JP2008239378A - Method for manufacturing monolayer carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a growth method of monolayer carbon nanotube by which carbon nanotubes can be grown at a low pressure and/or a low temperature. <P>SOLUTION: The method comprises heating a substrate provided with a catalyst in an ultrahigh vacuum space and then introducing a source material gas to grow monolayer carbon nanotubes, wherein the pressure in the ultrahigh vacuum space just before heating the substrate is not more than 1/1000 of the pressure in the ultrahigh vacuum space when introduction of the source material gas is finished. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing single-walled carbon nanotubes.

The growth method of single-walled carbon nanotubes (hereinafter abbreviated as “SWNTs”) using a chemical vapor deposition method using a catalyst (hereinafter abbreviated as “CCVD”) can be integrated. Is attracting attention as a new growth method. However, since CCVD using conventionally known methane gas as a raw material has been performed at a high pressure (for example, 50 kPa) and a high temperature (for example, 900 ° C.), its application has been limited.
Therefore, as described in Non-Patent Document 1, a method for growing SWNTs at low pressure (1.5 kPa) and low temperature (550 ° C.) using alcohol has been developed. However, even in this method, when SWNTs are grown on a silicon device or a gallium arsenide device, the temperature is too high and the silicon device or the gallium arsenide device is broken.
For example, a hybrid device composed of SWNTs and a GaAs / AlGaAs substrate is manufactured by growing SWNTs on the substrate. It will come off and the substrate will be destroyed. For this purpose, SWNTs grown by other growth methods are currently dispersed on the substrate. Such an indirect growth method has an important disadvantage that the SWNTs are likely to be damaged due to an increase in the number of processes and cannot be integrated.

In addition, SWNTs can flow a large current of 3 digits or more compared to an integrated circuit using a copper material that has been used conventionally, and since the allowable current density is high and the thermal conductivity is also high. It is attracting attention as the next wiring material. However, since the interlayer wiring of the integrated circuit is normally performed at the final step of the manufacturing process, if the growth temperature of the SWNTs wiring is high, the interlayer insulating layer and the device under the wiring are greatly affected. For this reason, it is required to lower the growth temperature.
Under such circumstances, Non-Patent Document 2 describes a method of growing SWNTs at 350 ° C. using an acetylene gas as a raw material and using an Al / Fe catalyst. This method requires treatment at the same temperature as the growth temperature (350 ° C.) in a high-pressure ammonia gas or hydrogen gas atmosphere in order to activate the catalyst. However, in such a high temperature treatment in a gas atmosphere, there is a problem that there is a high possibility that etching of a low dielectric constant insulator on a silicon device or nitriding of the surface of a GaAs substrate occurs.

Chem. Phys. Lett., 360, 229 (2002) Nano.Lett. 6, 1107 (2006)

  The present invention aims to solve the above-described problems, and provides a novel method for growing SWNTs.

  The inventor of the present application performs a series of operations in an ultra-high vacuum space and heats the substrate in a method of growing a single-walled carbon nanotube after introducing a source gas after heating a substrate provided with a catalyst. The pressure in the ultra-high vacuum space (hereinafter sometimes referred to as “initial pressure”) just before the start is the pressure in the ultra-high vacuum space (hereinafter also referred to as “growth pressure”) when the introduction of the source gas is completed. It was found that good SWNTs can be grown even at low temperatures and / or low pressures by setting the ratio to 1/1000 or less. In particular, the present invention is characterized in that the work is performed in an ultra-high vacuum space and the ratio between the initial pressure and the growth pressure is set to a specific value. For example, the method described in Non-Patent Document 2 (Nano. Lett. 6, 1107 (2006)) succeeds in growing SWNTs at 350 ° C., but is not performed in an ultrahigh vacuum space. No mention is made of the importance of the ratio of initial pressure to growth pressure.

