KR102528880B1 - Fabrication of nanostructrues by secondary interference effect between microstructures using electrohydrodynamic instability patterning technology and method of manufacturing superhydrophobic surface - Google Patents

Abstract

상기 식1에서, λ_m은 고유파장이고, γ는 유체 박막의 표면장력, ε_r는 유체 박막의 유전율, ε₀는 진공 유전율, U는 인가되는 전압의 세기, h는 유체 박막의 두께, d는 양 전극 사이의 거리이다.The present invention relates to a method for forming a microstructure capable of realizing an anisotropic wett on a surface using electrohydrodynamic instability, and includes protrusion and non-protrusion on the top of a fluid thin film positioned on a lower electrode layer. A first step of disposing an upper electrode having a master pattern comprising a first distance from the surface of the fluid thin film by a first distance and a second step of applying a voltage between the upper electrode and the lower electrode, The natural wavelength (λ _m ) derived from Equation 1 is characterized in that the period (λ _p ) of the projection is smaller than:
<Equation 1>

In Equation 1, λ _m is the natural wavelength, γ is the surface tension of the fluid film, ε _r is the permittivity of the fluid film, ε ₀ is the vacuum permittivity, U is the applied voltage, h is the thickness of the fluid film, d is the distance between the two electrodes.

Description

Fabrication of ultrafine structures and superhydrophobic surface formation method by secondary interference effect between microstructures of pattern manufacturing technology using electrohydrodynamic instability SURFACE}

The present invention relates to a method for forming a microstructure on a surface, and specifically, using secondary interference of electrohydrodynamic instability generated in a fluidic thin film through application of an electric field. It relates to a method for controlling surface structural characteristics by simultaneously fabricating a secondary structure between existing surface structures.

Anisotropic wetting based on the surface structure is effective only when the density and continuity of the three-phase contact line in which solid-liquid-air are in simultaneous contact are precisely controlled. Accordingly, the prior art attempted to fabricate a microstructure exhibiting directional orientation in various ways.

One of these conventional techniques, chemical patterning method (Langmuir 2010, 26(17), 14276 ? 14283, Langmuir 2005, 21, 911-918) is a method of controlling the discontinuity of a triplet by directionally arranging a hydrophilic group and a hydrophobic group. . However, when this method is used, there is a problem in that the control effect of surface energy due to chemical treatment easily disappears at a specific temperature, humidity, and frequent contact with water because of the durability problem.

Recently, it has been revealed that micro-level anisotropic structures on the surface of rice leaves and nano-level fine papilles located between them greatly contribute to anisotropic wetting. in progress However, the fabrication process studied so far has a problem of technical complexity that must be patterned at least twice.

Most of them use a contact process based on an imprinting technique. For example, there is a technique of fabricating a micro-level structure and then fabricating a nano structure therebetween (Langmuir 2007, 23, 7793-7798). . However, in this technique-based process, it is difficult to secondaryly form nanostructures positioned therebetween without affecting the primarily fabricated microstructures.

Accordingly, a method of inducing the formation of a nanostructure through chemical synthesis and coating (Adv. Funct. Mater. 2013, 23, 547-553) secondarily on the patterned structure was proposed, but mechanical and chemical durability There is a disadvantage in that a complicated process procedure must be performed along with the problem of Therefore, there is a demand for a manufacturing technology capable of producing an anisotropic structure in a simple and single process in relation to surface fabrication that implements anisotropic wetting.

On the other hand, the structure formation through the electrohydrodynamic instability of the fluid thin film is simple and has the advantage of being able to control various surface structures in a single process. Therefore, currently, a promising method related to the fabrication of anisotropic structures is to use secondary electrohydrodynamic instability that induces the formation of secondary structures between primarily formed structures (Thin Solid Films 642 (2017) 241-251). However, in-depth research related to this is currently absent, and strategies to effectively induce this phenomenon have not been studied at present.

One object of the present invention is to provide a method for easily forming a microstructure capable of implementing anisotropic wetting on a surface by using electrohydrodynamic instability.

Another object of the present invention is to manufacture an ultra-fine structure by the secondary interference effect between the micro structures of the pattern manufacturing technology using electrohydrodynamic instability.

