JP2010504268A - Growth of carbon nanotubes using metal-free nanoparticles - Google Patents

Growth of carbon nanotubes using metal-free nanoparticles Download PDF

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JP2010504268A
JP2010504268A JP2009528558A JP2009528558A JP2010504268A JP 2010504268 A JP2010504268 A JP 2010504268A JP 2009528558 A JP2009528558 A JP 2009528558A JP 2009528558 A JP2009528558 A JP 2009528558A JP 2010504268 A JP2010504268 A JP 2010504268A
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metal
nanoparticles
substrate
carbon
free catalyst
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キャロライン・ウィーラン
サンティアゴ・クルス・エスコンハウレギ
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アイメックImec
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00Manufacture or treatment of nanostructures
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/08Silica
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/14Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of germanium, tin or lead
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/20Carbon compounds
    • B01J27/22Carbides
    • B01J27/224Silicon carbide
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00Carbon; Compounds thereof
    • C01B32/15Nano-sized carbon materials
    • C01B32/158Carbon nanotubes
    • C01B32/16Preparation
    • C01B32/162Preparation characterised by catalysts

Abstract

The present invention provides a method of forming at least one carbon nanotube (16) using metal-free catalytic nanoparticles (14) such as nanoparticles comprising Si or Ge. The method of the present invention uses the steps of decomposing the carbon source gas and forming carbon fragments that recombine in the metal-free catalyst nanoparticles (14) to later grow carbon nanotubes (16). Methods according to embodiments of the present invention result in carbon nanotubes (16) that are free of metal impurities.
[Selection] Figure 1

Description

  The present invention relates to the growth of carbon nanotubes. In particular, the present invention relates to the growth of carbon nanotubes using metal-free (or metal-free) nanoparticles.

  Carbon nanotubes (CNT) generally exhibit very good electrical and mechanical properties. Therefore, CNTs are expected to find many industrial uses. One of these applications would be the use of both passive and active components in nanoelectronic devices.

  The most widely accepted growth mechanism for CNTs is based on the catalytic decomposition of the carbon source (or carbon source) at the surface of the metal nanoparticles (or metal nanoparticles) that act as catalysts in CNT synthesis. In this growth mechanism, the hydrocarbon source decomposes at the exposed outermost surface of the metal nanoparticles, releasing hydrogen and carbon dissolved in the nanoparticles. The dissolved carbon diffuses in the metal nanoparticles and precipitates (or aggregates) to start the formation of CNTs.

  One of the important problems in the growth mechanism shown in the known technology is that it requires catalytic metal particles (or metal catalyst particles) to initiate the growth of carbon nanotubes. The disadvantage of this is that impurities are present in the CNTs on which the catalytic metal particles are grown. These impurities need to be removed before CNTs can be used in many applications. To remove undesirable metal impurities from CNTs, extensive chemical and thermal oxidation processes are usually required. For example, a multi-stage purification method involving the use of nitric acid reflux and thermal oxidation can be used.

  Catalyst-free (or catalyst-free) growth of CNTs using laser absorption and arc discharge has been performed previously. However, these methods require very high temperatures, i.e. temperatures exceeding 3000 ° C. Due to such high temperatures, these methods are not suitable for in-situ growth of CNTs and therefore require an ex-situ approach. In addition, these methods will yield lower yields when compared to CVD methods that can be performed at relatively low temperatures (450-1100 ° C.), are in situ or ex situ, and yield yields that can be mass produced. .

  Nanoletters, 2002 Vol. 2, No. 10, 1043-1046 (by Derycke et al.) Reports uncatalyzed growth of CNTs on SiC (111) at temperatures above 1500 ° C. In this document, the non-catalytic growth of CNT is realized by repeatedly annealing the carbon surface of hexagonal silicon carbide in a vacuum within a predetermined temperature range. CNTs are produced without a metal catalyst, but these CNTs have an axis parallel to the surface, in other words, are oriented and grown on the substrate, and mass production of CNTs is not considered feasible.

