JP7494582B2 - Gas detection device and gas detection method - Google Patents

Description

This disclosure relates to technology for detecting gases, and in particular to technology for detecting gases by optical methods.

Gas sensors using plasmon resonance induced in periodic metal wires fabricated on a semiconductor substrate have been studied as reusable gas sensors capable of detecting minute amounts of gas. The plasmon resonance wavelength is determined by the period of the metal wires and the refractive index of the medium. Therefore, when a minute amount of gas molecules is adsorbed on the metal wires, the effective refractive index changes slightly, and the plasmon resonance wavelength shifts. Gas can be detected by observing the shift in the plasmon resonance wavelength through spectroscopic measurement. Such technology is disclosed, for example, in Patent Document 1 and Non-Patent Document 1. Such gas sensors using plasmon resonance have the advantages of a fast response speed from gas adsorption to a signal and the ability to be reused after gas desorption.

JP 2018-128681 A

A. Tittl et al., ”Palladium-Based Plasmonic Perfect Absorber in the Visible Wavelength Range and Its Application to Hydrogen Sensing”, Nano Lett. 2011, 11, 4366-4368.

In the technology disclosed in Patent Document 1 and Non-Patent Document 1, spectroscopic measurement is required to observe the shift in plasmon resonance wavelength due to gas adsorption. Therefore, there is a problem in that it is necessary to use large-scale and expensive measuring equipment such as a spectrometer or Fourier transform infrared spectrometer in addition to a photodetector.

One of the objectives of the present disclosure is to provide a gas detection device and the like that can reduce the cost of detecting gas using plasmon resonance.

A gas detection device according to one aspect of the present disclosure includes a reflecting means having a structure that induces localized plasmon resonance, a light emitting means that irradiates the reflecting means with light, a bandpass means that transmits light of a predetermined range of wavelengths including a predetermined wavelength, and a detecting means that measures the intensity of the light based on a first reflected light of the light by the reflecting means that has transmitted through the bandpass means, and detects gas on the surface of the reflecting means based on the intensity.

A gas detection method according to one aspect of the present disclosure includes a light emitting means for irradiating light onto a reflecting means having a structure for inducing localized plasmon resonance, and measures the intensity of the light based on a first reflected light of the light by the reflecting means that has passed through a bandpass means that transmits light of a predetermined range of wavelengths including a predetermined wavelength, and detects gas on the surface of the reflecting means based on the intensity.

The present disclosure has the advantage of reducing the cost of detecting gases using plasmon resonance.

FIG. 1 is a diagram illustrating an outline of a gas detection device according to a first embodiment of the present disclosure. FIG. 2 is a schematic diagram of a cross-sectional view of a front-illuminated photodetector and a back-illuminated photodetector. FIG. 3 is a diagram illustrating an enlarged cross-sectional view of the semiconductor photodetector according to the first embodiment of the present disclosure. FIG. 4 is a schematic diagram illustrating incident light on the semiconductor photodetector according to the first embodiment of the present disclosure, and reflected and transmitted light related to the incident light. FIG. 5 is a diagram showing the results of measuring the wavelength dependency of sensitivity (spectral sensitivity) of a photodetector actually fabricated by the manufacturing method according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating the relationship between the resonance wavelength of a localized plasmon and the spectral sensitivity of the semiconductor photodetector according to the first embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of a change in intensity of the output signal of the semiconductor photodetector according to the first embodiment of the present disclosure, which occurs with an increase in the amount of adsorbed gas. FIG. 8 is a schematic diagram showing an example of a semiconductor photodetector and an optical path of incident light. FIG. 9 is a schematic diagram showing an example of the structure of a semiconductor photodetector according to the second embodiment of the present disclosure. FIG. 10 is a schematic diagram showing an example of a light path when the incident light is not perpendicular to the back surface. FIG. 11 is a block diagram illustrating a schematic example of a configuration of a gas detection device according to a third embodiment of the present disclosure. FIG. 12 is a flowchart illustrating an example of the operation of the gas detection device according to the third embodiment of the present disclosure. FIG. 13 is a block diagram illustrating a schematic example of a configuration of a detection device according to a fourth embodiment of the present disclosure. FIG. 14 is a block diagram illustrating a schematic example of a configuration of a gas detection device according to the fourth embodiment of the present disclosure. FIG. 15 is a flowchart illustrating an example of the operation of the gas detection device according to the fourth embodiment of the present disclosure.

FIG. 16 is a flowchart illustrating an example of the operation of the detection device according to the fourth embodiment of the present disclosure. FIG. 17 is a block diagram illustrating an example of a configuration of a computer capable of implementing a detection device according to a fourth embodiment of the present disclosure.

First Embodiment
(Structural Description)
A gas detection device (also simply referred to as a detection device) according to a first embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same elements are commonly represented by the same reference numerals. Unless otherwise specified, duplicated descriptions will be omitted.

First, the outline of the gas detection device 1 according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram showing the outline of the gas detection device according to this embodiment. The gas detection device 1 includes a gas chamber 11, a semiconductor chip 12, a light source 13, a semiconductor photodetector 14, and a bandpass filter 15. A gas to be detected (i.e., a gas to be measured) is injected into the gas chamber 11. The gas chamber 11 introduces the injected gas into the semiconductor chip 12. It is preferable that the gas chamber 11 is kept in a vacuum before the gas to be measured is introduced. In addition, an aperture (window) 16 is formed in the gas chamber 11. The aperture 16 is formed so that the excitation light described later passes through the aperture 16 into the gas chamber 11, and the plasmon resonance light described later passes through the aperture 16 to the outside of the gas chamber 11. The semiconductor chip 12 is installed in the gas chamber 11. Specifically, the semiconductor chip 12 is installed in a cavity inside the gas chamber 11. A structure for inducing plasmons is formed on the surface of the semiconductor chip 12. For example, a periodic metal thin-line structure as disclosed in Non-Patent Document 1 can be used as the structure for inducing plasmons. However, the structure for inducing plasmons is not limited to this. The light source 13 irradiates the semiconductor chip 12 with excitation light through the aperture 16. By irradiating the semiconductor chip 12 with excitation light, plasmon resonance light is induced on the surface of the semiconductor chip 12 irradiated with the excitation light. The plasmon resonance light is incident on the semiconductor photodetector 14 through the aperture 16. The semiconductor photodetector 14 detects the plasmon resonance light induced on the surface of the semiconductor chip 12 by irradiating the semiconductor chip 12 with excitation light. The bandpass filter 15 is installed between the semiconductor chip 12 and the semiconductor photodetector 14. In the example shown in FIG. 1, the bandpass filter 15 is attached to the aperture 16.