Specifically, the above problem has been achieved by the following means.
(1) A method of growing a single-walled carbon nanotube by introducing a source gas after heating a substrate provided with a catalyst in an ultra-high vacuum space, wherein the ultra-high vacuum space just before heating the substrate A method for growing single-walled carbon nanotubes, wherein the pressure is 1/1000 or less of the pressure in the ultra-high vacuum space when the introduction of the source gas is completed.
(2) In an ultra-high vacuum space, a method is provided in which a catalyst is provided on a substrate, the substrate provided with the catalyst is heated, a source gas is introduced, and single-walled carbon nanotubes are grown. A method for growing single-walled carbon nanotubes, wherein the pressure in the ultra-high vacuum space immediately before is less than 1/1000 of the pressure in the ultra-high vacuum space at the time when the introduction of the source gas is completed.
(3) A method of growing single-walled carbon nanotubes by cleaning a substrate in an ultra-high vacuum space, providing a catalyst on the substrate, heating the substrate provided with the catalyst, and then introducing a source gas. The method for growing single-walled carbon nanotubes, wherein the pressure in the ultra-high vacuum space immediately before heating the substrate is 1/1000 or less of the pressure in the ultra-high vacuum space when the introduction of the source gas is completed.
(4) The growth method according to (3), wherein the substrate is cleaned with argon gas.
(5) The growth method according to (3) or (4), wherein the cleaning is performed at 700 to 800 ° C.
(6) The method for growing single-walled carbon nanotubes according to any one of (1) to (5), wherein the heating temperature of the substrate provided with the catalyst is 430 ° C. or lower.
(7) The growth method according to any one of (1) to (6), wherein the single-walled carbon nanotube is grown at a rate of 10 nm / min or less.
(8) The growth method according to any one of (1) to (7), wherein the pressure in the ultra-high vacuum space immediately before heating the substrate is 2 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Pa. .
(9) The growth method according to any one of (1) to (8), wherein the pressure in the ultrahigh vacuum space at the time when the introduction of the source gas is completed is 0.001 to 0.2 Pa.
(10) The pressure in the ultra-high vacuum space immediately before heating the substrate is 1/1000 to 1/10000 of the pressure in the ultra-high vacuum space at the time when the introduction of the source gas is completed. The growth method according to any one of 9).
(11) The growth method according to any one of (1) to (10), wherein the source gas is a hydrocarbon-based gas.
(12) The growth method according to any one of (1) to (10), wherein the source gas is an alcohol-based gas.
(13) The growth method according to any one of (1) to (10), wherein the source gas is ethyl alcohol.
(14) The growth method according to any one of (1) to (13), wherein the catalyst contains cobalt.
(15) A method in which a substrate provided with a catalyst is heated to 350 to 750 ° C. in an ultra-high vacuum space, and then a raw material gas is introduced to grow single-walled carbon nanotubes immediately before heating the substrate. Single layer in which the pressure in the ultra-high vacuum space is 2 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Pa, and the pressure in the ultra-high vacuum space is 0.002 to 0.2 Pa when the introduction of the source gas is completed Carbon nanotube growth method.

  By employing the growth method of the present invention, it has become possible to grow SWNTs even at low temperatures (for example, less than 400 ° C.) and / or low pressure.

  Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

In the present invention, in a method of heating a substrate provided with a catalyst, introducing a source gas, and growing SWNTs, these operations are performed in an ultrahigh vacuum space, and the initial pressure is 1/1000 of the growth pressure. The following adjustments have been made. Here, the ultra-high vacuum space means a pressure state of 1 × 10 ⁻⁵ Pa or less.
The initial pressure is preferably 1/1000 to 1/10000 of the growth pressure, and more preferably 1/1000 to 1/100000. By adopting such means, even if the growth temperature of SWNTs is low, good SWNTs can be grown without problems such as substrate damage.
In the present invention, the initial pressure is preferably 1 × 10 ⁻⁵ to 2 × 10 ⁻⁷ Pa, more preferably 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁸ Pa. Adjustment of the initial pressure is usually performed by adjusting the exhaust time in an ultra-high vacuum apparatus. The exhaust time can be appropriately adjusted according to the initial pressure to be set, and is usually 10 to 120 minutes. However, it goes without saying that the pressure adjustment work is not necessary when the pressure in the ultra-high vacuum space is a pressure suitable for the initial pressure before the pressure adjustment.
Furthermore, in the present invention, the growth pressure can be 0.001 Pa to 0.1 Pa, and further can be 0.002 to 0.05 Pa. The growth pressure is usually adjusted by a flow controller by introducing the raw material gas. The specific introduction amount is usually 0.24 to 24 cc / min.

