JP4608335B2 - Method for producing mesoporous metal film - Google Patents

Description

  The present invention relates to a method for producing a mesoporous metal film, and more particularly to a method for producing a mesoporous metal film in fine grooves and holes.

  With the downsizing and widespread use of electronic devices, there is a demand for downsizing batteries and the like that are energy sources. In addition, it is required that a metal body having a high surface area and an array of regular pores, which is required for a microreactor, a microsensor, etc., be formed in a microchannel or a desired fine structure. Yes. The technology to uniformly create a mesoporous metal with a high surface area and regular pore arrangement can be used to create a new battery configuration such as a fuel cell that uses a microchannel, even on fine irregularities. Enables the creation of new electronic functional devices based on microelectrochemical systems (MEMS), such as sensors and microreactors that use mesoporous metals other than batteries as reaction fields, and uses a unique reaction field called mesostructure. New physical properties can be expected.

  As a method of forming a metal body having such a high surface area and regularly arranged fine pores, a sol-gel method using a precursor solution made of a metal alkoxide, particularly silicon alkoxide and a surfactant, has been conventionally used. Processes for creating mesoporous structures in a so-called manner are known. This method is known as a method for creating a mesoporous structure by hydrolysis and polymerization reaction of silicon alkoxide on a template of lyotropic liquid crystal (LLC) formed by a surfactant. (For example, Patent Document 1) This method is limited to a mesoporous structure made of an inorganic oxide, and is inappropriate for forming a mesoporous structure with a metal. Moreover, since the viscosity of the solution is high, a mesoporous structure cannot be formed in a fine part.

  Conventionally, in order to create a mesoporous structure with a fine pattern, a precursor solution composed of a metal alkoxide (especially silicon alkoxide), an organic solvent, water, and a surfactant is used to flow into a fine pattern region. A process is known in which an LLC liquid crystal is formed as a result of volatilization, and a mesoporous structure is formed through a hydrolysis / polycondensation reaction of a metal alkoxide. (For example, Non-Patent Document 1) However, in these methods, the skeleton of the mesoporous structure is limited to inorganic oxides such as silica and cannot be applied to the production of a mesoporous metal having a metal skeleton.

  On the other hand, a mesoporous metal having a metal skeleton was reported by G. S. Attard et al. In 1997 by a synthesis method using lyotropic (LLC) liquid crystal as a direct template. (For example, Patent Document 1 and Non-Patent Document 2) With this technique, mesoporous metals having a wide range of metal compositions can be synthesized. However, this method can not be applied to the part of the fine pattern because the viscosity of the LLC liquid crystal used as a template is very high, and in order to deposit metal around the lyotropic liquid crystal Therefore, it is difficult to control it, and it is difficult to form a uniform mesoporous metal constantly.

As described above, in a conventionally known method called a sol-gel method or a method of forming a mesoporous metal by a method using a conventional precursor solution LLC liquid crystal directly, the mesoporous metal is made into fine grooves or holes. It was impossible to form a uniform and uniform pattern in a controlled state.
JP H10-226514 A Jong-Ah Paik et al., J. Mater. Res., Vol. 17, No8, (2002) p2122-2123 George S. Attard et al., Angew. Chem. Int. Ed. Engl., 36, No12 (1997) p1315-1317

  An object of the present invention is to provide a method for constantly and uniformly forming a mesoporous metal film in a controlled state at a pattern site such as a fine groove or hole.

  The invention described in claim 1 makes a solution obtained by adding a metal ion source dissolved in pure water to a surfactant that forms a lyotropic liquid crystal, and dilutes the solution with a water-soluble volatile organic solvent. After the diluted solution is applied to a substrate, the solvent is volatilized to form a lyotropic liquid crystal, and a metal is deposited around the formed lyotropic liquid crystal to remove the lyotropic liquid crystal. And a method for producing a mesoporous metal film.

  A solution of a surfactant that forms lyotropic liquid crystals with a metal ion source dissolved in pure water has a high viscosity. By diluting with a water-soluble volatile organic solvent, the mesoporous metal film is uniformly formed in a fine pattern. To be formed.

  The invention described in claim 2 is a mesostructure that is finally formed by selecting the metal ion concentration and the type and concentration of the surfactant that forms the lyotropic liquid crystal, and by adding an additive. Therefore, the mesoporous metal film can be uniformly formed in a constantly controlled state.

