Composite materials and methods for making and using them

Abstract

This specification discloses composite materials and methods of making and using them. The composite material can include a porous periodic nanolattice layer having a first refractive index and a continuous layer having a second refractive index disposed on the porous periodic nanolattice layer, wherein the first refractive index and the second refractive index are different, the porous periodic nanolattice layer includes a plurality of pores defined by a nanolattice formed of hollow members, and the plurality of pores are periodic. Also disclosed herein is a method of making a composite material, the method including forming a patterned layer, depositing a first material on the patterned layer to thereby form a coated patterned layer, depositing a buffer material layer on the coated patterned layer to thereby form a planarized layer, depositing a continuous layer on the planarized layer, and removing the buffer material layer and the patterned layer to thereby form the composite material.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 347,195, filed May 31, 2022, the entire contents of which are incorporated herein by reference.

[0002] Statement Regarding Government Support This invention was made with government support under Grant No. CMMI1552424 awarded by the National Science Foundation. The government has certain rights in this invention.

Background Art

[0003] The advent of nanofabrication has opened up great opportunities for the acoustic, photonics, and electronics industries, enabling mass production with better properties than bulk materials and exhibiting unexpected effects due to scaling laws. The presence of periodic nanostructures can further amplify the effects due to their regular shapes.

[0004] Photonic crystals have a periodic dielectric profile and can block the propagation of light with a specific wavelength in a specific polarization direction within the crystal.

[0005] Currently, there are no multilayer photonic crystals with high / low refractive index mismatches. Furthermore, there is a lack of integration of solid layers within multilayer 3D stacked structures. The compositions, devices, methods, and systems contemplated herein address these and other needs.

Summary of the Invention

[0006] In accordance with the objects of the disclosed compositions, devices, methods, and systems, as embodied and broadly described herein, the disclosed subject matter relates to composite materials, and methods of making and using the same.

[0007] For example, this specification describes a composite material including a porous periodic nanolattice layer and a continuous layer, where the continuous layer is disposed on the porous periodic nanolattice layer. The porous periodic nanolattice layer has a first refractive index, the continuous layer has a second refractive index, and the first refractive index is different from the second refractive index. The porous periodic nanolattice layer includes a plurality of pores defined by a nanolattice formed of hollow members, and the plurality of pores are periodic (e.g., arranged in a regular array).

[0008] In some examples, the first refractive index is from 1 to 1.35. In some examples, the second refractive index is from 1 to 4. In some examples, the difference between the first refractive index and the second refractive index is 0.5 or more, 1 or more, or 2 or more.

[0009] In some examples, the porous periodic nanolattice layer has a porosity of 90% or more or 95% or more. In some examples, the plurality of pores have an average pore diameter of 10 nanometers (nm) to 1 micrometer (μm). In some examples, the plurality of pores have a periodicity of 1 nanometer (nm) to 1 micrometer (μm).

[0010] In some examples, the hollow member includes a wall that defines an internal void space. In some examples, the wall includes a dielectric material, a metal, or a combination thereof. In some examples, the wall includes a metal oxide. In some examples, the wall includes Al2O3, ZnO, SiO2, TiO2, or a combination thereof. In some examples, the wall includes Al2O3. In some examples, the wall has an average thickness of 1 nanometer (nm) to 250 nm. In some examples, the wall has an average thickness of 1 nm to 100 nm, 5 nm to 75 nm, or 10 nm to 50 nm. In some examples, the wall further includes a first dopant.

[0011] In some examples, the porous periodic nanolattice layer has an average thickness of 1 nanometer (nm) to 1 micrometer (μm). In some examples, the porous periodic nanolattice layer has sufficient mechanical rigidity to support the continuous layer.

[0012] In some examples, the continuous layer includes a dielectric material, a metal, or a combination thereof. In some examples, the continuous layer includes a metal oxide. In some examples, the continuous layer includes TiO2, Al2O3, ZnO, or a combination thereof. In some examples, the continuous layer has an average thickness of 1 nanometer (nm) to 1 micrometer (μm). In some examples, the continuous layer has an average thickness of 10 nm to 500 nm, 50 nm to 250 nm, or 50 nm to 100 nm. In some examples, the continuous layer further includes a second dopant. In some examples, the continuous layer has sufficient mechanical rigidity to support a porous periodic nanolattice layer.

[0013] In some examples, the composite material further includes a substrate, and the porous periodic nanolattice layer is disposed on the substrate such that the porous periodic nanolattice layer is sandwiched between the substrate and the continuous layer.

[0014] In some examples, the composite material further includes a substrate, and the continuous layer is disposed on the substrate such that the continuous layer is sandwiched between the substrate and the porous periodic nanolattice layer.

[0015] In some examples, the composite material further includes one or more additional layers disposed on the porous periodic nanolattice layer such that the porous periodic nanolattice layer is sandwiched between the continuous layer and the one or more additional layers.

[0016] In some examples, the composite material further includes one or more additional layers disposed on the continuous layer such that the continuous layer is sandwiched between the porous periodic nanolattice layer and the one or more additional layers.

[0017] In some examples, the continuous layer and / or the porous periodic nanolattice layer independently have sufficient mechanical rigidity to support one or more additional layers.

[0018] In some examples, each of the one or more additional layers comprises a material having a refractive index, and the refractive index of a given layer is different from the refractive index of the preceding and / or subsequent layers. In some examples, each of the one or more additional layers independently has an average thickness of from 1 nanometer (nm) to 1 micrometer (μm).

[0019] In some examples, the composite material comprises a laminate including a plurality of alternating layers of a porous periodic nanogrid layer and a continuous layer.

[0020] In some examples, the composite material has a total number of layers from 2 to 100. In some examples, the total number of layers is 2 or more. In some examples, the total number of layers is 4 or more, 6 or more, or 8 or more.

[0021] In some examples, the composite material includes a Bragg reflector. In some examples, the composite material includes a one-dimensional photonic crystal.

[0022] In some examples, the composite material reflects one or more wavelengths of the solar spectrum with a reflectivity of 80% or more. In some examples, the composite material has an average specular reflectivity of 80% or more over at least a portion of the solar spectrum. In some examples, the composite material has a reflectivity peak, and the full width at half maximum (FWHM) of the reflectivity peak is 300 nm or more.

[0023] In some examples, the composite material is a low-k dielectric. In some examples, the composite material has a low thermal conductivity, a low refractive index, a low stiffness, or a combination thereof.

[0024] Also disclosed herein is a method of making any of the composite materials disclosed herein.

[0025] Also disclosed herein is a method of making a composite material, the method comprising: (a) forming a patterned layer; (b) depositing a first material on the patterned layer, thereby forming a coated patterned layer; (c) depositing a buffer material layer on the coated patterned layer, thereby forming a planarized layer; (d) depositing a continuous layer on the planarized layer; and (e) removing the buffer material layer and the patterned layer, thereby forming a composite material, the composite material comprising a porous periodic nanolattice layer and a continuous layer, the continuous layer being disposed on the porous periodic nanolattice layer, the porous periodic nanolattice layer having a first refractive index, the continuous layer having a second refractive index, the first refractive index and the second refractive index being different, the porous periodic nanolattice layer comprising a plurality of pores defined by a nanolattice formed of hollow members, the plurality of pores being periodic (e.g., arranged in a regular array).

[0026] In some examples, the method further comprises repeating steps (a)-(d) one or more times before performing removal step (e).

[0027] In some examples, the method further comprises depositing one or more additional layers before performing removal step (e).

[0028] In some examples, a composite material made by the method disclosed herein comprises any of the composite materials disclosed herein.

[0029] In some examples, forming the patterned layer includes 3D nanolithography, nanosphere lithography, phase-shift lithography, holographic lithography, additive manufacturing processes, imprint processes, self-assembly processes, or combinations thereof. In some examples, forming the patterned layer includes nanosphere lithography, near-field phase-shift lithography, or combinations thereof.

[0030] In some examples, forming the patterned layer includes depositing a photoresist layer, forming a monolayer of nanospheres on the photoresist layer, irradiating the monolayer of nanospheres with light configured to pattern the photoresist layer, and removing the nanospheres. In some examples, the photoresist layer is deposited using spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, or combinations thereof. In some examples, the photoresist layer is deposited on a substrate. In some examples, the substrate further includes an anti-reflection layer, and the method includes depositing the photoresist layer on the anti-reflection layer. In some examples, the nanospheres include a polymer, a dielectric material, a metal oxide, a metal, or combinations thereof. In some examples, the nanospheres have an average diameter of 1 nm to 1 μm. In some examples, the nanospheres have an average diameter of 100 nm to 1 μm, 100 nm to 750 nm, or 300 nm to 500 nm. In some examples, the monolayer of nanospheres is formed via self-assembly, Langmuir-Blodgett deposition, dip coating, spin coating, solvent evaporation, forced assembly methods, air-water interface methods, blade coating, or combinations thereof. In some examples, the light includes UV light.

[0031] In some examples, the first material is deposited using electroplating, lithographic deposition, electron beam deposition, thermal deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, the first material is deposited using atomic layer deposition (ALD).

[0032] In some examples, the buffer material layer is deposited using spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, or combinations thereof.

[0033] In some examples, the continuous layer is deposited using electroplating, lithographic deposition, electron beam deposition, thermal deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, the continuous layer is deposited using atomic layer deposition (ALD).

[0034] In some examples, the removal process includes a thermal cycle, plasma etching, wet etching, solvent removal, or combinations thereof.

[0035] Also disclosed herein are methods of using any of the composite materials disclosed herein and / or any of the composite materials made by any of the methods disclosed herein. In some examples, the method includes using the composite material in an optical device, an electronic device, or an optoelectronic device. In some examples, the method includes using the composite material in a photonic application, an electronic application, a thermal application, or combinations thereof. In some examples, the method includes using the composite material as a photonic crystal, as a dielectric mirror, for thermal insulation, for selective reflection, or combinations thereof. In some examples, the method includes using the composite material as a Bragg reflector, an electrical insulator, a thermal insulator, or combinations thereof. In some examples, the method includes using the composite material in a mechanical device, an energy dissipation device, an energy storage device, a spring system, or combinations thereof. In some examples, the method includes using the composite material in a filter device.

[0036] Also disclosed herein are manufactured articles and / or devices that include any of the composite materials disclosed herein and / or any of the composite materials made by any of the methods disclosed herein. In some examples, the article and / or device includes an optical device, an electronic device, or an optoelectronic device. In some examples, the article and / or device includes a photonic crystal, a dielectric mirror, a Bragg reflector, or a combination thereof. In some examples, the article and / or device includes a mechanical device, an energy dissipation device, an energy storage device, a spring system, or a combination thereof. In some examples, the article and / or device includes a filter device.

[0037] Additional advantages of the disclosed compositions, devices, systems, and methods will be described in part in the following description and will in part be apparent from the description. The advantages of the disclosed compositions, devices, systems, and methods will be realized and achieved by the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed compositions, devices, systems, and methods as claimed.

[0038] Details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will become apparent from the description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate some aspects of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0040]

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DETAILED DESCRIPTION OF THE INVENTION

[0041] The compositions, devices, methods, and systems described herein can be more readily understood by reference to the following detailed description of specific embodiments of the disclosed subject matter and the examples contained therein.

[0042] Prior to the disclosure and description of the present compositions, devices, methods, and systems, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents and can, of course, vary. It should also be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0043] Also, throughout this specification, various publications are referenced. For the purpose of more fully describing the state of the art to which the disclosed matter pertains, the disclosures of these publications are hereby incorporated by reference in their entirety into this application. The disclosed references are also individually and specifically incorporated by reference herein for the materials contained therein, which are discussed in the context in which the reference is relied upon.

[0044] In this specification and the appended claims, reference is made to several terms that are defined to have the following meanings.

[0045] Throughout the description of this specification and the claims, the term "comprise", "comprising", and other forms of this term such as "comprises" are not limiting, but are not intended to exclude, for example, other additional elements, components, integers, or steps.

[0046] As used in the specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise. Thus, for example, reference to "a composition" includes mixtures of two or more such compositions, reference to "an agent" includes mixtures of two or more such agents, reference to "a component" includes mixtures of two or more such components, and the like.

[0047] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and the description includes instances where the event or circumstance occurs and instances where it does not.

[0048] In this specification, a range can be expressed from one particular value using "about" and / or to another particular value using "about". "About" means within 5% of the value, for example, within 4%, 3%, 2%, or 1% of the value. When such a range is expressed, another embodiment includes from one particular value and / or to another particular value. Similarly, when a value is expressed as an approximation by use of the preceding "about", it will be understood that the particular value otherwise makes a difference. It will be further understood that each of the endpoints of the range is significant whether related to the other endpoint or independent of the other endpoint.

[0049] "Exemplary" means "an example of" and is not intended to convey an indication of a preferred or ideal embodiment. "Such as" is used for illustrative purposes and not in a limiting sense.

[0050] Values can be expressed herein as "average" values. "Average" generally refers to a statistical average value.

[0051] "Substantially" means within 5% of, for example, within 4%, 3%, 2%, or 1% of.

[0052] Throughout this specification, it should be understood that the identifiers "first" and "second" are used solely to aid in distinguishing various components and steps of the disclosed subject matter. The identifiers "first" and "second" are not intended to imply any particular order, quantity, preference, or importance to the components or steps modified by these terms.