  In the present invention, the heating temperature of the substrate provided with the catalyst corresponds to the growth temperature of SWNTs. In the method of the present invention, the heating temperature of the substrate can be, for example, 430 ° C. or lower, and further lower than 400 ° C. In this way, by lowering the substrate heating temperature, SWNTs can be grown with little damage and can be integrated. In the method of the present invention, since the growth temperature can be adjusted by adjusting the initial pressure and the growth pressure, the lower limit value of the growth temperature is not particularly defined. That is, it is possible to grow good SWNTs regardless of whether the growth temperature is low or high.

  In the growth method of the present invention, after introducing the source gas, the time for growing SWNTs (hereinafter sometimes referred to as “growth time”) can be appropriately determined according to the initial pressure, growth pressure, growth temperature, etc. For example, when an alcohol-based gas is used as a raw material gas, it is 50 to 2000 minutes.

In particular, in the invention, when the heating temperature of the substrate provided with the catalyst is 350 to 450 ° C. (preferably 360 to 450 ° C.), the initial pressure is 2 × 10 ⁷ to 2 × 10 ⁻⁶ Pa, and the growth pressure is 0.002. It is preferable that it is -0.02 Pa, and it is preferable that the growth time in this case is 500-2000 minutes.
When the heating temperature of the substrate provided with the catalyst is 450 to 650 ° C., it is preferable that the initial pressure is 2 × 10 ^{−6 to} 5 × 10 ⁻⁶ Pa and the growth pressure is 0.02 to 0.05 Pa. In this case, the growth time is preferably 500 to 200 minutes.
In particular, when the heating temperature of the substrate provided with the catalyst is 650 to 750 ° C., the initial pressure is preferably 1 × 10 ^{−6 to} 5 × 10 ⁻⁶ Pa and the growth pressure is 0.05 to 0.2 Pa. In this case, the growth time is preferably 200 to 50 minutes.

  In the present invention, the single-walled carbon nanotubes are preferably grown at a rate of 10 nm / min or less, more preferably 1 nm / min or less. By growing at such a low speed, there is an advantage that control in the length direction can be performed with high accuracy. Such a slow growth rate is achieved by a synergistic effect that the SWNTs in the present invention are grown in an ultra-high vacuum space and the initial pressure is 1/1000 or less of the growth pressure.

In the present invention, SWNTs may be grown using a catalyst provided on a substrate, but the catalyst is preferably provided on the substrate in an ultra-high vacuum space. By providing the catalyst on the substrate in the ultra-high vacuum space, there is an advantage that the oxidation and contamination of the catalyst can be extremely reduced. Although a known method can be adopted as a method for providing the catalyst, it is usually provided by depositing a catalyst material on the substrate.
Here, the type of catalyst in the growth method of the present invention is not particularly defined unless it deviates from the gist of the present invention. For example, an iron group such as Ni, Fe, and Co, and a platinum group such as Pd, Pt, and Rh And selected from one or more of single metals, alloys or compounds containing rare earth metals such as La, Y, and transition metals such as Mo and Mn. Of these, metals or compounds containing at least one selected from the group consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, La, Y, Mo, and Mn are preferred, and Co and More preferably, Pt is contained, and Co is further preferably contained.

  The type of the substrate can be appropriately determined according to the use of the grown SWNTs, for example, a crystal substrate such as silicon, quartz, sapphire, MgO, an amorphous substrate such as alumina, glass, and the like. A metal substrate can be used. In the present invention, since the growth temperature of SWNTs can be lowered, a substrate having low heat resistance can also be employed.

