Electronic devices, sensor elements, and gas sensors

Abstract

Provided are a material for a device capable of selectively identifying substances, a material for a sensor, a sensor element, and a gas sensor. The material for an electronic device according to the present invention comprises an n-type conductor and carbon nanotubes having a semiconductor carbon nanotube purity of 80 mass% or more.

Description

[Technical Field]

[0001] The present invention relates to an electronic device. vinegar, The present invention relates to a sensor element and a gas sensor, and more particularly to a gas sensor using a semiconducting carbon nanotube. [Background technology]

[0002] In recent years, due to environmental issues such as global warming, food safety, and growing health consciousness, there are high expectations for a variety of applications for technology (sensors) for detecting trace amounts of chemical substances, such as detecting VOCs (volatile organic compounds) in the atmosphere, managing freshness during food distribution, managing and diagnosing health conditions by detecting skin gases emitted by the human body, improving comfort by detecting odors in spaces used by multiple users such as airplanes, trains, and automobiles, reducing the burden on caregivers and improving the quality of life of those receiving care by detecting gases derived from excrement, and improving security by detecting harmful gases. In particular, the healthcare field is a field where demand is increasing significantly. Analysis of gases contained in exhaled breath has attracted attention in recent years because many of the substances contained therein are relatively simple and easy to analyze, making it easy to use for disease detection and health management through simple tests.

[0003] Demand is particularly increasing for gas sensor technology, which requires real-time, highly sensitive, and selective detection of gases. In addition to the healthcare field, many other fields where demand is on the rise require sensors with high detection sensitivity on the order of ppb and the ability to selectively detect a wide variety of gases. However, the main gas sensors available on the market have insufficient detection sensitivity (on the order of ppm), high power consumption due to high operating temperatures (200-500°C), rapid deterioration, and almost no ability to distinguish between gas species, so they are unable to meet demand.As a result, in reality, the sensor is often replaced by a device incorporating or combining specialized analytical equipment used in laboratories that is specialized for a single field, but because it is extremely expensive and not versatile, it only meets a very limited portion of demand.

[0004] To address the lack of detection sensitivity of gas sensors, methods being considered include nanosizing the materials used in the sensors to increase their surface area, making it easier to detect trace molecules and improving sensitivity (Non-Patent Document 1), and hybridizing multiple materials to amplify the signal intensity and improve sensitivity (Non-Patent Document 2). Furthermore, to address the high power consumption and degradation caused by high operating temperatures (200 to 500° C.), development studies are being conducted to achieve both low-temperature operation and high sensitivity by using nanocarbon materials (Patent Document 1). Furthermore, it has been reported that sensitivity can be further improved by using a nanocarbon material with high semiconductor purity (Non-Patent Document 3).

[0005] On the other hand, most gas sensors currently in general use use a mechanism that detects electrical changes on the surface when oxygen on the metal oxide surface reacts with gas molecules at high temperatures (200-500°C). Therefore, they detect all gas molecules that undergo oxidation reactions and are not gas selective, except for some gases such as carbon dioxide. Therefore, gas selection is currently performed by controlling the temperature of the heater to control the reactivity of the detection surface, eliminating non-target gases with a filter, or attaching a device to the outside of the sensor to read the detected waveform and performing waveform analysis, but this only allows for a combination of two or three selectivities that are broadly divided into two categories, such as the combustion temperature of the gas or the molecular diameter of the gas, making it difficult to achieve selectivity for a wide variety of gases, making it difficult to apply this to applications with a large number of contaminating gases, such as the healthcare field, where demand is expected to be highest. Furthermore, while it is technically possible to combine multiple types of filters, this leads to reduced detection sensitivity and higher costs and is not practical. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-185495 [Non-patent literature]

[0007] [Non-Patent Document 1] ACS Omega.3,p.14592-14596(2018) [Non-patent document 2] Sens.Actuat.B170p,67-74(2012) [Non-patent document 3] ASC Sens.3,79-86(2018) Summary of the Invention [Problem to be solved by the invention]

[0008] While electronic device materials are becoming increasingly important in the field of sensing devices, where demand is growing, there are few materials that can selectively identify substances. In particular, there are few electronic device materials with substance (molecule) selectivity among sensor materials themselves, so when combining peripheral devices to achieve selectivity, the range of substance selectivity tends to be narrow. Furthermore, none of the methods in Patent Document 1 and Non-Patent Documents 1 to 3 solves the problem of gas sensing materials used in commercially available sensors, which have almost no ability to distinguish between gases.

[0009] The present invention aims to provide a material for a device capable of selectively identifying chemical substances. In particular, in the field of gas sensors, it is possible to provide an electronic device that can be used as a gas sensor having low-temperature operation, high sensitivity, and the ability to selectively detect gas molecules. vinegar, To provide a sensor element and a gas sensor. [Means for solving the problem]

[0010] That is, the present invention is (1) A material for electronic devices comprising carbon nanotubes having a purity of 80% by mass or more of semiconducting carbon nanotubes and an n-type semiconductor; (2) The material for electronic devices according to (1), wherein the carbon nanotubes are carbon nanotube composites having a polymer attached to at least a part of the surface thereof. (3) The material for electronic devices according to (2), wherein the polymer is a semiconducting polymer. (4) The material for electronic devices according to any one of (1) to (3), wherein the n-type semiconductor has a nanostructure. (5) The material for an electronic device according to any one of (1) to (4), wherein the n-type semiconductor is an oxide semiconductor. (6) The material for an electronic device according to any one of (1) to (5), which is a gas-sensitive material. (7) An electronic device comprising the material for electronic devices according to any one of (1) to (6). (8) A sensor element comprising the material for an electronic device according to any one of (1) to (6). (9) A gas sensor using the sensor element according to (8). is. [Effects of the Invention]

