Patent Application
20170096338
The present invention relates to a nanotube-nanohorn complex and a method of manufacturing the same.
Carbon nanotubes comprise such characteristics that they have a high aspect ratio, are chemically stable, and are mechanically strong. Therefore, carbon nanotubes have greatly been expected as field emission luminous elements as disclosed in Japanese laid-open patent publications Nos. 2001-143645 (Patent Literature 1) and 2000-86219 (Patent Literature 2) and have diligently been studied.
In most cases where carbon nanotubes are used as field emission elements as disclosed in Japanese laid-open patent publications No. 2007-103313 (Patent Literature 3) and 2007-265749 (Patent Literature 4), it has been customary to mix a binder or the like so as to produce paste for application onto an electrode by spraying, screen printing, or the like. However, the dispersibility of carbon nanotubes is so poor that homogeneous paste cannot be obtained. Accordingly, there has been a large problem in uniformity of the light emission. Aggregates of carbon nanohorns, which comprise a horn structure with a sheath structure like a carbon nanotube and a closed end, have been found in recent years. The unique structure of a carbon nanohorn has industrially attracted attention as a fuel cell as shown in Japanese laid-open patent publication No. 2002-159851 (Patent Literature 5) or a catalyst carrier for steam reforming to produce hydrogen from hydrocarbon such as methane as shown in disclosed in Japanese laid-open patent publication No. 2007-7599 (Patent Literature 6). Recently, carbon nanohorns have also greatly been expected as field emission elements as disclosed in Japanese laid-open patent publications Nos. 2003-77385 (Patent Literature 7) and 2009-76314 (Patent Literature 8).
It has already been known that carbon nanohorns are nanocarbon having high conductivity because they comprise a tubular structure. Carbon nanohorns are spherical aggregates having a diameter of 1 nm to 5 nm in which the length of a sheath comprising a horn structure is in a range of 30 nm to 200 nm. Although carbon nanohorns have higher dispersibility than carbon nanotubes, an aspect ratio of carbon nanohorns is so low that carbon nanohorns are unsuitable to field emission elements and the like.
In Japanese patent application No. 2008-169942 (Patent Literature 9), the applicant has proposed a nanotube-nanohorn complex having a high aspect ratio, also having high dispersibility, and allowing a carbon nanotube to grow with controlled diameter.
The nanotube-nanohorn complex described in Patent Literature 9 is an excellent invention in that it has a high aspect ratio, also high dispersibility, and allowing a carbon nanotube to grow with controlled diameter.
In order to produce the nanotube-nanohorn complex described in Patent Literature 9, however, carbon nanotubes should be synthesized from catalyst-carried carbon nanohorns by a chemical vapor deposition method (CVD method). Thus, there is a room for further improvement in cost reduction and mass synthesis. Additionally, a CVD method has a low synthesis temperature, resulting in low crystallinity. Thus, there is also a room for improvement in durability as a field emission element.
The invention of the present application has been made in view of the foregoing circumstances. It is, therefore, an object of the invention to solve problems in the prior art and to provide a nanotube-nanohorn complex having a high aspect ratio, also having high dispersibility, allowing a carbon nanotube to grow with controlled diameter, and having high durability at a low cost.
Therefore, in order to solve the above problems, the invention of the present application comprises the following features.
Specifically, a first aspect of the invention of the present application is a nanotube-nanohorn complex wherein a carbon nanotube grows from a catalyst, which is surrounded by a carbon nanohorn aggregate.
Furthermore, a second aspect of the invention of the present application is a method of manufacturing a nanotube-nanohorn complex, the method comprising evaporating a carbon target containing a catalyst with a laser ablation method to synthesize a structure including both of a carbon nanohorn aggregate and a carbon nanotube.
Moreover, a third aspect of the invention of the present application is a method of manufacturing a nanotube-nanohorn complex, the method comprising evaporating a carbon target containing a catalyst with a laser ablation method to synthesize a structure in which a carbon nanotube grows from the catalyst, which is surrounded by a carbon nanohorn aggregate.
