WO2017111546A1 - Broadband high-refractive index metamaterial nano-composite structure - Google Patents

Abstract

The present invention relates to a metamaterial nano-composite structure comprising a plurality of unit structures densely arrayed in three dimensions, each comprising a nanoparticle and a host material, and an optical film comprising the metamaterial nano-composite structure.

Description

High refractive index metamaterial nano composite structure with broadband characteristics

The present application relates to a high refractive index metamaterial nanocomposite structure having broadband characteristics and an optical film including the metamaterial nanocomposite structure.

The development of the semiconductor industry is based on improving the precision of micro processes in semiconductor processes. The main core technology of semiconductor microprocessing depends on how finely the pattern of etching resist can be controlled during photolithography process, and the resolution of the optical system is needed to finely etch the pattern. Do. Today's best photolithography device is an excimer laser that can produce devices with a minimum wiring width of 14 nm using light at wavelengths of 248 nm and 193 nm. However, to overcome this limitation, other alternatives are needed.

The oil immersion technology uses transparent oils with specific optical and viscosity properties between the objective lens and the sample in the optical microscope. As the oil properties improve, the wiring width can be reduced by several nanometers. It is expected. Currently, highly purified water is used in place of oil in semiconductor processes.

The size relationship of the fine patterns that can be realized by the optical system is that the size of the fine patterns (δ) = λ / (2NA), where λ is the wavelength of light, NA is the numerical aperture of the lens, and NA = nsin ₀ , where n is the refractive index of the material filling the lens and the pattern, such as oil or water, and α ₀ is the angle spread by the objective lens seen in the sample. In actual semiconductor processes, various techniques such as double exposure and resist development conditions are applied to reduce the line width even further, and thus, a line width smaller than the size determined by the simple relationship is obtained. Therefore, a smaller line width can be obtained by fundamentally reducing the resolution shown in the above relation. From the above two relations, it can be seen that the resolution of the fine pattern size is inversely proportional to the refractive index of the oil between the objective lens and the sample, and the high resolution requires immersion oil of high refractive index. However, in this case, the development of high refractive index oil, which is an optical characteristic of the oil, which must be improved, is currently delayed due to the absence of high refractive index oil and difficulty in making it.

Over the past few years, negative refractive index metamaterials have been developed in a range of wavelengths ranging from microwave and visible light to negative effective refractive indices and effective permeability. However, research on metamaterials with opposite high amounts of high refractive index has been relatively less studied, with a focus on theoretical feasibility. While previous studies have shown an increase in refractive index in the use of electrical resonances in separate ring resonators, such designs inherently have a high refractive index in a narrow frequency band. The metamaterial exhibits strong dispersion near the resonant frequency and maintains the desired refractive index only in the narrow frequency range. Although metamaterials made of sub-wavelength (sub-wavelength) capacitor (capacitor) arrays have been proposed to have high permittivity at broadband, they also have problems due to the strong diamagnetic effect of suppressing the magnetic permeability value. Only recently have broadband theoretical high refractive index metamaterials been proposed to reduce this diamagnetic effect. However, the proposed structure also has not been the target of easy implementation due to its three-dimensional features.

Korean Patent Laid-Open No. 2012-0007819 relates to a meta material and a method for manufacturing the same, and discloses a meta material including a nano pattern structure having a negative refractive index in a natural state and a method for manufacturing the same.

In one embodiment of the present invention by close-packed nanoparticles of very small size than the wavelength (3D), the meta-material nano having a high refractive index while exhibiting broadband characteristics in the visible, ultraviolet and / or infrared wavelength band It is intended to provide an optical film including a composite structure and the metamaterial nano composite structure.

However, the problem to be solved by the present application is not limited to the above-mentioned problem, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A first aspect of the present disclosure provides a unit structure comprising nanoparticles and a host material, wherein the unit structure is arranged in three dimensions, provides a metamaterial nano composite structure.

The second aspect of the present application provides an optical film comprising the metamaterial nanocomposite structure according to the first aspect of the present application.

According to one embodiment of the present application, a high refractive index metamaterial nano composite structure exhibiting broadband characteristics may be provided. The unit structure of the metamaterial nanocomposite structure according to the embodiment of the present invention is formed to a size smaller than the wavelength (about 1/10 or less of the wavelength in the vacuum) and the unit structures are densely arranged in three dimensions. packed, so that the whole structure can produce optical effects as if it were a single material with a high refractive index.

According to the exemplary embodiment of the present invention, the size of the nanoparticles corresponding to or smaller than the skin depth of the nanoparticles induces magnetic penetration into the nanoparticle part, thereby providing an effective permeability of the nanoparticles. By preventing the decrease of, high refractive index can be achieved. In addition, the dielectric constant may be freely adjusted through a simple structure without noticeable change in permeability by changing the width of the gap (gap) with the adjacent nanoparticles while maintaining the size of the unit structure to a constant value. In other words, by reducing the width of the gap, a high permittivity and a high refractive index can be achieved, and the adjustment of the permittivity and permeability is important for designing the impedance and other optical properties of the material, so that for lithography and imaging It can be applied in a variety of optical devices, from submerged lenses, waveguide couplers, modulators, light detectors and energy devices.

According to one embodiment of the present application, the metamaterial nanocomposite structure has the effect of overcoming the bandwidth limitations of other metamaterials directly dependent on surface plasmon resonance.

According to one embodiment of the present application, the metamaterial nanocomposites have the same effect on other nanoparticle morphologies and lattice types, thus providing the potential for multiple bottom-up nanoparticle synthesis instead of expensive and complex top-down nanofabrication processes. Can be.

FIG. 1 is a schematic diagram (a) of a cubic metamaterial nanocomposite structure densely arranged in three dimensions, and a schematic diagram (b) showing metal particle size conditions for achieving high refractive index.

2 is a schematic of a finite difference time domain method (FDTD) simulation in one embodiment of the present application.

3 is, in one embodiment of the present application, material data used for FDTD simulation.

