Gas sensor device used for detecting nitrogen dioxide gas and method for measuring nitrogen dioxide gas concentration

Abstract

To provide a gas sensor device having high sensitivity and high selectivity at 50°C or lower, and a method for measuring concentration of a gas to be detected.SOLUTION: A gas sensor device includes: a gas sensor element 10 having a substrate having electrical insulation, a pair of electrodes formed on a surface of the substrate, and a gas sensitive layer 15 connected to the electrode and containing an aggregate of a tin oxide plate crystal; and a light source 20 for emitting light to the gas sensitive layer 15 of the gas sensor element 10. An average value of a ratio (an aspect ratio) of a maximum length to thickness of the tin oxide plate crystal is preferably from 2.5 to 100.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas sensor device and a gas concentration measurement method used for measuring the concentration of a gas to be detected.

Background Art

[0002] A gas sensor device including a sensor element using a metal oxide (such as tin oxide, zinc oxide, γ-Fe2O3, etc.) that is sensitive to a gas to be detected is widely used industrially and is expected to have extremely high demand in future industries. Such a gas sensor device uses the surface of a sensor element made of a metal oxide as a reaction site, but since the control of the surface reaction of the metal oxide greatly affects the characteristics of the device, a technique for controlling the surface reaction is strongly required.

[0003] Patent Document 1 discloses a sensor in which a structure is formed on a substrate including two metal electrodes, the structure has tin oxide nanocrystals (sheet-like crystals) on the surface of an aggregate of nanoparticles, and the aggregate of nanoparticles includes tin oxide nanoparticles and noble metal nanoparticles. Further, the present inventors evaluated, in Patent Document 2, a composite obtained by forming an aggregate of sheet-like tin oxide on the surface of a glass substrate with a comb-shaped electrode as a gas sensor for hydrogen and methane. However, since the gas sensors of Patent Documents 1 and 2 control the surface reaction through the control of the driving temperature, they exhibit detection characteristics at a high temperature of 250°C or higher. That is, sufficient sensitivity could not be obtained at room temperature.

[0004] Non-Patent Document 1 discloses a technique for irradiating a sensor element made of a tin oxide thin film with light (visible light to UV-A region) to obtain a sensor response to nitrogen dioxide, but its sensitivity is slight.

[0005] Non-Patent Document 2 discloses that at room temperature, a sensor composed of single-crystalline SnO2 nanowires, a sensor composed of single-crystalline ZnO nanowires, or a sensor composed of nanowires having a core portion made of single-crystalline SnO2 and a shell portion made of single-crystalline ZnO was irradiated with ultraviolet rays (wavelength: 365 nm) to confirm the sensitivity to nitrogen dioxide.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Since some of the gases to be detected are flammable, for example, from the viewpoint of safety when detecting or measuring the concentration of hydrogen, acetone, isoprene, toluene, or ethanol, a gas sensor device and a gas concentration measurement method having sufficient sensitivity at a temperature up to at least 150°C are required. Depending on the type of gas to be detected, the upper limit of the temperature when using a gas sensor device near the skin of a living body is usually a temperature slightly higher than the body temperature. An object of the present invention is to provide a gas sensor device having high sensitivity and high selectivity at 50°C or lower and a method for measuring the concentration of a gas to be detected.

Means for Solving the Problem

[0009] The present invention is as follows.

[0010] 〔1〕A gas sensor device comprising a substrate having electrical insulation, a pair of electrodes formed on the surface of the substrate, and a gas-sensitive layer connected to the electrodes and containing an aggregate of tin oxide plate-like crystals, and a light source that emits light to the gas-sensitive layer of the gas sensor element. 〔2〕The gas sensor device according to 〔1〕 above, wherein the light is ultraviolet light. 〔3〕The gas sensor device according to 〔1〕 or 〔2〕 above, wherein the average value of the ratio (aspect ratio) of the maximum length to the thickness of the tin oxide plate-like crystals is 2.5 to 100. 〔4〕The gas sensor device according to any one of 〔1〕 to 〔3〕 above, wherein the main exposed surface of the tin oxide plate-like crystals is the (101) crystal plane. 〔5〕A gas concentration measurement method, comprising bringing a gas to be detected into contact with a gas-sensitive layer of a gas sensor element having a substrate having electrical insulation, a pair of electrodes formed on the surface of the substrate, and a gas-sensitive layer connected to the electrodes and containing an aggregate of tin oxide plate-like crystals, while irradiating the gas-sensitive layer with light, and measuring the concentration of the gas to be detected. 〔6〕The gas concentration measurement method according to 〔6〕 above, wherein the average value of the ratio (aspect ratio) of the maximum length to the thickness of the tin oxide plate-like crystals is 2.5 to 100. 〔7〕The gas concentration measurement method according to any one of 〔5〕 to 〔7〕 above, wherein the main exposed surface of the tin oxide plate-like crystals is the (101) crystal plane. 〔8〕The gas concentration measurement method according to 〔7〕 above, wherein the light is ultraviolet light. 〔9〕The gas concentration measurement method according to any one of 〔5〕 to 〔8〕 above, wherein the gas to be detected is nitrogen dioxide. 〔10〕The gas concentration measurement method according to 〔8〕 or 〔9〕 above, wherein the wavelength of the ultraviolet light is 310 to 400 nm.

Advantages of the Invention

[0011] According to the gas sensor device of the present invention, since the surface activity of the tin oxide plate-like crystals constituting the gas-sensitive layer of the gas sensor element can be controlled by the wavelength and intensity of light, the concentration of the gas to be detected can be efficiently measured at 50°C or lower without the need for the high temperature required conventionally. According to the gas concentration measurement method of the present invention, when the gas to be detected is brought into contact with the gas-sensitive layer of the gas sensor element and irradiated with light, the gas to be detected can be efficiently adsorbed onto the tin oxide plate-like crystals of the gas-sensitive layer at 50°C or lower without the need for the high temperature required conventionally. Therefore, the concentration of the gas to be detected can be easily obtained economically. At this time, for example, the change amount of the electrical physical property value (resistance value, conductivity, etc.) between a pair of electrodes can be utilized. Further, when the irradiated light is ultraviolet light and the gas to be detected is nitrogen dioxide, the gas concentration can be measured more efficiently. Further, according to another aspect of the present invention, different response values can be obtained for the gas to be detected depending on the wavelength and intensity of light. Data analysis is performed using the obtained response value data, and the type of the gas to be detected can be identified. Further, according to another aspect of the present invention, since the gas to be detected can be measured or identified near room temperature, it can be used even near the skin or a material.

Brief Description of Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] The gas sensor device of the present invention includes, for example, as shown in FIGS. 1, 2, 3, 4, and 5, a gas sensor element 10 and a light source 20. The gas sensor element 10 includes, for example, as shown in FIG. 6, a substrate 11 having electrical insulation, an electrode-attached substrate 14 composed of a pair of electrodes 12, 12 formed on the surface of the substrate 11, and a gas-sensitive layer 15 including an aggregate of tin oxide plate-like crystals that connects the electrodes 12, 12 to each other.

[0014] When measuring a gas to be detected using the gas sensor device of the present invention, light is irradiated while the gas to be detected is in contact with the gas-sensitive layer 15 of the gas sensor element 10, that is, an aggregate of tin oxide plate-like crystals. When the gas to be detected adsorbs to the tin oxide plate-like crystals, the electrical properties such as the resistance value and conductivity between the electrodes 12, 12 change compared to the state before contact with the gas to be detected. Therefore, the concentration of the gas to be detected can be obtained using the amount of change. Although not shown in FIGS. 1, 2, 3, 4, and 5, the gas sensor device of the present invention can further include, for example, when using the resistance value as an index, a resistance measuring device or a potentiometer that measures the resistance value between the electrodes 12, 12 from the current flowing through the gas-sensitive layer 15 and the voltage applied to the gas-sensitive layer 15 via the electrodes 12, 12.

[0015] In the gas sensor device of the present invention, the gas-sensitive layer 15 constituting the gas sensor element 10 is configured as an aggregate of a plurality of tin oxide plate-like crystals. FIG. 7 is a schematic diagram showing a preferred inclusion form of the tin oxide plate-like crystals 13 in the gas-sensitive layer 15. That is, each tin oxide plate-like crystal 13 is preferably oriented in the vertical direction with respect to the substrate 11 (or the electrode 12). The gas-sensitive layer 15 according to the present invention is not limited to this aspect, and may be an aspect in which a plurality of tin oxide plate-like crystals 13 are randomly mixed, or an aspect in which a plurality of tin oxide plate-like crystals 13 are sequentially stacked from the surface of the substrate 11.

[0016] The crystal structure, shape, and size of the tin oxide plate-like crystals are not particularly limited. The crystal structure of the tin oxide plate-like crystals is preferably a rutile type.

[0017] In the present invention, as shown in FIG. 7, it is preferable that the main exposed surface of the tin oxide plate-like crystal 13 is the (101) crystal plane. By being such a crystal, the gas to be detected can be efficiently adsorbed on the tin oxide plate-like crystal 13. The fact that it is the (101) crystal plane can be confirmed as follows. (a) From an image of the tin oxide plate-like crystal obtained using a transmission electron microscope (TEM) (see FIG. 8), measure the interval between lattice fringes that coincides with the (101) crystal plane of tin oxide. (b) On the other hand, calculate the crystallite size using the diffraction image obtained by X-ray diffraction measurement, and examine the presence or absence of the dependence of the crystallite size of the tin oxide plate-like crystal on the synthesis time. (c) When the dependence of the crystallite size in the

[0101] orientation is low, it means that almost no crystal growth has occurred in the

[0101] direction, and it can be determined that the main exposed surface is the (101) crystal plane.

[0018] The shape of the tin oxide plate-like crystal may be either a flat surface or a curved surface, or a combination thereof. The length and thickness of the tin oxide plate-like crystal are not particularly limited. The thickness of the tin oxide plate-like crystal is preferably 2 to 50 nm, more preferably 3 to 10 nm. Also, from the viewpoint of gas sensitivity, the average value of the ratio (L / T: aspect ratio) of the maximum length L to the thickness T calculated based on FIG. 9 is preferably 2.5 to 100, more preferably 3.5 to 85, still more preferably 7 to 70, and particularly preferably 10 to 50. The gas sensing layer 15 may contain tin oxide plate-like crystals having an aspect ratio of less than 2.5, but most of the exposed tin oxide plate-like crystals (for example, 50% or more of the exposed surface) are preferably tin oxide plate-like crystals having an aspect ratio exceeding 2.5.

