JP2012240880A - Device and method for producing nitrogen-including fullerene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem wherein, though nitrogen-including fullerene is a novel material having anticipation of application to a quantum computer or the like, when using a conventional production device of the nitrogen-including fullerene, the yield is low such as 10to 10%.SOLUTION: A production device including a potential-controllable grid electrode and an end plate electrode individually near a deposition substrate is used, and a nitrogen gas pressure is heightened, and the temperature of a fullerene sublimation oven is set at a high temperature over 700°C, and each potential of the electrodes and the deposition substrate is controlled respectively independently, to thereby synthesize nitrogen-including fullerene. Thus, the world highest synthesis purity 0.5% can be obtained by optimizing conditions of the synthesis process.

Description

  The present invention relates to a production apparatus and production method for nitrogen-encapsulated fullerene in which nitrogen atoms are encapsulated in fullerene molecules.

The endohedral fullerene is a substance in which atoms are encapsulated in a hollow portion of a cage-like fullerene molecule, and has a unique property that differs greatly from an empty fullerene in terms of electronic structure and physical properties. Nitrogen-encapsulated fullerene is a substance represented by the chemical formula N @ C _n (n = 60, 70, 76, 78, 80, 82...), And the encapsulated nitrogen atom has a small interaction with the carbon cage. , Trapped isolated in the center of the fullerene cage. Therefore, the line width of the electron spin resonance (ESR) spectrum is narrow and the life of the aligned electron spin is long, and application to, for example, a quantum computer is expected.
It has been reported that nitrogen-encapsulated fullerenes can be synthesized by plasma methods such as ion beam method, glow discharge method, arc discharge method, radio frequency (RF) discharge method, electron cyclotron resonance (ECR) discharge method. The endohedral fullerene is obtained by generating a plasma composed of ions containing encapsulated atoms, reacting with the fullerene, obtaining a product containing the endohedral fullerene, and removing impurities by purification. According to the synthesis of nitrogen-encapsulated fullerene using a conventional production apparatus, the amount of impurities including empty fullerene is much larger than the amount of endohedral fullerene, and it is impossible to synthesize endohedral fullerene in high yield. there were.

Patent Document 1 discloses a production method for synthesizing nitrogen-encapsulated fullerene N @ C ₆₀ by sublimating fullerene C ₆₀ in a glow discharge under a nitrogen atmosphere. It is described that the ratio of the yield N @ C ₆₀ / C ₆₀ was 10 ⁶ to 10 ⁵ , that is, 10 ⁴ to 10 ³ %, when the ESR measurement of the collected deposit was performed. Including the case of the glow discharge method described in Patent Document 1, the yield of nitrogen-encapsulated fullerene synthesized by the conventional method for producing nitrogen-encapsulated fullerene is about 10 ⁴ to 10 ³ %. Therefore, in order to produce nitrogen-encapsulated fullerene at the development level or at the practical level, it has been desired to realize a method capable of synthesizing nitrogen-encapsulated fullerene with higher yield.
Patent Document 2 describes a method of synthesizing nitrogen-containing fullerene by reacting nitrogen atoms and fullerene molecules in high-frequency induction plasma. The manufacturing apparatus includes a fullerene molecule supply source 27 disposed in a plasma generation chamber 21 on a counter electrode including a plasma electrode 25 and a ground electrode 29 and a heating plate 30 provided between the counter electrodes and connected to a DC heat source 28. And a gas introduction tube 23 and a vacuum suction tube 22. Nitrogen gas is introduced from the gas introduction tube 23 into the reduced pressure plasma generation chamber 21, high frequency power is applied to the counter electrode to generate plasma, and react with the fullerene vaporized by heating. A deposit 26 is deposited. Paragraph 0066 states that “the yield was between 10 ^{4 and} 10 ³ , which was almost equal to or higher than the yield by ion implantation”. Since the yield of endohedral fullerene synthesized by the ion beam method in the presentations of conventional academic conferences and papers has been reported as low as 10 ⁴ to 10 ³ %, the unit of numerical values relating to the yield of Patent Document 2 Is also considered to be%. Even when the production method described in Patent Document 2 is used, there is a problem that only an amount of nitrogen-encapsulated fullerene that is insufficient for application as a functional material can be synthesized.
Non-Patent Document 1 describes an experimental apparatus that generates N @ C ₆₀ by colliding a cation (positive ion) generated by discharge of nitrogen molecules with C ₆₀ molecules. FIG. 10 is a cross-sectional view of the experimental apparatus disclosed in Non-Patent Document 1. By flowing nitrogen gas into the vacuum vessel and applying a high-frequency electric field to the water-cooled coil, ionized gas is generated, the generated cations are guided downstream through the aperture, and the cylindrical water-cooled electrode with a stainless steel mesh stretched around the inlet. Collected by applying -80V. At the same time, C ₆₀ powder inside a small electric furnace installed downstream of the cylindrical electrode was sublimated and deposited on the inner wall of the cylindrical electrode. The molecules are then bombarded by cations and nitrogen-encapsulated fullerenes are produced on the inner wall of the cylindrical electrode. However, even when the endohedral fullerene was synthesized using the production apparatus described in Non-Patent Document 1, there was a problem that a sufficiently high yield could not be obtained.

