JPH06287745A - Production of composite superfine particle - Google Patents

Abstract

PURPOSE:To stably produce a composite superfine particle excellent in selectivity of a superfine particle and a coating-film metal by forming a coating film of metal vapor on a part or the whole of the surface of the superfine particle formed by thermal vaporization. CONSTITUTION:A vaporization chamber 1 contg. a target 4 by a CdTe wafer, for example, as a superfine particle material is evacuated, the target 4 is irradiated with a laser beam, heated and vaporized, an inert gas such as Ar is supplied from an inlet tube 6 to cool and solidify the vapor of the target 4, and a superfine particle of CdTe is produced. In this case, the pressure in the vapor- contg. chamber 1 is controlled to 5Torr, the CdTe superfine particle is introduced into a reaction chamber 2 connected to the chamber 1 through a pipe 10a and with the internal pressure kept at 0.05Torr by the pressure difference, Au is vaporized from a Knudsen cell 7 contg. the metallic material such as Au and deposited on a part or the whole of the surface of the CdTe superfine particle to form a composite superfine particle, which is introduced into a collecting chamber 3 with the internal pressure held at 10<-3>Torr by the pressure difference, and the composite superfine particle is collected on the surface of a quartz collecting sheet 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing composite ultrafine particles in which a part or the whole surface of fine particles is coated with a metal film, and in particular, ultrafine particles produced in the gas phase are coated with a metal film in the gas phase. The present invention relates to a method for producing composite ultrafine particles, which comprises applying various types of metal coatings to various semiconductor, metal or organic fine particles that can be produced in a gas phase by applying the treatment.

[0002]

2. Description of the Related Art Ultrafine particles are known to have properties different from those of bulk, and are expected to be applied as functional materials. For example, ultrafine compound semiconductor particles such as CdS have a so-called quantum size effect in which the band structure becomes discrete as the particle size decreases, and the absorption edge shifts to the high energy side (for example, AJ Nozice
t al., J. Phys. Chem., 89, 397 (1987)). It is also known that such a material having a quantum size effect has a large non-linear optical effect, and thus it can be applied to an optical control element using the non-linear optical effect such as an ultrafast optical switch or an optical logic element. Is expected.

As a method for producing ultrafine particles, a method for obtaining ultrafine particles as a colloidal dispersion system using an oxidation-reduction reaction in a solution has long been known. For example, a gold (Au) colloid can be easily produced by adding an appropriate reducing agent such as hydrogen peroxide or citric acid to a potassium chloroaurate solution. Also, as an example of a compound colloid, cadmium sulfide (CdS)
In the case of, cadmium perchlorate (Cd (Cl
When a sodium sulfide (Na ₂ S) solution is added to the O ₄ ) ₂ ) solution, a redox reaction occurs to obtain a CdS dispersion system (for example, R. Rossetti et al., J. Chem. Phys. 82, 5).
52 (1985)). Although the particle diameter of the obtained ultrafine particles differs depending on the manufacturing conditions, colloidal particles having a diameter of 5 nm or less and a small particle size distribution dispersion can be easily manufactured.

As a method for producing ultrafine particles, an evaporation method in a gas is known in addition to the above method utilizing the oxidation-reduction / precipitation reaction in a liquid phase. This is because when a substance is heated and evaporated in an atmosphere of an inert gas such as argon (Ar), the vapor collides with atmospheric gas molecules, loses kinetic energy, and is rapidly cooled to form fine particles of the substance. The size of the particles changes depending on the distance from the evaporation source, and ultrafine particles having a small particle size can be obtained by collecting the particles in the vicinity of the evaporation source. Further, oxide fine particles can be produced by reacting the generated particles with, for example, oxygen (O ₂ ) gas.

When the ultrafine particles produced by these methods are applied to a light control element or the like, a technique of dispersing the ultrafine particles in a solid matrix is required.

