JPH05305227A - Method and apparatus for producing diamond - Google Patents

Abstract

PURPOSE:To produce single crystal diamond in a small scale with high productivity by using a carbon powder based on a C60 and/or carbon nanno-tube as a starting material powder to press the same with a pressure gradient and irradiating the pressed powder with laser beam at the time of the max. pressure. CONSTITUTION:A cylindrical high pressure container 2 is packed with a powder 6 based on a C60 and/or carbon nanno-tube and the powder is pressed by an upper pressure element having a truncated cone-shape diamond window material 5 so as to provide a pressure gradient. At the same time, the powder 6 is irradiated with laser beam from the window material 5. Whereupon, the diamond window material 5 becomes a sead crystal and diamond can epitaxially be grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high pressure synthesis method of diamond using an anvil type press,
The present invention relates to a diamond manufacturing method and a diamond manufacturing apparatus using a powder mainly containing C ₆₀ and / or carbon nanotubes as a raw material powder and using a laser beam as a heating means of the raw material powder.

[0002]

2. Description of the Related Art Currently, two methods are used for synthesizing diamond: a vapor phase synthesis method represented by CVD and a high pressure synthesis method in which powders of graphite, diamond, etc. are made into crystalline diamond under high temperature and high pressure. Has been. The high-pressure synthesis method is further classified into the following three types.

1. Impact method The raw material powder is instantly pressurized to a high pressure by the explosive force of explosives or impact such as high-speed collision, and the graphite structure is directly converted to the diamond structure to synthesize the particulate diamond. Although two kinds of pressing devices described later are not used, it is more difficult to adjust the size of the diamond product or the like as compared with them.

2. Direct conversion method By encapsulating the raw material powder in a high-pressure container and adding a static high pressure of 13 to 16 GPa and a high temperature environment of 3000 to 4000 ° C to form a diamond stable region, decomposition of graphite and formation of a diamond structure are performed. It performs recombination and direct phase conversion to diamond.

3. Fluxing method Like the direct conversion method, this method uses static pressure and high temperature. This method uses a flux such as Ni or Fe to form diamond crystals at a lower pressure and temperature than the direct conversion method. I do. The purpose of this method is to facilitate the above recombination by using a flux. In this method, a flux is packed in a high-pressure container so as to wrap it with high-purity graphite which is a raw material powder, and 4 to 6 GP is packed.
Heat to about 1500-2000 ° C. under pressure of a. The flux becomes a solution while dissolving graphite, and becomes a saturated solution of graphite. At this time, since the interior of the high-pressure container is a stable phase of diamond in terms of pressure, the solubility of graphite in the flux is much higher than that of diamond. As a result, the phenomena of crystallization of diamond and dissolution of graphite in the flux occur inside the container.

Of these high-pressure synthesis methods, particularly, a press machine was used.2. And 3. With the advent of belt devices, ampil-type devices, etc., this method is virtually impossible with the gas phase synthesis method,
It is widely used because it has made it possible to produce single-crystal diamond with a size of several millimeters.

In the above-mentioned high-pressure synthesis method, a member called anvil made of cemented carbide is used as a means for applying pressure, and this anvil is made of diamond to achieve a high-pressure condition that has never existed before. Trials are being made.

[Problems of Prior Art] However, these high-pressure synthesis methods have many problems. What they have in common is
This is a poor productivity due to the need for a large-scale pressurizing device of several meters. Attempts have been made to improve mass productivity by replacing the high-pressure container and the like, but it is not possible to omit or simultaneously carry out a part of the series of steps of pressurization-heating-cooling-depressurization after replacing the container.

In the high-pressure synthesis method, as described above, it has become clear that a continuous process of heating a pressurized sample, cooling after completion of the reaction, depressurizing and taking out the sample is absolutely necessary. Further, it is necessary to simultaneously perform heating by means other than pressurization, but there is a problem with this heating method. As a method of heating a sample in the conventional high-pressure synthesis method, a method of heating by directly energizing the sample is generally used. However, since the electrical resistance inside the sample increases as the reaction progresses, it is very difficult to keep the sample temperature constant during the reaction. Therefore, in the synthesis of high-quality single crystal diamond, which requires the temperature to be stabilized for a relatively long time, the heating method by energizing this sample was unsuitable.

