JP6124266B2 - Mesoporous metal film - Google Patents

Description

The present invention relates to the mesoporous metal film.

  Due to the development of unprecedented chemical and physical properties, the nanostructure control of substances is extremely important in the field of material chemistry. In particular, the nano (meso) porous structure can reliably provide a surface having many functional sites that are essential for solving urgent problems. Up to now, it has been reported that many mesoporous materials with various compositions were produced by self-organization of amphiphilic organic molecules, and gas occlusion, separation, catalyst, ion exchange, sensing, polymer polymerization, There has been strong interest due to its wide applicability including drug delivery and the like (Non-Patent Documents 1 to 3).

  In particular, metal mesoporous materials can exhibit significant carrier density, thereby providing a remarkable photoresponse. This cannot be achieved by using mesoporous materials having other compositions (for example, silica compositions (Non-Patent Documents 4 and 5), carbon-based compositions (Non-Patent Documents 6 and 7), etc.). For example, the free space radiation wavelength of light in the near infrared (NIR) to visible (VIS) region is such that when it interacts with plasma oscillations of free electrons on the metal surface, 1 to 2 digits smaller (Non-Patent Documents 8 and 9). Excited surface plasma oscillation or surface plasmon provides the remarkable property that it can be manipulated flexibly by controlling the surface morphology of the metal on the nanometer scale (Non-Patent Documents 10-13). . A three-dimensional (3-D) spread metal framework is urgently needed to investigate the mechanism of operation of metal nanoparticles that are often constrained by the tendency to become large agglomerates due to sintering It will surely result in abundant reaction / adsorption sites, which are crucial for designing the functions that are considered.

Nanostructured gold (Au) materials in the form of membranes and particles showed a high degree of catalytic activity in some oxidation reactions (eg CO, glucose, methanol oxidation reactions) and O ₂ reduction reactions (non- Not only Patent Documents 14 to 18) but also unique optical properties due to its localized surface plasmon resonance (Non-Patent Documents 19 to 21). Various mesoporous metals and alloys have been produced by the soft template method and the hard template method (Non-Patent Documents 22 to 26), but a gold thin film having uniform mesopores has not yet been produced by such a method. This is because it is difficult to control the crystal growth of Au around the template. In almost all cases using hard templates, nanostructured Au materials were only obtained as nanoparticles, nanosheets and nanowires without mesoporous structures (Non-Patent Documents 27 and 28). The colloidal crystal template method is one of effective techniques for forming a macroporous (3-D ordered macroporous, also called 3-DOM) material having a three-dimensional order (Non-Patent Documents 29 to 32). It is very difficult to synthesize Au materials having typical mesoporous structures (for example, inverted opals similar to 3-D hexagonal structures) (Non-patent Document 33). As far as the inventor of the present application knows, the only way to create a mesoporous / nanoporous Au material has been reported by dealloying (Non-Patent Documents 34 to 36). This is a process for creating a porous structure by selectively eluting a specific metal from an alloy (two or more) (Non-patent Documents 37 and 38). However, this dealloying technique has poor controllability over structural parameters and requires a process under rigorous experimental conditions. Nevertheless, the resulting holes are irregular in size and shape. Therefore, it is very difficult to make the Au crystal shape into a nanoporous structure. In addition to Au, iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), tin (Sn It is very difficult to obtain a mesoporous metal film for metals such as). In addition, it is extremely difficult to produce a mesoporous metal film having a stable quality and further adjust the mesopore size in a wide range.

  An object of the present invention is to provide a novel mesoporous metal film using a metal such as Au, which has not been obtained by the above-described prior art, and to provide a novel method for producing a mesoporous metal film.

According to one aspect of the present invention, a metal film having mesopores (nanopores), the metal being Au, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Sn, and A mesoporous metal film that is at least one selected from the group consisting of these two or more alloys is provided.
Here, the mesopores may have an average diameter of 5 nm to 100 nm.
The mesoporous metal film may be formed on a conductive substrate.
The average wall thickness between adjacent mesopores may be 10 nm to 50 nm.
The film thickness may be more than 0 nm and less than 10 mm.
Further, the proportion of mesopores having a diameter in the range of average diameter × 0.9 to average diameter × 1.1 may be 60% to 100% in all mesopores.
According to another aspect of the present invention, a voltage is applied between electrodes immersed in an electrolyte solution containing micelles of an amphiphilic block copolymer and a metal compound, and the metal and the block copolymer are formed on one electrode. The metal is selected from the group consisting of Au, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Pt, Sn, and alloys of two or more thereof. A method for producing a mesoporous metal film is provided.
Here, a step of removing the block copolymer from the composite on the one electrode after completion of the deposition may be included.
The electrolyte solution may further include a solvent that dissolves the hydrophobic block in the amphiphilic block copolymer.
The solvent may be a cyclic ether solvent.
Moreover, you may adjust the average diameter of the mesopores of the mesoporous metal film manufactured by changing the quantity of the said solvent in the said electrolyte solution.
Moreover, you may adjust the average diameter of the mesopores of the mesoporous metal film manufactured by adding a hydrophobic organic compound in the electrolyte solution.
The hydrophobic organic compound may be 1,3,5-triisopropylbenzene.

  According to the present invention, a metal film made of Au or the like having a mesoporous structure that has not been obtained in the past can be provided, so that a novel application can be expected. In addition, the production method of the present invention is easy to execute, can produce a mesoporous metal film having a stable quality, and can easily adjust the size and wall thickness of mesopores in a wide range.

