Multilayer object and production method therefor

Abstract

[Problem] To provide a method for producing a multilayer object using an inkjet process, in which intra-dot nanopatterns that are expressed in nanodots can be stably adjusted into desired shapes in accordance with the application. [Solution] The method for producing a multilayer object at least includes: a printing step in which nanofluid droplets are ejected by an inkjet process onto a substrate on which a coating film may have been formed; and a drying step in which the ejected nanofluid droplets are dried to form a plurality of nanodots. The nanofluid droplets each comprise a dispersion medium and nanoparticles dispersed therein. In the printing step and the drying step, intra-dot nanopatterns expressed in the plurality of nanodots are adjusted by adjusting the Marangoni number Ma, the ratio kev of contact angle relaxation time to evaporation time, and the Péclet number Pe.

Description

Multilayer body and method for producing the same

[0001] The present invention relates to a multilayer body and a method for producing the same.

[0002] With the development of an advanced information and communications society, the performance standards required for various electronic devices are steadily increasing year by year. This has led to progress in semiconductors becoming more highly integrated and thinner, and various companies are currently attempting to improve their semiconductor production technologies.

[0003] Conventionally, semiconductors have been manufactured mainly using photolithography technology. Photolithography technology is a microfabrication technology that uses actinic radiation to form a precise thin-film pattern on a substrate such as a silicon wafer. More specifically, a photosensitive resin composition is applied to the substrate, and then exposed and developed using a photomask to form a fine pattern. Depending on the type of semiconductor element to be manufactured, thermal processing may be performed as necessary, and the shape of the fine pattern may be adjusted by heating and melting.

[0004] However, while photolithography can produce extremely fine and precise patterns, the process itself is expensive and has a high environmental impact, which is why alternative technologies to photolithography have been explored.

[0005] Printed electronics technology is a technology that can form fine patterns on various substrates using printing technology. Printed electronics technology is mainly used to form circuits on substrates using conductive inks containing metal nanoparticles, etc. Printed electronics technology is considered to have higher productivity and less environmental impact than the above-mentioned photolithography technology. Furthermore, printed electronics can also form electrodes on thin plastic substrates, and can be applied to the manufacture of flexible devices (see, for example, Patent Document 1).

[0006] JP 2024-017543 A

[0007] Printed electronics technology involves a printing process in which nanofluid droplets are ejected using an inkjet process, followed by a drying process in which the droplets are dried to form multiple nanodots. However, it has been difficult to consistently adjust the nanopatterns within the nanodots, depending on the characteristics of the substrate and nanofluid droplets, and the drying conditions for the fine nanodots. This can lead to yield problems in device manufacturing and reduced device production.

[0008] In printed electronics, it is desirable to form uniform nanoparticle dots in continuous lines, avoiding patterns such as coffee rings. Nanodots with coffee ring patterns, where particles are clustered along the nanodot's circumference like coffee stains, are expected to be used individually, in arrays, or in multi-line structures, not only in electronics but also in photonic crystals, sensors, solar cells, biochemical analysis, and other fields. Furthermore, by forming continuous coffee ring patterns or spoke patterns, where multiple lines radiate from the center to the circumference, it is possible to achieve properties (e.g., conductivity) with a small number of nanoparticles. Furthermore, it is possible to fabricate novel two-dimensional materials with non-equilibrium patterns based on the spoke patterns. Therefore, efficient methods for finding optimal conditions for forming nanodot patterns tailored to desired applications, not just uniform nanoparticle dot patterns, and materials with such patterns are essential in a variety of fields.

[0009] The present invention has been made in consideration of such problems, and aims to provide a method for manufacturing a multilayer body using an inkjet process, which allows the intra-dot nanopatterns expressed in the nanodots to be consistently adjusted in a desired form depending on the application.

[0010] As a result of extensive research, the present inventors have discovered that in a method for manufacturing a multilayer body that includes at least a printing step of ejecting nanofluid droplets by an inkjet process and a drying step of drying the droplets to form a plurality of nanodots, it is possible to adjust the intra-dot nanopatterns that appear in the plurality of nanodots to a consistent level by adjusting three parameters, and have thus completed the present invention. Specifically, the present invention provides the following:

[0011] The invention according to a first aspect is a method for producing a multilayer body, which includes at least a printing step of ejecting nanofluid droplets by an inkjet process onto a substrate on which a coating may be formed, and a drying step of drying the ejected nanofluid droplets to form a plurality of nanodots, wherein the nanofluid droplets contain nanoparticles dispersed in a dispersion medium, and in the printing step and the drying step, Ma and k represented by the following formulas (1) to (3) are formed. ｅｖ and Pe, thereby adjusting the intra-dot nanopattern appearing in the plurality of nanodots. (where Ma is a dimensionless number called the Marangoni number, dσ / dT is the temperature coefficient of the surface tension of the nanofluid (N / (m·K)), h ０ is the droplet height (m) of the nanofluid droplet on the substrate at the time of maximum expansion, μ is the viscosity of the nanofluid (Pa s), and α is the thermal diffusivity of the nanofluid (m 2 / s), ΔT is the temperature difference (K) formed within the droplet. (where k ｅｖ is the contact angle relaxation time τ re Evaporation time τ ev is a dimensionless number that indicates the ratio to the viscosity of the nanofluid (Pa s), and V ０ is the droplet volume at maximum expansion (m 3 ) where σ is the surface tension of the nanofluid droplet (mN / m) and θ ０ indicates the contact angle (rad.) at the time of maximum droplet spreading, where τ ev is the evaporation time (s) of the nanofluid droplets. ０ Use.) (Here, Pe is a dimensionless number called the Peclet number, U is the advection velocity (m / s) of nanoparticles due to capillary flow and Marangoni convection, and h ０ indicates the droplet height (m) at the time of maximum expansion of the droplet, and D ｐ is the diffusion coefficient of the nanoparticles in the dispersion medium.)

[0012] The second aspect of the invention is the first aspect of the invention, and provides a manufacturing method in which, in the printing step, at least one condition selected from the group consisting of the discharge amount of nanofluid droplets, atmospheric temperature, and ventilation conditions is adjusted, and / or, in the drying step, at least one condition selected from the group consisting of the drying time, drying temperature, and ventilation conditions is adjusted.

[0013] The third aspect of the invention is the invention according to the first or second aspect, and further provides a manufacturing method for adjusting the contact angle of the nanofluid droplets with respect to the surface of the substrate, which may have a coating formed thereon, adjusting the difference in SP value between the dispersion medium contained in the nanofluid and the nanoparticles, and / or adjusting the processing intensity in the dispersion processing of the nanofluid.

[0014] The invention according to a fourth aspect is an invention according to any one of the first to third aspects, and provides a manufacturing method for adjusting the intra-dot nanopattern expressed in the plurality of nanodots into a spoke pattern.

[0015] The fifth aspect of the invention is an invention according to any one of the first to third aspects, and provides a manufacturing method for adjusting the intra-dot nanopattern expressed in the plurality of nanodots into a coffee ring.

[0016] The sixth aspect of the invention is the invention according to any one of the first to third aspects, and provides a manufacturing method for adjusting the intra-dot nanopatterns appearing in the plurality of nanodots to a uniform pattern.

[0017] The seventh feature of the invention is the invention according to any one of the first to third features, and provides a manufacturing method for adjusting the intra-dot nanopatterns expressed in the multiple nanodots into a multi-ring.

[0018] The invention relating to its eighth feature provides a multilayer body in which a plurality of nanodots are formed on a substrate on which a coating may be formed, and intra-dot nanopatterns expressed in the plurality of nanodots are continuously formed as a uniform pattern.

[0019] The ninth aspect of the invention is the eighth aspect of the invention, and provides a multilayer body in which the intra-dot nanopattern is continuously formed as a spoke pattern. The tenth aspect of the invention is the ninth aspect of the invention, and provides a multilayer body in which the spoke pattern is a pattern of four or more radially extending stripes, and the diameter of the nanodots is 5000 μm or less. The eleventh aspect of the invention is the tenth aspect of the invention, and provides a multilayer body in which the difference in unevenness between the convex portions constituting the stripes and the concave portions constituting the spaces between adjacent stripes is 10 nm or more and 100 nm or less.

[0020] The invention according to a twelfth feature provides a multilayer body according to the eighth feature, in which the intra-dot nanopattern is continuously formed as a coffee ring. The invention according to a thirteenth feature provides a multilayer body according to the twelfth feature, in which the coffee ring is a pattern in which nanoparticles are accumulated along the circumference of the nanodot, the width of the rings constituting the coffee ring is 100 nm to 500 μm, and the diameter of the nanodots is 5,000 μm or less. The invention according to a fourteenth feature provides a multilayer body according to the thirteenth feature, in which adjacent rings form unevenness, and the difference in unevenness is 10 nm to 100 nm.

[0021] The invention according to the fifteenth feature is the invention according to the eighth feature, and provides a multilayer body in which the intra-dot nanopattern is continuously formed as a uniform pattern, and the film thickness variation, which is the standard deviation with respect to the average film thickness of the film constituting the uniform pattern, is less than 30 nm.

[0022] The invention according to a sixteenth feature provides a multilayer body according to the eighth feature, in which the intra-dot nanopattern is continuously formed as a multi-ring. The invention according to a seventeenth feature provides a multilayer body according to the sixteenth feature, in which the multi-ring is a pattern formed by accumulating a plurality of approximately concentric rings, the width of the rings constituting the multi-ring is 100 nm to 500 μm, and the diameter of the nanodots is 5,000 μm or less. The invention according to an eighteenth feature provides a multilayer body according to the seventeenth feature, in which adjacent rings form unevenness, and the difference in unevenness is 10 nm to 100 nm.