Next, the difference between a front-illuminated photodetector and a back-illuminated photodetector will be described with reference to FIG. 2. FIG. 2 is a schematic diagram of a cross-section of a front-illuminated photodetector and a back-illuminated photodetector. The semiconductor photodetector 14 may be a single-pixel detector having only one pixel, or a detector array having many pixels. In this description, a pixel may refer to, for example, an element of a detector that outputs one independent detection result. In the following description, the semiconductor photodetector 14 is a single-pixel detector. FIG. 2(a) is a schematic diagram of a cross-section of a front-illuminated single-pixel detector. The semiconductor photodetector has a light-receiving layer 21 that converts incident light into an electrical signal. In the example shown in FIG. 2, a region in which the "width" of the light-receiving layer 21 is narrower than the semiconductor base material 22 represents one pixel. However, the method of realizing a pixel is not limited to this. Generally, when a semiconductor photodetector is manufactured, microfabrication such as the manufacture of a metal electrode 23 for electrically contacting such a light-receiving layer is performed. For example, in a light detector such as a bolometer, the light-receiving layer itself may be manufactured by microfabrication. In the following description, the surface of the semiconductor wafer on which the above-mentioned microfabrication has been performed is called the "front surface," and the surface opposite the "front surface" is called the "back surface." As shown in the example of FIG. 2(a), a front-incident type photodetector is a type of photodetector in which the incident light 25 to be detected is incident from the front surface. In the case of a front-incident type photodetector, either nothing is provided on the element surface so as not to prevent the incident light 25 to be detected from reaching the light receiving layer 21, or even if there is a metal electrode 23 or the like on the element surface, an aperture 24 for passing the incident light (in FIG. 2(a), the aperture 24 is written as "metal electrode aperture 24") is provided. In other words, the element surface cannot be covered with a metal film or the like.

On the other hand, FIG. 2(b) is a schematic diagram of a cross section of a back-illuminated single pixel detector. A type of photodetector in which light to be detected is incident from the back surface is a back-illuminated photodetector as shown in FIG. 2(b). In the case of a back-illuminated photodetector, the incident light 25 to be detected is incident from the back surface that is not subjected to microfabrication, so all or most of the surface of the element can be covered with a metal film or the like. The metal film may also serve as the metal electrode 23. In addition, the back surface can be mirror-polished to prevent scattering of the incident light on the back surface. In the definition in this description, mirror-polishing of the back surface means polishing so that the RMS grain size value of the unevenness on the back surface is equal to or less than the wavelength of the incident light. In addition, the mirror surface means a state in which the surface is polished so that the RMS grain size value of the unevenness of the surface is equal to or less than the wavelength of the incident light. In this embodiment, a back-illuminated photodetector is used as the semiconductor photodetector 14. In the following description, the "back surface" of the semiconductor photodetector 14, which is a back-illuminated photodetector, may be referred to as the "incident surface". Additionally, the "front surface" of the semiconductor photodetector 14, which is a back-illuminated photodetector, is sometimes referred to as the "reflective surface."

The back-illuminated photodetector used in this embodiment is characterized in that its front surface is covered with a light-reflective structure such as a metal film, and its back surface is mirror-polished. The back-illuminated photodetector used in this embodiment has a structure in which the reflective surface of the front surface of the substrate and the mirror surface of the back surface of the substrate are parallel.

(Description of Manufacturing Method)
Next, a method for manufacturing the semiconductor photodetector 14 will be described. FIG. 3 is a diagram showing a schematic enlarged view of the cross section of the semiconductor photodetector 14 in FIG. 2. However, in FIG. 3, the illustration of the pixel structure, such as the difference in the width of the light-receiving layer shown in FIG. 2, is omitted. In FIG. 3, the region showing the light-receiving layer 21 and the semiconductor base material 22 is shown together as "semiconductor base material and light-receiving layer 31". The method of microfabrication or the like for manufacturing the semiconductor photodetector may be a general normal manufacturing method, and detailed description thereof will be omitted here. After manufacturing the semiconductor photodetector, a surface reflection structure 32 that reflects light is manufactured on the surface of the semiconductor base material and the light-receiving layer 31. The surface reflection structure 32 may be a metal film or a distributed Bragg reflector made of a dielectric multilayer film. Next, the thickness of the semiconductor base material and the light-receiving layer 31 is thinned by grinding the back surface of the semiconductor photodetector with a grinder or the like. At this time, the grinding is performed so that the back surface after grinding is parallel to the surface reflection structure 32. The thickness of the semiconductor base material and light receiving layer 31 after grinding is preferably 100 times or less the wavelength in the semiconductor of incident light 25 to be detected. The reason for this will be described later. The back surface after grinding is subjected to a mirror finish. The creation of the reflective structure and the grinding and mirror finish of the back surface described above are manufacturing processes specific to the semiconductor photodetector used in gas detection device 1 of this embodiment.

(Explanation of operation)
First, the operation of the semiconductor photodetector 14 manufactured as described above will be described. The behavior of the semiconductor photodetector 14 when light to be detected is incident thereon will be described with reference to the schematic diagram shown in FIG. 4. FIG. 4 is a schematic diagram illustrating incident light to the semiconductor photodetector 14 and reflected and transmitted light related to the incident light. When incident light 25 is incident from the back surface of the semiconductor photodetector 14 shown in FIG. 4 in a direction perpendicular to the back surface, the light of the incident light 25 that is not reflected by the back surface and is transmitted is reflected downward in the drawing by the front surface reflection structure 32. Note that a part of the incident light 25 is reflected by the back surface. The light reflected by the back surface is omitted in FIG. 4. In this description, the light reflected downward in the drawing by the front surface reflection structure 32 is referred to as the reflected light 41 on the front surface. Hereinafter, the reflected light 41 on the front surface is also simply referred to as the reflected light 41. When the reflected light 41 from the front surface reaches the rear surface of the semiconductor photodetector 14, a part of the reflected light 41 from the front surface goes out of the detector as transmitted light 42 (in FIG. 4, it is written as "transmitted light 42 from the rear surface"), and the rest returns to the upper direction in FIG. 4 as re-reflected light 43 from the rear surface. The "re-reflected light 43 from the rear surface" in FIG. 4 is also written as "re-reflected light 43" below. As described in the explanation of the structure, the mirror-finished rear surface and the front surface reflection structure 32 are made to be parallel to each other. Therefore, when the incident light 25 is incident from a direction perpendicular to the rear surface, the reflected light 41 from the front surface and the re-reflected light 43 from the rear surface pass through the same place in the plane extending in the left-right and depth directions of the paper surface of FIG. 4 in the semiconductor photodetector 14. In other words, the optical path of the incident light 25, the optical path of the reflected light 41 from the front surface, and the optical path of the re-reflected light 43 from the rear surface are the same. 4, in order to prevent the diagram from becoming complicated, the arrows indicating the incident light 25, the reflected light 41 from the front surface, and the re-reflected light 43 from the back surface are drawn shifted to the left and right. However, if these three arrows are drawn to show the actual positions of the optical paths of the light represented by these three arrows, the three arrows will overlap.