Further, as a problem in the case of the flux method / electric heating, the flux exists in the center between both electrode surfaces and the unreacted graphite is deposited in the vicinity of the electrodes so as to sandwich the diamondified portion, Internal non-uniformity occurs. This phenomenon is the same whether the current is direct current or alternating current. Although this is an unavoidable phenomenon, it cannot be denied that this phenomenon is linked to a decrease in product yield.

In order to solve these problems, there is a technique in which a heater is provided around the sample.
There was another problem that the volume of the synthesizable sample had to be made extremely small and could not contribute so much to the improvement of the yield.

Proposals for heating with laser light have been made, but a method for effectively using laser light that can only locally heat is not known.

However, the method using a high-pressure press is the only method capable of synthesizing a single crystal or a diamond material having a grain size on the order of μm to mm, and improvement work to make the most of its characteristics is important.

[0014]

DISCLOSURE OF THE INVENTION The present invention produces a single crystal diamond which can be obtained by the above-mentioned conventional method using a high-pressure press in a smaller scale and with higher productivity than the method using a high-pressure press. It is an object of the present invention to provide a method and a manufacturing apparatus therefor.

[0015]

DISCLOSURE OF THE INVENTION The present invention provides a diamond synthesizing method in which pressure is applied to a starting material powder with a pressure gradient, and a laser beam is applied to a portion of the maximum pressure through a window made of diamond as a constituent material. , Starting material powder C
_The main constitution is to facilitate the formation of diamond by using a carbon powder containing ₆₀ and / or carbon nanotubes as a main component.

The present invention is directed to synthesizing diamond by irradiating laser light to the maximum portion of the pressure having a gradient applied to the starting material C ₆₀ and / or carbon nanotube-based powder material. However, at this time, by using a diamond material as the material of the window for introducing the laser beam, it is possible to synthesize diamond from the powder material by using the diamond material forming the window material as a seed crystal. Characterize.

Further, C which is a starting material of diamond
It is characterized in that a pressure generating indenter having a taper shape is used to apply a pressure to a powder material containing ₆₀ and / or carbon nanotubes as a main component with a pressure gradient. Examples of the shape of the pressure generating indenter having a tapered shape include a truncated cone and a truncated pyramid.
The truncated cone means a shape obtained by cutting a cone in a plane parallel to the bottom surface, and the truncated pyramid means a shape obtained by cutting a pyramid in a plane parallel to the bottom surface. still,
A truncated pyramid has a shape similar to a truncated cone if the number of corners is large.

The meaning of using a raw material powder containing C ₆₀ and / or carbon nanotubes as a main component instead of the graphite-based raw material powder is as follows. The carbon atoms that make up a diamond crystal are four-coordinate (regular triangular pyramid) with sp ³ hybrid orbitals, and graphite is
It is a known fact that a three-coordinate sheet-like continuous body having an sp ² hybrid orbital is formed. Therefore, in the case of synthesizing diamond from graphite, it is necessary to recombine completely from tri-coordinate to tetra-coordinate. It is this part that requires a large amount of energy to synthesize diamond from the graphite-based raw material powder.

However, C ₆₀ is a spherical molecule, and sp ²
It has a bond with a degree of hybridization intermediate to that of sp ³ , and is therefore easier to form a diamond structure with lower energy than graphite. Of course, there have been reports on high-pressure diamond synthesis using C ₆₀ as a starting material, but in that report, only mixed-phase crystal fine particles of diamond and graphite were obtained without epitaxial growth of diamond alone. It was

Instead of C ₆₀ , carbon nanotubes, which are a tubular crystal structure of carbon, can be used, and the reactivity in that case is considered to be further enhanced. Although the exact physical properties of the carbon nanotube are not clear, it is known that the carbon atom ring is formed into a sheet by spirally connecting the carbon atom rings, and the carbon atom sheet forms a cylindrical crystal. According to the report, the thickness of the tubular crystal formed changes depending on the synthesis conditions, the tubular crystal is sealed, and the change in the number of carbon atoms due to the formation of the five-membered ring or the seven-membered ring is observed at the deformation point. It is predicted that the bond state of carbon varies depending on the synthesis conditions, and abundant intermediary hybrid bonds such as C ₆₀ exist.

