Two-dimensional colloidal crystal structure and method for producing same

Abstract

The present invention addresses the problem of providing a two-dimensional colloidal crystal structure having few defects in the crystal structure. A titanium dioxide-containing layer (2) is formed on a substrate (1), and a two-dimensional colloidal crystal layer (4) is further formed on the titanium dioxide-containing layer (2). This structure is manufactured by: 1) a substrate preparation step (S1) in which a metal oxide layer (2) is formed on the surface of a substrate (1); 2) as a colloidal crystal dispersion preparation step (S2), preparing a dispersion (6) having a charged three-dimensional colloidal crystal (5) having a surface charge opposite to the surface charge of the metal oxide layer (2); and 3) as a two-dimensional colloidal crystal formation step (S3), a dispersion liquid (6) of the charged three-dimensional colloidal crystal (5) is brought into contact with the metal oxide layer (2).

Description

Technical Field

[0001] The present invention relates to a two-dimensional colloidal crystal structure and a method for producing the same. A two-dimensional colloidal crystal structure herein refers to a monolayer structure in which particles of uniform particle size are regularly arranged on a plane. Furthermore, a two-dimensional colloidal crystal structure refers to a structure in which a layer composed of two-dimensional colloidal crystals is formed on the surface of a substrate. Background Art

[0002] Two-dimensional colloidal crystal structures are attracting attention as new functional materials. For example, proposals have been made to use them as transducers in various sensors that utilize surface adsorption, converting the amount of adsorbed matter into other signals, or in spectral analysis using surface plasmon resonance (SPR).

[0003] As a method for producing a two-dimensional colloidal crystal structure, the following method is known: a dispersion of three-dimensional colloidal crystals containing particles of uniform particle size arranged in a three-dimensionally regular pattern is brought into contact with a substrate, and the two-dimensional colloidal crystals are transferred from the surface of the three-dimensional colloidal crystals to the substrate by electrostatic attraction (for example, Patent Document 1). This method enables the production of a two-dimensional colloidal crystal structure without using complex patterning techniques for controlling the arrangement of the particles.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-34543 Summary of the Invention

[0007] However, the method for producing a two-dimensional colloidal crystal structure described in Patent Document 1 has many defects in the crystal structure. Therefore, a two-dimensional colloidal crystal structure having fewer defects is desired.

[0008] The present invention has been made in view of the above-mentioned conventional situation, and an object of the present invention is to provide a two-dimensional colloidal crystal structure having few defects in the crystal structure.

[0009] The method for producing a two-dimensional colloidal crystal structure of the present invention comprises:

[0010] a substrate preparation step of preparing a substrate having a metal oxide layer having a surface isoelectric point of 4 to 8;

[0011] a colloidal crystal dispersion preparation step of preparing a dispersion of charged three-dimensional colloidal crystals composed of colloidal particles having a surface charge having the same sign as the surface charge of the metal oxide layer; and

[0012] The two-dimensional colloidal crystal formation process is to bring the dispersion of the charged three-dimensional colloidal crystals into contact with the metal oxide layer, adjust the surface charge of the metal oxide layer so that it has a sign different from the surface potential of the colloidal particles constituting the charged three-dimensional colloidal crystals, and transfer the two-dimensional colloidal crystals to the substrate.

[0013] In the method for manufacturing two-dimensional colloidal crystals of the present invention, a substrate having a metal oxide layer with an isoelectric point of 4 to 8 on the surface is prepared (substrate preparation step). In addition, a dispersion of charged three-dimensional colloidal crystals composed of colloidal particles having a surface charge of the same sign as the surface charge of the metal oxide layer is prepared (colloidal crystal dispersion preparation step). Then, as a two-dimensional colloidal crystal forming step, the dispersion of the charged three-dimensional colloidal crystals is brought into contact with the metal oxide layer. At this time, an electrostatic repulsion is generated between the charged three-dimensional colloidal crystals and the metal oxide layer, maintaining an unadsorbed state. However, thereafter, by adjusting the surface charge of the metal oxide layer of the substrate so that it has a sign different from the surface charge of the particles constituting the charged three-dimensional colloidal crystals, an electrostatic attraction is generated between the charged three-dimensional colloidal crystals and the metal oxide layer, and the two-dimensional colloidal crystals are transferred to the substrate.

[0014] As a method for adjusting the sign of the surface charge inverted during the two-dimensional colloidal crystal formation process, this can be easily performed by adjusting the pH of the dispersion of the charged three-dimensional colloidal crystals within a pH range spanning the isoelectric point. The concentrations of acid and base required to adjust the pH of the dispersion to a range spanning the isoelectric point of 4 to 8 are lower than those for isoelectric points less than 4 or greater than 8, thereby reducing the salt concentration of the dispersion of the charged three-dimensional colloidal crystals. As a result, the electric double layer becomes thicker, preventing the aggregation of colloidal particles and the dissolution of the colloidal crystal structure. Therefore, the transfer of the two-dimensional colloidal crystals to the substrate can be carried out smoothly, and defects in the crystal structure are reduced.

[0015] According to the experimental results of the inventors, by changing the pH of the dispersion liquid of charged three-dimensional colloidal crystals in the two-dimensional colloidal crystal formation process to below 4 and the salt concentration to below 150 μM, the transfer of two-dimensional colloidal crystals to the substrate can be carried out more smoothly and the defects of the crystal structure can be reliably reduced.

[0016] As a method for adjusting the surface charge of the metal oxide layer so that it has a different sign from the surface charge of the particles constituting the charged three-dimensional colloidal crystals, it can be easily performed by adjusting the pH of the dispersion of the charged three-dimensional colloidal crystals within a pH range that spans the isoelectric point. Examples include 1) adding an acid or base solution, 2) using a cation exchange resin or anion exchange resin to adsorb hydrogen ions and hydroxide ions, and 3) adsorbing a gaseous acid (e.g., hydrogen chloride gas) or base (e.g., ammonia gas, carbon dioxide, etc.). In the case of using carbon dioxide, carbon dioxide contained in the atmosphere can be utilized.

[0017] From the perspective of reducing defects in the two-dimensional colloidal crystal structure, the isoelectric point of the metal oxide layer is in the range of 4 to 8, preferably 4.5 to 7.5. As a metal oxide layer with an isoelectric point of 4 to 8, for example, a titanium dioxide layer with an isoelectric point of around 6 or an aluminum oxide layer with an isoelectric point of 8 can be used. In addition, a layer composed of a mixed metal composite oxide in which the metal elements are at least two of Ti, Si and Al can also be used. In particular, from the perspective of obtaining an isoelectric point of 4 to 8, titanium dioxide-silicon dioxide system, aluminum oxide-silicon dioxide system, and titanium dioxide-aluminum oxide system can be appropriately used. By changing the content ratio of each metal, the metal composite oxide can be more precisely controlled to achieve a specified isoelectric point.

