JP2016175798A - Nano-crystal diamond and production method and production apparatus of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce nano-crystal diamond having a uniform particle diameter without pulverizing massive diamond.SOLUTION: Silicon and carbon included in a raw material gas are isolated in plasma environment by supplying the raw material gas including silicon and carbon to a plasma space (P) formed in a reaction chamber (2), and carbon is made to be covalent bonded to the periphery of silicon having an SP3 crystal structure as a crystal nucleus by vapor phase synthesis, and is recovered by negatively charging a recovery vessel (5) arranged directly under the plasma space (P).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nanocrystalline diamond that exhibits fluorescence when irradiated with excitation light, a manufacturing method thereof, and a manufacturing apparatus.

Fluorescence imaging has become an essential fundamental technology for biological science research.
Fluorescence imaging is a technique that enables high-sensitivity, multicolor, and dynamic imaging by imparting fluorescence to a biological observation target substance. Fluorescent probes used as biosensors are biological, medical, pharmaceutical, etc. It is an important elemental technology that supports fluorescence imaging in the field.
Fluorescent probes emit “fluorescence” only under specific conditions, such as irradiation with excitation light, so that they are not only in vitro (in vitro) but also in “living biological samples” (in vivo). It is possible to observe the dynamics of physiologically active substances in real time.

As such a fluorescent probe, conventionally, when using a fluorescent dye of a low molecular weight organic compound such as rhodamine, the other is a case where a fluorescent protein such as GFP is used. In addition to fluorescent dyes, fluorescent probes using semiconductor quantum dots and nanocrystalline diamond particles have been actively developed.
Semiconductor quantum dots are suitable as probes for single-molecule imaging in vivo due to their high fluorescence intensity and monochromaticity and strong light resistance compared to conventional fluorescent dyes, but they contain cadmium and are therefore cultured. In the test with cells, there is a problem that the eluted cadmium causes cell death.
It is possible to reduce elution of cadmium by devising the surface coating, but it goes without saying that it is safer not to use cadmium.

On the other hand, nano crystalline diamond is non-toxic, harmless and has high biocompatibility, so its application range is expanding in the biological and medical fields.
Currently, in order to realize fluorescence imaging using fluorescent nanocrystalline diamond (3 to 100 nm), a function that can be stably dissolved in the living body for a long period of time and can be selectively incorporated into the target site, A method for fluorescence observation of these by photoexcitation or magnetic resonance has been studied.

As a standard method for producing fluorescent nanocrystalline diamond, an ion implantation method (see Patent Documents 1 and 2) is known.
In this method, synthetic diamond particles having no fluorescence are generated in advance by a high-temperature and high-pressure method such as a detonation method (detonation method), and this is classified by size by centrifugation and dispersed in a slurry. Is applied onto a silicon substrate to form a diamond thin film having a thickness of about 380 nm.
In this state, in a vacuum chamber, the silicon substrate is irradiated with an ion beam containing magnetic metal element ions while being scanned to impart fluorescence, and then the diamond thin film is mechanically peeled and ground from the substrate. An annealing treatment is performed to form fluorescent NCD.
Here, metal element ions as impurities implanted in diamond impart fluorescence.

In addition, instead of implanting magnetic metal ions, nitrogen dispersed as impurities in synthetic diamond particles is used to form nitrogen vacancies (N-V centers) that serve as fluorescence centers to form fluorescent NCD. A manufacturing method has also been proposed (see Patent Document 3).
This method utilizes the fact that nitrogen is dispersed as an impurity in the synthetic diamond particles produced by the high-temperature and high-pressure method. The synthetic diamond particles are laid in layers in an appropriate box and irradiated with an electron beam. Thus, vacancies are formed in the crystal lattice. Next, by annealing this, nitrogen atoms dispersed in the synthetic diamond as impurities are combined with vacancies to form fluorescent centers (N-V centers), and layered diamond aggregates to form diamond. A lump of crystal structure is formed, and if this is pulverized and atomized, fluorescent nanocrystalline diamond can be obtained.

  Nanocrystalline diamond produced by either method is terminated with a carboxyl group and chemically modified with a polymer, enabling dissolution in a living environment and selective uptake into cancer cells, etc., as a fluorescent probe Can be used.

However, both of them are not only complicated in process, but also have the problem of poor productivity because mechanical grinding of diamond is necessary when finally producing NCD.
In addition, the nanocrystalline diamond produced by the detonation method is not uniform in size and contains particles of various sizes, so classification is required to form a uniform diamond film or diamond layer. .

