JP2008008931A - Manufacturing method of 3-dimensional photonic crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a 3-dimensional photonic crystal which has uniform crystal surface directions, no defective structure and large area by utilizing an electrophoresis of high manufacturing efficiency. <P>SOLUTION: In the manufacturing method of the 3-dimensional photonic crystal having real spherical particles (P) as a constitutional unit, dispersion liquid of the real spherical particles (P) with positive or negative charge is supplied onto a template substrate (Q) having a cavity and the real spherical particles (P) are accumulated in the cavity by applying an electric field opposite to charge of the real spherical particles (P) to an electrode installed at a rear surface of the template substrate (Q). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a highly uniform three-dimensional photonic crystal using electrophoresis of fine particles.

A photonic crystal is a structure having a periodic refractive index change equivalent to the wavelength of light, and has a photonic band gap that prohibits the presence of light corresponding to the periodic structure or the like. Utilizing the effects such as the photonic band gap, application research for various uses such as light emitting elements such as LEDs and semiconductor lasers, sensors, displays, and optical switches has been actively conducted. In particular, a three-dimensional photonic crystal has a large effect of a photonic band gap, and is expected to have a higher function than a two-dimensional photonic crystal.
Therefore, a method for producing a three-dimensional photonic crystal with high production efficiency is demanded, and a method for using fine particles as a constituent unit of a three-dimensional photonic crystal has been proposed. Specifically, a natural sedimentation method in which fine particles are sedimented by gravity and a method of accumulating by liquid crosslinking force or capillary force have been actively studied.

However, the natural sedimentation method, the method of accumulating by liquid crosslinking force and capillary force requires a relatively long process time, and it is difficult to produce a large-area three-dimensional photonic crystal used in an actual device. It is.
As a method for shortening these process times, a method of collecting by centrifugal force (Non-Patent Document 1) and a method of collecting by electrophoresis (hereinafter referred to as “electrophoresis”) (Non-Patent Documents 2, 3, and 4) ) Has been proposed. According to these two methods, it is possible to greatly reduce the process time.
In particular, the electrophoresis method can form various fine particle accumulation patterns by changing the position of the electrode, and can shorten the process time as compared with the method using centrifugal force. It is an excellent manufacturing method.

On the other hand, as in the natural precipitation method, it is difficult to produce a three-dimensional photonic crystal having a large area and having no defect structure in the electrophoresis method.
In addition, in order to improve the performance of devices such as light emitting elements, sensors, and displays, it is important that not only the defect structure does not exist, but also the orientation of the crystal plane is aligned. Has not been proposed for a method for producing a large-area three-dimensional photonic crystal having a defect structure with aligned crystal plane directions.

J. et al. W. Wu et. al. , J .; Korean Physical Soc. , Vol. 45, 108, 2004 The world of particle integration technology C. Lopez et. al. Langmuir. , Vol. 15, 4701, 1999 G. A. Ragoisha et. al. , J .; chem. Mater. , Vol. 12, 2721, 2000

  That is, an object of the present invention is to provide a method for producing a large-area three-dimensional photonic crystal having a defect structure with a uniform crystal plane direction using an electrophoresis method with high production efficiency.

  The production method of the present invention is a method for producing a three-dimensional photonic crystal having a spherical particle (P) as a structural unit, and a spherical shape having a positive or negative charge on a template substrate (Q) having a depression. By supplying a dispersion of particles (P) and applying an electric field opposite to the charge of the spherical particles (P) to the electrodes placed on the back of the template substrate (Q), the spherical particles (P ).

  According to the manufacturing method of the present invention, since the electrophoresis method is used, the production efficiency is high, and the large area 3 having no defect structure in which the crystal plane directions are aligned due to the effect of the template substrate (Q) having the depressions. It is possible to produce a two-dimensional photonic crystal.

