Plasmonic structure, light source, and wavelength-selective absorber

Abstract

To widen a band having large absorptivity and emissivity in comparison with a conventional plasmonic structure.SOLUTION: In a plasmonic structure (1), a first conductor layer (13), a dielectric layer (12), and a second conductor layer (11) are stacked in this order. The second conductor layer includes a plurality of conductor patterns (111) that is two-dimensionally and periodically arranged, each of the plurality of conductor patterns having a circular shape or a regular polygonal shape. A diameter D of a circle circumscribed on each of the plurality of conductor patterns (111) satisfies 200 nm≤D≤800 nm. A thickness g of the dielectric layer (12) and the diameter D satisfy 0.3≤g / D≤0.6.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a plasmonic structure, a light source, and a wavelength-selective absorber. [Background technology]

[0002] In order to use energy efficiently, the process of thermal radiation, which is a part of the energy transport process, is extremely important. However, generally, thermal radiation from an object occurs in a wide wavelength band, i.e., a broad band. Therefore, energy loss due to thermal radiation occurs in unnecessary wavelength bands. For example, in an incandescent light bulb, most of the input power is emitted as infrared radiation that is not required for lighting. In other words, most of the input power is wasted without being used for lighting. Therefore, wavelength-selective radiators have attracted attention from the viewpoint of improving the efficiency of energy use. A wavelength-selective radiator controls the spectral emissivity of the material surface to improve the emissivity in a desired wavelength band while suppressing the emissivity outside the desired wavelength band.

[0003] According to Kirchhoff's law, the emissivity of an object is equal to its absorptivity. Therefore, a wavelength-selective radiator can be obtained by controlling the wavelength dependency of the absorptivity of the material surface (also called the absorption characteristics). However, it is difficult to arbitrarily control the radiated wavelength by using the method that utilizes the inherent absorption characteristics of the material. Therefore, this method cannot be said to have a high degree of freedom.

[0004] Meanwhile, a technology that controls the spectral emissivity by forming a microstructure on the surface of a material has been attracting attention in recent years. This is because this technology makes it possible to control the spectral emissivity by controlling the size and period of the microstructure, without being limited by the inherent optical properties of the material. This method has a higher degree of freedom than the method of controlling the absorption properties of the material surface.

[0005] Among microstructures, a structure called a plasmonic structure has been proposed in recent years. The plasmonic structure is a structure that generates plasmon resonance when irradiated with light. Therefore, the electric field is strengthened and the amount of light absorbed increases. Highly efficient thermal radiation can be achieved by the same principle as that of highly efficient light absorption. For example, Patent Document 1 is an example of a document that discloses a technology for controlling the absorption / emission rate using a plasmonic structure.

[0006] Patent Document 1 discloses a plasmonic structure that can have a relatively high melting point and a relatively high light absorptance and emissivity. The plasmon resonance structure described in Patent Document 1 exhibits a large light absorptance and emissivity in the visible light region (400 nm or more and 800 nm or less) and the near-infrared region (2 μm or more and 5.5 μm or less). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-77007 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method of increasing the absorptance by forming a plasmonic structure on the surface of a material, as shown in Patent Document 1, the bandwidth of the wavelength band in which the absorptance and emissivity are high (for example, 90% or more) tends to become narrow.

[0009] One aspect of the present invention has been made in consideration of the above-described problems, and has an object to broaden the band in which the absorptance and emissivity are high, as compared with conventional plasmonic structures. [Means for solving the problem]

[0010] In order to achieve the above objectives, the plasmonic structure of the first aspect of the present invention employs a structure in which a first conductor layer covering a specific surface, a dielectric layer, and a second conductor layer consisting of a plurality of conductor patterns arranged two-dimensionally and periodically, each of which is a circle or a regular polygon, are stacked in this order.

[0011] In addition, in the plasmonic structure of the first embodiment, a diameter D of a circle circumscribing each of the multiple conductor patterns satisfies 200 nm≦D≦800 nm, and the thickness g and diameter D of the dielectric layer satisfy 0.3≦g / D≦0.6.

[0012] In order to solve the above problems, a light source according to a sixth aspect of the present invention includes a substrate and a plasmonic structure according to any one of the first to fifth aspects described above, in which the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and the plasmonic structure emits light in a specific wavelength band when heated.