[0023] A nineteenth aspect of the present invention provides a multilayer body produced by the method for producing a multilayer body according to any one of the first to third aspects.

[0024] The invention according to the twentieth feature is the invention according to the nineteenth feature, and provides a multilayer body in which intra-dot nanopatterns that appear in multiple nanodots formed on a substrate, which may have a coating formed thereon, are continuously formed as a spoke pattern.

[0025] The invention relating to the 21st feature is the invention relating to the 19th feature, and provides a multilayer body in which intra-dot nanopatterns that appear in multiple nanodots formed on a substrate, which may have a coating formed thereon, are continuously formed as coffee rings.

[0026] The invention relating to the 22nd feature is the invention relating to the 19th feature, and provides a multilayer body in which intra-dot nanopatterns that appear in multiple nanodots formed on a substrate, which may have a coating formed thereon, are continuously formed as a uniform pattern.

[0027] The invention relating to the 23rd feature is the invention relating to the 19th feature, and provides a multilayer body in which intra-dot nanopatterns that appear in multiple nanodots formed on a substrate, which may have a coating formed thereon, are continuously formed as multi-rings.

[0028] According to the present invention, in a method for manufacturing a multilayer body by an inkjet process, the intra-dot nanopatterns expressed in a plurality of nanodots can be adjusted to a desired and consistent shape depending on the application.

[0029] Figure 1 shows time-series images of droplets dropped onto a Si substrate. Figure 2 shows nanoparticle deposition patterns obtained by a phase-shift deflectometer. Figure 3 shows a micrometer-thick liquid film profile near the droplet contact line in the radial direction r from the droplet center. Figure 4 shows the normalized contact radius R / R for an n-octane sample. ０ and normalized time t / t ０ 1 shows the relationship between the Péclet number Pe and the ratio of the contact angle relaxation time to the evaporation time τ. 2 shows the nanometer-thick liquid film shape along the radial direction r and the nanoparticle deposition layer. 3 shows a schematic diagram illustrating the relationship between the convection inside the droplet and the contact line motion that induces spoke, coffee ring, multi-ring, and uniform patterns. 4 shows the dimensionless numbers calculated under each experimental condition. 5 shows the Peclet number Pe and the ratio of the contact angle relaxation time to the evaporation time τ. ｒｅ / τ ｅｖ FIG.

[0030] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0031] <Method for manufacturing a multilayer body> The method for manufacturing a multilayer body according to this embodiment includes at least a printing step and a drying step. Here, the printing step is a step of ejecting nanofluid droplets by an inkjet process onto a substrate on which a coating may be formed. Furthermore, the drying step is a step of drying the ejected nanofluid droplets to form a plurality of nanodots.

[0032] The nanofluid droplets contain nanoparticles dispersed in a dispersion medium.

[0033] In this embodiment, in the method for manufacturing such a multilayer body, the Marangoni number Ma and the ratio k of the contact angle relaxation time to the evaporation time, which are expressed by the following formulas (1) to (3), are used in the printing process and the drying process. ｅｖBy adjusting the P.sub.e and the Peclet number Pe, the nanopattern within the dots that appears in the multiple nanodots can be adjusted.

[0034] In this specification, nanodots refer to dots formed by self-organization using nanoparticles. Because nanodots are dots formed by self-organization using nanoparticles, the diameter of the nanodots is not necessarily on the order of nanometers, but can also be on the order of micrometers or millimeters.

[0035] [Printing Step] The printing step is a step of ejecting nanofluid droplets by an inkjet process onto a substrate which may have a coating formed thereon.

[0036] In the inkjet process, nanofluid droplets are generated from ink in a channel and ejected from a head, where they are deposited on a substrate. The diameter of the nanofluid droplets is 10 to 150 μm, roughly corresponding to the diameter of the nozzle. This allows for the formation of patterned thin films on the substrate.

[0037] When discharging nanofluid droplets onto a substrate on which a coating may be formed, it is preferable to perform positioning etc. so that the nanofluid droplets adhere to the substrate at precisely the desired positions. Positioning is performed through processes such as identifying each pixel of the print pattern, accurately moving the inkjet head to that pixel, and adjusting the timing of the inkjet head movement and the discharging of the nanofluid droplets.

[0038] Inkjet processes are classified into continuous inkjet and drop-on-demand inkjet. Drop-on-demand inkjet is further classified into thermal inkjet, piezoelectric inkjet, and electrostatic inkjet. Any of these inkjet processes can be used in the printing step of the method for producing a multilayer body of this embodiment.

[0039] As will be described later, in the method for manufacturing a multilayer body according to this embodiment, the Marangoni number Ma and the ratio k of the contact angle relaxation time to the evaporation time ｅｖThe nanopattern within the nanodots that appears in the nanodots can be adjusted by adjusting the P(ρ) and Peclet number Pe. To adjust these three parameters, it is preferable to adjust at least one condition selected from the group consisting of the discharge amount of nanofluid droplets, the ambient temperature, and the ventilation conditions in the printing process.

[0040] Among these, the discharge amount of nanofluid droplets affects the evaporation rate of the dispersion medium and the size of the droplets dropped. This affects the Marangoni number Ma and the ratio k of the contact angle relaxation time and evaporation time. ｅｖ , and the Peclet number Pe have their own unique influences. In addition, the ambient temperature affects the evaporation rate of the dispersion medium, etc. As a result, the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k ｅｖ , and the Peclet number Pe. Furthermore, the ventilation conditions affect the evaporation rate of the dispersion medium through the vapor partial pressure of the dispersion medium. This affects the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k, ｅｖ , and the Peclet number Pe each have their own specific influence.

[0041] Specific printing process conditions may be adjusted by performing simulations based on various mathematical formulas described below.

[0042] [Nanofluid] In this embodiment, the nanofluid droplets contain at least a dispersion medium and nanoparticles dispersed in the dispersion medium. Nanoparticles and dispersion mediums that can be used to prepare nanofluids for forming nanofluid droplets by the inkjet process may be any nanoparticles and dispersion mediums that are conventionally known in the field of printed electronics technology.

[0043] For example, nanoparticles may be made of metals such as Au, Ag, and Cu, or TiO ２ , CeO ２ and metal oxides such as ITO.

[0044] These nanoparticles may also be modified with known functional groups. The type of organic modifying group is not particularly limited, and examples thereof include an optionally substituted linear or branched alkyl group, an optionally substituted cyclic alkyl group, an optionally substituted aryl group, an optionally substituted aralkyl group, and an optionally substituted saturated or unsaturated heterocyclic group.

[0045] Examples of the substituent include a carboxy group, a cyano group, a nitro group, a halogen atom, an ester group, an amide group, a ketone group, a formyl group, an ether group, a hydroxyl group, an amino group, a sulfonyl group, -O-, -NH-, and -S-.

[0046] The organically modified nanoparticles may have one type of organic modifying group on the surface, or may have multiple types of organic modifying groups.

[0047] Examples of the dispersion medium include linear or branched hydrocarbons having 6 to 11 carbon atoms, as well as alicyclic hydrocarbons. More specifically, examples of linear hydrocarbons include hexane, heptane, octane, nonane, decane, and undecane. Examples of alicyclic hydrocarbons include cyclohexane, cycloheptane, and cyclooctane.

[0048] These nanoparticles and dispersion media may be used alone or in combination. In order to completely disperse the nanofluid droplets, it is preferable that the dispersion media and nanoparticles used in the nanofluid have solubility parameters close to each other.

[0049] In order for nanodots to form a desired pattern in the inkjet process, nanoparticles must be uniformly dispersed in the dispersion medium in the nanofluid. For example, the nanofluid can be made uniform by the following steps:

[0050] (1) The weights of the nanoparticles and dispersion medium are measured, and the nanoparticles and dispersion medium are mixed to prepare a mixture. (2) The mixture is poured into a sealed screw tube, and then ultrasonic waves are applied to the mixture in the screw tube using an ultrasonic cleaner. (3) The mixture is transferred to a centrifuge container and centrifuged at a rotation speed of, for example, approximately 10,000 rpm, to precipitate only the aggregated nanoparticles to the bottom of the container. The supernatant is then transferred to a new container and stored in a sealed container. (4) A conventional method such as dynamic light scattering is used to confirm that the nanoparticles are dispersed in the dispersion medium.

[0051] In the printing process, the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k ｅｖ In adjusting the P(ρ) and the Peclet number Pe, it is desirable to adjust the contact angle of the nanofluid droplet with respect to the surface of the substrate, which may have a coating formed thereon. The contact angle of the nanofluid droplet with respect to the surface of the substrate, which may have a coating formed thereon, can be adjusted, for example, by performing a surface treatment on the substrate. When the substrate is a silicon wafer, the surface treatment can be performed using conventionally known techniques such as ODS treatment, hydrophobic surface treatment (HMDS treatment), etching, polishing, epitaxial growth, UV treatment, etc. For the ODS treatment, a conventional silane coupling agent can be used.

[0052] [Drying Process] The drying process is a process in which the ejected nanofluid droplets are dried to form multiple nanodots. Through this drying process, the nanodots are fixed on the substrate, enabling them to exhibit desired properties. Various methods can be used for the drying process depending on the type of dispersion medium, nanoparticles, and other additives that make up the nanofluid.