  In the invention described in claim 3, by using two or more kinds of metal ions in the solution, a mesoporous metal film made of an alloy suitable for the application can be uniformly formed in a constantly controlled state. It is a thing. Furthermore, by controlling the composition of the metal ion concentration contained in the solution, a desired alloy composition can be obtained.

  In the invention according to claim 4, by diluting with 25 wt% or more of the organic solvent with respect to the amount of the surfactant that forms the lyotropic liquid crystal, the viscosity can be controlled by the ratio of the diluting organic solvent. According to the state of the pattern, the state of the mesoporous metal film to be formed can be controlled.

  In the invention according to claim 5, since the method of depositing the metal is a method by electrolytic deposition, the deposition rate can be controlled by voltage or current when electrolytically depositing the metal film. A mesoporous metal film can be constantly and uniformly formed in a controlled state at a site.

  According to the present invention, a solution obtained by adding a metal ion source dissolved in pure water to a surfactant that forms a lyotropic liquid crystal is diluted with a water-soluble volatile organic solvent, whereby a mesoporous material is formed in a fine pattern region. There is an effect that the metal film can be formed constantly and uniformly in a controlled state.

  The method for producing a mesoporous metal film according to the present invention will be described in detail below.

  First, a surfactant that forms a highly concentrated lyotropic liquid crystal is added to a solution in which a metal ion source dissolved in pure water is added. As shown in FIG. 1, in such a liquid 1, the micelle 2 shown typically is formed, and a lyotropic liquid crystal is formed. In the micelle 2, the hydrophobic group is oriented inward and the hydrophilic group is oriented in the solution side.

  The metal ion source can be added as a metal salt that is soluble in a solvent. Examples thereof include platinum, gold, silver, copper, nickel, cobalt, and palladium, but are not limited thereto. As these salts, chlorides and sulfates such as nickel chloride and nickel sulfate can be used. Also, for example, by adding platinum and ruthenium ion sources to form a platinum ruthenium mesoporous metal film, by adding two or more metal ion sources at the same time, and further controlling the metal ion composition, An alloy mesoporous metal film can be manufactured.

  As the surfactant that forms the lyotropic liquid crystal phase, for example, nonionic surfactants, ionic surfactants including alkyltrimethylammonium halide, alkyltrimethylammonium bromide, and the like can be used. It is preferable to use a nonionic surfactant which is an amphiphilic polymer.

Examples of the nonionic surfactant include octaethylene glycol monohexadecyl ether, C ₁₆ EO ₈ , C ₁₆ EO ₄ , Brij 56 (C ₁₆ H ₃₃ (OCH ₂ CH ₂ ) _n OH, manufactured by Aldrich, n is 10 Brij 78 (C ₁₈ H ₃₇ (OCH ₂ CH ₂ ) _n OH, n is mainly 20), Brij 76 (C ₁₈ H ₃₇ (OCH ₂ CH ₂ ) _n OH, n is mainly 10 Or Brij58 (C ₁₆ H ₃₃ (OCH ₂ CH ₂ ) _n OH, n is mainly 20) (Brij is a registered trademark) or the like. _{Furthermore, L121 ((PEO) 5 -} (PPO) 68 - (PEO) 5), P123 ((PEO) 20 - (PPO) 69 - (PEO) 20), F127 ((PEO) 97 - (PPO) 68 - It can also be applied to a triblock polymer (PEO-PPO-PEO type) system such as (PEO) ₉₇ ). Thus, an amphiphilic block copolymer is advantageous, but not limited thereto.

  In general, when the surfactant concentration is 30 wt% or more, a liquid crystal state is formed, and depending on the surfactant concentration, or the temperature and the type / concentration of metal ions, various lamellar structures, 2D-hexagonal structures, cubic structures, etc. Takes mesostructure.

  A solution in which a surfactant that forms a high-concentration lyotropic liquid crystal is added to a solution in which a metal ion source dissolved in pure water is added has a high viscosity butter shape. Therefore, dilute the solution to reduce the viscosity. As the solvent, a solvent that is easily volatilized and has a relatively low viscosity (specifically, acetone, isopropanol, ethanol, etc.) is preferable. For example, when ethanol is used as the organic solvent, the mesostructure of the LLC liquid crystal is determined on the basis of the final LLC liquid crystal composition after the ethanol is completely volatilized. That is, a phase diagram of LLC liquid crystal (metal ion species / surfactant / water) that does not contain a diluting solvent can be used.

