Method for producing anatase-type titanium oxide film

Abstract

To provide a method for producing an anatase-type titanium oxide film with high orientation by a solvothermal process.SOLUTION: A method for producing an anatase-type titanium oxide film comprises preparing a titanium-containing liquid containing water, an alcohol, a diketone, an acid, a titanium alkoxide and a fluorine atom-containing titanium compound, and immersing a substrate in the titanium-containing liquid to form an anatase-type titanium oxide film on the substrate by a solvothermal process.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing anatase titanium oxide film.

Background Art

[0002] Titanium oxide has continued to attract attention in various technical fields such as photocatalysts and n-type semiconductors. For example, in photocatalysts, anatase titanium oxide is known to exhibit higher activity than rutile titanium oxide. Since the required properties of titanium oxide vary depending on each application, methods for manufacturing titanium oxide suitable for the intended application have been studied.

[0003] Since anatase titanium oxide irreversibly changes to rutile titanium oxide at high temperatures, most of the single crystals of anatase titanium oxide are manufactured using epitaxial growth. For example, Patent Document 1 below discloses a method for producing a single crystal thin film of titanium dioxide having an anatase crystal structure on a single crystal substrate by a laser ablation film formation method.

[0004] Titanium oxide may be manufactured using a liquid phase method such as a hydrothermal synthesis method. The hydrothermal synthesis method is a substance synthesis method classified as a solvothermal method. For example, Patent Document 2 below discloses a method for synthesizing anatase titanium oxide particles. The method for synthesizing titanium oxide particles disclosed in Patent Document 2 below includes a step of reacting a titanium alkoxide with a hydroxyl group-containing amine to obtain a titanium oxide source, and a step of adding an organic acid amine salt obtained by reacting an organic acid having 8 or more carbon atoms with an amine in an aqueous solution in which the obtained titanium oxide source is dissolved, and performing hydrothermal synthesis.

[0005] The hydrothermal synthesis method is also used for manufacturing a composite titanium oxide film. For example, Patent Document 3 below discloses a method for forming a composite titanium oxide film on a substrate by a hydrothermal synthesis method. In Patent Document 3 below, the composite titanium oxide film is selectively formed only on the patterned Ti metal.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2002-030417 Patent Document 2 Japanese Patent Application Laid-Open No. 2015-059053 Patent Document 3 Japanese Patent Application Laid-Open No. 10-182154 Summary of the Invention Problems to be Solved by the Invention

[0007] Vapor-phase methods such as laser ablation have problems such as high manufacturing costs and high technical level requirements. For example, vapor-phase methods require expensive film-forming equipment. Not only is the film-forming equipment expensive, but also a high level of understanding and skills are required for handling the film-forming equipment. In addition to the above problems, vapor-phase methods are not suitable for manufacturing a large-area and uniform titanium oxide film.

[0008] Liquid-phase methods such as the solvothermal method may be able to solve the problems of the above-mentioned vapor-phase methods. However, the application of the conventional solvothermal method to the production of titanium oxide films cannot sufficiently grow anatase-type titanium oxide films having high orientation.

[0009] An object of an embodiment of the present disclosure is to provide a method for manufacturing an anatase-type titanium oxide film having high orientation by a solvothermal method. Means for Solving the Problems