[0053] Typically, methods known include natural drying, in which nanofluid droplets are dried naturally, and thermal drying, in which nanofluid droplets are dried using an oven or heater. A person skilled in the art can select an appropriate method depending on the type and state of the desired pattern.

[0054] As will be described later, in the method for manufacturing a multilayer body according to this embodiment, the Marangoni number Ma and the ratio k of the contact angle relaxation time to the evaporation timeｅｖ The nanopattern within the nanodots is adjusted by adjusting the P(ρ) and the Peclet number Pe. In order to adjust these three parameters, it is preferable to adjust at least one condition selected from the group consisting of drying time, drying temperature, and ventilation conditions in the drying step.

[0055] Among these, the drying time is the ratio k of the contact angle relaxation time to the evaporation time ｅｖ The drying temperature also affects the evaporation rate of the dispersion medium. This directly affects the Marangoni number Ma and the ratio of the contact angle relaxation time to the evaporation time k ｅｖ , and the Peclet number Pe. Furthermore, the ventilation conditions affect the evaporation rate of the dispersion medium through the vapor partial pressure of the dispersion medium. This affects the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k, ｅｖ , and the Peclet number Pe each have their own specific influence.

[0056] Specific conditions for the drying process may be adjusted by carrying out simulations based on various mathematical formulas described below.

[0057] [Marangoni Number Ma] In the method for producing a multilayer body according to this embodiment, the Marangoni number Ma, which is expressed by the following formula (1), is adjusted in the printing step and the drying step. (where Ma is a dimensionless number called the Marangoni number, dσ / dT is the temperature coefficient of surface tension (N / (m·K)), h ０ is the droplet height (m) of the nanofluid droplet on the substrate at the time of maximum expansion, μ is the viscosity of the nanofluid (Pa s), and α is the thermal diffusivity of the nanofluid (m 2 / s), ΔT is the temperature difference (K) formed within the droplet.

[0058] The Marangoni number Ma is a dimensionless number that indicates the ratio of the stress (Marangoni stress) based on the surface tension gradient to the viscous stress.

[0059] More specifically, when a temperature gradient occurs in the thickness direction of a nanofluid droplet, if the Marangoni number Ma expressed by equation (1) is equal to or greater than a certain value, cellular convection occurs in the nanofluid (Marangoni instability), and this convection is called Marangoni-Bénard convection.

[0060] Marangoni-Bénard convection and the significance of the Marangoni number Ma are explained in various publications, such as Int. J. Microgravity Sci. No. 31 Supplement 2014 and Int. J. Heat Mass Transf., 134, 784-795 (2019). The contents of the above-mentioned publications are incorporated by reference as part of this specification, but the contents of this specification take precedence over any matters specifically stated in this specification.

[0061] In the method for manufacturing a multilayer body according to this embodiment, when adjusting the intra-dot nanopatterns appearing in the nanodots, it is desirable to control the Marangoni-Bénard convection in the nanofluid droplets. Therefore, in the method for manufacturing a multilayer body according to this embodiment, it is possible to adjust the intra-dot nanopatterns by adjusting the process conditions of the printing and drying steps so as to adjust the Marangoni number Ma.

[0062] In this specification, the temperature coefficient of surface tension dσ / dT of nanofluids is measured using the pendant drop method. dσ / dT can also be used for dispersion media values ​​listed in publicly available literature, such as NIST Chemistry WebBook (URL: https: / / webbook.nist.gov / chemistry / ), PubChem (URL: https: / / pubchem.ncbi.nlm.nih.gov / ), and "Chemistry Handbook, Revised 5th Edition" (edited by the Chemical Society of Japan, Maruzen Publishing). However, depending on the combination of surface-modified chains and dispersion media, nanoparticles (surface-modified nanoparticles) may adsorb to the surface, resulting in a lower surface tension compared to the dispersion media (indicating interfacial activity). Therefore, in this specification, values ​​listed in publicly available literature will not be used, and values ​​measured using the pendant drop method will be used.

[0063] The droplet height h of the nanofluid droplet on the substrate at maximum expansion ０can be calculated from image analysis data obtained using, for example, a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd., DMo series) or a CMOS camera (manufactured by Baumer, VCXU-91M).

[0064] The viscosity μ of the nanofluid can be measured at a temperature of 20°C in accordance with JIS Z 8803:2011 "Method for measuring viscosity of liquids."

[0065] The thermal diffusivity α of the nanofluid is determined by measuring it using the laser flash method.

[0066] The temperature difference ΔT formed within the droplet can be estimated using the following equation (4): Therefore, there is no need to directly measure the temperature difference formed within the nanofluid droplet. (where D ｇ is the diffusion coefficient of the dispersion medium in the ambient atmosphere (m 2 / s), and ρ is the density of the dispersion medium (kg / m 3 ), ρ S is the saturated vapor density of the dispersion medium (kg / m 3 ) and ρ ∞ is the ambient density of the dispersion medium (kg / m 3 ) and ΔH ｖａｐ indicates the latent heat of vaporization of the dispersion medium (J / kg), and h ０ denotes the droplet height (m) of the nanofluid droplet on the substrate at the time of maximum expansion, and k Ｌ indicates the thermal conductivity of the nanofluid (W / (m·K)), and r ０ indicates the maximum contact radius (m) of the nanofluid droplet, and π is the constant of the circumference of a circle (=3.14).

[0067] Diffusion coefficient D of the dispersion medium in the ambient atmosphere ｇ , saturated vapor density of dispersion medium ρ S The values ​​are taken from Phys. Chem. Chem. Phys., 1999, 1, 149E153.

[0068] Ambient density of dispersion medium ρ ∞ is a value set in an experiment and can be calculated from the partial vapor pressure of the atmosphere.

[0069] Thermal conductivity k of nanofluid Ｌ is calculated from the measurements made by the thin wire heating method.

[0070] Latent heat of vaporization of dispersion medium ΔH ｖａｐ is 3.5 x 10 ５ J / kg.

[0071] Maximum contact radius of nanofluid droplets r ０ can be calculated from image analysis data obtained using, for example, a CMOS camera (manufactured by Baumer, VCXU-91M).

[0072] [Conditions Affecting the Marangoni Number Ma] The Marangoni number Ma can be adjusted by adjusting the type of dispersion medium and the type of modification chain bonded to the nanoparticles. The Marangoni number Ma can also be adjusted by adjusting the evaporation rate of the dispersion medium and the droplet size of the nanofluid droplets. The evaporation rate of the dispersion medium can be adjusted by adjusting the temperature and the partial pressure of the dispersion medium vapor in the ambient atmosphere. The partial pressure of the dispersion medium vapor in the ambient atmosphere can be adjusted by adjusting the ventilation conditions in the chamber, etc. The droplet size of the nanofluid droplets can be adjusted by adjusting the amount of nanofluid discharged from the inkjet printer.

[0073] [The ratio of the contact angle relaxation time to the evaporation time k ｅｖ In the method for producing a multilayer body according to this embodiment, in the printing step and the drying step, the ratio k of the contact angle relaxation time to the evaporation time, which is expressed by the following formula (2), ｅｖ is adjusted. (where k ｅｖ is the contact angle relaxation time τ re Evaporation time τ ev is a dimensionless number that indicates the ratio to the viscosity of the nanofluid (Pa s), and V ０ is the droplet volume at maximum expansion (m 3 ) where σ is the surface tension of the nanofluid droplet (mN / m) and θ ０ indicates the contact angle (rad.) at the time of maximum droplet spreading, where τ ev is the evaporation time (s) of the nanofluid droplets. ０ Use.)

[0074] Here, the contact angle relaxation time τ re is μV ０ １／３ / (σθ ０ ３ ) and the evaporation time is τ ｅｖ = t ０ It is expressed as k ｅｖ = τ re / τ ｅｖ As k ｅｖ By calculating , this determines whether stick-slip behavior occurs or not, depending on whether evaporation of the dispersion medium or retraction of the droplet is dominant.

[0075] The viscosity μ of the nanofluid can be measured at a temperature of 20°C in accordance with JIS Z 8803:2011 "Method for measuring viscosity of liquids."

[0076] The surface tension σ of nanofluid droplets is measured using the pendant drop method. The σ values ​​for dispersion media listed in publicly available literature, such as NIST Chemistry WebBook (URL: https: / / webbook.nist.gov / chemistry / ), PubChem (URL: https: / / pubchem.ncbi.nlm.nih.gov / ), and "Chemistry Handbook, Revised 5th Edition" (edited by the Chemical Society of Japan, Maruzen Publishing), can also be used. However, depending on the combination of surface-modified chains and dispersion media, nanoparticles (surface-modified nanoparticles) may adsorb to the surface, resulting in a lower surface tension compared to the dispersion media (exhibiting interfacial activity). Therefore, in this specification, values ​​listed in publicly available literature will not be used, and values ​​measured using the pendant drop method will be used.

[0077] Droplet volume at maximum expansion V ０ , and the contact angle θ at the time of maximum droplet expansion ０ can be calculated from image analysis data obtained using, for example, a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd., DMo series) or a CMOS camera (manufactured by Baumer, VCXU-91M).

[0078] [The ratio of contact angle relaxation time to evaporation time k ｅｖ Ratio k of contact angle relaxation time to evaporation timeｅｖ can be adjusted by adjusting the type of dispersion medium and the type of modification chain bonded to the nanoparticles. ｅｖ can be adjusted by adjusting the evaporation rate of the dispersion medium and the size of the nanofluid droplets. The evaporation rate of the dispersion medium can be adjusted by adjusting the temperature and the partial pressure of the dispersion medium vapor in the surrounding atmosphere. The partial pressure of the dispersion medium vapor in the surrounding atmosphere can be adjusted by adjusting the ventilation conditions in the chamber, etc. Furthermore, the size of the nanofluid droplets can be adjusted by adjusting the amount of nanofluid discharged from the inkjet printer.