  FIG. 2 is a conceptual diagram of a process for forming a mesoporous metal film. FIG. 2A shows a substrate 10 coated with a liquid diluted with the above solvent called a precursor solution 11. Since the precursor solution 11 has a low viscosity, it can be uniformly applied to patterns such as fine grooves and holes by utilizing capillary action. In this state, the solution may be left at room temperature, but by controlling the temperature, the solvent can be volatilized and the mesostructure of the LLC liquid crystal can be controlled.

  By evaporating the solvent, an LLC liquid crystal as shown in FIG. 2B is formed. That is, the LLC liquid crystal 12 in which the micelles 2 are regularly arranged.

  Subsequently, by subjecting the LLC liquid crystal 12 to electrolysis, metal ions dissolved in the solution are deposited around the micelle 2. Finally, the micelle 2 is washed away with a solvent to form a mesoporous metal film 13 as shown in FIG. As the solvent, for example, a solvent that dissolves a surfactant such as pure water, ethanol, and acetone can be used.

  In the method according to the present invention, when preparing the LLC liquid crystal solution, the metal ion concentration was examined in the range of 0.1M-5M. As a result, the most regular meso at a metal ion concentration of 1.9M. A structure was obtained. The reason for this is that if the metal ion concentration is too high, the metal deposition rate will increase, making it difficult to deposit the metal to cover the mold. Conversely, if the metal ion concentration is too low, the metal deposition will be insufficient, It is considered that a mesostructure cannot be generated.

Next, the concentration of the surfactant was examined. For example, in the case of using 1.9M platinum solution and C ₁₆ EO ₈ as a surfactant, as a result of examination in a range of 0 wt% to 100 wt% at room temperature, a 2D-hexagonal structure of about 35-80 wt%, about A cubic structure was formed at 80-85 wt%, and a lamellar structure was formed at about 85-90 wt%. Therefore, the composition (metal ion species, surfactant, water) excluding the solvent of the precursor solution can be adjusted according to the target mesostructure in the final product.

As another simple method, when a surfactant having a very small head group (hydrophilic portion) such as C ₁₆ EO ₄ is used, a lamella structure is easily obtained in terms of packing parameters (structurally). Thus, the mesostructure of the LLC liquid crystal can also be defined by the structure of the surfactant.

Furthermore, the mesostructure can be controlled by additives. For example, in the case of Brij56 (C ₁₆ H ₃₃ (OCH ₂ CH ₂ ) _n OH, where n is mainly 10), an additive such as heptane, nonane, decane or the like is added, and the final meso is controlled by controlling the temperature. It is possible to control the form of the structure as 2D-hexagonal structure, lamella structure, solid phase, cubic structure, 3D-hexagonal structure. This is possible with other surfactants and additives, but is not limited thereto.

  Regarding the amount of the organic solvent to be diluted, when an easily volatile solvent such as ethanol is used, the viscosity of the precursor solution decreases as the amount of the solvent added to the precursor solution is increased. As the viscosity of the precursor solution decreases, it becomes possible to fill the LLC liquid crystal in fine locations. Specifically, it is desirable to add 25 wt% or more of an organic solvent to the surfactant. Specifically, in the case of a fine groove of about 100 μm, the solvent should be added in such an amount that the micelle of 30 wt% or more is dispersed with respect to the amount of the surfactant (concentration of critical micelle or less). Is desirable. This is because when the addition amount is 30 wt% or less, since the precursor solution has high viscosity, the capillary phenomenon does not function well and the LLC liquid crystal cannot be filled.

  Methods for depositing metal around micelles include electroless deposition in which a reducing agent is added, and electrodeposition similar to so-called electroplating in which an electric field is applied to cause current to flow to deposit metal. Either method can be applied, but electrodeposition has the advantage that the mesoporous structure can be controlled more precisely.

  The mesoporous structure formed by electrodeposition varies depending on the type of metal ion, but when the deposition rate of the metal is too high, it is difficult to deposit the metal while including the rod of the LLC liquid crystal, and a porous structure cannot be obtained. The appropriate potential varies depending on the metal species, but in the case of platinum, as a result of examination at +0.1 to −0.4 V (vs. SCE), +0.1 to −0.1 V (vs. SCE). ) Showed an excellent mesoporous structure. This is because, when carried out at a potential of −0.1 V (vs. SCE) or less, the deposition rate of platinum metal deposition becomes too fast, making it difficult to deposit the metal to cover the mold. Since this voltage varies depending on the type of metal ion, the voltage is not limited to this example.