[0011] The material for electronic devices of the present invention can be used as a gas sensor that operates at low temperature, has high sensitivity, and has gas discrimination ability. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a sensor element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating gas detection using the sensor element according to the embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing the detection results of ammonia using the sensor element according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the detection results of nitric oxide using the sensor element according to the embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing the detection results of ammonia using a sensor element according to a comparative example. [Figure 6]FIG. 6 is a diagram showing the detection results of nitric oxide using a sensor element according to a comparative example. [Figure 7] FIG. 7 is a graph for comparing the detection results of ammonia and nitric oxide using the sensor element according to the embodiment of the present invention. [Figure 8] FIG. 8 is a graph for comparing the detection results of ammonia, methane, toluene, cyclohexane, and nitric oxide using the sensor element according to the embodiment of the present invention. [Figure 9] FIG. 9 is a graph for comparing the detection results of ammonia and nitrogen monoxide using the sensor element according to the comparative example. [Figure 10] FIG. 10 is a graph for comparing the detection results of ammonia and nitrogen monoxide using the sensor element according to the comparative example. [Figure 11] FIG. 11 is a graph for comparing the detection results of ammonia, methane, toluene, cyclohexane, and nitrogen monoxide using the sensor element according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the material for an electronic device according to the present invention, which comprises semiconducting carbon nanotubes (hereinafter referred to as "CNTs") having a purity of 80 mass % or more and an n-type semiconductor, will be described in detail. However, the present invention is not limited to the following embodiments, and can be practiced with various modifications depending on the purpose and application.

[0014] First, we will describe the electronic device material of the present invention, which is composed of CNTs and n-type semiconductors with a semiconducting CNT purity of 80% by mass or more. A semiconducting CNT purity of 80% by mass means that the ratio of semiconducting CNTs to the total CNTs is 80% by mass or more. Typically, CNTs are a mixture of semiconducting CNTs and metallic CNTs in a 2:1 mass ratio, resulting in a semiconducting CNT purity of 66.7% by mass. Semiconducting CNTs have thresholds for current flow and non-flow depending on the voltage applied to the device, whereas metallic CNTs have no particular threshold. Therefore, a high ratio of metallic CNTs easily creates paths connecting metallic CNTs in the CNT network connecting electrodes, making the on / off boundary of the current unclear. As a result, in electronic devices, the boundary between switching and signal detection (the boundary between signal and noise) becomes unclear. When such CNTs are used in sensor elements, noise increases, leading to reduced sensitivity. The higher the purity of semiconducting CNT, the better, since it is advantageous in terms of switching and signal detection, and as will be described later, a higher semiconducting purity is also better in terms of selectivity for the detection molecule. The CNT used in the present invention must have a semiconducting CNT purity of 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and best 95% by mass or more.

[0015] The semiconducting CNTs required for the present invention, which have a purity of 80% by mass or more, are effective as a sensor element in one form. By combining semiconducting CNTs with a purity of 80% by mass or more with an n-type semiconductor, the sensor element material exhibits selectivity to external substances that differs from that of the single material. Although the principle behind this difference in selectivity is unclear, under normal atmospheric conditions, semiconducting CNTs exhibit the properties of p-type semiconductors, in which holes are the carriers of electricity. Therefore, by combining them with n-type semiconductors to form a junction, the material for electronic devices exhibits diode-like rectifying properties. Alternatively, it is speculated that the combination results in an imbalance in the electronic state, with the CNTs becoming hole-rich and the n-type semiconductor becoming electron-rich. This results in a composite with electron donor / acceptor capabilities that differ from those of the p-type and n-type semiconductors individually. Therefore, it is speculated that selectivity in electron donor / acceptor behavior occurs when the composite material comes into contact with or adheres to chemicals. For example, when the external chemical substance is a gas molecule, some gases undergo electron transfer depending on the oxidizing and reducing power of the gas molecules, while others do not. Therefore, when the material for an electronic device of the present invention is used as a material for a sensor element, it can be used as a gas sensor with selectivity in gas response. Furthermore, in the case of liquids and other substances, selectivity occurs depending on the oxidizing and reducing power of the chemical substance that constitutes the liquid, so the material for an electronic device of the present invention can be used as a material for a sensor element for all chemical substances.

[0016] Selectivity to external substances is thought to be a characteristic resulting from the rectification properties of the contact (junction) between p-type and n-type semiconductors, or the charge imbalance that occurs when p-type and n-type semiconductors come into contact, and if a large amount of metallic CNTs, which do not have semiconducting properties, are mixed in, the p-type semiconducting properties of the CNTs as a whole are reduced, reducing their effectiveness (the leakage current from the metallic CNTs increases noise components and reduces the rectification properties or charge imbalance characteristics). For this reason, as described in Non-Patent Document 2, a composite of CNTs and n-type semiconductors with a purity of 66.7 mass% (general semiconducting CNTs, where the purity of the semiconducting CNTs has not been particularly increased) shows no selectivity in response to external chemical substances, particularly gases.

