Gallium-doped zinc oxide particles, film containing gallium-doped zinc oxide particles, transparent conductive film, electronic device, and method for producing gallium-doped zinc oxide particles

Abstract

Provided are gallium-doped zinc oxide particles doped with Ga and having an average particle size of more than 0 nm to 30 nm and a resistivity of 0.08 to 1.4 MΩ·cm.

Description

[Technical Field]

[0001] The present invention relates to gallium-doped zinc oxide particles, a film containing the gallium-doped zinc oxide particles, a transparent conductive film, an electronic device, and a method for producing the gallium-doped zinc oxide particles. This invention claims priority from Japanese Patent Application No. 2020-101499, filed on June 11, 2020, and the contents of that application are incorporated by reference into the present application in designated states where incorporation by reference of documents is permitted. [Background technology]

[0002] Conventionally, a method for producing a ZnO-based thin film, which is a transparent electrode material, by vacuum film formation such as sputtering has been known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-236219 Summary of the Invention

[0004] In the first aspect of the present invention, the average particle size is greater than 0 nm and is 30 nm, and the resistivity is 0.08 MΩ cm to 1.4 MΩ cm. (Excluding those with a value between 0.47MΩ·cm and 0.52MΩ·cm) gallium-doped zinc oxide particles. The gallium-doped zinc oxide particles have an average particle diameter of more than 0 nm and up to 30 nm, a resistivity of 0.08 MΩ·cm to 1.4 MΩ·cm, and an ellipsoidal projected shape.

[0005] A second aspect of the present invention is a film comprising the gallium-doped zinc oxide particles described above.

[0006] A third aspect of the present invention is a transparent conductive film comprising the above-described film.

[0007] A fourth aspect of the present invention is an electronic device comprising the transparent conductive film described above.

[0008] A fifth aspect of the present invention is a method for producing gallium-doped zinc oxide particles, the method comprising: a base introducing step of introducing a base containing at least sodium methoxide into a mixed solution containing a zinc raw material, a gallium raw material, and a solvent; a heating step of heating the mixed solution into which the base has been introduced at a temperature higher than the boiling point of the solvent to obtain gallium-doped zinc oxide particles; and a drying step of drying the gallium-doped zinc oxide particles.

[0009] A sixth aspect of the present invention is a method for producing a film containing gallium-doped zinc oxide particles, the method comprising: a dispersion preparation step of dispersing gallium-doped zinc oxide particles obtained by the method for producing gallium-doped zinc oxide particles according to the fifth aspect in a liquid to obtain a dispersion; a mist-forming step of misting the dispersion; and a supply step of supplying the misted dispersion to a substrate.

[0010] A seventh aspect of the present invention is a method for producing a crystalline silicate having an average particle size of more than 0 nm to 30 nm and a resistivity of 0.08 MΩ cm to 1.4 MΩ cm. (Excluding those with a value between 0.47MΩ·cm and 0.52MΩ·cm) The method for producing a film containing gallium-doped zinc oxide particles includes a dispersion preparation step of dispersing gallium-doped zinc oxide particles, which are represented by the formula (I), in a liquid to obtain a dispersion, a mist-forming step of turning the dispersion into a mist, and a supply step of supplying the mist-formed dispersion onto a substrate. Also, there is provided a method for producing a film containing gallium-doped zinc oxide particles, the method comprising: a dispersion preparation step of dispersing gallium-doped zinc oxide particles, the particles having an average particle diameter of more than 0 nm but up to 30 nm, a resistivity of 0.08 MΩ cm to 1.4 MΩ cm, and an ellipsoidal projected particle shape, in a liquid to obtain a dispersion; a mist-forming step of turning the dispersion into a mist; and a supply step of supplying the misted dispersion to a substrate.

[0011] A seventh aspect of the present invention is a method for producing a film containing gallium-doped zinc oxide particles, the method comprising: a dispersion preparation step of dispersing gallium-doped zinc oxide particles having an average particle diameter of 10 nm to 15 nm and gallium-doped zinc oxide particles having an average particle diameter of 16 nm to 36 nm in a liquid to obtain a dispersion; and an application step of applying the dispersion. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a conceptual diagram showing an example of a film forming apparatus using a mist method according to this embodiment. [Figure 2]Figure 2 is a transmission electron microscope (TEM) photograph of gallium-doped zinc oxide particles. [Figure 3] Figure 3 is a graph of the resistivity of the film when formed with different compounding ratios. [Figure 4] Figure 4 is a graph of the resistivity of the film when formed with different heat treatment (annealing) temperatures.

Embodiments for Carrying out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an exemplification for explaining the present invention and is not intended to limit the present invention to the following contents. In the drawings, the positional relationships such as up and down, left and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0014] <Method for Producing <ZnO:Ga> Nanoparticles (Gallium-Doped Zinc Oxide Particles)> The method for producing gallium-doped zinc oxide particles according to the present embodiment includes a base introduction step of introducing a base containing at least sodium methoxide into a mixed solution containing a zinc raw material, a gallium raw material, and a solvent, a heating step of heating the mixed solution into which the base has been introduced at a temperature higher than the boiling point of the solvent to obtain zinc gallium-containing particles, and a drying step of drying the obtained particles.