Furthermore, a fourth aspect of the invention of the present application is a paste for field emission comprising the nanotube-nanohorn complex as recited in the first aspect.
Moreover, a fifth aspect of the invention of the present application is a cold cathode electron source comprising the paste for field emission as recited in the third aspect.
Furthermore, a sixth aspect of the invention of the present application is a light emitting device using the cold cathode electron source as recited in the fourth aspect.
Moreover, a seventh aspect of the invention of the present application is an illuminating apparatus using the light emitting device as recited in the fifth aspect.
Furthermore, an eighth aspect of the invention of the present application is a light emitting method using the illuminating apparatus as recited in the sixth aspect.
According to the invention of the present application, there can be provided a nanotube-nanohorn complex having a high aspect ratio, also having high dispersibility, allowing a carbon nanotube to grow with controlled diameter, and having high durability at a low cost.
1 nanotube-nanohorn complex
100 carbon nanohorn aggregate
101 catalyst
102 carbon nanotube
103 graphene
104 carbon nanohorn
The invention of the present application comprises features as described above. Embodiments of the present invention will be described below.
An outlined structure of a nanotube-nanohorn complex 1 according to the present embodiment will be described with reference to
Referring to
At that time, as shown in the conceptual diagrams of
Furthermore, the carbon nanotube 102 preferably has the following size in view of limitation on a manufacturing process or a size with which the carbon nanotube 102 can be synthesized: In the case of a single layer, the diameter is in a range of 0.4 nm to 4 nm. In the case of two layers, the inside diameter is in a range of 0.4 nm to 20 nm, and the outside diameter is in a range of 0.7 nm to 22 nm. In the case of multiple layers, the inside diameter is in a range of 0.4 nm to 200 nm, and the outside diameter is in a range of 0.7 nm to 500 nm.
Next, a method of manufacturing a nanotube-nanohorn complex 1 according to the present embodiment will be described.
A method of manufacturing a nanotube-nanohorn complex 1 according to an embodiment of the present invention is not limited to a specific one as long as it produces the aforementioned structure. Nevertheless, the aforementioned structure is suitably synthesized by evaporating a carbon target containing a catalyst with a laser ablation method.
Specific manufacturing methods will be described below.
A CO2 laser, a YAG (Yttrium Aluminum Garnet) laser, or an excimer laser can be used as a laser for the laser ablation. A CO2 laser is the most suitable one for the following reasons: A CO2 laser utilizes transitions of vibrational and rotational levels of CO2 molecules. The quantum efficiency is about 40% to about 50% and is thus very high. Furthermore, the oscillation efficiency is high. Therefore, an output of the laser can readily be increased. Thus, a CO2 laser is suitable for evaporation of a carbon target. An output of 1 kW/cm2 to 1000 W/cm2 can be used for CO2 laser ablation, which can be performed by continuous irradiation and pulse irradiation. Furthermore, the synthesis can continuously be performed by rotating a target. At that time, it is the most effective to set a laser output to be 30 kW/cm2 to 50 kW/cm2. If a laser output is lower than 15 kW/cm2, then a target is hardly evaporated. Thus, it is difficult to synthesize a large amount of nanotube-nanohorn complex. Furthermore, if a laser output is 65 kW/cm2 or higher, then a nanotube-nanohorn complex 1 can be synthesized. However, amorphous carbon improperly increases.
An irradiation area can be controlled by a laser output and the degree of convergence of a lens. An available irradiation area is in a range of 0.01 cm2 to 1 cm2.
A laser beam can be emitted in a direction substantially perpendicular to a surface of a carbon target substance or in a direction inclined at an angle less than 90 degrees with respect to the orthogonal line to a surface of a carbon target substance.
