JP6800450B2 - Method for manufacturing metal oxide nanocrystals, method for manufacturing metal oxide nanocrystal film-immobilized substrate - Google Patents

Description

The present invention relates to a metal oxide nanocrystal film-immobilized substrate, a method for producing metal oxide nanocrystals, and a method for producing a metal oxide nanocrystal film-immobilized substrate.
The present application claims priority based on Japanese Patent Application No. 2017-129716 filed in Japan on June 30, 2017, the contents of which are incorporated herein by reference.

Lead titanate (PT) and lead zirconate titanate (PZT), which are metal oxides, are known as piezoelectric bodies that exhibit an excellent piezoelectric effect. Such nanocrystals (nanocubes) of lead titanate and lead zirconate titanate exhibit characteristic physical properties due to their size, and are expected to be applied as new materials.

As a conventional method for producing lead zirconate titanate, for example, in Non-Patent Document 1, lead acetate powder and EDTA are dispersed in water, and titanium oxide powder and raw material powder in which zirconium oxychloride is dispersed in water are added thereto. It is described that a powder of lead zirconate titanate is produced by hydrothermal synthesis using an autoclave.
According to the method for producing lead zirconate titanate described in Non-Patent Document 1, it is said that fine particles of lead zirconate titanate having a cubic shape and having a size of about several μm can be produced.

Further, in Patent Document 1, a lead compound, a titanium compound, and a zirconium compound are mixed at a mixing ratio in a specific range, and the mixed raw material is aged in a specific pH range, and then a basic substance is added for hydrothermal synthesis. It is described that the lead zirconate titanate having micron size particles such as 0.5 to 10 μm can be obtained.

Japanese Unexamined Patent Publication No. 2014-162685

R.E.Riman et al., Langmuir 2005,21,3207-3212

However, in the method for producing fine particles of lead zirconate titanate described in Non-Patent Document 1 and Patent Document 1, it is expected that characteristic physical properties due to the size thereof are exhibited, for example, the size is from several tens of nm. It is difficult to stably produce nanocrystals (nanocubes) of lead titanate and lead zirconate titanate having a size of several hundred nm.

In addition, conventionally, such fine particles of lead titanate and lead zirconate titanate are used to form a film in which fine particles of lead titanate and lead zirconate titanate are arranged and accumulated on the surface of a substrate, or the fine particles are dispersed alone on a substrate. In the formation of the film (hereinafter referred to as immobilization), complicated steps such as firing the substrate after forming the film and etching to form irregularities on the substrate were required. Therefore, a method for easily producing a substrate on which a film containing fine particles of lead titanate or lead zirconate titanate is formed at low cost is desired.

The present invention is a method for producing metal oxide nanocrystals capable of producing nanocrystals (nanocubes) of lead titanate and lead zirconate titanate, which are metal oxides, and metal oxide nanos by a simple process. An object of the present invention is to provide a method for producing a metal oxide nanocrystal film-immobilized substrate capable of immobilizing a crystal film on the surface of the substrate.

As a result of diligent studies to achieve the above object, the present inventor has obtained an aqueous solution of lead acetate and an aqueous solution of a water-soluble titanium complex, an aqueous solution of a water-soluble titanium complex, an aqueous solution of a water-soluble zirconate complex, and a quaternary ammonium compound. By mixing with and to obtain a mixed solution and heating and synthesizing this mixed solution, nano-sized lead titanate nanocrystals and lead zirconate titanate nanocrystals having a hexahedral structure can be obtained. I found it and came up with the present invention.

[ 1 ] The method for producing a metal oxide nanocrystal according to one aspect of the present invention is a method for producing a metal oxide nanocrystal containing a metal oxide composed of lead titanate or lead zirconate titanate. A mixed solution forming step of mixing an aqueous solution, a water-soluble titanium complex aqueous solution, a water-soluble titanium complex aqueous solution, a water-soluble zirconium complex aqueous solution, and a quaternary ammonium compound to form a mixed solution, and heating the mixed solution. It includes a heating step for synthesizing the metal oxide nanocrystals and a separation step for separating the metal oxide nanocrystals from the residual solution.

According to the above aspect, nanocrystals (nanocubes) of lead titanate and lead zirconate titanate can be stably synthesized by a simple method.

[ 2 ] In the method for producing metal oxide nanocrystals according to the above [ 1 ], it is preferable that the ligand of the water-soluble titanium complex is a hydroxycarboxylic acid.

[ 3 ] In the method for producing metal oxide nanocrystals according to any one of [ 1 ] or [ 2 ] above, it is preferable that the ligand of the water-soluble zirconium complex is a hydroxycarboxylic acid.

[ 4 ] In the method for producing metal oxide nanocrystals according to any one of the above [ 1 ] to [ 3 ], it is preferable that the quaternary ammonium compound is tetramethylammonium hydroxide.

[ 5 ] In the method for producing metal oxide nanocrystals according to any one of the above [ 1 ] to [ 4 ], the molar ratio of titanium and zirconium in the mixed solution is 100: 0 to 30:70. It is preferably in the range of.

[6] In the method for producing metal oxide nanocrystals according to any one of [ 1 ] to [ 5 ] above, the molar ratio of lead to titanium or titanium and zirconium in the mixed solution is 1: 1. It is preferably 1 or more and 2: 1 or less.

[ 7 ] In the method for producing metal oxide nanocrystals according to any one of [ 1 ] to [ 6 ] above, the mixed solution has 2 or more and 100 or less moles of the quaternary ammonium compound with respect to 1 mol of lead. Is preferable.

[ 8 ] In the method for producing metal oxide nanocrystals according to any one of [ 1 ] to [ 7 ] above, the heating step is performed in a temperature range of 140 ° C. or higher and 240 ° C. or lower, and for 1 hour or longer and 120. It is preferable to carry out in a time range of less than an hour.