  Applied Surface 245 (2005) 21-25 (by Wang et al.) Using plasma-enhanced hot filament chemical vapor deposition with a mixture of methane, ammonia and hydrogen as the reaction gas The carbon nanotips are grown on a silicon substrate without using a catalyst. The formation of carbon nanotips is recognized by the first growth of the carbon film on the length of the silicon substrate for an hour. The combination of further carbon film growth and ion irradiation by applying a negative bias of 430V to the silicon substrate creates a glow discharge and allows the growth of carbon nanotips.

  An object of embodiments of the present invention is to provide an excellent method of growing carbon nanotubes on a substrate.

  The above objective is accomplished by a method according to the present invention.

  An advantage of the method according to embodiments of the present invention is that the carbon nanotubes grown by this method are substantially free of metallic impurities.

  The chemical vapor deposition method can be used in the method according to the embodiment of the present invention.

The present invention provides a method for producing at least one carbon nanotube. The method is
Providing at least one metal-free (or metal-free) catalytic nanoparticle in a chemical vapor deposition reactor (or reactor);
Forming a reactive carbon fragment by decomposing the carbon source gas (or carbon source gas) in a chemical vapor deposition reactor;
Recombining reactive carbon fragments at the top of at least one metal-free catalyst nanoparticle to grow at least one carbon nanotube;
including.

  The method according to embodiments of the present invention results in the formation of carbon nanotubes that are free of metallic impurities.

  During decomposition of the carbon source gas and growth of at least one carbon nanotube, the substrate temperature may be maintained between 800 ° C and 1000 ° C.

In an embodiment of the invention, supplying at least one metal-free catalyst nanoparticle to a chemical vapor deposition reactor comprises
Supplying at least one metal-free catalyst nanoparticle to the substrate;
It may be carried out by moving a substrate with at least one metal-free nanoparticle thereon onto a chemical vapor deposition reactor.

  In these embodiments, at least one carbon nanotube can be formed on the substrate.

  In an embodiment of the present invention, the decomposition of the carbon source gas may be performed using a hot filament (or hot filament), using plasma, or a combination of a hot filament and plasma.

  The hot filament may be a metal filament such as a W filament or a Ta filament. The hot filament may be at a temperature suitable for cracking or cracking the carbon source gas. For example, when a hot filament is used for decomposition of the carbon source gas, the hot filament may be maintained at 950 ° C.

  In an embodiment of the present invention, supplying at least one metal-free catalytic nanoparticle to a chemical vapor deposition reactor comprises at least one semiconductor comprising nanoparticles, such as nanoparticles comprising Si or Ge, for example. May be implemented.

The at least one Si-containing nanoparticle may be, for example, a SiC, SiO 2 or pure Si nanoparticle.

The nanoparticles comprising at least one Ge may be, for example, GeO 2 or pure Ge nanoparticles.

In an embodiment of the invention, supplying at least one metal-free catalyst nanoparticle to the substrate comprises
Supplying a thin layer of metal-free catalyst material, for example a semiconductor catalyst material, to the substrate;
Annealing a thin layer of metal-free material to divide to form at least one metal-free nanoparticle;
To implement.

  Annealing can be performed at temperatures between 500 ° C and 800 ° C.

  In embodiments of the invention, the at least one metal free catalyst nanoparticle may have a diameter between 0.4 nm and 100 nm, or between 0.4 nm and 50 nm.

  In an embodiment of the invention, the method prevents the interaction of at least one metal-free catalyst nanoparticle with the substrate, such as chemical interaction, before supplying the substrate with at least one metal-free nanoparticle. It may further comprise providing a barrier layer (or barrier layer) for the substrate.

In a further embodiment of the invention, the method further comprises pretreating the at least one metal free catalyst nanoparticle prior to feeding the at least one metal free catalyst nanoparticle to the chemical vapor deposition reactor. May be included. An example of such a pre-treatment is a native oxide (or native oxide) (eg, SiO in the case of Si nanoparticles), for example, by immersion in HF (eg, 5 minutes immersion in 2% HF). 2 ) may be removed.

In embodiments of the present invention, the carbon source may be a hydrocarbon having 1 (C1) to 3 (C3) carbon atoms. The carbon source gas may be, for example, CH 4 , C 2 H 4 , C 2 H 2 or C 3 H 6 .