Furthermore, since crystallinity is inferior, it is very difficult to form a luminescent center even if it is intended to impart fluorescence by injecting metal atoms or using nitrogen contained as an impurity. there were.
And finally, since this must be grind | pulverized, there existed a problem that production efficiency was low and control of a particle size was difficult.

JP 2012-206863 A JP 2010-013718 A Special table 2010-526746

  Therefore, the present invention can form fluorescent centers easily and efficiently in diamond particles without using synthetic diamond having poor crystallinity, and it is not necessary to grind massive diamonds. The technical challenge is to be able to produce uniform nanocrystalline diamond.

In order to solve this problem, the present invention is a method for producing nanocrystalline diamond in which carbon is covalently bonded with an SP3 crystal structure,
By supplying a source gas containing silicon and carbon to the plasma space formed in the reaction chamber, the silicon and carbon contained in the source gas are liberated in a plasma environment,
It is characterized in that silicon having an SP3 crystal structure is used as a crystal nucleus and carbon is covalently bonded around it by vapor phase synthesis.

The nanocrystalline diamond manufacturing apparatus according to the present invention includes a source gas supply system that supplies a source gas containing silicon and carbon, a plasma torch that forms a plasma space in a reaction chamber, and a generation generated in the plasma space. Equipped with a collection container to collect items,
The plasma torch is provided with a needle-like electrode arranged at the center of the nozzle through which the source gas flows, and the plasma space is formed between the tip opening of the nozzle and the needle-like electrode,
The collection container is characterized in that the negative electrode is charged and disposed immediately below the tip opening of the nozzle.

  Further, the nanocrystalline diamond produced by the above production method was synthesized by vapor-phase synthesis of silicon and carbon liberated in a plasma environment, and carbon was sequentially covalently bonded around silicon having an SP3 crystal structure as a crystal nucleus. It is characterized by that.

According to the method for producing fluorescent nanocrystalline diamond particles according to the present invention, by supplying the source gas to the plasma space, silicon and carbon contained in the source gas are liberated into silicon radicals and carbon radicals.
At this time, by controlling the supply amount of the source gas, the supply amount of silicon and carbon and the plasma residence time of silicon radicals and carbon radicals can be controlled.

Here, if the type and supply amount of the source gas are set so that the silicon concentration is lower than the carbon concentration, a sufficient amount of carbon radicals exist around the silicon radicals.
Since silicon has larger atoms than carbon, carbon is bonded around silicon as a crystal nucleus, but silicon is covalently bonded only in the same SP3 crystal structure as diamond, and therefore, carbon is SP3 crystal relative to silicon. Bonded by the structure, and further, another carbon is successively bonded to the carbon by the SP3 crystal structure, and the crystal grows.

  In this way, nanocrystalline diamond is vapor-phase synthesized by bonding carbon radicals around silicon radicals as crystal nuclei in the plasma space, so it is possible to classify synthetic diamonds or diamonds implanted with metal ions, etc. There is no need for peeling and crushing.

In addition, since silicon is used as the crystal nucleus, silicon always exists in the nucleus of the generated nanocrystalline diamond. Since silicon and carbon have different atomic sizes, the silicon periphery is distorted and the silicon empty It is presumed that a hole is formed, and this becomes a fluorescence center to impart fluorescence.
Accordingly, all of the produced nanocrystalline diamond is given fluorescence.

  Furthermore, since carbon binds to silicon, which is the crystal nucleus in the plasma space, the reaction time can be set by adjusting the time for the source gas to pass through the plasma, and the particle size of the nanocrystalline diamond produced thereby Can be controlled.

The schematic diagram which shows the molecular structure of the nanocrystal diamond which concerns on this invention. The graph which shows the fluorescence spectrum of the nanocrystal diamond which concerns on this invention. Explanatory drawing which shows the manufacturing apparatus of the nanocrystal diamond which concerns on this invention.

In this example, it is possible to easily form fluorescent centers in diamond particles without using synthetic diamond having poor crystallinity, and it is not necessary to grind massive diamonds, so that the particle diameters are uniform. In order to achieve the goal of producing efficient nanocrystalline diamond particles,
By supplying a source gas containing silicon and carbon to the plasma space formed in the reaction chamber, the silicon and carbon contained in the source gas are liberated in a plasma environment,
Using silicon having an SP3 crystal structure as a crystal nucleus, carbon was covalently bonded to the periphery by vapor phase synthesis.

