JP2013157303A - Plasma generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma generation device capable of efficiently generating plasma by taking an electromagnetic wave out of a space irradiated with the electromagnetic wave and generating the plasma by supplying the taken-out electromagnetic wave to a reaction vessel.SOLUTION: A plasma generation device comprises a closed space 6 irradiated with an electromagnetic wave, an antenna 4 having one end 7 inserted into the closed space 6 and the other end 8 provided outside the closed space 6, a reaction vessel 3 placed outside the closed space 6 while a tip 9 of the other end of the antenna 4 is put inside the reaction vessel, and impedance adjusting means 15 which is present to match impedance in the closed space 6, the antenna 4 receiving an electromagnetic wave of a stationary wave at the one end 7 and generating plasma at the tip 9 of the other end 8.

Description

  The present invention relates to a plasma generating apparatus that receives standing electromagnetic waves and efficiently generates air or liquid plasma.

  Conventionally, vapor deposition technology using vapor phase plasma has been widely used as a deposition technology using plasma. The submerged plasma generator and submerged plasma generating method described in Patent Document 1 can generate high-energy plasma in a liquid with a simple apparatus and method. Or it is applied as a decomposition furnace of a harmful substance, and applying a microwave oven is indicated.

  Japanese Patent No. 3769625

  However, since the conventional in-liquid plasma generator has a structure that generates plasma in a space where electromagnetic waves are irradiated, the electromagnetic wave is absorbed by a conductive substance existing in the space, and the temperature of the substance increases. However, there is a problem that electromagnetic energy is consumed and plasma cannot be generated efficiently.

  Therefore, the present inventors take out the 2.45 GHz electromagnetic wave generated in the general-purpose microwave oven to the outside, and supplies the extracted electromagnetic wave to the reactor (reaction vessel) to generate the plasma, thereby efficiently generating the plasma. The following first experiment was attempted with the idea of being able to make it possible.

  FIG. 1 is a schematic view of a plasma generator, and a microwave oven (electromagnetic wave generation container) is used. This apparatus 1 is configured to connect a microwave oven 2 and a reactor (reaction vessel) 3 via an electromagnetic wave receiving / transmitting electrode (antenna) 4 composed of an electromagnetic wave receiving side electrode (one end) and an electromagnetic wave transmitting side electrode (the other end). It has a combined structure.

  The electromagnetic wave (2.45 GHz) transmitted from the magnetron (electromagnetic wave generating means) 5 installed in the microwave oven 2 enters the cooking chamber (closed space) 6 in the microwave oven 2 and is reflected on the cooking chamber wall for cooking. Accumulate in chamber 6. If the impedance seen from the receiving side electrode 7 of the electromagnetic wave receiving / transmitting electrode 4 inserted from the upper part of the microwave oven 2 is equal to the impedance of the microwave cooking chamber 6, the transmission of the electromagnetic wave receiving / transmitting electrode 4 is performed. An electromagnetic wave is transmitted into the reactor 3 through the side electrode 8. The electromagnetic wave (microwave) transmitted into the reactor 3 has the highest intensity at the tip 9 of the transmission electrode 8 and plasma is generated at the tip 9. When the medium contained in the reactor 3 is gas, air plasma is generated, and when it is liquid, liquid plasma is generated. If impedance matching is correctly performed, all electromagnetic waves generated in the microwave oven 2 are consumed for maintaining the plasma. Since the electromagnetic wave output of the general-purpose microwave oven is about 800 W at maximum, plasma of up to 800 W can be generated, and the electromagnetic wave output of the microwave oven is adjusted by controlling the high voltage (about 0 to 2 kV) applied to the magnetron 5. Can do.

  Specifically, the in-liquid plasma generator shown in FIG. 2 was used. As shown in FIG. 2, a solution in which methanol and ethanol are mixed at 95: 5 is put into the reactor 3, and the inside of the reactor 3 is evacuated by the aspirator 10, and when plasma is generated, it is mixed with air so as not to burn and explode. Secured safety. This mixed solution is usually a solution used for diamond formation in the in-liquid plasma CVD method.

  In the first experiment, the magnetron high voltage of the microwave oven 2 was adjusted to generate 800 W (full power) and 300 W electromagnetic waves. While keeping the pressure and temperature of the mixed solution as equal as possible, the length of the receiving electrode 7 was changed to examine how many seconds the in-liquid plasma was generated.

