Infrared spectrometer

Abstract

To provide an infrared spectrometer with a compact configuration which can divide infrared light by using SPR.SOLUTION: An infrared spectrometer 1A includes: a metal thin film 20 having a diffraction grating structure 23 in a front surface 21, the metal thin film being capable of exciting a surface plasmon resonance in the surface when infrared light enters the front surface 21 at a specific incidence angle (a specific angle θa); a power generation unit 30 provided on a back surface 22 of the metal thin film 20, the power generation unit being capable of generating power by transmission of infrared light into the inside of the power generation unit; and a current detection unit 70 for detecting a current flowing in the power generation unit 30 by power generation by the power generation unit 30.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present disclosure relates to an infrared spectroscopic device that utilizes surface plasmon resonance. [Background technology]

[0002] Various devices that utilize surface plasmon resonance (SPR) are known.

[0003] Patent Document 1 discloses a sensor having a photoelectric conversion element having a light receiving surface that converts incident light into an electric signal and outputs it, a grating structure formed in a stripe shape on the light receiving surface by a light-transmitting resist material and inducing surface plasmons when irradiated with incident light, a conductor formed to cover the grating structure and the exposed light receiving surface, and an output electrode that outputs a voltage signal generated by the photoelectric conversion element. According to the sensor disclosed in Patent Document 1, the angle of incidence at which SPR occurs can be detected by detecting a current excited by SPR generated when light passes through the diffraction grating structure on the sensor surface, and the gas passing through the sensor can be identified based on the detected angle of incidence.

[0004] Patent Document 2 discloses a photodetector having a semiconductor layer, an organic semiconductor having a convex portion provided on the semiconductor layer, and a metal layer provided on the semiconductor layer and the convex portion and having a metal that promotes plasmon resonance. According to the photodetector disclosed in Patent Document 2, the detection sensitivity can be improved by optimizing the size of the diffraction grating using an organic semiconductor.

[0005] Patent Document 3 discloses a spectroscopic device including a plate-shaped rotating part having a light receiving surface, a fixed part formed so as to be fixed to a support member, a connection part connected to a part of the outer edge of the rotating part to connect the rotating part and the fixed part, and an electrode part electrically connected to the light receiving surface of the rotating part. The rotating part of this spectroscopic device rotates in the vertical direction of the light receiving surface, and is configured so that surface plasmon resonance occurs when light of a predetermined wavelength is irradiated onto the light receiving surface. According to the spectroscopic device disclosed in Patent Document 3, the incident angle for generating surface plasmon resonance can be changed using MEMS technology. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-233779 A [Patent Document 2] Patent No. 6245495 specification [Patent Document 3] JP 2019-128157 A Summary of the Invention

[0007] (Problem to be solved by the invention) The techniques disclosed in Patent Documents 1, 2, and 3 are all techniques for detecting the angle of incidence of light by detecting electrons excited by SPR caused by light incident at a specific angle as a current. However, the current excited by SPR is very small, and no technique for increasing the output has yet been found. In addition, the longer the wavelength of light, the smaller the light energy, and therefore the energy of electrons excited by SPR caused by infrared light with a long wavelength is particularly small.

[0008] In addition, the electrons excited by SPR must overcome the Schottky barrier when moving to the semiconductor layer. Here, as described above, the energy of the electrons excited by SPR caused by infrared rays is particularly small, so there is a high possibility that they cannot overcome the Schottky barrier. When using a normal silicon substrate, the Bardeen model is applied in which the height of the Schottky barrier is always constant regardless of the type of metal thin film used to cause SPR. This is also known as the pinning phenomenon, and the height of the Schottky barrier cannot be lowered. Therefore, it is difficult to observe the electrons excited by SPR as a current. Therefore, in the past, a prism was used to split the light into different refractive indices for each wavelength of the incident infrared rays, and an infrared detection element was placed in the path of each split light, and the infrared rays were detected from the relationship between the position of the element that detected the infrared rays and the wavelength. However, such a configuration is not preferable because it leads to an increase in size.

[0009] An object of the present disclosure is to provide an infrared spectroscopy device having a compact configuration that can disperse infrared light using SPR. [Means for solving the problem]

[0010] The present inventors have developed a spectroscopic device capable of dispersing infrared light by utilizing the fact that the intensity of light passing through a metal thin film having a diffraction grating structure formed on its surface increases significantly when SPR occurs due to light incident on the surface of the metal thin film. That is, the present disclosure provides an infrared spectroscopic device comprising: a metal thin film having a diffraction grating structure formed on its surface and configured to excite surface plasmon resonance when infrared light is incident on the surface at a specific incident angle, a power generation unit provided on the back side of the metal thin film and configured to generate electricity by infrared light passing through the inside, and a current detection unit that detects a current flowing through the power generation unit due to power generation in the power generation unit.

[0011] According to the present disclosure, it is possible to provide an infrared spectroscopy device having a compact configuration that can disperse infrared light using SPR. [Brief description of the drawings]

[0012] [Figure 1A] FIG. 1 is a diagram showing the most basic configuration of an infrared spectroscope according to an embodiment. [Figure 1B] FIG. 2 is a diagram showing another infrared spectroscopy device according to the present embodiment. [Figure 1C] FIG. 13 is a diagram showing still another infrared spectroscopy device according to the present embodiment. [Diagram 2] FIG. 13 is a diagram showing a modified example of the sensor chip. [Diagram 3] FIG. 13 is a diagram showing another modified example of the sensor chip. [Figure 4] FIG. 13 is a diagram showing yet another modified example of the sensor chip. [Diagram 5] FIG. 13 is a diagram showing yet another modified example of the sensor chip. [Figure 6] FIG. 13 is a diagram showing yet another modified example of the sensor chip. [Figure 7] FIG. 13 is a diagram showing yet another modified example of the sensor chip. [Figure 8] 1 is a graph showing the results of a simulation of how the reflectance, absorptance, and transmittance of light change with the angle of incidence when infrared light with a wavelength of 2000 nm is incident on a thin metal film with a flat surface. [Figure 9] 13 is a graph showing the results of a simulation of how the reflectance, absorptance, and transmittance of light change with the angle of incidence when infrared light with a wavelength of 2000 nm is incident on a metal thin film having a diffraction grating structure formed on its surface. [Figure 10] FIG. 1 is a diagram showing the structure of a model of a sensor chip used in a simulation for investigating the effect of the thickness of a thin metal film on infrared transmittance. [Figure 11] FIG. 11 is a diagram showing the results of a simulation performed using the model shown in FIG. [Figure 12]1 is a graph showing the relationship between the peak difference ΔTpeak and the film thickness of a metal thin film. [Figure 13] 1 is a graph showing the relationship between the peak ratio Rpeak and the film thickness of a metal thin film. [Figure 14] FIG. 13 is a diagram showing the structure of a model of a sensor chip used in a simulation for investigating the effect of the wavelength of incident infrared light on the peak position of transmittance. [Figure 15] FIG. 13 shows the results of a simulation performed using a model in which the thickness of the transmissive layer is set to 50 nm. [Figure 16] FIG. 13 shows the results of a simulation performed using a model in which the thickness of the transmissive layer is set to 100 nm. [Figure 17] FIG. 13 is a diagram showing another modified example of the infrared spectroscope according to the embodiment. [Figure 18] FIG. 13 is a diagram showing another modified example of the sensor chip according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0014] 1A shows the most basic configuration of an infrared spectroscopy device according to this embodiment. As shown in FIG 1A, the infrared spectroscopy device 1A according to this embodiment includes a sensor chip 10A and a current detection unit 70. The sensor chip 10A includes a metal thin film 20 and a power generation unit 30.