When incident light 25 is incident perpendicularly on the back surface of the semiconductor photodetector 14 having the above-mentioned structure, at the position of the light receiving layer 21, the reflected light 41 on the front surface and the re-reflected light 43 on the back surface pass through the same place in the plane extending in the left-right and depth directions of the paper surface of the semiconductor photodetector 14. Therefore, when the phases of the reflected light 41 on the front surface and the re-reflected light 43 on the back surface are aligned, constructive interference occurs, and when the phases are shifted by exactly π, destructive interference occurs. The condition for constructive interference to occur is that the difference in the optical path length between the reflected light 41 on the front surface and the re-reflected light 43 on the back surface is an integer multiple of the wavelength of the light in the semiconductor. The condition for destructive interference to occur is that the difference in the optical path length is a half-integer multiple of the wavelength of the light in the semiconductor. Therefore, when the incident light is white light composed of various wavelength components of light, constructive interference occurs at a certain wavelength in the light receiving layer 21. When scanning the wavelength from the wavelength at which constructive interference occurs to a longer wavelength, the constructive interference weakens and destructive interference occurs, and as the wavelength becomes longer, the constructive interference becomes stronger and constructive interference occurs, and this is repeated. The same is true when scanning the wavelength to a shorter wavelength. For example, assume that the sensitivity of the semiconductor photodetector 14 is the same for each wavelength, and that the intensity of the output signal of the semiconductor photodetector 14 is proportional to or positively correlated with the intensity of the light in the light receiving layer. Furthermore, assume that the wavelength of the incident light is changed to be longer or shorter while the intensity of the incident light is kept constant for each wavelength, and as a result of the constructive and destructive interference described above, the output signal of the semiconductor photodetector 14 oscillates with the change in wavelength. In other words, the spectral sensitivity of the semiconductor photodetector 14 is expressed as an oscillation with respect to the change in wavelength.

Figure 5 shows the results of measuring the wavelength dependence (spectral sensitivity) of the sensitivity of a photodetector actually fabricated using the above-mentioned manufacturing method. Figure 5 shows how the sensitivity of this photodetector fluctuates finely with respect to the wavelength, as described in the explanation of its operation.

Next, the operation of gas detection using the setup shown in FIG. 1 including the semiconductor photodetector 14 will be described. When the semiconductor chip 12 is irradiated with white excitation light 17 from the light source 13, localized plasmon resonance occurs due to the periodic metal wires and the like fabricated on the semiconductor chip 12. The electric field strength due to the localized plasmon resonance is enhanced only near the surface. In other words, the light having a resonant wavelength among the white light of the light source is localized near the surface. This weakens the electric field strength going out of the semiconductor chip 12 as reflected light. Therefore, as disclosed in Non-Patent Document 1, when the spectrum of the reflected light 18 of the excitation light 17 reflected on the surface of the semiconductor chip 12 is measured, a dip is observed only at the plasmon resonance wavelength. The plasmon resonance wavelength is determined by the period of the metal wires fabricated on the semiconductor chip 12 and the refractive index of the material near the surface. Therefore, when a small amount of gas molecules are adsorbed on the surface of the semiconductor chip, the effective refractive index is modulated, and the plasmon resonance wavelength shifts. In other words, the wavelength of the dip that appears in the spectrum of the reflected light 18 shifts.

In the gas detection method according to the present embodiment, the resonance wavelength of the localized plasmon induced on the semiconductor chip 12 is made to coincide with one of the peaks of the vibration structure of the spectral sensitivity of the semiconductor photodetector 14, for example. In order to easily explain the method of detecting gas in this case, the case where the bandpass filter 15 is not present will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the relationship between the resonance wavelength of the localized plasmon and the spectral sensitivity of the semiconductor photodetector 14, for example. Broadly speaking, the left side of FIG. 6 is a part explaining the state before gas adsorption, and the right side of FIG. 6 is a part explaining the state after gas adsorption. Of the six curves shown in FIG. 6, the top two represent the spectrum of the reflected light 18. The middle two represent the wavelength dependency of the semiconductor photodetector 14. The bottom two represent the spectral sensitivity when the reflected light 18 is measured by the semiconductor photodetector 14. In all of these, the horizontal axis is the wavelength. The horizontal axis is common to the three curves on the left. Similarly, the horizontal axis is common to the three curves on the right. A more detailed explanation will be given below.

6 shows the spectrum 61 (hereinafter referred to as "spectrum 61") of the reflected light 18 before gas adsorption (e.g., in a vacuum state). The dip wavelength of the spectrum 61 corresponds to the localized plasmon resonance wavelength induced on the semiconductor chip 12. The localized plasmon resonance wavelength induced on the semiconductor chip 12 before gas adsorption is indicated by the dotted lines drawn on both the left and right sides of FIG. 6. The center part on the left side of FIG. 6 shows the wavelength dependence 62 (hereinafter referred to simply as "wavelength dependence 62") of the sensitivity of the semiconductor photodetector 14 before gas adsorption. As in the example of FIG. 5, the sensitivity oscillates with respect to the wavelength. The lower part on the left side of FIG. 6 shows the spectral sensitivity 63 (hereinafter referred to as "spectral sensitivity 63") when the reflected light 18 is measured by the semiconductor photodetector 14 having the wavelength dependence of the sensitivity as shown in the center part on the left side of FIG. 6. The spectral sensitivity 63 when the reflected light 18 is measured by the semiconductor photodetector 14 is a spectrum obtained by superimposing the spectrum 61 of the reflected light 18 in the upper left part of FIG. 6 and the wavelength dependency 62 in the center left part of FIG. 6. When the output signal intensity of the semiconductor photodetector 14 is proportional to or positively correlated with the intensity of the light in the light receiving layer, the spectral sensitivity 63 when the reflected light 18 is measured by the semiconductor photodetector 14 will generally have such a spectrum. Therefore, a small dip is seen in the spectral sensitivity 63 at the plasmon resonance wavelength indicated by the dotted line on the left side of FIG. 6.