  In another embodiment of the present invention, the carbon source gas may be CO.

  A CVD reactor for carrying out the method according to the invention may contain an inert gas and hydrogen. The inert gas may be nitrogen, for example.

The gas flow in the CVD reactor may be, for example, 4 liters / minute N 2 , 2 liters / minute H 2 , 0.5 liters / minute C 2 H 2 or 0.1 liters C 2 H 2 .

  In a further aspect, the present invention results in the growth of carbon nanotubes from metal-free catalyst nanoparticles. The advantage is that these nanotubes do not contain metal impurities.

  In a still further aspect, the present invention provides for the use of metal free catalyst nanoparticles so that carbon nanotubes grow. The advantage is that these nanotubes do not contain metal impurities.

  Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. The technical features according to the dependent claims may be combined as appropriate with the technical features of the independent claims or the technical features of other dependent claims other than those explicitly stated in the claims.

  Although there are certain improvements, changes, and evolutions of devices in the art, it is believed that the concept of the present invention represents a substantially new and novel improvement, and deviates from known techniques. Including the provision of a device with this property that is more efficient, stable and reliable.

  These and other features, technical features and advantages of the present invention will become apparent from the following description and accompanying drawings which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached figures.

FIG. 1 shows a method of forming metal-free CNTs on Si particles according to an embodiment of the present invention. 2 and 3 schematically illustrate a reactor that can be used to grow metal-free CNTs on a substrate, according to an embodiment of the present invention. 2 and 3 schematically illustrate a reactor that can be used to grow metal-free CNTs on a substrate, according to an embodiment of the present invention. 4, 5 and 6 show scanning electron microscope images after growth of CNTs on Si nanoparticles according to an embodiment of the present invention. 4, 5 and 6 show scanning electron microscope images after growth of CNTs on Si nanoparticles according to an embodiment of the present invention. 4, 5 and 6 show scanning electron microscope images after growth of CNTs on Si nanoparticles according to an embodiment of the present invention.

  All figures are intended to illustrate aspects and embodiments of the present invention. Not all alternatives and options are shown, and thus the invention is not limited to the concepts of the diagrams given. Like numbers are used to indicate like parts in different figures.

  The same reference symbols in different figures indicate the same or similar elements.

  The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The figures shown are only schematic and are not limiting. In the figures, the dimensions of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and relative dimensions do not correspond to the actual scale for carrying out the invention.

  The term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, it is interpreted as specifying that the mentioned feature, integer value, process or member exists as mentioned, and excludes one or more other features, integer values, steps or members or populations thereof. It is not a thing. Therefore, the technical scope of the expression “apparatus comprising means A and B” should not be limited to an apparatus consisting only of elements A and B. In the context of the present invention, it is intended that the meaningful elements of the device are A and B.

  As used herein, “an embodiment” or “an embodiment” means that a particular feature, structure, or characteristic illustrated in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in many places in the specification are not necessarily all referring to the same embodiment, but may be. Further, as will be apparent to those skilled in the art from the disclosure herein, the particular features, structures or characteristics in one or more embodiments may be combined in any suitable manner.

  Similarly, it should be understood that various features of the present invention are described in the description of exemplary embodiments of the invention in order to provide an efficient disclosure and to assist in understanding one or more of the various inventive aspects. Often together in one embodiment, figure or description thereof. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims indicate, aspects of the invention are less than all the features of a single disclosed embodiment. Thus, each claim is based on each separate embodiment of the invention, and the claims following the detailed description are hereby expressly incorporated into this detailed description.

  Further, although some embodiments shown herein include some features that are different from other features included in other embodiments, it will be understood by those skilled in the art that features of different embodiments Combinations are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, the embodiments described in any claim can be used in any combination.

  In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, concepts and techniques have not been shown in detail in order not to obscure the understanding of this description.

  The invention will be illustrated by a detailed description of several embodiments of the invention. It will be apparent to those skilled in the art that other embodiments of the invention may be made without departing from the true spirit or technical teaching of the invention, and that the invention resides in the claims hereinafter appended. Limited only by terminology.

