WO2006120780A1

WO2006120780A1 - Carbon nanotube aggregate and method for producing same

Info

Publication number: WO2006120780A1
Application number: PCT/JP2006/300981
Authority: WO
Inventors: Masaru Hori; Mineo Hiramatsu; Hiroyuki Kano
Original assignee: Nu Eco Engineering Co., Ltd.
Priority date: 2005-05-10
Filing date: 2006-01-23
Publication date: 2006-11-16
Also published as: JP4834818B2; JP2006315882A

Abstract

[PROBLEMS] To provide a carbon nanotube of novel structure. [MEANS FOR SOLVING PROBLEMS] A buffer layer composed of TiN is formed on an Si substrate. Co nano particles having a particle size of 5 nm or less are deposited on the buffer layer by generating a pulse arc about 3-150 times by using a pulse arc plasma under a vacuum of 1×10-5 Torr. When a carbon nanotube is grown subsequently, a pyramidal punctate aggregate of carbon nanotubes having a mean outside diameter of 4 nm and a mean inside diameter of 3 nm is formed. The aggregate exhibits high field electron emission efficiency.

Description

Specification

Carbon nanotube aggregate and method for producing the same

Technical field

The present invention relates to a carbon nanotube aggregate and a method for producing the same.

Background art

[0002] Conventionally, many studies have been made on the use of carbon nanostructured materials such as carbon nanotubes as conductors for microelectronic devices, field emission electrodes, electrical wiring, microstructures, high-strength material adsorbents, and the like.

[0003] This carbon nanotube has a shape in which a graphite sheet is rounded into a cylindrical shape, and is classified into a single-walled carbon nanotube with a single sheet and a multi-walled carbon nanotube in which a plurality of sheets are nested. be able to.

[0004] Patent Documents 1 and 2 below disclose the use of carbon nanotubes for wiring between stages of an electronic device. As a method of forming carbon nanotubes, in Patent Document 1, transition metal particles having a particle size of 0.4 to 20 nm are formed on the bottom surface of a via hole by electroless plating, and this is used as a catalyst to form a via hole. Further, it is disclosed that carbon nanotubes are grown by a plasma CVD method or the like.

[0005] Further, Patent Document 2 below discloses a method of selectively forming a carbon nanotube at the bottom of a high aspect ratio via hole. In this method, after forming metal fine particles by laser ablation and selecting the particle size, a flow of fine particles is obtained parallel to the height direction of the via hole, and Ni nanoparticles having a particle size of 5 nm are formed at the bottom of the via hole. This is a method for growing carbon nanotubes using this as a catalyst.

[0006] Patent Document 3 below discloses a method of forming an ultrafine Si thin film by sputtering using helicon plasma, although it is not a method of forming carbon nanotubes.

[0007] Further, Patent Document 4 discloses a sharp end multi-walled carbon nanotube radial assembly in which a plurality of spire-shaped multi-walled carbon nanotubes and a common root portion are gathered radially. Patent Document 1: JP 2005-72171

Patent Document 2: JP 2005-22886

Patent Document 3: JP 2002-167671

Patent Document 4: JP 2003-206116

Disclosure of the invention

Problems to be solved by the invention

[0008] However, the carbon nanotubes of Patent Documents 1 and 2 are formed in parallel and cannot be used as a force field emission electrode, which can be used as a wiring. Further, Patent Document 4 discloses use as a field emission electrode. However, the force-bonn nanotube of this document is essentially a multi-walled carbon nanotube with a large number of layers, and has a sharp tip. Is.

However, development of other structures having a high field emission effect is expected.

Unlike the conventional structure, the present invention is a force-bonn nanotube aggregate having a completely new structure that has never existed so far.

By using this structure, for example, the field emission effect can be enhanced, and application to other fields is expected.

Accordingly, an object of the present invention is to provide a carbon nanotube aggregate having a novel structure.

Means for solving the problem

[0009] The invention of claim 1 is a carbon nanotube aggregate in which tips of a plurality of carbon nanotubes are aggregated in a conical shape.

When a large number of carbon nanotubes are grown on the substrate, the tips of the carbon nanotubes contained in each region are gathered in a conical shape for each region. Therefore, a large number of aggregates of carbon nanotubes are formed. However, by limiting the growth region, the number of aggregates of carbon nanotubes can be controlled, and a single aggregate of carbon nanotubes with one aggregated end is within the scope of the present invention. .

[0010] In the invention of claim 2, the portion excluding the tip of the carbon nanotube is substantially the same as the base. 2. The carbon nanotube aggregate according to claim 1, wherein the carbon nanotube aggregate is formed vertically.

That is, the roots and intermediate portions of the plurality of carbon nanotubes are formed substantially perpendicular to the substrate and are formed in parallel to each other, and the tip portions of the plurality of carbon nanotubes are assembled in a dot shape. .

[0011] The invention of claim 3 is the carbon nanotube aggregate according to claim 1 or claim 2, wherein the carbon nanotube is a single-layer or a double-wall.

The present invention is characterized in that each carbon nanotube constituting the aggregate is a single wall or a double wall. With this structure, it becomes easy to gather the tip portions in a dot shape.