Therefore, the carbon nanotube is rich in a crystal structure having a large deviation in the balance of the degree of hybridization above C ₆₀ because the symmetry in the arrangement of carbon rings such as C ₆₀ is small, and therefore lower. High productivity can be obtained if the conversion to the diamond structure by energy can be easily performed and the stable supply of the raw material is possible.

However, the superiority of carbon nanotubes with respect to C _{60 in} improving the productivity is largely due to the mass productivity of the raw material itself. It has been known in recent years that carbon nanotubes have a yield much higher than that of fullerenes such as C _{60. In} the latest report, helium gas discharges using a graphite electrode near atmospheric pressure. has a was formed of carbon nanotubes at about three times the yield of C _60, and at the same time quickly can execute structural conversion to diamond compared to C _60, it has the feature that the raw material supply is facilitated.

In addition, carbon nanotubes are easier to add various impurities into carbon molecules than C ₆₀ . When trying to create a device material or the like using C ₆₀ , it is very difficult to perform the operation of dissociating the bond between carbons and substituting with an impurity because C ₆₀ is a completely spherical body. On the other hand, in the case of carbon nanotubes, the degree of hybridization is unbalanced to C ₆₀ or more, so that partial bond dissociation and carbon substitution with impurities can be easily performed.

The pressure gradient as referred to in the constitution of the present invention means a pressure gradient obtained by intentionally creating a strong pressure spot and a weak pressure spot to form a pressure distribution having a strong and weak pressure. As a method of applying the pressure gradient, it is desirable that the pressure distribution is such that the pressure is highest in the central portion of the pressure generating indenter and the pressure becomes smaller as it goes toward the surroundings. One of the optimum shapes of the pressure generating indenter capable of obtaining such a pressure gradient is a truncated cone shape.

In the method of the present invention, a flux such as Ni or Fe as described in the section of the prior art can be used, except for the unavoidable case where the gasket for holding the sample is melted. As a countermeasure against impurities, it is better to avoid adding a flux.

According to the present invention, the diamond indenter and the indenter facing it are conical, and when the distance between both indenters is shortened and pressure is applied to the powder material between both indenters, the tip of the indenter and the indenter are contained in the raw material powder. It is based on the experimental finding that the high-pressure synthesis of diamond proceeds in a chain reaction by making the pressure non-uniform, that is, a pressure gradient, at the periphery.

Particularly, regarding the shape of the pressure generating indenter,
The optimum form of the pressure gradient generation mechanism was searched, and some preliminary experiments were conducted to confirm its effectiveness. The diamond anvil (frustroconical indenter) has a flat tip.
This is based on the finding that the combination of the and the conical indenter is the most effective.

Based on the above facts, the indenter for pressure generation (a member generally called an anvil for applying pressure to the starting material) has a truncated cone shape, and the indenter facing it has a conical shape, and the indenter in the raw material powder is used. When non-uniformity in pressure, that is, a pressure gradient, is caused between the tip and the indenter peripheral portion, and at the same time, laser light is irradiated to the maximum pressure portion and energy is supplied, high-pressure diamond synthesis by C ₆₀ proceeds in a chain reaction. It depends on what I found.

The present inventors consider the difference in the progress form of the chain reaction between so-called fullerenes such as C ₆₀ and tubular carbon crystals such as carbon nanotubes as follows. In the case of spherical or near-spherical fullerenes, the inside of the carbon molecule is structurally uniform, and the effect of pressurization propagates uniformly inside the carbon molecule.

On the other hand, in the case of carbon nanotubes, when the number of carbon atoms in the carbon ring changes in the sealing portion at the tip, the taper structure portion, etc., the binding energy of carbon becomes a singular point which is biased, resulting in a structural change. It seems to be the starting point. This reaction propagates to the intermediate hybrid cylindrical graphite and other adjacent carbon tubes, thereby expanding the diamond structure formation.

Here, the preliminary experiment will be described in detail. Conventionally, since a pressure gradient is generated in the raw material powder, it is possible to disperse fine tips of carbon steel called a steel material dispersion method in the powder to generate a pressure gradient and form diamond at around room temperature. Has been reported. Therefore, the present inventors also tried a similar method in a preliminary experiment. As a result, although formation of diamond was confirmed, only fine particles of 10 μm at maximum were obtained. In this case, it may be possible to perform heating using a laser beam or a heater, but mixing of impurities is unavoidable. Further, when a heater is used, the size of the device is expected to be considerably large, considering the examples of the high-pressure synthesis method so far.