[0053] As used herein, the term "plurality" means two or more (e.g., three or more, four or more, five or more, ten or more, fifteen or more, twenty or more, twenty-five or more, thirty or more, forty or more, fifty or more, seventy-five or more, one hundred or more, one hundred and fifty or more, two hundred or more, two hundred and fifty or more, three hundred or more, four hundred or more, five hundred or more, seven hundred and fifty or more, one thousand or more, one thousand five hundred or more, two thousand or more, two thousand five hundred or more, three thousand or more, four thousand or more, or five thousand or more).

[0054] As used herein, the term "or combinations thereof" refers to all replacements and combinations of the listed items preceding that term. For example, "A, B, C, or combinations thereof" is intended to include at least one of the following: A, B, C, AB, AC, BC, or ABC, and also, where order is important in a particular situation, BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, combinations including repetitions of one or more items or terms such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, etc. are explicitly included. Unless otherwise apparent from the context, one of ordinary skill in the art will understand that typically there is no limit to the number of items or terms in any combination.

[0055] As used herein, "phase" generally refers to a region of material having a substantially uniform composition that physically separates portions of a clearly different and heterogeneous system. The term "phase" does not mean that the material constituting the phase is a chemically pure substance, but only that the chemical and / or physical properties of the material constituting the phase are essentially uniform throughout the material and that these chemical and / or physical properties are significantly different from the chemical and / or physical properties of another phase within the material. Examples of physical properties include density, thickness, aspect ratio, specific surface area, porosity, and dimensionality. Examples of chemical properties include chemical composition.

[0056] "Continuous" means a phase in which all points within the phase are directly connected, so that for any two points within the continuous phase, there exists a path connecting the two points without leaving the phase.

[0057] "Hollow" means the case where two void phases are completely separated by three continuous phases that prevent any direct contact between the two void phases.

[0058] A "bicontinuous" material contains two distinct continuous phases where each phase is continuous and the two phases mutually penetrate. It is impossible to separate the two structures without tearing one of them.

[0059] Composite material Disclosed herein is a composite material comprising a porous periodic nanolattice layer and a continuous layer, the continuous layer being disposed (fabricated thereon or grown thereon) on the porous periodic nanolattice layer, the porous periodic nanolattice layer having a first refractive index, the continuous layer having a second refractive index, and the first refractive index and the second refractive index being different.

[0060] For example, the first refractive index can be 1 or more (e.g., 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, 1.05 or more, 1.06 or more, 1.07 or more, 1.08 or more, 1.09 or more, 1.10 or more, 1.11 or more, 1.12 or more, 1.13 or more, 1.14 or more, 1.15 or more, 1.16 or more, 1.17 or more, 1.18 or more, 1.19 or more, 1.20 or more, 1.21 or more, 1.22 or more, 1.23 or more, 1.24 or more, 1.25 or more, 1.26 or more, 1.27 or more, 1.28 or more, 1.29 or more, 1.3 or more, 1.31 or more, 1.32 or more, 1.33 or more, 1.34 or more, 1.35 or more, 1.36 or more, 1.37 or more, 1.38 or more, or 1.39 or more). In some examples, the first refractive index can be 1.4 or less (e.g., 1.39 or less, 1.38 or less, 1.37 or less, 1.36 or less, 1.35 or less, 1.34 or less, 1.33 or less, 1.32 or less, 1.31 or less, 1.30 or less, 1.29 or less, 1.28 or less, 1.27 or less, 1.26 or less, 1.25 or less, 1.24 or less, 1.23 or less, 1.22 or less, 1.21 or less, 1.20 or less, 1.19 or less, 1.18 or less, 1.17 or less, 1.16 or less, 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, 1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, 1.05 or less, 1.04 or less, 1.03 or less, or 1.02 or less). The first refractive index can be in the range from any of the above minimum values to any of the above maximum values. For example, the first refractive index can be 1 to 1.35 (e.g., 1 to 1.2, 1.2 to 1.4, 1 to 1.1, 1.1 to 1.2, 1.2 to 1.3, 1.3 to 1.4, 1 to 1.05, 1.05 to 1.10, 1.10 to 1.15, 1.15 to 1.20, 1.20 to 1.25, 1.25 to 1.30, 1.30 to 1.35, 1.35 to 1.4, 1 to 1.35, 1 to 1.30, 1 to 1.25, 1 to 1.2, 1 to 1.15, 1.02 to 1.4, 1.03 to 1.4, 1.04 to 1.4, 1.05 to 1.4, 1.06 to 1.4, 1.07 to 1.4, 1.08 to 1.4, 1.09 to 1.4, 1.10 to 1.4, 1.15 to 1.4, 1.02 to 1.35, 1.02 to 1.3, 1.02 to 1.2, or 1.02 to 1.1).

[0061] In some examples, the second refractive index can be 1 or more (e.g., 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, 1.05 or more, 1.06 or more, 1.07 or more, 1.08 or more, 1.09 or more, 1.10 or more, 1.11 or more, 1.12 or more, 1.13 or more, 1.14 or more, 1.15 or more, 1.16 or more, 1.17 or more, 1.18 or more, 1.19 or more, 1.20 or more, 1.21 or more, 1.22 or more, 1.23 or more, 1.24 or more, 1.25 or more, 1.26 or more, 1.27 or more, 1.28 or more, 1.29 or more, 1.3 or more, 1.31 or more, 1.32 or more, 1.33 or more, 1.34 or more, 1.35 or more, 1.36 or more, 1.37 or more, 1.38 or more, 1.39 or more, 1.4 or more, 1.45 or more, 1.5 or more, 1.55 or more, 1.6 or more, 1.65 or more, 1.7 or more, 1.75 or more, 1.8 or more, 1.85 or more, 1.9 or more, 1.95 or more, 2 or more, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, 2.5 or more, 2.75 or more, 3 or more, 3.25 or more, 3.5 or more, or 3.75 or more). In some examples, the second refractive index can be 4 or less (e.g., 3.75 or less, 3.5 or less, 3.25 or less, 3 or less, 2.75 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2 or less, 1.95 or less, 1.9 or less, 1.85 or less, 1.8 or less, 1.75 or less, 1.7 or less, 1.65 or less, 1.6 or less, 1.55 or less, 1.5 or less, 1.45 or less, 1.4 or less, 1.39 or less, 1.38 or less, 1.37 or less, 1.36 or less, 1.35 or less, 1.34 or less, 1.33 or less, 1.32 or less, 1.31 or less, 1.30 or less, 1.29 or less, 1.28 or less, 1.27 or less, 1.26 or less, 1.25 or less, 1.24 or less, 1.23 or less, 1.22 or less, 1.21 or less, 1.20 or less, 1.19 or less, 1.18 or less, 1.17 or less, 1.16 or less, 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, 1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, 1.05 or less, 1.04 or less, 1.03 or less, or 1.02 or less). The second refractive index can be in the range from any of the above minimum values to any of the above maximum values.For example, the first refractive index can be 1 to 4 (e.g., 1 to 2.5, 2.5 to 4, 1 to 2, 2 to 3, 3 to 4, 1 to 3.5, 1 to 3, 1 to 2.5, 1 to 2, 1 to 1.9, 1 to 1.8, 1 to 1.7, 1 to 1.6, 1 to 1.5, 1 to 1.4, 1.01 to 4, 1.02 to 4, 1.03 to 4, 1.04 to 4, 1.05 to 4, 1.1 to 4, 1.2 to 4, 1.3 to 4, 1.4 to 4, 1.5 to 4, 1.75 to 4, 1.01 to 3.75, 1.02 to 3.5, 1.03 to 3, 1.04 to 2.75, 1.05 to 2, or 1.01 to 1.4).

[0062] In some examples, the difference between the first refractive index and the second refractive index can be 0.5 or more (e.g., 0.75 or more, 1 or more, 1.25 or more, 1.5 or more, 1.75 or more, 2 or more, 2.5 or more, or 3 or more).

[0063] The porous periodic nanolattice layer includes a plurality of pores defined by a nanolattice formed of a hollow member, and the plurality of pores are periodic (e.g., arranged in a regular array).

[0064] In some examples, the plurality of holes may have a periodicity of 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, the plurality of holes may have a periodicity of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, or 2 nm or less). The periodicity of the plurality of holes can be in the range from any of the above minimum values to any of the above maximum values.For example, the plurality of pores may have a periodicity of 1 nanometer (nm) to 1 micrometer (μm) (for example, 1 nm to 500 nm, 500 nm to 1000 nm, 1 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 1 nm to 900 nm, 1 nm to 800 nm, 1 nm to 700 nm, 1 nm to 600 nm, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 100 nm, 5 nm to 1000 nm, 10 nm to 1000 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 5 nm to 950 nm, or 10 nm to 900 nm).

[0065] The plurality of pores may have any shape, for example, a polyhedron (for example, a regular polyhedron, a prism, a pyramid), a cylinder, a semi-cylinder, an elliptical cylinder, a semi-elliptical cylinder, a cone, a semi-cone, etc.

[0066] The plurality of pores may have an average pore diameter. As used herein, "pore diameter" refers to the maximum cross-sectional dimension of the pore in a plane perpendicular to the longitudinal axis of the pore. For example, in the case of a substantially cylindrical pore, the pore diameter is the diameter of the pore. In some examples, the average pore diameter may be substantially the same throughout the thickness of the layer. In some examples, the average pore diameter may vary depending on the thickness of the layer (for example, a tapered or conical pore). The average pore diameter can be determined, for example, using electron microscopy (for example, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM)), Brunauer-Emmett-Teller (BET) measurement, porosity measurement, or a combination thereof.

[0067] For example, the plurality of pores may have an average pore diameter of 10 nanometers (nm) or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, the plurality of pores may have an average pore diameter of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average pore diameter of the plurality of pores can range from any of the above minimum values to any of the above maximum values.For example, the plurality of pores may have an average pore diameter of 10 nanometers (nm) to 1 micrometer (μm) (e.g., 10 nm to 500 nm, 500 nm to 1000 nm, 10 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 10 nm to 900 nm, 10 nm to 800 nm, 10 nm to 700 nm, 10 nm to 600 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 100 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 15 nm to 950 nm, or 20 nm to 900 nm).

[0068] In some examples, the plurality of pores may be substantially monodisperse. As used herein, "monodisperse" and "uniform size distribution" generally refer to a population of pores in which all pores are the same or approximately the same size. As used herein, a monodisperse distribution refers to a pore distribution in which 80% (e.g., 85%, 90%, or 95% of the distribution) is within 25% of the median pore diameter (e.g., within 20% of the median pore diameter, within 15% of the median pore diameter, within 10% of the median pore diameter, or within 5% of the median pore diameter).

[0069] The hollow member may include, for example, a wall that defines an internal void space. The wall of the hollow member can form a continuous phase in some examples. In some examples, the porous periodic nanolattice layer includes two continuous void phases that are completely separated by a third continuous phase (e.g., the wall of the hollow member) that prevents any direct contact between the two continuous void phases.

[0070] The wall of the hollow member can have an average thickness of, for example, 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, or 225 nm or more). In some examples, the wall of the hollow member can have an average thickness of 250 nm or less (e.g., 240 nm or less, 230 nm or less, 220 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, or 2 nm or less). The average thickness of the wall of the hollow member can be in the range from any of the above minimum values to any of the above maximum values. For example, the wall of the hollow member can have an average thickness of 1 nanometer (nm) to 250 nm (e.g., 1 nm to 125 nm, 125 nm to 250 nm, 1 nm to 50 nm, 50 nm to 100 nm, 100 nm to 150 nm, 150 nm to 200 nm, 200 nm to 250 nm, 1 nm to 225 nm, 1 nm to 200 nm, 1 nm to 175 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 75 nm, 5 nm to 250 nm, 10 nm to 250 nm, 15 nm to 250 nm, 20 nm to 250 nm, 25 nm to 250 nm, 30 nm to 250 nm, 40 nm to 250 nm, 50 nm to 250 nm, 75 nm to 250 nm, 100 nm to 250 nm, 150 nm to 250 nm, 5 nm to 225 nm, 10 nm to 100 nm, or 10 nm to 50 nm).

[0071] In some examples, the hollow member is in the form of a flat wall. "In the form of a flat wall" means that the wall thickness is substantially uniform or monodisperse, and 80% (e.g., 85%, 90%, or 95% of the distribution) of the distribution is within 25% of the central wall thickness (e.g., within 20% of the central wall thickness, within 15% of the central wall thickness, within 10% of the central wall thickness, or within 5% of the central wall thickness).

[0072] The wall of the hollow member can include any suitable material. For example, the wall of the hollow member can include a dielectric material, a metal, or a combination thereof.

[0073] In some examples, the wall of the hollow member can include a metal chalcogenide (e.g., a compound containing a metal and a chalcogen), a metal halide (e.g., a compound containing a metal and a halogen), or a combination thereof. As used herein, "chalcogen" refers to any element from Group 16 such as oxygen, sulfur, selenium, tellurium, and polonium. Thus, metal chalcogenides can include, inter alia, metal oxides, metal sulfides, metal selenides, and metal tellurides. As used herein, "halide" or "halogen" or "halo" refers to fluorine, chlorine, bromine, and iodine.