A method of forming a microstructure for one purpose of the present invention is based on using electrohydrodynamic instability, and includes a protrusion and a non-protrusion on top of a fluid thin film positioned on a lower electrode layer. A first step of disposing an upper electrode on which a master pattern is formed so as to be spaced apart from the surface of the fluid thin film by a first distance and a second step of applying a voltage between the upper electrode and the lower electrode, and from Equation 1 below The derived natural wavelength (λ _m ) is characterized in that the period (λ _p ) of the projection is smaller than:

<Equation 1>

In Equation 1, λ _m is the natural wavelength, γ is the surface tension of the fluid film, ε _r is the permittivity of the fluid film, ε ₀ is the vacuum permittivity, U is the applied voltage, h is the thickness of the fluid film, d is the distance between the two electrodes.

In one embodiment, a first pattern is formed on the surface of the fluid thin film facing the protrusion of the upper electrode, and is provided on the surface of the fluid thin film facing the non-protrusion of the upper electrode. 2 patterns can be formed.

In one embodiment, the first interval may be 2 μm to 10 μm.

In one embodiment, the distance between the fluid thin film and the protrusion may be 1 μm or less.

)를 의미하는 것으로, 종횡비를 제어함으로써 고유파장(λ_m)을 돌출부의 주기(

)는 보다 작게 제어할 수 있다.In one embodiment, the aspect ratio of the protrusion may be 0.1 to less than 1. The aspect ratio is the height (width) of the protrusion (width)

), and by controlling the aspect ratio, the natural wavelength (λ _m ) is changed to the period of the protrusion (

) can be controlled to be smaller.

In one embodiment, the fluid thin film may be formed of a Newtonian fluid.

In one embodiment, the first and second steps may be performed at a glass transition temperature or higher when the fluid thin film is a polymer material.

In one embodiment, the thickness of the fluid thin film may be 300 to 1000 nm.

In one embodiment, the voltage may be 50 to 200 V.

According to the present invention, it is possible to form a microstructure capable of easily implementing anisotropic wetting on the surface of a fluid thin film in a single process compared to the prior art, and the thin film on which the microstructure is formed moves the fluid in the microstructure arrangement direction without a separate external driving force. It has the advantage of being able to flow with a specific direction. Therefore, it can be applied to fields such as microfluidic devices, and also has the advantage of being able to waterproof treatment on various surfaces through microstructures.

1 is a view showing a conventional method for forming a microstructure and a method for forming a microstructure according to the present invention.
2 is a view for explaining the formation of a microstructure by induction of secondary electrohydrodynamic instability according to the present invention.
3 is a view showing (a) a scanning electron microscope image and (b) a three-dimensional interfacial height of each surface of a microstructure manufactured according to the prior art and the method for forming a microstructure of the present invention. In the microstructure manufactured according to the method for forming the microstructure of the present invention, it can be confirmed that the pattern is also formed in the region of the fluid thin film corresponding to the non-protrusion.
FIG. 4 is a diagram showing an electroscanning microscope image and a contact angle analysis result of each microstructure manufactured according to the characteristic wavelength/period of the protrusion (λ _m /λ _p ). It can be seen that the hydrophobicity improves as the contact angle increases as λ _m /λ _p decreases.
5 is a view showing the results of anisotropic wetting analysis by transferring the microstructure prepared according to the present invention onto a curved surface.

Hereinafter, embodiments of the present invention will be described in detail. Since the present invention can have various changes and various forms, specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific form disclosed, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

Terms used in this application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, step, operation, component, part, or combination thereof described in the specification, but one or more other features or steps However, it should be understood that it does not preclude the possibility of existence or addition of operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

1 is a view showing each method to compare and explain a conventional method for forming a microstructure and a method for forming a microstructure according to the present invention.

Referring to FIG. 1, the conventional microstructure formation method and the microstructure formation method of the present invention are methods based on electrohydrodynamic instability. refers to the phenomenon of undulation.

Specifically, when a high electric field (for example, >10 ⁷ V/m) is applied in a direction perpendicular to the surface of a thin film of fluid, the fluid grows in the same direction as the electric field to lower the free energy inside the system, and tens of microns Fine structures ranging from meters to tens of nanometers can be formed.

The formation process of the structure by 'electrohydrodynamic instability' can be described as a competitive relationship between the electrostatic pressure that destabilizes the surface and the Laplace pressure that stabilizes the surface, and the numerical description here is from Equation 1 below. It can be given as the derived 'characteristic wavelength, λ _m '.

