JP5016976B2 - Method for producing fine particle film - Google Patents

Description

  The present invention relates to a method for producing a fine particle film using a coaxial vacuum arc deposition source.

  Cobalt particles have attracted attention as carbon nanotube base films (catalyst layers) and catalytic metal carriers for fuel cells, and platinum nanoparticles have attracted attention as nanoparticle catalysts for solid polymer fuel cells and methanol fuel cells. In recent years, for example, as described in Patent Document 1, attempts have been made to form cobalt nanoparticles and platinum nanoparticles on a collecting plate using a coaxial vacuum arc deposition source.

  A coaxial vacuum arc deposition source includes a cylindrical anode electrode, a cathode electrode having a deposition material disposed in the anode electrode, a trigger electrode disposed in the anode electrode apart from the cathode electrode, and an anode electrode And a cathode voltage electrode, and a capacitor connected in parallel to the DC voltage source. The opening of the anode electrode and the substrate as the collection plate are installed inside the vacuum chamber. When a trigger discharge is generated between the trigger electrode and the cathode electrode, an arc discharge is induced between the deposition material of the cathode electrode and the anode electrode. At this time, fine particles of the vapor deposition material are released into the vacuum chamber, and when the fine particles reach the substrate surface, a film or layer (hereinafter also simply referred to as “fine particle film”) made of the fine particles is formed on the substrate. .

  In the coaxial vacuum arc deposition source, the arc discharge is generated in a pulse manner between the anode electrode and the cathode electrode by periodically generating the trigger discharge. The discharge time and arc current per arc discharge are appropriately set according to the distance between the anode electrode and the cathode electrode (spatial impedance), discharge voltage, capacitor capacity, wiring length, and the like. For example, when the distance between the electrodes, the discharge voltage, and the wiring length are constant, the longer the discharge time and the larger the arc current are obtained as the capacitance of the capacitor connected to the DC voltage source is larger. In addition, the discharge voltage of the conventional coaxial arc vapor deposition source is 100 V or more.

JP 2004-307241 A

  However, in the conventional method for producing a fine particle film, when fine particles of the vapor deposition material are released from the coaxial vacuum arc vapor deposition source, unintended large particles (for example, a particle size of 10 nm or more) may be simultaneously emitted. In addition, there is a problem that only a fine particle film having a predetermined particle size (for example, a particle size of 1 to 5 nm) cannot be selectively formed on a substrate.

  The cause of the generation of the giant particles as described above is not necessarily clear, but it is considered not to be due to grain growth on the substrate in a vacuum. The reason is that if the grain growth on the substrate is the cause, when the substrate is at a low temperature, the presence of the giant particle is confirmed even though it does not grow. The presence of such large particles in the fine particle film may cause variations in catalyst performance or variations in diameter and number of layers when forming carbon nanotubes.

  This invention is made in view of the above-mentioned problem, and makes it a subject to provide the manufacturing method of the fine particle film which can form the fine particle film with uniform particle size.

  In solving the above problems, the method for producing a fine particle film of the present invention includes a cylindrical anode electrode, a cathode electrode having a vapor deposition material disposed in the anode electrode, and the anode spaced apart from the cathode electrode. A coaxial vacuum arc evaporation source comprising a trigger electrode disposed in an electrode, a DC voltage source disposed between the anode electrode and the cathode electrode, and a capacitor connected in parallel to the DC voltage source Is used, a trigger discharge is generated between the trigger electrode and the cathode electrode, an arc discharge is induced between the vapor deposition material of the cathode electrode and the anode electrode, and fine particles of the vapor deposition material are placed in a vacuum chamber. A method of manufacturing a fine particle film to be deposited on a surface of an installed substrate, wherein a discharge voltage between the anode electrode and the cathode electrode is 50 V or more and 100 V or less. Characterized by a.