[0074] In some examples, the wall of the hollow member can include a metal oxide. Examples of metal oxides include simple metal oxides (e.g., having a simple metal element) and mixed metal oxides (e.g., having different metal elements). In some examples, the wall of the hollow member can include Al2O3, ZnO, SiO2, TiO2, or a combination thereof. In some examples, the wall of the hollow member can include Al2O3.

[0075] In some examples, the wall of the hollow member may further include a dopant (e.g., a first dopant). The dopant may include any suitable dopant for the wall material. The dopant may be selected, for example, to adjust the optical, electronic, and / or thermal properties of the porous periodic nanolattice layer. In some examples, the concentration and / or identity of the dopant within the wall may vary, for example, by thickness and / or radially.

[0076] The porous periodic nanolattice layer may have, for example, a porosity of 90% or more (e.g., 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more). In some examples, the porosity of the porous periodic nanolattice layer may be selected in consideration of the desired refractive index of the layer (e.g., in consideration of the desired first refractive index).

[0077] In some examples, the porous periodic nanolattice layer has an average thickness of 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, the porous periodic nanolattice layer has an average thickness of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less). The average thickness of the porous periodic nanolattice layer can range from any of the above minimum values to any of the above maximum values.For example, the porous periodic nanolattice layer may have an average thickness of 1 nanometer (nm) to 1 micrometer (μm) (e.g., 1 nm to 500 nm, 500 nm to 1000 nm, 1 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 1 nm to 900 nm, 1 nm to 800 nm, 1 nm to 700 nm, 1 nm to 600 nm, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 100 nm, 5 nm to 1000 nm, 10 nm to 1000 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 5 nm to 950 nm, 10 nm to 900 nm, 100 nm to 500 nm, 100 nm to 250 nm, or 100 nm to 150 nm).

[0078] In some examples, the average thickness of the porous periodic nanolattice layer, the average thickness of the wall of the hollow member, the composition of the wall of the hollow member, the average pore diameter, the plurality of pore periodicities, the porosity of the porous periodic nanolattice layer, the presence of a dopant, the concentration of the dopant, the distribution of the dopant, or a combination thereof may be selected such that the porous periodic nanolattice layer has desired mechanical properties (e.g., mechanical rigidity), optical properties (e.g., refractive index), electrical properties, thermal properties, or a combination thereof.

[0079] The porous periodic nanolattice layer may have, for example, sufficient mechanical rigidity to support a continuous layer.

[0080] The continuous layer may include any suitable material. For example, the continuous layer may include a dielectric material, a metal, or a combination thereof.

[0081] In some examples, the continuous layer can include a metal chalcogenide (e.g., a compound containing a metal and a chalcogen), a metal halide (e.g., a compound containing a metal and a halogen), or a combination thereof. In some examples, the continuous layer can include a metal oxide. Examples of metal oxides include simple metal oxides (e.g., having a simple metal element) and mixed metal oxides (e.g., having different metal elements). In some examples, the continuous layer includes TiO2, Al2O3, ZnO, or a combination thereof.

[0082] In some examples, the continuous layer can further include a dopant (e.g., a second dopant). The dopant can include any suitable dopant for the continuous layer material. The dopant can be selected, for example, to adjust the optical, electronic, and / or thermal properties of the continuous layer. In some examples, the concentration and / or identity of the dopant within the continuous layer can vary, for example, by thickness and / or lateral dimension (e.g., concentration gradient by thickness).

[0083] The continuous layer may have an average thickness of, for example, 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, the continuous layer has an average thickness of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less). The average thickness of the continuous layer can range from any of the above minimum values to any of the above maximum values.For example, the continuous layer can have an average thickness of 1 nanometer (nm) to 1 micrometer (μm) (e.g., 1 nm to 500 nm, 500 nm to 1000 nm, 1 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 1 nm to 900 nm, 1 nm to 800 nm, 1 nm to 700 nm, 1 nm to 600 nm, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 100 nm, 5 nm to 1000 nm, 10 nm to 1000 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 5 nm to 950 nm, 10 nm to 900 nm, 10 nm to 500 nm, 50 nm to 250 nm, or 50 nm to 100 nm).

[0084] In some examples, the average thickness of the continuous layer, the composition of the continuous layer, the presence of the dopant, the concentration of the dopant, the distribution of the dopant, or combinations thereof can be selected such that the continuous layer has desired mechanical properties (e.g., mechanical rigidity), optical properties (e.g., refractive index), electrical properties, thermal properties, or combinations thereof.

[0085] The continuous layer can have, for example, sufficient mechanical rigidity to support a porous periodic nanolattice layer.

[0086] In some examples, the composite material can further include a substrate. In some examples, the porous periodic nanolattice layer is disposed on the substrate such that the porous periodic nanolattice layer is sandwiched between the substrate and the continuous layer. In some examples, the continuous layer is disposed on the substrate such that the continuous layer is sandwiched between the substrate and the porous periodic nanolattice layer.

[0087] The substrate may include a suitable material. For example, the substrate may include a dielectric, semiconductor, ceramic, transparent conductive oxide, polymer, metal, or a combination thereof. In some examples, the substrate may be permeable. As used herein, "permeable substrate" means any substrate that is permeable at the wavelength or wavelength region of interest. Examples of substrates include, but are not limited to, silicon, III-V semiconductors, glass, quartz, parylene, silicon dioxide, sapphire, mica, poly(methyl methacrylate), polyamide, polycarbonate, polyester, polypropylene, polytetrafluoroethylene, polydimethylsiloxane (PDMS), hafnium oxide, hafnium silicate, tantalum pentoxide, zirconium dioxide, zirconium silicate, and combinations thereof.

[0088] In some examples, the composite material may further include one or more additional layers. In some examples, one or more additional layers are disposed on the porous periodic nanolattice layer such that the porous periodic nanolattice layer is sandwiched between the continuous layer and the one or more additional layers. In some examples, one or more additional layers are disposed on the continuous layer such that the continuous layer is sandwiched between the porous periodic nanolattice layer and the one or more additional layers. In some examples, the continuous layer and / or the porous periodic nanolattice layer independently have sufficient mechanical rigidity to support one or more additional layers.

[0089] In some examples, each of the one or more additional layers includes a material having a refractive index, and the refractive index of a given layer is different from the refractive index of the preceding layer and / or the succeeding layer. Each of the one or more additional layers may independently include any suitable material, including, but not limited to, dielectric materials, semiconductors, ceramics, transparent conductive oxides, phase change materials, polymers, metals, and combinations thereof.

[0090] Each of the one or more additional layers independently has an average thickness of 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, each of the one or more additional layers independently can have an average thickness of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less). The average thickness of each of the one or more additional layers can independently range from any of the above minimum values to any of the above maximum values.For example, each of the one or more additional layers can independently have an average thickness of 1 nanometer (nm) to 1 micrometer (μm) (e.g., 1 nm to 500 nm, 500 nm to 1000 nm, 1 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 1 nm to 900 nm, 1 nm to 800 nm, 1 nm to 700 nm, 1 nm to 600 nm, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 100 nm, 5 nm to 1000 nm, 10 nm to 1000 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 5 nm to 950 nm, 10 nm to 900 nm, or 100 nm to 500 nm).

[0091] In some examples, here, the composite material includes a laminate including a plurality of alternating layers of a porous periodic nanolattice layer and a continuous layer.

[0092] The total number of layers in the composite material can be, for example, 2 or more (e.g., 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 45 or more, 50 or more, 55 or more, 60 or more, 65 or more, 70 or more, 75 or more, 80 or more, 85 or more, 90 or more, or 95 or more). In some examples, the total number of layers in the composite material can be 100 or less (e.g., 95 or less, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, or 3 or less). The total number of layers in the composite material can be in the range from any of the above minimum values to any of the above maximum values. For example, the total number of layers in the composite material can be 2 to 100 (e.g., 2 to 50, 50 to 100, 2 to 20, 20 to 40, 40 to 60, 60 to 80, 80 to 100, 2 to 95, 2 to 90, 2 to 80, 2 to 70, 2 to 60, 2 to 40, 2 to 10, 3 to 100, 4 to 100, 5 to 100, 6 to 100, 7 to 100, 8 to 100, 9 to 100, 10 to 100, 15 to 100, 20 to 100, 25 to 100, 30 to 100, 40 to 100, 60 to 100, 70 to 100, 3 to 95, 4 to 90, or 5 to 85).

[0093] In some examples, the composite material includes a Bragg reflector.

[0094] In some examples, the composite material includes a one-dimensional photonic crystal.

[0095] In some examples, the composite material reflects one or more wavelengths of the solar spectrum having a reflectivity of 80% or more (e.g., 85% or more, 90% or more, 95% or more, or 99% or more). In some examples, the composite material has an average normal reflectivity of 80% or more (e.g., 85% or more, 90% or more, 95% or more, or 99% or more) over at least a portion of the solar spectrum.

[0096] In some examples, the composite material has a reflectance peak, and the full width at half maximum (FWHM) of the reflectance peak is 300 nm or more (e.g., 325 nm or more, 350 nm or more, 375 nm or more, 400 nm or more, 425 nm or more, 450 nm or more, 475 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, or 750 nm or more).

[0097] In some examples, the composite material is a low-k dielectric.

[0098] In some examples, the composite material has a low thermal conductivity.

[0099] In some examples, the composite material has a low refractive index.

[0100] In some examples, the composite material has low rigidity.

[0101] Fabrication method Also disclosed herein is a method for fabricating any of the composite materials disclosed herein.

[0102] Also disclosed herein is a method of making a composite material, the method comprising: (a) forming a patterned layer; (b) depositing a first material on the patterned layer, thereby forming a coated patterned layer; (c) depositing a buffer material layer on the coated patterned layer, thereby forming a planarized layer; (d) depositing a continuous layer on the planarized layer; and (e) removing the buffer material layer and the patterned layer, thereby forming a composite material. The composite material can include, for example, a porous periodic nanolattice layer and a continuous layer, the continuous layer being disposed on the porous periodic nanolattice layer, the porous periodic nanolattice layer having a first refractive index, the continuous layer having a second refractive index, the first refractive index and the second refractive index being different, the porous periodic nanolattice layer including a plurality of pores defined by nanolattices formed of hollow members, the plurality of pores being periodic (e.g., arranged in a regular array). For example, the composite materials made by these methods can include any of the composite materials described herein.

[0103] In some examples, the method can further include repeating steps (a)-(d) one or more times before performing removal step (e).

[0104] In some examples, the method can further include depositing one or more additional layers before performing removal step (e).

[0105] Forming the patterned layer can include, for example, 3D nanolithography, nanosphere lithography, phase shift lithography, holographic lithography, additive manufacturing processes, imprint processes, self-assembly processes, or combinations thereof. In some examples, forming a patterned photoresist layer includes nanosphere lithography, proximity phase shift lithography, or combinations thereof.

[0106] In some examples, forming the patterned layer includes depositing a photoresist layer, forming a monolayer of nanospheres on the photoresist layer, irradiating the monolayer of nanospheres with light configured to pattern the photoresist layer, and removing the nanospheres.

[0107] The photoresist layer can be deposited using, for example, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, or combinations thereof. In some examples, the photoresist layer is deposited on a substrate. In some examples, the substrate further includes an anti-reflection layer, and the method includes depositing the photoresist layer on the anti-reflection layer.

[0108] The nanospheres can include any suitable material. For example, the nanospheres can include a polymer (e.g., polystyrene), a dielectric material (e.g., silica), a metal oxide, a metal, or combinations thereof.

[0109] In some examples, the nanospheres can have an average diameter of 1 nanometer (nm) or more (e.g., 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 275 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, or 950 nm or more). In some examples, the nanospheres can have an average diameter of 1 micrometer (μm) or less (e.g., 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 275 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, or 2 nm or less). The average diameter of the nanospheres can be in the range from any of the above minimum values to any of the above maximum values.For example, the nanospheres can have an average diameter of 1 nanometer (nm) to 1 micrometer (μm) (e.g., 1 nm to 500 nm, 500 nm to 1000 nm, 1 nm to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1000 nm, 1 nm to 900 nm, 1 nm to 800 nm, 1 nm to 700 nm, 1 nm to 600 nm, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 100 nm, 5 nm to 1000 nm, 10 nm to 1000 nm, 15 nm to 1000 nm, 20 nm to 1000 nm, 25 nm to 1000 nm, 30 nm to 1000 nm, 40 nm to 1000 nm, 50 nm to 1000 nm, 75 nm to 1000 nm, 100 nm to 1000 nm, 200 nm to 1000 nm, 300 nm to 1000 nm, 400 nm to 1000 nm, 600 nm to 1000 nm, 700 nm to 1000 nm, 5 nm to 950 nm, 10 nm to 900 nm, 100 nm to 1 μm, 100 nm to 750 nm, or 300 nm to 500 nm). In some examples, the nanospheres can be substantially monodisperse. The average diameter of the nanospheres can be selected, for example, to control the average pore diameter and / or periodicity of the plurality of pores of the porous periodic nanolattice layer.

[0110] A monolayer of nanospheres can be formed, for example, via self-assembly, Langmuir-Blodgett deposition, dip coating, spin coating, solvent evaporation, forced assembly methods, air-water interface methods, drop-casting, zone casting, blade coating, or combinations thereof.

[0111] In some examples, the monolayer of nanospheres is irradiated with UV light. In some examples, the monolayer of nanospheres is irradiated with a dose suitable for a photoresist.