In the present invention, the three-dimensional photonic crystal is defined as a structure having a three-dimensional periodic refractive index change equivalent to the wavelength of light, and the periodic refractive index change is a spherical particle (P). And a substance filled between the particles. Here, “three-dimensional” means a multilayer structure, and does not include a single-layer structure or a small-layer structure that is not functionally different from a two-dimensional photonic crystal. The number of layers varies depending on the application, but in order to exhibit the function of the three-dimensional photonic crystal, it is preferably at least 3 layers, more preferably 4 layers or more, particularly preferably 5 layers. That's it.
As the substance filled between the particles, any of gas, liquid, and solid can be used. In the present invention, the substance is not particularly limited, and liquid or solid can be filled between the particles. . As a 3D photonic crystal filled with liquid or solid between particles, after depositing and filling photonic crystal or silicon etc. whose optical properties are changed by voltage control filled with liquid crystal, the spherical particles (P) A photonic crystal having a reverse face-centered cubic lattice structure removed by melting or the like has been studied.
However, the material filled between the particles is generally air or an inert gas such as air, and is intangible, so the aggregate of spherical particles (P) is a three-dimensional photonic crystal. It can be said that.

The three-dimensional photonic crystal of the present invention has a spherical unit (P) as a structural unit, and must have a regular structure, that is, a structure that is integrated so as to have periodicity. The periodic structure is at least one of a cubic close-packed structure and a hexagonal close-packed structure.
Here, the cubic close-packed structure and the hexagonal close-packed structure are both close-packed structures, and the filling rate is 74% by volume.
The cubic close-packed structure is also called a face-centered cubic lattice structure, and has a structure in which particles are positioned at the vertices of the regular tetragonal unit cell and the center of each surface, and the close-packed surfaces are stacked in the order ABCCABBC.
In the hexagonal close-packed structure, the unit cell is represented by a regular hexagonal column, and there are three particles at each corner and center of the top and bottom surfaces of this regular hexagonal column and at a height of 1/2 inside the hexagonal column. The atom located in the center of the bottom is in contact with the 6 particles at the corner of the bottom and 3 particles above and below (12 particles in total), and has the structure in which the most dense surfaces are stacked in the order of ABABAB.
The structure obtained by accumulating the spherical particles (P) with high production efficiency and constant regularity, ie, periodicity, is a cubic close packed structure or a hexagonal close packed structure, usually both The structure becomes a mixed structure. In the present invention, since a template substrate (Q) having a depression is used, a single crystal structure consisting only of a cubic close-packed structure, not a mixed crystal, can be produced.

As the template substrate (Q), various substrates can be used as long as they can regularly collect fine particles. However, a substrate in which depressions are formed so that fine particles are three-dimensionally integrated is used. There is a need. The shape and size of the obtained three-dimensional photonic crystal are determined by the shape of the depression. Therefore, in order to produce a highly uniform three-dimensional photonic crystal, a substrate with a uniform recess size is required.
As a material constituting the template substrate (Q), use a material made of an inorganic compound such as silicon, silica, titanium oxide or a material made of a synthetic polymer such as an acrylic resin, an epoxy resin, a polyimide resin, or a photosensitive resin. Can do.

The shape of the template substrate (Q) in which the depression is formed is a quadrangular pyramid shape (Fig. 1), a cone shape, a hexagonal pyramid shape, or a trapezoidal or triangular shape (with V groove). And the like (see Fig. 2). Here, the groove means an elongated recess. Among these shapes, from the viewpoint of improving the uniformity of the obtained three-dimensional photonic crystal, it is preferably a quadrangular pyramid type (FIG. 1) or a V-groove type (FIG. 2).
The size (μm) of the cross section of the depression is preferably 1 to 10000, more preferably 5 to 1000, and particularly preferably 10 to 100. If the size is within this range, the minor axis It may be a groove type having a long diameter.
The depth (μm) of the depression is preferably 1 to 1000, more preferably 5 to 500, and particularly preferably 10 to 100. If the depth is within this range, a three-dimensional photonic crystal having a multilayer structure can be produced, and the uniformity thereof is further improved.