[0079] [Peclet number Pe] In the method for producing a multilayer body according to this embodiment, the Peclet number P, expressed by the following formula (3), is used in the printing step and the drying step. ｅ is adjusted. (Here, Pe is a dimensionless number called the Peclet number, U is the advection velocity (m / s) of nanoparticles due to capillary flow and Marangoni convection, and h ０ denotes the droplet height (m) of the nanofluid droplet on the substrate at the time of maximum expansion, and D ｐ is the diffusion coefficient of the nanoparticles in the dispersion medium.

[0080] The Peclet number is a dimensionless number related to transport phenomena in continuums. Generally, when referring to the Peclet number, there are two types: the Peclet number in the context of mass transfer and the Peclet number in the context of heat transfer. Of these, the Peclet number in the context of mass transfer is expressed as the product of the Reynolds number and the Schmidt number, while the Peclet number in the context of heat transfer is expressed as the product of the Reynolds number and the Prandtl number.

[0081] The Péclet number Pe referred to in the method for producing a multilayer body according to this embodiment refers to the Péclet number in the context of mass transfer. More specifically, the Péclet number Pe is defined as the ratio of the advection rate of nanoparticles due to a flow to the diffusion rate of the same amount driven by an appropriate gradient.

[0082] In the method for producing a multilayer body according to this embodiment, when adjusting the intra-dot nanopattern appearing in the nanodots, it is desirable to adjust the advection velocity and diffusion velocity within the nanofluid droplets. Therefore, in the method for producing a multilayer body according to this embodiment, the intra-dot nanopattern can be adjusted by adjusting the process conditions of the printing and drying steps so as to adjust the Peclet number Pe.

[0083] In equation (3), U is the capillary flow velocity u derived from the mass conservation equation. Ca and the Marangoni convection velocity u Ma It is estimated by the following equation (5) as the sum of (where r0 is the maximum contact radius of the nanofluid droplet (m), and V0 is the volume of the nanofluid droplet at its maximum expansion (m 3 ), and (dV / dt)0 is the evaporation rate of the dispersion medium at the time of maximum expansion of the droplet (m 3 / s), (dσ / dT) is the temperature coefficient of surface tension (N / (m·K)), ΔT is the temperature difference within the droplet (K), h0 is the droplet height (m) at maximum expansion of the nanofluid droplet, and μ is the viscosity of the nanofluid.

[0084] Also, D ｐ can be expressed by the Stokes-Einstein equation, Equation (6) below. (where k Ｂ is the Boltzmann constant (1.38 × 10 ‐２３ J.K. ‐１ ), T represents temperature (K), π represents the constant of the circumference of a circle (3.14), μ represents the viscosity of the dispersion medium (Pa s), and d p indicates the average primary particle diameter (m) of the nanoparticles.

[0085] The evaporation rate of the dispersion medium at the time of maximum droplet expansion (dV / dt) ０ is the drip rate (m 3 ) divided by the evaporation time (s), and can be calculated by measuring the drop amount and evaporation time from image analysis data using, for example, a CMOS camera (manufactured by Baumer, VCXU-91M).

[0086] The viscosity μ of the dispersion medium can be measured at a temperature of 20°C in accordance with JIS Z 8803:2011 "Method for measuring viscosity of liquids."

[0087] Maximum contact radius of nanofluid droplets r ０ , the droplet height h of the nanofluid droplet on the substrate at maximum expansion ０ , and the maximum expansion volume of the nanofluid droplet V ０ can be calculated from image analysis data obtained using, for example, a CMOS camera (manufactured by Baumer, VCXU-91M).

[0088] Average primary particle diameter d of nanoparticles p was determined by dynamic light scattering (DLS) using, for example, a dynamic light scattering measuring device (DLS, Nano ZS, manufactured by Malvern Instruments Ltd.).

[0089] [Conditions Affecting the Péclet Number Pe] The Péclet number Pe can be adjusted by adjusting the type of dispersion medium and the type of modification chain bonded to the nanoparticles. The Péclet number Pe can also be adjusted by adjusting the evaporation rate of the dispersion medium and the droplet size of the nanofluid droplets. The evaporation rate of the dispersion medium can be adjusted by adjusting the temperature and the partial pressure of the dispersion medium vapor in the surrounding atmosphere. The partial pressure of the dispersion medium vapor in the surrounding atmosphere can be adjusted by adjusting the ventilation conditions in the chamber, etc. The droplet size of the nanofluid droplets can also be adjusted by adjusting the amount of nanofluid ejected from the inkjet printer.

[0090] [Nanodot pattern appearing by adjusting parameters] Marangoni number Ma, ratio of contact angle relaxation time to evaporation time k ｅｖ By adjusting the Marangoni number Ma and the Peclet number Pe, the nanopattern within the dot that appears after the nanofluid droplet dries can be adjusted. For example, if the Marangoni number Ma is greater than about 80, a "spoke pattern" is formed, with multiple lines extending radially from the center to the circumference. In this case, the Peclet number should be Pe > 10. ２ Satisfy the following.

[0091] As the Péclet number decreases, the pattern transitions to the coffee ring region. Specifically, when the Péclet number Pe is 10 or greater, a "coffee ring" pattern is formed, in which particles are accumulated along the circumference of the nanodot, similar to a coffee stain. As the Péclet number Pe decreases further, a "uniform pattern" is formed, in which particles are distributed approximately uniformly within the nanodot and no nanopattern is apparent. The transition zone between the coffee ring and the uniform pattern generally occurs in the range of Pe≈1 to 10, and when Pe<1, the coffee ring is suppressed.

[0092] The ratio of contact angle relaxation time to evaporation time k ｅｖ Regarding k ｅｖ is the critical value 1×10 －４ If Pe is smaller than 10, a "multi-ring pattern" will be formed, in which multiple rings that are close to concentric circles are accumulated. All conditions for forming a multi-ring pattern satisfy the condition for forming a coffee ring, which is that Pe is 10 or more.

[0093] When the Marangoni number Ma exceeds a critical value, a convection called Marangoni-Bénard convection is induced, and the spoke pattern is formed due to the structure of this convection. The critical value of the Marangoni number Ma is theoretically derived from linear stability theory. On the other hand, the ratio of the contact angle relaxation time to the evaporation time k ｅｖ The critical values ​​of the ρ and the Peclet number Pe are experimentally derived by observing patterns formed under different conditions.

[0094] Thus, the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k ｅｖ By adjusting the ρ and the Peclet number Pe, it is possible to manufacture a multilayer body in which nanodots having a desired intradot nanopattern are continuously formed in a constant pattern.

[0095] <Multilayer Body> The multilayer body according to this embodiment also relates to a multilayer body in which a plurality of nanodots are formed on a substrate on which a coating may be formed, and the intra-dot nanopatterns expressed in the plurality of nanodots are continuously formed as a uniform pattern. This multilayer body can be manufactured by the above-mentioned method for manufacturing a multilayer body. The intra-dot nanopatterns expressed in the plurality of nanodots may be any of a "uniform pattern," a "spoke pattern," a "coffee ring," and a "multi-ring." As mentioned above, these are determined by the Marangoni number Ma, the ratio of the contact angle relaxation time to the evaporation time k, ｅｖ , and the Peclet number Pe, respectively.

[0096] [Uniform Pattern] A uniform pattern refers to a pattern in which uniform nanoparticle dots are continuously formed. In this case, the film thickness variation, which is the standard deviation of the average film thickness of the film constituting the uniform pattern, is preferably less than 30 nm, more preferably less than 20 nm, and even more preferably less than 10 nm.

[0097] Until now, if the unevenness of the film was not visible, it was perceived as a uniform pattern regardless of the size of the standard deviation relative to the average film thickness. As experimentally demonstrated in Fig. 8 described later, according to the invention described in this embodiment, by adjusting the Peclet number Pe, it is possible to continuously form a plurality of nanodots made of a film that is truly free of unevenness in the sense that the standard deviation is small, i.e., a uniform pattern.

[0098] The upper limit of the diameter of the nanodots constituting the deposition pattern, i.e., the uniform pattern, is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. On the other hand, the lower limit of the diameter of the nanodots constituting the uniform pattern is not particularly limited, but in consideration of the manufacturing stability of the nanodots, it is, for example, preferably 10 nm or more, and more preferably 100 nm or more.

[0099] It should be noted that nanodots are dots formed by self-organization using nanoparticles, and therefore the diameter of the nanodots is not necessarily on the order of nanometers, but can be on the order of micrometers or millimeters, as is the case with other patterns.

[0100] [Spoke Pattern] A spoke pattern refers to a pattern in which multiple lines extend radially. In this case, the number of lines is preferably four or more, more preferably eight or more, and even more preferably twelve or more.

[0101] The upper limit of the diameter of the nanodots constituting the deposition pattern, i.e., the spoke pattern, is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. On the other hand, the lower limit of the diameter of the nanodots constituting the spoke pattern is not particularly limited, but in consideration of the manufacturing stability of the nanodots, it is, for example, preferably 10 nm or more, and more preferably 100 nm or more.

[0102] The lower limit of the difference in unevenness between the convex portions that form the stripes of the spoke pattern and the concave portions that form the spaces between adjacent stripes is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more, which allows the presence or absence of the spoke pattern to be clearly recognized.