  The raw material gas in the growth method of the present invention is preferably a hydrocarbon gas, particularly preferably an alcohol gas such as ethyl alcohol, and acetylene.

In the present invention, it is preferable to clean the substrate when the catalyst is provided on the substrate. In this case, cleaning is also preferably performed in an ultra-high vacuum space. In the method for growing SWNTs according to the present invention, by performing a series of operations including cleaning of a substrate in an ultra-high vacuum space, low-temperature growth can be achieved with low pressure, and SWNTs can be obtained under advantageous conditions. There is a synergistic advantage. Further, in the present invention, since the catalyst can be provided after the substrate is cleaned, there is an advantage of preventing oxidation and contamination of the catalyst.
Cleaning is preferably performed by introducing a gas such as a rare gas, ammonia, or hydrogen, and more preferably by introducing argon gas because there is no unnecessary reaction with the substrate. Furthermore, it is more preferable to carry out in an ultrahigh vacuum. The gas introduction temperature is usually about the same as the growth temperature, the pressure of the introduction gas is usually about 0.1 to 1.0 Pa, and the gas introduction time is usually 10 to 60 minutes.

  In particular, in the present invention, the initial pressure is 1/1000 or less of the growth pressure, and the growth rate of SWNTs can be controlled by employing a means for providing a catalyst on a cleaned substrate in an ultra-high vacuum. It is the speed, the amount of SWNTs grown is large, and the obtained SWNTs are good. In particular, these effects are exhibited synergistically by employing a combination of the above means.

  SWNTs grown by the growth method of the present invention can be used for various transistors and wiring materials.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

Example 1
Cleaning the substrate The SiO ₂ / Si substrate was introduced into an ultra-high vacuum apparatus (manufacturer: Katagiri Engineering Co., Ltd., product number: UHV-400X, and cleaned at 800 ° C. for 2 hours in an ultra-high vacuum at 10 ⁻⁷ Pa. Went.

Deposition of catalyst Cobalt was deposited on the surface of the cleaned substrate in an ultrahigh vacuum apparatus so that the average film thickness was 0.1 nm.

Setting of initial pressure The substrate on which the catalyst was deposited was moved to a growth chamber in an ultra-high vacuum apparatus, and the pressure in the growth chamber was adjusted to 10 ⁻⁷ Pa.

Substrate heating After the initial pressure reached 10 ⁻⁷ Pa, the substrate on which the catalyst was deposited was heated to a growth temperature (380 ° C.).

Introduction of source gas After the substrate reached the growth temperature (380 ° C.), ethyl alcohol was introduced so that the pressure (growth pressure) in the ultra-high vacuum apparatus was 2 × 10 ⁻³ Pa. SWNTs were grown in the same state (1000 minutes).

Analysis by Raman spectroscopy After the temperature of the grown SWNTs decreased, analysis was performed by Raman spectroscopy. As a result, the SWNTs are formed on the substrate from several peaks depending on the diameter of the low frequency part peculiar to SWNTs (FIG. 1 (a)) and G-band splitting around 1600 cm ⁻¹ (FIG. 1 (b)). Confirmed growing up. The result by Raman spectroscopy is shown in FIG.

Example 2
In Example 1, the growth temperature was 380 ° C., the growth time was 200 minutes, and the others were performed in the same manner. As a result, as shown in FIG. 2, this results in several peaks (FIG. 2 (a)) depending on the diameter of the low-frequency part peculiar to SWNTs, as well as the splitting of the G-band in the vicinity of 1600 cm ⁻¹ (FIG. 2). From (b)), it was confirmed that SWNTs were grown on the substrate. Moreover, compared with Example 1, it turned out that the production amount of SWNTs is 10 times or more, and the diameter distribution of SWNTs obtained is wide. In addition, the substrate was not damaged.

Comparative Example 1
In Example 1, the SWNTs did not grow at the growth temperature (380 ° C.) even when the same procedure was performed in place of ultrahigh vacuum in the pressure of 1 kPa.