Next, when the gas to be measured is introduced into the gas chamber 11 in a vacuum state, a portion of the gas is adsorbed onto the surface of the semiconductor chip 12, which shifts the plasmon resonance wavelength. This is shown on the right side of FIG. 6. On the right side of FIG. 6, the dotted line indicates the plasmon resonance wavelength before gas adsorption. The dashed line indicates the plasmon resonance wavelength after gas adsorption. After gas adsorption, the dip wavelength seen in the spectrum 61 of the reflected light 18 shifts to the wavelength of the dashed line. Therefore, the spectral sensitivity 63 when the reflected light 18 is measured by the semiconductor photodetector 14 is as shown in the lower part on the right side of FIG. 6. In the spectral sensitivity 63, a large dip exists at the wavelength indicated by the dashed line, while the spectral sensitivity increases (i.e., recovers) at the plasmon resonance wavelength before gas adsorption indicated by the dotted line.

In order to measure the spectral sensitivity 63 shown in FIG. 6, it is necessary to use an expensive and large-scale measuring device such as an FTIR (Fourier transform infrared spectrometer). In other words, when measuring the spectral sensitivity 63, the problem of high cost cannot be solved. For this purpose, the bandpass filter 15 shown in FIG. 1 is used. The bandpass filter 15 is a filter that transmits only light of a specific wavelength (hereinafter referred to as the transmission wavelength). The bandpass filter 15 may be a filter that transmits light of a wavelength included in a specific wavelength range (hereinafter referred to as the transmission range) including the transmission wavelength and attenuates light of other wavelengths. When the bandpass filter 15 is used, the output signal of the semiconductor photodetector 14 indicates the amount obtained by integrating the spectral sensitivity 63 in the transmission range (for example, a very narrow wavelength range near the transmission wavelength of the bandpass filter 15). Therefore, when gas is introduced into the gas chamber 11 in a state where the transmission wavelength of the bandpass filter 15 coincides with the plasmon resonance wavelength before gas adsorption, the output signal of the semiconductor photodetector 14 increases as the amount of gas adsorption increases (see FIG. 7). FIG. 7 is a diagram showing an example of the change in the output signal strength of the photodetector (i.e., the strength of the output signal of the semiconductor photodetector 14) with an increase in the amount of gas adsorbed. Therefore, by using the method according to this embodiment, it is possible to detect the adsorption of gas from an increase in the output signal by simply monitoring the output signal of the semiconductor photodetector 14 without measuring the spectral sensitivity 63.

The above explanation is for the case where the resonance wavelength of the localized plasmon coincides with one of the peaks of the vibration structure of the spectral sensitivity of the semiconductor photodetector 14. The same explanation is also valid for the case where the resonance wavelength of the localized plasmon coincides with one of the dips of the vibration structure of the spectral sensitivity of the semiconductor photodetector 14. In this case, the above explanation is valid as it is if the right side of FIG. 6 represents the state before gas adsorption, the left side of FIG. 6 represents the state after gas adsorption, the dashed line indicates the plasmon resonance wavelength before gas adsorption, and the dotted line indicates the plasmon resonance wavelength after gas adsorption. However, if the plasmon resonance wavelength shifts to the long wavelength side due to gas adsorption, the position of the dotted line shown on the right side of FIG. 6 will be the long wavelength side of the dip of the dashed line in the wavelength dependence 62. In this case, if the direction of the horizontal axis of FIG. 6 is all reversed from the above explanation, the positional relationship between the dotted line and the dashed line will be the same as in FIG. 6.

More specifically, even if the dip in the spectrum 61 of the reflected light 18 before gas adsorption does not necessarily coincide with the peak or dip in the wavelength dependence 62 of the sensitivity, it is possible to perform gas detection by observing the modulation of the signal intensity of the semiconductor photodetector 14 through the above operation. However, it goes without saying that the effect is greater when the dip wavelength of the spectrum 61 coincides with the peak or dip in the wavelength dependence 62 of the sensitivity than when it does not.

(Explanation of effects)
By using the gas detection device 1 of this embodiment, it is possible to detect gases simply by observing modulation of the signal intensity of a photodetector, without using large-scale and expensive measuring devices such as a spectroscope, a Fourier transform infrared spectrometer, etc. Therefore, the gas detection device 1 according to this embodiment can reduce the cost of detecting gases using plasmon resonance.

Second Embodiment
As described in the explanation of the operation of the first embodiment, the first embodiment uses the constructive interference effect between the reflected light 41 at the front-surface reflection structure 32 of the semiconductor photodetector 14 and the re-reflected light 43 at the rear surface of the reflected light 41. Therefore, it is required that the front-surface reflection structure 32 and the rear surface of the semiconductor photodetector 14 are parallel. However, in actual fabrication of the element, it is difficult to fabricate them perfectly parallel. Therefore, the results of considering the extent to which deviation from parallelism is acceptable are described below.

As described in the explanation of the operation of the first embodiment, it is assumed that the incident light 25 is incident perpendicular to the back surface. In addition, consider the case where the surface reflection structure 32 is tilted from parallel to the back surface of the semiconductor photodetector 14 by an angle α. FIG. 8 is a schematic diagram showing an example of the optical path of the semiconductor photodetector 14 and the incident light 25, depicting the optical path in the above situation. In the example shown in FIG. 8, the incident light 25 is incident at an angle α from the normal direction of the surface reflection structure 32. Therefore, it is reflected at an angle 2α from the normal to the back surface. If the thickness of the semiconductor base material and the light receiving layer 31 is d, the position where the reflected light 41 reaches the back surface at this time is shifted by a distance expressed by the following formula within the plane of the semiconductor photodetector 14 (i.e., within the plane represented by the left-right direction in FIG. 8).