[0103] The upper limit of the difference between the protrusions and recesses is not particularly limited, but from the viewpoint of continuously forming the spoke pattern as a uniform pattern, it is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less.

[0104] [Coffee Ring] A coffee ring is a pattern in which nanoparticles are accumulated along the circumference of a nanodot. In this case, the width of the ring constituting the coffee ring is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 100 μm or less. The width of the ring is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more.

[0105] The upper limit of the diameter of the nanodots constituting the deposition pattern, i.e., the coffee ring, is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. On the other hand, the lower limit of the diameter of the nanodots constituting the coffee ring is not particularly limited, but considering the manufacturing stability of the nanodots, it is preferably 10 nm or more, and more preferably 100 nm or more.

[0106] In the coffee ring, adjacent rings have unevenness, and the lower limit of the difference in unevenness is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. This allows the presence or absence of a coffee ring to be clearly recognized.

[0107] The upper limit of the difference between the protrusions and recesses is not particularly limited, but from the viewpoint of continuously forming coffee rings in a uniform pattern, it is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less.

[0108] [Multi-ring] The multi-ring refers to a pattern in which multiple, approximately concentric rings are accumulated. In this case, the number of rings in a nanodot is preferably 3 or more, more preferably 6 or more, and even more preferably 10 or more.

[0109] The width of the rings constituting the multi-ring is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 100 μm or less, and is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more.

[0110] The upper limit of the diameter of the nanodots constituting the deposition pattern, i.e., the multi-ring, is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. On the other hand, the lower limit of the diameter of the nanodots constituting the multi-ring is not particularly limited, but considering the manufacturing stability of the nanodots, it is preferably 10 nm or more, and more preferably 100 nm or more.

[0111] In the multi-ring, adjacent rings have unevenness between them, and the lower limit of the difference in unevenness is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. This allows the presence or absence of a multi-ring to be clearly recognized.

[0112] The upper limit of the difference between the protrusions and recesses is not particularly limited, but from the viewpoint of continuously forming multi-rings in a uniform pattern, it is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less.

[0113] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0114] <Obtaining and preparing experimental materials> The types, sources, and preparation methods of the experimental materials used in the experiments are outlined below.

[0115] [Preparation of Nanoparticles] The nanoparticles dispersed in the dispersion medium in the following examples were decanoic acid-modified CeO ２ The nanoparticles were synthesized by supercritical hydrothermal method and consisted of CeO ２ The nanoparticles are surface-modified with decanoic acid, which allows them to exhibit high dispersibility in organic solvents such as alkanes. ２Detailed preparation methods for the nanoparticles are described in J. Colloid Interface Sci. 587, 574-580 2021, the contents of which are incorporated herein by reference, but the matters specifically mentioned herein shall take precedence.

[0116] Decanoic acid modified CeO ２ The reagents required for preparing the nanoparticles were reagent-grade compounds from ITEC Co., Ltd., Fujifilm Wako Pure Chemical Industries, Ltd. (manufacturers), and other companies.

[0117] [Dispersion medium] The dispersion medium used in the following examples was hexane (n-C ６ H １４ ), heptane (n-C ７ H １６ ), octane (n-C ８ H １８ ), nonane (n-C ９ H ２０ ), decane (n-C １０ H ２２ ) as a dispersion medium. １１ H ２４ ), cyclohexane (C ６ H １２ The organic solvents used were reagent-grade organic solvents from Fujifilm Wako Pure Chemical Industries, Ltd. (manufacturer).

[0118] <Conditions for Various Experiments> Experimental conditions such as the conditions for preparing the nanofluid, the conditions for the substrate onto which the droplets are dropped, the method for preparing the atmosphere around the substrate, and the method for dropping by the inkjet process are outlined below.

[0119] [Preparation of Nanofluid] Decanoic acid modified CeO ２ Nanofluids were prepared by dispersing nanoparticles in various organic solvents. In this example, to observe the difference in behavior depending on the nanoparticle concentration, nanofluids containing low concentrations (0.1 wt%) and high concentrations (0.5 wt%) of nanoparticles were prepared. Specific nanofluid preparation methods are outlined below.

[0120] (1) The weight of the nanoparticles was measured using an electronic balance, and each organic solvent was mixed to achieve the desired concentration. (2) The premix was placed in a screw tube, and the tube was sealed and subjected to ultrasonic irradiation for 30 minutes using an ultrasonic cleaner. (3) The mixture was transferred to a centrifuge container, and centrifuged at 10,100 rpm for 30 minutes. This process allowed the aggregated nanoparticles in the nanofluid to settle, and the supernatant was used in the experiment. (4) The particle size distribution of the nanoparticles in the nanofluid was measured using dynamic light scattering (DLS), confirming that the nanoparticles were dispersed.

[0121] Throughout the entire process, the concentration changed by up to 0.07 wt% due to nanoparticle precipitation caused by centrifugation and evaporation during preparation. However, since the concentration did not change significantly from before centrifugation, experiments were carried out with nanofluid concentrations of approximately 0.1 wt% and approximately 0.5 wt%, respectively. In the experiments using silanized Si substrates described below, the nanofluid concentration was adjusted to approximately 0.1 wt%.

[0122] [Substrate Preparation] In this example, a Si substrate (silicon wafer) and a silanized Si substrate were used as the substrate. The silanization treatment changes the free surface energy of the substrate and the interaction between the silicon wafer and the substrate, which is thought to result in changes in wetting behavior and the nanoparticle pattern after drying. Below, we will explain the method for cleaning the Si substrate and the silanization treatment process.

[0123] [Cleaning of Si Substrate] The Si substrate was cleaned according to the following procedure.

[0124] (1) The Si substrate was immersed in ethanol and subjected to ultrasonic irradiation for 10 minutes using an ultrasonic cleaner. (2) The Si substrate was naturally dried and then washed with H ２ SO ４ and H ２ O ２A Piranha solution was prepared by mixing the above in a volume ratio of approximately 7:3, and the Si substrate was immersed in the solution at 60°C for at least 6 hours. (3) The Si substrate was removed from the Piranha solution and immersed in pure water, where it was subjected to ultrasonic irradiation for 10 minutes. The pure water was then replaced, and ultrasonic irradiation was repeated. (4) The pure water was evaporated, and the Si substrate was stored in a desiccator under reduced pressure to prevent water vapor in the air from adhering to the substrate.

[0125] On the Si substrate exposed to the atmosphere, a SiO film with a thickness of about 2 nm was formed. ２ It is known that a natural oxide film is formed, and in this test, SiO ２ In addition, the surface roughness of the Si substrate washed with Piranha solution was measured using the dynamic force mode (DFM) of a scanning probe microscope (SPM), and it was found that the surface roughness of the Si substrate was within a range that did not affect the wetting behavior.

[0126] [Silanization Treatment of Si Substrate] To change the physical properties of the substrate, the Si substrate was subjected to silanization treatment (ODS treatment). Octadecyltriethoxysilane (manufactured by Combi-Blocks: hereinafter also referred to as "ODS") was used as a silane coupling agent. After Piranha cleaning, the silanization treatment was carried out according to the following procedure.

[0127] (1) The Si substrate was immersed in a cyclohexane solution containing 0.01 M ODS at 60°C for 1 hour to perform a silanization treatment on the surface. (2) The silanized Si substrate was immersed in acetone and subjected to ultrasonic irradiation for 10 minutes. The substrate surface was then rinsed with pure water. (3) The Si substrate was heated at 120°C for 2 hours to evaporate the organic solvent, and then stored in a desiccator under reduced pressure.

[0128] Although not shown in the figure, the surface roughness of the silanized Si substrate was measured using the dynamic force mode (DFM) of a scanning probe microscope (SPM). The surface roughness of the silanized Si substrate was found to be within a range that did not affect the wetting behavior.

[0129] [Controlling the atmosphere around the substrate] Changing the organic solvent used as the dispersion medium is thought to change the viscosity, evaporation rate, and surface energy of the nanofluid. However, to evaluate the effect of differences in capillary flow velocity on particle patterns, it was necessary to change only the evaporation rate. Therefore, experiments were conducted using two types of atmospheres around the substrate: an open system and an evaporation-suppressed system. In the open system, there are no barriers around the substrate to prevent evaporation, and evaporation proceeds through gas diffusion. On the other hand, in the evaporation-suppressed system (EvMod), the substrate was surrounded on all four sides by a copper container, and organic solvent was injected into the reservoir to increase the vapor concentration and decrease the evaporation rate.

[0130] For observation with the measuring device, an optical glass window was installed on the wall of the copper container to allow the laser light to pass through.In the evaporation suppression system experiment, experiments were conducted with pure organic solvent and approximately 0.1 wt% nanofluid to compare with the open system.

[0131] [Inkjet Dropping] An inkjet device was used to drop droplets onto the substrate. By using an inkjet, the drop volume can be controlled on the picoliter to nanoliter scale. The inkjet nozzle used was IJHB-1000 manufactured by Microjet Corporation.

[0132] To examine the droplet volume per ejection, a droplet observation camera was used to observe the flying droplets ejected from the inkjet nozzle.

[0133] The nanofluid samples used were approximately 0.1 wt.% nanofluids, in which nanoparticles were dispersed in five types of organic solvents. To measure droplet volume, visualized images of 50 flying droplets in each experiment were analyzed using imageJ image analysis software (developed by Wayne Rasband, NIH). The average volume per droplet was calculated from the long and short sides of the approximated ellipse. The calculated volume per droplet ranged from 230 pL to 280 pL. In this example, the number of droplets was varied between 10, 50, and 100 (approximately 2.5, 25, and 125 nL, respectively), and the contact radius and evaporation time were also varied. The inkjet head settings were also adjusted to ensure stable droplet ejection.