  It is known that plasma in liquid is generated when vapor bubbles are generated by induction heating of the electrode 9 at the tip 9 of the transmission-side electrode 8. If the length of the reception side electrode 7 is appropriate, impedance matching is performed and a large amount of power is introduced to the transmission side electrode tip 9 positioned in the reactor 3, so that the tip temperature rises in a short time and the steam bubbles Will occur. Therefore, impedance matching can be measured by the time required for plasma generation. The experimental results are shown in Tables 1, 2 and 3. FIG. 3 is a graph showing the time until plasma is generated when an electromagnetic length of 300 W is generated with the electrode length as the X axis and the plasma generation time as the Y axis.

  In the table, “x” indicates that plasma was not generated within 30 seconds, and “electrode length” is the sum of the length of the reception side electrode 7 and the length of the transmission side electrode 8. 4 lengths.

  In-liquid plasma was generated at electrode lengths of 80 to 85 mm, 132 to 153 mm, and 220 to 244 mm. Since the wavelength of the electromagnetic wave (2.45 GHz) generated in the microwave oven is about 122 mm, it can be seen that the interval of the length at which the plasma in liquid can be generated is about a half wavelength. However, it does not seem to be exactly half a wavelength. This is due to the effect of impedance matching. In this experiment, the strongest plasma was generated when the length of the antenna 4 was 220 mm or longer. It was confirmed that powerful plasma was generated outside the electromagnetic wave irradiation space. In addition, although the mixed solution in this experiment was put into the plasma generator disclosed in Patent Document 1 to try to generate plasma, only the temperature of the solution increased and no plasma was generated.

  Subsequently, the present inventors further attempted the following second experiment in order to stably generate plasma that can be heated to a temperature at which diamond can be formed.

  In order to generate plasma stably, it is necessary to match the impedance in the coaxial circuit constituting the electromagnetic wave receiving / transmitting electrode 4 with the impedance in the microwave oven 2 and to convert the microwave (electromagnetic wave) coaxially well. Therefore, as shown in FIG. 4, the magnetron 5 of the microwave oven 2 is replaced with the antenna probe 11, and the impedance measuring device 12 in which the antenna probe 11 attached instead of the magnetron 5 and the network analyzer 13 are connected by the coaxial cable 14 is manufactured. Then, the electrode length was changed in the same manner as the lengths shown in Table 1, Table 2, and Table 3, and the reflection of the microwave of the entire device 12 was measured. The result is shown in FIG. 5 in which the graph of the reflection coefficient is superimposed on the plasma generation graph of FIG. In FIG. 5, the numerical value on the right X-axis is the reflection coefficient.

  FIG. 5 shows that the length of the electromagnetic wave reception / transmission electrode 4 in which the plasma is generated is independent of impedance matching, and the length of the electromagnetic wave reception / transmission electrode 4 in which the plasma is generated is used. The idea was that plasma could be generated stably if the impedance was adjusted by another mechanism.

  Therefore, from the bottom of the microwave oven 2 to which the reactor 3 is attached, three copper bars (impedance adjusting bars) 16 are inserted as a mechanism (impedance adjusting means) 15 for adjusting the impedance, and the copper bars 16 are attached. A third experiment was conducted in which the impedance inside the microwave oven 2 was adjusted by moving it back and forth. FIG. 6 is an explanatory diagram of a mechanism for adjusting impedance (hereinafter referred to as “impedance adjusting mechanism”).

  Using the plasma generator 17 provided with the impedance adjusting mechanism 15 shown in FIG. 6, the diamond was tried to be generated in the same manner as in the first experiment.

  First, as shown in FIG. 7, the impedance adjusting mechanism 15 (see FIG. 6) is attached to the microwave oven 2 of the impedance measuring device 12 (see FIG. 4), and the copper rod 16 is moved forward and backward to match the impedance in the present device 12. I let you. At that time, since plasma in liquid is generated in bubbles generated in the liquid, impedance to be matched must be in a state where bubbles are generated at the tip 9 of the electromagnetic wave reception / transmission electrode 4. Matching was performed while the inside of 3 was filled with the vapor of the solution. Moreover, the attachment position of the copper rod 16 of the plasma generator 17 shown in FIG. 6 and the attachment position of the copper rod 16 of the impedance measuring device 12 shown in FIG. 7 are the same positions.