The re-reflected light 43 that is re-reflected on the back surface is also re-reflected at an angle of 2α. Therefore, the position where the re-reflected light 43 reaches the surface reflection structure 32 is shifted from the position where the incident light 25 reaches the surface reflection structure by a distance in the above-mentioned plane expressed by the following equation:

For constructive interference to occur in the light receiving layer, the positional shift in the plane between the reflected light 41 and the re-reflected light 43 must be within a range of at least the wavelength of light (in the material in which the optical path of the semiconductor photodetector 14 exists). The most stringent condition for the inclination angle α from parallelism is when the light receiving layer 21 is in the vicinity of the surface reflection structure 32. The mathematical formula that expresses this condition is as follows:

Here, λ is the wavelength of the incident light 25 in a vacuum, and n is the effective refractive index of the semiconductor base material and the light receiving layer 31. From this formula, it can be seen that the thinner the thickness d of the semiconductor base material and the light receiving layer 31, and the longer the wavelength λ of the incident light, the more lenient the allowable conditions for the angle α become. In other words, infrared light, which has a longer wavelength than visible light, is more suitable for gas detection according to this embodiment. Furthermore, if the plasmon resonance wavelength is in the infrared wavelength region instead of visible light, the period of the periodic metal thin line structure of the semiconductor chip 12 can also be made longer than that of visible light. Therefore, the plasmon resonance wavelength of infrared light also has the advantage of making it easier to fabricate devices.

Equation 3 is an inequality that gives an upper limit for α when d, n, and λ are fixed. On the other hand, this equation can also be considered as the condition for thickness d for constructive interference to occur when a certain deviation angle α from parallelism is expected as the limit of device fabrication precision. Transforming equation 3 gives the following equation.

The left side of equation 4 indicates how many times the thickness d of the semiconductor base material and light receiving layer 31 corresponds to the wavelength in the semiconductor. Experimental results by the authors of this disclosure have shown that when this value is 225, almost no interference effect occurs, and when it is 37.5, a sufficient interference effect occurs. Therefore, in order to obtain the interference effect, it is preferable that the thickness d of the semiconductor base material and light receiving layer 31 is approximately 100 times or less the wavelength in the semiconductor.

However, when actually fabricating a photodetector, in addition to the problem of fabrication accuracy, such as the parallelism between the back surface and the front reflection structure 32, there is also the issue of the difficulty of making the direction of propagation of the incident light 25 completely perpendicular to the back surface. A structure to solve this problem is proposed in the second embodiment.

(Structural Description)
The overall configuration of the gas detector according to this embodiment is the same as that of the gas detector according to the first embodiment. As shown in FIG. 1, the gas detector includes a gas chamber 11, a semiconductor chip 12, a light source 13 for irradiating the semiconductor chip 12 with excitation light 17, a semiconductor photodetector 14 for receiving reflected light 18 from the semiconductor chip 12, and a bandpass filter 15. As described above, the semiconductor chip 12 is installed in the cavity of the gas chamber 11. The bandpass filter 15 is installed between the light source 13 and the semiconductor photodetector 14. Compared to the first embodiment, the structure of the semiconductor photodetector 14 is partially different. A schematic diagram for explaining this is shown in FIG. 9. FIG. 9 is a schematic diagram showing an example of the structure of the semiconductor photodetector 14 according to this embodiment. As shown in FIG. 9, a concave-convex structure 91 having a size of about the wavelength of the light to be detected in the semiconductor of the semiconductor photodetector 14 is fabricated on the surface side of the semiconductor base material and the light receiving layer 31 of the semiconductor photodetector 14 according to the second embodiment. The concave-convex structure 91 may be, for example, a cylindrical or prismatic structure, or may be a hemispherical or pyramidal structure. The uneven structure 91 may be a structure carved out from the surface, such as a circular hole or a square hole. The surface reflecting structure 32 is formed so as to cover such an uneven structure 91.

(Description of Manufacturing Method)
The method for producing the semiconductor base material and the light receiving layer 31 of the semiconductor photodetector 14 of this embodiment may be any of the known production methods, as in the first embodiment. The method for producing the semiconductor base material and the light receiving layer 31 of the semiconductor photodetector 14 of this embodiment is not limited to a specific production method. Therefore, the description of the method for producing the semiconductor base material and the light receiving layer 31 of the semiconductor photodetector 14 of this embodiment will be omitted. After the semiconductor base material and the light receiving layer 31 are produced, the uneven structure 91 is produced. As a method for producing the uneven structure 91, for example, a method using lithography and etching can be used. The etching method may be dry etching or wet etching. Next, the front surface reflection structure is produced. However, since the front surface reflection structure of the first embodiment is formed on a flat surface, it may be formed of a dielectric multilayer film, but in the front surface reflection structure of the second embodiment, the uneven structure 91 exists, so that the light reflection surface is not necessarily parallel to the back surface (or the surface before the uneven structure is formed). Therefore, it is desirable to produce the front surface reflection structure of the second embodiment with a metal film.

(Explanation of operation)
In this embodiment, even if the back surface and the front surface reflection structure 32 are not completely parallel, the reflected light 41 and the re-reflected light 43 on the back surface are likely to interfere with each other, thanks to the presence of the uneven structure 91 as described in the description of the structure. Even if the traveling direction of the incident light 25 is not completely perpendicular to the back surface, the reflected light 41 and the re-reflected light 43 on the back surface are likely to interfere with each other, thanks to the presence of the uneven structure 91 as described in the description of the structure. Even if the back surface and the front surface reflection structure 32 are not completely parallel and the traveling direction of the incident light 25 is not completely perpendicular to the back surface, the reflected light 41 and the re-reflected light 43 on the back surface are likely to interfere with each other, thanks to the presence of the uneven structure 91 as described in the description of the structure. This will be described with reference to FIG. 10. FIG. 10 is a schematic diagram showing an example of a light path when the incident light 25 is not perpendicular to the back surface. If the uneven structure 91 does not exist in the front-surface reflection structure 32 and the front-surface reflection structure 32 is a flat surface horizontal to the rear surface, the reflected light 41 will not be perpendicular to the rear surface, and the condition for interference between the reflected light 41 and the re-reflected light 43 in the light-receiving layer may not be satisfied. On the other hand, if the uneven structure 91 as shown in FIG. 9 exists, the interface between the uneven structure 91 and the front-surface reflection structure 32 is not horizontal to the rear surface but faces at various angles. Therefore, a part of the incident light is reflected in a direction completely perpendicular to the rear surface. In other words, the incident light 25 is diffusely reflected by the uneven structure 91, and a part of it is reflected in a direction perpendicular to the rear surface. In FIG. 10, the reflected light 101 is reflected in a direction perpendicular to the rear surface. The re-reflected light 102, which is the reflected light 101 re-reflected by the rear surface, also propagates in a direction perpendicular to the rear surface and passes through the same position in the light-receiving layer as the position where the reflected light 101 passes through within the surface of the semiconductor photodetector 14. Therefore, the reflected light 101 and the re-reflected light 102 can interfere with each other. The method of gas detection using the vibration structure of the spectral sensitivity caused by the interference is the same as that of the first embodiment. Therefore, the description will be omitted. Similarly, if the back surface excluding the uneven structure 91 and the front surface reflection structure 32 are not completely parallel, the reflected light 41 should not propagate perpendicular to the back surface if the uneven structure 91 does not exist (see FIG. 8). However, even in this case, the reflected light 101, which is a part of the diffuse reflection by the uneven structure 91, propagates perpendicular to the back surface. Therefore, it can interfere with the re-reflected light 102 on the back surface.

