Mesoporous metal thin film and method for producing mesoporous metal thin film

Abstract

The purpose of the present invention is to newly provide a mesoporous metal thin film and a method for producing a mesoporous metal thin film.　This mesoporous metal thin film is formed on a substrate, wherein (i) the surface of the substrate is made of an insulating material, or (ii) the material constituting the surface of the substrate is a metal having a higher ionization tendency than the metal forming the mesoporous metal thin film, and a gap is partially provided between the substrate and the mesoporous metal thin film.

Description

Mesoporous metal thin film and method for producing mesoporous metal thin film

[0001] The present invention relates to a mesoporous metal thin film and a method for producing a mesoporous metal thin film.

[0002] Metals are widely used as structural materials, electronic materials, etc. In particular, precious metals are used as catalysts, sensing reaction sites, etc., taking advantage of the chemical activity on their surfaces. In applications that utilize the chemical activity of metals, techniques such as microparticulating metals and making metals porous are important in order to increase the surface area per unit weight of the metal.

[0003] Known methods for producing metal microparticles include physical methods such as gas evaporation and chemical methods that chemically reduce metal precursors. By making metal microparticles porous, it is possible to further increase the specific surface area. Patent Document 1 and Non-Patent Document 1 disclose a technique for producing mesoporous metal microparticles in which an assembly of amphiphilic molecules serves as a template by reducing a metal precursor in the coexistence of amphiphilic molecules.

[0004] Although mesoporous metals can be used in the form of particles for catalysts, etc., thin mesoporous metal films can be patterned and can be used in sensing devices, etc. Patent Document 2 and Non-Patent Document 2 disclose a technique for producing mesoporous metal thin films by electrochemically reducing a metal precursor on an electrode in the presence of amphiphilic molecules.

[0005] JP 2015-089958 Public Relations JP 2012-167300 Public Relations

[0006] Nature Communications, Vol. 6, Article No. 7608; Journal of the American Chemical Society, Vol. 132, pp. 208-214

[0007] An object of the present invention is to provide a novel mesoporous metal thin film and a method for producing the same.

[0008] Conventionally, mesoporous metal thin films have been produced by electrochemical methods.

[0009] Conventionally, when reducing metal precursors by electrochemical techniques, the substrate for fabricating mesoporous metal thin films has been limited to metals with good electrical conductivity. Furthermore, even when using metals, it has been difficult to fabricate uniform and high-quality mesoporous metal thin films in isolated regions when the substrate has high in-plane resistance or a complex morphology, such as a thin film.

[0010] Conventionally, when producing a mesoporous metal thin film by an electrochemical method, equipment such as a power source and an electrochemical reaction control device is required.

[0011] The present inventors have found that mesoporous metal thin films can be produced on substrates by (i) preparing an aqueous solution containing ions containing a metal element, an amphipathic compound, and a compound capable of reducing the metal (metal element) contained in the ions, and then holding a substrate having an insulating surface in the aqueous solution, or (ii) preparing an aqueous solution containing ions containing a metal element and an amphipathic compound, and then holding a substrate having a metal surface in the aqueous solution.

[0012] The present invention encompasses the following mesoporous metal thin film and its manufacturing method.

[0013] Item 1. A mesoporous metal thin film formed on a substrate, wherein (i) the surface of the substrate is made of an insulating material, or (ii) the material of the surface of the substrate is a metal that has a higher ionization tendency than the metal that forms the mesoporous metal thin film, and the mesoporous metal thin film has voids in some parts between the substrate and the mesoporous metal thin film.

[0014] Item 2. (i) The mesoporous metal thin film according to Item 1, wherein the surface of the substrate is made of an insulating material, and the mesoporous metal thin film is formed directly on the surface of the substrate.

[0015] Item 3. (i) The mesoporous metal thin film according to Item 1, wherein the insulating material is an oxide having an isoelectric point of 5 or more.

[0016] Item 4. The mesoporous metal thin film according to Item 1, wherein the surface of the substrate is formed on the insulating material by a material including a site that is positively charged in an aqueous solution.

[0017] Item 5. The mesoporous metal thin film according to Item 4, wherein the positively charged sites are positive ions.

[0018] Item 6. (ii) The mesoporous metal thin film according to Item 1, wherein the material of the surface of the substrate is a metal having a higher ionization tendency than the metal forming the mesoporous metal thin film, and a portion between the substrate and the mesoporous metal thin film has voids different from the mesoporous structure.

[0019] Item 7. The mesoporous metal thin film according to Item 1, wherein the mesoporous metal material is at least one material selected from the group consisting of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture of these materials.

[0020] Item 8. A method for producing a mesoporous metal thin film (i), comprising: (1) preparing an aqueous solution containing ions containing a metal element, an amphipathic compound, and a compound that reduces the metal (metal element) contained in the ions; and (2) retaining a substrate having an insulating surface material in the aqueous solution prepared in step (1), wherein the surface of the substrate carries a charge of opposite polarity to the charge of the ions containing the metal element in the aqueous solution.

[0021] Item 9. (3) The method for producing a mesoporous metal thin film according to Item 8, further comprising the step of forming ionic sites on the surface of the substrate after the step (1) and before the step (2).

[0022] Item 10. A method for producing a mesoporous metal thin film (ii), comprising: (1) preparing an aqueous solution containing ions containing a metal element and an amphipathic compound; and (2) retaining a substrate having a metal surface in the aqueous solution prepared in step (1), wherein the metal on the surface of the substrate has a higher ionization tendency than the metal constituting the mesoporous metal thin film.

[0023] Item 11. The method for producing a mesoporous metal thin film according to Item 8 or 10, wherein step (2) is a step of holding the substrate in the aqueous solution and forming a mesoporous metal thin film on the substrate.

[0024] The present invention provides a technology for producing uniform mesoporous metal thin films over a large area without requiring any special equipment and without being restricted by the shape of the substrate or the deposition area, and can provide mesoporous metal thin films with a variety of compositions and morphologies that can be achieved thereby.

[0025] The mesoporous metal thin film of the present invention is useful for applications such as catalysts, sensors, and electrodes.

[0026] The present invention can provide a new mesoporous metal thin film and a method for producing a mesoporous metal thin film.

[0027] FIG. 1 is a cross-sectional schematic diagram illustrating the structure of a mesoporous metal thin film of the present invention. FIG. 2 is a cross-sectional schematic diagram illustrating the pore structure of a mesoporous metal thin film of the present invention. FIG. 3 is a cross-sectional schematic diagram illustrating the structure of a substrate of a first embodiment of a mesoporous metal thin film of the present invention (a mesoporous metal thin film formed directly on the surface of a substrate made of an insulating material). FIG. 4 is a cross-sectional schematic diagram illustrating the structure of a second embodiment of a mesoporous metal thin film of the present invention (a mesoporous metal thin film formed on a substrate having a surface containing a metal material with a higher ionization tendency than the metal forming the mesoporous metal thin film). FIG. 5 is a scanning electron microscope image of the surface of a mesoporous platinum thin film formed on a silicon substrate coated with alumina in Example 1. (a) Mesoporous structure with pores of approximately 20 nm on average. (b) Mesoporous structure after heat treatment. FIG. 6 is a scanning electron microscope image of the surface of a mesoporous platinum thin film formed on a quartz glass substrate coated with zirconium oxide in Example 2. Figure 7 is a scanning electron microscope image of the surface of a mesoporous platinum thin film produced on a quartz glass substrate whose surface was modified with 3-aminopropyltriethoxysilane in Example 3. Figure 8 is a scanning electron microscope image of the surface and cross section of a mesoporous platinum thin film produced on a silver plate substrate in Example 6. (a) Mesoporous structure with pores of approximately 20 nm on average. (b) Voids between the substrate and the mesoporous platinum thin film that are partially different from the voids of the mesoporous structure. Figure 9 is a scanning electron microscope image of the surface of a mesoporous platinum thin film produced on a copper plate substrate in Example 9. Figure 10 is a scanning electron microscope image of the surface of a mesoporous platinum thin film produced on the cut surface of a partially cut tin particle in Example 10. Figure 11 is a scanning electron microscope image of the surface of a mesoporous palladium thin film produced on the cut surface of a partially cut tin particle in Example 11. Fig. 12 is a scanning electron microscope image of the surface of a mesoporous platinum thin film formed on a silicon substrate with a cerium oxide film formed thereon in Example 13. Fig. 13 is a scanning electron microscope image of the surface of a mesoporous platinum thin film formed on a foamed nickel substrate in Example 14. Fig. 14 is a scanning electron microscope image of the surface of a mesoporous palladium thin film formed on a foamed nickel substrate in Example 15.Fig. 15 is a scanning electron microscope image of the surface of a mesoporous palladium thin film formed on a flat copper substrate in Example 16. Fig. 16 is a scanning electron microscope image of the surface of a mesoporous silver thin film formed on a flat copper substrate in Example 17. Fig. 17 is a scanning electron microscope image of the surface of a mesoporous gold thin film formed on a flat nickel substrate in Example 18. Fig. 18 is a scanning electron microscope image of the surface of a mesoporous platinum thin film formed on a steel wool substrate in Example 19.