[0012] The invention of claim 4 is characterized in that the carbon nanotubes are formed by a particulate catalyst having a particle diameter of 5 nm or less formed on a substrate. The aggregate of carbon nanotubes according to any one of the above items.

The particulate catalyst formed on the substrate is characterized by a particle size of 5 nm or less. With this configuration, it is easy to gather the tip portions in a dot shape.

The invention of claim 5 is characterized in that the carbon nanotube is formed by a particulate catalyst having a particle diameter of 2 nm or more and 4 nm or less formed on a substrate. Or an aggregate of carbon nanotubes according to item 1.

With this configuration, it is easy to gather the tip portions in a dot shape.

[0013] The invention of claim 6 is characterized in that the density of the particulate catalyst is 1 x 10 ¹² m ^{2 to} 5 x 10 ¹³ m ^2. The aggregate of carbon nanotubes described in the item. A desirable range of the density of the particulate catalyst is 3 × 10 ¹² 111 ^{2 to} 3 × 10 ¹³ 111 ² . A more desirable range is 1 10 ¹³ 01 ^{2 to} 3 10 ¹³ 01 ² . In this desirable range, a high-quality force-bonbon nanotube aggregate in which the tips of a plurality of carbon nanotubes are gathered in a conical shape can be reliably obtained.

The invention of claim 7 is the aggregate of carbon nanotubes according to claims 1 to 6, wherein the diameter of the carbon nanotube is 2 nm or more and 5 nm or less.

In the invention of claim 8, the average outer diameter of the carbon nanotube is 4 nm and the average inner diameter is 3 nm. The carbon nanotube assembly according to any one of claims 1 to 7, wherein the aggregate is a nanometer.

According to the invention of claim 9, a particulate catalyst having a particle size of 5 nm or less is deposited on a substrate in a density range of 1 × 10 ¹² m ^{2 to} 5 × 10 cm ² , and thereafter, two layers are formed by plasma CVD. Alternatively, it is a method for producing a carbon nanotube aggregate in which single-bonn nanotubes are grown and the tips of a plurality of carbon nanotubes are aggregated into a cone shape. By concentrating the tip of multiple carbon nanotubes in a cone shape, the particle size of the particulate catalyst is 5 nm or less and the density is in the range of 1 x 10 ¹² m ^{2 to} 5 x 10 ¹³ m ^2. Is possible. A desirable range for the density of the particulate catalyst is 3 10 ¹² 111 ^{2 to} 3 10 ¹³ 111 ² . Further, the desirable range of the density of the particulate catalyst is 1 × 10 ¹³ m ^{2 to} 3 × 10 ¹³ m ² .

The invention of claim 10, the particulate catalyst, 1 in X 10- ⁴ Torr or less degree of vacuum, the carbon nanotube aggregate according to claim 9, characterized in that it is produced by the pulsed arc plasma It is a manufacturing method.

The invention of claim 11 is the method for producing a carbon nanotube aggregate according to claims 9 to 10, wherein the particulate catalyst is cobalt or a cobalt alloy.

In the invention of claim 12, the gas phase density above the substrate of the particulate catalyst formed by the pulsed arc plasma is measured by absorption spectroscopy, and the particulate matter deposited on the substrate is determined from the measured gas phase density. 12. The carbon nanotube aggregate manufacturing method according to claim 10, wherein the number of pulses of the pulse arc plasma is controlled so that the density of the catalyst becomes a desired value.

A laser or a holo-power sword lamp can be used as a light source for absorption spectroscopy. The density of the particulate catalyst deposited on the substrate and the density and number of pulses of the gas phase particulate catalyst scattered in the atmosphere by the pulsed arc plasma (generally, the density of the gas phase particulate catalyst x the number of pulses) Is previously measured. When the particulate catalyst is actually deposited on the substrate, the gas phase particulate catalyst density is measured by absorption spectroscopy, and the number of pulses is controlled so that a predetermined density of the particulate catalyst is obtained on the substrate. To do. Thereby, the desired optimum density of the particulate catalyst can be obtained on the substrate. At this time, the pulse width and the pulse voltage It ’s good to control it.

[0015] Plasma CVD is a method in which a raw material gas of carbon nanotubes is turned into plasma to form a plasma atmosphere, and carbon nanotubes are grown on the substrate using a particulate catalyst deposited on the substrate. A plasma atmosphere is a state in which at least some of the substances that make up the atmosphere are ionized (ie, charged particles such as ions and electrons of atoms and molecules, and neutral particles such as radicals of atoms and molecules) Atmosphere (in a plasma state)).

The invention's effect

[0016] In the inventions of claims 1 and 2, by using a carbon nanotube aggregate in which the tip portions of a plurality of carbon nanotubes are gathered in a cone shape, when used for a field emission electrode, Field electron emission efficiency is improved. In addition, since a large number of carbon nanotubes are gathered in the form of dots, the mechanical strength of the field emission electrode is improved. According to the invention of claim 3, since the carbon nanotubes are single-walled or double-walled, the electrical characteristics of each carbon nanotube are uniform, and it is possible to obtain a carbon nanotube aggregate with uniform characteristics.