A carbon target substance irradiated with a laser beam may contain, as a catalyst, a trace of metal including at least one of Fe, Ni, Co, Pt, Au, Cu, Mo, W, Mg, Pd, Rh, Ti, Nb, Ru, Y, and B, or a precursor thereof, or an alloy thereof. In this case, it is preferable to include a catalyst at an element ratio of 0.1 atomic % to 30 atomic % to carbon. The optimum element ratio is 0.1 atomic % to 5 atomic %. This carbon target substance containing a catalyst is housed in a chamber, and a laser beam is concentrated by a ZnSe lens or the like and emitted to the carbon target substance. At that time, the temperature of the chamber can be adjusted from a room temperature to 1500° C. It is preferable to set the temperature of the chamber at a room temperature in view of mass synthesis, cost reduction, and the like.
Inert gas, hydrogen, air, carbon monoxide, carbon dioxide, and the like can be introduced into a chamber in which a laser ablation is performed. The gas passes through the chamber, and a flow of the gas allows produced substances to be recovered. A closed atmosphere may be used depending upon the gas being introduced. Ar or Kr is suitable for an atmosphere gas. In a case where an inert gas is used, amorphous carbon tends to be included when the gas has a relatively small atomic weight. Petal-like nanohorns are likely to be produced when the gas has a relatively large atomic weight. The flow rate of the atmosphere gas may be set at any value. Nevertheless, the flow rate of the atmosphere gas is preferably in a range of 0.5 L/min to 100 L/min.
The gas pressure of the chamber after the introduction of the gas is about 0.01 Torr (0.013×102 Pa) to about 760 Ton (1013×102 Pa). At that time, in order to increase a ratio of the carbon nanotube 102, a pressure that is not more than 400 Torr (533×102 Pa) is suitable for the gas pressure of the chamber. In order to increase a ratio of the carbon nanohorn aggregate, it is preferable to set the gas pressure of the chamber at not less than 400 Torr (533×102 Pa).
Thus, according to the present embodiment, the carbon nanotube 102 grows from the catalyst 101 in the nanotube-nanohorn complex 1, and the carbon nanohorn aggregate 100 surrounds the catalyst 101. Therefore, the nanotube-nanohorn complex 1 has a high aspect ratio also has high dispersibility. At the same time, the nanotube-nanohorn complex 1 has controlled diameter and has high durability at a low cost.
Moreover, according to the present embodiment, a nanotube-nanohorn complex 1 is synthesized by evaporating a carbon target containing a catalyst with a laser ablation method.
Accordingly, the nanotube-nanohorn complex 1 comprises an inexpensive structure in which its diameter has been controlled at a desired value.
Examples will be shown below to illustrate and explain the present invention in greater detail. However, the present invention is not limited to the following examples.
A carbon target containing a catalyst was evaporated under a constant gas pressure by a laser ablation method while a laser output was varied. Thus, nanotube-nanohorn complexes 1 were produced by way of trial. The following specific steps were performed.
First, a carbon target containing a catalyst having a diameter of 2.5 cm and a length of 10 cm was placed in a chamber. An inert gas of Ar was supplied so that a gas pressure was 150 Torr (200×102 Pa). The interior of the chamber was held at a room temperature. A flow rate of Ar was set to be 10 L/min. The target containing a catalyst included Co at 0.6 atomic % and Ni at 0.6 atomic %. A target rotation mechanism was provided within the chamber so that a laser beam could continuously be emitted, and was adjusted so that a uniform target surface was produced at the time of continuous emission.
Then the target containing a catalyst was irradiated with a CO2 laser while the output of the CO2 laser was set to be 15 kW/cm 2, 30 kW/cm2, 50 kW/cm2, 65 kW/cm2, and 75 kW/cm2, respectively. Samples were synthesized under the respective conditions. Measurement of the
Raman spectrum of the obtained samples and observation of surfaces of the obtained samples were conducted.
Furthermore, it was confirmed that a G/D ratio of the Raman spectrum of NTNH synthesized under the aforementioned conditions of 30 kW/cm2 to 50 kW/cm2 was higher than a G/D ratio of NTNH synthesized by a CVD method. It was also confirmed that NTNH synthesized under the aforementioned conditions of 30 kW/cm2 to 50 kW/cm2 had higher crystallinity.