[0010] The present disclosure includes the following aspects. <1> Preparing a titanium-containing liquid including water, alcohol, diketone, acid, titanium alkoxide, and a fluorine atom-containing titanium compound, and dipping a substrate into the titanium-containing liquid to form an anatase-type titanium oxide film on the substrate by a solvothermal method. A method for manufacturing an anatase-type titanium oxide film. <2> The preparation of the titanium-containing liquid includes preparing a mixture containing the water, the alcohol, the diketone, and the acid, and mixing the mixture with the titanium alkoxide and the fluorine atom-containing titanium compound. The method for producing an anatase-type titanium oxide film according to <1>. <3> The method for producing an anatase-type titanium oxide film according to <1> or <2>, wherein the alcohol contains ethanol. <4> The method for producing an anatase-type titanium oxide film according to any one of <1> to <3>, wherein the diketone contains β-diketone. <5> The method for producing an anatase-type titanium oxide film according to any one of <1> to <3>, wherein the diketone contains acetylacetone. <6> The method for producing an anatase-type titanium oxide film according to any one of <1> to <5>, wherein the acid contains hydrogen halide. <7> The method for producing an anatase-type titanium oxide film according to any one of <1> to <5>, wherein the acid contains hydrogen chloride. <8> The method for producing an anatase-type titanium oxide film according to any one of <1> to <7>, wherein the number of carbon atoms of the alkoxy group in the titanium alkoxide is from 1 to 8. <9> The method for producing an anatase-type titanium oxide film according to any one of <1> to <8>, wherein the titanium alkoxide contains titanium tetraisopropoxide. <10> The fluorine atom-containing titanium compound contains a salt containing TiF6 2- The method for producing an anatase-type titanium oxide film according to any one of <1> to <9>. <11> The method for producing an anatase-type titanium oxide film according to any one of <1> to <9>, wherein the fluorine atom-containing titanium compound contains ammonium hexafluorotitanate. <12> The method for producing an anatase-type titanium oxide film according to any one of <1> to <11>, wherein the substrate is a LaAlO3 substrate or a SrTiO3 substrate. <13> The manufacturing method of the anatase titanium oxide film according to any one of <1> to <12>, wherein the heating temperature in the solvothermal method is 110°C to 170°C.

Advantages of the Invention

[0011] According to one embodiment of the present disclosure, a method for manufacturing an anatase titanium oxide film having high orientation by a solvothermal method is provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments. The following embodiments may be appropriately changed within the scope of the object of the present disclosure.

[0014] In the present disclosure, a numerical range represented by "~" means a range including the numerical values described before and after "~" as a lower limit value and an upper limit value.

[0015] In the numerical ranges described step by step in the present disclosure, the upper limit value described in a certain numerical range may be replaced with the upper limit value of the numerical range described in other step-by-step descriptions, and the lower limit value described in a certain numerical range may be replaced with the lower limit value of the numerical range described in other step-by-step descriptions. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0016] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps when the intended purpose is achieved.

[0017] In the present disclosure, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition means the total amount of the plurality of substances present in the composition.

[0018] In the present disclosure, a combination of preferred embodiments is a more preferred embodiment.

[0019] <Method for producing anatase-type titanium oxide film> Hereinafter, a method for producing anatase-type titanium oxide film according to the present disclosure will be described. In one embodiment of the present disclosure, the method for producing anatase-type titanium oxide film includes the following (1) to (2). (1) Preparing a titanium-containing liquid containing water, alcohol, diketone, acid, titanium alkoxide, and a fluorine atom-containing titanium compound (hereinafter sometimes referred to as "step (1)"). (2) Immersing a substrate in the titanium-containing liquid and forming an anatase-type titanium oxide film on the substrate by a solvothermal method (hereinafter sometimes referred to as "step (2)").

[0020] The above-described embodiments provide a method for producing anatase-type titanium oxide films having high orientation by the solvothermal method. It is presumed that the reason for obtaining the titanium oxide films as described above is that the titanium-containing solution constructs an environment suitable for the growth of anatase-type titanium oxide films having high orientation. For example, an acid serves as a catalyst for the dehydration condensation reaction of reaction intermediates (e.g., hydrolysis products of titanium alkoxides) in step (2) by adjusting the acidity of the titanium-containing solution. For example, diketones can form titanium-diketone complexes in the titanium-containing solution. The formation of titanium-diketone complexes can maintain the titanium concentration in the solution without increasing the amount of acid. Therefore, the use of diketones and acids can achieve the titanium concentration necessary for the growth of the target anatase-type titanium oxide films in the titanium-containing solution while preventing or reducing the dissolution of the substrate caused by the acid, as compared with the case of using only an acid without using both diketones and acids. Furthermore, the use of a fluorine atom-containing titanium compound contributes to the preferential growth of anatase-type titanium oxide films having high orientation. Although the detailed mechanism is not clear, it is considered that the action of fluorine atoms in the fluorine atom-containing titanium compound affects the crystal structure and orientation of the titanium oxide film. Therefore, anatase-type titanium oxide films having high orientation are formed.