[0017] The purity of the semiconducting CNTs required for the CNTs used in this invention varies depending on the application form of the electronic device. However, a semiconducting CNT purity of 80% by mass or higher provides selectivity for chemicals as a composite material. A purity of 90% by mass or higher provides clear selectivity, and a purity of 95% by mass or higher is preferable because it practically eliminates noise. For example, when the electronic device material of this invention is used as a sensor element, the signal represented by the difference between the current when the voltage is turned on and the current when the voltage is turned off (leakage current, i.e., noise) is smaller. The signal change is clearer and easier to read, making even small signals readable. While a clearer current ratio between when the voltage is turned on and when it is off is preferable, because metallic CNTs are prone to current flow, the more metallic CNTs there are, the higher the leakage current when the voltage is off, making it difficult to read the current difference between the on and off states, and thus hindering improvement in sensor performance. In other words, the sensitivity of the sensor is poor. Conversely, the higher the purity of the semiconducting CNT, the smaller the leakage current when the voltage is off and the less noise is generated, making the signal easier to read, resulting in a highly sensitive sensor and clearly demonstrating selectivity.

[0018] If a highly sensitive sensor element is required, it is preferable to increase the purity of the semiconducting CNT within the CNT, but if it is 80% by mass or more, even when the CNT is used as an electrode, there will be almost no three-dimensional connections made only of metallic CNT, and if it is 90% by mass or more, the metallic CNT will be more easily isolated, making it less likely for leakage current to flow and resulting in a highly sensitive and selective sensor element. In reality, a purity of 95% by mass or more of the semiconducting CNT is best, as the influence of the metallic CNT will be very small.

[0019] The electronic device material according to the present invention can be used as a sensor element material, and is particularly useful as a gas sensor material. The electronic device material according to the present invention can be applied as a sensor element that does not require heating, because it utilizes the phenomenon in which a resistance change (current change) occurs simply when a gas comes into contact with or adheres to the CNT. Furthermore, because the CNTs used are nanomaterials and therefore have a substantially high surface area, they can be used as highly sensitive gas sensors with a large contact area with gases, and can be used as a sensor material that is selective for chemical species without the use of an external device. The electronic device material of the present invention utilizes the high surface area of ​​the CNTs, enabling detection of trace amounts of chemical substances at ppm levels, and under appropriate conditions, even at ppb and even ppt levels. For example, by connecting a measuring device such as a digital multimeter capable of detecting nanoampere-order current changes and measuring the current change, chemical substances at ppt levels can be detected. Furthermore, the higher the semiconductor purity of the CNTs, the easier it is to detect trace amounts of chemical substances. While there are no restrictions on semiconductor purity if detection of the target substance is at ppm levels, a semiconductor purity of 80% by mass or higher is preferred. If detection at ppb levels is required, a semiconductor purity of 90% by mass or higher is preferred. A semiconductor purity of 95% by mass or higher enables detection of trace amounts of chemical substances of 100 ppt or less.

[0020] Known methods can be used to achieve a semiconducting CNT purity of 80% by mass or higher in CNT. Examples include ultracentrifugation in the presence of a density gradient agent to increase the purity, selectively attaching specific compounds to the surface of semiconducting CNT or metallic CNT and separating metallic CNT from semiconducting CNT by utilizing the difference in solubility, and electrophoresis, which utilizes the difference in electrical properties to increase the semiconducting CNT purity. Methods for measuring the semiconducting CNT content in CNT include calculation from the absorption area ratio in visible-near-infrared absorption spectra and calculation from the intensity ratio in Raman spectra.

[0021] As described above, the electronic device material according to the present invention is capable of selectively detecting trace chemical substances by combining CNTs with increased semiconductor purity with an n-type semiconductor. For example, in the case of an electronic device material that combines CNTs with increased semiconductor purity with tin oxide (SnO2) as an n-type semiconductor, the material will exhibit high sensitivity to reducing compounds but low sensitivity or no sensitivity to oxidizing compounds, making it possible to distinguish between oxidizing chemical substances and reducing chemical substances. In this case, examples of oxidizing chemical substances include nitrogen monoxide, nitrogen dioxide, nitric acid, nitrous acid, chloric acid, perchloric acid, hypochlorous acid, sulfur monoxide, sulfur dioxide, sulfur peroxide, ozone, hydrogen peroxide, halogens such as fluorine, chlorine, bromine, and iodine, and gases such as hydrogen fluoride, hydrogen chloride, and hydrogen bromide. Examples of reducing chemical substances include ammonia, hydrogen, and carbon monoxide, and examples of chemical substances that exhibit weak reducing properties include aldehydes such as formaldehyde and acetaldehyde, alcohols such as methanol and ethanol, organic compounds having π electrons such as alkynes such as acetylene, alkenes such as ethylene, and aromatic compounds such as toluene. Furthermore, the electronic device material of the present invention, which combines an n-type semiconductor such as tin oxide (SnO) with CNTs of enhanced semiconductor purity, exhibits excellent response to alkanes such as methane, ethane, and cyclohexane, as well as near-neutral chemicals such as carbon dioxide. The ability to detect these weakly reducing compounds and near-neutral chemicals is believed to be due to the use of CNTs, which, as generally described in published literature, undergo electrical fluctuations depending on the amount of chemicals attached. (It is believed that the CNTs convert changes in the surrounding environment into electrical behavior.) Therefore, the material exhibits electrical response without undergoing a chemical reaction, even to chemicals that do not undergo complete oxidation or reduction, resulting in the transfer of electrons. Furthermore, by utilizing the properties of CNTs and adjusting the work function of the CNTs in a composite material with an n-type semiconductor, it is possible to adjust the selectivity threshold and achieve more specific selectivity for chemical substances (selectivity between compounds that exhibit reducing properties, selectivity between compounds that exhibit oxidizing properties).