[0134] [Film Thickness Measurement] In the present invention, the thickness of the dried nanoparticle layer is measured using phase-shifting ellipsometry (E. Shoji et al., Optics and Lasers in Engineering, 112 (2019) 145-150). For the analysis, the effective medium approximation (EMA) is applied, and the nanoparticle layer is considered to be a single layer consisting of nanoparticles and air with a volume fraction of 0.5, and its refractive index is set to 1.42 based on the refractive index of the nanoparticles (1.81) and the refractive index of air (1.000).

[0135] Experimental Results Figure 1 shows time-series images of droplets deposited on a Si substrate. These images show the phase difference Δ between the P and S polarization states and represent contours of the liquid film thickness. The samples included pure n-octane, n-octane nanofluids containing 0.1 wt % and 0.5 wt % nanoparticles, and 0.1 wt % nanofluid in an evaporation-reduced system (EvMod). t represents time, and t ０ denotes the evaporation time listed in Table 1, with t = 0 corresponding to the moment the droplet was deposited on the substrate. Visualization revealed a region of interference fringes representing a liquid film of microscale thickness coexisting with a uniformly colored region representing the substrate. The region from the first interference fringe to the substrate corresponds to the nano-liquid film region. Evaporation time t under each condition for a droplet volume of 25 nL ０ Values ​​represent the average of three or more experiments.

[0136] After deposition, the droplet spread rapidly on the substrate, exhibiting axisymmetric spreading accompanied by liquid evaporation. During the early stages of droplet spreading in an open system, certain regions within the droplet may appear white or black, indicating areas of steep film thickness gradients, resulting in dense interference fringes. These dense regions are not axisymmetric due to the oblique incidence of light in the ellipsometer. In these cases, side-on observations of the droplet were used to interpolate the data. Furthermore, for pure liquids, the t / t ０ No deposit remained after complete evaporation at ρ = 1.0, but a deposition pattern of nanoparticles was observed for the nanofluid.

[0137] Figure 2 shows the two-dimensional film thickness distribution of the dried particles after the droplets on the substrate evaporated. The droplet amounts were 2.5 nL, 25 nL, and 125 nL under all conditions. Figure 2(a) shows the particle pattern on an open-system Si substrate with a nanofluid concentration of approximately 0.1 wt%, Figure 2(b) shows the particle pattern on an open-system Si substrate with a nanofluid concentration of approximately 0.5 wt%, and Figure 2(c) shows the particle pattern on an evaporation-suppressed Si substrate with a nanofluid concentration of approximately 0.1 wt%.

[0138] Various droplet patterns emerged depending on the experimental conditions. While the droplet volume and nanoparticle concentration had minimal effects, the type of solvent significantly affected the pattern formation. A spoke pattern was observed with hexane nanofluid, while coffee rings were formed with heptane, octane, and nonane nanofluids. Decane nanofluid showed a uniform pattern at 0.1 wt %, but a multi-ring pattern appeared at 0.5 wt %. Furthermore, the evaporation rate played an important role, and in the evaporation-suppressed system (EvMod), the characteristic pattern disappeared, resulting in a nearly uniform pattern.

[0139] To define dimensionless numbers and analyze the internal convection and contact line motion of the droplet, we extracted wetting parameters, such as contact radius, contact angle, and droplet height, with high accuracy from the micrometer-scale liquid film thickness profile shown in Figure 3. The thickness distribution shows that the 0.1 wt% octane nanofluid spreads the most and exhibits the smallest dynamic contact angle θ. Furthermore, the maximum contact radius for the evaporation-inhibited system (EvMod) was approximately 0.9 mm, while the radius of the circle defined by the nanoparticle layer was approximately 0.5 mm (see Figure 2(c)). In other words, unlike the typical coffee-ring formation, the maximum contact radius did not match the size of the nanoparticle layer.

[0140] Wetting parameters were extracted with high accuracy from the measured liquid film thickness based on the definitions shown in Figure 3(d). Specifically, the contact angle θ was defined as the slope of the tangent at the inflection point, and the apparent contact line, used to calculate the contact radius R, was determined as the point where the tangent intersected the substrate. A nanometer-scale liquid film (Figure 3(d)) was confirmed ahead of the contact line by measurements using a phase-shifting ellipsometer. Such a thin liquid film is usually called a leading film, but in this study, this film was observed during both the expansion and contraction processes, so we refer to it as a nanoliquid film rather than a leading film.

[0141] Figure 4 shows the normalized contact radius R / R for all n-octane samples. ０ (listed in Table 2) and normalized time t / t ０ All samples show the relationship between t / t ０ The maximum expansion was observed in the range of ρ = 0.1 to 0.3, followed by gradual evaporation and droplet contraction. In particular, the octane nanofluid in the open system formed coffee rings without typical pinning, and the maximum contact radius did not correspond to the size of the nanoparticle layer. Therefore, the results of this study revealed that coffee rings can form even without pinning, whereas many previous studies have attributed coffee ring formation to a pinning mechanism and aimed to prevent pinning as a coffee ring suppression method. The maximum radius R0 under each condition at a droplet volume of 25 nL. Values ​​represent the average of three or more experiments.

[0142] Generally, droplets with high saturated vapor pressure have a short evaporation time and a large contact angle, so it is expected that the expansion (maximum contact radius) in an open system will be smaller than that in an evaporation-suppressed system. However, from Tables 1 and 2, it can be seen that droplets in an open system have a short evaporation time (t ０ ) is shorter, it can expand significantly more than the droplets in the evaporation retardant (EvMod) system.

[0143] As shown in Figure 5, the coffee ring formation process in octane nanofluid was observed for the first time using phase-shifting ellipsometry.

[0144] Figure 5 reveals that the evaporation-inhibited (EvMod) system using 0.1 wt% octane nanofluid exhibits nanofilm morphology similar to that of previously reported non-evaporative systems. This behavior is due to the low nanoparticle concentration near the contact line, as evidenced by the absence of a nanoparticle layer after drying (shown in Figure 5(d)), and is supported by the discrepancy between the maximum contact radius of the droplet and the size of the nanoparticle layer (shown in Figures 2 and 3).

[0145] However, the open system exhibited a different behavior, with both the pure liquid and the nanofluid thinning to a film thickness of approximately 10-20 nm near the contact line. Beyond this region, the nanofluid film thickened slightly, increasing in thickness by approximately 10 nm. Furthermore, in this thickened region, nanoparticle deposition was observed, suggesting the formation of a coffee ring.

[0146] This finding is particularly noteworthy because it suggests that the nanoparticles exist within an ultrathin liquid film of 10-20 nm, which is likely due to the nanoparticles' very small size.

[0147] <Discussion> [Nanoparticle deposition patterns induced by droplet internal flow and contact line motion] Nanoparticle deposition patterns arise as a result of the complex interaction of multiple factors. Here, we discuss the transitions between spoke, coffee-ring, multi-ring, and uniform deposition patterns observed in experimental results. The main phenomena affecting these patterns include capillary flow, Marangoni convection, Marangoni-Bénard convection, and stick-slip motion of the contact line, as shown in Figure 6. Before discussing specific details, we outline four applied assumptions.

[0148] The first assumption is that nanoparticles exhibit high followability to the flow inside the droplet, and sedimentation due to gravity can be ignored. The followability of nanoparticles can be evaluated using the Stokes number. The Stokes number is St = ρ ｐ d ｐ ２ U / 18 μL, where ρ ｐ is the density of the nanoparticles, d ｐis the diameter of the nanoparticle, U is the velocity of capillary flow, μ is the viscosity of the liquid, and L is the characteristic length. If St is small enough, the nanoparticles closely follow the movement of the fluid. For example, CeO ２ Nanoparticles (ρ ｐ = 7.22 x 10 ３ kg / m ３ ) density, nanoparticle diameter d ｐ = 5.8 x 10 －９ m, maximum estimated flow velocity U≒10 －２ m / s, maximum contact radius L=R ０ ≒10 －３ m, and viscosity of n-hexane μ = 3.129 × 10 －４ Using Pa s, the calculated Stokes number is St ≈ 5 × 10 －１０ <<1. This very small value confirms that the nanoparticles have high followability to the droplet flow.

[0149] The second assumption is that the nanoparticles in this system do not significantly adsorb at either the gas-liquid or solid-liquid interfaces, preventing their immediate accumulation. At the gas-liquid interface, the surface tension of the nanofluid has been measured using the pendant drop method, and no significant change has been observed thus far, suggesting minimal nanoparticle adsorption.

[0150] The interaction potential between the surface-modified nanoparticles and the related substances at the solid-liquid interface was evaluated using an interaction potential model. Here, the electrostatic force of the nanoparticles can be ignored because the surface charge of the nanoparticles is zero in the organic solvent. The surface of the silicon substrate is usually coated with SiO ２ The SiO layer on our substrate is oxidized to form a ２ The thickness of the layer was about 2 nm, and SiO ２ Since the Hammerker constant of is smaller than that of pure Si, considering ２ Considering the potential, it can be assumed that nanoparticles are not easily adsorbed at the solid-liquid interface.