[0018] Alternatively, a metal oxide layer can be easily obtained by hydrolysis and polycondensation of metal alkoxides (the so-called sol-gel method). By adjusting the ratio of the various metal alkoxides used in the sol-gel method, the isoelectric point of the metal oxide layer can be more precisely controlled.

[0019] The coefficient of variation of the particle size of the colloidal particles constituting the charged three-dimensional colloidal crystal is preferably 20% or less. When the coefficient of variation of the particle size is 20% or less, the colloidal crystal structure is more easily formed, and defects in the crystal structure are reduced. The coefficient of variation (CV) of the particle size here refers to (standard deviation of the particle size × 100 / average particle size), and is preferably 15% or less, more preferably 10% or less, and most preferably approximately 5% or less.

[0020] The average particle size of the colloidal particles constituting the charged three-dimensional colloidal crystals is preferably between 50 nm and 500 nm. When the average particle size of the colloidal particles is 500 nm or less, the sedimentation rate in the dispersion is slow, making it easier to form three-dimensional colloidal crystals. Furthermore, when the average particle size of the colloidal particles is 50 nm or greater, thermal motion is less intense, making it easier to form charged colloidal crystals.

[0021] Furthermore, the charge of the colloidal particles forming the colloidal crystal can be either positive or negative. For negatively charged colloidal particles, the substrate is first charged negatively to prevent adsorption, generating a sufficiently regular three-dimensional colloidal crystal. The substrate is then reversed to a positive charge to allow adsorption, producing a two-dimensional colloidal crystal. For positively charged colloidal particles, the substrate is first charged positively to prevent adsorption, generating a sufficiently regular three-dimensional colloidal crystal. The substrate is then reversed to a negative charge to allow adsorption, producing a two-dimensional colloidal crystal.

[0022] The two-dimensional colloidal crystal structure of the present invention comprises a metal oxide layer having an isoelectric point of 4 to 8 formed on a substrate, and a two-dimensional colloidal crystal layer formed on the metal oxide layer. The two-dimensional colloidal crystal structure can be produced by the method for producing two-dimensional colloidal crystals of the present invention.

[0023] Furthermore, the two-dimensional colloidal crystal layer may be composed of metal colloidal particles. Furthermore, the metal colloidal particles may be metal colloidal particles of the platinum group such as gold colloidal particles and platinum colloidal particles, or silver colloidal particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a two-dimensional colloidal crystal structure.

[0025] Figure 2 This is a process diagram showing a method for producing a two-dimensional colloidal crystal structure.

[0026] Figure 3 This is a schematic diagram of using MPS to modify the surface of gold colloidal particles.

[0027] Figure 4 This is a graph showing the presence or absence of adsorption of silica colloidal particles to the surface-modified glass substrates of Test Examples 1 to 4 in which the mixing ratio of TTIP and TEOS was changed at various pH values.

[0028] Figure 5 These are the results of measuring the isoelectric points of the surface-modified glass substrates of Test Examples 1 to 4 in which the mixing ratio of TTIP and TEOS was varied.

[0029] Figure 6 The graph shows the presence or absence of adsorption of silica colloidal particles to the surface-modified glass substrates of Test Examples 5 to 8 in which the mixing ratio of ALIP and TEOS was varied at various pH values.

[0030] Figure 7 These are the results of measuring the isoelectric points of the surface-modified glass substrates of Test Examples 5 to 8 in which the mixing ratio of ALIP and TEOS was varied.

[0031] Figure 8 This graph shows the calcination temperature and the presence or absence of adsorption of TTIP surface-modified glass substrates.

[0032] Figure 9 The diagram and photograph show an apparatus for producing a glass substrate having its surface coated with a metal oxide by dip coating.

[0033] Figure 10 This is a graph showing the relationship between the liquid level lowering rate and the minimum HCl concentration when silica colloidal particles are adsorbed.

[0034] Figure 11 This is a graph showing the presence or absence of adsorption of silica colloidal particles to the surface-modified glass substrates of Test Examples 9 to 12 in which the mixing ratio of TTIP and ALIP was changed at various pH values.

[0035] Figure 12 These are the results of measuring the isoelectric points of the surface-modified glass substrates of Test Examples 9 to 12 in which the mixing ratio of TTIP and ALIP was varied.

[0036] Figure 13 These are optical microscope photographs of the two-dimensional gold colloidal crystal structure of Comparative Example 1 (when no alkali is added) and radial distribution functions obtained from these photographs.

[0037] Figure 14 These are optical microscope photographs of the two-dimensional gold colloidal crystal structure of Comparative Example 1 (when alkali is added) and radial distribution functions obtained from these photographs.

[0038] Figure 15 Schematic diagram showing the method for fabricating two-dimensional charged colloidal crystals.

[0039] Figure 16 It is a graph showing the relationship between the NaHCO3 concentration and the primary peak height h of g(r).

[0040] Figure 17 This is a graph showing the relationship between the surface potential of SiO2, TiO2, Al2O3 and APTES-modified SiO2 and pH.

[0041] Figure 18 This is an optical microscope photograph of the two-dimensional gold colloidal crystal of Example 2 obtained under the condition of [NaHCO3] = 100 μM.

[0042] Figure 19 It is from Figure 18 The radial distribution function is obtained from the photo.

[0043] Figure 20 This is an optical microscope photograph of the two-dimensional silica colloidal crystal of Example 3.

[0044] Figure 21 This is an optical microscope photograph of the two-dimensional polystyrene colloidal crystal of Example 4.

[0045] Figure 22 This is an optical microscope photograph of the two-dimensional polystyrene colloidal crystal of Example 5.

[0046] Figure 23 It represents the HCl concentration and the particle concentration at the crystalline-amorphous phase boundary. A diagram of the relationship.

[0047] Figure 24 yes Optical micrographs of silica colloid at HCl concentration = 100 μM and HCl concentration = 200 μM.

[0048] Figure 25This is an optical microscope photograph showing the passage of time when an HCl solution was diffused. DETAILED DESCRIPTION

[0049] Embodiments of the present invention will be described.

[0050] <Structure of Two-Dimensional Colloidal Crystal Structure>

[0051] Two-dimensional colloidal crystal structures such as Figure 1 As shown, a metal oxide layer 2 is stacked on a substrate 1, and a two-dimensional colloidal crystal layer 4 is formed on the surface of the metal oxide layer 2, in which colloidal particles 3 are regularly arranged in a single layer. The isoelectric point of the metal oxide layer 2 is 4 to 8. As such a metal oxide, titanium dioxide having an isoelectric point of approximately 6 can be used. In addition, composite oxides such as silicon dioxide and titanium dioxide, silicon dioxide and aluminum oxide, or titanium dioxide and aluminum oxide can also be used. As the substrate 1, an insulating substrate (e.g., a glass substrate, a plastic substrate, etc.) or a conductive substrate (e.g., a metal substrate, etc.) can be used.