  Next, the three copper rods 16 in the impedance matching state are attached to the same attachment position of the plasma generator 17 shown in FIG. 6 while maintaining the position of the copper rod 16 in the cooking chamber 6, and the impedance measuring device 12. The reactor 3 attached to was moved to the plasma generator 17, the reactor 3 was filled with the mixed solution, and the microwave oven 2 was turned on.

  As a result, plasma was stably generated and the temperature of the substrate could be raised. It was possible to generate diamond by adjusting the voltage applied to the microwave oven 2 to adjust the temperature of the substrate. The diamond on the substrate was confirmed as shown in FIGS. 8, 9, and 10, and the diamond was confirmed as shown in FIGS. 11 and 12. The substrate temperature was 650 ° C.

  Based on the results of the first experiment, the present invention achieves the technical problem by introducing electromagnetic waves from the space where the electromagnetic waves are irradiated to the outside and generating plasma outside the spaces.

  Further, based on the second experiment and the third experiment, the present invention further adjusts the impedance in the space where the electromagnetic wave is radiated, and guides a standing-wave microwave (electromagnetic wave) to the outside. The above technical problem has been achieved by generating plasma.

  The technical problem can be solved by the present invention as follows.

  That is, a plasma generator according to the present invention includes a closed space that radiates electromagnetic waves, an antenna having one end inserted into the closed space and the other end provided outside the closed space, and the other end of the antenna. It comprises a reaction vessel disposed outside the enclosed space with an end at the end, receiving electromagnetic waves at one end of the antenna and generating plasma at the end at the other end. .

  The plasma generator according to the present invention includes a closed space that radiates electromagnetic waves, an antenna having one end inserted into the closed space and the other end provided outside the closed space, and the other of the antennas. A reaction vessel disposed outside the closed space with an end tip provided therein, and impedance adjusting means for matching the impedance in the closed space when present, and at one end of the antenna It receives electromagnetic waves and generates plasma at the tip of the other end.

  Further, according to the present invention, in the plasma generator provided with the impedance adjusting means, the impedance adjusting means is made of a copper rod.

  Furthermore, according to the present invention, in any one of the above plasma generators, a closed space in which electromagnetic waves are irradiated is a cooking chamber of a microwave oven.

  According to the present invention, one end of an antenna that receives electromagnetic waves is positioned in a closed space irradiated with electromagnetic waves, the other end is positioned outside the closed space, and electromagnetic waves are received at one end, and the other ends. Since the plasma is generated at the tip of the electrode, it is not affected by the electromagnetic wave irradiated on the other end side, so that the electromagnetic wave can be efficiently consumed for generating the plasma.

  In addition, since the impedance adjusting means for adjusting and matching the impedance in the closed space where the electromagnetic wave is irradiated due to the presence thereof is positioned in the space, the standing wave electromagnetic wave is transmitted to the tip where the plasma is generated. Therefore, electromagnetic waves can be consumed for generating plasma efficiently, and plasma can be generated in a high temperature state. Therefore, for example, diamond can be generated efficiently.

  It is the schematic explaining the plasma generator which concerns on this invention.   It is explanatory drawing of the plasma generator which concerns on this invention.   It is a graph showing time until plasma is generated.   It is explanatory drawing of an impedance measuring device.   It is a graph showing a reflection coefficient.   It is explanatory drawing of the plasma generator which concerns on this invention.   It is explanatory drawing of an impedance measuring device.   2 is a scanning electron micrograph of a diamond film formed on a substrate.   It is a scanning electron microscope enlarged photograph of the diamond film position 1 shown in FIG.   It is a scanning electron microscope enlarged photograph of the diamond film position 2 shown in FIG.   It is a laser Raman spectroscopy analysis graph of the diamond film | membrane position shown in FIG.   It is a laser Raman spectroscopy analysis graph of the diamond film | membrane position shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.

