deposition of hydrocarbons (Ivanov et al., Chem. Phys. Lett. 223: 329 (1994); Li et al., Science 274: 1701 (1996)). Multi-walled carbon nanotubes can be produced on an industrial scale by catalytic hydrocarbon cracking, whereas single-walled carbon nanotubes can still be produced only in grams by laser technology.

  Single-walled carbon nanotubes are generally preferred over multi-walled carbon nanotubes because they have fewer defects, are stronger, and are more conductive when compared at the same diameter. In the case of multi-walled carbon nanotubes, some of the defects are compensated by cross-linking between unsaturated carbon valances, but in the case of single-walled carbon nanotubes, there is no adjacent wall and the defects cannot be compensated. Therefore, it is difficult to produce single-walled carbon nanotubes having defects. Defect-free single-walled nanotubes are expected to have significant mechanical, electronic, and magnetic properties that can be adjusted by changing the tube diameter, coaxial shell number, and chirality.

  Single-walled carbon nanotubes are manufactured by simultaneously evaporating carbon and a small amount of a Group VIII transition metal from the anode of an arc discharge device (Saito et al., Chem. Phys. Lett. 236: 419 (1995). )). It has also been shown that the use of transition metal mixtures increases the yield of single-walled carbon nanotubes in the arc discharge apparatus. However, the yield of nanotubes is still low, there are significant variations in structure and dimensions between individual nanotubes in the mixture, and it is difficult to separate the nanotubes from other reaction products. In a typical arc discharge process, a carbon anode filled with a catalyst material (generally nickel / cobalt, nickel / cobalt / iron, or a combination of metals such as nickel and transition elements such as yttrium) is consumed by arc plasma. Single-walled carbon nanotubes are grown by evaporating the catalyst and carbon and condensing the carbon on the concentrated liquid catalyst. Sulfur compounds such as iron sulfide, sulfur, and hydrogen sulfide are generally used as a promoter for maximizing the product yield.

  A general laser cutting method for producing single-walled carbon nanotubes is disclosed by Andreas Thess et al. (1996). Metal catalyst particles such as nickel-cobalt alloy are mixed with graphite powder at a predetermined ratio, and the mixture is compressed to obtain pellets. The pellet is irradiated with a laser beam. The laser beam evaporates the carbon and nickel-cobalt alloy and condenses the carbon vapor in the presence of the metal catalyst. Single-walled carbon nanotubes with a non-constant diameter are present during condensation. However, if a second laser is provided in the process and a pulse is given 50 nanoseconds after the pulse of the first laser, a large number of 10,10 structures (10 hexagonal chains on the outer periphery of the nanotube) are obtained. The product is composed of fibers having a diameter of about 10 to 20 nm and a length of several micrometers, and the fibers contain single-walled nanotubes each having a diameter of about 1.38 nm, which are randomly arranged.

  Unlike the laser method and the arc method, carbon deposition on a transition metal catalyst tends to generate mainly multi-walled carbon nanotubes instead of single-walled carbon nanotubes. However, in some cases, the catalytic hydrocarbon decomposition method has succeeded in producing most single-walled carbon nanotubes. Dai et al. (Chem. Phys. Lett 260: 471 (1996)) heated a temperature of 1200 ° C. together with a molybdenum (Mo) catalyst supported on alumina to disproportionate carbon monoxide (CO). Single-walled carbon nanotubes are produced. The diameter of single-walled carbon nanotubes generally ranges from 1 nm to 5 nm, but could be controlled by the Mo particle size. An electron microscopic image of the product revealed that Mo metal was attached to the tip of the nanotube. A bundle of rope-like single-walled carbon nanotubes is obtained by thermally decomposing benzene at 1100 to 1200 ° C. together with an iron catalyst and a sulfur additive. The synthesized single-walled carbon nanotubes are coarsely arranged in rows and knitted in the same manner as those obtained by laser evaporation or electric arc method. Use of a metal catalyst containing iron and at least one element selected from group V (V, Nb and Ta), group VI (Cr, Mo and W), group VII (Mn, Tc and Re) and lanthanide Has also been proposed (see US Pat. No. 5,707,916).

  Currently available carbon nanotube synthesis methods yield large quantities of carbon nanotubes that are generally intertwined. In addition, the nanotube may have structural defects at the molecular level that adversely affect properties. Therefore, in the current method, carbon nanotubes cannot be generated at a preselected position. For example, as one use of carbon nanotubes, circuit connection wiring is considered. U.S. Pat. No. 6,574,130 discloses a hybrid memory cell in which each cell has a nanotube ribbon crossbar junction. Individual nanotube ribbons are formed from entangled nanotubes and placed at the desired location in the memory cell. The above process can be simplified if there is a method for efficiently producing individual carbon nanotubes at different positions.

  US Pat. No. 6,146,227 discloses a method of manufacturing carbon nanotubes as elements of a microelectromechanical system (MEMS) device. Nano-sized pores or nanoscale catalyst holding structures are formed in the MEMS substrate layer, and the nanotube growth catalyst is deposited inside. As a result, nanotubes grow inside the nano-sized pores. That is, in this method, the position and size of the nanotube are controlled by providing a nanoscale catalyst holding structure at a specific position on the MEMS substrate.

  In the method disclosed in US Pat. No. 6,401,526, the location of the nanotubes is determined by installing a silicon pyramid. A silicon pyramid is placed at a specific position, dip-coated with a liquid phase catalyst, and carbon is chemically deposited to create a single-walled carbon nanotube probe tip for atomic force microscopy. The nanotubes are then shrunk to the desired length.