It is a figure explaining the manufacturing method of the mesoporous Au film | membrane of one Example of this invention, (A) The figure which illustrates notionally the mechanism of mesoporous Au film | membrane formation from a micelle aggregate. (B) TEM image of PS _18000- b-PEO ₇₅₀₀ micelles formed in the liquid phase (using 3 mL of THF). (B-1) when the HAuCl ₄ sources without, when using the (B-2) HAuCl ₄ source. In the TEM image of (B), the black dots are Au nanoparticles formed on the surface of the micelle by electron beam irradiation. (B-1) and (B-2) In the upper right inset, the Tyndall phenomenon in each case is shown. (A-1) and (A-2) Upper side of a mesoporous Au film made using a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL THF as solvent in one embodiment of the present invention. SEM image of the surface. Here, the deposition time was 1000 seconds. (B-1) to (B-3) In one embodiment of the present invention, the upper side of a mesoporous Au film prepared using three types of electrolytes containing PS ₁₈₀₀₀ -b-PEO ₇₅₀₀ micelles and different amounts of THF SEM image of the surface (THF amount: (B-1) 1 mL, (B-2) 2 mL, (B-3) 3 mL). (C-1) to (C-3) High mesoporous Au film prepared using a typical electrolyte containing PS ₁₈₀₀₀ -b-PEO ₇₅₀₀ micelles and 3 mL THF as solvent in one embodiment of the present invention. Magnification TEM image. The crystal lattice assignment is shown in FIG. In one embodiment of the present invention, two electrolytes comprising PS _18000- b-PEO ₇₅₀₀ micelles and different solvent compositions (Sample II: 3 mL THF, Sample III: 3 mL THF + 40 μL 1,3,5-TIPBz) (S-1) and (B-1)) of the mesoporous Au film prepared in step 1 and the electric field distribution under the corresponding excitation at 532 nm ((A-2), (B- 2), (B-3)). The electric field magnitudes of (A-2) and (B-2) were obtained at a depth of 10 nm in the film, and the appropriate E field magnitude is the pore surface as shown by the dashed square. Observed clearly inside or around. The electric field distribution of (B-3) is obtained from the film surface and shows a strong electric field (hot spot) around the protruding object (marked by a solid square). (B-4) is a cross-sectional electric field distribution on the mesoporous Au film (sample III). (C-1), (C-2), (D-1), (D-2) an enlarged SEM image of a region indicated by a dashed square in (A-1) and (A-2), respectively, and The figure which shows the electric field distribution in the area | region shown with the square of the broken line in (B-1) and (B-2). The figure which shows the surface enhancement Raman scattering (SERS) measurement of the Nile blue molecule | numerator coat | covered on the mesoporous Au film | membrane of one Example of this invention. (A) Photograph of a mesoporous Au film (sample III) prepared using an electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL of THF + 40 μL of 1,3,5-TIPBz solvent. (B) The figure which shows the corresponding SERS spectrum mapping about vibration intensity. (C) Representative SERS spectrum on mesoporous Au film (Sample III). Both mesoporous Au regions (deposited regions) and non-porous regions (non-deposited regions) were measured. (D) Three types including PS _18000- b-PEO ₇₅₀₀ micelles and different solvent compositions (Sample I: 1 mL THF, Sample II: 3 mL THF, Sample III: 3 mL THF + 40 μL 1,3,5-TIPBz) A typical SERS spectrum on a mesoporous Au film prepared with an electrolytic solution. For comparison, data for a sputtered Au film without mesopores is also shown. The SERS spectrum variation is ± 5% for each. This variation is due to the surface roughness and non-uniformity of the adsorbed molecular layer. SEM image of the top surface of a mesoporous Au film made with three electrolytes containing PS _18000- b-PEO ₇₅₀₀ micelles and different amounts of THF ((A): 1 mL, (B): 2 mL, (C): 3 mL) The figure which shows the corresponding pore size distribution curve. The average pore size was (A): 19 nm, (B): 24 nm, and (C): 25 nm. (A1) SEM image of PS ₁₈₀₀₀ -b-PEO ₇₅₀₀ micelles formed in an aqueous solution containing 3 mL THF but no HAuCl ₄ source. (B1) SEM image of PS _18000- b-PEO ₇₅₀₀ micelles formed in an aqueous solution containing 3 mL of THF and HAuCl ₄ source. (A2) and (B2) The micelle size distribution histograms of (A1) and (B1), respectively. The SEM image of the upper surface of the mesoporous Au film | membrane produced with very short deposition time ((A): 10 second, (B): 30 second, (C): 100 second). All films shown here were made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL of THF as solvent. Four types of electrolysis including PS _18000- b-PEO ₇₅₀₀ micelles and different amounts of 1,3,5-TIPBz ((A): 10 μL, (B): 20 μL, (C): 30 μL and (D): 40 μL)) The figure which shows the SEM image of the conditions of the mesoporous Au film | membrane produced with the liquid, and a corresponding pore size distribution curve. The amount of THF in the electrolyte was fixed at 3 mL. The average mesopore size was (A): 32 nm, (B): 32 nm, (C): 40 nm, and (D): 40 nm. SEM images and corresponding pore size distribution curves of mesoporous Au films prepared with two different electrolytes including (A): PS _18000- b-PEO ₇₅₀₀ micelles and (B): PS _63000- b-PEO ₂₆₀₀₀ micelles. FIG. The amount of THF in the electrolyte was fixed at 3 mL. The average mesopore size was (A): 25 nm and (B): 60 nm. The figure which shows the relationship between deposition time and a film thickness. (A to E) Cross-sectional SEM images of mesoporous Au films prepared using a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL of THF as solvent. Deposition times were (A): 600 seconds, (B): 1000 seconds, (C): 1800 seconds, (D): 2500 seconds, and (E): 3600 seconds. (F) shows the growth rate of the mesoporous Au film. Graph showing the calculation results of the ECSA (electrochemically active surface area) of the mesoporous Au film fabricated by typical electrolyte containing THF in 3mL as PS _{18000 -b-PEO 7500} micelles and solvent. (A) Cyclic voltammograms (CV) of mesoporous Au films of various thicknesses in an acidic solution (0.5 MH ₂ SO ₄ ). (B) The figure which shows the relationship between ECSA and a film thickness. (C) A diagram showing the relationship between total ECSA and film deposition. The conceptual diagram which shows the mesopore arrangement | positioning model in a single layer mesoporous Au film | membrane. High magnification TEM image of a mesoporous Au film made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL THF as solvent. In (A), some defects such as (a) stacking faults, (b) dislocations, (c) kink bands are indicated by arrows. The scale bar (A) is 5 nm, (B) to (G) are 1 nm, and the zone axis is the [110] direction. (A) to (c) are XPS spectra of mesoporous Au films prepared by a typical electrolyte containing PS ₁₈₀₀₀ -b-PEO ₇₅₀₀ micelles and 3 mL of THF as a solvent (measuring object: (a) polymer micelles removed) (B) Mesoporous Au film after etching (removed 5 nm thick portion from the upper surface), (c) Mesostructured Au film before removal of polymer micelles). (D) is an XPS spectrum of a non-porous Au film produced by a sputtering method. The figure which shows the measurement result for investigating the coordination state (Auordination environment) of Au seed | species melt | dissolved in electrolyte solution. (A) UV-bis spectra of various solutions (a solvent containing both PS-b-PEO micelles and HAuCl ₄ , a solvent containing only PS-b-PEO micelles, and a solvent containing only HAuCl ₄ ). (B) Raman spectrum of the same solvent. (C) The enlarged view of the rectangular area of the left end of (B). SEM images of various positions of a mesoporous Au film made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and THF as solvent. Two membranes were made separately from two separately prepared batches of electrolyte. (A) A photograph of a typical mesoporous Au film before the peel test. (B) SEM image of a typical mesoporous Au film before the peel test. (C) A photograph of a typical mesoporous Au film after the peel test. (D) SEM image of a typical mesoporous Au film after the peel test. The sample to be tested, the mesoporous Au film, was made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and THF as the solvent. Plot of current measurement results during the deposition process of mesoporous Au film under various temperatures. All deposition processes were performed under a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL of THF as solvent. SEM images of Au films prepared at various temperatures ((A) 0 ° C., (B) 25 ° C., (C) 40 ° C., and (D) 60 ° C.). All membranes were made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ micelles and 3 mL of THF as solvent. (A) SEM images of mesoporous Au films prepared with three types of electrolytes. Here, the three kinds of electrolytes are PS _18000- b-PEO ₇₅₀₀ micelles and three kinds of solvent compositions as solvent, respectively (sample I) 1 mL THF, (sample II) 3 mL THF, and (sample III) 3 mL THF + 40 μL 1,3.5-TIPBz was used. (B) Scattering spectra of mesoporous Au films (Sample I, Sample II, and Sample III). For comparison, a sputtered Au film without mesopores was also measured. (C) The graph which shows the position dependence on the film | membrane of the scattering spectrum of a mesoporous Au film | membrane (sample III). The broadband spectrum seen in the graph of (B) is due to the combined effect of optical responses from various types of mesopores and nanoprotrusions in the film. (A-1), (B-1), (C-1) SEM images of mesoporous Au films prepared with three types of electrolytes. Here, the three kinds of electrolytes are PS _18000- b-PEO ₇₅₀₀ micelles and three kinds of solvent compositions as solvent, respectively (sample I) 1 mL THF, (sample II) 3 mL THF, and (sample III) 3 mL THF + 40 μL 1,3,5-TIPBz was used. (A-2), (B-2), (C-2) on mesoporous Au films corresponding respectively to (A-1), (B-1) and (C-1) under excitation at 532 nm The figure which shows E field distribution. The field enhancement on the mesoporous Au structure increases with increasing pore size. FT-IR absorption spectrum of bovine serum albumin self-assembled monolayer (SAM-BSA) on mesoporous Au film (Sample I). For comparison, the FT-IR absorption spectrum of SAM-BSA on a flat Au surface without mesopores (the smaller of the two spectra in the figure) is also shown. No FT-IR signal was detected from the BSA film on bare silicon (Si). Cyclic voltammograms of mesoporous Au films (sample II and sample III) made with two different electrolytes to investigate the electrochemical properties of the mesoporous Au film. For comparison, an Au film prepared by sputtering and having no mesopores was also measured. The solution used to obtain the cyclic voltammogram was obtained by adding 2 M CH ₃ OH to 0.1 M KOH, and the running speed was 50 mVs ⁻¹ . The figure which shows the measurement result of the detection performance of several types of mesoporous Au film | membranes from which film thickness differs by the same pore size (25 nm). The difference in film thickness of the mesoporous Au film was realized by changing the electrodeposition time in three ways: 300 seconds, 600 seconds and 1500 seconds. For comparison, an Au film prepared by sputtering and having no mesopores was also measured. (A) Dynamic amperometric response at 0.3 V of the above three kinds of mesoporous Au films and an Au film prepared by sputtering when glucose is continuously added from 0.0 mM to 18 mM. (B) Calibration curves respectively corresponding to the three types of mesoporous Au films to be measured in (a) and an Au film produced by sputtering. (C) Dynamic ampero at 0.3 V of the mesoporous Au film having the electrodeposition time of 1500 seconds when glucose is continuously added from 0.00 mM to 0.18 mM in a low concentration range. Metric response. (D) A calibration curve corresponding to a mesoporous Au film having an electrodeposition time of 1500 seconds, which is a measurement target of (c). The measurement result of the dynamic amperometry response in FIG. 24A (mesoporous Au film has an electrodeposition time of 1500 seconds) and the mesoporous Pt film of Patent Document 1 (thickness is almost the same as the mesoporous Au film, average The figure which compares with the experimental result performed on the same conditions using mesopore size 18nm). This figure also shows the measurement results for an Au film produced by sputtering that does not have mesopores. (A) SEM image of a mesoporous Cu film produced with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ . (B) SE image of a mesoporous Ag base alloy made with a typical electrolyte containing PS _18000- b-PEO ₇₅₀₀ . The conceptual diagram of the electrochemical cell used in order to produce the mesoporous Au film | membrane of an Example.