[0021] [Step (1)] Step (1) is to prepare a titanium-containing solution containing water, alcohol, diketone, acid, titanium alkoxide, and a fluorine atom-containing titanium compound. Step (1) may include producing the titanium-containing solution.

[0022] Water mainly serves as a solvent. Furthermore, water is involved in the hydrolysis of titanium alkoxide in step (2).

[0023] Examples of the water include purified water. Examples of the method for producing purified water include filtration, distillation, and ion exchange.

[0024] The proportion of water in the titanium-containing liquid is preferably 5% to 45% by volume, more preferably 15% to 25% by volume on a volume basis. The "proportion of water in the titanium-containing liquid" means the proportion of the total amount of water in the titanium-containing liquid to the total amount of the titanium-containing liquid.

[0025] Alcohol mainly serves as a solvent. Furthermore, alcohol can contribute to the promotion of the hydrolysis of titanium alkoxide in step (2). The promotion of the hydrolysis of titanium alkoxide is considered to be due to the substitution of at least one alkoxy group in the titanium alkoxide by an alkoxy group derived from alcohol.

[0026] Examples of alcohol include aliphatic alcohols and aromatic alcohols. The aliphatic alcohol may be a saturated aliphatic alcohol or an unsaturated aliphatic alcohol. Examples of the aliphatic alcohol include methanol, ethanol, 1-propanol, 2-propanol (alias: isopropanol), 2-methyl-1-propanol (alias: isobutyl alcohol), 2-methyl-2-propanol (alias: tert-butyl alcohol), 1-butanol, and 2-butanol. Examples of the aromatic alcohol include benzyl alcohol. From the viewpoints of solubility, miscibility, and the promotion of the hydrolysis of titanium alkoxide in step (2), alcohol preferably contains an aliphatic alcohol, preferably contains at least one selected from the group consisting of ethanol and 2-propanol, and more preferably contains ethanol.

[0027] From the viewpoints of solubility, miscibility, and the promotion of the hydrolysis of titanium alkoxide in step (2), the number of carbon atoms of the alcohol is preferably 1 to 8, more preferably 1 to 6, and still more preferably 2 to 4.

[0028] The titanium-containing liquid may contain one or more alcohols.

[0029] From the viewpoints of solubility, miscibility, and acceleration of hydrolysis of titanium alkoxide in step (2), the proportion of alcohol in the titanium-containing liquid is preferably 5 to 45% by volume, more preferably 15 to 25% by volume on a volume basis. The "proportion of alcohol in the titanium-containing liquid" means the proportion of the total amount of alcohol in the titanium-containing liquid to the total amount of the titanium-containing liquid.

[0030] From the viewpoints of solubility and control of hydrolysis rate, the ratio of the alcohol content to the titanium alkoxide content in the titanium-containing liquid is preferably 10 to 50, more preferably 15 to 30 on a volume basis.

[0031] The diketone mainly plays a role of forming a titanium-diketone complex in the titanium-containing liquid to maintain the titanium concentration necessary for the growth of the target anatase-type titanium oxide film. The diketone also serves as a solvent.

[0032] Examples of the diketone include β-diketone and γ-diketone. Examples of the β-diketone include acetylacetone (alias: 2,4-pentanedione) and methylacetylacetone (alias: 3-methyl-2,4-pentanedione). Examples of the γ-diketone include 2,5-hexanedione.

