JP4837409B2 - Nanoparticle production method - Google Patents

Description

  The present invention relates to a technology for producing nanoparticles.

  Cobalt nanoparticles are attracting attention as a carbon nanotube underlayer (catalyst layer) and catalytic metal carrier for fuel cells, and platinum nanoparticles are attracting attention as nanoparticle catalysts for polymer electrolyte fuel cells and methanol fuel cells. Attempts have been made to form cobalt nanoparticles and platinum nanoparticles on a collecting plate using a coaxial arc deposition source.

However, in the prior art, when generating, for example, cobalt vapor from a coaxial arc evaporation source, droplets of molten cobalt are discharged into the vacuum chamber together with the cobalt vapor, and as shown in FIG. Coarse particles were attached together with the cobalt nanoparticles, and it was not possible to selectively form only the cobalt nanoparticles.
A technique for producing nano-sized fine particles using a coaxial arc vapor deposition source is described in, for example, Patent Document 1 below.
JP 2004-307241 A

  The present invention was created to solve the above-described problems of the prior art, and provides a technique capable of selectively forming nanoparticles.

In order to solve the above problems, the present invention relates to a vacuum chamber, a cylindrical anode electrode, a cathode electrode having an evaporation material disposed in the anode electrode, and the cathode electrode disposed in the anode electrode. and a spaced trigger electrode, to generate a trigger discharge between the trigger electrode and the cathode electrode, an arc evaporation source Ru is induce arc discharge between the evaporating material and the anode electrode of the cathode electrode A method for producing nanoparticles, wherein a capacitor having a capacity of 2200 μF or less is connected to the cathode electrode, the capacitor is set to a voltage of 100 V or more and 800 V or less, and the arc discharge is performed once in a discharge time of 300 μsec or less. This is a method for producing nanoparticles by setting the discharge peak current to 1800 A or more and releasing nanoparticles of the evaporating material into the vacuum chamber. .
Moreover, this invention is a nanoparticle manufacturing method which repeats the said trigger discharge in multiple times, induces the said arc discharge for every said trigger discharge, and discharge | releases the nanoparticle of the said evaporation material repeatedly.
Moreover, this invention is a nanoparticle manufacturing method which makes the said trigger discharge generate | occur | produce 1 to 10 times per second.
Further, the present invention evacuates the inside of the vacuum chamber, introduces helium gas into the vacuum chamber to a pressure lower than atmospheric pressure, and in the atmosphere of the helium gas, the nanomaterial of the evaporation material is placed in the vacuum chamber. A method for producing nanoparticles by releasing particles.

  In the present invention, the wiring length of the capacitor is shortened to 50 mm or less so that the peak current of arc discharge of the coaxial arc deposition source used for the production of nanoparticles is 1800 A or more, and the capacitance of the capacitor connected to the cathode electrode is reduced. Arc discharge was generated by setting the discharge voltage to 2200 μF or less, the discharge voltage to 100 V to 800 V, and the discharge time to 300 μsec or less.

  Arc discharge is induced once by one trigger discharge. The arc current flows for 300 μsec or less, but it takes time to charge the capacitor. Therefore, the trigger discharge generation cycle is set to 1 to 10 Hz, and the capacitor is charged so that arc discharge can be generated at that cycle. Thus, nanoparticles having a size of about 1 to 100 nm can be obtained.

  Nanoparticles of about 1 to 100 nm that do not contain giant particles due to droplets can be obtained.

A nanoparticle production apparatus used in the present invention is denoted by reference numeral 1 in FIG.
The nanoparticle manufacturing apparatus 1 has a cylindrical vacuum chamber 10, and a substrate stage 17 is horizontally disposed in the vacuum chamber 10. A rotation introducing mechanism 18 is inserted in the vacuum chamber 10 in an airtight manner, and the substrate stage 17 is configured to rotate in a horizontal plane when the motor 19 disposed outside the vacuum chamber 10 is operated.

One or more collecting plates 20 are cooled and held at a room temperature or lower on the surface of the substrate stage 17 facing vertically downward.
One or a plurality of coaxial arc vapor deposition sources 13 are arranged at a position facing the vertically downward surface of the substrate stage 17.