<Equation 1>

In Equation 1, λ _m is the natural wavelength, γ is the surface tension of the fluid film, ε _r is the permittivity of the fluid film, ε ₀ is the vacuum permittivity, U is the applied voltage, h is the thickness of the fluid film, d is the distance between the two electrodes.

The intrinsic wavelength (λ _m ) corresponds to the length/size scale at which the surface structural deformation of the fluid thin film observed according to the film undulation by the electric field is exhibited. That is, theoretically, microstructures due to electrohydrodynamic instability follow the size of the natural wavelength (λ _m ) at the level of spatial size/length, and therefore, realizing a smaller natural wavelength can be very advantageous in forming a microstructure.

Referring to (a) of FIG. 1, in the conventional method for forming a microstructure, an upper electrode is formed with a master pattern including protrusions and non-protrusions on top of a fluid thin film positioned on a lower electrode layer. It may include disposing them to be spaced apart from the surface of the fluid thin film by a first distance (d) and applying a voltage between the upper electrode and the lower electrode.

When a voltage is applied here, the structured upper electrode including the protruding portion and the non-protruding portion generates an electric field difference due to a difference in height (h _p ) of the protruding portion and the non-protruding portion. At this time, the surface of the fluid thin film facing the protrusion may receive a higher electric field than the surface of the fluid thin film facing the non-protrusion.

As a result, the formation of the structure may be concentrated only in the region of the fluid thin film facing the protrusion receiving a high electric field, and a relatively low electric field may be received in the region of the thin fluid facing the non-protrusion. A structure may be previously formed in a region of the thin film of fluid facing the protrusion that receives a high electric field in time, and at the same time, the fluid in the region of the thin film of fluid facing the non-protrusion may be moved to the region of the thin film of fluid facing the protrusion. Through this process, the fluid in the fluid thin film region facing the non-protrusion is exhausted by forming the structure on the surface of the thin fluid film facing the protrusion, making it difficult to form an additional structure on the surface of the thin fluid film region facing the non-protrusion. there is.

In the present invention, a coating having a sufficient thickness was performed so that the fluid thin film remains even after the first pattern is produced on the non-protrusion part. The difference between the strength of the electric field acting at the non-protrusion and the strength of the electric field acting at the protrusion is clear due to the protrusion of the upper electrode having a low aspect ratio in the fluid thin film of the remaining non-protrusion area through the 'secondary electrohydrodynamic instability'. It is possible to form an additional microstructure because it does not occur. In the present invention, the secondary electrohydrodynamic instability can be distinguished from the electrohydrodynamic instability first induced through the protrusion of the upper electrode. In the present invention, the electrohydrodynamic instability first induced through the protrusion of the upper electrode in time is defined as 'primary electrohydrodynamic instability'. The electrohydrodynamic instability induced through the non-protrusion of the upper electrode following the occurrence of the first electrohydrodynamic instability is defined as 'secondary electrohydrodynamic instability'.

Hereinafter, the secondary electrohydrodynamic instability will be described with reference to the drawings.

2 is a schematic diagram of secondary electrohydrodynamic instability.

Referring to FIG. 2, it can be seen that the secondary electrohydrodynamic instability follows the size of the natural wavelength (λ _m ) at the spatial size/length level, and the formation of additional structures is determined according to the period (λ _p ) of the upper electrode protrusion. can When the period (λ _p ) of the protrusions is constant, as the natural wavelength (λ _m ) decreases, microstructures can be formed in the region of the fluid film facing the non-protrusions, and as the natural wavelength (λ _m ) decreases, the density It can be seen that increases and the size of the structure decreases. That is, it can be confirmed that the secondary electrohydrodynamic instability is induced when the spatial distribution of the electric field intensity given by the topology of the upper electrode is properly controlled.

Referring back to (b) of FIG. 1, in the method for forming a microstructure of the present invention, a master pattern including a protrusion and a non-protrusion is formed on the top of a fluid thin film positioned on the lower electrode layer. It may include a first step of disposing an electrode spaced apart from the surface of the fluid thin film by a first distance and a second step of applying a voltage between the upper electrode and the lower electrode.