[0033] At least one carbonyl group (-CO-) contained in the diketone may be part of an ester bond (-COO-). For example, the term "diketone" in the present disclosure includes β-ketoester. Examples of the β-ketoester include methyl acetoacetate, ethyl acetoacetate, and tert-butyl acetoacetate.

[0034] From the viewpoint of the formability of the titanium-diketone complex, the diketone preferably contains β-diketone, more preferably contains at least one selected from the group consisting of acetylacetone and ethyl acetoacetate, and still more preferably contains acetylacetone.

[0035] From the viewpoint of the formation of the titanium-diketone complex, the number of carbon atoms of the diketone is preferably from 5 to 10, more preferably from 5 to 8, and still more preferably from 5 to 6.

[0036] The titanium-containing liquid may contain one or more diketones.

[0037] From the viewpoint of preventing or reducing the dissolution of the substrate due to the acid and maintaining the titanium concentration necessary for the growth of the target anatase-type titanium oxide film in the titanium-containing liquid, the ratio of the diketone in the titanium-containing liquid is preferably from 15% to 50% by volume, and more preferably from 35% to 50% by volume, based on volume. The "ratio of the diketone in the titanium-containing liquid" means the ratio of the total amount of the diketone in the titanium-containing liquid to the total amount of the titanium-containing liquid.

[0038] From the viewpoint of the formation of the titanium-diketone complex, the ratio of the content of the diketone to the content of the titanium alkoxide in the titanium-containing liquid is preferably from 3 to 200, and more preferably from 6 to 100, on a molar basis.

[0039] The acid mainly serves as a catalyst for the dehydration condensation reaction of the reaction intermediate (for example, the hydrolyzate of the titanium alkoxide) in step (2) by adjusting the acidity of the titanium-containing liquid.

[0040] Examples of the acid include phosphoric acid (H3PO4), nitric acid (HNO3), sulfuric acid (H2SO4), acetic acid (CH3COOH), and hydrogen halide. Examples of the hydrogen halide include hydrogen chloride and hydrogen bromide. In the production of the titanium-containing liquid, the hydrogen halide is preferably added as an aqueous solution of the hydrogen halide. For example, an aqueous solution of hydrogen chloride is called hydrochloric acid. From the viewpoint of efficient growth of the highly oriented film, the acid preferably contains a hydrogen halide, and more preferably contains hydrogen chloride.

[0041] The titanium-containing liquid may contain one or more acids.

[0042] From the perspective of promoting the dehydration condensation reaction of the reaction intermediate in step (2) while preventing or reducing the dissolution of the substrate caused by the acid, the pH of the titanium-containing liquid at 25 °C is preferably 2 to 4, and more preferably 2 to 2.5. The pH of the titanium-containing liquid is measured with a commercially available pH test paper using the titanium-containing liquid at 25 °C. Examples of commercially available pH test papers include "Stick pH Test Paper pH0 - 14.0 (MACHEREY-NAGEL)".

[0043] The titanium alkoxide serves as a titanium oxide source. The titanium alkoxide forms titanium oxide through hydrolysis and dehydration condensation in step (2).

[0044] Examples of the titanium alkoxide include titanium tetramethoxide, titanium tetraethoxide, titanium tetraisopropoxide, titanium tetra-n-butoxide, and titanium tetra-tert-butoxide. From the perspective of the hydrolyzability of the titanium alkoxide in step (2), the titanium alkoxide preferably contains titanium tetraisopropoxide.

[0045] From the perspective of the hydrolyzability of the titanium alkoxide in step (2), the number of carbon atoms of the alkoxy group in the titanium alkoxide is preferably 1 to 8, more preferably 2 to 8, and even more preferably 2 to 6. When the titanium alkoxide contains a plurality of alkoxy groups, "the number of carbon atoms of the alkoxy group" refers to "the number of carbon atoms of each alkoxy group".

