JPH09308681A - Metallic material having bone conductivity and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metallic material which has bone conductivity and is capable of improving the precipitation rate of hydroxyapatite(HAP) and a process for producing the same. SOLUTION: All of calcium is made to exist in the form of oxide or hydroxide as a surface treatment layer 3 on the surface of a base material metal 2 for the living body and the oxide of the base material metallic elements is made to exist therein. The metallic material is so formed that at least part of the oxides descried above are an amorphous structure or a crystal structure (described as a nano crystal structure) having a crystal grain size of <=100m. As a result, the inadequateness of the calcium in the metallic state to the living body is eliminated and the metallic material having the excellent bone conductivity without having the ordinary crystal structure is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal material for a living body to be implanted in a living body such as an artificial tooth root and an artificial joint and a method for producing the same, and is intended to improve bone conductivity and the like.

[0002]

2. Description of the Related Art One of the characteristics required for a metallic material for a living body to be implanted in a living body such as an artificial tooth root or an artificial joint is one of the properties of the osteoconductive property of a metallic material having an interface with a living body, especially a bone cell. It is necessary to generate a substance called hydroxyapatite (HAP) derived from a living body on the surface of the material, and it is required to efficiently increase the deposition rate of hydroxyapatite (HAP).

For this reason, it has been proposed that calcium is present on the surface by a method of immersing in a solution containing an alkali or alkaline earth metal ion and then performing a heat treatment or a method of ion-implanting calcium.

[0004]

As a result of research on improving the efficiency of the precipitation rate of such hydroxyapatite (HAP), osteoconductivity depends on the state of calcium present on the surface of the base metal material and its crystal structure. It was found to have a great effect on sex.

The present invention aims to provide a metal material having osteoconductivity capable of improving the deposition rate of hydroxyapatite (HAP) based on the above research results, and a method for producing the same.

[0006]

In order to solve the above-mentioned problems, the metal material having osteoconductivity according to claim 1 of the present invention has a surface of a base metal material for a living body, and calcium oxide or hydroxide. In addition to being present as an object, an oxide of the base metal element is present, at least a part of which is provided with a surface-treated layer having an amorphous structure or a crystal structure having a crystal grain size of 100 nm or less. Is.

According to the present invention, as the surface treatment layer on the surface of the base metal for living body, all of calcium is present as the oxide or hydroxide, and the oxide of the base metal element is present. At least a part of them has an amorphous structure or a crystal structure with a crystal grain size of 100 nm or less (herein referred to as a nanocrystal structure), which eliminates the incompatibility of the metallic calcium with the living body, and The metal material having excellent osteoconductivity can be obtained without having the crystal structure of.

According to a second aspect of the present invention, there is provided a method for producing a metal material having osteoconductivity, which comprises injecting calcium into a surface of a base metal material for living body by an ion implantation method and then in a gas containing oxygen. At a temperature of 600 ° C. or lower to oxidize a part or all of the metal elements of the surface treatment layer to allow calcium to exist as an oxide or hydroxide, and to allow the oxide of the base metal element to exist. At least a part of the surface treatment layer has an amorphous structure or a crystal structure having a crystal grain size of 100 nm or less.

According to the present invention, after the calcium is injected into the surface of the base metal material for living body by the ion implantation method, the metal element of the surface treatment layer is exposed by exposing it to a gas containing oxygen at a temperature of 600 ° C. or lower. The surface treatment layer on the surface of the base metal material for living body is composed of calcium in the oxide or hydroxide state and the oxide of the base metal element, At least a part of them can have an amorphous structure or a crystal structure having a crystal grain size of 100 nm or less, and it becomes possible to manufacture a metal material having high biocompatibility and excellent osteoconductivity.

Further, in the method for producing a metal material having osteoconductivity according to claim 3 of the present invention, calcium ions are irradiated by an ion mixing method instead of the ion implantation method having the structure according to claim 2. It is characterized by having done.

According to the present invention, after irradiating calcium atoms by the ion mixing method instead of the ion implantation method,
Oxidation treatment is performed, and in this case as well, it becomes possible to similarly improve the compatibility with the living body and to produce a metal material having excellent osteoconductivity.