[0052] It should be noted that as long as the isoelectric point of the substrate 1 itself is 4 to 8, the substrate 1 and the metal oxide layer 2 may be made of the same homogeneous material.

[0053] <Method for producing two-dimensional colloidal crystal structures>

[0054] Implementation Method 1

[0055] Figure 2 This is a process diagram showing a method for producing a two-dimensional colloidal crystal structure. Each process is described below.

[0056] Substrate preparation process (S1)

[0057] A substrate 1 is prepared, and a metal oxide layer 2 having an isoelectric point of 4 to 8 is formed on the surface thereof. Examples of a method for forming the metal oxide layer 2 on the surface of the substrate 1 include a wet method and a dry method.

[0058] Examples of wet methods include sol-gel methods using metal alkoxides such as titanium alkoxide, aluminum alkoxide, and silicon alkoxide as raw materials, and methods in which titanium or aluminum substrates are anodized in an electrolyte. In wet methods utilizing the sol-gel method, the substrate 1 is immersed in a solution containing a metal alkoxide, hydrolyzed using acid and water, then pulled from the solution and heated for polycondensation to form a titanium dioxide layer. Alternatively, the substrate 1 can be immersed in a solution containing a mixture of multiple metal alkoxides, then pulled from the solution and heated for polycondensation, thereby forming metal composite oxides with various ratios depending on the composition of the solution. It should be noted that when pulling the substrate 1 from the immersion solution, the film thickness can be controlled by controlling the pulling speed.

[0059] In addition, dry methods include vacuum evaporation, sputtering, CVD, etc. In these dry methods, in addition to using titanium dioxide, silicon dioxide, and aluminum oxide as a metal source, methods such as reacting Ti and oxygen in the system to generate titanium dioxide can also be used.

[0060] ·Colloidal crystal dispersion preparation step (S2)

[0061] Prepare a dispersion 6 of charged three-dimensional colloidal crystals 5. Charged three-dimensional colloidal crystals are colloidal crystals that are three-dimensionally arranged in a regular pattern due to electrostatic interactions between charged colloidal particles. The colloidal particles 3 that constitute the charged three-dimensional colloidal crystals 5 can be metal particles such as gold and platinum, particles made of silicon dioxide or silicates, or particles made of organic polymers such as polystyrene.

[0062] In order to prepare a dispersion 6 of charged three-dimensional colloidal crystals 5, various soluble ionic compounds that change the surface potential of the colloidal particles 3 can be added. In addition, when metal colloidal particles are used, the surface can be modified with a compound having anionic functional groups. When gold is used as the metal colloidal particles, an organic compound having a thiol group and anionic functional groups (such as 3-mercapto-1-propanesulfonic acid sodium salt, etc.) can be appropriately used. This is because the thiol group combines with the surface of gold to form a self-organized film, and thus becomes a gold colloidal particle with a negative charge through the anionic functional group (refer to Figure 3 ).

[0063] In addition, the salt concentration of the dispersion 6 is 150 μM or less.

[0064] Two-dimensional colloidal crystal formation process (S3)

[0065] The pH of the dispersion 6 was adjusted in two stages as follows.

[0066] That is, 1) by adjusting the pH of the dispersion 6, the surface potential of the metal oxide layer 2 and the surface charge of the colloidal particles 3 become the same sign, so that the charged three-dimensional colloidal crystals 5 can grow fully, and then 2) the pH is readjusted so that the surface charge of the metal oxide layer 2 and the surface charge of the colloidal particles 3 become the opposite sign, so that the charged three-dimensional colloidal crystals 5 are electrostatically adsorbed on the surface of the metal oxide layer 2.

[0067] By performing such two-step pH adjustment, it is possible to prevent the colloidal particles 3 from being randomly adsorbed to the metal oxide layer 2 before the charged three-dimensional colloidal crystals 5 are formed, thereby reducing defects in the crystal structure of the two-dimensional colloidal crystal layer 4 .

[0068] In addition, as a method for readjusting the pH, a method of lowering the pH by absorbing carbon dioxide contained in the air may also be used.

[0069] As a method for forming the two-dimensional colloidal crystal layer 4 on the metal oxide layer 2 , a method of dropping a dispersion liquid 6 of three-dimensional colloidal crystals 5 onto the substrate 1 on which the metal oxide layer 2 is formed can be used.

[0070] (Effect)

[0071] In the method for producing a two-dimensional colloidal crystal structure according to the embodiment, since the isoelectric point of the metal oxide layer 2 is between 4 and 8, even if the pH of the dispersion liquid 6 containing the three-dimensional colloidal crystals 5 is set to a value greater than 8 or less than 4, the surface charge of the three-dimensional colloidal crystals 5 is opposite to that of the metal oxide layer 2, resulting in electrostatic adsorption of the three-dimensional colloidal crystals 5 to the substrate 1. Therefore, the melting and particle aggregation of the three-dimensional colloidal crystals 5 caused by increased ionic strength can be suppressed, and the two-dimensional gold colloidal crystals 4 with minimal crystal structure defects can be transferred to the metal oxide layer 2.

[0072] Generally speaking, in a substrate utilizing surface plasmon resonance (SPR), a distance between the particle surfaces of 300 to 600 nm is required (refer to Scientific Reports, Volume 5, Article number: 14419 (2015).). The present inventors have found that in order to produce three-dimensional charged colloidal crystals having such a wide inter-particle distance, it is effective to adjust the three-dimensional charged colloid under conditions of low salt concentrations such as below 150 μM. By using the manufacturing method of the above embodiment, the three-dimensional charged colloid can be adjusted under conditions of low salt concentrations such as below 150 μM, so that the three-dimensional charged colloidal crystals can be fixed to the substrate under low salt concentration conditions, and two-dimensional charged colloidal crystals can be produced.

[0073] Example

[0074] - Fabrication of a Glass Substrate with a Metal Oxide Layer -

[0075] In order to measure the isoelectric point of the metal oxide layer, glass substrates having metal oxide layers formed thereon according to Test Examples 1 to 12 shown below were prepared.

[0076] The reagents used to form the metal oxide layer are as follows.

[0077] Titanium tetraisopropoxide (TTIP): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0078] Tetraethoxysilane (abbreviation: TEOS): manufactured by Shin-Etsu Chemical Co., Ltd.