[0046] The titanium-containing liquid may contain one or more titanium alkoxides.

[0047] From the perspective of promoting the growth of the titanium oxide film in step (2), the ratio of the titanium alkoxide in the titanium-containing liquid is preferably 1.5% to 5% by volume, more preferably 1.5% to 3% by volume based on volume. The "ratio of the titanium alkoxide in the titanium-containing liquid" means the ratio of the total amount of the titanium alkoxide in the titanium-containing liquid to the total amount of the titanium-containing liquid.

[0048] From the perspective of producing an anatase-type titanium oxide film having a sufficient film thickness, the ratio of the content of the titanium alkoxide to the content of the fluorine-containing titanium compound in the titanium-containing liquid is preferably 2 / 3 to 2, more preferably 1 to 2 based on volume.

[0049] The fluorine atom-containing titanium compound mainly plays a role in contributing to the preferential growth of the anatase-type titanium oxide film having a high orientation.

[0050] Examples of the fluorine atom-containing titanium compound include salts containing TiF6 2- . Examples of the counter ion of TiF6 2- include metal ions and ammonium ions. Examples of the salts containing TiF6 2- include sodium hexafluorotitanate (Na2TiF6), potassium hexafluorotitanate (K2TiF6), and ammonium hexafluorotitanate ((NH4)2TiF6). From the perspective of the preferential growth of the anatase-type titanium oxide film having a high orientation, the fluorine atom-containing titanium compound preferably contains a salt containing TiF6 2- and more preferably contains ammonium hexafluorotitanate.

[0051] The titanium-containing liquid may contain one or more fluorine atom-containing titanium compounds.

[0052] From the perspective of the preferential growth of anatase-type titanium oxide films having high orientation, the ratio of the titanium compound containing fluorine atoms in the titanium-containing liquid is preferably 0.8% to 3.5% by volume, more preferably 1% to 2% by volume, based on volume. The "ratio of the titanium compound containing fluorine atoms in the titanium-containing liquid" means the ratio of the total amount of the titanium compound containing fluorine atoms in the titanium-containing liquid to the total amount of the titanium-containing liquid.

[0053] From the perspective of the preferential growth of anatase-type titanium oxide films having high orientation, the ratio of the content of the titanium compound containing fluorine atoms to the content of titanium alkoxide in the titanium-containing liquid is preferably 0.5 to 1.5, more preferably 0.5 to 1, based on volume.

[0054] The titanium-containing liquid may contain other components as long as it does not deviate from the gist of the present disclosure. Examples of other components include nitrates and other metal alkoxides.

[0055] As long as a titanium-containing liquid capable of producing the target titanium oxide film can be obtained, the production method of the titanium-containing liquid is not limited. For example, the titanium-containing liquid is produced by mixing water, alcohol, diketone, acid, titanium alkoxide, and a titanium compound containing fluorine atoms. The mixing method may be selected from known mixing methods. The addition of each raw material may be carried out at once or in several portions.

[0056] Step (1), that is, preparing the titanium-containing liquid preferably includes the following (1) to (2). (1) Preparing a mixture containing water, alcohol, diketone, and acid (hereinafter sometimes referred to as "mixture (A)"). (2) Mixing mixture (A) with titanium alkoxide and a titanium compound containing fluorine atoms.

[0057] For example, the mixture (A) is produced by mixing water, alcohol, diketone, and an acid. The mixing method may be selected from known mixing methods. The addition of each raw material may be carried out all at once or in several portions. The diketone and the acid are preferably added to a mixture containing water and alcohol. Further, the addition of the acid is preferably carried out after the addition of the diketone.