[0112] The first material can be deposited using, for example, electroplating, lithographic deposition, electron beam deposition, thermal deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulse layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, the first material is deposited using atomic layer deposition (ALD).

[0113] The first material can include any suitable material. The first material forms the wall of the hollow member.

[0114] The buffer material layer can be deposited using, for example, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, or combinations thereof. The buffer material can include any suitable material such as a second photoresist material.

[0115] The continuous layer can be deposited using, for example, electroplating, lithographic deposition, electron beam deposition, thermal deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulse layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, the continuous layer is deposited using atomic layer deposition (ALD).

[0116] In some examples, the removal process includes a thermal cycle, plasma etching, wet etching, solvent removal, or combinations thereof. The removal process can be performed in a manner that minimizes or avoids, for example, the disintegration and / or deformation of the composite material.

[0117] Method of Use Also disclosed herein is a method of using any of the composite materials disclosed herein. For example, the method can include using the composite material in an optical device, an electronic device, or an optoelectronic device. In some examples, the method can include using the composite material in photonic applications, electronic applications, thermal applications, or combinations thereof. In some examples, the method includes using the composite material as a photonic crystal, as a dielectric mirror, for thermal insulation, for selective reflection, or combinations thereof. In some examples, the method includes using the composite material as a Bragg reflector, an electrical insulator, a thermal insulator, or combinations thereof. In some examples, the method includes using the composite material as a porous filter. In some examples, the method includes using the composite material as a mechanical damping system. In some examples, the method can include using the composite material in a mechanical device, an energy dissipation device, an energy storage device, a spring system, or combinations thereof. In some examples, the method can include using the composite material in a filter device.

[0118] Device Also disclosed herein are devices and / or articles of manufacture that include any of the composite materials disclosed herein. For example, the article and / or device can include an optical device, an electronic device, or an optoelectronic device. In some examples, the article and / or device includes a photonic crystal, a dielectric mirror, a Bragg reflector, or combinations thereof. In some examples, the article and / or device includes a porous filter. In some examples, the article and / or device includes a mechanical damping system.

[0119] In some examples, the article and / or device can include a mechanical device, an energy dissipation device, an energy storage device, a spring system, or combinations thereof. In some examples, the article and / or device can include a filter device.

[0120] Some embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the present invention. Accordingly, other embodiments are within the scope of the appended claims.

[0121] The following examples are intended to further illustrate specific aspects of the systems and methods described herein and are not intended to limit the scope of the claims.

Example

[0122] The following examples are described below to illustrate methods and results related to the disclosed subject matter. These examples are not intended to include all aspects of the subject matter disclosed herein, but rather are intended to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention that will be apparent to those skilled in the art.

[0123] Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.), but some errors and deviations should be taken into account. Unless otherwise specified, parts are parts by weight, temperature is in °C or ambient temperature, and pressure is atmospheric or near atmospheric. There are numerous variations and combinations for measurement conditions, such as component concentrations, temperature, pressure, and other measurement ranges, as well as conditions that can be used to optimize the described processes.

[0124] Example 1 - Nanolattice Dielectric Mirror with Selective Reflectivity Band Cooling strategies have been an important energy topic for decades. As global warming becomes increasingly apparent, active cooling methods consume a significant amount of energy and have become one of the largest electricity demands. The US Department of Energy estimates that nearly one-sixth of the primary energy consumed by buildings in the United States is used by air conditioning systems. As a result, highly reliable passive cooling techniques that can cool systems without energy consumption are attracting increasing attention.

[0125] Among various passive cooling methods, radiative cooling (which has the advantage of all-day cooling) has become one of the most popular topics in recent years (Raman et al. Nature, 2014, 515, 40 - 44; Lim, Nature, 2019, 577, 18 - 20; Pech-May et al. Nanoscale Adv. 2020, 2, 249 - 255). Radiative cooling technology maintains a device temperature below that of the ambient air by radiating heat into outer space through the Earth's atmospheric transmission window, which is generally between wavelengths of 8 - 13 μm. Since the device receives radiant heat from the sun during the day, the radiative cooler must also exhibit good reflectivity to the solar spectrum. Therefore, dielectric mirrors containing 1D photonic crystals are good candidates for radiative cooling because the dispersion behavior is a flexible basis for the bandgap design of the periodic stack of photonic crystals. In this specification, the design and optical property evaluation of dielectric mirrors for radiative cooling are considered.

[0126] Design of nanogrid photonic crystal reflectors. The radiation wavelength of an object at room temperature (293 K) is approximately 9.9 μm, which is within the atmospheric transmission window (8 - 13 μm), so passive cooling at night is spontaneous. This means that thermal energy can be radiated into outer space. However, the transfer of thermal energy from the environment increases in correspondence with the temperature difference between the device and the environment. Therefore, the cooling power of a passive cooler at night under steady-state conditions is given by (Raman et al. Nature, 2014, 515, 40 - 44): P c(T)=P rad (T)-P air rad (T amb )-P cond -P conv

[0127] Here, P rad (T) is the radiation from the device to outer space, and P air rad (T amb ) is the radiation from the ambient air to the device, and P cond and P conv are, respectively, heat conduction and heat convection from the environment.

[0128] However, since the passive cooler is exposed to solar radiation during the day, it obtains additional thermal energy from this solar radiation, and thus, the total cooling power is as follows: P c (T)=P rad (T)-P sun -P air rad (Tamb)-P cond -P conv

[0129] In the formula, P sun is the solar irradiance. In the case of blackbody radiation, P sun is much larger than P rad (T), and thus, passive cooling does not function for most materials during the day. However, if the cooler surface is highly reflective in the solar spectrum to overwhelm P sun , the solar radiation to the system can be significantly reduced.

[0130] Since the reflectivity of the dielectric mirror can be adjusted by using different material pairings for the alternating optical materials while maintaining a high emissivity in the infrared, the dielectric mirror is a good candidate for achieving a high reflectivity in the solar spectrum and a transmittance in the atmospheric transmission window. The bandwidth of the bandgap frequency of the 1D photonic crystal is proportional to the refractive index contrast between the alternating materials, which can be calculated as follows (Fink et al. Science 1998, 282, 1679 - 1682):

Number

[0131] Here, Δf is the bandwidth of the stop band, f0 is the center frequency of the band gap, and n1 and n2 are the refractive indices of the alternating materials, respectively. Since most of the solar irradiance is in the range of 250 nm to 2.5 μm, a plurality of dielectric mirrors having a range of periods are required to cover the entire spectrum.

[0132] In this specification, a nano-grid layer fabricated with a nanostructure having a period of 500 nm coated with 10 nm of Al2O3 (ALD thin film) (n ≈ 1.1), and a TiO2 film (n ≈ 2.3) fabricated by e-beam evaporation were adopted as the low-refractive-index and high-refractive-index materials, respectively. As a result, the calculated Δf / f0 of the nano-grid-TiO2 pair is approximately 0.46.

[0133] In this study, three reflectors with nanogrid / TiO2 pairs of various thicknesses are used, specifically having thickness pairs of 180 nm / 80 nm, 300 nm / 135 nm, and 500 nm / 220 nm. As shown in FIGS. 1-4, rigorous coupled-wave analysis (RCWA) was used to simulate the obtained reflection of dielectric mirrors with different numbers of repeating pairs of low / high refractive index materials. FIG. 1 demonstrates the reflectivity of the dielectric mirror in the range of 400 nm to 3.4 μm. Reflectors with five pairs of nanogrid / TiO2 repeating units having thicknesses of 180 / 80, 300 / 135, and 500 / 220 nm were simulated. Further, "combination laminate" reflectors each containing the 180 / 80, 300 / 135, and 500 / 220 nm nanogrid / TiO2 pairs (a total of one repeating unit) were also simulated. Mirrors with a single period (e.g., five pairs of nanogrid / TiO2 repeating units having thicknesses of 180 / 80, 300 / 135, and 500 / 220 nm) have center frequencies of 835, 1400, and 2315 nm, respectively, and bandwidths of 430, 740, and 1230 nm (FIG. 1). The reflectivity of the dielectric mirror in the wavelength range of 0 to a maximum of 13 μm is shown in FIG. 2. These results demonstrate that the sum of the emissivity and transmission of all reflectors is higher than 80% in the atmospheric transmission window. Note that the emissivity is the absorption rate at thermal equilibrium equal to 1 - R - T. FIGS. 3 and 4 show the results of mirrors with three pairs of repeating units. The comparison between FIGS. 1 and 3, and FIGS. 2 and 4 illustrates that as the number of repetitions of the low / high reflectivity materials decreases, the stop-band phenomenon also becomes less prominent. However, the results from mirrors with only three repeating units still satisfy the dispersion behavior required for the desired reflection / transmission intervals.

[0134] Fabrication of a nano-lattice photonic crystal reflector. The fabrication process for a nano-lattice photonic crystal dielectric mirror is illustrated in FIG. 5. As shown in panel (a) of FIG. 5, a nanostructure is first patterned using 3D phase lithography with colloidal particles. As demonstrated in panel (b) of FIG. 5, the nanostructure is adopted as a template for the ALD process to construct a conformal film on the surface of the nanostructure. Next, as shown in panel (c) of FIG. 5, a photoresist buffer layer coating process is applied to cover the underlying nano-lattice, thereby flattening the structure. Then, as shown in panel (d) of FIG. 5, a continuous TiO2 film is deposited by an electron beam evaporation process to construct a high refractive index layer within the dielectric mirror. As shown in panel (e) of FIG. 5, by repeating the processes shown in panels (a)-(d) of FIG. 5, a multi-layer of nano-lattice-TiO2 laminate can be fabricated. Then, as shown in panel (f) of FIG. 5, a thermal cycle or plasma etching process is used to remove the photoresist and buffer layer materials to form a low refractive index and self-supporting nano-lattice layer between the high refractive index TiO2 films, resulting in a high contrast photonic crystal dielectric mirror. The thickness of the low refractive index nano-lattice layer can be controlled by the thickness of the photoresist used for nanostructure patterning, and the thickness of the high refractive index TiO2 film can be controlled by the vapor deposition process. In this specification, reflectors with three different repetition periods were investigated and fabricated. Based on the rigorous coupled wave analysis simulation, dielectric reflectors with nano-lattice / TiO2 thickness ratios of 180 nm / 80 nm, 300 nm / 135 nm, and 500 nm / 220 nm were fabricated to construct a broadband reflector that can cover the solar spectrum.

[0135] The rigorous coupled wave analysis results shown in FIGS. 3 and 4 illustrate that a nano-lattice photonic crystal mirror with three pairs of repeating units can achieve an appropriate broadband reflectivity. As a result, dielectric mirrors with three pairs of 180 nm / 80 nm, 300 nm / 135 nm, and 500 nm / 220 nm nano-lattice / TiO2 alternating laminates were fabricated and their optical properties were characterized.

[0136] In these experiments, silicon wafers (100-mm single-side polished Si wafers, University Wafer) coated with a 100-nm thick antireflection coating (ARC i-con-16, Brewer Science) were used as substrates. Hexagonally close-packed 500-nm diameter polystyrene nanosphere self-assemblies were employed as periodic phase elements for the near-field phase-shift lithography process to pattern periodic nanostructures in a photoresist (PFi-88A2, Sumitomo). PGMEA (≥99.5% propylene glycol monomethyl ether acetate, Sigma Aldrich) was used to dilute the photoresist to reach the desired thickness. An 11.5-nm thick Al2O3 film was deposited on the nanostructures by a commercially available ALD system (ALD TM 200, Cambridge NanoTech Inc.). An additional layer of photoresist was spin-coated on the ALD-coated nanostructures, which served as a buffer layer. Subsequently, an e-beam evaporation process (PVD75 e-beam and sputtering system, Kurt J. Lesker) was applied to deposit a TiO2 layer with the corresponding thickness on the buffer layer. Lithography, ALD, planarization, and e-beam evaporation were repeated three times to form three alternating photonic crystal layers. As shown in FIGS. 6 to 8, the photoresist was removed by a thermal cycle up to 550 °C, resulting in an alternating low-high refractive index laminate.

[0137] The cross-sectional SEM images of FIGS. 6 to 8 show a pair of 180 / 80, 300 / 135, and 500 / 220 nm Al2O3 nanolattices / TiO2 laminates, respectively. In the case of the 180 / 80 nm pair, the thickness of the TiO2 layer was approximately 80 nm as the designed height, but the nanolattice thickness was only approximately 130 nm. The side walls of the nanolattice were slightly curved, and it was found that this could cause a 19.2% difference between the desired height and the actually fabricated height of the nanolattice layer in the 180 / 80 nm pair. The same phenomenon, but to a more severe extent, was also observed for the 300 / 135 nm and 500 / 220 nm pairs. The obtained heights of the nanolattice layers were approximately 167.0 and 249.1 nm, which represent height decreases of 30.6% and 34.8% of the repeating unit, respectively. The cross-sectional SEM images of FIGS. 7 and 8 also demonstrate the disintegration and deformation of the nanolattice layer under the solid TiO2 film.

