WO2007108132A1

WO2007108132A1 - Process for producing carbon nanotube

Info

Publication number: WO2007108132A1
Application number: PCT/JP2006/305866
Authority: WO
Inventors: Akio Kawabata
Original assignee: Fujitsu Limited
Priority date: 2006-03-23
Filing date: 2006-03-23
Publication date: 2007-09-27
Also published as: JP4850900B2; JPWO2007108132A1

Abstract

A process for producing carbon nanotubes, comprising providing first substrate (10) furnished with multiple projections on its surface; forming multiple microparticles of a catalyst material on a second substrate; bringing the multiple projections (12) on the first substrate into contact with the catalyst material microparticles on the second substrate to thereby adhere the catalyst material microparticles to the multiple projections; and placing the first substrate in a carbonaceous gas atmosphere to thereby grow carbon nanotubes on the catalyst material microparticles. Thus, carbon nanotubes isolated between projections are formed.

Description

Specification

Method for producing carbon nanotubes

Technical field

The present invention relates to a method for producing carbon nanotubes, and more particularly to a method for producing carbon nanotubes that can be produced by crosslinking isolated carbon nanotubes.

Background art

[0002] Research on electronic devices using carbon nano-tubes (CNTs) has been actively conducted. Carbon nanotubes basically have a structure in which a dalaphen sheet with a hexagonal network structure of carbon atoms is rolled into a cylindrical shape. When carbon nanotubes are miniaturized to become single-walled carbon nanotubes (single-walled nanotubes (SWNT)) or double-walled single-bonn nanotubes (double-walled nanotubes (DWNT)), the difference in diameter and strength is due to the difference in irritation. Carbon nanotubes with electrical or semiconducting electrical properties and semiconducting electrical properties can be expected to be applied to electronic devices. Although it is still a basic research stage, various examples of application of carbon nanotubes to electronic devices have been reported.

[0003] For example, Patent Document 1 proposes a structure of an electrode that is electrically connected to a multi-walled carbon nanotube. According to this, the carbon nanotube is cut immediately before forming the electrode, and a metal that forms a strong and ionic bond with the carbon atom is formed on the cut carbon nanotube to form the electrode. As a result, the contact resistance between the electrode and the carbon nanotube is reduced, and it is attempted to be applied to electronic devices!

[0004] Patent Document 2 proposes a field effect transistor in which a metallic inner layer of a double-walled carbon nanotube is used as a gate electrode and a semiconducting outer layer is used as a channel. Patent Document 2 also discloses a field effect transistor in which a semiconducting inner layer of two-walled carbon nanotubes is used as a channel region and a metallic outer layer is used as a gate electrode as a prior art.

[0005] As described above, application to electronic devices using carbon nanotubes has been reported. However, only a few methods have been reported to produce single- or double-walled carbon nanotubes with semiconducting properties with good reproducibility. Since it is still difficult to produce single-walled or double-walled carbon nanotubes with semiconducting properties with good reproducibility, Raman spectroscopy and fluorescence characteristics of many randomly generated carbon nanotubes were evaluated and desired Carbon nanotubes with these characteristics are selected and used only for the formation of electronic devices.

[0006] In order to evaluate Raman spectroscopy and fluorescence characteristics, carbon nanotubes need to be generated in a state of being isolated and hanging in a hollow state without contacting the substrate. If the carbon nanotubes are in contact with the substrate, the characteristic evaluation signal will be weak, and if multiple carbon nanotubes are bundled (bundled), fluorescence will not be seen. This is because evaluation becomes difficult. Therefore, the present condition is to select the carbon nanotubes that are in a state of floating in the air alone from the many grown carbon nanotubes, and to characterize them. However, if the force grows in a bundled state, it becomes difficult to take out single bonn nanotubes with the desired characteristics and support them on the substrate.

[0007] In Patent Document 3, fine protrusions are formed on the surface of a silicon substrate, a portion other than the protrusion tips is coated with a photosensitive resist, a catalyst metal is applied only to the protrusion tips, and a desired metal is applied to the catalyst metal by CVD. The production of carbon nanotubes of diameter is described. According to this method, it is expected to generate carbon nanotubes with the tip force of the protrusions, and it is expected to reproduce the state of being hung alone.

Patent Literature l: WO 02 / 063693A1

Patent Document 2: JP 2004-171903 A

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-182537

Disclosure of the invention

Problems to be solved by the invention

[0008] The generation method of Patent Document 3 described above requires a process of forming protrusions on the surface of the silicon substrate, and covering with a photosensitive resist leaving the tip. However, in this process, it is necessary to control the height of the protrusion and the film thickness of the photosensitive resist with high precision, which is not a realistic generation method. Depending on the size of the catalyst metal formed at the tip of the protrusion, the growth Although the diameter and the number of layers of the carbon nanotubes can be controlled, it is difficult to control the size of the catalyst metal with good reproducibility for the same reason as above.