[0028] The present invention will be described in detail below. The embodiments of the present invention are intended to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the content of the invention.

[0029] In this specification, the terms "comprise" and "contain" are concepts that encompass all of "comprise," "consist essentially of," and "consist only of."

[0030] In this specification, when a numerical range is expressed as "A to B," it means "A or more, and B or less."

[0031] In this specification, the terms "parts," "%," etc. are generally used to represent parts by mass, parts by weight, mass %, and weight % (wt%).

[0032] The present invention includes the following mesoporous metal thin film and a method for producing a mesoporous metal thin film. The present invention includes the following first and second aspects, and embodiments will be described.

[0033] [1] Mesoporous metal thin film Figure 1 is a schematic diagram of a cross section of a mesoporous metal thin film of the present invention. In Figure 1, 11 is a substrate, 12 is a pore wall made of metal, and 13 is a mesopore. Mesoporous metal thin films include those in which pores are formed across multiple layers as shown in Figure 1 (a), those with a single-layer pore structure as shown in Figure 1 (b), and those in which only a portion of a single layer is formed as shown in Figure 1 (c).

[0034] The thickness of the mesoporous metal thin film is not limited, but is preferably in the range of 1 nm to 10 μm, more preferably in the range of 10 nm to 1 μm, and even more preferably in the range of 20 nm to 500 nm.

[0035] Figure 2 is a schematic diagram of the pore structure of the mesoporous metal thin film of the present invention. Typical mesoporous metal thin films in Figure 2 include those with a structure in which spherical pores are arranged in a cubic crystal pattern, as shown in (a), and those with cylindrical pores arranged hexagonally, as shown in (b). The mesoporous structure is not limited to these. The mesoporous structure may have any pore structure, such as a structure with random pore shapes or a bicontinuous pore structure.

[0036] "Mesoporous" refers to a porous material with pores ranging in diameter from 2 to 50 nm, and the pore size is generally estimated from gas adsorption isotherm measurements, electron microscope observations, etc.

[0037] The mesoporous metal thin film of the present invention is characterized by having mesopores with diameters of 2 to 50 nm. The mesoporous metal thin film may also contain micropores with diameters of less than 2 nm and macropores with diameters of more than 50 nm.

[0038] The material of the mesoporous metal of the present invention is not limited. The mesoporous metal material is preferably a metal material that can be easily chemically reduced from a precursor, can stably exist in a metallic state under an oxidizing environment, and has a low ionization tendency (compared to the ionization tendency of the metal formed on the substrate surface). The mesoporous metal material is preferably any one of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture thereof.

[0039] [2] First embodiment of mesoporous metal thin film Mesoporous metal thin film (i) The mesoporous metal thin film of the present invention is formed on a substrate, and the surface of the substrate is made of an insulating material.

[0040] The insulating material on the substrate surface is preferably an oxide, and preferably has an isoelectric point greater than 5. A material containing sites that are positively charged in an aqueous solution is preferably formed on a portion of the substrate surface. The positively charged sites are preferably positive ions.

[0041] The mesoporous metal material is preferably any one of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture of these materials.

[0042] The present invention is a mesoporous metal thin film (i) formed on a substrate, the surface of which is a mesoporous metal thin film made of an insulating material.

[0043] In the mesoporous metal thin film (i) of the present invention, the surface of the substrate is preferably made of an insulating material, and the mesoporous metal thin film is formed directly on the surface of the substrate.

[0044] In the mesoporous metal thin film (i) of the present invention, the insulating material is preferably an oxide having an isoelectric point greater than 5. In this embodiment, by using an oxide having an isoelectric point greater than 5, the surface can be positively charged in an acidic solution, enabling the formation of a mesoporous metal film.

[0045] In the mesoporous metal thin film (i) of the present invention, the surface of the substrate is preferably formed on the insulating material from a material containing a site that is positively charged in an aqueous solution. This embodiment makes it possible to form a mesoporous metal film by providing a positively charged material on the surface, even without using an oxide with an isoelectric point greater than 5. This embodiment also makes it possible to provide a positively charged material on the surface, even when using an oxide with an isoelectric point greater than 5.

[0046] In the mesoporous metal thin film (i) of the present invention, the positively charged sites are preferably positive ions.

[0047] In the mesoporous metal thin film (i) of the present invention, the mesoporous metal material is preferably at least one material selected from the group consisting of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture of these materials.

[0048] A first aspect of the present invention is a mesoporous metal thin film formed directly on the surface of a substrate made of an insulating material.

[0049] FIG. 3 shows the structure of a mesoporous metal thin film on a substrate according to the first embodiment of the present invention.

[0050] 3(a) shows a two-layer structure consisting of an insulating substrate 31 and a mesoporous metal thin film (12: pore walls made of metal, 13: mesopores). In this structure, the substrate 31 is preferably an oxide whose isoelectric point is greater than 5.

[0051] The material of the substrate 31 (base) on which the mesoporous metal thin film of the first embodiment is formed is not limited as long as it is an insulating material, and specifically, preferred materials for the substrate 31 include aluminum oxide (alumina, sintered alumina, etc.), zirconium oxide, cerium oxide, lanthanum oxide, yttrium oxide, magnesium oxide, etc.

[0052] The substrate 31 may be made of a plurality of materials as long as they have an isoelectric point of 5 or more.

[0053] FIG. 3(b) shows a configuration in which a mesoporous metal thin film is formed on a substrate 33 made of any material, on which an oxide layer 32 having an isoelectric point greater than 5 is formed. The oxide layer 32 can be formed using a known film formation method. The film formation method is not limited. The film formation method preferably uses sputtering, vacuum deposition, coating and baking of a precursor solution, or the like.

[0054] The present invention uses an oxide with an isoelectric point greater than 5, thereby making it possible to positively charge the surface in an acidic solution and form a mesoporous metal film.

[0055] 3(c) shows a configuration in which a mesoporous metal thin film is formed on a substrate 33 of any material, on which a material 34 having portions that are positively charged in aqueous solution is formed. In configuration (c), the positively charged portions of material 34 having portions that are positively charged in aqueous solution are preferably positive ions. In configuration (c), material 34 having portions that are positively charged in aqueous solution is depicted as a layer having a certain thickness, but it also includes, for example, a monolayer on the surface.

[0056] The present invention makes it possible to form a mesoporous metal film by providing a positively charged material on the surface, even without using an oxide with an isoelectric point greater than 5. This embodiment also makes it possible to provide a positively charged material on the surface, even when using an oxide with an isoelectric point greater than 5.

[0057] In FIG. 3(c), a material 34 containing a site that is positively charged in an aqueous solution and formed on the surface is, for example, a silane coupling agent having an amino group. The material 34 in FIG. 3(c) is not limited. Preferably, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltriethoxysilane, or the like is used for the material 34 in FIG. 3(c). When a silane coupling agent having an amino group is used, the amino group is quaternized in water to become a positive ion.