As an example thereof, there is a melt quenching method for simultaneously producing ultrafine particles and glass holding them. In this method, the raw material for the fine particles and the glass raw material are mixed,
After heating above the melting temperature, it is rapidly cooled and reheated at a lower temperature to precipitate fine particles. With this method, a diameter of 10
So-called fine particle-dispersed glass in which compound fine particles having a particle size of nm or less are dispersed in glass can be produced.

As another example, there is also known a method of embedding compound semiconductor ultrafine particles in a solution in glass by using a sol-gel method.

On the other hand, recently, when not only the fine particles are confined in the solid matrix as they are, but also the fine particle surfaces are covered with a metal film and then confined in the solid matrix, a material having a new function due to the interaction between the metal thin film and the fine particle surface is obtained. There have been several studies suggesting that it will be obtained (eg MH Birnboim and WP Ma, Mat. Res. Sy.
mp. Proc. Vol. 164, 277 (1990)). Hereinafter, such fine particles will be referred to as composite ultrafine particles.

As an attempt to actually produce composite ultrafine particles, for example, hydrogen sulfide (H ₂ S) was introduced into a solution containing cadmium ions (Cd ²⁺ ) to produce CdS,
Furthermore, there is an example in which rhodium ions (Rh ³⁺ ) are added to grow rhodium on the surface of CdS fine particles (YM Tricot
and JH Fendler, J. Am. Chem. Soc. 106, 7359 (1
984)).

[0010]

However, the above method is a method that can be applied only to fine particles or colloids that can be produced in a solution, and has a problem that a metal coating cannot be applied to arbitrary fine particles. Further, there is also a problem that the kind of metal that coats the surface of the fine particles is limited to the metal that can be generated by a chemical reaction in a solution. This problem becomes a great obstacle to selection of a combination of materials for maximizing the effect when the application to a nonlinear optical material is considered.

That is, in the composite ultrafine particles, the magnitude of the optical non-linearity depends on the combination of the core particles and the metal on the surface. Therefore, it is desirable that the degree of freedom of the combination is as large as possible in the material search. In addition, the magnitude of nonlinearity of a material generally has wavelength dependency, and the wavelength at which the optical nonlinearity becomes maximum varies depending on the combination of materials. Therefore, depending on the type (wavelength) of the light source used, it is necessary to select a material having large optical nonlinearity at that wavelength. In order to meet these requirements, in the production of composite ultrafine particles in existing solutions, there are many restrictions on the combination of materials, which is a major obstacle in selecting materials.

An object of the present invention is to solve the above problems and to provide a method for producing composite ultrafine particles which is excellent in both the selectivity of the ultrafine particles and the selectivity of the metal coating material.

[0013]

The above object of the present invention can be achieved by the following constitutions.

That is, the raw material of the ultrafine particles is heated and evaporated in an inert gas to form the ultrafine particles of the raw material,
This is a method for producing composite ultrafine particles in which a metal raw material is evaporated by heating in the presence of ultrafine particles to form a metal film on a part or the whole surface of the ultrafine particles.

One of the methods for producing fine particles is an in-gas evaporation method. In this method, fine particles are produced by evaporating a raw material in an inert gas such as Ar and quenching the evaporated element in the gas. In particular, when using a so-called laser heating gas vaporization method in which the raw material is instantly vaporized by using a high-power laser beam for vaporization of the raw material, the number of types of fine particles that can be produced is dramatically increased.

The present invention is for producing composite ultrafine particles by covering the ultrafine particles synthesized in the gas phase by the gas evaporation method or the like with a metal film in the gas phase. The composite ultrafine particles are produced by covering a part or the whole surface of the ultrafine particles with a metal film in the vapor phase by heating and evaporating the metal while moving the particles using a differential pressure.