  Thus, there is a need for a method of synthesizing individual carbon nanotubes at preselected locations on a substrate. Such a method preferably grows a controlled number of carbon nanotubes at preselected locations on the substrate. Such a method is further preferably one that allows individual growth of the desired type of carbon nanotubes, for example single-walled nanotubes.

SUMMARY OF THE INVENTION The present invention provides methods and processes for growing carbon nanotubes at target locations on a substrate. In one embodiment, a mask layer is provided on the substrate and selected portions of the substrate are exposed. An organometallic precursor film is then deposited on the substrate. The precursor film is deposited using a dry method on both the mask portion and the exposed portion of the substrate. After depositing the precursor film, the mask layer is removed from the substrate. The organometallic film remaining on the substrate is pyrolyzed to form metal nanoparticles. The obtained metal nanoparticles are used as a growth catalyst for growing carbon nanotubes.

  In one aspect, the present invention provides a method for synthesizing carbon nanostructures. The method includes providing a substrate with a deposition mask; depositing an organometallic layer on the substrate such that at least a portion of the organometallic layer is deposited on a non-masked portion of the substrate; removing the deposition mask from the substrate. Oxidizing a portion of the organometallic layer deposited on the non-masked portion of the substrate to form a growth catalyst on the substrate; and exposing the substrate to a carbon precursor gas at a deposition temperature to form a carbon nanostructure. Including that. The vapor deposition mask may be a metal oxide such as silicon oxide or aluminum oxide. The organometallic layer may consist of iron phthalocyanine, molybdenum phthalocyanine or a combination thereof. The carbon precursor gas may be methane, and may further contain other gases such as argon and hydrogen.

  In another aspect, the present invention provides a system for producing carbon nanotubes. The system supports a plurality of temperature zones and can have a hermetic chamber with a carbon precursor gas source and an inert gas source; a sample holder disposed in a first temperature zone; a second A masked substrate disposed in the temperature zone; and an exhaust system connected to the reactor and exhausting gas from the chamber. The vapor deposition mask may be a metal oxide such as silicon oxide or aluminum oxide. The organometallic layer may consist of iron phthalocyanine, molybdenum phthalocyanine or a combination thereof. The carbon precursor gas may be methane, and may further contain other gases such as argon and hydrogen. An organometallic layer is deposited on the masked substrate and oxidized to form metal catalyst particles of specific dimensions. The mask is removed either before or after the oxidation step. Next, the metal catalyst particles are brought into contact with the carbon precursor gas, and carbon nanotubes are formed by chemical vapor deposition.

  In another embodiment, the present invention deposits an organometallic layer on a substrate comprising a deposition mask; oxidizes the deposited organometallic layer on a non-masked portion of the substrate; and causes the substrate to contact a carbon precursor gas at a deposition temperature. Thus, a carbon nanotube structure manufactured by a process of forming a carbon nanotube structure is provided. The vapor deposition mask may be a metal oxide such as silicon oxide or aluminum oxide. The organometallic layer may consist of iron phthalocyanine, molybdenum phthalocyanine or a combination thereof. The carbon precursor gas may be methane, and may further contain other gases such as argon and hydrogen.

The flowchart of the manufacturing method of the one-dimensional carbon nanostructure of this invention is shown. 1 shows a horizontal apparatus suitable for producing a one-dimensional carbon nanostructure of the present invention. 1 shows an apparatus having a plurality of temperature zones used in the production of a one-dimensional carbon nanostructure of the present invention. 1 shows a vertical apparatus suitable for the practice of the present invention. 1 shows a schematic of a masked substrate used in the method of the present invention. Mask 325 covers substrate 305, while target area 335 on the substrate is unmasked.

Detailed Description of the Invention Definitions Unless otherwise stated, the following terms used in this application, including the specification and claims, are defined as follows: Note that the singular forms “a (an)” and “the (the)” used in the specification and the claims include the plural unless the context clearly indicates otherwise. Definitions of common chemical terms are, for example, Carey and Sundberg (1992) “Advanced Organic Chemistry 3rd Edition” Volumes A and B, Plenum Press (New York); and Cotton et al. (1999) “Advanced Inorganic Chemistry. 6th edition ", Wiley (New York).

  In this application, the terms “single-walled carbon nanotube” or “one-dimensional carbon nanotube” are used interchangeably and have a wall substantially composed of a single layer of carbon atoms, and have a hexagonal crystal structure with a graphite-type bond. Means a thin sheet of carbon atoms arranged in a cylindrical shape.

  In the present application, the term “multi-walled carbon nanotube” means a nanotube composed of two or more coaxial tubes.

  The terms “metalorganic” or “organometallic” are used interchangeably and refer to a coordination compound of an organic compound and a metal, transition metal or metal halide.

II. SUMMARY The present invention discloses a method, apparatus, and process for producing a structure consisting of carbon nanotubes and single-walled nanotubes at preselected locations on a substrate.

  In one embodiment, one surface of the substrate has a mask covered area and an uncovered or non-masked area. By non-masked region is meant a region that is a target for synthesizing nanotubes or nanostructures. Catalyst particles such as metal are selectively deposited in the non-masked region. In general, an organic metal compound layer is deposited on a non-mask region, and organic components are removed by oxidation or the like to obtain catalytic metal particles at specific positions on the substrate. Next, the substrate on which the catalyst particles are formed is brought into contact with the carbon precursor gas to obtain single-walled carbon nanotubes and nanostructures. As a result, carbon nanotubes and nanostructures are produced by chemical vapor deposition (CVD) at positions where catalyst particles are present. A flowchart of this method is shown in FIG. By controlling the size of the catalyst particles deposited on the non-masked surface of the substrate, the size and type of carbon nanostructures formed during chemical vapor deposition can be controlled.

