Five-layer thin film structure containing metallic iron absorber

Abstract

To provide multilayer thin film structures that provide omnidirectional structural color and comprise materials suitable for consumer application.SOLUTION: A five-layer thin film structure includes a reflector, a high refractive index layer overlying or encapsulating the reflector, and a metallic iron absorber layer overlying or encapsulating the high refractive index layer. The reflector has a thickness from 10 nm to 5,000 nm, the high refractive index layer has a thickness from 5 nm to 500 nm, and the metallic iron absorber layer has a thickness greater than 0 nm and less than or equal to 50 nm.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates to five-layer thin film structures, and more particularly to omnidirectional structural color five-layer thin film structures including a metallic iron absorber. [Background technology]

[0002] Previously disclosed multilayer thin-film structures that provide omnidirectional structural color (OSC) include a layer of metal oxide with a high refractive index and a thin layer of metal as an absorber. However, some metal oxides used as the high refractive index layer, and some metals used as the metal absorber, may not be suitable for certain consumer applications, such as cosmetics and textiles. [Overview of the project] [Problems that the invention aims to solve]

[0003] Therefore, there is a need for multilayer thin-film structures that provide OSCs and contain materials suitable for consumer applications. [Means for solving the problem]

[0004] According to one embodiment, the five-layer thin-film structure includes a reflector, a high refractive index layer on or enclosing the reflector, and a metallic iron absorber layer on or enclosing the high refractive index layer.

[0005] According to the embodiment, the reflector has a thickness of 10 nm to 5000 nm, the high refractive index layer has a thickness of 5 nm to 500 nm, and the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

[0006] According to one embodiment, the five-layer thin film structure includes an aluminum reflector, an iron oxide high refractive index layer on or enclosing the aluminum reflector, and a metallic iron absorber layer on or enclosing the iron oxide high refractive index layer.

[0007] According to the embodiment, the aluminum reflector has a thickness of 10 nm to 5000 nm, the iron oxide high refractive index layer has a thickness of 5 nm to 500 nm, and the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

[0008] Further features and advantages are described below in detail, some of which will be readily apparent to those skilled in the art from the detailed description, or will be recognized by carrying out the embodiments described in this disclosure, including the detailed description below, the claims, and the accompanying drawings.

[0009] It should be understood that both the general description above and the detailed description below are intended to describe various embodiments and provide an overview or framework for understanding the nature and features of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, are incorporated herein, and constitute part of this specification. The drawings illustrate the various embodiments described herein and, together with the detailed description, help to illustrate the principles and operation of the claimed subject matter. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a graph showing the refractive index (n) and extinction coefficient (k) of chromium and iron.

[0011] [Figure 2A] Figure 2A is a schematic diagram showing a cross-section of a five-layer thin-film structure according to the embodiments disclosed and described herein.

[0012] [Figure 2B]Figure 2B is a schematic diagram showing a cross-section of an encapsulated five-layer thin-film structure according to the embodiments disclosed and described herein.

[0013] [Figure 3] Figure 3 schematically shows a thin film structure in which a high refractive index layer extends on a substrate layer and is exposed to electromagnetic radiation at an angle θ with respect to the direction normal to the outer surface of the high refractive index layer.

[0014] [Figure 4A-4E] Figures 4A to 4E are photographs of a three-layer thin-film structure for comparison and a five-layer thin-film structure according to the embodiments disclosed and described herein. [Modes for carrying out the invention]

[0015] As mentioned above, some metal oxides used as high refractive index layers, and some metals used as absorber layers, are not suitable for use in consumer products. For example, chromium (Cr) is a commonly used metal absorber material because it is a good absorber and easy to deposit. However, some forms of chromium may be toxic and are therefore not suitable for all consumer applications, such as cosmetics and textiles. Therefore, it is desirable to replace chromium as an absorber material in 5-layer thin film structures with an absorber material that is more consumer-friendly and exhibits good OSC properties. Furthermore, it is desirable that the absorber material replacing chromium in 5-layer thin film structures can be safely deposited in 5-layer thin film structures in both small-scale and large-scale production processes.

[0016] Conventionally, high refractive index metal oxide layers and metal absorber layers can be applied in a five-layer thin film structure by methods such as physical vapor deposition (PVD) and sputtering. In some cases, the five-layer thin film is first formed as a large sheet that includes a reflector layer and various combinations of high refractive index metal oxide layers and metal absorber layers. This large sheet can then be divided by mechanical means and processed to form small particles of the five-layer thin film structure that can be used as pigments in products such as paints, cosmetics, and textiles.

