WO2023058704A1 - Method for producing thin film formed from dense single layer film of nanosheet and usage of thin film - Google Patents

Abstract

The purpose of the present invention is to newly provide a method for producing a thin film formed from a dense single layer film of a nanosheet. This thin film production method forms a thin film formed from a dense single layer film of a nanosheet.

Description

Method for producing thin film composed of dense monolayer film of nanosheets, and use of the thin film

The present invention relates to a method for producing a thin film consisting of a dense monolayer film of nanosheets, and uses of the thin film.

As a method for producing thin films of nanosheets, for example, Non-Patent Document 1 discloses the Langmuir-Blodgett (LB) method. In this technique, after the nanosheet colloidal dispersion is spread in a trough, surface pressure is applied to adsorb the nanosheets to the air-liquid interface, and then the nanosheets are transferred to the substrate to obtain an arrayed nanosheet monolayer film. . However, this technique has problems such as a long film-forming time, a need for a special apparatus, a complicated film-forming operation, and a small area of a substrate on which a film can be formed.

As a method for producing thin films of nanosheets, for example, Non-Patent Document 2 discloses a spin coating method. In this technique, a small amount of an organic solvent sol in which nanosheets are dispersed in an organic solvent is dropped onto a substrate and spin-coated to obtain a densely-packed monolayer film of nanosheets. However, this technique has problems such as the need for pretreatment of the solution and the need for precise setting of conditions.

In addition, the techniques of Non-Patent Documents 1 and 2 require a large amount of solution consumption, and as a result, 95% or more of the solution is discarded.

The purpose of the present invention is to newly provide a method for producing a thin film consisting of a dense monolayer film of nanosheets.

The inventors of the present invention have devoted themselves to research in order to achieve the above objectives.

The inventors
(1) A colloidal aqueous solution in which nanosheets from which a layered compound is exfoliated is dispersed is developed in pure water, and then
(2) forming a densely aligned film of the nanosheets at the air/water interface, and then (3) transferring the densely aligned film of the nanosheets to a substrate,
Developed to manufacture thin films.

The present inventors have found that this nanosheet densely-arranged film can solve the problems remaining in conventional nanosheet thin film manufacturing methods.

That is, the present invention relates to the following method for producing a thin film composed of a dense monolayer film of nanosheets and uses of the thin film.

Section 1.
A method for producing a thin film,
(1) A process of developing a colloidal aqueous solution in which nanosheets are dispersed on the water surface,
(2) forming a dense monolayer film of the nanosheets at the gas-liquid interface; and (3) transferring the dense monolayer film of the nanosheets to a substrate,
forming a thin film consisting of a dense monolayer film of said nanosheets;
Thin film manufacturing method.

Section 2.
The nanosheet is a nanosheet in which a layered compound is delaminated,
2. A method for producing a thin film according to item 1 above.

Item 3.
Compounds constituting the layered compound include titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, and molybdenum oxide. , ruthenium oxide, graphene, graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and at least one compound selected from the group consisting of transition metal carbide,
3. A method for producing a thin film according to item 2 above.

Section 4.
The colloidal aqueous solution is an alcohol-containing colloidal aqueous solution,
4. A method for producing a thin film according to any one of 1 to 3 above.

Item 5.
By repeating the steps (1) to (3),
forming a stack of dense monolayer films of the nanosheets;
5. A method for producing a thin film according to any one of Items 1 to 4.

Item 6.
In at least one step of steps (1) to (3),
(4) a step of irradiating the nanosheet with ultraviolet rays to remove organic substances between single layers of the nanosheet;
6. The method for producing a thin film according to any one of Items 1 to 5, comprising

Item 7.
An optical thin film comprising a thin film produced by the method for producing a thin film according to any one of Items 1 to 6.

Item 8.
A dielectric thin film comprising a thin film produced by the method for producing a thin film according to any one of Items 1 to 6.

Item 9.
A conductive thin film comprising a thin film produced by the method for producing a thin film according to any one of Items 1 to 6.

Item 10.
A thin film having a release agent content of 100 ppmwt or less, produced by the method for producing a thin film according to any one of Items 1 to 6 above.

Item 11.
a thin film,
Consisting of a dense monolayer film of nanosheets,
The nanosheets include titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, molybdenum oxide, ruthenium oxide, and graphene. , graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and transition metal carbide.
A thin film having a release agent content of 100 ppmwt or less.

According to the method for producing a thin film composed of a dense monolayer film of nanosheets of the present invention (the method for producing a thin film of the present invention), a film is formed on a colloidal aqueous solution in which nanosheets are suspended, and transferred to a substrate to form a thin film. It is possible to The thin film manufacturing method of the present invention can shorten the nanosheet manufacturing time compared to conventional manufacturing methods such as dip coating and spin coating, and the manufactured nanosheet thin film has a denser structure. The nanosheet (TiO ₂ , RuO _{2 ,} etc.) thin film (the thin film of the present invention) produced by the thin film production method of the present invention has a dense and large-area coating structure.

The present invention can newly provide a method for producing a thin film consisting of a dense monolayer film of nanosheets.

FIG. 1 shows an example of a method for producing a thin film of the present invention. FIG. 2 presents an illustration of the monolayer coverage of the thin films of the present invention. FIG. 3 shows examples of thin films (single-layer films and multilayer films) of the present invention. FIG. 4 shows an application example of the thin film manufacturing method of the present invention. FIG. 5 shows an example (Example 1) of the method for producing a thin film of the present invention. FIG. 6 shows an example of the method for producing a thin film of the present invention (Example 2). FIG. 7 shows an example (Example 3) of the method for producing a thin film of the present invention. FIG. 8 shows an example (Example 4) of the method for producing a thin film of the present invention. FIG. 9 shows an example of the method for producing a thin film of the present invention (Example 5). FIG. 10 shows an example of the method for producing a thin film of the present invention (Example 6). FIG. 11 shows the superiority of the thin film manufacturing method of the present invention.