The mesoporous metal film according to the present invention is a mesoporous metal film having mesopores, and the metal includes Au, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Sn, and two kinds thereof. It is at least one selected from the group consisting of the above alloys. Among the metals, gold is preferable in terms of catalytic activity, optical properties, and the like.
In this specification, the “metal film” is a film having a pair of main planes and having a portion in which one main plane and the other main plane are connected by a metal bond. And / or a portion having a portion connected by a metal bond over a distance of more than 1000 nm in the plane direction.

  The average diameter of the mesopores is not particularly limited, and is preferably 5 nm to 100 nm, more preferably 10 nm to 90 nm, and still more preferably, from the viewpoint of the characteristics of the mesoporous metal film and the ease of production. 20 nm to 70 nm. In the present specification, “diameter of mesopores” means that measured from an SEM image, and “average diameter of mesopores” means the diameter of mesopores measured from an SEM image. It is calculated from the distribution curve. Further, in the present specification, “the diameter of mesopores” is also referred to as “mesopore size”, and “average diameter of mesopores” is also referred to as “average mesopore size”.

  The mesoporous metal film according to the present invention is preferably formed on a conductive substrate from the viewpoint of ease of production and use. The conductive substrate is not particularly limited, and examples thereof include a Si wafer on which a conductive metal such as Au, Pt, or Cu is deposited on the surface. Specific examples of the conductive substrate include an Au—Si wafer, a Pt—Si wafer, a Cu—Si wafer, and the like. From the viewpoint of characteristics and the like, an Au—Si wafer and a Pt—Si wafer are preferable.

  The average wall thickness between the adjacent mesopores is not particularly limited, and is preferably 10 nm to 40 nm, more preferably 15 nm to 35 nm, from the viewpoint of the characteristics of the mesoporous metal film and the ease of production. Even more preferably, it is 20 nm to 30 nm. In this specification, “wall thickness between adjacent mesopores” refers to a value measured from an SEM image, and “average wall thickness between adjacent mesopores” refers to an SEM image. Calculated from a distribution curve of wall thickness between mesopores measured from.

  The film thickness of the mesoporous metal film according to the present invention can be controlled in any way. Specifically, it can be set to a desired value by adjusting the plating time. In principle, a film thickness on the order of millimeters can also be realized. Therefore, the film thickness of the mesoporous metal film according to the present invention is not particularly limited, and is preferably more than 0 nm and less than 10 mm, and more preferably more than 0 nm and less than 1 μm from the viewpoint of the uniformity of the film surface and the few cracks. And even more preferably from 0.5 nm to 500 nm.

  In the mesoporous metal film according to the present invention, the distribution range of the mesopore diameter is not particularly limited, and the uniformity of the mesopore diameter is likely to be high, and the characteristics of the obtained mesoporous metal film are likely to be favorable. The proportion of mesopores having a diameter in the range of average diameter × 0.9 to average diameter × 1.1 is preferably 60% to 100%, more preferably 70% to 100% in all mesopores. %, Even more preferably from 80% to 100%, particularly preferably from 90% to 100%.

  In the method for producing a mesoporous metal film according to the present invention, a voltage is applied between electrodes immersed in an electrolyte solution containing a micelle of an amphiphilic block copolymer and a metal compound, and the metal and the block are formed on one electrode. Depositing a composite with a copolymer (hereinafter also referred to as composite micelle), wherein the metal is gold, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, tin, and two of these It is at least one selected from the group consisting of more than one type of alloy. Among the metals, gold is preferable in terms of catalytic activity, optical properties, and the like.

  The amphiphilic block copolymer refers to a block copolymer including a hydrophobic portion and a hydrophilic portion, and even a block copolymer of a hydrophobic polymer and a hydrophilic polymer includes a hydrophobic portion and a hydrophilic portion. A block copolymer of two different kinds of polymers may be used, and a block copolymer of a hydrophobic polymer and a hydrophilic polymer is preferable from the viewpoint of micelle forming ability and the like. The amphiphilic block copolymer may be a diblock copolymer composed of two kinds of polymers, or may be a triblock copolymer or more composed of three or more kinds of blocks. Therefore, a diblock copolymer or a triblock copolymer is preferable.

  Hereinafter, the case where the amphiphilic block copolymer is a block copolymer of a hydrophobic polymer and a hydrophilic polymer will be described. The hydrophobic polymer is not particularly limited, and examples thereof include phenolic hydroxyl group-containing polymers such as polystyrene (sometimes referred to as “PS”), which are more rigid and easily form micelles that are superior in function as a structure-directing agent. From the viewpoint, polystyrene is preferable. The hydrophilic polymer is not particularly limited, and poly (oxyalkylene) such as poly (oxyethylene) (sometimes referred to as “PEO”); polysiloxane such as dimethylpolysiloxane; polyacrylic acid, polymethacrylic acid, etc. Carboxyl group-containing polymers; poly (N-methyl-2-vinylpyridinium) iodine salts and the like, and hydrophobic (especially, the difference in hydrophilicity / hydrophobicity from polystyrene) tends to increase. preferable. As a block copolymer of a hydrophobic polymer and a hydrophilic polymer, a phenolic hydroxyl group-containing polymer-poly (oxyalkylene) block copolymer is preferable from the viewpoint of micelle forming ability and the like.

  Specific examples of amphiphilic block copolymers include polystyrene-b-poly (oxyethylene), polystyrene-b-poly (2-vinylpyridine) -b-poly (oxyethylene), and poly (2-vinylpyridine) -b. -Dimethylpolysiloxane, polystyrene-b-polyacrylic acid, polystyrene-b-poly (N-methyl-2-vinylpyridinium) iodine salt, and the like. From the viewpoint of micelle formation ability, polystyrene-b-poly (oxy Ethylene) is preferred. “-B-” means that the polymers form a block copolymer.

  The molecular weight of the polymer constituting each block in the amphiphilic block copolymer is preferably from 3000 to 100,000, more preferably from 5000 to 70000, from the viewpoint of micelle forming ability. When the amphiphilic block copolymer is a block copolymer of a hydrophobic polymer and a hydrophilic polymer, the molecular weight of the hydrophobic polymer is preferably 7000 to 100,000, more preferably 10,000 to 70,000 from the viewpoint of micelle forming ability and the like. The molecular weight of the conductive polymer is preferably 3000 to 50000, more preferably 5000 to 30000.

