Nickel-aluminum film, method for producing the same, device for conversion between light and heat, thermo-photovoltaic power generation device, heat-assisted magnetic recording device, electronic device, and sheet-like heating heater

Abstract

To provide a NiAl film that exhibits excellent optical response appropriate for conversion between light and heat and the like.SOLUTION: A NiAl film, having an atomic ratio of Ni to Al of 1:1, a preferential orientation plane of (110), and a root mean square surface roughness on the surface of 6 nm or less, demonstrates excellent optical response. The NiAl film can be fabricated, for example, by laminating another NiAl film under conditions that improve flatness on a NiAl film formed under conditions in which the (110) plane is preferentially oriented, followed by post-annealing the laminated film at 700 K or more and 940 K or less. The NiAl film is applicable as, for example, a heater that radiates infrared light with a sharp peak at a desired wavelength upon heating, an infrared sensor that achieves high wavelength resolution by strongly absorbing light of a specific wavelength and converting it into heat, optical radiation or heating that makes use of electromagnetic field enhancement or near-field, and various other applications other than light-heat conversion.SELECTED DRAWING: Figure 34

Description

[Technical Field]

[0001] The present invention relates to a material used in devices that convert light to heat using plasmon resonance, and more specifically to a film of an alloy of nickel (Ni) and aluminum (Al) that is used for such applications, etc. The present invention also relates to a method for producing a film that is particularly suitable for such applications, etc. [Background technology]

[0002] Photo-thermal converters are key elements in infrared device technology. Recently, photo-thermal converters based on two-dimensionally lithographically patterned metal nanostructures have been proposed and fabricated to specify wavelength ranges for use in infrared detectors and heaters. Another common type of spectroscopic photo-thermal converter is the distributed Bragg reflector (DBR)-based IR device. Specific structures of this type of photo-thermal converter are described in, for example, U.S. Patent No. 5,929,231 and U.S. Patent No. 5,929,231.

[0003] When using this type of light-to-heat converter, enhancing the wavelength selectivity of light is extremely useful. Specifically, when converting heat into light (infrared light) and irradiating it to heat an object noncontact, the efficiency of heating can be improved if infrared light of a wavelength that is efficiently absorbed by a specific component of the object can be irradiated. This wavelength selectivity is also useful, for example, when selectively volatilizing a specific component in a liquid. Conversely, to avoid problems such as thermal decomposition or deformation during heating or to minimize the amount of volatilization of a specific component in a liquid, it is possible to irradiate the object with infrared light of a wavelength that is poorly absorbed by the component. This wavelength selectivity is also useful in applications where light is converted into heat. For example, when using such a converter as a sensor, by enhancing the wavelength selectivity of light, the intensity of the component of a specific wavelength in the light input to the converter can be measured by measuring the heat generated by converting light of a specific wavelength into heat. Of course, it can also be used as a thermal sensor by converting heat into light.

[0004] Plasmon resonance can be utilized to improve the wavelength selectivity described above. More specifically, a plasmonic perfect absorber (PA) also functions as a wavelength-selective infrared emitter with an emission spectrum equivalent to its absorption spectrum, according to Kirchhoff's law for thermal radiation. By utilizing this property, a light-to-heat converter can be provided that can convert light and heat mutually with high wavelength selectivity using a plasmonic perfect absorber. For information on such a light-to-heat converter, see, for example, Patent Document 2.

[0005] Furthermore, photoelectric conversion, that is, conversion between light and electricity, is possible as well as photothermal conversion, and here too the selectivity of the wavelength of light is useful. Summary of the Invention [Problem to be solved by the invention]

[0006] Photo-thermal converters are often used in environments much higher than room temperature (denoted as RT in drawings, etc.). For example, when using a photo-thermal converter as an infrared source for infrared heating, it is often desirable to maximize the intensity of the infrared radiation generated by heating the photo-thermal converter to a high temperature. Therefore, in order to use a material with plasmonic properties (more precisely, optical response, hereafter referred to as optical response) in a photo-thermal converter, it is desirable that such a material not only have good optical response but also be able to withstand high temperatures. Note that a good optical response means that the real part ε1 of its complex dielectric constant is large on the negative side and the imaginary part ε2 is small. Furthermore, since it would be advantageous if a photo-thermal converter could be used without additional protective measures in a high-temperature oxidizing atmosphere containing oxygen, water vapor, or the like, it is also desirable that materials for the photo-thermal converter, which may come into contact with such an atmosphere, be highly resistant to high-temperature oxidizing atmospheres. Furthermore, when a photo-thermal converter is used as an optical sensor for infrared light, etc., it is often used not only at room temperature but also in a high-temperature oxidizing atmosphere, so resistance to oxidizing atmospheres is also desirable in this case.

[0007] Gold (Au) is well known as a material with good optical response. However, Au is not only expensive, but also has a relatively low melting point of approximately 1337 K. Furthermore, Au softens or peels off into droplets at temperatures significantly lower than its melting point, making it unsuitable for use in optical-thermal converters used at high temperatures. Therefore, there is a need for optical-thermal converter materials that have good optical response and can be used in oxidizing atmospheres at high temperatures.

[0008] A thermal-to-light converter that uses a plasmonic perfect absorber made of a metal other than gold (Au) or platinum (Pt) and can operate at relatively high temperatures has been proposed, for example, using a molybdenum (Mo)-based material (Non-Patent Document 1). However, while such a thermal-to-light converter can operate up to 1273 K in a vacuum, it oxidizes and is damaged in air at temperatures of, for example, 873 K. In fact, when a thin film of molybdenum is exposed to air at 873 K, it discolors to a white color that is clearly visible to the naked eye, making it unusable as a material for a thermal-to-light converter that utilizes optical response. Furthermore, tungsten (W) oxidizes to almost the same extent under the same conditions, so it cannot be used for this purpose either.

[0009] Additionally, the fabrication of aluminum (Al)- and indium tin oxide (ITO)-based thermal-to-optical converters has also been reported (Non-Patent Documents 2 and 3). These optical-to-thermal converters exhibit good wavelength tunability and can be operated in air. However, at temperatures above 573 K and 673 K, respectively, Al begins to dissolve from its surface, and the optical properties of ITO rapidly deteriorate. Furthermore, when other materials, such as titanium (Ti)-based oxides and nitrides, are used, the plasmon resonance becomes significantly broader and corrosion begins when operated at temperatures above 650 K.

[0010] In a previously published paper, Non-Patent Document 4, the inventors of the present application focused on the fact that high-temperature resistant alloys (also called superalloys), known for their use as materials for jet engine turbine blades and other applications that operate under high mechanical loads in oxidizing environments at high temperatures, have the potential to be used in high-temperature oxidizing environments. They investigated the possibility of using these alloys as optically responsive materials for light-to-heat converters and other applications that can be used in high-temperature oxidizing environments. As a result, they found that, among high-temperature resistant alloys, NiAl (cesium chloride lattice structure, space group Pm-3m, lattice constant 2.88 Å), whose crystal structure is shown in Figure 1, is suitable for solving the above-mentioned problems. The table below compares the basic properties of NiAl with those of typical high-temperature resistant alloys, NiTi and Ni3Al.

[0011] [Table 1]

[0012] As is clear from the table above, of NiTi, Ni3Al, and NiAl, NiAl has the highest melting point, making it the preferred material for light-to-heat converters, which are often exposed to high temperatures. Furthermore, NiAl has an electrical resistivity that is one-third or less that of the other two materials, minimizing loss, and its thermal conductivity is more than twice as high, making it advantageous for supplying heat to be converted into light, extracting heat converted from light, and cooling to prevent excessive temperature rise.

[0013] NiAl can also be used as a bulk material in optical-to-thermal converters, and the best properties are expected when NiAl single crystals are used. However, as is well known in the field of heat-resistant alloys, NiAl has poor workability to be formed into desired shapes, sizes, and thicknesses, which poses a problem for applications such as optical-to-thermal converters. Furthermore, the furnace and crucible temperatures required to grow NiAl single crystals exceed 1900 K, making it difficult to produce well-oriented bulk crystals. In fact, while NiAl can be used as a heat-resistant coating material, its use as a heat-resistant single-crystal bulk component itself is considered difficult. Therefore, when nickel-aluminum alloys are used for the main body of heat-resistant components, Ni3Al is usually used.

[0014] Non-Patent Document 4 clarifies that by forming a NiAl film by magnetron sputtering on a substrate heated to a relatively high temperature (specifically, 744 K to 889 K) but sufficiently lower than the melting point of NiAl, 1956 K, a uniaxial (110) NiAl thin film with good crystallinity and a preferred orientation of the (110) plane can be formed, and that this polycrystalline NiAl film has optical properties sufficiently close to those of single-crystal NiAl. Because this NiAl film has such good optical properties, i.e., good optical response, it can be used much more easily than bulk NiAl in sensors, optical-thermal converters, and the like, and can demonstrate high performance, and therefore this thin film can be used in sensors, optical-thermal converters, and the like.

[0015] The film formation method described in Non-Patent Document 4 provides NiAl films with excellent optical response and high resistance to high-temperature oxidizing atmospheres, making them suitable for a wide range of applications, including sensors and photothermal converters. However, this NiAl film suffers from the problem of impaired surface flatness (increased surface roughness) due to gaps formed between the NiAl crystal grains as they grow on the substrate. This not only increases film loss (i.e., the imaginary part of the complex dielectric constant), but also leads to the appearance of structures on the film surface measuring several tens to several hundreds of nanometers, resulting in the NiAl film itself possessing a resonator structure due to localized surface plasmons and the Mie resonance effect. This may manifest as unintended peaks or background in the absorption / emission spectra of photothermal converters using the NiAl film. Furthermore, the gaps between the crystal grains tend to be quite deep, which may allow the atmosphere to penetrate through the gaps and into the film when used in a high-temperature oxidizing atmosphere. If this occurs, the NiAl film, which is expected to also function as a protective film for light-to-heat converters and sensors, will lose its function early, and the lifespan of these types of devices may vary greatly, which is an extremely undesirable situation from the standpoint of quality control. The NiAl film produced by the method shown in Non-Patent Document 4 exhibits better optical response (specifically, the figure of merit FOM, described below) at higher temperatures within the substrate temperature range of 744 K to 889 K mentioned above. However, the problem of increased surface roughness becomes more pronounced, and so as long as NiAl films are produced according to this document, it is often the case that the optical response cannot be optimized, which is a major problem.

[0016] In addition to the importance of environmental resistance as described above, in order to be useful as a sensor for light, particularly near-infrared light, it is necessary to use a material with a sufficiently low Schottky barrier as the plasmonic perfect absorber material. [Means for solving the problem]

[0017] According to one aspect of the present invention, there is provided a nickel aluminum film having an atomic ratio of Ni to Al of 1:1, a (110) plane as a preferred orientation plane, and a surface root mean square roughness of 6 nm or less. Here, the figure of merit of the optical response may be 3 or more within the wavelength range of 0.8 μm to 2.5 μm. The figure of merit of the optical response may be 2 or more within the wavelength range of 0.6 μm to 2 μm. The figure of merit of the optical response may be 2 or more within the wavelength range of 1.2 μm to 4 μm. Furthermore, the integrated intensity of the peak corresponding to the (110) plane in the XRD pattern may be 65% or more of the total integrated intensity. The film thickness may be in the range of 1 nm to 30 nm. According to another aspect of the present invention, there is provided a nickel aluminum film having a thickness in the range of 2 nm or more and less than 20 nm and an atomic ratio of Ni to Al of 1:1. According to yet another aspect of the present invention, there is provided a method for producing a nickel-aluminum film in which the atomic ratio of nickel to aluminum is 1:1, the (110) plane is the preferred orientation plane, and the root-mean-square roughness of the surface is 6 nm or less, by post-annealing a nickel-aluminum film having an atomic ratio of nickel to aluminum of 1:1 at 700 K or more and 940 K or less. Here, the post-annealing temperature may be 930K or less. The nickel aluminum film to be post-annealed may be formed by magnetron sputtering on a substrate at room temperature. According to yet another aspect of the present invention, there is provided a method for producing a nickel-aluminum film having an atomic ratio of nickel to aluminum of 1:1, a preferred orientation plane of the (110) plane, and a surface root-mean-square roughness of 6 nm or less, by forming a second nickel-aluminum film having a surface roughness smaller than that of the first nickel-aluminum film on the first nickel-aluminum film having an atomic ratio of nickel to aluminum of 1:1, and the second nickel-aluminum film having a surface roughness smaller than that of the first nickel-aluminum film, and post-annealing the nickel-aluminum film at a temperature of 700 K or more and 940 K or less. Here, the first nickel aluminum film may be formed by magnetron sputtering at a substrate temperature of 700K or more and 940K or less. The second nickel aluminum film may be formed by magnetron sputtering on the first nickel aluminum film at room temperature. According to yet another aspect of the present invention, there is provided a device for converting light to heat using any of the nickel aluminum films described above. According to yet another aspect of the present invention, there is provided a thermophotovoltaic power generation device using any of the above nickel aluminum films as a near-infrared emitter. According to yet another aspect of the present invention, there is provided a thermally assisted magnetic recording device in which any one of the nickel aluminum films described above is used in a near-field light generating element for forming a light spot for heating a magnetic recording medium. According to yet another aspect of the present invention, there is provided an electronic device for absorbing / emitting light utilizing optical response, which uses any one of the nickel aluminum films described above as an electrode material. According to yet another aspect of the present invention, there is provided a planar heater that generates heat by passing an electric current through any one of the nickel aluminum films described above. [Effects of the Invention]

[0018] According to the present invention, by using a NiAl film with small surface roughness, it is possible to provide a material for optical-thermal converters and optical-electrical converters that has good optical response, reduces unnecessary peaks and background in the absorption / emission spectrum compared to previously proposed materials, and exhibits stable resistance to high-temperature oxidizing atmospheres. Furthermore, the NiAl film of the present invention can maintain its continuous film form even when its thickness is around 20 nm or even thinner. Furthermore, since the Schottky barrier of this material is sufficiently low, it is also useful as a material for optical-electrical converters. Furthermore, by utilizing the good optical response and heat resistance of the NiAl film of the present invention, various other applications are possible. Furthermore, by appropriately selecting the film formation method and film formation conditions, the optical response can be further improved. [Brief explanation of the drawings]

