JPH04281433A - Superfine particle dispersion thin film - Google Patents

Abstract

PURPOSE:To offer a thin film useful for a nonlinear optical material which shows 0-th dimensional behavior of electron or exciton, so-called quantum sizing effect, due to three-dimensional sealing effect. CONSTITUTION:The superfine particle dispersion thin film is formed by dispersing superfine particles of metal or semiconductor at a concn. as high as >=15 atomic % in a transparent matrix, and forming a columnar structure perpendicular to the film plane in the film so as to regularly align the superfine particles of metal and semiconductor in the vertical direction. The thin film can be used for an optical bistable element, optical gate, optical switch, wavelength converter, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to ultrafine particle-dispersed thin films, and more specifically, they are useful as nonlinear optical materials due to the so-called "quantum size effect" in which electrons and excitons exhibit zero-dimensional behavior due to a three-dimensional confinement effect. , relates to a thin film in which ultrafine particles are dispersed in a transparent matrix. This ultrafine particle dispersed thin film can be used for optical bistable devices, optical gate optical switches, wavelength conversion devices, etc.

0002

BACKGROUND OF THE INVENTION The quantum size effect of fine particle dispersed glass has recently been discovered and is attracting attention. Generally, transparent insulating materials such as glass and polymers (
It is formed by dispersing ultrafine semiconductor or metal particles with a particle diameter of several hundred angstroms or less in a matrix) and forming an embedded thin film, and it is said that it can be expected to greatly increase nonlinearity due to the quantum size effect.

[0003] As an example, "Optics" Vol. 19, No. 1 (January 1990), pages 10-16 and 17-
24 pages, “Applied Physics” Vol. 59, No. 2 (1990), pp. 155 (23) to 162 (30), “Applied Physics” No. 5
Volume 9, No. 6 (1990), Nos. 738 (52) to 745 (
Research on third-order optical nonlinearity in ultrafine semiconductor and metal particles in various matrices has been published on page 59).

However, as far as the literature published so far has been considered, at present, (1) the average size of the ultrafine particles is determined depending on the substrate temperature and the heat treatment after film formation when forming the ultrafine particles into a thin film. (2) The content of the ultrafine particles in the matrix is as low as 15 atomic% at most; It is said to be difficult to contain.

[0005] The average size (particle diameter) of ultrafine particles is generally controlled by the substrate temperature (150 to 400°C) during film formation and heat treatment after film formation. The heat treatment is optionally carried out at 600-700° C., which has the disadvantage that plastics cannot be used for the substrate. On the other hand, the reason why the content of ultrafine particles in a thin film has been suppressed to a few percent to 15 atomic percent is that it is limited to the FR sputtering method, and that This is because a later heating means was used, and there is a disadvantage that the amount of light must be increased in order to make the optical nonlinearity function. Conversely, if the content of ultrafine particles in the thin film can be increased, optical nonlinearity can be activated with a small amount of light.

[0006]

SUMMARY OF THE INVENTION The present invention allows the use of plastic for the substrate and provides a thin film in which the content of ultrafine particles in the transparent matrix is 15 atomic % or more.

[0007]

[Means for Solving the Problems] The ultrafine particle-dispersed thin film of the present invention has 15 atomic% or more of ultrafine particles of metal or semiconductor dispersed in a transparent matrix, and has a columnar structure, and the columnar structure is perpendicular to the film surface. And it is characterized by being formed in the surface of the film.

The present invention will be explained in more detail below.
Prior to that, I will briefly touch on the "nonlinear optical effect" and "quantum size effect" and the relationship between them. Nonlinear effect is a phenomenon in which optical properties such as the absorption coefficient and refractive index of a material that is irradiated with light change depending on the intensity of light, and by using this, it is possible to control light with light. , it is possible to realize an all-optical logic element that uses only light for input and output. The quantum size effect means that electrons and holes in semiconductor ultrafine particles embedded in transparent glass or the like in the visible light region are three-dimensionally confined by the deep potential created by the glass or the like. Therefore, if we think of electrons as waves, the wave mode is limited to a specific one within a small box, so the electronic state mentioned above in the quantum size effect becomes discrete, and the oscillator strength and nonlinear sensitivity rate increases.

The thin film according to the present invention has ultrafine metal or semiconductor particles dispersed in a transparent matrix and a transparent matrix at a high concentration of 15 atomic% or more in the visible light region, and has a columnar structure perpendicular to the film surface. By forming them in a film, ultrafine metal/semiconductor particles are arranged vertically in an orderly manner, and by adopting this structure, the particle size can be controlled by controlling the substrate temperature or heating such as heat treatment. Therefore, it is possible to easily control the column diameter of the columnar structure and change the particle diameter within the column.

[0010] The diameter of the columnar structure is determined to be 100 to 500 Å because, for example, if ion beam sputtering is used, the behavior (migration) of atoms on the substrate can be controlled by the amount of gas introduced and the intensity of the ion beam. It can be changed. Since the probability of ultrafine particles existing between the pillars is extremely reduced, ultrafine particles can be arranged vertically at a high concentration. In the case of an optical device, the light is incident on the film surface as perpendicularly as possible, so this columnar structure rarely interferes with the transmission of light.

As mentioned above, the columnar structure has a uniform column diameter depending on the film forming conditions and is formed vertically and regularly, so microfabrication techniques such as electron beam lithography and reactive ion etching are used. without any
It can easily be made into a vertical nonlinear optical thin film. The spacing between columns can also be controlled by the gas pressure introduced.