[0022] One method for adjusting the work function of CNTs is to change the type of substance that is previously contacted with the CNTs as part of the electronic device material. The most influential adjustment method is to change the type of n-type semiconductor. Changing the type of n-type semiconductor is used to significantly adjust the work function of the CNTs. To precisely control the work function of the CNTs, one method is to wrap the CNTs in a semiconducting polymer beforehand and then change the type of wrapping polymer, which allows for fine adjustment of the work function. Another method for further fine-tuning the selectivity threshold is to change the environmental temperature in which the electronic device material of the present invention is used. This is presumably due to the fact that changing the temperature changes the probability of free electrons existing in the conduction band of the CNTs.

[0023] In the electronic device material according to the present invention, the CNTs are preferably a CNT / polymer composite having a polymer attached to at least a portion of the surface. Here, the polymer is a compound whose repeating unit has a conjugated structure and a degree of polymerization of 2 or more. Composites of CNTs with polymers are preferred in that they prevent the CNTs from bundling and allow the surface area of ​​the CNTs to be used effectively. As the polymer, it is more preferable to use a semiconducting polymer in terms of improving the precision of selectivity. By combining CNTs with semiconducting polymers, it is possible to adjust the work function of the CNT / semiconducting polymer composite, which is considered a p-type semiconductor. Therefore, by combining semiconducting polymers with CNTs, it is possible to prepare materials with more precise material selectivity and greater effectiveness. While there are no particular restrictions on the semiconducting polymer, the most preferable form of combination is to use the semiconducting polymer as a dispersant for the CNTs, which allows for the preparation of an ink in which the CNTs are uniformly dispersed. Mixing this ink with an n-type semiconductor is preferred, as it makes it easier to create a state in which the CNTs are homogeneously in contact with the n-type semiconductor.

[0024] If the semiconducting polymer cannot be used as a dispersant, the effect of the CNT / semiconducting polymer composite can be obtained simply by mixing a solution of the semiconducting polymer dissolved in a solvent in which the semiconducting polymer is soluble with CNT and using the resulting mixture as a suspension, paste, etc. by kneading or other methods. From the viewpoint of suppressing detection noise when used as a sensor element, it is preferable that the suspension, paste, etc. containing the semiconducting polymer and CNT be mixed uniformly. If the amount of semiconducting polymer used is too large, the CNTs will be buried in the semiconducting polymer and the properties of the material will become those of the semiconducting polymer, so the amount of semiconducting polymer used relative to the CNTs should preferably be less than 10 times by mass, and if it is used in a manner that also serves as a dispersant, it is preferable to use less than 3 times. Furthermore, if you want to avoid any influence on the properties of the semiconducting polymer itself as much as possible, it is also a good idea to remove the semiconducting polymer that is not attached to the CNTs by classification, washing, etc.

[0025] Particularly preferred semiconducting polymers, which do not impair the semiconducting properties of CNTs, include those described in Japanese Patent Nos. 5470763 and 5454139. These semiconducting polymers can also be used as dispersants for CNTs. Commercially available semiconducting polymers such as poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)] (F8BT) and poly(3-hexylthiophene) (P3HT) can also be used.

[0026] In the present invention, by appropriately combining p-type semiconducting CNTs with a purity of 80% by mass or higher with an n-type semiconductor to form a composite material, it is possible to produce a material for electronic devices that exhibits selectivity for external substances that come into contact with or adhere to them. The selectivity of the electronic device material of the present invention is thought to be due to a diode-like rectification effect or charge imbalance at the interface between the p-type semiconductor (CNT) and the n-type semiconductor. Therefore, the selectivity of the electronic device material of the present invention becomes clearer the more the composite material is formed so that the contact area between the CNT and the n-type semiconductor is increased. While there are no particular limitations on the mixing method if the contact area is increased, it is preferable to form the CNTs into an ink, apply it to or mix it with the n-type semiconductor, and then dry it, as this facilitates adhesion of the CNTs to the n-type semiconductor. In the present invention, by bringing the CNTs into contact with the n-type semiconductor, the charge state on the CNTs is biased toward the CNTs due to the influence of the contacting n-type semiconductor, compared to the case of CNTs alone. As a result, there is the advantage that the response speed is improved due to the excess charge compared to the case of CNTs alone. This also makes it possible to use CNTs as a sensor material with higher sensitivity than when either CNTs or n-type semiconductors are used alone, and the signal (S) to noise (N) ratio (S / N) can be S / N = 3 to 500 even when detecting trace amounts of chemical substances on the order of ppb. Even when detecting trace amounts of chemical substances on the order of ppt, S / N = 3 to 300 is possible.