According to a fourth aspect of the present invention, there is provided a method for producing a metallic material having osteoconductivity, in addition to the configuration of the third aspect,
The ion mixing method is characterized in that oxygen ions are used to irradiate calcium atoms.

According to the present invention, when the calcium atoms are irradiated by the ion mixing method, oxygen ions are used, and then the oxidation treatment is carried out to further promote the generation of oxides in the surface treatment layer, Similarly, it becomes possible to manufacture a metal material having high biocompatibility and excellent osteoconductivity.

Further, in the method for producing a metal material having osteoconductivity according to claim 5 of the present invention, calcium is obtained by irradiating the surface of a base metal material for living body with calcium atoms by using oxygen ions by an ion mixing method. Is present as an oxide or a hydroxide, and an oxide of the above-mentioned base metal element is present so that at least a part of these becomes a surface-treated layer having an amorphous structure or a crystal structure with a crystal grain size of 100 nm or less. It is characterized by having done.

According to the present invention, the surface treatment layer of the base metal material is obtained by only irradiating calcium atoms with oxygen ions by the ion mixing method, and no post-treatment of oxide formation is required. Further, it becomes possible to more easily make a metal material having high biocompatibility and excellent osteoconductivity.

Here, as the base metal material for a living body, a metal material such as titanium, a titanium alloy, a cobalt-chromium-molybdenum alloy, or a ceramic material such as alumina is used. Titanium is industrial pure titanium. Meaning,
The alloying elements of the titanium alloy are Ca, P, O, Fe and A.
l, V, Sn, Pd, etc. can be mentioned.

The term "osteoconductivity" refers to biocompatibility, osteogenicity, cell-inducing ability, etc. Usually, a material excellent in osteoconductivity is subjected to a hydroxy solution during immersion in Hank's solution having a composition close to that of extracellular fluid. Since it is known that apatite (HAP) precipitates rapidly on the material surface, the rate of hydroxyapatite (HAP) precipitation was evaluated.

Further, in the surface-treated layer, calcium is present in the state of all oxides or hydroxides, and the base metal element is present in the state of part or all of the oxides. A part or all of the layer has an amorphous structure or a nanocrystal structure. The surface treatment layer has a crystalline, amorphous structure, and a crystal grain size of 10 by a transmission electron microscope structure or X-ray photoelectron spectroscopy analysis.
It is possible to determine whether or not the crystal structure is 0 nm or less (nanocrystal structure) and whether or not it is in the oxide state.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The osteoconductive metal material and the method for producing the same according to the present invention will be specifically described below.

The metal material 1 having osteoconductivity is shown in FIG.
As shown in the cross-sectional structure in FIG. 1, calcium is used as the surface treatment layer 3 on the surface of the base metal material 2 such as pure titanium (industrial pure titanium) that has been conventionally used as a biomedical metal or a biocompatible titanium alloy. Is present in the form of an oxide or hydroxide, and an oxide containing a base metal element as a main component is present, and these have an amorphous structure or a crystalline structure state with a crystal grain size of 100 nm or less (hereinafter, nanocrystalline structure). Called)).

That is, in the surface treatment layer 3, all the calcium is an oxide or hydroxide, and the surface treatment layer 3
At least a part of the base metal element of is an oxide, and the calcium oxide or calcium hydroxide and the oxide mainly of the base metal element have an amorphous structure and no crystal structure? Or, even if it has a crystal structure, it has a fine crystal structure with a crystal grain size of 100 nm or less.

The metal material 1 having osteoconductivity provided with such a surface-treated layer 3 can efficiently increase the deposition rate of hydroxyapatite (HAP) derived from a living body and is excellent in biocompatibility. I understood.

As a concrete manufacturing method of such a metal material 1 having osteoconductivity, several methods shown in FIG. 2 are used.

First, since it is necessary to allow calcium to exist on the surface of the base metal material 2, calcium is injected into the surface of the base metal 2 by an ion implantation method or an ion mixing method. Produces a surface layer of inclusions.

In this case, in the ion implantation method, a calcium-containing surface layer is formed by applying energy to calcium ions to irradiate them, and in the ion mixing method, calcium atoms are converted into other ions, for example, ions of an inert gas. Is mixed with the base metal element to form a calcium-containing surface layer.