[0058] Figure 3(d) shows a mesoporous metal thin film in which a material 34 containing positively charged sites in an aqueous solution is further formed on the surface of the substrate having the structure shown in Figure 3(b). Even when using a substrate with an isoelectric point higher than 5, a better mesoporous metal thin film can sometimes be obtained by forming a material 34 containing positively charged sites on the surface.

[0059] In the case of the mesoporous metal thin films of Figures 3(c) and 3(d), if the material 34 containing positively charged sites formed on the surface is organic, this organic material will be lost by heat treatment. When the organic material (material 34) is lost by heat treatment, the mesoporous metal thin film of Figure 3(c) changes to the mesoporous metal thin film structure of Figure 3(e). When the organic material (material 34) is lost by heat treatment, the mesoporous metal thin film of Figure 3(d) changes to the mesoporous metal thin film structure of Figure 3(b). The mesoporous metal thin film of the present invention also includes a thin film formed directly on a substrate of any material.

[0060] The potential and isoelectric point of the substrate surface in solution can be determined using a zeta potential measuring device. The isoelectric point is determined by measuring the surface potential while changing the pH, and determining the pH at which the surface potential becomes zero.

[0061] In Figures 1 to 3, the substrate used to form the mesoporous metal thin film of the present invention is depicted as a flat plate. The shape of the substrate on which the mesoporous metal thin film is formed is not limited to these. A wide range of substrate shapes are applicable, including curved surfaces, substrates with complex surface structures, and porous materials with complex internal structures. The substrate shape can be any shape, including fine substrates such as particles and powders.

[0062] Manufacturing Method of Mesoporous Metal Thin Film (i) The manufacturing method of a mesoporous metal thin film of the present invention first prepares an aqueous solution containing ions containing a metal element, an amphipathic compound, and a compound capable of reducing the metal (metal element) contained in the ions, and then places a substrate having an insulating surface in the aqueous solution to form a mesoporous metal thin film on the substrate. In the aqueous solution, the substrate surface carries a charge of opposite polarity to that of the ions containing the metal element. In the manufacturing method of a mesoporous metal thin film, after preparing the aqueous solution, a material containing ionic sites is preferably formed on the surface of the substrate.

[0063] The method for producing a mesoporous metal thin film (i) of the present invention includes the steps of: (1) preparing an aqueous solution containing ions containing a metal element, an amphiphilic compound, and a compound that reduces the metal (metal element) contained in the ions; and (2) retaining a substrate having an insulating surface in the aqueous solution prepared in step (1).

[0064] In the method for producing a mesoporous metal thin film (i) of the present invention, the surface of the substrate is charged in the aqueous solution with a charge of a polarity opposite to that of the ions containing the metal element.

[0065] The method for producing the mesoporous metal thin film (i) of the present invention preferably includes the step of: (3) forming ionic sites on the surface of the substrate after the step (1) and before the step (2).

[0066] In the method for producing a mesoporous metal thin film (i) of the present invention, the step (2) is preferably a step of holding the substrate in the aqueous solution and forming a mesoporous metal thin film on the substrate.

[0067] Preparation of Aqueous Solution of Metal Precursor In the first embodiment of the method for producing a mesoporous metal thin film of the present invention, first, an aqueous solution of a metal precursor is prepared.

[0068] The metal precursor to be used is not limited. The metal precursor preferably includes a metal chloride complex, a metal chloride, or the like. The metal precursor preferably includes potassium tetrachloroplatinate, potassium hexachloroplatinate, potassium tetrachloroaurate, sodium tetrachloroaurate, potassium tetrachloropalladate, potassium hexachloroiridate, sodium hexachlororhodiumate, potassium hexachloroosmate, potassium hexachlororuthenate, or the like.

[0069] An aqueous solution of these complexes is prepared. The concentration of the aqueous solution of the complex is not limited. The concentration of the aqueous solution of the complex is preferably in the range of 0.001 M (mol / L concentration) to 0.1 M, more preferably in the range of 0.002 M to 0.05 M. The amount of the aqueous solution is optimized taking into account the total area of ​​the substrate to be used, etc.

[0070] Examples of ions containing metal elements: [PtCl4] 2- is a negative ion, and the substrate surface is positively charged with the opposite polarity to this negative ion. [PtCl4] 2- is a negative ion and cannot be reduced to form a metal. [PtCl4] 2- is [Pt 2+ (Cl - )4] 2- and Pt 2＋ is reduced to Pt. In other words, what is reduced is an ion containing a metal element ([PtCl4] 2- ) contained in the metal (Pt 2＋ )

[0071] Preparation of a Solution of Amphiphilic Material Next, a solution of an amphiphilic material that forms molecular aggregates (micelles) that serve as templates for forming pores in the mesoporous metal thin film is prepared.

[0072] The amphiphilic material is not limited. Preferably, the amphiphilic material is a block copolymer containing polyethylene oxide as a hydrophilic block. Preferably, the amphiphilic material is a polymethyl methacrylate-polyethylene oxide block copolymer, a polystyrene-polyethylene oxide block copolymer, a polypropylene oxide-polyethylene oxide block copolymer, or the like.

[0073] An additive may be added to adjust the hydrophilicity or hydrophobicity of each block. The additive is not limited. Preferably, trimethylbenzene or the like is used as the additive.

[0074] The solvent used to dissolve the amphiphilic material should be one that is miscible with the aqueous metal precursor solution. The preferred solvents for dissolving the amphiphilic material include tetrahydrofuran, ethanol, 2-propanol, dimethylformamide, and water. The concentration of the amphiphilic material is optimized in consideration of the molecular weight, solubility, critical micelle concentration, and other factors of the amphiphilic material used.

[0075] Adjusting the pH of the solution to suit the self-assembly process The metal precursor solution and the amphiphilic material are mixed, and the solution is adjusted to a pH suitable for the self-assembly process. Generally, the polyethylene oxide block is positively charged in an acidic environment and interacts with the metal precursor, so an acid is often added. The acid used is not limited. Hydrochloric acid is generally used.

[0076] A reducing agent is added to the pH-adjusted solution (a reaction solution whose pH has been adjusted to be acidic). The reducing agent is not limited. As the reducing agent, ascorbic acid, glucose, hydroquinone, etc. are preferably used. The type, concentration, and amount of the reducing agent are optimized in consideration of the type of metal precursor used, the total area of ​​the substrate, etc. The reducing agent may be added after the substrate is brought into contact with a mixed solution of the metal precursor and amphiphilic material whose pH has been adjusted.

[0077] Contacting the Reaction Solution with a Substrate The reaction solution prepared by the above procedure, which contains a metal precursor, an amphiphilic solution, and a reducing agent and whose pH has been adjusted to be acidic, is brought into contact with a substrate.

[0078] The surface of the substrate on which the mesoporous metal thin film is to be formed is preferably one that is free of impurities such as organic deposits as much as possible, and is preferably subjected to a pretreatment for surface cleaning.

[0079] In the case of a substrate having an oxide surface, UV-ozone treatment, sputtering treatment, treatment with piranha solution, etc. are preferably performed. When using a substrate whose surface has been modified with a material that positively charges, in order to achieve uniform modification, it is preferable to perform a cleaning treatment similar to the above process before modification. When the material to be modified is an organic substance, it is not possible to perform pre-cleaning treatment on the surface after modification, so it is preferable to store the modified substrate so that the surface does not become contaminated.

[0080] The substrate is held in the solution in a manner that does not prevent the formation of a mesoporous metal thin film on the surface. There are no particular limitations on the method for holding the substrate. The substrate is preferably held using a substrate holder so that the surface that has been surface-treated faces downward.

[0081] A mesoporous metal thin film is formed on the substrate by holding the substrate in the reaction solution. The holding time and holding temperature are adjusted to optimal conditions depending on the substrate used, the mesoporous metal species to be produced, and the film thickness.

[0082] The holding time is preferably selected from the range of 1 minute to 100 hours. The thickness of the mesoporous metal thin film does not increase in proportion to the holding time. A typical holding time is about 15 minutes to 24 hours.