[0019] [Figure 1] Diagram showing the crystal structure of NiAl. [Figure 2] FIG. 2 is a diagram schematically showing a second method (two-stage film formation method) for producing a NiAl film according to the present invention. [Figure 3A] FIG. 10 is a SEM image of the surface of a NiAl film produced at a substrate temperature of 744 K using a comparative example of a NiAl film production method (in-situ film formation method). [Figure 3B] 3B is a graph showing the relationship between the complex dielectric constant and wavelength (referred to as dielectric function and wavelength in the figure, respectively; the same applies below) of the NiAl film shown in FIG. 3A. [Figure 3C] FIG. 3B shows an AFM image of the NiAl film shown in FIG. 3A. [Figure 4A] FIG. 10 is a SEM image of the surface of a NiAl film produced at a substrate temperature of 814 K using a comparative example of a NiAl film production method (in-situ film formation method). [Figure 4B] FIG. 4B is a diagram showing the complex dielectric constant of the NiAl film shown in FIG. 4A. [Figure 4C] FIG. 4B shows an AFM image of the NiAl film shown in FIG. 4A. [Figure 5A]FIG. 10 is a SEM image of the surface of a NiAl film produced at a substrate temperature of 889 K using a comparative example of a NiAl film production method (in-situ film formation method). [Figure 5B] FIG. 5B is a diagram showing the complex dielectric constant of the NiAl film shown in FIG. 5A. [Figure 5C] FIG. 5B shows an AFM image of the NiAl film shown in FIG. 5A. [Figure 6A] FIG. 10 is a SEM image of the surface of a NiAl film produced at a substrate temperature of 967 K using a comparative example of a NiAl film production method (in-situ film formation method). [Figure 6B] FIG. 6B is a diagram showing the complex dielectric constant of the NiAl film shown in FIG. 6A. [Figure 6C] FIG. 6B shows an AFM image of the NiAl film shown in FIG. 6A. [Figure 7A] 6A , 6B, 6C, and 6D are SEM images of the surface of a NiAl film produced under the same conditions as the NiAl film shown in FIG. 3A, FIG. 4A, FIG. 5A, and FIG. 6A by a comparative example production method (in-situ film formation method), except that the substrate temperature was room temperature. [Figure 7B] 7B is a graph showing the complex dielectric constant of the NiAl film shown in FIG. 7A. [Figure 7C] FIG. 7B is an AFM image of the NiAl film shown in FIG. 7A. [Figure 8] 3A, 4A, 5A, 6A, and 7A, and a sample of NiAl single crystal cut on the (110) plane. FIG. [Figure 9] Figure 3A, 4A, 5A, 6A, and 7A show the figure of merit (FOM) of the NiAl film and the NiAl single crystal cut on the (110) plane. The FOMs of lanthanum hexaboride (LaB6), gold (Au), tungsten (W), molybdenum (Mo), and titanium nitride (TiN) are also shown. [Figure 10] This figure compares the FOM of the NiAl film (substrate temperature 889 K) in Figure 5A, which gives the best FOM among the NiAl films produced by the comparative example method, with the FOMs of a sample cut from a NiAl single crystal on the (110) plane, LaB6, Au, W, Mo, and TiN. [Figure 11]This figure compares the real part of the complex dielectric constant (ε1) of the NiAl film (substrate temperature 889 K) in Figure 5A, which gives the best FOM among the NiAl films produced by the comparative example method, with the real part of the complex dielectric constant (ε1) of a sample cut from a NiAl single crystal along the (110) plane, LaB6, Au, W, Mo, and TiN. [Figure 12] This figure compares the imaginary part (ε2) of the complex permittivity (denoted as "imaginary part" in the figure; the same applies below) of the NiAl film (Fig. 5A) that gives the best FOM among the NiAl films produced by the comparative example method (substrate temperature 889 K), with the imaginary part (ε2) of the complex permittivity of a sample cut from a NiAl single crystal along the (110) plane, LaB6, Au, W, Mo, and TiN. [Figure 13A] 1 shows an SEM image of the surface of an NiAl film according to an embodiment of the present invention, which was produced using the first NiAl film production method (post-annealing method) at a post-annealing temperature of 776 K. A cross-sectional SEM image near the surface is also shown as an inset in the upper right corner. [Figure 13B] FIG. 13B is an AFM image of the NiAl film shown in FIG. 13A. [Figure 14A] 1 shows an SEM image of the surface of an NiAl film according to an embodiment of the present invention, which was produced using the first NiAl film production method (post-annealing method) at a post-annealing temperature of 851 K. A cross-sectional SEM image near the surface is also shown as an inset in the upper right corner. [Figure 14B] FIG. 14B shows an AFM image of the NiAl film shown in FIG. 14A. [Figure 15A] 1 shows an SEM image of the surface of an NiAl film according to an embodiment of the present invention, which was produced using the first NiAl film production method (post-annealing method) at a post-annealing temperature of 928 K. A cross-sectional SEM image near the surface is also shown as an inset in the upper right corner. [Figure 15B] FIG. 15B is an AFM image of the NiAl film shown in FIG. 15A. [Figure 16A] 1 shows an SEM image of the surface of an NiAl film according to an embodiment of the present invention, which was produced using the first NiAl film production method (post-annealing method) at a post-annealing temperature of 967 K. A cross-sectional SEM image near the surface is also shown as an inset in the upper right corner. [Figure 16B] FIG. 16B shows an AFM image of the NiAl film shown in FIG. 16A. [Figure 17] 15A , 15B, and 15C show SEM images of the surface of a comparative NiAl film produced under the same conditions as those of the example of the second production method of the present invention shown in FIGS. 13A, 14A, and 15A, except that post-annealing was not performed. A cross-sectional SEM image near the surface is also shown as an inset in the upper right corner. [Figure 18] 13A, 14A, 15A, and 16A show XRD patterns of the NiAl films of the examples of the present invention, the NiAl film shown in FIG. 17 formed under the same conditions except for the absence of post-annealing (i.e., the film was formed as is with the substrate temperature at room temperature), and a sample of NiAl single crystal cut on the (110) plane. [Figure 19] FIG. 18 is a graph comparing the FOM of the NiAl film of an embodiment of the present invention, which was fabricated using the first NiAl film fabrication method (post-annealing method) of the present invention, with the FOM of the NiAl film formed under the same conditions except for the absence of post-annealing, as shown in FIG. [Figure 20] This figure compares the FOM of the NiAl film (post-annealing temperature 928 K) that gives the best FOM among the NiAl films produced by the first NiAl film production method (post-annealing method) of the present invention with the FOM of the NiAl film (substrate temperature 889 K) that gives the best FOM among the NiAl films produced by the comparative method and a sample of NiAl single crystal cut on the (110) plane. [Figure 21] FIG. 18 is a graph comparing the real part of the complex dielectric constant of the NiAl film of an example of the present invention, which was produced using the first manufacturing method (post-annealing method) of the NiAl film of the present invention, with the real parts of the complex dielectric constant of the NiAl film formed under the same conditions except for not performing post-annealing, the NiAl film (substrate temperature 889 K) which gives the best FOM among the NiAl films produced by the method of the comparative example, and a sample in which the NiAl single crystal is cut on the (110) plane. [Figure 22]FIG. 18 is a graph comparing the imaginary part of the complex dielectric constant of the NiAl film of an example of the present invention, which was produced using the first manufacturing method (post-annealing method) of the NiAl film of the present invention, with the imaginary part of the complex dielectric constant of the NiAl film formed under the same conditions except for not performing post-annealing, the NiAl film (substrate temperature 889 K) which gives the best FOM among the NiAl films produced by the method of the comparative example, and a sample in which the NiAl single crystal is cut on the (110) plane. [Figure 23A] 1 is an SEM image of the surface of a first sample of a NiAl film (post-annealing temperature 928K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for a NiAl film according to the present invention. [Figure 23B] 10 is an SEM image of the surface of a second sample of the NiAl film (post-annealing temperature 928K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for the NiAl film of the present invention. [Figure 23C] 10 is an SEM image of the surface of a third sample of the NiAl film (post-annealing temperature 928K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for the NiAl film of the present invention. [Figure 24A] 1 is an SEM image of the surface of a first sample of a NiAl film (post-annealing temperature 967 K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for a NiAl film according to the present invention. [Figure 24B] 10 is an SEM image of the surface of a second sample of the NiAl film (post-annealing temperature 967 K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for the NiAl film of the present invention. [Figure 24C] 10 is an SEM image of the surface of a third sample of the NiAl film (post-annealing temperature 967 K) according to an example of the present invention, which was produced using the first manufacturing method (post-annealing method) for the NiAl film of the present invention. [Figure 25A] 1 is an SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a quartz substrate using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 25B] 1 is a high-magnification SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a quartz substrate using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 25C]1 is an SEM image of a cross section of a 20 nm thick NiAl film produced on a quartz substrate by the first NiAl film production method (post-annealing method) of the present invention according to an example of the present invention. [Figure 26A] 1 is an SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a sapphire substrate with a C-plane orientation using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 26B] 1 is a high-magnification SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a sapphire substrate with a C-plane orientation using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 26C] 1 is an SEM image of a cross section of a 20 nm thick NiAl film according to an example of the present invention, which was fabricated on a sapphire substrate having a C-plane orientation using the first method (post-annealing method) for fabricating a NiAl film according to the present invention. [Figure 27A] 1 is an SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a sapphire substrate with an R-plane orientation using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 27B] 1 is a high-magnification SEM image of the surface of a 20 nm thick NiAl film according to an example of the present invention, which was produced on a sapphire substrate with an R-plane orientation using the first method (post-annealing method) for producing a NiAl film according to the present invention. [Figure 27C] 1 is an SEM image of a cross section of a 20 nm thick NiAl film according to an example of the present invention, which was fabricated on a sapphire substrate with an R-plane orientation using the first method (post-annealing method) for fabricating a NiAl film according to the present invention. [Figure 28] This diagram explains why, in the case of NiAl crystals, no polarization occurs perpendicular to the plane even when the crystal is cut along any (110) plane, and therefore the (110) plane tends to be the preferred orientation plane. [Figure 29A] 1 is an SEM image of the surface of a NiAl film according to an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 858K. [Figure 29B] FIG. 10 is a graph showing the complex dielectric constant of the NiAl film according to an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 858K. [Figure 29C] FIG. 10 is a diagram showing an AFM image of a NiAl film according to an example of the present invention, which was produced at a post-annealing temperature of 858 K using the second NiAl film production method (two-stage film formation method) of the present invention. [Figure 30A] 1 is an SEM image of the surface of a NiAl film according to an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 916K. [Figure 30B] FIG. 10 is a diagram showing the complex dielectric constant of the NiAl film of an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 916 K. [Figure 30C] FIG. 10 is a diagram showing an AFM image of a NiAl film according to an example of the present invention, which was produced at a post-annealing temperature of 916 K using the second NiAl film production method (two-stage film formation method) of the present invention. [Figure 31A] 1 is an SEM image of the surface of a NiAl film according to an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 928K. [Figure 31B] FIG. 10 is a diagram showing the complex dielectric constant of the NiAl film of an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 928K. [Figure 31C] FIG. 10 is a diagram showing an AFM image of a NiAl film according to an example of the present invention, which was produced at a post-annealing temperature of 928 K using the second NiAl film production method (two-stage film formation method) of the present invention. [Figure 32A] 1 is an SEM image of the surface of a NiAl film according to an example of the present invention, which was produced at a post-annealing temperature of 967K using the second NiAl film production method (two-stage film formation method) of the present invention. [Figure 32B] FIG. 10 is a diagram showing the complex dielectric constant of the NiAl film of an example of the present invention, which was produced using the second NiAl film production method (two-stage film formation method) of the present invention at a post-annealing temperature of 967 K. [Figure 32C] FIG. 10 is a diagram showing an AFM image of a NiAl film according to an example of the present invention, which was produced at a post-annealing temperature of 967 K using the second NiAl film production method (two-stage film formation method) of the present invention. [Figure 33]31A and 32A show XRD patterns of the NiAl film and NiAl single crystal samples cut on the (110) plane according to the examples of the present invention. [Figure 34] FIG. 10 is a diagram showing the FOM of a NiAl film according to an embodiment of the present invention, which is produced using the second manufacturing method (two-stage film formation method) of the NiAl film according to the present invention. [Figure 35] 1 is a conceptual diagram of a manufacturing process of an example of a NiAl infrared absorber using a NiAl film of the present invention. [Figure 36] 36 is a schematic perspective view of a strip-like structure appearing on the surface of the NiAl infrared absorber obtained as a result of the manufacturing process shown in FIG. 35. [Figure 37A] SEM image of the surface of an example NiAl infrared absorber (p=4.26 μm) obtained as a result of the fabrication process shown in FIG. 35. [Figure 37B] SEM image of the surface of an example NiAl infrared absorber (p=5.74 μm) obtained as a result of the fabrication process shown in FIG. 35. [Figure 38A] 36 is a cross-sectional SEM image of an example NiAl infrared absorber (p=4.26 μm) obtained as a result of the fabrication process shown in FIG. 35. [Figure 38B] 36 is a cross-sectional SEM image of an example NiAl infrared absorber (p=5.74 μm) obtained as a result of the fabrication process shown in FIG. 35. [Figure 39A] FIG. 36 compares the absorption spectrum of the NiAl infrared absorber obtained as a result of the manufacturing process shown in FIG. 35 with the absorption spectrum of a comparative NiAl infrared absorber (p=4.26 μm) having the same structure except that the NiAl film used therein is fabricated using the comparative example film formation method (in-situ film formation method), and with the simulation results of the absorption spectrum of a NiAl infrared absorber having the same structure except that it is assumed that the NiAl film has ideal characteristics. [Figure 39B]FIG. 36 compares the absorption spectrum of the NiAl infrared absorber (p=5.74 μm) obtained as a result of the manufacturing process shown in FIG. 35 with the absorption spectrum of a comparative NiAl infrared absorber having the same structure except that the NiAl film used therein is fabricated using the comparative example film formation method (in-situ film formation method), and with the simulation results of the absorption spectrum of a NiAl infrared absorber having the same structure except that it is assumed that the NiAl film has ideal characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0020] In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits. In order to solve the above-mentioned problems of the prior art, particularly the problems of the NiAl film produced by the method described in Non-Patent Document 4, the present invention provides a nickel-aluminum film having an atomic ratio of Ni to Al of 1:1, a (110) plane as the preferred orientation plane, and a surface root-mean-square roughness of 6 nm or less. Hereinafter, the root-mean-square roughness of the surface will also be referred to simply as surface roughness. Even if the atomic ratio of Ni to Al deviates slightly from 1:1, results are obtained that are approximately equivalent to those obtained when the ratio is 1:1. Therefore, throughout the present specification and claims, when the atomic ratio of Ni to Al is expressed as 1:1 or NiAl, it is acceptable for the composition ratio to deviate from 1:1 by ±10% (the ratio value is within the range of 0.9 to 1.1), i.e., when the above notation is used, it is acceptable for the Ni to Al atomic ratio to deviate from 1:1 by ±10%. x Al (where 0.9≦x≦1.1). The preferred orientation plane can be determined as the plane of orientation corresponding to the peak with the greatest intensity (integrated intensity) in the XRD pattern.