Figure 4, in one embodiment of the present application, the image showing the unit structure of the metamaterial nano composite structure and the complete electrical conductor [(a), (d), and (g)], Ex-field distribution of each unit structure [(b), (e), and (h)] are FDTD simulation results showing the Hy-field distribution [(c), (f), and (i)] of each unit structure.

5 (a) and 5 (b) show FDTD simulation results showing an effective dielectric constant, an effective permeability, and an effective refractive index of a gold metamaterial nanocomposite structure having a host material of Si02 in an example of the present application.

6 (a) to 6 (f) show an asymptotic value of a fully electric conductor and a gold metamaterial nanocomposite structure in which a gap width is changed under a constant unit structure size in one embodiment of the present application [(a) and ( d)], FDTD simulation results showing permeability [(b) and (e)] and refractive index [(c) and (f)].

7 (a) to 7 (d) are schematic diagrams ((a) and (b)] showing cubic nanoparticles in a cubic lattice and spherical nanoparticles in a hexagonal lattice in one embodiment of the present application, and a multilayer FDTD simulation results [(c) and (d)].

FIG. 8 is an image illustrating a manufacturing process of a hole pattern by block copolymer lithography in an embodiment of the present disclosure.

FIG. 9 is an image illustrating an ion milling process of the aluminum metamaterial nanocomposite structure in one embodiment of the present application.

10 (a) to 10 (d) are SEM images of the aluminum metamaterial nanocomposite structure in one embodiment of the present application.

11A and 11B are AFM images of an aluminum metamaterial nanocomposite structure in one embodiment of the present application.

12 is a UV-VIS spectrometer spectrum showing the measured transmittance of the aluminum metamaterial nanocomposite structure in one embodiment of the present application.

FIG. 13 is an FDTD simulation graph showing a calculated transmittance of an aluminum metamaterial nanocomposite structure in one embodiment of the present application. FIG.

14 is an FDTD simulation graph showing the derived effective refractive index of the metamaterial nanocomposite structure in one embodiment of the present application.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present disclosure. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted for simplicity of explanation, and like reference numerals designate like parts throughout the specification.

Throughout this specification, when a part is said to be "connected" with another part, this includes not only the "directly connected" but also the "electrically connected" between other elements in between. do.

Throughout this specification, when a member is located “on” another member, this includes not only when one member is in contact with another member but also when another member exists between the two members.

Throughout this specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding the other components unless otherwise stated. As used throughout this specification, the terms “about”, “substantially”, and the like, are used at, or in close proximity to, numerical values when manufacturing and material tolerances inherent in the meanings indicated are provided, and an understanding of the present application may occur. Accurate or absolute figures are used to assist in the prevention of unfair use by unscrupulous infringers. As used throughout this specification, the term “step of” or “step of” does not mean “step for”.

Throughout this specification, the term "combination (s) thereof" included in the expression of a makushi form refers to one or more mixtures or combinations selected from the group consisting of components described in the expression of makushi form, It means to include one or more selected from the group consisting of the above components.

Throughout this specification, the description of “A and / or B” means “A or B, or A and B”.

Throughout this specification, the term "metamaterial" is a material made of an array of meta atoms designed with a metal or dielectric material made to a size much smaller than the wavelength of light, which is difficult for natural materials to have. It means the artificially designed and made to have optical properties.

Throughout this specification, the term "close-packed" refers to a state in which nanoparticles or unit structures are densely arranged in three dimensions with a certain unit size and gap width in the host material. To indicate. The densely arranged nanoparticles and the densely arranged unit structures according to the present invention exhibit broadband properties from visible light to ultraviolet and / or infrared wavelength bands and at the same time have a high refractive index. The unit structure size and the width of the gap of the nanoparticles and unit structures may be several nanometers or less, but may not be limited thereto.

Throughout this specification, the term "skin depth" refers to the depth indicating how far electromagnetic waves can penetrate into the surface of the medium. In the medium, depending on the skin effect, the current density tends to be close to the surface of the medium and decreases as it penetrates into the conductor. The current flows mainly at the "surface" of the conductor, which is between the outer surface and the level called the skin depth, so that the penetration depth is more specifically 1 / e (such as current density or electric field at the surface). 37%).

Throughout this specification, the term "refractive index" refers to the rate of velocity of waves traveling in two media as light travels from one media to another. The refractive index varies with wavelength, and at the interface of the media with different refractive indices, the light bends according to Snell's law and some reflects according to the angle of incidence. The refractive index can be expressed as the square root of the product of relative permittivity and relative permeability for Equation 1, and as the refractive index value increases, the resolution, which is the ability to distinguish two objects from each other in an optical device, is increased. Because it improves, the resolution increases:

 [Equation 1]

n = (εμ) ^1/2 (n = refractive index, ε = relative dielectric constant, μ = relative permeability)

Hereinafter, embodiments of the present disclosure have been described in detail, but the present disclosure may not be limited thereto.

A first aspect of the present application provides a metamaterial nanocomposite structure comprising unit structures comprising nanoparticles and a host material, wherein the unit structures are arranged in three dimensions.

In one embodiment of the present application, the unit structure may be close-packed in three dimensions.

In one embodiment of the present application, the metamaterial nano composite structure may have a high refractive index in a wavelength band selected from visible light, ultraviolet light, infrared light, and combinations thereof, but may not be limited thereto. For example, the metamaterial nanocomposite structure may exhibit a high refractive index by controlling the size of the nanoparticles of the metamaterial nanocomposite structure and / or the width of the gap, which is a gap with adjacent nanoparticles, but is not limited thereto. Can be.

The high refractive index metamaterial, which has been proposed for the terahertz frequency in the related art, has a disadvantage in that it is difficult to apply directly at the visible wavelength due to the difficulty of nanofabrication due to a complicated structure. However, the high refractive index meta-material nanocomposite structure according to one embodiment of the present application is selected by appropriately selecting the width of the gap that is the gap between the nanoparticle size and the adjacent nanoparticles in the unit structure, a simple structure without lowering the effective permeability This can lead to an improvement in the effective dielectric constant and refractive index.

In one embodiment of the present application, the unit structure may be one that is isotropic (isotropy) or anisotropic (anisotropy) are densely arranged in three dimensions.

