JP3627021B2 - Method for producing tube-like substance with different elements introduced - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a tube-like substance into which a different element is introduced, which has excellent electrical conduction characteristics and is useful as an electronic material.
[0002]
[Prior art]
Carbon nanotubes discovered in 1991 (Nature, 354, 56-58, 1991) are materials in which a graphite sheet is rolled on a tube, and their electrical properties can be either metallic or semiconducting depending on the structure. It is predicted. Carbon nanotubes have a diameter of 1 to several tens of nanometers and a length of several tens of micrometers, and are therefore expected to exhibit typical one-dimensional electrical conduction.
[0003]
By the way, it is extremely important to control the electrical conduction characteristics of such a tube-shaped substance, and for that purpose, it is necessary to introduce a different element into the tube-shaped substance to control the valence state. Yes.
[0004]
Conventionally, tube-like substances into which such different elements have been introduced are introduced into the gas phase or liquid phase containing the different elements to which the tube-like substance is to be introduced, thereby introducing the different elements by intrusion substitution reaction or surface adsorption. The way to do is taken.
However, the conventional method of introducing a different element from an intrusive substitution reaction or surface adsorption is an equilibrium process, so the amount of the different element introduced is limited, and the concentration of the different element to be introduced exceeds the solid solution limit. It is theoretically impossible to introduce these elements, and furthermore, it is difficult to control the implantation concentration.
[0005]
On the other hand, as a technique for introducing a different element, for example, in silicon semiconductor technology, an ion implantation technique is used in addition to a method of introducing a desired amount of a different element in a silicon wafer manufacturing process. In this ion implantation technique, ions accelerated to energy of kiloelectron volts to megaelectron volts are implanted into a surface layer portion having a depth of several nanometers to several micrometers from the surface of a solid, and the physical properties thereof are controlled.
This ion implantation technique can (1) introduce elements into a sample at room temperature, (2) count the number of ions and control the concentration from a low concentration to a high concentration, and (3) select any region. (4) Since it is a non-equilibrium process, the element can be introduced beyond the solid solution limit.
[0006]
However, when a different element is introduced into the tube-shaped material by using such a conventional ion implantation method, the ion energy is too high and the implanted ions pass through the tube-shaped material, so that the desired different element is contained in the tube-shaped material. In addition, there is a problem that the tube-shaped substance is damaged by ion irradiation and defects are introduced into the inside.
For this reason, there has been a strong demand for a method of introducing a different element with a controlled concentration without damaging the tubular material.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve such problems of the prior art, and enables introduction of a wide variety of different elements without damaging the tube-shaped material, and ion implantation of the different elements. An object of the present invention is to provide an industrially extremely useful method for producing a tubular inorganic substance into which a different element is introduced, the amount of which can be controlled appropriately.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by setting the degree of vacuum and irradiation energy at the time of implanting different types of ions to specific conditions, thereby completing the present invention. It came to.
That is, according to the present invention, the following inventions are provided.
(1) A tube-like inorganic substance into which a heterogeneous element is implanted, characterized in that ions of different elements are implanted into the tubular inorganic substance under a vacuum degree of 1 × 10 ⁻⁵ Pa or less and an irradiation energy of 20 to 200 eV . Production method.
(2) The method for producing a tubular inorganic material into which a different element is injected according to the above (1), wherein the tubular inorganic material is a carbon nanotube.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing a tubular inorganic material into which a different element is injected according to the present invention is to implant ions of a different element into the tubular inorganic material under a vacuum degree of 1 × 10 ⁻⁵ Pa or less and an irradiation energy of 20 to 200 eV. It is a feature.
[0010]
In the conventional ion beam apparatus, since the degree of vacuum during ion beam irradiation is not sufficient in the conventional ion beam apparatus, charge exchange occurs due to collision between the ion beam and the residual gas, and high-speed neutral particles are generated and irradiated. It was found to damage the target. As a result of further investigations, ions were extracted from the ion source, only ions were selected by the mass separator, ion divergence was prevented by the ion focusing mechanism, and the ion deflection mechanism caused the charge exchange action. When ionizing particles are removed and the irradiation energy is controlled to a low energy by an ion deceleration mechanism under ultra-vacuum, a desired amount of different element ions such as nitrogen ions enter the carbon nanotube without damaging the structure of the carbon nanotube. It was found that it can be introduced accurately. The present invention has been made based on such findings.