JP 2005-53748 A JP 2005-272159 A

Molecular Science Symposium 2008 Fukuoka, 1P038, Kinki University, Wakabayashi Tomonari, Kuroda Takayoshi R.F.Boivin and E.E.Scime, Plasma SourcesSci.Technol. 14 (2005) 238-292 K. Shiga, K. Ohno, T. Ohtsuki, and Y. Kawazoe, Materials Transactions, 42 (2001) 2189-2193.

  An object of this invention is to implement | achieve the manufacturing apparatus and manufacturing method which can synthesize | combine the nitrogen inclusion fullerene with a high yield.

In the present invention (1), nitrogen gas is introduced into a vacuum vessel, plasma including electrons is generated by a plasma generating means, and a bias voltage V _ep is applied to an end plate electrode disposed in the vacuum vessel. controls space potential of the plasma, accelerating the electrons by the potential of the grid electrode disposed in the vacuum container to apply a bias voltage V _g to the grid electrode so that the negative potential than the spatial potential of the plasma The electrons collide with nitrogen molecules in the nitrogen gas to generate nitrogen ions, and at the same time, fullerenes are heated to generate vapors composed of fullerene molecules, toward a deposition substrate disposed in the vacuum vessel. by injecting the steam, the potential of the deposition substrate is applied a bias voltage V _sub to the deposition substrate to be a negative potential than the space potential The nitrogen-encapsulated fullerene is produced by accelerating nitrogen ions and causing the nitrogen ions to collide with the fullerene molecules to generate nitrogen-encapsulated fullerene, wherein the pressure of the nitrogen gas is 15 Pa to 35 Pa, and the heating temperature of the fullerene Is a method for producing fullerene containing nitrogen, characterized in that the temperature is 700 ° C to 1000 ° C.
The present invention (2) is the method for producing a nitrogen-containing fullerene according to the invention (1), wherein the nitrogen ions are nitrogen molecular ions.
The present invention (3) is characterized in that the plasma generating means is a plasma generating means using high frequency induction, and the high frequency power applied for plasma generation is 100 to 700 W. It is a manufacturing method of the nitrogen inclusion fullerene of (2).
The present invention (4) is a method for producing nitrogen-encapsulated fullerene according to any one of the inventions (1) to (3), wherein the vapor comprising fullerene molecules is jetted toward the deposition substrate through a metal mesh. It is.
The present invention (5), the fullerene is the invention (1) to the production method of the nitrogen endohedral fullerenes of the invention (4), which is a C ₆₀ or C _70.
The present invention (6) is the production of a nitrogen-containing fullerene according to any one of the inventions (1) to (5), wherein the V _g is -200 to 0 V and the V _ep is -70 to +70 V Is the method.
The present invention (7) is the production of a nitrogen-containing fullerene according to any one of the inventions (1) to (6), wherein the V _sub is -200 to 0 V and the V _ep is -70 to +70 V Is the method.
The present invention (8) includes a vacuum vessel, nitrogen gas introduction means for introducing nitrogen gas into the vacuum vessel, plasma generation means for generating plasma containing electrons in the vacuum vessel, and the spatial potential of the plasma. Means for controlling, means for accelerating the electrons, means for colliding the accelerated electrons with nitrogen molecules in the nitrogen gas to generate nitrogen ions, and introducing vapor made of fullerene molecules into the vacuum vessel. Nitrogen comprising a sublimation oven, means for accelerating the nitrogen ions, means for colliding the accelerated nitrogen ions with the fullerene molecules to generate nitrogen-containing fullerenes, and a deposition substrate for depositing and collecting the nitrogen-containing fullerenes It is an endohedral fullerene production apparatus.
The present invention (9) is the nitrogen-encapsulated fullerene production apparatus according to the invention (8), wherein the plasma generating means is a plasma generating means using high-frequency induction.
The present invention (10) is the apparatus for producing nitrogen-encapsulated fullerene according to the invention (8) or the invention (9), wherein a metal mesh is arranged inside the sublimation oven.
The present invention (11) is characterized in that the means for controlling the space potential of the plasma is a grid electrode disposed in the plasma and capable of applying a bias voltage V _ep. It is a manufacturing apparatus of the nitrogen inclusion fullerene of invention (10).
The present invention (12), the means for accelerating said electrons is disposed between the deposition substrate the plasma generating means, the invention which is characterized in that an electrode of the bias voltage V _g and can be applied grid-like (8) It is a manufacturing apparatus of the nitrogen inclusion fullerene of the said invention (11).
According to the present invention (13), in the nitrogen-containing fullerene according to any one of the inventions (8) to (12), the means for accelerating the nitrogen ions is the deposition substrate to which a bias voltage V _sub can be applied. It is a manufacturing device.

According to the present invention (1) to (13), the end plate electrode 8 fixes the plasma space potential to a constant value, and a negative potential is applied to the grid electrode 7 to generate a high energy electron beam. It is possible to synthesize a large amount of nitrogen-encapsulated fullerene by generating nitrogen ions with high efficiency, reducing excited nitrogen radicals, accelerating nitrogen ions by applying a negative potential to the deposition substrate 8 and irradiating the fullerenes. become. Furthermore, the synthesis of nitrogen-encapsulated fullerene with the world's highest synthetic purity was realized by setting the gas pressure to about 25 Pa.
According to the present invention (4) and (10), synthesis of nitrogen-encapsulated fullerene having a synthesis purity of 0.5% was realized by inserting a high-density metal mesh into the oven and raising the temperature to 700 ° C. or higher.

