High-thermal-emissivity metamaterial

Abstract

The invention relates to a metamaterial comprising at least two components, including a first component that comprises, and preferably consists of, a dielectric oxide of at least one of the elements chosen from among Al, Ti, Ca, Mg, Ta, Hf and Zr; and a second component that comprises, and preferably consists of, a transparent electron-conductive oxide, the oxide being an oxide of at least one element chosen from among Zn, Sn, Ni, Ga, In and Cd, the conductive and dielectric oxides being inert with respect to one another at a temperature of 1000°C and at a pressure of 0.1 MPa, the components being present in the metamaterial in the form of a plurality of layers of the two components or of a wall consisting of one of the components on which a layer of the other component is deposited, the thickness of each layer or wall being less than 300 nanometers and the maximum distance between the two closest walls or layers of the same component being less than 300 nanometers.

Description

[0001]Description Title: METAMATERIAL WITH HIGH THERMAL EMISSIVITY Technical field The invention relates to a nanostructured material, preferably refractory, whose thermal emissivity is high and adjustable in the infrared range, in particular wavelengths less than or equal to 5000 nanometers, in particular in the range of 1 to 5 micrometers. The invention also relates to a method for manufacturing such a material and its use in order to improve the performance of: - thermal energy conversion installations, for example thermo-photovoltaic systems, in particular to reduce the energy of the radiation emitted outside the wavelength range effective for the cell; - installations emitting heat by radiation, in industrial processes for manufacturing materials, for example baking ovens or thermoforming devices,in order to reduce their energy consumption and / or in order to adjust the emissivity and in particular the spectral emission range according to the absorption spectral bands of the target material to be thermoformed or fired, for example to heat the material either on the surface or deeper depending on the semi-transparency bands of said material to be heated. - thermal barriers to maximize the heat re-emitted by radiation and thus limit the temperature rise at the thermal barrier / substrate interface; - heat exchangers or heating elements to maximize their efficiency. Prior art: Among the refractory materials with high thermal emissivity, rare earth oxides are known. US5668072A describes, for example, a material based on Cerium oxide. These materials have a high cost. In addition, their emission peak is fixed solely by the nature of the element. More recently,nanostructured composite materials or metamaterials have been proposed, in particular in the form of regular stacks of alternating layers of an electronically conductive material and a dielectric material or in the form of a two-component comprising electronically conductive wires of nanometric diameter embedded in a dielectric matrix. CA2833151 describes this concept of metamaterial which consists of a periodic structure capable of optimizing its optical properties at the atomic scale so as to control the emission spectrum. CA2833151 discloses in particular an embodiment in the form of a multilayer comprising an electronic conductor such as titanium nitride, tantalum (metal) or a transparent semiconducting oxide such as an aluminum and zinc oxide,more thermally stable than metals such as silver or gold. Titanium nitride can in particular be deposited by atomic layer in the form of a deposit below the nanometer. The nature of the dielectric material is however not specified. US2017085212A1 also proposed a selective thermal emitter comprising a material for a thermo-photovoltaic application in the form of a multilayer resistant to a temperature above 1000°C comprising a first rear layer of platinum, covered with a dielectric deposit of alumina 150 nanometers thick, itself covered with regular cross-shaped patterns of platinum 45 nanometers thick and approximately 150 to 300 nanometers wide, a fourth protective layer of alumina 150 nanometers thick. The use of noble metal conductors makes this system expensive, however. In addition, in an oxidizing environment, in the presence of corrosive or alkaline vapors,The metallic components listed by US20170885212A1 are susceptible to oxidation, which makes such a system insufficiently robust. Even more recently, US20190339418A1 described metamaterials exhibiting high emissivity at low wavelengths. These materials are in particular formed from nanometric-thick layers of different oxides, in particular aluminum-doped zinc oxide deposited alternately with layers of zinc oxide. The resistance of such materials to a temperature above 1000°C is, however, insufficient. There is a continual need for improvement and in particular for adjustment of materials with high thermal emissivity in the low wavelength range, i.e. below 5000 nanometers, in particular below 2000 nanometers,which resist a temperature above 1000°C in an oxidizing environment and in difficult conditions, in particular corrosive environments. The object of the present invention is therefore to propose a new metamaterial whose thermal emissivity is adjustable in the low wavelength range and which has greatly improved mechanical and chemical resistance at a temperature