[0015] The metal thin film 20 is a thin film having a front surface 21 perpendicular to the thickness direction and a back surface 22 on the opposite side. The metal thin film 20 is a metal thin film made of a plasmonic material capable of exciting surface plasmon resonance when infrared light is incident on the front surface 21 or the back surface 22 at a specific incident angle. The metal thin film 20 may be made of a metal alone or may be made of a substance containing a metal. Examples of materials for the metal thin film 20 include metals, metal nitrides, and metal oxides, and one of these may be used alone or a composite material using two or more of them. Examples of metals that are preferable for the material of the metal thin film 20 include gold (Au), silver (Ag), aluminum (Al), copper (Cu), platinum (Pt), palladium (Pd), zinc (Zn), and sodium (Na). Examples of metal nitrides that are preferable for the material of the metal thin film 20 include titanium oxide (TiN). Examples of metal oxides that are preferable for the material of the metal thin film 20 include ITO (indium tin oxide), FTO (fluorine-doped tin oxide), and ZnO doped with other elements (aluminum, gallium, etc.). Among them, the material of the metal thin film 20 is preferably at least one selected from the group consisting of Au, Ag, Al, Cu, Pt, Pd, and TiN, and more preferably at least one selected from the group consisting of Au, Ag, Al, Cu, and Pt.

[0016] As shown in Fig. 1A, a diffraction grating structure 23 is formed on a surface 21 of a metal thin film 20. The diffraction grating structure 23 is a structure in which convex portions 23a (ridges) and concave portions 23b (grooves) extending in parallel along one direction (predetermined direction) among the in-plane directions of the surface 21 of the metal thin film 20 are continuously (periodically) repeated. That is, a plurality of parallel grooves formed by a plurality of convex portions 23a and a plurality of concave portions 23b are formed on the surface 21 of the metal thin film 20, and the diffraction grating structure 23 is formed by these grooves. Fig. 1A shows a cross section of the diffraction grating structure 23 cut along a plane perpendicular to the direction in which the convex portions 23a and the concave portions 23b extend.

[0017] The shape of the diffraction grating structure 23, for example, the width a of the convex portion 23a and the pitch b (the width of the convex portion 23a+the width of the concave portion 23b) can be adjusted so that it can function as a diffraction grating when infrared light is incident. More preferably, the width a and the pitch b of the convex portion 23a are adjusted so that the diffraction grating structure 23 can function as a transmission type diffraction grating when near infrared light is incident. Here, infrared light is an electromagnetic wave having a longer wavelength than visible light and a shorter wavelength than radio waves. The wavelength of infrared light is approximately in the range of 700 nm or more and 1 mm or less. Moreover, near infrared light is infrared light with a short wavelength, and its wavelength is approximately 700 nm or more and 2500 nm or less.

[0018] The thickness of the metal thin film 20, i.e., the length from the front surface 21 to the back surface 22 of the metal thin film 20, is preferably 100 nm or less, more preferably 20 nm to 50 nm, and even more preferably 30 nm to 50 nm. Here, in the example shown in Fig. 1A, the thickness of the portion of the metal thin film 20 constituting the convex portion 23a of the diffraction grating structure 23 is equal to the thickness of the portion constituting the concave portion 23b. Thus, the thickness of the metal thin film 20 is the thickness of the convex portion 23a and the concave portion 23b of the diffraction grating structure 23.

[0019] The power generating unit 30 is provided on the rear surface 22 side of the metal thin film 20. The power generating unit 30 may be in direct contact with the rear surface 22 of the metal thin film 20. The power generating unit 30 does not have to be in direct contact with the rear surface 22 of the metal thin film 20. In this case, it is preferable that the power generating unit 30 is in indirect contact with the rear surface 22 of the metal thin film 20 via another layer (such as the transmissive layer 50 described below).

[0020] In FIG. 1A, the power generating section 30 has a surface 31 that is in direct contact with the back surface 22 of the metal thin film 20. Here, as shown in FIG. 1A, an uneven structure corresponding to the convex portions 23a and concave portions 23b formed on the front surface 21 is formed on the back surface 22 of the metal thin film 20. Therefore, an uneven structure corresponding to the uneven structure formed on the back surface 22 of the metal thin film 20 is also formed on the front surface 31 of the power generating section 30. Note that, during actual manufacturing, the uneven structure is first formed on the front surface 31 of the power generating section 30. Next, the metal thin film 20 is formed (deposited) on the front surface 31 of the power generating section 30. As a result, a diffraction grating structure 23 consisting of an uneven structure corresponding to the uneven structure of the front surface 31 of the power generating section 30 is formed on the front surface 21 of the metal thin film 20.

[0021] The power generating unit 30 is configured to have electrical conductivity and to have a function of absorbing infrared rays passing through the inside to generate electricity. In particular, the power generating unit 30 is preferably configured to have a function of absorbing near-infrared rays (infrared rays with wavelengths in the range of 700 nm to 2500 nm) to generate electricity. The power generating unit 30 is also configured to generate more electricity as the intensity of the infrared rays passing through the inside increases. The power generating unit 30 may be made of a semiconductor.

[0022] The material constituting the power generating unit 30 is preferably at least one selected from the group consisting of InGaAs, GeSi, PbS, PbSe, HgCdTe, GaAlAs, InSb, InAsSb, and PtSi. The power generating unit 30 may also be a plasmonic material such as Au, Ag, Cu, Al, Ni, Pd, V, or indium tin oxide (ITO) processed into a nanostructure such as nanoparticles. Furthermore, the power generating unit 30 may be an element configured as an infrared photodetector. Here, the element configured as an infrared photodetector includes a photodiode made of the above-mentioned materials and a thermopile-type infrared sensor utilizing the pyroelectric effect.