The present invention provides a method for producing at least one carbon nanotube (CNT). The manufacturing method is
Providing at least one metal-free (or metal-free) catalytic nanoparticle in a chemical vapor deposition reactor (or reactor);
Forming a reactive carbon fragment by decomposing the carbon source gas (or carbon source gas) in a chemical vapor deposition reactor;
Recombining reactive carbon fragments at the top of at least one metal-free catalyst nanoparticle to grow at least one carbon nanotube;
including.

  In an embodiment of the present invention, at least one carbon nanotube can be formed on a substrate. In these embodiments, the substrate can be provided with at least one metal-free catalyst nanoparticle and the substrate with at least one metal-free catalyst nanoparticle may be transferred to a CVD reactor for CNT growth. .

  The CVD method used for CNT growth may be thermal CVD or plasma enhanced (or plasma enhanced) CVD (PE-CVD).

  The method according to an embodiment of the present invention can be applied to the growth of CNTs by the base growth principle or the tip growth principle. Whether a particular type of growth principle occurs depends on the interaction between the catalyst nanoparticles and the underlying substrate. The term “base growth”, also called “rooth growth”, refers to a growth mechanism in which the nanoparticles used to initiate CNT growth remain on the substrate during growth. The term “tip growth”, also called “top down growth”, is the growth mechanism of CNT growth with CNTs located on the surface during growth and catalyst nanoparticles at the tip of the CNTs. Means.

Furthermore, the term “non-metal containing” nanoparticle means a nanoparticle comprising a material different from a metal and suitable for use as a catalyst nanoparticle for initiating CNT growth. In an embodiment of the present invention, any metal-free nanoparticles can be used. In embodiments of the invention, the nanoparticles may comprise a semiconductor material such as silicon or germanium. For example, the nanoparticles may be nanoparticles containing silicon, and may be, for example, pure Si, SiO 2 or SiC, or may be germanium-containing nanoparticles, such as pure Ge or GeO 2 . In certain embodiments of the invention, the nanoparticles may be pure Si nanoparticles or pure Ge nanoparticles. In the specification of the present invention, the term “catalyst nanoparticle” must be understood to mean a catalyst nanoparticle which does not contain a metal.

  The method according to embodiments of the present invention allows the synthesis of CNTs free of metal impurities since growth starts from suitable metal-free catalyst particles that can undergo CNT growth according to embodiments of the present invention. To. Therefore, no purification (or purification) step is required after CNT formation.

  Furthermore, the method according to embodiments of the present invention is suitable for use in growing large amounts of CNTs and can be used for high production yield applications.

  In general, the size of the catalyst nanoparticles can affect the final diameter of the formed CNTs. Or, in other words, the final diameter of the CNT can be determined. Catalyst nanoparticles suitable for use for the growth of CNTs according to the method of embodiments of the present invention have a diameter in the range between 0.4 nm and 100 nm or between 0.4 nm and 50 nm. Good.

  Below, the growth method of CNT is demonstrated using FIG. It should be understood that the order of steps described below is not intended to limit the invention in any way.

First, the substrate 10 is supplied in the process (see FIG. 1). In embodiments of the invention, the term “substrate” can include any underlying single material or multiple materials on which CNTs can be grown or used to grow. In embodiments, the term “substrate” refers to, for example, doped or undoped silicon, gallium arsenide (GaAs), gallium arsenide phosphorus (GaAsP), indium phosphide (InP), germanium (Ge), or silicon germanium (SiGe). A semiconductor substrate such as a substrate may be included. The “substrate” may include, for example, an insulating layer such as a SiO 2 or Si 3 N 4 layer in addition to the semiconductor substrate portion. Thus, the term “substrate” also includes glass, plastic, ceramic, silicon-on-glass, silicon-on-sapphire substrates. The term “substrate” is thus generally used in the specific embodiment of the invention, which is used to define the elements of the layer located below or of interest, in particular in the present invention the layer on which the CNTs are grown. The substrate 10 may be a semiconductor wafer such as a Si wafer or a Ge wafer. In embodiments of the present invention, the major surface of the substrate 10 must be inert to the growth of CNTs or not interact with the catalyst nanoparticles formed on the substrate 10. Thus, in embodiments of the present invention, the barrier layer 11 may be provided on the substrate before the catalyst nanoparticles are formed thereon (see further below).

