JPH05142597A - Organic nonlinear optical thin film and production thereof - Google Patents

Abstract

PURPOSE:To obtain the org. nonlinear optical thin film which is excellent in both of a nonlinear optical characteristic and laser resistance by using sapphire as a substrate for vapor deposition and depositing fluorene compds. by evaporation on the sapphire substrate, thereby forming thin films CONSTITUTION:The sapphire is used as the substrate for vapor deposition and the fluorene compds. are deposited as an optical medium having a nonlinear refractive index by evaporation alone or in combination with other compds. on the sapphire substrate to form the thin film. A thin film of CaF2 or the like is deposited by evaporation as a 2nd layer on the vapor deposited thin film of the fluorene compd. alone or the mixture composed of the fluorene compd. and the other compds. The structure of the fluorene compds. of C60 and C70 are evidently extremely stable and the vapor deposition operation is possible without thermal decomposition even at a high temp. of 320 deg.C from the results of the direct ionization mass analysis of the mixture composed of the C60 and C70 fluorenes at 320 deg.C. Then, the thin films of the fluorene compds. having the high laser resistance characteristic and the large cubic nonlinear constant are produced by the vapor deposition method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic nonlinear optical thin film and a method for producing the same.

[0002]

2. Description of the Related Art In the field of optoelectronics, third-order organic nonlinear optical materials have been actively developed. Of these materials, the polydiacetylene derivative is one of the materials that exhibits the largest third-order nonlinear optical property, and χ ⁽³⁾
A thin film with a value of more than 10 ^-10 esu has been obtained (TK
anakete, K, Ishikawa, T .; Hase
Gawa, T .; Koda, K .; Takeda, M .; Ha
segawa, K .; Kubodera and H.M. K
obayashi, Appl. Phys. Lett. ，
54 , 2287 (1989)).

A thin film manufacturing technique is required for making a third-order nonlinear optical material into a device. Generally, a thin film of a third-order nonlinear optical material is produced by a Langmuir-Blodgett (LB) film method, a casting method, a spin casting method, an evaporation method, or the like. In the LB film method, it is necessary to introduce a long chain substituent into the molecule, and it is necessary to start the study from the method of compound synthesis. Further, there are disadvantages that the introduction of substituents causes a relative decrease in non-linearity and that film formation takes a long time. The casting method and the spin casting method are limited in application because it is necessary to use a solvent in which the nonlinear optical material dissolves without causing a chemical reaction or a decomposition reaction as a solvent.
In addition, the solvent remaining during film formation gradually volatilizes and tends to form voids.

In the vapor deposition method, the compound is evaporated or sublimated as it is to form a film, so that the characteristics of the nonlinear optical material can be utilized to the maximum extent. In order to form a thin film of a polydiacetylene compound by a vapor deposition method, it is necessary to polymerize the diacetylene monomer by light or heat after forming a film by the vapor deposition method (TK
antake, K .; Ishikawa, T .; Kod
a, Y. Tokuura and K.K. Takeda, A
ppl. Phys. Lett. , 51 , 1957 (19
87)). In this case, in order to prevent decomposition during vapor deposition of the monomer, it is necessary to perform the vapor deposition operation at a low temperature, and the vapor deposition rate is 2%.
It has a drawback that it is very small, about 00Å / hour. In addition, since it polymerizes after vapor deposition, the film quality is likely to change,
When the film thickness is 500 nm or more, there is also a drawback that the film quality is sharply deteriorated due to polycrystallization accompanying polymerization.

In applying a device of the third-order nonlinear optical material, it is necessary to form a thin film having a film thickness of about 1 μm or more. Therefore, it is possible to form a thin film by a vapor deposition method and it is high without performing a polymerization reaction after vapor deposition. Development of a method for producing an organic nonlinear optical thin film that can obtain a thin film having χ ⁽³⁾ is desired.