As described above, the shape of the depression is preferably a quadrangular pyramid type or a V-groove type, but more specifically, by anisotropically etching a silicon substrate whose surface is a (100) plane or a (110) plane. A depression having a (111) plane on the surface is preferable. When a silicon substrate having a (100) surface is anisotropically etched, a quadrangular pyramid-shaped depression as shown in FIG. 1 or a V-groove as shown in FIG. 2 forming 54.74 ° with the substrate surface is formed. When a silicon substrate having a (100) surface is anisotropically etched, a depression that forms 35.27 ° with the substrate surface is formed.
A single-crystal three-dimensional photonic crystal consisting only of a face-centered cubic lattice structure can be obtained by supplying fine particle slurry and accumulating it under appropriate conditions on the template substrate (Q) having a depression by anisotropic etching. Can be produced. By controlling the crystal lattice structure, it is possible to produce a highly uniform and large surface area three-dimensional photonic crystal.

A specific method for producing a template substrate (Q) having depressions by anisotropic etching will be described using a silicon substrate having a (100) plane on a surface having a side of 1 cm as a raw material substrate.
An oxide film is formed by heating a silicon substrate with a side of 1 cm at 1000 ° C for 1.5 hours in the air, and then using a piranha solution (a mixture of sulfuric acid and 30% hydrogen peroxide in a volume ratio of 1: 9). Washing to completely remove organic matter.
After drying, a resist was applied by a spin coater, and a resist film having a thickness of about 400 nm was formed on a silicon substrate (prebaked at 180 ° C. for 3 minutes). As the resist, α-methylstyrene-α-chloroacrylate copolymer (ZEP520 (positive resist), manufactured by Nippon Zeon Co., Ltd.) was used.
A pattern was drawn on the resist film by an electron beam drawing apparatus so as to correspond to the size of an appropriate depression cross section, and then immersed in a developer (ZEP-RD, manufactured by Nippon Zeon Co., Ltd.) to prepare a mask pattern.
An aqueous solution consisting of potassium hydroxide (30%) and isopropyl alcohol (12%) after being immersed in BHF (a mixture of ammonium fluoride and hydrofluoric acid at a volume ratio of 1: 9) for several minutes to remove only the oxide film. For 1 hour to perform anisotropic etching. Finally, the oxide film is removed with BHF to obtain a template substrate (Q) having a quadrangular pyramid-shaped or V-groove-shaped depression as shown in FIG. 1 or 2 that forms 54.74 ° with the substrate surface.

The interval between the depressions formed in the template substrate (Q) is preferably 0 or an integer multiple of the diameter of the fine particles as the constituent unit.
Here, the space | interval of a hollow means the space | interval between the edges of a hollow, as shown in FIG. In FIG. 3, the interval between the recesses is D.
When the interval between the recesses satisfies the above-described conditions, it becomes easy to form a continuous particle accumulation layer (A ′) on the layer (A) having a particle accumulation body according to the shape of the depression described later. Here, the interval between the recesses is 0, as shown in FIG. 4, when the edge of the recess overlaps the edge of the other recess. That is, D is O.
The space between the depressions can be controlled by the electron beam drawing conditions.

As the spherical particles (P) having a positive or negative charge, fine particles having various compositions can be used.
The composition of the fine particles is not particularly limited, and various resins and metal compounds can be used. Particles made of a polymer mainly composed of styrene or methyl methacrylate or a metal oxide such as silica can be easily synthesized by a known method. For example, when styrene is the main component, an emulsion polymerization method, a suspension polymerization method, a soap-free emulsion polymerization method, and the like can be mentioned. In the case of silica, a sol-gel method and the like can be mentioned. Many spherical particles having the above-mentioned preferable average particle diameter and particle size distribution are commercially available, and those commercially available products can also be used.
It is also possible to use true spherical monodisperse fine particles (P) in which pigments such as carbon black and vermilion are dispersed and colored.
The refractive index of the true spherical particles (P) is preferably 1.3 or more and 3.0 or less, more preferably 1.4 or more and 2.9 or less, and particularly preferably 1.5 or more and 2.8 or less. When the refractive index is within this range, the photonic band gap is increased, the wavelength range of the reflected light is expanded, and the intensity of the reflected light is increased.
The refractive index of the true spherical monodisperse fine particles (P) is often derived from the composition, and it is preferable to use titanium oxide, zirconia, or the like.