[0151] The third assumption is related to the evaporation process, specifically that the evaporated liquid is transported by diffusion rather than by convection. To verify this assumption, the potential influence of natural convection outside the droplet, which affects the behavior of the evaporated liquid in the gas phase and thus the estimated temperature difference within the droplet, is calculated using the Grashof number Gr = (ρ ｓａｔ -ρ ∞ ) gR ０ ３ / (ρ ∞ ν ∞ ２ ) where ν ∞ represents the kinematic viscosity of the surrounding gas, g is the gravitational acceleration, and the subscripts "sat" and "∞" refer to saturation and a position sufficiently far from the droplet, respectively. The effect of natural convection around the droplet is 0.310 × Gr, which shows the effect of convection on the evaporation rate. ０．２１６ Under the experimental conditions used in this study, the maximum contact radius R was used at a droplet volume of 150 nL. For the solvents used, the 0.310 × Gr for hexane, heptane, octane, nonane, and decane nanofluids was used. ０．２１６ The corresponding values ​​of σ were calculated as 0.592, 0.609, 0.580, 0.459, and 0.363, respectively. These values ​​indicate that the experiment was conducted under diffusion-dominated evaporation conditions, and the influence of natural convection was negligible. This assumption is important for accurately estimating the temperature gradient within the droplet and evaluating the Marangoni effect.

[0152] The fourth assumption concerns the thermophysical properties of the system. Due to the characteristics of nanoparticles and their low concentration, the thermophysical properties of nanofluids were assumed to be nearly identical to those of the solvent. As mentioned previously, the surface tension of nanofluids can be considered equivalent to that of a pure liquid. Furthermore, the viscosity of nanofluids is nearly constant within the concentration range studied. Therefore, the values ​​listed in Table 3 were used to calculate the dimensionless numbers. Furthermore, the diffusion coefficient D of nanoparticles is ｐ is the Stokes-Einstein equation D ｐ = k Ｂ T / (3πμd ｐ ) where k Ｂ represents the Boltzmann constant, and T represents the absolute temperature. Thermophysical properties used to derive dimensionless parameters: density ρ, viscosity μ, thermal conductivity k ｌ , thermal diffusivity α, and surface tension σ are values ​​at 20°C. Vapor diffusion coefficient D in air ｇ Only the values ​​are those at 25°C.

[0153] Based on these assumptions, the phenomena involved in the formation of the nanoparticle deposition pattern shown in FIG. 6 will now be explained.

[0154] Coffee Ring-Péclet Number The nanoparticles used in this study exhibited a high diffusion coefficient due to their small size and high dispersity. Nanoparticle diffusion may hinder pattern formation by opposing transport due to the flow inside the droplet. However, convection inside the droplet significantly contributed to transporting nanoparticles to the contact line. To quantify the relative influence of convection and diffusion, the Péclet number is defined by equation (3) above: where U denotes the advection velocity of the nanoparticles, and h ０ represents the droplet height at maximum expansion of the nanofluid droplet on the substrate. Pe>>1 indicates that convective transport dominates diffusion, thereby promoting pattern formation, while a small value of Pe suggests that diffusion suppresses pattern formation. The diffusion coefficient of the nanoparticles used in this study is D ｐ ≒10 －１０ m ２ / s, which reflects the small size and high dispersibility of the nanoparticles.

[0155] Two types of convection inside the droplet were considered: capillary flow and Marangoni convection. It is known that the coffee ring pattern is the result of capillary flow driven by solvent evaporation and geometric constraints that maintain the spherical droplet shape. This outward flow carries the nanoparticles to the droplet edge.

[0156] In addition to capillary flow, Marangoni convection, driven by the temperature gradient along the gas-liquid interface due to evaporative cooling, also has a significant effect on particle deposition. When using a solvent with a high vapor pressure, evaporation causes a significant temperature gradient. This temperature gradient creates a difference in surface tension, generating Marangoni convection from regions with low surface tension (warmer) to regions with high surface tension (cooler).

[0157] Because the solvent is single-component and surfactant-free, and the nanoparticles used are not adsorbed at the gas-liquid interface, only the temperature difference Marangoni effect was considered. Evaporation causes heat loss due to latent heat, cooling the gas-liquid interface. As shown by capillary flow, evaporation is more intense near the contact line than at the droplet apex. However, the high thermal conductivity of the silicon substrate ensures sufficient heat supply to the gas-liquid interface with a thin liquid film near the contact line. As a result, the temperature at the droplet apex is lower than that near the contact line, which typically induces Marangoni convection along the gas-liquid interface from the contact line toward the droplet center.

[0158] Temperature difference Marangoni convection velocity u Ｍａ can be estimated by the following formula: Here, dσ / dT represents the temperature coefficient of surface tension, and ΔT represents the temperature difference at the interface. The temperature difference ΔT is expressed as follows: where ρ is the density of the solvent, ΔH ｖａｐ is the latent heat of vaporization, k ｌ indicates the thermal conductivity of the solvent. The evaporation rate parameter β ｅｖ is defined as follows: β ｅｖ =D ｇ (ρ ｓａｔ -ρ ∞ ) / ρ where D ｇ indicates the vapor diffusion coefficient of the solvent in air.

[0159] In this study, we hypothesized that Marangoni convection and capillary flow combine to generate a circulating flow, as shown in Figure 6(b), and that both flows contribute to the formation of the coffee ring. Particles near the droplet surface are initially transported inward toward the droplet apex by Marangoni convection. Upon reaching the apex, these particles descend along the droplet centerline and reach the substrate. At this point, the particles may either be adsorbed near the droplet center or transported outward along the substrate by the circulating flow. If transported outward, the particles may return to the droplet apex via the free surface, repeating the cycle. This flow pattern indicates that Marangoni convection, although initially inward, repeatedly delivers particles to the outward capillary flow, ultimately promoting particle deposition at the contact line.

[0160] According to the interaction model of surface-modified nanoparticles with substrates, nanoparticles are known to adhere weakly to the substrate. As a result, even if nanoparticles descend from the droplet apex through the flow and then approach the substrate, they are unlikely to immediately adhere to the substrate. Instead, nanoparticles are expected to recirculate toward the contact line. Once the droplet reaches its maximum spreading point and the contact line begins to recede, nanoparticles are unable to return to the droplet center and instead accumulate near the contact line, forming a coffee ring. The results in Figure 2 confirm this behavior, showing that heptane nanofluid, which exhibits a stronger Marangoni flow compared to nonane nanofluid, produces a more pronounced coffee ring pattern under our experimental conditions.

[0161] In this experiment, Marangoni convection was identified as the driving factor for the coffee ring formation, and the magnitude of its velocity was determined to be the velocity u of the temperature difference Marangoni flow mentioned above. Ｍａ In calculating the Peclet number Pe, the specific flow velocity U includes the contributions of both capillary flow and Marangoni convection, and is simply U = u Ｃａ +u Ｍａ The contribution of Marangoni convection is important, and this has a major impact on the formation of the coffee ring.

[0162] Spoke-Marangoni Number: The spoke pattern was observed only in experiments conducted under open-system conditions using n-hexane as the solvent. This pattern is due to Marangoni-Bénard convection. Unlike radial convection from the droplet apex toward the contact line, Marangoni-Bénard convection is due to a temperature gradient along the droplet height and occurs when the liquid film is thin.

[0163] When the thermal diffusivity of the nanofluid is α, the Marangoni number Ma can be calculated from the above-mentioned formula (1).

[0164] Critical Marangoni number M ａｃ ≒80 is Biot number Bi = hh ０ / k ｌ The Biot number is defined as the heat transfer coefficient at the gas-liquid interface, h. In most microdroplet systems, h ０ Since is small, Bi ≒ 0 holds. For example, in the results of this test, the maximum droplet height h of a 150 nL droplet of 0.5 wt% decane nanofluid is ０ h ０ ≒ approx. 8×10 －５ It has been shown that Marangoni-Bénard convection occurs in an evaporating droplet when Ma exceeds a critical value. In this case, the Péclet number Pe in equation (3) is usually large, indicating that convective transport dominates diffusion. Therefore, the combination of Marangoni-Bénard convection and capillary flow forms convective cells, resulting in a spoke pattern in particle deposition.

[0165] Multi-ring pattern - ratio of contact angle relaxation time to evaporation time The multi-ring pattern is due to the stick-slip motion of the contact line, which alternates between sticking and slipping as the contact line retreats. During the stick stage, particles are transported and deposited near the contact line by the same mechanism as described for coffee-ring formation.

[0166] In this test, the contact line relaxation time τ ｒｅ and evaporation time τ ｅｖ A dimensionless number k defined as the ratio of evThe stick-slip motion was predicted using this non-dimensional number, which is expressed by the following equation (2). Here, the contact angle relaxation time is τ ｒｅ = μV ０ １／３ / (σθ ０ ３ ) and the evaporation time is τ ｅｖ = t ０ It is defined as follows.

[0167] k ev Below a certain threshold, the droplet contact line exhibits stick-slip behavior. Furthermore, when the Peclet number Pe exceeds a critical value, the resulting particle film structure is predicted to form a multi-ring pattern.

[0168] Correlation between Experimental Results and Estimated Dimensionless Numbers The calculated dimensionless numbers under each experimental condition are shown in Figure 7. As Figure 7 shows, the droplet volume has minimal effect on the observed patterns, so the results shown in Figure 7 correspond to a 25 nL droplet. Figure 7 also highlights the critical region of each dimensionless number, with a reference line for the Marangoni number Ma at Ma ≈ 80 and bands showing the estimated critical regions for the other two dimensionless numbers.