Third Embodiment
Next, a third embodiment of the present disclosure will be described in detail with reference to the drawings.

(composition)
11 is a block diagram showing an example of the configuration of gas detection device 100 according to this embodiment. Gas detection device 100 includes a reflecting section 112, a light emitting section 113, a detecting section 114, and a bandpass section 115.

The reflecting section 112 has a structure that induces localized plasmon resonance. The light emitting section 113 irradiates the reflecting section 112 with light (e.g., excitation light). The bandpass section 115 transmits a predetermined percentage or more of light having a wavelength in a predetermined range including a predetermined wavelength (e.g., the above-mentioned transmission wavelength). The bandpass section 115 does not transmit a predetermined percentage or more of light having a wavelength not included in the predetermined range. The predetermined wavelength is the plasmon resonance wavelength of the reflecting section 112 when the gas is not present on the surface. The detection section 114 measures the intensity based on the first reflected light, which is the reflected light by the reflecting section 112 of the irradiated light that has passed through the bandpass section 115, and detects the gas on the surface of the reflecting section 112 based on the measured intensity. The detection section 114 may detect the amount of gas adsorbed on the surface of the reflecting section 112.

In addition, the light that has passed through the bandpass section 115 (i.e., the incident light in the first and second embodiments) among the reflected light by the reflecting section 112 of the above-mentioned excitation light that the light emitting section 113 irradiates to the reflecting section 112 may also be referred to as the first reflected light. In addition, the detecting section 114 is realized by the semiconductor photodetector 14, which is a back-illuminated photodetector as described above, and the back surface (i.e., the incident surface) on which the light is incident may be mirror-polished. In addition, a surface reflection structure that reflects light may be generated on the above-mentioned front surface (i.e., the reflection surface), which is the surface of the detecting section 114 opposite to the incident surface. Furthermore, a light receiving layer that converts light into an electrical signal may be generated between the back surface (i.e., the incident surface) and the front surface (i.e., the reflection surface). And, a material that transmits light may be used between the back surface and the front surface. The reflected light of the first reflected light (i.e., the incident light 25 in the first and second embodiments) reflected by the surface reflection structure of the front surface is also referred to as the second reflected light. The second reflected light is the light referred to as reflected light 41 in the first and second embodiments. The light reflected by the mirror-polished back surface of the detection unit 114 is also referred to as the third reflected light. The third reflected light is the re-reflected light 43 in the first and second embodiments. The second reflected light and the third reflected light reflected by the incident surface of the detection unit 114 interfere with each other inside the detection unit 114. The intensity of the light resulting from the interference in the light receiving layer of the detection unit 114 is converted into a signal by the light receiving layer of the detection unit 114. The intensity based on the first reflected light described above may be the intensity of the light resulting from the interference of the second reflected light and the third reflected light in the light receiving layer of the detection unit 114.

The gas detection device 100 is realized by the gas detection device 1 of the first embodiment or the gas detection device 1 of the second embodiment. The semiconductor chip 12 of the first or second embodiment operates as the reflector 112. The light source 13 of the first or second embodiment operates as the light emitter 113. The semiconductor photodetector 14 of the first or second embodiment operates as the detector 114. The bandpass filter 15 of the first or second embodiment operates as the bandpass section 115.

(motion)
Next, the operation of gas detection device 100 of this embodiment will be described.

Figure 12 is a flow chart showing an example of the operation of the gas detection device 100 of this embodiment. In the example shown in Figure 12, the light emitting unit 113 irradiates light onto the reflecting unit 112 having a structure that induces localized plasmon resonance (step S1). The gas detection device 100 transmits the light reflected by the reflecting unit 112 through the bandpass unit 115, which transmits light of a predetermined range of wavelengths including a predetermined wavelength (step S2). The detecting unit 114 measures the intensity based on the first reflected light, which is the transmitted light, out of the reflected light (step S3). The detecting unit 114 detects gas on the surface of the reflecting unit 112 based on the measured intensity (step S4).

(effect)
This embodiment has the same effects as the first embodiment, for the same reasons as those for which the first embodiment has the effects.

Fourth Embodiment
Next, a fourth embodiment of the present disclosure will be described.

(composition)
Fig. 13 is a block diagram showing an example of the configuration of detection device 200 of the present embodiment. Detection device 200 shown in Fig. 13 includes gas detection device 100A, a receiving unit 201, a generating unit 202, and an output unit 203. Gas detection device 1 of the first embodiment or gas detection device 1 of the second embodiment operates as gas detection device 100.

The receiving unit 201 receives the above-mentioned output signal from the gas detection device 100A. The receiving unit 201 sends an output value, which is a value represented by the received output signal, to the generating unit 202. The generating unit 202 receives the output value from the generating unit 202.

The generating unit 202 generates information representing the result of gas detection based on the received output value. The generating unit 202 may generate information representing whether or not gas is present based on the result of comparing the output value with a predetermined threshold value, for example. For example, a case will be described in which a threshold value is set so that it is determined that gas is present when the output value is greater than the predetermined threshold value. In this case, the threshold value may be determined in advance, for example, experimentally. If the output value exceeds the threshold value, the generating unit 202 generates information representing the presence of gas. If the output value does not exceed the threshold value, the generating unit 202 generates information representing the absence of gas. The generating unit 202 may generate information representing the amount of gas adsorption based on the relationship between the magnitude of the output value and the amount of gas adsorption, for example, as shown in FIG. 8. The generating unit 202 outputs the generated information representing the gas detection result to the output unit 203.