[0013] In order to achieve the above object, a wavelength-selective absorption element according to a seventh aspect of the present invention employs a configuration comprising a substrate, and a plasmonic structure according to any one of the first to fifth aspects described above, in which the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and the plasmonic structure absorbs light in a specific wavelength band. Effect of the Invention

[0014] According to a plasmonic structure according to one aspect of the present invention, the band in which the absorptance and emissivity are high can be broadened as compared with conventional plasmonic structures. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is an enlarged perspective view of a portion of a plasmonic structure according to one embodiment of the present invention. [Diagram 2] 2 is a plan view of a portion of the plasmonic structure shown in FIG. 1. [Diagram 3] 2 is a cross-sectional view of a portion of the plasmonic structure shown in FIG. 1. [Figure 4] 1. FIG. 4 is a plan view showing another example of a periodic two-dimensional arrangement of a plurality of conductor patterns included in the plasmonic structure shown in FIG. [Diagram 5] 1A to 1C are schematic diagrams showing a method for manufacturing a plasmonic structure according to one embodiment of the present invention. [Figure 6] 1 is an image showing the relationship between reflectance, period, and wavelength in a plasmonic structure according to one embodiment of the present invention. [Figure 7] 1 is a graph showing the wavelength dependence of reflectance in plasmonic structures according to first to fourth examples of the present invention. [Figure 8] 11 is an SEM image of a plasmonic structure according to a second embodiment of the present invention. [Figure 9] 13 is a graph showing measurement results and calculation results of the wavelength dependence of reflectance in a plasmonic structure according to a second embodiment of the present invention. [Figure 10] 1 is an image showing the relationship between reflectance, period, and wavelength in a plasmonic structure according to a first comparative example of the present invention. [Figure 11] 13 is an image showing the relationship between reflectance, period, and wavelength in a plasmonic structure according to a second comparative example of the present invention. [Figure 12] 13 is a graph showing the wavelength dependence of reflectance in the plasmonic structures according to the second example, the first comparative example, and the second comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A plasmonic structure 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is an enlarged perspective view of a part of the plasmonic structure 1. FIG. 2 is a plan view of a part of the plasmonic structure 1 shown in FIG. 1. The plan view of FIG. 2 is obtained by viewing the plasmonic structure 1 from the conductor layer 11 side in the direction of a normal to the main surface of the plasmonic structure 1. FIG. 3 is a cross-sectional view of a part of the plasmonic structure 1 shown in FIGS. 1 and 2. FIG. 3 shows a cross section taken along line AA shown in FIG. 2. FIG. 4 is a plan view showing another example of a periodic two-dimensional arrangement of a plurality of conductor patterns 111 included in the plasmonic structure 1. FIG. 5 is a schematic view showing an example of a method for manufacturing the plasmonic structure 1.

[0017] [Overview of Plasmonic Structures] It is assumed that the plasmonic structure 1 is formed on the surface of a substrate not shown in FIG. 1. In this embodiment, the plasmonic structure 1 including the substrate is made of a material that can be heated to a high temperature (for example, 500° C. or higher). The method of heating the plasmonic structure 1 including the substrate is not limited, and examples thereof include a method using a heater and a method of passing a current through the plasmonic structure 1 including the substrate. The plasmonic structure 1 heated by the heater or the plasmonic structure 1 heated by Joule heat caused by the current passed therethrough emits light having an emission intensity corresponding to the temperature reached. When the plasmonic structure 1 is heated by passing a current, at least a pair of electrodes may be provided on either the substrate (in the case of a dielectric) or the conductor layer 13. The electrodes may be connected to the same member of the substrate or the conductor layer 13, or may be connected to different members. The material constituting the substrate may have any conductivity. That is, the conductive property of the material constituting the substrate may be metallic or semiconducting. The material constituting the substrate may be an insulator or a dielectric.

[0018] The material constituting the substrate is not limited, and may be any of semiconductors, glass, metals, and semi-metals. An example of a semiconductor is silicon (Si). An example of a glass is quartz. Examples of metals are platinum (Pt), gold (Au), silver (Ag), tungsten (W), tantalum (Ta), and nickel-chromium (Ni-Cr) alloys. An example of a semi-metal is a carbon material.

[0019] 1 to 3 show an enlarged portion of the plasmonic structure 1. Therefore, only nine conductor patterns 111 are shown in Fig. 1 and Fig. 2, and only three conductor patterns 111 are shown in Fig. 3. However, the size of the plasmonic structure 1 when the main surface of the plasmonic structure 1 is viewed in plan can be determined arbitrarily in accordance with the size of the substrate. That is, the number of conductor patterns 111 constituting the conductor layer 11 of the plasmonic structure 1 can be determined arbitrarily in accordance with the size of the substrate.