[0021] Here, the root mean square roughness value is the value obtained by operating an atomic force microscope (AFM) in tapping mode using a silicon cantilever as the probe. The AFM actually used in the experiments described in the examples was a Multimode Nanoscoper IIIA manufactured by Bruker USA, and the silicon cantilever was an SI-DF20 silicon cantilever manufactured by Hitachi High-Tech Corporation.

[0022] Here, it will be explained that it is desirable that the NiAl film not only has good crystallinity but also has a surface that is as flat as possible, in other words, that the surface roughness is as small as possible.

[0023] The first reason is that the imaginary part (ε2) of the complex dielectric constant, i.e., the loss component, increases when the film surface has irregularities or pores. More specifically, an increase in ε2 increases ohmic loss, which inhibits the optical response (dielectric response) and rapidly attenuates plasmon vibrations, thereby degrading the optical response. Furthermore, such optical loss can be detrimental even when the NiAl film is used simply as a mirror, rather than as a surface plasmon effect. For example, in the inventor's invention of a stacked emitter (Patent Document 1, etc.), even when a NiAl film is used as a bottom mirror (e.g., the metallic total reflection layer formed in a mirror-like shape in Patent Document 1), optical loss in the film can cause problems such as a wide wavelength band or reduced radiation of the light emitted from the emitter.

[0024] The second reason is that when the film surface deviates from a perfectly flat surface due to irregularities or holes, the film surface itself has spatial nonuniformity, resulting in periodicity of several tens to several hundreds of nanometers, and the film itself has many plasmon resonance wavelengths. Therefore, sensors and light-to-heat converters fabricated using such films have a desired light emission / absorption spectrum built into the converter structure that is superimposed by the film's inherent light emission / absorption spectrum resulting from the film's surface roughness, leading to problems such as the appearance of unintended peaks in the spectrum and a rise in the spectral baseline.

[0025] The third reason is that in the case of NiAl films with high surface roughness, the film becomes porous, increasing the likelihood that the atmosphere present near the film surface will penetrate deep into the film and even reach the backside. The NiAl film of the present invention is formed as an aggregate of numerous crystal grains, and one cause of the deterioration of the surface roughness of the NiAl film is the widening or increase in the gaps between these crystal grains. For this, please refer to the SEM image of the surface of a NiAl film produced by a conventional technology (the method described in Non-Patent Document 4) shown as a comparative example in the Examples section. These gaps make the film porous, and when devices using such NiAl films, such as sensors or photo-thermal converters, are used in high-temperature oxidizing atmospheres, harmful atmospheres may reach other components, such as electrodes, covered by the NiAl film through the pores in the film, potentially destroying the device.

[0026] In producing the NiAl film of the present invention, a NiAl film having an atomic ratio of Ni to Al of 1:1 is annealed at 700K or more and 940K or less.

[0027] Various methods can be used to form NiAl films, including, but not limited to, magnetron sputtering, electron beam evaporation, chemical vapor deposition, and molecular beam epitaxy. DC magnetron sputtering was used in the experiments shown in the examples. Although DC magnetron sputtering was used in the experiments shown in the examples, AC magnetron sputtering may also be used. Regarding the difference between DC and AC magnetron sputtering, when sputtering an insulating material, the material to be sputtered is not conductive, making it impossible to form a film using DC sputtering. Therefore, AC sputtering, which uses an expensive high-frequency power supply to apply AC to electrodes to generate plasma, can be used to form a film. However, in the present invention, since the target is conductive, DC sputtering is sufficient, which is simpler. Therefore, DC magnetron sputtering was used in the examples. Of course, AC magnetron sputtering can also be used, but the results obtained will be essentially the same.

[0028] However, when the Ni source and the Al source are prepared separately when forming the NiAl film, depending on the film formation method used, a film with a composition different from NiAl, i.e., Ni x Al y It is easy to form a film with a composition where x≠y, or the values of x and y vary depending on the location on the film. When such a compositional deviation occurs, the resulting film has insufficient crystallinity, resulting in a problem of reduced optical response. Controlling the Ni:Al atomic ratio in the film to fall within the desired narrow range to avoid this problem is often difficult if the Ni source and Al source are kept separate. Therefore, when forming a NiAl thin film by sputtering, for example, it is preferable to use a single target with a Ni:Al atomic ratio of 1:1, i.e., a NiAl alloy target. Of course, this does not necessarily apply if the separately provided Ni source and Al source can be controlled with the required precision.

[0029] In order to improve both the crystallinity and flatness of the surface of the NiAl film, the film formation method is selected and various parameters during film formation are optimized. Because this is partly related to the present invention, the NiAl film manufacturing method shown in Non-Patent Document 4 will be described in detail below as a comparative manufacturing method (also called an in situ film formation method; indicated as in situ in the figure) in addition to the two methods of manufacturing the NiAl film according to the present invention.

[0030] In the first of the two methods for manufacturing NiAl films according to the present invention, a NiAl film is first deposited and then annealed at a relatively high temperature (hereinafter also referred to as post-annealing; denoted "Post-anneal" in the figures) to improve the flatness of the NiAl film. This method will be described in more detail below as the first manufacturing method (post-annealing method). The other method is similar to the first method in that it involves post-annealing, but in order to further improve the crystallinity of the film surface after post-annealing, the NiAl film to be post-annealed is configured as a stack of multiple films with different properties. More specifically, by adjusting the film formation method and film formation parameters, a multilayer NiAl film is formed in which a NiAl film with good flatness is placed on a NiAl film with good crystallinity, and this is then post-annealed. This will be described in more detail below as the second manufacturing method (two-stage film formation method; denoted "comb." in the figures). The post-annealing time did not significantly affect the results. In the examples of the present invention, post-annealing for approximately 15 minutes significantly improved surface roughness and crystallinity. Further extending the post-annealing time to approximately 1 hour resulted in some improvement, but longer post-annealing times did not significantly affect the results. While this depends heavily on the performance of the equipment, the post-annealing time is expected to be approximately 15 minutes to 1 hour. However, post-annealing for longer than 1 hour does not adversely affect the above-mentioned properties. Furthermore, since NiAl has high resistance to high-temperature oxidizing atmospheres, a normal atmosphere is unlikely to have much of an effect during post-annealing. However, to avoid the risk of highly reactive components being mixed into the atmosphere, post-annealing in a vacuum environment within the deposition equipment may be considered as a precaution. In the examples of the present invention, post-annealing was performed in a vacuum for 15 minutes to 1 hour.

[0031] Here, the manufacturing method of the comparative example and the two manufacturing methods of the NiAl film of the present invention will be described in more detail. Of course, it should be noted that there is no intention to exclude other manufacturing methods from the technical scope of the present invention.

[0032] <NiAl film formation by a manufacturing method (in-situ film formation method) as a comparative example and NiAl film produced thereby> In the comparative manufacturing method (in situ deposition), NiAl films were formed on silicon (Si) (100) by DC magnetron sputtering using NiAl as a target. X-ray diffraction analysis of the resulting NiAl films revealed that the (100) plane was the preferred orientation when deposited at room temperature, but the (110) plane was preferred at substrate temperatures of 744 K to 967 K (hereinafter, temperature refers to the substrate temperature unless otherwise specified), resulting in a diffraction pattern similar to that of a sample cut from a NiAl single crystal on the (110) plane (in Figure 28, this plane is referred to as NiAl <0110>). In particular, the height of the sharp peak (2θ ≒ 44.7°) corresponding to the (110) plane in the diffraction pattern was greatest when the film was deposited at a substrate temperature of 889 K. Scanning electron micrographs of the films also revealed that the grains of the NiAl films formed at this substrate temperature were the largest, with the intergranular gaps being smallest. Measurements of the complex dielectric constant of these films also revealed that the (110) oriented NiAl film obtained when deposited at a substrate temperature of 889K exhibited the best optical response.

[0033] Furthermore, scanning electron microscope photographs and complex dielectric constants of NiAl films obtained by DC magnetron sputtering at multiple substrate temperatures revealed that the preferred substrate temperature range during magnetron sputtering is 700K to 940K. As the substrate temperature increases, once it exceeds 889K, the crystal grains become larger, the gaps between the crystal grains also become larger, and the absolute value of the real part of the complex dielectric constant (ε1) of the NiAl film rapidly decreases. It is believed that some discontinuous change occurs in the crystalline state, etc., when the substrate temperature is around 930K to 940K. Therefore, in the comparative example, it is considered preferable to set the upper limit of the substrate temperature to 930K or 940K. More preferably, the upper limit should be 900K. Based on the results of DC magnetron sputtering at multiple substrate temperatures, it is determined that the preferred lower limit of the substrate temperature range is 700K, and more preferably 800K.

[0034] However, the (110)-oriented NiAl film obtained in this way had a porous surface with gaps formed between the crystal grains, even when it was deposited at the optimum substrate temperature of 889 K, resulting in a large surface roughness. The specific measurement results of the surface roughness (root-mean-square roughness) of the NiAl film deposited at 889 K were R RMS = 10.0 nm. As mentioned above, when the film was formed at 967 K, which is a higher temperature than the preferable substrate temperature in terms of the complex dielectric constant, the gaps between the crystal grains became even larger, and the surface roughness measured under the same conditions also worsened to 13.1 nm.

[0035] <NiAl film formation by the first manufacturing method (post-annealing method) and NiAl film produced thereby> To solve or mitigate this problem, the first NiAl film fabrication method (post-annealing method) of the present invention involves post-annealing the NiAl film, i.e., annealing after film formation. This reduces the surface roughness of the film surface after film formation. It is desirable that the NiAl film to be post-annealed has low surface roughness before the process (details will be described later). It has been found that when a NiAl film is formed by DC magnetron sputtering, the surface roughness is reduced when the substrate temperature is set to room temperature. When post-annealing was performed on a NiAl film formed by DC magnetron sputtering at room temperature, the surface roughness was further reduced compared to the NiAl film as formed. Furthermore, the X-ray diffraction pattern of the post-annealed NiAl film changed to a pattern similar to that of a sample cut from a NiAl single crystal along the (110) plane. This allows for the production of a (110)-oriented NiAl film with good optical response.

[0036] In this example, Si was used as the substrate on which the NiAl film was formed, but the substrate material is not limited to this. Furthermore, the NiAl film may be directly deposited on the substrate, or an intermediate layer (e.g., an insulator, semiconductor, etc.) may be interposed between the substrate and the NiAl film. In this sense, the substrate with the intermediate layer formed thereon can be collectively referred to as a "substrate." As a non-limiting example of the application of the intermediate layer, a rectifying effect is also exhibited when a nanometer-order oxide film is inserted between Si and NiAl. This phenomenon can be utilized to realize a self-powered sensor that generates voltage when irradiated with light. Naturally, the above points also apply to the second film formation method described below and the NiAl film formed thereby.

[0037] In the present invention, room temperature refers to a broader range than the commonly used range of 20°C to 25°C (293K to 298K), namely, approximately 20°C to 40°C (293K to 323K). In special cases where temperatures are particularly high, the range can be approximately 20°C to 50°C (293K to 323K). This is because, due to the presence of a heat source within the sputtering apparatus, even if a substrate at normal room temperature, i.e., approximately 20°C to 25°C (293K to 298K), is placed in the sputtering apparatus and sputtering is performed without any temperature control, such as heating, the heat from the surrounding heat source may cause the temperature to rise to approximately 40°C to 50°C (313K to 323K). NiAl films obtained by magnetron sputtering at substrate temperatures in the range of approximately 20°C to 50°C (293K to 323K) show little difference in film surface roughness or crystallinity due to substrate temperature within this range.

[0038] Here, we will first consider the upper limit of the temperature range for post-annealing. As already mentioned in the explanation of the comparative example method, there is some kind of discontinuity in the crystals around 930K to 940K, and it is believed that the temperature must be lower than the temperature at which the discontinuity occurs, whether it is crystallization during sputtering or recrystallization during annealing. Therefore, the upper limit of the post-annealing treatment should also be 930K to 940K. The lower limit of the post-annealing temperature should be 700K, taking into account the results of performing the treatment at several temperatures. In addition, the annealing atmosphere should be 4.0 x 10 to suppress surface reactions such as surface oxidation. -2 It is desirable to create a vacuum of 100 Pa or less.