[0023] The current detection unit 70 is configured to be able to detect a current flowing inside the power generation unit 30 due to power generation in the power generation unit 30. The current detection unit 70 can be configured to include a first lead wire 71 having one end connected to the metal thin film 20, a second lead wire 72 having one end connected to the power generation unit 30, and an ammeter 73 connected to the other end of the first lead wire 71 and the other end of the second lead wire 72. In this case, the ammeter 73 detects the current flowing inside the power generation unit 30.

[0024] FIG. 1B is a diagram showing another infrared spectroscopy device 1B according to the present embodiment. This infrared spectroscopy device 1B includes a sensor chip 10B and a current detection unit 70. The sensor chip 10B includes a metal thin film 20, a power generation unit 30, and an electrode 41. The configurations of the metal thin film 20 and the current detection unit 70 are the same as those of the metal thin film 20 and the current detection unit 70 included in the infrared spectroscopy device 1A shown in FIG. 1A, and therefore the description thereof will be omitted. As shown in FIG. 1B, the power generation unit 30 has a front surface 31 that contacts the back surface 22 of the metal thin film 20, and a back surface 32 opposite to the front surface 31. An electrode 41 is provided on the back surface 32 of the power generation unit 30. The material of the electrode 41 can be appropriately selected from those conventionally used as electrodes in the semiconductor field. Examples of materials for the electrode 41 include transparent conductive materials such as copper (Cu), gold (Au), silver (Ag), platinum (Pt), zinc (Zn), chromium (Cr), aluminum (Al), titanium (Ti), titanium nitride (TiN), ITO (indium tin oxide), FTO (fluorine-doped tin oxide), and metal oxides such as ZnO doped with other elements (aluminum, gallium, etc.). One end of a first lead wire 71 of the current detection unit 70 is connected to the metal thin film 20, and one end of a second lead wire 72 is connected to the electrode 41.

[0025] FIG. 1C is a diagram showing another infrared spectroscopy device 1C according to the present embodiment. The infrared spectroscopy device 1C includes a sensor chip 10C and a current detection unit 70. The sensor chip 10C includes a metal thin film 20, a power generation unit 30, and an electrode 42. The configurations of the metal thin film 20 and the current detection unit 70 are the same as those of the metal thin film 20 and the current detection unit 70 included in the infrared spectroscopy device 1A shown in FIG. 1A and the infrared spectroscopy device 1B shown in FIG. 1B, and therefore the description thereof will be omitted. The surface 31 of the power generation unit 30 has a portion on which the metal thin film 20 is formed and an exposed portion on which the metal thin film 20 is not formed. An electrode 42 is formed on the exposed portion. The material constituting the electrode 42 can be exemplified by the material constituting the electrode 41 described above. One end of the first lead wire 71 of the current detection unit 70 is connected to the metal thin film 20, and one end of the second lead wire 72 is connected to the electrode 42.

[0026] FIG. 2 shows the deformability of the sensor chip. The sensor chip 10D shown in FIG. 2(a) is a modified version of the sensor chip 10A shown in FIG. 1A, the sensor chip 10E shown in FIG. 2(b) is a modified version of the sensor chip 10B shown in FIG. 1B, and the sensor chip 10F shown in FIG. 2(c) is a modified version of the sensor chip 10C shown in FIG. 1C. The sensor chips 10D, 10E, and 10F shown in FIG. 2 further include a transmission layer 50 provided on the back surface 22 side of the metal thin film 20 so as to be interposed between the metal thin film 20 and the power generation unit 30. The transmission layer 50 is made of a material having a function of transmitting infrared rays. An example of a material constituting such a transmission layer 50 is silicon. Other examples of materials constituting the transmission layer 50 include germanium and chalcogenide glass.

[0027] The transmissive layer 50 has a front surface 51 and a back surface 52 on the opposite side. The power generating unit 30 is disposed on the back surface 52 side of the transmissive layer 50 so that the front surface 31 of the power generating unit 30 is in contact with the back surface 52 of the transmissive layer 50. In addition, a concave-convex structure is formed on the front surface 51 of the transmissive layer 50. This concave-convex structure is formed in the same manner as the concave-convex structure formed on the front surface 31 of the power generating unit 30 shown in FIGS. 1A, 1B, and 1C. The metal thin film 20 is formed on the concave-convex structure on the front surface 51 of the transmissive layer 50. As a result, a diffraction grating structure 23 consisting of a concave-convex structure corresponding to the concave-convex structure on the front surface 51 of the transmissive layer 50 is formed on the front surface 21 of the metal thin film 20.

[0028] Fig. 3 shows other modified examples of the sensor chips 10A, 10B, and 10C shown in Fig. 1A, 1B, and 1C. The sensor chip 10G shown in Fig. 3(a) is a modified example of the sensor chip 10A in Fig. 1A, the sensor chip 10H shown in Fig. 3(b) is a modified example of the sensor chip 10B in Fig. 1B, and the sensor chip 10I shown in Fig. 3(c) is a modified example of the sensor chip 10C in Fig. 1C. In the sensor chips 10G, 10H, and 10I shown in Fig. 3, the rear surface 22 of the metal thin film 20 is formed into a flat surface. The flat surface 31 of the power generation unit 30 is in direct contact with the rear surface 22 of the metal thin film 20.

[0029] FIG. 4 shows a modified example of the sensor chip 10H shown in FIG. 3(b). FIG. 5 shows another modified example of the sensor chip 10B shown in FIG. 1B. In the example shown in FIG. 4 and FIG. 5, the power generation unit 30 is composed of a plurality of metal fine particles. The diameter of the metal fine particles is about 1 nm to 100 nm. That is, the power generation unit 30 is formed of a plurality of metal nanoparticles. The metal nanoparticles are desirably composed of a plasmonic material capable of exciting surface plasmon resonance. For example, gold can be used as the material of the metal nanoparticles.

[0030] In each of the sensor chips shown in Fig. 4 and Fig. 5, a permeable layer 50 is provided on the back surface 22 side of the metal thin film 20. The front surface (upper surface) of the permeable layer 50 is in contact with the back surface 22 of the metal thin film 20. In the sensor chip 10J shown in Fig. 4(a) and the sensor chip 10L shown in Fig. 5(a), metal nanoparticles serving as the power generation unit 30 are disposed at the contact interface between the back surface 22 of the metal thin film 20 and the front surface (upper surface) of the permeable layer 50. In contrast, in the sensor chip 10K shown in Fig. 4(b) and the sensor chip 10M shown in Fig. 5(b), the metal nanoparticles serving as the power generation unit 30 are disposed inside the permeable layer 50.