[0020] In this way, a light source comprising a substrate and a plasmonic structure 1 having a conductor layer 13, a dielectric layer 12, and a conductor layer 11 stacked in this order on the surface of the substrate, and which emits light in a specific wavelength band when heated, is also included in the scope of the present invention.

[0021] Such a light source can improve the emissivity in a desired wavelength band while suppressing the emissivity in wavelengths other than the desired wavelength band, thereby improving the efficiency of energy utilization, as compared to a normal infrared light source. When such a light source is applied to a spectrometer or the like, the temperature rise of the spectrometer can be suppressed. Furthermore, the plasmonic structure 1 can adjust the central wavelength (the central emission wavelength in the case of a light source) in a specific wavelength band by controlling the diameter D of the conductor pattern. Note that the central emission wavelength becomes longer as the diameter D increases. By controlling the diameter D, the central emission wavelength can be adjusted, for example, within a range of 500 nm or more and 4 μm or less.

[0022] In addition, a wavelength-selective absorption element having a plasmonic structure 1 in which a conductor layer 13, a dielectric layer 12, and a conductor layer 11 are stacked in this order on the surface of a substrate and which absorbs light in a specific wavelength band is also included in the scope of the present invention.

[0023] An example of the application of such a wavelength-selective absorption element is a solar thermophotovoltaic power generation system (Solar-TPV). In a solar-TPV, all solar energy is converted into thermal energy using a solar light absorber, and then a thermal radiation emitter emits thermal radiation light that is easy for a solar cell to generate electricity. The light emitted from the sun has a wide wavelength distribution. However, a single-junction solar cell can only convert light with a wavelength shorter than the band gap of the semiconductor material used into electricity. In other words, light with a wavelength longer than the band gap is not converted into electricity and is lost. The plasmonic structure 1 can convert the solar spectrum with a wide wavelength distribution into electricity without waste by expanding the wavelength range that can be absorbed. Therefore, the plasmonic structure 1 can be applied as a wavelength-selective absorption element or a thermal radiation emitter. In this case, a specific example of a specific wavelength band is 600 nm or more and 1.5 μm or less.

[0024] Another application example of such a wavelength-selective absorption element is a substrate used in surface-enhanced Raman scattering analysis. As described above, the plasmonic structure 1 absorbs light in a specific wavelength band according to the diameter D of the conductor pattern. The plasmonic structure 1 can enhance the Raman signal of molecules adsorbed on the surface by utilizing the energy of the absorbed light. Therefore, by applying the plasmonic structure 1 to a substrate used in surface-enhanced Raman scattering analysis, highly sensitive Raman scattering analysis can be performed with near-infrared light that penetrates a living body. In this case, a specific example of the specific wavelength band is 900 nm or more and 2 μm or less.

[0025] [Configuration of Plasmonic Structure] 1, the plasmonic structure 1 includes a conductor layer 11, a dielectric layer 12, and a conductor layer 13. The conductor layer 11 is an example of a second conductor layer, and the conductor layer 13 is an example of a first conductor layer.

[0026] <First conductive film> The conductor layer 13 is composed of a conductor film formed on the surface of the substrate so as to cover the surface of the substrate. The surface of the substrate is an example of a specific surface. Although not shown in Figs. 1 and 3, the substrate is disposed below the main surface of the conductor layer 13 that is located on the lower side.

[0027] In this embodiment, hafnium nitride (HfN) is used as the material constituting the conductor layer 13. However, the material constituting the conductor layer 13 is not limited to HfN, and any material having metallic conductive properties may be used. When the plasmonic structure 1 is formed on the surface of a substrate that is expected to become hot during use, it is preferable that the material constituting the conductor layer 13 is a material with a high melting point such as HfN.

[0028] The region of the surface of the substrate where the plasmonic structure 1 is formed (i.e., the region where the conductor layer 13 is formed) may be the entire surface of the substrate or a part of the surface of the substrate, and can be determined as appropriate.

[0029] In this embodiment, a thickness of 100 nm is adopted as the thickness of the conductor layer 13. However, the thickness of the conductor layer 13 is not limited and can be appropriately determined within the range of, for example, 100 nm or more.

[0030] <Dielectric film> The dielectric layer 12 is composed of a dielectric film formed on the principal surface of the conductor layer 13 opposite the substrate so as to cover the principal surface opposite the substrate. In Fig. 1 and Fig. 3, the dielectric layer 12 is provided on the principal surface located above the conductor layer 13.