  A thin layer 12 of non-metal material (also referred to as metal free) is supplied, for example, to be deposited on the main surface of the substrate 10. This layer 12 comprises a semiconductor material such as, for example, Si or Ge. For example, in the case of a material containing Si, this thin layer 12 is formed by a commonly used deposition method such as CVD (chemical vapor deposition), for example poly-Si (polycrystalline silicon), amorphous silicon or dioxide. It may be a uniformly deposited thin film such as silicon. The thickness of the thin layer 12 may be less than 15 nm, for example, a thickness between 0.4 nm and 5 nm. In the embodiment of the present invention, the thin layer 12 may be a non-uniform sub-atomic layer (or sub-atomic layer) deposited by, for example, ALD (Atomic Layer Deposition). In another embodiment, a uniform thin layer 12 can be deposited using spin-off and dip coating methods.

If necessary, the barrier layer 11 can be deposited on the substrate 10 before the thin layer 12 is deposited (see FIG. 1). For example, the barrier layer 11 prevents nanoparticles from reacting with the lower substrate 10 and / or forms nanoparticles with the lower substrate 10, for example, a semiconductor layer such as Si or Ge. It can be used to prevent this. The barrier layer 11 may be any other layer that prevents the reaction between the substrate 10 and the material of Si 3 N 4 or the thin layer 12, for example.

  After the thin layer 12 is deposited, an annealing step may be performed to divide the thin layer 12 and form nanoparticles 14 (see step 13 in FIG. 1). The formed nanoparticles 14 can have a diameter between 0.4 nm and 100 nm, for example, a diameter between 0.4 nm and 50 nm. FIG. 1 shows the formation of nanoparticles 14. The thickness of the deposited thin layer 12 and the temperature and time of the annealing process may be controlled or appropriately selected to control the dimensions, and more particularly to control the diameter of the nanoparticles 14. The optimum temperature and time for making the nanoparticles depends on the type and thickness of the thin layer 12 metal-free material. For example, the annealing temperature may be in the range of 500 ° C to 800 ° C. The annealing step can be performed in a reactor. In the reactor, for example, nitrogen and / or hydrogen can be used as the atmospheric gas.

In another embodiment, a dielectric thin film 14 in which nanoparticles 14, which may comprise a pure semiconductor material (such as pure Si), are provided, for example, by deposition, for example by CVD, on a substrate 10 such as a semiconductor wafer. It can be formed into a layer (eg a SiO 2 layer). After the SiO 2 thin layer is deposited, Si nanocrystals may be formed by an annealing process after low energy Si ion implantation is performed on the SiO 2 layer. Then, a SiO 2 is removed by applying a dissolution treatment such as HF treatment (for example, HF vapor or dilute solution) so that Si nanoparticles suitable for use as a CNT growth initiator remain in the substrate 10. it can.

  In yet another embodiment of the invention, the substrate 10 on which the nanoparticles 14 are formed or deposited may be formed of a porous (or porous) material. Examples of suitable porous materials for use in embodiments of the present invention may be zeolites and porous low-k materials that are widely used in the semiconductor process and are commercially available. The use of a porous material, in other words, the use of the substrate 10 having inner pores allows the thin layer 12 to be deposited not only in the main surface of the substrate 10 but also in these internal pores of the substrate 10. . This significantly increases the surface area on which the nanoparticles 14 can be formed. As a result, the amount of CNT that can be formed by the method according to the embodiment of the present invention can also be significantly increased.

  In the case of such a porous substrate 10, for example, a continuous or non-continuous thin layer 12 made of a semiconductor material (eg, Si) is deposited on the main surface of the porous substrate 10 and the surface of the internal pores of the porous substrate 10. it can. After performing the above-described annealing step so as to form nanoparticles, the nanoparticles 14 can be formed on the main surface of the substrate 10 and the internal pores of the substrate 10. These nanoparticles 14 can be used as a catalyst for growing CNTs.