[0031] Fig. 6 shows another modified example of the sensor chip. The sensor chip 10N shown in Fig. 6(a) is another modified example of the sensor chip 10H shown in Fig. 3(b), and the sensor chip 10O shown in Fig. 6(b) is another modified example of the sensor chip 10B shown in Fig. 1B. In these sensor chips 10N and 10O, the power generation section 30 is composed of a p-type semiconductor layer 30a and an n-type semiconductor layer 30b that are excited by infrared rays. Therefore, when infrared rays pass through the inside of the power generation section 30, power is generated by an internal photoelectric effect that occurs at the junction interface between the p-type semiconductor layer 30a and the n-type semiconductor layer 30b.

[0032] Fig. 7 is a modified example of the sensor chip 10O shown in Fig. 6(b). In the sensor chip 10P shown in Fig. 7, the power generation section 30 includes a p-type semiconductor layer 30a, an intrinsic semiconductor layer 30c, and an n-type semiconductor layer 30b. In this example, the p-type semiconductor layer 30a is a p-type InP (indium phosphide) layer, the intrinsic semiconductor layer is an InGaAs (indium gallium arsenide) layer, and the n-type semiconductor layer is an n-type InP (indium phosphide) layer. Providing a PIN junction structure in the power generation section 30 in this way also allows power generation using infrared rays.

[0033] 1A, 1B, and 1C, an infrared spectroscopy device according to this embodiment equipped with the sensor chip having the above configuration is irradiated with infrared rays emitted from a light source 100. The infrared rays emitted from the light source 100 are incident on a surface 21 of a metal thin film 20. When an incident angle θ of the infrared rays on the surface 21 of the metal thin film 20 is a specific angle θa, plasmon resonance is excited. This increases the absorptance of the incident light and decreases the reflectance.

[0034] Incidentally, when the surface of the metal thin film on which plasmon resonance is excited is a flat surface, that is, when a diffraction grating structure is not formed on the surface, when the incident angle θ of light is equal to or greater than the critical angle θc, the light incident on the metal thin film is totally reflected and does not pass through the metal thin film. FIG. 8 is a graph showing the results of a simulation of how the reflectance, absorptance, and transmittance of light change with respect to the incident angle when light (infrared light) with a wavelength of 2000 nm is incident on a metal thin film (thickness 20 nm) with a flat surface. In FIG. 8, the horizontal axis is the incident angle θ [°] of light on the metal thin film, and the vertical axis is the ratio [%] of the intensity of each light (reflected light, transmitted light, absorbed light). In FIG. 8, the graph A1 shown by the solid line represents the reflectance, the graph B1 shown by the dashed line represents the transmittance, and the graph C1 shown by the dashed line represents the absorptance. As shown in FIG. 8, when the incident angle θ is equal to or greater than the critical angle θc, the transmittance is 0%, and the light does not pass through the metal thin film. Furthermore, when the incident angle θ is a resonance angle θs that is slightly larger than the critical angle θc, plasmon resonance is excited on the surface of the metal thin film. This results in a large decrease in reflectance and a large increase in absorptance. The resonance angle θs is the incident angle at which plasmon resonance can be excited when light is incident on the interface of the metal thin film.

[0035] FIG. 9 is a graph showing the results of a simulation of how the reflectance, absorptance, and transmittance of light change with respect to the angle of incidence when light (infrared light) with a wavelength of 2000 nm is incident on a metal thin film (thickness 50 nm) on which a diffraction grating structure is formed on the surface. All simulations disclosed in this specification were performed using "Ansys Lumerical FDTD", an electromagnetic field simulation software. In FIG. 9, the horizontal axis is the incident angle θ [°] of light on the metal thin film, and the vertical axis is the ratio [%] of the intensity of each light (reflected light, transmitted light, absorbed light). In FIG. 9, graph A2 shown by a solid line represents the reflectance, graph B2 shown by a dashed line represents the transmittance, and graph C2 shown by a dashed line represents the absorptance. As can be seen from FIG. 9, when a diffraction grating structure is formed on the surface of the metal thin film, the incident light is slightly transmitted through the metal thin film regardless of the angle of incidence θ. When the incident angle θ is a specific angle θa (=24.8°, 49.2°), the reflectance drops significantly, while the transmittance as well as the absorptance increases significantly. Thus, the transmittance changes according to the incident angle θ so that a peak is formed when the incident angle θ is the specific angle θa.

[0036] When light is incident on the surface of a metal thin film with a diffraction grating structure formed on its surface, the incident light is transmitted through the metal thin film at a specified diffraction angle due to the diffraction grating structure. At this time, diffracted light of multiple diffraction orders (e.g., first-order diffracted light, third-order diffracted light, fifth-order diffracted light) is transmitted through the metal thin film. If, among the diffracted light transmitted through the metal thin film, there is diffracted light whose diffraction angle at the interface (e.g., the back surface) of the metal thin film matches the resonance angle θs, plasmon resonance is excited. This reduces the reflectance and increases the absorptance, but it is presumed that at the same time, the transmittance also increases significantly.

[0037] In Figure 9, when the incident angle θ of the infrared ray to the surface of the metal thin film is 24.8°, the diffraction angle of the first-order diffracted light coincides with the resonance angle θs, exciting plasmon resonance and increasing the transmittance. When the incident angle θ of the infrared ray is 49.2°, the diffraction angle of the third-order diffracted light coincides with the resonance angle θs, exciting plasmon resonance and increasing the transmittance.

[0038] In this way, when the incident angle θ of the infrared ray irradiated onto the surface 21 of the metal thin film 20 of the infrared spectroscopy device of this embodiment is a specific angle θa, that is, an angle at which any of the diffracted lights passing through the metal thin film 20 induces plasmon resonance, an anomalous transmission phenomenon occurs in which the transmittance of the infrared ray passing through the metal thin film 20 increases significantly.

[0039] The infrared rays that have passed through the thin metal film 20 pass through the inside of the power generation unit 30 provided on the back surface 22 side of the thin metal film 20. This causes power generation in the power generation unit 30, and this power generation causes a current to flow in a circuit formed by the thin metal film 20, the power generation unit 30, and the current detection unit 70. This current is detected by the current detection unit 70. Therefore, by having the current detection unit 70 detect the current while changing the incident angle θ of the infrared rays, the relationship between the incident angle θ and the current value can be obtained.

[0040] Moreover, the power generation amount in the power generation unit 30 increases as the intensity of the infrared rays passing through the inside increases. In other words, the power generation amount in the power generation unit 30 increases as the transmittance of the infrared rays passing through the metal thin film 20 increases. As described above, the transmittance of the infrared rays passing through the metal thin film 20 reaches a peak when the incident angle θ is a specific angle θa, so that the peak of the current value is detected when the incident angle θ is a specific angle θa. In other words, the incident angle θ at which the peak of the current value is detected can be determined as the specific angle θa. This specific angle θa changes depending on the wavelength of the infrared rays incident on the metal thin film 20, as described later. Therefore, by identifying the specific angle θa, i.e., the peak position of the current value, the wavelength of the incident infrared rays can be identified.