above or equal to 1000°C. Summary of the invention: The present invention relates to a metamaterial (or nanostructured composite material) comprising: -an inorganic support, said support being porous and having open pores with a median size less than or equal to 300 nanometers, and -at least two components including: -a first component comprising, and preferably consisting of, a dielectric oxide of at least one of the elements chosen from Al, Ti, Ca, Mg, Ta, Hf and Zr, preferably chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7,HfO2 and ZrO2; and - a second component comprising, and preferably consisting of, a transparent electronically conductive oxide, said oxide being an oxide of at least one element chosen from Zn, Sn, Ni, Ga, In, Cd, said oxide being hereinafter called "conductive oxide" for the sake of simplification, preferably chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3; and said conductive and dielectric oxides being inert to each other at a temperature of 1000°C and a pressure of 0.1 Mpa, preferably at a temperature of 1100°C, preferably at a temperature of 1200°C, preferably at a temperature of 1300°C, or even 1400°C or even 1500°C, also at a pressure of 0.1 Mpa; and said components being present in said metamaterial in the form of: - a plurality of layers of said two components, each layer of one component being in contact with at least one layer of the other component,or - a plurality of walls constituted by one of said components on which is deposited a layer of the other component, preferably one of said components constituting said support, said support comprising said plurality of walls on which is deposited said layer of the other component, and the thickness of each layer or wall being less than 300 nanometers, preferably less than 250 nanometers, and the maximum distance between two walls or two closest layers of the same component being less than 300 nanometers, preferably less than 250 nm. The inventors have discovered that such a metamaterial presents the best compromise between high thermal emissivity at short wavelengths and very good resistance to a temperature above 1000°C, or even above 1200°C, or even above 1300°C, in an oxidizing environment. According to a preferred embodiment,the relative difference in the coefficient of thermal expansion between the conductive oxide and the dielectric oxide is less than 15%, preferably less than 10%, preferably less than 5%, relative to the arithmetic mean of said coefficients measured according to ISO 17562:2016. The relative difference in the coefficient of thermal expansion is equal to the difference in absolute value of the coefficient of thermal expansion of said conductive oxide and that of said dielectric oxide divided by the coefficient of thermal expansion of said conductive oxide. Preferably, these are the coefficients of thermal expansion measured between 20°C and 1000°C. The metamaterial according to the invention thus has improved thermal stability at a temperature above 1000°C. According to a preferred embodiment, the melting temperature at a pressure of 0.1 Mpa of said conductive and dielectric oxides is greater than 1200°C, preferably greater than a temperature of 1300°C,or even greater than 1400°C or even greater than 1500°C. Preferably, said oxides are refractory oxides. Preferably, at least one conductive oxide of the second component is chosen from ZnO, SnO2, CdO, NiO, In2O3 or Ga2O3. The second component may also comprise a mixture of at least two of these oxides, in particular a mixture of SnO2 and In2O3 (ITO). The conductive oxides according to the invention may also comprise another chemical element (different from that or those of the oxide) chosen from B, Al, Ga, In, Si, Ge, Sn, Ti, Zr, Hf, F, Cl, Na, Sb, Ta, in particular in the form of a dopant, to increase the electrical conduction. Preferably at least one dielectric oxide of the first component is selected from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2. The first component may also comprise a mixture of at least two of these oxides. In particular the pair of conductive and dielectric oxides included in, or consisting of,respectively the second and first components, can be chosen from ZnO and ZnAl2O4, ZnO and ZnTa2O6, SnO2 and Al2O3, CdO and CdAl2O4, NiO and NiAl2O4, NiO and NiTiO3, Ga2O3 and GaTaO4, Ga2O3 and CaGa4O7. These pairs of oxides are in fact particularly advantageous because they do not exhibit any chemical reactivity between them and the thermal expansion coefficients of the conductive and dielectric oxides are very close. Various preferred embodiments of the present invention are described below, which can of course, if necessary, be combined with each other: - the thickness of the layer or even of the wall of each component, preferably the thickness of each layer is less than 200 nanometers, preferably less than 100 nanometers. - the metamaterial comprises an inorganic support, preferably ceramic. - said support comprises at least one wall on which, preferably a plurality of walls on which,a layer of one of said components is deposited. - one of said components, in particular the dielectric oxide, constitutes the walls of said support. - the support of said metamaterial is porous and has open pores with a median size less than or equal to 300 nanometers, preferably less than 250 nanometers, preferably less than 200 nanometers. - the two components are