Accordingly, an object of the present invention is to provide a carbon nanotube production method capable of producing a large amount of hollow carbon nanotubes with good reproducibility.

Means for solving the problem

[0010] To achieve the above object, according to the first aspect of the present invention, there is provided a first step of preparing a first substrate having a plurality of protrusions formed on the surface, and a second substrate. A second step of generating a plurality of fine particles comprising a catalyst material, and contacting a plurality of protrusions formed on the first substrate with the fine particles of the catalyst material formed on the second substrate, A third step of attaching the fine particles of the catalyst material to the plurality of protrusions, and a fourth step of growing the carbon nanotubes on the fine particles of the catalyst material by placing the first substrate in a carbon-containing gas atmosphere. It is the production method of the carbon nanotube which has.

[0011] In the first aspect described above, according to a preferred embodiment, the catalyst material is a transition metal containing at least cobalt, iron, and nickel. Alternatively, the catalyst material is an alloy of a transition metal containing at least cobalt, iron, or nickel and a metal of Ti, Al, Ta, TiN, or Ti02.

[0012] Further, according to a preferred aspect of the first aspect described above, in the third step, the protrusion of the first substrate is in contact with the fine particles of the catalyst material of the second substrate. , Heat to a predetermined temperature to attach fine particles of catalyst material to the protrusions.

[0013] Further, in the first aspect described above, according to a preferred embodiment, prior to the third step, Ti, Al are formed on the plurality of protrusion surfaces of the first substrate prepared in the first step. , Ta, TiN, Ti02 (V, having a fifth step of forming a metal layer of any one.

[0014] In the first aspect, preferably, the transition material fine particles are transition metal fine particles having a diameter of 0.5 to LOnm, and the carbon nanotubes grown in the fourth step are 1 to 4nm in diameter. Single or double layered in diameter.

[0015] In order to achieve the above object, according to the second aspect of the present invention, a first step of preparing a first substrate having a plurality of protrusions formed on the surface, and a step on the second substrate Made of catalyst material A second step of generating a plurality of fine particles; and a plurality of protrusions formed on the first substrate are brought into contact with the fine particles of the catalyst material formed on the second substrate; A method for producing a fine wire substance, comprising: a third step of attaching fine particles of material; and a fourth step of placing the first substrate in a growth gas atmosphere to grow fine wire substance on the fine particles of the catalyst material. is there.

[0016] In the second aspect, according to a preferred embodiment, the catalyst material is Au, and the fine wire substance is a group IIIV compound semiconductor containing GaAs, InP, InAs, and a fourth process force. This is a metalorganic chemical vapor deposition method using III group V metal gas as the growth gas.

[0017] In order to achieve the above object, according to a third aspect of the present invention, a first step of generating a plurality of fine particles of a catalyst material on a substrate, Etching with the fine particles as a mask to form a plurality of protrusions having the fine particles attached to the tips, and placing the substrate in a growth gas atmosphere to grow fine wire substances on the fine particles of the catalyst material And a third step of producing a fine wire substance.

The invention's effect

[0018] According to the present invention, since the fine particles of the catalyst material are attached to the tips of the protrusions of the first substrate, it is possible to grow isolated carbon nanotubes or fine wire substances there with good reproducibility.

Brief Description of Drawings

FIG. 1 is a cross-sectional view showing a carbon nanotube production process according to the first embodiment. FIG. 2 is a cross-sectional view showing a carbon nanotube production process according to the first embodiment. It is a figure explaining the laser abrasion method.

FIG. 4 is a cross-sectional view showing a production process of carbon nanotubes according to the first embodiment

FIG. 5 is a sectional view showing a carbon nanotube production step according to the first embodiment. FIG. 6 is a cross-sectional view showing a carbon nanotube production step according to the first embodiment.

FIG. 7 is a schematic configuration diagram of a CVD apparatus.

FIG. 8 is a view showing a carbon nanotube CNT generated by the third embodiment.

FIG. 9 is a cross-sectional view showing a production process of the fifth embodiment.

Explanation of symbols

[0020] 10: First substrate 12: Projection

22: Fine particles of catalyst material CNT: Carbon nanotube

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and their equivalents.