[0019] The thickness of the gas-sensitive layer 15 (the thickness from the surface of the substrate 11 or the thickness from the surface of the electrode 12) is not particularly limited. The thickness of the gas-sensitive layer 15 as viewed from the surface of the substrate 11 is preferably 5 to 1000 nm, more preferably 20 to 200 nm. Note that the thickness of the gas-sensitive layer 15 may be either uniform or non-uniform over its entire surface.

[0020] As described above, as shown in FIG. 6, the gas sensor element 10 includes a substrate 11, a pair of electrodes 12, 12 formed on the surface of the substrate 11, and a gas-sensitive layer 15 connecting the electrodes 12, 12. FIG. 6 shows that the entire pair of electrodes 12, 12 is covered by the gas-sensitive layer 15, but the present invention is not limited thereto, and the gas-sensitive layer may be formed such that a part of the surface of each electrode 12, 12 is exposed.

[0021] The constituent material, structure, shape, and size of the substrate 11 constituting the gas sensor element 10 are not particularly limited. The constituent material of the substrate 11 may be either an inorganic material or an organic material. Among these, an inorganic material is preferable, and it can be a metal, ceramics (oxides, nitrides, carbides, oxynitrides, etc.).

[0022] The constituent material and film thickness of the electrodes 12, 12 are not particularly limited. The constituent material of the electrode 12 is usually platinum (Pt), palladium (Pd), gold (Au), silver (Ag), copper (Cu), nickel (Ni), titanium (Ti), chromium (Cr), aluminum (Al), tin (Sn), indium (In), molybdenum (Mo), ruthenium (Ru), etc. On the substrate 11, the electrodes 12, 12 are usually patterned, and the shape thereof can be, for example, the comb shape shown in FIG. 10 or FIG. 11, but is not limited thereto.

[0023] The gas sensor element 10 can be obtained, for example, by immersing a substrate (substrate with electrodes) having a pair of electrodes on its surface in a raw material liquid containing a precursor for tin oxide plate-like crystals, and generating tin oxide plate-like crystals on the surface of the substrate on the side having the electrodes so as to connect the pair of electrodes. In this manufacturing method, the raw material liquid is preferably an aqueous solution containing tin ions. The aqueous solution containing tin ions can be obtained by dissolving SnF4 (tin fluoride), SnCl4 (tin tetrachloride), SnCl2 (tin dichloride), SnCl2·2H2O (tin chloride dihydrate), SnCl4·5H2O (tin chloride pentahydrate), SnBr2 (tin bromide), SnI2 (tin iodide), SnI4 (tin iodide), tin acetate, tin oxalate, tin stearate, tin sulfate, tin tartrate, tin tetrafluoroborate, tin trifluoromethanesulfonate, etc. in water. A particularly preferred raw material liquid is an aqueous solution of tin fluoride. Since an aggregate of tin oxide plate-like crystals having the above preferred aspect ratio is efficiently formed on the surface of the substrate or the electrodes, the concentration of the aqueous solution of tin fluoride is preferably 20 to 600 mM, more preferably 50 to 400 mM, and even more preferably 100 to 300 mM. The temperature of the raw material liquid when immersing the substrate with electrodes is not particularly limited, but is preferably 20°C to 99°C, more preferably 40°C to 95°C, and even more preferably 70°C to 92°C. Also, the immersion time is appropriately selected depending on the size of the substrate with electrodes, etc., but is usually 30 minutes or more in order to ensure the thickness of the gas-sensitive layer containing tin oxide plate-like crystals.

[0024] The gas sensor device of the present invention includes a light source 20 that emits light to the gas-sensitive layer 15 of the gas sensor element 10. The type of light is not particularly limited and can be, for example, ultraviolet light, visible light, etc., but ultraviolet light is preferred. The light source 20 that emits ultraviolet light can be any of a light source that emits ultraviolet light in the UV-A region (wavelength 310 - 400 nm), a light source that emits ultraviolet light in the UV-B region (wavelength 280 - 310 nm), and a light source that emits ultraviolet light in the UV-C region (wavelength 100 - 280 nm). Among these, a light source that emits ultraviolet light in the UV-A region (wavelength 310 - 400 nm) is preferred. Specifically, as the light source 20, a light-emitting diode (LED), a high-pressure mercury lamp, a metal halide lamp, an ultraviolet (UV) electrodeless lamp, an ultraviolet laser, etc. can be used. Also, an optical fiber may be used in combination. In addition, the number of the light sources 20 included in the gas sensor device of the present invention is appropriately selected according to the application and may be one or a plurality. In the case of a plurality, they may be light sources that emit ultraviolet light of different wavelengths from each other.

[0025] FIG. 1 is a schematic diagram showing the gas sensor device of the present invention. The light source 20 can be arranged at any position where the distance from the gas-sensitive layer 15 of the gas sensor element 10 is not limited as long as it can emit light to the gas-sensitive layer 15 of the gas sensor element 10.

[0026] FIG. 2 (FIG. 3), FIG. 4, and FIG. 5 are specific examples of the gas sensor device of the present invention. As shown in FIG. 3, FIG. 2 shows a gas sensor device 1A that protects the gas-sensitive layer 15 of the gas sensor element 10 with a lid 40 having an opening 41 at the center of the upper surface. It is a device that introduces the gas to be detected from the opening 41 into a contact state with the gas-sensitive layer 15 of the gas sensor element 10 and irradiates light from the light source 20 protected by the lid 40 in the same way. Note that FIGS. 2 and 3 include the lid 40 and the number of the openings 41 is one, but the gas sensor device of the present invention is not limited to this. When a lid is provided, it may be on the side surface. Also, if the opening can ensure air permeability, a mesh may be provided. FIG. 4 shows a gas sensor device 1B in which the light source 20 is arranged outside the lid 40, and the light from the light source 20 is irradiated onto the gas-sensitive layer 15 through the opening 41. FIG. 5 shows a gas sensor device 1C in which the light from the light source 20 arranged outside the lid 40 is irradiated onto the gas-sensitive layer 15 using the optical fiber 22.

[0027] Next, the gas concentration measurement method of the present invention is a method for measuring the concentration of a gas to be detected by bringing the gas to be detected into contact with a gas-sensitive layer of a gas sensor element having a substrate having electrical insulation, a pair of electrodes formed on the surface of the substrate, and a gas-sensitive layer including an aggregate of tin oxide plate-like crystals connected to the electrodes while irradiating light on the gas-sensitive layer. The gas concentration measurement method of the present invention may use any device as long as it can irradiate light on the gas-sensitive layer of the gas sensor element. However, a gas sensor device having the configuration of FIG. 2 (FIG. 3), FIG. 4, or FIG. 5 and using a light source that emits ultraviolet rays is preferably used. Further, the preferable properties of the tin oxide plate-like crystals constituting the gas-sensitive layer are as described above.

[0028] When using the gas sensor device of FIG. 2, FIG. 4, or FIG. 5, for example, in the absence of the gas to be detected, while irradiating the gas-sensitive layer of the gas sensor element with light (preferably ultraviolet light having a wavelength of 400 nm or less), the electrical resistance value between the pair of electrodes (hereinafter referred to as "resistance value R1") is measured. Then, the gas to be detected is brought into contact with the gas-sensitive layer, and while irradiating the gas-sensitive layer with light, the electrical resistance value (hereinafter referred to as "resistance value R2") is measured in the same manner. The concentration of the gas to be detected can be calculated from the change amount between the above resistance values R1 and R2 and a calibration curve prepared in advance using a gas to be detected having a known concentration. When bringing the gas to be detected into contact with the gas-sensitive layer, it is preferable to bring it into contact with a mixed gas with air, a mixed gas with synthetic air, an inert gas, or a mixed gas with oxygen.

[0029] In the gas concentration measurement method of the present invention, when the above gas sensor device is used, when the gas to be detected is brought into contact with the gas sensitive layer of the gas sensor element and the gas sensitive layer is irradiated with light, it is possible to efficiently adsorb the gas to be detected onto the tin oxide plate-like crystals of the gas sensitive layer at 50 ° C. or lower without the need for the conventionally required high temperature. Therefore, the concentration of the gas to be detected can be obtained economically and easily. Further, the following operational effects can be obtained. (1) The nitrogen dioxide gas concentration dependency value of the sensor response value (hereinafter simply referred to as "response value") can be preferably 0.2 to 100, more preferably 1.5 to 55. (2) When irradiating light with a wavelength in the range of 100 to 400 nm, the nitrogen dioxide gas concentration dependency value of the response value is preferably 10 to 100,000 times, more preferably 30 to 80,000 times higher than that of hydrogen, acetone, isoprene, toluene, ethanol or ammonia. (3) When irradiating light with a wavelength in the range of 310 to 400 nm, the ammonia gas concentration dependency value of the response value can be preferably 0.001 to 1, more preferably 0.1 to 0.5. (4) When irradiating light with a wavelength in the range of 310 to 400 nm, the ammonia gas concentration dependency value of the response value is preferably 10 to 10,000 times, more preferably 100 to 2,500 times higher than that of hydrogen, acetone, isoprene, toluene or ethanol. (5) When irradiating light with a wavelength in the range of 100 to 280 nm, the ethanol gas concentration dependency value of the response value can be preferably 0.001 to 0.1, more preferably 0.1 to 0.05. (6) When irradiating light with a wavelength in the range of 100 to 280 nm, the ethanol gas concentration dependency value of the response value is preferably 1.5 to 500 times, more preferably 5 to 250 times higher than that of hydrogen, acetone, isoprene, toluene or ammonia.

[0030] The gas concentration dependency values for the above respective gases are y with the response value on the axis xIt is the coefficient a when the axis is plotted with the gas concentration, and the intercept b in the formula F(x)=ax + b of the obtained approximate straight line is taken as the noise value.

Example

[0031] Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. However, the examples are merely illustrative, and the present invention is not limited by the examples in any way.