The spherical particles (P) need to have a positive or negative charge, and a known method can be used as a method for imparting a charge.
The spherical particles (P) need to be supplied in the form of a dispersion as described later, and it is preferable to change the method of imparting charge depending on the type of solvent of the dispersion, and each of the aqueous liquid and non-aqueous liquid It is preferable to use the following method.

In the case of dispersing in an aqueous liquid, a method of introducing an ionic group into the true spherical particles (P) is preferable. For example, a negative charge can be imparted by introducing an anionic group such as a carboxylic acid group, a sulfonic acid group, or a hydroxyl group, and a positive charge can be imparted by introducing a cationic group such as an amino group. Examples of the introduction method include a method of using monomers having these substituents at the time of synthesis and a method of adding a modifier such as a silane coupling agent having these substituents after the synthesis. In addition, the amount of charge can be adjusted in advance by adjusting the pH or adding an inorganic salt such as sodium chloride or potassium chloride.
In the case of dispersing in a non-aqueous liquid, a method using a charge control agent or a method using acid-base dissociation is preferable. As the charge control agent, a known charge control agent can be used, and examples thereof include an acrylic base M type series and an acrylic base L type series (manufactured by Fujikura Kasei Co., Ltd.).
In the method using acid-base dissociation, a positive or negative charge is imparted by acid-base dissociation occurring between the base or acid on the surface of the spherical particle (P) and the acid or base dissolved in the non-aqueous liquid. In this method, when a base is present on the surface of the spherical particles (P) and the acid is dissolved in the non-aqueous liquid, a positive charge can be imparted. For example, the case where an amino group is introduced into the surface of a true spherical particle (P) and an oligomer having a carboxylic acid group is dissolved in a non-aqueous liquid can be mentioned.

As the number average particle diameter of the true spherical particles (P), the preferred range varies depending on the application, but when using a photonic crystal for a device such as a light emitting element or a display for controlling visible light, 100 nm to 700 nm. More preferably, it is 120 nm or more and 500 nm or less, and particularly preferably 150 nm or more and 300 nm or less.
The particle size distribution of the fine particles is preferably sharp, and specifically, the coefficient of variation is preferably 3% or less, more preferably 2% or less, and particularly preferably 1.5% or less. Here, the variation coefficient means a percentage of a value obtained by dividing the standard deviation by the average value.
When the particle size distribution is within this range, it is possible to produce a photonic crystal with very few defects and high uniformity.

Spherical particles (P) are supplied as a dispersion and applied to the electrodes placed on the back side of the template substrate (Q) by applying an electric field opposite to the charge of the spherical particles (P) to form spherical particles in the depressions. (P) is accumulated.
The spherical particles (P) are not used as they are, but are used as a dispersion. The reason why it is used as a dispersion is to give particles mobility. When there is no solvent, or when the solvent is not evaporated, the solidification occurs immediately between the particles or between the particle and the substrate, and the mobility of the particles is lost. Therefore, a highly uniform three-dimensional photonic crystal cannot be produced. Because.
As a solvent, water (including ion-exchanged water, ultrapure water, etc.), alcohols (methanol, ethanol, butanol, etc.), general-purpose organic solvents (acetone, tetrahydrofuran, methyl ethyl ketone, toluene, etc.) or a mixture thereof should be used. Can do. Of these, water (including ion-exchanged water, ultrapure water, etc.), alcohols (methanol, ethanol, butanol, etc.) and a mixed solution of these and a general-purpose organic solvent are preferred, and water (ion-exchanged water) is more preferred. Water, ultrapure water, etc.) and alcohols (methanol, ethanol, butanol, etc.).
In the present invention, the integrated driving force of the spherical particles (P) is an electric field, and is characterized by using a so-called electrophoresis method. It is possible to increase the production efficiency of the photonic crystal and to produce a three-dimensional photonic crystal having a small periodic structure unit with high uniformity, which is difficult to produce by a conventional method.