deposited in the form of layers on the surface or in the open porosity of said inorganic support. - said first component is in the form of a layer surrounded by two layers of the second component and in contact with said second component, the assembly forming a tri-layer. - said second component is in the form of a layer surrounded by two layers of said first component and in contact with it, the assembly forming a tri-layer. - the support, preferably porous, constitutes one of the two components, preferably the dielectric oxide,preferably an aluminum oxide (Al2O3). - said metamaterial comprises a surface layer of said dielectric oxide, preferably a dielectric oxide layer, preferably Al2O3 or ZnAl2O4, with a thickness of less than 500 nanometers, preferably less than 300 nanometers and / or greater than 1 nanometer, preferably greater than 3 nanometers, preferably greater than 10 nanometers, more preferably greater than 100 nanometers. Preferably the porosity of said surface layer is less than 5% by volume of said surface layer, in order to improve the protection of said material against corrosion. - said conductive oxide and / or said dielectric oxide have grains whose equivalent median grain diameter is less than 30 nanometers. -said conductive oxide is zinc oxide, to which is preferably added at least one chemical element chosen from B, Al, Ga, In, Si, Ge, Sn, Ti, Zr, Hf, F, Cl, Na, Sb, Ta. Preferably,to the conductive oxide is added a chemical element of the dielectric oxide, preferably between 1 and 5 mol% of said conductive oxide. More preferably the conductive oxide is zinc oxide to which is added between 1 and 5 mol% of aluminum. - said conductive oxide is tin oxide, to which is preferably added at least one chemical element chosen from Sb, F, In, Cl, Ga, Ta. - said dielectric oxide is Al2O3, preferably if the conductive oxide is tin oxide, or said dielectric oxide is ZnAl2O4, preferably if the conductive oxide is zinc oxide. - the porosity of the conductive and / or dielectric oxide(s) is between 0.5% and 10% by volume. - the volume ratio of said conductive oxide is between 1% and 90%, preferably between 3% and 50%, more preferably between 3 and 30%,the complement to 100% being constituted by said dielectric oxide and the possible porosity; Advantageously the volume rate makes it possible to adjust the emissivity curve in the wavelength range between 1 and 5 µm. - the mass content of dielectric oxide of the dielectric oxide layer, including the possible dopant(s), is greater than 99%, preferably greater than 99.5%, preferably greater than 99.9%. - the mass content of conductive oxide of the conductive oxide layer, including the possible dopant(s), is greater than 99%, preferably greater than 99.5%, preferably greater than 99.9%. The present invention also relates to a method for manufacturing said metamaterial, said method comprising the following steps: a) preparation of an inorganic support, preferably ceramic; b) if said support has a surface made of a dielectric oxide, chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7,HfO2 and ZrO2 deposition on said surface of a layer of electronically conductive oxide, said oxide being an oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3 with a thickness less than or equal to 300 nanometers, preferably less than 250 nanometers, preferably less than 200 nanometers, in order to at least partially cover the surface or the porosity of said support, optionally followed by deposition of a layer of dielectric oxide, chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2, with a thickness less than or equal to 300 nanometers, preferably less than 250 nanometers, preferably less than 200 nanometers; or b') if said support has a surface made of an electronically conductive oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3, deposition on said surface of a layer of a dielectric oxide chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO, 2,with a thickness less than or equal to 300 nanometers, preferably less than 250 nanometers, preferably less than 200 nanometers, in order to at least partially cover the surface or the porosity of said support, optionally followed by deposition of a layer of electronically conductive oxide, said oxide being an oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3, with a thickness less than or equal to 300 nanometers, preferably less than 250 nanometers, preferably less than 200 nanometers; c) optionally separation of said layers from said support. The conductive oxide may comprise a mixture of at least two of said oxides chosen from SnO2, CdO, NiO, In2O3 and Ga2O3. The dielectric oxide may comprise a mixture of at least two of said oxides selected from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO 2.According to one possible embodiment, if said support has a surface made of a material that is not inert with respect to said conductive or dielectric oxides at a temperature of at least 600°C, in particular at a temperature above 800°C, or even above 1000°C, a barrier layer is deposited on said surface in order to limit any reactivity with a subsequent deposition of a dielectric or conductive oxide layer. Preferably, the barrier layer consists either of the product of the temperature reaction between the deposited oxide and the material of the support, or of a material that is inert with respect to the support and the oxide above. Inert is