[0041] (Effect of metal thin film thickness on transmittance) Next, the influence of the thickness of the metal thin film on the transmittance of light passing through the metal thin film was investigated. In this case, a simulation was performed using a model M1 of a sensor chip shown in FIG. 10. The model M1 shown in FIG. 10 is similar to the configuration of the sensor chip 10D shown in FIG. 2(a) except that the power generation unit 30 is removed. Specifically, the model M1 is composed of a metal thin film 20 having a diffraction grating structure 23 formed on a front surface 21, and a transmission layer 50 provided on the back surface 22 side of the metal thin film 20. In this example, the transmission layer 50 is a silicon layer. This silicon layer has a function of transmitting infrared rays. In addition, in the model M1, a concave-convex structure is formed on a front surface 51 of the transmission layer 50. This concave-convex structure is the same structure as the concave-convex structure of the front surface 51 of the transmission layer 50 of the sensor chip 10D shown in FIG. 2(a).

[0042] The thin metal film 20 is provided on the surface 51 of the transmissive layer 50. Therefore, the surface 21 of the thin metal film 20 has an uneven structure corresponding to the uneven structure formed on the surface 51 of the transmissive layer 50. Specifically, the surface 21 of the thin metal film 20 has an uneven structure in which convex portions 23a (ridges) and concave portions 23b (grooves) extending in parallel along one direction (direction perpendicular to the paper surface in FIG. 10) of the in-plane direction of the surface 21 are continuously (periodically) repeated. The uneven structure formed on the surface 21 of the thin metal film 20 forms a diffraction grating structure 23. The thickness of the portion of the thin metal film 20 that forms the convex portions 23a of the diffraction grating structure 23 is equal to the thickness of the portion of the thin metal film 20 that forms the concave portions 23b. Therefore, the film thickness of the thin metal film 20 (the thickness of the convex portions 23a and the thickness of the concave portions 23b) is uniform. The width c of the convex portions 23a of the diffraction grating structure 23 is set to 1600 nm, and the pitch d of the diffraction grating structure 23 is set to 3400 nm.

[0043] The transmittance of infrared rays (transmitted light) passing through the metal thin film 20 was calculated when infrared rays with a wavelength of 2000 nm were incident at various angles of incidence θ on the surface 21 of the metal thin film 20 included in the model M1 shown in Fig. 10. In this case, the film thickness of the metal thin film 20 was changed from 10 nm to 100 nm in 10 nm intervals, and the transmittance was calculated for each film thickness. The transmittance was calculated based on the intensity of infrared rays passing through position P inside the transmission layer 50 shown in Fig. 10. Position P is a position 2000 nm away from the lowest position of the metal thin film 20 as shown in Fig. 10.

[0044] FIG. 11 is a diagram showing the results of the above-mentioned simulation using the model M1 shown in FIG. 10. In FIG. 11, the horizontal axis is the incident angle θ [°] of the infrared ray to the surface 21 of the metal thin film 20, and the vertical axis is the transmittance [%] of the infrared ray (transmitted light) transmitted through the metal thin film 20. Here, the incident angle θ is the angle between the perpendicular line L1 to the surface 21 of the metal thin film 20 and the incident direction L2 of the infrared ray as viewed from the direction shown in FIG. 10 (the extension direction of the convex portion 23a and the concave portion 23b of the diffraction grating structure 23). Also, FIG. 10 shows ten graphs. Among these, graph A3 shows the simulation results of the transmittance when a metal thin film 20 having a film thickness of 10 nm is used. Similarly, graph B3 shows the simulation results of the transmittance when a metal thin film 20 with a thickness of 20 nm is used, graph C3 shows the simulation results of the metal thin film 20 with a thickness of 30 nm, graph D3 shows the simulation results of the metal thin film 20 with a thickness of 40 nm, graph E3 shows the simulation results of the metal thin film 20 with a thickness of 50 nm, graph F3 shows the simulation results of the metal thin film 20 with a thickness of 60 nm, and graph G3 shows the simulation results of the transmittance when a metal thin film 20 with a thickness of 70 nm is used. Note that although the simulation results of the transmittance when a metal thin film 20 with a thickness of 80 nm, 90 nm, and 100 nm is used are also shown in FIG. 11, the graphs overlap and therefore cannot be shown individually.

[0045] 11, when the thickness of the thin metal film 20 is in the range of 10 nm to 100 nm, the incidence angle θ (i.e., the specific angle θa) at which the transmittance peak occurs is the same angle (=24.8°, 49.2°). This result shows that even if the thickness of the thin metal film 20 changes, the specific angle θa indicating the transmittance peak, i.e., the position of the transmittance peak, does not change as long as the wavelength of the incident infrared ray is the same.

[0046] It is also clear that the transmittance peak value (Tpeak) is larger as the thickness of the thin metal film 20 is thinner. Furthermore, it is also clear that the transmittance is larger as the thickness of the thin metal film 20 is thinner when compared at the same incident angle θ.

[0047] FIG. 12 is a graph showing the relationship between the peak difference ΔTpeak of each peak of the transmittance shown when the incident angle θ is a specific angle θa (=24.8°, 49.2°) in FIG. 11 and the film thickness of the metal thin film 20. In FIG. 12, the horizontal axis is the film thickness [nm] of the metal thin film 20, and the vertical axis is the peak difference ΔTpeak [%]. Here, the peak difference ΔTpeak is the rise amount of the transmittance peak calculated when the incident angle θ is increased from 0°. Specifically, the peak difference ΔTpeak is represented by the difference (Tpeak-Tprep) between the peak value Tpeak [%] of the transmittance shown in each graph in FIG. 11 and the transmittance value Tprep [%] calculated at the incident angle just before the peak rises. In FIG. 12, the ■ mark indicates the peak difference ΔTpeak obtained when the incident angle θ=24.8°, and the ◯ mark indicates the peak difference ΔTpeak obtained when the incident angle θ=49.2°.