  In yet another embodiment, bulk catalyst nanoparticles may be provided without a substrate, but to grow CNTs. The bulk nanoparticles must allow the carbon source gas to flow between adjacent nanoparticles so that CNTs can grow on the catalyst nanoparticles when the bulk catalyst nanoparticles are fed to the reactor (see below). See further).

In an embodiment of the invention, nanoparticles 14 such as semiconductor nanoparticles such as Si or Ge nanoparticles can be pretreated before CNT growth begins. An example of such a pre-treatment may be removal of natural oxides (eg, SiO 2 in the case of Si nanoparticles) by, for example, HF immersion (eg, 5% immersion in 2% HF).

  After forming the metal-free nanoparticles 14, the substrate 10 on which the nanoparticles are formed or the bulk nanoparticles according to another embodiment are grown into CNT 16, such as a chemical vapor deposition (CVD) reactor. To the appropriate reactor chamber (see step 15 in FIG. 1). The CVD reactor can be, for example, a plasma enhanced CVD reactor or a thermal CVD reactor or a thermal reactor. In the CVD reactor, the carbon source gas is decomposed or cracked by heating the carbon source gas. Cracking of the carbon source results in the formation of different carbon fragments, which can be recombined with catalyst nanoparticles to form CNTs. Thus, recombination occurs at the surface of the formed nanoparticles 14 (eg, nanoparticles comprising semiconductors such as nanoparticles comprising Si or Ge).

  In an embodiment of the present invention, the heating of the carbon source gas can be performed using a hot filament, using plasma, or using a combination of a hot filament and plasma. When hot filaments are used to decompose the carbon source gas, the hot filaments are used in the reactor so that cracked or decomposed carbon species do not recombine before reaching the catalyst nanoparticles so that the CNTs grow. It may be located in the chamber (see further below). The hot filament may be a metal filament and may include W (tungsten) or Ta (tantalum) and is held at a high temperature. The height of the temperature depends on the carbon source used and needs to be high enough to crack the carbon source. For example, the temperature of the hot filament may be 950 ° C. or higher.

  During the formation of reactive carbon fragments by decomposing the carbon source gas and during subsequent CNT growth, the temperature of the catalyst nanoparticles 14 and / or the substrate 10 on which the catalyst nanoparticles 14 are formed. The temperature may range between 800 ° C and 1000 ° C.

Any suitable carbon source gas known by those skilled in the art can be used in embodiments of the present invention. For example, the carbon source gas may be a hydrocarbon source and may be a hydrocarbon gas having from 1 (C1) to 3 (C3) carbon atoms. Examples of suitable hydrocarbon gases used for the growth of CNTs assisted by CVD may be CH 4 , C 2 H 4 , C 2 H 2 or C 3 H 6 . In other embodiments, another carbon source such as carbon monoxide (CO) can also be used as the carbon source. The amount of carbon source gas used in the reactor chamber determines the growth, morphology and characteristics of the CNT formed. The amount of carbon gas in the reactor chamber and / or the amount of cracked carbon fragments should be sufficient, i.e., sufficient to carry out the growth of CNTs, but on the other hand, such that CNT growth does not occur, It should be small enough to avoid the formation of amorphous carbon on the catalyst nanoparticles.

The CVD reactor chamber may further include an inert gas and hydrogen. The inert gas may be, for example, argon. As an example, the total flow rate of the CVD reactor of gas between the process of forming the CNT16 is approximately 4 liters / min N 2 and 2 liters / minute between H 2 0.01 to 1 l / min C 2 H Carbon gas like 2 may be sufficient. A suitable gas flow rate is a carbon gas such as 4 liters / minute N 2 , 2 liters / minute H 2 and 0.1 liters / minute C 2 H 2 .