[0015] In conventional synthesis of gallium-doped zinc oxide particles, water initially formed through condensation of metal oxides promotes the formation of layered double hydroxides (LDHs) as by-products, further accelerating Ostwald ripening and reducing the amount of gallium ions doped. These behaviors have been considered serious problems in obtaining gallium-doped zinc oxide particles with small particle size and low resistivity. The inventors have discovered that gallium-doped zinc oxide particles doped with several atomic percent of Ga can be synthesized by introducing a base containing at least sodium methoxide into a mixed solution in which a zinc source and a gallium source are dissolved in a solvent selected from the group consisting of methanol, ethanol, ethylene glycol, or a combination thereof, and then heating the resulting mixed solution at a temperature higher than the boiling point of the solvent, preferably at a high temperature of 200°C or higher, preferably for about 24 hours, followed by drying. The average particle size of the synthesized gallium-doped zinc oxide particles is greater than 0 nm to 36 nm, preferably greater than 0 nm to 30 nm, and more preferably greater than 0 nm to 26 nm. The resistivity is 0.08 MΩ·cm to 1.4 MΩ·cm, preferably 0.08 MΩ·cm to 1.3 MΩ·cm, and more preferably 0.08 MΩ·cm to 1.0 MΩ·cm.

[0016] [Zinc raw material] According to the method of this embodiment, the zinc raw material is not particularly limited, but examples thereof include zinc chloride (ZnCl), zinc nitrate (Zn(NO)), zinc sulfate (ZnSO), zinc acetate (Zn(CHCOO)), zinc acetylacetonate (Zn(CHCOCHCOCH)), hydrates thereof, and combinations thereof.

[0017] [Gallium raw material] According to the method of this embodiment, the gallium source is not particularly limited, but examples thereof include gallium chloride (GaCl), gallium nitrate (Ga(NO)), gallium sulfate (Ga(SO)), gallium acetate (Ga(CHCOO)), gallium acetylacetonate (Ga(CHCOCHCOCH)), hydrates thereof, and combinations thereof.

[0018] [Solvent in the base introduction step] The solvent used in the base introduction step is methanol, ethanol, ethylene glycol, or a combination thereof. By using these solvents, it is possible to synthesize more uniform and / or finer gallium-doped zinc oxide particles, i.e., gallium-doped zinc oxide particles with a narrower particle size distribution and / or a smaller particle diameter, compared to when other solvents are used. Therefore, by forming a film using the gallium-doped zinc oxide particles synthesized in this manner by a conventionally known method such as a printing method or the mist method described below, it is possible to produce a film containing gallium-doped zinc oxide with significantly improved resistivity. The solvent may contain a small amount of water.

[0019] [base] In the production method according to this embodiment, the use of at least sodium methoxide (NaOMe) as a base suppresses the formation of layered double hydroxides (LDHs), reduces resistivity, and further reduces the particle size of gallium-doped zinc oxide. To promote Ga doping into the particles, other bases may be used in combination. Examples include, but are not limited to, sodium hydroxide (NaOH), monoethanolamine (HNCHCHOH), or a combination thereof. The base used in combination with sodium methoxide is preferably sodium hydroxide (NaOH). A base containing at least sodium methoxide is introduced into a mixed solution containing a zinc raw material, a gallium raw material, and a solvent.

[0020] When sodium methoxide (NaOMe) is used in combination with another base, the other base is used in a mixing ratio of [other base] / ([other base]+[NaOMe])=20-80%, preferably [other base] / ([other base]+[NaOMe])=about 60%. Preferably, the other base is sodium hydroxide (NaOH).

[0021] [Heating process] In the heating step of the production method according to this embodiment, a mixed solution containing a zinc source, a gallium source, a solvent, and a base containing at least sodium methoxide is heated, with stirring as necessary, to a temperature higher than the boiling point of the solvent, for example, 150°C or higher, preferably 200°C or higher, more preferably 230°C or higher, and generally 350°C or lower, thereby producing particles containing zinc and gallium. The heating time is 1 hour or longer, preferably 3 to 24 hours; a shorter heating time can suppress the growth of gallium-doped zinc oxide particles.

[0022] [Drying process] In the drying step of the production method according to this embodiment, the zinc- and gallium-containing particles obtained in the heating step are washed with an alcohol such as ethanol or water such as ion-exchanged water as needed, and then dried, for example, under reduced pressure or normal pressure at a temperature of about 40° C. to about 150° C. Finally, gallium-doped zinc oxide particles having an average particle size of more than 0 nm to 36 nm, preferably more than 0 nm to 30 nm, and more preferably more than 0 nm to 26 nm are synthesized.

[0023] [Powder compaction process] In the compacting step of the manufacturing method according to this embodiment, the gallium-doped zinc oxide particles obtained in the drying step are compressed to a predetermined shape to obtain a compact of gallium-doped zinc oxide particles. The resistivity of the compact is 0.08 MΩ·cm to 1.4 MΩ·cm, preferably 0.08 MΩ·cm to 1.3 MΩ·cm, and more preferably 0.08 MΩ·cm to 1.0 MΩ·cm.