[0032] As described below, on the platinum electrode surface of an alumina substrate (size: 3.3 mm × 3.3 mm × 0.32 mm, hereinafter referred to as "alumina substrate with electrodes") having a pair of platinum electrodes on the surface (a modified pattern shape of FIG. 10, patterned in a comb shape at intervals of 150 μm in width), a film (gas sensing layer) composed of an aggregate of rutile-type tin oxide plate-like crystals (hereinafter referred to as "nanosheet-type tin oxide") was formed to fabricate a gas sensor element. Then, a light source equipped with an LED element that emits ultraviolet rays was arranged above the gas sensing layer in this gas sensor element to obtain a gas sensor device (see FIGS. 2 and 3). Thereafter, hydrogen, acetone, isoprene, toluene, ethanol, nitrogen dioxide, or ammonia was used as the gas to be detected, and the sensor characteristics were evaluated for the mixed gas of this gas to be detected and air.

[0033] Example 1 (Manufacture and Evaluation of a Gas Sensor Device Containing Nanosheet-Type Tin Oxide with an Average Aspect Ratio of 10.87) Tin fluoride (SnF2) (manufactured by Morita Chemical Industries Co., Ltd.) was dissolved in distilled water at 90 °C to obtain a 280 mM aqueous solution of tin fluoride. Subsequently, an alumina substrate with electrodes was immersed in this aqueous solution of tin fluoride and held at 90 °C for 6 hours to form a film (hereinafter also referred to as "gas-sensitive layer α") composed of an aggregate of nanosheet-type tin oxide on the entire surface including a pair of platinum electrodes, thereby obtaining a gas sensor element. The size L of the nanosheet-type tin oxide corresponding to the thickness of the gas-sensitive layer α on the platinum electrode was about 150 nm. Thereafter, the back side of the obtained gas sensor element was placed on the metal semiconductor package 30 and platinum wire welded. Next, an ultraviolet light source 20 was arranged above the gas-sensitive layer 15 of the gas sensor element 10, and further, a metal semiconductor package lid 40 having an opening 41 at the center of the upper surface was attached to fabricate a gas sensor device 1A (see FIGS. 2 and 3). FIG. 12 is a scanning electron microscope (SEM) image of the gas-sensitive layer α formed on the platinum electrode of the alumina substrate with electrodes. The aspect ratios calculated by image analysis of some of the nanosheet-type tin oxides in this FIG. 12 were 3.65 to 17.75, and the average was 10.87.

[0034] 〔A〕Fabrication of Sensor α1 As an ultraviolet light source, an LED element (manufactured by OSA OPTO) that emits light with a wavelength of 360 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor α1").

[0035] 〔B〕Fabrication of Sensor α2 As an ultraviolet light source, an LED element (manufactured by Seoul Viosys) that emits light with a wavelength of 275 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor α2").

[0036] 〔C〕Evaluation of Sensor Characteristics of Gas Sensor Device Next, using the obtained gas sensors α1 and α2, sensor characteristics evaluation was performed on a mixed gas of hydrogen, acetone, isoprene, toluene, ethanol, nitrogen dioxide, or ammonia as the gas to be detected and air (a mixed gas with the gas to be detected at a predetermined concentration). The measurement temperature was 25 °C, hereinafter referred to as "room temperature". Specifically, in an atmosphere of only air, the gas sensitive layer was irradiated with ultraviolet light (wavelength: 360 nm or 275 nm), and after 1800 seconds had elapsed, the electrical resistance value between the pair of electrodes was measured (electrical resistance value: Ra). Next, a mixed gas with a known concentration of the gas to be detected was brought into contact with the gas sensitive layer, and in this state, the gas sensitive layer was irradiated with ultraviolet light (wavelength: 360 nm or 275 nm), and the electrical resistance value between the pair of electrodes was measured (electrical resistance value: Rg) until 1200 seconds had elapsed since the start of irradiation. Each electrical resistance value was measured using a multi-channel digital multimeter (manufactured by Keithley Instruments, Inc.; model number 2700 and manufactured by Samwha Corporation; model number PWON-GS-4 modified).

[0037] The evaluation items of the gas sensor were as follows, and the evaluation results are shown in Table 1 and Table 2. (1) Response value When the electrical resistance value increased and Ra < Rg after contact with the mixed gas, Rg / Ra was calculated and used as the response value. When the electrical resistance value decreased and Ra > Rg after contact with the mixed gas, Ra / Rg was calculated and used as the response value. (2) Noise Ra / (standard deviation of Ra - Ra) was calculated. (3) Signal value From the response value and noise obtained above, the difference (response value - noise) was calculated. (4) 90% response time With Ra at 0% and Rg at 100%, the time until Rg reached 90% after the mixed gas was circulated was measured. (5) 90% recovery time With Rg at 0% and Ra at 100%, after contacting with the mixed gas, it was switched to air, and the time until Ra reached 90% was measured.

[0038] 〔D〕Regarding the sensor characteristics of sensor α1 Sensor α1 showed sensitivity as its signal value was 5.76 (signal value ≥ 0.30 and < 10.00) for 1 ppm nitrogen dioxide. Also, its signal value was 0.08 (signal value ≥ 0.03 and < 0.30) for ammonia at the same concentration, showing slight sensitivity. However, its signal value was < 0.03 for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, showing almost no sensitivity.

[0039] The response value for 1 ppm nitrogen dioxide was greater than that for other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 6.73, nitrogen dioxide / acetone: 6.54, nitrogen dioxide / isoprene: 6.50, nitrogen dioxide / toluene: 6.69, nitrogen dioxide / ethanol: 6.75, nitrogen dioxide / ammonia: 6.14, and the response value ratio was ≥ 2.00 and < 10.00.

[0040] The response value for 1 ppm ammonia was slightly greater than that for other gases at the same measured concentration excluding nitrogen dioxide at the same concentration. That is, ammonia / hydrogen: 1.10, ammonia / acetone: 1.06, ammonia / isoprene: 1.06, ammonia / toluene: 1.09, ammonia / ethanol: 1.10, and the response value ratio was ≥ 1.01 and < 2.00.

[0041] Sensor α1 showed high sensitivity as its signal value was 32.71 (signal value ≥ 10.00 and < 100.00) for 5 ppm nitrogen dioxide. Also, its signal value was 0.56 (signal value ≥ 0.30 and < 10.00) for ammonia at the same concentration, showing sensitivity. However, its signal value was < 0.03 for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, showing almost no sensitivity.

[0042] The response value to 5 ppm nitrogen dioxide was significantly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 33.41, nitrogen dioxide / acetone: 33.55, nitrogen dioxide / isoprene: 32.98, nitrogen dioxide / toluene: 33.07, nitrogen dioxide / ethanol: 32.70, nitrogen dioxide / ammonia: 21.22, and the response value ratio was 10 or more.

[0043] The response value to 5 ppm ammonia was slightly greater than that to other gases at the same measured concentration excluding nitrogen dioxide. That is, ammonia / hydrogen: 1.57, ammonia / acetone: 1.53, ammonia / isoprene: 1.55, ammonia / toluene: 1.56, ammonia / ethanol: 1.54, and the response value ratio was 1.01 or more and less than 2.00.

[0044] Sensor α1 had a signal value of 168.57 (signal value 100.00 or more) for 20 ppm nitrogen dioxide, showing extremely high sensitivity. Also, it had a signal value of 3.43 (signal value 0.30 or more and less than 10.00) for ammonia at the same concentration, showing sensitivity. However, for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, the signal value was less than 0.03, showing almost no sensitivity.

[0045] The response value to 20 ppm nitrogen dioxide was significantly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 166.31, nitrogen dioxide / acetone: 168.69, nitrogen dioxide / isoprene: 161.01, nitrogen dioxide / toluene: 169.78, nitrogen dioxide / ethanol: 165.71, nitrogen dioxide / ammonia: 38.07, and the response value ratio was 10 or more.

[0046] The response value to 20 ppm ammonia was greater than that to other gases excluding nitrogen dioxide at the same measured concentration. That is, ammonia / hydrogen: 4.37, ammonia / acetone: 4.43, ammonia / isoprene: 4.23, ammonia / toluene: 4.46, ammonia / ethanol: 4.35, and the response value ratio was 2.00 or more and less than 10.00.

[0047] 〔E〕Regarding the sensor characteristics of sensor α2 For sensor α2, the signal value for 1 ppm nitrogen dioxide was 0.53 (signal value 0.30 or more and less than 10.00), indicating sensitivity. Also, for hydrogen, acetone, isoprene, toluene, ethanol, and ammonia at the same concentration, the signal value was 0.03 or more and less than 10.00, showing slight sensitivity.

[0048] The response value to 1 ppm nitrogen dioxide was slightly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 1.42, nitrogen dioxide / acetone: 1.39, nitrogen dioxide / isoprene: 1.40, nitrogen dioxide / toluene: 1.40, nitrogen dioxide / ethanol: 1.39, nitrogen dioxide / ammonia: 1.40, and the response value ratio was 1.01 or more and less than 2.00.

[0049] For sensor α2, the signal value for 5 ppm nitrogen dioxide was 4.48 (signal value 0.30 or more and less than 10.00), indicating sensitivity. Also, for hydrogen, acetone, isoprene, toluene, ethanol, and ammonia at the same concentration, the signal value was 0.03 or more and less than 10.00, showing slight sensitivity.

[0050] The response value to 5 ppm nitrogen dioxide was greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 5.19, nitrogen dioxide / acetone: 4.89, nitrogen dioxide / isoprene: 5.09, nitrogen dioxide / toluene: 5.10, nitrogen dioxide / ethanol: 4.66, nitrogen dioxide / ammonia: 4.68, and the response value ratio was 2.00 or more and less than 10.00.

[0051] Sensor α2 showed a signal value of 168.57 (signal value ≥ 10.00 and < 100.00) for 20 ppm nitrogen dioxide, indicating high sensitivity. Also, for ethanol and ammonia at the same concentration, the signal values were 0.52 and 0.30 respectively (both signal values ≥ 0.30 and < 10.00), showing sensitivity. Furthermore, for hydrogen, acetone, isoprene, and toluene at the same concentration, the signal values were ≥ 0.03 and < 0.30, showing slight sensitivity.

[0052] The response value for 20 ppm nitrogen dioxide was significantly greater than that for other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 166.31, nitrogen dioxide / acetone: 168.69, nitrogen dioxide / isoprene: 161.01, nitrogen dioxide / toluene: 169.78, nitrogen dioxide / ethanol: 165.71, nitrogen dioxide / ammonia: 38.07, and the response value ratio was ≥ 10.