Examples of the metal compound include gold, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, tin, or an oxide, chloride, fluoride, bromide, or iodide of two or more of these metals. , Hydroxides, sulfides, inorganic acid salts (sulfates, nitrates, etc.), complexes and the like. From the viewpoints of reactivity, stability, availability, etc., the above metal complexes are preferred, and HAuCl ₄ More preferred are halogeno complexes of the above metals.

The electrolyte solution can be obtained, for example, by mixing a solution of an amphiphilic block copolymer and an aqueous solution of a metal compound and forming micelles of the amphiphilic block copolymer in the presence of water. Therefore, examples of the solvent in the electrolyte solution include a solvent and water in an amphiphilic block copolymer solution. The solvent in the solution of the amphiphilic block copolymer is not particularly limited as long as the amphiphilic block copolymer can be dissolved, and examples thereof include a solvent that dissolves the hydrophobic block in the amphiphilic block copolymer. Cyclic ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 4,4-dimethyl-1,3-dioxane are preferred, and tetrahydrofuran is more preferable because excellent solubility is easily obtained. preferable. The hydrophobic block in the amphiphilic block copolymer means a portion showing hydrophobicity in the amphiphilic block copolymer, and the amphiphilic block copolymer is a block copolymer of a hydrophobic polymer and a hydrophilic polymer. The term refers to a hydrophobic polymer, and when the amphiphilic block copolymer is a block copolymer of two different polymers containing a hydrophobic portion and a hydrophilic portion, it refers to a hydrophobic portion.
The electrolyte solution may further contain alcohol such as ethanol as a solvent.

  Examples of the concentration of the amphiphilic block copolymer in the electrolyte solution include 0.25 mg / mL to 2.5 mg / mL, and 0.5 mg / mL to 2.0 mg / mL are preferable.

  Examples of the concentration of the metal compound in the electrolyte solution include 1 mM to 10 mM, and 3 mM to 8 mM are preferable.

  The voltage applied between the electrodes follows a normal standard electrode potential. From the viewpoint of the characteristics of the obtained mesoporous metal film, the efficiency of deposition of the composite of metal and block copolymer, etc., there is no problem even if it is applied in the direction of increasing the current value (increasing the deposition rate).

The method for producing a mesoporous metal film according to the present invention may include a step of removing the block copolymer from the composite on the one electrode after completion of the deposition of the composite on the one electrode. The portion where the block copolymer is removed in the above step is converted into mesopores, and a mesoporous metal film is obtained. The method for removing the block copolymer is not particularly limited. For example, a dry removal method such as a method for decomposing the block copolymer in the complex using a UV ozone cleaner, O ₂ plasma treatment, or the like, Examples thereof include a wet removal method such as a method of dissolving the block copolymer in the complex with the above-mentioned solvent in the solution of the amphiphilic block copolymer.

  In the method for producing a mesoporous metal film according to the present invention, the average diameter of the mesopores of the produced mesoporous metal film dissolves the solvent in the electrolyte solution (that is, the hydrophobic block in the amphiphilic block copolymer). It can be adjusted by changing the amount of the solvent) and / or by adding a hydrophobic organic compound to the electrolyte solution.

  In the electrolyte solution, the amount of the solvent that dissolves the hydrophobic block in the amphiphilic block copolymer is, for example, 5% to 50% by volume, and preferably 10% to 45% by volume. The average diameter of the mesopores tends to increase as the concentration increases within this range. In addition, in this specification, the numerical value regarding a volume is a value in room temperature (specifically 20-30 degreeC) unless there is particular notice.

  The hydrophobic organic compound is not particularly limited, and examples thereof include 1,3,5-triisopropylbenzene, n-heptane, 1,3,5-trimethylbenzene, 1,3,5-triethylbenzene and the like. It is done. Examples of the concentration of the hydrophobic organic compound in the electrolyte solution include 0.25 μL / mL to 10 μL / mL, and 0.5 μL / mL to 7 μL / mL are preferable. The average diameter of the mesopores tends to increase as the concentration increases within this range.

  The mesoporous metal film according to the present invention can be used for various applications based on excellent characteristics resulting from mesopores. Examples of such applications include oxidation and / or reduction catalysts having the mesoporous metal film, molecular sensors having the mesoporous metal film, and lithium ion battery electrodes having the mesoporous metal film. Examples of the oxidation and / or reduction catalyst include a methanol oxidation catalyst. The oxidation and / or reduction catalyst including the mesoporous metal film according to the present invention is expected to be applied to, for example, a fuel cell electrode catalyst. Examples of the molecular sensor include a glucose sensor and a pH sensor. The lithium ion battery electrode can be used as a negative electrode, for example. In addition to the mesoporous metal film according to the present invention, the oxidation and / or reduction catalyst, the molecular sensor, and the lithium ion battery electrode include a base material that supports the mesoporous metal film, an inorganic film other than the mesoporous metal film, Inorganic particles, organic films, organic particles and the like may be provided.

  The mesoporous metal thin film (especially mesoporous gold thin film) according to the present invention has catalytic activity, light absorption characteristics, compared with other mesoporous metal materials such as other mesoporous platinum films (Patent Document 1) and mesoporous metal powders. It is excellent in properties such as light scattering properties and adsorption properties, and its application to catalyst materials, molecular sensors, electrode materials, adsorbent materials, etc. is much expected. In particular, since it is in the form of a thin film, it can be used as it is as an electrode.

It is well known that a large electromagnetic field enhancement effect occurs in the nanoscale gap formed between metal particles, but considering the optical principle of the Babinet principle, the opposite mesopores Electromagnetic field enhancement effect also appears around thin walls and protrusions present in The material proposed in the present invention is not only a light scattering effect but also a molecular detection because of many “electromagnetic field hot spots” formed in the mesopores and also near the thin walls and protrusions between the pores. High performance is also exhibited by surface enhanced Raman scattering (SERS) for (Non-Patent Document 39). As shown in FIG. 1A, the inventor of the present application uses a polystyrene-block-poly (oxyethylene, PS-b-PEO) diblock copolymer as a soft template. Have found an efficient method for producing a mesoporous Au film with finely tuned pore size, in which HAuCl ₄ is decomposed into H ₃ O ⁺ ions and AuCl ₄ ⁻ ions in an electrolyte solution, and hydrogen Bonding interacts with the micelle's oxyethyl (EO) shell, this interaction being greater with H ₃ O ⁺ than with AuCl ₄ ⁻ , resulting in positively charged micelles toward the working electrode surface. Here, the AuCl ₄ ⁻ ions are reduced to the metallic Au as the micelles are electrochemically deposited. The mesoporous Au film actually showed high scattering performance and thus showed high activity for molecular detection as seen in SERS (Non-Patent Document 40) and Surface Enhanced Infrared Absorption (SEIRA) (Non-Patent Document 41). The magnitude of the electric field (E-field), greatly enhanced by localized surface plasmons (LSPR), was clearly seen in and around the mesopores. It can be easily adjusted simply by adjusting the size of the holes, and this method provides a novel means for adjusting the optical function with a simple soft template method.

  Furthermore, by the same method, not only Au but also mesoporous metal films of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Pt, Sn, and alloys thereof can be formed.

  Hereinafter, the present invention will be described in more detail based on examples. Here, it should be noted that the following examples are not intended to limit the present invention, but are described only to help understanding. The technical scope of the present invention is defined only by the claims.