[0083] The holding temperature significantly affects the shape of the mesoporous metal thin film that is formed. The holding temperature is not limited to a specific range as long as it satisfies the conditions for forming a mesoporous metal thin film. The holding temperature is preferably in the range of -10°C to 80°C, and more preferably in the range of -10°C to 60°C. When an amphiphilic substance with polyethylene oxide as the hydrophilic moiety is used, it may lose its hydrophilicity at high temperatures and no longer exhibit self-assembly behavior.

[0084] Obtaining a mesoporous metal thin film The substrate that has been in contact with the reaction solution is removed from the reaction solution, and excess components are then washed away. The solvent used in the reaction solution is often used for washing. There are no particular limitations on the washing solvent, as long as it can remove the amphiphilic material and metal precursor. A mixed solution of tetrahydrofuran and water is preferably used as the washing solvent. Ultrasonic treatment may be added to the washing process to remove by-product particles adhering to the surface.

[0085] After the above cleaning process, the substrate is dried to obtain a mesoporous metal thin film on the substrate.

[0086] Even after the washing process, amphiphilic substances may remain in the mesopores of the mesoporous metal thin film produced by the above process. If it is necessary to completely remove the organic matter in the pores, the mesoporous metal thin film on the substrate is subjected to a heat treatment process. The organic matter can be removed by heat treatment at approximately 200°C to 500°C. The treatment temperature, heating rate, and heat treatment time should be selected appropriately taking into account the material of the substrate and the material of the mesoporous metal thin film. The heat treatment atmosphere is often air. Heat treatment can be performed, for example, in an atmosphere with a controlled oxygen concentration or in a vacuum.

[0087] [3] Second embodiment of mesoporous metal thin film Mesoporous metal thin film (ii) The second embodiment of the mesoporous metal thin film (ii) of the present invention is formed on a substrate.

[0088] The surface of the substrate is made of a metal with a higher ionization tendency than the metal forming the mesoporous metal thin film. A void exists between the substrate and the mesoporous metal thin film. The void exists between the substrate and the mesoporous metal thin film and is different from the mesoporous structure.

[0089] The mesoporous metal material is preferably at least one material selected from the group consisting of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture of these materials.

[0090] FIG. 4 shows the structure of a mesoporous metal thin film according to a second embodiment of the present invention.

[0091] Figure 4(a) shows a typical configuration of the second embodiment of the present invention. The metal substrate 41 is made of a metal with a higher ionization tendency than the metal constituting the pore walls 12 of the mesoporous metal thin film. Between the substrate 41 and the mesoporous metal thin film, there are voids 42 that are different from the voids of the mesoporous structure (13: mesopores). The voids 42 between the substrate 41 and the mesoporous metal thin film (12: pore walls made of metal, 13: mesopores) are amorphous.

[0092] The metal substrate 41 forming the mesoporous metal thin film of the second embodiment is not limited as long as it has a higher ionization tendency than the metal constituting the mesoporous metal thin film. The material of the metal substrate 41 is appropriately selected based on the ionization tendency of the metal constituting the mesoporous metal thin film. Specific examples of preferred materials include silver (silver plate, silver particles, silver thin film, etc.), copper (copper plate, etc.), tin (tin particles, etc.), nickel (nickel foam, nickel plate, etc.), and iron (steel wool, etc.).

[0093] Examples of embodiments: Substrate of silver (plate, particles, thin film, etc.): mesoporous platinum thin film Substrate of copper (plate, etc.): mesoporous platinum thin film, palladium thin film, silver thin film Substrate of tin (particles, etc.): mesoporous platinum thin film, palladium thin film Substrate of nickel (foamed nickel, plate, etc.): mesoporous platinum thin film, palladium thin film, mesoporous gold thin film Substrate of iron (steel wool, etc.): mesoporous platinum thin film

[0094] In the present invention, the entire substrate does not need to be made of a metal that satisfies the above conditions. For example, a substrate 43 (FIGS. 4(b) and 4(d)) made of any material may be provided with a metal having a higher ionization tendency than the metal that constitutes the pore walls 12 of the mesoporous metal thin film in the form of a thin film.

[0095] The mesoporous metal thin film may be formed in multiple layers as shown in Figures 4(a) and (b), or in a single layer as shown in Figures 4(c) and (d).

[0096] In FIG. 4, the substrate used to form the mesoporous metal thin film of the present invention is depicted as a flat plate. However, the shape of the substrate on which the mesoporous metal thin film is formed is not limited to this. A wide range of substrate shapes are applicable, including curved surfaces, substrates with complex surface structures, and porous materials with complex internal structures. The substrate shape can be any shape, including fine substrates such as particles and powders.

[0097] The method for producing a mesoporous metal thin film (ii) of the present invention involves first preparing an aqueous solution containing ions containing a metal element and an amphipathic compound, then placing a substrate whose surface (at least a portion of the surface) is made of a metal in the aqueous solution, and forming a mesoporous metal thin film on the substrate. The ionization tendency of the metal formed on the substrate surface is higher than that of the metal constituting the mesoporous metal thin film.

[0098] The method for producing a mesoporous metal thin film (ii) of the present invention comprises the steps of: (1) preparing an aqueous solution containing ions containing a metal element and an amphiphilic compound; and (2) retaining a substrate whose surface is made of a metal in the aqueous solution prepared in step (1).

[0099] In the method for producing a mesoporous metal thin film (ii) of the present invention, the ionization tendency of the metal on the surface of the substrate is higher than that of the metal constituting the mesoporous metal thin film.

[0100] In the method for producing a mesoporous metal thin film (ii) of the present invention, the step (2) is preferably a step of holding the substrate in the aqueous solution and forming a mesoporous metal thin film on the substrate.

[0101] Preparation of Aqueous Solution of Metal Precursor In the second embodiment of the method for producing a mesoporous metal thin film of the present invention, first, an aqueous solution of a metal precursor is prepared.

[0102] The metal precursor to be used is not limited. The metal precursor preferably includes a metal chloride complex, a metal chloride, or the like. The metal precursor preferably includes potassium tetrachloroplatinate, potassium hexachloroplatinate, potassium tetrachloroaurate, sodium tetrachloroaurate, potassium tetrachloropalladate, potassium hexachloroiridate, sodium hexachlororhodiumate, potassium hexachloroosmate, potassium hexachlororuthenate, or the like.

[0103] An aqueous solution of these complexes is prepared. The concentration of the aqueous solution of the complex is not limited. The concentration of the aqueous solution of the complex is preferably in the range of 0.001 M (mol / L concentration) to 0.1 M, more preferably in the range of 0.002 M to 0.05 M. The amount of the aqueous solution is optimized taking into account the total area of ​​the substrate to be used, etc.

[0104] Preparation of a Solution of Amphiphilic Material Next, a solution of an amphiphilic material that forms molecular aggregates (micelles) that serve as templates for forming pores in the mesoporous metal thin film is prepared.

[0105] The amphiphilic material is not limited. Preferably, the amphiphilic material is a block copolymer containing polyethylene oxide as a hydrophilic block. Preferably, the amphiphilic material is a polymethyl methacrylate-polyethylene oxide block copolymer, a polystyrene-polyethylene oxide block copolymer, a polypropylene oxide-polyethylene oxide block copolymer, or the like.

[0106] An additive may be added to adjust the hydrophilicity or hydrophobicity of each block. The additive is not limited. Preferably, trimethylbenzene or the like is used as the additive.

[0107] The solvent used to dissolve the amphiphilic material should be one that is miscible with the aqueous metal precursor solution. The preferred solvents for dissolving the amphiphilic material include tetrahydrofuran, ethanol, 2-propanol, dimethylformamide, and water. The concentration of the amphiphilic material is optimized in consideration of the molecular weight, solubility, critical micelle concentration, and other factors of the amphiphilic material used.