[0031] In this embodiment, silicon oxide (SiO2) is used as the material constituting the dielectric layer 12. However, the material constituting the dielectric layer 12 is not limited to SiO2, and may be any material that is transparent to light in a predetermined wavelength band and is an insulator. An example of such a material is an insulating oxide. When the plasmonic structure 1 is formed on the surface of a substrate that is expected to become hot during use, the material constituting the dielectric layer 12 is preferably any one of SiO2, Al2O3, and a mixture of SiO2 and Al2O3.

[0032] The thickness g (see FIG. 3) of the dielectric layer 12 is determined corresponding to the diameter D (see FIG. 3) of each conductor pattern 111 described below. Specifically, the thickness g and the diameter D are each determined to satisfy 0.3≦g / D≦0.6. That is, the thickness g is determined to satisfy 0.3×D≦g≦0.6×D.

[0033] <Second conductor layer> The conductor layer 11 is formed on one of the principal surfaces of the dielectric layer 12, the principal surface being opposite to the dielectric layer 12. In Fig. 1 and Fig. 3, the conductor layer 11 is provided on the principal surface located above the dielectric layer 12.

[0034] The conductor layer 11 is made up of a plurality of conductor patterns 111 (nine in Figs. 1 and 2) each having a circular shape. However, the shape of each conductor pattern 111 is not limited to a circular shape, and may be a regular polygonal shape. A preferred example of the regular polygonal shape is a regular hexagonal shape. In the following, a circular shape includes a circle and a shape having a circle as a base and non-isotropic variations and irregular variations in its contour due to the manufacturing process. For example, the shape of the conductor pattern 111 included in the second embodiment of the present invention shown in Fig. 8 is an example of a circle. Similarly, a regular polygonal shape includes a regular polygonal shape and a shape having a regular polygonal shape as a base and non-isotropic variations and irregular variations in its contour due to the manufacturing process.

[0035] Note that the reference numeral 111 is given to only one of the plurality of conductor patterns 111. As shown in Figs. 1 and 2, the plurality of conductor patterns 111 are two-dimensionally and periodically arranged on the main surface of the dielectric layer 12. In this embodiment, as shown in Fig. 2, a square arrangement is adopted as the periodic two-dimensional arrangement of the conductor patterns 111. However, this periodic two-dimensional arrangement is not limited to a square arrangement, and may be, for example, a hexagonal arrangement as shown in Fig. 4.

[0036] The diameter D of the circle circumscribing each conductor pattern 111 is determined to satisfy 200 nm≦D≦800 nm. When each conductor pattern 111 has a circular shape as in this embodiment, the circle circumscribing each conductor pattern 111 approximately matches the shape of each conductor pattern 111. There is a positive correlation between the diameter D and the center wavelength in the absorption band caused by the mode in which the diffraction mode and the plasmo mode are coupled. Therefore, by appropriately setting the diameter D within the range of 200 nm≦D≦800 nm, the center wavelength in the absorption band of the plasmon absorption can be adjusted arbitrarily. The range in which the center wavelength can be adjusted is, for example, approximately 1 μm or more, as shown in FIG. 7. 2.7 μm or less.

[0037] Furthermore, a period P, which is the center-to-center distance between adjacent conductor patterns 111 among the multiple conductor patterns 111, is determined in accordance with the diameter D. Specifically, each of the period P and the diameter D is determined to satisfy 1.3≦P / D≦2.0. That is, the period P is determined to satisfy 1.3×D≦P≦2.0×D.

[0038] Furthermore, the thickness h of each conductor pattern 111 is 40 nm in this embodiment, but the thickness h is not limited to this and can be determined appropriately.

[0039] [Method for manufacturing a plasmonic structure] An example of a method for manufacturing the plasmonic structure 1 will be described with reference to FIG. 5. In this embodiment, electron beam lithography is used to pattern the multiple conductor patterns 111 constituting the conductor layer 11. However, the lithography used in this patterning is not limited to electron beam lithography as long as it is a lithography that can realize a desired resolution. An example of lithography other than electron beam lithography is UV lithography. The wavelength of the ultraviolet light used in UV lithography can be appropriately selected. The wavelength of the ultraviolet light may be, for example, included in the DUV (Deep ultraviolet) region or the EUV (Extreme ultraviolet) region.