[0048] As can be seen from FIG. 12, when the thickness of the metal thin film 20 is 10 nm and when it is 70 nm or more, ΔTpeak in both cases (ΔTpeak represented by ■ and ΔTpeak represented by ◯) is 5% or less. In contrast, when the thickness of the metal thin film 20 is 20 nm or more and 60 nm or less, at least one of the ΔTpeaks is 5% or more. When any of the ΔTpeaks is 5% or more, the peak is easy to detect. Furthermore, when the ΔTpeak is 5% or more, an improvement in the SN ratio can be expected. Therefore, from the viewpoint of the ease of detecting the peak and the improvement in the SN ratio, the thickness of the metal thin film 20 is preferably in the range of 20 nm or more and 60 nm or less. Furthermore, when the thickness of the metal thin film 20 is 20 nm or more and 50 nm or less, at least one of the ΔTpeaks is 10% or more. When any of the ΔTpeaks is 10% or more, the peak is easier to detect and the SN ratio is further improved. Therefore, the thickness of the metal thin film 20 is more preferably in the range of 20 nm or more and 50 nm or less.

[0049] 13 is a graph showing the relationship between the peak ratio Rpeak of each peak of the transmittance shown when the incident angle θ is a specific angle θa (=24.8°, 49.2°) in FIG. 11 and the film thickness of the metal thin film 20. The horizontal axis of FIG. 13 is the film thickness [nm] of the metal thin film 20, and the vertical axis is the peak ratio Rpeak [-]. Here, the peak ratio Rpeak is the ratio (ΔTpeak / Tpeak) of the peak difference ΔTpeak to the peak value Tpeak at each peak of the transmittance shown in each graph of FIG. 11. In FIG. 13, the ■ mark indicates the peak ratio Rpeak obtained when the incident angle θ=24.8°, and the ◯ mark indicates the peak ratio Rpeak obtained when the incident angle θ=49.2°.

[0050] 13, when the thickness of the metal thin film 20 is 10 nm, the peak ratio Rpeak is small. In contrast, when the thickness of the metal thin film 20 is 30 nm or more, the peak ratio Rpeak is large, at 0.8 or more. When the peak ratio Rpeak is small, the detection accuracy of the transmittance peak is low, and when the peak ratio Rpeak is large, the detection accuracy of the transmittance peak is high. Therefore, from the viewpoint of detection accuracy, the thickness of the metal thin film 20 is preferably 30 nm or more.

[0051] From the above, when the thickness of the metal thin film 20 is 30 nm or more and 60 nm or less, more preferably when the thickness of the metal thin film 20 is 30 nm or more and 50 nm or less, the transmittance peak is easily detected, the S / N ratio is high, and the detection accuracy of the peak is high. Therefore, the thickness of the metal thin film 20 is preferably 30 nm or more and 60 nm or less, and more preferably 30 nm or more and 50 nm or less.

[0052] (Relationship between the wavelength of incident infrared light and the peak position of the current value) Next, the relationship between the wavelength of infrared light incident on the surface 21 of the metal thin film 20 and the peak position (specific angle θa) of the current value detected by the current detection unit 70 was investigated. In this case, a simulation was performed using a model M2 of a sensor chip shown in FIG. 14. As shown in FIG. 14, the model M2 includes a metal thin film 20, a power generation unit 30, and a transmission layer 50. These are configured in a laminated state, with the transmission layer 50 being interposed between the metal thin film 20 and the power generation unit 30. This model M2 has a configuration similar to that of the sensor chip 10D shown in FIG. 2(a).

[0053] The transmissive layer 50 is made of a material capable of transmitting infrared rays. In model M2, the transmissive layer 50 is made of a silicon thin film. The transmissive layer 50 has a front surface 51 and a back surface 52 that face each other in the thickness direction. A concave-convex structure is formed on the front surface 51 of the transmissive layer 50. The back surface 52 of the transmissive layer 50 is a flat surface.

[0054] The thin metal film 20 is provided on the surface 51 of the transmissive layer 50. In the model M2, the thin metal film 20 is a gold film having a thickness (length in the thickness direction (vertical direction in FIG. 14)) of 50 nm. Since an uneven structure is formed on the surface 51 of the transmissive layer 50, an uneven structure corresponding to the uneven structure formed on the surface 51 of the transmissive layer 50 is also formed on the surface 21 of the thin metal film 20 above it. As a result, an uneven structure corresponding to the uneven structure formed on the surface 51 of the transmissive layer 50 is formed on the surface 21 of the thin metal film 20. Specifically, an uneven structure is formed on the surface 21 of the thin metal film 20 in which convex portions 23a (ridges) and concave portions 23b (grooves) extending in parallel along one direction of the in-plane directions of the surface 21 (direction perpendicular to the paper surface in FIG. 14) are continuously (periodically) repeated. A diffraction grating structure 23 is formed by the uneven structure formed on the surface 21 of the thin metal film 20.

[0055] In the model M2, the power generating unit 30 is composed of a laminate of a p-type InAs (indium arsenide) semiconductor thin film 35 and an n-type GaAs (gallium arsenide) semiconductor thin film 36. One surface (upper surface) of the p-type InAs semiconductor thin film 35 is provided so as to contact the rear surface 52 of the transmission layer 50, and one surface (upper surface) of the n-type GaAs semiconductor thin film 36 is provided so as to contact the other surface (lower surface) of the p-type IsAs semiconductor thin film 36. When infrared rays pass through the interface between the p-type InAs semiconductor thin film 35 and the n-type GaAs semiconductor thin film 36, electricity is generated by the internal photoelectric effect. The amount of electricity generated is greater as the intensity of the infrared rays passing through the interface is higher. Also, the intensity of the infrared rays passing through the interface is higher as the transmittance of the infrared rays passing through the metal thin film 20 is higher. Therefore, the amount of electricity generated in the power generating unit 30 is greater as the transmittance of the infrared rays passing through the metal thin film 20 is higher.

[0056] In the model M2, the width e of the convex portion formed on the surface 51 of the transmissive layer 50 (≈ the width of the convex portion 23a of the diffraction grating structure 23 formed on the surface 21 of the metal thin film 20) was set to 1600 nm, and the pitch f of the diffraction grating structure 23 (the width of the convex portion 23a of the diffraction grating structure 23 plus the width of the concave portion 23b) was set to 3400 nm. Simulations were also performed with two patterns in which the thickness tsi of the transmissive layer 50 was 50 nm and 100 nm. Here, the thickness tsi of the transmissive layer 50 is the distance in the thickness direction from the bottom surface of the concave portion formed on the surface 51 of the transmissive layer 50 to the back surface 52 of the transmissive layer 50.

[0057] In the simulation, when infrared rays of various wavelengths are incident at various angles on the surface 21 of the thin metal film 20 of the model M2 of the sensor chip configured as described above, the transmittance of the infrared rays passing through the thin metal film 20 is calculated. Furthermore, the current flowing through the power generation unit 30 due to the power generation that occurs when the infrared rays with the calculated transmittance pass through the power generation unit 30 is calculated. This current is calculated as the current per unit energy (W) of the incident infrared rays.