[0108] Adjusting the pH of the solution to suit the self-assembly process The metal precursor solution and the amphiphilic material are mixed, and the solution is adjusted to a pH suitable for the self-assembly process. Generally, the polyethylene oxide block is positively charged in an acidic environment and interacts with the metal precursor, so an acid is often added. The acid used is not limited. Hydrochloric acid is generally used.

[0109] In the second embodiment of the present invention, the metal of the substrate is ionized, and the electrons released during this process reduce ions of the mesoporous metal precursor in the solution, forming a mesoporous metal thin film.

[0110] In the second embodiment of the present invention, the addition of a reducing agent, which is used in the first embodiment, is basically not necessary, although the addition of a reducing agent does not prevent the formation of a mesoporous metal thin film.

[0111] Contact of the Reaction Solution with the Substrate The reaction solution, which contains the metal precursor and the amphiphilic solution and has been adjusted to an acidic pH, prepared by the procedure described above, is brought into contact with the metal of the substrate.

[0112] The surface of the metal substrate on which the mesoporous metal thin film is to be formed is preferably free of organic deposits and oxide layers, and is preferably subjected to a pretreatment for surface cleaning.

[0113] The surface cleaning pretreatment method varies depending on the metal material of the substrate. There are no limitations on the surface cleaning treatment method. When the metal material of the substrate is a metal that does not easily form an oxide, UV-ozone treatment, sputtering treatment, treatment with piranha solution, etc. are preferably performed. When the metal material of the substrate is a metal that easily forms an oxide, sputtering treatment is preferably performed.

[0114] The substrate that has undergone the surface cleaning treatment is held in the solution in a manner that does not prevent the formation of a mesoporous metal thin film on the surface. There are no particular limitations on the method for holding the substrate. The substrate is preferably held using a substrate holder so that the surface that has been surface-treated faces downward.

[0115] A mesoporous metal thin film is formed on the substrate by holding the substrate in the reaction solution. The holding time and temperature are adjusted to optimal conditions depending on the substrate used, the mesoporous metal species to be produced, and the film thickness.

[0116] The holding time is preferably selected from the range of 1 minute to 100 hours. The thickness of the mesoporous metal thin film does not increase in proportion to the holding time. A typical holding time is about 15 minutes to 24 hours.

[0117] The holding temperature significantly affects the shape of the mesoporous metal thin film that is formed. The holding temperature is not limited to a specific range as long as it satisfies the conditions for forming a mesoporous metal thin film. The holding temperature is preferably in the range of -10°C to 80°C, and more preferably in the range of -10°C to 60°C. When an amphiphilic substance with polyethylene oxide as the hydrophilic moiety is used, it may lose its hydrophilicity at high temperatures and no longer exhibit self-assembly behavior.

[0118] Obtaining a mesoporous metal thin film The substrate that has been brought into contact with the reaction solution is removed from the reaction solution and washed to remove excess components. The solvent used in the reaction solution is often used for washing. There are no particular restrictions on the washing solvent, as long as it can remove the amphiphilic material and metal precursor. A mixed solution of tetrahydrofuran and water is preferably used as the washing solvent. In the washing process, ultrasonic treatment may be added to remove by-product particles adhering to the surface.

[0119] After the above cleaning process, the substrate is dried to obtain a mesoporous metal thin film on the substrate.

[0120] Even after the washing process, amphiphilic substances may remain in the mesopores of the mesoporous metal thin film produced by the above process. If it is necessary to completely remove the organic matter in the pores, the mesoporous metal thin film on the substrate is subjected to a heat treatment process. The organic matter can be removed by heat treatment at approximately 200°C to 500°C. The treatment temperature, heating rate, and heat treatment time should be selected appropriately taking into account the material of the substrate and the material of the mesoporous metal thin film. The heat treatment atmosphere is often air. Heat treatment can be performed, for example, in an atmosphere with a controlled oxygen concentration or in a vacuum.

[0121] [4] Use of Mesoporous Metal Thin Film The mesoporous metal thin film of the present invention is useful for applications such as catalysts, sensors, and electrodes.

[0122] The present invention provides a technology for producing uniform mesoporous metal thin films over a large area without requiring any special equipment and without being restricted by the shape of the substrate or the deposition area, and can provide mesoporous metal thin films with a variety of compositions and morphologies that can be achieved thereby.

[0123] The present invention makes it possible to produce mesoporous metal thin films with few restrictions on the form of the substrate, the size and shape of the film to be formed, and the material of the substrate.The present invention makes it possible to produce mesoporous metal thin films without using special equipment or requiring large amounts of power.

[0124] The present invention will be described in detail below based on examples.

[0125] The present invention is not limited to these examples.

[0126] [1] Production of the first type of mesoporous metal thin film: Examples 1 to 5 Example 1 (Fig. 5) Insulating material on the surface of the substrate: alumina Mesoporous metal thin film: mesoporous platinum thin film

[0127] Example 1 is an example in which a mesoporous platinum thin film was formed on a substrate on the surface of which an alumina film was formed by sputtering.

[0128] A 200 nm thick alumina film was deposited on a silicon substrate by ion beam sputtering. Zeta potential measurements of the alumina film surface revealed that the isoelectric point of alumina was 8.2. This substrate was cut into a 10 mm square and cleaned with a UV-ozone surface treatment device. It was then placed face-down in a 10 mL container using spacers to prevent the coated surface from touching the bottom of the container.

[0129] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 1.0 mL of a 0.02 M (mol / L) aqueous solution of potassium tetrachloroplatinate, 1.0 mL of 0.1 M HCl, and 1.52 mL of pure water were mixed and stirred for 30 minutes. This mixture was heated to 60 °C in a water bath, and 2.0 mL of a 0.1 M aqueous solution of ascorbic acid was added while stirring. The solution immediately after the addition of ascorbic acid was transferred to the 10 mL container containing the substrate and kept at 60 °C for 3 hours. After 3 hours, the substrate was removed from the solution, thoroughly washed with a 1:1 tetrahydrofuran:pure water mixture, and air-dried.

[0130] The formation of a film on the substrate was confirmed with the naked eye. Observation of the film on the substrate with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores of approximately 20 nm on average, as shown in Figure 5(a).

[0131] The film on the substrate was heated in air at 400°C for 4 hours to completely remove the organic components. After the heat treatment, the film on the substrate maintained its mesoporous structure, as shown in Figure 5(b).

[0132] In Example 1, a mesoporous platinum thin film was successfully obtained on an alumina substrate.

[0133] Example 2 (Fig. 6) Insulating material on the surface of the substrate: zirconium oxide Mesoporous metal thin film: mesoporous platinum thin film

[0134] Example 2 is an example in which a mesoporous platinum thin film was formed on a substrate on the surface of which a zirconium oxide film was formed by sputtering.

[0135] A 200 nm thick zirconium oxide film was formed on a quartz glass substrate by RF sputtering. Zeta potential measurements of the zirconium oxide film surface revealed that the isoelectric point of zirconium oxide was 7.8. This substrate was cut into a 10 mm square and cleaned with a UV-ozone surface treatment device. The substrate was then placed in a 10 mL container with the film side facing downwards, using spacers to prevent the film surface from contacting the bottom of the container.

[0136] As in Example 1, a tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, an aqueous potassium tetrachloroplatinate solution, 0.1 M HCl, and pure water were mixed and stirred for 30 minutes. As in Example 1, this mixture was heated in a water bath (60°C), and an aqueous ascorbic acid solution was added while stirring. The solution immediately after the addition of ascorbic acid was transferred to the 10 mL container containing the substrate and kept at 60°C for 3 hours. After keeping for 3 hours, the substrate was removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried.

[0137] The formation of a film on the substrate was confirmed with the naked eye. Observation of this film on the substrate with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores of approximately 20 nm on average, as shown in Figure 6.

[0138] Example 3 (Figure 7) Insulating material on the surface of the substrate: quartz glass Mesoporous metal thin film: mesoporous platinum thin film

[0139] Example 3 is an example in which a mesoporous platinum thin film was formed on a quartz glass substrate whose surface was modified with 3-aminopropyltriethoxysilane.