[ 9 ] In the method for producing metal oxide nanocrystals according to any one of [ 1 ] to [ 8 ] above, in the separation step, the metal oxide nanocrystals are separated and recovered by centrifugation from the residual liquid. It is preferable that the process is performed.

[ 10 ] The method for producing a metal oxide nanocrystal film-immobilized substrate according to one aspect of the present invention includes a substrate and a nanocrystal film composed of metal oxide nanocrystals arranged or immobilized on the substrate. The metal oxide constituting the metal oxide nanocrystals is a method for producing a metal oxide nanocrystal film-immobilized substrate which is lead titanate or lead zirconate titanate, and is described in each of the above items [ 1]. ] To [ 9 ] The metal oxide nanocrystals obtained by the method for producing metal oxide nanocrystals according to any one of [ 9 ] are dispersed in an alcohol solvent or an acidic solvent having a pH of 3 or less, and then centrifuged to obtain a supernatant. A dispersion step of recovering the nanocrystal dispersion liquid to obtain a nanocrystal dispersion liquid, and an immobilization step of immobilizing the nanocrystal film on the substrate by applying the nanocrystal dispersion liquid on the substrate and then drying it. Have.

According to the present invention, a method for producing metal oxide nanocrystals capable of producing nanocrystals (nanocubes) of lead titanate or lead zirconate titanate, and a film of metal oxide nanocrystals in a simple process. It becomes possible to provide a method for producing a metal oxide nanocrystal film-immobilized substrate, which can be immobilized on the surface of the substrate.

6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead titanate nanocrystals prepared in Example 1 on a silicon wafer substrate at room temperature. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead titanate nanocrystals prepared in Example 2 on a silicon wafer substrate at room temperature. It is a graph which shows the result of having carried out the powder XRD measurement using the X-ray diffractometer about the lead titanate nanocrystal produced in Example 2. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead nanocrystals of lead zirconate titanate prepared in Example 3 on a silicon wafer substrate at room temperature. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead nanocrystals of lead zirconate titanate prepared in Example 4 on a silicon wafer substrate at room temperature. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead nanocrystals of lead zirconate titanate prepared in Example 5 on a silicon wafer substrate at room temperature. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead nanocrystals of lead zirconate titanate prepared in Example 6 on a silicon wafer substrate at room temperature. It is a graph which shows the result of having carried out the powder XRD measurement using the X-ray diffractometer about the lead titanate nanocrystal produced in Example 3. It is a graph which shows the result of having carried out the powder XRD measurement using the X-ray diffractometer about the lead titanate nanocrystal produced in Examples 4-6. 6 is an SEM image of the surface of a sample prepared by dropping and drying the dispersion liquid containing lead nanocrystals of lead zirconate titanate prepared in Example 7 on a silicon wafer substrate at room temperature. It is a graph which shows the result of having carried out the powder XRD measurement using the X-ray diffractometer about the lead titanate nanocrystal produced in Example 7. It is an SEM image of a sample in which a nanocrystal film is immobilized on a substrate with a mold attached after drying. It is an SPM image of a sample in which a nanocrystal film is immobilized on a substrate with a mold attached after drying. It is a graph which shows the measurement result (1) of the piezoelectric property using the metal oxide nanocrystal film-immobilized substrate. It is a graph which shows the measurement result (2) of the piezoelectric property using the metal oxide nanocrystal film-immobilized substrate. It is a graph which shows the measurement result (3) of the piezoelectric property using the metal oxide nanocrystal film-immobilized substrate. It is a graph which shows the measurement result (4) of the piezoelectric property using the metal oxide nanocrystal film-immobilized substrate. 6 is an SEM image of a sample prepared by allowing the supernatant liquid adjusted for pH with hydrochloric acid to stand for one day and then dropping and drying it on a silicon wafer substrate at room temperature. It is an SEM image of a sample in which a nanocrystal film is immobilized on a substrate with a polyimide mold attached. It is an SEM image of a sample in which a nanocrystal film is immobilized on a substrate with a polyimide mold attached. It is an SEM image of a sample in which a nanocrystal film is immobilized on a substrate with a silicon mold attached. It is a table summarizing the SEM image of the lead zirconate titanate nanocrystal and the measurement result about the center line average roughness and the average surface roughness of the lead zirconate titanate nanocrystal. It is a table summarizing the SEM image of the lead zirconate titanate nanocrystal and the measurement result about the center line average roughness and the average surface roughness of the lead zirconate titanate nanocrystal.

Hereinafter, with reference to the drawings, a metal oxide nanocrystal film-immobilized substrate, a method for producing metal oxide nanocrystals, and a method for producing a metal oxide nanocrystal film-immobilized substrate according to an embodiment of the present invention will be described. It should be noted that each of the embodiments shown below is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified. Further, in the drawings used in the following description, in order to make the features of the present invention easy to understand, the main parts may be enlarged for convenience, and the dimensional ratios of the respective components are the same as the actual ones. Is not always the case. In this specification, when the numerical range is indicated by using "~", the numerical values at both ends are included.

First, the method for producing metal oxide nanocrystals of the present invention and the metal oxide nanocrystals obtained by the method will be described.
In addition to the so-called nanocube, which is a hexahedral crystal, the term "nanocrystal" as used herein refers to an incomplete hexahedron in which the apex of the hexahedron is chamfered, which is simultaneously synthesized in the process of synthesizing or producing the nanocube. Also includes shaped crystals. The incomplete hexahedral crystal in which the apex of the hexahedron is chamfered is in the process of becoming a hexahedral crystal. The size of the crystal is not limited as long as it is a nanometer size in which lead titanate or lead zirconate titanate can be hexahedral, but it is assumed to be in the range of 10 nm or more and 1500 nm or less, for example. be able to. Further, this size is preferably 100 nm or more and 1500 nm or less, and more preferably 800 nm or more and 1500 nm or less. The size here means the maximum length of one side when each surface of each nanocrystal is viewed in a plan view.