Accumulation of spherical particles (P) by electrophoresis is performed by placing an electrode on the back of the template substrate (Q) and applying an electric field opposite to the charge of the spherical particles (P) to this electrode. Is called.
As a method of installing the electrode on the back surface of the template substrate (Q), the back surface of the template substrate (Q), that is, the spherical particles (P) having depressions are accumulated on a thin metal plate made of aluminum or nickel. The method of making it contact the surface opposite to a surface is mentioned. Contacting means a state that can be easily removed after the accumulation process without using an adhesive or the like.
By applying an electric field opposite to the charge of the true spherical particles (P) to the electrode made of a thin metal plate brought into contact with the back surface of the template substrate (Q), the true spherical particles (P) are removed from the template substrate (Q). Accumulated in the depression.

The strength of the applied electric field varies depending on the dispersion to be used, the particle diameter and the specific gravity of the particles, but is preferably stronger from the viewpoint of improving the production rate. However, in order to produce a highly regular and uniform 3D photonic crystal, not only the strength of the electric field, but also the voltage application time, the concentration of the spherical particles (P), the charge of the spherical particles (P), It is necessary to optimize parameters such as the properties of the template substrate surface.
For example, regarding the strength of the electric field, when the spherical particles (P) are negatively charged particles having a number average particle diameter of 300 nm and a zeta potential of 22 mV, and the solvent of the dispersion is a mixed solution of water and ethanol 0.1 to 3.0 V, more preferably 0.5 to 2.5 V, and particularly preferably 0.7 to 2 V.
The treatment time varies depending on the strength of the electric field, but is preferably 0.1 to 60 minutes, more preferably 0.5 to 30 minutes, and particularly preferably 1 to 15 minutes.
The concentration of the spherical particles (P) in the dispersion is preferably 0.01 to 20% by weight, more preferably 0.02 to 15% by weight, and particularly preferably 0.05 to 10% by weight.
As a method for preparing a dispersion of true spherical particles (P), it can be prepared by dispersing the true spherical particles (P) in a solvent using a surfactant or an ultrasonic disperser. It is preferable to use it as a dispersion of spherical particles (P) as it is.

The three-dimensional photonic crystal produced in the recess of the template substrate (Q) can be taken out from the template substrate (Q) without breaking the periodic structure by fixing the particles to each other.
As a method of immobilizing particles, a method of thermally adhering is common, and the method can be applied not only when the spherical particles (P) are made of an organic compound but also when it is made of an inorganic compound. For example, when the spherical particles (P) are made of polystyrene, they can be fixed by heat treatment at around 90 ° C. for about 1 to 5 minutes, and in the case of silica at 1 to 5 minutes at around 500 ° C. It can be fixed by heat treatment to some extent.
As other methods, a method in which a reactive functional group is introduced into the spherical particles (P) and a cross-linking agent having a group that reacts with the functional group is added and chemically bonded is exemplified.
When using without removing from the template substrate (Q), the particles are physically adsorbed by van der Waals force or electrostatic attraction, etc. There is.
As a specific method of removing from the template substrate (Q), a method of physically removing the 3D photonic crystal fixed by the above method by attaching an adhesive tape or the like to the surface, or removing the template substrate (Q) with acid or Examples of the method include removal using an alkali or an organic solvent.

Examples of evaluation methods related to uniformity such as single crystallinity, crystal plane direction, and defect structure of a three-dimensional photonic crystal include a method of measuring a reflection spectrum, a method of observation with an electron microscope, and a method of observing reflected light with the naked eye. It is done.
The peak of the reflection spectrum is derived from the photonic band gap, and is detected when the photonic crystal is irradiated with light having a specific wavelength corresponding to the gap. When the uniformity of the three-dimensional photonic crystal is high, the peak is detected sharply, and when the uniformity is low, the peak is broad and broadened. In addition, when the uniformity is low, the peak intensity tends to be weakened. When the uniformity is extremely low, reflected light composed of a large number of colors is mixed, and a whitish light reflected light is observed with the naked eye. .
A general-purpose spectrophotometer or the like can be used as the reflection spectrum detection device. For example, spectrophotometer PMA-11 (manufactured by Hamamatsu Photonics), multi spectrophotometer ATRAS-25, FTIR-IRT-3000 (manufactured by JASCO), UV-visible near infrared spectrophotometer UV-3600 (manufactured by Shimadzu) ), Reflection measuring device MCPD-3000 (manufactured by Otsuka Electronics Co., Ltd.), and the like.
The wavelength of the reflection spectrum obtained by irradiating a periodic structure with light of a specific wavelength mainly corresponds to the periodic size of the photonic crystal, and is composed of, for example, true spherical particles (P) with an average particle diameter of 200 to 300 nm. In the case of a photonic crystal having a cubic close-packed structure, a reflection spectrum appears in the vicinity of 200 to 500 nm.