In the following examples, a mesoporous Au film is prepared by a novel manufacturing method conceptually shown in FIG. 1A, and various characteristics thereof are examined. This manufacturing method is based on electrochemical methods that have been used in practice for the production of continuous metal films. In order to perform Au plating on the electrode surface in the presence of PS-b-PEO micelles, a precursor solution was prepared as follows. The PS-b-PEO diblock copolymer was completely dissolved in tetrahydrofuran (tetrahydrofuran, THF), which is a good solvent for the PS block as its unimer. Neither micelles nor aggregates were detected in the transparent PS-b-PEO / THF solution as measured by dynamic light scattering (DLS). In making this, THF was essential. This is because PS-b-PEO cannot be dissolved in water or ethanol without THF. After continuously adding ethanol, an aqueous solution of HAuCl ₄ was slowly dropped into this solution. As a result, PS-b— having PS as the core due to the lower solubility of polystyrene (PS) block in water. PEO spherical micelles were formed. As shown in FIG. 1B, spherical micelles constructed with a PS core and a PEO shell were observed with a transmission electron microscope (TEM), and their average diameter was about 25 nm. As shown in FIG. 1B, a Tyndall phenomenon was also observed in the electrolyte. As shown in FIG. 1A, the hydrophilic EO block can interact with the water-HAuCl ₄ complex in the vicinity of the outer layer of the micelle. This will be described later. In order to directly confirm the presence of PS-b-PEO micelles in the electrolyte, uniform-sized polymer micelles in Brownian motion were visualized using a confocal scanning laser microscope. Composite micelles that interact with Au species by applying an electric potential (a state in which Au compound ions are partially taken into the EO shell of the block copolymer or Au compound ions are attracted around the EO shell, ie, block Copolymer micelles and Au compound ions) were brought close to the working electrode and deposited as mesoporous Au material on the working electrode.

  Block copolymers such as PS-b-PEO, poly (ethylene-co-butylene) -b-PEO (KLE) are often used on the basis of sol-gel reactions as templates for the synthesis of mesoporous metal oxides (non- Patent Documents 41 and 42). In these cases, regularly arranged mesostructures formed in advance by evaporation of the solution are formed. Here, the inorganic framework is reliably induced in this phase. This is a kind of situation similar to the outline of the mesoporous Pt generation process (Non-patent Document 22). In contrast, the method of the present application is based on a “micelle assembly” caused by an electrical driving force. Here, metal deposition (framework construction) and micelle accumulation occur simultaneously. This is because the electrochemical deposition process of spherical composite micelles proceeds completely in the liquid phase without solvent evaporation. Therefore, the method of the present application is different in concept from the preceding method for producing a mesoporous film (referred to as evaporation-induced self-assembly, EISA).

  In order to more clearly confirm the role of micelles, the growth of mesostructures was examined using SEM at its initial stage (10, 30, and 100 seconds after initiation). After 10 seconds, a large amount of initial Au seeds was formed as indicated by arrows in FIG. 7 (A). The curved surface of the Au branch as shown by the slanted ellipse in FIG. 7A is due to the directing effect of the micelles. When the deposition time was further extended to 30 seconds, a large number of mesopores were observed as shown in FIG. 7B, but the formation of each mesopore was not completely completed. When the deposition was advanced to 100 seconds, the estimated film thickness reached almost half of the mesopore size, and the Au skeleton was sufficiently constructed as shown in FIG.

  Here, the film thickness of the Au film shown in FIG. 7 will be described. Since the Au film does not grow uniformly on the substrate in the initial stage of Au deposition, it is difficult to show an accurate film thickness. . However, as shown in FIG. 10, when it is assumed that the Au film thickness increases at a constant growth rate, the average film thicknesses are (A) (after 10 seconds) and (B) (after 30 seconds) in FIG. And (C) (after 100 seconds) are estimated to be 1 nm, 4 nm and 11 nm, respectively.

  After completely removing PS-b-PEO micelles, a mesoporous Au film was obtained. Its properties were carefully measured. As shown in FIG. 2 (A), cage-like uniform mesopores connected to each other over the entire membrane were observed. As shown in FIGS. 2A and 5C, the scanning electron microscope (SEM) image of the upper surface of the mesoporous Au film has a uniform size (average 25 ± 5 nm) and a wall thickness of 25 nm ± 5 nm. The presence of pores was indicated. The size of the pores formed in the mesoporous Au film (FIG. 2A) was almost the same as the size of the spherical micelles observed by TEM (FIG. 1B) and SEM (FIG. 6). This means that the spherical micelle acts as a mold.

  In addition to this, the pore size of the mesoporous Au film was very easily controllable by changing the amount of THF. The amount of THF was changed here from 1 mL to 3 mL. This is the most important technique for adjusting the optical properties of the mesoporous Au film caused by the concave Au surface. Since THF is a good solvent for PS blocks, the PS core in micelles gradually shrinks as the amount of THF is reduced. In fact, by reducing the amount of THF, the pore size could be controlled to be reduced to about 19 nm without causing a large change in the wall thickness as shown in FIGS. 2 (B) and 5. Even using the minimum amount of THF (1 mL) to completely dissolve PS-b-PEO, the polymer micelles were able to stably maintain their original form in a reduced form. The mesopores were actually spherical in shape as shown in FIG. 2 (B-1). The average pore size and wall thickness were about 19 nm and about 25 nm, respectively.

  On the other hand, the pore size can be increased by adding a hydrophobic organic compound. When 1,3,5-triisopropylbenzene (1,3,5-TIPBz) is used as the pore expansion agent, the effective pore size is 1,3,5-TIPBz. From 25 nm without, 32 nm (10 μL 1,3,5-TIPBz), 32 nm (20 μL 1,3,5-TIPBz), 40 nm (30 μL 1,3,5- TIPBz) and 40 nm (40 μL of 1,3,5-TIPBz). As the pore size increased, the pore walls became more like protrusions.

In addition, as shown in FIG. 9, the molecular weight of the PS block in PS-b-PEO can also be used to control the pore size. As estimated by SEM, the average pore size of the mesoporous Au film produced using PS _63000- b-PEO ₂₆₀₀₀ was about 60 nm. In addition, from this experimental result, the influence of the molecular weight on the PEO block side was hardly confirmed.

Unlike the method of manufacturing a mesoporous metal oxide film using the sol-gel method, the manufacturing method of the present application has an advantage that the film growth rate can be easily and accurately controlled by electrochemical deposition. Brought about. That is, by using this method, the film thickness can be finely adjusted simply by adjusting the deposition time. The film thickness of the mesoporous Au film produced using PS _18000- b-PEO ₇₅₀₀ shown in FIG. 10 is 70 nm when the deposition time is 600 seconds, 1000 seconds, 1800 seconds, 2500 seconds and 3600 seconds, respectively. 140 nm, 170 nm, 230 nm, and 440 nm, and the growth rate in this case was calculated to be approximately 0.1 nm / second.

In addition, as shown in FIG. 11, the electrochemically active surface area (ECSA) was also calculated using cyclic voltammetry in an acidic medium (0.5 MH ₂ SO ₄ ).

  Here, if FIG. 11 is supplementarily explained, the ideal surface area can be estimated by the following calculation. First, consider a single-layer mesoporous Au film shown in FIG. The average pore size and average wall thickness are assumed to be 25 nm and 25 nm, respectively. Further, as shown in FIG. 12, it is assumed that this film is a rectangular parallelepiped having a length of 125 nm, a width of 100 nm, and a height of 25 nm, and has three spherical mesopores and four hemispherical mesopores.

By using the model of FIG. 12, the total surface area S in the mesopores can be determined by examining five spherical mesopores.
S = 5 × 4 · π · R ² = 5 × 4 × 3.14 × (12.5 × 10 ⁻⁹ ) ² = 9.8125 × 10 ⁻¹⁵ (m ² )
Further, the bulk film deposition V of this model can be obtained as follows.
V = (125 × 10 ⁻⁷ ) × (100 × 10 ⁻⁷ ) × (25 × 10 ⁻⁷ ) = 3.125 × 10 ⁻¹⁶ (cm ³ )
Therefore, the surface area P normalized by volume can be obtained as follows.
P = S · V ⁻¹ = 31.4 (m ² · cm ⁻³ )
This calculation result is slightly smaller than the value 49.1 m ² · cm ⁻³ (described later) obtained by electrochemical measurement. The reason is that the surface of the actual pores in the mesoporous Au film is uneven (that is, not flat). The high-resolution TEM images of FIGS. 2 and 13 also show uneven surfaces having atomic size steps and bends, but these increase the surface area than expected.

