JPH06167728A - Nonlinear optical material and its production - Google Patents

Abstract

PURPOSE:To provide a nonlinear optical material having the large value of a cubic nonlinear sensitivity (3) by separating metallic particulates of at least one of metals selected from copper (Cu) and silver (Aq) by the oxide thin films of the above-mentioned metals, thereby uniformly dispersing the metallic particulates at a high density into the thin films. CONSTITUTION:The Cu particulates 2 are formed on a quartz glass substrate 1. The Cu particulates 2 are oxidized to form the oxide thin films on the surfaces of the Cu particulates 2. Electron cyclotron resonance (ECR) plasma of gaseous oxygen is used as means for oxidizing the surfaces of the Cu particulates 2 in such a case. The Cu particulates 2 are again formed on the oxide thin films 3 and the surfaces of the Cu particulates 2 are oxidized by the ECR plasma. The nonlinear optical material is produced by alternately repeating plural times the formation of the Cu particulates 2 and the oxidation of the surfaces of the Cu particulates (the formation of the oxide thin films 2) in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material in which fine metal particles useful as an element of an optical device utilizing the non-linear optical effect are dispersed, and a method for producing the same.

[0002]

2. Description of the Related Art By dispersing fine metal particles in glass, optical nonlinearity, especially third-order nonlinear susceptibility χ ⁽³⁾
Optics letters, vol. 10, p. 511 (Optics Letters, 10,
p. 511 (1985)). In this case, Au and Ag are used as the metal fine particles, and a metal salt reduction method is used as a method for producing the metal fine particle-dispersed glass. In addition, a metal called “colored glass” in which metal colloids such as gold, silver, and copper are deposited by mixing fine metal particles into a glass raw material using a melting method and then performing heat treatment to deposit a specific metal. Fine particle dispersed glass is also manufactured.

[0003]

However, the third-order nonlinear susceptibility χ ⁽³⁾ of the metal fine particle-dispersed glass thus produced is 10 ^-13 to 10 ^-12 esu, and other nonlinear optical materials are used. Very small compared to. It is considered that this is because the value of the third-order nonlinear susceptibility χ ⁽³⁾ is small because the dispersion amount of the metal fine particles is 5 ppm or less. On the other hand, when the amount of dispersion was increased by the conventional manufacturing method, it was not possible to disperse uniformly.

Further, even when the formation of the metal fine particles and the glass are controlled independently, there is a limit in increasing the dispersion amount of the metal fine particles. This is because in order to separate the metal fine particles from each other, the thickness of the glass must be about several times the diameter of the fine particles.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a non-linear optical material in which metal fine particles are uniformly dispersed in a thin film with high density and a method for producing the same.

[0006]

In order to achieve the above object, the non-linear optical material according to the present invention is such that at least one metal fine particle selected from copper (Cu) and silver (Ag) is an oxide of the metal. Separated by a thin film, and
The metal fine particles are dispersed to form a layered structure.

In the above structure, it is preferable that the size of the metal fine particles is in the range of 0.5 to 20 nm and the film thickness of the oxide thin film is in the range of 0.5 to 50 nm.
Further, in the method for producing a nonlinear optical material according to the present invention, fine particles of at least one metal selected from copper (Cu) and silver (Ag) are separated by the oxide thin film of the metal to produce the nonlinear optical material. The method is characterized in that after forming the metal fine particles, the step of oxidizing the surface of the metal fine particles is repeated.

In the above-mentioned method of the present invention, the size of the metal fine particles is in the range of 0.5 to 20 nm, and
The film thickness of the oxide thin film is preferably in the range of 0.5 to 50 nm.

Further, in the constitution of the method of the present invention,
It is preferable to use electron cyclotron resonance (ECR) plasma of an oxidizing gas as a means for oxidizing the metal fine particles.

[0010]

According to the above-mentioned constitution of the present invention, since Cu ₂ O or Ag ₂ O which is an oxide of copper (Cu) or silver (Ag) is transparent in the optically active region, copper (Cu) or Silver (A
It is possible to obtain a non-linear optical material in which the metal fine particles of g) are densely and uniformly dispersed, and as a result, the value of the third-order non-linear susceptibility χ ⁽³⁾ can be increased.