[0017] According to the invention of claim 4, the carbon nanotube can be formed into a single-walled or double-walled carbon nanotube by forming it with a particulate catalyst having a particle diameter of 5 nm or less formed on the substrate. . The outer diameter of each carbon nanotube can be reduced to 5 nm or less, and the tips can be assembled in the form of dots.

The invention of claim 5 is to increase the ratio of single-walled or double-walled carbon nanotubes by forming carbon nanotubes with a particulate catalyst having a particle diameter of 2 nm or more and 4 nm or less formed on a substrate. This makes it possible to make the electrical properties of the carbon nanotube aggregate in which the tip ends gather like dots.

[0018] According to the invention of claim 6, the tip portion can be assembled in the form of dots by setting the density of the particulate catalyst to 1 × 10 ¹² m ^{2 to} 5 × 10 ¹³ m ² . By adjusting the distance between the target and the substrate, it is possible to form a carbon nanotube aggregate in which the tips of a plurality of carbon nanotubes are aggregated in a conical shape. Desirably, 3 10 ¹² 111 ^{2 to} 3 10 ¹³ 111 ² . Further, it is preferably 1 × 10 ¹³ 111 ^{2 to} 3 × 10 ¹³ 111 ² . When in this range, make sure The tip portions can be assembled in the form of dots.

In the invention of claim 7, the diameter of the carbon nanotubes is 2 nm or more and 5 nm or less, so that the ratio of single-walled or double-walled carbon nanotubes can be increased, and the tips are gathered in the form of dots. It is possible to make the electrical characteristics of the carbon nanotube aggregate uniform.

[0019] In the invention of claim 9, a particulate catalyst having a particle size of 5 nm or less is deposited on a substrate in a density range of 1 x 10 ¹² m ^{2 to} 5 x 10 ¹³ / cm ² , and then plasma CVD By growing double-layer or single-layer carbon nanotubes by the method, it is possible to produce a carbon nanotube aggregate in which the tips of a plurality of carbon nanotubes are aggregated in a conical shape. The larger the diameter of the particulate catalyst, the more multilayered, and the smaller the particle diameter, the more monolayered. In the present invention, when the number of the layers is two or less, it becomes easy to manufacture a carbon nanotube aggregate having a pyramidal shape with aggregated tips.

By this method, an aggregate of carbon nanotubes whose tips are assembled in a dot shape can be easily and uniformly produced. When the density of the particulate catalyst is in the range of 1 X 10 ¹² / cm ² to 5 X 10 ¹³ / cm¾, the tips of multiple carbon nanotubes can be conically shaped by adjusting the distance between the target and the substrate. It becomes possible to form aggregated carbon nanotube aggregates. Desirably, 3 10 ¹² 111 ^{2 to} 3 10 ¹³ 111 ² . Furthermore, 1 X 10 1 ³ 111 ^{2 to} 3 10 ¹³ 1 11 ^{2 is} desirable. In this range, it is possible to reliably gather the tips in the form of dots.

[0020] Further, in the invention of claim 10, the particulate catalyst is in the degree of vacuum of 1 X 10- ⁴ Torr, it is generated by the pulse arc plasma, to less 5nm particle size of the particulate catalyst It is possible to make each carbon nanotube as a single layer or a double layer and to assemble the tips in a dot shape.

In addition, in the invention of claim 11, by using cobalt or a cobalt alloy as the particulate catalyst, it is possible to produce a carbon nanotube aggregate in which the tip ends are gathered in a dot shape uniformly and at high speed. .

Further, according to the invention of claim 12, since the gas phase density of the particulate catalyst above the substrate is measured by absorption spectroscopy and the measured value power pulse number is controlled, it is deposited on the substrate. It is possible to accurately control the density of the particulate catalyst to be produced, and it is possible to produce high-quality carbon nanotubes.

Brief Description of Drawings

FIG. 1 is a configuration diagram showing an apparatus for depositing a particulate catalyst.

FIG. 2 is a configuration diagram showing the principle of the arc gun of the device.

FIG. 3 is a table showing conditions for depositing a buffer layer and a particulate catalyst.

[Figure 4] AFM image of substrate surface on which Co nanoparticles were deposited.

FIG. 5 is a configuration diagram showing an apparatus for growing carbon nanotubes.

[Fig. 6] Measurement diagram showing the relationship between the deposition rate of carbon nanotubes and the number of pulse arcs when depositing Co nanoparticles.

[Fig. 7] SEM image showing the surface structure of an aggregate of carbon nanotubes grown on a substrate on which a particulate catalyst has been formed by 50 pulse arcs.

[Fig.8] Magnified image of SEM image of Fig.7.

[Fig. 9] SEM image showing the side structure of an aggregate of carbon nanotubes grown on a substrate with a particulate catalyst formed by 50 pulse arcs.

FIG. 10 is an SEM image showing the surface structure of a carbon nanotube aggregate grown on a substrate on which a particulate catalyst has been formed by 250 pulsed arcs.