[0140] The surface of a quartz glass substrate was cleaned using a UV-ozone surface treatment device, and then spin-coated with a solution of 1 mL of 3-aminopropyltriethoxysilane dissolved in 15 mL of ethanol. The substrate was then dried at 60°C for 10 minutes and used as a substrate. 3-aminopropyltriethoxysilane reacts with silanol groups on the quartz glass surface to form a monolayer. Because it has an amino group at its terminal, it forms ammonium ions under acidic conditions and becomes positively charged.

[0141] This substrate was shaped into a 10 mm square and held in a 10 mL container with the modified surface facing downwards using a spacer so that the modified surface did not come into contact with the bottom of the container.

[0142] As in Example 1, the substrate was placed in a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloroplatinate, HCl, and ascorbic acid under the same conditions as in Example 1, and was maintained at 60°C for 3 hours.

[0143] After being kept in the solution for 3 hours, the substrate was taken out, thoroughly washed with a mixed solvent of tetrahydrofuran:pure water=1:1, and then air-dried.

[0144] It was confirmed with the naked eye that a film had been formed on the substrate. When the film on the substrate was observed with a scanning electron microscope, it was confirmed that the thin film formed had a mesoporous structure with pores of approximately 20 nm on average, as shown in Figure 7.

[0145] Example 4 (Fig. 7) Insulating material on the surface of the substrate: sintered alumina Mesoporous metal thin film: mesoporous platinum thin film

[0146] Example 4 is an example in which a mesoporous platinum thin film was formed on a sintered alumina substrate.

[0147] A commercially available alumina sintered body was cut into a 10 mm square and cleaned with a UV-ozone surface treatment device. The treated surface was placed face down in a 10 mL container using a spacer to prevent the modified surface from contacting the bottom of the container. The isoelectric point of the alumina sintered body used was determined to be 8.4 by measuring the zeta potential of the surface.

[0148] As in Example 1, the substrate was placed in a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloroplatinate, HCl, and ascorbic acid under the same conditions as in Example 1, and was maintained at 60°C for 3 hours.

[0149] After being kept in the solution for 3 hours, the substrate was taken out, thoroughly washed with a mixed solvent of tetrahydrofuran:pure water=1:1, and then air-dried.

[0150] The formation of a film on the substrate was confirmed with the naked eye, and when the film on the substrate was observed with a scanning electron microscope, it was confirmed that the thin film formed had a mesoporous structure with pores of approximately 20 nm on average.

[0151] Example 5 Insulating material on the surface of the substrate: alumina Mesoporous metal thin film: mesoporous palladium thin film

[0152] Example 5 is an example in which a mesoporous palladium thin film was formed on the substrate (insulating material) used in Example 1, on whose surface an alumina film had been formed by sputtering.

[0153] The silicon substrate with alumina coating used in Example 1 was shaped into a 10 mm square and cleaned with a UV-ozone surface treatment device. The surface was then placed face down in a 10 mL container using spacers so that the coated surface did not come into contact with the bottom of the container.

[0154] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 1.0 mL of a 0.02 M aqueous solution of potassium tetrachloropalladate, 1.0 mL of 0.1 M HCl, and 1.52 mL of pure water were mixed and stirred for 30 minutes. This mixture was heated to 60°C in a water bath, and 2.0 mL of a 0.1 M aqueous solution of ascorbic acid was added while stirring. The solution immediately after the addition of ascorbic acid was transferred to the 10 mL container containing the substrate and kept at room temperature for 3 hours.

[0155] After being kept in the solution for 3 hours, the substrate was taken out, thoroughly washed with a mixed solvent of tetrahydrofuran:pure water=1:1, and then air-dried.

[0156] It was confirmed with the naked eye that a film had been formed on the substrate.

[0157] Observation of the film on the substrate using a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores of approximately 20 nm on average.

[0158] [2] Production of second type of mesoporous metal thin film: Examples 6 to 12 Example 6 (Figure 8) Substrate surface material: silver plate (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in some parts between the substrate and the mesoporous metal thin film.

[0159] Example 6 is an example in which a silver plate was used as a substrate and a mesoporous platinum thin film was formed on the surface of the substrate. Silver is a metal with a higher ionization tendency than platinum.

[0160] A 1 mm thick silver plate was cut into a 10 mm square, and after cleaning the surface with a plasma sputtering device, it was placed in a 10 mL container with the treated surface facing downwards using a spacer so that the film-forming surface did not come into contact with the bottom of the container.

[0161] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 1.0 mL of a 0.02 M aqueous solution of potassium tetrachloroplatinate, 1.0 mL of 0.1 M HCl, and 3.52 mL of pure water were mixed and stirred for 30 minutes while heating in a water bath to 60° C. This solution was transferred into the 10 mL container containing the substrate and kept at 60° C. for 3 hours.

[0162] After 3 hours in the solution, the substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, followed by air drying. The metallic luster of the substrate surface was not lost. Observation of the film on the substrate with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores averaging approximately 20 nm in size, as shown in Figure 8(a).

[0163] The cross section of this mesoporous platinum thin film was processed with an argon ion beam and observed with a scanning electron microscope. As a result, as shown in Figure 8(b), voids 83, which differ from the voids in the mesoporous structure, were partially present between the substrate 81 and the mesoporous platinum thin film 82. This is due to the reaction process that occurs during the mesoporous platinum thin film formation process, in which the silver in the substrate dissolves and ionizes, and the platinum ions are reduced by the electrons released during this process. This is one of the structural features of the mesoporous metal thin film of the present invention.

[0164] Example 7 Substrate surface material: silver particles (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in parts between the substrate and mesoporous metal thin film.

[0165] In Example 7, instead of the silver plate used in Example 6, silver particles having a diameter of about 1 mm were used as the substrate, and a mesoporous platinum thin film was formed on the surface of the silver particles.

[0166] Ten silver particles with a diameter of approximately 1 mm were placed in a 10 mL container after their surfaces had been cleaned using a plasma sputtering device.

[0167] The silver particles were kept in a reaction solution containing the same polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer as used in Example 6, potassium tetrachloroplatinate, and HCl at 60° C. for 3 hours.

[0168] After 3 hours of storage, the silver particles were removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried. Observation of the particles under a scanning electron microscope confirmed the formation of a mesoporous platinum film on the particle surface, confirming a mesoporous structure with pores averaging approximately 20 nm in size.

[0169] When this mesoporous platinum thin film was cross-sectionally processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure had partially formed between the silver particle surface and the mesoporous platinum thin film.

[0170] Example 8 Substrate surface material: silver thin film (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in parts between the substrate and the mesoporous metal thin film.

[0171] Example 8 is an example in which a mesoporous platinum thin film was formed on a base in which a thin silver film was formed on a general substrate of any material.

[0172] A 200 nm thick silver film was deposited on a quartz glass substrate using ion beam sputtering, with a 5 nm thick Ti layer as an adhesive layer. This substrate was then shaped into a 10 mm square and cleaned using a plasma sputtering device. The treated surface was then placed face down in a 10 mL container using spacers to prevent the coated surface from contacting the bottom of the container.

[0173] The same reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloroplatinate, and HCl as used in Example 6 was placed in the vessel, and the substrate was maintained at 60° C. for 3 hours.

[0174] After 3 hours of storage, the silver particles were removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried. Observation of the particles under a scanning electron microscope confirmed the formation of a mesoporous platinum film on the substrate surface, confirming a mesoporous structure with pores averaging approximately 20 nm in size.

[0175] When this mesoporous platinum thin film was cross-sectionally processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure had partially formed between the surface of the silver thin film on the substrate and the mesoporous platinum thin film.

[0176] Example 9 (Fig. 9) Substrate surface material: copper plate (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in parts between the substrate and mesoporous metal thin film.

[0177] Example 9 is an example in which a copper plate was used as a substrate and a mesoporous platinum thin film was formed on the surface of the substrate. Copper is a metal with a higher ionization tendency than platinum.