The structure of the coaxial arc deposition source 13 will be described. Each coaxial arc deposition source 13 includes a cylindrical (here cylindrical) anode electrode 131, a cathode electrode 132, and a trigger electrode 134.
The cathode electrode 132 and the trigger electrode 134 are disposed inside the anode electrode 131.

The cathode electrode 132 has a columnar shape, one end is made of an evaporation material 135 and the other end is made of a rod-like electrode 136. Here, metallic cobalt is used for the evaporating material 135, and the evaporating material 135 is attached to the tip of the rod-shaped electrode 136 and arranged on the discharge port 137 side.
The cathode electrode 132 is inserted through a ring-shaped trigger electrode 134 and a washer insulator 133.

  The washer insulator 133 is disposed between the evaporation material 135 and the trigger electrode 134, and the evaporation material 135, the washer insulator 133, and the trigger electrode 134 are arranged in this order from the discharge port 137 side. It is arrange | positioned in the position far from the discharge outlet 137.

  Although not shown in detail in the drawing, the three parts of the cathode electrode 132, the washer insulator 133, and the trigger electrode 134 are attached in close contact with screws. The anode electrode 131 is made of stainless steel.

  The anode electrode 131, the trigger electrode 134, and the cathode electrode 132 are insulated from each other, the cathode electrode 132 is connected to the arc power supply 141, the trigger electrode 134 is connected to the trigger power supply 142, and each of the electrodes 131, 132, 134 is configured to be able to apply different voltages.

  The arc power supply 141 has a DC voltage source 144 and a capacitor unit 145. Both ends of the capacitor unit 145 are connected to the anode electrode 131 and the cathode electrode 132. The capacitor unit 145 and the DC voltage source 144 are connected in parallel.

  The DC voltage source 144 has a capability of flowing a current of several A at 800 V, and the capacitor unit 145 is configured to be charged by the DC voltage source 144 in a fixed charging time.

  The trigger power supply 142 is composed of a pulse transformer, and is configured to boost the input voltage of 200 V μs by about 17 times to output 3.4 kV (several μA). It is connected so as to be applied to the trigger electrode 134 with a positive polarity with respect to the electrode 132.

The vacuum chamber 10 is connected to an evacuation system 31, and the inside of the vacuum chamber 10 is evacuated to form a vacuum atmosphere of 10 ⁻⁵ Pa. The evacuation system 31 includes a turbo molecular pump and a rotary pump.
The anode electrode 131 and the vacuum chamber 10 are connected to the ground potential.

  First, the capacity of the capacitor unit 145 is set to 2200 μF, a voltage of 100 V is output from the DC voltage source 144, the capacitor unit 145 is charged with the voltage, and the charging voltage of the capacitor unit 145 is between the anode electrode 131 and the cathode electrode 132. Applied. A negative voltage output from the capacitor unit 145 is applied to the evaporation material 135 via the rod-shaped electrode 136.

  In this state, when a pulsed trigger voltage of 3.4 kV is output from the trigger power source 142 and applied between the cathode electrode 132 and the trigger electrode 134, trigger discharge (creeping discharge) is generated on the surface of the washer insulator 133. Electrons are emitted from the joint between the cathode electrode 132 and the washer insulator 133.

  With this trigger discharge, the withstand voltage between the anode electrode 131 and the cathode electrode 132 decreases, and an arc discharge occurs between the inner peripheral surface of the anode electrode 131 and the side surface of the cathode electrode 132.

  Due to the discharge of the electric charge charged in the capacitor unit 145, an arc current having a peak current of 1800 A or more flows for about 200 μsec, cobalt vapor is emitted from the side surface of the cathode electrode 132, and cobalt plasma is formed.

  At this time, the evaporation material 135 and the rod-shaped electrode 136 of the cathode electrode 132 in which nanoparticles of several nanometers are formed by cobalt atomic ions or clustered cobalt are disposed on the central axis of the anode electrode 131. The arc power supply 141 is connected to the end of the rod-shaped electrode 136 opposite to the evaporation material 135, and the arc current flows on the central axis of the rod-shaped electrode 136, and a magnetic field is formed in the anode electrode 131.

  The electrons emitted into the anode electrode 131 are subjected to a Lorentz force in the direction opposite to the direction in which the current flows due to the magnetic field formed by the arc current, and are emitted from the emission port 137 into the vacuum chamber 10.