  When the anode electrode is grounded, a positive potential is applied to the trigger electrode, and a negative potential is applied to the cathode electrode, a trigger discharge is generated between the trigger electrode and the cathode electrode (evaporation material). When electrons and ions are generated by the trigger discharge, the withstand voltage between the anode electrode and the vapor deposition material decreases, and arc discharge is induced between the anode electrode and the vapor deposition material. When the arc discharge is induced, the capacitor is discharged, an arc current flows, and evaporated particles are generated from the surface of the vapor deposition material.

  The particles emitted from the vapor deposition material include neutral particles and charged particles. Among these, fine charged particles having a relatively large charge mass ratio (charge / mass) are subjected to electromagnetic force generated in the anode electrode by the generation of arc current, and bend the flight direction toward the opening of the anode electrode. And released into the vacuum chamber. On the other hand, neutral particles and huge charged particles having a relatively small charge-mass ratio (charge / mass) move straight into the vacuum chamber without being bent by the electromagnetic force in the anode electrode. Release is suppressed.

  In the conventional method of forming a fine particle film using a coaxial vacuum arc deposition source, the discharge voltage between the anode electrode and the cathode electrode is set to 100 V or higher, for example, 200 V or 400 V. The electromagnetic force generated due to the arc current during discharge is proportional to the magnitude of the discharge voltage, and the higher the discharge voltage, the greater the generated electromagnetic force. Therefore, under a condition where the discharge voltage is high, there is a high possibility that huge particles having a relatively small charge mass ratio are mixed in charged particles emitted from the opening of the anode electrode.

  Therefore, in the present invention, the discharge voltage between the anode electrode and the cathode electrode is set to 50 V or more and less than 100 V. By limiting the discharge voltage in this way, the size of the electromagnetic force generated at the time of discharge is limited, thereby avoiding the mixing of large particles with a certain size or more in the charged particles emitted from the opening of the anode electrode. Only fine charged particles below a certain level are emitted. For this reason, if the substrate is disposed at a position opposite to the opening of the anode electrode, the charged particles reach the substrate, and a thin film having a good film quality is formed on the substrate surface.

  When the magnitude of the discharge voltage is 100 V or more, as described above, it is difficult for large particles having a particle diameter of 10 nm or more to be mixed in the formed fine particle film, and a dense film or a uniform layer of fine particles is obtained. It becomes difficult. Further, when the discharge voltage is less than 50 V, there is a possibility that stable discharge cannot be obtained between the anode electrode and the cathode electrode.

  According to the method for producing a fine particle film of the present invention, fine particles having a uniform particle diameter can be generated from a vapor deposition source, so that a fine particle film having excellent film quality can be produced.

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

  FIG. 1 is a schematic configuration diagram of a fine particle film manufacturing apparatus 1 used in an embodiment of the present invention. The fine particle film manufacturing apparatus 1 includes a cylindrical vacuum chamber 10 and a coaxial vacuum arc vapor deposition source 13 installed in the vacuum chamber 10.

  A substrate stage 17 is disposed horizontally in the vacuum chamber 10. The substrate stage 17 is connected to a rotation introducing mechanism 18 that is airtightly inserted into the top plate of the vacuum chamber 10, and is configured to be rotatable by driving a motor 19. A plurality of substrates (collecting plates) W are installed at the same radial position on the substrate stage 17. Reference numeral 20 denotes a heater for heating the substrate.

An evacuation system 30 is connected to the vacuum chamber 10 so that the inside can be evacuated and maintained in a vacuum atmosphere of 10 ⁻⁵ Pa or less. The vacuum exhaust system 30 includes a variable valve 31, a turbo molecular pump 32, a valve 33, and a rotary pump 34. The vacuum chamber 10 is connected to the ground potential.

  A plurality of coaxial type vacuum arc vapor deposition sources 13 are installed at the bottom of the vacuum chamber 10 so as to face the substrate stage 17. Each coaxial type vacuum arc vapor deposition source 13 is disposed in the anode electrode 21 having a cylindrical anode electrode 21, a cathode electrode 22 having a vapor deposition material disposed in the anode electrode 21, and spaced apart from the cathode electrode 22. And a trigger electrode 23.