[0017] Initially, tungsten (W) was considered to be a good alternative to chromium as a metal absorber material. In small-scale production, tungsten showed fairly good performance, and a five-layer thin film structure including a tungsten metal absorber layer provided OSC characteristics equivalent to those of a five-layer thin film structure having a chromium metal absorber layer. However, in order to apply tungsten as a metal absorber layer in a five-layer thin film structure, it is necessary to reduce tungsten oxide to metallic tungsten. The reduction of tungsten oxide has conventionally been carried out under high temperature and high pressure conditions in the presence of hydrogen. When tungsten oxide is deposited on an aluminum reflector layer, which is a common reflector layer used in the five-layer thin film structure of OSC, and reduced, the aluminum reflector layer may undergo exothermic oxidation. This exothermic oxidation of aluminum, combined with the hydrogen-based atmosphere used to reduce tungsten oxide, can result in a harmful mixture, especially when carried out in large-scale production. Therefore, although tungsten may be suitable as an alternative to a chromium absorber in small-scale applications, it is not a good candidate for large-scale applications. Thus, an alternative metal absorber material is desired.

[0018] Another material that can be a suitable alternative to chromium as a metal absorber material is metallic iron. As used herein, "metallic iron" refers to any iron isotope and does not include iron oxides. However, it should be understood that a metallic iron layer as described in this disclosure may, according to embodiments, contain trace amounts of iron oxide that are inadvertently formed when the various layers of the 5-layer thin film are deposited on top of each other.

[0019] One reason metallic iron can be a good alternative to chromium is that metallic iron has optical properties very similar to chromium. Here, referring to FIG. 1, the refractive index (n) and extinction coefficient (k) of chromium and iron are compared. As is generally known, the refractive index (n) of a substance is the ratio of the speed of light in a vacuum to the phase velocity of light in the medium. This relationship is

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[0020] As used herein, the terms “electromagnetic wave,” “electromagnetic radiation,” and “light” may interchangeably refer to light of various wavelengths incident on a five-layer thin-film structure, and such light may have wavelengths in the ultraviolet (UV), infrared (IR), and visible regions of the electromagnetic spectrum.

[0021] In addition to possessing optical properties similar to chromium, metallic iron is also a good alternative to chromium as a metal absorber in a five-layer thin film structure because it can be deposited in the structure by low-cost methods such as known chemical vapor deposition (CVD) or other wet chemical methods. This reduces the need for more expensive deposition methods such as PVD or atomic layer deposition (ALD). According to embodiments, and as will be described in more detail below, the iron oxide layer can be deposited in the appropriate location on the five-layer thin film structure by any suitable method, such as CVD or other wet chemical methods. In some embodiments, the entire deposited iron oxide layer is then reduced to form a metallic iron absorber layer. In other embodiments, only a portion of the iron oxide layer is reduced to form a metallic iron absorber layer. Since the reduction of iron does not require the stringent conditions required for the reduction of tungsten, the exothermic oxidation of the aluminum reflector layer does not occur to the same extent as in the reduction of tungsten. Furthermore, this method allows for the control of the metallic iron absorber layer thickness to the nanometer scale, which is important when forming a five-layer thin film of OSC, as even slight changes in the thickness of various layers in the five-layer thin film can dramatically affect the OSC properties of the five-layer thin film. By forming the metallic iron absorber layer in this way, oxidation of the metallic iron layer during deposition or weathering tests can be prevented.

[0022] A five-layer thin-film structure 200 according to one or more embodiments disclosed and described in this disclosure is provided in Figure 2A. The five-layer thin-film structure 200 of the embodiment disclosed in Figure 2A includes a reflector 210, a first high refractive index layer 220a on one side of the reflector 210, a second high refractive index layer 220b on a second surface of the reflector 210, a first metallic iron absorber layer 230a on the first high refractive index layer 220a, and a second metallic iron absorber layer 230b on the second high refractive index layer 220b. As can be seen from Figure 2A, the five-layer thin-film structure 200 includes symmetrical layers on both sides of the reflector 210, the first and second high refractive index layers 220a and 220b are made from the same material, and the first and second metallic iron absorber layers 230a and 230b are made from the same material.