[Fig. 11] SEM image showing the side structure of an aggregate of carbon nanotubes grown on a substrate with a particulate catalyst formed by 50 pulse arcs.

[Fig. 12] SEM image of the side of an aggregate of carbon nanotubes with tips gathered in a pyramid shape.

[Fig. 13] SEM image showing the surface structure of an aggregate of carbon nanotubes grown at 600 ° C on a substrate on which a particulate catalyst has been formed by 50 pulse arcs.

[Fig. 14] SEM image showing the surface structure of an aggregate of carbon nanotubes grown at 700 ° C for 5 minutes on a substrate with a particulate catalyst formed by 50 pulsed arcs.

[Fig. 15] TEM image of the side of the carbon nanotube aggregate.

FIG. 16 is an SEM image showing the surface structure of a carbon nanotube aggregate grown on a substrate on which a particulate catalyst has been formed by 30 pulse arcs.

[Fig.17] Carbon grown on substrate with particulate catalyst formed by 50 pulse arcs SEM image showing the surface structure of the aggregate of nanotubes.

Sono 18] A SEM image showing the surface structure of an aggregate of carbon nanotubes grown on a substrate on which a particulate catalyst has been formed by 70 pulsed arcs.

Sono 19] SEM image showing the surface structure of a carbon nanotube aggregate grown on a substrate on which a particulate catalyst has been formed by 100 pulsed arcs.

Sono]] SEM image showing the surface structure of carbon nanotube aggregates grown on a substrate on which particulate catalyst is formed by 200 pulse arcs.

[Sen 21] A configuration diagram showing an apparatus for measuring the field electron emission effect from the tip of the pyramidal carbon nanotube aggregate of this example.

Sono 22] A measurement diagram showing the relationship between the electric field and emission current measured by the device.

Sono 23] A measurement diagram showing the relationship between the electric field and emission current measured by the device.

Sono 24] Measurement diagram of the pyramidal carbon nanotube aggregate of this example by Raman spectroscopy.

Sono 25] A schematic diagram illustrating the principle of the formation of a pyramidal carbon nanotube aggregate of this example.

Gon 26] A schematic diagram showing the relationship between the density of the particulate catalyst and the properties of the carbon nanotubes formed.

Explanation of symbols

[0022] 10- · '-Anti, solstice

11 -'- susceptor

12- · •• Si substrate

13 -'- Halogen run

15 -... Cathode

16 -... Insulator

17 'trigger electrode

18 '' Anode

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] Hereinafter, preferred embodiments of the present invention will be described. Technical matters other than those specifically mentioned above and matters necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on the prior art. The present invention can be implemented based on the technical contents disclosed in this specification and the common general technical knowledge in the field.

[0024] As a raw material used for the production of carbon nanotubes, various substances having at least carbon as a constituent element can be selected. Examples of the elements that can form the source material together with carbon include one or more selected from hydrogen, fluorine, chlorine, bromine, nitrogen, oxygen, and the like. Preferred raw material materials include a raw material material substantially composed of carbon and hydrogen, a raw material material substantially composed of carbon and fluorine, and a raw material material substantially composed of carbon, hydrogen and fluorine. The Saturated or unsaturated hydrocarbons (eg CH

4, C H), Fluorocarbon (eg C F), Fluorohydride Carbo 2 2 2 6

(For example, CHF) can be preferably used. Linear, branched, or cyclic

Three

Those having the molecular structure can also be used. It is usually preferable to use a source material (source gas) that exhibits a gaseous state at normal temperature and pressure. Two or more kinds of materials may be used in any proportion, or only one kind of material may be used as a raw material. The type (composition) of the raw material used may vary depending on the production stage, which may be constant throughout the production stage (for example, the growth process) of carbon nanotubes. Depending on the properties and / or characteristics (for example, electrical characteristics) of the target carbon nanostructure, the type (composition) of the raw material used, the supply method, and the like can be appropriately selected.

[0025] As the radical source substance, a substance containing at least hydrogen as a constituent element can be preferably used. It is preferable to use a radical source material (radical source gas) that exhibits a gaseous state at normal temperature and pressure. A particularly preferred radical source material is hydrogen gas (H 2). Also, ha

2

Substances that can generate H radicals by decomposition, such as id carbon (CH etc.)

Four

It can also be used as a source material. Only one type of material may be used as the radical source material, or two or more types of materials may be used in any ratio.

In one preferred embodiment of the manufacturing method, the plasma atmosphere is formed by converting the raw material into plasma in the reaction chamber. Alternatively, the source material is plasmaized outside the reaction chamber, and the plasma is introduced into the reaction chamber to form a plasma atmosphere in the reaction chamber. Good.

Desirably, radicals are injected into the plasma atmosphere from the outside of the atmosphere. It is preferable to decompose radical source materials in a radical generation chamber outside the chamber forming the reaction chamber to generate radicals, which are then injected into the plasma atmosphere in the reaction chamber. Alternatively, a radical generation chamber in the same chamber as the reaction chamber may be decomposed outside the plasma atmosphere, and radicals generated thereby may be injected into the plasma atmosphere. In short, radicals are generated in a region different from the processing region where film formation or processing is performed by plasma of the raw material, and only these radicals are injected into the cache region to control film formation and processing. Carbon nanotubes may be grown.