[0169] First, we examined the open system in which various patterns were observed. Among the nanofluids used in this study, only hexane nanofluid showed a spoke pattern, and its Marangoni number was the critical value M ａｃ The value exceeded 80. Furthermore, the hexane nanofluid exhibited a high Peclet number Pe, suggesting that the synergistic effect of Marangoni-Bénard convection and radial flow contributes to the formation of the spoke pattern.

[0170] Heptane, octane, and nonane nanofluids have a critical Marangoni number M ａｃThe Péclet numbers Pe of these nanofluids ranged from 0.7 to 250, indicating that convective transport dominated nanoparticle diffusion. The large Péclet numbers of heptane nanofluids and the large particle film thicknesses observed at the sample edges are consistent with the implications of these dimensionless numbers.

[0171] The deposition patterns of the nanofluid droplets described above were independent of nanoparticle concentration, except for the decane nanofluid, which showed distinctly different patterns at different concentrations. At 0.1 wt%, the pattern was nearly uniform, but at 0.5 wt%, a multi-ring pattern was observed. This behavior is due to the very small k value exhibited by the 0.5 wt% decane nanofluid. ev ≒10 －５ This low k ev is due to the larger contact angle and longer evaporation time compared to the other samples. The Peclet number, Pe≈100, is consistent with coffee ring formation during the stick stage. On the other hand, none of the dimensionless numbers for the 0.1 wt% decane nanofluid reached a critical value, which is also true for all droplets in the evaporation-suppressed system. This indicates that no pattern formation-related phenomena were induced.

[0172] Finally, for all samples, the Peclet number Pe and the ratio of the contact angle relaxation time to the evaporation time k ev The correlation between Ma and Pe is shown in Figure 8, with deposition patterns indicated by markers. Because there is a correlation between Ma and Pe and a threshold value is defined for the Marangoni number, the Marangoni number Ma was removed from the axis in Figure 8 for easier viewing.

[0173] High Peclet number Pe>10 ２In the region of , the observed deposition pattern was spoked. As the Péclet number decreased, the pattern transitioned to a coffee ring region, and with further decrease, it changed to a uniform deposition region. The transition zone between the coffee ring and the uniform pattern occurred roughly in the range of Pe≈1 to 10. For Pe<1, the coffee ring was suppressed.

[0174] Ratio of contact angle relaxation time and evaporation time k ev Regarding k ev <10 －４ Importantly, all conditions for forming multirings were within the range of Pe≈10. ２ The conditions for coffee ring formation were met.

[0175] Furthermore, to demonstrate the applicability of this map, we included data from studies that met the assumptions of this study and provided the necessary parameters. Both of these studies focused on coffee ring formation and used tens of picoliters of droplets of 755 nm polystyrene (PS) particles stabilized with poly(N-vinylpyrrolidone) (PVP) in isopropyl alcohol (IPA) (Non-Patent Documents 1, 2). These studies used a different solvent (IPA) and larger particle size (755 nm) than this study, making them suitable for validating this map. As shown in Figure 8, the k evThe Péclet numbers were similar, but the Péclet numbers were higher, satisfying the conditions for coffee ring formation. These results highlight the applicability of the dimensionless framework proposed in this study to predict deposition patterns in diverse systems with different fluid properties and particle sizes. Non-patent document 1: AA Pahlavan, L. Yang, CD Bain, HA Stone, Evaporation of binary-mixture liquid droplets : The formation of picoliter pancakelike shapes, Physical Review Letters 127 (2) (2021) 24501-24501. doi:10.1103 / PhysRevLett.127.024501. Non-patent document 2: L. Yang, AA Pahlavan, HA Stone, CD Bain, Evaporation of alcohol droplets on surfaces in moist air, Proceedings of the National Academy of Sciences 120 (38) (2023) e2302653120. doi:doi:10.1073 / pnas.2302653120.

Claims

1. A method for producing a multilayer body, comprising at least a printing step of discharging nanofluid droplets by an inkjet process onto a substrate on which a coating may be formed, and a drying step of drying the discharged nanofluid droplets to form a plurality of nanodots, wherein the nanofluid droplets contain nanoparticles dispersed in a dispersion medium, and in the printing step and the drying step, Ma and k represented by the following formulas (1) to (3) are used. ｅｖ and Pe, thereby adjusting the intra-dot nanopattern appearing in the plurality of nanodots. (where Ma is a dimensionless number called the Marangoni number, dσ / dT is the temperature coefficient of surface tension (N / (m·K)), h ０ is the droplet height (m) of the nanofluid droplet on the substrate at the time of maximum expansion, μ is the viscosity of the nanofluid (Pa s), and α is the thermal diffusivity of the nanofluid (m 2 / s), ΔT is the temperature difference (K) formed within the droplet. (where k ｅｖ is the contact angle relaxation time τ re Evaporation time τ ev is a dimensionless number that indicates the ratio to the viscosity of the nanofluid (Pa s), and V ０ is the droplet volume at maximum expansion (m 3 ) where σ is the surface tension of the nanofluid droplet (mN / m) and θ ０ indicates the contact angle (rad.) at the time of maximum droplet spreading, where τ ev is the evaporation time (s) of the nanofluid droplets. ０ Use.) (Here, Pe is a dimensionless number called the Peclet number, U is the advection velocity (m / s) of nanoparticles due to capillary flow and Marangoni convection, and h ０ indicates the droplet height (m) at the time of maximum expansion of the droplet, and D ｐ is the diffusion coefficient of the nanoparticles in the dispersion medium.) 2. The method for producing a multilayer body according to claim 1, wherein in the printing step, at least one condition selected from the group consisting of the amount of nanofluid droplets ejected, the atmospheric temperature, and the ventilation conditions is adjusted, and / or in the drying step, at least one condition selected from the group consisting of the drying time, the drying temperature, and the ventilation conditions is adjusted.

3. The method for producing a multilayer body according to claim 1, further comprising adjusting the contact angle of the nanofluid droplets with respect to the surface of the substrate, which may have a coating formed thereon, adjusting the difference in SP value between the dispersion medium contained in the nanofluid and the nanoparticles, and / or adjusting the treatment intensity in the dispersion treatment of the nanofluid.

4. A method for producing a multilayer body according to any one of claims 1 to 3, wherein the intra-dot nanopattern expressed in the plurality of nanodots is adjusted to a spoke pattern.

5. A method for producing a multilayer body according to any one of claims 1 to 3, wherein the nanopattern within the dots expressed in the plurality of nanodots is adjusted to a coffee ring.

6. A method for producing a multilayer body according to any one of claims 1 to 3, wherein the intra-dot nanopatterns expressed in the plurality of nanodots are adjusted to a uniform pattern.

7. A method for producing a multilayer body according to any one of claims 1 to 3, wherein the intra-dot nanopatterns expressed in the plurality of nanodots are adjusted to a multi-ring.

8. A multilayer body in which a plurality of nanodots are formed on a substrate on which a coating may be formed, and the intra-dot nanopatterns expressed in the plurality of nanodots are continuously formed as a fixed pattern.

9. The multilayer body according to claim 8, wherein the intradot nanopattern is continuously formed as a spoke pattern.

10. The multilayer body according to claim 9, wherein the spoke pattern is a pattern of four or more radially extending stripes, and the diameter of the nanodots is 5000 μm or less.

11. The multilayer body according to claim 10, wherein the difference in unevenness between the convex portions constituting the streaks and the concave portions constituting the spaces between adjacent streaks is 10 nm or more and 100 nm or less.

12. The multilayer body according to claim 8, wherein the intradot nanopattern is continuously formed as a coffee ring.

13. The multilayer body described in claim 12, wherein the coffee ring is a pattern in which nanoparticles are accumulated along the circumference of the nanodot, the width of the annulus constituting the coffee ring is 100 nm or more and 500 μm or less, and the diameter of the nanodot is 5000 μm or less.

14. The multilayer body according to claim 13, wherein adjacent rings have irregularities, the difference in irregularities being 10 nm or more and 100 nm or less.

15. The multilayer body according to claim 8, wherein the intra-dot nanopattern is continuously formed as a uniform pattern, and the film thickness variation, which is the standard deviation of the average film thickness of the film constituting the uniform pattern, is less than 30 nm.

16. The multilayer body according to claim 8, wherein the intradot nanopattern is continuously formed as multiple rings.

17. The multilayer body according to claim 16, wherein the multi-ring is a pattern in which a plurality of approximately concentric rings are integrated, the width of the rings constituting the multi-ring is 100 nm or more and 500 μm or less, and the diameter of the nanodots is 5000 μm or less.

18. The multilayer body according to claim 17, wherein adjacent rings have irregularities, the difference in irregularities being 10 nm or more and 100 nm or less.

19. A multilayer body produced by the method for producing a multilayer body according to any one of claims 1 to 3.

20. The multilayer body according to claim 19, wherein the intradot nanopattern, which appears in a plurality of nanodots formed on a substrate on which a coating may be formed, is continuously formed as a spoke pattern.

21. The multilayer body according to claim 19, wherein the intradot nanopattern, which appears in a plurality of nanodots formed on a substrate on which a coating may be formed, is continuously formed as a coffee ring.

22. The multilayer body according to claim 19, wherein the intradot nanopattern, which appears in a plurality of nanodots formed on a substrate on which a coating may be formed, is formed continuously as a uniform pattern.

23. The multilayer body according to claim 19, wherein the intra-dot nanopatterns expressed in a plurality of nanodots formed on a substrate on which a coating may be formed are continuously formed as multiple rings.

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