[0058] The method of mixing the mixture (A), titanium alkoxide, and a titanium compound containing a fluorine atom may be selected from known mixing methods. From the viewpoint of the uniformity of the liquid, the mixing time is preferably 5 to 10 hours. The addition of each raw material may be carried out all at once or in several portions. The titanium alkoxide and the titanium compound containing a fluorine atom are preferably added to the mixture (A). Further, the addition of the titanium compound containing a fluorine atom is preferably carried out after the addition of the titanium alkoxide.

[0059] [Step (2)] Step (2) is to dip a substrate into a titanium-containing solution and form anatase-type titanium oxide film on the substrate by the sol-gel thermal method.

[0060] Examples of the substrate include LaAlO3 substrate and SrTiO3 substrate. From the viewpoint of the orientation of the titanium oxide film, the substrate is preferably a LaAlO3 substrate or a SrTiO3 substrate, more preferably a LaAlO3 substrate, and even more preferably a (001)-plane-oriented LaAlO3 substrate. The surface of the substrate (preferably the surface on which the titanium oxide film is formed) may be mirror-finished.

[0061] Examples of the reaction apparatus for accommodating the titanium-containing liquid and the substrate include heat-resistant and pressure-resistant containers. Examples of the heat-resistant and pressure-resistant containers include autoclaves. The autoclave may be a known autoclave. The heat-resistant and pressure-resistant container may accommodate a crucible. For example, the crucible disposed in the heat-resistant and pressure-resistant container is used as a container for accommodating the titanium-containing liquid and the substrate. Examples of the component of the crucible include fluororesins. Examples of the fluororesin include polytetrafluoroethylene.

[0062] As long as the target titanium oxide film can be obtained, the conditions of the solvothermal method (for example, heating temperature and heating time) are not limited. From the viewpoint of the growth of the target titanium oxide film, the heating temperature in the solvothermal method is preferably 110°C to 170°C, more preferably 120°C to 160°C. From the viewpoint of the growth of the target titanium oxide film, the heating time in the solvothermal method is preferably 15 hours or more, more preferably 20 hours or more. The upper limit of the heating time may be 48 hours or 30 hours. The heating time may be determined in consideration of the thickness of the titanium oxide film.

[0063] The anatase-type titanium oxide film formed by the solvothermal method may be washed. Examples of the solvent used for washing include alcohol and water.

[0064] The anatase-type titanium oxide film formed by the solvothermal method may be dried. Examples of the drying method include heat drying.

[0065] The thickness of the anatase-type titanium oxide film is not limited. The thickness of the anatase-type titanium oxide film may be determined in consideration of the application. The thickness of the anatase-type titanium oxide film may be 0.2 μm to 3 μm.

[0066] In the X-ray diffraction pattern of the anatase-type titanium oxide film, the ratio of the peak intensity derived from the (211) plane of rutile-type titanium oxide to the peak intensity derived from the (004) plane of anatase-type titanium oxide is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. Further, the above ratio is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. The above ratio may be 0%.

[0067] Examples of the use of the anatase-type titanium oxide film include photocatalysts and n-type semiconductors.

Example

[0068] Hereinafter, the present disclosure will be described in detail by way of examples. However, the present disclosure is not limited to the following examples. The matters shown in the following examples may be appropriately changed without departing from the spirit of the present disclosure.