[Example]
EXAMPLES Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples without departing from the gist of the present invention. Unless otherwise specified, “part” means “part by weight” and “%” means “% by weight”.

<Preparation of template substrate (Q1)>
Appearance image: Fig. 1
Indentation shape: Square pyramid Indentation size: One side: 5 μm, depth: 6 μm, angle with substrate surface: 54 ° (AN in FIG. 3 is 54 °)
Indentation interval: 0 (D in Figure 3 is 0)
The size of the substrate; a square with a side of 10 cm, and a dent is formed on the front surface leaving the edge of the substrate at 1 cm.
After forming an oxide film by heating a silicon substrate (substrate (Q)) (with a (100) surface) with a side of 10 cm at 1000 ° C in the air for 1.5 hours, piranha solution (30% excess with sulfuric acid) The mixture was washed with hydrogen oxide water mixed at a volume ratio of 1: 9 to completely remove organic substances.
After drying, a resist was applied by a spin coater, and a resist film having a thickness of about 400 nm was formed on a silicon substrate (prebaked at 180 ° C. for 3 minutes). As the resist, α-methylstyrene-α-chloroacrylate copolymer (ZEP520 (positive resist), manufactured by Nippon Zeon Co., Ltd.) was used.

A pattern was formed on the resist film with an electron beam drawing apparatus. The pattern was drawn by preparing CAD data (manufactured by A & Aco., LTD) so as to correspond to the size of the pits (one side; 5 μm, dent interval 0) and transferring it to an electron beam drawing apparatus. After pattern drawing, it was immersed in a developing solution (ZEP-RD, manufactured by Nippon Zeon Co., Ltd.) to prepare a mask pattern.
An aqueous solution consisting of potassium hydroxide (30%) and isopropyl alcohol (12%) after being immersed in BHF (a mixture of ammonium fluoride and hydrofluoric acid at a volume ratio of 1: 9) for several minutes to remove only the oxide film. For 1 hour to perform anisotropic etching. Finally, the oxide film was removed with BHF to produce a template substrate for a nanoimprint substrate (the surface has a (111) plane).
Using this template substrate, a nanoimprint substrate made of nickel was obtained.
A PET film having a thickness of 50 μm was prepared, the nanoimprint substrate was pressed to form a recess, and then cut into a 10 cm square to obtain a substrate (Q1).

<Preparation of template substrate (Q2)>
Appearance image: Fig. 2
Indentation shape: V-groove Indentation size: One side: 10 μm × 100 μm, depth: 12 μm, angle with substrate surface: 54 °
Indentation spacing: 7.5 μm (D in FIG. 3 is 7.5 μm)
The size of the substrate; a square with a side of 10 cm, and a dent is formed on the front surface leaving the edge of the substrate at 1 cm.
Prepare a PET film with a thickness of 20μm as a substrate film, create CAD data corresponding to the size of the above-mentioned recesses (one side; 10μm x 100μm, spacing between recesses 1.08μm), and transfer it to the electron beam lithography system A template substrate (Q2) was obtained in the same manner as the template substrate (Q1), except that the resist film was drawn on the substrate.

