A layer structure for gas sensitive detection and preparation method thereof

Abstract

The present invention relates to a layer structure for gas sensitive detection, which includes: a sensing layer capable of changing its own electrical properties based on contact and sensing reaction of the gas to be detected; a catalyst layer for accelerating the process of changing its own electrical properties when the sensing layer undergoes a sensing reaction; a double-pass AAO nanotube for providing a carrier required for the deposition of the sensing layer and the catalyst layer and transmitting the electrical parameters of the sensing layer; the sensing layer and the catalyst layer are sequentially deposited on the inner wall of the double-pass AAO nanotube, wherein a portion of catalyst particles made of the same material as the catalyst layer are embedded in the sensing layer in a manner in which the density decreases linearly with increasing depth of the sensing layer. The present invention also deposits catalyst particles in the sensing layer whose density decreases as the distribution of the gas molecules to be detected in the sensing layer gradually decreases from the surface to the interior, so that the time for the sensing reaction of the entire sensing layer is basically consistent, thereby avoiding errors in sensing current measurement caused by different sensing reaction rates at different locations.

Description

Technical Field

[0001] The present invention relates to the field of sensor equipment, and in particular to a layer structure for gas sensitive detection and a preparation method thereof. Background Art

[0002] Gas sensing equipment is a device that converts information such as gas composition and concentration into information that can be used by personnel, instruments, computers, etc. There are various types of gas sensors on the market, which are widely used in civil, industrial, and environmental testing.

[0003] The detection principle of common gas sensors is to convert information related to gas type and concentration into changes in electrical signals. Based on the changes in these electrical signals, the qualitative and quantitative identification and judgment of the gas to be tested in the environment can be achieved, thereby enabling real-time detection, monitoring, and alarm of specific gases.

[0004] Furthermore, with the rapid development of today's society, wireless connectivity, networking, and electronics technologies are becoming increasingly integrated, leading to higher demands for intelligent and user-friendly technologies. Combining gas sensors with wireless connectivity and networking technologies for simultaneous detection and real-time monitoring of toxic gases greatly facilitates timely detection. Therefore, the development of a miniature, reliable, portable, highly sensitive detection system capable of real-time monitoring of various toxic gases is of paramount importance.

[0005] In the prior art, a patent document with publication number CN105900236B discloses a semiconductor sensor device, including: a substrate; a non-suitable seed layer located above the substrate; at least one electrode located above the non-suitable seed layer; and a porous sensing layer directly supported by the non-suitable seed layer and electrically communicating with the at least one electrode, wherein the porous sensing layer defines a plurality of grain boundaries formed by spaced-apart nucleation on the non-suitable seed layer using atomic layer deposition.

[0006] CN102818834B provides a gas sensor that reduces cracks or breakage in a gas sensor element held by a sealing member passing through the inside of a body component, thereby reducing costs. The gas sensor comprises: a plate-shaped gas sensor element (oxygen sensor element); a cylindrical body component that passes the gas sensor element through a through hole and holds it; and a sealing member (powder filling layer) disposed between the inner surface of the body component and the outer surface of the gas sensor element to maintain the airtightness of the gap between the gas sensor element and the body component. The gas sensor comprises a metal filler having a substantially rectangular through hole for the gas sensor element to pass through. The metal filler's own flat surface directly contacts the rear end surface of the sealing member, pressing the sealing member toward the front end. The outer diameter of the metal filler's flat surface is greater than or equal to the outer diameter of the rear end surface of the sealing member. The size of the gap between the inner end of the metal filler's flat surface and the surface of the gas sensor element is less than half the thickness of the gas sensor element.

[0007] The above application document provides a method for detecting gas by using a porous sensing layer to adsorb the gas to be detected and then generate a sensing reaction, especially judging the type of the gas to be detected based on changes in the electrical properties of the sensing layer. Furthermore, in order to increase the sensing rate, catalytic particles are provided on the sensing layer. However, in the prior art, catalytic particles are only provided on the surface of the sensing layer that is easy to generate a sensing reaction with the gas to be detected, and no sensing particles are provided inside the sensing layer. Therefore, when a sensing reaction can also occur inside the sensing layer, there is a time difference between the internal sensing rate and the surface sensing efficiency, which will undoubtedly affect the sensing current during the sensing reaction, and easily cause the sensing current to be reduced or superimposed.