[0069] <Example 1> [Manufacture of Titanium Oxide Film] A titanium oxide film was manufactured according to the following procedure. (1) 14.5 mL of purified water and 15 mL of ethanol were mixed and stirred for 5 minutes. (2) 30 mL of acetylacetone was added to the mixture obtained in (1) above, and then the resulting mixture was stirred for 5 minutes. (3) 51 μL of 12 mol / L hydrochloric acid was added to the mixture obtained in (2) above, and then the resulting mixture was stirred for 5 minutes. (4) 1 mL of titanium tetraisopropoxide was added to the mixture obtained in (3) above in 5 portions of 200 μm each. When the resulting mixture was stirred for 5 minutes, a yellow transparent liquid was obtained. (5) 1 mL of a 1 mol / L aqueous solution of ammonium hexafluorotitanate was added to the yellow transparent liquid obtained in (4) above. The resulting mixture was stirred for 10 hours to obtain a titanium-containing liquid. The pH of the titanium-containing liquid at 25 °C was in the range of 2 to 2.5. (6) Two one-side mirror-finished LaAlO3 (001) substrates were prepared. Each LaAlO3 substrate was ultrasonically cleaned using each solvent in the order of acetone, ethanol, and purified water. The cleaning time for each solvent was 15 minutes. The liquid adhering to the mirror-finished surface of the LaAlO3 substrate was removed with a blower, and the liquid adhering to the non-mirror-finished surface of the LaAlO3 substrate was wiped off. (7) The titanium-containing liquid obtained in (5) above was poured into a Teflon (registered trademark) crucible having a capacity of 100 mL, and then the two cleaned LaAlO3 substrates were immersed in the titanium-containing liquid. Regarding the arrangement of each LaAlO3 substrate, each LaAlO3 substrate was leaned against the inner wall surface of the Teflon (registered trademark) crucible, and the mirror-finished surface of each LaAlO3 substrate was directed toward the bottom of the Teflon (registered trademark) crucible. When the mirror-finished surface of each LaAlO3 substrate is directed toward the bottom of the Teflon (registered trademark) crucible, it is possible to prevent impurities from adhering or mixing into the titanium oxide film. (8) The Teflon (registered trademark) crucible was placed in a stainless steel autoclave and heated at 140 °C for 24 hours to form a titanium oxide film on the mirror-finished surface of the LaAlO3 substrate. After the heating was completed, the autoclave was naturally cooled to room temperature. The LaAlO3 substrate taken out from the Teflon (registered trademark) crucible was rinsed with ethanol and purified water and dried on a hot plate. The thickness of the obtained titanium oxide film was about 2.5 μm.

[0070] [X-ray diffraction method] The crystal phase, crystallinity, and orientation of the titanium oxide film were evaluated by X-ray diffraction method. The measuring device was an X-ray diffractometer (RINT Ultima III) manufactured by Rigaku Corporation. The measurement conditions are shown in Table 1.

[0071]

Table 1

[0072] Hereinafter, the measurement result of "θ / 2θ scan" is referred to as "XRD pattern" (that is, X-ray diffraction pattern). In the X-ray diffraction method, CuK αLine and CuK β Since the line was used without any special separation operation, peaks reflecting two types of X-rays occurred in the XRD pattern. Therefore, in the XRD pattern, the peak caused by the CuK β line is denoted as "CuK β ". On the other hand, peaks without any specific notation other than the plane indices in the XRD pattern are peaks caused by the CuK α line.

[0073] The XRD pattern of the titanium oxide film is shown in Fig. 1. The pole figure of the titanium oxide film is shown in Fig. 2. Fig. 1 shows that anatase-type titanium oxide grows preferentially. The ratio of the intensity of the peak derived from the (211) plane of rutile-type titanium oxide to the intensity of the peak derived from the (004) plane of anatase-type titanium oxide was about 1%. Figs. 1 and 2 show that anatase-type titanium oxide has good orientation in all three directions of the direction perpendicular to the plane and the in-plane direction. Similar to the known examples prepared by the vapor phase method, the c-axis of anatase-type titanium oxide is aligned in the direction perpendicular to the plane, and the a-axis of anatase-type titanium oxide is aligned in the in-plane direction. That is, the titanium oxide film has grown by inheriting the crystal lattice of the substrate and is epitaxially grown.

[0074] <Example 2> [Manufacture of Titanium Oxide Film] A titanium oxide film was manufactured by the same procedure as in Example 1 described above, except that the heating temperature in the stainless steel autoclave was changed from 140°C to 160°C. The thickness of the obtained titanium oxide film is about 2.5 μm.