[0138] As shown in FIGS. 9 to 14, the same situation was found for samples of two and three pairs of Al2O3 nanolattice / TiO2 repeating units having thicknesses of 180 / 80, 300 / 135, and 500 / 220 nm. Cross-sectional SEM images of the 180 / 80 nm samples with two and three repeating pairs show well-defined nanolattice structures (FIGS. 9 and 12). However, as shown in FIGS. 10, 11, 13, and 14, systematic deformation and collapse of the nanolattice structures were found in the 300 / 135 and 500 / 220 nm structures, resulting in considerably lower nanolattice heights in the samples. The decrease in nanolattice height was 19.1% and 34.4% for the two-pair samples, and the height decreases for the three-pair samples were 10.8% and 20.1%, respectively. The decrease in the repeating unit height for the 300 / 135 and 500 / 220 nanolattice photonic crystals was not consistent from one pair to three pairs. Furthermore, the reduction ratios of each nanolattice layer in the nanolattice photonic crystal were not uniform. The deformation of the nanolattice may be due to the photoresist removal process. During the thermal cycle, the resist changes from solid to liquid and gas phases, resulting in non-uniform surface tension acting on the nanolattice. The layered shape of the nanolattice photonic crystal also suppresses the outflow of the photoresist flow, thereby further degrading the nanolattice layer that causes shrinkage and collapse of the nanolattice layer. The nanolattice collapse problem can potentially be alleviated by employing a plasma etching process to remove the photoresist or increase the ALD film thickness of the nanolattice.

[0139] Characterization of the optical properties of a nanolattice photonic crystal reflector. The refractive indices of Al2O3 nanolattices and TiO2 layers with different thicknesses were investigated by ellipsometry. As shown in Fig. 15, since the nanolattices are highly porous, the refractive indices of the nanolattices with various thicknesses are close to 1.1. It should be noted that since the ALD thickness of the nanolattices is kept constant, the refractive index is fairly constant and independent of the film thickness. Slight refractive index variations in the UV at about 400 nm were observed due to material dispersion. The measured refractive indices of the TiO2 layers fabricated by the e-beam evaporation process are about 2.2 - 2.0, which results in a contrast between low- and high-reflectivity materials of about 1.0.

[0140] As shown in FIGS. 16 to 19, the normal reflectance of the 180 nm / 80 nm Al2O3 nanolattice / TiO2 reflector was characterized by 633 and 532 nm lasers. The TE-mode reflectance of the 532 nm laser over different incident angles is shown in FIG. 16. Here, the nanolattice photonic crystal having one to three low-high refractive index repetition times was characterized by the 532 nm laser having incident angles of 0° to 70°, shown by the solid line, and the corresponding rigorous coupled-wave analysis model is shown by the dashed line (FIG. 16). For the nanolattice photonic crystal having a pair of 180 / 80 nm Al2O3 / TiO2 laminates, the normal reflectance is 70.8% at normal incidence and 84.5% at 70°. The rigorous coupled-wave analysis simulation demonstrates the same tendency that the normal reflectance is 77.8% and 95.9% at 0° and 70°, respectively. In these simulations, as shown by the cross-sectional SEM image, the nanolattice / TiO2 layer thickness is adjusted to 125 nm / 80 nm. It can be observed that as the number of repeating pairs increases from one to three, the nanolattice photonic crystal reflector can achieve a higher reflectance. In the case of the reflector having two repeating pairs, the normal reflectance reaches 76.2% and 86.7% at incident angles of 0° and 70°, respectively. When the number of pairs increases to three, the normal reflectance can be as high as 84% and 87.2% at 0° and 70° incidence. However, this experimental result indicates that the improvement in reflectance as the number of pairs increases is not as much as predicted by the simulation. This may be due to defects in the laminate. The yield rate decreases exponentially as the manufacturing process increases, resulting in higher scattering losses. The mismatch in normal reflectance becomes worse under higher incident angles, which may be due to the projected area of the laser beam proportional to 1 / cosθ, meaning that higher angles are associated with more defects. As shown in FIG. 17, the same phenomenon can be found in the case of TM. The normal reflectance of the TE and TM modes at the 633 nm wavelength is shown in FIGS. 18 and 19. The measurement results also generally follow the tendency predicted by the simulation, but the efficiency is slightly lower. Note that the sharp drop in TM reflection is observed at high incident angles due to the Brewster angle effect.

[0141] As shown in FIGS. 20 to 23, the broadband normal reflectance from 400 to 1000 nm under normal incidence was measured by spectroscopic analysis (HR4PRO-UV-VIS-ES, OceanView) and spectrophotometry (Cary 000 UV-Vis-NIR, Agilent). An optical spectrometer was employed for the initial investigation. Two measurement systems were used to investigate the systematic error in the measurement system. The reflectance of a reflector having a pair of nano-gratings-TiO2 is shown in FIG. 20. The measurement results of both the optical spectrometer and the spectrophotometer were in fairly good agreement with the rigorous coupled-wave analysis simulation (FIG. 20). In the simulation, a maximum reflectance of 75.2% was predicted at 580 nm, and the optical spectrometer and the spectrophotometer obtained peak values of 73.1% and 75.9% at 502 nm and 538 nm, respectively (FIG. 20). There is a region of reflectance with significant noise in the spectrophotometer measurement in the range of 800 to 900 nm, which is due to the change of the diffraction grating and the detector in the system.

[0142] The calculated reflectance of a nano-grating reflector having two repeating pairs was over 80% in the range of 490 to 730 nm as shown in FIG. 21, and the calculated peak value was 92.1% at 80 nm by the rigorous coupled-wave analysis simulation. The experimental results conform to this trend, and the data from the optical spectrometer show that the reflectance reaches 80% at 440 to 650 nm and reaches a peak value of 93.3% at 477 nm (FIG. 21). The spectrophotometer measurement shows that the reflectance of the reflector is over 80% in the range of 458 to 690 nm and has a peak value of 89.9% at 525 nm (FIG. 21).

[0143] The measurements of the optical spectrometer and the spectrophotometer of a reflector having three repeating units showed reflectances over 80% in the ranges of 460 to 728 nm and 470 to 732 nm, respectively, and had peak values of 95.3% at 488 nm and 91.9% at 527 nm (FIG. 22). The corresponding simulation results predicted an 80 percent reflectance, the range was 490 to 750 nm, and had a peak value of 97.8% at 80 nm (FIG. 22).

[0144] The experimental results of reflectors with one pair, two pairs, and three pairs of repetitions indicate that the stop band of the periodic laminate is slightly shifted from the simulation. This could be due to defects or breakdown of the nanogrid, resulting in an average nanogrid height shorter than the value observed in the cross-sectional SEM image.

[0145] Figure 23 demonstrates the reflectivity of 180 / 80 nm dielectric mirrors with different numbers of repeating units across the entire solar spectrum. The stop band of the 180 / 80 nm dielectric mirror is located in the range of 500 - 750 nm and has a reflectivity outside the stop band range of less than 40%, which is similar to the reflectivity of the silicon surface.

[0146] As shown in FIGS. 24 to 25, the broadband reflectivity of a nanolattice photonic crystal reflector having 300 / 135 and 500 / 220 nm Al2O3 / TiO2 units was also characterized by a spectrophotometer. The experimental and simulated normal reflectivities of the 300 / 135 nm reflector from 250 to 2500 nm are shown in FIG. 24. In the simulation, as illustrated by the cross-sectional SEM image, the periodic unit thickness in the model is set to 220 / 135 nm because the nanolattice has a systematic breakdown. The broadband reflectivity measurements show that the reflectivity increases as the number of unit pairs increases. The observed bandgap positions satisfied the predictions from the rigorous coupled-wave analysis simulations, e.g., 800 to 1500 nm. However, the measured reflectivity of the reflector with three repeating pairs barely reaches 60%, which is much lower than the simulation results. The stopband of the reflector is based on the refractive index contrast of the alternating layers, and the breakdown of the nanolattice layer increases the effective refractive index of the nanolattice layer and thus worsens the results. As shown in FIG. 25, the same phenomenon can be found in the 500 / 220 nm reflector. The maximum reflectivity of the dielectric mirror with three pairs of repeating units is 64.7% at 1427 nm, however, the corresponding reflectivity from the simulation is 96.3%. As a result, by improving the structural stability of the nanolattice layer in the fabrication of dielectric mirrors, their experimental performance can be improved.

[0147] Problem. The nano-lattice / TiO2 photonic crystal reflector in this specification has demonstrated the feasibility of achieving high reflectivity in the solar spectrum, which is predicted in the rigorous coupled-wave analysis simulation. Using a nano-lattice layer with a 180 / 80 nm repeating unit, the proof-of-concept principle has been successfully demonstrated, which was in fairly good agreement with the prediction of numerical simulations. The high contrast between the nano-lattice and TiO2 also results in a wider bandgap with fewer repeating units. The proposed nano-lattice photonic crystal achieved a peak reflectivity of 91.9% with a FWHM of 347 nm using only three pairs of repeating units, which is in fairly good agreement with the rigorous coupled-wave analysis results (FWHM of 335 nm, 465 nm to 800 nm). At the same time, existing investigations using the oblique angle deposition (OAD) method to control the refractive index contrast require the use of two sets of five repeating pairs to reach a peak reflectivity of 95% with a FWHM of 320 nm (Leem et al. Opt. Express, OE 2014, 22, 1819-1826).

[0148] The experimental reflectance behavior of nanolattice photonic crystal reflectors with thicker nanolattice layers did not demonstrate the corresponding predicted optical properties. The main reason for this is that, as shown in FIGS. 26-27, these nanolattice layers are likely to collapse or deform during the photoresist removal process, resulting in inconsistencies in nanolattice thickness and volume fraction. In FIG. 26, it can be seen that the bottom layer of the nanolattice is dramatically deformed by systematic collapse, and thus the nanolattice thickness is significantly reduced. Since the stop band of the dielectric reflector scales with the refractive index that varies periodically along the thickness direction, as shown in FIGS. 24-25, the deformation of the nanolattice layer reduces the periodicity and further reduces the reflectance. This becomes a greater problem when the collapse is not uniform, resulting in aperiodic refractive index modulation, which in turn reduces the photonic crystal response. This problem can be solved by using thicker ALD layers for stronger nanolattice layers. Another issue with this approach is the defects in the reflector, which can be due to the particle assembly process. These defects lead to diffuse reflection and non-uniformity of the nanolattice layer. The problem of defects can be remedied by improving the lithography yield and optimizing the photoresist removal process.

[0149] Conclusion. Two applications of the nanolattice multilayer fabrication technique for photonics have been demonstrated herein. Using this process, a four-layer gradient refractive index (GRIN) antireflection structure was fabricated that reduces the normal reflectance by more than 90% at a wavelength of 633 nm and reflects less than 6% broadband from a silicon substrate. A multilayer nanolattice approach was also employed for the fabrication of all-dielectric photonic crystal reflectors with high refractive index contrast. The resulting reflectors had high reflectivity in the visible range and high transmissivity in the NIR spectrum. By combining multiple photonic crystal reflectors with different stop bands, reflectors with selective dispersion behavior can be achieved. The potential of the nanolattice multilayer stacking technology has been demonstrated in this study, which can be applied to optical multilayer films, radiation shielding, and radiative cooling.

[0150] Fabrication of a Multilayer Photonic Reflector Using a Periodic Nanolattice: Example 2 The advent of nanofabrication has opened up great opportunities for the acoustic, photonics, and electronics industries, enabling mass production with properties superior to those of bulk materials and exhibiting unexpected effects according to scaling laws (Jang et al. Adv. Funct. Mater. 2007, 17, 3027 - 3041; Jeon et al. PNAS, 2004, 101, 12428 - 12433). The presence of periodic nanostructures can further amplify the effects due to their regular shapes. At the macroscale, nanostructures provide an improved strength-to-weight ratio and result in enhanced stiffness for a given density. Regarding thermal properties, porous nanostructures can potentially reduce the thermal conductivity. Optically, the presence of porous nanostructures can reduce the effective refractive index, approaching that of air (Zhang et al. Adv. Funct. Materials, 2015, 25, 6644 - 6649). This enables the nanostructures to act as low-refractive-index media in Bragg reflectors or one-dimensional photonic crystals with multiple layers of high and low refractive indices, achieving perfect reflectivity over a wavelength band. The proposed investigation involves using a multilayer nanostructure fabricated by stacking a porous nanolattice and solid layers, which can result in a very effective dielectric mirror.

[0151] A schematic diagram of the sample fabrication for the nanolattice reflector is depicted in Fig. 28. In this study, the self-assembly of colloidal nanospheres with a diameter of 500 nm is achieved due to the tendency of the surface to maintain the lowest surface energy. The assembled spheres are used as a near-field phase-shift mask, and then the sample is irradiated with 90, 100, 110, and 120 mJ / cm 2It was subjected to UV lithography using a 325 nm laser with a dose of exposure (panel (b) of FIG. 28). The monolayer of nanospheres results in the formation of periodic 3D nanostructures such as those governed by the Talbot effect (Chang et al. Nano Lett. 2011, 11(6), 2533-2537). On this structure, atomic layer deposition (ALD) was used to deposit a conformal coating of Al2O3 to a thickness of 20 nm in the structure (panel (c) of FIG. 28). As a compromise between a tall structure with a strong but low aspect ratio and a high porosity but low strength, the layer height of the porous nanostructure was maintained at 120 nm. The conformal coating enables the photoresist to act as a sacrificial template for the nanogrid (Chen at al. Adv. Materials Interfaces, 2021, 17, 2170092). Subsequently, another layer of about 350 nm of PFI 88 resist was coated to planarize the nanogrid, and then 80 nm thick TiO2 was deposited using electron beam evaporation to create a solid layer (panel (d) of FIG. 28). A series of steps can be repeated with different exposure parameters and different materials to stack the 3D layers to the desired thickness. Finally, the structure was baked in an oven at 550 °C to remove the photoresist.