[0040] 4, when the periodic two-dimensional pattern in the plurality of conductor patterns 111 is a hexagonal arrangement, interference exposure can also be used in the above-mentioned patterning. This is because in interference exposure, a region where the intensity of interference light is high becomes a pattern corresponding to the hexagonal arrangement.

[0041] A simple explanation of interference exposure is as follows. When a diffraction grating is placed under spatially coherent illumination, an intensity pattern with the same period as the diffraction grating is formed at a specific distance from the diffraction grating. Interference exposure is a technique for integrating the intensity distribution in one period caused by the Talbot effect. By using interference exposure when exposing the photoresist R, cross-order interference can be eliminated.

[0042] 5, the manufacturing method of the plasmonic structure 1 includes a film forming step S11, a spin-coating step S12, a lithography step S13, a film forming step S14, and a lift-off step S15. In this manufacturing method, a Si wafer is used as a base material B on which the plasmonic structure 1 is formed.

[0043] The film formation step S11 is a step of forming the conductor layer 13 and the dielectric layer 12 to a predetermined thickness on one main surface of the substrate B. In the present embodiment, a sputtering method is used as a method for forming the conductor layer 13 and the dielectric layer 12. However, the method for forming the conductor layer 13 and the dielectric layer 12 is not limited thereto.

[0044] The spin-coating step S12 is a step carried out after the film-forming step S11, and is a step of applying a photoresist R by spin-coating onto one of the main surfaces of the dielectric layer 12, which is the main surface opposite the conductor layer 13.

[0045] The lithography step S13 is a step carried out after the spin coating step S12, in which the photoresist R is exposed to light in a manner corresponding to the plurality of conductor patterns 111 by using electron beam lithography, and the photoresist R is developed.

[0046] The film formation step S14 is a step performed after the lithography step S13, and is a step of forming a conductor layer 11 on one main surface of the photoresist R, which is the main surface opposite the dielectric layer 12. In this embodiment, a sputtering method is used as a method for forming the conductor layer 11. However, the method for forming the conductor layer 11 is not limited to this.

[0047] The lift-off process S15 is a process carried out after the film-forming process S14, and is a process of removing the photoresist R by using a solvent. By this process, the conductor layer 11 formed on the photoresist R is removed together with the photoresist R.

[0048] By carrying out the above steps, the plasmonic structure 1 can be manufactured. EXAMPLES

[0049] The plasmonic structure 1, which is the first to fourth examples constituting the embodiment group of the present invention, will be described with reference to Figs. 6 to 9. In addition, the plasmonic structures, which are the first and second comparative examples of the present invention, will be described with reference to Figs. 10 to 12, in comparison with the first to fourth examples. Fig. 6 is an image showing the relationship between the reflectance, the period, and the wavelength in the second example. Fig. 7 is a graph showing the wavelength dependence of the reflectance in the first to fourth examples. Fig. 8 is an SEM image of the second example. Fig. 9 is a graph showing the measurement results and the calculation results of the wavelength dependence of the reflectance in the second example. Fig. 10 is an image showing the relationship between the reflectance, the period, and the wavelength in the first comparative example. Fig. 11 is an image showing the relationship between the reflectance, the period, and the wavelength in the second comparative example. Fig. 12 is a graph showing the wavelength dependence of the reflectance in the second example, the first comparative example, and the second comparative example.

[0050] In each of the first to fourth examples, the design parameters of the plasmonic structure 1, diameter D, period P, thickness g, and thickness h, were set as follows. g / D and P / D are also shown. The dimensions indicated by the diameter D, period P, thickness g, and thickness h are as shown in FIG. 3.

[0051] First Example: D=200 nm, P=300 nm, g=100 nm, h=40 nm, g / D=0.5, P / D=1.5 Second Example: D=400 nm, P=650 nm, g=180 nm, h=40 nm, g / D=0.45, P / D=1.625 Third Example: D=600 nm, P=1050 nm, g=240 nm, h=40 nm, g / D=0.4, P / D=1.75 Fourth Example: D=800 nm, P=1400 nm, g=340 nm, h=40 nm, g / D=0.425, P / D=1.1.75 In the first and second comparative examples, the thickness g was changed as follows based on the configuration of the second comparative example. g / D is also shown.

[0052] First Comparative Example: g=80 nm, g / D=0.2 Second Comparative Example: g=280 nm, g / D=0.7 As described above, the first comparative example has a g / D smaller than 0.3, and the second comparative example has a g / D larger than 0.6.