Further, according to the constitution of the method of the present invention, since the metal fine particles are formed and then the metal fine particles are oxidized, C which is an oxide of copper (Cu) or silver (Ag) is used.
u ₂ O or Ag ₂ O can be easily formed to separate the metal fine particles from each other. In addition, since the steps of forming the metal fine particles and oxidizing the surface of the metal fine particles (formation of the oxide thin film) are repeated, the oxide thin film can be formed as compared with the case of forming the oxide thin film by the conventional synthesis method after the metal fine particles are formed. Can be formed uniformly and thinly, and as a result, the metal fine particles can be dispersed at a high density.

In the method of the present invention, according to a preferred structure in which electron cyclotron resonance (ECR) plasma of an oxidizing gas is used as a means for oxidizing the metal fine particles, atomic oxygen which plays an important role in the oxidizing action is removed. A large amount can be generated and low pressure (for example, 10 ^{-3 to} 10 P)
Since the plasma can be generated in a), the generated atomic oxygen can be transported to the surface of the Cu or Ag metal fine particles without colliding with other particles, and as a result, the surface of the metal fine particles can be reliably and easily oxidized. You can

[0013]

[Example] The nonlinear optical effect in the glass in which metal particles are dispersed is exhibited by the absorption of surface plasmons generated at the interface between the metal particles and the glass by light irradiation. This surface plasmon occurs in the optically active region where the real part of the dielectric function of metal is negative. The optically active region extends from the visible light region to the infrared light region, and the resonance absorption peak of the surface plasmon is such that the absolute value of the real part of the dielectric function of the metal is the dielectric constant (refractive index of the refractive index of the material around the metal fine particles. It appears at a wavelength equal to twice (squared). As long as the material around the metal fine particles is satisfied, any material may be used as long as it is not glass but transparent in the optically active region, and the resonance absorption peak wavelength of the surface plasmon is within the band gap of the semiconductor. Alternatively, a semiconductor may be used.

Therefore, if the compound of the metal fine particles themselves, especially the oxide which is easy to manufacture, is transparent in the optically active region, the metal fine particles can be easily separated from each other and the metal fine particles can be dispersed at a high density.

By the way, the optically active region of copper (Cu) extends from 400 nm to the infrared region. The oxide of Cu is Cu ₂ O, which is an oxide semiconductor, and its refractive index and band gap are about 2.17 and about 500 nm, respectively, so that it is transparent in the optically active region, and the resonance peak wavelength of the surface plasmon. Is about 610 nm.

Even if the semiconductor or the like is absorbed in the optically active region, the resonance absorption peak of the surface plasmon can be observed by forming the semiconductor layer extremely thin and suppressing the absorption by the semiconductor. For example, in the case of silver (Ag), the optically active area is 40% like Cu.
It extends from 0 nm to the infrared region. The band gap of Ag ₂ O, which is an oxide of Ag, is about 780 nm, but when the film thickness of Ag ₂ O is set to 50 nm or less, light penetrates to the Ag particles and the resonance absorption peak of the surface plasmon due to the Ag particles. Can be observed.

The present inventors have paid attention to the above facts and have completed the present invention. That is, Cu or Ag metal fine particles are mixed with each other to form Cu ₂ O or Ag ₂ O which is an oxide thereof.
By separating by, it was possible to obtain a non-linear optical material in which Cu or Ag metal fine particles were densely and uniformly dispersed.

The size of the fine metal particles in the nonlinear optical material of the present invention is preferably about 0.5 to 20 nm, and metal oxides (Cu ₂ O, Ag _2).
The film thickness of O) is preferably about 0.5 to 40 nm.

The present invention will be described in more detail below with reference to examples. FIG. 1 is a schematic configuration diagram of a sputtering apparatus used in this embodiment, and FIG. 2 is a process schematic diagram showing a method for manufacturing a nonlinear optical material of this embodiment.

As shown in FIG. 1, the sputtering apparatus 4 supplies voltage and current to the metal target 5, the shutter 6, the electron cyclotron resonance (ECR) plasma gun 7 for generating atomic oxygen, the substrate 1, and the target 5. The DC power supply 8 is provided for the operation. Quartz glass is used as the substrate 1, and Cu is used as the metal target 5.
The ECR plasma gun 7 is composed of a microwave waveguide 9 for introducing microwaves, a quartz plate 10, an electromagnet 11 for generating ECR plasma, and an inlet 12 for introducing oxygen gas.