understood to mean a material that does not exhibit any chemical reactivity between them in such a way that no new phase detectable by X-ray diffraction analysis is formed by reaction between these components, up to at least 1500°C.Various preferred embodiments of the present invention are described below, which can of course, if necessary, be combined with each other: -The separation of the support is carried out by a heat treatment, a chemical treatment or local exposure to high-intensity radiation. -after the deposition step b), a thermal stabilization treatment, preferably an annealing, is carried out at a temperature below the softening temperature of the support, preferably at a temperature between 50 and 80% of the melting temperature of the lowest oxide constituting the layers of the metamaterial, preferably at a temperature above 600°C, preferably above 700°C and / or below 1400°C, preferably below 1200°C, preferably below 1100°C, preferably below 1000°C, under oxidizing gas, preferably under air. The temperature range depends on the conductive and dielectric oxides.A too high stabilization or annealing temperature may be detrimental in particular to the electronic conduction properties of the conductive oxide. -step b) or b') is repeated in order to obtain a plurality of bilayers formed of an electronically conductive oxide and a successive dielectric oxide, each bilayer having a thickness of less than 600 nanometers, preferably less than 500 nanometers, preferably less than 400 nanometers, preferably less than 300 nanometers. -the support is a nanoporous ceramic, the median equivalent pore diameter of which is preferably less than or equal to 300 nanometers. Preferably, the nanoporous ceramic support comprises at least one surface layer of dielectric oxide, of at least one of the elements chosen from Al, Ti, Ca, Mg, Ta, Hf and Zr. -the support is a nanoporous membrane of dielectric oxide, of at least one of the elements chosen from Al, Ti, Ca, Mg, Ta, Hf and Zr. ,preferably an oxide chosen from Al2O3, ZnAl2O4, MgO, HfO2 and ZrO2, preferably the support is an alumina membrane. -the deposition in step b) or b') can be carried out from a precursor of the element of the oxide to be formed using lithography, nano-imprint lithography, micro-contact printing, atomic layer deposition (or "atomic layer deposition" in English) techniques and in particular for a metamaterial in lamellar or multilayer form, the sol-gel method ("dip coating" or "spin coating" in English) and magnetron deposition. - the deposition is carried out by atomic layer deposition (or "atomic layer deposition" in English) from one or more organometallic compounds, preferably metal halide or alkyl, comprising the element(s) of the chemical formula of said conductive oxide. The deposition is preferably carried out at a temperature below 500°C.- the deposition of conductive oxide, in particular zinc oxide to which aluminum is added, is carried out by successive depositions from an aluminum precursor and a zinc precursor at a temperature of at least 50°C. According to one possible embodiment, the metamaterial according to the invention is obtained by deposition of atomic layers of conductive oxide on a nanoporous membrane, preferably a membrane whose median pore size is between 1 and 300 nanometers, preferably an alumina membrane. According to another possible embodiment, each layer of the bilayer of the metamaterial according to the invention is obtained by a succession of atomic layer depositions and the total thickness of all the atomic layer depositions for each layer of the metamaterial bilayer has a maximum thickness of less than 200 nanometers.The present invention further relates to the use of the metamaterial as previously described for coating: - all or part of the emitting surface of a thermophotovoltaic device, in particular to reduce the energy of the radiation emitted outside the effective wavelength range for the cell; and / or - a heating installation emitting heat by radiation in an industrial process for manufacturing materials, for example a baking oven or a thermoforming device, with the aim of reducing their energy consumption and / or in order to adjust the emissivity and in particular the spectral range of emission according to the absorption spectral bands of the target material to be thermoformed or baked, to heat the material either on the surface or more deeply according to the semi-transparency bands of the material to be heated.In particular, it may be a furnace or an installation implementing a heating process, in particular at a temperature above 600°C, or even above 1000°C, in order to reduce their energy consumption; and / or - a thermal barrier to maximize the heat re-emitted by radiation and thus limit the temperature rise at the thermal barrier interface with its substrate; and / or - a heat exchanger or a heating element to maximize their efficiency. Definitions: The following indications and definitions are given, in relation to the preceding description of the present invention: By "inorganic" is meant a non-organic product, that is to say not comprising carbon-hydrogenated chains as one of its main components. The family of inorganic materials includes metals, glasses and ceramics and composites made of these materials.By "ceramic" is meant a product that is neither metallic nor organic. In the context of the present invention, sapphire