After the calcium-containing surface layer is formed on the surface of the base metal material 1 in this manner, 600
An exposure process is performed at a temperature of ℃ or below to oxidize calcium and base metal elements. In addition, near room temperature (100 ℃
When exposed to the atmosphere (below), calcium mainly undergoes a hydration reaction with water in the air to form calcium hydroxide.

In these treatments, all of the calcium is oxidized or hydrated to a calcium oxide or hydroxide state, and a part or all of the base metal element is oxidized.

When oxygen ions are used as the other ions used in the ion mixing method, irradiation of oxygen ions causes calcium to form a film at the same time as oxidation, which causes oxidation of the base metal material. This oxidation treatment may be omitted, but at least all the calcium must be present as an oxide.

On the surface of the base metal material 2 thus obtained,
All calcium is present as an oxide or hydroxide, a part or all of the base metal element is present as an oxide, and these form the surface-treated layer 3 having an amorphous structure or a nanocrystal structure.

It has been found that any metal material having osteoconductivity produced by such a manufacturing method can efficiently increase the deposition rate of hydroxyapatite (HAP) derived from a living body and is excellent in biocompatibility. It was

Next, a detailed description will be given of an experiment conducted by comparing the amorphous structure or the nanocrystal structure, which is the surface structure required for the surface treatment layer 3, with the case of the crystalline structure. Pure titanium was used as a base metal material for living organisms, calcium ions were implanted at 20 KeV (ion implantation method), and then exposed to the atmosphere as an oxidation treatment to obtain a sample, which was designated as Ca-Ti20.

Pure titanium is used as a base metal material for living organisms, and a calcium thin film is formed to a thickness of 500 nm on its surface.
After implanting argon ions at 20 KeV (ion mixing method), the sample was obtained by exposing it to the atmosphere as an oxidation treatment and used as IM-Ti20.

Further, for comparison, a sample Ca-Ti20 obtained by the above-mentioned ion implantation method was further heat-treated in an argon gas at 700 ° C. as an oxidation treatment to obtain a sample, which was Ca-Ti20H.
T.

The three samples Ca-Ti20 and IM-Ti2 thus obtained
In order to investigate the structure near the surface of 0, Ca-Ti20HT, the tissue was observed using a high resolution transmission electron microscope, and the results are shown in FIG.

As is clear from these high-resolution transmission electron microscope structures, the two samples Ca-Ti20 and IM-Ti20 have an amorphous structure or a crystal grain size that does not have a clear crystal structure up to about 30 nm from the surface. It can be seen that it has a nanocrystal structure of about 10 nm.

On the other hand, in the sample Ca-Ti20HT, only a small number of surfaces
Only nm has an amorphous structure, but all others are crystalline.

Next, these three samples Ca-Ti20 and IM-Ti2
In order to investigate the elemental distribution in the depth direction near the surface of 0, Ca-Ti20HT, an Auger electron spectroscopic analysis was performed, and the results are shown in FIG.

Three samples Ca-Ti20, IM-Ti20, Ca-Ti20H
In each of T, calcium exists up to a depth of about 30 nm from the surface, and in the two samples Ca-Ti20 and IM-Ti20,
The region in which calcium is present matches the region having an amorphous structure or a nanocrystal structure of about 10 nm.

Further, three samples Ca-Ti20, IM-Ti20,
X-ray photoelectron spectroscopy analysis of Ca-Ti20HT shows the binding energy spectrum of p2p electrons of Ca in FIG.

Three samples Ca-Ti20, IM-Ti20, Ca-Ti20H
It can be seen that calcium is in an oxide state at any of T.

Samples Ca-Ti20 having an amorphous structure and samples IM-Ti20 having a nanocrystal structure have such surface treatment layers.
, 3 samples of crystalline Ca-Ti20HT were examined in order to investigate the osteoconductivity of 3 samples in Hank's solution containing no organic matter.
After soaking for 0 day, the surface product was analyzed. In addition,
In the immersion test, the temperature of Hank's solution was 37 ° C and the pH was 7.
I kept it from 2 to 7.6.

The Hank's solution used here is an aqueous electrolyte solution having a composition (mol / l) as shown in Table 1, which is close to the extracellular fluid composition.
It is known that, when an immersion test in a s solution is performed, hydroxyapatite (HAP) is rapidly deposited on the sample surface in a material having excellent osteoconductivity.