[0053] [Simulation results] Based on the design parameters of the second embodiment, a simulation of the reflectance was performed when the period P was changed between 0.4 μm and 1.2 μm. In this simulation, linearly polarized light was incident on the plasmonic structure 1 from the direction of the normal to the main surface of the plasmonic structure 1. The simulation was performed based on the finite difference time domain method (FDTD method). The wavelength of the linearly polarized light was set to 400 nm or more and 3 μm or less. In FIG. 6, the reflectance is represented by a gray scale bar. Here, the reflectance can be read as the absorptance by using the relational expression between the reflectance and the absorptance (absorptance=1-reflectance). In the following, the wavelength band where the absorptance is 90% or more (i.e., the wavelength band where the reflectance is 10% or less) is regarded as the band where the absorptance is high (i.e., the band where the emissivity is high).

[0054] According to FIG. 6, it was found that in the plasmonic structure 1 based on the design parameters of the second embodiment, the absorption band of the absorption mode in which the diffraction mode and the plasmo mode are coupled exists over a wide wavelength range.

[0055] 12, it was found that the second embodiment had an absorptance of 90% or more in the wavelength band of approximately 1.0 μm to 2.2 μm inclusive. In other words, it was found that the bandwidth with high absorptance in the second embodiment was approximately 1.2 μm.

[0056] According to FIG. 10, it was found that in the plasmonic structure based on the design parameters of the first comparative example, the diffraction mode and the plasmo mode are induced independently.

[0057] 12, the first comparative example (g=80 nm) shows that the first comparative example has an absorptance of 90% or more in the wavelength band of approximately 0.7 μm or more and 0.8 μm or less. That is, in the first comparative example, the bandwidth with high absorptance is approximately 0.1 μm.

[0058] According to FIG. 11, it was found that in the plasmonic structure based on the design parameters of the second comparative example, the mode in which the diffraction mode and the plasmo mode are coupled disappears.

[0059] 12, the plot of the second comparative example (g=280 nm) shows that the second comparative example does not have a wavelength band in which the absorptance is 90% or more. This shows that if the thickness g is too thick, plasmon resonance accompanied by strong absorption cannot be induced.

[0060] Next, the results of a similar simulation performed on the first to fourth examples will be described.

[0061] According to the plot of the first embodiment in Fig. 7, it was found that the first embodiment has an absorptance of 90% or more in the wavelength band of approximately 0.65 μm or more and 1.45 μm or less. That is, in the first embodiment, it was found that the bandwidth with high absorptance was approximately 0.8 μm. Also, it was found that the central wavelength of the absorption band with high absorptance was approximately 1.0 μm.

[0062] According to the plot of the second embodiment in Fig. 7, it was found that the second embodiment has an absorptance of 90% or more in the wavelength band of approximately 1.0 μm or more and 2.2 μm or less. That is, in the second embodiment, it was found that the bandwidth with high absorptance was approximately 1.2 μm. Also, it was found that the central wavelength of the absorption band with high absorptance was approximately 1.6 μm.

[0063] According to the plot of the third embodiment in Fig. 7, it was found that the third embodiment has an absorptance of 90% or more in the wavelength band of approximately 1.4 μm or more and 2.7 μm or less. That is, in the third embodiment, it was found that the bandwidth with high absorptance was approximately 1.3 μm. Also, it was found that the central wavelength of the absorption band with high absorptance was approximately 2.1 μm.

[0064] According to the plot of the fourth embodiment in Fig. 7, it was found that the fourth embodiment has an absorptance of 90% or more in the wavelength band of approximately 1.9 μm or more and 3.5 μm or less. That is, in the second embodiment, it was found that the bandwidth with high absorptance was approximately 1.6 μm. Also, it was found that the central wavelength of the absorption band with high absorptance was approximately 2.7 μm.

[0065] As described above, it was found that the central wavelength can be adjusted within the range of approximately 1.0 μm to 2.7 μm by appropriately setting the diameter D within the range of 200 nm≦D≦800 nm.

[0066] In the above simulation, the characteristics of a specific wavelength band with high absorptivity for the structure (parameter settings) of the plasmonic structure 1 in each embodiment are shown, but these characteristics also show similar characteristics in light emission caused by heating the plasmonic structure. This is because, according to Kirchhoff's law, the emissivity of an object is equal to the absorptivity. In this way, by appropriately setting each parameter of the plasmonic structure, it is possible to configure a plasmonic structure (i.e., a wavelength-selective absorption element) that absorbs light in any specific wavelength band from the visible light region to the infrared region, and a plasmonic structure (i.e., a light source) that emits light in any specific wavelength band from the visible light region to the infrared region.