[0039] Surface roughness R RMSRegarding the surface roughness, when post-annealed at 928K, it was greatly improved from 6.4nm when the film was formed at room temperature to 1.4nm. Therefore, if a light-to-heat converter or the like is fabricated using a NiAl film with such small surface roughness, it will be possible to reduce unintended peaks that appear in the absorption / emission spectrum. Furthermore, as can be seen from the SEM image of the surface of the NiAl film after post-annealing, almost no gaps between the crystal grains are observed, so the possibility of harmful atmospheres penetrating into the film through such gaps is naturally very small. Incidentally, the surface roughness R when post-annealed at 967K was RMS The thickness was 12.1 nm, which was worse than the value immediately after film formation at room temperature, but was still better than the value of 13.1 nm obtained immediately after DC magnetron sputtering at 967K.

[0040] However, since the film is annealed at a temperature significantly lower than its melting point, the atomic rearrangement due to atomic movement during annealing is more limited than during sputtering. Therefore, it is advantageous to select deposition conditions that minimize surface irregularities and pores for the film to be post-annealed, since this minimizes the distance that atoms must travel before the surface is flat. This is why it is recommended to use a film deposited at room temperature for post-annealing. As shown in the examples below, NiAl films deposited at room temperature have low surface roughness immediately after deposition. However, NiAl films deposited at room temperature are close to an amorphous state and have poor crystallinity. Therefore, the crystallinity of the film after post-annealing may be poorer than that of films deposited by DC magnetron sputtering under appropriate conditions. As a result, it is possible that the optical response may not be satisfactory.

[0041] <NiAl film formation by the second manufacturing method (two-stage film formation method) and the NiAl film produced thereby> Therefore, the present inventors further improved the first manufacturing method, which aimed to achieve both high crystallinity and flatness with a single NiAl film, and came up with the idea of a second manufacturing method (two-step film formation method) for NiAl films of the present invention, in which a NiAl film with good crystallinity is first formed on the lower layer and a NiAl film with low surface roughness is formed on the upper layer, followed by post-annealing. The steps of the second manufacturing method are described in more detail with reference to the conceptual diagram in Figure 2. First, a (110)-oriented NiAl film with good crystallinity (referred to as "highly crystalline NiAl" in Figure 2) is formed in situ on a substrate such as silicon. The film formation conditions, such as the substrate temperature, are preferably selected to ensure good crystallinity of the NiAl film, for example, by DC magnetron sputtering at a relatively high substrate temperature, as described in the description of the comparative manufacturing method. On the lower (110)-oriented NiAl film thus obtained, an upper NiAl film (referred to as "room-temperature planarized NiAl" in Figure 2) is then deposited under conditions that do not require strict crystallinity but instead favor good flatness (low surface roughness). As a result, the upper surface (opposite the substrate) of the upper NiAl film (referred to as "room-temperature planarized NiAl") is improved in flatness compared to the upper surface of the lower NiAl film. By post-annealing in this state, the NiAl grains with good crystallinity in the lower layer act as a kind of seed crystals, promoting the growth of the NiAl grains with good crystallinity in the upper layer during post-annealing. As a result, a NiAl film (referred to as "highly crystallinity-highly planar NiAl" in Figure 2) is obtained that satisfies both the requirements of good crystallinity and film surface flatness (the upper right of Figure 2 shows an example of an SEM image of the flat NiAl film surface after post-annealing).

[0042] To produce a laminated NiAl film using this two-stage deposition method, the lower layer is deposited under conditions that result in a film with good crystallinity, such as a substrate temperature of 889 K, as described above for the DC magnetron sputtering method described in the comparative manufacturing method. Next, a second NiAl film is deposited on the NiAl film under conditions that result in high flatness, resulting in a lower surface roughness compared to the lower layer. This two-stage deposition is then performed, and a post-annealing treatment is then performed under appropriate conditions to form a NiAl film with high crystallinity and low surface roughness. The upper NiAl film is not required to have high crystallinity before the post-annealing treatment; the deposition conditions for each layer can be selected to achieve good flatness from the beginning and further improve the flatness after the post-annealing treatment. In forming the upper NiAl film, for example, a NiAl film with relatively small surface roughness is prepared at room temperature by DC magnetron sputtering, and then post-annealed under the conditions described for the post-annealing of the NiAl film in the first manufacturing method, for example, in the range of a lower limit of 700 K and an upper limit of 930 to 940 K. As a result, a NiAl film with good crystallinity and flatness on its surface can be obtained.

[0043] Regarding the structure of the NiAl film fabricated by the second manufacturing method, as can be seen from the cross-sectional SEM images of the film shown in the Examples described later (in the cross-sectional SEM images of the device using the NiAl film shown in Figures 38A and 38B, the six or four trapezoidal sections are cross-sections of the NiAl film fabricated by this method), in the NiAl film fabricated by this manufacturing method, the lower NiAl and the upper NiAl are almost integrated, and at least in these cross-sectional SEM images, the boundary between the two is not visible. This suggests that the lower NiAl crystals grew upward using the upper NiAl during post-annealing, resulting in the two being almost integrated.

[0044] According to the second manufacturing method, the surface roughness R of the NiAl film after post-annealing RMSThe surface roughness R of the NiAl film after post-annealing at 928K was 2.2nm. This is the same as the surface roughness R of the NiAl film fabricated by the first manufacturing method after post-annealing under the same conditions. RMS This difference in surface roughness is due to the fact that the room-temperature magnetron sputtered film that is the target of post-annealing in the first manufacturing method has very good flatness (surface roughness R RMS In the second manufacturing method, the lower NiAl film is formed on a Si substrate with a surface roughness of R RMS This is because the surface roughness of the NiAl film fabricated by the second manufacturing method was relatively poor, with a thickness of 10.2 nm. In other words, the low surface roughness of the lower layer adversely affected the surface smoothness of the laminated NiAl film, and this relatively low surface smoothness before post-annealing was reflected in the surface smoothness after the process. Another possible reason is that the extremely thin upper layer, approximately 20 nm, of the room-temperature magnetron sputtered film may have been unable to fully restore the low surface smoothness of the lower NiAl film fabricated at 889 K. However, as can be seen by comparing the AFM images of the NiAl film surfaces fabricated by the two methods with a post-annealing temperature of 928 K (Figure 15B) (first manufacturing method) and Figure 31C (second manufacturing method), the NiAl film surface fabricated by the second manufacturing method certainly had more pronounced fine irregularities, but it also had larger openings and significantly fewer deep pores. The small number of such pores is an advantageous structural feature in that when the NiAl film of the present invention is used in an oxidizing atmosphere at high temperatures, the possibility of the atmosphere penetrating deep into the film or reaching the back surface of the film is reduced.

[0045] However, although the NiAl film fabricated by the second manufacturing method is inferior in flatness to that of the first manufacturing method as described above, the NiAl film fabricated by the second manufacturing method has a better optical response figure of merit (FOM), calculated as [real part of complex dielectric constant × (-1)] / [imaginary part of complex dielectric constant], due to the good crystallinity of the upper layer as described above.

[0046] The difference in FOM between the NiAl films fabricated by the first and second fabrication methods can be further explained based on specific measurement results. While the FOM of both NiAl films decreases from a certain point between 1 μm and 2 μm toward longer wavelengths, the NiAl film fabricated by the second fabrication method exhibits a smaller rate of decrease, maintaining a relatively large FOM up to the longer wavelength range. Specifically, Figure 19, which shows the measurement results of FOM versus wavelength change for the first fabrication method in the example, shows that even at a post-annealing temperature of 928 K, which is the condition that provides the maximum FOM, the FOM is already slightly below 1 at a wavelength of 7.5 μm. Furthermore, at a slightly lower post-annealing temperature of 851 K, the FOM becomes 1 at wavelengths less than 3 μm. 34, which shows the wavelength variation of the FOM for the second manufacturing method, also shows that the maximum FOM is obtained at a post-annealing temperature of 928 K (specifically, the FOM value is maintained at 3 or greater in the near-infrared region). However, in the case of the second manufacturing method, the FOM value is almost 3 or greater not only at 928 K, where the maximum FOM is obtained, but also at 916 K throughout the near-infrared region, and the FOM remains 1 or greater at a wavelength of 7.5 μm down to 858 K, considerably lower. If we compare the FOMs of the NiAl films fabricated by these two manufacturing methods in the wavelength range where the FOM value is 2 or greater, the NiAl films fabricated by the first manufacturing method (post-annealing method) have an FOM of 2 or greater in the wavelength range of 0.6 μm to 2 μm, whereas the NiAl films fabricated by the second manufacturing method (two-stage film formation method) have an FOM of 2 or greater in the wavelength range of 1.2 μm to 4 μm. Therefore, the NiAl film fabricated using the second manufacturing method maintains good optical response over the entire near-infrared range and part of the long-infrared range, and can therefore be suitably used in devices that absorb / emit or detect infrared radiation in this range.

[0047] As mentioned above, the NiAl films fabricated by the second manufacturing method exhibited minimal change in FOM with respect to post-annealing temperature, as can be seen from the FOM measurement results shown in the examples. The small change in FOM with post-annealing temperature is believed to be due to the fact that the lower NiAl crystals, with their excellent crystallinity, function sufficiently as seed crystals for the growth of the upper NiAl crystals at relatively low temperatures within a reasonable time frame. This means that there is a large tolerance for post-annealing temperature fluctuations, and by utilizing this tolerance, it is possible to obtain NiAl films whose optical response is not significantly reduced compared to films obtained by post-annealing at the optimal temperature, even when post-annealing is performed at temperatures significantly lower than the optimal temperature. This is advantageous for the industrial production of NiAl films with excellent optical response.

[0048] The small change in FOM with post-annealing temperature, as mentioned above, is presumed to suggest that the crystallinity of the upper NiAl layer after post-annealing, which is dominated by the crystallinity of the lower NiAl layer, reaches or approaches its upper limit even when post-annealed at a low temperature, rather than at a high temperature. Alternatively, it may suggest that in the second manufacturing method, post-annealing was essentially completed or reached a state close to completion at a relatively early stage of post-annealing in the examples. If this presumption is correct, it may be possible to shorten the post-annealing time by adjusting the processing conditions, which is effective in shortening manufacturing time.

[0049] As mentioned above, the NiAl film of the present invention is a (110)-oriented NiAl film. However, while it is not necessary for the NiAl film to be as perfectly (110)-oriented as the (110) plane of a NiAl single crystal, the (110) plane is the preferred orientation plane. In this application, the (110) plane being the preferred orientation plane means that, in terms of the integrated intensity of the XRD peak, the integrated intensity of the peak corresponding to the (110) orientation accounts for 65% or more, and more preferably 70% or more, of the total integrated intensity. Note that, in calculating the percentage of integrated intensity, the baseline of the XRD pattern measured in advance was normalized to zero, and the XRD peak due to the substrate was excluded.

[0050] <Ultra-thin NiAl film of the present invention> Using the first manufacturing method, we confirmed that even extremely thin NiAl films, approximately 20 nm thick, can achieve film uniformity, including post-annealing planarization (reduced surface roughness). Furthermore, even when a voltage of 10 V was repeatedly applied to this extremely thin 20-nm NiAl film, no film breakdown or atomic migration due to the applied voltage was observed, confirming the film's electrical robustness. For many materials, such as Au, thinning to this thickness can cause the material to deform from a thin, spread-out state on the substrate surface into small globules during annealing, resulting in film fracture and a rough morphology. This, of course, also degrades the film's optical response. In this application, a material that is dispersed in a globular form on the substrate surface is not considered a film. Therefore, common sense predicts similar problems when fabricating NiAl films. Therefore, it is unthinkable to limit the film thickness to 30 nm or even 25 nm or less when fabricating NiAl films for optical-to-thermal converters, or even for other applications. However, in actual fabrication experiments conducted by the present inventors, it was confirmed that such a phenomenon does not occur when annealing NiAl, and that NiAl films with very few defects that impair continuity, such as film fractures, can be obtained. As a result, in the present invention, even extremely thin NiAl films formed at room temperature do not suffer from deterioration of morphology due to fractures or the like during post-annealing, and therefore the planarization effect of post-annealing can still be achieved. Furthermore, considering that even at a film thickness of 20 nm, extremely good levels of flatness and continuity are maintained, it is certain that a film that is substantially free of defects that cause discontinuities, such as holes, can be obtained even when the film thickness is reduced to less than 20 nm, for example, 10 nm. The maintenance of the planarization effect when thinning the film was confirmed using SiO2 and sapphire substrates (two types of sapphire substrates with C-plane and R-plane orientations were used).

[0051] Furthermore, NiAl films with thicknesses of 100 nm, 20 nm, and 10 nm were fabricated on Si substrates, and a 6 nm NiAl film was fabricated on a glass substrate, and the electrical resistance between a pair of electrical contacts formed on these films was measured. As will be explained in detail in the Examples, good electrical conduction was observed even in the case of an ultrathin film with a thickness of 6 nm. These measurement results confirmed that NiAl films with thicknesses of 10 nm and even 6 nm were substantially free of defects that would cause discontinuities such as holes. Furthermore, given the tendency for electrical resistance to increase as the film thickness is reduced, it is believed that films with high continuity, in the sense that there are no or very few discontinuities such as holes, can be obtained even when the film thickness is reduced to, for example, 3 nm or 2 nm. Furthermore, maintaining the above-mentioned continuity also means that the flatness of such ultrathin films is very good. A surface roughness value that is significant relative to the film thickness means that the underlying film is exposed everywhere.

[0052] Although the reasons for the extremely thin NiAl films described above are not fully understood, it is believed that because NiAl preferentially grows along the (110) plane, the NiAl island-like microdomains that appear at the very beginning of NiAl film growth on the substrate preferentially grow laterally (parallel to the substrate surface) while maintaining their crystal orientation. In other words, a flat, extremely thin, continuous NiAl film with uniform crystal orientation rapidly covers the substrate surface, and then this film grows perpendicular to the surface, maintaining its initial flatness and continuity. Therefore, even if the NiAl film growth is stopped at a very early stage, the resulting NiAl film remains flat and continuous. For similar two-dimensional growth of extremely thin films, although the film composition is different, please refer to our previous papers, Non-Patent Documents 5 and 6. Also, please refer to the explanation provided below, with reference to Non-Patent Document 7, that a similar ultrathin film may also be achieved using a comparative manufacturing method. Another reason why extremely thin NiAl films can be formed and that the films have a high degree of flatness and continuity is that the two-component system of Ni and Al used for thinning may cause the film to grow in a different manner than single-component systems. Furthermore, NiAl, being a two-component system, is less likely to migrate from its original position once formed than single-component systems. Furthermore, the two-component system may contribute to the tendency for the film to be preferentially oriented in the (110) plane. It is also possible that the material generated at the interface between the NiAl and substrate materials by their reaction may somehow contribute to the thinning process.