In one embodiment of the present application, the metamaterial nano composite structure may have a maximum refractive index of about 1.5 or more at a wavelength of about 200 nm or less, but may not be limited thereto.

In one embodiment of the present application, the metamaterial nano composite structure may have a maximum refractive index of about 2 or more at an ultraviolet wavelength of about 200 nm to about 400 nm, but may not be limited thereto.

In one embodiment of the present application, the metamaterial nano composite structure may have a maximum refractive index of about 4 or more at a visible light wavelength of about 400 nm to about 700 nm, but may not be limited thereto.

In one embodiment of the present application, the metamaterial nano composite structure may have a maximum refractive index of about 5 or more at an infrared wavelength of about 700 nm or more, but may not be limited thereto.

Figure 1 (a) is an image showing an example of a three-dimensionally arranged cubic metamaterial nano composite structure contained in a dielectric host material for achieving a high refractive index according to an embodiment of the present application. As in Figure 1, the blue and gray areas represent the dielectric and metal, respectively. In [b (i)] of FIG. 1 surrounded by a green dotted rectangle, the arrow represents the electric field and the field intensity is weakened by the electrons of the metal. In [b (ii)] of FIG. 1, the length of the arrow indicates the strength of the magnetic field and the propagation strength becomes weak when the magnetic field penetrates into the metal.

In one embodiment of the present application, the size of the nanoparticles in the unit structure may correspond to or smaller than the penetration depth of the nanoparticles, but may not be limited thereto.

In one embodiment of the present application, the penetration depth may be different depending on the type of the nanoparticles, but may not be limited thereto. The penetration depth is not only in the metal but also in the heavily doped semiconductor, or in a material where the real part of the dielectric constant is negative, so that the magnetic field does not enter well and decreases exponentially with distance from the surface. Has a unique penetration depth. Here, the penetration depth is a depth indicating how far the electromagnetic wave can penetrate from the surface of the medium, and the intensity of the electromagnetic wave decreases by 1 / e when the penetration depth penetrates. When producing nanoparticles of smaller or corresponding size to the penetration depth, the magnetic field is distributed almost uniformly across the unit structure, which prevents the reduction of the effective permeability of the metamaterial nanocomposite structure, resulting in a high refractive index. Metamaterial nanocomposites can be created. For example, the size of the nanoparticles corresponding to or smaller than the depth of penetration can lead to high refractive indices according to the formula of Equation 2:

[Equation 2]

n _eff = (ε _{effμ eff} ) ^1/2 = (a / g) ^1/2

In the above induction formula, n _eff is an effective refractive index, ε _eff is an effective permittivity, ε _eff is an effective permeability, a is the size of a unit structure (unit cell), and g is a width of a gap, which is an interval between adjacent nanoparticles. Metamaterial nanocomposites have a high effective dielectric constant that is nearly constant over a wide range of wavelengths due to the capacitive effect determined by geometry. In general, the DC or low-frequency permittivity of a less known (meta) material is the same as the capacitance of a parallel plate capacitor with a test material that fills the entire space between the plates, but with a known permittivity. It can be quantified by comparing the capacitance of a parallel plate capacitor filled with a reference material having. When the capacitance of the parallel plate capacitor is expressed as C = Q / V = ε _cap (C, Q, and V are capacitance, total charge, and total voltage drop, respectively, while ε _cap , A, and d are Respectively, the dielectric constant, area and distance of the dielectric material between the plates), and the capacitance is directly proportional to ε _cap . Thus, the ratio of the capacitance is the ratio of the dielectric constant of the test material and the reference material. When the metamaterial nanocomposite is inserted between the plates and charges + Q and-Q are applied to the capacitor plate, the longitudinal electric field due to the charge is present only in the gap region between the metal particles and excluded from the inside of the particles. This is because the longitudinal electric field, typically a unit of sub-angstrom, cannot penetrate into the metal beyond the Thomas-Fermi screening length. This fact is shown in Fig. 1B. The strength of the electric field in the dielectric gap region of the metamaterial nanocomposite is equal to the strength of the electric field in the reference case where the space between the capacitor plates is filled with the same material (permittivity, εh) as the gap dielectric. Since the voltage drop is a linear integration of the electric field, the total voltage drop in the presence of the metamaterial nanocomposite is reduced to g / a of the voltage drop in the reference case, which means that the capacitance is improved by a / g. Thus, ε _eff of the metamaterial nanocomposite structure is also improved by a / g, meaning a / gε _h . As a result, the meta-material nanocomposites require 'close-packed' arrays for high refractive index due to the a / g factor.

In one embodiment of the present application, the nanoparticles in the unit structure may be coated or surrounded by the host material (wraaping), but may not be limited thereto. For example, the unit structure may be a core-shell structure in which spherical nanoparticles are surrounded by a host material and then arranged in another host material, but may not be limited thereto. For example, the unit structure may be formed by arranging cylindrical nanoparticles such as carbon nanotubes in a host material, but may not be limited thereto. For example, the arrangement of the nanoparticles may be a core-shell structure or a close-pack, but may not be limited thereto.

In one embodiment of the present application, the material of the nanoparticles is gold (Au), silver (Ag), aluminum (Al), copper (Cu), nickel (Ni), platinum (Pt), titanium (Ti), tin (Sn), and a metal core selected from the group consisting of combinations thereof may be in a form surrounded by a nonmetallic shell, but may not be limited thereto.

In one embodiment of the present application, when the nanoparticles are semiconductors, although the nanoparticles are larger in size, they may exhibit a high refractive index, but may not be limited thereto. Since the semiconductor nanoparticles have a longer penetration depth than the metal nanoparticles, the magnetic field can penetrate deeper. Therefore, even if the nanoparticles have a larger size than the metal nanoparticles, they may exhibit a high refractive index. Can be.