[0011]
The tube-shaped inorganic substance into which the different element of the present invention is introduced is an ion beam of a different element from the element constituting the tube-shaped inorganic substance under an irradiation energy of a vacuum degree of 1 × 10 ⁻⁵ Pa or less and 20 to 200 eV. Obtained by injection.
[0012]
The term “tubular inorganic substance” as used herein means a substance having a hollow structure with a diameter of 5 nm to 500 nm and an aspect ratio of the diameter to the length of 10 or more, and representative examples include carbon nanotubes and boron nitride nanotubes. be able to.
As an ion beam of a different element, an ion beam of nitrogen, an ion beam of boron, fluorine, phosphorus, gallium, lithium, calcium, potassium, or the like can be used.
[0013]
In the present invention, when irradiating these ion beams, it is important that at least the degree of vacuum in the vacuum vessel is 1 × 10 ⁻⁵ Pa or less.
When the degree of vacuum in the vacuum container exceeds 1 × 10 ⁻⁵ Pa, charge exchange occurs due to collision between the ion beam and the residual gas, and high-speed neutral particles are generated, damaging the tubular inorganic substance; Therefore, the intended object of the present invention cannot be achieved. Moreover, in this invention, it is necessary to set ion irradiation energy to 20-200 eV energy with the said pressure conditions (vacuum degree).
If the ion irradiation energy is less than 20 eV, no ion element is introduced into the tubular inorganic material, and if it exceeds 200 eV, the tubular inorganic material is damaged by the ion energy, which is not preferable.
[0014]
The ion irradiation conditions of the present invention are sufficient if the above two requirements are satisfied, and other conditions may be appropriately selected as necessary. Usually, the ion implantation amount is 1 × 10 ⁻¹² ions / cm ² to 1 ×. 10 ⁻¹⁷ ions / cm ² , preferably 1 × 10 ⁻¹³ ions / cm ² to 1 × 10 ⁻¹⁵ ions / cm ² .
[0015]
In order to produce a hollow inorganic substance into which a different element is introduced by the method of the present invention, for example, ions are extracted from an ion source, only ions are selected by a mass separator, and ions are diffused by space charge by an ion focusing mechanism. The carbon nanotubes are placed in a vacuum vessel of an ion implantation apparatus that can prevent, remove high-speed neutral particles generated by the charge exchange action by the ion deflection mechanism, and control the irradiation energy to a low energy by the ion deceleration mechanism in an ultra vacuum. Then, nitrogen ions may be irradiated to the carbon nanotubes by irradiating the carbon nanotubes with nitrogen ions under an irradiation energy of 1 × 10 ⁻⁵ Pa or less and 20 to 200 eV.
[0016]
The tubular inorganic material introduced with the different element obtained by the method of the present invention has significantly improved semiconductor electronic conduction characteristics as compared with the tubular inorganic material into which the different element is not introduced. It can be applied as an electron conductor.
[0017]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
[0018]
Example 1
The ion implantation apparatus includes an ion source for generating ions, a mechanism for extracting ions from the ion source, an ion mass separation mechanism, an ion focusing mechanism, an ion deflection mechanism, an ion decelerating mechanism, and a vacuum container for depositing ions on a substrate. A manufacturing apparatus was used. A sector-type electromagnet as the ion mass separation mechanism, an electromagnetic lens composed of three quadrupole electromagnets as the ion focusing mechanism, a sector-type electromagnet as the ion deflection mechanism, and an electrode that forms an electrostatic field as the ion deceleration mechanism Using.
Two cryopumps are attached to the ion source part, one between the mass separation mechanism and the ion focusing mechanism, one between the ion focusing mechanism and the ion deflection mechanism, and one in the vacuum vessel part. A pumping mechanism consisting of a rotary pump and a turbo molecular pump was installed as a pump, and evacuation was performed. By these evacuation mechanisms, after the ultimate vacuum, the vacuum vessel portion was 3 × 10 ⁻⁸ Pa, the ion deflection mechanism portion was 8 × 10 ⁻⁷ Pa, and the mass separation mechanism portion was 5 × 10 ⁻⁵ Pa.