[0027] A preferred method for generating radicals from a radical source material includes a method of irradiating the radical source material with electromagnetic waves. The electromagnetic wave used in this method can be selected from either microphone mouth waves or high-frequency waves (UHF waves, VHF waves, or RF waves). It is particularly preferable to irradiate VH F wave or RF wave. According to the method, it is possible to easily adjust the decomposition strength (radical generation amount) of the radical source material, for example, by changing the frequency and / or the input power. Therefore, there is an advantage that the production conditions of carbon nanotubes (such as the amount of radicals supplied into the plasma atmosphere) can be easily controlled.

[0028] Here, as is well known, "microwave" refers to an electromagnetic wave of about 1 GHz or more. “UHF wave” refers to electromagnetic waves of about 300 to 3000 MHz, “VHF waves” refers to electromagnetic waves of about 30 to 300 MHz, and “RF waves” refers to electromagnetic waves of about 3 to 30 MHz.

Another preferred method and method for generating radicals from a radical source material is a method of applying a DC voltage to the radical source material. It is also possible to employ a method of irradiating the radical source material with light (eg, visible light or ultraviolet light), a method of irradiating an electron beam, a method of heating the radical source material, or the like. Alternatively, a member having a catalytic metal may be heated and a radical source material may be brought into contact with the member (ie, by heat and catalysis) to generate a radical. As the catalyst metal for generating radicals, one or more selected from Pt, Pd, W, Mo, Ni and the like can be used.

[0029] The radicals injected into the plasma atmosphere are at least hydrogen radicals (that is, hydrogen atoms). Child. Hereinafter, it may be referred to as “H radical”. ) Is preferably included. It is preferable to decompose a radical source material containing at least hydrogen as a constituent element to generate H radicals and inject the H radicals into a plasma atmosphere. Particularly preferred as such a radical source material is hydrogen gas (H 2).

In particular, when only H radicals are supplied, carbon nanotubes can be generated satisfactorily. In addition, it seems that the formation of carbon nanotubes is facilitated by the presence of moderately OH and O radicals.

[0030] Based on the concentration of at least one kind of radical in the reaction chamber (for example, the concentration of at least one kind of radical among a carbon radical, a hydrogen radical, and a fluorine radical), at least one of the carbon nanotube production conditions is adjusted. It is desirable to do. Examples of manufacturing conditions that can be adjusted based on such radical concentrations include the amount of raw material supplied, the plasma intensity of the raw material (the severity of the plasma conditions), and the injection of radicals (typically H radio canore). Amount and the like. Such production conditions are preferably controlled by feedback of the radical concentration. According to a powerful production method, it is possible to more efficiently produce carbon nanotubes having properties and / or characteristics according to the purpose.

[0031] As a method for measuring radicals, a radical emission line (that is, a carbon atom emission line) is emitted into the reaction chamber, the emitted emission line is received, and the radio-canole concentration is measured from the light absorption spectrum. Can do. Therefore, it is possible to efficiently produce carbon nanotubes having properties and / or characteristics according to the purpose. The emission line specific to the carbon radical (carbon atom) can be obtained, for example, by applying appropriate energy to a gas containing at least carbon as a constituent element. It can be configured to emit a light beam specific to a carbon radical (carbon atom).

[0032] Monitors and control targets are not limited to C, H, and F radicals, and C, CF, CF, CF, and CF (x≥l, y≥l) may be used as target radicals. Examples of manufacturing conditions that can be adjusted based on such measurement results include the amount of raw material supplied, the intensity of plasma of the raw material, the amount of radicals (typically H radicals) injected, the amount of radical source material supplied, Radical strength of the radio-canole source material. Such production conditions are determined based on the radical concentration. It is preferable to control the measurement result by feedback. According to such a production method, it becomes possible to produce carbon nanotubes having properties and / or characteristics according to the purpose homogeneously and more efficiently.

[0033] Similarly, the amount of radicals injected into the reaction chamber is determined by measuring radicals, particularly H radicals, in the radical generating chamber for generating radicals to be injected or in the inlet for injecting radicals into the reaction chamber. Therefore, it is desirable to control the supply amount of the radical source material and the electric power applied to the radical source material. In this way, the amount of radicals injected into the reaction chamber, particularly H radicals, can be controlled in real time during the growth process, and high-quality carbon nanotubes can be generated.

[0034] A member having a metal catalyst (Pt, Pd, W, Mo, Ni, etc.) for generating radicals is disposed facing the radical generation chamber, and radical generating means is provided so that the metal catalyst can be heated. May be configured. For example, a wavy Ni wire (catalytic metal member) can be arranged inside the radical generation chamber. Introduce H as a radionocule source material into contact with the heater that passed a current through the wire. As a result, H radicals can be generated by the catalytic action of Ni. The heating temperature of the catalyst metal can be, for example, about 300 to 800 ° C, and is usually preferably about 400 to 600 ° C. The plasma discharge means is preferably configured as a capacitively coupled plasma (CCP) generation mechanism.