[0027] While there are no particular limitations on the structure of the n-type semiconductor required to achieve the effects of the electronic device material of the present invention, nanostructures offer the advantage of increased surface area and therefore improved sensitivity, making them a preferred structure for use as sensor element materials. The term "nanostructure" refers to an aggregate of particles, sheets, crystals, or the like, with at least one dimension (length, width, or height) on the nanoscale (1.0 nm to 999.9 nm), or an aggregate of nanoscale pores. Examples of nanostructure structures include metal-organic frameworks (MOFs), zeolites, mesoporous materials, mesoporous materials, macroporous materials, layered compounds, clay minerals, metal complexes, porous organic-silica hybrid materials, ionic crystals, nanosheet liquid crystals, colloidal template materials, and colloidal crystals. Nanostructure identification can be achieved by cross-sectional analysis of the material components using an electron microscope (transmission electron microscope or scanning electron microscope) and measuring the length, width, and height of the particles, sheets, crystals, or pores. When the electronic device material of the present invention is used as a sensor material, it is often required that the signal intensity be clearly defined relative to noise. While sufficient signal intensity can be obtained simply by mixing CNTs and n-type semiconductors so that they form a junction, a preferred form for obtaining a more sufficient signal intensity as a sensor element is that the n-type semiconductor is nanostructured. Because p-type CNTs are nanostructured, they have a high specific surface area. The required signal intensity can be obtained even without a nanostructured n-type semiconductor. However, when both the p-type and n-type semiconductors are nanostructured, the specific surface area as a sensor material is increased, and the increased contact area with external substances increases the signal intensity, making the signal-to-noise ratio clearer.

[0028] Furthermore, by forming the n-type semiconductor into a nanostructure, both the p-type and n-type semiconductors have a short diode configuration in which the electrodes are closer than the diffusion length of the diffusion current from the p / n junction surface, which is thought to result in a larger current value than in a normal diode, amplifying the signal strength and improving detection sensitivity.

[0029] In the electronic device material of the present invention, the n-type semiconductor used in combination with semiconducting CNTs having a purity of 80% by mass or more can achieve the effect of the present invention on selectivity for detecting chemical substances, regardless of the type of n-type semiconductor. However, by changing the type of n-type semiconductor, the work function value of the n-type semiconductor can be adjusted, and therefore, when used as a sensor, it is also possible to adjust the selectivity for molecular species that come into contact with the electronic device material of the present invention. An oxide semiconductor can be suitably used as the n-type semiconductor. Oxide semiconductors are preferred because they allow easy preparation of nanocrystal aggregates by crystal growth, and also because nanocrystal structures can be prepared without using large-scale equipment. Examples of oxide semiconductors that can be used include tin oxide, titanium oxide, indium oxide, ITO, lead oxide, zinc oxide, and tungsten oxide.

[0030] Furthermore, the CNTs used in the electronic device material of the present invention are not particularly limited as long as they have a semiconducting CNT purity of 80% by mass or more. However, CNTs with a smaller diameter are preferable because they have a larger effective surface area and a larger contact area with gas. If the CNTs are too thick, their shape will be distorted by their own weight, changing their semiconducting properties and the material properties as a composite material. The diameter of the CNTs is preferably 3.0 nm or less, more preferably 2.0 nm or less, and even more preferably 1.5 nm or less. If the CNTs are too thin, they will not maintain their shape. The lower limit for maintaining a cylindrical shape is 0.4 nm, but the practical lower limit for industrial production at present is 0.7 nm. The longer the CNT length, the better. This is because the network structure of CNTs connecting electrodes reduces contact resistance, improving the conductivity of the CNT film and improving responsiveness. While the longer the CNT length, the better in terms of the conductivity of the CNT network, if the CNT length is too long, a single CNT is likely to coil into a ring-like shape or become twisted. It also becomes more likely to be bundled, making it difficult to effectively utilize the high surface area and ballistic electrical conductivity of CNTs. Therefore, if the CNT length is too long, the responsiveness and selectivity of the resulting device will decrease. The practical upper limit of the length that can be handled without impairing the CNT properties is 10 μm, with a preferred length being 0.3 nm to 10.0 μm. A more preferred length is 0.4 nm to 5.0 μm, and most preferably 0.5 nm to 3.0 μm. Furthermore, the use of CNTs enables the detection of trace chemical substances even in temperature ranges where oxide semiconductors commonly available as products are not suitable. Because CNTs exhibit electrical responsiveness simply by adhering to trace chemical substances, the electronic device material of the present invention exhibits responsiveness even at temperatures below freezing (−80°C) to 0°C, and the upper usable temperature limit is a temperature at which the CNTs do not burn. When used in an air atmosphere, it can be used up to 500°C, but at higher temperatures, the detection sensitivity decreases due to the effects of thermal vibration. There is no particular limit on the lower limit as long as there is no effect of condensation or freezing. However, when used in air, it is preferable to use it at 0°C or above to avoid the effects of surface condensation. Therefore, the temperature range in which the detection sensitivity is good in air and can be used generally is 0°C to 200°C. From the perspective of ease of use in device fabrication, it can be used with good sensitivity even at 0°C to 100°C.

[0031] Furthermore, when the material for electronic devices of the present invention is used as a sensor material for detecting chemical substances, the change in electrical signal can be read simply by the attachment and desorption of chemical substances, and therefore the material also exhibits good repeatability. The temperature range in which the repeatability is good must be changed depending on what is being detected, as the adsorption strength of the CNT varies depending on the chemical substance being detected, but good repeatability is mainly exhibited in the temperature range of 0°C to 200°C or less.