In one embodiment of the present application, the nanoparticles in the unit structure may include a material in which the real part of the dielectric constant is negative, and the host material may include a material in which the real part of the dielectric constant is positive, but is not limited thereto. Can be. For example, the nanoparticles are metals such as gold (Au), silver (Ag), aluminum (Al), copper (Cu), nickel (Ni), platinum (Pt), titanium (Ti), tin (Sn), and the like. matter; Two or more kinds of metal alloys; Carbon-based materials such as graphite, carbon nanotubes, and fullerenes; Silicon, germanium, cadmium telluride (CdTe), lead sulfide (PbS), indium arsenide (InAs), indium phosphide (InP), indium antimonide (InSb), gallium phosphide (GaP), gallium nitride (GaN), non Semiconductor materials such as gallium hydride (GaAs); Or a compound semiconductor material of three or more elements such as InGaAsP, but may not be limited thereto. For example, the host material may be silicon dioxide (SiO ₂ ), copper oxide (CuO ₂ ), aluminum oxide (Al ₂ O ₃ ), vanadium oxide, titanium oxide, silver oxide Oxides such as these; Nitrides such as silicon nitride (Si ₃ N ₄ ), sialon and the like; Silicon, germanium, cadmium telluride (CdTe), lead sulfide (PbS), indium arsenide (InAs), indium phosphide (InP), indium antimonide (InSb), gallium phosphide (GaP), gallium nitride (GaN), non Semiconductor materials such as gallium hydride (GaAs); Compound semiconductor materials of three or more kinds of elements such as InGaAsP; Polymeric materials; Carbon-based materials such as graphite; Organic materials such as polydopamine, oleylamine; Or liquid materials such as water, oils, organic solvents, and the like, but may not be limited thereto.

In one embodiment of the present application, when the host material is a liquid material such as water, oil, the host material is used after applying on the sample using a spin coating method, spray coating method, immersion method, or a drop method It may be, but may not be limited thereto.

In one embodiment of the present application, by using aluminum (Al) is a highly reactive metal as the nanoparticles, it is possible to improve the refractive index of the metamaterial nano composite structure, but may not be limited thereto.

In one embodiment of the present invention, the nanoparticles in the unit structure is tetrahedral, hexahedral, octahedral, octahedral, tetrahedral, icosahedron, rod, concave tetrahedron, tetrahedral It may include, but not limited to, twin, spherical, ellipsoidal, cylindrical, such as hexagonal plate, triangular plate, circular pentagonal twin.

In one embodiment of the present application, the nanoparticles may have an isotropic sphere, tetrahedron, cube, octahedron, dodecahedron, dodecahedral, or dodecahedron. It may not be limited.

In one embodiment of the present application, the nanoparticles formed in the unit structure may have a width of a gap, which is a gap with adjacent nanoparticles, of about 10 nm or less, but may not be limited thereto. For example, the width of the gap, which is the distance between the nanoparticles and adjacent nanoparticles, may be about 10 nm or less, about 9 nm or less, about 8 nm or less, about 7 nm or less, about 6 nm or less, or about 5 nm or less. It may be, but may not be limited thereto.

In one embodiment of the present application, the dielectric constant of the nanoparticles can be freely adjusted without noticeable change in permeability, by changing the width of the gap while maintaining the size of the unit structure at a constant value under the depth of penetration, but is not limited thereto. Can be. While the permeability is nearly constant for the nanoparticles, the permittivity is inversely proportional to the width of the gap, thereby reducing the gap width to achieve high permittivity and high refractive index.

In one embodiment of the present application, the material in which the real part of the dielectric constant of the nanoparticles is negative is a material selected from the group consisting of metal material, carbon-based material, semiconductor material having improved carrier density by doping, and combinations thereof It may be to include, but may not be limited thereto. For example, the nanoparticles are metals such as gold (Au), silver (Ag), aluminum (Al), copper (Cu), nickel (Ni), platinum (Pt), titanium (Ti), tin (Sn), and the like. matter; Two or more kinds of metal alloys; Carbon-based materials such as graphite, carbon nanotubes, and fullerenes; Silicon, germanium, cadmium telluride (CdTe), lead sulfide (PbS), indium arsenide (InAs), indium phosphide (InP), indium antimonide (InSb), gallium phosphide (GaP), gallium nitride (GaN), non Semiconductor materials such as gallium hydride (GaAs); Or a compound semiconductor material of three or more elements such as InGaAsP, but may not be limited thereto.

In one embodiment of the present application, the material of which the real part of the dielectric constant of the host material is positive is selected from the group consisting of oxides, nitrides, low-density semiconductor materials, high-molecular materials, organic materials, liquid materials, and combinations thereof It may be to include the material, but may not be limited thereto. For example, the host material may be silicon dioxide (SiO ₂ ), copper oxide (CuO ₂ ), aluminum oxide (Al ₂ O ₃ ), vanadium oxide, titanium oxide, silver oxide Oxides such as these; Nitrides such as silicon nitride (Si ₃ N ₄ ), sialon and the like; Silicon, germanium, cadmium telluride (CdTe), lead sulfide (PbS), indium arsenide (InAs), indium phosphide (InP), indium antimonide (InSb), gallium phosphide (GaP), gallium nitride (GaN), arsenide Semiconductor materials such as gallium (GaAs); Compound semiconductor materials of three or more kinds of elements such as InGaAsP; Polymeric materials; Carbon-based materials such as graphite, carbon nanotubes, and fullerenes; Organic materials such as polydopamine, oleylamine; Or liquid materials such as water, oils, organic solvents, and the like, but may not be limited thereto.

In one embodiment of the present application, when the host material is a liquid material such as water, oil, the host material is used after applying on the sample using a spin coating method, spray coating method, immersion method, or a drop method It may be, but may not be limited thereto.

The second aspect of the present application provides an optical film comprising the metamaterial nanocomposite structure according to the first aspect.

In one embodiment of the present application, the metamaterial nano composite structure includes unit structures including nanoparticles and a host material, and the unit structures may be close-packed in three dimensions. This may not be limited.

In one embodiment of the present application, the optical film may be to improve the resolution of an optical system such as optical lithography or an optical microscope using a high refractive index, but may not be limited thereto.