Here, returning to FIG. 11, the area of the peak indicated by the dashed ellipse in FIG. 11A corresponds to the reduction of the Au oxide species. Based on the assumption that the charge corresponding to the reduction of the oxide species on the Au surface is 400 μCcm ⁻² (Non-Patent Documents 45 and 46), ECSA in the film was theoretically calculated from the observed charge. As shown in FIGS. 11B and 11C, the total surface area of the mesoporous Au film increased proportionally. ECSA normalized by volume (per membrane volume (cm ³ )) was approximately 49.1 m ² cm ^{−3 as} shown in FIG. 11 (C) and was almost constant until the film thickness reached 5 μm. . Therefore, even in the case of a thick film, the inside of the mesoporous Au film can operate as a surface having electrochemical activity, and it has been proved that the mesoporous structure is uniformly formed inside the film. .

  In order to investigate the atomic structure of Au in the pore wall extensively and carefully, a single-layer mesoporous Au film was prepared, and a sample of the cross section was observed by TEM as shown in FIG. 2 (C) and FIG. From these TEM images, it was found that the spherical mesopores were surrounded by a continuous network of crystallized Au. Lattice fringes associated with Au fcc crystals were clearly observed inside the pore walls. The high-resolution TEM image seen along the [001] direction shown in FIG. 13 showed (111) lattice fringes together with single crystal stacking faults in the mesoporous Au film. As shown in FIG. 2 (C), several crystal domains were sequentially joined to produce a concave surface that exposes higher order surfaces. As indicated by arrows in FIG. 13A, there were some defects such as (a) stacking faults, (b) dislocations, and (c) bent bands. These defects may be due to local strain during Au crystal growth and / or electrochemical deposition of mesoporous films accompanying reduction of soluble Au species. XPS was used to determine the surface composition and oxidation state of the Au film. As shown in FIG. 14, the high-resolution Au 4f scan shows 87.7 eV and 84.0 eV doublets separated by 3.7 eV due to spin orbit coupling, and there is an Au (0) species in the film. Was confirmed.

The electrolyte solution was examined by UV-Vis absorption and Raman spectroscopy as shown in FIG. In the ultraviolet spectrum, the peak around 324 nm corresponds to the typical dd transition of the AuCl ₄ ⁻ species. Another band around 278 nm appears due to the presence of a benzene ring in the PS block. The Raman spectra, AuCl ₄ in solution ^- species symmetric mode _{(A 1 g),} the half symmetric mode _{(B 2 g)} and bending mode _{(B 1 g),} respectively ^347cm -1, a peak at 324cm ^-1 and 171cm ^-1 appear. All other peaks were associated with solvent and PS-b-PEO diblock copolymer. From both UV-Vis absorption and the Raman spectrum, it can be seen that the Au species is considered to be Au (III) in which Cl ^- is a ligand. Therefore, the method for obtaining a mesoporous Au film in the present application is realized by the interaction between PS-b-PEO micelles and soluble Au species. That is, as shown in FIG. 1A, HAuCl ₄ is decomposed into H ₃ O ⁺ and AuCl ₄ ⁻ and interacts with the EO shell region of the PS-b-PEO micelle by hydrogen bonding. Furthermore, AuCl ₄ ⁻ is considered to be a free ion not only in solution but also in the hydrophilic region of PS-b-PEO micelles. A micelle containing AuCl ₄ ⁻ may be electrically neutral, or may be negatively or positively charged, depending on the H ₃ O ⁺ / AuCl ₄ ⁻ ratio in the EO shell portion. Under the experimental conditions of the present application, the micelle solution after the addition of the HAuCl ₄ aqueous solution was slightly positive at the zeta potential. Therefore, micelles rich in H3O ⁺ were positively charged and moved to the working electrode (negative electrode) surface.

  As shown in FIG. 16, the method of the present invention exhibits very high reproducibility (100%). In fact, the inventor of the present application repeated the same experimental procedure many times and obtained the same mesoporous structure exactly every time. Even at the edge portion, the same mesoporous structure was reliably formed. In order to show the high reproducibility of this method, FIG. 16 shows two films A and B separately prepared and showing SEM images at many positions P1 to P9 for each. As can be seen, the SEM images of the films A and B and the positions P1 to P9 are very similar.

  As shown in FIG. 17, the electrodeposited mesoporous Au film adhered well on the substrate (that is, the working electrode). The peel test whose result is shown in FIG. 17 is a 90 ° peel test in which adhesion between an electrodeposited mesoporous Au film and a substrate is performed on a film sample using Scotch Tape (registered trademark) of 3M Company. It is. The tape was peeled from the mesoporous Au film at a constant force of 5.0 ± 0.1 N and a test distance of 20 mm. After the peel test, it was observed that the deposited Au film was still attached on the substrate. Samples before and after the peel test were observed with an SEM, and it was confirmed that the original mesoporous structure was maintained well without deformation of mesopores and formation of cracks and scratches.

  In order to realize a good mesoporous structure, the crystal growth rate, that is, the resulting crystal size is the most important factor. According to Non-Patent Document 23, Wiesner et al. Found that the diameter of the nanoparticles as building blocks must be below the critical point for the size of the blocks with which these nanoparticles interact. According to Non-Patent Document 44, in the case of mesoporous metal oxides, the mesoporous structure is sufficiently maintained only when the wall thickness is larger than the crystal size controlled by the nucleation and grain growth rates. In the electrochemical method of the present application, the Au crystal size is governed by the Au growth rate. The bath temperature for deposition is one of the important factors for controlling the Au growth rate. From the plots of current measurement results for mesoporous Au film deposition under various temperatures shown in FIG. 18, it was found that the reduction current increases (that is, the deposition rate increases) as the bath temperature increases. As shown in FIG. 19, it was clearly confirmed that a mesoporous structure was formed only when the temperature was 25 ° C. or lower. In contrast, when the temperature was 40 ° C. or higher, the Au crystal growth rate was increased, and large bulk Au crystals were mainly formed. As a result, the mesoporous structure did not develop well.

In order to investigate the basic optical properties of mesoporous Au films, three typical films with different pore sizes were compared. Here, PS _18000- b-PEO ₇₅₀₀ micelles and three types of solvent composition (Sample I: 1 mL of THF (average pore size 15 nm), Sample II: 3 mL of THF (25 nm)), and Sample III: 3 mL of THF And 40 μL of 1,3,5-TIPBz (40 nm) were used to select mesoporous Au films prepared with three types of electrolytes.
Using a custom-made dark field spectroscopic microscope, the representative scattering spectrum shown in FIG. 20 was measured and compared with a spectrum obtained from an Au film having no mesopores prepared by sputtering. As can be seen from FIG. 20B, the scattered light intensity increased systematically as the pore size increased. This indicates that the interaction between the mesopore surface and electromagnetic waves in the visible frequency region has increased. This result suggests that the interaction between the Au surface and light has increased. This may be due to the increased electromagnetic field around the individual mesopores. This is because as the pore size increases, the Au volume exposed to the electromagnetic field (E field) of the incident light increases, so that the charge induced on the surface of the pores also increases. Another reason for this is that when the pore size is increased, the pore size approaches the wavelength of the charge density wave that vibrates on the Au surface where it is induced by visible light. It may be related to being able to respond more efficiently to it. Note that the charge density wave wavelength of (localized) surface plasmons is in the range below 100 nm. As can be seen from FIG. 20C, the points on the Au surface respond in different ways with different scattering intensities and different resonance frequencies, reflecting their different morphology at the nanometer scale. Therefore, as shown in FIG. 20B, the broadband scattering spectrum is due to the effect of summing up a large number of mesopores in the film.

    In order to gain deeper insight into the observed spectrum, the electric field distribution was evaluated based on simulations using a finite-difference time domain (FDTD) algorithm. As can be clearly seen, the tendency of the scattering intensity of the three types of films shown in FIG. 20 observed experimentally clearly corresponds to the electric field strengths in FIGS. As can be seen from FIG. 21, the magnitude of the electric field increased with increasing pore size. As can be seen from FIGS. 3C and 3D, a considerable electric field was clearly observed in or around the mesopores. On the other hand, for larger pores, as clearly shown in FIG. 3B-3, there is a clear tendency that a strong electric field point (hot spot) appears around the protrusion. Also from the cross-sectional image of FIG. 3 (B-4), the above characteristics indicating that a strong electric field is generated inside the mesopores are confirmed. In particular, for sample III, as shown in FIG. 3 (B-3), the pores have a conglomerated and bent pore wall with prominent nano-sized protrusions, and the electric field is concentrated there. And has a tendency to give large strength. Such protrusions on the stretched wall exhibit a plasmon resonance frequency in the longer wavelength (near infrared) region. In contrast, the other two membranes (Sample I and Sample II with smaller pores) have fewer corrugated surfaces and protrusions and a slightly higher resonance frequency (ie shorter wavelength), Electric field and scattering are smaller.

