JPH04280802A - Production of metal oxide thin film - Google Patents

Abstract

PURPOSE:To obtain a multilayer porous metal oxide thin film having various kinds of shapes, and a structure controlled in the molecular level by a develop ing method modified in the kinds and the producing conditions on an amphiphatic compound used. CONSTITUTION:A compound having a fluorocarbon chain as a hydrophobic group and a polar group bound to both the molecular ends is used as an amphiphatic compound. A developing liquid is developed on a proper substrate and then dried to afford a composite film. The amphiphathic compound is extracted from the composite film to prepare the objective metal oxide thin film. The amphiphatic compound used in this invention does not promote hydrolysis of a metal alkoxide, because the compound can be prepared in the developing liquid prepared by using a non-aqueous solvent. As a result, various metal alkoxides can be as starting materials of the oxide thin film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multilayered, porous metal oxide thin film whose structure is controlled at the molecular level.

0002

[Prior Art] Metal oxide thin films formed by the sol-gel method are described in "Science of the Sol-Gel Method" (written by Masao Sakuhana, published by Agne Seifusha, 1988), pp. 85-153. Along with physical properties, manufacturing methods and usage forms are introduced. The metal alkoxide solution used is prepared by adding the desired metal oxide to a solvent such as alcohol, water, acid, or ammonia. When a metal oxide thin film is produced by the sol-gel method, cracks are likely to occur during thin film formation because the volume shrinks due to evaporation of the solvent and a crosslinking reaction due to the formation of methanoxane bonds (M-O-M). Furthermore, it is difficult to obtain a thin film with a uniform structure and thickness. Moreover, since it is highly hydrolyzable, precipitation may occur in the solution.

[0003] Furthermore, since a substrate and a supporting film are used, the substrate is required to have good adhesion between the coating film and the substrate and mechanical strength to withstand volume shrinkage during film formation. Restrictions are added to the material. Moreover, the thickness of the coating film is 10 to 20 μm when it is thick and 0.0 μm when it is thin.
The limit is about 1 μm. Such a thick film cannot be made into a thin film whose structure is controlled at the molecular level.

Metal oxide thin films produced by the sol-gel method are three-dimensionally crosslinked, so the pore diameter is 10 to 2.
The pore size is approximately 0.00 angstroms and has an amorphous pore structure. It is difficult to make the pore diameter larger than this, and therefore it is unsuitable as a carrier for catalysts and the like. Furthermore, the orientation of surface active groups cannot be controlled.

As described above, in the conventional sol-gel method, it is difficult to control the thickness, pore structure, orientation of surface active groups, etc. of a metal oxide thin film at the molecular level.

[0006] As a means to prevent these defects, in the synthesis of bulk bodies, a method of adding an organic solvent such as formamide, dimethylformamide, etc. as a drying control agent has been adopted in some cases. However, this method is limited to producing a bulk body, and it is considered impossible to produce a film-like thin film by the sol-gel method. For example, even if a drying control agent such as an organic solvent is added to prevent cracks in the thin film, if the developing solution is water, no matter what kind of hydrophilic organic solvent is used, the amount added will be There are limits. Therefore, it does not reach the point where it exhibits hardening as a drying control agent, and crack generation cannot be completely suppressed.

Therefore, in order to improve the conventional sol-gel method, a developing solution containing an amphiphilic compound having a polar group and a hydrophobic group added to both ends of the molecule and a metal alkoxide was prepared, and this developing solution was Patent Application No. 1999 discloses that a thin film containing an amphiphilic compound and a metal alkoxysilane substance as a thin film precursor can be prepared by removing the solvent from the composite film formed on the substrate after being developed on the substrate. -1314
Proposed in No. 78. The resulting thin film is a multilayered and porous film whose structure is controlled at the molecular level because the metal alkoxysilane substance is distributed using the amphiphilic compound molecular assembly as a template. It becomes a metal oxide thin film. It has also been introduced that the thin film can be modified by promoting hydrolytic polycondensation reactions such as M (OR)n and M (OH)n from the composite membrane from which the solvent has been removed.