(A) is sectional drawing of the manufacturing apparatus of the nitrogen inclusion fullerene which concerns on the Example of this invention. (B) is a figure for demonstrating the production | generation reaction of nitrogen inclusion fullerene. It is a figure which shows the potential structure of the deposition substrate vicinity in the manufacturing apparatus of nitrogen inclusion fullerene. (A) And (b) is a graph which shows the dependence with respect to the grid voltage and nitrogen gas pressure of the purity of nitrogen inclusion fullerene. It is a graph of the grid electric potential dependence of a plasma emission spectroscopy spectrum (OES) intensity | strength, the excitation of a nitrogen molecule, and the grid electric potential dependence of an ionization cross section. It is a table | surface of the reaction type in nitrogen plasma. It is a graph which shows the dependence with respect to the high frequency electric power and nitrogen gas pressure of the purity and solubility of nitrogen inclusion fullerene. It is a graph which shows the dependence with respect to the deposition substrate voltage and nitrogen gas pressure of the purity of nitrogen inclusion fullerene. It is a graph which shows the dependence with respect to the fullerene sublimation oven temperature of the purity of nitrogen inclusion fullerene. (A) is sectional drawing of a fullerene sublimation oven. (B) is a graph of the sublimation temperature dependence of the purity of nitrogen-encapsulated fullerene synthesized using the fullerene sublimation oven shown in FIG. It is sectional drawing of the manufacturing apparatus of the conventional nitrogen inclusion fullerene.

  The best mode of the present invention will be described below.

The inventors of the present application have conducted intensive studies for the purpose of highly efficient synthesis of nitrogen atom-encapsulated fullerene, and as a result of experiments, the following useful findings have been obtained.
First, an end plate electrode was provided in a position in contact with the plasma inside the production apparatus for nitrogen atom-encapsulating fullerene, so that the plasma space potential could be controlled, and the plasma space potential was fixed during the synthesis process. Next, a large amount of high-energy electrons are generated in the plasma by applying a negative voltage with respect to the plasma space potential to the grid electrode provided at the position where it is in contact with the plasma. As a result, a large amount of nitrogen positive ions are generated. Produced and reduced excited nitrogen radicals. Furthermore, high-efficiency synthesis of nitrogen-encapsulated fullerene was realized by applying a negative voltage relative to the plasma space potential to the deposition substrate and accelerating the nitrogen positive ions to collide with the fullerene. At that time, by increasing the nitrogen gas pressure, the synthesis purity and solubility of the nitrogen-encapsulated fullerene increased, and the yield increased overwhelmingly. These results are thought to be caused by an increase in the density of nitrogen molecular ions due to collision of high energy electrons with nitrogen gas. In addition, by controlling the fullerene oven temperature to increase the sublimation amount of fullerene by increasing the temperature to 700 ° C or higher, and providing a high-density metal mesh inside the fullerene sublimation oven, fullerene bumps are prevented, It was clarified that the synthesis purity of nitrogen-encapsulated fullerene can be increased by reducing the probability of sublimation in the state. Through the above control, we have succeeded in achieving the world's best nitrogen-containing fullerene synthesis purity of 0.5%.