[0043]

[Table 1]

In the dipping test, an untreated pure titanium plate was also dipped in Hank's solution for comparison.

As a result of such immersion test in Hank's solution, hydroxyapatite (H
The amount of phosphorus derived from (AP) was analyzed by X-ray photoelectron spectroscopy, and the results are shown in Table 2. The greater the amount of phosphorus, the greater the amount of precipitated hydroxyapatite (HAP).

[0046]

[Table 2]

Of these four samples, two samples Ca-T
Remaining two samples Ca-T compared to i20 and sample IM-Ti20
It can be seen that the amount of phosphorus on the surface of i20HT and pure titanium is small.

That is, the difference between these two groups of samples is mainly in the surface structure, and in the two samples Ca-Ti20 and IM-Ti20 in which a large amount of phosphorus is precipitated, the former has an amorphous structure and the latter has an amorphous structure. Has a nanocrystalline structure, whereas the other samples, Ca-Ti20HT and pure titanium, which have less precipitation of phosphorus, are both crystalline.

Therefore, it was found that the material in which the surface treatment layer 3 on the surface of the base metal material 2 has an amorphous structure or a nanocrystal structure has higher osteoconductivity than a material having a crystal structure.

Next, the fact that all the calcium necessary for the surface treatment layer 3 is present as an oxide will be described in detail with respect to the experiment conducted in comparison with the case of the metallic state. Pure titanium is used as the base metal material for the living body.
After injecting calcium ions at 0 KeV (ion implantation method), a sample was prepared by exposing it to the atmosphere at room temperature for 1 hour as an oxidation treatment, and this was subjected to thin film X-ray diffraction, and its diffraction chart is shown in FIG.

As is clear from this thin film X-ray diffraction chart, in this sample, in addition to the peaks of titanium as the base metal material and the oxides of implanted calcium, clear peaks of calcium metal are recognized.

On the other hand, pure titanium was used as the base metal material for the living body, calcium ions were implanted at 50 KeV (ion implantation method), and then the sample was prepared by exposing it to the atmosphere at room temperature for 1 hour for oxidation treatment. As a result of performing thin film X-ray diffraction on this, from the diffraction chart, it was found that titanium as the base metal material,
The oxide peak of the implanted calcium was observed, but the distinct peak of metallic calcium was not observed.

Samples in which metal calcium is present in the surface treatment layer 3 on the surface of the base metal material 2 and samples in which no metal calcium is present are prepared, and Hank 'is used as described above.
s A 30-day immersion test in a solution was performed, and the surface product of the sample was analyzed by X-ray photoelectron spectroscopy.

As a result, in all the samples, the amount of phosphorus derived from hydroxyapatite (HAP) precipitation was larger than that in pure titanium, but in the sample containing metallic calcium (200 KeV injection material), immediately after the start of the immersion test. It foamed from the surface and became extremely rough with irregularities on the surface.

This is because the calcium in the metallic state reacted violently with water in the aqueous solution, and is considered to be a phenomenon not suitable as a biomaterial.

Therefore, the sample containing the metallic calcium (200 KeV injection material) is exposed to various temperatures from room temperature to 700 ° C. for 1 hour in each of pure argon, 10% oxygen-argon and the atmosphere. After the treatment, the compound was identified by thin film X-ray diffraction, and the results are shown in Table 3.

[0057]

[Table 3]

As is clear from the table, peaks derived from metallic calcium are still clearly observed in the sample exposed to room temperature and the sample exposed to pure argon, but in other samples, the temperature was 600 ° C or No peak derived from metallic calcium was observed in the sample exposed at 700 ° C. in a 10% oxygen-argon atmosphere in which oxygen is present or in the air.

Next, the 9 different samples obtained by changing the temperature and atmosphere of the surface treatment were subjected to the immersion test in the Hank's solution for 30 days in the same manner as described above, and the X-ray photoelectrons of the surface products of the samples were examined. Analysis by spectroscopic analysis and observation by a scanning electron microscope were performed, and the results are shown in Table 4.