[0008]

In this proposed method, an aqueous developing solution can be used since alkoxysilane has a lower hydrolyzability than other metal alkoxides. However, when a highly hydrolyzable metal alkoxide is used as a thin film precursor, precipitation is likely to occur during preparation of a developing solution. In this regard, the proposed method
It is considered difficult to manufacture metal oxide thin films other than polysiloxane films.

[0009] Furthermore, the molecular aggregates necessary to obtain a thin film whose structure is controlled at the molecular level are formed only in an aqueous solution, and not in a non-aqueous solvent. Therefore,
Metal alkoxides used as thin film precursors also have a fast hydrolysis rate and are extremely unstable, reacting to moisture in the air. Moreover, it is difficult to manufacture thin films incorporating Ti, Zr, Sn, etc., and there are restrictions on the types of thin films that can be obtained. Furthermore, since the hydrolytic polycondensation reaction of metal alkoxides proceeds easily in the presence of a large amount of water,
It is also difficult to control the degree of polycondensation.

The present invention was devised to solve these problems, and utilizes the aggregate state of amphiphilic compounds present in a solvent to produce a thin film whose structure is controlled at the molecular level. In this method, a developing solution containing an amphiphilic compound and a metal alkoxide as a thin film precursor is prepared in a non-aqueous solvent to prevent precipitation of the metal alkoxide during development preparation, and furthermore, development from the prepared developing solution is prevented. The purpose of this invention is to obtain a metal oxide thin film in which the occurrence of cracks is suppressed when the film is formed by a method.

[0011]

[Means for Solving the Problems] In order to achieve the object, the production method of the present invention uses a parent compound having a fluorocarbon chain, a group having no affinity for organic solvents, and a polar group added to both ends of the molecule. A developing solution containing a medium compound and a metal alkoxide is prepared using a non-aqueous solvent, and after the developing solution is developed on the surface of a substrate, the solvent is removed from the composite film formed on the substrate. .

A small amount of water can also be added to the developing solution in order to actively carry out the partial hydrolysis and polycondensation reaction of the metal alkoxide. Alternatively, the amphiphilic compound may be extracted after the composite membrane from which the solvent has been removed is subjected to a chemical treatment or thermal treatment that promotes the decomposition polycondensation reaction.

[0013] The amphiphilic compound used in the present invention is a compound having both a polar group and a hydrophobic group in the same molecule. Polar groups include sulfonate, sulfate, ammonium salt, polyamine salt, carboxylate, sulfonyl salt,
Polyols and combinations of these groups can be used, including phosphates, phosphonates, phosphonium salts, polyethers, alcohols, sulfonium salts, sugar residues, etc. On the other hand, as groups that have no affinity for organic solvents (hereinafter referred to as solvophobic groups), alkyl groups containing fluorocarbons, alkylaryl groups, alicyclic groups, fused polycyclic groups, and combinations of these groups can be used. can.

The amphiphilic compounds used in the present invention include fluoroalkylcarboxylic acids having 2 to 20 carbon atoms, perfluoroalkylcarboxylic acids having 7 to 13 carbon atoms, and N-propyl-N-(2-hydroxyethyl). Examples include fluorine-based surfactants such as perfluorooctane sulfonamide, and amphiphilic compounds that combine a fluorocarbon chain and a hydrocarbon chain with higher molecular orientation, as introduced in Japanese Patent Application No. 2-59019. be done. These amphiphilic compounds form an aggregated state not only in water but also in various solvents, and a thin film with regular orientation can be obtained by film formation by a spreading method.

[0015] The metal alkoxide which is the precursor of the metal oxide thin film is represented by the general formula M (OR)n. However, M represents a metal element, R represents an alkyl group, and n represents the oxidation number of the metal element M, respectively.