  An example of a simplified reactor that can be used to perform CNT growth according to an embodiment of the present invention is schematically illustrated in FIGS. The difference between FIG. 2 and FIG. 3 is the position of the hot filament 2. The reactor comprises a quartz tube 6 on which a substrate 10 comprising nanoparticles 14 such as nanoparticles comprising Si or Ge, for example nanoparticles comprising a semiconductor, is disposed. The furnace 3 is placed outside the quartz tube 6 and used to bring the inside of the quartz tube 6 to an optimum reaction temperature. The optimum temperature means the temperature at which CNT growth occurs. In the example given by FIG. 2, a hot filament 2 is placed at the inlet or gas inlet of the reactor into a fragment that can be recombined at a nanoparticle 14 later to form a CNT, for example a carbon source such as a carbon source gas. To divide. In another embodiment shown in FIG. 3, the hot filament 2 is located on top of the substrate 10. In the latter case, larger scale growth of CNTs can be obtained. In this case, the cracked carbon species does not have to travel a long path to reach the nanoparticles 14 and is therefore less likely to recombine before assisting CNT growth compared to the case shown in FIG. It is.

  For example, a simple opening process such as chemical dissolution of the substrate 10 can be performed so as to open the CNTs 16 formed on the substrate 10 such as the mass-produced CNTs 16.

  Several examples are shown below. It should be understood that these are only for ease of understanding of the invention and are not intended to limit the invention in any way.

1. Preparation of nanoparticles A silicon wafer was prepared as a substrate 10 on which CNTs 16 were grown. A Si 3 N 4 barrier layer 11 was first deposited on the silicon substrate 10 in a vacuum reactor. A thin layer 12 of 5 nm poly-Si was deposited on the Si 3 N 4 barrier layer 11. The sample was annealed under the condition that the thin layer 12 was divided into nanoparticles 14 without breaking the vacuum. An annealing step for splitting the poly-Si layer 12 into Si nanoparticles 14 was performed at 530 ° C. for 20 minutes. The obtained Si nanoparticles 14 had a diameter of about 5 nm.

2. Pretreatment of Catalyst Nanoparticles Substrate 10 with nanoparticles 14 thereon is then treated for several minutes at room temperature to remove any native oxide that may form and exist after the nanoparticles are exposed to air ( Placed in standard HF solution (2% HF), eg 5 minutes. Immediately after removing the native oxide, the substrate 10 containing Si nanoparticles 14 was placed in a CVD reactor at 900 ° C. for 5 minutes. Reactor gas (reactor gas) was 4 liters / min N 2 with a ratio 4 liter / min H 2 N 2 and H 2. It has been found that Si nanoparticles 14 are suitable for the growth of CNTs 16 according to the method of the present invention. Nanoparticles 14 are suitable that they can function as templates (or templates) or precursors (or precursors) for CNT formation, ie they initiate CNT growth It can be used to

3. Growth of CNT After forming the Si catalyst nanoparticles 14 in the CVD reactor, C 2 H 2 gas was added to the reactor at a flow rate of 0.5 liter / min. During CNT growth, N 2 and H 2 were also present at a ratio of 4 liters / minute N 2 to 2 liters / minute H 2 . The substrate temperature was in the range between 800 ° C. and 1000 ° C., for example 900 ° C.

During CNT growth, the W or Ta filament 2 located at the inlet 1 of the gas inlet of the reactor is such that the incoming C 2 H 2 gas is a stable species such as CH 4 or C 2 H 2 as well as C—C. , C—H, and heated to break up into different carbon fragments such as CH 3 radicals. Temperature of the filaments was about 950 ° C. (filament current was 6 1/2 ~6 3/4 A.). FIG. 4 shows a scanning electron microscope (SEM) image of CNT grown on Si catalyst nanoparticles. From FIG. 4, it can be found that the nanotubes grow on the μm scale in the experiment conducted.

4). Growth of large amounts of CNTs Prior to performing CNT growth, the substrate 10 with nanoparticles 14 is removed in HF (2%) at room temperature to remove any native oxides that may be present from the Si nanoparticles 14. Etched for 1 minute.

The sample was placed in a CVD reactor under a reducing atmosphere of N 2 : H 2 (4: 2 liter / min) in the temperature range between 600 ° C. and 900 ° C. for 5 minutes at atmospheric pressure.

A W wire was used as the hot filament 2 and was placed on top of the substrate 10 including the catalyst nanoparticles 14. The carbon source was decomposed by flowing acetylene, ethylene or methane through the hot filament 2 in addition to other gas (N 2 : H 2 ) in addition to a flow rate of 0.1 liter / min. The gas composition used in this experiment was N 2 : H 2 : C at a ratio of 4: 2: 0.1 liter / min. The carbon source used was either acetylene, ethylene or methane. CNT16 was grown for half an hour at atmospheric pressure.