(Nitrogen-containing fullerene production equipment)
Fig.1 (a) is sectional drawing of the manufacturing apparatus of the nitrogen inclusion fullerene which concerns on the Example of this invention. An apparatus for producing nitrogen-encapsulated fullerene according to an embodiment of the present invention is a production apparatus that synthesizes nitrogen-encapsulated fullerene by a reaction between nitrogen plasma generated by high frequency induction and sublimated fullerene molecules. The manufacturing apparatus shown in FIG. 1A includes, for example, a cylindrical vacuum vessel 1, a vacuum pump 4 connected to the vacuum vessel 1, a gas introduction pipe 5 for introducing nitrogen gas into the vacuum vessel 1, and a nitrogen gas. Between the induction plasma coil 6 for generating nitrogen plasma, a high frequency power source 10 and a matching box 9, a fullerene sublimation oven 3 for heating and sublimating fullerene, and a nitrogen plasma generation device and a fullerene sublimation oven 3. And a cylindrical deposition substrate 2 for depositing a product obtained by reacting sublimated fullerene molecules and nitrogen ions in the plasma, and a plasma generating apparatus and the deposition substrate 14 to arrange the energy of electrons in the plasma. A grid electrode 7 to be controlled, and an end plate disposed between the deposition substrate 2 and the fullerene sublimation oven 3 to control the space potential of the plasma. It consists of over gate electrode 8. The potentials of the grid electrode 7, the deposition substrate 2, and the end plate electrode 8 are controlled by a grid potential control power source 11, a deposition substrate potential control power source 12, and an end plate potential control power source 13, respectively. The upper part from the grid electrode in such a manufacturing apparatus is called a plasma generation region, and the lower part from the grid electrode is called a synthesis process region. The vacuum vessel 1 is, for example, a glass cylinder having a length of about 1 m and a diameter of about 10 cm.
The method for producing fullerene containing nitrogen according to the present invention is characterized by the apparatus structure in addition to the optimization of process conditions such as nitrogen gas pressure and fullerene oven temperature. An end plate electrode is disposed below the deposition substrate, and a control voltage is applied to fix the plasma space potential Φ _s . Further, a grid electrode is disposed between the plasma generation region and the deposition substrate, and a control voltage is applied so that the potential of the grid electrode is set to a negative potential with respect to the space potential. Thus, electrons are accelerated from the grid electrode toward the plasma, and nitrogen positive ions are generated by collision of the accelerated high-energy electrons and nitrogen molecules. A bias voltage is also applied to the deposition substrate so that the potential of the deposition substrate is more negative than the space potential. As a result, nitrogen positive ions are accelerated from the plasma toward the deposition substrate, and high energy nitrogen positive ions collide with fullerene molecules on or near the deposition substrate, thereby increasing the yield of encapsulated fullerene.
In the manufacturing apparatus shown in FIG. 1A, the lower end portion of the deposition substrate 2 is shown as a structure located below the position of the end plate electrode 8 or the fullerene sublimation oven 3, but the excellent effect according to the present invention is shown. In order to obtain the above, it is not always necessary to have such a structure. What is necessary is just to arrange | position the end plate electrode 8 in the position which contacts plasma. Further, the positional relationship between the fullerene sublimation oven and the deposition substrate may be arranged at a position where the fullerene sublimated from the oven can be efficiently recovered.
In the manufacturing apparatus according to the embodiment of the present invention shown in FIG. 1A, the vacuum container is a glass cylinder divided into an upper part and a lower part of the deposition substrate, and the deposition substrate is a metal cylinder. When collecting the deposit, the upper and lower glass cylinders and the deposition substrate are disassembled, the deposition substrate is removed, and the deposit is peeled off and collected. The conventional endohedral fullerene production apparatus shown in FIG. 9 has a structure in which a deposition substrate is inserted into a glass container. To cool the deposition substrate with water or to apply a bias voltage, FIG. The structure of the manufacturing apparatus according to the embodiment of the present invention shown in a) can be more easily implemented. The water cooling temperature is preferably about 5 ° C to 25 ° C.

(Method for producing nitrogen-encapsulated fullerene)
In the endohedral fullerene production apparatus shown in FIG. 1A, the inside of the vacuum vessel 1 is evacuated to a background vacuum of about 10 ³ Pa by a vacuum pump such as a diffusion pump. Nitrogen gas is introduced from the gas introduction pipe 5 and the N ₂ gas pressure is set to 1 to 100 Pa, for example. In the plasma generating apparatus, power of 100 to 700 W is supplied from the high frequency power supply 10 to the induction coil 6 at a frequency of 13.56 MHz to excite the N ₂ gas to generate nitrogen plasma consisting of N ⁺ ions, N ₂ ⁺ ions, and electrons. . Although not shown in FIG. 1A, a plasma state is observed using a Langmuir probe or the like. In a fullerene sublimation oven, a bowl-like fullerene is placed inside the oven, heated, and fullerene vapor is injected. The heating temperature is preferably 700 to 850 ° C. FIG. 1 (b) is a diagram for explaining a reaction for generating nitrogen-encapsulated fullerene. Fullerene molecules constituting the injected fullerene vapor adhere to the cylindrical deposition substrate and form a thin film. At that time, N ₂ ⁺ ions in the plasma collide with the fullerene molecule to form two N atoms or N ⁺ ions, and also have the effect of distorting the fullerene structure. The N atom or N ⁺ ion is inserted into the interior from between the six-membered rings in which the fullerene is distorted and widened to synthesize nitrogen-containing fullerene.
FIG. 2 is a diagram showing a potential structure in the vicinity of the deposition substrate in the apparatus for producing nitrogen-encapsulated fullerene. Applied voltage _{V g} of the grid electrode 7 is preferably controlled in the range of -200～0V. The applied voltage V _sub of the deposition substrate 2 is preferably controlled in the range of −200 to 0V. The applied voltage V _ep of the end plate 8 is preferably controlled in the range of −70 to 70V.
The space potential Φ _{s of the} plasma is controlled by the voltage V _ep of the end plate electrode. V _g is preferably a negative potential with _respect to V _ep . That is, it is preferable that V _g <V _ep . Electrons in the plasma generation region are accelerated from the grid electrode toward the plasma in the synthesis process region, collide with nitrogen molecules in the vacuum chamber 1, and nitrogen atom ions (N ⁺ ) or nitrogen molecule ions (N ₂ ⁺ ). Is produced with high efficiency. _Increasing V _g in the negative direction with respect to V _ep and increasing electron energy increases the probability of generating nitrogen molecular ions and reduces the generation of excited N ₂ radicals that generate harmful ultraviolet radiation. It is desirable to suppress ultraviolet rays because they polymerize fullerenes, lower the solubility, and deteriorate the yield.
Furthermore, V _sub is preferably negative with _respect to V _ep . That is, it is preferable that V _sub <V _ep . When V _ep is controlled in this way, the generated nitrogen positive ions are accelerated from the plasma toward the deposition substrate 2 and collide with the fullerene molecules sublimated from the fullerene sublimation oven 3, thereby generating nitrogen-encapsulated fullerene with high efficiency. . The nitrogen molecular ion collides with the fullerene to form two nitrogen atom ions, and then is encapsulated in the fullerene through the fullerene six-membered ring. Since the fullerene vapor comes out radially from the sublimation cylinder, it is deposited on the cylindrical deposition substrate. By fixing the plasma space potential with the end plate potential V _ep , the sheath electric field formed in the vicinity of the grid electrode and the deposition substrate can be controlled with high precision by V _g and V _sub, so that the synthesis reaction of nitrogen-encapsulated fullerene is high. It becomes possible to optimize with reproducibility.
Also, this time from the synthesis of N @ C ₆₀ was confirmed by using a manufacturing method according to the present invention, it goes without saying for the other larger fullerenes are possible synthesis of nitrogen containing fullerene.