[0016] As the metal element M, Ti, Al, Zr,
Si, etc. are listed. Examples of alkoxides of these metal elements M include Ti(iso-OC3 H7)4, A
l(iso-OC3 H7)3, Zr(OCH3)4,
Si(OCH3)4,Si(OC4H9)4,Si(
OC2 H5)4, Ba(OC2 H5)2, etc. In addition to these metal alkoxides, Ge, B
, Li, Na, Fe, Ga, Mg, P, Sb, Sn, T
Metal alkoxides such as a, V, etc. are used. Regarding other metal alkoxides, any metal alkoxide that can be generally used in the sol-gel method can be used in the production method of the present invention.

Metal alkoxide M (OR)n undergoes hydrolysis to generate M (OH)n group, and M(OH)n
Mutual dehydration reaction or M (OH)n and M (OR)n
A polycondensation reaction is carried out by the dealcoholization reaction between
Crosslinking occurs due to the formation of methanoxane bonds M-O-M, and a thin film is formed.

The reaction at this time can be expressed as follows. Hydrolysis reaction: M (OR) n+xH2 O→M
(OH)x (OR)n-x+xROH Polycondensation reaction: (dehydration) -M-OH+H-O-M→-M-O-M
+H2O (Dealcoholization) -M-O
H+R-O-M→-M-O-M+ROH

R in the metal alkoxide M (OR)n needs to be hydrolyzed to produce an M (OH)n group. Specifically, methyl, ethyl, propyl, butyl,
Examples of R include acetoxy, acetylacenato, and the like. In addition to these normal alkoxides, there are also isomers such as secondary butoxide, tertiary butoxide, and isobutoxide.

The metal alkoxide M (OR)n can be used alone or in combination of two or more. Further, in order to form a metal oxide thin film, the metal alkoxide used as a precursor needs only to have at least one alkoxy group OR bonded to an M atom in one molecule. In particular, in the case of a combination of two or more metal alkoxides, it is possible to set their hydrolytic polycondensation reaction rates to be the same to form a uniform composite crosslinked product, or to reduce the crosslinking density to prevent changes in the thin film structure and residual M ( OH)n and M(O
It is also possible to use a metal alkoxide having a lower crosslinking property than the metal alkoxide described above for the purpose of sealing R)n.

[0021] Taking Si as an example of metal alkoxides with low crosslinking properties, there are the following.

[0022]

[Chemical formula 1]

However, R3 to R6 may be the same or different, and can be selected from the same groups as R. In addition, R includes methyl, ethyl, propyl, butyl, octyl, octadecyl, phenyl, naphthyl, fluoroalkyl, vinyl, allyl, γ-chloropropyl, γ-
Aminopropyl, N-(β-aminoethyl)-γ-aminopropyl, γ-mercaptopropyl, γ-glycidoxypropyl, γ-methacryloxypropyl, etc. can be selected.

[0024] Further, as R2, there are the following.

[Case 2]

Furthermore, there are no restrictions as to the other metal alkoxides, and metal alkoxides having all different alkoxide groups can be used as well.

Since the above-mentioned amphiphilic compound having a fluorocarbon chain as a solvophobic group forms an aggregated state, alcohols, ethers, ketones, esters, and halogenated alkanes, which are less polar than water, are used as a developing solution. nitrites, organic acids, organic bases, aromatic hydrocarbons,
Organic solvents such as saturated and unsaturated hydrocarbons can be used. At this time, when adjusting the amount of water added to the developing solution, taking into consideration the hydrolyzability of the metal alkoxide and the effect of the acidic catalyst of moisture taken in from the air and CO2 gas, the amount of water added to the developing solution is adjusted. It is possible to control the degree of As a result, it is possible to produce a thin film with a structure that is varied in porosity or layered structure depending on the purpose. Furthermore, a small amount of an acidic or basic substance may be added to promote hydrolysis of the M (OR)n group.