[0053] As the NiAl film becomes thinner, defects such as irregularities in the film surface, gaps between crystal grains, deep holes, and discontinuities in the film surface, pinholes, etc. are likely to occur. In this regard, unlike the manufacturing method of the comparative example, the first manufacturing method significantly reduces the surface roughness by post-annealing, making it possible to suppress the increase in the above defects when the film thickness is reduced.

[0054] The NiAl film of the present invention can be used for various applications, primarily in light-to-thermal converters. When using a metal film for such optical applications, a thickness of approximately 20 nm is sufficient to block most of the light. Therefore, a film thickness of approximately 20 nm is sufficient. If the NiAl film can be thinned to the minimum thickness required to obtain sufficient optical properties in a light-to-thermal converter, the time required for NiAl film deposition during the manufacturing process can be shortened, and the consumption of targets and other NiAl sources used during the process can be reduced. This is particularly important when fabricating large-area light-to-thermal converters. Even when a NiAl film is not required to be as thin as approximately 20 nm, the fact that it can be sufficiently thinned to approximately 20 nm is useful for designing manufacturing processes. Furthermore, the ease of forming extremely thin and highly continuous NiAl films on substrates or other films suggests that highly continuous films of other materials can be easily formed on the NiAl film, and that such continuous films can be made extremely thin. Therefore, when it is difficult or impossible to form an ultrathin or continuous film of a first material directly on a second material, the interposition of a NiAl film as a kind of "surfactant" between the two may facilitate the growth of the first material on the second material film or substrate. In such cases, it is believed that a thinner NiAl film is better able to reduce the impact on various properties of the laminated structure of the first and second material films. Therefore, it is useful to be able to reduce the thickness of the NiAl film to 20 nm or even thinner, as described below. Of course, even thinner NiAl films may be required for specific applications, and the present invention can fully address such cases.

[0055] In addition, experiments with the comparative manufacturing method only confirmed that a NiAl film with a thickness of approximately 100 nm could be produced. However, the point described with respect to the first manufacturing method remains the same: the NiAl island-like micro-regions that appear at the very beginning of the NiAl film growth on the substrate preferentially grow laterally while maintaining their crystal orientation. Therefore, it is believed that the film can be made extremely thin, similar to the first manufacturing method. Here, as with the comparative manufacturing method, Non-Patent Document 7 published by the present inventors shows that, when deposited on a heated substrate, crystals that preferentially grow in a specific orientation on the substrate, like NiAl, first grow laterally (toward the substrate surface), and the film thus formed on the substrate surface then grows in the thickness direction (perpendicular to the substrate surface).

[0056] To explain Non-Patent Document 7 in more detail, it describes the growth of a LaB6 film deposited by electron beam deposition (EBD) on a Si(001) substrate heated to 800 °C (Fig. 5(a) → (b) → (c)). In the experiment described in Non-Patent Document 7, the LaB6 film on the substrate grows somewhat in the thickness direction from the stage of multiple, spaced islands (Fig. 5(b)). Therefore, the film thickness immediately after these islands fuse together (between Fig. 5(b) and Fig. 5(c)) is expected to be thicker than the NiAl film at the corresponding point in the film deposition process using the comparative manufacturing method. Nevertheless, the film thickness immediately after the multiple islands fuse should be between 10 nm in Fig. 5(b) and 100 nm in Fig. 5(c). Considering this, the NiAl film fabricated by the comparative manufacturing method should not aggregate into small globules from the initial stage of film formation, but should preferentially grow laterally in the form of multiple thin, layer-like fragments (relatively short islands), and when growth in the thickness direction does not progress much, the islands should fuse to form an integrated film. Therefore, even with the comparative manufacturing method, it is thought that by appropriately adjusting the film formation time, rate, and other conditions, it is possible to obtain films that are considerably thinner than the approximately 100 nm thick film obtained in the experiment. Specifically, as mentioned above, it should be possible to achieve extremely thin films such as 20 nm, 10 nm, 6 nm, and even 3 nm and 2 nm.

[0057] As a result of experiments to demonstrate that the thickness of the above-mentioned NiAl film can be further reduced, it was possible to fabricate continuous NiAl films thinner than the initially obtained thickness of up to 6 nm, specifically continuous films with thicknesses of 3 nm, 2 nm, and 1.4 nm, and it is fully expected that the thickness can be further reduced to around 1 nm. Furthermore, the fact that the NiAl films obtained in this way with thicknesses of less than 6 nm are continuous films was confirmed by the fact that the films exhibit sufficient electrical conductivity.

[0058] In the second manufacturing method, the final film obtained is almost the same as the NiAl film obtained by stacking the NiAl film obtained by the manufacturing method of the comparative example and the NiAl film obtained by the first manufacturing method, so the thickness of the entire laminated film may be somewhat larger. However, considering the high probability that the film obtained by the first manufacturing method can be thinned to a few nm to 1 nm as described above, it is thought that the thickness of the entire laminated film will not be so large. Therefore, even when the second manufacturing method is used, a NiAl film that is highly structurally uniform and electrically strong can be obtained, even when the film is thinned to a thickness of 20 nm, 10 nm, 6 nm, or even thinner, such as 3 nm, 2 nm, 1.4 nm, or 1 nm, within the above-mentioned thickness range.

[0059] <Oxidation resistance of the NiAl film of the present invention at high temperatures> The NiAl film of the present invention does not oxidize up to high temperatures in an oxidizing atmosphere compared with Mo and W films. As mentioned above, Mo and W films are rapidly oxidized in air at 600°C, causing their surfaces to turn clearly white. In contrast, the NiAl film of the present invention does not oxidize in air at 600°C, and its surface only turns slightly white even in air at 700°C. Therefore, the NiAl film of the present invention can be used in an oxidizing atmosphere without special surface protection measures up to at least 600°C, and is actually believed to be usable up to a temperature between 600°C and 700°C. Furthermore, since the NiAl film of the present invention has low surface roughness, there are fewer pores and gaps leading from the surface to the interior of the film, making it a protective film that functions satisfactorily for a long period of time for various components placed below the NiAl film.

[0060] This high-temperature oxidation resistance is achieved by the reaction of Al in NiAl with oxygen, forming a dense aluminum oxide film on the surface. The high-temperature oxidation resistance of NiAl due to the formation of this aluminum oxide film is known in the technical field of heat-resistant structural materials for machine parts operating in high-temperature oxidizing environments, such as gas turbines.

[0061] However, this knowledge about oxidation resistance in the field of heat-resistant structural materials for mechanical components cannot be directly applied to optical-thermal converters or sensors that use plasmon resonance to convert light to heat or electricity. This is because, when NiAl is used as a material for such high-temperature mechanical components, a sufficiently thick aluminum oxide film is formed on the surface to maximize heat and oxidation resistance, and the actual thickness reaches the micrometer order. Furthermore, such aluminum oxide films have poor surface flatness and are prone to pitting and cracking. Because optical response is not utilized in these types of mechanical components, no consideration is given to whether the surface is made of a material that adversely affects the optical response or whether it has surface roughness that degrades the optical response. In reality, plasmons are a phenomenon that appears on the surface of components, so the metallicity and flatness of the surface on the nanometer order are crucial for good optical response. The inventors of the present application are not aware of any reports measuring the optical response of NiAl members used in conventional high-temperature materials. However, even if such measurements were made, the surface would likely be covered with a thick aluminum oxide film (insulating film), and the surface roughness of the NiAl portion on the surface of the insulating film and below the insulating film would be very large when considering the optical response. In fact, the interface between aluminum oxide and NiAl is not sharp, so such a film is not suitable for the light-to-heat converter application that is the primary purpose of the NiAl film of the present invention. Therefore, even if a person skilled in the art had knowledge of NiAl in the field of heat-resistant materials according to the prior art, it would clearly not have been able to easily implement the present invention based on that knowledge.

[0062] In the examples of the present invention, the resistance to high-temperature oxidizing atmospheres (air) was tested with a naturally formed aluminum oxide film on the surface. In other words, in this test, no special treatment was performed to optimize the thickness of the oxide film on the surface of the NiAl film, nor was any treatment performed to adjust various parameters of the NiAl film to impart high resistance to oxidizing atmospheres to such natural oxide films. Despite this, the NiAl film of the present invention was hardly oxidized up to 600 °C, and only slight oxidation was observed at 700 °C in air, turning the surface slightly white, confirming its high resistance to high-temperature oxidizing atmospheres. The oxidation of the NiAl film observed here is thought to be caused by the oxidizing atmosphere penetrating through minute pores and cracks in the surface aluminum oxide film. Therefore, the resistance of the NiAl film of the present invention to high-temperature oxidizing atmospheres can be further improved by appropriately controlling the thickness and morphology of the aluminum oxide film, provided that the degradation of optical response due to thickness and surface roughness is within the desired range.

[0063] Furthermore, as specifically shown in the examples, experiments by the inventors of the present application have shown that the Schottky barrier of a NiAl film grown on a Si substrate is as low as about 0.7 V, making this material usable not only for conversion between heat and light, but also for conversion between near-infrared light and electricity. Furthermore, this material can be used not only for power generation, where electrical energy is directly extracted by irradiating light, but also as a sensor that detects light, particularly at high temperatures and in a strongly oxidizing atmosphere. In particular, growing a NiAl film on a P-type Si substrate reduces the Schottky barrier, making it suitable for use as a near-infrared sensor.

[0064] Other applications include thermophotovoltaic (PTV) power generation and heat-assisted magnetic recording (HAMR). PTV power generation involves generating near-infrared rays from a near-infrared emitter heated by a heat source and converting the near-infrared rays into electricity using a PTV cell. Here, the near-infrared emitter and the light-receiving surface of the PTV cell are placed in close proximity to each other, thereby utilizing the near-field light emitted from the near-infrared emitter surface, greatly improving power generation efficiency. Because the near-infrared emitter is heated to temperatures ranging from several hundred degrees Celsius to over 1000 degrees Celsius, it is required that it not only have excellent optical response but also high heat resistance, such as resistance to oxidation, deformation, and mechanical strength degradation even when used for long periods at such high temperatures. Therefore, the NiAl film of the present invention can be suitably applied to the near-infrared emitter of a PTV power generation device. HAMR is a magnetic recording method in which light is irradiated onto a narrow area on the surface of a high-coercivity magnetic recording medium, heating it to approximately 400 to 900 degrees Celsius, and writing is performed while the coercivity is reduced. Here, the diameter of the narrow region (light spot) is on the order of tens of nanometers, and because such a narrow light spot cannot be formed by ordinary light irradiation, near-field light is utilized. Initially, Au and other materials were used as materials for near-field light generating elements that generate such near-field light. However, because this element itself becomes hot just like the object being heated, there is a problem that the recording device cannot withstand long-term use if Au and other materials are used. The NiAl film of the present invention satisfies both the requirements of good optical response and heat resistance, and can therefore be suitably used in devices that generate near-field light in HAMR.

[0065] <Applications other than those utilizing the optical response of the NiAl film of the present invention> Although the NiAl film of the present invention has been described above as being primarily intended for applications utilizing its optical response, it goes without saying that it can also be used for other applications. For example, as shown in the examples below, NiAl films obtained by the manufacturing method of the present invention have low electrical resistivity even when made extremely thin, making them suitable for use as electrodes on various electronic devices. In particular, these NiAl films are suitable for use as electrodes on electronic devices that utilize optical response to absorb and / or emit infrared light. This is not simply because electrodes using NiAl films exhibit high resistance to high temperatures and oxidizing atmospheres. Because NiAl film electrodes exhibit high continuity with very few cracks or pinholes and have low surface roughness, even when large-area NiAl film electrodes are installed on such devices, there are very few irregularities on a scale close to the wavelength of light. Therefore, no structures exhibiting resonant optical response are observed, and significant absorption / emission due to the optical response of the electrode does not occur. Therefore, the inherent absorption / emission characteristics of such electronic devices are not superimposed as noise by the electrodes. Furthermore, because it is possible to form a homogeneous NiAl film with high continuity, even when the electrode film is made extremely thin, it is possible to prevent a decrease in the effective electrode area due to film separation, and to prevent variations and instability in the electrical connection. Note that the term "electrode" here is used in a broad sense to include not only electrodes that serve as terminals for electrically connecting a device to the outside world, but also electrodes that serve as conductors sandwiching layers such as dielectrics in ultrathin capacitors.

[0066] As a non-limiting example of another application, the NiAl film of the present invention can be used to realize a heater that generates heat in a planar manner by passing an electric current through it. The NiAl film of the present invention has high heat resistance, and as shown in the above-described examples, even when it is extremely thin, it can be easily fabricated with high continuity, just as when it is relatively thick. This allows for control of electrical resistance over a wide range. Furthermore, the high film continuity ensures that the current density on the film is constant regardless of location, thereby enabling a constant amount of heat generated per unit area throughout the surface. Therefore, the NiAl film of the present invention can be suitably used, for example, as a planar heater for uniformly heating a film of a desired area placed on it. Furthermore, when used as a heater, the electrode itself generates little heat, reducing unnecessary heat radiation and thermal radiation noise. [Example]

[0067] The present invention will be described in more detail below with reference to examples of the present invention and comparative examples based on the method described in Non-Patent Document 4. Needless to say, it should be noted that these examples are presented for the purpose of aiding understanding of the present invention, and are not intended to limit the present invention.