In another embodiment, the steps of producing carbon nanotubes and nanostructures are performed in the apparatus. Nanotubes are produced using a reactor having multiple temperature zones. A substrate having a masked area and an unmasked area is placed in one temperature zone. An organometallic compound is placed in another temperature zone. The temperature and pressure in the reaction vessel are controlled so that the organometallic compound forms a predetermined thickness layer on the non-masked portion of the substrate by physical vapor deposition. The organometallic layer on the non-masked substrate is treated to obtain metal particles. Preferably the metal catalyst essentially comprises iron, molybdenum, cobalt, nickel or mixtures thereof. Using these metal particles as a catalyst, nanotubes and nanostructures are synthesized by CVD. In addition, the reaction chamber may be filled with a heat transfer gas and an inert carrier gas. Preferably, the atmosphere contains an inert gas, argon or helium, or may optionally contain some hydrogen. The atmosphere is maintained at a pressure in the range of 10 ⁻⁵ Torr to 760 Torr, preferably 10 ⁻⁴ Torr to 10 ⁻³ Torr.

III. Reaction Vessel In one aspect of the present invention, a system for producing carbon nanotubes is provided. The system supports a plurality of temperature zones and can have a hermetic chamber with a carbon precursor gas source and an inert gas source; a sample holder disposed in a first temperature zone; a second A masked substrate disposed in the temperature zone; and an exhaust system connected to the reactor and exhausting gas from the chamber. The system, process and method of the present invention will now be described with reference to the accompanying figures, wherein like reference numbers indicate identical or functionally equivalent elements. Further, in the figure, the leftmost digit of each reference number corresponds to the figure number in which the reference number was first used.

  FIG. 2 is a schematic diagram of a “horizontal” reactor 100 that can be used to practice various aspects of the present invention. As the reaction furnace 100, any conventionally known furnace may be used as long as it can control the gas flow in the heated reaction chamber. For example, Carbolite TZF 12/65/550 is a suitable horizontal three-zone furnace for carrying out various aspects of the present invention.

  As shown in FIG. 2, a quartz tube 110 is disposed in a reaction furnace 100 and used as a reaction chamber. The quartz tube functions as the reaction chamber 110 of the reaction furnace 100, and the reaction furnace supplies all the heat necessary for the process. The reaction chamber 110 includes gas inlets 121 to 123 and a gas outlet 125, thereby controlling the atmosphere composition in the quartz tube. Depending on the conditions required for a given process, additional gas inlets may be provided or unnecessary gas inlets may be blocked. Alternatively, a vacuum pump (not shown) may be provided at the gas outlet 125 so that the reaction chamber can be operated at a low pressure. Other types of reaction chambers 110 that can be suitably used in the present invention will be apparent to those skilled in the art. During operation of the reaction furnace 100, a sample holder 130, such as a quartz boat, a quartz substrate or other type of reaction vessel or substrate, can be placed in the quartz tube 110. In general, the sample holder 130 is used to easily introduce or remove material from the quartz tube or the reaction chamber 110. The material to be processed is placed in the sample holder 130 during the gas flow / heating stage in the desired process.

  Another horizontal reaction vessel with multiple temperature zones is shown in FIG. The reaction furnace 100 is configured to perform a physical vapor deposition process. Similar to FIG. 2, the reactor 100 includes a quartz tube 110 that functions as a reaction chamber. In order to perform the physical vapor deposition process, the reactor is configured to include at least two temperature zones 405 and 406. Although the reaction furnace 100 is shown separately in FIG. 3, it is merely for emphasizing the existence of the temperature zones 405 and 406, and all the portions of the reaction furnace 100 support a plurality of temperature zones. It may be a part of a conventionally known reaction furnace capable of

  In normal operation, the sample holder 430 carrying the organometallic precursor can be placed in the temperature zone 405 of the reaction chamber 110. A masked substrate 435 can be placed in the temperature zone 406 of the reaction chamber 110. Then, the pressure in the reaction chamber 110 can be reduced by the vacuum pump 440. The vacuum pump 440 may use any conventionally known vacuum pump. When the internal pressure of the reaction chamber 110 reaches a desired pressure, the temperature of the temperature zones 405 and 406 is adjusted to start the physical vapor deposition process.

  The temperature of the temperature zones 405 and 406 is adjusted so that a temperature gradient is created to promote the formation of a distinctly thick organometallic layer on the masked substrate 435 located in the temperature zone 406. In one embodiment, all temperature zones can be heated to different temperatures. In another aspect, the temperature zone 405 can be heated and the other temperature zones can be prevented from being heated. In this case, since only the sample holder on which the organometallic compound is placed is heated, a temperature gradient is generated. The temperature in the temperature zone can be selected according to the selected organometallic compound, the composition of the substrate, the composition of the mask material, the desired thickness of the organometallic layer, the capacity of the reaction chamber, the gas used for heat conduction, and the like. Preferably, the temperature of temperature zone 405 is selected such that the organometallic compound disposed therein sublimes. The temperature of the temperature zone 406 can be selected to be deposited as a layer on the organometallic masked surface.