The substrate on which the developing solution is developed includes a glass plate,
There are quartz plates, fluoropores, graphite plates, silicon plates, Teflon plates, dense polymer films, porous polymer films, etc. The surface of the substrate may be subjected to hydrophilic treatment or hydrophobic treatment depending on the type of developing solution. For example, so that the developing solution is spread over a predetermined area on the substrate surface,
It is also effective to make part of the substrate surface hydrophilic and the remaining surface hydrophobic.

The solvent is removed from the developing solution spread on the substrate, and a composite thin film of the amphiphilic compound and metal alkoxide is formed. At this time, it is preferable to remove the solvent gradually, since the metal alkoxide exists according to the regularity of the molecular assembly of the amphiphilic compound, and in order to suppress partial hydrolysis due to moisture in the air. Further, by removing the solvent in a dry container such as a dry box, it is possible to further suppress partial hydrolysis of the metal alkoxide due to moisture in the air or CO2 gas.

Subsequently, chemical treatment or thermal treatment is performed to advance the hydrolytic polycondensation reaction of M (OR)n and M (OH)n groups. Chemical treatments include treatments using acidic substances and basic substances. For example, hydrochloric acid,
Treatments in which the composite thin film is directly immersed in liquids or solutions such as nitric acid, sulfuric acid, acetic acid, ammonia, amines, and sodium hydroxide, and treatments in which the composite thin film is exposed to vapors of these acidic or basic substances are effective. Another effective method is to heat-treat the composite thin film at several hundred degrees Celsius.

[0030] The composite thin film produced in this way is made into a metal oxide thin film whose structure is controlled at the molecular level by extracting and removing the amphipathic compound using an extractant selected depending on the type of amphiphilic compound. Become.

[0031]

[Function] The present inventors focused on amphiphilic compounds having fluorocarbon chains that form various molecular organizations even in non-aqueous organic solvents, and discovered that the regular molecular assemblies formed by these amphipathic compounds When applying the sol-gel method as a molecular template, it is possible to produce metal oxide thin films with structural control at the molecular level, even with metal alkoxides that are highly hydrolyzable and cause precipitation in aqueous solvents. Thought. Based on this consideration, as a result of intensive research, we have completed the present invention.

[0032] Amphiphilic compounds having a polar group and a solvophobic group having a fluorocarbon chain at both ends of the molecule are known to form molecular aggregates not only in water but also in organic solvents. The details are explained in Japanese Patent Application No. 2-59019 and will not be repeated here, but the amphiphiles have a solvophobic group that is a combination of a highly hydrophobic fluorocarbon chain and a hydrocarbon chain with a higher molecular orientation. A thin film with regular orientation at the molecular level can be obtained by dissolving or dispersing the compound in an organic solvent and spreading it on a suitable substrate.

On the other hand, amphiphilic compounds with only hydrocarbon chains without fluorocarbon chains in their solvophobic groups form molecular aggregates when dispersed in water, but when dispersed in organic solvents, they form molecular aggregates. is difficult to form. Since this matter is explained in detail in Japanese Patent Application No. 1-58889, it will be omitted here.

[0034] By adding a highly hydrolyzable metal alkoxide to a developing solution in which an amphiphilic compound having a fluorocarbon chain is dissolved or dispersed in an organic solvent, an amphiphilic compound forms a molecule with regular orientation. Using the aggregate as a template, the metal alkoxide is fixed in the developing solution. Furthermore, if a metal alkoxide that has undergone a partial hydrolytic polycondensation reaction by adding a small amount of water is added to the developing solution, or a developing solution is prepared by dispersing a small amount of water in the developing solution, the metal alkoxide is immobilized by proceeding with a hydrolytic polycondensation reaction using a molecular assembly of amphiphilic compounds as a template, forming a certain degree of crosslinking. These methods differ in the preparation method depending on the type of amphiphilic compound or metal alkoxide and the amount added. Therefore,
By selecting appropriate conditions, it is possible to change the speed of the hydrolytic polycondensation reaction of the metal alkoxide and control the structural form of the thin film at the molecular level.