[0023] An alternative five-layer thin-film structure 200, following one or more embodiments disclosed and described herein, is provided in Figure 2B. The five-layer thin-film structure of the embodiment shown in Figure 2B is formed using an encapsulation method to deposit the layers of the five-layer thin-film structure 200. The five-layer thin-film structure 200 of the embodiment shown in Figure 2B includes a reflector 210, a high refractive index layer 220 encapsulating the reflector 210, and a metallic iron absorber layer 230 encapsulating the high refractive index layer 220. By using an encapsulation method, the high refractive index layer 220 is deposited symmetrically on all sides of the reflector 210, and the metallic iron absorber layer 230 is deposited symmetrically on all sides of the high refractive index layer 220, thereby having a structure similar to the five-layer thin-film 200 in Figure 2A, except that all sides of the five-layer thin-film 200 in Figure 2B include the high refractive index layer 220 and the metallic iron absorber layer 230. As used herein, “encase” means that the encasement layer covers all sides of the layer being encasement. It should be understood that “encase” includes embodiments in which the deposition method used for encasement does not unintentionally cover any portion of the layer being encasement by that deposition method.

[0024] Referring again to Figures 2A and 2B, a structure 200 according to the embodiments disclosed and described herein includes a reflector 210, a high refractive index layer 220 on or enclosing the reflector 210, and a metallic iron absorber layer 230 on or enclosing the high refractive index layer 220.

[0025] In this embodiment, the position of the metallic iron absorber layer 230 may be selected to increase absorption of light wavelengths within a certain range, but to reflect light of other wavelengths. For example, the position of the metallic iron absorber layer may be selected to increase absorption of light waves below 550 nm, but to reflect light waves of about 650 nm, such as visible light outside the 10° to 30° hue. Therefore, the electric field (|E|) 2 ) The absorber layer is arranged with a smaller thickness at a wavelength of 550 nm than at a wavelength of 650 nm. Mathematically,

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[0026] Figure 3 and the following discussion provide a method for calculating the thickness of a zero or near-zero electric field point at a given wavelength of light, according to an embodiment. For the purposes of this specification, the term “near-zero” means |E| 2 It is defined as ≤10. Figure 3 shows the refractive index "n s The present invention relates to a five-layer thin film comprising a substrate layer 2 having a total thickness "D", an incremental thickness "d", and a refractive index "n", and a high refractive index layer 4 on top of that substrate layer 2 having a substrate layer 2 having a high refractive index layer 4 having a total thickness "D", an incremental thickness "d", and a refractive index "n". The substrate layer 2 can be a reflector of the five-layer thin film. Incident light strikes the outer surface 5 of the high refractive index layer 4 at an angle θ with respect to a line 6 perpendicular to the outer surface 5, and is reflected from the outer surface 5 at the same angle θ. The incident light passes through the outer surface 5 into the high refractive index layer 4 at an angle θ with respect to the line 6. F It enters at an angle θ to the surface 3 of the base material layer 2. s It hits. In the case of a single high refractive index layer, θ s =θ F Therefore, the energy / electric field (E) can be expressed as E(z) when z=d. From Maxwell's equations, the electric field for s-polarized light is

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[0027] It should be understood that the fluctuations in the electric field along the Z direction of the high refractive index layer 4 can be estimated by calculating the unknown parameters u(z) and v(z), and here,

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[0028]

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[0029] According to the above, the thickness of the high refractive index layer and the metallic iron absorber can be changed to have a thickness that satisfies a nearly zero electric field as described above. For example, there are locations where nearly zero energy exists and locations where |Ed=d0|=0 exists. If a thin metallic iron absorber layer is placed at this point (d0) for a specific wavelength A, no energy to be absorbed at that wavelength will be found, but other wavelengths with non-zero energy will be absorbed. For example, in the case of a wavelength of 434 nm, the 434 nm light will not be absorbed and will remain transparent, but the position of the metallic iron absorber when |E|d=d0=0 can be selected so that other wavelengths with a non-zero electric field are absorbed.