The present invention will be described in detail below.

As used herein, "contain" is a concept that includes all of "comprise", "consist essentially of", and "consist of". Further, in this specification, when a numerical range is indicated by "A to B", it means A or more and B or less.

[1] Method for producing thin films consisting of dense monolayer films of nanosheets (Figs. 1 and 2)
The method for producing a thin film composed of a dense monolayer film of nanosheets of the present invention (the method for producing a thin film of the present invention) comprises:
(1) A process of developing a colloidal aqueous solution in which nanosheets are dispersed on the water surface,
(2) forming a dense monolayer film of the nanosheets at the gas-liquid interface; and (3) transferring the dense monolayer film of the nanosheets to a substrate,
It is characterized by forming a thin film composed of a dense monolayer film of the nanosheet.

The thin film manufacturing method of the present invention employs an interfacial transfer method in which a dense monolayer film of nanosheets is formed on the gas-liquid interface, and then the dense monolayer film of nanosheets is transferred to a substrate.

Figure 1: Examples of nanosheet manufacturing methods The thin film manufacturing method of the present invention includes, for example, (1) a colloidal aqueous solution (TiO ₂ , RuO ₂ , nanosheet ink such as GO) is developed (ink drop), then (2) step of forming a nanosheet densely arranged film at the air/water interface (formation of dense film), then (3) ) includes the step of transferring (substrate transfer) a nanosheet densely arranged film (Film) to a substrate (Substrate, metal, glass, PET, etc.).

According to the thin film manufacturing method of the present invention, a dense monolayer film of nanosheets (Ti _0.87 O ₂ etc.) can be produced in a large area in a short time (about 30 seconds) with a simple operation (low cost etc.). I can do things. In the method for producing a thin film of the present invention, preferably, an alcohol-added solution is used as the colloidal aqueous solution, so that a high-quality nanosheet monolayer film in which nanosheets are densely arranged can be produced by a simple operation in a short time. It can be manufactured.

Definition of Dense in a Dense Monolayer of Nanosheets (Fig. 2(A))
The dense monolayer film of nanosheets of the present invention (interfacial integration method) maximizes the excellent functions of nanosheets and is useful for the fabrication of devices.

Conventionally, it was difficult to produce a nanosheet film with a coverage rate of 80% or more even on a small substrate of 1 cm ² square. In the production of nanosheet films by the conventional spin coating method, the coverage rate of the nanosheets was about 80%, and the void portions (defective portions) of the nanosheets were about 20%.

The dense monolayer film of the nanosheets of the present invention is in a state in which the nanosheets are densely arranged without gaps. The coverage ratio (single layer portion) of the dense monolayer film of the nanosheet is usually about 90% or more (area ratio). The gap portion (defective portion) of the nanosheet is usually in the range of 0% or more and about 10% or less (area ratio).

In the dense monolayer film of the nanosheets of the present invention, the monolayer coverage of the nanosheets is preferably 90% or more, more preferably 95% or more, and still more preferably 97% or more in terms of area ratio. Yes, and particularly preferably 98% or more. The area ratio of gaps (defective parts) in the nanosheet is preferably 10% or less, more preferably 5% or less, and still more preferably 2% or less.

Numerical limitation of coverage (measurement method) (Fig. 2 (B))
The dense monolayer film coverage of the nanosheets of the present invention can be evaluated by atomic force microscopy, confocal laser scanning microscopy, or scanning electron microscopy.

With an atomic force microscope, it is possible to evaluate the unevenness of a dense monolayer film of nanosheets at the atomic level. Atomic force microscopy distinguishes between single-layered and multi-layered parts (overlapping single-layered parts, overlapping parts, bright parts) and defect parts (parts without nanosheets, dark parts). By evaluating the area ratio with other portions, it is possible to evaluate the single layer coverage.

With a confocal laser microscope or a scanning electron microscope, the dense monolayer film of nanosheets is analyzed based on the contrast between the optical image and the secondary electron image. The single layer coverage can be evaluated by distinguishing from the dark portion and evaluating the area ratio of the single layer portion and the other portions.

The thin film production method (interface integration method) of the present invention makes it possible to produce a dense monolayer film of nanosheets with a nanosheet coverage of 95% or more in a large area and at a high yield.

(1) Step of developing a colloidal aqueous solution in which nanosheets are dispersed on a water surface The water surface is preferably a pure water surface.

The nanosheet is preferably a nanosheet in which a layered compound is delaminated.

A stripping agent such as tetrabutylammonium ion (TBA ⁺ ) is used for single layer stripping. A stripping agent is used to strip the surfactant.

The compound constituting the layered compound is preferably titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, oxide At least one compound selected from the group consisting of molybdenum oxide, ruthenium oxide, graphene, graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and transition metal carbide.

The layered titanium oxide can preferably be synthesized by a solid-phase synthesis method.

Representative substances constituting layered compounds are preferably graphene, graphene oxide, oxides, hydroxides, hexagonal boron nitride, transition metal chalcogenites, transition metal carbides, and the like. Nanosheets obtained by single-layer exfoliation of these layered compounds are sheet-like nanomaterials with high two-dimensional anisotropy of lateral size of several hundred nm to several tens of μm with respect to the thickness of several atoms. Nanosheets composed of these layered compounds reflect their chemical composition and structure, and have excellent electronic and ionic conductivity, semiconductor properties, insulating properties, high dielectric properties, ferroelectric properties, ferromagnetism, fluorescence properties, photocatalytic properties, etc. characterize.