(Differences from conventional nitrogen-containing fullerene production equipment)
The conventional nitrogen-encapsulated fullerene production apparatus shown in FIG. 9 differs from the production apparatus according to the present invention in that the substrate and the grid are integrated, and even if a bias voltage can be applied to the deposition substrate, the acceleration energy of electrons And the irradiation energy of nitrogen ions cannot be controlled independently. Since electrons cannot be accelerated, that is, there is no mechanism for generating an electron beam, in the ionization reaction of nitrogen, not only nitrogen ions but also nitrogen molecular radicals are generated in large quantities. For this reason, there is a problem that generation of nitrogen-encapsulated fullerene is difficult to occur due to ultraviolet rays emitted from nitrogen molecular radicals, and polymerization of fullerene occurs, both of which are factors that reduce the yield of nitrogen-encapsulated fullerene.
In contrast, in the manufacturing apparatus according to the present invention, the bias voltage can be applied to each of the grid electrode and the deposition substrate independently of the bias voltage for controlling and fixing the space potential of the plasma. Can be optimized for the generation of endohedral fullerenes.

(Purification of nitrogen-containing fullerene)
The deposit recovered from the deposition substrate contains impurities such as empty fullerene and heterofullerene in addition to the nitrogen-containing fullerene. The deposit is put in a solvent such as toluene and separated into one that is soluble in the solvent and one that is not soluble. Impurities such as heterofullerene do not dissolve in toluene and can be separated here. Empty fullerene and nitrogen-containing fullerene are dissolved in the solvent. By analyzing the sample dissolved in the solvent by ESR, the synthesis amount of nitrogen-encapsulated fullerene (N @ C ₆₀ (mol / l)) can be determined. Also, by measuring the UV / vis absorption spectrum, the amount of empty fullerenes and nitrogen endohedral fullerene _{(C 60 + N @ C 60} (mol / l)) can be measured. The purity (Purity) used in the specification of the present application is represented by purity = N @ C ₆₀ / (C ₆₀ + N @ C ₆₀ ) ≈N @ C ₆₀ / C ₆₀ . On the other hand, the yield (Yield) is expressed as Yield = Purity × Solubility, and represents the absolute amount of N @ C ₆₀ in the deposit containing the recovered impurities. Therefore, it is necessary to increase the solubility as well as the purity.
The high synthesis efficiency of the endohedral fullerene means that the endohedral fullerene can be synthesized with a high yield by using the production apparatus and production method according to the present invention.

(Fullerene)
As described above, fullerene as a raw material for the endohedral fullerene is a carbon compound having a chemical formula represented by C _n (n = 60, 70, 76, 78, 80, 82...). Among fullerenes, for example, it is preferable to produce N @ C ₆₀ or N @ C ₇₀ using typical C ₆₀ or C ₇₀ having a low material cost.

  EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

Example 1
(Dependence of endohedral fullerene purity on V _g and P _N2 )
FIG. 3A is a graph of V _g dependency of purity and solubility in the case of P _N2 = 5 Pa. Further, FIG. 3 _(b), in the case of P N2 = 25 Pa, a _{V g} dependence graph of purity and solubility. Synthesis of nitrogen-encapsulated fullerene is as follows: V _sub = −90 V, V _ep = + 30 V, P _RF = 500 W, T (synthesis time) = 60 min, T _ov (fullerene sublimation oven temperature) = 850 ° C., V _g = −120 to 0 V It went on condition of. The deposit formed on the deposition substrate was collected, and the endohedral fullerene was dissolved and extracted using toluene as a solvent, and the purity and solubility were evaluated. As a result, it was found that in both cases of P _N2 = 5 Pa and 25 Pa, the purity increases as V _g increases on the negative side, and decreases after reaching the peak value. When P _N2 = 5 Pa, the purity peak value is 0.024% when V _g = −40 V, and when P _N2 = 25 Pa, the purity peak value is 0.25% when V _g = −90 V. Met. From this, it was found that the peak value of the purity of the endohedral fullerene increases as the nitrogen gas pressure increases. The nitrogen gas pressure dependence of purity will be described in detail later with reference to FIG. For the V _g dependence, until a purity reaches a peak value, V _g is greater on the negative side, the purity increases as electron energy accelerated by V _g is high, negative further V _g after reaching a peak It was found that the purity decreased as the value increased to the side.
In addition, when V _g is increased to the negative side, the yield of the apparatus is further increased because the amount of excited nitrogen radicals is reduced and the solubility is increased.