The output unit 203 outputs information representing the gas detection result generated by the generation unit 202. The output unit 203 may be, for example, a display. In this case, the generation unit 202 may display information representing the gas detection result (for example, information representing the presence or absence of gas, or the amount of gas adsorption) on the output unit 203. The output unit 203 may be, for example, an indicator such as a lamp or a buzzer that indicates the presence or absence of gas. In this case, the generation unit 202 may set the state of the indicator so that the indicator indicates the result of the gas detection. The output unit 203 may be, for example, a meter that indicates the amount of gas adsorption. In this case, the generation unit 202 may set the state of the meter so that the pointer of the meter indicates the amount of gas adsorption.

Next, we will explain the gas detection device 100A.

Figure 14 is a block diagram showing an example of the configuration of the gas detection device 100A of this embodiment.

The gas detection device 100A of this embodiment includes an introduction section 111 in addition to the elements of the gas detection device 100 of the third embodiment. The introduction section 111 introduces gas into the reflection section 112. An aperture 16 similar to the aperture 16 of the first and second embodiments is formed in the introduction section 111. The gas detection section 101A is also realized by the gas detection device 1 of the first embodiment or the gas detection device 1 of the second embodiment. The gas chamber 11 of the first or second embodiment operates as the introduction section 111. The other elements of the gas detection device 100A are the same as the elements of the gas detection device 100 of the third embodiment that are given the same names and symbols.

(motion)
Next, the operation of the present embodiment will be described First, the operation of gas detection device 100A of the present embodiment will be described.

Figure 15 is a flowchart showing an example of the basic operation of the gas detection device 100A of this embodiment. The operation of the gas detection device 100A of this embodiment may be the same as the operation of the gas detection device 1 of the first embodiment. The operation of the gas detection device 100A of this embodiment may be the same as the operation of the gas detection device 1 of the second embodiment.

In the example shown in FIG. 15, the light emitting unit 113 irradiates the reflecting unit 112 with light (step S101). The bandpass unit 115, which transmits the plasmon resonance wavelength of the reflecting unit 112, transmits the light of the plasmon resonance wavelength of the reflecting unit 112 from the light reflected by the reflecting unit 112 (step S102). The first reflected light, which is the light that has transmitted through the bandpass unit 115, enters the detecting unit 114 from the incident surface (i.e., the "rear surface"). The reflecting surface of the detecting unit 114 (i.e., the surface reflection structure of the "front surface") reflects the first reflected light that has transmitted through the bandpass unit 115 at its reflecting surface (step S103). The incident surface of the detecting unit 114 reflects the second reflected light reflected by the reflecting layer of the detecting unit 114 at its incident surface (step S104). The second reflected light and the third reflected light reflected by the incident surface of the detecting unit 114 interfere inside the detecting unit 114. The intensity of the light resulting from the interference in the light receiving layer of the detection unit 114 is converted into a signal by the light receiving layer of the detection unit 114. In other words, the detection unit 114 causes the second reflected light to interfere with the third reflected light reflected by the incident surface of the detection unit 114 (step S105). The detection unit 114 then measures the intensity of the interfered light (step S106). The detection unit 114 outputs a signal representing the measured intensity as a result of gas detection (step S107).

Next, the operation of the detection device 200 of this embodiment will be described.

Figure 16 is a flowchart showing an example of the operation of the detection device 200 of this embodiment.

In the example shown in FIG. 16, first, gas detection device 100A detects gas (step S201). Specifically, the operation in step S201 may be the operation of gas detection device 100A shown in FIG. 15. Receiving unit 201 receives a signal representing the result of the detection from gas detection device 100A (step S202). Generating unit 202 generates information representing the result of the detection based on the received signal (step S203). Generating unit 202 displays the generated information representing the result of the detection on output unit 203 (step S204).

(Other configurations)
The detection device 200 of the present embodiment can be realized by a dedicated circuit. The dedicated circuit may be realized by one circuit. The dedicated circuit may be realized by a plurality of circuits communicably connected to each other. The detection device 200 of the present embodiment may be realized by one computer controlled by a program. The detection device 200 of the present embodiment may be realized by a plurality of computers each controlled by a program and communicably connected to each other.

Figure 17 is a diagram showing an example of the hardware configuration of a computer 1000 that can realize the detection device 200 of this embodiment. Referring to Figure 17, the computer 1000 includes a processor 1001, a memory 1002, a storage device 1003, and an I/O (Input/Output) interface 1004. The computer 1000 can also access a storage medium 1005. The memory 1002 and the storage device 1003 are, for example, storage devices such as RAM (Random Access Memory) and a hard disk. The storage medium 1005 is, for example, a storage device such as RAM or a hard disk, a ROM (Read Only Memory), or a portable storage medium. The storage device 1003 may be the storage medium 1005. The processor 1001 can read and write data and programs from the memory 1002 and the storage device 1003. The processor 1001 can access, for example, the gas detection device 100A via the I/O interface 1004. The processor 1001 can access the storage medium 1005. The storage medium 1005 stores a program that causes the computer 1000 to operate as the detection device 200.

The processor 1001 loads a program stored in the storage medium 1005, which causes the computer 1000 to operate as the detection device 200, into the memory 1002. The processor 1001 then executes the program loaded into the memory 1002, causing the computer 1000 to operate as the detection device 200.

The receiving unit 201, the generating unit 202, and the output unit 203 can be realized, for example, by a processor 1001 that executes a program loaded into a memory 1002 from a storage medium 1005 that stores the program. A part or all of the receiving unit 201, the generating unit 202, and the output unit 203 can also be realized by a dedicated circuit that realizes the function of each unit.

(effect)
This embodiment has the same effects as the first embodiment, for the same reasons as those for which the first embodiment has the effects.

In addition, some or all of the above embodiments can be described as follows, but are not limited to the following:

(Appendix 1)
A reflecting means having a structure for inducing localized plasmon resonance;
A light emitting means for irradiating the reflecting means with light;
a bandpass means for transmitting light having a predetermined range of wavelengths including the predetermined wavelength;
a detection means for measuring an intensity based on a first reflected light of the light by the reflecting means that has been transmitted through the bandpass means, and detecting a gas on a surface of the reflecting means based on the intensity;
A gas detection device comprising:

(Appendix 2)
2. The gas detection device according to claim 1, wherein the predetermined wavelength is a plasmon resonance wavelength of the reflecting means when the gas is not present on the surface of the reflecting means.