[0067] [Actual measurement results] Next, the plasmonic structure 1 of the second example was manufactured using the manufacturing method shown in Fig. 5. It was found that the plasmonic structure 1 actually manufactured also had a plurality of conductor patterns 111 periodically arranged two-dimensionally (see Fig. 8).

[0068] 9, it was found that the second embodiment actually manufactured had an absorptance of 90% or more in the wavelength band of approximately 1.0 μm or more and 2.0 μm or less. That is, it was found that the bandwidth with high absorptance was approximately 1.0 μm in the second embodiment actually manufactured. It was also found that the central wavelength of the absorption band with high absorptance was approximately 1.5 μm.

[0069] From the above results, it was found that a mode in which the diffraction mode and the plasmo mode are coupled is induced in the actually manufactured plasmonic structure 1, and that it exhibits high absorptance in a wide band. In addition, when the reflection characteristics of the actually manufactured plasmonic structure 1 were compared with those obtained by simulation, it was found that although the bandwidth with high absorptance was slightly narrower, they showed a similar tendency and were generally consistent.

[0070] 〔summary〕 The plasmonic structure according to the first aspect of the present invention employs a structure in which a first conductor layer covering a specific surface, a dielectric layer, and a second conductor layer consisting of a plurality of conductor patterns arranged two-dimensionally and periodically, each of which is a circle or a regular polygon, are stacked in this order.

[0071] In addition, in the plasmonic structure of the first embodiment, a diameter D of a circle circumscribing each of the multiple conductor patterns satisfies 200 nm≦D≦800 nm, and the thickness g and diameter D of the dielectric layer satisfy 0.3≦g / D≦0.6.

[0072] In conventional plasmonic structures, plasmon absorption due to surface plasmon resonance is mainly used, and therefore the bandwidth of the absorption band obtained by the conventional plasmonic structures is mainly determined by the diameter of the conductor pattern and is narrow.

[0073] According to the above configuration, a thickness g that is thicker than that of a conventional plasmonic structure is adopted, and the thickness g and the diameter D satisfy 0.3≦g / D, so that a mode in which a diffraction mode and a plasmo mode are coupled can be induced. Therefore, the plasmonic structure according to the first aspect can utilize absorption caused by a mode in which a diffraction mode and a plasmo mode are coupled.

[0074] The mode in which the diffraction mode and the plasmo mode are coupled is induced in a wider band than the plasmo mode. Therefore, the plasmonic structure according to the first embodiment can broaden the band in which the absorption rate is high compared to the conventional plasmonic structures. According to Kirchhoff's law, the emissivity of an object is equal to the absorptivity, so the plasmonic structure according to the first embodiment can broaden the band in which the emissivity is high compared to the conventional plasmonic structures.

[0075] If the thickness g is too large, the plasmo mode becomes weak, and it becomes impossible to induce a mode in which the diffraction mode and the plasmo mode are coupled. According to the above configuration, by making the thickness g and the diameter D satisfy g / D≦0.6, it is possible to avoid the inability to induce a mode in which the diffraction mode and the plasmo mode are coupled.

[0076] In addition, in a plasmonic structure according to a second aspect of the present invention, in addition to the configuration of the plasmonic structure according to the first aspect described above, the first conductor layer and the second conductor layer are made of HfN.

[0077] HfN (hafnium nitride) has a melting point of 2573°C, which is higher than Ag (silver), Au (gold), Cu (copper), Cr (chromium), Al (aluminum), and Fe (iron), which are often used as materials for forming plasmonic structures. Therefore, the plasmonic structure according to the second embodiment can have higher heat resistance than the plasmonic structure containing the above-mentioned metal material. W (tungsten), Ta (tantalum), and Mo (molybdenum) are known as high-melting-point metals having melting points of about 3000°C. However, these high-melting-point metals have a negative real part of the dielectric constant in the infrared range, but a positive real part of the dielectric constant in the visible range. Therefore, these high-melting-point metals do not produce a plasmonic effect in the visible range. In order to exhibit the plasmonic effect over a wide wavelength range including visible light, HfN, which has a high melting point and a negative dielectric constant even in the visible range, is suitable as the material constituting the first conductor layer and the second conductor layer.