[0079] Aluminum isopropoxide (ALIP): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0080] (Test Examples 1 to 4)

[0081] <Production of glass substrates formed with titanium dioxide and titanium dioxide-silicon dioxide composite oxide layers>

[0082] TEOS 50 μL, ethanol 92.5 mL, 0.1 M HCl 4.5 mL and Milli-Q water 5.6 μL were put into a glass bottle and mixed, kept at 40 ° C for 10 minutes, thereby preparing the hydrolyzed solution of TEOS. Then, EtOH, TTIP, the hydrolyzed solution of TEOS, 0.1 MHCl solution and pure water (hereinafter referred to as "Milli-Q water") prepared by a Milli-Q water manufacturing device were added to the glass bottle in the ratio shown in Table 1 and stirred at 300 rpm for 20 hours. The reaction solution was transferred to a polypropylene staining jar (Fisher Scientific) and impregnated with a cover glass (NEO micro cover glass 24 mm × 60 mm, Songlang Glass Industry) as a glass substrate for 1 hour. After impregnation, the glass substrate was taken out and kept in a 50 ° C oven for 1 hour, then the glass surface was cleaned with Milli-Q water and dried in an 80 ° C oven. In this manner, the titanium dioxide layer-formed glass substrate of Test Example 1 and the titanium dioxide-silicon dioxide composite oxide layer-formed glass substrates of Test Examples 2 to 4 were produced.

[0083] [Table 1]

[0084]

[0085] (Test Examples 5 to 8)

[0086] <Production of Glass Substrates Formed with Alumina and Alumina-Silica Composite Oxide Layers>

[0087] EtOH, ALIP in EtOH, TEOS hydrolyzate, 0.1M HCl solution and Milli-Q water were added to a glass bottle in the proportions shown in Table 2 and stirred at 300 rpm for 20 hours. The reaction solution was transferred to a polypropylene staining jar (Fisher Scientific) and the same glass substrate used in Test Examples 1 to 4 was immersed for 1 hour. Then, the glass substrate was taken out and kept in a 50°C oven for 1 hour, and then the glass surface was washed with Milli-Q water and dried in an 80°C oven. In this way, the aluminum oxide layer-forming glass substrate of Test Example 5 and the aluminum oxide-silicon dioxide composite oxide layer-forming glass substrates of Test Examples 6 to 8 were prepared.

[0088] [Table 2]

[0089]

[0090] *: ALIP was added in the form of 0.29 wt% ethanol solution.

[0091] <Production of a glass substrate with a titanium dioxide-aluminum oxide composite layer>

[0092] EtOH, TTIP, ALIP, 0.1M HCl solution, and Milli-Q water were placed in a glass bottle in the proportions shown in Table 3 and stirred at 300 rpm for 20 hours. The reaction solution was transferred to a polypropylene staining jar (Fisher Scientific) and the same glass substrate used in Experimental Examples 1 to 4 was immersed in it for 1 hour. The glass substrate was then removed and kept in a 50°C oven for 1 hour. The glass surface was then rinsed with Milli-Q water and dried in an 80°C oven. In this way, the titanium dioxide-aluminum oxide composite oxide layer-forming glass substrates of Experimental Examples 9 to 12 were prepared.

[0093] [Table 3]

[0094]

[0095] *: ALIP was added as a 0.097 wt% ethanol solution.

[0096] - Determination of isoelectric point -

[0097] The isoelectric point of the surface-modified glass substrates of Test Examples 1 to 12 was measured. The surface potential of these surface-modified glass substrates varies according to the pH, so the pH at which the surface potential is 0 becomes the isoelectric point. Particles with charges of opposite signs to the surface potential of the substrate are electrostatically adsorbed on the substrate. Therefore, the isoelectric point is determined based on the presence or absence of adsorption of silica colloidal particles to the substrate. HCl and NaOH dispersions of different concentrations containing 0.1 vol% silica colloidal particles were prepared, added dropwise to the prepared glass substrates, and the presence or absence of particle adsorption was observed using an inverted optical microscope (ECLIPSE, Ti-S, Nikon). The results are shown below.

[0098] (Isoelectric point of titanium dioxide-silicon dioxide composite oxide modified glass substrate)

[0099] For the surface-modified glass substrates of Test Examples 1 to 4, the presence or absence of adsorption of silica colloidal particles to the glass substrates was observed. The minimum HCl concentration at which silica colloidal particles adsorb to the substrates was as follows: Figure 4 As shown, the isoelectric point of the surface-modified glass substrate in Experimental Example 1 was 40 μM, that in Experimental Example 2 was 50 μM, that in Experimental Example 3 was 200 μM, and that in Experimental Example 4 was 600 μM. These results show that the isoelectric point of the surface-modified glass substrate can be controlled by varying the ratio of TTIP to TEOS.

[0100] In addition, the results of determining the pH corresponding to the isoelectric point measurement results of the surface-modified glass substrates of titanium dioxide-silicon dioxide composite oxide modified glass substrates of Test Examples 1 to 4 are shown in FIG. Figure 5 This figure shows that the isoelectric point of the surface potential can be controlled by changing the mixing ratio of TTIP and TEOS. It should be noted that in Test Example 1, where no TEOS was mixed, the isoelectric point of titanium dioxide was lower than the predicted value of 6 because a portion of the glass substrate surface was not modified with TTIP.

[0101] (Isoelectric point of alumina-silica composite oxide modified glass substrate)

[0102] For the surface-modified glass substrates of Test Examples 5 to 8, the presence or absence of adsorption of silica colloidal particles to the glass substrates was observed. The minimum concentration of silica colloidal particles adsorbed on the substrates was as follows: Figure 6 As shown, the isoelectric point of the surface-modified glass substrate in Test Example 5 was 600 μM NaOH, the surface-modified glass substrate in Test Example 6 was 600 μM NaOH, the surface-modified glass substrate in Test Example 7 was 100 μM NaOH, and the surface-modified glass substrate in Test Example 8 was 550 μM HCl. These results show that the isoelectric point of the surface-modified glass substrate can be controlled over a wide range by varying the ratio of ALIP to TEOS.

[0103] In addition, the results of determining the pH corresponding to the isoelectric point measurement results of the surface-modified glass substrates of the alumina-silica composite oxide modified glass substrates of Test Examples 5 to 8 are shown in FIG. Figure 7 As can be seen from the figure, the isoelectric point of the surface potential can be controlled by changing the mixing ratio of ALIP and TEOS.

[0104] <Relationship between calcination temperature and isoelectric point in TTIP-modified glass substrates>

[0105] The relationship between the calcination temperature and isoelectric point of glass substrates surface-modified with TTIP was investigated.