[0068] [Experimental methods, etc.] <Common matters> The NiAl film was deposited on a Si(100) substrate (p-type, 10 Ω·cm, 1 mm thick) using a commercially available NiAl alloy target (Furuuchi Chemical Co., Ltd., 99.9% purity, approximately 75 mm diameter, 6 mm thick) with a sputtering system I-Miller (Shibaura Mechatronics Co., Ltd.). The Si substrate was ultrasonically cleaned in acetone, ethanol, and isopropyl alcohol, in that order, for 5 minutes each before use. The base pressure in the sputtering chamber was approximately 2.3 × 10 -5It was maintained at Pa, and residual gas, especially water, was removed as much as possible. Also, the DC sputtering power was set to 200 W. While deposition was being carried out, high-purity argon gas was introduced into the chamber at 20 sccm, and the working pressure was set to 0.51 Pa.

[0069] <Film formation of NiAl: Manufacturing method of comparative example (in-situ film formation method)> When forming a NiAl film by the manufacturing method of the comparative example, the substrate temperature was set to four levels of 744 K, 814 K, 889 K, and 967 K, and film formation was carried out by DC magnetron sputtering. Furthermore, for comparison, the substrate temperature was set to room temperature (298 K), and film formation was carried out under the same conditions otherwise.

[0070] <Film formation of NiAl: First manufacturing method (post-annealing method)> In the film formation of the NiAl film by the first manufacturing method, first, the substrate temperature was set to room temperature, and a NiAl film was formed under the same conditions as the manufacturing method of the comparative example otherwise. The NiAl film thus obtained was post-annealed at 776 K, 851 K, 928 K, and 967 K for 1 hour under a vacuum of 4.0×10 -2 Pa or less.

[0071] <Film formation of NiAl: Second manufacturing method (two-step film formation method)> In the second manufacturing method, first, the substrate temperature was set to 889 K, at which the NiAl film with the best optical response was obtained by the manufacturing method of the comparative example, and film formation was carried out under the same conditions as the comparative example and the first manufacturing method otherwise. After cooling the substrate on which the NiAl film thus obtained was formed to room temperature, with the substrate temperature remaining at room temperature, an upper-layer NiAl film was formed by the manufacturing method of the comparative example. The resulting laminate was post-annealed at 858 K, 916 K, 928 K, and 967 K under the same conditions as the first manufacturing method.

[0072] <Measurement method of NiAl film> Information about the crystallinity of the NiAl films obtained as described above was obtained by X-ray diffraction (XRD) using a Rigaku SmartLab. Cu Kα radiation (λ = 1.5425 Å) was used. The morphology and surface roughness of the NiAl films were measured using a scanning electron microscope (SEM) Hitachi S-4800 (Hitachi High-Tech Corp.) and an atomic force microscope (AFM) Multimode Nanoscoper IIIA (Bruker USA). The AFM measurements were performed using a Hitachi High-Tech SI-DF20 silicon cantilever operated in tapping mode. The complex permittivity over the deep ultraviolet to far infrared range was obtained using a spectroscopic ellipsometry instrument (SENTEC Instruments GmbH, Berlin, Germany) using the Drude-Lorentz model with three Lorentz oscillators for all fittings.

[0073] <Method for manufacturing a light-to-heat converter using a NiAl film by the second manufacturing method> As described above, the optimal deposition conditions for the second fabrication method were determined by combining the deposition conditions that yielded the maximum FOM in the comparative fabrication method with the post-annealing conditions that yielded the maximum FOM in the first fabrication method. Using the obtained dielectric function, precise numerical simulations were performed to determine the configuration of a photothermal converter using a NiAl film obtained by the second fabrication method. To fabricate a photothermal converter with a NiAl-Al2O3-NiAl metal-insulator-metal (MIM) structure and a NiAl strip resonator array, a 0.18 μm thick NiAl film was first deposited on a Si(100) substrate at a substrate temperature of 889 K using the comparative fabrication method. After the deposition was completed and the substrate was cooled to room temperature, a 0.02 μm thick NiAl film was immediately deposited on the NiAl film. Subsequently, the entire NiAl film stack was post-annealed at 928 K for 1 hour. After the post-annealed NiAl film was cooled to room temperature, a 20 cm thick NiAl film was deposited on top of it by AC sputtering at a sputtering power of 450 W and an operating pressure of 0.54 Pa. 3A 0.2 μm Al2O3 insulating layer was deposited from an Al2O3 target under an argon gas flow of 1 / min. The first NiAl layer deposition process was then repeated, but the thicknesses of the layers were different from the first NiAl layer: 0.15 μm and 0.4 μm, respectively. The NiAl layer was then post-annealed in the same manner as the first NiAl layer.

[0074] <Structure and properties of NiAl film produced by the comparative manufacturing method (in-situ film formation method)> 3A to 6C show SEM images, complex permittivity, and AFM images of the surfaces of NiAl films (substrate temperatures of 744K, 814K, 889K, and 967K, respectively) produced by the comparative manufacturing method. Furthermore, FIGS. 7A to 7C show SEM images, complex permittivity, and AFM images of the surfaces of NiAl films produced by DC magnetron sputtering with the substrate temperature set to room temperature. As can be seen from these figures, the NiAl films produced by the comparative manufacturing method have a larger surface roughness than NiAl films produced under the same conditions except for the substrate temperature being room temperature, but they exhibit high metallicity as can be seen from the real part ε1 of the complex permittivity. In particular, it can be seen that the NiAl film produced with the substrate temperature set to 889K exhibits the highest metallicity. Regarding surface roughness, the surface roughness R of the NiAl film produced increases as the substrate temperature is increased from 744K. RMS The value of increases. The fact that surface roughness increases as the substrate temperature increases can be intuitively understood from the SEM images of these NiAl films. In particular, when comparing the SEM images of the NiAl film surfaces obtained at substrate temperatures of 889 K and 967 K, it is clear that at the 889 K substrate temperature stage, the grains that appear on the surface already become larger, resulting in noticeable surface irregularities. At 967 K, a significant change in the surface structure is observed, with numerous pores or gaps that are significantly larger in diameter and extend deep into the surface.

[0075] The table below shows the average particle size of NiAl particles appearing on the surface of the NiAl film for each of the four examples at these substrate temperatures and at room temperature (RT). The average particle size in the table below was calculated from the width of the peak corresponding to (110) in the XRD pattern ( FIG. 8 ) at the corresponding substrate temperature. The average particle size thus determined and listed in the table shows essentially the same tendency as the average particle size determined from SEM images of the NiAl film surface shown in FIGS. 3A, 4A, 5A, 6A, and 7A (some SEM images of the film cross section are also shown in the examples described below). Furthermore, the trends in the peak intensity and background, which reflect the number of particles and lattice defect density, also tend to qualitatively match those of the SEM images and optical properties. However, because factors affecting the calculation results do not completely coincide between the average particle size calculated from the XRD peak width and the average particle size calculated from the SEM image, these two values of average particle size calculated from the same sample are not necessarily quantitatively the same, and the impression given by observing the SEM image may appear to contradict the value calculated from the XRD peak width. This also applies to the average particle size described in the two examples shown later.

[0076] [Table 2]

[0077] Furthermore, the crystal orientation of each NiAl film obtained at different substrate temperatures was measured by XRD. The results are shown in Figure 8. In addition to the XRD patterns of the NiAl films obtained at substrate temperatures of 744, 814, 889, and 967 K, Figure 8 also shows the XRD patterns of NiAl films obtained at room temperature (RT) and a sample cut from a NiAl single crystal along the (110) plane (Single Crystal (110)). Comparing the XRD patterns in Figure 8 reveals that the NiAl film obtained at room temperature has a preferred crystal orientation of (100) rather than (110). This crystal orientation reduces the metallicity of the NiAl film, as indicated by the complex dielectric constant of the NiAl film shown in Figure 7B. Furthermore, among the NiAl films obtained by increasing the substrate temperature, the NiAl film obtained at a substrate temperature of 889 K exhibited the XRD pattern closest to that of a (110)-cut NiAl single crystal specimen, which exhibited almost perfect (110) orientation. As mentioned above, NiAl single crystals are extremely difficult to produce, and even if they could be produced at a laboratory level, their use in industrial products is impractical. Furthermore, even if bulk single crystals could be produced, it would be equally difficult to thin them down and incorporate them into light-to-heat converters. Therefore, among the examples of Manufacturing Method 1, the one produced at a substrate temperature of 889 K is optimal in terms of NiAl film orientation. Furthermore, considering industrial applications, even if we include NiAl single crystals in addition to the examples above, the 889 K substrate temperature remains optimal.

[0078] Furthermore, Fig. 9 shows the FOM values from the deep ultraviolet region to a wavelength of 15 μm, calculated from the complex dielectric constant of each NiAl film obtained when the substrate temperature was changed. In addition to the FOM values of the NiAl films obtained at substrate temperatures of 744 K, 814 K, 889 K, and 967 K, Fig. 9 also shows the FOM values of NiAl films obtained at room temperature (RT) and a sample of NiAl single crystal cut on the (110) plane (NiAl (110)), as well as the FOMs of lanthanum hexaboride (LaB6), gold (Au), tungsten (W), molybdenum (Mo), and titanium nitride (TiN) films. Furthermore, in Figure 10, to facilitate comparison between the NiAl film, which exhibits the best optical response among the four examples, and various comparative samples, the graph format is the same as in Figure 9, but the comparative samples are plotted as in Figure 9, while the example samples are plotted only for the NiAl film at a substrate temperature of 889 K. In addition, similar to Figure 10, Figures 11 and 12 show the wavelength-dependent changes in the real and imaginary parts of the complex permittivity of the various samples shown in Figure 10, respectively.

[0079] As can be seen from the wavelength-dependent changes in FOM shown in Figures 9 and 10, the comparative examples (substrate temperatures of 744K, 814K, 889K, and 967K) exhibited better optical responses than many heat-resistant materials, particularly in the near-infrared region (wavelengths of 0.8µm to 2.5µm). The optical response of the NiAl film fabricated at a substrate temperature of 889K was particularly good, as can be seen from Figures 10 to 12. The optical responses at substrate temperatures of 744K and 814K were also relatively close to those at a substrate temperature of 889K. In contrast, when the substrate temperature was increased to 967K, the optical response was significantly degraded, even though the temperature was only increased by 78K from 889K. This may indicate that a significant change occurs in the crystalline structure of the NiAl film formed on the substrate at a certain substrate temperature between 889K and 967K.

[0080] <Structure and properties of NiAl film produced by the first manufacturing method (post-annealing method)> For the first manufacturing method, an experiment roughly corresponding to the above-mentioned comparative example was carried out, and roughly corresponding measurements were also carried out on the NiAl film obtained as a result.

[0081] Figures 13A to 16B show SEM and AFM images of the surface of an NiAl film (post-annealing temperatures of 776 K, 851 K, 928 K, and 967 K, respectively) according to an embodiment of the present invention, fabricated by the first manufacturing method. The SEM images shown in Figures 13A, 14A, 15A, and 16A also include insets of cross-sectional images of the NiAl film and the substrate immediately below the film. For comparison, Figure 17 shows an SEM image (also with an inset) of the surface of a NiAl film in the as-is state after DC magnetron sputtering (i.e., no post-annealing) with the substrate temperature set to room temperature. See Figure 7C for an AFM image of the NiAl film surface. As can be seen from Figures 17, 7C, and 13A to 15B, the surface roughness of the NiAl film fabricated by the first manufacturing method decreased as the post-annealing temperature increased. However, when the post-annealing temperature was increased from 928 K (FIGS. 15A and 15B) to 967 K, the surface roughness R RMS The thickness suddenly deteriorated from 1.4 nm to 12.1 nm. This is thought to be due to a discontinuous change such as a phase change in the NiAl crystal at a temperature between 928 K and 967 K.

[0082] In fact, looking at the XRD patterns shown in Fig. 18, as the post-annealing temperature is increased from 776 K to 851 K to 928 K, the (110) peak becomes larger, while the other peaks decrease, whereas this trend is completely reversed when the post-annealing temperature is increased to 967 K. Furthermore, as for the FOM shown in Fig. 19 and Fig. 20, the FOM when the post-annealing temperature is 928 K is significantly larger than those at the annealing temperatures before and after that (specifically, the FOM value is 3 or more in the near-infrared region), which indicates that the crystallinity is at its best at 928 K.

[0083] Furthermore, when examining the complex permittivity shown in Figures 21 and 22, when post-annealing is performed at 928 K, the absolute value of the real part ε1 is larger than when post-annealing is performed at higher or lower temperatures (except for NiAl single crystals) (and even when film formation is performed at the optimal substrate temperature of 889 K using the in-situ film formation method in the comparative example), thus indicating high metallicity. Furthermore, the imaginary part ε2, which represents loss, also varies less with post-annealing temperature than the real part ε1, but is smallest at 928 K among the four post-annealing temperatures. This is reflected in the FOM shown in Figure 19 mentioned above.

[0084] Furthermore, we investigated the reproducibility of the NiAl films formed by the first manufacturing method. Specifically, SEM images of the surfaces of three samples obtained under the same experimental conditions, with the post-annealing temperature set to the optimal temperature of 928 K, are shown in Figures 23A to 23C. As can be seen from these figures, the three samples exhibited similar surface morphologies and excellent flatness. Furthermore, the flatness was better than that of any NiAl films formed in situ on substrates heated by the first manufacturing method.

[0085] 24A to 24C show SEM images of the surfaces of three NiAl film samples obtained at a post-annealing temperature one step higher than the optimum post-annealing temperature of 928 K, i.e., 967 K. Although the results at these one-step higher post-annealing temperatures were inferior to the optimum post-annealing temperature of 928 K, the surface flatness was still better than that of the NiAl film formed in situ using the comparative manufacturing method.

[0086] The surface shapes were compared for the comparative manufacturing method and manufacturing method 1 at the substrate temperature / post-annealing temperature that optimizes FOM (889 K and 928 K, respectively), and at temperatures one step higher (967 K in both cases). In the comparative manufacturing method, both surfaces exhibit significant porosity (FIGS. 5A and 6A). On the other hand, in manufacturing method 1, even at temperatures higher than the optimal temperature (FIG. 16A), flatness is worse than at the optimal temperature (FIG. 15A), but there is a notable difference in that few or no pores are observed.