[0035] As the particulate catalyst for growing carbon nanotubes, transition metals such as Ni, Fe, Co, Pd, and Pt, alloys of these transition metals, transition metals and other metals are used. An alloy with a semiconductor can be used. As a method for depositing the particulate catalyst on the substrate, it is desirable to use a no-less arc plasma deposition method. For example, 10 at ⁴ Torr or less degree of vacuum, by generating an arc to a target consisting of transition metals such as Co, plasma is generated in the transition metal, particulate catalyst particle size of less than 5nm on a substrate Power to deposit S. To less 10- ⁴ Torr is to reduce the collision probability of atoms or molecules, in order to reduce the particle size. If the substrate is Si, catalyst particles and Si are alloyed to form silicide, so it is desirable to form a buffer layer such as TiN or AlO. In addition, when CoTi is used for the catalyst particles, it does not react with Si, so that the particulate catalyst can be deposited directly on the Si substrate. Hereinafter, the present invention will be described based on specific examples, but the present invention is not limited to the following examples.

Example 1

[0037] First, a Si substrate was used as a substrate as a base. The coaxial vacuum arc deposition apparatus shown in Fig. 1 deposited a TiN buffer layer on a Si substrate and a particulate catalyst made of Co on the TiN buffer layer. In FIG. 1, a susceptor 11 is provided in a reaction chamber 10, and a Si substrate 12 is provided thereon. Under the susceptor 11, a halogen lamp 13 for heating the Si substrate 12 is provided. A plasma gun 14 is provided above the reaction chamber 10. FIG. 2 is a principle diagram of the plasma gun 14. A cylindrical cathode 15 is provided at the center, a cylindrical insulator 16 is provided around the cathode 15, and a ring-shaped trigger electrode 17 is provided outside thereof. In addition, a cylindrical anode 18 is provided coaxially with the cathode 15 and outside the insulator 16. A target 19 made of Co is provided on the end face of the cathode 15, and a cap 30 is provided on the end face of the target 19. Further, a plate-like insulator 31 is provided on the end face of the trigger one electrode 17. By applying an electric field between the cathode 15 and the anode 18 and applying a pulse voltage to the trigger electrode 17, a pulse arc is generated and constituent atoms of the target 19 are scattered. In this example, Ti was used for the target 19 when the buffer layer was formed, and Co was used when the particulate catalyst was formed.

FIG. 3 shows the formation conditions of the TiN buffer layer and the particulate catalyst. To form the TiN buffer layer, the distance between the target 19 and the Si substrate 12 and 10 cm, the temperature of the Si substrate 12 and 4 00 ° C, 3 X 10- 2 Torr the pressure in the reaction chamber 10, the N While flowing into reaction chamber 10,

2

A pulsed arc plasma was generated 900 times by applying a voltage. As a result, a TiN buffer layer having a thickness of 20 nm was formed on the Si substrate 12. The buffer layer is used to prevent the particulate catalyst and Si from reacting to form silicide.

[0039] Further, the deposition of the particulate catalyst consisting of Co, the temperature of the Si substrate 12 to room temperature, 1 X 10- ⁵ Torr pressure in the reaction chamber 10 to Nag and scores flow of gas, 30 a pulse voltage : Applied 100 times to generate pulsed arc plasma. As a result, Co nanoparticles having a particle diameter of 5 nm or less were deposited on the TiN buffer layer in the range of 1 × 10 ¹² m ^{2 to} 5 × 10 ¹³ 111 ² .

Figure 4 shows the substrate surface when Co particles are deposited on the substrate using 10 pulsed arcs. An atomic force microscope image (AFM image) is shown. From this image, the particle size was determined to be 2-3 nm and the density was 3 × 10 ¹² m ² . Therefore, it was found that the density of Co nanoparticles deposited in a single no-arc was 3 X 10 ¹ cm ² .

Next, carbon nanotubes were grown on the Si substrate 12 on which the TiN buffer layer was formed, using the microwave plasma CVD apparatus of FIG. In the reaction chamber 20, a susceptor 21 made of Mo is provided, and a substrate 12 is provided thereon. A carbon heater 22 for heating the substrate 12 is provided under the susceptor 21. From the top of the reaction chamber 20, a 2.45 GHz microwave is introduced into the reaction chamber 20. The reaction chamber 20 is provided with an exhaust port 24, which is evacuated by a vacuum pump so that a certain degree of vacuum can be obtained in the reaction chamber 20. Further, from the intake port 23 provided in the reaction chamber 20, H and CH gas are introduced into the reaction chamber 20 via the mass flow controllers 25 and 26, respectively.