Recently, in order to achieve the above object, the non-linear optical characteristics of a vapor-deposited film of C60 fullerene vapor-deposited on a quartz glass substrate have been studied, and an Nd: YAG laser 1.06 μm has been studied.
For the wavelength of m, χ ⁽³⁾ = 2 × 10 ^-10 esu is obtained (H. Hoshi, N. Nakamura,
Y. Maruyama, T .; Nakagawa, S .; S
uzuki, H .; Shiromarunu Y. Ac
hiba, Jpn. J. Appl. Phys. , 30 ,
L1397 (1991)). In this case, the wavelength of the third harmonic generation (THG) is 355 nm, which is a measured value in the resonance region substantially matching the absorption maximum wavelength (350 nm) of the C60 thin film. In general, it is known that a χ ⁽³⁾ value that is one digit or more larger than that in the non-resonance condition is observed under the resonance condition, and thus the measured value may be greater than that in the non-resonance condition. is expected. Further, under the resonance condition, the mechanism of the non-linear effect is caused by absorption, so that it is expected that the response time becomes slower than the non-linear optical effect caused by ordinary electronic polarization. 0.8 to 1.
Since it is used in a wide wavelength range of 0 μm, 1.3 μm and 1.55 μm band, the nonlinear optical thin film needs to have a large χ ⁽³⁾ value even under non-resonant conditions. However, the C60 thin film vapor-deposited on a quartz glass substrate has a drawback that molecules in the thin film evaporate due to irradiation of laser light having a wavelength of 1.9 μm, which is generally measured in the past, and the laser resistance is poor. Further, there is a drawback that the intensity of the laser light that enables the measurement of χ ⁽³⁾ is small, and that even the weak light is gradually evaporated, the measured value changes over time, making accurate measurement difficult. Therefore, it has been desired to propose a method for producing a fullerene thin film having excellent laser resistance in a wide wavelength range.

[0007]

The present invention is a vapor deposition method,
It is an object of the present invention to provide an organic nonlinear optical thin film using a fullerene compound having a large χ ⁽³⁾ with improved laser resistance and a method for producing the same.

[0008]

In order to achieve the above object, the inventors of the present invention have been keenly aware of a thin film manufacturing method in order to find a device material having excellent optical nonlinearity and laser resistance using a fullerene compound as a thin film material. As a result of the examination, the present invention has been achieved.

In the method for producing an organic nonlinear optical thin film of the present invention, sapphire is used as a substrate for vapor deposition, and a fullerene compound is used alone as an optical medium having a nonlinear refractive index.
Alternatively, it is characterized by forming a thin film by mixing with another compound and depositing it on the sapphire substrate.

The organic nonlinear optical thin film of the present invention is characterized by comprising a vapor-deposited thin film of a fullerene compound alone or a mixture with another compound, and a second layer provided on the vapor-deposited thin film. ..

[0011]

Function: Mixture of C60 and C70 fullerene at 320 ℃
The result of the direct ionization mass spectrometry at is shown in FIG. m /
Divalent ions of C60 and C70 are observed around e: 360 and 420, and monovalent ions around m / e: 720 and 840. Since other fragment ions are hardly observed, it is clear that the structures of fullerene compounds such as C60 and C70 are extremely stable, and vapor deposition work can be performed even at a high temperature of 320 ° C. without thermal decomposition.
In the present invention, a thin film of a fullerene compound having high laser resistance and a large third-order nonlinear optical constant of χ ⁽³⁾ ≧ 10 ⁻¹⁰ esu can be produced by the vapor deposition method.
Further, in order to improve the laser resistance property and the third-order nonlinear optical property of the fullerene thin film, the pressure inside the vacuum apparatus at the time of vapor deposition should be lowered, and sapphire, which is crystalline and has high thermal conductivity, should be used as the vapor deposition substrate. There are effects such as increasing the substrate temperature during vapor deposition, and providing a second layer on the prepared fullerene thin film. Further, the thin film of the fullerene compound produced by the method of the present invention has a large non-linear refractive index coefficient because of its large third-order nonlinear effect.