[0030] Referring again to Figures 2A and 2B, according to the embodiment, the reflector 210 may be a layer formed from a reflective material, or the reflector 210 may be discrete particles having any shape. In the embodiment, the reflector 210 may have a thickness of 10 nm to 5000 nm (5 microns (μm)), for example, 50 nm to 1000 nm, 100 nm to 600 nm, 125 nm to 400 nm, 150 nm to 300 nm, or 175 nm to 250 nm. In embodiments, the reflector 210 has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. In embodiments, the reflector 210 can be made from at least one of the "gray metal" materials such as Al, Ag, Pt, Sn; at least one of the "colorful metal" materials such as Au, Cu, brass, bronze, TiN, Cr, or a combination thereof. In some embodiments, the reflector is Al.

[0031] According to the embodiment, the high refractive index layer 220 is deposited on or encapsulates the reflector 210. The high refractive index layer 220 can be deposited on the reflector 210 by any suitable method such as CVD, ALD, wet chemical processes, and PVD. According to the embodiment, the high refractive index layer 220 can have a thickness of 5 nm to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. In some embodiments, the high refractive index layer 220 can have a thickness of 5 nm to 450 nm, for example, 5 nm to 400 nm, 5 nm to 350 nm, 5 nm to 300 nm, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 150 nm, 5 nm to 100 nm, or 5 nm to 50 nm. In embodiments, the high refractive index layer 220 can have a thickness of 50 nm to 450 nm, for example, 100 nm to 400 nm, 150 nm to 350 nm, or 200 nm to 300 nm. In embodiments, the high refractive index layer 220 can be made from at least one colorful dielectric material such as Fe2O3, TiN, or a combination thereof. In other embodiments, the high refractive index layer 220 can be a dielectric material selected from the group consisting of ZnS, ZrO2, CeO2, HfO2, TiO2, or a combination thereof. According to some embodiments, the high refractive index layer 220 may be selected from ZnS, Fe2O3, TiO2, or a combination thereof. According to one or more embodiments, the TiO2 may be a rutile phase, anatase phase, or a combination thereof. In embodiments, the high refractive index layer 220 is composed of one or more metal oxides.

[0032] In some embodiments, the metallic iron absorber layer 230 may be deposited on the high refractive index layer 220, or the high refractive index layer 220 may be encapsulated within it. In some embodiments, the metallic iron absorber layer 230 may have a thickness greater than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, or 15 nm to 20 nm. In some embodiments, the metallic iron absorber layer 230 may have a thickness of 5 nm to 15 nm, for example, 5 nm to 10 nm, or 10 nm to 15 nm. In some embodiments, the metallic iron absorber layer 230 is made from metallic iron (Fe).

[0033] In embodiments where the high refractive index layer 220 is iron oxide (Fe2O3), the metallic iron absorber layer 230 is formed by exposing the iron oxide high refractive index layer 220 to a reducing agent to reduce the iron oxide to metallic iron, thereby forming the metallic iron absorber layer. The thickness of the metallic iron absorber layer 230 can be controlled by adjusting the amount of reducing agent used, by adjusting the conditions under which reduction occurs (such as temperature and pressure), or by adjusting the reduction time. In embodiments where the high refractive index layer 220 is iron oxide, it should be understood that the thickness of the iron oxide deposited as the high refractive index layer 220 should be adjusted (i.e., increased) in consideration of the thickness of the metallic iron absorber layer 230. As an example, in embodiments where the high refractive index layer 220 is iron oxide, the desired thickness of the high refractive index layer 220 is 200 nm, and the desired thickness of the metallic iron absorber layer is 20 nm, iron oxide having a thickness of 220 nm should be deposited on the reflector 210 (i.e., the desired thickness of the metallic iron absorber layer 230 plus the desired thickness of the high refractive index layer 220).

[0034] The metallic iron layer can be obtained by the high-temperature reaction of a deposited iron oxide layer with a reducing gas, such as hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), or a mixture containing H2-CO, CO-CO2, H2-CO-CO2, H2-CO-CO2-CH4. In embodiments, the various iron oxides may be hematite (Fe2O3), magnetite (Fe3O4), ferrous oxide (FeO), or mixtures of these iron oxides. For the purposes of this explanation, we will use hematite (Fe2O3).