[0032] While there are no particular limitations on the applications of the electronic device material of the present invention, its use as a sensor material is preferred. It is particularly preferred that the electronic device material be a gas sensor. When the electronic device material of the present invention is used in sensor materials, sensor elements, and gas sensors, the gas selectivity of the material itself allows for the elimination of gas selection functions that rely on peripheral equipment, which is advantageous in that it leads to improved productivity. Furthermore, the use of CNTs enables the development of low-power sensors, and furthermore, the nanostructured n-type semiconductor allows for the nanosizing of materials, thereby enabling the miniaturization of sensors. Furthermore, the electronic device material of the present invention allows for the combination of p-type and n-type semiconductor materials, which does not require large-scale facilities such as clean rooms, and therefore significantly simplifies the sensor manufacturing process. For example, it is possible to manufacture a sensor element by printing a CNT ink and a tin oxide nanocrystal ink separately onto a substrate. When the electronic device material of the present invention is used as a sensor material, as described above, simply attaching a chemical substance to the CNT causes an electrical change corresponding to the amount of attached chemical substance, so the material can be used to detect chemical substances even in an environment with 0% oxygen. As long as the oxygen concentration in the environment is constant, the material can be used regardless of the oxygen concentration, even in a range greater than 0% and less than 50%.

[0033] When the material for electronic devices of the present invention is used as a sensor element, there are no particular restrictions on the substrate to be used, and glass, quartz, silicon with an oxide film, metal oxide, sintered ceramic, resin film, etc. can be used. When the material for electronic devices of the present invention is used as a sensor element, the basic structure is defined by attaching a metal electrode to the material for electronic devices of the present invention. As the metal electrode, a conventionally known electrode can be used as it is. Examples of such a metal electrode include gold, platinum, silver, aluminum, nickel, chromium, and copper. When the electronic device material of the present invention is used as a sensor element, there is no restriction on the spacing between the metal electrodes, as long as it is large. However, a narrower spacing is preferable, as it allows for device miniaturization. Using the electronic device material of the present invention, elements with an electrode spacing of 0.1 to 1,000 μm can be prepared. In a preferred embodiment, elements with an electrode spacing of 0.1 to 100 μm can be prepared, preferably 0.1 to 100 μm, more preferably 0.1 to 10 μm, and even more preferably 0.1 to 5 μm. The narrower the electrode spacing, the less noise is introduced, making it suitable for more sensitive sensor elements and gas sensors (detecting trace amounts of chemical substances). Furthermore, a comb-like electrode shape is also preferred to increase detection sensitivity. [Example]

[0034] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples. [Example] (Preparation of CNT / semiconductor polymer composite dispersion) To prepare the CNT / semiconducting polymer composite dispersions used in Example 1, Example 2, and Comparative Example 1, first, aqueous solutions of semiconducting CNT with purities of 90% by mass and 94% by mass were prepared using CNTs manufactured by NoPo Nanotechnologies India Private Limited using the method disclosed in Japanese Patent Application Laid-Open No. 2012-36041. The prepared semiconducting CNT aqueous solution was filtered using 0.1 μm filter paper, washed on the filter paper with approximately 200 mL of methanol, and then washed with approximately 200 mL of water to remove excess surfactant. Finally, the water was replaced with methanol, and the solution was dried to remove the solvent, yielding semiconducting CNTs. 1.5 mg of the resulting semiconducting CNTs and 1.5 mg of the semiconducting polymer F8BT (poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)]; Sigma-Aldrich) were added to 15 mL of chloroform and subjected to ultrasonic stirring for 30 minutes at 250 W using an ultrasonic homogenizer (Tokyo Rikakikai Co., Ltd. VCX-500) while cooling on ice. This resulted in CNT / semiconducting polymer composite dispersion A (CNT / semiconducting polymer composite concentration relative to the solvent: 0.1 g / L, semiconducting CNT purity: 90% by mass) and CNT / semiconducting polymer composite dispersion B (CNT / semiconducting polymer composite concentration relative to the solvent: 0.1 g / L, semiconducting CNT purity: 94% by mass). Next, this dispersion was diluted with chloroform to produce CNT / semiconducting polymer composite solutions A and B with a CNT composite concentration of 0.625 mg / L.

[0035] (Preparation of tin oxide nanocrystallite-forming solution) The tin oxide nanocrystallite forming solution was prepared by dissolving SnF2 (manufactured by Wako Pure Chemical Industries, Ltd., mass number 156.71 g, purity 90.0%) in distilled water at 90°C to a concentration of 5 mM. (Preparation of nano-tin oxide particle ethanol dispersion) Tin(IV) oxide powder (Kanto Chemical Co., Ltd.: average particle size 15.9-136.7 nm (D BET )) 100 mg was mixed with 15 mL of ethanol in a 20 mL glass vial, and the mixture was subjected to ultrasonic irradiation for 60 minutes using an ultrasonic bath (Bransonic (CPX2800H-J)), and then allowed to stand at room temperature for 48 hours. The supernatant was used as a dispersion of nano-tin oxide microparticles in ethanol.

