JPH07100136B2 - Manufacturing method of fine particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fine particles or a thin film, and particularly to a method for controlling the crystal structure thereof.

(Prior Art) In recent years, attention has been paid to ultrafine particles as a material for magnetic materials, catalysts, special ceramics, etc., because they may exceed the limits of conventional materials. Known methods for producing fine particles of these metals or oxides, particularly ultrafine particles, include reduction of chloride and organometallic vapor with hydrogen, precipitation from a metal salt solution, and gas evaporation.

(Problems to be Solved by the Invention) Although various methods for producing fine particles have been tried as described above, a method for controlling the crystal structure of produced fine particles has not been established.

A method of controlling the crystal structure of fine particles by radiant heating or plasma heating during the manufacturing process, although at the research stage, has been reported. However, in these methods, the apparatus becomes complicated and large in size, and besides, it is difficult to handle, and the crystal structure has not been sufficiently controlled.

Therefore, the structure of the fine particles was determined by the initial production conditions, and only a specific structure could be obtained.

In addition, it is generally considered to be extremely difficult to manufacture and maintain an amorphous film or a structure of a high temperature phase at room temperature.

(Means for Solving the Problem) In the present invention, when the generated fine particles are collected by the collection substrate in the gas evaporation method, the crystal structure of the fine particles is changed by changing the collision condition of the fine particles. The inventors have discovered a phenomenon, and by utilizing this phenomenon, it is possible to generate not only a high temperature phase crystal structure and an amorphous structure but also fine particles of a whisker-like single crystal, which have been difficult to obtain conventionally.

(Example) Hereinafter, the present invention will be described in detail by taking as an example a method of obtaining a room temperature phase, an amorphous and a whisker-like single crystal in iron fine particles.

The fine particles having various crystal structures described above can be obtained by the same manufacturing apparatus, and an example of the apparatus is shown in FIG.

The apparatus is composed of a particle generation chamber 1, an acceleration tube 2 and a collection chamber 3. The particle generation chamber 1 is similar to an apparatus for generating particles by a normal gas evaporation method. For example, an exhaust system 4 including a turbo molecular pump and an oil rotary pump, a gas introduction system 5 are connected, and an evaporation source 6 is built in. However, a vacuum gauge 7 is provided.

The accelerating tube 2 is, for example, a stainless tube having a total of 1 mm, one end of which is 100 mm directly above the evaporation source 6 is fixed, and the other end of the accelerating tube 2 is arranged to face the collection substrate 9 in the collection chamber 3. The collection chamber 3 is additionally provided with a vacuum gauge 8, and an oil rotary pump is provided via a valve 10.
Connected to 11.

After exhausting the particle generation chamber 1 to the level of 10 ^-7 Torr, Ar gas was discharged.
Introduce up to 100 Torr and evaporate pure iron (99.9%) in the atmosphere. At this time, the pressure in the collection chamber 3 is 0.1 to 10 several Tor.
Adjustable up to r with valve 10. The evaporated iron condenses into fine particles and rises as smoke. This state can be observed with the naked eye.

The iron fine particles obtained under these conditions have a size of 10 to 50 nm,
All have a room temperature phase structure (body centered cubic structure). The rising smoke-like particles are sucked into the accelerating tube 2, placed on Ar gas flowing in the collection chamber 3 to be accelerated, and collide with the collection substrate 9. The particle velocity is about a maximum when the particle size is 20 nm under the above conditions.
It is 8 km / sec.

As a collecting substrate, a microgrid for an electron microscope was attached to a mirror-polished stainless holder and used, and the structure of the produced fine particles or film was determined by a transmission electron microscope.

Example 1 The pressure in the iron fine particle collection chamber 3 having the face-centered cubic structure (high temperature phase) was 0.1 Torr and the temperature of the collection substrate was room temperature (about 25 ° C.),
Fine particles that were off the central axis and entered a solid angle of 0.2 to 3 degrees were collected from the exit of the accelerating tube. An electron micrograph of the obtained fine particles is shown in FIG. 2, and it can be seen that fine particles having a face-centered cubic structure with a particle size of 20 to 50 nm are obtained.