Under the same conditions as in Example 1 except for a constant laser output (50 kW/cm2) and a varying pressure of Ar, nanotube-nanohorn complexes were produced by way of trial. Measurement of the Raman spectrum of the obtained samples and observation of surfaces of the obtained samples were conducted.
It can be seen from
Under the same conditions as in Example 1 except that a catalyst had a different composition with a constant laser output (50 kW/cm2), Ar pressure (150 Torr (200×102 Pa)), and flow rate (10 L/min), nanotube-nanohorn complexes were produced by way of trial. Measurement of the Raman spectrum of the obtained samples was conducted.
It can be seen from
Under the same conditions as in Example 1 expect that an Ar gas and a Kr gas were respectively used with a constant laser output (50 kW/cm2), nanotube-nanohorn complexes were produced by way of trial. Measurement of the Raman spectrum of the obtained samples was conducted.
It can be seen from the RBM of
Field emission paste was produced using the samples produced with a laser output of 50 kW/cm2 among the samples produced in Example 1. The field emission characteristics of the paste were evaluated.
Specifically, the sample was first subjected to ultrasonic dispersion in α-terpineol (15 ml) for 30 minutes. The dispersion was mixed with a cellulose type organic binder of 200 mg and glass frit of 400 mg and then subjected to ultrasonic dispersion for 30 minutes. The paste was screen-printed on a glass substrate on which ITO (Indium Tin Oxide) had been sputtered so that the paste had a thickness of about 100 μm. Thereafter, a heat treatment was performed at 500° C. in nitrogen to remove the organic binder. Furthermore, for a purpose of comparison, paste was produced using only carbon nanohorns in the same manner described above, and an electrode was produced. The current-voltage characteristics of a cathode were measured in a state in which a degree of vacuum was 0−6 Torr (1.3×10−4 Pa).
Some or all of the above embodiments can be described as in the following notes.
Nevertheless, the present invention is not limited to those notes.
A nanotube-nanohorn complex wherein a carbon nanotube grows from a catalyst, which is surrounded by a carbon nanohorn aggregate.
The nanotube-nanohorn complex as recited in Note 1, wherein the carbon nanohorns comprise one of a dahlia-like form, a bud-like form, a seed-like form, and a petal-like form.
The nanotube-nanohorn complex as recited in one of Notes 1 and 2, wherein the carbon nanotube has a single layer, and the carbon nanotube has a diameter of 0.4 nm to 4 nm.
The nanotube-nanohorn complex as recited in one of Notes 1 and 2, wherein the carbon nanotube has two layers, and the carbon nanotube has an inside diameter of 0.4 nm to 20 nm and an outside diameter of 0.7 nm to 22 nm.
The nanotube-nanohorn complex as recited in one of Notes 1 and 2, wherein the carbon nanotube has multiple layers, and the carbon nanotube has an inside diameter of 0.4 nm to 200 nm and an outside diameter of 0.7 nm to 500 nm.
The nanotube-nanohorn complex as recited in one of Notes 1 to 5, wherein the nanotube-nanohorn complex is synthesized by evaporating a carbon target containing a catalyst with a laser ablation method.
The nanotube-nanohorn complex as recited in Note 6, wherein the catalyst includes at least one of Fe, Ni, Co, Pt, Au, Cu, Mo, W, Mg, Pd, Rh, Ti, Nb, Ru, Y, and B, or a precursor thereof, or an alloy thereof.
The nanotube-nanohorn complex as recited in one of Notes 6 and 7, wherein the nanotube-nanohorn complex is synthesized with a laser output of 1 kW/cm2 to 1000 kW/cm2.