In one embodiment of the present application, the optical film may be formed using a deposition method, a spray method, a immersion method, a drop method, etc., but may not be limited thereto.

Although the second aspect of the present application omits a detailed description of the overlapping parts of the first aspect of the present application, the description of the first aspect of the present application may be equally applied even if the description is omitted in the second aspect of the present application. have.

Here, a three-dimensionally arranged array of metal nanoparticles has been proposed to achieve broadband high refractive index in the visible and infrared regions. In densely arranged metamaterial nanocomposites, small gap-to-period ratios lead to improved effective permittivity from strongly sealed electric fields within the dielectric gap. At the same time, the nanometer diameter of tens of metal particles prevents the undesired drop in effective permeability, since the size of the nanoparticles corresponding to or smaller than the penetration depth allows the penetration of the magnetic field through the metal particles. This difference in electrical and magnetic field behavior is due to the large difference between Thomas-Fermi screening length and penetration depth. As a result, the effective refractive index of the metamaterial nanocomposite is much higher than natural materials in the visible and infrared regions and can be easily controlled by varying the gap width. The proposed metamaterial nanocomposite overcomes the bandwidth limitations of other metamaterials directly dependent on surface plasmon resonance. Another advantage of metamaterial nanocomposites is the weak dependence of the effective refractive index on the particle morphology and lattice type, which allows the possibility for many bottom-up particle synthesis methods in lieu of expensive and complex top-down nanofabrication processes. Since the ability to adjust the dielectric constant and permeability is important not only in achieving high refractive index but also in designing impedance and other optical properties of the material, the proposed technique is a waveguide coupler in submerged lenses for lithography and imaging. Applications can be found in a variety of optical devices, from couplers, modulators, photo detectors and energy devices.

Hereinafter, the present invention will be described in more detail with reference to examples of the present application, but the following examples are merely illustrated to aid the understanding of the present application, and the content of the present application is not limited to the following examples.

[ Example ]

Example 1 FDTD Simulation Analysis

FDTD  Simulation condition

FDTD simulation was performed using Lumerical Solutions' product (version 8.7.4). The entire FDTD simulation was performed in three dimensions. In Figure 2, the schematic of the FDTD simulation in the XZ plane of the metamaterial nanocomposite structure. Light with X-polarized light propagates along the Z-direction, and the light source wavelength ranges from 200 nm to 3,000 nm. Because metamaterial nanocomposites consist of repeated unit structures in the XY plane, periodic boundary conditions were used in the X- and Y-directions to save computer time. On both sides in the Z-direction, a perfectly matched layer (PML) was used. Two monitors were placed below and above to characterize metamaterial nanocomposites using the S-parameter method. In all simulations, the minimum mesh size was designed to be one tenth of the smallest structure. In addition, the minimum mesh size was designed by first conducting a convergence test. For gold metamaterial nanocomposite simulations, Johnson and Christy material data apply from 200 nm to 3,000 nm. Palik material data is used for the simulation of silver and aluminum metamaterial nanocomposites, and material data such as refractive indices for the materials (gold, silver, and aluminum) used in the simulation are plotted in FIG. 3. Silicon dioxide was selected as the dielectric host material with a refractive index of 1.473.

1-1: Depending on nanoparticle size Metamaterial  Electric "G magnetic field distribution of nanocomposites

In order to check the refractive index change according to the nanoparticle size of the metal, FDTD simulation was used. As shown in FIG. 4, in the case of the metal material, perfect electric conductor (PEC) and gold were compared. (A), (d), and (g) of FIG. 4 are schematic diagrams of the metamaterial nanocomposite structure, and red squares each represent one unit structure. (B), (e), and (h) of FIG. 4 show an Ex-field distribution of one metamaterial nanocomposite unit structure in a z-normal view as shown in (a) of FIG. , (f), and (i) represent the Hy-field distribution. Ex-field and Hy-field distributions were normalized by the maximum at the edge of the unit structure, which coincided with the red squares of FIGS. 4 (a), (d), and (g). The central coordinate of the cross section of the unit structure is typically (0, 0). PEC had a Thomas-Fermi screening length and a penetration depth of zero, and the particle size was always larger than both lengths. For gold at near-infrared and visible wavelengths above the interband transition wavelengths, the lengths were sub-angstrom scale and 22 nm, respectively. Thus, two cases with different particle sizes of 18 nm and 270 nm were compared. These were each smaller and larger than the depth of penetration. The particle size to gap ratio was fixed at 9: 1. As shown in (b), (e), and (h) of FIG. 4, the electric field was strongly localized in the dielectric gap between the metal particles regardless of the metal particle size and clearly identified whether the metal is PEC or gold. This is because the Thomas-Fermi length is much shorter than both the particle and gap widths in three cases. Because of this electric field confinement, the effective permittivity should be close to ten times the dielectric in all three cases. In contrast, the magnetic field distribution varies considerably with material and size. As shown in FIG. 4C, the magnetic field existed only outside the PEC particles. This shows strong diamagnetic properties. In the case of gold particles, the magnetic field penetrated into the particles. Empirically, this distribution could be investigated with a primary hyperbolic cosine function. Therefore, when the size of the gold particles was larger than the depth of penetration, the magnetic field did not penetrate mostly from the inner region of the particles, and the field profile exhibited strong diamagnetism and was close to that of the PEC particles (Fig. 4 (i)). However, when the size of the gold nanoparticles is 18 nm (unit structure size 20 nm, gap 2 nm), when normalized to the maximum value in the dielectric gap, the magnetic field has a minimum value of 0.9465 at the center of the nanoparticles. It was expressed that it was distributed almost uniformly over [FIG. 4 (f)]. Therefore, the size of the metal nanoparticles corresponding to or smaller than the penetration depth of the nanoparticles is an important key for inducing magnetic penetration through the metal, which prevents a significant reduction in the effective permeability of the metamaterial nanocomposites. Directly induces The result of the magnetic field corresponds to the idea proposed in FIG. 1 (c), and the penetration depth corresponding to the metal particles is n _eff = (ε _eff μ _eff ) ^1/2 = (a / g · ε _h ) ^1/2 Phosphorus high refractive index can be realized.