for example or a carbon material such as diamond, graphite, graphene, carbides and cermets are considered as ceramic materials. By "inert" is meant that said conductive and dielectric oxides do not exhibit any chemical reactivity between them. Such a characteristic is for example measured by X-ray diffraction analysis by verifying by this method that no new phase is formed by reaction between said oxides up to at least 1000°C, or even up to 1500°C, at their contact zone(s). By "refractory" is meant a material having a melting temperature above 1500°C. This definition is commonly used by those skilled in the art and cited in "Refractory materials and technical ceramics (ceramic and technology elements)", G.Aliprandi, Septima Paris, 1979. This work also gives on pages 297 to 301 examples of refractory materials, in particular oxides, carbides and nitrides. An electronically conductive oxide is understood to mean an oxide whose electronic conductivity is greater than 0.5 S / cm, preferably greater than 1 S / cm, preferably greater than 10 S / cm. A "dielectric oxide" is understood to mean an oxide whose electronic conductivity is less than 0.05 S / cm, preferably less than 0.01 S / cm, preferably less than 0.01 S / cm, preferably less than 0.001 S / cm. A layer forms a continuous structure of the same material, porous or not, extending over two dimensions of space, the third dimension, the smallest forming the thickness of said layer. In the present application, a layer can be obtained by successive depositions, for example by atomic deposition techniques.Material thickness means the smallest dimension of the material, which may be in the form of a nanolayer or a nanowire. In the case of a nanowire, the thickness thus corresponds to the minimum diameter of said nanowire. Equivalent grain or particle diameter means the half-sum of the greatest length of the grain and the greatest width of the grain, measured in a direction perpendicular to said greatest length. The maximum and median equivalent particle or pore diameters, the distances between pores or between components, and the dimensions of the components are conventionally determined from the observation of the microstructure of the material, conventionally using images taken with a SEM (scanning electron microscope) on a section of said material.The term "median diameter" or "median size" of a set of particles or pores, in particular of a powder or of a material, is used to describe the D50 percentile, i.e. the size dividing the particles or pores into first and second populations equal in volume, these first and second populations comprising only particles or pores having a size greater than or less than the median size. The volume of open pores of the support and the porosity of the surface layer can also be determined from observation of the microstructure of the material, conventionally using images taken with a SEM on a section of said material. "Matrix" means a crystallized or non-crystalline phase, providing a substantially continuous structure surrounding a second phase (or a second component) present in discrete form.^ The volume ratio can be determined by observation and analysis of images obtained by a scanning microscope equipped with a localized ion beam in order to reconstruct the microstructure in three spatial dimensions. The phase composition of the material is normally obtained by X-ray diffraction and Rietveld analysis. This method is also useful for determining the absence of chemical reactivity between the conductive oxide and the dielectric oxide. By molar percentage addition in an oxide of element X of an element Y is meant the ratio of the molar mass of element Y multiplied by 100 to the sum of the molar masses of elements X and Y. By impurities is meant the unavoidable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated.By "containing a", "comprising a" or "comprising a" is meant "comprising at least one", unless otherwise indicated. Unless otherwise indicated, in the present description, all percentages are mass percentages. Unless otherwise stated, all averages are arithmetic averages. Figures: Figure 1 shows a schematic section of an embodiment of the metamaterial according to the present invention (example 3). The support in the form of a nanoporous membrane comprising walls 1 and pores 2 whose median size is approximately 100 nanometers. According to the invention, the pores are filled with components. Thus, the surface of the membrane and the pores are covered with a first layer 3 of dielectric oxide, ZnAl2O4, itself covered with a second layer 4 of electronically conductive oxide of ZnO with 2 mol% of Al (elemental Aluminum), these layers having been obtained by atomic layer deposition.A low residual porosity may persist 5. Detailed description: The ceramic support may be, for example, a single crystal of alumina oriented perpendicular to the c axis to obtain a nanostructured material in lamellar form or a porous membrane to obtain a structure in the form of nanowires. The dielectric oxide layer, for example ZnAl2O4, may be obtained by depositing atomic layers of Al2O3 and then ZnO according to several successive cycles. The total number of cycles is typically more than 1000, the number of Al2O3 deposition cycles being greater than that of the ZnO deposition. The deposition is carried out at 100°C. The electronic conductor layer, for example ZnO, may be