[0036] (Fabrication of sensor element) <Sensor element I> A Metrohm DropSense interdigitated electrode substrate (platinum electrode / 10 μm line gap / glass substrate) was completely immersed in the prepared tin oxide nanocrystallite-forming solution at a 45° angle relative to the liquid surface (upper surface). The electrode surface was oriented downward. The temperature of the tin oxide nanocrystallite-forming solution was maintained at 90°C, and a tin oxide film was grown on the electrode substrate for 20 minutes. The electrode substrate was then removed from the tin oxide nanocrystallite-forming solution, washed with running water, and allowed to dry at room temperature. Using a pipette, 25 μL of CNT / semiconductor polymer composite solution A with a CNT concentration of 0.625 mg / L was dropped onto the electrode substrate on which the tin oxide film had been grown so as to cover the entire interdigitated electrode, and the solution was dried at 60°C for 30 minutes in a nitrogen atmosphere. Next, the tin oxide nanocrystal formation solution was left to stand at 90°C for 20 minutes and then cooled to room temperature to prepare a tin oxide suspension solution in which only tin oxide had grown in the solution. 25 μL of the tin oxide suspension was dropped onto the top surface of the interdigitated electrode of an electrode substrate coated and dried with CNT / semiconductor polymer composite solution A, covering the entire surface. This was then dried at 90°C for 30 minutes under a nitrogen atmosphere to produce sensor element I. A schematic diagram of the fabricated sensor element is shown in Figure 1. Sensor element I consists of a glass substrate 1 with a 10 μm line gap, a interdigitated platinum electrode 2, a nanostructured tin oxide layer 3 on the platinum electrode 2, a CNT / semiconductor polymer composite layer 4 on the tin oxide layer 3, and a nanostructured tin oxide layer 4 on the CNT / semiconductor polymer composite layer 4.

[0037] <Sensor element II> A Metrohm DropSense interdigitated electrode substrate (gold electrode / 10 μm line gap / glass substrate) was completely immersed in the prepared tin oxide nanocrystallite-forming solution at a 45° angle relative to the liquid surface (upper surface). The electrode surface was oriented downward. The temperature of the tin oxide nanocrystallite-forming solution was maintained at 90°C, and a tin oxide film was grown on the electrode substrate for 2 hours. The electrode substrate was then removed from the tin oxide nanocrystallite-forming solution, washed with running water, and allowed to dry at room temperature. Next, 25 μL of CNT / semiconductor polymer composite solution B with a CNT concentration of 0.625 mg / L was dropped using a pipette onto the electrode substrate on which the tin oxide film had been grown so as to cover the entire interdigitated electrode, and the substrate was dried at 60°C for 30 minutes in a nitrogen atmosphere. The electrode substrate was then completely immersed again in the prepared tin oxide nanocrystallite-forming solution, with the electrode surface facing downward at an angle of 45° relative to the liquid surface (upper surface). The temperature of the tin oxide nanocrystallite-forming solution was maintained at 90°C, and a tin oxide film was grown on the electrode substrate for 30 minutes. The electrode substrate was then removed from the tin oxide nanocrystallite-forming solution, washed with running water, and left to dry at room temperature to produce sensor element II.

[0038] <Sensor element III> On a Metrohm DropSense interdigital electrode substrate (platinum electrode / 10 μm line gap / glass substrate), 25 μL of CNT / semiconductor polymer composite solution A with a CNT concentration of 0.625 mg / L was dropped using a pipette onto the electrode substrate so as to cover the entire interdigital electrode, and the electrode was dried at 60°C for 30 minutes in a nitrogen atmosphere to produce sensor element III.

[0039] <Sensor element IV> A Metrohm DropSense interdigitated electrode substrate (gold electrode / 10 μm line gap / glass substrate) was completely immersed in the prepared tin oxide nanocrystallite-forming solution at a 45° angle relative to the liquid surface (upper surface). The electrode surface was then oriented downward. The temperature of the tin oxide nanocrystallite-forming solution was maintained at 90°C, and a tin oxide film was grown on the electrode substrate for 6 hours. The electrode substrate was then removed from the tin oxide nanocrystallite-forming solution, washed with running water, and allowed to dry at room temperature to produce sensor element IV, which consisted solely of tin oxide.

[0040] <Sensor element V> A Metrohm DropSense interdigitated electrode substrate (gold electrode / 10 μm line gap / glass substrate) was placed on a hot plate heated to 120°C. 25 μL of nano-tin oxide nanoparticle ethanol dispersion was dropped onto the entire surface of the interdigitated electrode using a pipette. This was then dried for 10 minutes at 120°C in a nitrogen atmosphere to form a nano-tin oxide film on the electrode. Next, 25 μL of CNT / semiconductor polymer composite solution B (CNT concentration: 0.625 mg / L) was dropped onto the interdigitated electrode with the nano-tin oxide film formed, completely covering the entire surface. This was then dried for 10 minutes at 120°C in a nitrogen atmosphere to form sensor element V.

[0041] (measurement) Using the fabricated sensor elements I to V and a glass tube 20 having the shape shown in Fig. 2, each sensor element was set in the glass tube 20, and the sensor was exposed to a sample gas prepared so that the oxygen concentration was 20% and the target detection gas had a concentration as described in the following examples. The change in resistance between the interdigitated electrodes was measured at room temperature (25°C) or 50°C. The results are shown in Examples 1 to 3 and Comparative Examples 1 and 2.