[0024] In this embodiment, unless otherwise specified, the term "average particle size" refers to the arithmetic mean value of the unidirectional diameters (Feret diameters) of 100 or more randomly selected particles measured using an electron microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0025] Furthermore, according to the method of this embodiment, it is possible to obtain gallium-doped zinc oxide particles having a Ga doping amount of more than 0 mol % to 4.0 mol %, preferably more than 0 mol % to 3.5 mol %, and more preferably more than 0 mol % to 3.0 mol %.

[0026] In this embodiment, the "Ga doping amount" refers to the ratio of the number of gallium atoms to the total number of zinc atoms and gallium atoms contained in the gallium-doped zinc oxide particles. Unless otherwise specified, the "Ga doping amount" in this embodiment refers to a measured value when the gallium-doped zinc oxide particles are analyzed by an optical method, for example, ICP (inductively coupled plasma) optical emission spectrometry.

[0027] <Method for producing a film containing gallium-doped zinc oxide> A first aspect of the method for producing a film containing gallium-doped zinc oxide according to the present embodiment includes a dispersion preparation step of dispersing gallium-doped zinc oxide particles having an average particle diameter of 10 to 15 nm, preferably 12 to 14 nm, and gallium-doped zinc oxide particles having an average particle diameter of 16.0 to 36.0 nm, preferably 20 to 30 nm, in a liquid to obtain a dispersion, and a coating step of coating the dispersion.

[0028] Each step will be described below.

[0029] [Dispersion liquid preparation process] According to the method of the present embodiment, in the dispersion preparation step, the gallium-doped zinc oxide particles are introduced into a liquid to prepare a dispersion. Although not particularly limited, for example, the gallium-doped zinc oxide particles can be introduced into a solvent in an amount such that the content of the gallium-doped zinc oxide particles in the solvent is in the range of 1 to 30 wt % based on the total mass of the gallium-doped zinc oxide particles and the solvent.

[0030] [Gallium-doped zinc oxide particles] The gallium-doped zinc oxide particles introduced into the solvent in the mixing step are doped with Ga and have an average particle size of more than 0 to 30 nm, preferably more than 0 to 28 nm, and more preferably more than 0 to 26 nm. The Ga doping amount in the gallium-doped zinc oxide particles is more than 0 mol% to 4.0 mol%, preferably more than 0 mol% to 3.5 mol%, and more preferably more than 0 mol% to 3.0 mol%.

[0031] Gallium-doped zinc oxide particles having these characteristics are not particularly limited, but can be synthesized, for example, by the method for synthesizing gallium-doped zinc oxide particles according to the present embodiment described above.

[0032] [Liquids used in dispersion preparation] The liquid used in the mixing step is not particularly limited, but may be, for example, an alcohol such as ethylene glycol, water, or a combination thereof. Preferably, the liquid is ethylene glycol or water.

[0033] [Ultrasonic treatment] According to the method of the present embodiment, in the mixing step, it is preferable to subject the dispersion liquid containing the gallium-doped zinc oxide particles and the liquid to ultrasonic vibration treatment, which applies ultrasonic vibration to the mixture liquid, thereby making it possible to reliably and uniformly disperse the gallium-doped zinc oxide particles in the liquid.

[0034] Any device known to those skilled in the art can be used to apply ultrasonic vibrations to the dispersion, including, but not limited to, an ultrasonic homogenizer.

[0035] The time for applying ultrasonic vibrations to a dispersion containing gallium-doped zinc oxide particles and a liquid may be appropriately set taking into consideration various parameters such as the type of liquid and the amount of gallium-doped zinc oxide particles introduced into the liquid, and is not particularly limited, but can be appropriately set within a range of, for example, several minutes to several tens of minutes or several hours, such as 5 minutes to 3 hours, 10 minutes to 2 hours, or 10 minutes to 1 hour.

[0036] [Coating process] According to the method of this embodiment, the dispersion is applied onto a substrate in the application step.

[0037] The dispersion liquid can be applied to the substrate by any method known to those skilled in the art. Although not particularly limited, for example, the dispersion liquid can be applied to the substrate by bar coating, spin coating, dip coating, spray coating, screen printing, gravure printing, offset printing, or inkjet printing. By applying the dispersion liquid to the substrate by such a method, it is possible to produce a film containing gallium-doped zinc oxide at low cost and with high yield without using a vacuum device, unlike the case of vacuum film formation such as sputtering.

[0038] [Base material] According to the method of this embodiment, it is preferable to use a transparent substrate as the substrate, and more preferably a glass substrate.

[0039] [Heat treatment process] According to the method of this embodiment, the substrate after the coating step is optionally dried, for example, in an air atmosphere for several minutes to several hours, and then heat-treated in a subsequent heat-treatment step in an oxidizing or reducing atmosphere.

[0040] After the coating step, the substrate is heat-treated at a predetermined temperature in an oxidizing atmosphere, for example, in the air, to decompose and remove organic components such as ethylene glycol, thereby forming a film containing gallium-doped zinc oxide in which gallium-doped zinc oxide particles are densely packed.