[0008] In addition, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventor studied a large number of documents and patents when making the present invention, but due to space limitations, not all details and contents are listed in detail. However, this does not mean that the present invention does not have the characteristics of these prior arts. On the contrary, the present invention already has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0009] In order to address at least some of the shortcomings of the above-mentioned prior art, the present application provides a layer structure for gas sensitive detection, which includes: a sensing layer, which can change its own electrical properties based on the contact and sensing reaction of the gas to be detected; a catalyst layer, which is used to accelerate the process of changing the sensing layer's own electrical properties when a sensing reaction occurs; a double-pass AAO nanotube, which is used to provide the carrier required for the deposition of the sensing layer and the catalyst layer and transmit the electrical parameters of the sensing layer; the sensing layer and the catalyst layer are deposited in sequence on the inner wall of the double-pass AAO nanotube, wherein a part of catalyst particles made of the same material as the catalyst layer are embedded in the sensing layer in a manner that the arrangement density decreases linearly as the depth of the sensing layer increases. The present invention uses a method of depositing catalyst particles on the surface of the sensing layer and inside the sensing layer to improve the efficiency of the sensing layer in contacting and reacting with the gas molecules to be detected. The density of the catalyst particles is set in a linear decreasing manner from the surface of the sensing layer to the inside of the sensing layer, so that it is arranged in a manner that matches the distribution density of the gas to be detected in the sensing layer and continuously decreases with the depth of the sensing layer. The ratio of the number of catalyst particles to the number of molecules of the gas to be detected per unit space is basically equal, thereby ensuring that the time required for the sensing reaction to occur at different positions on the sensing layer remains equal, reducing the reduction or superposition of electrical property changes caused by different sensing reaction times. Furthermore, the present invention increases the gap between the sensing particles by arranging catalyst particles of different particle size from the sensing particles in the sensing layer, encouraging the gas molecules to be detected to enter the sensing layer for detection, and improving the utilization rate of the sensing particles on the sensing layer.

[0010] Preferably, before depositing the sensing layer and catalyst layer on the inner wall of the double-pass AAO nanotube, the double-pass AAO nanotube is roughened to encourage the sensing layer to be deposited and integrated on the inner wall of the double-pass AAO nanotube in a non-matching manner. The present invention uses erosion or impact grinding to groove or embed holes in the inner wall of the double-pass AAO nanotube, so that the sensing layer and the catalyst layer are not tightly stacked on the inner wall. The presence of the grooves or embedded holes provides an integration foundation for the smooth deposition and integration of the sensing layer and the catalyst layer on the inner wall of the nanotube, allowing the sensing layer and the catalyst layer to be easily integrated.

[0011] Preferably, the sensing particles that make up the sensing layer are deposited in a mismatched manner so that the sensing particles have at least one contact point with other particles on their defined particle boundaries, and the contact points form a wall field that can accommodate the gas molecules to be detected. When the sensing particles are not stacked in a close-fitting manner, the gas molecules to be detected can enter the wall field formed by the sensing particles through the pores between the sensing particles and react with the sensing particles. Under the influence of the wall field, the gas molecules that enter the wall field can maintain contact with the sensing particles and are not easily desorbed from the sensing particles, resulting in sensing interruption and detection failure.

[0012] Preferably, the two ends of the nanotubes of the double-channel AAO nanotubes are connected, and the nanotubes are arranged in a uniform array without gaps between them. When using the double-channel AAO nanotubes with both ends connected to detect the gas molecules to be detected, it can reduce the problems of poor gas fluidity caused by one end being closed and the sensing layer deep in the AAO nanotubes being unable to perform detection work, and greatly improve the detection sensitivity of the detection layer structure of the gas-sensitive detection.

[0013] Preferably, a first conductive plate and a second conductive plate are respectively arranged at both ends of the double-channel AAO nanotubes in the third direction, and the first conductive plate and the second conductive plate are arranged opposite to each other.

[0014] Preferably, a heat conduction layer is arranged in the negative direction of the third direction of the second conductive plate, and a heating layer is arranged in the negative direction of the third direction of the heat conduction layer. The heat conduction layer can transfer the heat generated by the heating layer into the double-channel AAO nanotubes in a uniform conduction manner. By setting a heat conduction layer between the double-channel AAO nanotubes and the heating layer, the rate of heat generated by the heating layer entering the double-channel AAO nanotubes can be controlled, preventing the situation that the detection of the double-channel AAO nanotubes fails due to too rapid temperature change.

[0015] Preferably, a reinforcing layer for enhancing the physical strength of the layer structure is arranged in the negative direction of the third direction of the heating layer. Adding a reinforcing layer (also called a substrate) to the nanosensor can enhance the mechanical strength of the sensor to prevent the three-dimensional nanosensor from being damaged during packaging, transportation and installation.