[0035] The reduction reaction of iron oxide to Fe by hydrogen: Fe2O3(s)+3H2(g)→2Fe(l)+3H2O(g)

[0036] The reduction reaction of iron oxide to iron by carbon monoxide: Fe2O3(s)+3CO(g)→2Fe(l)+3CO2(g)

[0037] The dynamics of the reduction reaction of iron oxide can be influenced by various parameters. Process parameters (e.g., temperature, pressure, and gas composition) and reaction time, as well as the properties of the material being reduced (e.g., grain size, morphology, and porosity), affect the reduction performance. To achieve precise control of the composition, density, and thickness of the metallic iron (Fe) layer, various reaction conditions can be fine-tuned in embodiments.

[0038] Generally, diffusion rates and phase boundary reactions accelerate with increasing temperature. From a thermodynamic standpoint, the reduction of iron oxide can proceed at low temperatures. However, gas utilization achievable at low temperatures is insufficient due to kinetic limitations. Therefore, a certain temperature, such as 220°C, is required to achieve gas utilization. However, higher temperatures are advantageous for both the thermodynamics and kinetics of the reduction of iron oxide. In this case, a low temperature range of 200-450°C is desirable to avoid damage to the Al core and to achieve better control of the Fe layer thickness. In addition to temperature, pressure can also affect the reduction rate. Increasing the pressure and keeping the partial pressure of reducing gases in the gas constant (higher morph flow) can sometimes lead to an increase in the reduction rate. The composition of the reducing gases is also an important factor governing the reduction rate.

[0039] In embodiments where the high refractive index layer 220 is not iron oxide (Fe2O3), the metallic iron absorption layer 230 is formed by first depositing an iron oxide layer on the high refractive index layer 220, or by encapsulating the high refractive index layer 220 with iron oxide. The iron oxide may be deposited on the high refractive index layer by CVD or a wet chemical process, or the high refractive index layer 220 may be encapsulated with iron oxide using CVD or a wet chemical process such that the iron oxide on the high refractive index layer 220 has a metallic iron absorption layer 230 of a desired thickness, for example, the thickness disclosed above. When iron oxide is present on the high refractive index layer 210, the iron oxide is exposed to a reducing agent and reduced from iron oxide to metallic iron, thereby forming a metallic iron absorber layer. In some embodiments, all of the iron oxide is reduced to metallic iron. In other embodiments, some of the iron oxide is reduced to metallic iron. In some embodiments where only some of the iron oxide is reduced to metallic iron, the thickness of the remaining iron oxide is minimized.

[0040] According to an embodiment, and also referring to Figure 2A, the five-layer thin film structure 200 may include an aluminum reflector 210; a high refractive index layer 220 containing iron oxide (Fe2O3) on the aluminum reflector 210; and a metallic iron absorber layer 230 on the iron oxide high refractive index layer 220. By changing the thickness of the high refractive index layer 220, and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic radiations in the visible spectrum.

[0041] The aluminum reflector has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. The iron oxide high refractive index layer has a thickness of 5 to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, 15 nm to 20 nm, 5 nm to 15 nm, 10 nm to 15 nm, or 5 nm to 10 nm.

[0042] According to the embodiment, and again referring to Figure 2A, the five-layer thin film structure 200 may include: an aluminum reflector 210; a high refractive index layer 220 containing TiO2 (rutile phase or anatase phase) on the aluminum reflector 210; and a metallic iron absorber layer 230 on the TiO2 (rutile phase or anatase phase) high refractive index layer 220. By changing the thickness of the high refractive index layer 220, and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic waves in the visible spectrum.

[0043] The aluminum reflector has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. The TiO2 (rutile phase or anatase phase) high refractive index layer has a thickness of 5 to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, 15 nm to 20 nm, 5 nm to 15 nm, 10 nm to 15 nm, or 5 nm to 10 nm.

[0044] According to an embodiment, and also referring to Figure 2A, the five-layer thin film structure 200 may include an aluminum reflector 210; a high refractive index layer 220 containing ZnS on the aluminum reflector 210; and a metallic iron absorber layer 230 on the ZnS high refractive index layer 220. By changing the thickness of the high refractive index layer 220 and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic waves in the visible spectrum.