  FIG. 1 (a) is an explanatory view showing silicon radicals and carbon radicals that are raw materials of a nanocrystalline diamond (hereinafter abbreviated as “NCD”) according to the present invention, and FIG. 1 (b) shows silicon radicals as crystal nuclei. It is explanatory drawing which shows the molecular structure of NCD in which the carbon radical was covalently bonded to SP3 crystal structure.

  As shown in FIG. 1A, silicon and carbon contained in the source gas are liberated by the silicon radical Si (r) and the carbon radical C (r) in the plasma space P, and the carbon radical C (r) Thus, by setting the type and supply amount of the source gas so that the concentration of the silicon radical Si (r) is lowered, the carbon radical C (r) is aggregated around the silicon radical Si (r).

In this state, as shown in FIG. 1B, with the silicon radical Si (r) as a crystal nucleus, carbon radicals C (r) are sequentially covalently bonded around the silicon nucleus, and only one silicon Si exists at the center. An NCD is generated.
This is because silicon Si has an atomic weight larger than that of carbon C, and thus it is considered that the bonding force between silicon and carbon is larger than the bonding force between carbons.
Further, since silicon can only have the same SP3 crystal structure as diamond, the carbon supplied and bonded to silicon exhibits an SP3 crystal structure.

In other words, a crystal structure in which only one carbon C located at the center of the diamond particle is replaced with silicon Si is obtained.
This crystal growth depends on the reaction time in the plasma space P, and the reaction time depends on the type and supply amount of the raw material gas. In this example, the raw material is grown so that the particle size of NCD is 3-100 nm. The gas type and supply amount are selected.

  In the NCD generated in this way, since the atomic weight of silicon serving as a crystal nucleus is larger than that of carbon, the periphery of the silicon is distorted to form silicon vacancies, which are the fluorescence centers (Si-Vac). It is presumed that fluorescence is imparted to the center.

  FIG. 2 shows a fluorescence spectrum measured when the thus generated NCD is irradiated with a laser diode excitation type SHG-Nd: YAG laser (wavelength: 532 nm) as excitation light. From the wavelength of the excitation light, FIG. In addition, it is considered that a fluorescence phenomenon occurs because a peak of light intensity is observed in the vicinity of a wavelength of 700 nm on the long wavelength side.

FIG. 3 is a schematic view showing an NCD manufacturing apparatus 1 according to the present invention.
In this manufacturing apparatus 1, a microwave plasma torch 3 is attached downward in a reaction chamber 2 formed of a vacuum chamber, and a silicon and carbon supplied from a source gas supply system 4 are formed at the tip of the plasma torch 3. Gas phase synthesis is performed in the space P, and the product is recovered in the recovery container 5.

The plasma torch 3 includes a coaxial cavity resonator 8 including a cylindrical cavity resonator 6 and an electrode antenna 7 disposed on the central axis thereof.
The cylindrical cavity resonator 6 is formed with a gas inflow port 9 through which the source gas supplied from the source gas supply system 4 flows.

  The electrode antenna 7 has a water-cooled double tube structure in which cooling water supplied from the upper end side inflow port 10a to the inner tube 11a flows into the outer tube 11b from the lower end side and is discharged from the upper end side outflow port 10b. The needle electrode 12 made of tungsten is attached to the tip.

The metal waveguide rod 13 for propagating microwaves to the electrode antenna 7 is penetrated to the cylindrical cavity resonator 6 via the insulating sleeve 13a, one end of which is connected to the outer tube 11b of the electrode antenna 7, and the other end is connected. It is provided through the waveguide 14 that propagates microwaves.
Note that a magnetron (not shown) having an output of 400 W that generates a microwave of 2.45 GHz is attached to the tube end of the waveguide 14.

  In the plasma torch 3, the tip of the cylindrical cavity resonator 6 is formed in the nozzle 15, the tip opening 15a of the nozzle 15 and the tip of the needle electrode 12 are arranged close to each other. (−100 V), and a microwave is supplied in a state where a DC voltage is applied so that the nozzle 15 becomes an anode (earth), thereby causing a discharge between the nozzle 15 and the needle electrode 12, and the tip of the nozzle 15. A plasma space P is formed.