[0041] Following the heat treatment in the oxidizing atmosphere, the substrate can be heat-treated at a predetermined temperature in a reducing atmosphere, such as a hydrogen-containing atmosphere, to form oxygen vacancies in ZnO:Ga and increase the carrier concentration, thereby improving the conductivity of the final film containing gallium-doped zinc oxide, i.e., achieving a lower resistivity in the final film containing gallium-doped zinc oxide.

[0042] The heat treatment in the oxidizing atmosphere can be carried out, for example, at a temperature above about 200°C, preferably above about 300°C, more preferably above about 350°C or above about 400°C, and below about 800°C, preferably below about 700°C, more preferably below about 600°C or below about 500°C, for a predetermined time, for example, about 15 minutes to about 5 hours, preferably about 30 minutes to about 3 hours. Similarly, the heat treatment in the reducing atmosphere can be carried out, for example, at a temperature above about 200°C, preferably above about 300°C, more preferably above about 350°C or above about 400°C, and below about 800°C, preferably below about 700°C, more preferably below about 600°C or below about 500°C, for a predetermined time, for example, about 15 minutes to about 5 hours, preferably about 30 minutes to about 3 hours.

[0043] The film containing gallium-doped zinc oxide obtained by the method according to this embodiment can be used in any suitable application. In particular, the film containing gallium-doped zinc oxide exhibits lower resistivity and higher transmittance than films containing gallium-doped zinc oxide obtained by conventional methods. Therefore, it can be used as a transparent conductive film or a transparent electrode. When the film containing gallium-doped zinc oxide obtained by the method according to this embodiment is used as an electrode material for solar cells or the like, it can exhibit improved performance compared to conventional films containing gallium-doped zinc oxide.

[0044] <Method for producing a film containing gallium-doped zinc oxide by mist deposition method> A second aspect of the method for producing a film containing gallium-doped zinc oxide according to the present embodiment includes a dispersion preparation step of dispersing gallium-doped zinc oxide particles having an average particle diameter of more than 0 nm to 30 nm, preferably more than 0 nm to 28 nm, and more preferably more than 0 nm to 26 nm and a resistivity of 0.08 MΩ·cm to 1.4 MΩ·cm, preferably 0.08 MΩ·cm to 1.3 MΩ·cm, and more preferably 0.08 MΩ·cm to 1.0 MΩ·cm in a liquid to obtain a dispersion; a mist-forming step of forming the dispersion into a mist; a supplying step of supplying the misted dispersion onto a substrate; and a drying step of drying the dispersion present on the substrate after the supplying step.

[0045] The gallium-doped zinc oxide particles according to this embodiment have high dispersibility in aqueous liquids, and therefore, it is possible to form a nanoparticle film by the above-described method. The nanoparticle film can be produced, for example, by spraying a nanoparticle-containing mist, which is obtained by misting (atomizing) a dispersion containing gallium-doped zinc oxide particles by the vibration of an ultrasonic pendulum in the MHz range, onto a substrate.

[0046] Furthermore, the above-described method does not require heat treatment of the substrate at high temperatures, which alleviates restrictions on the substrate material. For example, film formation is possible on flexible substrates made of resin materials with low softening points.

[0047] Each step will be described below.

[0048] (1) For the dispersion preparation step, the conditions described for the step performed in the first embodiment of the method for producing a film containing gallium-doped zinc oxide described above can be employed, except that gallium-doped zinc oxide particles are used that have an average particle size of more than 0 nm to 30 nm, preferably more than 0 nm to 328 nm, and more preferably more than 0 nm to 26 nm, and a resistivity of 0.08 MΩ cm to 1.4 MΩ cm, preferably 0.08 MΩ cm to 1.3 MΩ cm, and more preferably 0.08 MΩ cm to 1.0 MΩ cm.

[0049] The mist-forming step (2) may be any method that can mist (atomize) the dispersion liquid containing the gallium-doped zinc oxide particles obtained in the step (1).

[0050] Known methods can be used to generate mist, such as pressurization, rotating disk, ultrasonic, electrostatic, orifice vibration, and steam. In this embodiment, since the dispersion liquid is a gallium-doped zinc oxide particle dispersion, a physical mist generation (atomization) method is preferred. This makes it easy to control the liquid temperature and droplet size.

[0051] In the mist-forming step, the mist of the dispersion liquid can be carried to the subsequent supply step by using a carrier gas, such as an inert gas such as argon, helium, or nitrogen.

[0052] Furthermore, between the steps (2) and (3), a step of homogenizing the mist using a mist trap or a retention step of providing a retention period (retention portion) for the mist may be performed.

[0053] The liquid for dispersing the particles may be water or an organic solvent such as ethanol, methanol, or propanol. For example, the above-mentioned component (C) or component (D) may be used as the liquid. The liquid may be one type alone or two or more types in combination. The frequency band for atomization is not limited to the above bands as long as it is suitable for each liquid. The material of the substrate is not limited, and may be glass, resin, metal, or the like, and it is preferable to provide a process for hydrophilizing the surface, such as UV irradiation.