[0022] [First embodiment]

FIGS. 1, 2, 4, 4, and 6 are cross-sectional views showing the carbon nanotube production process according to the first embodiment. In the process of FIG. 1, a substrate having a plurality of fine needle-like protrusions 12 formed on the surface, for example, a silicon substrate 10 is prepared. The fine protrusions 12 are formed, for example, by forming a resist layer having a predetermined pattern on the surface of the silicon substrate 10 and etching the substrate surface using the mask as a mask to form irregularities having a rectangular cross section. This can be achieved by processing the concavo-convex protrusion into a protrusion 12 with a sharp tip by a wet etching method having anisotropy in a predetermined crystal direction.

In addition to the process of FIG. 1, in the process of FIG. 2, fine particles 22 of catalyst material are supported on the surface of a substrate 20 such as silicon. This catalyst material is a transition metal containing, for example, nickel, iron, and cobalt when growing carbon nanotubes. Or transition metal and Ti,

It is an alloy formed by mixing any one of Al, Ta, TiN and Ti02. The diameter of the fine particles is controlled to about 0.5 to: LOnm, preferably about 1 to 4 nm.

As shown in FIG. 2, 0.5˜: Fine particles whose diameter is controlled to about LOnm are generated on the substrate surface by the laser ablation method developed by the present inventors. The method of producing these fine particles is It is introduced in detail in Chemical Physics Letters 382 (2003) 361.

FIG. 3 is a diagram for explaining the laser ablation method. The method is briefly described below. First, an iron target 32 is set in a chamber 30 containing He gas and having a pressure of 1.5 KPa, and the target is irradiated with a laser beam 36 from an Nd, YAG laser 34 to ablate the iron target 32 ( Excise). The iron of the target 32 evaporates by irradiation with a single laser beam 36 having energy, and immediately after that, solidifies to produce fine particles 40. These fine particles are annealed when passing through the vicinity of the tube-shaped heating means 42 by the He gas flow, and the crystal state thereof is improved.

[0026] However, since the particle size of the iron fine particles 40 to be generated has a certain variation, the particle size is 0.5 to: LOnm, preferably 1.0 to 4 by DM A (Differential Mobility Analyzer) 44. Fine particles having a particle size of Onm are selected, introduced into the chamber 46, and supported on the surface of the second substrate 20 as fine particles 22 of the catalyst material. In order to accumulate the fine particles 22 on the surface of the second substrate 20, a voltage is applied to the stage 28 of the substrate 20, and the charged fine particles 22 fall on the surface of the substrate 20 due to a potential difference.

Next, in the process of FIG. 4, the first substrate 10 having a plurality of protrusions formed on the surface is turned upside down so as to face the second substrate 20 carrying a large number of fine particles 22 of catalyst material. Then, the tip of the protrusion 12 is brought into contact with the fine particle 22 to attach the fine particle 22 to the tip of the protrusion. As a result, as shown in FIG. 5, one particle 22 is attached to the tip of the protrusion 12 of the first substrate 10.

In the step of FIG. 4, the fine particles can be more efficiently attached to the tips of the protrusions by heating to, for example, about 300 ° C. while the tips of the protrusions 12 are in contact with the fine particles 22. This heating temperature is considerably lower than the melting point of catalytic metals such as iron, but the metal is easily attached by heating.

In FIGS. 3 and 4, the fine particles 22 are supported on the surface of the substrate 20 without gaps. However, if there are gaps between the fine particles 22 to some extent, the projection 12 is more effective in the adhesion process of FIG. One fine particle 22 can be separated and attached to the tip of the substrate. As described above, the particle size of the catalyst metal fine particles 22 is adjusted to a desired value, and by using the catalyst metal fine particles 22 having such a controlled particle size, carbon nanotubes having a uniform diameter are grown. To let it can. Therefore, it is desirable to attach a single particle 22 to the tip of each protrusion.

Next, in the process of FIG. 6, the first substrate is introduced into the chamber of the thermal CVD apparatus, and while the substrate is heated to about 600 ° C., argon (Ar), acetylene (C2H2), hydrogen Carbon nanotubes CNT are grown on the catalytic metal fine particles 22 in an atmosphere of 0.1 to lKPa in a mixed gas of (H2) (ratio 90: 10: 1000). Carbon nanotubes CNT start growing at a diameter corresponding to the particle size of the fine particles 22, and the tip reaches the surface of the adjacent protrusion. By setting the above CVD growth time to a predetermined time, for example, 30 minutes, the length of the carbon nanotube CNT can be controlled, and the carbon nanotube isolated in the hollow from the catalytic metal fine particle 22 to the adjacent protrusion 22 CNT can be grown.