(Dependence of plasma emission spectrum (OES) intensity on grid potential, excitation of nitrogen molecule and ionization cross section on grid potential)
FIG. 4 is a graph of the dependence of the plasma emission spectroscopy spectrum (OES) intensity on the grid potential, the excitation of nitrogen molecules, and the grid potential dependence of the ionization cross section. The graph on the upper left of FIG. 4 is a graph of the _Vg dependence of the plasma emission intensity. The synthesis conditions of the evaluated samples were V _sub = −90 V, P _N2 = 25 Pa, V _ep = + 30 V, P _RF = 500 W, T = 60 min, V _g = −120 to 0V. A circle represents a curve corresponding to the nitrogen molecular ion N ₂ ⁺ . The curve indicated by (1) is a curve corresponding to the nitrogen molecular radical N ₂ ^* . The graph on the lower left of FIG. 4 is a graph showing wavelengths corresponding to the corresponding ions and radicals. It can be seen that increasing V _g to the negative side increases ionized N ₂ ^{+ and} decreases non-ionized N ₂ ^* . The electron beam system, the nitrogen ions are generated efficiently, V _g by it can be seen that the amount of ions can be controlled. FIG. 5 is a table of reaction equations in nitrogen plasma described in Non-Patent Document 2. When electrons are collided with nitrogen molecules constituting nitrogen gas to generate nitrogen ions, when the electron energy is increased, the electron energy is 6.17 eV or more as shown in the formula (1). As shown in equation (5), nitrogen molecular ions are generated at 15.58 eV or more, and at 24.32 eV or more, nitrogen molecules are converted into nitrogen atoms as shown in equation (6). It can be seen that it dissociates and is further ionized. The graph on the right side of FIG. 4 is a graph disclosed in Non-Patent Document 2, and is data indicating changes in the probability that the reactions shown in (1) to (6) of FIG. 5 occur as the electron energy increases. When the electron energy increases, the generation of nitrogen molecular ions starts at 15.58 eV. When the electron energy increases, the amount of nitrogen molecular ions generated increases rapidly. However, when the electron energy is further increased, the increase in nitrogen molecular ions is slow. It turns out that it becomes. Therefore, in FIG. 3, it has a peak value purity when increasing V _g on the negative side, then a reason to decrease again, are involved in the generation of nitrogen molecular ions by electron collision, the nitrogen molecular ion density The increase in the probability of formation of nitrogen-encapsulated fullerenes increases the purity. On the other hand, the excited nitrogen radical is generated from 6.17 eV, and the generation probability increases up to about 15 eV, but the generation probability decreases conversely at larger electron energy. Therefore, large electron energy increases nitrogen ions and decreases excited nitrogen radicals, which is extremely convenient for high yield synthesis. The reason why the purity of the nitrogen-encapsulated fullerene increases as the nitrogen gas pressure increases is that when the gas pressure is increased, the density of nitrogen molecules in the vacuum vessel increases. As a result, the amount of nitrogen-encapsulated fullerene synthesized is increased.

(Dependence on the purity of the _{P N2} and _{P RF} of endohedral fullerenes)
FIG. 6 is a graph showing the dependence of the yield and solubility of nitrogen-containing fullerene on high-frequency power and nitrogen gas pressure. The synthesis conditions of the evaluated samples were V _g = −90 V, V _sub = −90 V, V _ep = + 30 V, and T = 60 min. As can be seen from the graph, the highest purity was obtained when P _RF = 500 W and P _N2 = 25 Pa, and a purity of 0.25% was obtained. When P _N2 is small, for example, when the 5Pa _{is P N2} is the remarkable increase in purity increases were _observed, when _{P N2} is large, for example, when _25Pa, increasing the _{P RF} It was found that the purity increased uniformly. _Further, when the P RF = 500 _W, the _{P N2} is _{P N2} than when the 5Pa is when 25Pa has been found to purity increases an order of magnitude. _Furthermore, it was found _{that P N2} purity decreases exceeds 25 Pa. This is because if P _N2 becomes too high, presumably because loss of energy nitrogen ions generated collides with the excess nitrogen molecules.
When the _PRF was 500 W or more, the plasma became unstable and the purity decreased, so it was found that an appropriate _PRF was necessary.
From the above results, as process parameters suitable for improving the purity of the nitrogen-encapsulated fullerene, P _N2 = 15 to 35 Pa, T _ov = 700 to 1000 ° C., and P _RF, V _g, V _sub, V _ep As described above, by setting P _RF = 100 to 700 W, V _g = −200 to 0 V, V _sub = −200 to 0 V, V _ep = −70 to +70 V, synthesis of nitrogen-encapsulated fullerene with high purity can be achieved. I knew it would be possible. Furthermore, the manufacturing conditions were narrowed down to P _N2 = 15 to 35 Pa, P _RF = 300 to 600 W, T _ov = 700 to 1000 ° C., V _g = −100 to −30 V, V _sub = −100 to −30 V, V _ep By setting = 0 to +50 V, it is possible to synthesize higher-purity nitrogen-encapsulated fullerenes, and by using the process conditions in such a range, it is possible to synthesize nitrogen-encapsulated fullerenes having a purity of 0.1% or more. I understood it.