[0054] (3) The supplying step is not particularly limited as long as it is a method for supplying a mist to a substrate, and known techniques can be used. For example, a method in which the fine droplets obtained in the mist-forming step are sprayed onto the substrate by a mist method can be mentioned. Examples of the mist method include ultrasonic spraying, mist CVD, the Sonia source method, and the hot wall method. These methods can be selected taking into consideration the film thickness of the film to be formed on the substrate, the size of the droplets to be sprayed, and the like.

[0055] The supply step may be carried out under atmospheric pressure, reduced pressure, or vacuum, but is preferably carried out under atmospheric pressure from the viewpoint of convenience.

[0056] Alternatively, the mist dispersion may be sprayed onto a masked substrate in accordance with a predetermined pattern to pattern a film containing gallium-doped zinc oxide particles, thereby enabling highly accurate dimensional control.

[0057] For example, a material that becomes relatively hydrophilic upon light irradiation may be used as the masking material. By irradiating the material with light corresponding to a predetermined pattern, relatively hydrophilic regions and relatively water-repellent regions are formed, and by spraying the mist of the dispersion liquid in this state, the mist of the dispersion liquid can be deposited only in the hydrophilic regions.

[0058] Furthermore, since material restrictions on the substrate are relaxed, thin, highly flexible film substrates (sometimes called "sheet substrates") can be used as the substrate. Furthermore, continuous production such as roll-to-roll production becomes possible.

[0059] The substrate may be made of known materials, such as glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate (CAP).

[0060] (4) In the drying process, the liquid of the dispersion sprayed onto the substrate is removed. For example, the liquid is vaporized by irradiation with infrared light or heating, thereby forming a film containing gallium-doped zinc oxide particles on the surface of the substrate. The heating temperature can be set taking into consideration the boiling point of the liquid, the softening point of the substrate, and other physical properties that affect the physical properties of the film. The softening point of the substrate here refers to the temperature at which the substrate softens and begins to deform when heated, and can be determined, for example, by a test method in accordance with JIS K7191-1.

[0061] After the step (4), if necessary, a UV irradiation step or the like may be carried out for the purpose of modifying the substrate, such as by imparting hydrophilicity.

[0062] Here, an example of a film forming apparatus that can be used in the manufacturing method according to this embodiment will be described.

[0063] FIG. 1 is a conceptual diagram showing an example of a film forming apparatus using a mist method according to this embodiment.

[0064] The film forming apparatus 1 has a first tank for misting a dispersion containing gallium-doped zinc oxide particles, a second tank which is a mist trap for homogenizing the mist, and a third tank for spraying the mist onto the substrate 10.

[0065] The first tank contains the above-mentioned dispersion liquid S containing gallium-doped zinc oxide particles.

[0066] Air 20 is flowed through the first tank to form a flow path for the mist.

[0067] The first tank is equipped with an ultrasonic vibrator 30. The ultrasonic vibrator 30 turns a dispersion liquid containing gallium-doped zinc oxide particles into mist. The particle diameter of the mist is not particularly limited, but is preferably 10 μm or less (for example, 1 to 10 μm). The mist generated in the first tank is transported to the second tank via a pipe provided in the first layer. In the second tank, excess mist accumulates at the bottom of the tank, and mist with a more uniform particle diameter is transported to the third layer via a pipe provided in the second tank. It is preferable that the configuration be such that mist with a particle diameter of 5 μm or less (for example, 1 to 5 μm) is transported from the second tank to the third tank.

[0068] Substrate 10 is placed in the third tank, and the mist transported from the second tank is sprayed onto the substrate. In the third tank, the mist is sprayed onto substrate 10 for a predetermined time. Then, the dispersion medium of the mist that has adhered to substrate 10 evaporates, thereby forming a film containing gallium-doped zinc oxide particles on the surface of substrate 10. Note that, if a certain amount of time has passed since spraying, new mist will adhere to substrate 10 before the mist evaporates, causing the droplets of dispersion to flow down, preventing the formation of a uniform film on substrate 10. The time to stop spraying the mist onto substrate 10 may be the time when the mist containing ZnO:Ga fine particles liquefies and flows down from substrate 10, or the time when a film with a desired thickness has been formed on substrate 10.

[0069] If the substrate 10 is heated excessively in the third tank, it may be softened and deformed. Therefore, it is preferable that the mist is sprayed in the third tank at a temperature lower than the softening point of the substrate to form a film. Furthermore, if the substrate 10 is heated above a predetermined temperature when the mist is sprayed, the ZnO:Ga particles attached to the substrate 10 will aggregate, deteriorating the uniformity of the film. Therefore, it is more preferable that the mist is sprayed at a temperature of 40°C or lower (for example, 10 to 40°C) to form a film.

[0070] When selectively forming a film on the substrate 10, a water-repellent film is selectively formed on the substrate 10 in advance, so that the mist is deposited only on relatively hydrophilic regions. In this case, if the substrate 10 is placed horizontally, the mist adhering to the relatively water-repellent regions is less likely to be repelled, and it may be impossible to selectively form a film. For this reason, in the third tank, it is preferable to spray the mist onto the substrate 10 that is tilted relative to the horizontal plane.