  The anode electrode 21 is made of a bottomed stainless steel cylinder having one end opened, and penetrates the bottom of the vacuum chamber 10 in an airtight manner toward the inside of the vacuum chamber 10 through the opening 21a. The cathode electrode 22 is installed at an axial center position inside the anode electrode 21. The cathode electrode 22 is formed integrally with the vapor deposition material or by the vapor deposition material itself. The cathode electrode 22 has a columnar shape, and an evaporation material (evaporation material) 22A is provided at one end thereof. The vapor deposition material 22A is composed of a constituent material of a fine particle film formed on the substrate W, and metallic cobalt is used in this embodiment.

  The trigger electrode 23 is attached to the outer peripheral side of the cathode electrode 22 (deposition material 22A) via an insulator 24. The trigger electrode 23 has a cylindrical shape, and is made of, for example, stainless steel. The insulator 24 is a hat type having a large diameter portion and a small diameter portion, and is made of a hard insulating material such as alumina. The insulator 24 is attached to the cathode electrode 22 (deposition material 22A) with its small diameter portion facing the opening 21a side of the anode electrode 21. The trigger electrode 23 is attached to the small diameter portion of the insulator 24.

  An arc power source 25 is installed outside the vacuum chamber 10. The arc power supply 25 has a DC voltage source 26 and a capacitor unit 27. The positive electrode and the negative electrode of the DC voltage source 26 are connected to the anode electrode 21 and the cathode electrode 22, respectively. The voltage of the DC voltage source 26 is set to 50 V or more and less than 100 V, and in this embodiment, is set to 60 V.

  The capacitor unit 27 is connected between the anode electrode 21 and the cathode electrode 22 in parallel with the DC voltage source 26. The capacitor unit 27 is formed by connecting a plurality of capacitors in parallel, and the total capacity thereof is set to, for example, 1000 μF or more and 9000 μF or less, and in this embodiment, is set to 8800 μF. The capacitor unit 27 is configured to be charged by the DC voltage source 26 at a constant charging time. For example, when the charging time is 1 second, charging / discharging of the capacitor unit 27 is repeated at a cycle of 1 Hz.

  A trigger power supply 28 is installed outside the vacuum chamber 10. The trigger power supply 28 is composed of a pulse transformer, and is configured to boost an input voltage of 200 V and a microsecond pulse voltage by about 17 times and output it to 3.4 kV (several μA). The boosted voltage is connected to the trigger power supply 21 with a positive polarity with respect to the cathode electrode 22.

  The configuration of the coaxial vacuum arc evaporation source 13 is not limited to the example shown in FIG. 1, and as shown schematically in FIG. You may employ | adopt what was attached and comprised along the 21 axial direction. In FIG. 2, parts corresponding to those in FIG. In FIG. 2, reference numeral 35 denotes a vacuum pump, and 36 denotes a gas introduction system such as an inert gas.

  Next, the operation of the fine particle film manufacturing apparatus 1 configured as described above will be described.

  Referring to FIG. 1 (or FIG. 2), a power supply voltage of a trigger power supply 28 is applied between the cathode electrode 22 and the trigger electrode 23 to generate creeping discharge (trigger discharge) through the surface of the insulator 24. When the trigger discharge occurs, the withstand voltage between the anode electrode 21 and the vapor deposition material 22A decreases, and an arc discharge is induced between the anode electrode 21 and the vapor deposition material 22A. When the arc discharge is induced, the capacitor unit 27 is discharged, and an arc current flows between the cathode electrode 22 (deposition material 22A) and the anode electrode 21. By this arc current, the surface of the vapor deposition material is heated, melted, and evaporated to form a metal cobalt plasma.