[0106] 40 mL of ethanol, 186 μL of 0.1 M HCl, 8 μL of Milli-Q water, and 40 μL of TTIP were added to a glass bottle and stirred at 300 rpm at room temperature for 20 hours. The reaction solution was transferred to a polypropylene staining jar and a cover glass for an optical microscope, serving as a glass substrate, was immersed in the jar for 1 hour. The glass substrate was then removed and placed in a 50°C oven for 1 hour. It was then placed in a calcining furnace and calcined at 200, 350, and 500°C for 30 minutes. The surface of the glass substrate removed from the calcining furnace was rinsed with Milli-Q water and dried in an 80°C oven. The calcined TTIP-surface-modified glass substrate obtained in this manner was subjected to the aforementioned isoelectric point measurement based on the presence or absence of adsorption of silica colloidal particles.

[0107] The results show that, if Figure 8 As shown, for glass substrates calcined at 200°C and 350°C, silica particles adsorbed to the substrates at HCl concentrations of 100 μM or higher, while for glass substrates calcined at 500°C, silica particles adsorbed at HCl concentrations of 200 μM or higher. This indicates that the isoelectric point shifts toward the acidic side at a calcination temperature of 500°C.

[0108] <Fabrication of TTIP-surface-modified glass substrates by dip coating>

[0109] A TTIP surface-modified glass substrate was produced by a dip coating method described in the following document.

[0110] Uchiyama,H.,Namba,W.,&Kozuka,H., "Spontaneous Formation of LinearStriations and Cell-like Patterns on Dip-Coating Titania Films Prepared fromAlkoxide Solutions," Langmuir,Vol.26,No.13,11479-11484,2010.

[0111] 40 mL of ethanol, 186 μL of 0.1 M HCl, 8 μL of Milli-Q water, and 40 μL of TTIP were added to a glass bottle and stirred at 300 rpm for 20 hours at room temperature. The resulting mixed solution was placed in a centrifuge tube or a bottle, and a cover glass for an optical microscope (NEO micro cover glass 24 mm × 60 mm, Matsunami Glass Industry) as a glass substrate was immersed in the solution. The mixed solution was slowly discharged from the discharge tube connected to the lower end of the centrifuge tube (or bottle) (refer to Figure 9The discharge rate was adjusted by varying the diameter of the discharge tube. The solution discharge rate was calculated from the rate of drop in the liquid level. After discharge, the glass substrate was removed and placed in a 50°C oven for 1 hour. The surface of the glass substrate was then rinsed with Milli-Q water and dried in an 80°C oven.

[0112] The TTIP surface-modified glass substrate produced by the above method was observed for the presence or absence of adsorption due to the adsorption of silica colloidal particles. The results are shown in Figure 10 . The horizontal axis represents the rate of decrease of the liquid level, and the vertical axis represents the minimum HCl concentration when the silica colloidal particles are adsorbed on each substrate. For glass substrates that have not been calcined, as the liquid level speed decreases, the isoelectric point moves toward the acidic side. From the above results, it can be seen that the surface of the glass substrate can be modified with TTIP even by the dip coating method. It should be noted that according to this method, there is an advantage in that the film thickness of the titanium dioxide-containing layer can be controlled by controlling the rate of decrease of the liquid level (i.e., the discharge rate of the liquid).

[0113] (Isoelectric point of glass substrate modified with titanium dioxide-aluminum oxide composite oxide)

[0114] For the surface-modified glass substrates of Test Examples 9 to 12, the presence or absence of adsorption of silica colloidal particles to the glass substrates was observed. The minimum concentration of silica colloidal particles adsorbed on the substrates was as follows: Figure 11 As shown, the surface-modified glass substrate of Test Example 9 was treated with 20 μM HCl, the surface-modified glass substrate of Test Example 10 was treated with 20 μM HCl, the surface-modified glass substrate of Test Example 11 was treated with no additives, and the surface-modified glass substrate of Test Example 12 was treated with 100 μM NaOH. These results show that the isoelectric point of the surface-modified glass substrate can be controlled by varying the ratio of TTIP to ALIP.

[0115] In addition, the results of determining the pH corresponding to the isoelectric point measurement results of the surface-modified glass substrates of the titanium dioxide-aluminum oxide composite oxide modified glass substrates of Test Examples 9 to 12 are shown in FIG. Figure 12 As can be seen from the figure, the isoelectric point of the surface potential can be controlled by changing the mixing ratio of TTIP to ALIP through pH.

[0116] -Fabrication of two-dimensional colloidal crystal structures-

[0117] <Fabrication of Two-Dimensional Gold Colloidal Crystal Structure>

[0118] (Comparative Example 1)

[0119] Fabrication of two-dimensional gold colloidal crystal structures on glass substrates modified with APTES

[0120] The same glass substrate as used in Test Examples 1 to 4 was used. An APTES hydrolyzate was prepared by adding 60 mL of Milli-Q water, 60 μL of 1 mol / l acetic acid, and 60 μL of aminopropyltriethoxysilane (APTES) to a polypropylene staining jar (Fisher Scientific), and the mixture was immersed in the glass substrate for 1 hour. Then, the glass substrate was taken out, the surface was washed with Milli-Q water, and dried in an oven at 40°C. In this way, a silica layer with amino groups introduced on the surface of the glass substrate was prepared by dehydration condensation of APTES with the silanol groups of the glass substrate.

[0121] A silicone frame with circular windows was placed on the APTES-modified glass substrate obtained in this way to form a depression, which was used as a well for microscopic observation. A gold colloidal particle dispersion was added dropwise to the well and the results were observed continuously using an optical microscope. The colloidal particles were adsorbed to the substrate before forming three-dimensional colloidal crystals, and no two-dimensional colloidal crystals were formed (see Figure 13 In addition, the radial distribution function g(r) was calculated, and the peak intensity was low, and multiple peaks were not observed, so no crystal structure was observed (refer to Figure 13 picture).

[0122] On the other hand, when NaHCO3 or NaOH is added to the gold colloidal particle dispersion to increase the pH, three-dimensional charged gold colloidal crystals are generated. Then, by adding ion exchange resin to desalinate and lowering the pH, a portion of the three-dimensional charged gold colloidal crystals is adsorbed on the substrate, and two-dimensional gold colloidal crystals are observed (refer to Figure 14 Photos and Figure 15 ). However, it was observed that its crystal structure has many defects. In addition, its radial distribution function g(r) was calculated, and multiple periodic peaks were observed together with the large peak, and the crystal structure was observed (refer to Figure 14 right). Figure 16 The relationship between the NaHCO3 concentration and the primary peak height h of g(r) is shown in the figure. As can be seen from the figure, the primary peak height h of g(r) reaches its maximum value when the NaHCO3 concentration is around 500 to 700 μM.