[0178] A 1 mm thick copper plate was cut into a 10 mm square, and after cleaning the surface with a plasma sputtering device, it was placed in a 10 mL container with the treated surface facing downwards using a spacer so that the film-forming surface did not come into contact with the bottom of the container.

[0179] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 0.4 mL of a 0.02 M aqueous solution of potassium tetrachloroplatinate, 1.0 mL of 0.1 M HCl, and 4.12 mL of pure water were mixed and stirred for 30 minutes while heating in a water bath to 60° C. The solution was transferred to the 10 mL container containing the substrate and kept at 60° C. for 3 hours.

[0180] After 3 hours of incubation, the substrate was removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried. A black product was visible on the substrate surface. Observation of the film on the substrate with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores averaging approximately 20 nm in size, as shown in Figure 9.

[0181] When this mesoporous platinum thin film was cross-sectionally processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure had partially formed between the substrate and the mesoporous platinum thin film.

[0182] Example 10 (FIG. 10) Substrate surface material: tin particles (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in parts between the substrate and mesoporous metal thin film.

[0183] Example 10 is an example in which tin particles are used as a substrate and a mesoporous platinum thin film is formed on the surface of the substrate. Tin is a metal with a higher ionization tendency than platinum.

[0184] Tin particles with a diameter of 2 mm were cut with a sharp knife to expose a clean surface, and 10 of these partially cut particles were placed in a 10 mL container.

[0185] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 1.0 mL of a 0.02 M aqueous solution of potassium tetrachloroplatinate, 1.0 mL of 0.1 M HCl, and 3.52 mL of purified water were mixed and stirred for 30 minutes. This solution was transferred to the 10 mL container containing the partially cut particles and kept at room temperature for 3 hours.

[0186] After 3 hours of storage, the particles were removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried. The formation of a product was confirmed with the naked eye on the cross section of the particles. Observation of the film on this cross section with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores averaging approximately 20 nm in size, as shown in Figure 10.

[0187] When the cross section of this mesoporous platinum thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure had partially formed between the particle cross section and the mesoporous platinum thin film.

[0188] Example 11 (FIG. 11) Substrate surface material: tin particles (metal with high ionization tendency) Mesoporous metal thin film: mesoporous palladium thin film (metal with low ionization tendency) There are voids in parts between the substrate and mesoporous metal thin film.

[0189] In this example, tin particles are used as a substrate, and a mesoporous palladium thin film is formed on the surface of the substrate. Tin is a metal with a higher ionization tendency than palladium.

[0190] Tin particles with a diameter of 2 mm were cut with a sharp knife to expose a clean surface, and 10 of these partially cut particles were placed in a 10 mL container.

[0191] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 2.0 mL of a 0.02 M aqueous solution of potassium tetrachloropalladate, 1.0 mL of 0.1 M HCl, and 2.52 mL of purified water were mixed and stirred for 30 minutes. This solution was transferred to the 10 mL container containing the partially cut particles and kept at room temperature for 3 hours.

[0192] After 3 hours of incubation, the particles were removed from the solution, thoroughly washed with a 1:1 tetrahydrofuran:pure water mixed solvent, and then air-dried. The formation of a product was confirmed with the naked eye on the cross section of the particles. Observation of the film on this cross section with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores averaging approximately 20 nm in size, as shown in Figure 11.

[0193] When the cross section of this mesoporous palladium thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure were partially formed between the particle cross section and the mesoporous palladium thin film.

[0194] Example 12 Substrate surface material: silver plate (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency) There are voids in parts between the substrate and mesoporous metal thin film.

[0195] In Example 12, similar to Example 6, a silver plate was used as a substrate, and a mesoporous platinum thin film was formed on the surface of the silver plate using polyethylene oxide (114)-b-polymethacrylic acid (41) as an amphiphilic material.

[0196] A 1 mm thick silver plate was cut into a 10 mm square, and after cleaning the surface with a plasma sputtering device, it was placed in a 10 mL container with the treated surface facing downwards using a spacer to prevent the film-forming surface from contacting the bottom of the container.

[0197] 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethacrylic acid (41) diblock copolymer, 1.0 mL of a 0.02 M aqueous solution of potassium tetrachloroplatinate, 1.0 mL of 0.1 M HCl, and 3.52 mL of pure water were mixed and stirred for 30 minutes while heating in a water bath to 60° C. This solution was transferred into the 10 mL container containing the substrate and kept at 60° C. for 3 hours.

[0198] After 3 hours of storage, the substrate was removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried. The formation of a film on the substrate surface was confirmed with the naked eye. Observation of the film on the substrate with a scanning electron microscope confirmed that the thin film formed had a mesoporous structure with pores averaging approximately 10 nm in size.

[0199] When this mesoporous platinum thin film was cross-sectionally processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids different from the voids in the mesoporous structure had partially formed between the substrate and the mesoporous platinum thin film.

[0200] [3] Production of the first type of mesoporous metal thin film: Example 13 Example 13 (Fig. 12, mesoporous metal film on insulator) Insulating material on the surface of the substrate: cerium oxide Mesoporous metal thin film: mesoporous platinum thin film

[0201] Example 13 is an example in which a mesoporous platinum thin film was formed on a substrate on the surface of which a cerium oxide film was formed by sputtering.

[0202] A 200 nm thick cerium oxide film was formed on a silicon substrate by RF sputtering, and this was used as the substrate. Zeta potential measurements of the cerium oxide film surface revealed that the isoelectric point of cerium oxide was 8.1. This substrate was cut into a 10 mm square and cleaned using a UV-ozone surface treatment device. Then, the substrate was placed in a 10 mL container with the film side facing downwards, using spacers to prevent the film surface from contacting the bottom of the container.

[0203] As in Example 1, a tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, an aqueous potassium tetrachloroplatinate solution, 0.1 M HCl, and pure water were mixed and stirred for 30 minutes. An aqueous ascorbic acid solution was added to the mixture while stirring at room temperature. The solution immediately after the addition of ascorbic acid was transferred to the 10 mL container containing the substrate and held at room temperature for 3 hours. After holding for 3 hours, the substrate was removed from the solution, thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, and then air-dried.

[0204] Observation of the substrate surface with a scanning electron microscope confirmed that a thin film of platinum with a mesoporous structure with pores of approximately 20 nm on average had been formed on the substrate surface, as shown in Figure 12.

[0205] [4] Preparation of second type mesoporous metal thin film: Examples 14 to 19 Example 14 (Fig. 13, mesoporous metal film on metal substrate) Substrate surface material: nickel (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency)

[0206] Example 14 is an example in which a mesoporous platinum thin film was formed on a foamed nickel substrate.

[0207] A commercially available foamed nickel substrate, 10 mm square and 1 mm thick, was hydrophilized by plasma exposure and placed in a 10 ml container.

[0208] As in Example 6, a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloroplatinate, and HCl was placed in the vessel, and the substrate was kept at room temperature for 3 hours.

[0209] After 3 hours in the solution, the foamable nickel substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, followed by air drying. The surface of the foamable nickel had turned black. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous platinum thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 13.

[0210] When the cross section of this mesoporous platinum thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that partial voids had formed between the surface of the foamed nickel substrate and the mesoporous platinum thin film.

[0211] Example 15 (Figure 14, mesoporous metal film on metal substrate) Substrate surface material: nickel (metal with high ionization tendency) Mesoporous metal thin film: mesoporous palladium thin film (metal with low ionization tendency)

[0212] Example 15 is an example in which a mesoporous palladium thin film was formed on a foamed nickel substrate.

[0213] A commercially available foamed nickel substrate, 10 mm square and 1 mm thick, was hydrophilized by plasma exposure and placed in a 10 ml container.

[0214] As in Example 11, a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloropalladate, and HCl was placed in the vessel, and the substrate was kept at room temperature for 3 hours.

[0215] After 3 hours in the solution, the foamable nickel substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, followed by air drying. The surface of the foamable nickel had turned black. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous palladium thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 14.

[0216] When the cross section of this mesoporous palladium thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids had formed partially between the surface of the foamed nickel substrate and the mesoporous palladium thin film.