Next, an attempt was made to provide a needle-like projection on one surface of the indenter facing the diamond anvil and to generate a pressure gradient in the needle-like projection. I couldn't get it. Further, no significant change occurred even when heating was further performed using a laser. On the other hand, a diamond anvil having a truncated cone shape that is tapered toward the center and a mirror-finished surface is used to form a gradient with respect to the powder material containing C ₆₀ as a main component. When the applied pressure was applied and the central part of the diamond anvil where the pressure was maximized was irradiated with laser light, the sample with the largest particle size was obtained.

[0033]

Although the role of the pressure gradient at this time is not clear, the present inventors consider that the pressure gradient may play the same role as Ni and Fe in the flux method. That is, the diamond structural component generated by heating is naturally collected in the high pressure portion and the graphite structural component in the low pressure portion according to the solubility under each pressure condition, and the size of the diamond phase in the central portion increases. It is thought to continue.

That is, according to the present invention, by setting an appropriate pressure gradient, a segregation effect of diamond similar to that of the fluxing method is brought about, and further, a seed crystal for epitaxial growth of diamond is formed at the maximum pressure portion for synthesizing diamond. By arranging the diamond window material, and irradiating the laser beam through the diamond window material to the maximum pressure part that synthesizes this diamond,
It forms the conditions for epitaxially growing diamond. Then, under the condition that the epitaxial growth of diamond occurs, a powder material containing C ₆₀ as a main component, which easily forms a diamond structure with low energy, is epitaxially grown using a diamond window material as a seed crystal to obtain diamond.

Further, under the above-mentioned conditions in which the epitaxial growth of diamond occurs, carbon nanotube powder that is easy to form a diamond structure with low energy and is excellent in supply efficiency is epitaxially grown using a diamond window material as a seed crystal to form large grains. This is to obtain a diamond of diameter.

In the constitution of the present invention, a good effect can be expected even if a mixed powder of C ₆₀ and carbon nanotubes is used as a starting material. In that case, considering the degree of carbon bond hybridization, it is likely that the carbon nanotubes will undergo structural conversion, forming a diamond structure in such a way as to enclose C _{60. In} that case, C ₆₀ and carbon The particle size and reaction rate of diamond obtained by adjusting the mixing ratio of the nanotubes can be adjusted.

[0037]

【Example】

[Embodiment 1] Hereinafter, an example of a diamond manufacturing apparatus utilizing the configuration of the present invention will be described. In this example, a powder containing C ₆₀ and / or carbon nanotubes as a main component was used as the raw material powder, a pressure was applied with a pressure gradient, and laser light was irradiated to the maximum pressure portion. The present invention relates to a diamond manufacturing apparatus capable of forming large diamond particles at a lower pressure and lower temperature than conventional high pressure synthesis methods.

FIG. 1 shows a diamond manufacturing apparatus of this embodiment. In FIG. 1, a cylinder type compression device (hereinafter,
This portion is referred to as a high pressure vessel). In this high-pressure container, a diamond window material 5 is provided at the tip of a pressure generating indenter 1 having a truncated cone shape (hereinafter, this pressure generating indenter portion is referred to as an upper indenter 1). Upper indenter 1
Moves along a spiral groove 4 provided inside the cylinder 2 and is held by a gasket 3 between another raw material indenter (hereinafter, this portion is referred to as a lower indenter 7). Then, use C ₆₀ powder.) 6 is compressed. At this time, in order to generate the above-mentioned pressure gradient, the upper indenter 1 has a truncated cone shape in which the top of the cone is cut off horizontally, and the lower indenter 7 has a conical shape. This applies pressure to the powder material with a pressure gradient, and the top 1 of the upper indenter 1
This is because the maximum pressure is applied at 0. Of course, both the upper indenter 1 and the lower indenter 7 may have a truncated cone shape.

The gasket 3 is for holding the powder material, and also acts to press the powder from the surroundings and apply pressure to the powder. The material of the gasket 3 is Fe, S
US or Ni can be used, and in this embodiment, F
e was used.