At this time, in the present invention, the natural wavelength (λ _m ) derived from Equation 1 is given a smaller period (λ _p ) of the protrusion by controlling the aspect ratio / height of the protrusion to induce the secondary electrohydrodynamic instability. It is characterized in that, it is possible to provide a method for manufacturing an anisotropic microstructure surface by forming additional microstructures by secondary electrohydrodynamic instability between microstructures replicated by primary electrohydrodynamic instability.

That is, compared to the prior art, the present invention not only forms a first pattern on the surface of the fluid thin film facing the protrusion of the upper electrode, but also faces the non-protrusion of the upper electrode. A second pattern may be formed on the surface of the fluid thin film. The first pattern may be a pattern replicated by the first electrohydrodynamic instability, and the second pattern may be a pattern replicated by the second electrohydrodynamic instability.

)의 크기에 영향을 미치지 않아, 종래의 미세 구조체 형성방법과 동일한 크기의 상부 전극의 돌출부(protrusion)와 마주보는 유체 박막의 표면에 제1 패턴(구조체)를 형성함과 동시에, 상기 상부 전극의 비돌출부(non-protrusion)와 마주보는 상기 유체박막의 표면에 제2 패턴(구조체)을 형성할 수 있다.In the present invention, only the aspect ratio/height of the protrusion is controlled while maintaining the distance between the fluid thin film and the protrusion (ie, the air layer), so that the natural wavelength (λ _m -(d-) affecting the formation of the first pattern

), the first pattern (structure) is formed on the surface of the fluid thin film facing the protrusion of the upper electrode having the same size as the conventional microstructure forming method, and at the same time, the upper electrode A second pattern (structure) may be formed on the surface of the fluid thin film facing the non-protrusion.

)를 감소시킴으로써 고유파장(λ_m)과 돌출부의 주기(λ_p)를 제어하여, 돌출부에 의해 형성된 구조체 사이로 제어된 고유파장(λ_m)의 크기에 대응하는 길이/크기 수준의 추가적인 미세 구조체를 형성시킬 수 있다.In the prior art, the natural wavelength (λ _m ) for the distance (d) between the electrodes is given greater than or equal to the period (λ _p ) of the protrusion, but in the present invention, the aspect ratio / height of the protrusion of the upper electrode (

) by reducing the natural wavelength (λ _m ) and the period (λ _p ) of the protrusions to create additional microstructures of a length/size level corresponding to the size of the controlled natural wavelength (λ _m ) between the structures formed by the protrusions. can form.

)를 의미하는 것으로, 일 실시예에서, 상기 돌출부의 종횡비(aspect ratio)는 0.1 내지 1 일 수 있다. 바람직하게는, 돌출부의 종횡비는 약 0.2 내지 0.5 일 수 있다.The aspect ratio is the height (width) of the protrusion (width)

), and in one embodiment, the aspect ratio of the protrusion may be 0.1 to 1. Preferably, the aspect ratio of the protrusions may be between about 0.2 and 0.5.

The upper electrode and the lower electrode are not particularly limited as long as they are substrates capable of supporting the fluid thin film and the master pattern. For example, the substrate may be formed of a glass substrate coated with silicon or ITO. In addition, since a high voltage is used in the present invention, the substrate may be formed of a strong insulating material. For example, glass or plastic substrates can also be used.

The fluid thin film may be formed of a material capable of having a certain fluidity and viscosity, and the fluid thin film may be formed of a Newtonian fluid material. Preferably, it may be formed of a Newtonian fluid material. For example, the fluid thin film may be a polystyrene thin film, which is a polymer material. However, the present invention is not necessarily limited thereto.

The fluid thin film may have a thickness of about 70 to 1000 nm. Preferably, the thickness of the fluid film may be about 300 to 1000 nm. For example, the fluid thin film may have a thickness of about 500 nm. However, in the present invention, the thickness of the fluid thin film is not particularly limited and the range can be easily adjusted according to the strength of the electric field.

The fluid thin film may be formed by coating a fluid material on the lower electrode. As the coating, spray coating, inkjet, drop casting, spin coating, and wet coating may be used. Preferably, the fluid thin film may be formed using wet coating.

The master pattern is a concavo-convex structure including a protrusion and a non-protrusion, and may mean a pattern to be replicated in the present invention. The master pattern may have a shape such as a line or a cylinder. The master pattern may be formed of an insulating material, for example, a material containing silicon. However, in the present invention, the shape and material of the master pattern are not particularly limited.