[0041] Next, when depositing the particulate catalyst composed of Co on the substrate 12, various samples were prepared in which the number of pulse arcs was changed. Carbon nanotubes were grown for each sample. It was found that the self-organized carbon nanotube aggregate in which the tips of multiple carbon nanotubes gathered into a pyramid was obtained when the number of pulse arcs was about 3 to 150 times. It was. That is, the density of Co nanoparticles depends on the distance between the substrate and the target, but in the case of 1 × 10 ¹² 111 ^{2 to} 5 × 10 ¹³ m ² , pyramidal self-organization occurs. I understood that. In addition, when the number of nano arcs is 30 to 100 times, that is, when the density of the particulate catalyst is 1 × 10 ^{13 to} 111 ^{2 to} 3 × 10 ¹³ m ² , the tips of the plurality of carbon nanotubes are surely attached. A self-organized carbon nanotube aggregate in an aggregated pyramid shape was obtained. In addition, when the number of pulse arcs is 10 to 100 times, that is, when the density of the particulate catalyst is 3 x 10 ¹² m ^{2 to} 3 x 10 ¹³ m ² , high quality pyramid self-assembly As a result, an assembled carbon nanotube tube was obtained. Figure 6 shows the relationship between the number of pulse arcs and the growth rate of carbon nanotubes.

[0042] Figure 7 shows that after depositing Co particles on the substrate by 50 pulse arcs, substrate temperature 700 ° C, microwave power 900W, pressure 70Torr, CH flow 50sccm, H flow 70sccm, growth time Scattered electrons on the surface when carbon nanotubes are grown for 5 seconds It is the image (SEM image) by a microscope. It can be seen that the tips of a plurality of carbon nanotubes are gathered in the form of dots in a pyramid shape. The density of this pyramid is 3 x 10 ⁸ m ² , and the average spacing is about 0.5 / im. Fig. 8 shows an enlarged image of Fig. 7. Figure 9 shows the side SEM images. It can be seen that the carbon nanotubes grow almost perpendicular to the substrate and the tips are gathered in a cone shape. In addition, as a result of imaging SEM images of the surface while changing the growth time, it was found that self-organization in which the tips gather in a cone shape can be seen from the initial stage of growth. Accordingly, it was found that pyramid-like self-organization occurred in the early stage of growth, and then the carbon nanotubes grew perpendicularly to the substrate from the root.

[0043] Next, SEM images of the surface when carbon nanotubes were grown were imaged by changing the number of pulse arcs for depositing Co nanoparticles, that is, the density of Co nanoparticles. As a result, the higher the density of Co nanoparticles, the more closely the carbon nanotubes grow, and the self-organization in which the tips of a plurality of carbon nanotubes gather in a conical shape is less likely to occur. Figures 10 and 11 show the SEM images at that time. Figure 10 shows 250 pulse arcs and Figure 11 shows 50 pulse arcs.

Next, FIG. 12 shows an SEM image of the side surface of the carbon nanotube aggregate with the tips assembled in a pyramid shape. It can be seen that the tip forming the pyramid grows straight, but the other intermediate and root portions are twisted and bent perpendicular to the substrate.

Example 2

[0045] Next, the growth temperature of the carbon nanotubes was changed. In the sample whose SEM image is shown in Fig. 7, the growth temperature was 700 ° C. Only the growth temperature was 600 ° C, and the other growth conditions were the same, and the carbon nanotubes were grown. Figure 13 shows the SEM image of the surface at that time. It can be seen that the aggregate of carbon nanotubes whose tips are gathered in a pyramid shape is obtained uniformly.

Example 3

[0046] Next, the growth time of the carbon nanotubes was changed. Fig. 14 shows the SEM image of the surface when carbon nanotubes were grown with a growth time of 5 seconds and a force of 5 minutes. Figure 15 shows an image (TEM image) obtained by a scanning electron microscope. Even if the growth time is lengthened, once the pyramid is formed, a carbon nanotube aggregate is obtained in which the tips of the middle part and the root part that do not disappear are gathered in a conical shape. Is understood.

Example 4

[0047] The density of the particulate catalyst was changed. 30 times (density 9 x 10 ¹² m ² ), 50 times (density 1.5 x 10 ¹³ m ² ), 70 times (density 2.1 x 10) ¹³ / cm ^2), 100 times (density 3 X 10 ¹³ I m @ 2), as 200 times (density 6 X 10 ¹³ I m ^2), FIG. 16 SEM images of the respective surface when grown carbon nano tube To Figure 20. When the number of panoramic arcs is 30 to 100, a carbon nanotube aggregate in which the tips are gathered in the shape of dots in a cone shape is observed. It can be seen that the density of the aggregate increases as the density of Co nanoparticles increases. However, as shown in Fig. 20, when the panoramic arc reaches 200 times, it can be seen that pyramid-like self-organization has not occurred.

[0048] In this way, the number of pulse arcs was changed in various ways, and as a result of imaging the growth rate of the carbon nanotube and the SEM image of the surface, the pulse arc of about 3 to 150 times was obtained. It was found that pyramid-like self-organization occurs when Co particles are deposited by the above method.