  The vacuum pump 440 continues to operate during the physical vapor deposition process. By operating the vacuum pump, not only can a low pressure environment be maintained, but a flow can be created in the reaction chamber 110 from the sample holder to the masked substrate. As a result, the organometallic vapor sublimated from the sample in the sample holder 430 moves from the temperature zone 405 to the temperature zone 406. Thus, in this step, the organometallic vapor moves to the masked substrate 435 and is physically deposited on the masked substrate by the lower temperature in the temperature zone 406.

  In another embodiment, the reaction vessel may be oriented in a “vertical” direction as shown in FIG. Reaction chamber 500 may be any conventionally known vertical reaction furnace or chamber that is suitable for performing vacuum processing. A conventionally known vacuum pump (not shown) can be connected to the reaction chamber 500 for the purpose of operating the reaction chamber under reduced pressure. In a standard method of performing a physical vapor deposition process using the system of FIG. 4, an organometallic sample 530 is placed in the reaction chamber 500 and a means for heating the reaction vessel 531 is provided. The organometallic sample 530 can be placed in a reaction vessel 531 such as a quartz boat. For example, the reaction vessel 531 can be disposed on a heater 510 such as a hot plate. Alternatively, a vertical furnace including a heater 510 for heating the reaction vessel 531 as an integral part of the reaction chamber, for example, a heating zone, can be used as the reaction chamber 500. In this case, the reaction vessel 531 is placed on a pedestal or other support for the purpose of correctly placing the organometallic sample 530 in the heating zone of the reaction chamber 500. A physical vapor deposition target such as a masked substrate 535 is also placed in the reaction chamber 500 so that the masked surface faces the organometallic sample. The distance between the organometallic sample 530 and the masked surface 535 can be selected from about 1 cm to about 30 cm, preferably about 3 cm to about 15 cm, more preferably about 5 cm to 10 cm, or any distance therebetween. Thus, 530 and 535 can be separated by 5 cm, 6 cm, 7 cm, 8 cm, 9 cm or 10 cm. Prior to initiating physical vapor deposition, the pressure in the reaction chamber 500 can be reduced with a vacuum pump. When the desired pressure is reached, turn off the vacuum pump. The heater 510 can then be actuated to raise the temperature of the organometallic sample to cause organometallic sublimation. When FePc is used as the organometallic, sample 530 is heated to about 480 ° C to about 550 ° C. The organometallic vapor generated by sublimation contacts the masked substrate 535, and an organometallic layer is deposited on the exposed surface. The masked substrate 535 need not be heated during this physical vapor deposition process. However, depending on the reaction chamber configuration and the organometallic sample used, it may be desirable to heat the masked substrate to 200 ° C. to 300 ° C. to improve the adhesion of the organometallic layer deposited on the masked substrate 535. is there. Alternatively, due to the proximity of the organometallic sample 530 and the heater 510, some heating of the masked substrate 535 can occur.

  In one embodiment, the boat with the organometallic is heated and the masked substrate is not heated. As the boat with the organic metal is heated, a temperature gradient occurs. In another embodiment, both the boat and the masked substrate are heated. Usually, the substrate is at a lower temperature, which creates a temperature gradient. The substrate may be heated for the purpose of obtaining better adhesion or controlling the thickness of the organometallic layer to be formed.

IV. Substrate In one embodiment of the present invention, single-walled carbon nanotubes can be stably bonded to the solid surface of the substrate 305 shown in FIG. The dimensions and position of the substrate can be such that nanotubes with controlled dimensions, shape, orientation and position can be synthesized, and the substrate can be a variety of materials such as plastic, ceramic, metal, gel, membrane, glass, beads, etc. Can be created from. Preferably, the substrate is made of a material suitable for use as a support when carbon nanotubes are synthesized using a metal growth catalyst described later. Such materials include crystalline silicon, polysilicon, silicon nitride, tungsten, magnesium, aluminum and their oxides, preferably silicon oxide, aluminum oxide and magnesium oxide. For example, an exposed region of silicon oxide on the silicon wafer surface can be used as the deposition target 335. The other regions of the substrate 305 may be configured using any suitable structural material.

  In one embodiment of the invention, the substrate is treated to provide specific locations for the growth of nanotubes and nanostructures. Such treatments include masking the substrate surface, providing unmasked areas, and performing electrochemical (EC) and photoelectrochemical (PEC) etching to form individual holes or structures at specific locations on the substrate, etc. Processing. As shown in FIG. 5, the substrate 305 preferably has a top surface 315 and an opposite surface. A portion covered with a removable mask 325 and a portion not covered (non-mask region 335) can be provided on the upper surface. The non-mask region 335 represents an area that is a target of carbon nanotube synthesis. Since the metal catalyst particles are positioned in the non-mask region by the physical vapor deposition process, the non-mask region may be hereinafter referred to as a vapor deposition target 335.

  The deposition target 335 is preferably made of a material suitable for use as a support during the synthesis of carbon nanotubes using a metal growth catalyst described below. Such materials include silicon oxide, aluminum oxide and magnesium oxide. For example, the deposition target 335 can be an exposed silicon oxide region.