Further, in the present specification, "lead zirconate titanate" is represented by the general formula PbZr _x Ti _(1-x) O ₃ (0 ≦ x ≦ 0.7). Then, in this general formula, the case of x = 0 is lead titanate.

In the method for producing metal oxide nanocrystals of the present invention, when producing lead titanoate nanocrystals having a crystal size of nanometer size, lead acetate aqueous solution, water-soluble titanium complex aqueous solution, and quaternary ammonium are used as raw materials. Compounds and compounds are prepared and mixed to form a mixed solution which is a raw material for synthesizing nanocrystals (mixed solution forming step).
When producing lead zirconate titanate having a crystal size of nanometer size, a lead acetate aqueous solution, a water-soluble titanium complex aqueous solution, a water-soluble zirconium complex aqueous solution, and a quaternary ammonium compound are prepared as raw materials. Then, they are mixed to form a mixed solution which is a synthetic raw material for nanocrystals (mixed solution forming step).

As the water-soluble titanium complex used in the present invention, a compound can be used in which the ligand is removed from the titanium atom after being dissolved in water to form a bond between the titanium atom and the oxygen atom. As such a compound, it is preferable that the ligand of the water-soluble titanium complex is a hydroxycarboxylic acid.

Specific examples of hydroxycarboxylic acid include lactic acid, malic acid, citric acid, tartaric acid, glyceric acid, 2-hydroxybutyric acid, leucic acid (= 2-hydroxy-4-methylpentanoic acid), quinic acid, and mandelic acid (= 2). -Hydroxy-2-phenylacetic acid), glycolic acid and the like can be mentioned. Examples of the water-soluble titanium complex include Titanium bis (ammonium lactate) dihydroxide (hereinafter referred to as "TALH") in which the ligand is lactic acid, and glycolic acid (HOCH ₂ COOH) in the ligand. Yes (NH ₄ ) ₆ [Ti ₄ (C ₂ H ₂ O ₃ ) ₄ (C ₂ H ₃ O ₃ ) ₂ (O ₂ ) ₄ O ₂ ] ・ 6H ₂ O, ligand is citrate ((CH ₂₎ COOH) ₂ C (OH) COOH) (NH ₄ ) ₈ [Ti ₄ (C ₆ H ₄ O ₇ ) ₄ (O ₂ ) ₄ ] ・ 8H ₂ O, or ligand is malic acid (CH ₂ CHOH) Examples include a titanium complex which is (COOH) ₂ ) or tartrate ((CHOH) ₂ (COOH) ₂ ).

In this embodiment, TALH is used as the water-soluble titanium complex. TALH is a precursor of an oxide containing titanium that is soluble in water, and the oxide formation reaction using TALH proceeds under mild conditions as compared with other methods, and TALH is soluble in water. Therefore, the reaction in an aqueous solution is possible. By using a water-soluble titanium complex in which such a ligand is a hydroxycarboxylic acid, it contributes to the synthesis of lead titanate nanocrystals and lead zirconate titanate nanocrystals having a controlled nanometer-sized hexahedral structure. ..

As the water-soluble zirconium complex used in the present invention, a compound that is dissolved in water and then the ligand is removed from the zirconium atom to form a bond between the zirconium atom and the oxygen atom can be used. As such a compound, it is preferable that the ligand of the water-soluble zirconium complex is a hydroxycarboxylic acid.

Specific examples of hydroxycarboxylic acid include lactic acid, malic acid, citric acid, tartaric acid, glyceric acid, 2-hydroxybutyric acid, leucic acid (= 2-hydroxy-4-methylpentanoic acid), quinic acid, and mandelic acid (= 2). -Hydroxy-2-phenylacetic acid), glycolic acid and the like can be mentioned. Examples of the water-soluble zirconium complex include zirconium lactate ammonium salt and the like.

In this embodiment, zirconium lactate ammonium salt as the water-soluble zirconium complex (Zr (OH) [(OCH (CH 3) COO -]. 3 (NH 4 +) 3) is used specifically, Orgatics ZC -300 (trade name, manufactured by Matsumoto Fine Chemicals). Zirconic acid titanate having a controlled nanometer-sized hexahedral structure by using a water-soluble zirconium complex in which such a ligand is a hydroxycarboxylic acid. Contributes to the synthesis of lead nanocrystals.

In the present invention, the water-soluble titanium complex and the water-soluble zirconium complex are mixed so that the molar ratio of titanium and zirconium is in the range of 100: 0 to 30:70 in the above-mentioned mixed solution. That is, the water-soluble titanium complex and the water-soluble zirconium complex so that the molar ratio of titanium is 30 or more and 100 or less, the molar ratio of zirconium is 0 or more and 70 or less, and the total molar ratio of titanium and zirconium is in the range of 100. And mix. When the molar ratio of zirconium is 0, it corresponds to the case of synthesizing lead titanate nanocrystals.

Further, in the present invention, after production (after synthesis), the number of moles of titanium is 0.3 times or more and 1 times or less the number of moles of lead, and the total number of moles of titanium and zirconium is lead. Lead acetate, a water-soluble titanium complex, and a water-soluble zirconium complex are mixed so as to have the same number of moles. Therefore, in the above-mentioned mixed solution, lead acetate is used so that the molar ratio of lead to titanium or lead to titanium and zirconium (Pb: Ti + Zr) is in the range of 1: 1 or more and 2: 1 or less. , A water-soluble titanium complex and a water-soluble zirconium complex are mixed. That is, at the start of mixing, the amount of lead is 1 mol or more and 2 mol or less with respect to 1 mol of titanium or 1 mol of a mixture of titanium and zirconium.