[0152] 100 mJ / cm 2 The cross-sectional SEM image of the sample with an exposure dose of is shown in FIG. 29. The cross-section of the layer is consistent for a dose of 100 mJ / cm higher than that used, indicating that the samples prepared using doses of 110 and 120 mJ / cm 2 were overexposed. Furthermore, the diameter of the exposed feature was 100 mJ / cm 2 2 ​It was larger at a higher dose. Information such as the depth, shape of the structure, and the filling rate of the periodic hexagonal close-packed arrangement can be investigated by the characteristic size taken from the SEM image. The result of laminating a solid film on top of the nanolattice is shown in Fig. 30. It was observed that the Al2O3 porous layer was 130 nm thick and the solid TiO2 film was 80 nm thick. The porous layer enables good thermal insulation, a low refractive index, and maintains mechanical strength, whereby the reflectivity can be improved as the number of layers increases. The aim of this research is to fabricate a three-layer nanostructure and characterize its optical properties. Furthermore, post-fabrication coating with aluminum (on top) improves the reflectivity of the sample. The structure has important applications in photonics for improving the reflectivity parameter.

[0153] Example 3 - Fabrication of a Multilayer Photonic Reflector Using a Periodic Nanolattice Applications of 3D nanostructures include, among others, heat transport and battery electrodes. The nanolattice exhibits high deformability, recoverability, and high rigidity. Heat transport occurs within the nanolattice composed of carbon and Al2O3 truss, resulting in thermal insulation. For example, nanorods can act as current collectors (e.g., Cu nanorods) and anodes (e.g., TiO2 nanorods) for microbatteries, thereby improving efficiency.

[0154] A photonic crystal has a periodic dielectric profile and can block the propagation of light with a specific wavelength in a specific polarization direction within the crystal.

[0155] An example of an application is a Bragg reflector having multiple layers of high and low refractive index materials. The thinner the nanolattice thickness, the more the contrast of the low / high refractive index pair can be increased. Low refractive index porous materials have porosity, low rigidity, and high scattering. An existing solid with a lower refractive index is CaF2, which has a refractive index of approximately 1.39. A large refractive index mismatch is essential for a Bragg reflector, and it is difficult to use conventional solid materials for fabricating photonic crystals with a high mismatch.

[0156] Using an array of nanospheres assembled as a layer element with a porosity of about 50%, a 3D periodic nanostructure can be fabricated (Chang et al. Nano Lett. 2011, 11(6), 2533 - 2537). This procedure eliminates the need for a physical mask and instead relies on self-assembly. The assembled spheres are used as a near-field phase-shifting mask and subjected to UV irradiation. A monolayer of nanospheres results in the formation of a periodic 3D nanostructure that is governed by the Talbot effect (e.g., an intensity pattern repeated with an axial period) (Chang et al. Nano Lett. 2011, 11(6), 2533 - 2537).

[0157] Atomic layer deposition (ALD) is a process for depositing thin films of different materials such as oxides and / or ceramics. A 3D thin-shell nanolattice can be formed by applying a conformal coating onto the above-described 3D periodic nanostructure using ALD. Subsequently, the photoresist can be removed to provide a hollow structure having a low refractive index, e.g., of about 1.025. Removal of the photoresist increases the porosity (void space) of the material to about 90%, which contributes to the low refractive index of the material, provides a better high / low refractive index contrast, and results in a higher reflectivity.

[0158] Currently, there are no multilayer photonic crystals having a high refractive index mismatch. Furthermore, there is a lack of integration of solid layers in multilayer 3D stacked structures and a lack of experimental results for depositing different shapes.

[0159] Disclosed herein is a process for integrating a multilayer nanolattice material having a high refractive index mismatch. For example, this multilayer nanolattice material can be used as a Bragg reflector. The reflectivity of these structures can be measured using spectrophotometry and compared with calculated values.

[0160] Multilayer 3D nanostructures are shown in FIGS. 5 and 28 and can be fabricated using procedures similar to those described above.

[0161] First, a PFI 88 positive resist (PR) (300 nm) and a 100 nm ARC coating are deposited to improve stability and reduce transmittance. Then, a monolayer of 300 nm diameter spheres is assembled thereon. Then, the assembled spheres are subjected to UV lithography using a dose of 110 mJ / cm 2 to form a periodic 3D nanostructure. On this structure, then, Al2O3 is deposited to a thickness of 20 nm (200 ALD cycles) using ALD. Then, a buffer layer resist layer is deposited for stability and planarization, and a buffer layer coating prevents disintegration and provides a stable base for subsequent processes. Then, a solid layer such as TiO2 (e.g., to a thickness of 80 nm) is deposited using, for example, PVD, ALD, etc. The period of the nanolattice photonic crystal is controlled by the thicknesses of the photoresist and TiO2 layers.

[0162] The monolayer of nanospheres self-assembles into a hexagonal close-packed structure based on low surface energy and capillary forces. As shown in FIGS. 31 and 32, shape defects and point defects can occur within the assembled nanosphere layer. Separation between the filling regions can lead to crack formation. Void formation is brought about by the presence of inclusions and high-energy regions.

[0163] Attempts were made to use porous nanostructures and single-layer inverse opal structures (schematically shown in FIG. 33) and multiple inverse opal laminates in the multilayer laminate. However, experimentally, these structures showed insufficient mechanical stability, and the overlap of the structures could cause refractive index deviations (FIGS. 34 - 38). As the number of inverse opal laminates increases, surface fluctuations increase (FIGS. 34 - 38). Polystyrene spheres after ultrasonic cleaning result in an inverse opal structure. By controlling the ultrasonic cleaning time, the structural stability is improved.

[0164] High thermal cycles and inclusions promote the formation of macro and micro cracks, and the inclusions initiate the formation of micro and nano cracks (Figs. 39 - 42). Clear thin layers of ARC and Al2O3 were observed (Figs. 43 - 44). Post - process baking removes all the resist and results in the deposition of Al2O3 on the ARC layer. Cracks occur only along the surface, and the inverse opal structures are not affected by high ramp rates.

[0165] A laminated nanolattice integrating a solid layer was formed from a structure with a 20 - nm - thick Al2O3 wall having a TiO2 film deposited on top of a porous layer. TiO2 deposition on the holes combined with the substrate causes the collapse of the porous layer (Figs. 45 - 47).

[0166] Photonic crystals were fabricated from nanolattices and TiO2 pairs having thicknesses of 180 nm and 80 nm, respectively. The broadband normal reflectivity of 180 / 80 - nm Al2O3 / TiO2 dielectric reflectors under normal incidence with one pair of repeating units, two pairs of repeating units, and three pairs of repeating units was experimentally measured and modeled using rigorous coupled - wave analysis (RCWA) (Fig. 48). The three - layer stack repeating unit showed a peak reflectivity of 91.9% at 527 nm with an FWHM of 347 nm (450 nm - 797 nm) (Fig. 48). Lower reflectivities were experimentally observed compared to the rigorous coupled - wave analysis model due to collective defects, structural collapse, film crack formation, etc. (Fig. 48).

[0167] In short, surface waves exist in multi - layer nanostructures with inverse opal - type structures and do not exist in multi - layer photonic crystals. The presence of the polystyrene layer helps in the fabrication of inverse opal - type structures with high refractive index mismatch and insufficient mechanical stability. Process parameters can be controlled to reduce surface waves and improve the mechanical properties of the inverse opal - type structures.

[0168] Fabrication of nanostructures by incorporating a solid high refractive index layer and a porous low refractive index layer provides the highest possible mismatch. The physical properties of the multilayer structure and their variations depending on the number of layers can be further investigated.

[0169] Example 4 - Multilayer Photonic Nanogrid Reflector Regarding existing Bragg reflector technology, two different types of dielectric materials are alternately laminated to fabricate a one-dimensional photonic crystal. However, when a solid flat dielectric layer is adopted, the minimum refractive index of the low refractive index layer is limited by the material properties of the dielectric material. The materials described herein adopt a nanogrid as the low refractive index layer capable of achieving a refractive index near 1, significantly increasing the refractive index contrast between the high refractive index material and the low refractive index material. The high contrast dielectric reflector results in a higher reflectivity and a wider bandwidth and can have fewer repeating units.

[0170] This specification describes a fabrication method for a high contrast nanogrid dielectric reflector by laminating a 3D nanogrid and a flat dielectric layer. This specification further describes a highly efficient broadband dielectric reflector having a low thermal conductivity and being lightweight. These dielectric reflectors result in a higher reflectivity and a wider bandwidth but have fewer repeating units. The materials can also be thermally insulating and lightweight.

[0171] Provided herein is a dielectric reflector prepared by alternately laminating a nanogrid and a dielectric layer. The periodic optical properties of the multilayer reflector can reach a high reflectivity for a specific wavelength band. The reflectivity of the reflector can be controlled by the thickness and refractive index of the nanogrid and the dielectric layer. This approach is based on the concept of a Bragg reflector including high and low refractive index films. Since the nanogrid layer can reach a refractive index near 1, the reflectivity and bandwidth of the materials described herein can be much higher than those of dielectric reflectors made of other alternating dielectric materials. The nanogrid reflector can be patterned using 3D nanolithography, phase-shift lithography, holographic lithography, or other additive manufacturing processes. Next, a thin shell of an oxide layer is deposited on the nanostructure by atomic layer deposition (ALD) to protect the underlying structure. Then, a layer of buffer material is coated on the ALD-protected nanostructure. The flat upper surface of the buffer material is used to deposit a flat layer of a high refractive index dielectric material. Optionally, after repeating these processes, the photoresist nanostructure and the buffer material can be removed by dry etching or a thermal cycle. The ALD oxide shell and the dielectric material remain, and thus, an alternating lamination of the nanogrid and the flat dielectric material can be performed.

[0172] Regarding the existing technology, two different types of dielectric materials are alternately laminated to fabricate a one-dimensional photonic crystal. However, when a solid flat dielectric layer is employed, the minimum refractive index of the low refractive index layer is limited by the material properties of the dielectric material (generally, about 1.39). The materials described herein employ a nanogrid as the low refractive index layer, whereby a refractive index near 1 can be achieved, and thus, the refractive index contrast of the layer is significantly increased. Therefore, the materials herein overcome the limitations of the refractive index contrast of the alternating lamination caused by available naturally occurring materials. The high contrast dielectric reflector results in a higher reflectivity and a wider bandwidth and can have fewer repeating units.

[0173] Defects within the nanolattice can lead to scattering and thus may reduce the reflectivity of the dielectric reflector. This problem can be solved, for example, by fabricating a periodic 3D nanostructure having a conformal phase mask.

[0174] The reflectors described herein can also have a low thermal conductivity due to the high porosity of the nanolattice. Thereby, the nanolattice reflector can also function as a thermal insulation material.

[0175] The materials described herein can be used, for example, as photonic crystals, as dielectric mirrors, for thermal insulation, for selective reflection, or in combinations thereof.

[0176] Example 5 - Precise Control of the Optical Refractive Index in a Nanolattice Abstract. Recent developments in photonic devices, light irradiation fields, and AR / VR displays have arisen from competitive developments in the industry towards the emergence of new technologies for improving the user experience in the optical field. These advancements can be due to the rise of nanofotonics and metasurfaces that can be designed to manipulate light more efficiently. In these elements, performance conveniently increases and decreases in accordance with the refractive index contrast, making the use of low refractive index materials important. Herein, the precise control of the refractive index of a low refractive index nanolattice material is investigated using 3D lithography and atomic layer deposition (ALD). This approach employs light diffraction from an array of colloidal aggregates to create a photoresist template for ALD, enabling precise control of the nanolattice shape and its refractive index. The refractive index of the fabricated nanolattice is characterized using spectroscopic ellipsometry and is in good agreement with the effective medium theory. By controlling the unit cell shape by designing the exposure and thickness of the ALD process, the effective refractive index of the nanolattice film can be precisely controlled up to 3×10 -4 Precisely. The proposed technique broadens any opportunities in refractive index control and enables better performance in nanofotonic elements used in displays and other integrated devices.

[0177] Introduction. The advent of the ability to fabricate nanostructures has brought about a spectrum of possible developments in the fields of integrated devices, materials science, and optics (CL Haynes et al. J. Phys. Chem. B, 2001, 105(24), 5599 - 5611; Kaushik Pal et al. “Nanofabrication for Smart Nanosensor Applications, Chapter - 2,” Micro and Nano Technologies MNT, 2020; M Cavallini et al. Synth. Met, 2004, 146(3), 283 - 286). These include improvements in functional materials, nanostructured surfaces, high - resolution sensors, nanoscale catalysts, and more efficient optoelectronics. Specifically, the field of photonics is facing a rapid increase in the number of applications of nanofabrication by techniques such as electron beam, interference, and two - photon lithography for the fabrication of nanostructures. Bottom - up self - assembly techniques involving colloidal elements, block copolymers, and biomolecules have also led to new photonic structures. In optoelectronics, nanofabrication has contributed to 3D displays, flexible wearable devices, and improvements in high - resolution patterning on displays (J Li et al. J. Display Technol. 2005, 1(1), 51 - 61; FF Muhammad et al. J Mater Sci: Mater Electron, 2017, 28, 14777 - 14786; TW Kelly et al. Optica, 2021, 8(6), 916 - 920; T Ishigure et al. J. Light. Technol., 1997, 15(11), 2095 - 2100).