  The mask 325 may be made of any material that can be removed if desired. That is, the mask is formed of a material that can be removed relatively easily by physical removal, dissolution in water or solvent, chemical or electrochemical etching, vaporization by heating, and the like. Examples of mask materials include water-soluble or solvent-soluble salts such as sodium chloride, silver chloride, potassium nitrate, copper sulfate, and indium chloride; and soluble organic materials such as sugar and glucose. The mask material may be a chemically etchable metal or alloy such as Cu, Ni, Fe, Co, Mo, V, Al, Zn, In, Ag, Cu-Ni alloy, Ni-Fe alloy, A base-soluble material such as Al may be used. The mask can be formed from a soluble polymer such as polyvinyl alcohol, polyvinyl acetate, polyacrylamide, acrylonitrile-butadiene-styrene. Alternatively, the removable mask may be a volatile (evaporable) material such as a PMMA polymer. These materials may be dissolved in an acid such as hydrochloric acid, aqua regia or nitric acid, or may be dissolved and removed with a base solution such as sodium hydroxide or ammonia. The removable layer or mask may be an evaporable material such as Zn that can be removed by thermal decomposition or combustion. The mask can be introduced physically on the substrate, by chemical deposition such as electroplating or electroless plating, by physical vapor deposition such as sputtering, evaporation, laser cutting, ion beam deposition, or chemical vapor deposition ( This can be done by chemical vapor decomposition.

  Thus, in one embodiment, the mask may be an aluminum foil. Aluminum foil can be given a structure by cutting and etching. This structure preferably exposes the vapor deposition target 335 on the substrate and denotes the position, size and / or orientation of the synthesized nanotubes and nanostructures. Such a structure may be, for example, a hole at a specific position for forming a nanotube at a specific position, or a V-shaped groove, a Y-shaped groove, a circle, It may be a trench or the like.

  In another embodiment, the mask 325 may be a metal oxide such as quartz or sapphire. The metal oxide may be printed out with a stencil or patterned in a desired structure such as a hole, circle or groove. In another embodiment, the deposition target can be formed by introducing impurities, local flaws or stress on the substrate or mask. Impurities, local flaws or stresses are X-ray lithography, deep UV lithography, scanning probe lithography, electron beam lithography, ion beam lithography, photolithography, electrochemical deposition, chemical deposition, electrolytic oxidation, electroplating, sputtering, thermal diffusion and It can be introduced by vapor deposition, physical vapor deposition, sol-gel deposition or chemical vapor deposition. In yet another aspect, the location and number of carbon nanotubes can be controlled by etching a desired location and not etching the region surrounding the desired location at all or at a different rate.

  In the method of manufacturing the nanotubes of the present invention, lithography techniques such as light and scanning probe lithography can be used for the purpose of forming holes or structures at specific locations on the substrate or mask. Using conventional light and scanning probe lithography techniques, holes can be formed at precise locations (controlled locations) on the substrate or mask with controlled diameters and controlled depths. Examples of such methods include X-ray lithography, deep ultraviolet lithography, scanning probe lithography, electron beam lithography, ion beam lithography, and optical lithography. Scanning probe lithography can be used to form structures such as holes while accurately controlling position and dimensions. Optical lithography is a technique that allows mass production of structures. It is possible to accurately control the position and dimensions of structures such as holes.

V. Catalyst Before the carbon nanotubes are grown in the unmasked region 335, a metal catalyst must be deposited in that region. The function of the metal catalyst in the carbon nanotube growth process is to decompose the carbon precursor and assist in the regular ordered deposition of carbon. Metal catalysts include Group V metals (such as vanadium), Group VI metals (such as Cr, W, Mo and mixtures thereof), Group VII metals (such as Mn), Group VIII metals (Co, Ni, Ru, Rh, Pd, Ir, Pt and mixtures thereof, etc.) and lanthanides (cerium etc.). The oxide of the material used for the substrate can also be used as a catalyst for carbon nanotube growth. Preferably, the metal catalyst is iron, molybdenum or a mixture thereof.

  In one embodiment, the metal catalyst may be complexed with an organic moiety to form an organometallic precursor compound. That is, a metal selected from the metals listed above can be complexed with, for example, phthalocyanine, porphorin, cyclopentyl and the like to form a precursor compound. In general, an organometallic compound is selected that gives properties such as high vapor pressure, high purity, high vapor deposition rate, ease of handling, non-toxicity, low cost, and suitable vapor deposition temperature. Various organometallic precursors can be used to form the organometallic precursor layer. An example of a suitable organometallic precursor material is iron phthalocyanine (FePc). FePc is a solid at room temperature. By heating the FePc sample at a temperature sufficient to cause sublimation of FePc, it is possible to obtain FePc vapor. Heating the FePc sample to about 480 ° C. to about 520 ° C. provides an amount of FePc vapor suitable for the physical vapor deposition process. Molybdenum phthalocyanine (MoPc) or a mixture of FePc and MoPc can also be used as the organometallic precursor. Preferably, an organometallic compound containing iron or molybdenum suitable for use in the physical vapor deposition process can be used. An example of such a compound is iron porphyrin.

  In one embodiment, the process of the present invention evaporates one or more organometallic precursor compounds, transfers the evaporated precursors to the masked substrate surface with a carrier gas, and forms a thin film on the substrate surface by a chemical reaction. To be implemented. The physical vapor deposition described above can be performed at a relatively low temperature. By changing the amount of the raw material and the carrier gas, the composition of the thin film and the deposition rate can be easily controlled, and the finally obtained thin film can damage the substrate surface. It is advantageous in that it has good uniformity without giving.

  During the physical vapor deposition process, an organometallic precursor layer is formed on all exposed surfaces of the substrate. That is, the organometallic layer is formed on the mask 325 as well as on the deposition target 335 (exposed portion of the upper surface 315). The thickness of the deposited organometallic layer is one of the factors affecting the final dimensions and shape of the carbon nanostructures produced using the present invention. The thickness of the organometallic layer is typically from about 1 micron to about 30 microns. However, organometallic layers can be formed using physical vapor deposition up to 50 microns or thicker if desired.