[0053] The response value for 20 ppm ethanol was greater than that for other gases at the same measured concentration excluding nitrogen dioxide and ammonia at the same concentration. That is, ethanol / hydrogen: 1.44, ethanol / acetone: 1.29, ethanol / isoprene: 1.38, ethanol / toluene: 1.45, and the response value ratio was ≥ 2.00 and < 10.00.

[0054] The response value for 20 ppm ammonia was slightly greater than that for other gases at the same measured concentration excluding nitrogen dioxide and ethanol at the same concentration. That is, ammonia / hydrogen: 4.37, ammonia / acetone: 4.43, ammonia / isoprene: 4.23, ammonia / toluene: 4.46, and the response value ratio was ≥ 1.01 and < 2.00.

[0055] Example 2 (Manufacture and Evaluation of a Gas Sensor Device Containing Nanoscale Sheet-Type Tin Oxide with an Average Aspect Ratio of 11.79) Tin fluoride (SnF2) (manufactured by Morita Chemical Industries Co., Ltd.) was dissolved in distilled water at 90 °C to obtain a 140 mM aqueous solution of tin fluoride. Subsequently, an alumina substrate with electrodes was immersed in this aqueous solution of tin fluoride and held at 90 °C for 6 hours, thereby forming a film (hereinafter also referred to as "gas-sensitive layer β") composed of an aggregate of nanosheet-type tin oxide on the entire surface including a pair of platinum electrodes, and a gas sensor element was obtained. The size L of the nanosheet-type tin oxide corresponding to the thickness of the gas-sensitive layer β on the platinum electrodes was about 100 nm. Thereafter, the back side of the obtained gas sensor element was placed on the metal semiconductor package 30 and platinum wire welded. Next, an ultraviolet light source 20 was disposed above the gas-sensitive layer 15 of the gas sensor element 10, and further, a metal semiconductor package lid 40 having an opening 41 at the center of the upper surface was attached to fabricate a gas sensor device 1A (see FIGS. 2 and 3). FIG. 13 is a scanning electron microscope (SEM) image of the gas-sensitive layer β formed on the platinum electrodes of the alumina substrate with electrodes. The aspect ratios calculated by image analysis of some of the nanosheet-type tin oxides in this FIG. 13 were 4.73 to 21.75, and the average was 11.79.

[0056] 〔A〕Fabrication of Sensor β1 As an ultraviolet light source, an LED element (manufactured by OSA OPTO) that emits light with a wavelength of 360 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor β1").

[0057] 〔B〕Fabrication of Sensor β2 As an ultraviolet light source, an LED element (manufactured by Seoul Viosys) that emits light with a wavelength of 275 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor β2").

[0058] 〔C〕Sensor Characteristic Evaluation In the same manner as in Example 1, the sensor characteristics of sensor β1 and sensor β2 were evaluated at room temperature. The evaluation results are shown in Tables 1 and 2.

[0059] 〔D〕Regarding the sensor characteristics of sensor β1 For sensor β1, the signal value was 12.68 (signal value: 10.00 or more and less than 100.00) for 1 ppm of nitrogen dioxide, indicating high sensitivity. Also, the signal value was 0.12 (signal value: 0.03 or more and less than 0.30) for ammonia at the same concentration, showing slight sensitivity. However, the signal value was less than 0.03 for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, showing almost no sensitivity.

[0060] The response value for 1 ppm of nitrogen dioxide was significantly larger than that for other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 13.52, nitrogen dioxide / acetone: 13.52, nitrogen dioxide / isoprene: 13.52, nitrogen dioxide / toluene: 13.57, nitrogen dioxide / ethanol: 13.60, nitrogen dioxide / ammonia: 12.14, and the response value ratio was 10.00 or more.

[0061] The response value for 1 ppm of ammonia was slightly larger than that for other gases at the same concentration excluding nitrogen dioxide measured. That is, ammonia / hydrogen: 1.11, ammonia / acetone: 1.11, ammonia / isoprene: 1.11, ammonia / toluene: 1.12, ammonia / ethanol: 1.12, and the response value ratio was 1.01 or more and less than 2.00.

[0062] For sensor β1, the signal value was 70.99 (signal value: 10.00 or more and less than 100.00) for 5 ppm of nitrogen dioxide, indicating high sensitivity. Also, the signal value was 2.58 (signal value: 0.30 or more and less than 10.00) for ammonia at the same concentration, showing sensitivity. However, the signal value was less than 0.03 for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, showing almost no sensitivity.

[0063] The response value to 5 ppm of nitrogen dioxide was significantly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 71.30, nitrogen dioxide / acetone: 70.65, nitrogen dioxide / isoprene: 71.37, nitrogen dioxide / toluene: 71.96, nitrogen dioxide / ethanol: 72.00, nitrogen dioxide / ammonia: 34.92, and the response value ratio was 10.00 or more.

[0064] The response value to 5 ppm of ammonia was slightly greater than that to other gases at the same measured concentration excluding nitrogen dioxide. That is, ammonia / hydrogen: 2.04, ammonia / acetone: 2.02, ammonia / isoprene: 2.04, ammonia / toluene: 2.06, ammonia / ethanol: 2.06, and the response value ratio was 1.01 or more and less than 2.00.

[0065] Sensor β1 had a signal value of 306.67 (signal value: 100.00 or more) for 20 ppm of nitrogen dioxide, indicating extremely high sensitivity. Also, it had a signal value of 9.24 (signal value 0.30 or more and less than 10.00) for ammonia at the same concentration, indicating sensitivity. Furthermore, it had a signal value of 0.01 (signal value 0.03 or more and less than 0.30) for ethanol at the same concentration, indicating slight sensitivity. However, for hydrogen, acetone, isoprene, toluene, and ethanol at the same concentration, the signal value was less than 0.03, indicating no sensitivity.

[0066] The response value to 20 ppm of nitrogen dioxide was significantly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 303.30, nitrogen dioxide / acetone: 286.91, nitrogen dioxide / isoprene: 306.87, nitrogen dioxide / toluene: 303.54, nitrogen dioxide / ethanol: 303.44, nitrogen dioxide / ammonia: 34.92, and the response value ratio was 10 or more.

[0067] The response value to 20 ppm of ammonia was significantly greater than that to other gases excluding nitrogen dioxide and acetone at the same measured concentration. That is, ammonia / hydrogen: 10.12, ammonia / isoprene: 10.22, ammonia / toluene: 10.11, ammonia / ethanol: 10.10, and the response value ratio was 10 or more. Also, the response value to this 20 ppm of ammonia was 9.55, the response value ratio was 2.00 or more and less than 10.00, and it was greater than that to acetone at the same concentration.

[0068] The response value to 20 ppm of acetone was slightly greater than that to other gases excluding nitrogen dioxide and ammonia at the same measured concentration. That is, acetone / hydrogen: 1.06, acetone / isoprene: 1.07, acetone / toluene: 1.06, acetone / ethanol: 1.06, and the response value ratio was 1.01 or more and less than 2.00.

[0069] 〔E〕Regarding the sensor characteristics of sensor β2 For sensor β2, the signal value was 0.78 (signal value: 0.30 or more and less than 10.00) for 1 ppm of nitrogen dioxide, indicating sensitivity. Also, the signal value was 0.04 (signal value: 0.03 or more and less than 0.30) for ethanol at the same concentration, showing slight sensitivity. However, the signal value was less than 0.03 for hydrogen, acetone, isoprene, toluene, and ammonia at the same concentration, showing almost no sensitivity.

[0070] The response value to 1 ppm of nitrogen dioxide was slightly greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 1.78, nitrogen dioxide / acetone: 1.78, nitrogen dioxide / isoprene: 1.78, nitrogen dioxide / toluene: 1.76, nitrogen dioxide / ethanol: 1.72, nitrogen dioxide / ammonia: 1.75, and the response value ratio was 1.01 or more and less than 2.00.

[0071] The response value to 1 ppm of ethanol was slightly greater than that to other gases excluding nitrogen dioxide at the same measured concentration. That is, ethanol / hydrogen: 1.03, ethanol / acetone: 1.04, ethanol / isoprene: 1.04, ethanol / toluene: 1.04, ethanol / ammonia: 1.02, and the response value ratio was 1.01 or more and less than 2.00.

[0072] Sensor β2 showed sensitivity with a signal value of 2.58 (signal value: 0.30 or more and less than 10.00) for 5 ppm of nitrogen dioxide. Also, it showed slight sensitivity with a signal value of 0.14 (signal value: 0.03 or more and less than 0.30) for ethanol at the same concentration. However, the signal value was less than 0.03 for hydrogen, acetone, isoprene, toluene, and ammonia at the same concentration, and it showed almost no sensitivity.

[0073] The response value to 5 ppm of nitrogen dioxide was greater than that to other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 3.57, nitrogen dioxide / acetone: 3.58, nitrogen dioxide / isoprene: 3.57, nitrogen dioxide / toluene: 3.50, nitrogen dioxide / ethanol: 3.14, nitrogen dioxide / ammonia: 3.50, and the response value ratio was 2.00 or more and less than 10.00.

[0074] The response value to 5 ppm of ethanol was slightly greater than that to other gases excluding nitrogen dioxide at the same measured concentration. That is, ethanol / hydrogen: 1.14, ethanol / acetone: 1.14, ethanol / isoprene: 1.13, ethanol / toluene: 1.11, ethanol / ammonia: 1.11, and the response value ratio was 1.01 or more and less than 2.00.

[0075] Sensor β2 showed sensitivity with signal values of 6.29 and 0.37 respectively for 20 ppm of nitrogen dioxide and 20 ppm of ethanol (both signal values: 0.30 or more and less than 10.00). Also, for toluene at the same concentration, the signal value was 0.07 (signal value: 0.03 or more and less than 0.30), showing slight sensitivity. However, for hydrogen, acetone, isoprene, and ammonia at the same concentration, the signal value was less than 0.03, showing almost no sensitivity.

[0076] The response value for 20 ppm of nitrogen dioxide was greater than that for other gases at the same measured concentration. That is, nitrogen dioxide / hydrogen: 7.28, nitrogen dioxide / acetone: 7.28, nitrogen dioxide / isoprene: 7.24, nitrogen dioxide / toluene: 6.83, nitrogen dioxide / ethanol: 5.31, nitrogen dioxide / ammonia: 7.28, and the response value ratio was 2.00 or more and less than 10.00.