<Preparation of spherical particles (P1)>
17 parts of titanium tetraethoxide was dissolved in 1000 parts of ethanol and charged into a reaction vessel with a stirring function. While stirring at 100 rpm, 4 parts of an aqueous solution of potassium chloride having a solid content concentration of 0.3% was added and reacted at room temperature for 120 minutes, whereby titanium oxide monodispersed fine particles having a number average particle size of 220 nm and a Cv value of 1.5% ( An ethanol dispersion of true spherical fine particles (P1) was obtained.
After completion of the reaction, heat treatment was performed at 80 ° C. to partially evaporate the solvent, and ethanol was added as necessary to adjust the solid content concentration to 1%. This dispersion contains 0.1% or less of water and a trace amount of potassium chloride.
When the zeta potential of the obtained fine particles (P1) was measured with a zeta potential measuring device (ELS-Z manufactured by Otsuka Electronics Co., Ltd.), it was found to have a negative charge of 22 mV. Titanium oxide is a highly transparent material having a refractive index of about 2.8 and hardly absorbing visible light.

<Production of spherical particles (P2)>
10 parts of tetrabutoxysilane was dissolved in 80 parts of butanol and charged into a reaction vessel with a stirring function. While stirring at 100 rpm, 10 parts of ion-exchanged water whose pH was adjusted to 11 with ammonia water was added and reacted at room temperature for 10 hours to obtain a silica monodispersed fine particle having a number average particle size of 270 nm and a Cv value of 1.4% ( An ethanol dispersion of spherical particles (P2) was obtained.
After the reaction, heat treatment was performed at about 80 ° C. to partially evaporate and remove the solvent, and butanol was added as necessary to adjust the solid content concentration to 1%. This dispersion contains 1% or less of water.
When the zeta potential of the obtained fine particles (P2) was measured with a zeta potential measuring device (ELS-Z manufactured by Otsuka Electronics Co., Ltd.), it was found to have a negative charge of 20 mV. Silica has a refractive index of about 1.5 and is a highly transparent material that hardly absorbs visible light.

<Example 1>
On the back surface of the template substrate (Q-1), an electrode made of an aluminum thin plate corresponding to the size of the recessed portion was installed. Another electrode made of an aluminum thin plate having the same size as the template substrate (Q-1) was prepared and used as a counter electrode.
Apply a sealant with a height of 1 mm around the extreme part, fill the central part surrounded by the sealant with a dispersion of spherical particles (P1), and then take care not to let air in the template substrate. Sealed with (Q1).
A voltage of 2 V was applied to the back electrode of the template substrate (Q-1) and held for 1 minute. By applying this voltage, the spherical particles (P1) are electrophoresed and accumulated in the depressions of the template substrate (Q-1).
After 1 minute, the counter electrode was removed and the plate was dried with a dryer at 60 ° C. for 5 hours to obtain a three-dimensional photonic crystal formed over the entire recessed portion of the template substrate (Q-1).
From the obtained three-dimensional photonic crystal, strong green reflected light was confirmed with the naked eye over the entire surface. When observed with an electron microscope, the thickness was about 3 μm from the top surface of the template substrate (Q-1), and the top surface was almost flat. Moreover, the crystal structure was a single crystal, the crystal planes were aligned, and there were no defects such as fine particle defects.

<Example 2>
Example except that instead of the template substrate (Q-1), the template substrate (Q-2) is replaced by a dispersion of true spherical fine particles (P1) instead of a dispersion of true spherical fine particles (P1). In the same manner as in 1, a three-dimensional photonic crystal was obtained.
From the obtained three-dimensional photonic crystal, strong red reflected light was confirmed with the naked eye over the entire surface. When observed with an electron microscope, the thickness was about 6 μm from the upper surface of the template substrate (Q-1), and the uppermost surface was almost flat. Moreover, the crystal structure was a single crystal, the crystal planes were aligned, and there were no defects such as fine particle defects.