[0123] The above results can be explained as follows (it should be noted that for reference, Figure 17 (shows the relationship between the surface potential of SiO2, TiO2, Al2O3 and APTES-modified SiO2 and pH).

[0124] When no base is added to the gold colloidal particle dispersion, the surface charge of the APTES-modified glass substrate is positive, and the negatively charged gold colloidal particles rapidly and randomly adsorb to the surface of the APTES-modified glass substrate before forming three-dimensional charged gold colloidal crystals. Consequently, two-dimensional gold colloidal crystals are not formed.

[0125] On the other hand, when alkali is added to the gold colloidal particle dispersion, the surface charge of the APTES-modified glass substrate becomes negative. The gold colloidal particles, which also have a negative surface charge, do not adsorb to the APTES-modified glass substrate surface, but instead grow into three-dimensional charged gold colloidal crystals. Subsequently, by adding an ion exchange resin to lower the pH, the amino groups on the surface of the APTES-modified glass substrate are ionized, resulting in a positive surface charge. Three-dimensional charged gold colloidal crystals are adsorbed, and two-dimensional gold colloidal crystals are transferred to the surface of the APTES-modified glass substrate. It should be noted that the significant defects observed in the crystal structure of the two-dimensional gold colloidal crystals are due to the thinning of the double layer caused by the addition of alkali, the melting of the three-dimensional charged gold colloidal crystals, or the aggregation of the gold colloidal particles.

[0126] Fabrication of a Two-Dimensional Gold Colloidal Crystal Structure Using TTIP-Modified Glass Substrate

[0127] (Example 1)

[0128] Preparation of TTIP-modified glass substrate (substrate preparation step S1)

[0129] 70 mL of MeOH, 30 mL of acetonitrile, 666 μL of Milli-Q water, and 0.746 g of dodecylamine were added to a fluororesin container and mixed. A coverslip treated with UV / O₃ and sulfuric acid was added, followed by 800 μL of TTIP. The mixture was shaken on a rotator for 1 hour. The coverslip was removed, and the surface of the glass substrate was rinsed with MeOH and then with Milli-Q water. The glass substrate was then placed in a vial filled with Milli-Q water and ultrasonically treated for 10 minutes. The coverslip was removed, rinsed with Milli-Q water, and dried at 80°C to obtain a TTIP-modified glass substrate.

[0130] Preparation of a Dispersion of Charged Gold Colloidal Particles (Colloidal Crystal Dispersion Preparation Step S2)

[0131] In a centrifuge tube, 4 mL of a 1.0 mM aqueous solution of 3-mercapto-1-propanesulfonic acid sodium salt (MPS, Sigma-Aldrich) was added to 4 mL of a dispersion of gold colloidal particles (average particle size: 156 nm, coefficient of variation: 9%) manufactured by Tanaka Kikinzoku Co., Ltd. (particle concentration 0.006 wt%), and ultrasonic treatment was performed for 10 minutes. The thiol group of MPS forms a strong coordination bond with gold, so sulfonic groups are introduced on the surface of the gold particles (see Figure 3Next, the mixture was centrifuged at 2000 rpm for 25 minutes, 5 mL of the supernatant was removed, and 5 mL of Milli-Q water was added for 5 minutes of ultrasonic treatment and redispersion. The centrifugation and redispersion washing steps were repeated three times, followed by another centrifugation at 2000 rpm for 25 minutes. The supernatant was removed, concentrated, and redispersion was performed to prepare a dispersion of MPS-modified gold colloidal particles.

[0132] Preparation of two-dimensional gold colloidal crystal structure (two-dimensional colloidal crystal formation step S3)

[0133] A silicone frame with circular windows was placed tightly against the surface of a TTIP-modified glass substrate to create a depression. 5 μL of a dispersion of MPS-modified gold colloid particles (concentration: 19 wt%) was dripped into the depression and allowed to stand for observation from the back using an optical microscope. The results showed that after the MPS-modified gold colloid particle dispersion was added, the gold colloid particles did not immediately adsorb to the glass substrate, but instead gradually formed three-dimensional charged gold colloidal crystals. Approximately 15 minutes after the gold colloid particle dispersion was added, it was confirmed that the gold colloid particles were adsorbed to the substrate while maintaining their crystalline structure. Unadsorbed gold colloid particles were then washed with Milli-Q water to obtain a two-dimensional charged gold colloidal crystal substrate.

[0134] From the above results, it can be seen that by using a TTIP-modified glass substrate (refer to Figure 17 ), a two-dimensional charged gold colloidal crystal substrate can be obtained.

[0135] In the two-dimensional colloidal crystal formation step S3 of Example 1, carbon dioxide in air is used to adjust the pH across the isoelectric point. The mechanism is as follows.

[0136] (1) CO2 in the atmosphere dissolves in water in the form of CO2 (gas)

[0137] (2) CO2 (gas) dissolved in water reacts with water to produce carbonic acid

[0138] CO2+H2O→H2CO3

[0139] (3) Carbonic acid dissociates to generate H + , pH decreases

[0140] H2CO3→H + +HCO3 -

[0141] The concentration of carbon dioxide in the atmosphere is 0.04%. When Henry's law is used to calculate the concentration in water at equilibrium, it is calculated to be 1.4×10 -5 M. H2CO3→H+ +HCO3 - The acid dissociation constant at 25°C is Ka = 4.4×10 -7 , calculated from this value [H + ]=2.8×10 -6 M, pH = 5.6. On the other hand, since the isoelectric point of the TTIP-modified glass substrate is 6.0, the sample was placed in air under the condition of 5.6 < the isoelectric point of the TTIP-modified glass substrate (6.0) < the initial pH of the sample. The carbon dioxide in the air then gradually dissolved, lowering the pH, and the pH changed across the isoelectric point of the substrate (6.0).

[0142] (Example 2)

[0143] Preparation of TTIP-modified glass substrate (substrate preparation step S1)

[0144] In a fluororesin container, 35 mL of MeOH, 15 mL of acetonitrile, 333 μL of Milli-Q water, and 0.373 g of dodecylamine were added and mixed. A coverslip treated with UV / O₃ and sulfuric acid was added, followed by 400 μL of TTIP and shaking for 1 hour. The coverslip was removed and placed in a bottle filled with Milli-Q water, where it was ultrasonically treated for 5 minutes. The surface was then rinsed with Milli-Q water and dried at 80°C.

[0145] Using the thus obtained TTIP-modified glass substrate, the same operation as in Example 1 was carried out to obtain a two-dimensional charged gold colloidal crystal substrate.