Titanium oxide (Ti _0.87 O ₂ ) nanosheets have a high refractive index and dielectric constant, and can be used for optical and dielectric applications. Nanosheets of titanium oxide (Ti _1-δ O ₂ ) exhibit properties such as semiconducting properties and photocatalytic properties.

Perovskite (Ca ₂ Nb ₃ O ₁₀ ) nanosheets have high dielectric constant (high dielectric) and insulating properties, and can be applied to dielectrics. Perovskite (Ca ₂ Nb ₃ O ₁₀ ) nanosheets exhibit properties such as high heat resistance.

Ruthenium oxide (RuO ₂ ) nanosheets have high conductivity (conductivity), can be applied to conductors, and function as excellent transparent conductive films.

　Graphene oxide (GO) nanosheets have electrical insulation and high ionic conductivity, and can be applied to electrocatalysts. Graphene oxide (GO) nanosheets exhibit properties such as semiconductivity.

Hexagonal boron nitride (h-BN) nanosheets have electrical insulation, high withstand voltage, and high thermal conductivity, and can be applied to insulating films and heat dissipation substrates.

Nanosheets _of photochromic films ( _Cs4W11O36 ) exhibit _photochromic properties.

Conductive two-dimensional (2D) carbide, nitride, and carbonitride nanosheets known as MXenes exhibit conductive properties. The general structure of MXene is M _n+1 X _n T _x . M is an early transition metal (Ti, V, Nb, etc.). X is C or N (or both). The range of n is 1-4. T _x represents the surface termination (typically -O, -OH, and -F), with n+1 layers of M covering n layers of X in the [MX] _n M arrangement.

Nanosheets composed of these layered compounds can be applied to inorganic nanosheets with various compositions and structures. The method for producing a thin film of the present invention is an extremely versatile film-forming technique that allows nanosheets composed of these layered compounds to be formed on various substrates.

As the colloidal aqueous solution, a colloidal aqueous solution (about 0.004% by mass) obtained by further diluting a colloidal aqueous solution containing about 0.4% by mass of a layered compound (layered titanium oxide, etc.) by 100 is preferably used.

In the thin film manufacturing method of the present invention, the colloidal aqueous solution is preferably an alcohol-containing colloidal aqueous solution.

In the thin film manufacturing method of the present invention, a dense nanosheet monolayer film can be easily manufactured by adding alcohol to the nanosheet colloidal solution.

In the thin film manufacturing method of the present invention, the concentration difference due to alcohol evaporation is used, and the convection phenomenon is used. When the colloidal aqueous solution in which the nanosheets are dispersed is dropped (developed) on the water surface, the dropped colloidal aqueous solution spreads over the water surface. At this time, since the nanosheet is charged, it interacts weakly with the water surface and is transported to the outside by convection. In the observation of the interface, when the colloidal aqueous solution droplets match the size of the container, alcohol evaporates quickly at the edge of the container. Arrange in a self-organizing manner.

In the method for producing a thin film of the present invention, by adding an alcohol (such as ethanol) to the colloidal aqueous solution, the surface tension of the colloidal aqueous solution is reduced, the evaporation rate of the dispersion medium in the colloidal aqueous solution added dropwise is increased, and the dispersion medium is It can promote the convection of the nanosheet inside.

There are no particular restrictions on the alcohol added to the colloid aqueous solution for film formation.

In addition to ethanol, it is preferable to use lower alcohols with 5 or less carbon atoms because they have good affinity with water.

The alcohol is preferably from methanol, ethanol, n-propyl alcohol (n-propanol), isopropyl alcohol (IPA), n-butyl alcohol (n-butanol), isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol. is the alcohol of choice. These alcohols are readily available and easy to handle.

As for the alcohol, one of these alcohols may be used alone, or two or more may be mixed (blended) and used.

Among alcohols, ethanol reduces the surface tension of the colloidal aqueous solution, increases the evaporation rate of droplets, and affects the inside of droplets of nanosheets (dispersion medium It is particularly suitable from the viewpoint of promoting convection in the medium).

The amount of alcohol to be added is preferably 0.5% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and still more preferably , 0.5% by mass or more and 3% by mass or less.

In addition to alcohol (preferably lower alcohol), or in addition to alcohol, a water-soluble organic solvent may be added to the colloid aqueous solution for film formation.

The water-soluble organic solvent is preferably an aprotic polar solvent selected from dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF) and formamide .

As for the aprotic polar solvent, one of these aprotic polar solvents may be used alone, or two or more may be mixed (blended) and used.

As for the alcohol and the aprotic polar solvent, these alcohols and aprotic polar solvents may be used alone, or two or more may be mixed (blended) and used.

The operation of developing the colloidal aqueous solution in which the nanosheets are dispersed on the water surface is performed, for example, by filling a Petra dish or the like with water (preferably ultrapure water) (about 100 mL), and then (ii) using a micropipette or the like. , by spreading a colloidal aqueous solution (about 12 μL) on the water surface.

(2) Step of forming a dense monolayer film of nanosheets at the gas-liquid interface The colloidal aqueous solution spread on the water surface forms a dense monolayer film of nanosheets at the gas-liquid interface.

(3) Step of transferring the dense monolayer film of the nanosheet to the substrate Preferably, a silicon (Si) substrate, a quartz glass substrate, a Pt substrate, a SrTiO ₃ :Nb substrate, a PET substrate, or the like is used as the substrate for film formation. .

For the film-forming substrate, the surface of the substrate is preferably subjected to a hydrophilic treatment by a cleaning treatment.