  Cobalt vapor emitted from the cathode electrode 132 includes ions (charged particles) and neutral particles, but giant charged particles and neutral particles such as droplets having a small charge-mass ratio (charge is smaller than mass). Goes straight and collides with the wall surface of the anode electrode 131, but charged particles having a large charge-mass ratio are attracted to electrons by the Coulomb force and discharged into the vacuum chamber 10 from the discharge port 137 of the anode electrode 131.

  At a position 100 mm away from each coaxial arc vapor deposition source 13, a collection plate 20 cooled and held at room temperature or lower by the substrate stage 17 rotates and moves on a concentric circle centered on the center of the substrate stage 17. When the cobalt vapor ions passing through and released into the vacuum chamber 10 reach the surface of the collecting plate 20, they adhere to the nanometer-order cobalt nanoparticles.

An arc discharge is induced once by one trigger discharge, and an arc current flows for 300 μsec.
When the charging time of the capacitor unit 145 is about 1 second, arc discharge can be generated with a period of 1 Hz.
The desired number of arc discharges are generated, and the cobalt nanoparticles formed on the surface of the collecting plate 20 are collected in a state of being attached to the surface of the collecting plate 20.

Code W ₁ in FIG. 1 shows the wiring length of the wiring connecting the capacitor unit 145 and the cathode electrode 132, reference numeral W ₂ indicates the wiring length of the wiring connecting the capacitor unit 145 and the anode electrode 131 ing.

FIG. 2A shows arc discharge when the capacitance of the capacitor unit is 2200 μF, the discharge voltage is 100 V, and the wiring length L (L = W ₁ + W ₂ ) between the capacitor unit 145 and the cathode electrode 132 is 50 mm. FIG. 5B is a SEM photograph of the surface of the collecting plate 20 at that time.

  FIG. 3A shows a waveform of arc discharge when the capacitance of the capacitor unit 145 is 8800 μF and the wiring length between the capacitor unit 145 and the cathode electrode 132 is 1 m, and FIG. It is a SEM photograph of the surface of the collecting plate 20 at the time.

Comparing FIG. 2 (a) and FIG. 3 (a), when the wiring length L is 50 mm, the peak current of arc discharge is 1850A and the discharge time is 250 μsec, whereas when 1 m, the peak current is 1950A. However, the discharge time is 500 μs.
Comparing FIG. 2 (b) and FIG. 3 (b), a droplet having a diameter of several μm observed in the case of 1 m is hardly observed in the case of 50 mm .

The capacity was set to 2200 μF, the wiring was super 50 mm, and arc discharge was generated twice, five times, or ten times to attach cobalt nanoparticles to the surface of the collection plate 20 made of amorphous carbon. FIGS. 4A, 4B, 5A, 5B, 6A, and 6B show TEM photographs in the case of 2 times, 5 times, and 10 times, respectively.
Further, EELS (Electron Energy-Loss Spectroscopy) data on the surface of the collection plate 20 are shown in FIGS.

  4 (a) and 4 (b), nanoparticles are not observed in the two trigger discharges, but are slightly detected in the graph of FIG. 7, and it can be seen that cobalt is present on the substrate. .

  On the other hand, from FIGS. 5A and 5B, cobalt nanoparticles are clearly observed when arc discharge is generated five times. Detection can also be confirmed from the EELS graph of FIG.

  Further, from FIGS. 6 (a) and 6 (b), it is clear that when the arc discharge is generated 10 times, the density of the cobalt nanoparticles is obviously higher than that in the case of 5 times. Also in the EELS graph of FIG. 9, the signal intensity is higher than in the case of five times.

FIG. 10 is an enlarged TEM photograph of FIG. From FIG. 10, it can be seen that about 5 nm of cobalt nanoparticles are uniformly dispersed.
In each of the above examples, the gas was not introduced into the vacuum chamber 10 and cobalt nanoparticles were generated in a high vacuum atmosphere. However, a gas introduction system 32 was connected to the vacuum chamber 10, and the vacuum chamber A gas inert to cobalt can be introduced into 10 while controlling the flow rate from a mass flow controller (not shown) to produce cobalt nanoparticles in an introduced gas atmosphere.

  Here, the gas introduction system 32 has a helium gas cylinder, helium gas was introduced at a flow rate of 5 sccm while evacuating, and the inside of the vacuum chamber 10 was made an introduction gas atmosphere of 10 Torr or more.