[0075] [X-ray Diffraction Method] The crystal phase, crystallinity, and orientation of the titanium oxide film were evaluated by the above-described X-ray diffraction method. The XRD pattern of the titanium oxide film is shown in Fig. 3. The pole figure of the titanium oxide film is shown in Fig. 4. Similar to Figs. 1 and 2, Figs. 3 and 4 show that anatase-type titanium oxide grows preferentially and that anatase-type titanium oxide has good orientation in all three directions of the perpendicular direction and the in-plane direction. The ratio of the peak intensity derived from the (211) plane of rutile-type titanium oxide to the peak intensity derived from the (004) plane of anatase-type titanium oxide was about 1%. No significant difference was observed between the titanium oxide film of Example 1 and the titanium oxide film of Example 2 in the XRD pattern and the pole figure.

[0076] <Comparative Example 1> An attempt was made to produce a titanium oxide film by the same procedure as in Example 1, except that an aqueous solution of ammonium hexafluorotitanate was not used and the volume deficit due to the non-use of the aqueous solution of ammonium hexafluorotitanate was supplemented with purified water. However, only the peak derived from LaAlO3 of the substrate was observed in the XRD pattern. This result indicates that no titanium oxide film was formed.

[0077] <Comparative Example 2> An attempt was made to produce a titanium oxide film by the same procedure as in Example 1, except that hydrochloric acid was not used and the volume deficit due to the non-use of hydrochloric acid was supplemented with purified water. However, only the peak derived from LaAlO3 of the substrate was observed in the XRD pattern. This result indicates that no titanium oxide film was formed.

Claims

1. Preparing a titanium-containing liquid comprising water, an alcohol, a diketone, an acid, a titanium alkoxide, and a fluorine atom-containing titanium compound; Immersing a substrate in the titanium-containing liquid and forming anatase-type titanium oxide film on the substrate by a solvothermal method. A method for producing anatase-type titanium oxide film.

2. The method for producing anatase-type titanium oxide film according to claim 1, wherein preparing the titanium-containing liquid includes preparing a mixture comprising the water, the alcohol, the diketone, and the acid, and mixing the mixture with the titanium alkoxide and the fluorine atom-containing titanium compound.

3. The method for producing anatase-type titanium oxide film according to claim 1 or claim 2, wherein the alcohol contains ethanol.

4. The method for producing anatase-type titanium oxide film according to any one of claims 1 to 3, wherein the diketone contains β-diketone.

5. The method for producing anatase-type titanium oxide film according to any one of claims 1 to 3, wherein the diketone contains acetylacetone.

6. The method for producing anatase-type titanium oxide film according to any one of claims 1 to 5, wherein the acid contains hydrogen halide.

7. The method for producing anatase-type titanium oxide film according to any one of claims 1 to 5, wherein the acid contains hydrogen chloride.

8. The method for producing anatase-type titanium oxide film according to any one of claims 1 to 7, wherein the number of carbon atoms of the alkoxy group in the titanium alkoxide is 1 to 8.

9. The manufacturing method of the anatase-type titanium oxide film according to any one of claims 1 to 8, wherein the titanium alkoxide contains titanium tetraisopropoxide.

10. The manufacturing method of the anatase-type titanium oxide film according to any one of claims 1 to 9, wherein the fluorine atom-containing titanium compound contains a salt containing TiF ６ ２－ .

11. The manufacturing method of the anatase-type titanium oxide film according to any one of claims 1 to 9, wherein the fluorine atom-containing titanium compound contains ammonium hexafluorotitanate.

12. The manufacturing method of the anatase-type titanium oxide film according to any one of claims 1 to 11, wherein the substrate is a LaAlO ３ substrate or a SrTiO ３ substrate.

13. The manufacturing method of the anatase-type titanium oxide film according to any one of claims 1 to 12, wherein the heating temperature in the solvothermal method is 110°C to 170°C.

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