In the cleaning process, first, the surface of the substrate is wiped with acetone to remove organic substances on the surface of the substrate, and then the substrate is placed in a mixed solution of methanol and hydrochloric acid (for example, mixed at a volume ratio of 1:1). It is immersed (about 30 minutes), then washed with ultrapure water, then immersed in concentrated hydrochloric acid (about 30 minutes), and washed again with ultrapure water. Si substrates, quartz glass substrates, etc. are preferably hydrophilized (hydrophilized substrates) by cleaning with acetone, a mixed solution of methanol and hydrochloric acid, ultrapure water, concentrated hydrochloric acid, etc. ) can be obtained.

The cleaning process is carried out by ultraviolet irradiation (about 15 to 30 minutes) in an ozone atmosphere. Pt substrates, SrTiO ₃ :Nb substrates, PET substrates, etc., can be satisfactorily hydrophilized (obtained hydrophilized substrates) by performing a cleaning treatment with UV irradiation in an ozone atmosphere. .

The operation of transferring the dense monolayer film of the nanosheet to the substrate is to scoop up the interfacial layer by inserting the colloidal aqueous solution developed on the surface of the water with tweezers or the like into the substrate from below the liquid surface. Thus, a monolayer film of nanosheets is obtained.

Although the dense (dense) monolayer film of the nanosheet of the present invention depends on the properties of the colloidal solution of the nanosheet, the nanosheet is usually a sheet material with a thickness of about 1 nm and a lateral size of several μm.

The dense monolayer film of the nanosheets of the present invention represents a state in which the nanosheets are densely arranged without gaps (densely). Thus, the defect-free dense monolayer film of nanosheets of the present invention can maximize the excellent functions of the nanosheets and is useful for the fabrication of devices.

The dense monolayer film of the nanosheets of the present invention is electrically charged, strongly bonded to the substrate due to electrostatic attraction, and exhibits excellent stability. A dense monolayer film of nanosheets formed on glass or silicon exhibits high durability in tape peeling tests, pencil scratch tests, and the like. On a substrate, the dense monolayer film of nanosheets of the present invention is difficult to peel off and exhibits excellent thin film durability.

Repeating steps (1) to (3) In the method for producing a thin film of the present invention, preferably, by repeating steps (1) to (3), a laminate of dense monolayer films (multilayers) of the nanosheets film) to produce a thin film.

First, a nanosheet monolayer film of a layered compound (titanium oxide (Ti _0.87 O ₂ ), etc.) is obtained on a substrate (quartz glass substrate, Si substrate, etc.) through the steps (1) to (3).

Next, the obtained nanosheet monolayer film on the substrate is heated (about 100° C. to 200° C. for about 15 minutes). This removes the release agent (tetrabutylammonium ion (TBA ⁺ )) remaining in the nanosheet monolayer film.

The nanosheet is preferably a nanosheet in which a layered compound is delaminated. A release agent is used for single layer release. A stripping agent is used to strip the surfactant. At least one release agent selected from the group consisting of tetrabutylammonium ions (TBA ⁺ ) and tetramethylammonium ions (TMA ⁺ ) is used as the release agent.

Next, the nanosheet monolayer film after heating is washed with pure water. This makes the aqueous colloidal solution more compatible.

Next, steps (1) to (3) are started, using a micropipette or the like to develop the colloidal aqueous solution on the surface of water (preferably ultrapure water), and using tweezers or the like to move the substrate below the liquid surface. Insert from the side and scoop up the interfacial layer.

By repeating these operations, it is possible to satisfactorily obtain a laminate of nanosheets (nanosheet multilayer film). For example, starting from a Ti _0.87 O ₂ nanosheet monolayer film on a Si substrate (n = 1, where n indicates the number of layers in which nanosheets are densely arranged), the film formation operation on the Si substrate is further By repeating the process 9 times, a multilayer film composed of Ti _0.87 O ₂ nanosheets (a total of 10 layers (n=10) nanosheet multilayer film) can be produced as a thin film.

In the thin film manufacturing method of the present invention, by repeating the film forming operation, nanosheets can be reliably multi-layered layer by layer as n increases. In the method for producing a thin film of the present invention, a dense monolayer film of nanosheets having a thickness of about 1 nm can usually be produced. (coating layer) can be formed.

(4) A step of irradiating the nanosheet with ultraviolet rays to remove organic substances between single-layer films of the nanosheet. In one step, further
(4) A step of irradiating the nanosheets with ultraviolet rays to remove organic substances between single layers of the nanosheets.

Tetrabutylammonium (TBA) and tetramethylammonium (TMA) are used to synthesize the dense monolayer of nanosheets of the present invention. These TBA and TMA can be decomposed by irradiating ultraviolet rays after forming a dense monolayer film of nanosheets.

TBA and TMA remain as NH ⁴⁺ ions after decomposition, and infrared spectroscopy can be used to analyze the remaining NH ⁴⁺ ions.

The irradiation with ultraviolet rays is preferably carried out by irradiating ultraviolet rays for each layer when forming the laminate to remove organic substances (release agents such as TBA ⁺ , TMA ^{+ ,} etc.). Organic substances may be removed by irradiating ultraviolet rays after fabrication.

The release agent is at least one release agent selected from the group consisting of tetrabutylammonium ion (TBA ⁺ ) and tetramethylammonium ion (TMA ⁺ ).

In the thin film manufacturing method of the present invention, the release agent is decomposed by irradiating the thin film (single layer film or laminated film) with ultraviolet rays.

The present invention includes a thin film having a release agent content (mass) of 100 ppmwt or less, produced by the method for producing a thin film of the present invention.

The present invention consists of a dense monolayer film of nanosheets,
The nanosheets include titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, molybdenum oxide, ruthenium oxide, and graphene. , graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and transition metal carbide.
This includes thin films in which the content (mass) of the release agent is 100 ppmwt or less.