  The mesoporous Au film is stable in water, and its high affinity with proteins and amino acids on the Au surface is greatly beneficial when the film is used as a substrate for biosensing. Most of the state-of-the-art aptamer-sensing is based on aptamers with thiol groups introduced, often with linker molecules rationally designed for specific target molecules. Therefore, the mesoporous Au film of the present application is considered to be the best substrate suitable for aptamer-based sensing SERS.

Here, as shown in FIG. 4, the above-mentioned three types of membranes having different pore sizes (sample I, sample II and sample III, which are denoted as Sample I, Sample II and Sample III respectively in all drawings) ) SERS performance was investigated. Specifically, a droplet (5 μL) of a Nile blue solution (10 ⁻⁶ M ethanol solution) is spread evenly on a mesoporous Au film (0.3 cm × 1.5 cm), and the substrate is expanded with nitrogen. Dry in air at room temperature under a gas stream. SERS spectra obtained from Nile blue molecules coated on mesoporous Au films by excitation with a laser of wavelength 532 nm were recorded. Optical microscope images and corresponding SERS spectrum mapping images for Sample III are shown in FIGS. Here, it is clearly visualized that the SERS signal greatly increases on the mesoporous Au region. The enhancement mechanism of the SERS effect is mainly due to the electromagnetic field enhancement effect caused by mesoporous Au. The surface of the sputtered Au film without mesopores (denoted as Sputtered Au in all figures) shows much less SERS signal intensity. The most dramatic effect caused by nanopore morphology is actually the field enhancement caused by the strong interaction between light and the gold surface, as can be seen from the enhanced light scattering shown in FIG. 20B. Therefore, this SERS effect can be attributed to electromagnetic origin, as shown in FIGS. In addition to this, the chemical SERS effect caused by molecular adsorption should be small. This is because the contribution of molecular adsorption to the SERS intensity is in the order of the lower curve in FIG. 4C where the magnitude of the electromagnetic field is significantly reduced compared to the mesoporous Au film. Furthermore, the chemical SERS effect is an adsorption monolayer effect determined by the nature of the local bond between the Nile blue molecule and the Au atom, and the adsorbed Nile blue should be multi-layered. So, if the difference in SERS intensity is attributed to the effect of surface morphology, it can be concluded without problems.

  Furthermore, as shown in FIG. 4D, the SERS signal intensity from the molecule increased as the mesopore size increased. This result shows the same tendency as the scattering intensity shown in FIG. 20B, and shows the influence of the pore structure of these films. That is, in the larger mesopores, the electric field enhancement due to localized surface plasmon excitation occurs more strongly, which results in stronger light scattering. The enhanced electric field results in a stronger SERS signal from the adsorbed molecule, as seen in the measurements herein. Note that the strongest SERS intensity is expected for a laser excitation wavelength near 670 nm, which is close to the wavelength of the peak position in the scattering spectrum. However, even the experiments of the present application using a 532 nm laser, which is not necessarily optimal, already show a sufficiently high SERS signal. This proves the high performance of the mesoporous Au substrate of the present application.

In order to estimate the SERS enhancement factor, a film of the same area sputtered with Au (ie, a non-SERS substrate) was added to a solution of Nile Blue's 10 ⁻³ M ethanol solution (to visualize weak signals of non-SERS). Covered with drops (5 μL). The result is shown in FIG. 4C (the Raman intensity is significantly lower). When the same measurement conditions are used, the SERS enhancement factor (EF) is simply calculated by the following equation.
EF = [I _SERS / C _SERS ] / [I _RS / C _RS ]
Here, I _SERS and I _RS are the Raman intensities of the SERS signal and the non-SERS signal, respectively, and C _SERS and C _RS are the concentrations of the molecules dropped on the SERS substrate and the non-SERS substrate, respectively. The strongest peak at 1642 cm ⁻¹ was used for this calculation, resulting in an enhancement index calculation of 1.2 × 10 ⁵ . The signal enhancement factor of the material of the present application is in the same order as that of the nanostructure sample (Non-Patent Documents 48 to 50) reported previously, but by using a mesoporous Au substrate, spectral mapping having high spatial resolution is used. This has led to a systematic understanding for associating local optical properties with fine-tuned morphology. Such information is definitely useful to elucidate the origin and mechanism of electromagnetic field enhancement.

In order to further clarify the large-sized mesopores, an example in which a large biomolecule (protein) is selectively detected on the mesoporous Au film of the present application will be described below with reference to FIG. Surface enhanced infrared absorption spectroscopy (SEIRA) was performed using an FT-IR configuration in attenuated total reflection (ATR) form. In this measurement, a self-assembled monolayer (SAM) of bovine serum albumin (BSA, average diameter 8.6 nm) adsorbed on a clean mesoporous substrate was used as a sample protein. A mesoporous Au film (sample II) (0.3 cm × 1.5 cm) was immersed in a BSA solution (10 ⁻³ M aqueous solution, pH = 7.1) for 24 hours, and then completely rinsed with distilled water to give a single BSA molecule The layer was left on the pore surface and finally dried in a stream of nitrogen gas. As shown in FIG. 22, protein bands (Amide-I and Amide-II) were clearly observed in the FT-IR absorption spectrum, showing evidence that the monolayer of BSA was adsorbed. . In the mesoporous Au film of the present application, a very large signal intensity of the SAM-BSA protein was observed. Note that the enhancement factor in the visible frequency region for SEIRA is proportional to (E / E _i ) ² , unlike (E / E _i ) ^{4 for} SERS (where E is It means the amplitude of the local electric field on the mesoporous Au substrate, and E _i means the amplitude of the electric field of the incident light). Considering the above-mentioned differences and the fact that the electromagnetic field intensity in the infrared region is smaller than that in the visible region in this sample, the signal enhancement of SEIRA shown here is sufficiently satisfactory.

  As indicated above, the electrochemically deposited mesoporous Au film with tunable pores of the present application is tuned by designing a uniform mesospace made with a soft template. Optical properties can be provided. Several efforts have been made to create mesoporous Au films, but continuous Au films with precisely designed mesopores are still realized due to the difficulty of controlling Au crystal growth It has not been. In order to overcome this problem, the electrochemical synthesis proposed here, utilizing a stable PS-b-PEO diblock copolymer as a pore directing agent, is extremely efficient. In the finished membrane, uniformly sized mesopores are distributed throughout the membrane, and this mesopore size can be increased from 19 nm by changing the molecular weight and electrolyte composition of the PS-b-PEO diblock copolymer. It is controlled within 60 nm or a wider range. This method not only shows a novel optical application of the mesoporous Au film, but also provides an innovative method of synthesizing mesoporous metal using a soft template. Such a three-dimensionally expanded metal framework can reliably provide sufficient adsorption and reaction sites for the molecules of interest, but this is extremely important to realize new functions in the future. is important. By the electrochemical method of the present application, it is possible to synthesize materials in which uniform mesopores are incorporated into other metals and alloys.

  In addition to the SARS application, the mesoporous Au film of the present application shows good performance as an electrode catalyst application such as a fuel cell catalyst and a sensor material such as an amperometric sensor. This will be described below with reference to experimental results.

  As shown in FIG. 23, it has been clarified that the mesoporous Au film of the present application exhibits extremely high electrocatalytic performance as compared with an Au film produced by sputtering without mesopores. Even after normalization by the surface area, the mesoporous Au film of the present application showed an activity three times higher than the Au film prepared by sputtering. This indicates a high catalytic efficiency of the mesoporous Au surface. Compared to other metal nanoparticle-supported carbon and other catalysts, the self-supporting Au porous system does not require a support and can be used as an electrode as it is, so it will be an ideal catalyst in the future.