[0017]

The following effects can be obtained with the composite ultrafine particles of the present invention. First, when fine particles are produced in the gas phase as described above, the types of fine particles that can be produced are dramatically increased. Second, the kind of metal that covers the fine particles can be selected from various metals that can be melted by resistance heating or electron beam heating. That is, the method for producing the composite ultrafine particles according to the present invention is an excellent production method in terms of both the selectivity of the ultrafine particles and the selectivity of the metal coating material. Solvable.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a manufacturing apparatus used for manufacturing composite ultrafine particles. This apparatus is composed of an evaporation chamber 1 for producing ultrafine particles in a gas, a reaction chamber 2 for coating the surface of the produced ultrafine particles with a metal coating, and a collection chamber 3 for collecting composite ultrafine particles coated with a metal coating. It consists of two chambers. The evaporation chamber 1 has a raw material target 4 which is a raw material for ultrafine particles, and irradiates this with a laser beam introduced through a laser introduction window 5 to heat and vaporize the raw material to produce ultrafine particles. An inert gas for quenching the evaporated raw material is introduced through the introduction pipe 6. The reaction chamber 2 has a Knuzen cell 7 containing a metal raw material, and heating the Knuzen cell 7 evaporates the metal material. A quartz substrate 11 was installed in the collection chamber 3 to collect the produced composite ultrafine particles. These three chambers are connected by pipes 10a and 10b, respectively, and the pressure of the evaporation chamber 1 is set to be the highest and the pressure of the collection chamber 3 is set to be the lowest by differential exhaust. Since the pressure in the reaction chamber 2 is lower than the pressure in the evaporation chamber 1, the generated ultrafine particles are introduced into the reaction chamber 2 via the pipe 10a due to the differential pressure. Similarly, the composite ultrafine particles generated in the reaction chamber are guided to the collection chamber through the pipe 10b due to the pressure difference between the ultrafine particles and the collection chamber. These differential pressures are very important factors in producing composite ultrafine particles, and the pressure difference between the evaporation chamber and the reaction chamber is one of the parameters that determine the particle size of the ultrafine particles. The pressure difference between the collection chambers is one of the parameters that determine the particle size of the composite ultrafine particles. In this manufacturing apparatus, the particle size of the ultrafine particles is determined by the pressure in the evaporation chamber, the laser light intensity, the distance from the raw material target 4 to the pipe 10a, the inner diameter of the pipe 10a, etc., in addition to the above pressure difference. On the other hand, the particle size of the composite ultrafine particles can also be controlled by the pressure in the reaction chamber, the flow rate of the ultrafine particles in the reaction chamber, which is determined by the inner diameter of the pipe 10b, the pressure difference from the collection chamber, and the like. The pressure of each chamber is the vacuum gauge 12a provided for each chamber,
It was measured by 12b and 12c.

A method for producing gold (Au) -coated cadmium telluride (CdTe) ultrafine particles (composite ultrafine particles) using this apparatus will be described. Commercially available CdTe polycrystalline wafer (2 inch diameter,
A thickness of 2 mm) was used. First, Ar gas was introduced into the evaporation chamber 1, and the pressure was controlled to about 5 Torr. The pressure in the reaction chamber 2 is 0.05 Torr, the wavelength is 532 nm, the pulse width is 70 ns, and the pulse power is 50 J / cm ² , Nd: Y.
Irradiate AG laser to evaporate CdTe, and pipe 10a
The CdTe ultrafine particles ejected from the sample were collected and analyzed, and it was found that the particle size was about 8 nm and the dispersion of the particle size distribution was very small.

Next, Au (purity 99.999) was used as a metal raw material.
%) In the Knudsen cell 7 attached to the reaction chamber 2 and then at a pressure of about 10 ⁻⁴ Torr,
The laser light was introduced into the evaporation chamber 1, and at the same time, the Knuzen cell was heated. The pressure in the collection chamber was set to about 10 ^-5 Torr. As a result, the intended composite ultrafine particles 20 adhered to the quartz substrate 11 in the collection chamber.