[0012] The size of the ultrafine particles contained in the matrix must be controlled to be less than the Bohr radius. however,
For example, the semiconductor CdSxSey (where y=1-x)
When ultrafine particles of 1 are scattered in the glass, the Bohr radius is 30 to 50 Å, but in the present invention, it is sufficient that it is 100 Å or less. This is because in the thin film of the present invention, the ultrafine particles are stacked vertically in a columnar manner. However, a feature of the present invention is that the particle size can be roughly controlled by the diameter of the columnar structure. That is, the particle size does not become larger than the column diameter. The column diameter can be controlled to 50 Å or more.

[0013] The fine particle material includes CdSxS as a semiconductor.
ey (however, y=1-x), CdS, CdSe, C
uCl, GaAs, ZnSe, InSb, InP, Cd
Examples include Te, metals such as Au and Ag, and oxides such as MnO.

The third-order nonlinear susceptibility, which represents the magnitude of nonlinearity, is proportional to the number density of ultrafine particles. Therefore, it is desirable that the number of ultrafine particles be large. However, when a film is formed by heating a substrate using conventional RF sputtering method, the content of ultrafine particles in the thin film is a few atoms, as mentioned above.
The average ic% is at most 15 atomic%. In contrast, in the present invention, the content of ultrafine particles in the thin film is 20 atomic% or more, which can be confirmed by, for example, XPS. Although the reason for this is not necessarily clear, it is thought that this is attributable to the fact that the present invention preferably uses ion beam sputtering to obtain a columnar structure, and manufactures the film while introducing gas during film formation.

[0015] If a film is formed by ion beam sputtering while introducing a gas, a columnar structure can be formed directly above the glass even if glass is used as the transparent substrate, for example. If you want to change the column diameter, you can change the gas pressure, but for example, you can use a film (such as Au, ZnO, TiO2
), and a columnar structure is provided on top of it, the column diameter can be controlled by being influenced by the particle size of the base.

The substrate may be of any material as long as it is transparent to visible light, and glass, quartz, polycarbonate, polyethylene terephthalate, or other plastics are used.

Film forming methods include ion beam sputtering, PV
D method, CVD method, etc. can be used, but ion beam sputtering method with good reactivity is preferable.

The film thickness is not particularly limited, but is 1
Approximately 00 Å to 1 μm is suitable.

[0019]

[Examples] Examples will be shown next, but the present invention is not limited thereto. In addition, a comparative example is also shown.

Example 1 A thin film approximately 1200 Å thick was prepared on a transparent glass substrate by ion beam sputtering under the following conditions. Here, by changing only the gas pressure of introduced oxygen, (A) (B) (
Four different types of thin films were prepared: C) and (D). Target AuSi
(Si50atomic%) Substrate heating
None Ionized gas
Ar (purity 99.999%) Introduced gas Oxygen (99.99%)
9%) Introduced gas pressure (A
)0.6/106Torr
(B) 0.8/106To
rr
(C) 1.0/106Torr
(D)1.2/
106Torr ion gun (voltage x current) 9KV
×1.7mA Ion incident angle
30 degrees base pressure 4/10
7Torr Target-board distance 14mm

[
When these transparent films were examined by X-ray diffraction, a broad minute peak of SiO2 and a minute peak of Au were observed. When the side cross section was observed using a TEM method, a columnar structure as shown below was found in the diameter. (A) Approximately 160
Å (B) Approx. 130 Å (C) Approx. 110 Å (D
) The average particle size of Au in each sample determined from the approximately 70 Å TEM image is (A) approximately 61 Å, (B) approximately 45 Å, (C) approximately 30 Å,
(D) It was about 21 Å. In addition, Au obtained from XPS
The composition ratio was about 20 atomic% or more.

Furthermore, from the measurement results of the optical absorption edge investigated using a spectrophotometer at room temperature, a clear high energy shift (
A blue shift) was observed in all samples, and its size was proportional to the square of the average particle diameter of the particles, confirming that it shows a quantum size effect.

Comparative Example 1 A thin film with a thickness of about 1200 Å was prepared on a transparent glass substrate using the RF sputtering method under the following conditions. In addition, the area ratio of Au/SiO2 in the target, the glass substrate temperature,
By changing the high frequency power (E) (F) (G) and (H)
Four different types of thin films were prepared. Placing the Au chip on the target SiO2 Introducing gas Ar (99
．． 999%) Introduced gas pressure 4
/103Torr glass substrate temperature
200-350℃ base pressure 5/
107Torr Target-board distance 50mm High frequency power 205~30
0W

The average particle size of Au in each sample is (E) approximately 7
7 Å, (F) about 52 Å, (G) about 33 Å, (H) about 29
Å, and no columnar structure was observed in any of the samples from the cross-sectional TEM images of the films. Further, from the X-ray diffraction pattern, a broad minute peak of SiO2 and a minute peak of Au were observed. From the measurement results of the optical absorption edge obtained from XPS, a high energy shift similar to that in Example 1 was observed, but it was not proportional to the square of the average particle size of the ultrafine Au particles.

[0025]

Effects of the Invention The ultrafine particle dispersed thin film of the present invention has the following advantages. (1) It contains a high concentration of ultrafine particles of approximately 100 Å or less and has a columnar structure, and it does not require substrate heating during film formation or heat treatment after film formation, so it is possible to use a plastic substrate etc. can. Therefore, it is easy to produce a film with high third-order nonlinear susceptibility. (2) Since the ultrafine particles are arranged in a direction perpendicular to the film surface, it is particularly effective for making use of light incident perpendicularly to the film.

Claims (2)

[Claims] Claim 1: Ultrafine particles of metal or semiconductor are dispersed in a transparent matrix at 15 atomic % or more and have a columnar structure, and the columnar structure is perpendicular to the film surface and formed in the film surface. Characteristic ultrafine particle dispersed thin film. 2. The ultrafine particle dispersed thin film according to claim 1, wherein the particle size of the ultrafine particles is 100 Å or less.