<Comparative Example 1>
A three-dimensional photonic crystal was prepared and evaluated in the same manner as in Example 1 except that a flat PET film (thickness 50 μm) having no depression on the surface was used instead of the template substrate (Q-1).
A strong green reflected light was confirmed with the naked eye from about half of the obtained three-dimensional photonic crystal. From other parts, light blue or yellow reflected light was confirmed. When observed with an electron microscope, the thickness was about 6 μm, and the uppermost surface was almost flat. On the other hand, the crystal structure was polycrystalline, and the orientation of the crystal plane was random. Furthermore, many defects such as fine particle defects existed in a portion where the orientation of the crystal plane changes.

<Evaluation method of three-dimensional photonic crystal of Examples 1 and 2 and Comparative Example 1>
The obtained three-dimensional photonic crystal was evaluated by the following method.

<Measurement of reflection spectrum>
The reflection spectrum of the three-dimensional photonic crystal obtained using a micro ultraviolet visible spectrophotometer MSV-350 (manufactured by JASCO Corporation) was measured. A peak is detected at a wavelength corresponding to the photonic band gap. From this peak, the uniformity of the three-dimensional photonic crystal, single crystallinity, unity of crystal plane direction, and the like can be determined. If the uniformity, single crystallinity, and unity of crystal plane direction are high, the peak becomes sharp, and only light having a wavelength corresponding to the photonic band gap is reflected. Accordingly, it is possible to confirm a strong single color reflected light even with the naked eye.

<Observation by electron microscope>
While observing the entire surface of the three-dimensional photonic crystal from the top, and observing it at an end from an oblique direction, the thickness and crystal structure of the photonic crystal were confirmed. When the crystal structure is monocrystalline, the orientation of crystal planes is uniform, and when it is polycrystalline, it becomes random. In addition, when the crystal uniformity is low, a large number of defect structures such as fine particle defects can be confirmed.

The reflection spectra of Examples 1 and 2 and Comparative Example 1 are shown in FIG.
In the three-dimensional photonic crystal of Example 1, a reflection spectrum peak with a very strong reflection intensity having a reflectance of almost 100% is detected in the vicinity of a wavelength of 520 to 570 nm, and the edge of this peak is very sharp. It can be seen that the crystal uniformity is extremely high.
On the other hand, in the three-dimensional photonic crystal of Comparative Example 1, a reflection spectrum peak was detected at a wavelength of 560 nm. This peak was broad and the reflection intensity was about half that in Example 1. Therefore, it can be seen that the crystal uniformity is low.
In the three-dimensional photonic crystal of Example 2, a reflection spectrum peak with a very high reflection intensity with a reflectance of almost 100% was detected in the vicinity of a wavelength of 700 nm, and the edge of this peak was very sharp. Is very high.
The reason why the uniformity of the three-dimensional photonic crystal of the example is high is that, as described above, it satisfies all the factors of single crystallinity, absence of defect structure, and orientation of crystal planes. is there.

  The three-dimensional photonic crystal obtained by the production method of the present invention can be applied to applications in which application research is actively conducted, such as light emitting elements such as LEDs and semiconductor lasers, sensors, displays, and optical switches.

Square pyramid-shaped depression V-groove depression Cross section of template substrate (Q) Sectional view of template substrate (Q) (when indent D is 0) Reflection spectrum measurement result

Explanation of symbols

P: Fine particle R: Fine particle diameter D: Indentation interval DI: Indentation AN: Angle with substrate surface

Claims (3)

  A method for producing a three-dimensional photonic crystal having a spherical particle (P) as a structural unit, and a dispersion of a spherical particle (P) having a positive or negative charge on a template substrate (Q) having a depression Is applied to the electrode placed on the back side of the template substrate (Q) to apply an electric field opposite to the electric charge of the spherical particles (P), thereby accumulating the spherical particles (P) in the depressions. A method for producing a three-dimensional photonic crystal.   2. The three-dimensional photonic crystal according to claim 1, wherein the interval between the depressions formed in the template substrate (Q) is 0 or an integer multiple of the diameter of the spherical particles (P) as a structural unit. Production method. The depression formed in the template substrate (Q) is a quadrangular pyramid type having a (111) surface on the surface, which is produced by anisotropic etching of a silicon substrate having a (100) surface. The method for producing a three-dimensional photonic crystal according to claim 1 or 2.