[0045] The aluminum reflector has a thickness of 10nm to 400nm, for example, 10nm to 375nm, 10nm to 350nm, 10nm to 325nm, 10nm to 300nm, 10nm to 275nm, 10nm to 250nm, 10nm to 225nm, 10nm to 200nm, 10nm to 175nm, 10nm to 150nm, 10nm to 125nm, 10nm to 100nm, 10nm to 75nm, 10nm to 50nm, or 10nm to 25nm, and the ZnS high refractive index layer has a thickness of 5 to 500nm, for example, 50nm to 500nm, 1 The layers have thicknesses such as 00nm~500nm, 150nm~500nm, 200nm~500nm, 250nm~500nm, 300nm~500nm, 350nm~500nm, 400nm~500nm, or 450nm~500nm, while the metallic iron absorber layer has thicknesses greater than 0nm and less than or equal to 50nm, for example, 1nm~40nm, 2nm~30nm, 3nm~20nm, 4nm~20nm, 5nm~20nm, 10nm~20nm, 15nm~20nm, 5nm~15nm, 10nm~15nm, or 5nm~10nm.

[0046] According to an embodiment, and also referring to Figure 2B, the five-layer thin film structure may include an aluminum reflector 210; a high refractive index layer 220 containing iron oxide (Fe2O3) enclosing the reflector 210; and a metallic iron absorber layer 230 enclosing the high refractive index layer 220 containing iron oxide (Fe2O3). By changing the thickness of the high refractive index layer 220, and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic waves in the visible spectrum.

[0047] The aluminum reflector has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. The iron oxide (Fe2O3) high refractive index layer has a thickness of 5 to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, or 15 nm to 20 nm.

[0048] According to an embodiment, and also referring to Figure 2B, the five-layer thin film structure may include: an aluminum reflector 210; a high refractive index layer 220 containing TiO2 (rutile phase or anatase phase) enclosing the reflector 210; and a metallic iron absorber layer 230 enclosing the high refractive index layer 220 containing TiO2 (rutile phase and anatase phase). By changing the thickness of the high refractive index layer 220, and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic waves in the visible spectrum.

[0049] The aluminum reflector has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. The TiO2 (rutile phase or anatase phase) high refractive index layer has a thickness of 5 to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, 15 nm to 20 nm, 5 nm to 15 nm, 10 nm to 15 nm, or 5 nm to 10 nm.

[0050] According to an embodiment, and also referring to Figure 2B, the five-layer thin film structure may include an aluminum reflector 210; a high refractive index layer 220 containing ZnS enclosing the reflector 210; and a metallic iron absorber layer 230 enclosing the high refractive index layer 220 containing ZnS. By changing the thickness of the high refractive index layer 220 and thereby changing the position of the metallic iron absorber layer, the five-layer thin film structure can reflect various electromagnetic waves in the visible spectrum.

[0051] The aluminum reflector has a thickness of 10 nm to 400 nm, for example, 10 nm to 375 nm, 10 nm to 350 nm, 10 nm to 325 nm, 10 nm to 300 nm, 10 nm to 275 nm, 10 nm to 250 nm, 10 nm to 225 nm, 10 nm to 200 nm, 10 nm to 175 nm, 10 nm to 150 nm, 10 nm to 125 nm, 10 nm to 100 nm, 10 nm to 75 nm, 10 nm to 50 nm, or 10 nm to 25 nm. The ZnS high refractive index layer has a thickness of 5 to 500 nm, for example, 50 nm to 500 nm, 100 nm to 500 nm, 150 nm to 500 nm, 200 nm to 500 nm, 250 nm to 500 nm, 300 nm to 500 nm, 350 nm to 500 nm, 400 nm to 500 nm, or 450 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm, for example, 1 nm to 40 nm, 2 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, or 15 nm to 20 nm.

[0052] The hue is tan -1 (a * / b * ) can be defined as the positive a of a given data point. * It can also be referred to as an angle with respect to an axis. The hue value provides a scale of the color (e.g., red, green, blue, yellow, etc.) exhibited by an object. Embodiments of the five-layer thin film described herein have hues from 0° to 120°, e.g., 0° to 100°, 0° to 80°, 0° to 60°, 0° to 40°, or 0° to 20°. In embodiments, the hue shift is less than 30° in the Lab color space, e.g., less than 25°, less than 20°, less than 15°, or less than 10° when observed at an angle of 0° to 45°.