Moreover, since the developing solution is prepared using an organic solvent, it is of course possible to use a developing solution that immediately precipitates when added to water.
Metal alkoxides that readily form precipitates even in air can be easily added to the developing solution. Furthermore, the organic solvent itself acts as a drying control agent and suppresses the occurrence of cracks and the like due to volume shrinkage associated with crosslinking reactions, which is generally a problem in the sol-gel method.

[0036]

[Examples] The present invention will be specifically explained below with reference to Examples. In addition, the amphipathic compound used in this example is
These are compounds represented by the following formulas 1 to 3.

[Chemical formula 3]

Example 1: After dissolving 100 mM of amphiphilic compound 1 in an organic solvent of ethylene glycol monomethyl ether, metal alkoxide Ti(O-isoC3H7)4 was added in a molar amount 5 times that of amphiphilic compound 1. The mixture was added and dispersed to prepare a developing solution. This developing solution was dropped onto a glass plate surrounded by a Teflon film frame (hereinafter simply referred to as a glass plate), and left in a dry box kept at room temperature with a humidity of 5% or less for 2 days to develop. A composite membrane was obtained by evaporating the organic solvent of the liquid. Thereafter, the composite membrane was placed in a closed container filled with ammonia vapor, left to stand at room temperature for one week, and amphipathic compound 1 was further extracted with chloroform. As a result, a white film-like titanium oxide thin film without cracks was produced. When the obtained thin film was observed using a scanning electron microscope (SEM), its fine structure was found to be multilayered.

Example 2: 1/10 part by weight of LiOC2 H5 was added to metal alkoxide Si(OCH3)4, and the liquid was heated to 100% by weight.
A developing solution was prepared by dispersing amphiphilic compound 2 (mM) in hexafluorobenzene at a ratio of 5 times the molar amount in terms of Si. This developing solution was developed in the same manner as in Example 1 to evaporate the solvent, treated with ammonia, and then extracted amphipathic compound 2 with chloroform. As a result, a uniform white film-like thin film without cracks was produced. When this thin film was observed by SEM, it had a network structure.

Example 3: Ba(OC4 H9)2, Y (OC4 H9)3 and Cu(OCH3)2 were prepared in a molar ratio of Ba:Y:Cu of 2.
: Weigh and mix so that the ratio is 1:3.
A developing solution was prepared by adding 5 times the molar amount of amphiphilic compound 3 at 0 mM to a mixed solvent of triethanolamine and perfluorohexane at a volume ratio of 1:4. Then, in the same manner as in Example 1, this developing solution was developed, the solvent was evaporated, and ammonia treatment was performed. Furthermore, heat treatment was performed at 900° C. in an air atmosphere, and then amphipathic compound 3 was completely extracted with chloroform to prepare a thin film. This thin film was white and transparent, and when observed by SEM, it had a multilayer film-like fine structure.

Example 4: An alkoxysilane solution was prepared in advance by adding 3 times the molar amount of water to metal alkoxide CH3Si(OCH3)3 and dispersing it, and 100mM of amphiphilic compound 2 was dissolved therein. A developing solution was prepared by adding 5 times, 10 times, 20 times, and 50 times the molar amount in terms of Si to the alkoxysilane solution to the hexafluorobenzene solution obtained. Each of these developing solutions was dropped onto a glass substrate and left to stand at room temperature for 3 days to evaporate the solvent in the developing solution to obtain a composite film. Thereafter, the composite membrane was inserted into a closed container filled with ammonia gas, and after being left at room temperature for one week, amphipathic compound 2 was extracted with chloroform to prepare a thin film. All of the obtained thin films were porous or multilayered, and had a white film shape without cracks.

Furthermore, metal alkoxide CH3Si(
A developing solution prepared without adding water to OCH3)3 was developed and processed in the same manner. In this case, regardless of the difference in the amount of alkoxysilane added, it became a white fine powder and no thin film was formed.