[0146] Figure 18 The two-dimensional gold colloidal crystals on the TTIP-modified glass substrate were obtained under the condition of [NaHCO3] = 100μM. Figure 18 The images observed were larger than those obtained on the APTES substrate. Figure 14 The two-dimensional gold colloidal crystal shown has a large area and few defects in the crystal structure. Figure 18 The radial distribution function obtained from the photo is shown in Figure 19 The radial distribution function was compared with the radial distribution function of the two-dimensional gold colloidal crystal obtained on the APTES substrate ( Figure 14 Comparison with the two-dimensional gold colloidal crystal (right) shows that more peaks are obtained, indicating that the crystal structure has fewer defects.

[0147] (Example 3)

[0148] Fabrication of a Two-Dimensional Colloidal Dioxide Crystal Structure Using TTIP-Modified Glass Substrate

[0149] A two-dimensional silica colloidal crystal structure was prepared using a silica colloidal particle dispersion (KE-P100 manufactured by Nippon Shokubai Co., Ltd., particle size 1 μm, concentration 3.0 vol%, salt-free).

[0150] Preparation of TTIP-modified glass substrate (substrate preparation step S1)

[0151] In a fluororesin container, 35 mL of MeOH, 15 mL of acetonitrile, 333 μL of Milli-Q water, and 0.373 g of dodecylamine were added and mixed. A coverslip treated with UV / O₃ and sulfuric acid was added, followed by 400 μL of TTIP and agitation for 1 hour. The coverslip was removed, and the surface of the glass substrate was rinsed with MeOH and then with Milli-Q water. The glass substrate was then placed in a vial filled with Milli-Q water and ultrasonically treated for 10 minutes. The coverslip was removed, rinsed with Milli-Q water, and dried at 80°C.

[0152] A silicone frame with circular windows was placed in close contact with the surface of the TTIP-modified glass substrate thus obtained to form a depression. 100 μL of a silica colloidal particle dispersion was dripped into the depression and observed under an optical microscope. The results confirmed the presence of three-dimensional silica colloidal crystals. Subsequently, 11.1 μL of 1 mM HCl was added to the dispersion to adjust the HCl concentration to 100 μM. The surface was then washed with Milli-Q water to remove excess silica particles. An optical microscope photograph of the surface of the resulting TTIP-modified glass substrate is shown in FIG. Figure 20 As can be seen from this photograph, two-dimensional silica colloidal crystals with very few defects in the crystal structure are formed on the surface of the TTIP-modified glass substrate.

[0153] (Example 4)

[0154] <Fabrication of a Two-Dimensional Polystyrene Colloidal Crystal Structure Using TTIP-Modified Glass Substrate>

[0155] A two-dimensional polystyrene colloidal crystal structure was prepared using a polystyrene particle dispersion (average particle size 430 nm, 10 vol%). Specifically, 5 μL of polystyrene particles (particle size 430 nm, 10 vol%) was added dropwise to the TTIP-modified glass substrate prepared in Experimental Example 1. After confirming the formation of a three-dimensional charged colloidal crystal, 4 μL of 200 μM HCl was added dropwise, and then the surface was washed with Milli-Q water to remove excess polystyrene particles. An optical microscope photograph of the surface of the TTIP-modified glass substrate thus obtained is shown in FIG. Figure 21 As can be seen from this photograph, two-dimensional polystyrene colloidal crystals with very few defects in the crystal structure are formed on the surface of the TTIP-modified glass substrate.

[0156] (Example 5)

[0157] <Fabrication of Two-Dimensional Colloidal Crystal Structures of Positively Charged Colloidal Particles>

[0158] A three-dimensional colloidal crystal dispersion of positively charged colloidal particles was prepared and adsorbed onto a glass substrate coated with a thin film of TEOS:ALIP (1:9). The substrate was initially positively charged, but the addition of alkali (NaOH) reversed the charge to negative, allowing the colloidal particles to adsorb.

[0159] Positively charged polystyrene particles were synthesized and used by the following method.

[0160] A mixture of 14 mL of Milli-Q water and 126 mL of ethanol was placed in a glass container, 10 g of polyvinyl pyrrolidone was added, and the mixture was stirred at 500 rpm for 10 minutes using a magnetic stirrer, followed by 5 minutes of nitrogen bubbling. 0.1388 g of azobisisobutyronitrile (reaction initiator), 0.2030 g of ammonium chloride (electrolyte), 0.0062 g of Nile Red (fluorescent pigment), 10 mL of styrene (monomer), and 0.5 mL of divinylbenzene (crosslinking agent) were added as polymerization initiators, and nitrogen bubbling was performed for 5 minutes while rotating with a stirrer. The mixture was placed in a water bath and reacted at 70°C for 24 hours, then removed from the water bath and cooled at room temperature while stirring at 300 rpm. Spherical particles were obtained by the above reaction. The particle size obtained by dynamic light scattering was 789 nm, and the zeta potential was +30.9 mV.

[0161] A thin film layer of TEOS:ALIP (1:9) was formed on the surface of a coverslip, and a silicon wafer with circular holes was attached to serve as a microscope observation cell. The bottom of the sample cell was observed using an inverted microscope. 50 μL of the positively charged polystyrene colloidal particles described above were added to the cell. After confirming the formation of three-dimensional charged colloidal crystals, 5 μL of 1 mM NaOH was added. The NaOH diffused into the colloidal sample over time, causing the particles to adhere to the substrate. The cell was rinsed with Milli-Q water to remove any unadsorbed polystyrene particles. Figure 22 This optical microscope photograph shows a substrate after water washing. The particles are adsorbed to the substrate while maintaining their two-dimensional crystalline structure. Image analysis revealed a center-to-center distance of approximately 960 nm and a particle concentration of approximately 41.1 vol%.

[0162] - Relationship between the distance between particles constituting colloidal crystals and salt concentration -

[0163] The relationship between the distance between particles in three-dimensional colloidal crystals used for preparing two-dimensional colloidal crystal structures and the salt concentration of the colloidal dispersion was investigated.

[0164] Preparation of three-dimensional colloidal crystals

[0165] Silica particles with a particle size of 1000 nm (KE-P100, Nippon Shokubai Co., Ltd.) were dispersed in pure water and deionized and purified in the presence of an ion exchange resin. The surface charge of the silica thus obtained was determined by particle conductivity measurement and found to be 10,460 particles / particle.

[0166] A silicon wafer with a circular hole was attached to a cover glass for an optical microscope, cleaned by sulfuric acid treatment, to serve as a microscope observation cell. Hydrochloric acid was then added to a deionized and purified silica particle dispersion to prepare silica particle dispersions of various hydrochloric acid concentrations. These dispersions were then filled into the observation cell and observed from the bottom surface of the sample using an inverted optical microscope.