[0016] Preferably, a blocking layer is deposited at the openings of the double-channel AAO nanotubes without complete closure. The thickness h of the blocking layer matches the diameter R of the double-channel AAO nanotubes. Preferably, the thickness of the blocking layer is set as: R / 10 < h < R / 2; more preferably: the thickness of the blocking layer is set as: R / 4 < h < R / 3. By depositing a blocking layer at least at one end opening of the double-channel AAO nanotubes, the present invention reduces the number of undetected gas molecules to be detected that directly escape from one end opening of the nanotube through the other end opening of the nanotube, and improves the detection sensitivity of the present device.

[0017] Preferably, when the layer structure of the blocking layer detects the gas molecules to be detected, some of the gas molecules to be detected can circulate in a way of forming eddies near the openings inside the tubes of the double-channel AAO nanotubes. The gas molecules to be detected near the nanotube wall form eddies near the blocking layer inside the tube under the action of their own molecular thermal motion and the airflow passing through from the axis position of the nanotube, and perform cyclic sensing at the nanotube openings under the action of the eddies, reducing the problem that only the gas molecules to be detected close to the nanotube wall can be detected, and improving the detection ability of the present device.

[0018] A method for preparing a gas-sensitive detection layer structure, based on the above-mentioned layer structure, sequentially deposits a sensing layer and a catalyst layer with catalyst particles on the inner wall of a roughened double-pass AAO nanotube, wherein the arrangement density of the catalyst particles decreases linearly as the depth of the sensing layer increases.

[0019] The present invention has at least the following advantages:

[0020] 1. High heating efficiency per unit area: The longitudinal heat conduction of AAO is better than the lateral heat conduction, which can make most of the heat be transmitted longitudinally along the nanotubes and reduce the lateral heat loss.

[0021] 2. Achieve higher sensitivity with lower power consumption: Depositing the gas-sensing material on the nanotube walls creates an extremely high surface area, enabling more complete contact with gas molecules and higher sensitivity, reducing the sensor's required operating temperature. Combined with a highly efficient micro-heater, this achieves higher sensitivity with lower power consumption.

[0022] 3. It can improve the sensing ability of the sensor when the concentration of the gas to be detected is low, and increase the probability of the gas molecules to be detected contacting the sensing layer to produce a sensing reaction, thereby amplifying the sensing effect.

[0023] 4. The ability of AAO nanotubes to detect gas molecules outside the tube is increased, thereby improving detection efficiency.

[0024] 5. Reduce the heat loss inside the AAO nanotube, improve energy utilization, and save energy during the detection process;

[0025] 6. By linearly embedding the catalyst particles inside the sensing layer, the overall detection efficiency of the sensing layer is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention;

[0027] Figure 2 It is a circuit connection diagram of the present invention;

[0028] Figure 3 This is a schematic diagram of the inner wall deposition of the double-pass AAO nanotube of the present invention;

[0029] Figure 4 is a longitudinal cross-sectional view of a single nanotube of the present invention;

[0030] Figure 5 is a top view of a single nanotube of the present invention;

[0031] Figure 6 It is a schematic diagram of the gas flow at the pipe mouth of the present invention.

[0032] Reference Signs List

[0033] 100: Layer structure for gas sensitive detection; 101: Layer structure device; 102: First power supply; 103: Second power supply; 104: Resistor; 105: Strengthening layer; 106: Heat conduction layer; 107: Temperature rising layer; 108: Catalytic particles; 109: First conductive plate; 110: Second conductive plate; 111: Sensing layer; 112: Catalytic layer; 113: Sensing particles; 114: Wall field; 115: Double-pass AAO nanotubes; 116: Blocking layer; 117: Eddy current. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings.

[0035] To make the above-mentioned purposes, features, and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0036] In the description of the present invention, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0037] In the description of the present invention, it should be understood that the “first direction” refers to a direction parallel to the axis X, the “second direction” refers to a direction parallel to the axis Y, and the “third direction” refers to a direction parallel to the axis Z.