[0087] The table below shows the average particle diameters of NiAl particles appearing on the surface of the NiAl films of the examples obtained by the first manufacturing method at four different post-annealing temperatures, i.e., 776 K, 851 K, 928 K, and 967 K, and the NiAl films obtained by simply depositing the film at room temperature (RT) without post-annealing (denoted as RT in the table).

[0088] [Table 3]

[0089] Furthermore, we confirmed that good films could be formed even when the NiAl film thickness was very thin. Specifically, 20-nm-thick NiAl films were formed on quartz substrates and sapphire substrates with C-plane and R-plane orientations using manufacturing method 1 at a post-annealing temperature of 928 K, and SEM images of the surfaces and cross sections of each were obtained. These images are shown in Figures 25A-25C, 26A-26C, and 27A-27C, respectively. In these figures, Figures 25A, 26A, and 27A are SEM images of the surfaces of three samples on which 20-nm-thick NiAl films were formed, respectively, and Figures 25B, 26B, and 27B are high-magnification SEM images of the surfaces of the three samples, respectively. Furthermore, Figures 25C, 26C, and 27C are SEM images of cross sections of the 20-nm-thick NiAl films on the surfaces of the three samples, cut perpendicular to the film surface together with the substrate. As is clear from these figures, the NiAl films formed on any type of substrate showed no island-like particles larger than the film thickness, or significant holes or cracks, either on the film surface or in the cross section, confirming the formation of extremely uniform and flat films. Furthermore, considering the fact that even a 20-nm film formed was uniform and flat with no observable defects, it is believed that NiAl films adequate for the purposes of this invention can be obtained even with a thickness of 10 nm or even a few nanometers. Regarding the orientation of such ultrathin NiAl films, as can be seen in Figure 28, the (110) plane maintains charge neutrality regardless of the plane cut (i.e., regardless of the horizontal plane cut in the lower diagram of Figure 28), whereas the (100) plane becomes either a + or - plane, resulting in an electrically unstable surface. This is thought to result in a more stable (110) plane. For more information on this, please also refer to Non-Patent Document 8. Although NiAl is not an ionic crystal like NaCl, and so may not have the same charge imbalance as an ionic crystal, the difference in electronegativity between Ni and Al makes it easy for charge imbalance to occur on the surface, and the above explanation still applies in this case. Therefore, under the post-annealing conditions where the (110) plane tends to be the preferred orientation plane as described above, a NiAl film strongly oriented in the (110) plane is naturally formed even when the film thickness is extremely thin.In the case of the second manufacturing method (two-step film formation method), in addition to the discussion of the number of bonds broken on the surface as performed in the first manufacturing method, it is also natural that NiAl crystals grow in a manner that inherits the same orientation plane as the preferred orientation plane of the underlying NiAl film during post-annealing of the upper NiAl film formed thereon, considering that the (110) is the preferred orientation plane of the underlying NiAl film in the first place.

[0090] To investigate the properties of this 20-nm-thick NiAl film, two probes were brazed onto the NiAl film using Ag, and a voltage of 10 V was repeatedly applied between the probes. Even with this repeated voltage application, stable measurements were obtained without any fluctuations. This means that the application of this voltage did not cause any destruction or other structural changes to the NiAl film, and that the application of voltage did not substantially cause any migration of electrode material elements into the NiAl film. Therefore, it was found that the 20-nm-thick NiAl film not only possesses a high degree of structural uniformity, but is also electrically strong and stable.

[0091] To investigate the possibility of further thinning, NiAl films with thicknesses of 100 nm, 20 nm, and 10 nm were fabricated on Si substrates, and a 6 nm NiAl film was fabricated on a glass substrate, and the electrical resistance between a pair of electrodes formed on these films was measured. In fabricating these NiAl films, the films on the Si substrates were fabricated by magnetron sputtering at a substrate temperature of 773 K (sputtering time was 1 hour for a film thickness of 10 nm), and the films on the glass substrates were fabricated by magnetron sputtering at room temperature, followed by post-annealing at 873 K for 1 hour.

[0092] This measurement was performed using the same measurement method as in the experiment to investigate the properties of the 20 nm thick NiAl film mentioned above. As a result, the measurement results shown in the table below were obtained stably. The table also shows the conductivity σ of the NiAl thin plate, calculated from the measured resistance R between the electrodes, based on the approximation that a current flows through a ribbon-shaped (ultra-thin rectangular parallelepiped) NiAl thin plate with two electrodes of width W (2 mm), distance d (2 mm) between these electrodes, and thickness t. In other words, in this model, σ=d / (WtR) By substituting the values of the width W and distance d, the formula is σ=1 / (tR) The conductivity σ was calculated by substituting the thickness t and the resistance value R into this equation.

[0093] [Table 4]

[0094] As shown in this table, good electrical conductivity was observed even in the case of an ultrathin film with a thickness of 6 nm. Such high conductivity means that NiAl films were obtained with very few defects that impair continuity, such as film ruptures, even when the film thickness was reduced to 10 nm or even 6 nm. For comparison, the resistance of a simple glass substrate without a NiAl film was also measured, and the results showed a much higher resistance than that of the 6-nm NiAl film. Furthermore, to confirm whether this phenomenon is due to the properties of the film itself or whether it is dependent on the substrate, three types of insulating substrates were selected: glass, sapphire, and lithium tantalate. Films were deposited at room temperature using magnetron sputtering to an effective thickness of 20 nm, followed by post-annealing at a substrate temperature of 873 K. The results showed metallic electrical conduction in all cases (0.7–1.0 × 10 -4 Ω -1 cm -1 ) The substrate dependence was found to be small. Furthermore, even when a 6 nm film was formed on a glass substrate at room temperature and post-annealed at 873 K, the-4 Ω -1 cm -1 It exhibited metallic electrical conductivity of .

[0095] Furthermore, the fact that such thin films maintain high continuity means that the surface roughness of these films is also very small, specifically, equivalent to or even better than the surface roughness measured in this example for the thicker NiAl films. That is, while the root-mean-square roughness of the surface in the thicker NiAl film examples is 6 nm or less, a surface roughness of this magnitude or greater would result in a film with poor continuity, with the underlying surface exposed throughout due to surface irregularities. From this perspective, even when the film is thinned to 6 nm, the root-mean-square roughness of the surface should be significantly smaller than 6 nm. Therefore, even when thinned to 6 nm, the film can be said to have high continuity and flatness (extremely small root-mean-square roughness).

[0096] As can be seen from the table above, the thinner the NiAl film is, the lower the conductivity σ becomes. The reason for this phenomenon is that, when considering the current flowing within the film in the direction of its expansion, the thinner the film is, the higher the proportion of current flowing in the immediate vicinity of the film surface becomes. More specifically, it is known that current (electrons) flowing in the immediate vicinity of the film surface tends to lose momentum due to interactions with the surface (in macroscopic terms, the conductivity of the film surface is lower than that of the interior). This means that the thinner the film is, the larger the proportion of the area in the entire film cross section where the drop in conductivity is significant in the immediate vicinity of the film surface becomes, resulting in a decrease in the conductivity of the film as a whole. In addition, although NiAl films have very good flatness, when considering that they have root-mean-square roughness on the order of nm, another reason is thought to be that the deviation from the assumption that current flows through a ribbon-shaped (ultrathin rectangular parallelepiped) thin plate with a completely uniform thickness, which is the model for calculating conductivity in the table above, becomes non-negligible when the film thickness is 10 to 20 nm or less.

[0097] As described above, even with a thickness of 30 nm or less, a smooth and continuous NiAl film can be obtained. Because of their excellent flatness, these ultrathin films naturally have the same excellent optical response as thicker NiAl films and can be used for similar purposes. Furthermore, because they maintain good electrical conductivity even at extremely thin thicknesses, NiAl's high resistance and mechanical strength in oxidizing high-temperature environments can be utilized for electrodes in microelectronic devices used in harsh environments. Depending on the manufacturing conditions of the NiAl film, the imaginary part of its complex permittivity, ε2, may be large. However, NiAl films with such high dielectric loss still have applications, such as use as a heat generating material in broadband heaters (light-to-heat converters), and such NiAl films are still useful.

[0098] To verify the feasibility of ultrathin NiAl films less than 6 nm thick and their electrical conductivity if they were realized, we fabricated NiAl films with thicknesses of 3 nm, 2 nm, and 1.4 nm. These NiAl films were fabricated using the same method as for the thicker NiAl films shown above, but the specific conditions were as follows: A 1.4 nm thick NiAl film was sputtered onto a glass substrate at room temperature, and then post-annealed in a vacuum at 200°C for 1 hour in a sputtering chamber. A 2-nm thick NiAl film was sputtered onto a glass substrate at room temperature, and then post-annealed in a vacuum at 200°C for 1 hour in a sputtering chamber. A 3 nm thick NiAl film was sputtered at room temperature, and then post-annealed in a vacuum at 600°C for 1 hour in a sputtering chamber. The electrical conductivity measurements of these NiAl films are shown in the table below.

[0099] [Table 5]

[0100] Here, in the measurements for film thicknesses of 6 nm, 10 nm, 20 nm, and 100 nm shown above, the electrical resistance between a pair of electrical contacts formed on the film was measured using a conventional resistance meter to determine the resistance value R. However, for film thicknesses of 3 nm, 2 nm, and 1.4 nm, measurements were performed using the van der Pauw method using a Toyo Corporation ResiTest 8400 series resistivity / Hall measurement system, which is believed to have resulted in more accurate measurement results. Furthermore, in the former measurements, conductive paste was used to electrically connect the resistance meter to the film, while in the latter measurements, indium wire was used to connect the measurement system to the NiAl film at four points, thereby reducing the electrical resistance inserted in series into the measurement system. This may have resulted in a higher conductivity observed with the latter measurement system, which may have also contributed to the difference in the two measurement results. Note that for ease of reading, the conductivity σ in the latter measurement results is expressed in Ω, which was used as the unit in the former measurement results. -1 m -1 Not Omega -1 cm -1 Note that the latter conductivity value is two orders of magnitude smaller because of the use of

[0101] As can be confirmed again from the above experimental results, the conductivity of the NiAl film decreases as the film thickness becomes thinner, just as it does when the film thickness is 20 nm or more. This is thought to be due to the reasons mentioned above, but it can also be seen that even at a film thickness of 1.4 nm, the film maintains sufficient continuity in terms of conductivity. From this, it cannot be said that 1.4 nm is the lower limit of the thickness of a continuous NiAl film, and it is thought that NiAl films that maintain continuity up to a thickness of at least ○ nm can be realized.

[0102] However, in this experiment, thinning the film to 1.4 nm further reduced the conductivity, which may make it unsuitable for use as a conductive line, depending on the requirements. However, the application of NiAl films is not limited to conductive line materials; they can also be used in fields that utilize their optical properties. For example, thinning NiAl films to a few nanometers increases their optical transparency. Taking advantage of this property, an ultrathin NiAl film (e.g., 1.4 nm) can be formed on a substrate, such as silicon, to produce an optical sensor that utilizes the phenomenon that occurs at the interface between the substrate material and the NiAl film when light passes through the NiAl film. While a similar result could be achieved by using a material with high optical transmittance on the substrate instead of the NiAl film or by thinning the substrate, this could lead to problems such as a complex manufacturing process or the inability to secure a large enough aperture area for light reception due to the placement of other components on the substrate. In such cases, an ultrathin NiAl film that allows light irradiation from the opposite side of the substrate would be extremely useful. Of course, it should be noted that the conductivity may be significantly improved beyond the experimental results by optimizing various parameters in the production of NiAl films.

[0103] <Structure and properties of NiAl film produced by the second manufacturing method (two-stage film formation method)> For the second manufacturing method, experiments were carried out that were roughly equivalent to those for the comparative example and the first manufacturing method described above, and roughly equivalent measurements were also carried out on the NiAl film obtained as a result.

[0104] 29A to 32C show SEM images, complex dielectric constants, and AFM images of the surface of NiAl films (post-annealing temperatures of 858K, 916K, 928K, and 976K, respectively) according to an embodiment of the present invention, fabricated by the second manufacturing method. As can be seen from these figures, particularly from FIGS. 29C, 30C, 31C, and 32C, which show the AFM images of the surface, the NiAl films obtained by the second manufacturing method showed the same tendency as in the first manufacturing method as the post-annealing temperature was increased. That is, between 858K and 928K, the surface roughness decreased as the post-annealing temperature was increased. However, when the post-annealing temperature was increased from 928K to 967K, the surface roughness R RMS The thickness of the NiAl film rapidly deteriorated from 2.2 nm to 12.5 nm. This is thought to be due to a discontinuous change, such as a phase change in the NiAl crystal, occurring at a temperature between 928 K and 967 K, as in the case of the first manufacturing method. This tendency is also confirmed by the XRD patterns (Fig. 33) and the change in FOM wavelength (Fig. 34) of the NiAl films obtained in this way for various post-annealing temperatures.

[0105] The table below shows the integrated intensities of the peaks in the XRD pattern of the NiAl film fabricated by the second manufacturing method shown in Figure 33. The percentage values in the table above represent the integrated intensities of the peaks corresponding to each orientation plane when the integrated intensity of the entire XRD pattern at each temperature is taken as 100%.

[0106] [Table 6]

[0107] From the above table, it can be determined that for a NiAl film to be uniform and have good optical response, the peak corresponding to the (110) plane in the XRD pattern must be at least 65%, preferably 70%. Although the specific values of the integrated intensities of the peaks in the XRD pattern of the NiAl film fabricated by the first manufacturing method shown in FIG. 18 were not calculated, a comparison of these two XRD patterns shows that they are very similar. Therefore, it can be determined that for the NiAl film fabricated by the first manufacturing method as well, for a NiAl film to be uniform and have good optical response, the peak corresponding to the (110) plane in the XRD pattern must be at least 65%, preferably 70%, as in the case of the second manufacturing method.