Examples of the quaternary ammonium compound used in the present invention include tetramethylammonium hydroxide (“TMAH”). TMAH exists in the form of a relatively stable solid pentahydrate, and when dissolved in water, the aqueous solution is strongly basic.

In the present invention, lead acetate and a quaternary ammonium compound are mixed so that the number of moles of the quaternary ammonium compound with respect to 1 mol of lead is in the range of 2 or more and 100 or less in the above-mentioned mixed solution. As a result, the nanocrystal synthesis reaction can be sufficiently advanced in the heating step described later, and the aggregation of the nanocrystals to be synthesized can be sufficiently suppressed to achieve a nanometer size.

When the number of moles of the quaternary ammonium compound with respect to 1 mole of lead is less than 2, the synthesis reaction does not proceed sufficiently in the heating step described later, and the shape of the nanocrystals is not sufficiently controlled, resulting in a clean hexahedron. There is a problem. Further, when the number of moles of the quaternary ammonium compound with respect to 1 mole of lead exceeds 100, there is a problem that it becomes difficult to completely remove the residue after the completion of the synthesis reaction in the heating step.

Next, the above-mentioned mixed solution is heated to synthesize metal oxide nanocrystals (heating step).
The reaction solution used in the present invention is preferably heated at a temperature of 140 ° C. or higher and 240 ° C. or lower. Further, it is more preferable to carry out at a temperature of 200 ° C. or higher and 230 ° C. or lower. When the heating temperature is less than 140 ° C., there is a problem that the synthesis reaction of nanocrystals does not proceed sufficiently. Further, when the heating temperature exceeds 240 ° C., there is a problem that a controlled hexahedral structure cannot be finally obtained.

The heating of the reaction solution used in the present invention is preferably carried out for 1 hour or more and 120 hours or less, and more preferably 70 hours or more and 100 hours or less. If the heating time is less than 1 hour, there is a problem that the nanocrystal synthesis reaction does not proceed sufficiently. Further, since the shape of the nanocrystals does not change so much even if the heating time exceeds 120 hours, it is considered that further heating is not necessary.

Various already known methods can be appropriately used to heat the reaction solution of the present invention to allow the reaction to proceed, but hydrothermal synthesis is preferred.

According to the method for producing metal oxide nanocrystals of the present invention, the nanocrystal synthesis reaction is sufficiently carried out by carrying out the heating step at a temperature of 140 ° C. or higher and 240 ° C. or lower and for 1 hour or longer and 120 hours or lower. It is possible to obtain nanometer-sized lead titanate nanocrystals and lead zirconate titanate nanocrystals having a controlled hexahedral structure without advancing and unnecessary heating.

After that, the mixed solution is centrifuged after synthesizing the metal oxide nanocrystals. Then, the metal oxide nanocrystals are precipitated and separated (separated and recovered) from the residual liquid by filtration or the like (separation step). By such a separation step, unnecessary small crystals and the like can be removed to obtain lead titanate nanocrystals and lead zirconate titanate nanocrystals having a hexahedral structure whose size is controlled.

The metal oxide nanocrystals (lead titanate nanocrystals, lead zirconate titanate nanocrystals) obtained by the above method for producing metal oxide nanocrystals of the present invention have the following characteristics.
(1) The crystal shape is hexahedron (shaped), and the crystal size is 10 nm or more and 1500 nm or less. Further, it is preferably 100 nm or more and 1500 nm or less. Further, it is more preferably 800 nm or more and 1500 nm or less. In addition, this size means the length of the maximum side when each nanocrystal is viewed in a plane.
(2) The average of the absolute values of the saturation values of the piezoelectric constants (d _33-PFM ) obtained by the piezoelectric response microscope (PFM) measurement is 25 pm / V or more. The d constant is a quantity indicating the ease of deformation when a voltage is applied, and d ₃₃ indicates expansion and contraction perpendicular to the electrode surface (thickness direction).
(3) In the shape image measured by SPM (scanning probe microscope), the average roughness of the center line on the diagonal of any one surface of the hexahedron (each surface constituting the hexahedron) is 5 nm or less, and any one surface of the hexahedron It has surface smoothness such that the average surface roughness in a region of 40% or more of the area is 30 nm or less. Inferring from the observation image of nanocrystals by SEM, the smoothness is basically maintained on the entire surface of the hexahedron.

Next, a method for manufacturing the metal oxide nanocrystal film-immobilized substrate of the present invention will be described.
The metal oxide nanocrystal film-immobilized substrate obtained by the method for producing a metal oxide nanocrystal film-immobilized substrate of the present invention is a nanocrystal composed of a substrate and metal oxide nanocrystals arranged or immobilized on the substrate. It is equipped with a membrane. The metal oxide constituting the metal oxide nanocrystal is lead titanate or lead zirconate titanate.

As the substrate, any substrate that is stable to a solvent and has no hygroscopicity can be applied, and a substrate having a flat surface is preferable. For example, FTO, ITO, glass, silicon, metal, ceramics, polymer, paper. , Rubber, and those selected from the group of low heat resistant substrates can be used.

Further, unevenness that can be removed by etching can be formed on the surface of the substrate. Due to these irregularities, the nanocrystal film can be formed into an arbitrary shape on the substrate. As the shape of the unevenness in a plan view from the thickness direction of the substrate, for example, any one of a linear shape, a curved shape, and a circular shape can be used.