  A plasma generator 1 shown in FIG. 1 includes an electromagnetic wave generation container (general-purpose microwave oven) 2 having a closed space (a microwave cooking chamber) 6 to which an electromagnetic wave is irradiated, and an electromagnetic wave generating means (magnetron) 5 that radiates the electromagnetic wave. An antenna (electromagnetic wave reception / transmission) composed of one end (electromagnetic wave reception side electrode) 7 that receives electromagnetic waves and the other end (electromagnetic wave transmission side electrode) 8 that transmits electromagnetic waves and generates plasma from the tip 9. Electrode) 4, one end 7 is inserted into the closed space 6, and the other end 8 protrudes outside the microwave oven 2 to generate various substances by generating plasma. ) Positioned within 3.

  The plasma generator 1 has a structure in which the microwave oven 2 and the reactor 3 are coupled via an antenna 4 having one end portion 7 and the other end portion 8, and electromagnetic waves (microwaves) flying in a closed space 6. ) Is received by the one end 7 of the antenna 4, the received electromagnetic wave (microwave) passes through the other end 8 and plasma is generated from the tip 9 of the other end 8.

  The electromagnetic wave transmitted from the magnetron 5 installed in the microwave oven 2 enters the cooking chamber 6 of the microwave oven 2, reflects off the wall of the cooking chamber 6 and accumulates in the cooking chamber 6. The inside of the cooking chamber 6 is adjusted so that the impedance viewed from one end 7 which is the receiving side electrode of the antenna 4 inserted in the cooking chamber 6 is matched with the impedance of the cooking chamber 6, and the reflected wave of the electromagnetic wave is generated. Since the fine adjustment is performed to minimize the electromagnetic wave, the electromagnetic wave is transmitted into the reactor 3 through the other end 8 serving as the transmission side electrode. The electromagnetic wave transmitted into the reactor 3 has the highest intensity at the tip 9 of the other end 8 and plasma is generated at the tip 9.

  The medium contained in the reactor 3 may be gas or liquid. In the case of gas, air plasma is generated, and in the case of liquid, liquid plasma is generated. Further, the closed space may be a space that is sealed by being closed, or may be a space that is in a sealed state.

  In the present embodiment, since the electrode tip where plasma is generated is positioned outside the closed space where the electromagnetic wave is irradiated, plasma can be generated efficiently. Moreover, since the impedance is adjusted and matched in the closed space, the electromagnetic wave generated in the microwave oven can be consumed for maintaining the plasma.

  Next, examples in the present embodiment will be described.

Examples 1-25:
As shown in FIG. 2, when plasma is generated when methanol and ethanol are mixed at a ratio of 95: 5 and a solution used for diamond formation in a submerged plasma CVD method is put into the reactor 3, and the inside of the reactor 3 is evacuated by the aspirator 10. The safety was ensured so that it would not explode when mixed with air.

  Next, the magnetron high voltage of the microwave oven 2 was adjusted, and electromagnetic waves of 800 W (full power) and 300 W were generated. While keeping the pressure and temperature of the solution as equal as possible, the length of the electromagnetic wave receiving electrode 7 inserted into the cooking chamber 6 was changed to examine how many seconds the plasma in the liquid was generated. The results are shown in Table 4.

  In the table, “electrode length” represents the total length of the electromagnetic wave reception side electrode 7 and the electromagnetic wave transmission side electrode 8, that is, the length of the antenna 4. Regardless of the length of the electrode, the position of the tip 9 of the electromagnetic wave transmission side electrode 8 in the reactor 3 remains unchanged.

  The in-liquid plasma is generated when vapor bubbles are generated at the tip 9 of the electromagnetic wave transmission side electrode 8 due to induction heating of the electrode. If the length of the electromagnetic wave reception side electrode 7 is appropriate, impedance matching is performed and a large amount of electric power is introduced into the distal end 9 of the electromagnetic wave transmission side electrode 8 installed in the reactor 3, so that the tip temperature of the electrode can be increased in a short time. As it rises and vapor bubbles are generated, impedance matching can be measured in the time required for plasma generation.

  In this example, in-liquid plasma was generated at lengths of 80 to 85 mm, 132 to 153 mm, and 220 to 244 mm. When the electrode length was 220 mm or more, the impedance was adjusted, and the strongest plasma was generated.

Embodiment 2. FIG.