[0060]

[Table 4]

As is clear from the table, in the sample exposed to room temperature and the five samples exposed to pure argon, peaks derived from metallic calcium were clearly observed, and as a result, foaming occurred from the surface immediately after the start of the immersion test. However, it is considered that the surface irregularities are extremely rough and not suitable as a biomaterial.

On the other hand, in the other four samples which were 600 ° C. or 700 ° C. and were exposed to a 10% oxygen-argon atmosphere in which oxygen is present or in the air, the peak derived from metallic calcium is Although not observed, the surface condition becomes smooth, but in the two samples at the treatment temperature of 700 ° C, the amount of phosphorus derived from hydroxyapatite (HAP) precipitation is about the same as that of pure titanium, which improves the osteoconductivity. Cannot be admitted.

However, in the two samples at the treatment temperature of 600 ° C., the amount of phosphorus derived from the hydroxyapatite (HAP) precipitation is larger than that of pure titanium, and it is clear that the improvement of osteoconductivity can be recognized. .

From the above results, as the oxidation treatment after the calcium ion implantation treatment by the ion implantation method or the ion mixing method, when the implantation energy is less than 200 KeV, it is exposed to a gas containing oxygen at a temperature of 600 ° C. or less. However, it has been found that it is effective to make all the calcium in the surface treatment layer 3 into an oxide state and oxidize a part or all of the base metal element.

Next, a detailed description will be given of an experiment in which calcium is injected, which is one of the methods for producing the metal material having osteoconductivity, by using oxygen ions by the ion mixing method.

First, pure titanium was used as a base metal material for living organisms, and a calcium thin film was vapor-deposited to a thickness of about 500 nm on the surface thereof to form a film, and then oxygen ions were injected at an injection energy of 25 KeV to prepare a sample. Obtained.

When this sample was observed using a high resolution transmission electron microscope, all the surface layers had a structure mainly composed of amorphous material, and further X-ray photoelectron spectroscopy analysis was conducted to show that the binding energy of p2p electrons of Ca was FIG. 7 shows the spectrum, and it can be seen that calcium is in an oxide state.

In order to examine the osteoconductivity of this sample, a dipping test in a Hank's solution for 30 days was carried out in the same manner as above.
The surface product of the sample was analyzed by X-ray photoelectron spectroscopy, and the results are shown in Table 5.

[0069]

[Table 5]

As is clear from the table, the amount of phosphorus derived from the hydroxyapatite (HAP) precipitation is larger than that of pure titanium in this sample as well, and it is clear that the improvement of osteoconductivity can be clearly recognized.

Therefore, the metal material obtained by injecting calcium using oxygen ions by the ion mixing method does not carry out an oxidation treatment after calcium injection, and all the calcium in the surface layer of the base metal material is oxidized. Exist in the state of, and the presence of an oxide mainly composed of the base metal element,
Moreover, the structure can be an amorphous structure,
A metal material having excellent osteoconductivity can be obtained.

Further, even when calcium is implanted by using oxygen ions in the ion mixing method, oxidation treatment may be performed after the implantation as in the ion implantation method or the ion mixing method using other ions. Oxidation of metal material elements can be promoted.

[0073]

As described above in detail with the embodiments, according to the metal material having osteoconductivity according to claim 1 of the present invention, a surface treatment layer is formed on the surface of the base metal for living body. In addition to making all of calcium exist as oxides or hydroxides, oxides of base metal elements are made to exist, and at least a part of them has an amorphous structure or a crystal structure with a crystal grain size of 100 nm or less. Therefore, it is possible to obtain a metal material excellent in osteoconductivity by eliminating the incompatibility of the calcium in the metallic state with the living body and without having a normal crystal structure.

Further, according to the method for producing a metal material having osteoconductivity according to claim 2 of the present invention, after calcium is injected into the surface of the base metal material for living body by the ion implantation method,
Since a part or all of the metal elements of the surface treatment layer were oxidized or hydroxide by exposing to a temperature of 600 ° C. or lower in a gas containing oxygen, the surface treatment layer on the surface of the base metal material for living body was formed. , Calcium in the oxide or hydroxide state and oxide of the base metal element, at least a part of which can have an amorphous structure or a crystal structure with a crystal grain size of 100 nm or less, which is compatible with living organisms. It is possible to make a metal material that is high and has excellent osteoconductivity.