[0077] The response value for 20 ppm of ethanol was slightly greater than that for other gases at the same concentration excluding nitrogen dioxide. That is, ethanol / hydrogen: 1.37, ethanol / acetone: 1.37, ethanol / isoprene: 1.36, ethanol / toluene: 1.29, ethanol / ammonia: 1.37, and the response value ratio was 1.01 or more and less than 2.00.

[0078] The response value for 20 ppm of toluene was slightly greater than that for other gases at the same concentration excluding nitrogen dioxide and ethanol. That is, toluene / hydrogen: 1.06, toluene / acetone: 1.06, toluene / isoprene: 1.06, toluene / ammonia: 1.06, and the response value ratio was 1.01 or more and less than 2.00.

[0079] [Table 1]

[0080] [Table 2]

[0081] Example 3 (Manufacture and Evaluation of Gas Sensor Device Containing Nanoplate-Type Tin Oxide with Average Aspect Ratio of 12.39) Tin fluoride (SnF2) (manufactured by Morita Chemical Industries Co., Ltd.) was dissolved in distilled water at 90 °C to obtain a 28 mM aqueous solution of tin fluoride. Subsequently, an alumina substrate with electrodes was immersed in this aqueous solution of tin fluoride and held at 90 °C for 6 hours, thereby forming a film composed of an aggregate of nanoplate-type tin oxide (hereinafter referred to as "gas-sensitive layer γ") on the entire surface including a pair of platinum electrodes, and a gas sensor element was obtained. The size L of the nanoplate-type tin oxide corresponding to the thickness of the gas-sensitive layer γ on the platinum electrode was about 80 nm. Thereafter, the back side of the obtained gas sensor element was placed on the metal semiconductor package 30 and platinum wire welded. Next, an ultraviolet light source 20 was disposed above the gas-sensitive layer 15 of the gas sensor element 10, and further, a metal semiconductor package lid 40 having an opening 41 at the center of the upper surface was attached to fabricate a gas sensor device 1A (see FIGS. 2 and 3). FIG. 14 is a scanning electron microscope (SEM) image of the gas-sensitive layer γ formed on the platinum electrode of the alumina substrate with electrodes. The aspect ratios calculated by image analysis of some of the nanoplate-type tin oxides in this FIG. 14 were 5.35 to 34.15, and the average was 12.39.

[0082] 〔A〕Fabrication of Sensor γ1 As an ultraviolet light source, an LED element (manufactured by OSA OPTO) that emits light with a wavelength of 360 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor γ1").

[0083] 〔B〕Fabrication of Sensor γ2 As an ultraviolet light source, an LED element (manufactured by Seoul Viosys) that emits light with a wavelength of 275 nm was disposed about 1.5 mm above the gas-sensitive layer to obtain a gas sensor device (hereinafter referred to as "sensor γ2").

[0084] Sensor characteristic evaluation of [C] In the same manner as in Example 1, the sensor characteristics of sensor γ1 and sensor γ2 were evaluated at room temperature. The evaluation results are shown in Tables 3 and 4.

[0085] 〔D〕Sensor characteristics for nitrogen dioxide For sensor γ1, the signal value was 49.57 (signal value: 10.00 or more and less than 100.00) for 1 ppm of nitrogen dioxide, indicating high sensitivity. For 5 ppm of nitrogen dioxide and 20 ppm of nitrogen dioxide, the signal values were 305.59 and 1003.31 (both signal values: 100.00 or more), respectively, indicating extremely high sensitivity.

[0086] For sensor γ2, the signal value was 3.39 (signal value: 0.03 or more and less than 10.00) for 1 ppm of nitrogen dioxide, indicating sensitivity. For 5 ppm of nitrogen dioxide and 20 ppm of nitrogen dioxide, the signal values were 14.69 and 36.74 (both signal values: 10.00 or more and less than 100.00), respectively, indicating high sensitivity.

[0087]

Table 3

Table 4

[0088] 〔E〕Gas concentration dependence of sensors α1, α2, β1, β2, γ1 and γ2 From the above results, the gas concentration dependence values of the response values of each sensor to the detected gas (hereinafter referred to as "sensor response values") were calculated and shown in Tables 5 and 6.

[0089] (I) Nitrogen dioxide When the gas sensitive layer was irradiated with light, the gas concentration dependence value of the sensor response value for nitrogen dioxide gas was 0.3277 to 50.807. Further, the average value was 13.045, and since it was 10 or more, it was interpreted as having an extremely strong gas concentration dependence. Furthermore, the coefficient of determination (R2 ) is 0.9989 and is 0.9 or more, so it is interpreted as having a high linear relationship.

[0090] When comparing with the wavelength of the irradiated light, when irradiating light with a wavelength of 360 nm, the nitrogen dioxide gas concentration dependency value of the sensor response value was 8.3117 to 50.807. Also, this average value was 24.793 and was 10 or more, so it is interpreted as having an extremely strong gas concentration dependency. Furthermore, the coefficient of determination (R 2 ) is 0.9989 and is 0.9 or more, so it is interpreted as having a high linear relationship. On the other hand, when irradiating light with a wavelength of 275 nm, the nitrogen dioxide gas concentration dependency value of the sensor response value was 0.3277 to 1.9053. Also, this average value was 1.2997 and was 1 or more. Also, the coefficient of determination (R 2 ) is 0.9993 and is 0.9 or more, so it is interpreted as having a strong gas concentration dependency and a high linear relationship.

[0091] When comparing with the thickness of the gas sensitive layer, when irradiating light on the gas sensitive layer α, the nitrogen dioxide gas concentration dependency value of the sensor response value was 1.6601 to 8.3117, and the average value was 4.9859. Also, the coefficient of determination (R 2 ) was 0.9971. In the case of the gas sensitive layer β, the nitrogen dioxide gas concentration dependency value of the sensor response value was 0.3277 to 15.2600, and the average value was 7.7940. Also, the coefficient of determination (R 2 ) was 0.9999. In the case of the gas sensitive layer γ, the nitrogen dioxide gas concentration dependency value of the sensor response value was 1.9053 to 50.807, and the average value was 26.356. Also, the coefficient of determination (R 2 ) was 0.9959. From these, when irradiating light on the gas sensitive layers α and β, it is interpreted as having a strong gas concentration dependency on nitrogen dioxide and showing a high linear relationship, and when irradiating light on the gas sensitive layer γ, it is interpreted as having an extremely strong gas concentration dependency and a high linear relationship.

[0092] (II) Ammonia When the gas-sensitive layer was irradiated with light, the ammonia gas concentration dependence value of the sensor response was 0.0004 to 0.4468. Also, the average value was 0.1578, which was 0.1 or more, indicating gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9914, which was 0.9 or more, and thus was interpreted to have a high linear relationship.

[0093] When compared by the wavelength of the irradiated light, when the light with a wavelength of 360 nm was irradiated, the ammonia gas concentration dependence value of the sensor response was 0.1681 to 0.4468. Also, the average value was 0.3074, which was 0.1 or more, and thus showed gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9906, which was 0.9 or more, and thus was interpreted to have a linear relationship. On the other hand, when the light with a wavelength of 275 nm was irradiated, the ammonia gas concentration dependence value of the sensor response was 0.0004 to 0.016. Also, the average value was 0.0082, which was less than 0.1, and thus showed a slight gas concentration dependence. Also, the coefficient of determination (R 2 ) was 0.9578, which was 0.9 or more, and thus was interpreted to have a high linear relationship.

[0094] When compared by the thickness of the gas-sensitive layer, when the light was irradiated on the gas-sensitive layer α, the ammonia gas concentration dependence value of the sensor response was 0.016 to 0.1681, the average value was 0.2227, which was 0.1 or more, and thus showed gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9886, which was 0.9 or more, and thus showed a high linear relationship. In the case of the gas-sensitive layer β, the ammonia gas concentration dependence value of the sensor response was 0.0004 to 0.4468, the average value was 0.0929, which was more than 0.01 and less than 0.1, and thus showed a slight gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9968, which was 0.9 or more, and thus was interpreted to have a high linear relationship.

[0095] (III) Ethanol When the gas-sensitive layer was irradiated with light, the ethanol gas concentration dependency values of the sensor response were in the range of -0.0012 to 0.0264. Also, the average value was 0.0114, which was in the range of 0.01 or more and less than 0.1, indicating a slight gas concentration dependency. Furthermore, the coefficient of determination (R 2 ) was 0.9989, which was interpreted as having a high linear relationship.

[0096] When compared by the wavelength of the irradiated light, when the light with a wavelength of 360 nm was irradiated, the ethanol gas concentration dependency values of the sensor response were in the range of -0.0012 to 0.0007. Also, the average value was -0.0001, indicating no gas concentration dependency. Also, the coefficient of determination (R 2 ) was 0.6639, which was in the range of 0.5 or more and less than 0.75, and was interpreted as having a slight linear relationship. On the other hand, when the light with a wavelength of 275 nm was irradiated, the ethanol gas concentration dependency values of the sensor response were in the range of 0.0193 to 0.0264, and the average value was 0.0229, which was in the range of 0.01 or more and less than 0.1, indicating a slight gas concentration dependency. Also, the coefficient of determination (R 2 ) was 0.9997, which was interpreted as having a high linear relationship.

[0097] When compared by the thickness of the gas-sensitive layer, when the light was irradiated on the gas-sensitive layer α, the ethanol gas concentration dependency values of the sensor response were in the range of -0.0012 to 0.0264, and the average value was 0.0128. Furthermore, the coefficient of determination (R 2 ) was 0.9999. Also, in the case of the gas-sensitive layer β, the ethanol gas concentration dependency values of the sensor response were in the range of 0.0007 to 0.0193, and the average value was 0.01. Furthermore, the coefficient of determination (R 2 ) was 0.9945. From these, when the gas-sensitive layers α and β were irradiated with light, it was interpreted that both had a high linear relationship with a slight gas concentration dependency for ethanol.

[0098] (IV) Toluene When the gas-sensitive layer was irradiated with light, the toluene gas concentration dependence value of the sensor response value was -0.0025 to 0.0029. Also, this average value was 0.0011, and it did not show gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.1047, which was less than 0.5, so it did not show a linear relationship.

[0099] (V) Isoprene When the gas-sensitive layer was irradiated with light, the isoprene gas concentration dependence value of the sensor response value was 0.0002 to 0.0056. Also, this average value was 0.0018, and it did not show gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.3203, which was less than 0.5, so it did not show a linear relationship.