1-2: Metamaterial  Refractive Index of Nanocomposite Structures

For quantitative analysis, s-parameter extraction was used to calculate effective material property values from FDTD simulations. The extracted effective values of refractive index, dielectric constant, and permeability for the gold metamaterial nanocomposite structure having a 20 nm unit structure and a 2 nm gap filled with SiO ₂ are plotted in FIG. 5. FIG. 5A shows the effective dielectric constant ε _eff and permeability μ _eff of the gold metamaterial nanocomposite structure, and FIG. 5B shows the effective refractive index and the actual imaginary part of the FOM. The unit structure size and gap width were 20 nm and 2 nm, respectively, and the host material used was SiO ₂ . In FIG. 5A, the green dotted line and the red dotted line at the bottom are asymptotes of the effective dielectric constant and permeability of the metamaterial nanocomposite structure. In FIG. 5B, the dotted green line is an asymptote of the effective refractive index of the metamaterial nanocomposite structure. The metamaterial nanocomposites have been shown to exhibit prominent resonance properties around 800 nm and to exhibit very high refractive indices that are nearly constant over a broad wavelength range after the resonance peak, which can be controlled by the shape and size of the particles. This is due to the dipolar resonance of. The asymptotic value of the effective material parameter at the long-wavelength limit, indicated by the dashed line in FIG. 5, is very close to the theoretical prediction. The permittivity, permeability, and resulting refractive indices of asymptotes were 21.2, 0.983, and 4.57, with theoretical values for a / gεSiO ₂ = 20/2 × 2.17 = 21.7, 0.998, and 4.65. The figure of merit (FOM), defined as Re (n) / Im (n), is considerably higher for metamaterials in the visible and near-infrared regions, which is currently dependent on current design studies, resonances and related strong dispersions. Unlike most of the metamaterials that have been proposed in the past, they are mainly due to the fact that they are independent of resonance.

1-3: Metamaterial  Refractive Index Control of Nanocomposite Structures

FDTD simulation was used to check the refractive index according to the size of the unit structure of the metamaterial nano composite structure and the width of the gap. The magnetic and electrical properties of the metamaterial nanocomposite can be independently controlled, while the permittivity is not so dependent on the relative size of the particles relative to the depth of penetration. As shown in Fig. 6, the permittivity can be freely adjusted without noticeable change in permeability by changing the width of the gap while maintaining the size of the unit structure at a constant value of 20 nm under the depth of penetration (Fig. 6 (a)). To (c)]. It can be seen that while the permeability is nearly constant for the gold metamaterial nanocomposite, the permittivity is inversely proportional to the width of the gap. Thus, high permeability and high refractive index can be achieved by reducing the width of the gap. On the other hand, the magnetic property is that there is little magnetic reaction by changing the size of the unit structure while maintaining a constant ratio between the size of the unit structure and the width of the gap to 10: 1 to maintain the same dielectric constant (near 1 Permeability) can be designed with a very strong diamagnetic (permeability near zero) (Fig. 6 (d) to (f)). The theoretical predictions based on geometry and penetration depth of gold are in good agreement with the FDTD results, further demonstrating the model herein. In comparison, the hypothesis is almost identical to the gold metamaterial nanocomposite when the Thomas-Fermi length is not negligible in both cases, while the PEC and the hypothetical made of PEC with zero penetration depth instead of 22 nm gold Metamaterial nanocomposites exhibit very different permeability. Using this independent control of electrical and magnetic properties, one can design broadband metamaterials with very high refractive indices or very high admittances and anything in between.

1-4: gold, silver, and aluminum Metamaterial  Nano composite structure

FDTD simulations were conducted on gold, silver, and aluminum to confirm that the theoretical model and analysis also apply to other metals. The results were compared in Table 1 and they showed that the effective values were not significantly different, due to the fact that these metals had similar penetration depths. However, the resonance wavelength is influenced by the surface plasmon frequency and is markedly short for aluminum metamaterial nanocomposites. This means that although aluminum has a small FOM due to large optical losses, aluminum metamaterial nanocomposites with 20 nm particle size are capable of broadband high refractive index in the visible range. It is also an optically transparent host medium that can utilize various types of dielectrics. Since the effective refractive index of the metamaterial nanocomposite is continuously proportional to the refractive index of the host medium, a higher effective refractive index can be achieved if the metamaterial nanocomposite is embedded in a host material having a higher refractive index than SiO ₂ .

1-5: Refractive Index Comparison by Grating Shape

FDTD simulations were performed to determine the refractive indices of metamaterial nanocomposites in different lattice shapes. Although the metamaterial nanocomposite of this embodiment is assumed to be cubic lattice and cubic particles, the principle remains the same for other particle shapes and lattice types and the high refractive index is lower-in the densely arranged configuration. It is achieved by sub-skin-depth-scale particles. For comparison, spheres in hexagonal lattice were considered. In Figure 7 (a) is a multi-layered schematic of the cube nanoparticles in the cubic lattice, Figure 7 (b) shows the nanospheres in the hexagonal array included in the host material. Figure 7 (c) is a multi-layer FDTD result of the gold cube and the size and width of the gap of the unit structure of the gold cube is 20 nm and 2 nm, respectively. 5 (d) shows the result of the multilayered FDTD of the gold spheres, the diameter and center-to-center distance of the spheres are 19 nm and 20 nm, respectively. In FIGS. 7C and 7D, 1 to 20 represent the number of layers. One subtle point is that the mono-layer of the sphere is not a true unit structure of the lattice, which also includes truncated spheres from the layers above and below. Thus, in contrast to the metahedral nanocomposite in the form of a gold cube in FIG. 7 (c), which is all data in the long wavelength regime closely overlapped with one another regardless of the number of layers, the hexagonal form The extracted refractive index of the metamaterial nanocomposite of showed a layer-number dependency for thin samples (FIG. 5 (d)). However, for samples with five or more layers of spheres, the effective refractive index was nearly saturated and its long-wavelength value was 4.10, which is significantly different from that of the metamaterial nanocomposite in the form of a cube (4.48). I didn't see it. This insensitiveness of the effective refractive index for the exact particle morphology allows for the various applications of metal nanoparticle synthesis methods previously reported.