[0038] like Figure 2 The exemplary embodiment of the layer structure 100 for gas sensitive detection shown includes a layer structure device 101 (shown as being electrically connected to a first power source 102), a second power source 103, and a resistor 104. The first power source 102 and the second power source 103 are DC voltage sources, which are used to maintain the voltage value of the AAO layer structure device 101 and maintain the heating power of the heater, respectively. The resistor 104 is an arbitrary resistor device with a known resistance value. Figure 1The layer structure device 101 shown includes a strengthening layer 105, a heat conduction layer 106, a temperature rising layer 107, a double-pass AAO nanotube 115, a first conductive plate 109, a second conductive plate 110 and a sensing layer 111. The strengthening layer 105 is usually formed by a silicon layer in a silicon crystal. The strengthening layer 105 is used to improve the physical strength of the layer structure 100 of the gas sensitive detection, which is the substrate in this field. The heat conduction layer 106 is located between the temperature rising layer 107 and the second conductive plate 110, and is configured to isolate the heat of the temperature rising layer 107 from being directly conducted to the AAO nanotube, thereby maintaining the heat conduction rate. Preferably, the heat conduction layer 106 can be formed of silicon dioxide (SiO2) or other insulating materials. The temperature rising layer 107 is located between the strengthening layer 105 and the heat conduction layer 106 and is electrically connected to the second power supply 103. The temperature rising layer 107 is a material that can convert electrical energy into thermal energy when current passes through it. The thermal power of temperature-elevating layer 107 is configured so that the heat generated by it is evenly conducted to sensing layer 111 through heat conduction layer 106, achieving a temperature suitable for sensing layer 111 to undergo a change in resistance upon contact with gas. Other suitable materials for forming temperature-elevating layer 107 include silicon dioxide, platinum, and composite materials.

[0039] like Figure 1 In the illustrated AAO layer structure device 101, the double-pass AAO nanotubes 115 are anodic aluminum oxide nanotubes, preferably with a thickness of 100 nm to 100 μm and a pore size of 100 nm to 1 μm. The double-pass AAO nanotubes 115 have a porous honeycomb structure. The nanopores of the double-pass AAO nanotubes 115 are test-tube-like structures, with the lower end closed and the upper end open to the outside world. A sensing layer 111 and a catalyst layer 112 are sequentially deposited on the pore walls of the double-pass AAO nanotubes 115. The sensing layer 111 is preferably SnO2; however, in other embodiments, the sensing layer 111 can also be made of metal oxides such as TiO2 or ZnO. A first conductive plate 109 and a second conductive plate 110, electrically connected to the first power source 102, are disposed on the upper and lower surfaces of the double-pass AAO nanotubes 115, respectively. The first and second conductive plates 109, 110 are disposed at the upper and lower ends of the double-pass AAO nanotubes 115, respectively, so as not to completely cover the surface of the double-pass AAO nanotubes 115. The first conductive plate 109 and the second conductive plate 110 are respectively attached to the surface of the double-pass AAO nanotube 115 and are in series contact with the AAO nanotube. The sensing layer 111 is located on the inner wall of the double-pass AAO nanotube 115. The sensing layer 111 and the double-pass AAO nanotube 115 are integrated in a mismatched manner. This integration method is suitable for the sensing layer 111 to be deposited on the wall of the double-pass AAO nanotube 115 in a spaced-apart, loosely adsorbed manner.

[0040] According to a preferred embodiment, the inner wall of the double-pass AAO nanotube 115 is "roughened" by etching or impact milling to encourage the sensing layer 111 to be deposited on the inner wall of the double-pass AAO nanotube 115. Preferably, "roughening" includes crystallizing the inner wall of the double-pass AAO nanotube 115 or forming certain partitions that separate the oxide of the sensing layer 111.

[0041] According to a preferred embodiment, the first and second conductive plates 109, 110 at the upper and lower ends of the dual-pass AAO nanotube 115 can be composed of any conductive material conceivable by those skilled in the art. Preferably, the first and second conductive plates 109, 110 are formed of titanium and electrically isolated from each other by the dual-pass AAO nanotube 115. The spacing between the first and second conductive plates 109, 110 is defined by the longitudinal length of the dual-pass AAO nanotube 115. The first and second conductive plates 109, 110 have vertically opposed portions, which are designated as the overlapping portions. A heat conduction layer 106 is disposed on the lower surface of the second conductive plate 110. A temperature-raising layer 107 is formed on the lower surface of the heat conduction layer 106, vertically opposing the overlapping portions. A strengthening layer 105 is disposed on the lower surface of the temperature-raising layer 107 to increase the physical strength of the device. Preferably, the area of ​​the strengthening layer 105 is larger than the area of ​​the heat conduction layer 106 and larger than the lateral area of ​​the dual-pass AAO nanotube 115.