FIG. 7 is a schematic configuration diagram of the above CVD apparatus. In this apparatus, a stage 52 and a heating means 54 made of hot filament are provided in a chamber 50. A voltage 56 is applied to the hot filament 54 to generate heat, and the surface of the first substrate placed on the stage 52 is heated. Then, a mixed gas of argon (Ar), acetylene (C2H2), and hydrogen (H2) (ratio 90: 10: 1000) 58 is introduced into the chamber 50 as the growth gas. maintained at lKPa. By heating the hot filament, the surface of the first substrate 10 is heated to about 600 ° C. As a result, carbon nanotube CNTs grow from the catalytic metal particles 22.

According to the present inventors, by adjusting the diameter of the iron fine particles 22 to about 0.5 to 4 nm, it was possible to grow one or two-layer carbon nanotubes with a diameter of about 1 to 4 nm. Therefore, by attaching a single iron fine particle 22 to the tip 12, carbon nanotubes having a uniform diameter and a uniform number of layers can be generated in isolation.

[0033] [Second Embodiment]

In the first embodiment, transition metals such as iron, cobalt, and nickel were used as catalyst materials. In the second embodiment, a mixture of these catalyst metals and any one of Ti, Al, Ta, TIN, and Ti02 is used. Therefore, the target 32 shown in Fig. 3 is replaced with the above mixed metal material. Thus, the mixed metal fine particles 22 can be supported on the surface of the second substrate 20 by the same manufacturing method. Other processes are the same as those in the first implementation. The form is the same.

[0034] As a specific example, in FIG. 3, fine particles mixed with both metals are generated by laser ablation using a mixed substrate of 80% coronate and 20% titanium as the target 32.

[0035] [Third embodiment]

In the third embodiment, a metal film of Ti, Al, Ta, TiN, or Ti02 is deposited on the surface of the needle-like protrusion 12 of the first substrate 10 shown in FIG. It is formed to a film thickness of about. Then, catalytic metal fine particles 22 such as cobalt are attached to the protrusions 12 according to the procedures shown in FIGS. 2, 4, and 5, and carbon nanotubes are grown by thermal CVD or hot filament CVD.

FIG. 8 is a diagram showing the carbon nanotube CNT generated by the third embodiment. A titanium film 12 is formed on the surface of the needle-like protrusion 12, and carbon nanotubes CNT grow on cobalt fine particles 22 attached on the titanium film 12. In this chemical vapor deposition of carbon nanotubes, the substrate is heated to, for example, 650 ° C, a mixed gas of alcohol and hydrogen such as argon and ethanol is introduced, maintained at a pressure of 0.1 KPa, and held for about 40 minutes.

As the titanium film 12 is preliminarily formed as described above, the growing carbon nanotube CNT forms an ohmic contact with low resistance between the titanium film 12. Similarly, the tip of the growing carbon nanotube CNT also forms a low-resistance ohmic contact with the titanium film. Regarding this point, our paper (Japanese Journal of Applied Physics Vol. 43, No. 4B, 2004,

pp.1856-1859).

[0038] The cobalt fine particles may be fine particles of other transition metals, fine particles of a mixture of transition metal and Ti, Al, Ta, TiN, Ti02 (V, any metal!

[0039] [Fourth embodiment]

In the first to third embodiments, the carbon nanotube generation method has been described. In the fourth embodiment, it is a method for producing a thin wire material that is not a carbon nanotube but a IIIV compound semiconductor.

In FIG. 1, a first substrate 10 having needle-like protrusions 12 is prepared. And in Fig. 2, the second A catalyst metal, for example, gold fine particles 22 is supported on the surface of the substrate 20. 4 and 5, gold fine particles 22 are attached to the tips of the protrusions 12 of the first substrate 10. After that, the first substrate is loaded into the MOCVD (Metal Organic Chemical Vapor Deposition) equipment, and the fine wire material, III-V compound semiconductor, is grown on the catalyst particles 22 in the III-V metal gas atmosphere. Let Similar to the carbon nanotube CNT shown in Fig. 6, this fine wire material grows from catalyst fine particles 22 and becomes a thin rod-like material that reaches the surface of the adjacent protrusion 12.

[0041] [Fifth embodiment]

FIG. 9 is a cross-sectional view showing the generation process of the fifth embodiment. In this method, as shown in step (a), fine particles 22 of the catalyst material are generated on the surface of the first substrate 10 by the method described above. Then, as shown in step (b), using the fine particles 22 as a mask, the surface of the first substrate 10 is etched by, for example, ion milling to form needle-like protrusions 12. As a result, it is possible to form a state in which fine particles 22 of the catalyst material adhere to the tips of the protrusions 12 on the surface of the substrate 10. In other words, this is the same state as in Fig. 5.