  5 and 6 show an SEM image after CNT grows on the Si nanoparticles according to the embodiment of the present example. Mass growth of CNT16 was observed. That is, the CNTs grew more densely than each other as compared with FIG. More concentrated growth was observed in the region where the Si nanoparticles were closer to the hot filament 2 (see CNT in the upper row of FIG. 5).

  While the specification has shown preferred embodiments, specific constructions and configurations for the apparatus according to the invention, it will be understood that forms and details may be understood without departing from the scope of the invention as defined by the appended claims. It should be understood that various modifications or improvements can be made.

Claims (18)

  1. Providing at least one metal-free catalyst nanoparticle (14);
    Growing carbon nanotubes (16) from metal-free catalyst nanoparticles (14);
    A method of forming at least one carbon nanotube (16) comprising:
  2. At least one metal-free catalyst nanoparticle (14) is fed into a chemical vapor phase reactor and growing carbon nanotubes (16)
    Forming reactive carbon fragments by decomposition of the carbon source gas in a chemical vapor phase reactor,
    Recombining reactive carbon fragments on the surface of at least one metal-free catalyst nanoparticle (14) to grow at least one carbon nanotube (16);
    The method of claim 1 comprising:
  3.   The method of claim 2, wherein the carbon source gas is a hydrocarbon gas having from one (C1) to a maximum of three (C3) carbon atoms.
  4. The method according to claim 3, wherein the carbon source gas is CH 4 , C 2 H 4 , C 2 H 2 or C 3 H 6 .
  5.   The method according to claim 2, wherein the carbon source gas is CO.
  6. Supplying at least one metal-free catalyst nanoparticle (14) to the substrate (10);
    Transferring a substrate (10) with at least one metal-free catalyst nanoparticle (14) thereon to a chemical vapor phase reactor;
    6. The process according to any one of claims 2 to 5, wherein at least one metal-free catalyst nanoparticle (14) is fed to the chemical vapor phase reactor by means of.
  7. Supplying a metal-free material layer (12) to the substrate (10);
    Annealing the metal free material layer (12) to form at least one metal free catalyst nanoparticle (14);
    The method according to claim 6, wherein at least one metal-free catalyst nanoparticle (14) is provided on the substrate (10) by means of.
  8.   The method according to claim 7, wherein the annealing is performed at a temperature between 500 ° C and 800 ° C.
  9.   Prior to supplying at least one metal-free catalyst nanoparticle (14) to the substrate (10), the substrate (10) is prevented so that the interaction between the at least one metal-free catalyst nanoparticle (14) and the substrate (10) is prevented. The method according to any one of claims 6 to 8, further comprising providing a barrier layer (11).
  10.   The temperature of the substrate (10) is maintained between 800 ° C and 1000 ° C while the carbon source gas decomposes and at least one carbon nanotube (16) grows. The method described.
  11.   The method according to any one of claims 2 to 10, wherein the carbon source gas is decomposed by using a hot filament (2), plasma or a combination of both.
  12.   The method according to claim 11, wherein the carbon source gas is decomposed at 950 ° C using a hot filament (2).
  13.   13. A method according to any one of the preceding claims, wherein at least one metal-free catalyst nanoparticle (14) is provided by supplying at least one semiconductor comprising nanoparticles (14).
  14. At least one semiconductor SiC comprising nanoparticles (14), SiO 2, pure Si, A method according to claim 13 which is GeO 2 or pure Ge nanoparticle.
  15.   15. A method according to any one of the preceding claims, wherein the at least one metal-free catalyst nanoparticle (14) has a diameter between 0.4 nm and 100 nm.
  16.   The method according to any of the preceding claims, further comprising pretreating at least one metal-free catalyst nanoparticle (14) before growing the carbon nanotubes (16).
  17.   Carbon nanotubes (16) grown from metal-free catalyst nanoparticles (14).
  18.   Use of metal-free catalyst nanoparticles (14) to grow carbon nanotubes (16).
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