The master pattern may be formed by etching with electron beam lithography. In order to prevent discharge that can easily occur near the edge of the master pattern, the size of the upper electrode and the master pattern may be formed to have a size difference of about 20% or more from each other. In addition, it may be desirable to provide a location at the top of the center of the fluid film to minimize the risk of arc discharge.

The upper electrode and the fluid thin film may be spaced apart from each other by the first distance, and the master pattern and the fluid thin film may face each other. Specifically, the first interval may mean a distance between the protrusion of the upper electrode and the fluid thin film.

In one embodiment, the first interval may be, for example, several to several tens of micrometers. More specifically, the first interval may be about 2 to 10 μm.

)를 의미하는 것일 수 있다. 전기수력학적 불안정성을 유도하기 위해 일반적으로 요구되는 전기장 세기 (10⁷~10⁸ V/m 이상, 20~200200 V 이용 시)를 만족시키기 위해, 유체 박막과 상기 돌출부 사이의 거리(공기층 두께)는 약 1 ㎛ 이하로 유지하는 것이 바람직하다.In one embodiment, a distance between the fluid thin film and the protrusion may be about 1 μm or less. At this time, the distance between the fluid thin film and the protrusion is the air layer thickness ((d-

) may mean. In order to satisfy the generally required electric field strength (10 ⁷ to 10 ⁸ V/m or more, when using 20 to 200 200 V) to induce electrohydrodynamic instability, the distance between the fluid film and the protrusion (air layer thickness) is It is desirable to keep it below about 1 μm.

The first and second steps are characterized in that they are performed above the glass transition temperature of the fluid thin film for fluidity of the fluid thin film. For example, when the fluid thin film is formed of polystyrene, the process may be performed at about 100° C. or higher, which is higher than the glass transition temperature of polystyrene. Since the glass transition temperature differs depending on the type of fluid material, it is preferable to perform at a temperature equal to or higher than the appropriate glass transition temperature according to the material.

In one embodiment, a voltage of 20 to 200 V may be applied to generate an electric field. In one embodiment, the power supply connected to the upper and lower electrodes applies a voltage (<200V) to generate an electric field, and at this time, the allowable current range is ±0.5 to prevent problems such as short circuit or insulation breakdown in advance. It can be performed by setting it to A or less.

In the microstructure formed according to the method of the present invention, surface roughness may increase due to the formation of additional microstructures, and thus wettability may increase. In addition, it is possible to realize anisotropic wetting according to the directional gradient of surface energy. Therefore, on the surface where the microstructures are formed, the fluid may tend to flow along the arrangement direction of the microstructures without a separate driving force.

In addition, the technology of the present invention can be applied to the prior art of forming a pattern through several processes. Even in the case of a thin film having a primary structure, if the resist, which is a fluid, can be uniformly coated, in the present invention, the primary and secondary patterns are formed at the same time, but since the primary pattern is pre-fabricated, the primary pattern The second pattern is formed at the same time as the process of thinly coating the first pattern by the electric field applied thereto, so that the same surface structure as the present technology can be formed.

Example 1

The upper electrode on which the master pattern including protrusions and non-protrusions was formed was fabricated as a line pattern through electron beam lithography and etching, and the fluid thin film was fabricated using polystyrene (PS). A PS mixed solution having a concentration of 2.5 wt % was prepared by mixing 10 mL of toluene as a solvent and a solute of 0.257 g of PS, heating at about 60° C. and stirring at about 800 rpm for 2 hours. Then, a thin film having a thickness of about 220 nm was formed on an ITO glass substrate or a silicon substrate using a spin coater at 3000 RPM for about 30 seconds to prepare a lower electrode having a PS fluid thin film.

After fixing the upper electrode on which the master pattern is formed and the lower electrode on which the thin film of fluid is formed are respectively fixed to the pattern stage and the sample stage, the distance between the upper electrode and the thin film of fluid is maintained at about 200 nm, and the condition of the glass transition temperature or higher of the thin film of fluid is maintained. A voltage was applied to form a fine pattern.

Experimental Example 1: Microstructure surface analysis

In order to compare and analyze the surfaces of the microstructures prepared according to the prior art and the microstructure formation method of the present invention, each scanning electron microscope image and three-dimensional interfacial height were obtained, and the results are shown in FIG. 3 .