[0053] According to embodiments, the five-layer thin film structures disclosed and described herein can be used in paints, polymers, or coatings. In embodiments, the multilayer thin film structures described herein may be incorporated into a liquid carrier, such as an organic or inorganic binder, or used in a paint or similar coating system, and the application of the paint or similar coating system to a product imparts the omnidirectional reflective properties of the five-layer thin film structure to that product. In some embodiments, the five-layer thin film structures may be dispersed in a polymer matrix so that they are randomly oriented within the polymer matrix. Subsequently, the paint, coating, or polymer containing the five-layer thin film structure may be deposited on a product by spraying, electrostatic charging, powder coating, etc. The deposited paint can then impart the reflectivity and shimmer of a metallic component, or the omnidirectional reflective properties of the five-layer thin film structure, to the article to which it is applied.

[0054] According to the embodiment, at least one of a paint binder and a filler can be used, and at least one of the paint binder and filler can be mixed with a pigment to provide a paint exhibiting omnidirectional structural color. Furthermore, other additives can be added to the five-layer thin film to improve its compatibility in the paint system. An example of a compatibility-improving additive is a silane surface treatment agent that coats the outside of the five-layer thin film and improves its compatibility in the paint system.

[0055] Note that the terms “substantially” and “about” may be used in this disclosure to describe the degree of inherent uncertainty that may arise from any quantitative comparison, value, measurement, or other representation. These terms may also be used in this disclosure to describe the extent to which a quantitative representation may differ from the stated criteria without altering the fundamental function of the subject matter in question. [Examples]

[0056] The embodiments will be further clarified by the following examples.

[0057] To demonstrate the effectiveness of a five-layer thin-film structure with a metallic iron absorber layer, one three-layer thin-film structure without the metallic iron absorber layer (comparative sample) was formed, and four five-layer thin-film structures with the metallic iron absorber layer (samples 1-4) were fabricated. The three-layer thin-film structure (comparative sample) contained an aluminum reflector encapsulated in a high-refractive-index iron oxide layer. This three-layer thin-film structure is commercially available from BASF Corporation.

[0058] To form four 5-layer thin-film structures (Samples 1-4) having a metallic iron absorber layer, the aforementioned 3-layer thin-film structures were exposed to a reducing agent, thereby forming a metallic iron layer on the outer surface of the iron oxide high refractive index layer. For each of the four 5-layer thin-film structures, the thickness of the metallic iron absorber layer was increased. The thickness of the metallic iron absorber layer was measured as a percentage of the iron oxide high refractive index layer. Therefore, if the thickness of the iron oxide high refractive index layer is 100 nm and the thickness of the metallic iron absorber layer is measured as 5%, the metallic iron absorber layer has a thickness of 5 nm. Table 1 below shows the thickness of the metallic iron absorber layer.

[0059] [Table 1]

[0060] Figures 4A-4E show the colors of the comparative sample and the structures of samples 1-4, respectively. Figures 4A-4E show that the red color of the structure can be adjusted by adjusting the thickness of the metallic iron absorber layer. Samples 3 and 4 (with metallic iron absorber layer thicknesses of 8% and 10%, respectively) have a dark, unattractive color. However, sample 2, with a metallic iron absorber layer thickness of 4%, has an attractive red color.