[0071] Similarly, in the third tank, it is preferable that the mist be sprayed onto the substrate 10 that is tilted with respect to a plane perpendicular to the direction of mist spraying, in order to remove excess fine particles adhering to areas that are relatively water-repellent with the force of the mist spray.

[0072] The film forming apparatus may omit the mist trap in the second tank.

[0073] In addition to the ultrasonic vibrator 30 described above, other methods for generating mist include an electrostatic method in which a voltage is applied directly to a capillary tube that sprays droplets to generate mist; a pressure method in which pressure is applied to increase the flow rate of gas and the resulting mist is dispersed by colliding it with the liquid; a rotating disk method in which droplets are dropped onto a rapidly rotating disk and the resulting mist is dispersed by centrifugal force; and an orifice vibration method in which droplets are passed through an orifice plate with micro-sized holes, and the droplets are cut by applying vibrations using a piezoelectric element or the like to generate micro-sized droplets. These methods can be selected as appropriate depending on cost, performance, and other factors. Furthermore, mist can be generated by combining multiple of the above methods.

[0074] A suitable example of a film obtained by the above-described production method is a film containing gallium-doped zinc oxide particles having an average particle size of 30 nm or less. Such a film can be suitably used as an anti-reflection film, etc., as described below.

[0075] The film according to the present embodiment may be a film in which gallium-doped zinc oxide particles are dispersed in a resin material. The components of the resin material can be selected appropriately depending on the application of the film. Examples of the resin material include polymethyl methacrylate resin.

[0076] Furthermore, the substrate after the coating step may optionally be dried in the air for several minutes to several hours, and then heat-treated in an oxidizing or reducing atmosphere.

[0077] The obtained film can be used as a transparent conductive film, a transparent electrode, etc., and can be used in various electronic devices. <Anti-reflective film> A suitable example of the film according to this embodiment is a film containing gallium-doped zinc oxide particles, and therefore can be suitably used, for example, as an optical thin film that suppresses light scattering. Therefore, the film according to this embodiment can be suitably used as a layer constituting an antireflection film. Such an antireflection film may have a single-layer structure or a multi-layer structure of two or more layers. For example, the antireflection film may include at least one layer of the film according to this embodiment.

[0078] The antireflection film according to this embodiment can be provided on the surface of an optical element such as an optical lens of various optical devices such as a camera, a microscope, etc. The optical element such as an optical lens provided with such an antireflection film can suppress surface reflection, thereby eliminating stray light. [Example]

[0079] The present embodiment will be described in more detail with reference to the following examples and comparative examples, but the present embodiment is not limited to the following examples.

[0080] [Example 1]

[0081] [Synthesis of Gallium-Doped Zinc Oxide Particles] In this example, gallium-doped zinc oxide particles were synthesized by the method according to this embodiment, and the properties of the synthesized gallium-doped zinc oxide particles were investigated.

[0082] Example 1A [Synthesis of Gallium-Doped Zinc Oxide Particles (Base Mixing Ratio: R0.2)] A 5 mL methanol solution containing 60 M zinc chloride and 10 mol % gallium chloride was prepared.

[0083] A 5 mL methanol solution of sodium hydroxide-sodium methoxide mixed base (mixing ratio R([sodium hydroxide] / ([sodium hydroxide] + [sodium methoxide])) = 0.2) was prepared. Zinc chloride, gallium chloride, methanol, sodium hydroxide, and sodium methoxide were all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0084] The methanol solution in which the zinc chloride and gallium chloride were dissolved was mixed with the methanol solution in which the mixed base of R0.2 was dissolved, and the mixture was stirred for 10 minutes, and then heated at 200° C. for 24 hours.

[0085] The mixed solution obtained after heating was washed with ethanol and ion-exchanged water, and then subjected to solid-liquid separation by centrifugation twice. The obtained solid was dried to obtain gallium-doped zinc oxide particles (R0.2).

[0086] Example 1B [Synthesis of Gallium-Doped Zinc Oxide Particles (Base Mixing Ratio: R0.4)] Gallium-doped zinc oxide particles (R0.4) were obtained in the same manner as in Example 1A, except that a mixed base of R0.4 ([sodium hydroxide] / ([sodium hydroxide]+[sodium methoxide])=0.4) was used.

[0087] Example 1C [Synthesis of Gallium-Doped Zinc Oxide Particles (Base Mixing Ratio: R0.6)] Gallium-doped zinc oxide particles (R0.6) were obtained in the same manner as in Example 1A, except that a mixed base of R0.6 ([sodium hydroxide] / ([sodium hydroxide]+[sodium methoxide])=0.6) was used.

[0088] Example 1D [Synthesis of Gallium-Doped Zinc Oxide Particles (Base Mixing Ratio: R0.8)] Gallium-doped zinc oxide particles (R0.8) were obtained in the same manner as in Example 1A, except that a mixed base of R0.8 ([sodium hydroxide] / ([sodium hydroxide]+[sodium methoxide])=0.8) was used.