[0042] Example 1 Using sensor element I and sensor element III, the responsiveness to 15 ppm of ammonia (NH3) and nitric oxide (NO) was evaluated at room temperature (25°C). Sensor element I of Example 1 is a sensor element in which the semiconductor purity of the CNT is 90 mass%, F8BT is used as the semiconducting polymer of the CNT / semiconducting polymer composite, and tin oxide is used as the n-type semiconductor. The results of Example 1 (sensor element I) are shown in FIGS. Figure 3 shows the results of exposing sensor element I to 15 ppm ammonia gas. The resistance between the interdigital electrodes increased as ammonia gas was introduced, and returned to normal when the supply of ammonia gas was stopped, confirming a clear response to ammonia gas. Furthermore, by combining semiconducting CNTs with a purity of 90 mass% with tin oxide, an n-type semiconductor, a clear increase in response speed was observed compared to the results of the sensor element shown in Comparative Example 1, in which only the CNT / semiconducting polymer composite was formed as a film on the interdigital electrodes (Figure 5). Figure 4 shows the results of exposing sensor element I to 15 ppm of nitric oxide. No change in resistance was observed when nitric oxide was introduced, and only noise was observed, with no responsiveness being observed. In addition, to compare the difference in detection intensity between Figures 3 and 4, the magnitude of the change in resistance value when exposed to a gas compared to the initial resistance value was expressed as the resistance change rate (if the initial resistance value is R0 and the resistance value after exposure to a gas is R, the resistance change rate = R0 / R or R / R0; when the resistance change rate = 1, there is no change and therefore no detection), and the results of evaluating the magnitude of the resistance change rate as the detection ability of the element material for each gas are shown in Figure 7. It can be clearly seen that there is a resistance change when exposed to ammonia, but no resistance change when exposed to nitric oxide.

[0043] Example 2 Using sensor element II, 400 ppb of ammonia (NH3), methane (CH4), toluene (C6H5CH3), cyclohexane (C6H 12 ) and responsiveness to nitric oxide (NO) were evaluated at room temperature (50°C). Sensor element II of Example 2 is a sensor element in which the semiconductor purity of the CNT is 94 mass%, F8BT is used as the semiconducting polymer of the CNT / semiconducting polymer composite, and tin oxide is used as the n-type semiconductor. Figure 8 shows the comparison results of the detection capabilities for each gas. Sensor element II showed a resistance change rate of 1.3 or more for ammonia, but a resistance change rate of 1.1 or less for other gases, demonstrating its ability to selectively detect ammonia gas among various gases.

[0044] Example 3 Using sensor element V, 1 ppm of ammonia (NH3), methane (CH4), toluene (C6H5CH3), cyclohexane (C6H 12 ) and responsiveness to nitric oxide (NO) were evaluated at room temperature (25°C). Sensor element V of Example 3 is a sensor element in which the semiconductor purity of the CNT is 94 mass%, F8BT is used as the semiconducting polymer of the CNT / semiconducting polymer composite, and nano-tin oxide particles are used as the n-type semiconductor. The results of comparing the detection capabilities for each gas are shown in Figure 11. Sensor element V showed a resistance change rate of 1.15 or more for ammonia, but the resistance change rate for other gases was 1.05 or less, demonstrating the ability to selectively detect ammonia gas among various gases.

[0045] (Comparative Example 1) Using sensor element III, the responsiveness to 15 ppm ammonia (NH3) and nitric oxide (NO) was evaluated at room temperature (25°C). Sensor element III does not use an n-type semiconductor, the semiconductor purity of the CNT is 90 mass%, and F8BT is used as the semiconducting polymer in the CNT / semiconducting polymer composite. The results are shown in Figures 5, 6 and 9. Responsiveness to ammonia gas and nitric oxide was measured in the same manner as in Example 1. Figure 5 shows the results of exposing sensor element III to 15 ppm ammonia gas, and the resistance between the interdigitated electrodes increased with the introduction of ammonia gas, indicating responsiveness. FIG. 6 shows the results of exposing sensor element III to 15 ppm of nitric oxide. As nitric oxide was introduced, the resistance value decreased, indicating responsiveness to the gas. The gas detection capabilities of the element materials are as shown in FIG. 9. Although there was a difference in sensitivity to gases in sensor element III, the difference was not as clear as in Example 1.

[0046] (Comparative Example 2) Using sensor element IV, the response to 16 ppm of ammonia (NH3) and nitric oxide (NO) was evaluated at room temperature (50°C). The results are shown in Figure 10. Sensor element IV showed no change in resistance for any of the gases, confirming that gas detection in the low temperature range is not possible using only tin oxide, which is an n-type semiconductor. [Explanation of symbols]

[0047] 1 Base material 2 electrodes 3 n-type semiconductor 4. Semiconducting CNT / semiconducting polymer composite 20 Glass tube

Claims

1. A method for distinguishing between oxidizing chemicals and reducing chemicals, including materials for electronic devices, the electronic device material comprises carbon nanotubes having a purity of 80 mass % or more of the semiconducting carbon nanotubes and an n-type semiconductor; The carbon nanotubes are carbon nanotube composites having a polymer attached to at least a portion of the surface. A sensor element characterized by:

2. The polymer is a semiconducting polymer 2. The sensor element according to claim 1.

3. The n-type semiconductor is a nanostructure.

3. The sensor element according to claim 1 or 2.

4. The n-type semiconductor is an oxide semiconductor. The sensor element according to any one of claims 1 to 3.

5. It is a gas-sensitive substance The sensor element according to any one of claims 1 to 4.

6. The sensor element according to any one of claims 1 to 5 is included. An electronic device characterized by:

7. The sensor element according to any one of claims 1 to 5 is used. A gas sensor characterized by:

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