  As shown in FIG. 6, the plasma generator 17 according to the present embodiment includes a closed space 6 that is irradiated with electromagnetic waves, a magnetron 5 that radiates electromagnetic waves, and one end that is positioned in the closed space 6 and receives electromagnetic waves. The antenna 4 is composed of a part 7 and the other end 8 positioned outside the closed space 6 for transmitting electromagnetic waves and generating plasma from the tip 9, and the antenna 4 disposed outside the closed space 6. The reaction vessel 3 is provided with the other end tip 9 and the impedance adjusting means 15 that is provided in the closed space 6 to match the impedance in the closed space 6.

  Next, a method for making the impedance in the closed space 6 match by being present will be described.

  As shown in FIG. 7, a plasma generator 17 having the same configuration as in FIG. 6 is prepared, the magnetron 5 is replaced with the antenna probe 11, and the antenna probe 11 and the network analyzer 13 attached instead of the magnetron 5 are connected by the coaxial cable 14. The impedance measuring device 12 was connected. The reaction vessel 3 and the impedance adjusting means 15 with the antenna 4 attached thereto were removed from the plasma generator 17 and attached to the impedance measuring device 12.

  Subsequently, the impedance adjusting rod 14 of the impedance adjusting means 15 is moved back and forth in the closed space 6 to match the impedance in the impedance measuring device 12.

  Next, the impedance adjusting means 15 in a state where the impedance is matched and the reactor 3 with the antenna 4 attached to the impedance measuring device 12 are moved to the plasma generating device 17.

  Thereby, the impedance is matched in the plasma generator 17 shown in FIG. 6 due to the presence of the impedance adjusting means 15.

  Next, examples in the present embodiment will be described.

Example 26:
In-liquid plasma was generated using the in-liquid plasma apparatus 17 to generate diamond.

  First, as shown in FIG. 7, impedance adjusting means 15 (see FIG. 6) is attached to the microwave oven 2 of the impedance measuring device 12, and the three copper rods 16 are moved forward and backward to match the impedance in the device 12. . At that time, the impedance was matched while the reactor 3 was filled with the vapor of the solution.

  Next, the three copper rods 16 in the impedance matching state are attached to the same attachment position of the plasma generator 17 shown in FIG. 6 while maintaining the position of the copper rod 16 in the cooking chamber 6, and the impedance measuring device 12. The reactor 3 attached to was moved to the plasma generator 17, the reactor 3 was filled with a solution in which methanol and ethanol were mixed at 95: 5, and the microwave oven 2 was turned on.

  Plasma was stably generated, the temperature of the substrate rose to 650 ° C., and diamond could be generated as shown in FIGS. 8, 9 and 10, 11 and 12.

  According to the present invention, electromagnetic waves can be efficiently consumed for generating plasma, and plasma can be generated at a high temperature, so that diamond can be generated efficiently. Furthermore, since a microwave oven can be applied, an inexpensive apparatus with a simple structure can be provided.

1, 17 Plasma generator 2 Microwave oven (electromagnetic wave generation container)
3 Reactor (reaction vessel)
4 Antenna (electromagnetic wave reception / transmission electrode)
5 Magnetron (electromagnetic wave generation means)
6 closed space (microwave cooking room)
7 Electromagnetic wave receiving electrode (one end)
8 Electromagnetic wave transmission side electrode (the other end)
9 Tip 10 Aspirator 11 Antenna probe 12 Impedance measuring device 13 Network analyzer 14 Coaxial cable 15 Impedance adjusting means 16 Impedance adjusting rod (copper rod)

Claims (4)

  A closed space for irradiating electromagnetic waves; an antenna having one end inserted into the closed space and the other end provided outside the closed space; and the closed space including the tip of the other end of the antenna. A plasma generating apparatus comprising: a reaction vessel disposed outside the antenna; and receiving electromagnetic waves at one end of the antenna to generate plasma at the tip of the other end.   A closed space for irradiating electromagnetic waves; an antenna having one end inserted into the closed space and the other end provided outside the closed space; and the closed space including the tip of the other end of the antenna. And an impedance adjusting means for matching the impedance in the enclosed space by being present, and receiving a standing wave electromagnetic wave at one end of the antenna to receive the tip of the other end A plasma generator characterized by generating plasma in   The plasma generator according to claim 2, wherein the impedance adjusting means is made of a copper rod.   The plasma generator according to any one of claims 1 to 3, wherein the closed space for irradiating electromagnetic waves is a cooking chamber of a microwave oven.

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