[0089] [Comparative Example 1] [Synthesis of Gallium-Doped Zinc Oxide Particles (Sodium Hydroxide Only: R1.0)] Gallium-doped zinc oxide particles (R1.0) were obtained in the same manner as in Example 1A, except that a base of R1.0 (sodium hydroxide alone) was used.

[0090] [Analysis of Gallium-Doped Zinc Oxide Particles] The gallium-doped zinc oxide particles obtained in Examples 1A to 1D and Comparative Example 1 were pressed using a hydraulic pallet press to form a predetermined shape, thereby obtaining a green compact. The surface resistance of the green compacts obtained was measured and the values ​​were compared (Loresta GP MCP-T610, Mitsubishi Chemical Analytech). The results are shown in Table 1.

[0091] Referring to Table 1, the gallium-doped zinc oxide particles (R0.2) of Example 1A had the smallest average particle diameter, and the gallium-doped zinc oxide particles (R0.8) of Example 1D had the smallest resistivity. In addition, when only sodium hydroxide was used as a base as in Comparative Example 1, the average particle diameter exceeded 30 nm.

[0092] Figure 2 shows transmission electron microscope (TEM) photographs of the compacts of gallium-doped zinc oxide particles obtained in Examples 1A to 1D and Comparative Example 1. Referring to the TEM photographs in Figure 2, it can be seen that very fine particles with an average particle size of approximately 13 to 30 nm were synthesized in Examples 1A to 1D. Furthermore, the Ga doping amount of these particles analyzed by ICP (inductively coupled plasma) optical emission spectrometry was found to be 2.5 to 3.3 mol%. The results are shown in Table 1.

[0093] [Table 1]

[0094] [Example 2] [Production of a film containing gallium-doped zinc oxide (a combination of R0.2 and R0.8 particles)] In this example, films containing gallium-doped zinc oxide were produced by the mist film-forming method according to this embodiment with different blending ratios, and the resistivities of these films were measured.

[0095] Example 2A [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=0:10)] Gallium-doped zinc oxide particles with a blending ratio of R0.2:R0.8=0:10 were introduced into liquid water in an amount of 3 wt% based on the total mass of the gallium-doped zinc oxide particles and water. Next, ultrasonic vibrations were applied to the resulting dispersion using an ultrasonic homogenizer for approximately 30 minutes to thoroughly disperse the gallium-doped zinc oxide particles in the water.

[0096] The resulting dispersion was then coated onto a glass substrate and dried in the air. Finally, the coated glass substrate was heat-treated at 300°C for 1 hour in the air, and then at 300°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere to produce a gallium-doped zinc oxide film on the glass substrate.

[0097] Example 2B [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=2:8)] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 2A, except that the compounding ratio of gallium-doped zinc oxide particles was R0.2:R0.8=2:8.

[0098] [Example 2C] [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=4:6)] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 2A, except that the compounding ratio of gallium-doped zinc oxide particles was R0.2:R0.8=4:6.

[0099] Example 2D [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=6:4)] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 2A, except that the compounding ratio of gallium-doped zinc oxide particles was R0.2:R0.8=6:4.

[0100] Example 2E [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=8:2)] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 2A, except that the compounding ratio of gallium-doped zinc oxide particles was R0.2:R0.8=8:2.

[0101] [Example 2F] [Production of a film containing gallium-doped zinc oxide (particle blending ratio R0.2:R0.8=10:0)] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 2A, except that the compounding ratio of gallium-doped zinc oxide particles was R0.2:R0.8=10:0.

[0102] The surface resistance of the films containing gallium-doped zinc oxide obtained in Examples 2A to 2F was measured (Loresta GP MCP-T610, Mitsubishi Chemical Analytech). The results are shown in Table 2 and FIG.

[0103] [Table 2]

[0104] Referring to Table 2, it was found that the film containing gallium-doped zinc oxide of Example 2D (composition ratio: R0.2 / (R0.2+R0.8)=60%) had the smallest resistivity.

[0105] [Example 3] [Production of films containing gallium-doped zinc oxide when formed at different heat treatment (annealing) temperatures] In this example, films were produced using dispersions of R0.2 gallium-doped zinc oxide particles (60%) and R0.8 gallium-doped zinc oxide particles (40%) prepared by the method according to this embodiment, with the heat treatment (annealing) temperature varied, and the resistivity of these films was measured.

[0106] Example 3A [Membrane production at 200°C heat treatment process] Using the same method as in Example 2A, 60% R0.2 gallium-doped zinc oxide particles and 40% R0.8 gallium-doped zinc oxide particles were dispersed in ethylene glycol. The dispersion was applied to a glass substrate and then dried in the air. The coated glass substrate was then heat-treated at 200°C for 1 hour in the air, and then heat-treated at 200°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere to produce a film containing gallium-doped zinc oxide on the glass substrate.

[0107] Example 3B [Membrane production at 300°C heat treatment process] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 3A, except that the glass substrate after coating with the dispersion was heat-treated at 300°C for 1 hour in an air atmosphere, and then heat-treated at 300°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere.