The nanotube-nanohorn complex as recited in one of Notes 6 to 8, wherein the nanotube-nanohorn complex is synthesized by evaporating the carbon target containing the catalyst with the laser ablation method in a gas atmosphere including Ar, N2, He, Ne, Kr, or Xe, or a mixture gas thereof.
The nanotube-nanohorn complex as recited in one of Notes 6 to 9, wherein the nanotube-nanohorn complex is synthesized by evaporating the carbon target containing the catalyst with the laser ablation method in a gas atmosphere at a pressure of 0.01 Torr to 760 Torr (0.013×102Pa to 1013×102 Pa).
The nanotube-nanohorn complex as recited in one of Notes 6 to 10, wherein the nanotube-nanohorn complex is synthesized by evaporating the carbon target containing the catalyst with the laser ablation method in a gas atmosphere at a gas flow rate of 0.1 L/min to 100 L/min.
A method of manufacturing a nanotube-nanohorn complex, the method comprising evaporating a carbon target containing a catalyst with a laser ablation method to synthesize a structure including both of a carbon nanohorn aggregate and a carbon nanotube.
A method of manufacturing a nanotube-nanohorn complex, the method comprising evaporating a carbon target containing a catalyst with a laser ablation method to synthesize a structure in which a carbon nanotube grows from the catalyst, which is surrounded by a carbon nanohorn aggregate.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 and 13, wherein the carbon nanohorns comprise one of a dahlia-like form, a bud-like form, a seed-like form, and a petal-like form.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 14, wherein the carbon nanotube has a single layer, and the carbon nanotube has a diameter of 0.4 nm to 4 nm.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 14, wherein the carbon nanotube has two layers, and the carbon nanotube has an inside diameter of 0.4 nm to 20 nm and an outside diameter of 0.7 nm to 22 nm.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 14, wherein the carbon nanotube has multiple layers, and the carbon nanotube has an inside diameter of 0.4 nm to 200 nm and an outside diameter of 0.7 nm to 500 nm.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 17, wherein the catalyst of the carbon target containing the catalyst includes at least one of Fe, Ni, Co, Pt, Au, Cu, Mo, W, Mg, Pd, Rh, Ti, Nb, Ru, Y, and B, or a precursor thereof, or an alloy thereof.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 18, wherein the laser ablation method is performed with a laser output of 1 kW/cm2 to 1000 kW/cm2.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 19, wherein the laser ablation method is performed in a gas atmosphere including Ar, N2, He, Ne, Kr, or Xe, or a mixture gas thereof.
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 20, wherein the laser ablation method is performed in a gas atmosphere at a pressure of 0.01 Torr to 760 Torr (0.013×102 Pa to 1013×102 Pa).
The method of manufacturing a nanotube-nanohorn complex as recited in one of Notes 12 to 21, wherein the laser ablation method is performed in a gas atmosphere at a gas flow rate of 0.1 L/min to 100 L/min.
A paste for field emission comprising the nanotube-nanohorn complex as recited in one of Notes 1 to 11.
A cold cathode electron source comprising the paste for field emission as recited in Note 23.
A light emitting device using the cold cathode electron source as recited in Note 24.
An illuminating apparatus using the light emitting device as recited in Note 25.
A light emitting method using the illuminating apparatus as recited in Note 26.
In the aforementioned embodiments and examples, the nanotube-nanohorn complex is used as a material of paste for field emission. However, the present invention is not limited to this example at all and is applicable to any structure using a nanotube-nanohorn complex.
Furthermore, paste field emission according to the present invention is applicable to a cold cathode electron source or a light emitting device such as an illuminating device using such a cold cathode electron source.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-238936 | Oct 2009 | JP | national |
This is a divisional application based upon U.S. patent application Ser. No. 13/502,055 filed Apr. 13, 2012, which is a U.S. National Stage of International Application No. PCT/JP2010/067990 filed Oct. 6, 2010, claiming priority based on Japanese Patent Application No. 2009-238936 filed Oct. 16, 2009, the contents of all of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13502055 | Apr 2012 | US |
| Child | 15383553 | US |