In the present embodiment, as such a substrate, a silicon wafer on which a platinum thin film is formed is used. Then, in order to form a large number of linear nanocrystal films on the substrate, a mold made of polyimide, for example, was formed in advance on the surface of the substrate in the form of stripes having a width of several microns.

Next, the lead titanate nanocrystals or lead zirconate titanate nanocrystals obtained by the method for producing metal oxide nanocrystals of the present invention described above are dispersed in an alcohol solvent or an acidic solvent having a pH of 3 or less, and then centrifuged. To obtain a nanocrystal dispersion liquid by recovering the supernatant (dispersion step).

Then, the nanocrystal dispersion liquid obtained in this dispersion step is applied onto the substrate and dried. As a result, the nanocrystal film in which the nanocrystal dispersion liquid is dried is immobilized on the substrate (immobilization step). After that, if the striped molds are removed as in the present embodiment, the nanocrystal films that have entered the grooves between the linear molds and are fixed remain, and the nanocrystals of the stripe pattern are left on the substrate. A metal oxide nanocrystal film-immobilized substrate provided with a crystal film can be obtained.

According to the method for producing a metal oxide nanocrystal film-immobilized substrate of the present invention, nanocrystal dispersion occurs when a nanocrystal film in which lead titanate nanocrystals and lead zirconate nanocrystals are dispersed is formed on the substrate. Since the nanocrystal film is immobilized on the substrate simply by applying the liquid to the substrate and drying it, it is necessary to perform heat treatment such as firing in order to form a fine crystal film on the substrate as in the conventional case. No. As a result, even if the substrate is formed of a low heat resistant substrate such as polymer, paper, or rubber, the nanocrystal film in which lead titanate nanocrystals and lead zirconate titanate nanocrystals are dispersed is immobilized. be able to.

Further, a metal oxide nanocrystal film-immobilized substrate can be easily obtained at low cost by a simple process of applying the nanocrystal dispersion liquid to the substrate and drying it.
Further, if irregularities that can be easily removed such as a mold of an arbitrary pattern are formed on the substrate in advance, lead titanate nanocrystals and lead zirconate titanate nanocrystals can be formed in an arbitrary pattern without etching the substrate in advance. A metal oxide nanocrystal film-immobilized substrate on which a nanocrystal film in which crystals are dispersed is immobilized can be easily formed.

Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

[Synthesis and identification of lead titanate nanocrystals]
(1) Synthesis (manufacturing) of lead titanate nanocrystals
Lead titanate nanocrystals were synthesized according to the following procedure. Lead acetate _{(Pb (CH 3 COO) 2} · 3H 2 O) 6mmol dissolved in water 15 ml. A TALH aqueous solution having a concentration of 6 mmol was added to the lead acetate aqueous solution with stirring, and then a TMAH aqueous solution in which 6.726 g of TMAH was dissolved in 15 ml of water was added to prepare a mixed solution (reaction solution). At this stage, the molar ratio (Pb: Ti) of lead and titanium contained in the mixed solution was adjusted to 2: 1. The resulting mixed solution was placed in an autoclave, sealed, heated for 24 hours and then cooled to room temperature. The one having a heating temperature of 180 ° C. at this time was designated as Example 1, and the one having a heating temperature of 200 ° C. was designated as Example 2.

(2) Identification of lead titanate nanocrystals The lead titanate nanocrystals were analyzed using a scanning electron microscope (JEOL, JSM-6335FM, 10 kV manufactured by JEOL Ltd.). The crystal phase was identified using an X-ray diffractometer (SmartLab, 40 kV / 30 mA, manufactured by Rigaku Co., Ltd.).

The various identification samples of lead titanate nanocrystals of Examples 1 and 2 are dried by dropping on a silicon wafer substrate at room temperature using a colloidal solution in which the powder recovered by centrifugation is redispersed in isopropyl alcohol. Made by After irradiating the sample with ultraviolet rays for 2 hours, the sample was kept at 200 ° C. for 1.5 hours in an incubator to clean the surface.

FIG. 1 shows a silicon wafer containing a dispersion containing lead titanate nanocrystals (molar ratio Pb: Ti = 2: 1 at the start of mixing, heating temperature 180 ° C.) prepared in Example 1 by the above sample preparation method. The SEM image of the surface of the sample prepared by dropping and drying on a substrate at room temperature is shown.
From the SEM image, it was confirmed that in Example 1, nanocrystals having a hexahedral shape and a size of about 100 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 1, nanocrystals having a size of 100 nm accounted for about 90% of the total.

FIG. 2 shows a silicon wafer containing a dispersion liquid containing lead titanate nanocrystals (molar ratio Pb: Ti = 2: 1 at the start of mixing, heating temperature 200 ° C.) prepared in Example 2 by the above sample preparation method. The SEM image of the surface of the sample prepared by dropping and drying on a substrate at room temperature is shown.
From the SEM image, it was confirmed that in Example 2, nanocrystals having a hexahedral shape and a size of about 100 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 2, the nanocrystals having a size of 100 nm accounted for about 80% of the total.

FIG. 3 shows the results of powder XRD measurement of the lead titanate nanocrystals produced in Example 2 using an X-ray diffractometer. The lead titanate nanocrystals produced in Example 1 have a peak at substantially the same position as PbTiO ₃ , and the crystal structure and its lattice constant are close to each other. From this result, it can be confirmed that among the produced (synthesized) lead titanate nanocrystals, the molar ratio (Pb: Ti) of lead to titanium is 1: 1.

