JPH0718081A - Thin polysilane film - Google Patents

Abstract

PURPOSE:To provide the film having excellent third-order nonlinear optical properties. CONSTITUTION:The film comprises first linear regions 2 containing polysilane molecules and having a width of 1mum or smaller and second linear regions 3 containing molecules which serve to separate the regions 2 so as to inhibit the electronic interaction of the polysilane molecules between adjacent regions 2, the two kinds of regions being arranged alternately on the film surface, with the polysilane molecules of the regions 3 being oriented in the direction of the length of the regions 2. Alternatively, the film has on its surface a sea- island pattern which comprises island regions 4 containing polysilane molecules and having a maximum inner diameter of 1mum or smaller and a sea region 5 surrounding the regions 4 and containing molecules which serve to separate the regions 4 so as to inhibit the electronic interaction of the polysilane molecules between adjacent regions 4.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polysilane thin film having excellent third-order nonlinear optical characteristics.

[0002]

2. Description of the Related Art Conventionally, carbon-based polymers in which carbon atoms are linearly bonded are often used as polymer materials. On the other hand, in recent years, polysilane, which is a polymer in which silicon atoms are linearly bonded, has been attracting attention as a next-generation material replacing carbon-based polymers. Unlike carbon-based polymers, polysilane has an optical property that it does not have absorption in the visible light region. Therefore, it is expected to be applied to optical semiconductors, nonlinear optical elements, and transparent conductive materials.

Despite such expectations, when attention is paid to χ ⁽³⁾ , which is a typical physical property value of nonlinear optical characteristics, the value of polysilane is not necessarily larger than that of carbon-based polymer (for example, , F. Kajar, J.M.
essier, and C.I. Rosilio, J .; Ap
pl. Phys. 60 (1986) 3040). This seems to be due to the following reasons.

The origin of the nonlinear optical properties of polysilane is considered to be the one-dimensional exciton state formed by the conjugated σ electron of the polysilane main chain composed of silicon atoms (eg, Yoshinori Tokura, Hiroaki Tachibana, Applied Physics, Volume 60 (1991)
990). However, in the conventionally reported oriented polysilane thin film, the one-dimensional property of the polysilane main chain is only realized microscopically. That is, the orientation direction of each polysilane molecule is not always completely constant, and in many cases, the orientation directions of adjacent molecules are slightly different from each other. Even if a certain molecule is excited in this state, the anisotropy of the exciton is reduced when the exciton state transits to the adjacent molecule, and macroscopically the one-dimensional property of the exciton is reduced.
Therefore, as described above, it is the current situation that the expected third-order nonlinear optical constant has not been obtained.

[0005]

As described above, in the conventional polysilane thin film, the one-dimensional exciton state formed by each polysilane molecule tends to be canceled out in the entire film, so that a large third-order nonlinear optical constant is generated. There was a problem that I could not get it. An object of the present invention is to solve the above problems and provide a polysilane thin film exhibiting excellent third-order nonlinear optical characteristics.

[0006]

Means and Actions for Solving the Problems A polysilane thin film of the first invention of the present application is a polysilane molecule containing a polysilane molecule and having a width of 1 μm or less and a polysilane molecule between adjacent first linear regions. Of second linear regions containing molecules that segregate the electronic interactions of the first linear region with polysilane molecules in the second linear region are formed alternately. It is characterized in that it is oriented in the longitudinal direction.

The polysilane thin film of the second invention of the present application has an island-shaped region having a maximum inner diameter of 1 μm or less containing the polysilane molecule, and the polysilane molecule between the adjacent island-shaped regions surrounding the island-shaped region. It is characterized in that a pattern composed of a separation region containing a molecule for separating electronic interaction is formed in the film surface.

The polysilane used in the present invention is
The main chain is composed of silicon-silicon (-Si-Si-) bonds and has both hydrophilic groups and hydrophobic groups in the side chains,
Alternatively, it has only a hydrophilic group or only a hydrophobic group. Examples of the hydrophilic group include a hydroxyl group, an amino group, a carboxyl group, and a functional group having at least one selected from the group consisting of an ester bond, an amide bond, an ether bond, a carbamate bond and a carbonate bond. As the hydrophobic group, a linear alkyl group, a branched alkyl group, an aryl group, a cyclic alkyl group,
Alternatively, there may be mentioned a hydrocarbon group formed by combining these.

In the present invention, among these, polysilanes having a repeating unit represented by the following general formula (I), in other words, amphipathic polysilanes having both a hydrophilic group and a hydrophobic group in the side chain, are Langmuir. -It is particularly preferable because a monomolecular cumulative film can be obtained by the blow jet method.