obtained, for example, by deposition of atomic layers, using the zinc diethyl precursor with H2O as a reagent, the total deposited layer may have a thickness of 200 nm. The deposition temperature is typically 100°C.The pulse, exposure and purge times can be optimized to obtain a growth per cycle of 0.2 nm. In the case of an electronic conductor layer, for example ZnO to which aluminum is added, deposited by atomic layers, Al2O3 is deposited according to a predetermined number of cycles using for example aluminum trimethyl as precursor and deionized water as co-reactant. The deposition is typically carried out at 100 ° C. Then ZnO is deposited according to a predetermined number of cycles by successively sending diethylzinc and deionized water as co-reactant. After the deposition of ZnO, the same number of Al2O3 deposition cycles as previously are repeated in order to obtain a desired atomic percentage of aluminum (Al) addition, preferably less than 4%.The metamaterial according to the invention may comprise a succession of an electronic conductor and dielectric layer alternately deposited, i.e. a plurality of bilayers of conductive oxide and dielectric oxide. For example, at least two, preferably more than three, or even more than five stacks of bilayers. According to one possible embodiment, the metamaterial according to the invention may comprise a succession of n layers of electronic conductor oxide and n layers of dielectric oxide, representing for example up to two thousand stacks of layers in total according to an individual thickness of each oxide layer preferably of at least five nanometers and for a total thickness of metamaterial excluding support preferably of ten micrometers or less.A possible example of such a succession comprising an alternation of dielectric / conductor layers is given below: 150 nm SnO2 (conductive oxide) - 50 nm Al2O3 (dielectric oxide), this elementary bilayer being repeated five times to form said succession. On the supports of alumina single crystal oriented perpendicular to the c axis, preferably a layer of ZnAl2O4 is deposited as a final protective layer. On the porous membranes a layer of ZnAl2O4 or Al2O3 is preferably deposited as a final protective layer. After each deposition or at the end of all the depositions, a stabilization heat treatment or annealing is preferably carried out at a temperature between 600 ° C and 1400 ° C. For example, a treatment at 900 ° C for 1 h with a ramp of 10 ° C / min makes it possible to obtain stable deposits of ZnO and ZnAl2O4.It is possible to verify the presence of this phase by X-ray diffraction analysis before depositing the second conductive oxide layer. In the particular case of an electronic conductor layer of SnO2, for example by atomic layer deposition, the precursor used is preferably SnCl4 with deionized water as co-reactant. The deposition is typically carried out at 300°C with successive injection, exposure and purging of each of the precursors, repeated as many times as necessary to obtain the desired thickness. After possible deposition of a protective layer of alumina, an annealing heat treatment at 800°C makes it possible to stabilize the metamaterial. The following examples are given purely for illustrative purposes and do not limit the scope of the present invention in any of the aspects described.Examples: Example 1 (comparative) Deposition of a ZnO layer with 2 mol% Al was performed on sapphire using a stationary ALD system, using trimethylaluminum (TMA) and diethylzinc (DEZ) as precursors for Al2O3 and ZnO, respectively. Deionized water (H2O) was used as a co-reactant for both processes, and all depositions were performed at 100 °C. Samples were held at 100 °C for 30 min before deposition. The deposition parameters were: precursor / exposure / purge pulse 0.4 s / 20 s / 30 s (TMA), 0.4 s / 20 s / 30 s (DEZ), and 2 s / 20 s / 30 s (H2O). The precursor pulse and purge step were performed with argon flows of 25 sccm and 100 sccm, respectively, as the gas carrier. A successive deposition of 1 cycle of TMA / H2O followed by 49 cycles of DEZ / H2O was repeated 20 times to achieve a total thickness of approximately 200 nm for all coatings.After ALD deposition, an annealing at 900°C for 1 hour with a ramp of 10°C / min was applied. Example 2 (invention) Unlike the previous example, a deposition of a ZnO layer with 2 mol% Al was carried out on sapphire on which a ZnAl2O4 layer had been previously formed. The deposition of the ZnAl2O4 layer was carried out in the same way as the ZnO layer with 2 mol% Al but with a different number of cycles: 25 cycles of TMA / H2O followed by 13 cycles of DEZ / H2O repeated 27 times to obtain a total thickness of approximately 200 nm. After ALD deposition, a heat treatment at 900°C for 1 hour with a ramp of 10°C / min was applied to form the ZnAl2O4 phase. Subsequent deposition of ZnO with 2 mol% Al was carried out in a similar manner to that of Example 1. It was followed by annealing at 900°C for 1 h with a ramp of 10°C / min.Example 3 (invention) For this example, a support marketed by the Fraunhofer Institute IKTS was used, in the form of an alumina membrane with an Al2O3 mass content greater than 99% and pores with an equivalent median diameter of 100 nanometers. The maximum distance or maximum wall thickness separating two neighboring pores was less than 300 nanometers in said membrane. This measurement was carried out