Referring to FIG. 3 , when the natural wavelength (λ _m ) and the period (λ _p ) of the protrusion are the same, it can be confirmed that only the pattern formed on the protrusion of the upper electrode is formed, whereas the natural wavelength (λ _m ) is the period of the protrusion ( When it is smaller than λ _p ) (λ _m /λ _p =0.3), it can be seen that patterns are formed not only on the protrusions of the upper electrode but also on the region of the fluid thin film corresponding to the non-protrusions.

Experimental Example 2: Analysis of the contact angle of the surface on which the microstructure is formed

According to the method of the present invention, each scanning electron microscope image and contact angle measurement result for analyzing the surface and contact angle of each microstructure according to the decrease (1 to 0.23) of the natural wavelength/period (λ _m /λ _p ) of the protrusion are shown. shown in 4. At this time, the process temperature and time were set to 150 degrees and 15 minutes, respectively, and the experiment was conducted in a voltage-controlled manner (30-200 V).

Referring to FIG. 4 , it can be seen that the density of additional microstructures formed as λ _m /λ _p decreases. In addition, the contact angle increased from 88 ° to 136 °, confirming that the hydrophobic property gradually increased.

Experimental Example 3: Anisotropic wetting analysis

In order to analyze the anisotropic wetting of the surface of the microstructure prepared in Example 1, the microstructure was transferred to a curved glass surface (eyeglasses), and water droplets along the vertical and horizontal directions to compare with the general glass surface (non-transfer surface). After dropping the result, the degree of flow was compared. The results are shown in FIG. 5 .

Referring to FIG. 5, the anisotropic microstructure made of polystyrene prepared according to Example 1 can be separated from water through unstable interfacial energy between hydrophilic glass substrates, and through this, it can be transferred onto various curved surfaces. (a) is a transfer image of an anisotropic microstructure made of polystyrene fabricated on the surface of a general eyeglass, and (b) is a scanning electron microscope image of the microstructure. (c) and (d) compare the degree of flow after dropping water droplets according to the structure arrangement direction to observe anisotropic wetting. It can be confirmed, and it can be confirmed that the flow of water droplets appears in the same direction as the anisotropic structure. Through this, it can be expected that the water droplet flow is more preferred along the anisotropic structure arrangement direction. In addition, it can be confirmed that it has more improved waterproofness in comparison with a general glass surface (non-transfer surface). In the present invention, by transferring a patterned thin film on a curved glass substrate, as can be seen through the transfer to eyeglasses in Example 3, transfer is possible on various surfaces and can be applied to electronic devices, optical devices, and bio devices. .

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand that you can.

Claims (9)

A first step of disposing an upper electrode on which a master pattern including a protrusion and a non-protrusion is formed on the top of the fluid thin film positioned on the lower electrode layer to be spaced apart from the surface of the fluid thin film by a first distance. and a second step of applying a voltage between the upper electrode and the lower electrode;
The natural wavelength (λm), which is the wavelength corresponding to the fluctuation most predominantly generated on the surface of the fluid thin film by the electric field applied between the upper electrode and the lower electrode derived from Equation 1 below, is the period (λp) of the protrusion. ) is characterized by being smaller than
Method for forming microstructures:
<Equation 1>

In Equation 1, λ _m is the natural wavelength, γ is the surface tension of the fluid film, ε _r is the permittivity of the fluid film, ε ₀ is the vacuum permittivity, U is the strength of the applied voltage, h is the thickness of the fluid film, d is the distance between both electrodes.
A method for forming a microstructure.
delete According to claim 1,
Characterized in that the first interval is 2 μm to 10 μm,
A method for forming a microstructure.
According to claim 1,
Characterized in that the distance between the fluid thin film and the protrusion is 1 μm or less,
A method for forming a microstructure.
According to claim 1,
Characterized in that the aspect ratio of the protrusion is 0.1 to less than 1,
A method for forming a microstructure.
According to claim 1,
Characterized in that the fluid thin film is a Newtonian fluid,
A method for forming a microstructure.
According to claim 1,
The first and second steps are characterized in that when the fluid thin film is a polymer material, it is performed at a glass transition temperature or higher.
A method for forming a microstructure.
According to claim 1,
Characterized in that the thickness of the fluid thin film is 300 to 1000 nm,
A method for forming a microstructure.
According to claim 1,
Characterized in that the voltage is 50 to 200 V,
A method for forming a microstructure.

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