The pressure was applied to the powder material, which is the starting material of diamond, by screwing the upper indenter 1 along the spiral 4. At this time, the lower indenter 7 was fixed. A carbon dioxide gas laser (hereinafter referred to as CO ₂ laser) that emits light in the infrared region through the diamond window material 5 is used as a raw material in a state where the powder 6 reaches a pressure of about 2 to 3 GPa between both indenters by applying pressure. Irradiation was performed in the powder direction. However, the laser output can be changed depending on the target temperature reached by heating. A schematic diagram showing the pattern of laser light injection is shown in FIG. At this time, the focus of the CO ₂ laser beam 8 is adjusted by the lens 9, and the powder 6 is irradiated through the diamond window material 5. The pressure was detected by measuring the rotational torque of the lower indenter 1 moving in the cylinder 2 while rotating along the spiral 4.

At this time, melting of the powder occurs in the heated portion irradiated with the laser light, that is, the highest pressure portion (the portion indicated by 10 in FIG. 1), and the diamond window material serving as the laser light irradiation window. 5 plays the same role as the seed crystal in the epitaxial growth method. As a result, the carbon of the C ₆₀ powder changes its arrangement into a diamond shape and is directly converted into diamond. This epitaxial growth effect becomes possible only by using the diamond window material portion where the maximum pressure is generated as in the present invention, the laser beam irradiated to that portion, and the C ₆₀ powder raw material. At this time, from the component of C ₆₀ -diamond + graphite structure generated in the highest pressure portion, only graphite moves to the peripheral slightly lower pressure portion, and high-purity epitaxial growth of diamond proceeds.

As the temperature rises, part of the gasket 3 also becomes molten. Generally, graphite that is inevitably produced in such a high-pressure diamond synthesis reaction is taken into the molten gasket 3, but since the central epitaxial growth is promoted by the pressure gradient as described above, the influence of the melting of the gasket 3 on diamond is not so great. Not big.

In the diamond manufacturing apparatus described above, since the cylinders can be sequentially exchanged and moved immediately after the laser light emitting port, the above steps can be easily repeated and continuous diamond high pressure synthesis can be performed. Becomes

[Embodiment 2] In this embodiment, an application example of the diamond producing method of the present invention using the diamond producing apparatus shown in FIG. By using the configuration of the present invention, it is possible to lower the required pressure and temperature compared to the conventional high pressure synthesis method using graphite powder,
It is possible to reduce the scale of the device. This embodiment uses a one-dimensional compression type device having a structure for applying a pressure in one-dimensional direction as shown in FIG.

However, if it is possible to form a pressure gradient having a maximum pressure at the tip of the upper indenter for introducing the laser beam, the lower indenter is divided into a plurality of types to press the powder as shown in FIG. The structure of In the apparatus shown in FIG. 3, reference numerals are the same as those in FIG. 1, 1 is an upper indenter, 7 is a lower indenter divided into a plurality of parts, and 5 is a diamond window material. Further, the shape of the indenter for pressurizing the powder as the starting material is not limited to a perfect truncated cone or a truncated pyramid, and a pressure having a gradient can be applied, and the diamond of the portion where the maximum pressure is generated is formed. Any structure may be used as long as it can irradiate laser light through the window material.

In this embodiment, the laser light source has a wavelength of 1
A 0.6 μm CO ₂ laser was used. The window material 5 of diamond for indenter / laser light introduction has a wavelength of 10.6 μm.
A 2a type single crystal diamond plate having a transmittance of 70% or more in m 2 was used. Further, the diamond window material 5 used was one whose end surface was processed into a taper state with a diameter of 10 mm, 5 mm, and a thickness of about 7 mm.

Of course, it is preferable to match the wavelength of the laser beam with the wavelength of the laser beam which can be transmitted by the diamond constituting the window material 5 of the diamond which is the indenter / laser beam introduction window, so that the laser light source can be stably irradiated. If so, the type of the window material 5 of diamond and the pressurizing method have a choice, and the present invention does not limit the type of laser light source and the type of diamond.

As the raw material powder 6, commercially available C ₆₀ powder (9
8% and the balance was C ₇₀ ). Approximately 5 of this powder in one step
~ 7g was used. Powder is lower indenter and Fe gasket 3
Were filled in a hole having a diameter of 4.5 mm and a depth of 25 mm. It is not preferable that the diameter of the powder filling hole exceeds the diameter of the diamond window material 5, which is the introduction window of the laser beam, also from the pressing effect of the indenter. However, with respect to the depth dimension, adjustments should be made based on consideration of quantity and quality and the ability of the gasket material. Of course, the diameter may be changed depending on the size of the diamond window material 5 that can be used.