  After depositing the organometallic precursor layer, the mask is removed from the substrate. The method for removing the mask depends on the type of the mask layer used. For example, if the mask is made of aluminum foil or a thin plastic layer, the mask can be lifted away from the underlying substrate. In this case, when the mask is physically removed, the organometallic layer deposited on the mask is also removed. Therefore, the organometallic layer remains only on the deposition target.

  After removing the mask, the portion of the organometallic layer remaining on the substrate is oxidized or pyrolyzed. When the organometallic layer is oxidized or pyrolyzed, the organic component of the organometallic compound is oxidized. Since the oxidation reaction product is volatile, it is removed from the substrate to leave metal from the organometallic layer. The metal remaining on the substrate fuses during oxidation to form particles or particle clusters. These metal or metal oxide particles act as a growth catalyst during the synthesis of carbon nanotubes. Since the organometallic layer is present only on the deposition target (the region that is not masked during the deposition of the organometallic layer), the metal growth catalyst particles are formed to the same extent on the deposition target.

One method of oxidizing the organometallic layer is to heat the substrate to about 450 ° C. to about 500 ° C. in the presence of an oxygenated atmosphere. For example, the reactor 100 shown in FIG. 2 can be configured to perform this type of process. A substrate on which the organometallic layer is formed is placed in the reaction chamber 110. The gas inlet 125 is connected to an ultra high purity oxygen (UHP O ₂ ) source. While flowing UHP O ₂ , the temperature of the furnace 100 is raised to 500 ° C. These process conditions are maintained for 2 to 4 hours in order to oxidize organic components in the organometallic layer and leave metal growth catalyst particles on the substrate. In addition, the oxidation environment used for formation of the metal growth catalyst particles in this step may partially oxidize the metal growth catalyst particles or may completely oxidize the metal growth catalyst particles. Accordingly, those skilled in the art will appreciate that the metal growth catalyst particles may be comprised of either metal or metal oxide.

  In another embodiment, the oxidation of the organometallic layer can be performed prior to removal of the vapor deposition mask. Vapor deposition masks made of materials such as sapphire are relatively inert when placed in the reaction conditions used for oxidation of the organometallic layer. When such a vapor deposition mask is used, the organometallic layer can be oxidized before removing the mask. Thus, oxidation of the organometallic layer forms metal particles in both the mask and the exposed areas of the substrate. When the deposition mask is removed from the substrate, the metal particles on the mask are removed. This provides the desired result of selectively placing metal particles to be used as a growth catalyst only on the substrate portion that was exposed during vapor deposition.

In another embodiment, the selected catalytic metal can be deposited directly on the unmasked region 335 without being complexed. Using conventional methods known to those skilled in the art, the metal catalyst material can be uniformly deposited in the non-masked areas. Conventional catalytic vapor deposition methods include electrochemical deposition, chemical deposition, electrolytic oxidation, electroplating, sputtering, thermal diffusion and vapor deposition, physical vapor deposition, spraying, coating, printing, imaging, sol-gel deposition and chemical vapor deposition. Can be mentioned. The metal to be deposited is usually a flat substrate such as quartz, glass or silicon, a silicon oxide surface support such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), MgO, Mg (Al) O (aluminum stabilized oxidation). Magnesium), ZrO ₂ , molecular sieve zeolite, or other supports known in the art.

  After forming the metal growth catalyst particles on the substrate surface, the metal oxide particles can be used as a growth catalyst for the synthesis of carbon nanotubes, nanofibers and other one-dimensional carbon nanostructures by a chemical vapor deposition (CVD) process. .

VI. Carbon Precursor Carbon nanotubes can be synthesized using a carbon precursor such as a carbon-containing gas. In general, any carbon-containing gas that does not thermally decompose to 800 ° C. to 1000 ° C. may be used. Examples of suitable carbon-containing gases include carbon monoxide; saturated and unsaturated aliphatic hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, ethylene, acetylene and propylene; oxygenates such as acetone and methanol Hydrocarbons; aromatic hydrocarbons such as benzene, toluene and naphthalene; and mixtures of the above gases such as a mixture of carbon monoxide and methane. In general, the use of acetylene promotes the formation of multi-walled carbon nanotubes, but CO and methane are preferred as the supply gas for forming single-walled carbon nanotubes. The carbon-containing gas may optionally be mixed with a diluent gas such as hydrogen, helium, argon, neon, krypton, xenon and mixtures thereof.

  The reaction temperature used depends on the type of catalyst and the type of precursor. The energy balance equation for each chemical reaction can be used to analyze and determine the optimum CVD reaction temperature for carbon nanotube growth. This determines the required reaction temperature range. The optimum reaction temperature also depends on the selected precursor and catalyst flow rates. In general, this method requires a CVD reaction temperature of 300 ° C to 900 ° C, more preferably a reaction temperature of 400 ° C to 600 ° C.

  The size and type of carbon nanostructures formed during the CVD process is somewhat dependent on the thickness of the organometallic layer deposited on each deposition target. During pyrolysis of the organometallic layer, the metal from the organometallic layer accumulates on the substrate surface. For a given region on the substrate, as the thickness of the organometallic layer increases, the amount of metal that accumulates in that region during organometallic oxidation increases. This is thought to affect the size of the metal particles formed on the substrate in two ways. First, a thicker organometallic layer results in larger metal growth catalyst particles. Secondly, the thicker organometallic layer makes it easier to obtain clusters of metal growth catalyst particles.