Example 2 Preparation of Actual Metamaterial Nanocomposite Structures

2-1: Block copolymer In lithography  Hole pattern manufacturing

To make very small nanoscale structures, hole patterns were fabricated using BCP lithography as shown in FIG. 8. 4 inch silicon wafers were cleaned using an ultrasonic bath (ultra-sonic bath). Washing was performed for 15 minutes in order of deionized water, acetone, isopropyl alcohol, and DI water. In order to make the substrate more hydrophilic, UV-ozone treatment was performed for 30 minutes. Prior to coating the PS-b-PMMA, a random brush solution was coated to modify the surface morphology of the substrate. The random brush solution was 1 wt%, dissolved in toluene solvent (99.8% purity, Sigma Aldrich), and the average molecular weight (Mn) of the (PS-r-PMMA) -OH random brush was 8 kg mol with styrene of 62%. Was -1. The substrate was then thermally annealed at 160 ° C. for 12 hours in a vacuum oven. On the wafer with the changed surface, 2 wt% PS-b-PMMA solution was spin-coated at 2,500 rpm for 1 minute. The PS-b-PMMA block copolymer had 140 kg mol-1 and 65 kg mol-1 Mn for PS and PMMA blocks, respectively. It was chosen to fabricate a cylinder structure with a diameter of 30 nm. The solution was dissolved in toluene solvent, 2 wt%. The coated wafers were thermally annealed at 250 ° C. for 6 hours in a vacuum oven to produce a periodic cylinder pattern.

After the thermal annealing process at 250 ° C., the diblock-copolymer (BCP) coated wafers were exposed with 2 J of UV light (UV cross-linker, Spectronics) to decompose the PMMA microphase and harden the microphase. . The wafers were stored for 10 minutes in acetic acid solution (99.9% purity, Junsei corp.) And then washed with deionized water for 10 minutes to remove the PMMA microphase. Acetic acid selectively removes the degraded PMMA, so after the chemical etching process, a 30 nm hole pattern was uniformly produced on the wafer.

2-2: Preparation of Aluminum Nanocomposite Structure

In order to fabricate the aluminum nanocomposite structure, an ion milling method was used as shown in FIG. 9. The prepared 30 nm pore pattern was separated from the original substrate using hydrofluoric acid (49% to 51% HF solution, JT Baker.). The separated hole pattern was transferred onto the aluminum thin film surface. An aluminum thin film was deposited on a transparent quartz substrate by the vapor deposition method. The aluminum thin film is deposited under high vacuum (resistance method, 10 ⁻⁷ torr). After the hole pattern was transferred onto the aluminum surface, oxygen reactive ion etching (RIE) was performed for 10 seconds to adjust the hole diameter and remove PMMA residue on the substrate. Thus, the diameter of the pores expanded to 40 nm after RIE treatment.

Alumina (Al ₂ O ₃ ) was deposited in the hole pattern transmitted by the deposition method under the same conditions as the aluminum thin film. By sonication in toluene bath, the BCP hole pattern with PS domain was removed from the aluminum surface. After removal of the polymer domain, only the alumina nanocomposite structure for the ion milling mask on the aluminum surface was left. The ion milling process was followed by a nano-sized hard mask and an alumina nanocomposite structure was made. The chamber base was conducted at 8 × 10 ⁻⁷ torr or less and the process vacuum was conducted at 2 × 10 ⁻⁴ torr or less with 6 sccm of Ar gas. The ion beam was accelerated by 100 V, 1 mA and the ion milling time was 5-12 minutes.

2-3: SEM  analysis

In order to observe the surface and side morphology of the manufactured aluminum nanocomposite structure, a field emission scanning electron microscope (FE-SEM, HITACHI) was used. All samples prepared had tens of nanometers in size, so there was no osmium or platinum coating on the samples. Since the thickness of this conductive material coating is more than a few tens of nanometers, the sample was observed without coating to prevent distortion of the surface morphology. FIG. 10A illustrates a plan view of a hole pattern manufactured by a PS-b-PMMA block copolymer, and FIG. 10B illustrates an SEM image of an alumina hard mask periodically arranged on an aluminum thin film. 10C and 10D illustrate samples prepared by an ion milling process. From the SEM images, it can be seen that the aluminum nanocomposite structures were fabricated using BCP hole patterns of very similar scale.

2-4: AFM  analysis

The surface morphology of the prepared aluminum nanocomposite structure was investigated using an atomic force microscope (AFM, XE-100, Park System and AFM, Nanoman, Veeco Instruments Inc.). An atomic force microscope produces a surface image by moving the probe over the surface of the sample. The probe consists of a cantilever with a well defined resonant frequency and a very sharp tip. When the tip is close to the surface it is attracted or repelled. All changes in vibration amplitude or frequency tip are converted to a topo-graphic map. Surface morphologies such as root mean square surface roughness, particle analysis, and line profile were analyzed. The surface topography of the aluminum nanostructures manufactured differently is shown in FIG. 11. Figure 11 (a) is an AFM image showing an aluminum nano hemisphere composite structure using a 10 nm aluminum film for ion milling, Figure 11 (b) is an aluminum nano hemisphere composite structure using a 20 nm aluminum film. As shown in FIG. 11, the surface of the fabricated aluminum nanocomposite structure is in good agreement with the SEM analysis. The heights of the two samples showed similarity. Since thinner aluminum films reduce the time for ion milling, the alumina nano-dots used in the mask may remain high during the ion milling process. Thus, the height analyzed by AFM showed a similarity between 10 nm and 20 nm samples of aluminum.