[0058] FIG. 15 is a diagram showing the results of a simulation performed using a model M2 in which the thickness tsi of the transmission layer 50 is set to 50 nm. FIG. 16 is a diagram showing the results of a simulation performed using a model M2 in which the thickness tsi of the transmission layer 50 is set to 100 nm. In FIG. 15 and FIG. 16, a graph showing the relationship between the incident angle θ of the infrared ray and the calculated current value for each wavelength of the infrared ray incident on the metal thin film 20 is also shown. Among the graphs shown in FIG. 15 and FIG. 16, the top graph is a graph showing the relationship between the calculated current value and the incident angle θ when infrared ray with a wavelength of 2000 nm is incident on the model M2. Similarly, among the graphs shown in FIG. 15 and FIG. 16, the second graph from the top is a graph showing the relationship between the calculated current value and the incident angle θ when infrared ray with a wavelength of 1800 nm, the third graph from the top is a graph showing the relationship between infrared ray with a wavelength of 1600 nm, the fourth graph from the top is a graph showing the relationship between infrared ray with a wavelength of 1400 nm, and the fifth graph from the top is a graph showing the relationship between the calculated current value and the incident angle θ when infrared ray with a wavelength of 1200 nm is incident on the model M2. The horizontal axis of each graph shown in Fig. 15 and Fig. 16 is the incident angle θ [°] of the infrared ray to the surface 21 of the thin metal film 20 of the model M2, and the vertical axis is the calculated current value [mA / W]. Here, the incident angle θ is the angle between the perpendicular line L3 to the surface 21 of the thin metal film 20 and the incident direction L4 of the infrared ray when viewed from the direction shown in Fig. 14 (the extension direction of the convex portion 23a and the concave portion 23b of the diffraction grating structure 23), and the angle when the incident direction L4 is tilted counterclockwise with respect to the perpendicular line L3 when viewed from the direction shown in Fig. 14 is defined as a positive angle, and the angle when it is tilted clockwise is defined as a negative angle. Note that the positive and negative angles may be reversed.

[0059] As shown in Figures 15 and 16, even when infrared rays of various wavelengths are incident on the surface 21 of the metal thin film 20, it can be seen that a peak in the current value occurs when the incident angle θ of the infrared rays is a specific incident angle (specific angle θa). It can also be seen that the position (specific angle θa) at which the peak in the current value occurs varies depending on the wavelength of the incident infrared rays. Therefore, by identifying the incident angle (specific angle θa) at which the peak in the current value is detected, it is possible to identify the wavelength of the incident infrared rays. This makes it possible to separate the infrared rays.

[0060] Also, as can be seen by comparing FIG. 15 and FIG. 16, when infrared rays of the same wavelength are incident on the metal thin film 20, the position (specific angle θa) at which the peak of the current value is detected is the same when the thickness tsi of the transmission layer 50 is 50 nm and when it is 100 nm. The height of the peak detected at the same position (specific angle θa) is slightly larger when the thickness tsi of the transmission layer 50 is 50 nm than when it is 100 nm, but there is no significant difference. This means that when the incident angle θ of the infrared rays is the specific angle θa, the infrared rays transmitted through the metal thin film 20 are hardly attenuated when passing through the transmission layer 50. Here, near-field light is generated at the specific angle θa at which the peak of the current value is detected because plasmon resonance is excited. The intensity of this near-field light attenuates exponentially as it moves away from the generation position. On the other hand, as described above, the infrared rays transmitted through the metal thin film 20 are hardly attenuated when passing through the transmission layer 50. In other words, the results shown in FIGS. 15 and 16 support the idea that the light passing through the transmission layer 50 is not near-field light but transmitted light of the incident infrared rays.

[0061] In a conventional spectrometer using SPR, the flow of electrons excited by SPR is measured as a current, so the measured current value is very small. For example, the current value caused by SPR when infrared light with a wavelength of 1200 nm is incident is estimated to be about 1.5 mA / W. In contrast, according to this embodiment, instead of focusing on the flow of electrons excited by SPR, the transmittance of light passing through the metal thin film 20 increases when SPR is caused, and power generation based on this transmitted light is detected as a current. Therefore, for example, according to the graph of FIG. 15, when infrared light (near infrared light) with a wavelength in the range of 1200 nm to 2000 nm is incident on the surface 21 of the metal thin film 20 at a specific angle θa that can cause SPR, the calculated current value (i.e., the peak value of the current value) is as large as 6.0 mA / W to 12.0 mA / W. Thus, according to the infrared spectrometer according to this embodiment, a larger peak current value can be detected, so that the detection sensitivity can be increased.

[0062] The infrared spectroscope according to this embodiment can be used to detect, for example, a specific gas or gas concentration. For example, by passing light containing infrared rays of various wavelengths through the gas to be measured, the infrared rays of the wavelengths corresponding to the gas are absorbed. By irradiating the metal thin film 20 with this light (light in which infrared rays of the wavelengths corresponding to the gas have been absorbed) at various angles and dispersing the light, the amount of reduction in the infrared rays of the wavelengths corresponding to the gas can be identified. In other words, the specific angle θa corresponding to the wavelength corresponding to the gas changes. The value of the current in the absence of absorption is measured in advance, and by comparing it with the measured value, the type of gas can be identified from the current value detected by the current detection unit 70.

[0063] As described above, the infrared spectroscopy device of this embodiment includes a metal thin film 20 having a diffraction grating structure 23 formed on its surface 21 and configured to excite surface plasmon resonance (SPR) when infrared light is incident on the surface 21 at a specific incident angle (specific angle θa), a power generation unit 30 provided on the back surface 22 side of the metal thin film 20 and configured to generate power by infrared light passing through the inside, and a current detection unit 70 that detects the current flowing through the power generation unit 30 due to power generation in the power generation unit 30.

[0064] According to the infrared spectroscopy device of this embodiment, infrared rays can be detected based on a peak in the current value detected by the current detection unit 70 due to the abnormal transmission phenomenon of infrared rays caused by SPR when the incident angle θ of infrared rays is a specific angle θa. Furthermore, the metal thin film 20, the power generation unit 30, and the current detection unit 70 make it possible to configure a compact infrared spectroscopy device compared to a conventional device that uses a prism and multiple detection elements to perform spectroscopy. Therefore, according to this embodiment, it is possible to provide an infrared spectroscopy device that utilizes SPR with a compact configuration.