  Without being bound by a particular theory, it is believed that larger diameter nanostructures are synthesized when larger metal growth catalyst particles are formed on the surface. For example, when a 1 micron FePc layer is pyrolyzed, metal growth catalyst particles capable of independently producing single-walled carbon nanotubes having a length of 10 microns and a diameter of 1 nm are obtained. When the 5-10 micron FePc layer is pyrolyzed under the same conditions, metal growth catalyst particles capable of independently producing carbon nanotubes having a diameter of 35 nm are obtained. This carbon nanotube is not a single-walled nanotube. Further, when an FePc layer having a thickness of 30 microns is used, metal growth catalyst particles capable of independently producing solid carbon nanofibers having a diameter of about 1 micron can be obtained by pyrolyzing the organometallic layer.

  Carbon nanotubes and nanostructures produced by the methods and processes described above can be used for field emission devices, memory devices (high density memory arrays, memory logic switching arrays), nano MEMS, AFM imaging probes, distributed diagnostic sensors and strain sensors. Etc. can be used. Other important applications include thermal control materials, ultra-strong and lightweight reinforcements and nanocomposites, EMI shielding materials, catalyst supports, gas storage materials, high surface area electrodes and lightweight lead cables and wires.

EXAMPLES Examples of specific embodiments for carrying out the present invention are described below. The examples are described solely for the purpose of illustrating the invention and are not intended to limit the scope of the invention in any way. Although attention was paid to the accuracy of the numerical values used (eg quantity, temperature, etc.), some experimental errors and deviations should of course be allowed.

Purification of the organometallic sample It is desirable to purify the organometallic precursor prior to vapor deposition on the masked substrate. For example, FePc samples may contain up to 20% by weight of other materials. This mixing can cause problems during the physical vapor deposition process that can adversely affect the reproducibility and reliability of the CVD process, such as variations in sublimation speed and contamination of the resulting physical vapor deposition layer. In order to reduce the effects of such contamination, the organometallic precursor sample can be purified prior to use in the physical vapor deposition process. In the purification, an organometallic sample to be purified is placed in the temperature zone 405 of the reactor shown in FIG. A deposition target for recovering the purified organometallic material is placed in the temperature zone 406. However, this is not essential because the physical vapor deposition process will deposit the organometallic material on all exposed surfaces in the temperature zone 406. Purification is performed under conditions similar to those used for vapor deposition on the masked substrate. For example, when purifying an FePc sample, the temperature in the temperature zone 405 is set to about 480 ° C. to about 520 ° C., and the temperature in the temperature zone 406 is set to about 200 ° C. to about 300 ° C. The physical vapor deposition process for purification is performed under a pressure of 10 ⁻⁴ Torr. The vacuum pump not only maintains the pressure in the reaction chamber 110 but also creates a flow in the reaction chamber 110 toward the deposition target. This process condition is maintained for about 10 hours or until all starting samples to be purified have sublimed. After the purification step, purified organometallic material is recovered from all exposed surfaces in temperature zone 406, such as all substrates disposed in temperature zone 406, walls of reaction chamber 110, and the like. If desired, the organometallic sample may be purified multiple times to obtain higher crystallinity and purity.

Synthesis of carbon nanotubes Carbolite TZF12 / 65/550 type having a horizontal three-zone furnace is used. Rectangular silicon oxide having a length of 4 cc, a width of 4 cm, and a thickness of 0.5 cm is selected as a substrate. One surface of the substrate is covered with aluminum foil, and holes with a diameter of about 10 nm are evenly provided in the aluminum foil. Place a quartz sample holder in one of the temperature zones. 0.5 g of an organometallic precursor compound, iron phthalocyanine (FeC ₃₂ H ₁₆ N ₈ ) is placed on the sample holder. The masked substrate prepared above is placed in another temperature zone. The reaction chamber pressure is reduced to about 10 ⁻⁴ Torr by a vacuum pump. When the internal pressure of the reaction chamber reaches about 10 ⁻⁴ Torr, the temperature in the furnace is raised and the physical vapor deposition process is started. The temperature of the temperature zone containing FePc is raised to about 480 ° C to about 520 ° C. The temperature zone containing the substrate is similarly heated to about 200 ° C. to about 300 ° C. These temperatures are maintained until an organometallic layer about 2 microns thick is formed on the masked substrate. After depositing the organometallic precursor layer, the aluminum foil mask is removed from the substrate. The furnace is connected to an ultra high purity oxygen (UHP O ₂ ) source. The furnace temperature is raised to 500 ° C. with UHP O ₂ flowing at 1000 cubic centimeters per minute. These process conditions are maintained for 2 to 4 hours in order to oxidize organic components in the organometallic layer and leave metal growth catalyst particles on the substrate. Without removing the resulting substrate with metal oxide particles from the reaction chamber, hydrogen (H ₂ ), carbon precursor gas methane (CH ₄ ), and inert carrier gas argon (Ar) from the gas inlet. Supply. The temperature in the reactor is raised to about 700 ° C. while exposing the substrate to 350 sccm H ₂ , 450 sccm Ar, and 12 sccm CH ₄ . The temperature and gas flow are maintained for about 15-60 minutes to form carbon nanostructures.

  Although the invention has been described in detail with reference to preferred embodiments and various alternative embodiments, those skilled in the art will recognize that various modifications and details are possible within the spirit and scope of the invention.