In order to apply pressure to the powder containing C ₆₀ as a starting material, C is applied to the hole formed by the lower indenter 7 and the gasket 3 (corresponding to the portion indicated by 6 in FIG. 1). ₆₀
With the powder filled, the upper indenter 1 incorporating the diamond window material 5 is rotated along the inner wall of the cylinder 2 and moved toward the lower indenter 7. The state of movement is shown in FIG. In a preliminary experiment, the pressure generated between the upper and lower indenters in the raw material powder was measured in advance from the torque applied to the upper indenter, and thereafter the position and movement amount of the upper indenter were determined based on the measured pressure value. In this embodiment, the pressure value between the upper and lower indenters is set to 3 G lower than that of the flux method.
It was Pa.

The internal pressure of the raw material powder is not uniform because a pressure gradient is applied. In particular, the pressure between the upper and lower indenters on the straight line 8 showing the laser beam in FIG. 1 is a value that is always higher than the pressure generated in other portions, that is, the maximum pressure. The pressure between the upper and lower indenters is the pressure of this maximum pressure portion (the portion indicated by 10 in FIG. 1).

After the C ₆₀ powder is filled in the cylinder 2 at a predetermined pressure in the state as shown in FIG. 1, this high-pressure filled container is attached to the CO ₂ laser emission port. The positional relationship of mounting was performed according to FIG. 2 described above. The focus of the laser light is adjusted by the lens 9 provided at the CO ₂ laser emission port. The diameter of the diamond window material exposed from the upper indenter to the outside is 4 mm.

It is necessary to focus the laser light on the C ₆₀ powder just behind the diamond window material without contacting the upper indenter. When the focus is on the C ₆₀ powder, melting occurs in the C ₆₀ powder, and epitaxial crystal growth is possible by recombining the structure with the diamond window material as the forming nucleus. However, if the focus is on the diamond side, the diamond window will be decomposed, and the diamond formation conditions will be broken due to the fracture due to strength deterioration. It is necessary to perform some preliminary experiments for this focus adjustment as well. In the experiment, it was confirmed that the mechanical strength of the diamond window material can withstand the heating of CO ₂ laser light sufficiently and that the C ₆₀ powder can be dissociated and recombined sufficiently if the focus is placed on the C ₆₀ powder side. did it.

Hold this pressurized / heated state for 2-3 hours,
After the reaction time had elapsed, the laser output was immediately reduced. When the reaction temperature at this time was measured using an optical thermometer, it seems that the maximum internal temperature is about 2000 ° C, but the adjustment of the focal length and the reliability of the optical thermometer Due to problems, accurate measurement seems difficult.

Then, the high-pressure container was removed from the CO ₂ laser emission port, the upper indenter was loosened to reduce the pressure, and the sample was taken out from the high-pressure container.

Example 3 In this example, an example of diamond synthesis using carbon nanotube powder as a raw material is shown.

Also in this example, as in Examples 1 and 2, a CO ₂ laser having a wavelength of 10.6 μm was used as the laser light source, and the diamond window material 5 was a 2a type single crystal diamond plate.

As the raw material powder 6, about 5 to 7 g of carbon powder containing about 25% of carbon nanotubes was used.
This powder was synthesized by the present inventors by a graphite electrode discharge in atmospheric pressure helium gas. Powder is lower indenter and F
filled in the hole formed by the e-made gasket 3,
The upper indenter 1 was rotated along the inner wall of the cylinder 2 in the state filled with carbon nanotubes, and moved toward the lower indenter 7 to apply pressure. Also in this embodiment, the pressure value is 3GP.
a. The pressure between the indenters is the pressure of the maximum pressure portion (the portion indicated by 10 in FIG. 1).

Cylinder 2 with carbon nanotube powder
After filling the inside of the container with a predetermined pressure, the container in the high-pressure filled state is attached to the CO ₂ laser emission port to adjust the focus of laser light. The laser light needs to be focused on the powder behind the diamond window material.