[0065] The thickness of the metal thin film 20 included in the infrared spectroscopy device according to this embodiment is preferably 20 nm or more and 60 nm or less, and more preferably 20 nm or more and 50 nm or less. This makes it easier to detect the peak of the transmittance of infrared light passing through the metal thin film 20, and improves the S / N ratio. Furthermore, it is better that the thickness of the metal thin film 20 is 30 nm or more and 60 nm or less, and more preferably 30 nm or more and 50 nm or less. This makes it easier to detect the peak of the transmittance of infrared light, improves the S / N ratio, and increases the detection accuracy.

[0066] The infrared spectroscopy device according to this embodiment can also be configured to include a transmission layer 50 made of a material that transmits infrared rays and provided on the rear surface 22 side of the metal thin film 20 so as to be interposed between the metal thin film 20 and the power generation unit 30. With this, a concave-convex structure is formed on the surface 51 of the transmission layer 50, and the metal thin film 20 is formed on the surface 51, so that a diffraction grating structure can be formed on the surface 21 of the metal thin film 20. In other words, with this configuration, it is not necessary to form a concave-convex structure on the surface 31 of the power generation unit 30 in order to form a diffraction grating structure on the surface 21 of the metal thin film 20. Since it is not necessary to perform surface processing on the power generation unit 30 in this way, safety can be improved.

[0067] Although the present embodiment has been described above, the present invention should not be interpreted as being limited to the above embodiment, and modifications are possible without departing from the spirit of the present invention. For example, an infrared spectroscopy device can be configured as shown in FIG. 17. The infrared spectroscopy device 1D shown in FIG. 17 includes a sensor chip 10Q including a metal thin film 20, a transmission layer 50, and a power generation unit 30, and a current detection unit 70. A diffraction grating structure 23 is formed on a front surface 21 of the metal thin film 20. A transmission layer 50 made of a silicon layer is provided on a rear surface 22 side of the metal thin film 20. The transmission layer 50 has a front surface 51 that contacts the rear surface 22 of the metal thin film 20 and a rear surface 52 on the opposite side. A power generation unit 30 is provided on the rear surface 52 side of the transmission layer 50.

[0068] The power generating unit 30 is configured with a photodetector such as a photodiode. In this case, the power generating unit 30 is disposed with respect to the transmissive layer 50 so that a light receiving surface 33 of the photodetector as the power generating unit 30 faces and contacts the rear surface 52 of the transmissive layer 50.

[0069] As in the above embodiment, the current detection unit 70 has a first lead wire 71, a second lead wire 72, and an ammeter 73. One end of the first lead wire 71 is connected to a positive electrode of a photodetector serving as the power generation unit 30, and one end of the second lead wire 72 is connected to a negative electrode of the photodetector serving as the power generation unit 30. The ammeter 73 is connected between the other end of the first lead wire 71 and the other end of the second lead wire 72.

[0070] In the infrared spectroscopy device 1D configured as described above, when the incident angle θ of the infrared ray incident on the surface 21 of the thin metal film 20 is a specific angle θa, SPR is excited and an abnormal transmission phenomenon of the infrared ray occurs. As a result, the infrared ray that transmits through the thin metal film 20 is received by the light receiving surface 33 of the photodetector serving as the power generation unit 30 via the transmission layer 50. As a result, a current flows in the power generation unit 30. By detecting this current with the current detection unit 70, the peak of the current value can be detected, and the wavelength of the incident infrared ray can be identified based on the incident angle θ of the infrared ray (specific angle θa) when the peak of the current value is detected.

[0071] Also, a sensor chip of an infrared spectrometer can be configured as shown in Fig. 18. This sensor chip 10R includes a metal thin film 20, a power generation unit 30, a reflective layer 60, and a silicon substrate 80. The metal thin film 20 and the power generation unit 30 can be configured in the same manner as the metal thin film 20 and the power generation unit 30 included in the sensor chip 10A shown in Fig. 1A. The reflective layer 60 is provided so as to be in contact with the back surface (the bottom surface in Fig. 18) of the power generation unit 30. This reflective layer 60 is made of a material capable of reflecting infrared rays. A silicon substrate 80 is provided on the back surface (the bottom surface in Fig. 18) of this reflective layer 60.

[0072] In the sensor chip 10Q shown in Fig. 18, when the incident angle θ of infrared light incident on the surface 21 of the thin metal film 20 is a specific angle θa, SPR is excited and an abnormal transmission phenomenon of infrared light occurs. As a result, the infrared light that penetrates the thin metal film 20 enters the power generation unit 30 and generates power. The infrared light that enters the power generation unit 30 is reflected by the surface (upper surface) of the reflective layer 60. This reflected light is reflected by the rear surface (lower surface) of the thin metal film 20. In this way, the infrared light in the power generation unit 30 is repeatedly reflected, and the current flowing through the power generation unit 30 can be amplified. This can further improve the detection sensitivity.

[0073] In the above embodiment, an example in which infrared light is incident on the surface 21 of the metal thin film 20 has been described, but light other than infrared light can also be incident on the metal thin film 20. For example, visible light or ultraviolet light can be incident on the surface 21 of the metal thin film 20. Even in this case, it is considered that the anomalous transmission phenomenon occurs when the incident angle θ is a specific angle θa. Therefore, by detecting the peak of the current due to the transmitted light, the wavelength of the incident light can be identified. [Explanation of symbols]

[0074] 1A, 1B, 1C, 1D... infrared spectrometer, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J, 10K, 10L, 10M, 10N, 10O, 10P, 10Q, 10R... sensor chip, 20... metal thin film, 21... front surface, 22... rear surface, 23... diffraction grating structure, 23a... convex portion, 23b... concave portion, 30... power generation portion, 31... front surface, 32... rear surface surface, 33...light receiving surface, 41, 42...electrodes, 50...transmissive layer, 51...front surface, 52...rear surface, 60...reflective layer, 70...current detection section, 71...first lead wire, 72...second lead wire, 73...ammeter, 80...silicon substrate, 100...light source, Rpeak...peak ratio, Tpeak...peak value, ΔTpeak...peak difference, θ...angle of incidence, θa...specific angle, θc...critical angle, θs...resonance angle

Claims

1. a metal thin film having a diffraction grating structure formed on a surface thereof and configured to excite surface plasmon resonance when infrared light is incident on the surface at a specific incident angle; a power generating section provided on the rear surface side of the metal thin film and configured to generate power by passing infrared rays therethrough; a current detection unit that detects a current flowing through the power generation unit due to power generation in the power generation unit; An infrared spectroscopy device comprising:

2. 2. The infrared spectroscopic device according to claim 1, The metal thin film has a thickness of 20 nm or more and 60 nm or less.

3. 3. The infrared spectroscopic device according to claim 1, an infrared spectroscopy device comprising: a transmission layer made of a material that transmits infrared rays, the transmission layer being provided on the rear side of the metal thin film so as to be interposed between the metal thin film and the power generation unit;

Images