[Synthesis and identification of lead nanocrystals of lead zirconate titanate (Pb (Zr _0.52 Ti _0.48 ) O ₃ ): Composition 1]
(1) Synthesis (manufacturing) of lead nanocrystals of lead zirconate titanate (Zr: Ti = 52: 48)
Lead zirconate titanate nanocrystals (composition 1) were synthesized according to the following procedure. Lead acetate _{(Pb (CH 3 COO) 2} · 3H 2 O) 0.3mmol, TALH0.072mmol, dissolved zirconium lactate ammonium salt (Matsumoto Fine Chemical Co., ZC-300 (trade name)) 0.078 mmol of water 15ml did. A mixed solution (reaction solution) was prepared by adding an aqueous TMAH solution prepared by dissolving 1.6815 g of TMAH in 15 ml of water to this aqueous solution. At this stage, the molar ratio (Pb: Zr + Ti) of lead to zirconium and titanium contained in the mixed solution was adjusted to 2: 1. The obtained mixed solution was placed in an autoclave, sealed, heated, and then cooled to room temperature. At this time, the heating temperature is 180 ° C. and the heating time is 24 hours in Example 3, the heating temperature is 180 ° C. and the heating time is 6 hours in Example 4, the heating temperature is 200 ° C. and the heating time is 6 hours. The one with the heating temperature of 220 ° C. and the heating time of 6 hours was designated as Example 5.

(2) Identification of lead zirconate titanate nanocrystals (Zr: Ti = 52: 48) Lead zirconate titanate nanocrystals were prepared using a scanning electron microscope (JEOL, JSM-6335FM, 10 kV, manufactured by JEOL Ltd.). Analyzed. The crystal phase was identified using an X-ray diffractometer (SmartLab, 40 kV / 30 mA, manufactured by Rigaku Co., Ltd.).

The various identification samples of lead zirconate titanate nanocrystals of Examples 3 to 6 are dried by dropping the powder recovered by centrifugation onto a silicon wafer substrate at room temperature using a colloidal solution in which the powder is redispersed in isopropyl alcohol. It was made by. After irradiating the sample with ultraviolet rays for 2 hours, the sample was kept at 200 ° C. for 1.5 hours in an incubator to clean the surface.

In FIG. 4, a dispersion liquid containing lead zirconate titanate nanocrystals (heating temperature 180 ° C., heating time 24 hours) prepared in Example 3 by the above sample preparation method is dropped and dried on a silicon wafer substrate at room temperature. The SEM image of the surface of the sample prepared by the above is shown.
From the SEM image, it was confirmed that in Example 3, nanocrystals having a substantially hexahedral shape and a size of 800 nm to 1000 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 3, nanocrystals having a size of 800 nm to 1000 nm accounted for about 90% of the total.

In FIG. 5, the dispersion liquid containing the lead zirconate titanate nanocrystals (heating temperature 180 ° C., heating time 6 hours) prepared in Example 4 by the above sample preparation method is dropped and dried on a silicon wafer substrate at room temperature. The SEM image of the surface of the sample prepared by the above is shown.
From the SEM image, it was confirmed that in Example 4, nanocrystals having a substantially hexahedral shape and a size of 1000 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthetic conditions, but in Example 4, the nanocrystals having a size of 1000 nm accounted for about 90% of the total.

In FIG. 6, the dispersion liquid containing the lead zirconate titanate nanocrystals (heating temperature 200 ° C., heating time 6 hours) prepared in Example 5 by the above sample preparation method is dropped and dried on a silicon wafer substrate at room temperature. The SEM image of the surface of the sample prepared by the above is shown.
From the SEM image, it was confirmed that in Example 5, nanocrystals having a substantially hexahedral shape and a size of 1200 nm to 1300 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 5, nanocrystals having a size of 1200 nm to 1300 nm accounted for about 90% of the total.

In FIG. 7, the dispersion liquid containing the lead zirconate titanate nanocrystals (heating temperature 220 ° C., heating time 6 hours) prepared in Example 6 by the above sample preparation method is dropped and dried on a silicon wafer substrate at room temperature. The SEM image of the surface of the sample prepared by the above is shown.
From the SEM image, it was confirmed that in Example 6, nanocrystals having a size of approximately square columnar, 1 μm in width and 5 to 10 μm in length could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 6, nanocrystals having a size of 1 μm in width and 5 to 10 μm in length were about 90% of the total.

FIG. 8 shows the results of powder XRD measurement of the lead zirconate titanate nanocrystals produced in Example 3 using an X-ray diffractometer. The lead titanate nanocrystals prepared in Example _{3, Pb (Zr 0.52 Ti 0.48} ) O 3 and has a peak at substantially the same position, it is closer crystal structure and the lattice constants. From this result, it can be confirmed that the molar ratio (Pb: Zr + Ti) of lead to zirconium and titanium among the prepared (synthesized) lead zirconate titanate nanocrystals is 1: 1. ..

FIG. 9 shows the results of powder XRD measurement of the lead titanate nanocrystals produced in Examples 4 to 6 using an X-ray diffractometer. Among the lead titanate nanocrystals produced in Examples 4 to 6, in Example 6 (heating temperature 220 ° C., heating time 6 hours), a perovskite structure showing a ternary transition metal oxide was not obtained. On the other hand, in Examples 4 and 5, a perovskite structure was obtained.

[Synthesis and identification of lead nanocrystals of lead zirconate titanate (Pb (Zr _0.7 Ti _0.3 ) O ₃ ): Composition 2]
(1) Synthesis (manufacturing) of lead nanocrystals of lead zirconate titanate (Zr: Ti = 70: 30)
Lead zirconate titanate nanocrystals (composition 2) were synthesized according to the following procedure. Lead acetate _{(Pb (CH 3 COO) 2} · 3H 2 O) 0.3mmol, TALH0.045mmol, dissolved zirconium lactate ammonium salt (Matsumoto Fine Chemical Co., ZC-300 (trade name)) 0.105 mmol of water 15ml did. A mixed solution (reaction solution) was prepared by adding an aqueous TMAH solution prepared by dissolving 1.6815 g of TMAH in 15 ml of water to this aqueous solution. At this stage, the molar ratio (Pb: Zr + Ti) of lead to zirconium and titanium contained in the mixed solution was adjusted to 2: 1. The obtained mixed solution was placed in an autoclave, sealed, heated at a heating temperature of 180 ° C. and a heating time of 6 hours, and then cooled to room temperature as Example 7.