The compound used as a mixture with the compound of the present invention does not necessarily have to exhibit optical nonlinearity. However, it is expected that the optical non-linearity will be further improved by mixing the compound showing the large optical non-linearity. Therefore, it is preferable to mix a compound having large optical non-linearity with the fullerene compound. Generally, it is difficult to obtain a smooth thin film because a compound exhibiting large optical non-linearity tends to be a polycrystalline thin film, but the smoothness can be improved by mixing with a fullerene compound used in the present invention. It also has the advantage. Examples of the compound mixed for such a purpose include a phthalocyanine derivative, a CT complex of perylene and tetracyanoquinodimethane (TCNQ), and the like.

Examples of the second layer formed on the vapor-deposited thin film of the fullerene compound of the present invention include SiO ₂ and Si.
Examples include vapor-deposited films of O, TiO ₂ , CaF ₂ , MgO, and MgF ₂ , spin-coated films of polyimide, polyamide, and nylon, cast films of silicone resin, epoxy resin, urethane resin, and the like.

[0014]

EXAMPLES The features of the present invention will be described below in more detail with reference to examples.

Example 1 A K-cell 2 for heating and vaporizing fullerene and a heater block 4 for controlling the substrate temperature during vapor deposition are installed in a vacuum vapor deposition apparatus 1 (FIG. 2). Into the quartz crucible 5 of the K-cell, 0.1 g of C60 fullerene was charged, and the single crystal sapphire substrate 6 was closely attached and fixed to the heater block 4, and the internal pressure of the apparatus was 2 × 10 ^-9 torr.
It is maintained in an ultrahigh vacuum condition of r or less. Gradually heat the fullerene in the K-cell to adjust the temperature to 325 ° C.
A C60 fullerene thin film of 00Å was obtained. Although the pressure inside the equipment increased due to heating, it was always about 8 × 10 ^-9 t during the evaporation work.
The pressure of orr was kept.

FIG. 3 shows the prepared C60 fullerene thin film having a wavelength of 1.9 μm, a pulse width of 6 ns, and a repetition rate of 10 Hz.
This is the result of measuring the THG light intensity that emerges while injecting a laser pulse light with an intensity of 20 MW / cm ² and rotating the sample around an axis perpendicular to the incident direction of the laser light. This pattern is called maker fringe. The efficiency of the third-order effect can be measured by measuring a material of known efficiency (here, quartz glass was used) with the same observation system and comparing it with the peak intensity of THG (for the measurement principle, solid Physics, vol.24, N
o. 11, 903 (1989)). From Figure 3
^{When (3)} was obtained, χ ⁽³⁾ = 1.4 × 10 ^-10 esu
Met.

For comparison, a C60 fullerene cast film was formed on a single crystal sapphire substrate using a benzene solution of C60 fullerene, and the nonlinear optical characteristics were measured. The result obtained by measuring the cast film under exactly the same conditions as the vapor-deposited film is χ ⁽³⁾ = 3.0 × 10 ^-11 e
It was found to be su and lower than that of the vapor deposition film. From the above, it has been clarified that the nonlinear optical characteristics can be enhanced by forming a thin film of fullerene molecules by the vapor deposition method.

On the other hand, when the non-linear optical characteristics of the C60 fullerene vapor-deposited on a quartz substrate were measured, the film disappeared at the same pump light intensity of 20 MW / cm ² as when the vapor-deposited film of the sapphire substrate was measured. When the pump light intensity was reduced and the measurement was performed at 10 MW / cm ² , it was confirmed that χ ⁽³⁾ = 2.0 × 10 ^-11 esu in the initial measurement and then gradually decreased due to the disappearance of the thin film. ..

As described above, the method for producing a fullerene thin film by vapor deposition using single crystal sapphire as the substrate has made it possible to enhance the laser resistance and obtain an organic nonlinear optical thin film having a large χ ⁽³⁾ .