In the thin film of the present invention, the content (mass) of the release agent is preferably 100 ppmwt or less.

The content of the release agent in the thin film of the present invention can be measured by analyzing it using infrared spectroscopy.

Figure 3: Examples of monolayer and multilayer nanosheets A thin film consisting of a dense monolayer of nanosheets of the present invention can be formed by stacking monolayers to form a multilayer (single layer A → A → A → multilayer). , it is possible to stack different single-layer films to form a multilayer film (single-layer film A → single-layer film B (hetero film) → A → B → superlattice hetero-multilayer film).

In the dense monolayer film of nanosheets of the present invention, the film size is not particularly limited. In the method for producing the thin film of the present invention, for example, by using a commercially available kitchen drain pad (size of 30 cm long x 30 cm wide), a large area of A4 size, consisting of a dense monolayer film of nanosheets A multilayer film (laminate) can be formed by stacking thin films or single-layer films.

A thin film composed of a dense monolayer film of nanosheets of the present invention is useful for two-dimensional ultra-thin microdevices, three-dimensional integration (multi-materialization), and the like.

It is possible to manufacture and apply devices using two-dimensional materials (graphene and inorganic nanosheets). Unlike bulk materials, two-dimensional materials exhibit excellent functions such as high electron mobility, flexibility, transparency, and high heat resistance.

Using the thin film composed of the dense monolayer film of nanosheets of the present invention, it is possible to manufacture high-quality nanosheet thin films over a large area and realize new devices.

In the thin film manufacturing method of the present invention, the nanosheets are arranged on the substrate without gaps to form a dense monolayer film. In the method for producing a thin film of the present invention, by repeating the formation of this dense monolayer film, that is, by repeating the operation of producing a monolayer film, a multi-layer film composed of a nanosheet dense monolayer film is obtained. Membranes and superlattices can be constructed.

[2] Thin film composed of a dense monolayer film of nanosheets According to the thin film production method of the present invention, the entire substrate (such as a Si substrate) is coated with nanosheets of a layered compound (such as titanium oxide (Ti _0.87 O ₂ )). It is possible to obtain a nanosheet monolayer film in which the nanosheets overlap each other and are densely arranged without gaps. The coverage of the nanosheets on the substrate is preferably about 95% for the single layer region, about 2% for overlap, and about 3% for gaps, and the nanosheets are densely arranged.

According to the thin film manufacturing method of the present invention, a uniform nanosheet monolayer film can be obtained over the entire large-area substrate.

The present invention includes optical thin films, dielectric thin films, and conductive thin films made of thin films (thin films consisting of nanosheet dense single-layer films) manufactured by the thin film manufacturing method of the present invention.

The present invention includes a thin film having a release agent content (mass) of 100 ppmwt or less, produced by the method for producing a thin film of the present invention.

The present invention consists of a dense monolayer film of nanosheets,
Titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, molybdenum oxide, ruthenium oxide, graphene, graphite oxide, A nanosheet obtained by exfoliating at least one layered compound selected from the group consisting of hexagonal boron nitride, mica, transition metal chalcogenite, and transition metal carbide,
This includes thin films in which the content (mass) of the release agent is 100 ppmwt or less.

The thin film of the present invention is a multilayer film and a superlattice composed of a dense monolayer film of nanosheets, and has excellent electronic and ionic conductivity, semiconducting properties, insulating properties, high dielectric properties, ferroelectric properties, ferromagnetism, and fluorescence properties. characteristics, such as photocatalytic properties.

Titanium oxide (Ti _0.87 O ₂ ) nanosheets have a high refractive index and dielectric constant, and can be used for optical and dielectric applications.

Perovskite (Ca ₂ Nb ₃ O ₁₀ ) nanosheets have high dielectric constant and insulating properties and can be applied to dielectrics.

Ruthenium oxide (RuO ₂ ) nanosheets have high conductivity, can be applied to conductors, and function as excellent transparent conductive films.

　Graphene oxide (GO) nanosheets have electrical insulation and high ionic conductivity, and can be applied to electrocatalysts.

Hexagonal boron nitride (h-BN) nanosheets have electrical insulation, high withstand voltage, and high thermal conductivity, and can be applied to insulating films and heat dissipation substrates.

[3] Usefulness of a thin film manufacturing method consisting of a dense monolayer film of nanosheets (Fig. 4)
Conventional methods for manufacturing nanosheet thin films include the dip coating method, Langmuir-Blodgett (LB) method, and spin coating method. There are problems such as the point that it takes time to

The method for producing a thin film composed of a dense monolayer film of nanosheets of the present invention (the method for producing a thin film of the present invention) is a method for producing a high-quality densely arranged film of nanosheets over a large area, simply, in a short time, and with a small amount of solution. , is a process that can be used to form a film.

The method for producing a thin film of the present invention includes, for example, (1) spreading one drop of a nanosheet-dispersed colloidal aqueous solution on a water surface, (2) forming a monolayer film composed of nanosheets at a gas-liquid interface, and then (3) A thin film is manufactured by transferring a monolayer film composed of the nanosheet to a substrate.

The thin film manufacturing method of the present invention can solve the problems of the conventional technology, develop nanosheet devices, and further advance industrialization. INDUSTRIAL APPLICABILITY The thin film manufacturing method of the present invention can significantly reduce the cost of thin film manufacturing, and is effective as an industrial thin film manufacturing method and nano-coating method.