  Au is also considered a good candidate for sensor applications. Here, as an example, the detection performance of the three types of mesoporous Au films of the present application in which the deposition time was changed with the same pore size as shown in FIG. The detection characteristics of the mesoporous Au film of the present application were compared with an Au film produced by sputtering without mesopores. The performance of the mesoporous Au film was dependent on the deposition time, that is, the film thickness. As shown in FIGS. 24 (a) and (b), over a wide concentration range of glucose (0.0 mM to 18.0 mM), the mesoporous Au film exhibits an excellent amperometric response and relatively little degradation. there were. Even when the glucose concentration was very low (in the range of 0.00 mM to 0.18 mM), the mesoporous Au membrane electrode showed the performance of being very sensitive to glucose. As a result of careful calculation, as shown in FIGS. 24C and 24D, a detection limit of 3.35 μM was obtained by using the currently obtained mesoporous Au film. Importantly, rinsing the membrane with water allows it to be washed back and returned to its original state, indicating that the sensor has great practicality in clinical laboratories. .

  In the above description, only the Au film has been described as the mesoporous metal film, but mesoporous metal films using other metals or alloys can be realized in the same manner.

  Here, in order to compare the mesoporous Au film used in FIG. 24A and the mesoporous Pt film of Patent Document 1, glucose was detected under the same experimental conditions as in FIG. The result is shown in FIG. As can be seen, the mesoporous Au film according to the present invention can obtain a detection output more than twice that of the mesoporous Pt film to be compared, confirming the suitability of the film of the present invention for a molecular sensor. It was.

  FIG. 26 shows an SEM image of an example of such a mesoporous metal film made of a metal other than Au. FIG. 26A shows an example of a mesoporous Cu film. As is well known, Cu salts readily dissolve in water to form aqua complexes. Therefore, these Cu aqua complexes effectively interact with the EO group (that is, the polymer micelle surface). In this way, the inventor of the present application similarly has a very small variation in pore size with respect to a wide range of metals such as Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Pt, and Sn other than Au. A mesoporous metal film could be created.

  Furthermore, as shown in FIG. 26B, it has been demonstrated that a similar mesoporous metal film can be realized not only by a single metal but also by an alloy, as shown in FIG.

  The mesoporous metal film shown in FIGS. 26A and 26B is a continuous film, although there are many surface irregularities compared to the case of Au shown above. Further, as can be naturally predicted from the above-mentioned formation mechanism, it can be seen from the figure that the variation in pore size is very small in any of these mesoporous metal films.

[Details of manufacturing method]
The production of the mesoporous Au film of the example is based on an electrochemical method. This electrochemical method has been used in practice for the general production of uniform metal films. Details of a typical method for manufacturing a mesoporous Au film already described as an example will be described below.

10 mg of polystyrene-b-poly (oxyethylene) (PS-b-PEO) was completely dissolved in 3 mL of THF at 40 ° C., and then 1.5 mL of ethanol was added to this solution. When an aqueous solution of HAuCl ₄ (final concentration 5 mM in 8 mL electrolyte) was slowly added to the clear PS-b-PEO solution, spherical micelles were formed due to the presence of water. The mixture was gently stirred at room temperature for 30 minutes so that the dissolved denomination was sufficiently taken into the PEO region outside the micelle. Finally, a transparent and light yellow electrolyte (pH = 2.5) was obtained and used as it was for electrodeposition.

Electrochemical deposition from the precursor solution was performed using an electrochemical device (CHI 842B electrochemical analyzer from CH Instruments, USA). Here, the electrochemical device used a conventional three-electrode system including platinum wire as the counter electrode, Ag / AgCl as the reference electrode, and a conductive substrate as the working electrode. A conceptual diagram of a typical electrodeposition cell is shown in FIG. In this example, a typical conductive substrate used was an Au—Si wafer having a typical size of 0.45 cm ² (0.3 cm × 1.5 cm), and was produced by a dicing cutter. Optimal Au electrodeposition was performed at a constant potential of -0.5 V (vs. Ag / AgCl) for 1000 seconds without stirring at room temperature. During the electrodeposition process, a stable current flowed due to the reduction of gold as shown in FIG. After Au deposition, micelles (used as a soft template) were completely removed by UV ozone cleaner or low power O ₂ plasma treatment. This was confirmed by IR analysis. Application of atmospheric calcination, a widely used technique to completely remove organic templates from mesoporous metal oxide films, applied the film to the film, but the template was removed, but the growth of Au particles resulted in a mesoporous structure. It collapsed.

[Characteristic evaluation method]
A number of measurement results have been shown in the above examples. The equipment used for these measurements is summarized below.

A scanning electron microscope (SEM) image was obtained by using an HR-SEM SU8000 microscope manufactured by Hitachi at an acceleration voltage of 5 kV. A transmission electron microscope (TEM) image was taken using JEM-2100F manufactured by JEOL Ltd. at an acceleration voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) spectra were recorded at room temperature using JPS-9010TR manufactured by JEOL with Mg Kα X-ray source. All binding energies were calibrated with reference to C1s (285.0 eV). The UV-Vis absorption spectrum was recorded with a V-570 UV-Vis-NIR spectrometer manufactured by JASCO. Raman spectra were recorded using a T64000 Raman spectroscopy system manufactured by Horiba-Jobin-Yvon, with a laser wavelength of 514.5 nm. Mesoporous Au film electrodeposition and cyclic voltammetry measurements were performed using the CHI 842B electrochemical analyzer (CH Instruments) described above. A conventional three-electrode cell was used containing a platinum wire as the counter electrode, Ag / AgCl as the reference electrode, and a working electrode. Scattering spectra and SERS property measurements were performed using a confocal Raman microscope (WItec Alpha 300S). The dark field and SERS scan spatial resolution were both about 300 nm (64 × 64 pixels on a 20 × 20 μm scan area) with an integration time of 0.2 sec / pixel. The dark field scattering characteristics were examined using a UV-NIR light source (halogen lamp HAL 100 manufactured by ZEISS) and a dark field lens (50 × / 0.55 NA manufactured by ZEISS). For measurement of SERS characteristics, a second harmonic diode pump Nd: VO ₄ laser (Witec) (0.5 mW) at 532 nm is used in Nile blue using a 100 × objective lens (Olympus, 0.9 NA). Focus was on the scanned area of the treated Au porous part. Prior to each measurement, the intensity was carefully calibrated by measuring the Si Raman peak intensity of the Si wafer. Surface enhanced infrared absorption spectroscopy (SEIRA) was performed using an FT-IR configuration (Nicolet IS50R-FTIR from Thermo Fisher Scientific) in attenuated total reflection (ATR) form. The electric field distribution of the Au mesoporous structure was calculated using a three-dimensional finite difference time domain (FDTD) method (using Synopsys micro-optical element design / analysis software Rsoft Fullwave). Three-dimensional modeling was performed based on the shape of a scanning electron micrograph of a mesoporous Au film. Excitation field propagation along which the electric vector oscillates along the xz plane along the z axis was injected from the top of the Au mesoporous surface.

JP 2012-167300 A

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Claims (6)

A mesoporous metal film having mesopores, wherein the metal is at least one selected from the group consisting of gold, copper, silver and alloys of two or more thereof;
The proportion of mesopores having a diameter in the range of average diameter × 0.9 to average diameter × 1.1 is 60% to 100% in all mesopores,
Mesoporous metal film.   The mesoporous metal film according to claim 1, wherein an average diameter of the mesopores is 5 nm to 100 nm.   The mesoporous metal film according to claim 1 or 2, formed on a conductive substrate.   The mesoporous metal film according to any one of claims 1 to 3, wherein an average wall thickness between adjacent mesopores is 10 nm to 50 nm.   The mesoporous metal film according to any one of claims 1 to 4, wherein the film thickness is more than 0 nm and less than 10 mm. The mesoporous metal film according to claim 1, wherein the mesopores are spherical.