[0010]

[Chemical 1] (In the formula, R ₁ is a substituted or unsubstituted alkyl group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 24 carbon atoms, or a substituted or unsubstituted aralkyl group having 7 to 24 carbon atoms, and R ₂ is Divalent organic group having 1 to 24 carbon atoms, X is a functional group having at least one selected from the group consisting of hydroxyl group, amino group, carboxyl group or ester bond, amide bond, ether bond, carbamate bond and carbonate bond. Group is shown).

In the present invention, the molecule for isolating the electronic interaction of the polysilane molecule is not particularly limited as long as it has an insulating property, but polysiloxane is preferable. What is important is that polysiloxane has a main chain composed of a silicon-oxygen bond, and can be easily produced by treating polysilane in an oxygen-containing atmosphere and inserting oxygen into the polysilane main chain as described later. Because you can.

Here, an example of a method for producing the polysilane thin film according to the first invention of the present application will be described. First, a uniaxially oriented polysilane thin film having a polysilane main chain oriented in one direction is formed on a predetermined substrate. For this purpose, the Langmuir-Blodgett method (hereinafter abbreviated as LB method) can be used, or a method such as uniaxially stretching after coating a substrate with polysilane.

In the LB method, an amphipathic polysilane having a repeating unit represented by the above general formula (I) is used.
Specifically, prepare a solution of polysilane molecules in a volatile solvent and drop it on the surface of a developing medium such as pure water to form a monomolecular film on the water surface. After compressing to a pressure, it is transferred to a substrate. Here, when the substrate is dipped perpendicularly to the water surface and pulled up, a monomolecular film in which the main chain of polysilane is oriented in the pulling direction is obtained. By repeating this pulling operation, a cumulative film in which the polysilane main chain is oriented in one direction can be obtained.

For polysilanes to which the LB method cannot be applied, that is, polysilanes having neither hydrophilic groups nor hydrophobic groups in their side chains, a non-oriented thin film is once formed on the substrate by spin coating or the like, and then uniaxially stretched. And other operations. Also by such a method, a thin film in which the main chain of polysilane is oriented in one direction can be obtained. In this uniaxial stretching operation, if the temperature is raised above the glass transition point of polysilane and the operation of slow cooling while applying stretching force is added, a more stable uniaxially oriented thin film can be obtained.

In the polysilane thin film of the first invention of the present application, when measuring the extinction coefficient when irradiated with ultraviolet light (3 to 4 eV in terms of energy) of the absorption wavelength of the conjugated σ electron of the polysilane main chain, The extinction coefficient when the polarization direction of the ultraviolet light is the direction in which the polysilane main chain is strongly oriented, that is, the direction in which the substrate is pulled up or the direction in which the uniaxial stretching operation is performed according to the LB method, and the polarization direction of the ultraviolet light are perpendicular to this Value of the extinction coefficient when the direction is different (dichroic ratio)
It is preferable to orient the polysilane molecules so that the ratio is 2 or more, and more preferably 5 or more.

Then, a predetermined region of the obtained uniaxially oriented thin film is irradiated with an energy beam to polysiloxane the polysilane in the energy beam irradiation portion, whereby the polysilane thin film of the first invention of the present application is formed. For this purpose, for example, a method is used in which a photomask having a striped light-shielding portion parallel to the orientation direction of polysilane molecules is opposed to the above-mentioned uniaxially oriented thin film, and ultraviolet rays are irradiated in an oxygen-containing atmosphere. As the photomask, for example, a quartz glass having a chromium film deposited thereon may be used. Further, a method of irradiating the above-mentioned uniaxially oriented thin film in an oxygen-containing atmosphere with a particle beam such as an electron beam or X-ray having a narrowed beam diameter or an electromagnetic wave while scanning in a direction parallel to the orientation direction of polysilane molecules. Can also be used. It is also possible to use a method of irradiating the surface of the uniaxially oriented thin film with electromagnetic waves in a state in which the direction of interference fringes generated by interference of coherent electromagnetic waves is arranged parallel to the orientation direction of polysilane molecules.

In the first invention of the present application, the width of the first linear region containing the polysilane molecule should be small enough to suppress the diffusion of the exciton state in the direction orthogonal to the orientation direction of the polysilane molecule. Actually, 1 μm or less is appropriate in consideration of the restriction of patterning technology.