[0167] The results showed that the higher the HCl concentration, the stronger the electrostatic interaction between particles was, making it difficult for colloidal crystallization to occur. Crystallization required a higher particle concentration. In addition, silica particles settle over time, and the particle concentration at the bottom of the pool Moreover, when the particle concentration When the particle concentration is Under sufficiently large conditions, the silica particles are regularly arranged, showing a colloidal crystal structure. The value of is determined by measuring the interparticle distance from microscope images.

[0168] Figure 23 The particle concentration at the crystalline-amorphous phase boundary at various HCl concentrations is shown. The value of (the curve is an approximate curve obtained by the least squares method). The lower salt concentration side than the boundary corresponds to the crystalline state. For example, when the HCl concentration = 100μM, the phase boundary is Table 4 shows the particle concentration and inter-surface distance of the phase boundary at various [HCl].

[0169] [Table 4]

[0170]

[0171] Figure 24 yes Optical micrographs of silica colloids at HCl concentration = 100 μM and HCl concentration = 200 μM. These conditions correspond to the crystalline (phase boundary) and amorphous states, respectively. The latter condition is Figure 23 The triangle symbol indicates that when 200 μM HCl is added, even if (Inter-particle surface distance = about 360 nm) No crystal structure with inter-particle spacing was generated.

[0172] Observation of the two-dimensional colloidal crystal formation process using an optical microscope

[0173] The method for producing a two-dimensional colloidal crystal structure according to the present invention is characterized by its ability to immobilize two-dimensional colloidal crystals even at salt concentrations of 100 μM or less. A mixed solution of TEOS:TTIP = 3:7 was prepared on the surface of a cover glass with an insulating layer formed by a sol-gel method. A silicon wafer with circular holes was attached to the solution and used as a microscopic observation cell. The bottom surface of the sample cell was observed using an inverted microscope.

[0174] Add 100 μl of silica gel to the cell Next, a pipette with a semipermeable membrane was inserted into the silica colloid, exposing it to a 100 μM HCl solution through the membrane. Over time, HCl diffused into the colloid, reaching a maximum HCl concentration of 100 μM.

[0175] The microscope images showing the passage of time are shown in Figure 25 . As time went on, the silica particles were adsorbed to the substrate, and after 100 minutes, all the silica particles in the field of view were adsorbed. When the pipette was removed 100 minutes after the start of diffusion, the pool was washed with Milli-Q water to remove the non-adsorbed silica particles, the particles were adsorbed to the substrate while maintaining the crystal structure even after washing with water. From the above results, it can be seen that even under low salt concentration conditions of 100μM, silica particles can be adsorbed to the substrate, and crystals with wide particle spacing can be fixed. Such a structure with a wide distance between particles means that high sensitivity can be achieved in colloidal crystals used as substrates for SPR measurements using metal particles.

[0176] The present invention is not limited to the above-mentioned embodiments and examples, but includes various modifications that can be easily conceived by those skilled in the art without departing from the scope of the patent claims.

[0177] Industrial applicability

[0178] The present invention can be used as a transducer in a sensor using surface adsorption, or used in spectral analysis using surface plasmon resonance (SPR).

[0179] Explanation of symbols

[0180] 1…Substrate, 2…Metal oxide layer, 3…Colloidal particles, 4…Two-dimensional colloidal crystal layer, 5…Three-dimensional gold colloidal crystal, 6…Dispersion liquid

[0181] S1...substrate preparation step, S2...colloidal crystal dispersion preparation step,

[0182] S3…Two-dimensional colloidal crystal formation process.

Claims

1. A method for producing a two-dimensional colloidal crystal structure, comprising the following steps: a substrate preparation step of preparing a substrate having a metal oxide layer having a surface isoelectric point of 4 to 8; a colloidal crystal dispersion preparation step of preparing a dispersion of charged three-dimensional colloidal crystals composed of colloidal particles having a surface charge of the same sign as the surface charge of the metal oxide layer; and The two-dimensional colloidal crystal formation process is to bring the dispersion of the charged three-dimensional colloidal crystals into contact with the metal oxide layer, adjust the surface charge of the metal oxide layer so that it has a sign different from the surface potential of the colloidal particles constituting the charged three-dimensional colloidal crystals, and transfer the two-dimensional colloidal crystals to the substrate.

2. The method for producing a two-dimensional colloidal crystal structure according to claim 1, wherein: The pH of the dispersion liquid of the charged three-dimensional colloidal crystals in the two-dimensional colloidal crystal forming step changes to 4 or less, and the salt concentration is 150 μM or less.

3. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The isoelectric point of the metal oxide layer is 4.5 to 7.

5.

4. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The metal element in the metal oxide layer is Ti or Al, or at least two of Ti, Si and Al.

5. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The metal oxide layer is composed of titanium dioxide or a composite oxide containing titanium dioxide.

6. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The substrate preparation step is performed by polycondensation of a hydrolyzate of a solution containing a metal alkoxide.

7. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The charged three-dimensional colloidal crystal is composed of metal colloidal particles.

8. The method for producing a two-dimensional colloidal crystal structure according to claim 7, wherein: The metal colloid particles are gold colloid particles.

9. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The coefficient of variation of the particle diameter of the colloidal particles constituting the charged three-dimensional colloidal crystal is 20% or less.

10. The method for producing a two-dimensional colloidal crystal structure according to claim 1 or 2, wherein: The average particle size of the colloidal particles constituting the charged three-dimensional colloidal crystal is 50 nm to 500 nm.

11. A two-dimensional colloidal crystal structure, comprising: a metal oxide layer having an isoelectric point of 4 to 8 formed on a substrate; and a two-dimensional colloidal crystal layer formed on the metal oxide layer.

12. The two-dimensional colloidal crystal structure according to claim 11, wherein The isoelectric point of the metal oxide layer is 4.5 to 7.

5.

13. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The metal element in the metal oxide layer is Ti or Al, or at least two of Ti, Si and Al.

14. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The metal oxide layer is composed of titanium dioxide or a composite oxide containing titanium dioxide.

15. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The metal oxide layer is composed of a hydrolysis-condensation product of a metal alkoxide.

16. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The two-dimensional colloidal crystal layer is composed of metal colloidal particles.

17. The two-dimensional colloidal crystal structure according to claim 16, wherein The metal colloid particles are gold colloid particles.

18. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The coefficient of variation of the particle diameter of the colloidal particles constituting the two-dimensional colloidal crystal layer is 20% or less.

19. The two-dimensional colloidal crystal structure according to claim 11 or 12, wherein The average particle size of the colloidal particles constituting the two-dimensional colloidal crystal layer is 50 nm to 500 nm.

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