  Due to the formation of the arc discharge, an electromagnetic force is generated in the cylindrical anode electrode 21 along the axial direction. This electromagnetic force is a Lorentz force or a Coulomb force that deflects the flight direction of positive ions emitted from the vapor deposition material 22A toward the inside of the vacuum chamber 10, that is, the substrate W on the substrate stage 17. Therefore, the charged particles emitted from the vapor deposition material 22A are classified into those that fly toward the substrate W and those that do not, depending on the magnitude of the charge mass ratio (charge / mass).

  Specifically, fine charged particles having a relatively large charge-mass ratio are subjected to electromagnetic force generated in the anode electrode 21 and bent in the flight direction toward the opening 21 a of the anode electrode 21, so that the vacuum chamber 10. Is released inside. On the other hand, large particles and neutral particles having a relatively small charge-mass ratio go straight without being bent by the electromagnetic force in the anode electrode 21 and adhere to, for example, a grounded anode electrode. Thereby, discharge | release in the vacuum chamber 10 of the said large sized particle and neutral particle is suppressed.

  As described above, charged particles (cobalt (Co) ions) having a particle diameter of a predetermined value or less are mainly emitted from the coaxial vacuum arc deposition source 13. Therefore, these fine charged particles reach and adhere to the surface of the substrate W arranged facing the vapor deposition source 13. During film formation, the substrate W is rotated by driving the motor 19 together with the substrate stage 17, and a film or layer made of the fine particles is formed on the surface of each substrate W with fine particles emitted from the plurality of vapor deposition sources 13.

  Here, the formation of fine particles by the coaxial vacuum arc deposition source 13 is performed intermittently corresponding to the period of the trigger discharge. Therefore, the occurrence of arc discharge between the anode electrode 21 and the vapor deposition material 22A is also pulsed. The discharge time and arc current per arc discharge are the distance (that is, spatial impedance) between the anode electrode 21 and the cathode electrode (here, the vapor deposition material 22A), the discharge voltage of the arc power supply 25, the capacity of the capacitor unit 27, and the wiring. It depends on the length. On the other hand, the electromagnetic force in the anode electrode 21 generated during arc discharge is related to the magnitude of the magnetic field generated in the anode electrode 21. The magnitude of the magnetic field is determined by the magnitude of the arc current. The arc current is almost proportional to the capacitor capacity and the discharge voltage.

  In the conventional fine particle film manufacturing method using a coaxial vacuum arc evaporation source, the discharge voltage between the anode electrode and the cathode electrode is set to 100 V or more, for example, 200 V to 400 V. The electromagnetic force generated due to the arc current during discharge is proportional to the magnitude of the discharge voltage, and the higher the discharge voltage, the greater the generated electromagnetic force. Therefore, under a condition where the discharge voltage is high, there is a high possibility that huge particles having a relatively small charge mass ratio are mixed in charged particles emitted from the opening of the anode electrode.

  3A to 3C are TEM photographs of a cobalt fine particle film formed using a coaxial vacuum arc deposition source. The number of discharges is 20 times, and the discharge voltages are 200 V (FIG. 3A), 300 V (FIG. 3B), and 400 V (FIG. 3C). As is apparent from FIG. 3, it can be seen that giant particles having a particle size of about 10 nm are mixed in a film or layer made of fine particles. It can also be seen that the higher the discharge voltage, the larger the entrainment ratio and particle size of the giant particles.

  On the other hand, in this embodiment, the discharge voltage (power supply voltage of the DC voltage source 26) between the anode electrode 21 and the cathode electrode 22 (deposition material 22A) is set to 60V. By limiting the discharge voltage in this way, the magnitude of the electromagnetic force generated at the time of discharge is limited, so that the charged particles emitted from the opening 21A of the anode electrode 21 have large particles having a certain particle size or more. Mixing is avoided, and only fine charged particles having a particle size of a certain value or less are released.

  Therefore, according to the present embodiment, only charged particles having a particle size of a certain size or less can be formed, and thus a film or layer made of fine particles having a particle size of a certain size or less is stably formed on the surface of the substrate W. It is possible to form a fine and fine particle film that can be formed. FIG. 4 is a TEM photograph of a cobalt fine particle film obtained at a discharge voltage of 60V. A fine particle film having a particle diameter of about 3 to 5 nm in a certain range can be obtained.