(Dependence of endohedral fullerene purity on V _sub and PN ₂ )
FIG. 7 is a graph showing the dependence of the yield of nitrogen-containing fullerene on the deposition substrate voltage and nitrogen gas pressure. The synthesis conditions of the evaluated samples were V _g = −90 V, P _RF = 500 W, V _ep = + 30 V, and T = 60 min. As can be seen from the graph, the highest purity was obtained when V _sub = −90 V and P _N2 = 25 Pa, and a purity of 0.25% was obtained. When V _sub is also increased on the negative side, the energy for accelerating nitrogen molecular ions is increased, so that the purity of the endohedral fullerene is increased. This is probably because the nitrogen molecular ion collides with the fullerene to become a nitrogen atom and a nitrogen atom ion, and the energy for expanding the fullerene six-membered ring becomes sufficiently large. However, if V _sub becomes too large on the negative side, the purity tends to decrease. If the acceleration energy is too large, the collision with the fullerene may lead to penetration or destruction of the fullerene molecule, thus increasing the probability that it cannot be obtained as nitrogen fullerene. The optimum energy of ions for generating nitrogen-containing fullerenes by collision of nitrogen molecular ions and fullerene molecules is predicted by simulation (Non-Patent Document 3), and is said to be about 80 eV. The optimum substrate potential in data shown in FIG. 7 is a -90V when P _N2 is 25 Pa, as measured plasma space potential has become about 50 V, although the nitrogen ions are obtained acceleration energy of 140 eV, In the case of such a gas pressure, it is considered that nitrogen ions collide with neutral nitrogen molecules to lose energy, and when colliding with fullerene, the acceleration energy is reduced to about 80 eV. This is because, for example, when the gas pressure is as low as 5 Pa, it is considered that the accelerated nitrogen ions collide with the fullerene with almost no collision with the nitrogen molecules, and the purity is maximized when the V _sub is −30V. Thus, the difference from the space potential of 50V becomes 80V, and the nitrogen ions are accelerated to 80eV, which shows that the simulation results are in good agreement. Therefore, in order to obtain nitrogen-containing fullerene with high purity, it is necessary to appropriately control V _sub according to the value of nitrogen gas pressure.

(Dependence of endohedral fullerene purity on oven temperature)
FIG. 8 is a graph showing the dependence of the purity of nitrogen-containing fullerene on the fullerene sublimation oven temperature T _ov . Conventionally, since fullerene starts sublimation from about 400 ° C., an apparatus for sublimating fullerene conventionally heats fullerene at a temperature of 550 ° C. to 600 ° C. However, when the synthesis was carried out at a sublimation temperature of fullerene of 700 ° C. or higher, the synthesis purity increased rapidly. In the graph of FIG. 8, it can be seen that ● indicates the synthetic purity, but the synthetic purity increases by an order of magnitude when the oven temperature is 700 ° C. or higher. (2) is the sublimation speed, and it can be seen that fullerene is sufficiently sublimated even at 600 ° C., for example. While the sublimation amount is not doubled compared to 600 ° C. and 850 ° C., the synthetic purity is rapidly increasing from 700 ° C. as a boundary. From this, for the synthesis of nitrogen-encapsulated fullerene, it has been found for the first time that the temperature of the fullerene sublimation oven needs to be 700 ° C. or higher. The reason is not clearly understood yet, but at less than 700 ° C, fullerene sublimes, but sublimates in a cluster form, and even when nitrogen ions collide, ions collide only with the outer fullerene molecules. Therefore, the synthesis purity is low, and at 700 ° C. or higher, it is presumed that endohedral fullerenes are likely to be formed due to separation and sublimation of fullerene molecules.

(Improvement of fullerene purity with nitrogen by improving fullerene sublimation oven)
In FIG. 8, the synthetic purity increases uniformly up to 850 ° C., but when the temperature is further increased and the temperature is in the range of 850 ° C. to 1000 ° C., the amount of fullerene sublimation increases so much that nitrogen ions are included. Therefore, it is expected that the purity of the fullerene that accumulates without increasing will become too low. This is because in the temperature range of this range, fullerenes are ejected as cluster-like molecules in which fullerene molecules are bonded to each other due to bumping. Even when nitrogen ions collide with the cluster-like fullerene molecule, the inclusion fullerene is limited to a part of the fullerene molecule on the cluster surface, and the purity of the inclusion fullerene is lowered. Therefore, in order to prevent the fullerene from sublimating in a cluster state, a synthesis experiment of nitrogen-encapsulated fullerene using a fullerene sublimation oven shown in FIG. As shown in FIG. 9A, the sublimation oven has a high-density metal mesh placed inside the fullerene, and the fullerene passes through the high-density metal mesh and sublimates, and is ejected into the vacuum vessel. It has become. Since bumping is suppressed by the high-density metal mesh and the mesh is at a high temperature, the cluster-like fullerene is decomposed into smaller clusters and molecules, so that the synthesis purity of the nitrogen-encapsulated fullerene is improved.
As the material of the metal mesh, it is preferable to use a metal material having high thermal conductivity. For example, it is preferable to use copper. The mesh size is preferably 40 to 200 mesh / cm, for example. Since the temperature of the metal mesh is in the oven, the temperature is the same as that in the oven during the synthesis process of the endohedral fullerene.
FIG. 9B is a graph of the synthesis purity of nitrogen-encapsulated fullerene when synthesis of nitrogen-encapsulated fullerene is performed using a fullerene sublimation oven equipped with a high-density mesh at a sublimation temperature of 700 to 1000 ° C. It can be seen that the higher the temperature, the higher the purity and the synthetic purity is 0.5% or more. This is an order of magnitude greater value for the synthesis purity of the nitrogen-encapsulated fullerene than the synthesis purity by the conventional method. It was found that by using a high-density metal mesh, even if the sublimation temperature exceeds 850 ° C., the synthesis purity of the nitrogen-encapsulated fullerene can be improved by suppressing the sublimation of the cluster fullerene without causing fullerene boiling.