  Similar to normal electroplating, the longer the electrodeposition time, the thicker the film thickness. When it is desired to obtain a thick film, ideally, an appropriate deposition potential of various metals may be used to increase the electrodeposition time. When it is desired to deposit a metal of a substance amount (mole) or more of metal ions contained in the formed LLC liquid crystal, after completion of the first electrodeposition, it is performed until the template is removed, and then the precursor solution is poured into a fine place again, Electrodeposition is performed after forming the LLC liquid crystal. Thereafter, the same method is repeated to adjust the thickness of the thin film. If the film thickness is about 100 nm, a single operation is sufficient.

Experimental example

The test results of this method will be described below. First, the fine solution is filled with the precursor solution. 0.42 g (7.1 × 10 ⁻⁴ mol) of nonionic surfactant C ₁₆ EO ₈ as LLC liquid crystal forming agent, 0.29 g (1.6 × 10 ⁻² mol) of pure water, and chloroplatinic acid as platinum ion species A precursor solution was prepared using 0.29 g (5.6 × 10 ⁻⁴ mol) of hexahydrate and 10 ml of ethanol as an organic solvent. This precursor solution was filled into a microchannel (fine groove: depth 100 μm, width 100 μm) 20 utilizing capillary action, and waited for ethanol to volatilize.

  In order to confirm the LLC liquid crystal filling, confirmation with an optical microscope was performed. As shown in FIG. 3 (a), after the first time, when the focus is changed from the surface of the substrate to the bottom of the channel, a focused portion is always observed along the inner wall. It is thought that the cross section is as shown on the right side of). After the second time, when observing the state of the LLC liquid crystal that is the electrodeposition bath from the horizontal direction, as shown in FIG. 3B, it was observed that the electrodeposition bath was raised with respect to the substrate. It was found that the channel was filled with the electrodeposition bath. From FIG. 3, it is considered that there is no bubble-like material in the channel, and after the ethanol is volatilized, the LLC liquid crystal is filled in the channel. From the above results, it is appropriate to pour the precursor solution at least twice for filling the LLC liquid crystal into the 100 μm microchannel 20.

  Subsequently, electrodes CE and RE as shown in the schematic diagram of FIG. 4 were provided between the substrate 10 side and the solution 11 side to perform electrodeposition. FIG. 5 shows a scanning electron microscope (SEM) photograph of the mesoporous metal formed in the groove 20 having a width of 100 μm. It can be confirmed that the metal is uniformly deposited in the microchannel. FIG. 6 shows a further enlarged SEM photograph. It can be seen from the photograph that a mesoporous structure is formed.

  The present invention is not limited to the embodiments described above, and modifications and substitutions easily made by those skilled in the art are within the scope of the present invention.

It is a figure which shows typically the formation of a micelle. It is a conceptual diagram of the process which forms a mesoporous metal film. It is a figure which shows the filling state of a precursor solution. It is a schematic diagram of electrode attachment. It is a SEM photograph of a mesoporous metal film formed in a fine groove. It is an enlarged SEM photograph of a mesoporous metal film.

Explanation of symbols

1 liquid 2 micelle 10 substrate 11 precursor solution 12 LLC liquid crystal 13 mesoporous metal film 20 microchannel

Claims (5)

After making a solution in which a metal ion source dissolved in pure water is added to a surfactant that forms a lyotropic liquid crystal, the solution is diluted with a water-soluble volatile organic solvent, and the diluted solution is applied to a substrate. A method for producing a mesoporous metal film, comprising: volatilizing the solvent to form a lyotropic liquid crystal, depositing a metal in the presence of the lyotropic liquid crystal, and removing the lyotropic liquid crystal. By selecting the metal ion concentration and the type / concentration of the surfactant that forms the lyotropic liquid crystal, and by adding additives, the mesostructure that is finally formed is changed to a lamellar structure or a 2D-hexagonal structure. The method for producing a mesoporous metal film according to claim 1, wherein the method is controlled to any one of cubic structures. The method for producing a mesoporous metal film according to claim 1, wherein a desired alloy composition is obtained by controlling the solution composition of two or more metal ions. 2. The method for producing a mesoporous metal film according to claim 1, wherein the organic solvent is diluted with 25 wt% or more of the organic solvent with respect to the amount of the surfactant that forms the lyotropic liquid crystal. 2. The method for producing a mesoporous metal film according to claim 1, wherein the metal is deposited by electrolytic deposition electrochemical deposition.