In this example, a nonlinear optical material was produced by repeating the steps of forming Cu fine particles on the substrate 1 and then oxidizing the surface of the Cu fine particles. First, the step of forming Cu fine particles on the substrate 1 will be described. Argon is used as the sputtering gas, the gas pressure is 5 Pa, the temperature of the substrate 1 is 150 ° C., and the Cu target 5 is used.
DC voltage and DC current supplied to
It was set to 0 mA. Since the deposition rate of Cu under these conditions is about 0.5 nm / sec, the shutter 6 is set to 40
Opened for a second. At this stage, as a result of observation using an electron microscope, it was confirmed that Cu fine particles 2 having a diameter of about 20 nm were formed on the substrate 1 (FIG. 2A).

Next, the step of oxidizing the surface of the Cu fine particles will be described. Oxygen gas was introduced into the ECR plasma gun 7 through the inlet 12 and the gas pressure was set to 0.1 Pa. Further, the microwave of 2.45 GHz is converted into the microwave waveguide 9
Then, it was introduced into the ECR plasma gun 7 through the quartz plate 10. The magnetic field strength satisfying the electron cyclotron resonance condition determined by the microwave frequency is 2.45 GHz.
In the case of, since it is 0.0875T, the magnetic field strength under this ECR condition was generated by the electromagnet 11. And EC
The Cu fine particles 2 were irradiated with the ECR plasma of oxygen gas generated in the R plasma gun 7 for about 10 minutes. The resonance absorption peak wavelength of surface plasmon was only about 560 nm before irradiation with ECR plasma of oxygen gas.
After irradiation, double peaks of about 560 nm and about 620 nm were obtained. This means that the Cu fine particles 2 are in contact with layers having different refractive indexes. That is, before the irradiation, only the quartz glass substrate 1 was in contact with the Cu fine particles 2, but after the irradiation, the Cu fine particles 2 had two layers of the quartz glass substrate 1 and the Cu oxide thin film (Cu ₂ O) 3. Means that they are in contact. Thus, it was confirmed that the oxide thin film 3 was formed on the surface of the Cu fine particles 2 (FIG. 2B).

Since the ECR plasma is highly excited and has a high density, it can generate a large amount of atomic oxygen which plays an important role in the oxidation action, and also has a low pressure (for example, 10 ^{-3 to} 10 Pa).
Since the plasma can be generated by, the generated atomic oxygen can be transported to the surface of the Cu fine particles 2 without colliding with other particles, and as a result, the surface of the Cu fine particles 2 can be reliably and easily oxidized.

Next, Cu fine particles 2 are formed again on the oxide thin film 3 formed as described above (see FIG. 2).
(C)), the surface of the Cu fine particles 2 was oxidized by ECR plasma.

As described above, the formation of Cu fine particles 2 and C
The oxidation of the surface of the u fine particles 2 (formation of the oxide thin film 3) is alternately repeated 30 times, and the thickness of the entire layer of the Cu fine particles 2 is set to 4
It was set to 00 nm. As a result, the resonance absorption peak wavelength of the surface plasmon was almost 620 nm, and the dispersion amount of the Cu fine particles 2 reached about 50%. As a result, the non-linear optical material in which the Cu particles 2 were separated from each other by the oxide thin film (Cu ₂ O) 3 and the Cu particles 2 were uniformly dispersed at a high density could be manufactured.

[0026] to produce a non-linear optical material as described above, when the nonlinear optical properties were measured by degenerate four wave mixing process of nitrogen laser excitation dye laser, about 10 ^-6 e
A very large third-order nonlinear susceptibility χ ⁽³⁾ called su was obtained.