Figure 4: Thin film application example The thin film manufacturing method of the present invention (interfacial transfer method) can be applied to (i) ceramics manufacturing technology and coating technology, (ii) high productivity and cost reduction, ( iii) It is possible to manufacture in small lots and on demand. The thin film of the present invention is super fine ceramics with ultra-high quality, ultra-high reliability, and ultra-durability.

Perovskite insulating film (Ca ₂ Nb ₃ O ₁₀ ): Achieves withstand voltage > 4 MV/cm, dielectric constant εr > 200, and heat resistance > 800°C. It is useful for insulating films, high withstand voltage substrates, material fields, and electric power fields.

Semiconductor film of titanium oxide (Ti _0.87 O ₂ ): realizes a high refractive index n>2.7. It is useful for optical filters, photocatalyst films, and optical fields.

Magnetic film (Ti _0.8 Co _0.2 O ₂ ): Electromagnetic field shield film, useful in the field of materials.

Conductive film of ruthenium oxide (RuO ₂ ): achieves resistivity of 10 ^-4 Ωcm (equivalent to ITO) and transmittance of >98%. It is useful for transparent conductive films and glass fields.

Hexagonal boron nitride insulating film (h-BN): achieves a thermal conductivity of >40W/mK. It is useful for insulating films, high withstand voltage substrates, heat dissipation substrates, material fields, and electric power fields.

Capacitance film (metal/dielectric multilayer film): RuO ₂ /Ca ₂ Nb ₃ O ₁₀ /RuO ₂ multilayer capacitor application, useful in the electronic field.

Photochromic film (Cs ₄ W ₁₁ O ₃₆ ) (light irradiation (UV, etc.): a film in which the molecular structure changes reversibly and the absorption spectrum changes accordingly (photochromism)). It is useful in the fields of smart windows, heat shield film materials, and automobiles.

Hereinafter, embodiments of the present invention will be described more specifically based on examples.

However, the present invention is not limited to the scope of the examples.

[1] Fabrication of a thin film consisting of a dense monolayer of nanosheets (Fig. 11)
Example 1 (FIG. 5): Preparation of monolayer film Layered titanium oxide (K _0.8 Ti _1.73 Li _0.27 O ₄ ) was used as a starting material to prepare titanium oxide (Ti _0.87 O ₂ ) nanosheets. A monolayer film (nanosheet monolayer film) composed of titanium oxide nanosheets was produced.

A layered titanium oxide (K _0.8 Ti _1.73 Li _0.27 O ₄ ) was synthesized by a solid phase synthesis method.

Raw material powders consisting of TiO ₂ (Rare Metallic, 99.99% purity), K ₂ CO ₃ (Rare Metallic, 99.99% purity), and Li ₂ CO ₃ (Rare Metallic, 99.99% purity) were chemically Based on the stoichiometric ratio TiO ₂ :K ₂ CO ₃ :Li ₂ CO ₃ =1:0.23:0.078, they were weighed, ground and mixed for 60 minutes using an alumina mortar. Since part of the alkali metal carbonates K ₂ CO ₃ and Li ₂ CO ₃ evaporates during the next firing, they were added in excess of 5% in terms of molar ratio.

The pulverized and mixed raw material powder was placed in a platinum crucible and calcined at 900° C. for 1 hour in an electric furnace. After that, the calcined raw material powder was again pulverized and mixed in an alumina mortar for 30 minutes. Next, the pulverized and mixed raw material powder was placed in a platinum crucible and fired at 1,000° C. for 20 hours to obtain layered titanium oxide K _0.8 Ti _1.73 Li _0.27 O ₄ .

The obtained layered titanium oxide (0.2 g) and hydrochloric acid aqueous solution (200 mL) were stirred in a beaker and subjected to acid treatment for 72 hours to obtain a hydrogen exchanger (H _1.07 Ti _1.73 O ₄ ·H ₂ O). got

Next, the hydrogen ion exchanger was mixed with an aqueous tetrabutylammonium hydroxide solution whose concentration was adjusted so that the ratio of tetrabutylammonium ion (TBA ⁺ )/H ⁺ was 1, at a rate of 4 g/L. A milky-white colloidal aqueous solution, represented by the compositional formula Ti _0.87 O ₂ , in which rectangular titanium oxide nanosheets with a thickness of about 1 nm and a lateral size of 5 μm to 10 μm are dispersed was prepared. .

Next, the prepared Ti _0.87 O ₂ nanosheets were used to prepare a coating solution for thin film production. 10 μL of ethanol was added to 10 μL of colloidal aqueous solution in which Ti _0.87 O ₂ nanosheets were dispersed in water to obtain a colloidal aqueous solution for membrane formation.

A silicon (Si) substrate (30mmφ) was used as the film-forming substrate. The surface of the substrate was hydrophilized by washing. In the cleaning treatment, first, the surface of the substrate was wiped with acetone to remove organic matter on the surface of the substrate. Next, this substrate is immersed in a mixed solution of methanol and hydrochloric acid (mixed at a volume ratio of 1:1) for 30 minutes, washed with ultrapure water, then immersed in concentrated hydrochloric acid for 30 minutes, and Washed with ultrapure water.

A Petra dish (4 inches) was filled with 100 mL of ultrapure water (Milli-Q Element ultrapure water device manufactured by Nihon Millipore). Then, using a micropipette, 12 μL of colloidal aqueous solution was spread on the ultrapure water surface. After 5 seconds, the substrate was inserted from below the liquid surface with tweezers, and the interfacial layer was scooped up to obtain a monolayer film of nanosheets.

The surface of the nanosheet monolayer film on the Si substrate (wafer) obtained in Example 1 was observed with a confocal laser microscope (CFLM) and an atomic force microscope (AFM). For CFLM observation, OLS4000 manufactured by Olympus Corporation was used. For AFM observation, an E-Sweep scanning probe microscope system manufactured by SII Nano Technology was used. A silicon cantilever (spring constant k=20 Nm ⁻¹ ) was used as the probe, and observation was made in the tapping mode.