Claims (39)

Providing a substrate with a deposition mask;
Depositing an organometallic layer comprising an organic component and an inorganic component including a transition metal on the substrate, and depositing at least a portion of the organometallic layer on an unmasked portion of the substrate;
Removing the deposition mask from the substrate;
Exposing a portion of the organometallic layer to air;
Volatilizing the organic component of a portion of the organometallic layer to form a growth catalyst;
A method of synthesizing a carbon nanostructure comprising contacting the substrate with a carbon precursor gas at a deposition temperature to form a carbon nanostructure. The method of claim 1, wherein the organometallic layer is selected from the group consisting of iron phthalocyanine, molybdenum phthalocyanine, nickel phthalocyanine, and mixtures thereof. The method of claim 1, wherein the organometallic layer is deposited by physical vapor deposition. The method of claim 1, wherein the organometallic layer is between about 1 micron and about 30 microns thick. The method according to claim 1, wherein the vapor deposition mask is made of a metal oxide. The method according to claim 1, wherein the vapor deposition mask is made of one selected from the group consisting of silicon oxide and aluminum oxide. The method of claim 1, wherein the non-masked portion of the substrate has a top surface comprising a metal oxide. 8. The method of claim 7, wherein the metal oxide is selected from the group consisting of silicon oxide, aluminum oxide, and magnesium oxide. The method of claim 1, wherein the organic component of the portion of the organometallic layer is volatilized by heating a portion of the organometallic layer to a temperature between 450 ° C and 500 ° C. The method according to claim 9, wherein a part of the organometallic layer is exposed to air for 2 to 4 hours. The method of claim 1, wherein the growth catalyst comprises metal growth catalyst particles. The method according to claim 1, wherein the carbon precursor gas is methane. The method of claim 1, wherein contacting the substrate with the carbon precursor gas comprises contacting the substrate with an atmosphere comprising methane, argon and hydrogen. The method according to claim 13, wherein the substrate is exposed to the carbon precursor gas for 15 to 60 minutes. The method according to claim 1, wherein the deposition temperature is 700 ° C. The method of claim 1, wherein the organometallic layer is manufactured from a refined organometallic material prior to vapor deposition of the organometallic layer. The method of claim 1, wherein a portion of the organometallic layer is exposed to air before removing the deposition mask from the substrate. The method according to claim 1, wherein the carbon nanostructure is a single-walled carbon nanotube. The method according to claim 1, wherein the carbon nanostructure is a one-dimensional carbon nanostructure. Having a reactor capable of supporting a plurality of temperature zones and having an airtight chamber with a carbon precursor gas source and an inert gas source;
Said hermetic chamber;
A sample holder located in the first temperature zone;
A system for producing carbon nanotubes, comprising: a masked substrate disposed in a second temperature zone; and a vacuum pump connected to the reactor and evacuating gas from the chamber. 21. The system of claim 20, wherein the first temperature zone is 150 [deg.] C. to 350 [deg.] C. higher than the second temperature zone. The system of claim 21, wherein the first temperature zone is 200 ° C. to 300 ° C. higher than the second temperature zone. 21. The system of claim 20, wherein the carbon precursor gas is selected from the group consisting of methane, ethane, propane, ethylene, propene, and carbon dioxide. 21. The system of claim 20, wherein the inert gas is selected from the group consisting of hydrogen, helium, argon, neon, krypton, xenon, and mixtures thereof. 21. The system of claim 20, wherein a catalyst is provided by the sample holder. The said catalyst contains the transition metal chosen from the group which consists of iron, molybdenum, nickel, and mixtures thereof, It is manufactured from the organic metal which consists of an organic substance component and the inorganic substance component containing the said transition metal. The system described in. 27. The system of claim 26, wherein the organometallic is selected from the group consisting of iron phthalocyanine, molybdenum phthalocyanine, nickel phthalocyanine, and mixtures thereof. Providing a substrate with a deposition mask;
An organic metal layer comprising an organic component and an inorganic component, comprising an organic component and an inorganic component including a transition metal, is deposited on the substrate, and at least a portion of the organometallic layer is deposited on a non-mask portion of the substrate. ;
Removing the deposition mask from the substrate;
Exposing a portion of the organometallic layer to air;
Volatilizing the organic component of a portion of the organometallic layer;
A carbon nanotube structure manufactured by a step of bringing the substrate into contact with a carbon precursor gas at a deposition temperature to form a carbon nanostructure. 29. The carbon nanotube structure according to claim 28, wherein the organic metal layer is deposited by physical vapor deposition. 29. The carbon nanotube structure of claim 28, wherein the organometallic layer is selected from the group consisting of iron phthalocyanine, molybdenum phthalocyanine, nickel phthalocyanine, copper phthalocyanine, and mixtures thereof. 29. The carbon nanotube structure according to claim 28, wherein the substrate is selected from the group consisting of silicon oxide, aluminum oxide, magnesium oxide and mixtures thereof. 29. The carbon nanotube structure according to claim 28, wherein the vapor deposition mask is selected from the group consisting of silicon oxide and aluminum oxide. The carbon nanotube structure of claim 32, wherein the vapor deposition mask is removed before the organometallic layer is exposed to air. The carbon nanotube structure according to claim 32, wherein the deposition mask is removed after the organometallic layer is exposed to air. 29. The carbon nanotube structure according to claim 28, wherein the carbon precursor gas is selected from the group consisting of methane, ethane, propane, ethylene, propene and carbon dioxide. The carbon nanotube structure according to claim 28, wherein the carbon precursor gas is methane. 36. The carbon nanotube structure according to claim 35, wherein the step further includes supplying an additional gas. 38. The carbon nanotube structure of claim 37, wherein the additional gas is selected from the group consisting of hydrogen, helium, argon, neon, krypton, xenon, and mixtures thereof. The carbon nanotube structure according to claim 36, wherein the step further includes supplying hydrogen and argon.

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