Further, silver (Ag) is used instead of Cu,
The formation of Ag fine particles is performed by a thermal vapor deposition method (vacuum degree: 5 × 10 ⁻⁴ P
a, substrate temperature: 100 ° C.), and an oxide thin film (Ag ₂ O) was formed using ECR plasma as in the case of Cu. In this case, the diameter of the Ag particles is about 1
0 nm, Ag oxide thin film (Ag ₂ O) film thickness is about 5 n
m, the formation of Ag fine particles and the oxidation of the surface of Ag fine particles (formation of an oxide thin film) were repeated 30 times, and as a result, a nonlinear optical thin film having a thickness of about 400 nm could be obtained. In this nonlinear optical thin film, the dispersion amount of Ag particles reached 60%, and the third-order nonlinear susceptibility χ ⁽³⁾ was about 1
It was 0 ^-6 esu. As a result, the Ag particles are separated from each other by the Ag oxide thin film (Ag ₂ O).
It was confirmed that the fine particles were densely and uniformly dispersed.

As a means for forming the metal fine particles,
From the viewpoint of controllability and the like, it is preferable to use the above-mentioned sputtering method or thermal evaporation method, but the method is not necessarily limited to these, and for example, a thermal CVD method or a plasma CVD method can be adopted.

As the oxidizing gas used for the ECR plasma, it is preferable to use the above-mentioned oxygen gas from the viewpoint that impurities are less likely to enter, but the oxidizing gas is not necessarily limited to this and exhibits oxidizing properties. If it is a gas, for example, nitric oxide or the like can be used.

[0030]

As described above, according to the nonlinear optical material of the present invention, Cu ₂ O or Ag ₂ O which is an oxide of copper (Cu) or silver (Ag) is transparent in the optically active region. Because of this, it is possible to obtain a non-linear optical material in which metal fine particles of copper (Cu) or silver (Ag) are densely and uniformly dispersed, and as a result, the value of the third-order non-linear susceptibility χ ⁽³⁾ is increased. can do.

According to the method of the present invention, since the metal fine particles are formed and then the metal fine particles are oxidized, Cu ₂ O which is an oxide of copper (Cu) or silver (Ag) is used.
Alternatively, Ag ₂ O can be easily formed to separate the metal fine particles from each other. Further, since a series of steps of forming the metal fine particles and oxidizing the surface of the metal fine particles (formation of the oxide thin film) is repeated, the oxidation process is more difficult than forming the oxide thin film by the conventional synthesis method after forming the metal fine particles. The material thin film can be formed uniformly and thinly, and as a result, the metal fine particles can be dispersed at a high density.

In the method of the present invention, according to a preferred structure in which electron cyclotron resonance (ECR) plasma of an oxidizing gas is used as a means for oxidizing the fine metal particles, atomic oxygen which plays an important role in the oxidizing action is removed. A large amount can be generated and low pressure (for example, 10 ^{-3 to} 10 P)
Since the plasma can be generated in a), the generated atomic oxygen can be transported to the surface of the Cu or Ag metal fine particles without colliding with other particles, and as a result, the surface of the metal fine particles can be reliably and easily oxidized. You can

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a sputtering apparatus used in an embodiment of the present invention.

FIG. 2 is a process schematic diagram showing a method for manufacturing a nonlinear optical material according to an embodiment of the present invention.

[Explanation of symbols]

 1 Substrate 2 Cu Fine Particles 3 Oxide Thin Film 4 Sputtering Device 5 Metal Target 6 Shutter 7 Electron Cyclotron Resonance (ECR) Plasma Gun 8 DC Power Supply 9 Microwave Waveguide 10 Quartz Plate 11 Electromagnet 12 Inlet Port

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Mikuro 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. Non-linear optics in which at least one metal fine particle selected from copper (Cu) and silver (Ag) is separated by the metal oxide thin film, and the metal fine particle is dispersed to form a layered structure. material. 2. The size of the metal fine particles is 0.5 to 20 nm.
And the film thickness of the oxide thin film is 0.5 to 50.
The nonlinear optical material according to claim 1, which is in the range of nm. 3. A method for producing a non-linear optical material by separating fine particles of at least one metal selected from copper (Cu) and silver (Ag) by an oxide thin film of the metal, and forming fine metal particles. And then repeating the step of oxidizing the surface of the metal fine particles. 4. The size of the metal fine particles is 0.5 to 20 nm.
And the film thickness of the oxide thin film is 0.5 to 50.
The method for producing a non-linear optical material according to claim 3, wherein the range is nm. 5. The method for producing a nonlinear optical material according to claim 2, wherein electron cyclotron resonance (ECR) plasma of an oxidizing gas is used as a means for oxidizing the metal fine particles.