The observation results are shown in FIG. According to FIG. 5, the entire Si substrate was covered with Ti _0.87 O ₂ nanosheets, and it was confirmed that the nanosheets overlapped with each other and a nanosheet monolayer film densely arranged without gaps was obtained. Image analysis was performed and the coverage was calculated. The single layer area was 95%, the overlap was 2%, and the gap was 3%, indicating that the nanosheets were densely arranged.

As described above, according to the method of the present invention, it was shown that a uniform nanosheet monolayer film can be obtained over the entire large-area substrate in a short time from Ti _0.87 O ₂ nanosheets.

Example 2 (Fig. 6): Substrate study (single layer film)
In Example 2, a monolayer film composed of titanium oxide nanosheets (Ti _0.87 O ₂ ) was produced in the same manner as in Example 1, except that the substrate was changed.

A Si substrate (30 mmφ), a quartz glass substrate (30 mmφ), a Pt substrate (30 mmφ), and a PET substrate (30 mmφ) were used as the film-forming substrates.

For the Si substrate (wafer) and quartz glass substrate, the same substrate cleaning treatment as in Example 1 was performed to obtain a hydrophilic substrate.

Other Pt and PET substrates were cleaned by irradiating them with ultraviolet rays for 15 minutes in an ozone atmosphere.

For the obtained nanosheet monolayer film, CFLM observation was measured in the same manner as in Example 1, and the influence of different substrates was examined.

Fig. 6 shows the observation results. According to FIG. 6, it was confirmed that the nanosheets overlapped with each other and a nanosheet monolayer film in which the nanosheets were densely arranged with no gaps was obtained on any of the substrates.

Example 3 (Fig. 7): Investigation of layered compound (monolayer film)
In Example 3, monolayer films were produced in the same manner as in Example 1 for nanosheets of various layered compounds.

Perovskite (Ca ₂ Nb ₃ O ₁₀ ) nanosheets: applicable to dielectrics.

Ruthenium oxide (RuO ₂ ) nanosheets: applicable to conductors.

Graphene oxide (GO) nanosheets: can be applied to ion-conducting membranes and electrode catalysts.

　Insulating film (h-BN): Application to insulating films and heat dissipation substrates.

The results are shown in Fig. 7. According to FIG. 7, it was confirmed that the nanosheets of all layered compounds overlapped with each other, and nanosheet monolayer films were obtained in which the nanosheets were densely arranged without gaps.

Example 4 (Fig. 8): Examination of alcohol and aprotic polar solvent (single layer film)
In Example 4, a monolayer film composed of titanium oxide nanosheets (Ti _0.87 O ₂ ) was produced in the same manner as in Example 1 using alcohol and an aprotic polar solvent.

Using the prepared Ti _0.87 O ₂ nanosheets, a coating solution for thin film fabrication was prepared.

10 μL of isopropyl alcohol (IPA) was added to 10 μL of colloidal aqueous solution in which Ti _0.87 O ₂ nanosheets were dispersed in water to obtain a colloidal aqueous solution for film formation.

10 μL of dimethyl sulfoxide (DMSO) was added to 10 μL of colloidal aqueous solution in which Ti _0.87 O ₂ nanosheets were dispersed in water to obtain a colloidal aqueous solution for membrane formation.

10 μL of N,N-dimethylformamide (DMF) was added to 10 μL of colloidal aqueous solution in which Ti _0.87 O ₂ nanosheets were dispersed in water to obtain a colloidal aqueous solution for membrane formation.

The results are shown in Fig. 8. According to FIG. 8, it was confirmed that nanosheets overlapped with each other and a nanosheet monolayer film densely arranged without gaps was obtained regardless of which alcohol and aprotic polar solvent were used.

Example 5 (Fig. 9): Examination of repeated operation (multilayer film)
In Example 5, using the experimental conditions of Example 1, multilayer films (nanosheet multilayer films) composed of titanium oxide (Ti _0.87 O ₂ ) nanosheets were produced on quartz glass substrates and Si substrates.

Starting from the Ti _0.87 O ₂ nanosheet monolayer film (where n=1, where n indicates the number of layers in which the nanosheets are densely arranged) on the Si substrate obtained in Example 1, in Example 4, the quartz glass substrate and The operation of Example 1 was repeated nine times on the Si substrate.

Specifically, first, the nanosheet monolayer film obtained in Example 1 was heated. Heating was carried out at 200° C. for 15 minutes. This removed the TBA ⁺ remaining in the nanosheet monolayer film. Then, the nanosheet monolayer film after heating was washed with pure water. This made the colloidal aqueous solution more compatible. Thereafter, in the same manner as in Example 1, 12 μL of the colloidal aqueous solution prepared in Example 1 was spread on the ultrapure water surface using a micropipette. After 5 seconds, the substrate was inserted from below the liquid surface with tweezers and the interfacial layer was scooped up.

The above steps were repeated 9 times to produce a multilayer film of Ti _0.87 O ₂ nanosheets (a total of 10 nanosheet multilayer films (n=10)) as a thin film. For the thin film obtained in each step, the absorption spectrum was measured and the absorbance was obtained.

The results are shown in Fig. 9. According to FIG. 9, it was found that the absorbance at a wavelength of 265 nm increased linearly as n increased. This fact shows that according to the method of the present invention, multilayering can be reliably performed layer by layer.

Example 6 (Fig. 10): Examination of film formation on large PET substrate (single layer film)
In Example 6, a monolayer film composed of titanium oxide nanosheets (Ti _0.87 O ₂ ) was produced in the same manner as in Example 1, except that the substrate and film forming container were changed.