Melting occurs at the in-focus portion, and epitaxial crystal growth proceeds due to the recombination of the structure having the diamond window material as a forming nucleus. 2 in this pressurized / heated state
It was maintained for ~ 3 hours, and the laser output was immediately reduced after the reaction time had elapsed. Then, the high-pressure container was removed from the CO ₂ laser emission port, the upper indenter was loosened to reduce the pressure, and the sample was collected.

[Embodiment 4] In this embodiment, a method for producing a semiconductor diamond using carbon nanotubes substitutionally doped with impurities will be described. When carbon nanotubes are used as the raw material powder in the constitution of the present invention, it is possible to easily add impurities and to manufacture semiconductor diamond, as compared with the conventional high pressure synthesis method using graphite powder or C ₆₀ powder. Is.

As the raw material powder 6, as in Example 2, about 5 to 7 g of carbon nanotubes of about 25% was used. However, this powder is made to flow about 0.1 to 25%, preferably 1 to 5% of nitrogen in atomic% during discharge synthesis in atmospheric pressure helium,
This is an attempt to replace the weak crown with nitrogen. not to mention,
It is known that its synthesis is very difficult,
The purpose is to be a raw material for n-type semiconductor diamond. When the target semiconductor is p-type, a boron compound gas may be used instead of nitrogen. Also, for the purpose of n-type, for example, a phosphorus compound gas may be used. However, at this stage, the existence state of carbon-nitrogen in the nanotube is not examined.

With the carbon powder obtained as described above being filled in the hole formed by the lower indenter 7 and the gasket 3, the upper indenter 1 incorporating the diamond window material 5 as before is replaced by the lower indenter. Pressurization is performed by moving in 7 directions. In this example, the pressure value between the upper and lower indenters was set to 4.2 GPa, which is slightly higher than those in Examples 1 to 3.

The method of applying a laser beam to the container in the high-pressure filled state is the same as in Examples 1-3. Ie C
It is attached to the O ₂ laser emission port and the laser beam is focused on the raw material powder behind the diamond window material. This pressurized / heated state was maintained for 2 to 3 hours, and after the reaction time had elapsed, the laser output was quickly reduced, the CO ₂ laser emission port was removed, the upper indenter was loosened to reduce the pressure, and the sample was recovered.

[Embodiment 5] It is expected that the quality of the obtained diamond will be changed by moving the focal length of the laser beam. This is because the distance between the window formed by the diamond window material 5 that also functions as a seed crystal and the focal point of the laser light changes. Therefore, in order to compare the influence of the focal length, the focal point of the laser beam was set at about 12 mm from the diamond window material. Other conditions were the same as in Example 1, and the reaction was carried out by holding the heated state for 2-3 hours.

[Evaluation of Samples Obtained in Examples] Example 1
Comparative evaluation of the samples obtained in Examples 5 to 5 will be described below. The evaluation items are the results of visual observation and evaluation of the size and color of the sample, and the quality estimated from Raman spectroscopy.

The sample prepared in Example 2 was the gasket 3
And 0.5 to 1.5 in diameter except that a thin skin-like precipitate which is considered as an impurity was observed at the interface between the lower indenter 7 and the sample.
A high quality single crystal diamond material of mm was obtained. On the other hand, in Example 5, about 20% was a precipitate mainly composed of amorphous carbon. It is considered that this is because in Example 2, the diamond window does not sufficiently serve as a seed crystal due to the shift of the focus of the laser beam. From the above, it was found that the setting of the focal length of the laser beam is very important in determining the quality of diamond.

Further, the diamond crystal grains produced in Example 5 and the thin film-shaped precipitates obtained in the peripheral portion were evaluated by Raman spectroscopy. The spectrum of the diamond crystal grains is shown in FIG. 5, and the spectrum of the thin film deposit is shown in FIG. From the peak height and full width at half maximum shown in this Raman spectrum, the particle sample in the central part (the part where maximum pressure is applied) was obtained as almost perfect single crystal particles, but in the peripheral part it was diamond. It was clarified that it was formed as a continuous deposit in the form of a thin film in which a large amount of amorphous carbon structure was mixed even though it had a structure.

The diamond produced from the carbon nanotube-containing powder in Example 3 showed almost the same result as that shown in FIG. 5 in Raman spectroscopic analysis, but it could be formed in one third of the time when C ₆₀ was used. That is a remarkable result.