[0061] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Accordingly, this specification is intended to cover various modifications and variations to the embodiments described herein, provided that such modifications and variations fall within the scope of the appended claims and equivalents thereof. Some embodiments of the present invention are shown below. [Embodiment 1] Reflector and A high refractive index layer on or enclosing the reflector, A metallic iron absorber layer on or enclosing the high refractive index layer, A 5-layer thin film structure including this. [Embodiment 2] The five-layer thin-film structure according to Embodiment 1, wherein the reflector contains aluminum. [Embodiment 3] The five-layer thin-film structure according to Embodiment 1, wherein the reflector has a thickness of 10 nm to 5000 nm. [Embodiment 4] The five-layer thin-film structure according to Embodiment 1, wherein the high refractive index layer comprises iron oxide, zinc sulfide, or titanium dioxide. [Embodiment 5] The five-layer thin-film structure according to Embodiment 1, wherein the high refractive index layer has a thickness of 5 nm to 500 nm. [Embodiment 6] The five-layer thin-film structure according to Embodiment 1, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. [Embodiment 7] The five-layer thin-film structure according to Embodiment 1, wherein the metallic iron absorber layer has a thickness of 5 nm to 20 nm. [Embodiment 8] The five-layer thin-film structure according to Embodiment 1, wherein the reflector is aluminum and the high refractive index layer is zinc sulfide. [Embodiment 9] The five-layer thin-film structure according to Embodiment 8, wherein the reflector has a thickness of 10 nm to 5000 nm. [Embodiment 10] The five-layer thin-film structure according to Embodiment 8, wherein the high refractive index layer has a thickness of 5 nm to 500 nm. [Embodiment 11] The five-layer thin-film structure according to Embodiment 8, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. [Embodiment 12] The five-layer thin-film structure according to Embodiment 1, wherein the reflector is aluminum and the high refractive index layer is titanium dioxide. [Embodiment 13] The five-layer thin-film structure according to Embodiment 1, wherein the reflector has a thickness of 10 nm to 5000 nm. [Embodiment 14] The five-layer thin-film structure according to Embodiment 12, wherein the high refractive index layer has a thickness of 5 nm to 500 nm. [Embodiment 15] The five-layer thin-film structure according to Embodiment 12, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. [Embodiment 16] Aluminum reflector, A high refractive index iron oxide layer on or enclosing the aluminum reflector, A metallic iron absorber layer on or enclosing the iron oxide high refractive index layer, A 5-layer thin film structure including this. [Embodiment 17] The five-layer thin-film structure according to Embodiment 16, wherein the aluminum reflector has a thickness of 10 nm to 5000 nm. [Embodiment 18] The five-layer thin-film structure according to Embodiment 16, wherein the iron oxide high refractive index layer has a thickness of 5 nm to 500 nm. [Embodiment 19] The five-layer thin-film structure according to Embodiment 16, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. [Embodiment 20] The aluminum reflector has a thickness of 10 nm to 5000 nm. The iron oxide high refractive index layer has a thickness of 5 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. A five-layer thin-film structure as described in Embodiment 16.

Claims

1. Reflector and A high refractive index layer containing the aforementioned reflector, A metallic iron absorber layer containing the aforementioned high refractive index layer, Includes, The high refractive index layer comprises iron oxide, zinc sulfide, or titanium dioxide. 5 layer thin film structure.

2. The five-layer thin film structure according to claim 1, wherein the reflector contains aluminum.

3. The five-layer thin film structure according to claim 1, wherein the reflector has a thickness of 10 nm to 5000 nm.

4. The five-layer thin-film structure according to claim 1, wherein the high refractive index layer has a thickness of 5 nm to 500 nm.

5. The five-layer thin film structure according to claim 1, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

6. The five-layer thin film structure according to claim 1, wherein the metallic iron absorber layer has a thickness of 5 nm to 20 nm.

7. The five-layer thin-film structure according to claim 1, wherein the reflector is aluminum and the high refractive index layer is zinc sulfide.

8. The five-layer thin film structure according to claim 7, wherein the reflector has a thickness of 10 nm to 5000 nm.

9. The five-layer thin film structure according to claim 7, wherein the high refractive index layer has a thickness of 5 nm to 500 nm.

10. The five-layer thin film structure according to claim 7, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

11. The five-layer thin-film structure according to claim 1, wherein the reflector is aluminum and the high refractive index layer is titanium dioxide.

12. The five-layer thin film structure according to claim 1, wherein the reflector has a thickness of 10 nm to 5000 nm.

13. The five-layer thin film structure according to claim 11, wherein the high refractive index layer has a thickness of 5 nm to 500 nm.

14. The five-layer thin film structure according to claim 11, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

15. Aluminum reflector, The iron oxide high refractive index layer enclosing the aforementioned aluminum reflector, The iron metal absorber layer containing the aforementioned iron oxide high refractive index layer, A five-layer thin film structure including this.

16. The five-layer thin-film structure according to claim 15, wherein the aluminum reflector has a thickness of 10 nm to 5000 nm.

17. The five-layer thin-film structure according to claim 15, wherein the iron oxide high refractive index layer has a thickness of 5 nm to 500 nm.

18. The five-layer thin film structure according to claim 15, wherein the metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm.

19. The aluminum reflector has a thickness of 10 nm to 5000 nm. The iron oxide high refractive index layer has a thickness of 5 nm to 500 nm. The metallic iron absorber layer has a thickness of more than 0 nm and less than or equal to 50 nm. The five-layer thin film structure according to claim 15.

20. The five-layer thin film structure according to any one of claims 1 to 19, wherein the five-layer thin film structure has a hue shift of less than 30° in the Lab color space when observed at an angle of 0° to 45°.

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