The capacitance of the capacitor is set to 300 μF to 1100 μF. When arc discharge is generated at a discharge voltage of 400 V to 800 V, cobalt vapor is released into the vacuum chamber 10 and flies toward the collection plate 20.
The cobalt vapor collides with the helium gas filled in the vacuum chamber, and the energy is reduced and agglomerates to form uniform cobalt nanoparticles.

  The gas introduced into the vacuum chamber is not limited to helium gas, but may be any gas that is inert to cobalt. Further, when the introduced gas is cooled, cobalt nanoparticles having a small diameter can be obtained.

  In addition, the present invention is not limited to the above cobalt, and nanoparticles can be formed similarly for Pt (platinum), for example. As in the case of cobalt, the nanoparticle production apparatus 1 of FIG. 1 is used, platinum (99.95%) is used as the evaporation material 135 of the coaxial arc evaporation source 13, the capacitance of the capacitor is 2200 μF, and the discharge voltage is 400V. The discharge was performed 10 times, and platinum nanoparticles were adhered to the surface of the collection plate 20 made of amorphous carbon provided at a position 80 mm away from the coaxial arc vapor deposition source 13. At this time, the collection plate 20 was cooled to room temperature or lower, the peak current of the arc discharge was 2000 A, and the discharge time was 200 μsec. Moreover, the TEM photograph of the obtained platinum nanoparticle is shown in FIG.

As is clear from FIG. 11, it can be seen that platinum nanoparticles having a diameter of 2 to 3 nm and a uniform particle diameter are uniformly dispersed and adhered.
Furthermore, even with metal materials other than cobalt and platinum, semiconductor materials, and non-metals (meltable materials), nanoparticles can be formed according to the method of the present invention.

  The present invention is used for supporting a catalytic metal on a carbon nanotube base film (catalyst layer) or a fuel cell.

Nanoparticle production apparatus used in the present invention (a): Voltage waveform of the present invention (capacitance 2200 μF, wiring length 50 mm ) (b): SEM photograph of collection plate surface in that case (a): Voltage waveform of conventional technology (capacitance 8800 μF, wiring length 1 m) (b): SEM photograph of collection plate surface in that case (a), (b): TEM photograph of the collector plate surface when arc discharge is generated twice (a), (b): TEM photograph of the surface of the collecting plate when arc discharge is generated five times (a), (b): TEM photograph of the surface of the collecting plate when arc discharge is generated 10 times EELS data on the surface of the collecting plate when arc discharge is generated twice EELS data on the surface of the collecting plate when arc discharge is generated 5 times EELS data on the surface of the collecting plate when arc discharge is generated 10 times Enlarged TEM picture of Fig. 6 (b) TEM picture of platinum nanoparticles

Explanation of symbols

10 …… Vacuum chamber 131 …… Anode electrode 132 …… Cathode electrode 134 …… Trigger electrode

Claims (4)

A vacuum chamber;
A cylindrical anode electrode;
A cathode electrode having an evaporating material disposed within the anode electrode;
A trigger electrode disposed in the anode electrode and spaced apart from the cathode electrode, generating a trigger discharge between the trigger electrode and the cathode electrode, and the evaporation material of the cathode electrode and the anode electrode a nanoparticle manufacturing method using the arc evaporation source Ru is induce arc discharge between,
A capacitor having a capacity of 2200 μF or less is connected to the cathode electrode;
The capacitor is set to a voltage of 100 V or more and 800 V or less and the arc discharge is performed once in a discharge time of 300 μsec or less
A method for producing nanoparticles, wherein a peak current of the arc discharge is set to 1800 A or more and nanoparticles of the evaporating material are released into the vacuum chamber.   The nanoparticle manufacturing method according to claim 1, wherein the trigger discharge is repeated a plurality of times, the arc discharge is induced for each trigger discharge, and the nanoparticles of the evaporation material are repeatedly released.   The method for producing nanoparticles according to claim 2, wherein the trigger discharge is generated once or more and not more than 10 times per second. Evacuating the inside of the vacuum chamber, introducing helium gas into the vacuum chamber to a pressure lower than atmospheric pressure,
The nanoparticle manufacturing method according to any one of claims 1 to 3 , wherein nanoparticles of the evaporating material are released into the vacuum chamber in the atmosphere of the helium gas.