2 and 3 show schematic views of observed images when the composite ultrafine particles 20 deposited on the substrate are observed with a high resolution transmission electron microscope. Several types of composite ultrafine particles 20 have been observed, most of which are shown in FIG.
Although a structure (manufacturing example 1) in which the Au metal fine particles 22 are attached to the surface of the CdTe ultrafine particles 21 as described above was taken, the entire surface of the CdTe fine particles 21 was slightly covered with the Au coating film 23 as shown in FIG. Ultrafine particles (Production Example 2) were also observed. The size of the attached Au fine particles 22 in Production Example 1 is several nm in diameter, and it is true that this is Au fine particles.
This was confirmed by the electron beam diffraction pattern and the plane spacing of the lattice plane image observed when the surface of the fine particles was observed at high magnification. In the case of the Au coating 23 of Production Example 2, its thickness is about 3 nm,
It was confirmed by a method similar to the above that the coating was indeed Au.

This time, the composite ultrafine particles 20 in which the CdTe ultrafine particles 21 are coated with Au have been described, but the present invention is not limited to this, and as described above, the gas evaporation method can be applied to the production of various kinds of ultrafine particles. CdSSe, Zn
2-6 group compound semiconductors including Se and CdS, G
a 3-5 group compound semiconductor such as aAs, InP, InGaAsP, or a magnetic recording material of iron (Fe), cobalt (Co), nickel (Ni) or their alloys or compounds with other elements, in oxygen gas It can be applied to various materials such as oxides obtained by evaporation of various metals. In this embodiment, laser heating evaporation is used for heating evaporation of the raw material,
Although resistance heating was used for evaporation of the metal raw material, other than this, various methods such as induction heating, electron beam heating, and arc discharge may be applied depending on the pressure in the evaporation chamber. of course,
It is also possible to evaporate the fine particle raw material and the metal raw material in the same manner.

In the present embodiment, only the case where Au is used as the metal raw material has been described, but in addition to this, various materials such as aluminum (Al), chromium (Cr) and tungsten (W) which can be evaporated in the reaction chamber are used. Can also be applied.

As a method for producing ultrafine particles in the gas phase,
In addition to the gas evaporation method described here, the sputtering method,
Various methods such as a plasma method have been devised and used for producing ultrafine particles, but the present invention can be applied to any method for producing ultrafine particles as long as the produced ultrafine particles can be transported to a reaction chamber by using an air stream.

[0025]

According to the present invention, since it is possible to coat the ultrafine particles produced in the vapor phase with the metal coating in the vapor phase,
The selectivity of ultrafine particles and metallic materials can be dramatically increased.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for producing composite ultrafine particles used in an example of the present invention.

FIG. 2 is a schematic view of composite ultrafine particles produced by an apparatus for producing composite ultrafine particles used in an example of the present invention (Production Example 1).

FIG. 3 is a schematic view of composite ultrafine particles produced by an apparatus for producing composite ultrafine particles used in an example of the present invention (Production Example 2).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Evaporation chamber, 2 ... Reaction chamber, 3 ... Collection chamber, 4 ... Raw material target, 5 ... Laser introduction window, 6 ... Introduction pipe, 7 ... Knuzen cell, 8a, 8b, 8c ... Gate valve, 10a, 10
b ... pipe, 11 ... quartz substrate, 12a, 12b, 12c
... vacuum gauge, 20 ... composite ultrafine particles, 21 ... CdTe ultrafine particles, 22 ... Au particles, 23 ... Au coating,

Front Page Continuation (72) Inventor Shunsuke Otsuka 3-5-11 Doshomachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd.

Claims (1)

[Claims] 1. A raw material of ultrafine particles is heated and evaporated in an inert gas to form ultrafine particles of the raw material, and the metal raw material is evaporated by heating and evaporation in the presence of the ultrafine particles, and the surface of the ultrafine particles is obtained. A method for producing composite ultrafine particles, which comprises forming a metal coating on a part or the whole surface of