  As described above, according to the present embodiment, since a fine particle film having a particle diameter of about 3 to 5 nm can be obtained in a certain range, when the fine particle film is used as a carbon nanotube base film, In addition, variations in the formation diameter and the number of layers of carbon nanotubes can be avoided. Further, when the fine particle film is used as a catalyst metal carrier of a fuel cell, the catalyst performance can be stabilized.

  The discharge voltage between the anode electrode and the cathode electrode can be appropriately set according to the particle diameter of the fine particles to be formed, the type of vapor deposition material, and the like. For example, in order to obtain fine particles having a particle size of about 1 nm, the discharge voltage may be further reduced. A suitable discharge voltage is 50 V or more and less than 100 V. In the case where the discharge voltage is 100 V or more, as described above, it is impossible to suppress the unintended mixture of huge particles in the formed fine particle film. Further, when the discharge voltage is less than 50V, there is a possibility that stable discharge cannot be obtained.

  The discharge time and arc current are preferably adjusted by adjusting the capacity of the capacitor unit 27. Specifically, the higher the capacitor capacity, the longer the discharge time and the greater the arc current. A preferable range of the capacitor capacity is 1000 μF or more and 9000 μF or less. If the capacitance is less than 1000 μF, effective arc discharge cannot be obtained and it becomes difficult to form desired fine particles. On the other hand, if the capacitor capacity exceeds 9000 μF, it is difficult to control the particle diameter, and a desired particle film cannot be obtained stably.

  As mentioned above, although embodiment of this invention was described, of course, this invention is not limited to this, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in the above embodiment, the method for producing a metal cobalt fine particle film using a coaxial arc vapor deposition source has been described. However, the vapor deposition material is not limited to metal cobalt, and platinum, palladium, and the like can also be applied.

  In the above embodiment, the arc discharge time and the arc current are adjusted according to the capacitor capacity. However, the present invention is not limited to this, and the arc length depends on the wiring length between the arc power source and the anode electrode or the cathode electrode. It is also possible to adjust the discharge time and the magnitude of the arc current.

It is a schematic block diagram of the fine particle film manufacturing apparatus demonstrated in embodiment of this invention. It is a figure which shows the modification of a structure of the fine particle film manufacturing apparatus shown in FIG. It is a TEM photograph of the cobalt fine particle film produced by setting discharge voltage to 200V, 300V, and 400V. It is a TEM photograph of a cobalt fine particle film produced at a discharge voltage of 60V.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fine particle film manufacturing apparatus 10 Vacuum tank 13 Coaxial type vacuum arc evaporation source 17 Substrate stage 21 Anode electrode 22 Cathode electrode 22A Vapor deposition material 23 Trigger electrode 24 Insulator 25 Arc power supply 26 DC voltage source 27 Capacitor unit 28 Trigger power supply 30 Vacuum exhaust system W substrate

Claims (1)

A cylindrical anode electrode; a cathode electrode having a deposition material disposed in the anode electrode; a trigger electrode disposed in the anode electrode spaced apart from the cathode electrode; and the anode electrode and the cathode electrode A coaxial vacuum arc deposition source comprising a direct current voltage source installed in between and a capacitor connected in parallel to the direct current voltage source is used,
A substrate in which a trigger discharge is generated between the trigger electrode and the cathode electrode, an arc discharge is induced between the evaporation material of the cathode electrode and the anode electrode, and fine particles of the evaporation material are placed in a vacuum chamber A method for producing a fine particle film to be deposited on the surface of
The evaporation material is metallic cobalt,
The capacitance of the capacitor is 1000 μF or more and 9000 μF or less,
A method for producing a fine particle film, wherein a discharge voltage between the anode electrode and the cathode electrode is 50 V or more and less than 60 V.