Using the above apparatus, the carbon nanotubes were irradiated with nitrogen ions as follows.
After a silicon single crystal (100) substrate in which carbon nanotubes were dispersed and coated in the apparatus was installed, the inside of the apparatus was evacuated to 3 × 10 ⁻⁸ Pa or less. Nitrogen gas was used as the injection gas. After generating a plasma of nitrogen gas in the ion source, ions were extracted at −35 kV with respect to the ground potential. At this time, the mechanism for extracting ions from the ion source, the ion mass separation mechanism, the ion focusing mechanism, and the ion deflection mechanism are all −35 kV. The ion source is set to a positive potential with respect to the ground potential, and the ion energy that finally reaches the carbon nanotube in the vacuum vessel is determined by this potential. Only nitrogen ions having an atomic weight of 14 were selected from the extracted ion bundle by a mass separation electromagnet, and converged so that the ion current was maximized by a quadrupole electromagnet lens as an ion focusing mechanism. Further, carbon ions were bent in the vacuum vessel by an ion deflection electromagnet and introduced into the vacuum vessel, and the ions were decelerated and irradiated onto the silicon substrate. The degree of vacuum in the vacuum vessel during ion irradiation was 4 × 10 ⁻⁷ Pa. The nitrogen ion current density was adjusted to be 0.01 mA / cm ² . Nitrogen was introduced by fixing the nitrogen ion energy to 100 eV and irradiating the carbon nanotubes in a vacuum of 4 × 10 ⁻⁷ Pa as described above.
[0019]
Comparative Example 1
Furthermore, by opening the valve between the vacuum vessel and the cryopump halfway, the carbon nanotubes were irradiated with nitrogen ions with a degree of vacuum of 4 × 10 ⁻⁵ Pa during ion irradiation. The latter is a vacuum condition at the time of ion irradiation in conventional ion implantation, and is performed for comparison in order to clarify the superiority of the present invention.
[0020]
The structure of the carbon nanotube into which nitrogen ions were introduced obtained in Example 1 and Comparative Example 1 was examined using a transmission electron microscope (TEM). In addition, nitrogen in carbon nanotubes was analyzed by electron beam energy loss spectroscopy.
The carbon nanotubes obtained in Example 1 had a hollow structure and the graphite sheet structure was clearly observed, and no damage was observed. It was also found that the carbon nanotube contained 1.5 atom% nitrogen atoms. On the other hand, the carbon nanotubes obtained in Comparative Example 1 had a hollow structure, but the graphite sheet structure was not observed and had an amorphous structure. This is because when produced in a vacuum of 4 × 10 ⁻⁵ Pa, nitrogen ions collide with the residual gas during transport to the carbon nanotubes to become neutral particles due to the charge exchange effect, and the carbon nanotubes are irradiated without being decelerated. This is thought to be due to damage.
[0021]
Example 2
Carbon nanotubes into which nitrogen ions were introduced were prepared in the same manner as in Example 1 except that the degree of vacuum and irradiation energy during ion irradiation in Example 1 were changed as shown in FIG. The observation results are shown in FIG.
It can be seen from FIG. 1 that nitrogen can be introduced without damaging the carbon nanotube by setting the degree of vacuum during ion irradiation to 1 × 10 ⁻⁵ Pa or less and the irradiation energy to 20 to 200 eV.
[0022]
【The invention's effect】
The method for producing a tubular inorganic material into which a heterogeneous element is implanted according to the present invention can introduce various heterogeneous elements without damaging the tubular material, and can accurately control the ion implantation amount. It can be said that the manufacturing method is extremely advantageous. Further, since the obtained tubular inorganic substance can control semiconductor electronic conduction characteristics, it can be applied as an electronic conductor of such a semiconductor.
[Brief description of the drawings]
FIG. 1 is a diagram of the relationship between ion energy, degree of vacuum during irradiation, and damage to tubular materials.

Claims (2)

Ion of different elements into tube-shaped inorganic substance, vacuum degree 1 × 10 ^-5 Pa 20 to 200 below eV A method for producing a tubular inorganic substance into which a different element is introduced, characterized by being injected under irradiation energy of. 2. The method for producing a tubular inorganic material into which a different element is introduced according to claim 1, wherein the tubular inorganic material is a carbon nanotube.

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