[0042] Thereafter, carbon nanotubes and the like are grown independently on the fine particles 22 of the catalyst material by the CVD method described in FIGS.

[0043] According to the fifth embodiment, it is possible to easily form a structure in which catalyst fine particles are isolated and attached to the tips of a plurality of protrusions.

[0044] The growth gas for chemical vapor deposition in the first to fifth embodiments described above may be a gas obtained by vaporizing a carbon-containing liquid in addition to acetylene and alcohol. In addition to hydrogen H2, nitrogen may also be used. N2 may be used, and in addition to argon Ar, helium He may be used. As the growth gas, a gas obtained by vaporizing a carbon-containing liquid such as hydrocarbon or alcohol may be used alone, or a mixed gas mixed with at least one of hydrogen, nitrogen, argon, and helium may be used. You can use it.

[0045] As described above, according to the present embodiment, it is possible to generate an isolated carbon nanotube or fine wire substance hanging in the air with good reproducibility. Therefore, it can contribute to mass production of carbon nanotubes with desired characteristics.

Industrial applicability According to the present invention, it is possible to generate a fine wire substance such as an isolated carbon nanotube with good reproducibility.

Claims

The scope of the claims

[1] a first step of preparing a first substrate having a plurality of protrusions formed on the surface;

A second step of generating a plurality of fine particles comprising a catalyst material on a second substrate; and a catalyst material having a plurality of protrusions formed on the first substrate formed on the second substrate. A third step of bringing the catalyst material fine particles into contact with the plurality of protrusions in contact with the fine particles;

And a fourth step of growing the carbon nanotubes on the fine particles of the catalyst material by placing the first substrate in a carbon-containing gas atmosphere.

[2] In claim 1,

A method for producing carbon nanotubes, wherein the catalyst material is a transition metal containing at least cobalt, iron, and nickel.

[3] In claim 1,

The catalyst material is a carbon nanotube produced by alloying a transition metal containing at least cobalt, iron, and nickel with any one of Ti, Al, Ta, TiN, and TiO.

2

How to complete.

[4] In claim 2 or 3,

In the third step, the carbon that adheres the fine particles of the catalyst material to the protrusions by heating to a predetermined temperature in a state where the protrusions of the first substrate are in contact with the fine particles of the catalyst material of the second substrate. Nanotube production method.

[5] In claim 1,

Before the third step, a fifth step of forming a metal layer of any one of Ti, Al, Ta, TiN, and TiO on the surface of the plurality of protrusions of the first substrate prepared in the first step Having power

2

A method for producing single-bonn nanotubes.

[6] In claim 1,

The transition material fine particles are transition metal fine particles having a diameter of 0.5 to: LOnm, and the carbon nanotubes grown in the fourth step are carbon with a diameter of 1 to 4 nm and a single-layer or double-layer structure. Nanotube production method.

[7] In claim 1,

In the second step, the catalyst material is irradiated with an energy beam to vaporize, the vaporized catalyst material is atomized, and fine particles having a predetermined diameter are selected from the fine particles, and the second substrate is selected. A method for producing carbon nanotubes to be stacked.

[8] In claim 1,

In the fourth step, the carbon-containing gas is a gas obtained by vaporizing a carbon-containing liquid such as hydrocarbon or alcohol, and the carbon-containing gas alone or H, N, A

A method for producing carbon nanotubes, which is chemical vapor deposition, which is a mixed gas mixed with at least one of 2 2 r and He.

[9] a first step of preparing a first substrate having a plurality of protrusions formed on the surface;

And a fourth step of growing the fine wire substance on the fine particles of the catalyst material by placing the first substrate in a growth gas atmosphere.

10. The method for producing a fine wire substance according to claim 9, wherein the catalyst material is Au and the fine wire substance force GaAs, InP, InAs is included in a group IIIV compound semiconductor.

[11] The method of producing a thin wire substance according to claim 10, wherein the fourth step is a metal organic chemical vapor deposition method using the group IIIV metal gas as a growth gas.

[12] a first step of generating a plurality of fine particles comprising a catalyst material on a substrate;

A second step of etching the surface of the substrate using the plurality of fine particles as a mask to form a plurality of protrusions having the fine particles attached to the tip;

And a third step of growing the fine line substance on the fine particles of the catalyst material by placing the substrate in a growth gas atmosphere.

13. The method for producing a fine line substance according to claim 12, wherein the catalyst material is a transition metal containing at least cobalt, iron, and nickel, and the fine line substance is a carbon nanotube.