Example 5

[0049] Next, the electron field emission characteristics of the carbon nanotube aggregates thus produced were measured using the apparatus shown in FIG. The results are shown in Figs. The characteristics of the aggregate of carbon nanotubes in the shape of a pyramid whose tips are gathered in a conical shape are shown as A, and the characteristics of high-density carbon nanotubes grown in parallel without pyramids are shown as B. In the case of the aggregate of the carbon nanotubes of the pyramid shape of this example, it can be seen that a current of 5 μA flows in an electric field of IV / μm and a current of 400 μΑ flows in an electric field of 2V / μm. . On the other hand, in the case of high-density carbon nanotubes without pyramids, it can be seen that a current of 400 / i A flows at an electric field of 3 ¥ / 111 and an electric field of 6.5 V // im. Obviously, the electron field emission characteristics are improved.

Next, Raman spectroscopic measurement of the pyramidal carbon nanotube aggregate of this example Went. The results are shown in FIG. G band and D band are observed. [Considerations about the principle]

[0051] The reason for the formation of the pyramid-shaped carbon nanotube aggregate in which the tips are gathered in a conical shape in the form of a dot is considered as follows. When the density of Co nanoparticles is low, the particle size is also small as 2-3 nm, and the diameter of the carbon nanotubes that grow using it as a catalyst is also small, so each carbon nanotube cannot stand independently and grow In the initial stage, the tip is considered to be integrated into a cone shape under the Van der Waals force. Then, in the subsequent growth, the aggregate stands on the substrate with a large number of carbon nanotubes as a large number of legs, so that the mechanical strength of the aggregate increases and the tip remains integrated while the root portion is integrated. It seems that the carbon nano tube aggregate with the tip integrated into the pyramid shape is formed. Figure 25 shows a schematic diagram of the growth mechanism at this time.

[0052] The shape change of the growing carbon nanotubes is considered as follows depending on the number of pulse arcs when depositing Co nanoparticles, and therefore the density of Co nanoparticles. If the density of Co nanoparticles is too low, the distance between adjacent carbon nanotubes is too large and there is no interaction, so it grows randomly and does not grow orderly and perpendicular to the substrate. On the other hand, if the density of Co nanoparticles is too high, the particles themselves will continue to form large lumps, so they will not grow in an orderly manner with respect to the substrate. When the density of Co nanoparticles is appropriate, it is likely that adjacent carbon nanotubes will grow in an orderly manner perpendicular to the substrate and parallel to each other. Figure 26 shows a schematic diagram of the growth mechanism at this time.

[0053] Such a pyramid-shaped carbon nanotube aggregate in which the tips are gathered in the shape of a cone is a field emission electrode, a field emission electrode array, an interstage wiring of a next generation VLSI, a planar wiring, a fine capacitance, a diode It can also be applied to transistors and the like.

Industrial applicability

[0054] The aggregate of carbon nanotubes of the present invention can be used as, for example, a field electron emission electrode, and can be used for displays and other electronic devices.

Claims

The scope of the claims

[I] A carbon nanotube aggregate in which tips of a plurality of carbon nanotubes are aggregated in a cone shape.

[2] The aggregate of carbon nanotubes according to [1], wherein a portion of the carbon nanotube other than the tip is formed substantially perpendicular to the substrate.

[3] The aggregate of carbon nanotubes according to claim 1 or claim 2, wherein the carbon nanotubes are single-walled or double-walled.

[4] The force according to any one of claims 1 to 3, wherein the carbon nanotube is formed by a particulate catalyst having a particle diameter of 5 nm or less formed on the substrate. Of carbon nanotubes.

[5] The carbon nanotube according to any one of claims 1 to 3, wherein the carbon nanotube is formed by a particulate catalyst having a particle diameter of 2 nm or more and 4 nm or less formed on the substrate. An aggregate of carbon nanotubes described in 1.

6. The carbon nanotube according to any one of claims 1 to 5, wherein the density of the particulate catalyst is 1 X 10 ¹² / cm ² to 5 X 10 ¹³ m ^2. Aggregation.

[7] The aggregate of carbon nanotubes according to claims 1 to 6, wherein a diameter of the carbon nanotube is 2 nm or more and 5 nm or less.

8. The carbon nanotube aggregate according to any one of claims 1 to 7, wherein the carbon nanotube has an average outer diameter of 4 nm and an average inner diameter of 3 nm.

[9] A particulate catalyst having a particle size of 5 nm or less is deposited on the substrate in the density range of 1 × 10 ¹² m ^{2 to} 5 × 10 ¹³ m ² , and then two layers or A method for producing a carbon nanotube aggregate in which single-walled carbon nanotubes are grown and the tips of a plurality of carbon nanotubes are aggregated into a cone.

[10] The particulate catalyst in 1 X 10- ⁴ Torr or less of vacuum, manufacturing method of a carbon nanotube aggregate according to claim 9, characterized in that it is more generated pulse arc plasma.

[II] The method for producing a carbon nanotube aggregate according to any one of claims 9 to 10, wherein the particulate catalyst is cobalt or a cobalt alloy. The gas phase density above the substrate of the particulate catalyst formed by the pulsed arc plasma is measured by absorption spectroscopy, and the particulate matter deposited on the substrate is determined from the measured gas phase density. 12. The method for producing a force-bonded nanotube assembly according to claim 10, wherein the number of pulses of the pulse arc plasma is controlled so that the density of the catalyst becomes a desired value.