(Appendix 3)
3. The gas detection device according to claim 1, wherein the detection means includes a light receiving layer that measures light intensity and is disposed between an incident surface on which the first reflected light is incident and a reflecting surface that reflects light from the incident surface, and the light receiving layer measures intensity of light resulting from interference between a second reflected light formed by reflection of the first reflected light at the reflecting surface and a third reflected light formed by reflection of the second reflected light at the incident surface.

(Appendix 4)
4. The gas detection device according to claim 3, wherein a thickness between the incident surface and the reflecting surface is equal to or less than 100 times the wavelength of light of the predetermined wavelength in a material between the incident surface and the reflecting surface.

(Appendix 5)
The detection means has a concave-convex structure on the reflecting surface,
5. The gas detection device according to claim 3, wherein a difference between a size of the uneven structure and a wavelength of the light of the specified wavelength within a material between the incident surface and the reflecting surface satisfies a specified condition.

(Appendix 6)
6. The gas detection device according to claim 1, further comprising an introduction means for introducing the gas into the reflecting means.

(Appendix 7)
A light emitting means for irradiating light onto a reflecting means having a structure for inducing localized plasmon resonance;
measuring an intensity based on a first reflected light of the light by the reflecting means, the first reflected light having passed through a bandpass means that transmits light having a wavelength in a predetermined range including the predetermined wavelength; and detecting a gas on a surface of the reflecting means based on the intensity;
Gas detection methods.

(Appendix 8)
The gas detection method according to claim 7, wherein the predetermined wavelength is a plasmon resonance wavelength of the reflecting means when the gas is not present on the surface of the reflecting means.

(Appendix 9)
9. The gas detection method according to claim 7 or 8, further comprising a light receiving layer for measuring a light intensity, disposed between an incident surface on which the first reflected light is incident and a reflecting surface that reflects the light from the incident surface, the light receiving layer measuring an intensity of light resulting from interference between a second reflected light formed by reflection of the first reflected light at the reflecting surface and a third reflected light formed by reflection of the second reflected light at the incident surface.

(Appendix 10)
10. The gas detection method according to claim 9, wherein a thickness between the incident surface and the reflecting surface is less than or equal to 100 times the wavelength of light of the predetermined wavelength in a material between the incident surface and the reflecting surface.

(Appendix 11)
The reflecting surface has an uneven structure,
11. The gas detection method according to claim 9, wherein a difference between a size of the uneven structure and a wavelength of the light of the specified wavelength within a material between the incident surface and the reflecting surface satisfies a specified condition.

(Appendix 12)
The gas detection method according to any one of claims 7 to 11, further comprising introducing the gas into the reflecting means.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

REFERENCE SIGNS LIST 11 gas chamber 12 semiconductor chip 13 light source 14 semiconductor photodetector 15 bandpass filter 16 aperture 17 excitation light 18 reflected light 21 light-receiving layer 22 semiconductor base material 23 metal electrode 24 aperture 25 incident light 31 semiconductor base material and light-receiving layer 32 surface reflection structure 41 reflected light 42 transmitted light 43 re-reflected light 61 spectrum 62 wavelength dependence 63 spectral sensitivity 91 uneven structure 100 gas detection device 100A gas detection device 101 reflected light 102 re-reflected light 200 detection device 201 receiving section 202 generating section 203 output section 1000 computer 1001 processor 1002 memory 1003 storage device 1004 I/O interface 1005 storage medium

Claims (10)

A reflecting means having a structure for inducing localized plasmon resonance;
A light emitting means for irradiating the reflecting means with light;
a bandpass means for transmitting light having a predetermined range of wavelengths including the predetermined wavelength;
a detection means for measuring an intensity based on a first reflected light of the light by the reflecting means that has been transmitted through the bandpass means, and detecting a gas on a surface of the reflecting means based on the intensity;
Equipped with
The reflecting means is disposed in a region where the gas is introduced, inside an introducing means that introduces the gas into the reflecting means;
The light emitting means irradiates the light to the reflecting means from outside the introducing means through an aperture formed in the introducing means through which the light passes;
The first reflected light is a reflected light by the reflecting means of the light that reaches the bandpass means through the aperture.
Gas detection equipment. 2. The gas detection device according to claim 1, wherein the predetermined wavelength is a plasmon resonance wavelength of the reflecting means when the gas is not present on the surface of the reflecting means. 3. The gas detection device according to claim 1, wherein the detection means includes a light receiving layer for measuring a light intensity between an incident surface on which the first reflected light is incident and a reflecting surface that reflects light from the incident surface, the light receiving layer measuring an intensity of light resulting from interference between a second reflected light formed by reflection of the first reflected light at the reflecting surface and a third reflected light formed by reflection of the second reflected light at the incident surface. 4. The gas detection device according to claim 3, wherein a thickness between the incident surface and the reflecting surface is equal to or less than 100 times a wavelength of light of the predetermined wavelength in a material between the incident surface and the reflecting surface. The detection means has a concave-convex structure on the reflecting surface,
5. The gas detection device according to claim 3, wherein a difference between a size of the uneven structure and a wavelength of the light of the predetermined wavelength in a material between the incident surface and the reflecting surface satisfies a predetermined condition. The gas detection device according to claim 1 , further comprising: an introducing means for introducing the gas into the reflecting means. a reflecting means disposed in a region where a gas is introduced inside an introducing means for introducing a gas into the reflecting means, the reflecting means having a structure for inducing localized plasmon resonance is irradiated with light from an outside of the introducing means through an aperture formed in the introducing means through which the light passes ;
measuring an intensity based on a first reflected light of the light by the reflecting means, the first reflected light having passed through a bandpass means that transmits light having a wavelength in a predetermined range including a predetermined wavelength; and detecting the gas on the surface of the reflecting means based on the intensity ;
The first reflected light is a reflected light by the reflecting means of the light that reaches the bandpass means through the aperture.
Gas detection methods. The gas detection method according to claim 7 , wherein the predetermined wavelength is a plasmon resonance wavelength of the reflecting means when the gas is not present on the surface of the reflecting means. 9. The gas detection method according to claim 7, further comprising a light receiving layer for measuring light intensity, disposed between an incident surface on which the first reflected light is incident and a reflecting surface that reflects light from the incident surface, the light receiving layer measuring the intensity of light resulting from interference between a second reflected light formed by reflection of the first reflected light at the reflecting surface and a third reflected light formed by reflection of the second reflected light at the incident surface. 10. The gas detection method according to claim 9, wherein a thickness between the incident surface and the reflecting surface is 100 times or less the wavelength of light of the predetermined wavelength in a material between the incident surface and the reflecting surface.

Images