An A4-sized PET substrate was used as the film-forming substrate, and was subjected to UV irradiation for 15 minutes in an ozone atmosphere for cleaning.

A draining vat measuring 36 cm long, 25 cm wide, and 5 cm deep was used as the film-forming container, and was filled with 3000 mL of ultrapure water (Milli-Q Element, an ultrapure water device manufactured by Nihon Millipore Co., Ltd.). Then, using a pipette, 10 mL of colloidal aqueous solution was spread on the ultrapure water surface. After 5 seconds, the substrate was inserted from below the liquid surface and the interfacial layer was scooped up to obtain a monolayer film of nanosheets.

The results are shown in Fig. 10. The resulting nanosheet monolayer film was observed by CFLM in the same manner as in Example 1, and a nanosheet monolayer film with overlapping nanosheets and densely arranged nanosheet monolayer films without gaps was obtained. Therefore, it was confirmed that it is possible to manufacture a nanosheet monolayer film even with a general-purpose container and a large substrate.

Figure 11: Advantages of the thin film manufacturing method of the present invention As demonstrated in the above examples, the thin film manufacturing method of the present invention (interfacial transfer method) is a Langmuir-Blodgett method that is a conventional nanosheet thin film manufacturing method. Compared to the (LB) method, spin coating method, etc., it is possible to form a high-quality densely aligned nanosheet film with a larger area, more easily, in a shorter time, and with a smaller amount of solution. It's a process.

Fig. 11 shows the superiority of the thin film manufacturing method of the present invention. In the method for producing a thin film of the present invention, (i) water can be used as the solvent, (ii) operability can be a simple pipette operation, and (iii) the film formation time is, for example, It takes about 30 seconds, and (iv) costs only a small amount of solution (about 1/100 of the LB method).

The thin film produced by the method for producing a thin film of the present invention is subjected to film quality evaluation (coverage and defect density) using an atomic force microscope, a confocal laser microscope, a scanning electron microscope, etc., and the film quality (e.g. , titanium oxide) has a single layer coverage of 95% or more and defects of 2% or less in terms of area ratio, and is a high-quality dense film.

According to the thin film production method of the present invention, it is possible to produce a dense single layer film with a single layer coverage (coating ratio) of 95% or more and no defects.

The thin film production method of the present invention reduces materials and costs, is a low environmental load process, and can produce thin films industrially.

[2] Usefulness of a thin film composed of a dense monolayer film of nanosheets According to the production method of the present invention, nanosheets are arranged in an orderly fashion on various substrate surfaces to form thin films, and high-quality nanosheet films can be produced on a large scale. It is possible to form a film with an area.

A thin film consisting of a dense monolayer film of nanosheets obtained by the production method of the present invention (the thin film of the present invention) is composed of two-dimensional materials (nanosheets) such as graphene and inorganic nanosheets. The thin film of the present invention exhibits high electron mobility, flexibility, transparency, high heat resistance, etc. due to its atomic-level thinness and two-dimensional nanostructure, and can be applied to next-generation electronic devices and energy fields. I can do things. The thin film of the present invention has properties such as excellent electronic and ionic conductivity, semiconducting properties, insulating properties, high dielectric properties, ferroelectric properties, ferromagnetism, fluorescent properties, and photocatalytic properties possessed by nanosheets. It can be applied as an important member of the device.

Claims (11)

1. A method for producing a thin film,
   (1) A process of developing a colloidal aqueous solution in which nanosheets are dispersed on the water surface,
   (2) forming a dense monolayer film of the nanosheets at the gas-liquid interface; and (3) transferring the dense monolayer film of the nanosheets to a substrate,
   forming a thin film consisting of a dense monolayer film of said nanosheets;
   Thin film manufacturing method.
2. The nanosheet is a nanosheet in which a layered compound is delaminated,
   A method for producing the thin film according to claim 1.
3. Compounds constituting the layered compound include titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, and molybdenum oxide. , ruthenium oxide, graphene, graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and at least one compound selected from the group consisting of transition metal carbide,
   3. A method for producing a thin film according to claim 2.
4. The colloidal aqueous solution is an alcohol-containing colloidal aqueous solution,
   A method for producing a thin film according to any one of claims 1 to 3.
5. By repeating the steps (1) to (3),
   forming a stack of dense monolayer films of the nanosheets;
   A method for producing a thin film according to any one of claims 1 to 4.
6. In at least one step of steps (1) to (3),
   (4) a step of irradiating the nanosheet with ultraviolet rays to remove organic substances between single layers of the nanosheet;
   The method for producing a thin film according to any one of claims 1 to 5, comprising
7. An optical thin film made of a thin film manufactured by the thin film manufacturing method according to any one of claims 1 to 6.
8. A dielectric thin film comprising a thin film manufactured by the method for manufacturing a thin film according to any one of claims 1 to 6.
9. A conductive thin film comprising a thin film manufactured by the thin film manufacturing method according to any one of claims 1 to 6.
10. A thin film having a release agent content of 100 ppmwt or less, manufactured by the thin film manufacturing method according to any one of claims 1 to 6.
11. a thin film,
    Consisting of a dense monolayer film of nanosheets,
    The nanosheets include titanium oxide, perovskite oxide, manganese oxide, cobalt oxide, silicon oxide, tungsten oxide, niobium oxide, tantalum oxide, titanium/niobium oxide, titanium/tantalum oxide, molybdenum oxide, ruthenium oxide, and graphene. , graphite oxide, hexagonal boron nitride, mica, transition metal chalcogenite, and transition metal carbide.
    The release agent content is 100 ppmwt or less,
    Thin film.

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