[0178] In photonics applications, the refractive index contrast of the materials used can be an important factor in device efficiency. Examples are those in Bragg reflectors and photonic crystals, which can be used to improve the color range of displays and act as wavelength-selective mirrors on 3D displays. They reflect specific wavelengths of light while transmitting other wavelengths, and the control of refractive index contrast is a parameter involved in the functionality of Bragg reflectors (C Marinelli et al. Appl. Phys. Lett., 2001, 79(25), 40 - 76; B S Kawasaki et al. Opt. Lett., 1978, 3(2), 66 - 68). Previous studies have shown that multilayer reflectors with alternating high and low refractive indices improve the efficiency of light reflection and transmission. In optoelectronics, higher light extraction efficiency in solid-state lighting can be achieved by incorporating low-refractive-index materials with LEDs / OLEDs (Xiangyu Fu et al. Adv. Mater., 2021, 33(9), 2006801). Achieving a high refractive index mismatch between the alternating layers of multilayer reflectors requires a better understanding of refractive index control by fabrication methods (Jing-Qi Wang et al. Optics Communications, 2023, 532, 129251; I T Chen et al. Adv. Mater. Interfaces, 2021, 8(17), 2100690; V A Premnath et al. J. Vac. Sci. Technol., 2022, 40(6), 062803).

[0179] Existing methods for fabricating low refractive index materials involve adjusting the effective refractive index by varying the size and density of latex particles in a silica solute, which results in the possibility of varying the porosity of the sol-gel film regardless of its thickness. The effective refractive index is affected by the change in the sol-gel mixture and the porous fraction measured by the volume fraction (F Guillemot et al. Chem. Mater. 2010, 22(9), 2822-2828). Furthermore, the researchers explored the possibility of using oblique angle deposition, or glancing angle deposition (GLAD), to demonstrate a SiO2 nanorod layer with a refractive index of approximately 1.08. Such materials can be implemented within a Bragg reflector as a low refractive index layer to increase the reflectivity (JQ Xi et al. Opt. Lett. 2006, 31(5), 601-603; EF Schubert et al. Phys. Status Solidi (b), 2007, 244(8), 3002-3008). However, these oblique deposition methods can achieve precise control of the refractive index. Another potential fabrication technique for improving the control of the refractive index is atomic layer deposition (ALD), which enables the deposition of thin layers of materials within the range of 1 angstrom due to the self-limiting chemical interactions between reactants (M. Lesleka et al. Angewandte Chemie, 2003, 42(45), 5548-5554; J Lu et al. Surf. Sci. Rep., 2016, 71(2), 410-472; JG Baker et al. Chem. Mater., 2020, 32(5), 1925-1936). Recent studies have achieved control of the refractive index by using alternating layers of Al2O3 and TiO2 grown by atomic layer deposition, which results in a slight change in the refractive index corresponding to the corresponding increase in the number of atomic layer deposition cycles, and only depicts the refractive index as a function of the number of growth cycles through this investigation.Recent investigations using ALD on sacrificial 3D polymer nanostructure templates have demonstrated low refractive index materials with refractive indices as low as about 1.025 (SI Zaitsu et al. Appl. Phys. Lett., 2002, 80(14), 2442 - 2444; DE Jung et al. ACS Appl. Nano Mater. 2023, 6(3), 2009 - 2019; XA Zhang et al. Adv. Funct. Mater., 2015, 25(42), 6644 - 6649). Existing research has demonstrated the fabrication of materials with refractive indices close to 1, but still, precisely controlling the refractive index at the sub - 1×10. -3 level is difficult.

[0180] The aim of this study is to demonstrate precise control of the refractive index in low - refractive - index nanolattice materials. This approach uses an array of nanospheres as a phase mask to create a 3D nanostructure, which then serves as a template for ALD to coat a conformal thin film on the surface of the structure. After removing the resist, the resulting nanolattice structure is highly porous and has a low refractive index. By controlling the unit cell shape of the 3D nanostructure template during lithography and the shell thickness during ALD, the refractive index of the nanolattice elements can be precisely controlled. Spectroscopic ellipsometry using the Cauchy isotropic model is used to measure the refractive index of the fabricated samples and investigate the influence of the nanolattice shape and ALD thickness. The fabricated shapes are modeled using the Maxwell - Garnett effective medium theory, which is in good agreement with the experimental data. Carefully monitoring and varying the number of ALD cycles to achieve a refractive index resolution within the range of less than 1×10 -3 The results demonstrate that the refractive index of the nanolattice can be precisely controlled and can find applications in nanophotonics, metasurfaces, and optoelectronic devices.

[0181] Experimental methodology. The proposed nanolattice film with a precisely controllable refractive index is illustrated in Fig. 49. The periodic structure includes tubular elements with thin shells, and this shape controls the porosity and effective refractive index of the film. In this study, the influence of the lattice unit cell, period, and shell thickness on the measured refractive index is investigated. A combination of colloidal lithography and ALD is used to fabricate the nanolattice. The silicon wafer is spin-coated with a 100 nm thick anti-reflection coating (Brewer Science i-con-7) to reduce the reflection attenuation, and subsequently spin-coated with a positive photoresist (Sumitomo PFI-88) with a thickness of 300 - 1000 nm. Polystyrene nanospheres (Polysciences) in an aqueous solution are diluted in ethanol and dispersed on the surface of water to form a hexagonal close-packed structure through a Langmuir - Blodgett assembly. Nanospheres with diameters of 750 nm, 500 nm, and 390 nm are used in the experiment. The colloidal assembly is transferred onto the silicon substrate with the photoresist and exposed using a 325 nm HeCd laser. Subsequently, the removal of the nanospheres and development using a developer (Microposit CD-26) are performed to obtain a 3D photoresist nanostructure. Finally, the sample is subjected to ALD to form a layer of Al2O3 with a normal thickness of 21 nm, and the photoresist is removed by post-exposure baking at 550 °C with a ramp rate of 1 °C / hour in a furnace. The sample is left at this high temperature for 2 hours and then cooled to room temperature at a rate of 5 °C / hour.

[0182] Cross-sectional SEM images of the fabricated samples are shown in Figs. 50 - 54, depicting the fabrication of the desired nanostructures on a large scale on the silicon substrate.

[0183] Theoretical modeling of the refractive index of nanolattices. A model of a nanolattice material based on the effective medium theory is created to predict the refractive index of the film. This model is useful for modeling these parameters to identify the refractive index values for a given set of structural constants. By performing reverse engineering on this model and calculating the refractive index that can be obtained, it becomes possible to fabricate low refractive index samples, which have a wide range of applications in the optical field and can generate various refractive indices for successive sets depending on specific parameters. The nanolattice sample includes a periodic arrangement of tubular elements, and the unit cell shape depends on the lithography conditions. The lattice can inherently be non-cubic and anisotropic, and the initial model is based on the Cauchy isotropic model. The refractive index value can increase as the thickness of the aluminum oxide shell increases, and as shown in Figure 56, this increase is promoted by the increase in the number of ALD cycles. In this study, nanolattice samples with different numbers of cycles of ALD layers from 215 to 225 cycles were investigated, corresponding to aluminum oxide thicknesses from 215 to 225 angstroms. The period of the structure can also have an impact since a larger period with a constant shell thickness results in higher porosity and lower refractive index. For convenience, all refractive index values are at a wavelength of 632 nm. Aluminum oxide has a refractive index of approximately 1.67 at 632 nm, and the other parts of the nanostructure are made of air with a refractive index of 1. Thus, the effective refractive index of the structure varies depending on the number of ALD cycles. The Maxwell-Garnett (MG) model is used to predict the effective refractive index n eff as given below,

Number

[0184] Results and Discussion. A plot showing the refractive index of the fabricated nanogrid and the effect of the number of ALD cycles on the effective isotropic refractive index, observed for various cycles of atomic layer deposition using a Cauchy model that tracks isotropic behavior, is shown in Fig. 56. In these results, all refractive index values obtained and compared were obtained at a wavelength of 632 nm. Tests of thickness (nm) and refractive index values were obtained using a spectroscopic ellipsometer with an angle of light incidence of 70 degrees and a wavelength varying between 400 nm and 1600 nm. The Cauchy model was adopted in ellipsometry for both the isotropic model and the anisotropic model used. While using the Cauchy model for isotropic behavior analysis, this model was placed on a thin layer of silicon dioxide to incorporate the changes caused by the oxidation of a bare poly-silicon wafer that essentially reacts to the oxide in its pure form. The sample was tested 10 times at different spots on the sample to confirm the confidence level and measurement error for the refractive index and thickness values. It was found that the standard deviation was 0.00377, which is well below the 5% error bar. Since each cycle of atomic layer deposition corresponds to the deposition of a 1 angstrom thickness of the layer, the samples used had aluminum oxide thickness values in the range of 215 angstroms (215 cycles) to 225 angstroms (225 cycles).

[0185] The isotropic model was examined using an ellipsometer, which showed no variation between the refractive index values in the X, Y, and Z directions. The refractive index values varied between 1.08303 and 1.09120 for a 10 angstrom difference, whereby a refractive index control of 0.000409 is achievable for a single cycle of atomic layer deposition corresponding to 1 angstrom of aluminum oxide.

[0186] The thickness value was desirably in the range of about 310 - 325 nm, whereas the measured value was within the range of 217 - 245 nm. This decrease in thickness can be explained by the decrease in height due to the collapse of the structure when heated in the oven, and these can be prevented by reducing the ramp-up rate of the temperature to prevent the structure from experiencing a sudden temperature increase (R Huang et al. Sci. Rep. 2014, 4, 7051). The ramp-up rate used for the current sample is about 1 °C per minute, leading to a heating time of about 8 hours and 45 minutes. Further reduction of the ramp-up rate resulted in a corresponding increase in the heating time to achieve a lamp high temperature of 550 °C. Similarly, the thickness of the silicon oxide surface below the Cauchy layer also varies between 0 nm and 10 nm, and these variations are due to the diverse oxide environments in which the sample is placed during storage and property evaluation. Another set of constants fitted to the curve to achieve the highest accuracy in refractive index prediction are the An, Bn, and Cn constants (Cauchy model constants). These constants were also not found to vary significantly during a small additional thickness of aluminum oxide by ALD, and the values for An, Bn, and Cn were in the ranges of 1.062, 0.009, and 0.0005, respectively. These constants determine the type of curve generated by the ellipsometer to fit the actual experimental data. From the information about the variation of the effective refractive index with respect to a given number of ALD cycles, it was observed that the gradient between the X-axis and the Y-axis gradually decreases as the number of cycles increases, indicating that the effect of the thickness of the aluminum oxide layer saturates after a certain thickness in the effective refractive index.

[0187] Verification of the isotropic behavior modeling. The results obtained from the previous experiment were verified by fabricating a new set of samples by varying the number of cycles for atomic layer deposition, and the corresponding variations in thickness, MSE values, and effective refractive index were also measured. The refractive index corresponding to the number of ALD cycles is plotted in FIG. 56 for different diameters of the nanospheres used in the near-field phase mask for comparison. Further, the variation of the refractive index corresponding to the incident light wavelength in ellipsometry is plotted in FIG. 55. The sample contains an 800 nm thick photoresist coating on the anti-reflection coating, thereby increasing the thickness of the sample. In addition to this, ALD was performed at a thickness of about 21 nm, and then the photoresist was removed from the sample. These processes were not varied because the sonication time and the resist removal process were sufficient to effectively remove the deposited nanospheres and resist, respectively.

[0188] The thickness values of the samples were found to have a maximum deviation of 9.58%, and the lowest measured value was for the 213-cycle sample in the case of 750 nm diameter sphere deposition. This thickness could be due to the collapse of the structures within the sample. Furthermore, the effect of structural collapse increases with the height of the photoresist, and taller resists produce thin-walled structures with high aspect ratios. Due to the effect of thermal expansion, the atoms within the nanostructures vibrate, thereby causing a change in the distance between the nanostructures. This change in distance can cause plastic deformation, which can lead to collapse. The aspect ratio of the sample increases when using smaller nanospheres for the lithography phase mask, leading to larger structural collapse. The MSE values were also found to be within an average range of 60 - 65, which could be due to defects in the arrangement of the nanostructures, sometimes due to noise from experimental data caused by the influence of multilayers and structures. The nanospheres may aggregate within the multilayers, resulting in the formation of two or more layers of this structure, which can cause a deviation in the detected polarization change by the ellipsometer. The structure also contains a very thin layer of native oxide silica formed just beneath the Cauchy layer, which also affects the degree of polarization of the high aspect ratio structure. Thus, as a common trend among samples with diameters of 750 nm, 500 nm, and 390 nm, the thickness values were found to deviate between 9.58 - 13.12%, and the MSE values varied between 43.7 - 77.2. Regarding the refractive index corresponding to the number of ALD layers, for 750 nm, 500 nm, and 390 nm nanospheres, there is an increase in the refractive index range between 1.0394, 1.06613, and 1.13022. This increase in refractive index due to the reduction in nanosphere size is due to the corresponding increase in the surface-to-volume ratio because more structures are formed within the same substrate size (H Chen et al. Langmuir, 2008, 24(10), 5233 - 5237). This leads to an increase in the surface energy of the material, which in turn changes the electronic structure of the photoresist, leading to a change in optical properties.Another reason for the increase in refractive index due to the reduction in nanosphere size is the quantum confinement effect, where the electronic properties of the material change at the nanoscale size. Similar to ALD in structures with a very high aspect ratio, when the material is confined to a very small scale, the electrons in the material are quantized, the energy levels are discrete, leading to an increase in the refractive index (JS Weiner, Appl. Phys. Lett., 1987, 50, 842 - 844). The formation of discrete energy levels increases the density of charges in the material, further leading to a stronger interaction between the electromagnetic field and the material, resulting in a higher shift in polarization and a corresponding high change in refractive index. Due to the quantization of energy levels and the corresponding increase in the interaction between the EM field and the ALD material, the refractive index values fluctuate up and down with a large error at very low wavelengths.