(2) Identification of lead zirconate titanate nanocrystals (Zr: Ti = 70: 30) Lead zirconate titanate nanocrystals were prepared using a scanning electron microscope (JEOL, JSM-6335FM, 10 kV, manufactured by JEOL Ltd.). Analyzed. The crystal phase was identified using an X-ray diffractometer (SmartLab, 40 kV / 30 mA, manufactured by Rigaku Co., Ltd.).

The sample for identifying the lead nanocrystals of lead zirconate titanate of Example 7 was prepared by dropping and drying the powder recovered by centrifugation on a silicon wafer substrate at room temperature using a colloidal solution in which the powder was redispersed in isopropyl alcohol. .. After irradiating the sample with ultraviolet rays for 2 hours, the sample was kept at 200 ° C. for 1.5 hours in an incubator to clean the surface.

In FIG. 10, a dispersion liquid containing lead zirconate titanate nanocrystals (heating temperature 180 ° C., heating time 6 hours) prepared in Example 7 by the above sample preparation method is dropped and dried on a silicon wafer substrate at room temperature. The SEM image of the surface of the sample prepared by the above is shown.
From the SEM image, it was confirmed that in Example 7, nanocrystals having a substantially hexahedral shape and a size of 1000 nm could be synthesized. The size of the nanocrystals and their distribution depend on the synthesis conditions, but in Example 7, nanocrystals having a size of 1000 nm accounted for about 90% of the total.

FIG. 11 shows the results of powder XRD measurement of the lead zirconate titanate nanocrystals produced in Example 7 using an X-ray diffractometer. The lead titanate nanocrystal produced in Example 7 has a peak at almost the same position as Pb (Zr _0.7 Ti _0.3 ) O ₃ , the crystal structure and its lattice constant are close, and the perovskite structure is similar. Has been obtained. From this result, it can be confirmed that the molar ratio (Pb: Zr + Ti) of lead to zirconium and titanium among the prepared (synthesized) lead zirconate titanate nanocrystals is 1: 1. ..

[Preparation of metal oxide nanocrystal film-immobilized substrate]
0.1 g of powder of lead zirconate titanate nanocrystals (Pb (Zr _0.52 Ti _0.48 ) O ₃ ) obtained in Example 3 described above is added to isopropyl alcohol (2-propanol) by ultrasonic waves. It was dispersed to obtain a nanocrystal dispersion liquid. Next, a substrate having a platinum film formed on a silicon wafer was prepared, and a mold (concavo-convex) having a striped micropattern (width 2-3 μm ) made of polyimide was formed on this substrate. Then, the nanocrystal dispersion liquid was dropped onto the substrate provided with this mold, and then dried.

FIG. 12 shows an SEM image of a sample in which the nanocrystal film is immobilized on the substrate with the dried mold attached. According to FIG. 12, a portion (circled dotted line portion) where lead zirconate titanate nanocrystals were accumulated was observed in the groove of the mold.

Next, an SPM (scanning probe microscope, NanoNaviReal manufactured by Hitachi High-Tech Science Corporation) image of the above-mentioned sample is shown in FIG. According to FIG. 13, since the nanocrystal film of lead zirconate titanate was immobilized on the substrate by dropping the nanocrystal dispersion liquid and drying it, the shape can be measured by SPM (scanning probe microscope). ing.

[Measurement of piezoelectric characteristics of lead zirconate titanate nanocrystals using a piezoelectric response microscope]
Using the above-mentioned metal oxide nanocrystal film-immobilized substrate as a sample, the piezoelectric characteristics of lead zirconate titanate nanocrystals were measured using a piezoelectric response microscope (PFM).
As the piezoelectric response microscope, a NanoNaviReal piezoelectric response microscope manufactured by Hitachi High-Tech Science Corporation was used for analysis. Four measurement positions were set on the substrate, and each measurement was performed a plurality of times.
The SPM images of the respective measurement positions and the measurement results (1) to (4) of the piezoelectric characteristics are shown in FIGS. 14 to 17.

From the measurement results of the piezoelectric characteristics shown in FIGS. 14 to 17, the average of the absolute values of the saturation values of the piezoelectric constants (d _33-PFM ) obtained by the piezoelectric response microscope measurement of the lead zirconate titanate nanocrystals of the present invention is 25 pm /. It was confirmed that it was V or higher.

[Preparation of nanocrystal dispersion, method of immobilizing nanocrystal film on substrate, observation of microstructure on substrate surface]
0.1 g of powder of lead zirconate titanate nanocrystals (Pb (Zr _0.52 Ti _0.48 ) O ₃ : heating temperature 180 ° C., heating time 6 hours) of Example 4 described above was added to isopropyl alcohol (2-propanol). ), And 15 ml of hydrochloric acid (10 mmol) was added to adjust the pH, and an attempt was made to disperse lead nanocrystals of lead zirconate titanate. Then, the mixture was stirred at a rotation speed of 5800 rpm for 5 minutes, and the supernatant was collected. The pH of this supernatant was 1.9. The pH of the supernatant without pH adjustment was 12.53.