On the other hand, the width of the second linear regions alternately arranged with the first linear regions is 1 to 1 of the width of the first linear regions.
It is preferably set to 0 times. The reason for this is that if the width of the first linear regions is too small, the electronic interaction of the polysilane molecules between the adjacent first linear regions cannot be sufficiently isolated, and conversely the second linear regions cannot be isolated. This is because if the width of the linear region is too large, a large third-order nonlinear optical constant may not be obtained for the entire film.

Further, in the first invention of the present application, it is preferable that the film thickness of the polysilane thin film is 1 μm or less. This is because if the film thickness of the polysilane thin film is too thick, excitons generated by certain polysilane molecules may diffuse in the film thickness direction, and the one-dimensional property of the excitons may be diluted.

In the polysilane thin film of the first invention of the present application as described above, the polysilane main chain is oriented in one direction in the first linear region, and the first linear region is formed with a width of 1 μm or less. Therefore, the exciton state is confined in the orientation direction of the polysilane molecule. As a result, there is no confinement of the exciton state, and the reduction in the one-dimensionality of the exciton is suppressed as compared with the case where the exciton state generated by a certain molecule diffuses largely in the direction orthogonal to the polysilane main chain. The non-linear optical constant increases dramatically. In addition, the electrical anisotropy that the electrical conductivity is high in the orientation direction of the polysilane molecules and is extremely low in the direction orthogonal thereto can be expected.

Further, the polysilane thin film of the second invention of the present application, for example, irradiates the above-described polysilane thin film of the first invention of the present invention with the same energy rays as described above along the direction orthogonal to the orientation direction of the polysilane molecules. It can be produced by

At this time, in the second invention of the present application, it is not necessary to irradiate the energy beam after forming the uniaxially oriented thin film, and it is sufficient to irradiate the predetermined region of the non-oriented thin film with the energy beam.

In this case, the size of the island region containing the polysilane molecule is set so that the maximum value of the inner diameter is 1 μm or less. Further, in the second invention of the present application, it is preferable that the area ratio of the island-shaped region containing the polysilane molecule and the separation region surrounding the island-shaped region is 1: 1 to 1:10. The reason is that if the area of the separation region is too small, the electronic interaction of the polysilane molecules between the adjacent island regions cannot be sufficiently isolated, and conversely if the area of the molecule region is too large,
This is because a large third-order nonlinear optical constant may not be obtained for the entire film. Further, in the second invention of the present application, it is more preferable that the closest distance between adjacent island regions is set to be equal to or larger than the maximum value of the inner diameter of the island regions, and the thickness of the polysilane thin film is the same as that of the first invention of the present application. It is preferably 1 μm or less.

In the polysilane thin film of the second invention of the present invention having such a structure, the polysilane molecules exist in a substantially fine particle state, and it can be considered that the exciton state is confined in a zero-dimensional manner. The oscillator strength of electronic transitions caused by excitons increases more than when the state is confined one-dimensionally. Therefore, due to the spatial confinement effect of the exciton state, physical properties different from those of the bulk material, the two-dimensional thin film, and the one-dimensional thin line, more specifically, the increase of the third-order nonlinear optical constant, the generation of ferromagnetism, Effects such as shift of optical absorption wavelength can be expected.

[0025]

EXAMPLES Examples of the present invention will be described below. Example 1 A molecular weight of 100,000 having an m-hydroxyphenyl group as a hydrophilic group and an n-butyl group as a hydrophobic group in a side chain (GP
A polysilane monomolecular film was accumulated on a quartz substrate by the LB method in the following manner using polysilane molecules of polystyrene conversion value by C measurement).

First, as a pretreatment of a quartz substrate, dipping in a mixed solution of sulfuric acid and hydrogen peroxide (SH), dipping in hydrofluoric acid, and OA.
P treatment (treatment with a mixed solution of hexamethylenedisilazane and dodecyltrichlorosilane) was performed in this order. This pretreatment makes the quartz substrate surface hydrophobic.

A commercially available LB film forming apparatus (manufactured by Kyowa Interface Science Co., Ltd.) was used. Pure water was used as the developing phase, and the cyclohexane solution of the polysilane molecule was dropped on the surface of the pure water by a microsyringe to develop the monomolecular film on the water surface. The film forming conditions are as follows: pH of developing phase is 5.0 to 6.0, substrate pulling rate is 5 mm / min, surface pressure is 20 dyn.
/ Cm, the water temperature was 13.0 to 15.0 ° C., and the monomolecular film was accumulated on the substrate by the vertical dipping method.

Under these conditions, an LB film was prepared by accumulating 100 monolayers. The obtained LB film had a dichroic ratio of 6 when irradiated with ultraviolet light having the absorption wavelength of the conjugated σ electron of the polysilane main chain as described above, and exhibited anisotropy (dichroism) of ultraviolet absorption. From this, it was confirmed that they were uniaxially oriented.