[0108] Example 3B [Membrane production at 300°C heat treatment process] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 3A, except that the glass substrate after coating with the dispersion was heat-treated at 300°C for 1 hour in an air atmosphere, and then heat-treated at 300°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere.

[0109] Example 3C [Membrane production at 400℃ heat treatment process] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 3A, except that the glass substrate after coating with the dispersion was heat-treated at 400°C for 1 hour in an air atmosphere, and then heat-treated at 400°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere.

[0110] Example 3D [Membrane production at 500℃ heat treatment process] A film containing gallium-doped zinc oxide was produced in the same manner as in Example 3A, except that the glass substrate after coating with the dispersion was heat-treated at 500°C for 1 hour in an air atmosphere, and then heat-treated at 500°C for 1 hour in an argon-hydrogen (4% hydrogen) atmosphere.

[0111] The surface resistance of each of the resulting films containing gallium-doped zinc oxide was measured (Loresta GP MCP-T610, Mitsubishi Chemical Analytech). The results are shown in Table 3 and FIG. 4.

[0112] [Table 3]

[0113] Referring to Table 3, it was found that films containing gallium doped zinc oxide obtained above 200° C. had low resistivity. [Explanation of symbols]

[0114] 1...film forming device, 10...substrate, 20...air, 30...ultrasonic vibrator, S...raw material solution

Claims

1. Gallium-doped zinc oxide particles having an average particle size of more than 0 nm to 30 nm and a resistivity of 0.08 MΩ·cm to 1.4 MΩ·cm (excluding those having a resistivity of 0.47 MΩ·cm to 0.52 MΩ·cm).

2. Gallium-doped zinc oxide particles having an average particle diameter of more than 0 nm to 30 nm, a resistivity of 0.08 MΩ·cm to 1.4 MΩ·cm, and an ellipsoidal projected particle shape.

3. Gallium-doped zinc oxide particles according to claim 1 or 2, wherein the doping amount of gallium is more than 0 mol% to 4.0 mol%.

4. A film comprising the gallium-doped zinc oxide particles according to any one of claims 1 to 3.

5. The film described in claim 4, having a surface resistivity of 0.03 to 1.0 MΩ·cm.

6. A transparent conductive film comprising the film according to claim 4 or 5.

7. An electronic device comprising the transparent conductive film according to claim 6 .

8. 1. A method for producing gallium-doped zinc oxide particles, comprising: a base introducing step of introducing a base containing at least sodium methoxide into a mixed solution containing a zinc raw material, a gallium raw material, and a solvent; a heating step of heating the mixed solution containing the base at a temperature higher than the boiling point of the solvent to obtain gallium-doped zinc oxide particles; and a drying step of drying the gallium-doped zinc oxide particles.

9. 9. The method for producing gallium-doped zinc oxide particles according to claim 8, further comprising sodium hydroxide as the base.

10. 10. The method for producing gallium-doped zinc oxide particles according to claim 8 or 9, wherein the solvent is selected from the group consisting of methanol, ethanol, ethylene glycol, and combinations thereof.

11. The method for producing gallium-doped zinc oxide particles according to any one of claims 8 to 10, wherein the gallium-doped zinc oxide particles have an average particle diameter of more than 0 nm to 30 nm and a resistivity of 0.08 MΩ cm to 1.4 MΩ cm.

12. a dispersion preparation step of dispersing the gallium-doped zinc oxide particles obtained by the method for producing gallium-doped zinc oxide particles according to any one of claims 8 to 11 in a liquid to obtain a dispersion; a mist-forming step of misting the dispersion; a supplying step of supplying the mist-formed dispersion onto a substrate; 1. A method for producing a film comprising gallium-doped zinc oxide particles, comprising:

13. 13. The method for producing a film containing gallium-doped zinc oxide particles according to claim 12, further comprising a heat treatment step of heat treating the film containing gallium-doped zinc oxide particles at a temperature of more than 200°C and not more than 800°C.

14. a dispersion preparation step of dispersing gallium-doped zinc oxide particles having an average particle size of more than 0 nm to 30 nm and a resistivity of 0.08 MΩ cm to 1.4 MΩ cm (excluding those having a resistivity of 0.47 MΩ cm to 0.52 MΩ cm) in a liquid to obtain a dispersion; a mist-forming step of misting the dispersion; a supplying step of supplying the mist-formed dispersion onto a substrate; 1. A method for producing a film comprising gallium-doped zinc oxide particles, comprising:

15. A dispersion liquid preparation step of dispersing gallium-doped zinc oxide particles, the particles having an average particle diameter of more than 0 nm to 30 nm, a resistivity of 0.08 MΩ cm to 1.4 MΩ cm, and an ellipsoidal projected particle shape, in a liquid to obtain a dispersion liquid; a mist-forming step of misting the dispersion; a supplying step of supplying the mist-formed dispersion onto a substrate; 1. A method for producing a film comprising gallium-doped zinc oxide particles, comprising:

16. 16. The method for producing a film containing gallium-doped zinc oxide particles according to claim 14 or 15, further comprising a heat treatment step of heat treating the film containing the gallium-doped zinc oxide particles at a temperature of more than 200°C and not more than 800°C.

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