FIG. 18 shows an SEM image of a sample prepared by allowing the supernatant liquid adjusted for pH with hydrochloric acid to stand for one day and then dropping and drying it on a silicon wafer substrate at room temperature.
In the SEM image of FIG. 18, a well-organized hexahedron having a size of about 800 nm to 1500 nm could be observed.

Next, a mold (concavo-convex) having a striped micropattern (width 2-3 μm ) made of polyimide is formed on a substrate on which a platinum film is formed on a silicon wafer, and a supernatant liquid (nanocrystal) after pH adjustment with hydrochloric acid is formed. The dispersion liquid) was added dropwise and then dried.
In addition, a mold (unevenness) having a striped micropattern (width 2-3 μm ) made of silicon is formed on a substrate having a platinum film formed on a silicon wafer, and a supernatant liquid (nanocrystal dispersion) after pH adjustment with hydrochloric acid is formed. After dropping the liquid), it was dried.

19 and 20 show SEM images of the sample in which the nanocrystal film is immobilized on the substrate with the above-mentioned polyimide mold attached. Further, FIG. 21 shows an SEM image of a sample in which the nanocrystal film is immobilized on the substrate with the silicon mold attached.
According to FIGS. 19 to 21, in both the polyimide and silicon molds, the locations where lead zirconate titanate nanocrystals were accumulated were observed in the grooves of the mold.

[Observation of centerline average roughness and average surface roughness of metal oxide nanocrystals]
The above-mentioned supernatant liquid (nanocrystal dispersion liquid) after pH adjustment with hydrochloric acid is applied to two substrates (platinum film on a silicon wafer) on which a mold (concavo-convex) having a striped micro pattern (width 2-3 μm) made of silicon is formed. Was formed), and each was dropped and dried. Using these metal oxide nanocrystal film-immobilized substrates, the center line of lead zirconate titanate nanocrystals (Pb (Zr _0.52 Ti _0.48 ) O ₃ : heating temperature 180 ° C., heating time 6 hours) The average roughness and the average surface roughness were measured.

The results of the two measurements are shown in FIGS. 22 and 23, respectively. Lead zirconate titanate nanocrystals (Pb (Zr _0.52 Ti _0.48 ) O ₃ : heating temperature 180 ° C., heating time 6 hours) The average roughness of the center line on the diagonal of any one side of the hexahedron is 4.7 nm. (FIG. 22) was 3.9 nm (FIG. 23). The average surface roughness of any one surface of the hexahedron of lead zirconate titanate nanocrystals was 27 nm (FIG. 22) and 28 nm (44%) (FIG. 23). From these results, the lead zirconate titanate nanocrystal of the present invention has a center line average roughness of 5 nm or less on the diagonal line of any one surface of the hexahedron, and an average surface roughness in a region of 40% or more of any one surface of the hexahedron. It was confirmed that the diameter was 30 nm or less.

The PZT cube is suitably used for piezoelectric device elements and ferroelectric memory elements.

Claims (10)

A method for producing metal oxide nanocrystals containing a metal oxide composed of lead titanate or lead zirconate titanate.
A mixed solution forming step of mixing a lead acetate aqueous solution, a water-soluble titanium complex aqueous solution, a water-soluble titanium complex aqueous solution, a water-soluble zirconium complex aqueous solution, and a quaternary ammonium compound to form a mixed solution, and the mixed solution. A method for producing a metal oxide nanocrystal, which comprises a heating step of heating to synthesize a metal oxide nanocrystal and a separation step of separating the metal oxide nanocrystal and a residual solution. The method for producing metal oxide nanocrystals according to claim 1 , wherein the ligand of the water-soluble titanium complex is a hydroxycarboxylic acid. The method for producing metal oxide nanocrystals according to claim 1 or 2 , wherein the ligand of the water-soluble zirconium complex is a hydroxycarboxylic acid. The method for producing metal oxide nanocrystals according to any one of claims 1 to 3, wherein the quaternary ammonium compound is tetramethylammonium hydroxide. The method for producing metal oxide nanocrystals according to any one of claims 1 to 4 , wherein the molar ratio of titanium and zirconium in the mixed solution is in the range of 100: 0 to 30:70. .. The metal oxidation according to any one of claims 1 to 5 , wherein in the mixed solution, the molar ratio of lead to titanium, or titanium and zirconium is 1: 1 or more and 2: 1 or less. A method for producing nanocrystals. The method for producing metal oxide nanocrystals according to any one of claims 1 to 6 , wherein the mixed solution has 2 or more and 100 or less moles of the quaternary ammonium compound with respect to 1 mol of lead. The metal oxide nano according to any one of claims 1 to 7 , wherein the heating step is carried out in a temperature range of 140 ° C. or higher and 240 ° C. or lower, and in a time range of 1 hour or more and 120 hours or less. Crystal manufacturing method. The method for producing metal oxide nanocrystals according to any one of claims 1 to 8 , wherein the separation step is a step of separating and recovering the metal oxide nanocrystals from the residual liquid by centrifugation. .. The metal oxide comprising a substrate and a nanocrystal film composed of metal oxide nanocrystals arranged or immobilized on the substrate and constituting the metal oxide nanocrystals is lead titanate or lead zirconate titanate. This is a method for manufacturing a metal oxide nanocrystal film-immobilized substrate.
The metal oxide nanocrystals obtained by the method for producing metal oxide nanocrystals according to any one of claims 1 to 9 are dispersed in an alcohol solvent or an acidic solvent having a pH of 3 or less, and then centrifuged to obtain a supernatant. It has a dispersion step of collecting and obtaining a nanocrystal dispersion liquid, and an immobilization step of immobilizing the nanocrystal film on the substrate by applying the nanocrystal dispersion liquid on the substrate and then drying it. A method for manufacturing a metal oxide nanocrystal film-immobilized substrate.