[0078] In addition, in a plasmonic structure according to a third aspect of the present invention, in addition to the configuration of the plasmonic structure according to the first or second aspect described above, a configuration is adopted in which the dielectric layer is composed of any one of SiO2, Al2O3, and a mixture of SiO2 and Al2O3.

[0079] According to the above configuration, the heat resistance of the plasmonic structure can be reliably improved.

[0080] Furthermore, in a plasmonic structure according to a fourth aspect of the present invention, in addition to the configuration of the plasmonic structure according to any one of the first to third aspects described above, a configuration is adopted in which the period P and diameter D in the two-dimensional arrangement of the multiple conductor patterns are 1.3≦P / D≦2.0.

[0081] According to the above configuration, since the plasmonic mode can be made sufficiently strong, a mode in which the diffraction mode and the plasmonic mode are coupled can be reliably induced. Therefore, the plasmonic structure according to the fourth aspect can reliably widen the band in which the absorption rate is high, compared with the conventional plasmonic structures.

[0082] Furthermore, a plasmonic structure according to a fifth aspect of the present invention has, in addition to the configuration of the plasmonic structure according to any one of the first to fourth aspects described above, a configuration in which the multiple conductor patterns are arranged hexagonally in the second conductor layer.

[0083] According to the above configuration, the plurality of conductor patterns can be easily fabricated as compared with a case where the plurality of conductor patterns are arranged in an arrangement other than a hexagonal arrangement, because interference exposure can be used instead of electron beam exposure when exposing the plurality of conductor patterns.

[0084] A light source according to a sixth aspect of the present invention includes a substrate and a plasmonic structure according to any one of the first to fifth aspects described above, in which the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and the plasmonic structure emits light in a specific wavelength band when heated.

[0085] According to the above configuration, the same effects as those of the plasmonic structure according to any one of the first to fifth aspects can be achieved. In addition, since the plasmonic structure according to any one of the first to fifth aspects can be used to control the spectral emissivity of the light source, it is possible to reduce energy loss in the light source.

[0086] A wavelength-selective absorption element according to a seventh aspect of the present invention employs a configuration including a substrate and a plasmonic structure according to any one of the first to fifth aspects described above, in which the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and the plasmonic structure absorbs light in a specific wavelength band.

[0087] According to the above configuration, the same effects as those of the plasmonic structure according to any one of the first to fifth aspects can be achieved. Moreover, by using the plasmonic structure according to any one of the first to fifth aspects, light in a specific wavelength band can be selected.

[0088] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0089] 1 Plasmonic structures 11 Conductive layer (second conductive layer) 111 Conductor Pattern 12 Dielectric layer 13 Conductive layer (first conductive layer)

Claims

1. A plasmonic structure in which a first conductor layer covering a specific surface, a dielectric layer, and a second conductor layer consisting of a plurality of conductor patterns arranged two-dimensionally and periodically, each of which has a circular or regular polygonal shape, are laminated in this order, a diameter D of a circle circumscribing each of the plurality of conductor patterns satisfies 200 nm≦D≦800 nm; the thickness g and diameter D of the dielectric layer satisfy 0.3≦g / D≦0.6, The central wavelength of a wavelength range in which the light absorptance in the plasmonic structure is 90% or more is within a wavelength range of 1.0 μm to 2.7 μm, and the bandwidth of the wavelength range is 0.8 μm to 1.6 μm. A plasmonic structure comprising:

2. The first conductor layer and the second conductor layer are made of HfN. The plasmonic structure of claim 1 .

3. The dielectric layer is made of SiO ２ , Al ２ O ３ , and SiO ２ and Al ２ O ３ or a mixture thereof. The plasmonic structure according to claim 1 or 2.

4. The period P and the diameter D in the two-dimensional arrangement of the plurality of conductor patterns are 1.3≦P / D≦2.

0. The plasmonic structure according to any one of claims 1 to 3.

5. In the second conductor layer, the plurality of conductor patterns are arranged in a hexagonal pattern. The plasmonic structure according to any one of claims 1 to 4.

6. A substrate; A light source comprising the plasmonic structure according to any one of claims 1 to 5, wherein the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and the plasmonic structure emits light in a specific wavelength band when heated.

7. A substrate; The plasmonic structure according to any one of claims 1 to 5, comprising: a plasmonic structure in which the first conductor layer, the dielectric layer, and the second conductor layer are stacked in this order on a surface of the substrate, and which absorbs light in a specific wavelength band. A wavelength-selective absorption element.

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