Table 1 shows the morphological characteristics of the silicon oxide thin film obtained. In addition, 10 times the molar amount of CH3Si (OCH
3) Figure 1 shows an SEM photograph of a thin film obtained from a developing solution containing 3.
SEM of a thin film obtained from a developing solution containing H3)3
The photograph is shown in Figure 2, which also shows 50 times the molar amount of CH3Si(O
SE of thin film obtained from developing solution containing CH3)3
A photograph of M is shown in Figure 3.

[0043]

[Table 1]

As is clear from Examples 1 to 4, by using various metal alkoxides as precursors and changing the type of amphiphilic compound used and manufacturing conditions, metal oxide thin films with various microstructures can be produced. Created. The resulting thin film has a variety of microstructures that are controlled at the molecular level by adjusting the type of amphiphilic compound and manufacturing conditions. Therefore, it has become possible to manufacture thin films that have functions tailored to their purposes. Thin films with predetermined pores and layered structures at the molecular level can be used, for example, as optical materials, permeable membranes for substance separation and adsorption, catalyst carriers, biochemical carriers for immobilized enzymes, combustion catalyst carriers, and optical It can be used for various purposes as a material for electrochemical membranes, ionic conductors, electronic conductors, superconductors, etc.

Example 5: After dissolving 100 mM of the fluorine-based surfactant disodium N-perfluorooctanesulfonylglutamate in an organic solvent of perfluorohexane, metal alkoxide Ti was added in an amount 10 times the molar amount of the surfactant. (O-is
oC4H9)4 was added and dispersed to prepare a developing solution. This developing solution was developed under the same conditions as in Example 1,
The solvent was evaporated, ammonia treated and the surfactant extracted with THF. As a result, a white film-like thin film was produced. When this thin film was observed with SEM,
It had a multilayered structure.

Comparative Example 1: An amphipathic compound of the following formula was used as an amphipathic compound.

[C4]

When this amphiphilic compound was dispersed in various organic solvents, it did not form a molecular assembly, and even when developed in the same manner as in Example 1, it showed molecular orientation and self-supporting properties. A film-like thin film was not produced, but only a powder-like product was obtained.

Further, 100 mM of the above amphiphilic compound was dispersed in water, and metal alkoxide Ti(O-isoC3 H7)4 was added in an amount 5 times the molar amount of the amphiphilic compound. At this time, metal alkoxide Ti (O-iso
Immediately after the addition of C3H7)4, a white precipitate was generated, making it impossible to prepare a developing solution.

[0049]

Effects of the Invention As explained above, in the present invention, by utilizing the characteristics of amphiphilic compounds that form molecular aggregates even in organic solvents, when a developing solution is developed on a substrate, the amphiphilic compounds A thin film of a metal oxide is produced from a metal alkoxide precursor using a molecular organization with regular molecular orientation formed from a metal alkoxide as a template. When this method is used, even if the alkoxide is highly hydrolyzable, the orientation is high and the structure can be controlled at the molecular level, resulting in a crack-free thin film. The thin films obtained in this way are used as highly functional substance separation membranes, various carriers, conductive films, etc. by taking advantage of their structural characteristics.

[Brief explanation of the drawing]

[Figure 1] 1 for 2 amphiphilic compounds containing water
SEM photograph of a thin film obtained from a developing solution containing 0 times the molar amount of CH3Si(OCH3)3

Claims (3)

[Claims] Claim 1: A developing solution containing a metal alkoxide and an amphiphilic compound having a fluorocarbon chain and a group having no affinity for organic solvents and a polar group added to both ends of the molecule is prepared in a non-aqueous solvent. A method for producing a metal oxide thin film, which comprises: after developing the developing solution on the substrate surface, removing the solvent from the liquid film formed on the substrate. 2. A method for producing a metal oxide thin film, wherein the developing solution according to claim 1 contains water as one component. 3. A method of extracting the amphipathic compound after subjecting the composite membrane according to claim 1 to a chemical treatment or thermal treatment for promoting a decomposition polycondensation reaction after removing the solvent. A method for producing a metal oxide thin film.