using a scanning electron microscope from cross-sections of the membrane, each transverse plane being substantially perpendicular to the median plane of the filtration front surface of said membrane. A first deposition of dielectric oxide ZnAl2O4 was carried out according to the same procedure as for the deposition of ZnAl2O4 in Example 2, but the operation was repeated 4 times instead of 27 times.A second deposition of electronically conductive oxide of ZnO with 2% Al was carried out according to the same procedure as for the deposition of example 2 but the operation was repeated 3 times instead of 20 times. Examples 4 (invention) According to these example 4, on a starting support identical to that of the previous example 3, the following deposits were carried out respectively: -example 4a: On a first support, a deposition of electronically conductive oxide of SnO2 is carried out at 300°C in a low pressure ALD reactor. The reactor was directly connected to the precursor and co-reactant lines by valves heated to 100°C to avoid condensation. The deposition of SnO2 was carried out using sequential exposures of SnCl4 and H2O separated by argon (Ar) purge steps with a flow rate of 100 sccm.An ALD cycle consists of a 0.2 s SnCl4 pulse, a 30 s exposure and a 30 s Ar purge, followed by a 1 s H2O pulse, a 30 s exposure and a 30 s Ar purge. This operation was repeated 625 times before obtaining a 50 nanometer deposit. - example 4b: On a second support, a first deposition of alumina (Al2O3) was carried out in a stationary ALD system, using trimethylaluminum (TMA) as a precursor and deionized water (H2O) as a co-reactant. The ambient temperature was set at 100°C and the pipes were heated to 100°C to avoid condensation. The samples were kept at 100°C for 30 min before deposition. The deposition parameters were: precursor / exposure / purge pulse followed by a co-reactant / exposure / purge pulse. Exposure was set to 30s and purge to 40s. The pulse time was set to 0.4s and 2s for TMA and H2O, respectively.The precursor pulse and the purge step were carried out with argon flows of 25 sccm and 100 sccm, respectively, as the gas carrier. This operation is repeated 100 times in order to obtain a 20 nanometer Al2O3 layer. A second deposit of electronically conductive oxide SnO2 was carried out using the same method as that used for Example 4 / a but with 380 repetitions to obtain a thickness of 30 nm of SnO2. Emissivity measurement: It was measured on each sample at temperatures ranging from room temperature to 1600°K in air using a set of two Fourier transform infrared spectrometers manufactured by Bruker (Vertex 80V and Vertex 70) allowing emission measurements in the range from 2000 to 14000 cm. -1(approximately 0.7 to 5 micrometers). The heating of the samples during the measurement was carried out by a CO2 laser (Diamond K500, Coherent Inc.) the beam follows a path passing through a separator and a set of mirrors allowing identical heating of both faces of the sample tested. Simultaneous measurements are carried out by the two spectrometers of the fluxes emitted by the sample and by the black body (Pyrox PY8 furnace) having a cylindrical cavity made of lanthanum chromite (LaCrO3) pierced with a lateral orifice) the latter having an emissivity equal to 1. Infrared spectrometers are also used as pyrometers for the temperature measurement of the sample. The method used is that of Christiansen.In the particular case of Examples 4a and 4b, since the material did not have a Christiansen point (it was not possible to calibrate the temperature), the emissivity was determined by reflectance and transmittance at room temperature using an Infragold® integrating sphere. The emissivity was deduced according to Kirchhoff's radiation law, which imposes Ɛ= A = 1 – R – T with Ɛ, the emissivity, A, the absorbance, R, the reflectance and T, the transmittance. In the following Table 1, the quasi-normal emissivities measured at 2, 3 and 4 micrometers, for different temperatures, are given.[Table 1] Emissivity = f( ^, T) Ɛ at 1 µm Ɛ at 2 µm Ɛ at 3 µm Ɛ at 4 µm T° Support of example 1 - - - 0.05 1100°C Example 1* - - - 0.05 1100°C Example 2* - 0.02 0.04 0.15 1100°C Support example 3 - - - 0.1 1050°C Example 3** <0.2 0.41 0.67 0.8 1050°C Example 4a** 0.7 0.97 0.96 0.95 20°C Example 4b** 0.2 0.67 0.92 0.95 20°C *with single crystal alumina of example 1 **with nanoporous membrane IKTS example 3 Analysis of the results: The emissivity measured on the material of example 1 (comparative) is not different from that of the support which is low. The material of example 2 (invention) has, compared to example 1, given the very low number of layers deposited, a much higher emissivity, particularly at the wavelength of 4 µm. A stack according to example 3 (invention) produced on a nanoporous support formed by an alumina membrane has a very high emissivity at 1050°C compared to the support alone.Examples 4 (invention) show the possibility of modulating the emissivity curve in the wavelength range between 1 and 5 microns. This is achieved by adjusting the volume fraction of conductor as shown by the emissivity differences of Examples 4a and 4b. between 1 and 3 µm wavelength. Of course, the present invention is not limited to the embodiments described and shown, provided as examples. In particular, combinations of the different embodiments described also fall within the scope of the invention.