[0100] (VI) Acetone When the gas-sensitive layer was irradiated with light, the acetone gas concentration dependence value of the sensor response value was -0.0021 to 0.0096. Also, this average value was 0.0029, and it did not show gas concentration dependence. On the other hand, the coefficient of determination (R 2 ) was 0.9991, which was 0.9 or more, so it was interpreted as having a high linear relationship.

[0101] (VII) Hydrogen When the gas-sensitive layer was irradiated with light, the hydrogen gas concentration dependence value of the sensor response value was -0.0008 to 0.0031. Also, this average value was 0.0008, and it did not show gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.1159, which was less than 0.5, so it did not show a linear relationship.

[0102]

Table 5

[0103]

Table 6

[0104] From Table 1, it can be seen that the sensor of the present invention is highly sensitive to nitrogen dioxide, and the response value is larger than that for other gases (hydrogen, acetone, isoprene, toluene, ethanol, ammonia) measured. That is, it is highly selective to nitrogen dioxide. In particular, the effect is more remarkable as the gas concentration increases.

[0105] In the present invention, when a sensor that emits light with a wavelength of 360 nm is used, it shows particular sensitivity to ammonia, and its response value is larger than that for other gases (hydrogen, acetone, isoprene, toluene, ethanol) excluding the measured nitrogen dioxide. That is, it shows selectivity to ammonia. In particular, the effect is more remarkable as the gas concentration increases.

[0106] In the present invention, when a sensor that emits light with a wavelength of 275 nm is used, it shows particular sensitivity to ethanol, and its response value is larger than that for other gases (hydrogen, acetone, isoprene, toluene, ammonia) excluding the measured nitrogen dioxide. That is, it shows selectivity to ethanol. In particular, the effect is more remarkable as the gas concentration increases.

[0107] Comparative Example 1 〔A〕Fabrication of Sensor α3 A gas sensor device obtained by removing the light source in the gas sensor device (sensor α1) of Example 1 was designated as "sensor α3".

[0108] 〔B〕Fabrication of Sensor α4 A gas sensor device obtained by removing the light source in the gas sensor device (sensor α1) of Example 1, and further comprising a gas sensor element having a platinum heater on the back side where the platinum electrode is not arranged on the alumina substrate was designated as "sensor α4".

[0109] 〔C〕Evaluation of Sensor Characteristics of Sensors α3 and α4 In the same manner as in Example 1, the sensor α3 was evaluated for its sensor characteristics at room temperature, and the sensor α4 was evaluated for its sensor characteristics at 300 °C by driving the platinum heater. The evaluation results are shown in Tables 7 and 8.

[0110] 〔D〕Regarding the sensor characteristics of sensor α3 For sensor α3, the signal value was 0.10 for 1 ppm of nitrogen dioxide, showing slightly sensitivity. However, for other gases at the same measured concentration, the signal value was less than 0.03, showing almost no sensitivity.

[0111] Sensor α3 showed sensitivity to 5 ppm and 20 ppm of nitrogen dioxide. However, for other gases at the same measured concentration, it showed almost no sensitivity.

[0112] 〔E〕Regarding the sensor characteristics of sensor α4 For sensor α4, the signal value was 0.30 or more for any of the gases to be measured, showing sensitivity.

[0113] Comparative Example 2 〔A〕Fabrication of sensor β3 A gas sensor device obtained by removing the light source from the gas sensor device (sensor β1) in Example 2 above was designated as "sensor β3".

[0114] 〔B〕Fabrication of sensor β4 A gas sensor device obtained by removing the light source from the gas sensor device (sensor β1) in Example 2 and further comprising a gas sensor element having a platinum heater on the back side where the platinum electrode is not arranged on the alumina substrate was designated as "sensor β4".

[0115] 〔C〕Evaluation of the sensor characteristics of sensors β3 and β4 In the same manner as in Example 1, the sensor β3 was evaluated for its sensor characteristics at room temperature, and the sensor β4 was evaluated for its sensor characteristics at 300 °C by driving the platinum heater. The evaluation results are shown in Tables 7 and 8.

[0116] 〔D〕Regarding the sensor characteristics of sensor β3 For sensor β3, the signal value was 0.06 for 1 ppm of nitrogen dioxide, showing slightly sensitivity. However, for other gases at the same measured concentration, the signal value was less than 0.03, showing almost no sensitivity.

[0117] Sensor β3 showed sensitivity to 5 ppm and 20 ppm of nitrogen dioxide. However, it showed almost no sensitivity to the gases at the same measured concentration.

[0118] 〔E〕Regarding the sensor characteristics of sensor β4 For sensor β4, the signal value was 0.30 or more for any of the measured 1 ppm gases, showing sensitivity.

[0119] Sensor β4 showed a signal value of 0.30 or more for any of 5 ppm of hydrogen, acetone, isoprene, toluene, ethanol, and nitrogen dioxide, showing sensitivity. However, for ammonia at the same concentration, the signal value was less than 0.30, showing slightly sensitivity.

[0120] For sensor β4, the signal value was 10.00 or more for any of 20 ppm of acetone, isoprene, and nitrogen dioxide, showing high sensitivity. However, for hydrogen, toluene, and ethanol at the same concentration, the signal value was 0.30 or more for any of them, showing sensitivity. Also, for ammonia at the same concentration, the signal value was 0.03 or more, showing slightly sensitivity.

[0121]

Table 7

[0122]

Table 8

[0123] Comparative Example 3 〔A〕Fabrication of Sensor γ3 A gas sensor device obtained by eliminating the light source in the gas sensor device (sensor α1) of Example 1 was designated as "sensor γ3".

[0124] 〔B〕Fabrication of Sensor γ4 A gas sensor device obtained by eliminating the light source in the gas sensor device (sensor α1) of Example 1, and further comprising a gas sensor element having a platinum heater on the back side of the alumina substrate where the platinum electrode is not disposed, was designated as "sensor γ4".

[0125] 〔C〕Evaluation of Sensor Characteristics of Sensors γ3 and γ4 In the same manner as in Example 1, the evaluation of sensor characteristics for nitrogen dioxide was carried out for sensor γ3 at room temperature and for sensor γ4 at 300 °C by driving the platinum heater, respectively. The evaluation results are shown in Tables 9 and 10.

[0126] 〔D〕Regarding the Sensor Characteristics of Sensors γ3 and γ4 For sensor γ3, the signal value was less than 0.30 for 1 ppm of nitrogen dioxide, showing slightly sensitivity. Also, it showed sensitivity for 5 ppm and 20 ppm of nitrogen dioxide.

[0127] Sensor γ4 showed sensitivity for 1 ppm and 5 ppm of nitrogen dioxide. In particular, it showed high sensitivity for 20 ppm of nitrogen dioxide.

[0128]

Table 9

[0129]

Table 10

[0130] 〔E〕Concentration Dependence of Sensors α3, α4, β3, β4, γ3 and γ4 Using the above results, in the same manner as in the case of sensor α1 and the like, the gas concentration dependency values of the sensor response values were calculated. These values are shown in Tables 11 and 12.

[0131] (I) Nitrogen dioxide The nitrogen dioxide gas concentration dependency values of the sensor response values at room temperature of the gas sensing layer were 0.0841 to 0.1944. Also, the average value was 0.1506, and since it was 0.1 or more, it was interpreted as having gas concentration dependency. Furthermore, the coefficient of determination (R 2 ) was 0.9996, and since it was 0.9 or more, it was interpreted as having a high linear relationship. On the other hand, the nitrogen dioxide gas concentration dependency values at 300 °C were 0.4262 to 2.0737. Also, the average value was 1.0813, and since it was 1 or more, it was interpreted as having a strong gas concentration dependency. Furthermore, the coefficient of determination (R 2 ) was 0.9999, and since it was 0.9 or more, it was interpreted as having a high linear relationship.

[0132] (II) Ammonia The ammonia gas concentration dependency values of the sensor response values at room temperature of the gas sensing layer were -0.0003 to 0.0001. Also, the average value was 0.0008, and since it was less than 0.01, it did not show gas concentration dependency. Also, the coefficient of determination (R 2 ) was 0.9578, and since it was 0.9 or more, it was interpreted as having a high linear relationship. On the other hand, the ammonia gas concentration dependency values at 300 °C were 0.0105 to 0.0312. Also, the average value was 0.3075, and since it was 0.1 or more, it was interpreted as having gas concentration dependency. Furthermore, the coefficient of determination (R 2 ) was 0.9906, and since it was 0.9 or more, it was interpreted as having a high linear relationship.

[0133] (III) Ethanol The ethanol gas concentration dependency values of the sensor response values at room temperature of the gas sensing layer were -0.0011 to -0.0001. Also, the average value was -0.0006, and since it was less than 0.01, it did not show gas concentration dependency. Also, the coefficient of determination (R2 ) was 0.0059, which was less than 0.5, so it did not show a linear relationship. On the other hand, the ethanol gas concentration dependence values at 300 °C were 0.1192 - 0.1219. Also, this average value was 0.1206, which was 0.1 or more, so it was interpreted as having gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.6511, which was 0.5 or more, so it was interpreted as having a slight linear relationship.

[0134] (IV) Toluene The toluene gas concentration dependence values of the sensor response values at room temperature of the gas sensing layer were -0.001 - -0.0003. Also, this average value was -0.0007, which was less than 0.01, so it did not show gas concentration dependence. Also, the coefficient of determination (R 2 ) was 0.0024, which was less than 0.5, so it did not show a linear relationship. On the other hand, the toluene gas concentration dependence values at 300 °C were 0.3644 - 0.0522. Also, this average value was 0.2083, which was 0.5 or more, so it was interpreted as having gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.6708, which was 0.5 or more, so it was interpreted as having a slight linear relationship.

[0135] (V) Isoprene The isoprene gas concentration dependence values of the sensor response values at room temperature of the gas sensing layer were -0.0009 - 0.0001. Also, this average value was -0.0004, which was less than 0.01, so it did not show gas concentration dependence. Also, the coefficient of determination (R 2 ) was 0.0728, which was less than 0.5, so it did not show a linear relationship. On the other hand, the isoprene gas concentration dependence values at 300 °C were 0.1004 - 0.5633. Also, this average value was 0.3319, which was 0.1 or more, so it was interpreted as having gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9042, which was 0.9 or more, so it was interpreted as having a high linear relationship.