Example 2 A C60 fullerene thin film was produced on each of a sapphire substrate and a quartz substrate by using the same vacuum device as in Example 1 and changing the internal pressure during vapor deposition. Figure 4 shows the pressure dependence of χ ⁽³⁾ . The measurement conditions for χ ⁽³⁾ are the same as in Example 1, and the pump light intensity is 20 MW / cm ² . It was clarified that χ ⁽³⁾ tends to increase when the internal pressure of the device during vapor deposition is lowered, and that the maximum value is obtained when the internal pressure of the device is low on the sapphire substrate. For a thin film deposited on a quartz substrate, χ ⁽³⁾ can be measured only when it is deposited under the condition of low equipment pressure. It was found that when the pressure inside the device was increased, the thin film disappeared due to light irradiation, and the laser resistance was greatly reduced.

Example 3 On a sapphire substrate prepared by the same method as in Example 2 and on a fullerene thin film on a quartz substrate, a CaF ₂ film or a MgF ₂ film was deposited by vacuum evaporation using a K-cell 3. A coated two layer thin film was prepared. CaF _{2 with a} thickness of 3 μm
The result of obtaining nonlinear optical properties for the samples coated with films in THG method by laser of Example 2 the same pump power and 20MW / cm ² shown in FIG. Since the thin film on the sapphire substrate shows χ ⁽³⁾ equivalent to that of Example 2, the overcoated CaF ₂ thin film does not affect the χ ⁽³⁾ value and can be used as a thin film for protecting C60 fullerene. Became clear. Furthermore, for thin films on a quartz substrate, χ ⁽³⁾ can be measured even when C60 is vapor-deposited under high equipment pressure conditions. Therefore, the CaF ₂ overcoat thin film is a thin film formed by laser irradiation. It was found that it is effective in preventing the loss and improving the laser resistance.

From the above results, it is possible to obtain a nonlinear optical thin film which protects the C60 fullerene thin film and enhances the thin film laser resistance by the method of providing the second layer on the vapor deposited fullerene thin film. Was confirmed. However, in order to obtain a large χ ⁽³⁾ value, needless to say, it is necessary to lower the pressure inside the apparatus during vapor deposition.

[0023]

As described above, according to the present invention,
It is possible to provide an organic nonlinear optical thin film excellent in both nonlinear optical characteristics and laser resistance and a method for producing the same.

[Brief description of drawings]

FIG. 1 is a chart showing the results of direct ionization mass spectrometry of a mixture of C60 and C70 fullerenes.

FIG. 2 is a schematic cross-sectional view of a vacuum vapor deposition device used in a method for producing an organic nonlinear optical thin film.

FIG. 3 is a graph showing a maker fringe pattern when measuring a third-order nonlinear optical constant of a C60 fullerene vapor-deposited thin film.

FIG. 4 C60 on a sapphire substrate and a quartz substrate.
6 is a graph showing the relationship between the apparatus internal pressure during vapor deposition and χ ⁽³⁾ of the thin film when only the fullerene thin film is provided by vapor deposition.

FIG. 5 C60 on a sapphire substrate and a quartz substrate.
When a fullerene thin film is provided by vapor deposition and a CaF ₂ film having a thickness of 3 μm is provided as the second layer by a vacuum vapor deposition method,
6 is a graph showing the relationship between the internal pressure of a device during vapor deposition and χ ⁽³⁾ of a thin film.

[Explanation of symbols]

1 vacuum deposition apparatus 2 K- for heating and vaporizing fullerene compounds
Cell 3 K-cell for heating and vaporizing the material for vapor deposition of the second layer 4 Heater block for controlling the substrate temperature during vapor deposition 5 K-cell quartz crucible 6 Sapphire substrate

Front page continuation (72) Akira Yamashita Akira Yamashita 1-16 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Co., Ltd. (72) Hirohisa Kambara 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph Phone Co., Ltd.

Claims (2)

[Claims] 1. A sapphire substrate is used as a vapor deposition substrate, and a fullerene compound is used as an optical medium having a non-linear refractive index, either alone or mixed with another compound, to form a thin film on the sapphire substrate by vapor deposition. A method for producing a characteristic organic nonlinear optical thin film. 2. An organic nonlinear optical thin film comprising a vapor-deposited thin film of a fullerene compound alone or a mixture with another compound, and a second layer provided on the vapor-deposited thin film.