[0189] Finally, the reduction in the size of the nanospheres increases the packing density and dielectric constant of the medium. The measured refractive index of the nanolattice increases towards that of Al2O3, which is approximately 1.67 for a lattice period of 632 nm. The presence of two different materials such as aluminum oxide and air, and the ability to deposit aluminum oxide, facilitate the control of the refractive index up to 1×10 -4 It can also be observed that the increase in the thickness of the photoresist deposition does not affect the refractive index variation, as the 800 nm height structures for 500 nm particles have refractive indices of 1.06613, 1.06663, and 1.06813 for 210, 211, and 213 cycles of ALD respectively. This is close to a refractive index value of approximately 1.08 for 500 nm spheres used at a resist height of 300 nm. This effect may be due to the fact that the photoresist is a sacrificial template and is removed before the measurement of the effective refractive index. The lowest observed effective refractive index is for 750 nm diameter and 210 cycles, having a value of approximately 1.03904, and the highest refractive index is obtained at 221 cycles, enabling a refractive index control of 7.48×10 -4 Similarly, for a 500 nm near - field phase mask, 5×10 -4The refractive index control was achieved, and for a mask of 390 nm, about 9.28×10 -4 was achieved. Finally, it is noted that the analytical model can successfully predict the value of the effective refractive index using the relationship between the normalized refractive index and the volume fraction calculated from the input of the nanosphere diameter, and the photoresist height. Accurate prediction has a close relationship with the calculation of the desired volume fraction considering the material for deposition and the target refractive index, which can be achieved using the proposed series of processes involving UV lithography and atomic layer deposition processes. These design and prediction capabilities result in the fabrication of nanolattices having a desired effective refractive index on the order of 1×10 -4 The conclusion. In this specification, 3D nanocylinders arranged in hexagonal close packing and having a shell thickness of 21 nm to 22.2 nm are fabricated and characterized for optical constants such as refractive index. It is observed that an increase in the number of atomic layer deposition cycles results in an increase in the corresponding refractive index due to an increase in the density of the structure, and the effective dielectric constant shifts to a higher value with an increase in the amount of aluminum oxide deposition. A model is created to understand the trend using the Maxwell-Garnett equation, and calculations are performed to predict the refractive index of the 3D nanostructure using this model. Further, the verification of these predicted calculations is performed by fabricating samples having various photoresist thicknesses and varying the diameter of the nanostructure in comparison with the initial sample. There is no significant change observed by increasing the height of the photoresist on the nanostructure, whereas a significant trend in the refractive index value is observed with the corresponding change in the diameter of the nanospheres used for the near-field mask prior to lithography for these samples. This is due to an increase in the surface-to-volume ratio between the aluminum oxide of the nanostructure and the air phase. Finally, in this investigation, a good method is obtained for fabricating nanostructures having a refractive index difference of about 0.000409 for samples having a resist height of 300 nm and a cylinder diameter of about 500 nm. For samples having a resist height of 800 nm, the refractive index variation per cycle is 7.48×10- for a cylinder diameter of 750 nm

[0190] ​4 - For a diameter of 500 nm, it is 5×10 -4 - For a diameter of 390 nm, it is 9.28×10 -4 This was achieved. The accuracy in the fabrication and control of the refractive index opens up several possibilities for applications in photonic crystals, specifically in improving the efficiency of Bragg reflectors.

[0191] Example 6 - Ultra-Precise Refractive Index Control of Nanolattices This specification describes the ultra-precise control of the effective refractive index of nanolattices by depositing very thin layers by a process called atomic layer deposition. This concept has been demonstrated in prototypes, fabricating nanolattice samples with layers having a thickness of 210 - 221 using ALD. The variation in the effective refractive index is measured using a technique called spectroscopic ellipsometry and the refractive index variations are logged along with the corresponding changes in the number of ALD cycles. The standard deviation of the measured refractive index is verified by measuring at multiple locations on the sample and subsequently taking the root mean square of the measurements. This enables the sample to have a very small refractive index difference of about 0.0001. This fabrication technique involves using 3D colloidal lithography to define periodic nanostructures in a photoresist. This is followed by a lithography process (using a UV laser in this case) and subsequently development using a developer. Then, a nanolattice is created using an atomic layer deposition process that helps create a thin shell-like structure and then the structure is either placed in a vacuum furnace or dissolved using a solvent or subjected to oxygen plasma etching to remove the photoresist. Only the ALD oxide shell remains, revealing a nanolattice that is about 20 nm thick. These are measured using ellipsometry for best fit of parameters and the Cauchy model for isotropic / anisotropic behavior.

[0192] The ability to simultaneously achieve a low refractive index and precise refractive index control has not been demonstrated previously. The ability to precisely control the refractive index to about 0.0001 enables numerous applications in gradient refractive index optics, nanofotonics, and multilayer waveguides, and in improving transmission efficiency in photonic integrated circuits. This can enable advanced precise control of photonic bandgaps in nanostructures. Separately, the ability to control the refractive index also leads to the accurate development of optical sensors and functional Bragg reflectors. Overall, by enhancing the sensitivity of the lattice structure, this enables better performance of photonic integrated circuits.

[0193] The method described herein can precisely control the refractive index to about 0.0001. This method can also accurately predict the effective refractive index and fabricate a nanolattice for a desired refractive index. This method can also effectively control the optical properties (such as photonic bandgap, waveguide efficiency, etc.) of the nanolattice.

[0194] Using current technology, a low refractive index can be fabricated, but precise control of the refractive index to about 10 -4 has not been demonstrated previously. Separately, the MATLAB model opens up the possibility of accurately predicting the geometric and fabrication parameters for a desired refractive index.

[0195] Currently, samples are fabricated on small-scale wafers. This process can be extended using scalable nanosphere deposition methods such as roll-to-roll phase mask assembly devices.

[0196] Since this method can predict the resist thickness required for deposition and the size of the nanospheres used in the phase mask to accurately generate a specific refractive index to about 0.0001, the method described herein enables researchers to fabricate samples with a desired refractive index.

[0197] Example 7 - Ultra-Precise Refractive Index Control of Nanolattices This specification describes a method that can precisely control the refractive index to about 0.0001. Also described herein is a method that can accurately predict the effective refractive index and fabricate a nanogrid for a desired refractive index.

[0198] Other methods do not provide precise control of refractive indices as low as about 0.0001. Furthermore, the proposed technology is for periodic structures on a large scale, which makes this technology suitable for photonic integrated circuits.

[0199] Samples fabricated from the proposed method provide precise control such that light is manipulated through the structure. The grid can be controlled in terms of the height and radius of the cylindrical structure, which directly affects the change in the refractive index of the sample. As a result, parameters corresponding to the desired refractive index can be modeled and fabricated with ultra-high precision.

[0200] The relationship developed from this model results in predictions of the sample refractive index up to about 0.0001. Samples can be fabricated with ultra-high precision.

[0201] The results of the investigation enable refractive index control that is about 100 times better compared to existing methods that result in better efficiency for photonic manipulation. This opens up various applications in optoelectronics and in the fabrication of photonic crystals.

[0202] Applications and markets for this technology include, but are not limited to, photonic devices, semiconductor devices and devices, aerospace and defense applications such as those focused on stealth technology, and 3D display technology.

[0203] Other advantages, which are clear and specific to the present invention, will be apparent to those skilled in the art. It will be understood that certain features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. This is contemplated by the claims and is within their scope. It should be understood that all matters described or shown in the accompanying drawings are illustrative and not limiting in any sense, since many possible embodiments of the invention can be formed without departing from the scope of the invention.

[0204] The method of the appended claims is not limited in scope by the specific methods described herein, but is intended as an illustration of some aspects of the claims, and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative method steps specifically disclosed herein are specifically described, other combinations of method steps, even if not specifically recited, are intended to fall within the scope of the appended claims. Thus, while steps, elements, components, or combinations thereof may be explicitly recited herein or below, other combinations of steps, elements, components, or combinations thereof are included even if not explicitly described.

Claims

1. It is a composite material, Porous periodic nanolattice layer, Includes continuous layers, The continuous layer is disposed on the porous periodic nanolattice layer, The porous periodic nanolattice layer has a first refractive index, and the continuous layer has a second refractive index. The first refractive index and the second refractive index are different. The porous periodic nanolattice layer includes a plurality of pores defined by a nanolattice formed of a hollow member, and the plurality of pores are arranged in a regular arrangement so as to be periodic. The hollow member is a composite material including a wall that defines the internal void space.

2. The first refractive index is between 1 and 1.35; The second refractive index is 1 to 4; The difference between the first refractive index and the second refractive index is 0.5 or greater; or The composite material according to claim 1, which is a combination of these.

3. The composite material according to claim 1, wherein the porous periodic nanolattice layer has a porosity of 90% or more or 95% or more.

4. The composite material according to claim 1, wherein the plurality of pores have an average pore diameter of 10 nanometers (nm) to 1 micrometer (μm).

5. The composite material according to claim 1, wherein the plurality of pores have a periodicity of 1 nanometer (nm) to 1 micrometer (μm).

6. The composite material according to claim 1, wherein the wall contains a metal oxide.

7. The aforementioned wall is Al ２ O ３ ZnO, SiO ２ , TiO ２ The composite material according to claim 1, or a combination thereof.

8. The composite material according to claim 1, wherein the wall has an average thickness of 1 nanometer (nm) to 250 nm.

9. The porous periodic nanolattice layer has an average thickness of 1 nanometer (nm) to 1 micrometer (μm); The continuous layer has an average thickness of 1 nanometer (nm) to 1 micrometer (μm); or The composite material according to claim 1, which is a combination of these.

10. The porous periodic nanolattice layer has sufficient mechanical rigidity to support the continuous layer; The continuous layer has sufficient mechanical rigidity to support the porous periodic nanolattice layer; or The composite material according to claim 1, which is a combination of these.

11. The composite material according to claim 1, wherein the continuous layer contains a metal oxide.

12. The continuous layer is TiO ２ Al ２ O ３ The composite material according to claim 1, comprising ZnO, or a combination thereof.

13. Further including a substrate, The porous periodic nanolattice layer is disposed on the substrate such that it is sandwiched between the substrate and the continuous layer; or The composite material according to claim 1, wherein the continuous layer is disposed on the substrate such that the continuous layer is sandwiched between the substrate and the porous periodic nanolattice layer.

14. Further comprising one or more additional layers, The one or more additional layers are disposed on the porous periodic nanolattice layer such that the porous periodic nanolattice layer is sandwiched between the continuous layer and the one or more additional layers; or The one or more additional layers are disposed on the continuous layer such that the continuous layer is sandwiched between the porous periodic nanolattice layer and the one or more additional layers; and The composite material according to claim 1, wherein the continuous layer and / or the porous periodic nanolattice layer independently have sufficient mechanical rigidity to support the one or more additional layers.

15. The composite material according to claim 1, wherein the composite material comprises a laminate including a plurality of alternating layers of the porous periodic nanolattice layer and the continuous layer.

16. The composite material according to claim 1, wherein the composite material reflects one or more wavelengths of the solar spectrum with a reflectance of 80% or more.

17. The composite material according to claim 1, wherein the composite material has a reflectance peak, and the FWHM of the reflectance peak is 300 nm or more.

18. A method for producing a composite material according to any one of claims 1 to 17, wherein the method is: a. Forming a patterned layer, b. Depositing the first material onto the patterned layer, thereby forming a coated patterned layer, c. Depositing a buffer material layer onto the coated patterned layer, thereby forming a planar layer, d. Depositing a continuous layer on the planarized layer, e. A method comprising removing the buffer material layer and the patterned layer, thereby forming the composite material.

19. A method of using a composite material according to any one of claims 1 to 17, The method comprises using the composite material in optical devices, electronic devices, optoelectronic devices, photonic applications, electronic applications, thermal applications, mechanical devices, energy dissipation devices, energy storage devices, spring systems, filter devices, or combinations thereof.

20. A manufactured article and / or device comprising a composite material according to any one of claims 1 to 17, The articles and / or devices mentioned above include optical devices, electronic devices, optoelectronic devices, mechanical devices, energy dissipation devices, energy storage devices, spring systems, filter devices, or combinations thereof.

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