Further, according to the method for producing a metal material having osteoconductivity according to claim 3 of the present invention, the oxidation treatment is performed after irradiating calcium atoms by the ion mixing method instead of the ion implantation method. Therefore, also in this case, it is possible to similarly improve the compatibility with the living body and to produce a metal material having excellent osteoconductivity.

Further, according to the method for producing a metal material having osteoconductivity according to claim 4 of the present invention, oxygen ions are used when irradiating calcium atoms by the ion mixing method, and then the oxidation treatment is performed. Therefore, it is possible to further promote the generation of oxides in the surface treatment layer, enhance the compatibility with the living body, and produce a metal material having excellent osteoconductivity.

Further, according to the method for producing a metal material having osteoconductivity according to claim 5 of the present invention, the surface treatment layer of the base metal material is irradiated with calcium atoms by using oxygen ions by the ion mixing method. Since it is obtained only by itself, the post-treatment of oxide generation is not required, and the compatibility with living body can be enhanced more easily, and a metal material excellent in osteoconductivity can be produced.

[Brief description of drawings]

FIG. 1 is a cross-sectional structural view near a surface according to an embodiment of a metal material having osteoconductivity of the present invention.

FIG. 2 is a schematic process drawing according to an embodiment of a method for producing a metal material having osteoconductivity according to the present invention.

FIG. 3 is a high-resolution transmission electron micrograph of the outermost surface of each sample according to an embodiment of the metal material having osteoconductivity of the present invention.

FIG. 4 is a graph showing the concentration of each element by Auger electron spectroscopy analysis of Ca, Ti, and O from the surface of each sample according to one embodiment of the metal material having osteoconductivity of the present invention.

FIG. 5 is a calcium p2p electron binding energy spectrum by X-ray photoelectron spectroscopy analysis of each sample according to one embodiment of the metal material having osteoconductivity of the present invention.

FIG. 6 shows a thin film X-ray diffraction result of a sample in which titanium in which calcium ions are implanted at 200 KeV according to an embodiment of the metal material having osteoconductivity of the present invention is cooled to room temperature and then exposed to the atmosphere for 1 hour. It is a graph.

FIG. 7 is a calcium p2p electron binding energy spectrum obtained by X-ray photoelectron spectroscopy analysis of a sample in which calcium ions according to one embodiment of the present invention having osteoconductivity are injected by an ion mixing method using oxygen ions. is there.

[Explanation of symbols]

 1 Metallic material having osteoconductivity 2 Base metal material 3 Surface treatment layer (surface layer)

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Koichi Murakami 3-15-1, Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries Ltd. Technical Research Institute (72) Inventor Hidemi Ukai 3-1-1, Toyosu, Koto-ku, Tokyo No. 15 Ishikawajima Harima Heavy Industries Ltd. Technical Research Institute

Claims (5)

[Claims] 1. On the surface of a base metal material for living body, calcium is made to exist as an oxide or a hydroxide, and an oxide of the base metal element is made to exist, at least a part of which has an amorphous structure or Crystal grain size is 10
A metal material having osteoconductivity, comprising a surface-treated layer having a crystal structure of 0 nm or less. 2. After implanting calcium into the surface of a base metal material for living organisms by an ion implantation method, 6 in a gas containing oxygen.
By exposing at a temperature of 00 ° C. or less to oxidize a part or all of the metal elements of the surface treatment layer to allow calcium to exist as an oxide or a hydroxide, and to allow an oxide of the base metal element to exist. A method for producing a metal material having osteoconductivity, characterized in that at least a part of the surface-treated layer has an amorphous structure or a crystal structure having a crystal grain size of 100 nm or less. 3. The method for producing a metal material having osteoconductivity according to claim 2, wherein irradiation with calcium atoms is carried out by an ion mixing method instead of the ion implantation method. 4. The method for producing a metal material having osteoconductivity according to claim 3, wherein oxygen ions are used to irradiate calcium atoms in the ion mixing method. 5. The surface of a base metal material for living body is irradiated with calcium atoms by using oxygen ions by an ion mixing method to allow calcium to exist as an oxide or a hydroxide, and an oxide of the base metal element. And at least a part of them is formed into a surface-treated layer having an amorphous structure or a crystal structure having a crystal grain size of 100 nm or less.