2-5: UV- VIS  Permeability measured by spectrometer

In order to observe the optical properties of the produced samples, the transmittance and reflectance were measured (Lambda 1050, PerkinElmer). Samples were prepared on a transparent quartz substrate and all samples were at least 1 cm ² in size. All data were generalized to the transmittance and reflectance of the quartz substrate. The measured wavelength ranged from 175 nm to 750 nm. This was measured at the KAIST Analytical Research Center. As shown in FIG. 12, the transmittance measured by the UV-VIS spectrometer at 175 nm to 750 nm is shown. Samples using 10 nm thick aluminum foil (thin film) show sharper peaks at 195 nm, while samples using 20 nm thick aluminum foil exhibit broad peaks from 190 nm to 220 nm. Over the visible wavelength, all samples showed transparent properties, and the measured transmittance of the 10 nm aluminum sample was almost 100%. The 20 nm aluminum sample showed low transmittance. The difference in the optical properties between the two samples lies in the improved absorption of the nanocomposite structure with the insensitivity of aluminum thickness.

2-6: FDTD  Electromagnetic Analysis Using Simulation

The prepared aluminum nanocomposite structure was analyzed by FDTD simulation. In the FDTD simulations, the structure was assumed to be a 3 nm native aluminum oxide layer. 13 shows the numerically calculated transmittance by FDTD simulation from 150 nm to 800 nm. The transmittance showed a difference between the measured result and the numerically calculated result. In FIG. 13, the depth of permeability was deeper than the measured result. The wavelength of the depth position was also a red-shift of the numerical simulation results, and the 10 nm aluminum sample showed a sharp peak at 220 nm where the measured result was 195 nm. The measured results showed one large peak at 190 nm with a small shoulder peak at 220 nm, while the 20 nm aluminum sample showed two broad peaks in the transmission spectrum. This difference comes from the structural difference between the FDTD simulation and the sample produced. In the simulation, the aluminum nanocomposite structure was assumed to have a diameter of 40 nm, a center-to-center distance of 60 nm, and the structure was assumed to be perfectly periodic and symmetrical. The optical response is highly dependent on the nanocomposite structure, and small differences in structural dimensions can lead to different optical responses. The produced sample has both particle size distribution and center-to-center distribution. In addition, since aluminum plasmon is highly dependent on the deposition environment, and the oxygen content of the aluminum nanocomposite structure affects the plasmonic reaction, it is difficult to accurately reproduce the fabricated aluminum nanocomposite structure by numerical simulation.

Although the fabricated structure differs from the proposed densely arranged unit structure because the gap is about 20 nm, the aluminum hemispherical nanocomposite structure realized by BCP lithography shows optical properties similar to the simulation results. In Figure 14, the effective refractive index was derived from numerical simulations. As the height increases, the width of the gap decreases because the diameter of the structure is constant at 40 nm. Therefore, samples with a thickness of 20 nm show higher effective refractive index values. Although the value derived above is not high, it shows the feasibility of a simple structure of visible light metamaterial, and higher refractive index can be obtained by reducing the gap of the current sample, which is 20 nm level to 10 nm or less, as confirmed in the simulation. Indicates.

The above description of the present application is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present application. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present application is indicated by the following claims rather than the above description, and it should be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalents are included in the scope of the present application.

Claims (17)

1. A unit structure comprising nanoparticles and a host material,

   The unit structure is arranged in three dimensions,

   Metamaterial Nanocomposites.
2. The method of claim 1,

   The metamaterial nano composite structure has a high refractive index in the wavelength band selected from visible light, ultraviolet light, infrared light, and combinations thereof, meta-material nano composite structure.
3. The method of claim 2,

   The metamaterial nanocomposite structure has a maximum refractive index of 1.5 or more at a wavelength of 200 nm or less, metamaterial nanocomposite structure.
4. The method of claim 2,

   The metamaterial nano composite structure will have a maximum refractive index of 2 or more at the ultraviolet wavelength of 200 nm to 400 nm, metamaterial nano composite structure.
5. The method of claim 2,

   The metamaterial nano composite structure will have a maximum refractive index of 4 or more at visible light wavelength of 400 nm to 700 nm, metamaterial nano composite structure.
6. The method of claim 2,

   The metamaterial nanocomposite structure has a maximum refractive index of 5 or more at an infrared wavelength of 700 nm or more, metamaterial nanocomposite structure.
7. The method of claim 1,

   The nanoparticles in the unit structure is surrounded by the host material, metamaterial nano composite structure.
8. The method of claim 1,

   The nanoparticles in the unit structure comprises a material in which the real part of the dielectric constant is negative, the host material comprises a material in which the real part of the dielectric constant is positive, metamaterial nano composite structure.
9. The method of claim 1,

   The size of the nanoparticles in the unit structure, the metamaterial nano composite structure corresponding to or smaller than the penetration depth of the nanoparticles.
10. The method of claim 1,

    The unit structure is an isotropic or anisotropic one is arranged in three dimensions, metamaterial nano composite structure.
11. The method of claim 1,

    In the unit structure, the nanoparticles are tetrahedral, hexahedral, octahedral, decahedral, tetrahedral, icosahedral, rod, concave tetrahedral, tetrahedral, twin, spherical, ellipsoidal, or cylindrical. The metamaterial nano composite structure comprising a.
12. The method of claim 1,

    Wherein the nanoparticles (isotropic) sphere, tetrahedron, hexahedral, octahedral, dodecahedral, dodecahedral, or dodecahedron form, including those having a metamaterial nanocomposite structure.
13. The method of claim 1,

    The nanoparticles in the unit structure, the distance between adjacent nanoparticles is less than 10 nm, metamaterial nano composite structure.
14. The method of claim 8,

    The negative material of the dielectric constant of the nanoparticles is a negative material includes a material selected from the group consisting of metal material, carbon-based material, semiconductor material having improved carrier density by doping, and combinations thereof Nanocomposite Structures.
15. The method of claim 8,

    The material in which the real part of the dielectric constant of the host material is positive is a material selected from the group consisting of oxides, nitrides, low-density semiconductor materials, polymer materials, organic materials, liquid materials, and combinations thereof, Metamaterial Nanocomposites.
16. The metamaterial nano composite structure according to any one of claims 1 to 15.

    It includes, the optical film.
17. The method of claim 16,

    The optical film is to improve the resolution of the optical lithography or optical microscope using a high refractive index, the optical film.

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