The diamond prepared from the carbon nanotube-containing powder doped with nitrogen in Example 4 was closer to that of FIG. 6 than that of FIG. 5 in Raman spectroscopic analysis, but a visible-ultraviolet absorption analysis was tried. Okay, I
It has a uniform nitrogen distribution similar to type b, and
It was found to be an n-type semiconductor diamond having a resistance value of Ω · cm or less (at least 76 Ω · cm).

[0070]

INDUSTRIAL APPLICABILITY As described above, the powder having C ₆₀ and / or carbon nanotubes, which is the starting material for synthesizing diamond, which is the constitution of the present invention, as a main component is applied with a pressure gradient so that the maximum pressure is obtained. By irradiating laser light through a window made of diamond as a constituent material, high-quality single crystal diamond can be obtained by a low temperature and low pressure process using a much smaller device than the conventional high pressure synthesis method. It became possible to synthesize easily. Moreover, since a high-pressure container smaller than the direct conversion method can be used, another effect that high mass productivity can be obtained by exchanging the high-pressure container was obtained. Furthermore, by using carbon nanotubes synthesized in an impurity atmosphere as the raw material powder, semiconductor diamond could be easily synthesized.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cylinder type high pressure container.

[Fig. 2] Schematic diagram of laser light injection

FIG. 3 is a schematic diagram of a lower indenter split type high pressure vessel.

FIG. 4 is a schematic diagram of a pressurizing mechanism.

FIG. 5 Raman spectrum diagram

FIG. 6 Raman spectrum diagram

[Explanation of symbols]

1 Upper indenter 2 Cylinder 3 Gasket 4 Spiral groove 5 Diamond window material 6 C ₆₀ powder 7 Lower indenter 8 Laser light 9 Laser light lens 10 Maximum pressure part

Claims (6)

[Claims] 1. A method for producing diamond by using a powder material containing carbon as a main component as a starting material and applying a high pressure to the powder material, wherein C is used as the powder material containing the carbon as a main component. ₆₀ and / or using a powder material containing carbon nanotubes as a main component, when applying a high pressure to the powder material containing carbon as a main component, a pressure is applied with a pressure gradient, and A method for producing diamond, which comprises irradiating a laser beam. 2. The carbon molecule and / or carbon crystal, which is the main component of the powder material according to claim 1, is nitrogen and / or a nitrogen compound, phosphorus and / or a phosphorus compound, boron and / or a boron compound in the carbon nanotube. The method for producing diamond is characterized in that by including in the structure thereof, a semiconductor diamond can be easily formed. 3. A method for producing diamond by using a powder material containing carbon as a main component as a starting material and applying a high pressure to the powder material, wherein the powder material containing carbon as the main component is C ₆₀ and / or using a powder material containing carbon nanotubes as a main component, when applying a high pressure to the powder material containing carbon as a main component, a pressure is applied with a pressure gradient, and A method for producing a diamond, comprising irradiating a laser beam through a window material of diamond to produce a diamond from a powder material containing carbon as a main component with the diamond constituting the window material as a seed crystal. 4. The carbon molecule and / or carbon crystal, which is the main component of the powder material according to claim 3, is nitrogen and / or a nitrogen compound, phosphorus and / or a phosphorus compound, and boron and / or a boron compound in the carbon nanotube. The method for producing diamond is characterized in that by including in the structure thereof, a semiconductor diamond can be easily formed. 5. Inside a reaction vessel having a cylindrical outer wall,
A diamond manufacturing apparatus including a pressure generating indenter, wherein the pressure generating indenter has a taper shape for applying a pressure having a pressure gradient to a powder that is a raw material of diamond, and The tip of the pressure generating indenter has a diamond window material, maximum pressure is applied to the diamond window material, and laser light is radiated to the powder as the raw material of diamond through the diamond window material. A diamond manufacturing apparatus having the above-mentioned configuration. 6. The carbon molecule and / or carbon crystal, which is the main component of the powder material according to claim 5, is nitrogen and / or a nitrogen compound, phosphorus and / or a phosphorus compound, boron and / or a boron compound in the carbon nanotube. The method for producing diamond is characterized in that by including in the structure thereof, a semiconductor diamond can be easily formed.