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Deposition substrate 3 Fullerene sublimation oven 4 Vacuum pump 5 Gas introduction pipe 6 Inductive coil 7 Grid electrode 8 End plate electrode 9 Matching box 10 High frequency power source 11 Grid potential control power source 12 Deposition substrate potential control power source 13 End plate potential control power source 14 Deposition substrate 15 Fullerene sublimation oven 21 Plasma generation chamber 22 Vacuum suction tube 23 Gas introduction tube 24 High frequency plasma power supply 25 Plasma electrode 26 Deposit 27 Fullerene molecule supply source 28 DC heat source 29 Ground electrode 30 Heating plate

Claims (13)

Nitrogen gas is introduced into the vacuum container, plasma including electrons is generated by the plasma generation means, and the bias voltage V _ep is applied to the end plate electrode disposed in the vacuum container to control the space potential of the plasma. the accelerating the electrons by the potential of the grid electrode arranged in a vacuum container to apply a bias voltage V _g to the grid electrode so that the negative potential than space potential of the plasma, the nitrogen the electronic Colliding with nitrogen molecules in the gas to generate nitrogen ions, and at the same time, generating fullerene vapor by generating fullerene molecule vapor, spraying the vapor toward the deposition substrate disposed in the vacuum vessel, the deposition substrate so that the potential of the deposition substrate has a negative potential than the space potential the nitrogen ions by applying a bias voltage V _sub A method for producing a nitrogen-encapsulated fullerene in which the nitrogen ions collide with the fullerene molecules to produce a nitrogen-encapsulated fullerene, wherein the pressure of the nitrogen gas is 15 Pa to 35 Pa, and the heating temperature of the fullerene is 700 ° C. to The manufacturing method of the nitrogen inclusion fullerene characterized by being 1000 degreeC. 2. The method for producing nitrogen-encapsulated fullerene according to claim 1, wherein the nitrogen ions are nitrogen molecular ions. 3. The nitrogen-containing fullerene according to claim 1, wherein the plasma generation means is a plasma generation means using high-frequency induction, and the high-frequency power applied for plasma generation is 100 to 700 W. Manufacturing method. 4. The method for producing nitrogen-encapsulated fullerene according to claim 1, wherein the vapor made of fullerene molecules is sprayed toward the deposition substrate through a metal mesh. 5. Claims 1 to 4 any one nitrogen containing preparation method of fullerene according to, wherein the fullerene is a C ₆₀ or C _70. 6. The method for producing fullerene containing nitrogen according to claim 1, wherein the V _g is −200 to 0 V and the V _ep is −70 to +70 V. 6. 7. The method for producing nitrogen-encapsulated fullerene according to claim 1, wherein the V _sub is −200 to 0 V and the V _ep is −70 to +70 V. 8. A vacuum vessel; nitrogen gas introduction means for introducing nitrogen gas into the vacuum vessel; plasma generation means for generating plasma containing electrons in the vacuum vessel; means for controlling the space potential of the plasma; A means for colliding the accelerated electrons with nitrogen molecules in the nitrogen gas to generate nitrogen ions, a sublimation oven for introducing a vapor made of fullerene molecules into the vacuum vessel, and the nitrogen ions A device for producing nitrogen-encapsulated fullerene, comprising: means for accelerating the nitrogen; means for generating nitrogen-encapsulated fullerene by colliding the accelerated nitrogen ions with the fullerene molecules; and a deposition substrate for depositing and collecting the nitrogen-encapsulated fullerene. 9. The apparatus for producing nitrogen-containing fullerene according to claim 8, wherein the plasma generating means is a plasma generating means using high frequency induction. The apparatus for producing fullerene containing nitrogen according to any one of claims 8 and 9, wherein a metal mesh is arranged inside the sublimation oven. 11. The nitrogen inclusion according to claim 8, wherein the means for controlling the space potential of the plasma is a grid electrode disposed in the plasma and capable of applying a bias voltage V _ep. Fullerene production equipment. Means for accelerating said electrons is disposed between the deposition substrate the plasma generation means, any one of claims 8 to 11, characterized in that an electrode of the bias voltage V _g and can be applied grid-like 1 The manufacturing apparatus of the nitrogen inclusion fullerene of Claim. 13. The apparatus for producing nitrogen-encapsulated fullerene according to claim 8, wherein the means for accelerating the nitrogen ions is the deposition substrate to which a bias voltage V _sub can be applied.

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