Comparative Example 2
In Example 1, if the initial pressure is 1 Pa, the growth pressure is 10 Pa, that is, the initial pressure is 1/10 times the growth pressure, and others are performed in the same manner, SWNTs do not grow. Furthermore, if the growth temperature is raised in the same manner, the growth of SWNTs is not recognized even when the growth temperature is raised to 600 ° C.

Comparative Example 3
In Example 1, the substrate was not cleaned, and a substrate on which the catalyst was vapor-deposited in an ultra-high vacuum apparatus was used. As a result, it was found that SWNTs do not grow. On the other hand, when the initial pressure was 1/1000 or less of the growth pressure, the growth temperature was higher than 380 ° C., and the same process was performed using a substrate on which the catalyst was deposited outside the ultrahigh vacuum apparatus. , A tendency for SWNTs to grow was observed. For example, when the growth temperature was 600 ° C., it was recognized that the amount of SWNTs about 400 times that of Example 1 was growing.

The spectrum of the Raman spectroscopy measured in Example 1 is shown. The spectrum of the Raman spectroscopy measured in Example 2 is shown.

Claims (15)

  In a super high vacuum space, after heating a substrate provided with a catalyst, a raw material gas is introduced to grow single-walled carbon nanotubes, and the pressure in the ultra high vacuum space immediately before heating the substrate is: A method for growing single-walled carbon nanotubes, which is 1/1000 or less of the pressure in an ultra-high vacuum space when the introduction of the source gas is completed.   In an ultra-high vacuum space, a catalyst is provided on a substrate, the substrate provided with the catalyst is heated, a source gas is introduced, and single-walled carbon nanotubes are grown. A method for growing single-walled carbon nanotubes, wherein the pressure in the high vacuum space is 1/1000 or less of the pressure in the ultra-high vacuum space when the introduction of the source gas is completed.   In the ultra-high vacuum space, after cleaning the substrate, a catalyst is provided on the substrate, the substrate provided with the catalyst is heated, a source gas is introduced, and single-walled carbon nanotubes are grown. A method for growing single-walled carbon nanotubes, wherein the pressure in the ultra-high vacuum space immediately before heating is 1/1000 or less of the pressure in the ultra-high vacuum space when the introduction of the raw material gas is completed.  The growth method according to claim 3, wherein the substrate is cleaned with argon gas.  The growth method according to claim 3 or 4, wherein the cleaning is performed at 700 to 800 ° C.   The method for growing single-walled carbon nanotubes according to any one of claims 1 to 5, wherein a heating temperature of the substrate on which the catalyst is provided is 430 ° C or lower.  The growth method according to any one of claims 1 to 6, wherein the single-walled carbon nanotube is grown at a rate of 10 nm / min or less. The growth method according to claim 1, wherein the pressure in the ultrahigh vacuum space immediately before heating the substrate is 2 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Pa.   The growth method according to any one of claims 1 to 8, wherein the pressure in the ultra-high vacuum space at the time when introduction of the source gas is completed is 0.001 to 0.2 Pa.  The pressure in the ultra-high vacuum space immediately before heating the substrate is 1/1000 to 1 / 10,000 of the pressure in the ultra-high vacuum space when the introduction of the source gas is completed. 2. The growth method according to item 1.  The growth method according to claim 1, wherein the source gas is a hydrocarbon-based gas.   The growth method according to claim 1, wherein the source gas is an alcohol-based gas.  The growth method according to claim 1, wherein the source gas is ethyl alcohol.  The growth method according to claim 1, wherein the catalyst contains cobalt. In an ultra-high vacuum space, a substrate provided with a catalyst is heated to 350 to 750 ° C., and then a raw material gas is introduced to grow single-walled carbon nanotubes. The ultra-high vacuum just before heating the substrate The pressure of the space is 2 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Pa, and the pressure of the ultra-high vacuum space when the introduction of the source gas is finished is 0.002 to 0.2 Pa. Growth method.

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