[0217] Example 16 (Figure 15, mesoporous metal film on metal substrate) Substrate surface material: copper (metal with high ionization tendency) Mesoporous metal thin film: mesoporous palladium thin film (metal with low ionization tendency)

[0218] Example 16 is an example in which a mesoporous palladium thin film was formed on a flat Cu substrate.

[0219] A 10 mm square Cu plate with a thickness of 0.2 mm was used as a substrate, the surface of which was subjected to a hydrophilic treatment by plasma exposure, and was placed in a 10 mL container.

[0220] As in Example 11, a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloropalladate, and HCl was placed in the vessel, and the substrate was kept at room temperature for 3 hours.

[0221] After 3 hours in the solution, the Cu substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and purified water, followed by air drying. Discoloration was observed on the Cu surface. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous palladium thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 15.

[0222] When the cross section of this mesoporous palladium thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids had formed partially between the Cu substrate surface and the mesoporous palladium thin film.

[0223] Example 17 (Figure 16, mesoporous metal film on metal substrate) Substrate surface material: copper (metal with high ionization tendency) Mesoporous metal thin film: mesoporous silver thin film (metal with low ionization tendency)

[0224] Example 17 is an example in which a mesoporous silver thin film was formed on a flat Cu substrate.

[0225] A 10 mm square Cu plate with a thickness of 0.2 mm was used as a substrate, the surface of which was subjected to a hydrophilic treatment by plasma exposure, and was placed in a 10 mL container.

[0226] A reaction solution was prepared by mixing 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 0.1 mL of a 0.02 M aqueous solution of silver nitrate, 1.0 mL of 0.05 M H2SO4, and 4.42 mL of pure water, and stirring at room temperature for 30 minutes. This reaction solution was then placed in the container, and the Cu substrate was then maintained at room temperature for 3 hours.

[0227] After 3 hours in the solution, the Cu substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, followed by air drying. Discoloration was observed on the Cu surface. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous silver thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 16.

[0228] When the cross section of this mesoporous silver thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids had formed partially between the Cu substrate surface and the mesoporous silver thin film.

[0229] Example 18 (Figure 17, mesoporous metal film on metal substrate) Substrate surface material: nickel (metal with high ionization tendency) Mesoporous metal thin film: mesoporous gold thin film (metal with low ionization tendency)

[0230] Example 18 is an example in which a mesoporous gold thin film was formed on a flat Ni substrate.

[0231] A 0.2 mm thick Ni plate cut into a 10 mm square was used as a substrate, the surface of which was hydrophilized by plasma exposure, and placed in a 10 mL container.

[0232] A reaction solution was prepared by mixing 0.48 mL of a 16.7 g / L tetrahydrofuran solution of polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, 0.06 mL of a 0.02 M aqueous solution of potassium tetrachloroaurate, 1.0 mL of 0.1 M HCl, and 4.46 mL of pure water, and stirring at room temperature for 30 minutes. This reaction solution was then placed in the container, and the Ni substrate was then maintained at room temperature for 3 hours.

[0233] After 3 hours in the solution, the Ni substrate was removed and thoroughly washed with a 1:1 mixed solvent of tetrahydrofuran and pure water, followed by air drying. Discoloration was observed on the Ni surface. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous gold thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 17.

[0234] When the cross section of this mesoporous gold thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids had formed partially between the Ni substrate surface and the mesoporous gold thin film.

[0235] Example 19 (Figure 18, mesoporous metal film on metal substrate) Substrate surface material: iron (metal with high ionization tendency) Mesoporous metal thin film: mesoporous platinum thin film (metal with low ionization tendency)

[0236] Example 19 is an example in which a mesoporous platinum thin film was formed on a steel wool substrate.

[0237] A commercially available steel wool substrate, molded into a 10 mm square x 5 mm thick piece, was subjected to a hydrophilic treatment using UV-ozone and placed in a 10 ml container.

[0238] As in Example 6, a reaction solution containing polyethylene oxide (114)-b-polymethyl methacrylate (150) diblock copolymer, potassium tetrachloroplatinate, and HCl was placed in the container, and the steel wool substrate was kept at room temperature for 3 hours.

[0239] After 3 hours in the solution, the steel wool substrate was removed and thoroughly washed with a 1:1 tetrahydrofuran:pure water mixed solvent, followed by air drying. Discoloration was observed on the surface of the steel wool. Observation of the substrate surface with a scanning electron microscope confirmed the formation of a mesoporous platinum thin film with pores averaging approximately 20 nm in size on the substrate surface, as shown in Figure 18.

[0240] When the cross section of this mesoporous gold thin film was processed with an argon ion beam and observed with a scanning electron microscope, it was confirmed that voids had formed partially between the steel wool substrate surface and the mesoporous platinum thin film.

[0241] [3] Industrial Applicability of Mesoporous Metal Thin Films The mesoporous metal thin films of the present invention are subject to few restrictions in terms of the form of the substrate, the size and shape of the film to be formed, and the material of the substrate, and are useful for applications such as catalysts, sensors, and electrodes.

[0242] 11 Substrate 12 Pore wall made of metal 13 Mesopore 31 Insulating base material made of oxide having an isoelectric point greater than 5 32 Oxide layer having an isoelectric point greater than 5 33 Substrate of unspecified material 34 Material including a site that is positively charged in an aqueous solution 41 Substrate made of metal having a higher ionization tendency than the metal that constitutes the pore wall of the mesoporous metal thin film 42 Voids different from the voids of the mesoporous structure 43 Substrate of unspecified material 81 Substrate 82 Mesoporous platinum thin film 83 Voids different from the voids of the mesoporous structure

Claims

1. A mesoporous metal thin film formed on a substrate, wherein: (i) the surface of the substrate is made of an insulating material; or (ii) the material of the surface of the substrate is a metal that has a higher ionization tendency than the metal that forms the mesoporous metal thin film, and there is a void between the substrate and the mesoporous metal thin film.

2. (i) A mesoporous metal thin film as described in claim 1, wherein the surface of the substrate is made of an insulating material and the mesoporous metal thin film is formed directly on the surface of the substrate.

3. (i) The mesoporous metal thin film described in claim 1, wherein the insulating material is an oxide having an isoelectric point greater than 5.

4. The mesoporous metal thin film according to claim 1, wherein the surface of the substrate is formed on the insulating material with a material that includes sites that are positively charged in an aqueous solution.

5. The mesoporous metal film of claim 4, wherein the positively charged sites are positive ions.

6. (ii) A mesoporous metal thin film as described in claim 1, wherein the material of the surface of the substrate is a metal having a higher ionization tendency than the metal forming the mesoporous metal thin film, and a portion between the substrate and the mesoporous metal thin film has voids different from the mesoporous structure.

7. The mesoporous metal thin film described in claim 1, wherein the mesoporous metal material is at least one material selected from the group consisting of gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, silver, and copper, or a mixture of these materials.

8. A method for producing a mesoporous metal thin film (i), comprising: (1) preparing an aqueous solution containing ions containing a metal element, an amphipathic compound, and a compound that reduces the metal contained in the ions; and (2) holding a substrate having an insulating surface in the aqueous solution prepared in (1), wherein the surface of the substrate carries a charge of opposite polarity to the charge of the ions containing the metal element in the aqueous solution.

9. A method for producing a mesoporous metal film as described in claim 8, comprising the step of forming ionic sites on the surface of the substrate after step (1) and before step (2).

10. A method for producing a mesoporous metal thin film (ii), comprising: (1) preparing an aqueous solution containing ions containing a metal element and an amphipathic compound; and (2) retaining a substrate having a metal surface in the aqueous solution prepared in (1), wherein the ionization tendency of the metal on the surface of the substrate is higher than that of the metal constituting the mesoporous metal thin film.

11. A method for producing a mesoporous metal thin film as described in claim 8 or 10, wherein the step (2) is a step of holding the substrate in the aqueous solution and forming a mesoporous metal thin film on the substrate.

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