The source gas supply system 4 suffices to be able to supply silicon Si and carbon C to the plasma space P, but it is not preferable to use a gas containing impurities that may be mixed in the gas-phase synthesized product. .
As this source gas, for example, an Si—C gas containing silicon and carbon can be used. As this Si—C gas, for example, monomethylsilane, tetramethylsilane, or triethylsilane is a main component. Gas is used.
In this example, tetramethylsilane was used so that the components supplied to the reaction chamber 2 were only silicon Si, carbon C, and hydrogen H.

Further, as the source gas, one or more types of silicon-based gas containing at least silicon and one or more types of carbon-based gas containing at least carbon may be mixed and supplied.
In this case, as the carbon-based gas, a gas mainly containing alkane, alkene, or alkyne can be used.

In the raw material gas supply system 4 of this example, a constant temperature tank 21 filled with liquid tetramethylsilane serving as a raw material gas is connected to a gas inlet port 9 of the plasma torch 3 via a flow rate control pump 22 and a carrier gas. A supply source 23 is connected to the constant temperature tank 21 via a regulator 24.
Hydrogen is supplied from the carrier gas supply source 23, and tetramethylsilane can be bubbled and vaporized to be supplied to the plasma torch 3.

A vacuum pump 25 is connected to the reaction chamber 2 and a pressure sensor 26 for measuring the pressure in the reaction chamber 2 is attached.
Further, inside the reaction chamber 2, a cup-shaped recovery vessel 5 made of molybdenum for recovering the product synthesized in the gas phase in the plasma space P is arranged immediately below the tip opening 15a of the nozzle 15. The collection container 5 is charged to the negative electrode through a ring-shaped bracket 27 that supports the collection container 5.

  Since the nanoparticles synthesized in the gas phase in the plasma space P are very fine and light, even if they try to capture and capture, the filter will soon clog up and cannot be captured efficiently. However, these nanoparticles are charged on the anode. Therefore, electrostatic capture is surely performed by charging the collection container 5 to the negative electrode opposite to the negative electrode.

Next, a method for manufacturing NCD will be described.
First, the vacuum pump 25 is driven to maintain the inside of the reaction chamber 2 at 30 torr, a 2.45 GHz microwave is supplied from a magnetron with an output of 400 W, discharge is caused at the tip of the plasma torch 3, and a plasma space P is formed. To do.
In this state, the regulator 24 and the flow rate control pump 22 are adjusted so that hydrogen is supplied to the constant temperature tank 21 and trimethylsilane is bubbled and vaporized, and 231 cc / min gas is continuously supplied to the plasma torch 3 for 20 minutes. did.
In the supply gas 231 cc / min, hydrogen gas as a carrier gas was 220 cc / min, and gasified trimethylsilane was 11 cc / min.

Tetramethylsilane is represented by the formula Si (CH _{3) 4,} silicon Si four methyl groups around the CH ₃ ^- but is one that is bound, in the plasma space P, and the elements of each are disconnected, The silicon radical Si (r) and the carbon radical C (r) are released and floated.

At this time, each element of tetramethylsilane Si (CH ₃ ) ₄ is completely liberated and silicon Si and carbon C are not present in the plasma space P in a ratio of 1: 4 exactly. It is considered that there are a large number of carbon radicals C (r) that can be covalently bonded to the silicon radicals Si (r) released from.
This is because some of the four methyl groups CH ₃ ^— of tetramethylsilane are replaced with hydrogen H, trimethylsilane SiH (CH ₃ ) ₃ , dimethylsilane SiH ₂ (CH ₃ ) ₂ , monomethylsilane SiH ₃ (CH ₃ It is considered that a sufficient amount of carbon radical C (r) is supplied.

  Since silicon can only have the same SP3 crystal structure as diamond, when the carbon radical C (r) aggregates around the silicon radical Si (r), the silicon radical Si (r) larger than carbon becomes a crystal nucleus, The carbon radical C (r) is covalently bonded to the silicon radical Si (r) in the SP3 crystal structure, and further, another carbon is bonded to the carbon one after another to grow a crystal, thereby generating NCD.

Since new source gas is continuously supplied from the source gas supply system 4, the NCD generated in the plasma space P flows out from the nozzle 15 into the reaction chamber 2 so as to be pushed out by the source gas.
At this time, since the recovery container 5 disposed immediately below the nozzle 15 is negatively charged and NCD is positively charged, the NCD flowing out from the nozzle 15 into the reaction chamber 2 is recovered by electrostatic action. Captured in the container 5.