[0136] (VI) Acetone The acetone gas concentration dependence value of the sensor response value of the gas sensitive layer at room temperature was -0.001 to 0.0004. Also, since this average value was -0.0003 and less than 0.01, it did not show gas concentration dependence. Incidentally, the coefficient of determination (R 2 ) was 0.9139 and since it was 0.9 or more, it is interpreted as having a high linear relationship. On the other hand, the acetone gas concentration dependence value at 300 °C was 0.1574 to 0.5489. Also, since this average value was 0.4032 and 0.1 or more, it is interpreted as having gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.9881 and since it was 0.9 or more, it is interpreted as having a high linear relationship.

[0137] (VII) Hydrogen The hydrogen gas concentration dependence value of the sensor response value of the gas sensitive layer at room temperature was -0.0011 to -0.0001. Also, since this average value was -0.0006 and less than 0.01, it did not show gas concentration dependence. Incidentally, the coefficient of determination (R 2 ) was 0.9491 and since it was 0.9 or more, it is interpreted as having a high linear relationship. On the other hand, the hydrogen gas concentration dependence value at 300 °C was 0.1306 to 0.2828. Also, since this average value was 0.2067 and 0.1 or more, it is interpreted as having gas concentration dependence. Furthermore, the coefficient of determination (R 2 ) was 0.8149 and since it was 0.75 or more, it is interpreted as having a linear relationship.

[0138]

Table 11

[0139]

Table 12

[0140] From Table 1 and Table 7, the following can be understood. In the case of the sensor α1 (Example) irradiated with ultraviolet rays, the absolute value of the signal value for 1 ppm of nitrogen dioxide at room temperature was larger than that of the sensor α3 (Comparative Example) not irradiated with ultraviolet rays (signal value ratio: 100 or more and less than 1000, nitrogen dioxide: 614.78). Also, the signal value of 1 ppm of nitrogen dioxide by the sensor α3 was slightly larger than that for the same concentration of ammonia by the sensor α1 (signal value ratio: 1.01 or more and less than 100, ammonia: 8.46).

[0141] In the case of the sensor α1 (Example) irradiated with ultraviolet rays, the absolute value of the signal value for 5 ppm of nitrogen dioxide at room temperature was significantly larger than that of the sensor α3 (Comparative Example) not irradiated with ultraviolet rays (signal value ratio: 1000 or more, nitrogen dioxide: 6102.66). Also, the signal value of 5 ppm of nitrogen dioxide by the sensor α3 was larger than that for the same concentration of ammonia by the sensor α1 (signal value ratio: 100 or more and less than 1000, ammonia: 105.23).

[0142] In the case of the sensor α1 (Example) irradiated with ultraviolet rays, the absolute value of the signal value for 20 ppm of nitrogen dioxide at room temperature was significantly larger than that of the sensor α3 (Comparative Example) not irradiated with ultraviolet rays (signal value ratio: 1000 or more, nitrogen dioxide: 34018.32). Also, the signal value of 20 ppm of nitrogen dioxide by the sensor α3 was larger than that for the same concentration of ammonia by the sensor α1 (signal value ratio: 100 or more and less than 1000, ammonia: 692.01).

[0143] In the case of the sensor α2 (Example) irradiated with ultraviolet rays, the absolute value of the signal value for any gas of 1 ppm at room temperature was slightly larger than those of the sensor α3 (Comparative Example) not irradiated with ultraviolet rays (signal value ratio: 1.01 or more and less than 100, hydrogen: 8.67, acetone: 10.88, isoprene: 9.67, toluene: 9.59, ethanol: 10.98, nitrogen dioxide: 56.96, ammonia: 10.74).

[0144] In the case of the sensor α2 (Example) irradiated with ultraviolet light, the absolute value of the signal value for 5 ppm of nitrogen dioxide at room temperature was greater than that of the sensor α3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 100 or more and less than 1000, nitrogen dioxide: 836.25). Also, the signal value of 5 ppm of nitrogen dioxide by the sensor α3 was slightly greater than those for other gases of the same concentration by the sensor α2 (signal value ratio: 1.01 or more and less than 100, hydrogen: 9.25, acetone: 21.09, isoprene: 12.70, toluene: 12.39, ethanol: 32.05, ammonia: 31.24).

[0145] In the case of the sensor α2 (Example) irradiated with ultraviolet light, the absolute value of the signal value for 20 ppm of nitrogen dioxide at room temperature was significantly greater than that of the sensor α3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 1000 or more, nitrogen dioxide: 6904.02). Also, the signal value of 20 ppm of nitrogen dioxide by the sensor α3 was greater than that for ethanol of the same concentration by the sensor α2 (signal value ratio: 100 or more and less than 1000, ethanol: 104.45). Furthermore, the signal value of 20 ppm of nitrogen dioxide by the sensor α3 was slightly greater than those for other gases other than ethanol of the same concentration by the sensor α2 (signal value ratio: 1.01 or more and less than 100, hydrogen: 9.99, acetone: 34.43, isoprene: 19.70, toluene: 8.29, ammonia: 60.55).

[0146] Next, in the case of the sensor β1 (Example) irradiated with ultraviolet light, the absolute value of the signal value for 1 ppm of nitrogen dioxide at room temperature was significantly greater than that of the sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 1000 or more, nitrogen dioxide: 15121.24). Also, the signal value of 1 ppm of nitrogen dioxide by the sensor β3 was greater than that for ammonia of the same concentration by the sensor β1 (signal value ratio: 100 or more and less than 1000, ammonia: 145.54).

[0147] In the case of sensor β1 (Example) irradiated with ultraviolet light, the absolute value of the signal value for 5 ppm of nitrogen dioxide at room temperature was significantly larger than that of sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio of 1000 or more, nitrogen dioxide: 6745.56). Also, the signal value of 5 ppm of nitrogen dioxide by sensor β3 was larger than that for the same concentration of ammonia by sensor β1 (signal value ratio of more than 100 and less than 1000, ammonia: 100.42).

[0148] In the case of sensor β1 (Example) irradiated with ultraviolet light, the absolute value of the signal value for 20 ppm of nitrogen dioxide at room temperature was significantly larger than that of sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio of 1000 or more, nitrogen dioxide: 14150.07). Also, the signal value of 20 ppm of nitrogen dioxide by sensor β3 was larger than that for the same concentration of ammonia by sensor β1 (signal value ratio of more than 100 and less than 1000, ammonia: 426.38).

[0149] The absolute value of the signal value for 1 ppm of nitrogen dioxide at room temperature of sensor β2 (Example) irradiated with ultraviolet light was larger than that of sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio of more than 100 and less than 1000, nitrogen dioxide: 929.94). Also, the signal value of 1 ppm of nitrogen dioxide by sensor β3 was slightly larger than that for the same concentration of ethanol by sensor β2 (signal value ratio of 1.01 or more and less than 100, ethanol: 44.02).

[0150] The absolute value of the signal value for 5 ppm of nitrogen dioxide at room temperature of sensor β2 (Example) irradiated with ultraviolet light was larger than that of sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio of more than 100 and less than 1000, nitrogen dioxide: 245.30). Also, the signal value of 5 ppm of nitrogen dioxide by sensor β3 was slightly larger than that for the same concentration of ethanol by sensor β2 (signal value ratio of 1.01 or more and less than 100, ethanol: 13.27).

[0151] The absolute value of the signal value of the sensor β2 (Example) irradiated with ultraviolet light for 20 ppm of nitrogen dioxide at room temperature was greater than that of the sensor β3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 100 or more and less than 1000, nitrogen dioxide: 290.45). Further, the signal value of 20 ppm of nitrogen dioxide by the sensor β3 was slightly greater than that for ethanol at the same concentration by the sensor β2 (signal value ratio: 1.01 or more and less than 100, ethanol: 17.27).

[0152] From Tables 3 and 9, the following can be understood. The absolute values of the signal values of the sensor γ1 (Example) irradiated with ultraviolet light for 1 ppm, 5 ppm, and 20 ppm of nitrogen dioxide at room temperature were greater than those of the sensor γ3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 100 or more and less than 1000, 1 ppm nitrogen dioxide: 186.53, 5 ppm nitrogen dioxide: 275.39, 20 ppm nitrogen dioxide: 260.68).

[0153] Further, the absolute values of the signal values of the sensor γ2 (Example) irradiated with ultraviolet light for 1 ppm, 5 ppm, and 20 ppm of nitrogen dioxide at room temperature were slightly greater than those of the sensor γ3 (Comparative Example) not irradiated with ultraviolet light (signal value ratio: 1.01 or more and less than 100, 1 ppm nitrogen dioxide: 11.53, 5 ppm nitrogen dioxide: 13.24, 20 ppm nitrogen dioxide: 9.55).

[0154] From these results, the following can be understood. (1) The absolute value of the signal value of the sensor in the Example (room temperature) for nitrogen dioxide was greater than that of the sensor in the Comparative Example (room temperature). Further, the gas concentration dependency value of the response value was greater than that of the sensor in the Comparative Example (room temperature). That is, by light irradiation, the absolute value of the signal value for nitrogen dioxide at room temperature could be increased. (2) The absolute value of the signal value of the sensor in the example (room temperature) irradiated with light of 360 nm with respect to ammonia was larger than that of the sensor in the comparative example (room temperature) irradiated with light of 360 nm. Furthermore, the gas concentration dependence value of the response value was larger than that of the sensor in the comparative example (room temperature). That is, by irradiating with light of 360 nm, the absolute value of the signal value with respect to ammonia at room temperature could be increased. (3) The absolute value of the signal value of the sensor in the example (room temperature) irradiated with light of 275 nm with respect to ethanol was larger than that of the sensor in the comparative example (room temperature) irradiated with light of 275 nm. Furthermore, the gas concentration dependence value of the response value was larger than that of the sensor in the comparative example (room temperature). That is, by irradiating with light of 275 nm, the absolute value of the signal value with respect to ethanol at room temperature could be increased.

[0155] Also, from FIG. 15, which is a graph showing the resistance value change with respect to 20 ppm of nitrogen dioxide in sensors α1, α2, α3, β1, β2, β3, γ1, γ2, and γ3, the following can be understood. The 90% response time at room temperature of sensor α1 (example) was shortened compared to that of sensor α3 (comparative example) not irradiated with ultraviolet light at room temperature (more than 25% and less than 50%, 1 - α1 / α3: 40%).