Claims

CLAIMS 1. Metamaterial comprising: - an inorganic support, said support being porous and having open pores with a median size less than or equal to 300 nanometers, and - at least two components including: - a first component comprising, and preferably consisting of, a dielectric oxide chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2; and - a second component comprising a transparent electronically conductive oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3;said conductive and dielectric oxides being inert to each other at a temperature of 1000°C and at a pressure of 0.1 Mpa, said components being present in said metamaterial in the form of: - a plurality of layers of said two components, each layer of one component being in contact with at least one layer of the other component, or - a plurality of walls constituted by one of said components, on which a layer of the other component is deposited, and - the thickness of each layer or wall being less than 300 nanometers;and -the maximum distance between two walls or two closest layers of the same component is less than 300 nanometers, preferably less than 250 nanometers.

2. Metamaterial according to the preceding claim, wherein one of said components constitutes said support, said support comprising said plurality of walls on which said layer of the other component is deposited.

3. Metamaterial according to one of the preceding claims, wherein the conductive / dielectric oxide pair is chosen from ZnO / ZnAl2O4, ZnO / ZnTa2O6, SnO2 / Al2O3, CdO / CdAl2O4, NiO / NiAl2O4, NiO / NiTiO3, Ga2O3 / GaTaO4, Ga2O3 / CaGa4O7.

4. Metamaterial according to one of the preceding claims wherein said support is ceramic.; 5. Metamaterial according to one of the preceding claims, the support has open pores with a median size less than or equal to 250 nanometers.

6. Metamaterial according to one of the preceding claims wherein the dielectric oxide constitutes the walls of said support.

7. Metamaterial according to one of claims 1 to 6 wherein the conductive oxide constitutes the walls of said support.

8. Metamaterial according to one of the preceding claims, wherein at least one of said two components is deposited in the form of layers on the surface or in the open porosity of said inorganic support.

9. Metamaterial according to the preceding claim, wherein said first component is in the form of a layer surrounded by two layers of said second component, and in contact with said second component, or vice versa, in order to form a tri-layer. 10.Metamaterial according to one of the preceding claims, wherein the two components are deposited in the form of layers on the surface or in the open porosity of said inorganic support, in the form of a succession of alternating layers of dielectric oxide and layers of conductive oxide.

11. Metamaterial according to one of the preceding claims, comprising a surface layer, preferably a layer of dielectric oxide with a thickness of less than 500 nanometers, the porosity of said surface layer preferably being less than 5% by volume.

12. Metamaterial according to one of the preceding claims, wherein the conductive oxide is zinc oxide, to which is preferably added at least one chemical element chosen from B, Al, Ga, In, Si, Ge, Sn, Ti, Zr, Hf, F, Cl, Na, Sb, Ta, or the conductive oxide is tin oxide, to which is added at least one chemical element chosen from Sb, F, In, Cl, Ga, Ta. 13.Metamaterial according to one of the preceding claims, wherein said dielectric oxide is Al2O3 or ZnAl2O4.

14. Metamaterial according to one of the preceding claims, wherein said dielectric oxide is Al2O3 if the conductive oxide is tin oxide or said dielectric oxide is ZnAl2O4 if the conductive oxide is zinc oxide.

15. Method for manufacturing the metamaterial according to one of the preceding claims, comprising the following steps: a) preparation of an inorganic support;b) if said support has a surface made of a dielectric oxide chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2, deposition on said surface of a layer of electronically conductive oxide, said oxide being an oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3 with a thickness less than or equal to 300 nanometers, in order to at least partially cover the surface or the porosity of said support, Optionally followed by deposition of a layer of dielectric oxide chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2, with a thickness less than or equal to 300 nanometers;or if said support has a surface made of an electronically conductive oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3, deposition on said surface of a layer of dielectric oxide chosen from Al2O3, ZnAl2O4, ZnTa2O6, CdAl2O4, NiAl2O4, NiTiO3, GaTaO4, CaGa4O7, HfO2 and ZrO2, with a thickness less than or equal to 300 nanometers, Optionally followed by deposition of a layer of electronically conductive oxide, said oxide being an oxide chosen from ZnO, SnO2, CdO, NiO, In2O3 and Ga2O3, with a thickness less than or equal to 300 nanometers; c) optionally separation of said layers from said support.

16. Manufacturing method according to the preceding claim in which the deposition is carried out by atomic layer ("atomic layer deposition" (ALD) in English).

17. Use of the metamaterial according to one of claims 1 to 14 as a coating:; - all or part of the emitting surface of a thermo-photovoltaic device; - a heating installation emitting heat by radiation in an industrial process for manufacturing materials, for example a cooking oven or a thermoforming device; - a thermal barrier; - a heat exchanger or a heating element.

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