[0108] However, as can be seen from the change in FOM with wavelength shown in Figure 34, the FOM value remains 3 or greater within the near-infrared region at the post-annealing temperature (928 K) that provides the best FOM, just as with the first manufacturing method. However, it is noteworthy that the degree of decrease in FOM is smaller when the post-annealing temperature is changed, as compared to the first manufacturing method, for example, even when the post-annealing temperature is 916 K, the FOM value remains approximately 3 or greater within the near-infrared region.

[0109] Furthermore, when comparing the surface roughness values between the first and second manufacturing methods, the first manufacturing method had smaller values at all post-annealing temperatures. As explained above, the reason for this is thought to be the difference in surface roughness between the NiAl film before post-annealing in the first manufacturing method and the underlying surface of the upper NiAl film in the second manufacturing method.

[0110] The average particle size of NiAl particles appearing on the surface of each NiAl film of the example for four different post-annealing temperatures for the second manufacturing method, namely 858K, 916K, 928K and 967K, is shown in the table below.

[0111] [Table 7]

[0112] Comparing the average grain size in the table above with the average grain size at the corresponding post-annealing temperature in the first manufacturing method, the average grain size is larger when the second manufacturing method is used at all temperatures. This result confirms that the good crystallinity of the lower NiAl film is reflected in the crystallinity of the upper NiAl film by post-annealing.

[0113] <NiAl infrared absorber using NiAl film by the second manufacturing method (two-stage film formation method)> In the following, to demonstrate that the NiAl film of the present invention can actually be used as a light-to-heat conversion device, an infrared absorber will be used as a non-limiting example to explain its manufacturing method, structure, characteristics, etc. Here, a device is shown that has a metal-insulator-metal (MIM) structure in which an insulator is sandwiched between metals on the top and bottom, uses a NiAl film for the metal part, and the NiAl film on the infrared receiving side has a structure in which many long, thin, rectangular NiAl pieces are arranged in parallel at equal intervals. Of course, there are many other known structures for this type of device that uses optically responsive materials, and any structure can be selected and adopted from these as needed.

[0114] <Infrared absorber manufacturing> FIG. 35 shows a conceptual diagram of the manufacturing process of an embodiment of a NiAl infrared absorber using a NiAl film of the present invention.

[0115] The Si-NiAl-Al2O3-NiAl-resist laminate used in the first step of the manufacturing process shown in Figure 35 was prepared as follows. First, a 0.18 μm thick NiAl film was formed as the lower metal layer on a Si(100) substrate at a substrate temperature of 889 K using the comparative manufacturing method (in-situ deposition method). Immediately after this NiAl film was cooled to room temperature, a 0.02 μm thick NiAl film was deposited on top. The entire two-layer NiAl film was then post-annealed at 928 K for 1 hour to form a NiAl film using the second manufacturing method (two-stage deposition method). The NiAl film thus formed was then cooled to room temperature, and a 0.2 μm thick Al2O3 insulating film was formed on top of it by radio frequency sputtering from an Al2O3 target. The sputtering power was 450 W, the operating pressure was 0.54 Pa, and the Ar gas flow was 20 sccm. Next, an upper NiAl film was fabricated under the same conditions as the lower NiAl film, but with two thicknesses of 0.15 μm and 0.4 μm. The 0.15 μm and 0.4 μm thick NiAl films were used in two examples, NiAl infrared absorber 1 and NiAl infrared absorber 2, respectively, which will be described later. Furthermore, a negative photoresist AZ-5214E (manufactured by MicroChemicals GmbH, Federal Republic of Germany; referred to as AZ photoresist in the figure) was spin-coated on top of the upper NiAl film at 6000 rpm for 60 seconds and baked on a hot plate at 90°C for 3 minutes. In order to prepare an infrared absorber for comparison, the upper and lower NiAl films were prepared using the comparative example's film formation method (in-situ film formation method) (that is, in preparing the upper and lower NiAl films, the process was the same as that of the comparative example, up to the point where the NiAl film was prepared using the in-situ film formation method, but the step of depositing a 0.02 μm thick NiAl film on top and post-annealing was omitted), and other than that, they were prepared using the same material, size, and process.

[0116] The manufacturing process shown in Figure 35 was applied to each of the four example and comparative stacks prepared above, starting from the leftmost step. First, in the leftmost step, a desired pattern was transferred onto the photoresist using a direct laser writing processor (μPG 101 manufactured by HEIDELBERG Instruments Mikrotechnik GmbH, Federal Republic of Germany; referred to as the Laser gun in the figure) at a wavelength of 405 nm. After the pattern writing process was completed, reversal baking was performed at 120 °C for 20 seconds, followed by full exposure to a UV lamp for 60 seconds. As shown in the second step from the left in Figure 35, the substrate was then developed for 30 seconds using NMD-3, rinsed with deionized water, and dried using a nitrogen gas gun. The following processes, shown as the third and fourth steps from the left in Figure 35, were then performed to remove excess NiAl particles around the substrate and wash away the remaining photoresist. Specifically, reactive ion etching (using ULVAC CE-3001; mixed gas: Ar (5 sccm)-BCl3 (10 sccm)-Cl2 (5 sccm); total pressure: 0.2 Pa; RF power: 100 W; RF bias power: 80 W; etching rate: 0.2 nm / sec) and oxygen plasma ashing (using Mory PB-600; 300 W power for 15 minutes) were performed.

[0117] Figure 36 shows a schematic perspective view of the strip-like structures (right end of Figure 35) that appear on the surface of each stack (i.e., the completed NiAl infrared absorber) obtained as a result of the above manufacturing process. As shown here, the lower NiAl film maintains its original shape when deposited, i.e., a shape that covers the entire Si substrate surface, while the upper NiAl film has been shaped by the above-mentioned etching process into a shape in which multiple strips are arranged in parallel. Let the repeating period of the arrangement of these strips be p, the width and height of each strip be w and h, respectively, and the thickness of the insulating Al2O3 layer be t (see Figure 36). Here, NiAl infrared absorbers of the following two sizes were fabricated. ·NiAl infrared absorber 1: p=4.26μm, w=2.2μm, h=0.15μm, t=0.2μm ·NiAl infrared absorber 2: p=5.74μm, w=2.0μm, h=0.4μm, t=0.2μm

[0118] Figures 37A and 37B are SEM images of the surfaces of NiAl infrared absorbers 1 and 2, respectively. In these figures, the light-colored vertical stripes are the upper NiAl film (the trapezoidal cross section in Figure 36) that remained during the etching process, and the dark-colored vertical stripes are the insulating Al2O3 layer that became visible after the upper NiAl film covering it was removed by the etching process.

[0119] Figures 38A and 38B are SEM images of the cross sections of NiAl infrared absorbers 1 and 2, respectively. In these figures, the lower half of the figure is the Si substrate, and the narrow, light-colored region extending horizontally between the left and right edges near the center is the insulating Al2O3 layer. Six (Figure 38A) or four (Figure 38B) light-colored bar-like regions extending horizontally are visible on the insulating Al2O3 layer. These are the NiAl portions with trapezoidal cross sections shown in Figure 36. In both Figures 38A and 38B, dark-colored shaded regions appear between the trapezoidal NiAl portions and the insulating Al2O3 layer. These are artifacts resulting from the placement of the SEM electron beam detector and are not considered to correspond to the actual structure.

[0120] The resonance characteristics of the above-mentioned minute structures (strip-like structures) for the two NiAl infrared absorbers of the examples and the two NiAl infrared absorbers for comparison were investigated using a Fourier transform infrared spectrometer (FTIR; iS50 manufactured by Thermo Scientific Nicolet, USA).

[0121]

number

[0122] The absorber was placed on a 1 × 1 cm square strip of NiAl. 3The region of the figure was investigated. The incident light beam on the NiAl infrared absorber surface was set at 0 degrees relative to the normal direction of the surface. The wavelength-absorbency characteristics (denoted as Absorptivity in the figure) obtained in this way, i.e., the absorption spectra, are shown in Figures 39A and 39B. Figure 39A shows the absorption spectra (denoted as Expt._comb.-NiAl and Expt._in situ-NiAl in the figure) of NiAl infrared absorber 1, an example of the present invention, and its corresponding comparative NiAl infrared absorber. Figure 39B shows the absorption spectra (denoted as Expt._comb.-NiAl and Expt._in situ-NiAl in the figure) of NiAl infrared absorber 2, an example of the present invention, and its corresponding comparative NiAl infrared absorber. These figures also show the simulation results (denoted as Sim. Abs. in the figure) of the wavelength-absorbency characteristics of NiAl infrared absorbers 1 and 2, examples of the present invention. The rigorous coupled-wave analysis method (RCWA) was used for this simulation.

[0123] When light is incident perpendicularly on the surface of these NiAl infrared absorbers, two main resonance bands, M1 and M2, appear in the absorption spectra. The main resonance band M1 on the short wavelength side is centered at 4.35 μm and 5.75 μm in the spectra shown in Figures 39A and 39B, respectively, while the main resonance band M2 on the long wavelength side is centered at 7.75 μm and 8.0 μm in the spectra shown in Figures 39A and 39B. As can be seen, the absorption wavelength can be changed by changing the period p of the NiAl strips in the NiAl infrared absorber. This indicates that the sharp absorption is brought about by the periodicity, and M1 and M2 are thought to be related to the finite-size confinement of the surface plasmon resonance in each NiAl strip.

[0124] As can be seen from comparing the NiAl infrared absorber of the example shown in Figures 39A and 39B with the NiAl infrared absorber prepared for comparison, the background level is lower than that of the NiAl infrared absorber for comparison, particularly in the short wavelength region (specifically, on the shorter wavelength side than the peak of M1), and is closer to the simulation result.

[0125] According to Kirchhoff's law of thermal radiation, the NiAl infrared absorber of the embodiment having such characteristics can also function as a good infrared radiator by heating. A specific configuration for heating the NiAl infrared absorber of the embodiment to operate as an infrared radiator is, for example, to generate Joule heat by passing an electric current through the lower NiAl film. These matters are well known and will not be described further. [Prior art documents] [Patent documents]

[0126] [Patent Document 1] Republished Patent Publication 2019 / 225726 [Patent Document 2] International Publication WO2021 / 024909 [Non-patent literature]

[0127] [Non-Patent Document 1] T. Yokoyama, TD Dao, K. Chen, S. Ishii, RP Sugavaneshwar, M. Kitajima, and T. Nagao, "Spectrally selective mid-infrared thermal emission from molybdenum plasmonic metamaterial operated up to 1000 ℃," Adv. Opt. Mater. 4(12), 1987-1992 (2016). [Non-patent document 2] TD Dao, K. Chen, S. Ishii, A. Ohi, T. Nabatame, M. Kitajima, and T. Nagao, "Infrared Perfect Absorbers Fabricated by Colloidal Mask Etching of Al-Al2O3-Al Trilayers," ACS Photonics 2(7), 964-970 (2015).

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Claims

1. A nickel-aluminum film having an atomic ratio of Ni to Al of 1:1, a (110) plane as a preferred orientation plane, and a surface root-mean-square roughness of 6 nm or less.

2. 2. The nickel aluminum film according to claim 1, wherein the figure of merit of the optical response is 3 or more in the wavelength range of 0.8 μm to 2.5 μm.

3. 2. The nickel aluminum film according to claim 1, wherein the figure of merit of the optical response is 2 or greater within the wavelength range of 0.6 μm to 2 μm.

4. 2. The nickel aluminum film of claim 1, wherein the figure of merit of the optical response is 2 or greater within the wavelength range of 1.2 μm to 4 μm.

5. 5. The nickel aluminum film according to claim 1, wherein the integrated intensity of the peak corresponding to the (110) plane in the XRD pattern is 65% or more of the total integrated intensity.

6. 6. The nickel aluminum film according to claim 1, wherein the film thickness is in the range of 2 nm to 30 nm.

7. A nickel aluminum film having a thickness in the range of 1 nm or more and less than 20 nm, and an atomic ratio of Ni to Al of 1:

1.

8. A method for producing a nickel-aluminum film, in which the atomic ratio of nickel to aluminum is 1:1, the (110) plane is the preferred orientation plane, and the root-mean-square roughness of the surface is 6 nm or less, is obtained by post-annealing a nickel-aluminum film having an atomic ratio of nickel to aluminum of 1:1 at 700 K or more and 940 K or less.

9. The method for producing a nickel aluminum film according to claim 8 , wherein the post-annealing temperature is 930 K or less.

10. 10. The method for producing a nickel aluminum film according to claim 8, wherein the nickel aluminum film to be post-annealed is formed by magnetron sputtering on a substrate at room temperature.

11. a second nickel-aluminum film having a nickel-to-aluminum atomic ratio of 1:1 and a surface roughness smaller than that of the first nickel-aluminum film is formed on a first nickel-aluminum film having a nickel-to-aluminum atomic ratio of 1:1 and a (110) plane as a preferred orientation plane, thereby producing a nickel-aluminum laminate film; post-annealing the nickel-aluminum laminated film at 700 K or more and 940 K or less; A method for producing a nickel-aluminum film, in which the atomic ratio of nickel to aluminum is 1:1, the (110) plane is the preferred orientation plane, and the root-mean-square roughness of the surface is 6 nm or less.

12. 12. The method for producing a nickel aluminum film according to claim 11, wherein the first nickel aluminum film is formed by magnetron sputtering at a substrate temperature of 700K or more and 940K or less.

13. 13. The method for producing a nickel aluminum film according to claim 12, wherein the second nickel aluminum film is formed on the first nickel aluminum film at room temperature by magnetron sputtering.

14. A device for converting between light and heat, using the nickel aluminum film according to any one of claims 1 to 7.

15. A thermophotovoltaic power generating device using the nickel aluminum film according to any one of claims 1 to 7 as a near-infrared emitter.

16. 8. A thermally assisted magnetic recording device, comprising a near-field light generating element for forming a light spot for heating a magnetic recording medium, the nickel aluminum film according to claim 1.

17. 8. An electronic device for absorbing / emitting light utilizing optical response, which uses the nickel aluminum film according to any one of claims 1 to 7 as an electrode material.

18. A planar heater that generates heat by passing an electric current through the nickel aluminum film according to any one of claims 1 to 7.

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