[0156] The 90% recovery time at room temperature of sensor α1 (example) was significantly shortened compared to that of sensor α3 (comparative example) not irradiated with ultraviolet light at room temperature (more than 50%, 1 - α1 / α3: 75%).

[0157] The 90% response time at room temperature of sensor α2 (example) was slightly shortened compared to that of sensor α3 (comparative example) not irradiated with ultraviolet light at room temperature (more than 1% and less than 25%, 1 - α2 / α3: 24%).

[0158] The 90% recovery time at room temperature of sensor α2 (example) was significantly shortened compared to that of sensor α3 (comparative example) not irradiated with ultraviolet light at room temperature (more than 50%, 1 - α2 / α3: 62%).

[0159] The 90% response time at room temperature of sensor β1 (Example) was significantly shortened compared to that of sensor β3 (Comparative Example) without UV irradiation (by more than 50%, 1 - β1 / β3: 62%).

[0160] The 90% recovery time at room temperature of sensor β1 (Example) was significantly shortened compared to that of sensor β3 (Comparative Example) without UV irradiation (by more than 50%, 1 - β1 / β3: 80%).

[0161] The 90% response time at room temperature of sensor β2 (Example) was shortened compared to that of sensor β3 (Comparative Example) without UV irradiation (by more than 25% and less than 50%, 1 - β2 / β3: 47%).

[0162] The 90% recovery time at room temperature of sensor β2 (Example) was shortened compared to that of sensor β3 (Comparative Example) without UV irradiation (by more than 25% and less than 50%, 1 - β2 / β3: 37%).

[0163] The 90% response time at room temperature of sensor γ1 (Example) was significantly shortened compared to that of sensor γ3 (Comparative Example) without UV irradiation (by more than 50%, 1 - γ2 / γ3: 72%).

[0164] The 90% recovery time at room temperature of sensor γ1 (Example) was significantly shortened compared to that of sensor γ3 (Comparative Example) without UV irradiation (by more than 50%, 1 - γ1 / γ3: 94%).

[0165] The 90% response time at room temperature of sensor γ2 (Example) was significantly shortened compared to that of sensor γ3 (Comparative Example) without UV irradiation (by more than 50%, 1 - γ2 / γ3: 90%).

[0166] The 90% recovery time at room temperature of sensor γ2 (Example) was significantly shortened compared to that of sensor γ3 (Comparative Example) without UV irradiation (by more than 50%, 1 - γ2 / γ3: 87%).

[0167] From the above, the 90% response time and 90% recovery time of the sensor in the example (room temperature) for nitrogen dioxide were shorter than those of the sensor in the comparative example (room temperature). That is, by light irradiation, the 90% response time and 90% recovery time for nitrogen dioxide at room temperature could be shortened.

[0168] Next, the findings obtained by comparing sensors α1, α2, β1, β2, γ1, and γ2 with the conventionally known sensors α4, β4, or γ4 are shown. The absolute value of the signal value of sensor α1 (example) for 1 ppm of nitrogen dioxide at room temperature was slightly larger than that of sensor α4 (comparative example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 16.93).

[0169] The absolute values of the signal values of sensor α1 (example) for 5 ppm of nitrogen dioxide and ammonia at room temperature were slightly larger than those of sensor α4 (comparative example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 26.48, ammonia: 1.14).

[0170] The absolute values of the signal values of sensor α1 (example) for 20 ppm of nitrogen dioxide and ammonia at room temperature were slightly larger than those of sensor α4 (comparative example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 19.26, ammonia: 6.66).

[0171] The absolute value of the signal value of sensor α2 (example) for 1 ppm of nitrogen dioxide at room temperature was slightly larger than that of sensor α4 (comparative example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 1.57).

[0172] The absolute value of the signal value of sensor α2 (example) for 5 ppm of nitrogen dioxide at room temperature was slightly larger than that of sensor α4 (comparative example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 3.63).

[0173] The absolute value of the signal value of Sensor α2 (Example) for 20 ppm of nitrogen dioxide at room temperature was slightly larger than that of Sensor α4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 3.91).

[0174] The absolute value of the signal value of Sensor β1 (Example) for 1 ppm of nitrogen dioxide at room temperature was slightly larger than that of Sensor β4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 25.32).

[0175] The absolute values of the signal values of Sensor β1 (Example) for 5 ppm of nitrogen dioxide and ammonia at room temperature were slightly larger than those of Sensor β4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 12.53, ammonia: 5.23).

[0176] The absolute values of the signal values of Sensor β1 (Example) for 20 ppm of nitrogen dioxide and ammonia at room temperature were slightly larger than those of Sensor β4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 7.18, ammonia: 60.92).

[0177] The absolute value of the signal value of Sensor β2 (Example) for 1 ppm of nitrogen dioxide at room temperature was slightly larger than that of Sensor β4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, nitrogen dioxide: 1.56).

[0178] The absolute value of the signal value of Sensor γ1 (Example) for nitrogen dioxide at room temperature was slightly larger than that of Sensor γ4 (Comparative Example) at 300 °C (signal value ratio: 1.01 or more and less than 100, 1 ppm nitrogen dioxide: 37.53, 5 ppm nitrogen dioxide: 33.94, 20 ppm nitrogen dioxide: 74.18).

[0179] The absolute value of the signal value of Sensor γ2 (Example) for nitrogen dioxide at room temperature was slightly larger than that of Sensor γ4 (Comparative Example) at 300 °C (signal value ratio of 1.01 or more and less than 100, 1 ppm nitrogen dioxide: 2.57, 5 ppm nitrogen dioxide: 1.63, 20 ppm nitrogen dioxide: 2.72).

[0180] From the above, the absolute value of the signal value of the sensor in the Example (room temperature) for nitrogen dioxide is larger than that of the sensor in the Comparative Example (300 °C). Furthermore, the gas concentration dependence value of the response value is larger than that of the sensor in the Comparative Example (300 °C). That is, the Example in which only light irradiation was performed without heating has an equivalent or greater effect of increasing the absolute value of the signal value for nitrogen dioxide compared to the Comparative Example heated to 300 °C.

[0181] These Examples showed higher sensor response values at room temperature than those in Non-Patent Document 1 above. That is, the sensor response value of the sensor material in Non-Patent Document 1 does not exceed 2 for 100 ppm of nitrogen dioxide, whereas in the above Examples, for 20 ppm of nitrogen dioxide at a lower concentration, Sensor α1 showed a sensor response value of 169.59, Sensor α2 showed 35.22, Sensor β1 showed 307.67, Sensor β2 showed 7.29, Sensor γ1 showed 1004.32, and Sensor γ2 showed 37.74 (see Table 13).

[0182]

Table 13

[0183] Example 4 (Manufacture and Evaluation of a Gas Sensor Device Containing a Nanoscale Sheet-Type Tin Oxide with an Average Aspect Ratio of 7.88) Tin fluoride (SnF2) (manufactured by Morita Chemical Industries Co., Ltd.) was dissolved in distilled water at 90 °C to obtain a 28 mM aqueous solution of tin fluoride. Subsequently, an alumina substrate with electrodes was immersed in this aqueous solution of tin fluoride and held at 90 °C for 24 hours, thereby forming a film (hereinafter referred to as "gas-sensitive layer δ") composed of an aggregate of nanosheet-type tin oxide on the entire surface including a pair of platinum electrodes, and a gas sensor element was obtained. The size L of the nanosheet-type tin oxide corresponding to the thickness of the gas-sensitive layer δ on the platinum electrodes was about 100 nm. Thereafter, the back side of the obtained gas sensor element was placed on the metal semiconductor package 30 and platinum wire welded. Next, an ultraviolet light source 20 was disposed above the gas-sensitive layer 15 of the gas sensor element 10, and further, a metal semiconductor package lid 40 having an opening 41 at the center of the upper surface was attached to fabricate a gas sensor device 1A (see FIGS. 2 and 3). FIG. 16 is a scanning electron microscope (SEM) image of the gas-sensitive layer δ formed on the platinum electrodes of the alumina substrate with electrodes. The aspect ratios calculated by image analysis of some of the nanosheet-type tin oxides in this FIG. 16 were 5.04 to 11.52, and the average was 7.88.

Industrial Applicability

[0184] The gas sensor device of the present invention is suitable for measuring the concentration of nitrogen dioxide (NO2) gas, and can be measured, for example, for combustion exhaust gases from incinerators such as garbage, boilers, etc.; exhaust gases from incinerators, vehicles, ships, etc., and exhaust gases from steel mills.

Explanation of Reference Numerals

[0185] 1, 1A, 1B and 1C: Gas sensor devices 10: Gas sensor element 11: Substrate 12: Electrodes 13: Tin oxide plate-like crystal 14: Substrate with electrodes 15: Gas-sensitive layer 20: Light source 30: Semiconductor package 40: Semiconductor package lid 41: Opening 50: Support

Claims

1. A gas sensor element having a substrate with electrical insulation, a pair of electrodes formed on the surface of the substrate, and a gas-sensitive layer including an aggregate of tin oxide plate-like crystals having an average value of the ratio of the maximum length to the thickness (aspect ratio) of 2.5 to 100, which is connected to the electrodes, and, A light source that emits ultraviolet rays to the gas-sensitive layer of the gas sensor element characterized by comprising a gas sensor device for detecting nitrogen dioxide gas.

2. The gas sensor device for detecting nitrogen dioxide gas according to Claim 1, wherein the wavelength of the ultraviolet ray is 310 to 400 nm.

3. The gas sensor device for detecting nitrogen dioxide gas according to Claim 1 or 2, wherein the main exposed surface of the tin oxide plate-like crystal is the (101) crystal plane.

4. A method for measuring the concentration of nitrogen dioxide gas, characterized by contacting nitrogen dioxide gas while irradiating ultraviolet rays to the gas-sensitive layer of a gas sensor element having a substrate with electrical insulation, a pair of electrodes formed on the surface of the substrate, and a gas-sensitive layer including an aggregate of tin oxide plate-like crystals having an average value of the ratio of the maximum length to the thickness (aspect ratio) of 2.5 to 100, which is connected to the electrodes, and measuring the concentration of the nitrogen dioxide gas.

5. The method for measuring the concentration of nitrogen dioxide gas according to Claim 4, wherein the wavelength of the ultraviolet ray is 310 to 400 nm.

6. The method for measuring the concentration of nitrogen dioxide gas according to Claim 4 or 5, wherein the main exposed surface of the tin oxide plate-like crystal is the (101) crystal plane.

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