A photomask having a line-and-space of 1 μm formed of a chromium vapor deposition film on a quartz substrate was adhered to the LB film. At this time, the orientations of the photomask and the LB film were adjusted so that the longitudinal direction of the light shielding portion of the photomask coincided with the orientation direction of the polysilane molecules. After that, the sample was exposed to i-line (365 nm) of a mercury lamp for 10 minutes in dry air for exposure. By this operation, the exposed portion is changed to polysiloxane. Therefore, as shown in FIG. 1, on the quartz substrate 1, the first linear regions 2 containing polysilane molecules and the second linear regions 3 containing polysiloxane molecules are parallel to each other in stripes each having a width of 1 μm. The polysilane thin film of the first invention of the present application having a structure in which the main chain of polysilane is oriented in the longitudinal direction of the first linear region 2 is obtained.

The third-order nonlinear optical characteristics of the obtained polysilane thin film were evaluated by the third-order harmonic generation (THG) method shown below. That is, Nd-YAG is added to the polysilane thin film.
The fundamental wave of the laser (wavelength 1.064 μm) was irradiated, and the intensity of the 355 nm third harmonic light generated from the polysilane thin film was measured. At this time, the polarization direction of the incident light is made parallel to the longitudinal direction of the first linear region containing polysilane molecules, and 3
The intensity of the polarization component parallel to the incident light in the next harmonic was measured. On the other hand, a quartz substrate with a known third-order nonlinear susceptibility is used as a reference sample, and the intensity of the third-order harmonic light is measured,
The third-order nonlinear susceptibility of the polysilane thin film was determined by comparing the intensities of the third-order harmonic light of both. As a result, the third-order nonlinear susceptibility of the polysilane thin film is 1.5 × 10 ⁻⁸ e
It turned out to be su. This value is remarkably increased as compared to the third-order nonlinear susceptibility of 1.5 × 10 ⁻¹⁰ esu of the same polysilane thin film except that the exposure process was not performed. The intensity of the third-order harmonic light having a polarization component orthogonal to the incident light was very weak, which was 1/1000 of the intensity of the third-order harmonic light having a polarization component parallel to the incident light. On the other hand, when the polarization direction of the incident light was set to the direction orthogonal to the longitudinal direction of the first linear region containing polysilane molecules, the third harmonic light was not detected.

Example 2 The same photomask as that used in Example 1 was adhered onto the polysilane thin film produced in Example 1 so that the longitudinal direction of the light-shielding portion was perpendicular to the orientation direction of polysilane molecules. Exposure was carried out in the same manner as in Example 1. As a result of such an operation, as shown in FIG. 2, a large number of 1 μm square island-shaped regions 4 containing polysilane molecules are surrounded by a separation region 5 containing polysiloxane molecules on the quartz substrate 1. The polysilane thin film according to the invention was obtained.

Then, the polarization direction of the incident light and the intensity of the third-order harmonic light for measuring the intensity are set parallel to the orientation direction of the polysilane molecules, and in the same manner as in Example 1, the third-order nonlinear susceptibility of the obtained polysilane thin film is set. Was measured to be 1.8 × 10
The value of ⁻⁷ esu was obtained, and it was found that the third-order nonlinear optical characteristic was further improved as compared with Example 1.

[0033]

As described in detail above, the polysilane thin film of the present invention exhibits extremely excellent third-order nonlinear optical characteristics.

[Brief description of drawings]

FIG. 1 is a perspective view of a polysilane thin film of the first invention of the present application produced in Example 1. FIG.

FIG. 2 is a perspective view of a polysilane thin film of the second invention of the present application produced in Example 2.

[Explanation of symbols]

1 ... Quartz substrate, 2 ... 1st linear region, 3 ... 2nd linear region, 4 ... Island region, 5 ... Separation region.

Claims (2)

[Claims] 1. A first linear region containing a polysilane molecule and having a width of 1 μm or less, and a second linear region containing a molecule that isolates an electronic interaction of the polysilane molecule between adjacent first linear regions. A polysilane thin film, wherein patterns each comprising regions are alternately formed in the film surface, and polysilane molecules in the second linear regions are oriented in the longitudinal direction of the first linear regions. 2. The maximum value of the inner diameter containing the polysilane molecule is 1
A pattern is formed in the film surface, which is composed of an island region having a size of less than or equal to μm and a separation region containing a molecule that surrounds the island region and isolates electronic interaction of polysilane molecules between adjacent island regions. A polysilane thin film characterized in that