Since the particle size of the NCD produced in this way is almost equal if the production conditions are equal, there is no need for any subsequent classification or pulverization, and the NCD can be produced very easily.
In addition, since silicon radicals and carbon radicals are covalently bonded in the plasma space P to grow crystals, the production time (type of raw material gas and supply amount, etc.) is adjusted, and the residence time (reaction time) in the plasma space P is adjusted. The particle size can be controlled by adjusting.

Furthermore, since silicon is crystal-grown with silicon as a crystal nucleus, silicon is always present in the nucleus of the generated NCD, and since fluorescence is imparted by this silicon, fluorescence Excellent particle production efficiency and crystallinity.
Then, the fluorescent NCD generated in this way is terminated with a carboxyl group and chemically modified with a polymer as in the conventional case, so that it dissolves in a living environment and selectively binds to cancer cells and the like. It can be used as a fluorescent probe.

  The source gas is not limited to tetramethylsilane as long as silicon Si and carbon C can be supplied to the plasma space P. For example, monomethylsilane, tetramethylsilane, or triethylsilane is the main component. A gas may be used.

Further, as the source gas, one or more types of silicon-based gas containing at least silicon and one or more types of carbon-based gas containing at least carbon may be mixed and supplied.
In this case, as the carbon-based gas, methane gas CH ₃ , ethylene gas C ₂ H ₂ , acetylene gas C ₂ H ₂ , propane gas C ₃ H _{8, and} other gases mainly composed of alkane, alkene, or alkyne can be used. .

  The present invention is used for the production of fluorescent probes for performing fluorescence imaging in the fields of biology, medicine, and pharmacy.

Si (r) ... Silicon radical C (r) ... Carbon radical P ... ... Plasma space Si ... Silicon C ... ... Carbon 1 ... NCD production equipment 2 ... ... Reaction chamber 3 ……………… Plasma torch 4 ……………… Source gas supply system 5 ……………… Recovery container 7 …………… Electrode antenna 12 ………… Needle electrode
15 ………… Nozzle
15a ......... Opening

Claims (8)

A method for producing nanocrystalline diamond in which carbon is covalently bonded with an SP3 crystal structure comprising:
By supplying a source gas containing silicon and carbon to the plasma space formed in the reaction chamber, the silicon and carbon contained in the source gas are liberated in a plasma environment,
A method for producing nanocrystalline diamond, characterized in that silicon having an SP3 crystal structure is used as a crystal nucleus and carbon is covalently bonded to the periphery by vapor phase synthesis.   2. The nanocrystalline diamond production according to claim 1, wherein a recovery container charged to the negative electrode is disposed immediately below the plasma space, and the crystal synthesized in the gas phase and charged to the positive electrode is recovered in the recovery container. Method.   The method for producing nanocrystalline diamond according to claim 1, wherein the source gas uses one or more kinds of Si-C-based gases containing both silicon and carbon.   The method for producing nanocrystalline diamond according to claim 3, wherein the Si-C-based gas is mainly composed of monomethylsilane, tetramethylsilane, or triethylsilane.   2. The method for producing nanocrystalline diamond according to claim 1, wherein at least one silicon-based gas containing at least silicon and at least one carbon-based gas containing at least carbon are used as the source gas.   The method for producing nanocrystalline diamond according to claim 5, wherein a gas mainly composed of alkane, alkene, or alkyne is used as the carbon-based gas. Nanocrystalline diamond covalently bonded with carbon in SP3 crystal structure,
A nanocrystalline diamond characterized in that silicon and carbon liberated in a plasma environment are synthesized in a gas phase, and silicon having an SP3 crystal structure is used as a crystal nucleus and carbon is sequentially covalently bonded around the silicon. An apparatus for producing nanocrystalline diamond in which carbon is covalently bonded in an SP3 crystal structure,
A source gas supply system for supplying a source gas containing silicon and carbon, a plasma torch for forming a plasma space in the reaction chamber, and a recovery container for recovering a product generated in the plasma space,
In the plasma torch, a needle electrode is arranged at the center of the nozzle through which the source gas flows, and the plasma space is formed between the tip opening of the nozzle and the needle electrode,
The apparatus for producing nanocrystalline diamond, wherein the collection container is arranged to be charged to the negative electrode immediately below the opening at the tip of the nozzle.

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