On the other hand, when the pressure in the collection chamber 3 was set to 1 Torr or more, it was confirmed that all the obtained fine particles had a body-centered cubic structure in a room temperature phase. It is considered that this is because the collision energy with the gas in the collection chamber is decelerated and the collision energy with respect to the collection substrate is reduced.

Although the reported methods using radiant heating and plasma heating are still in the research stage, they are difficult to control, require a large-scale and complicated apparatus, and are expensive, and uniform particles cannot be obtained. However, in this method, homogeneous high-temperature phase fine particles were easily obtained only by controlling the pressure in the collection chamber.

Example 2 Formation of Amorphous Film The pressure in the collection chamber 3 was 0.1 Torr, the temperature of the collection substrate was room temperature (about 25 ° C.), and the fine particles within a solid angle of 0.1 degree along the central axis from the exit of the accelerating tube 2. Is collected, an amorphous iron thin film is obtained as shown in the electron micrograph in FIG.

Amorphous metal is extremely difficult to produce, and a method for producing it from fine particles is not known. According to this method, there are few restrictions on material components, and various amorphous films can be produced.

Example 3 Formation of a whisker-shaped single crystal The pressure in the collection chamber 3 was 0.1 Torr, and the collection substrate temperature was 200 ° C.
Fig. 4 shows an electron micrograph of the material in which the amount of fine particles deposited was collected to a thickness of about 1 µm. Width 3μm, length 60μ
It can be seen that a beard-shaped single crystal of m face-centered cubic structure is growing.

In the first place, the phenomenon that whiskers grow up to several 100 nm under electron beam irradiation was observed even in the places where no whiskers were observed. Up to now, there have been only reported examples of growing whiskers on the order of μm in a special device such as a field emission electron microscope.
Moreover, it is still in the research stage and is not a practical method. On the other hand, according to this method, a large whisker-shaped single crystal having a size of several tens of μm was obtained very easily and efficiently.

(Effects of the Invention) The method for producing fine particles of the present invention facilitates the crystal structure of fine particles or films deposited on the collecting substrate by controlling the collision conditions of the fine particles on the collecting substrate in the gas evaporation method. In addition, it is possible to control with certainty, and it becomes possible to easily perform the previously difficult things such as the production of fine particles having a high temperature phase crystal structure at room temperature, the production of an amorphous film and a whisker-shaped single crystal. The application range of fine particles is dramatically expanded.

In addition, although the example shows the case where pure iron is used as a material as an example, it is clear from the above description that the desired fine particles can be obtained by controlling the crystal structure of other materials.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out the method for producing fine particles of the present invention, FIG. 2 is an electron micrograph showing the grain structure of the high temperature phase produced in Example 1, and FIG. (A) is an electron micrograph showing the metal structure of the amorphous iron thin film produced in Example 2, Fig. 3 (b) is a partially enlarged photograph thereof, and Fig. 4 is a whiskers produced in Example 3. It is an electron micrograph which shows the particle structure of a single crystal. 1: Particle generation chamber, 2: Accelerator tube 3: Particle collection chamber, 4: Exhaust system 5: Gas introduction system, 6: Evaporation source 7, 8: Vacuum gauge, 9: Collection substrate 10: Valve, 11: Oil Rotary pump

Claims (9)

[Claims] 1. When the fine particles produced by the in-gas evaporation method collide with a collector and are collected, the collision conditions are controlled to control the crystal structure of the fine particles or film deposited on the collector. For producing fine particles, etc. 2. The method for producing fine particles and the like according to claim 1, wherein the control of the collision condition is performed by controlling the speed at which the generated fine particles collide with the collector. 3. The method for producing fine particles and the like according to claim 2, wherein the control of the collision speed is performed by connecting the fine particle generating chamber and the collecting chamber and controlling the pressure difference therebetween. 4. The control of the collision speed is performed by controlling the pressure in the collection chamber.
Method for producing fine particles of 5. The control of the collision condition is performed by controlling the state of the collector.
Method for producing fine particles of 6. A method for producing fine particles or the like according to claim 1, wherein fine particles having a high temperature phase crystal structure are produced. 7. A method for producing fine particles or the like according to claim 1, wherein an amorphous film is produced. 8. A method for producing fine particles or the like according to claim 1, wherein a whisker-shaped single crystal is produced. 9. The material as claimed in claim 6, wherein the material is iron.
To the method for producing fine particles, etc.