[0042] According to a preferred embodiment, the sensing layer 111 is deposited on the inner wall of the double-pass AAO nanotube 115. Due to the extremely high specific surface area of ​​the AAO nanotube, the gas molecules can fully contact the sensing layer 111 and fully react to obtain higher sensitivity. The overlapping portion of the temperature-raising layer 107 and the first conductive plate 109 and the second conductive plate 110 are arranged relative to each other in the longitudinal direction of the double-pass AAO nanotube 115. Since the heat conduction efficiency of the double-pass AAO nanotube 115 along the axial direction is higher than the heat conduction efficiency along its radial direction, the arrangement of the temperature-raising layer 107 and the electrode can achieve better gas sensing sensitivity with lower heat loss. The heat conduction layer 106 acts as an insulating layer. While isolating the temperature-raising layer 107 from the double-pass AAO nanotube 115, it also transmits the heat of the temperature-raising layer 107 to the sensing mechanism in a uniform conduction manner and maintains a constant temperature environment at the location of the double-pass AAO nanotube 115. Preferably, the heat conducting layer 106 can be a layered structure composed of SiO2. To ensure that all heat transferred from the temperature-elevating layer 107 to the double-pass AAO nanotubes 115 is conducted through the heat conducting layer 106, the area of ​​the heat conducting layer 106 is set to be larger than the area of ​​the temperature-elevating layer 107. Preferably, although the number of electrodes is shown as two in this embodiment, the number of electrode plates can also be any number arranged longitudinally opposite each other.

[0043] According to a preferred embodiment, sensing layer 111 is deposited on the roughened inner wall of a double-pass AAO nanotube 115 between first and second conductive plates 109, 110. Sensing layer 111 is in electrical communication with first and second conductive plates 109, 110, enabling current to flow between the first and second conductive plates 109, 110 through sensing layer 111. The thickness of sensing layer 111 is less than the nanotube radius of double-pass AAO nanotube 115. The deposition thickness of sensing layer 111 is determined by the desired thickness of layer structure device 101, ensuring that as many constituent particles of sensing layer 111 as possible are deposited without affecting gas flow through double-pass AAO nanotube 115. Preferably, the deposition material used to form sensing layer 111 can be a metal oxide such as tin dioxide (SnO2), zinc oxide (ZnO), or tungsten trioxide (WO3). Sensing layer 111, first and second conductive plates 109, 110 are connected in series to resistor 104 and first power supply 102.

[0044] According to a preferred embodiment, Figure 3 As shown, the pore wall of the double-pass AAO nanotube 115 is a double-layer deposition structure. Before depositing the catalyst layer 112 on the pore wall of the double-pass AAO nanotube 115, the sensing layer 111 is first deposited on the pore wall of the double-pass AAO nanotube 115. The sensing layer 111 is integrated on the pore surface of the double-pass AAO nanotube 115 in a non-matching manner. On the basis of the sensing layer 111 being integrated on the double-pass AAO nanotube 115 in a non-matching manner, the catalyst layer 112 is further integrated on the surface of the sensing layer 111 in a non-matching manner. The catalyst layer 112 is used to accelerate the reaction rate when the sensing layer 111 adsorbs and reacts with the gas to be detected to improve the detection sensitivity of the layer structure device 101. According to the attached Figure 3 The sensing particles 113 are deposited on the pore walls of the "roughened" double-pass AAO nanotubes 115 in a mismatched and integrated manner. The presence of the sensing particles 113 further causes the catalyst layer 112 to be deposited on the catalyst particles 108 in a further mismatched and integrated manner. The sensing layer 111 is an incompletely fitted structure formed by a plurality of sensing particles 113. Each sensing particle 113 is in contact with at least one other sensing particle 113 on its defined particle boundary, and the space surrounded by multiple contact points is called a wall field 114. The sensing particles 113 are configured to form as many contact points as possible so that the sensing layer 111 can form as many wall fields 114 as possible when deposited. The gas molecules to be detected can contact and react with the sensing particles 113 through the wall field 114, so that the sensing layer 111 can more easily contact and detect the gas molecules to be detected.

[0045] According to a preferred embodiment, "mismatch" means that any one of the integrated sensor particles 113 is surrounded by multiple other sensor particles 113, and the sensor particle 113 has at least one contact point with the other sensor particles 113, and there is also a contact point between two adjacent sensor particles 113 of the other sensor particles 113. The contact points between the sensor particles 113 and the other sensor particles 113 cooperate with the contact points of the adjacent sensor particles 113 to form an incompletely closed wall field 114 surrounded by multiple contact points. Any two adjacent wall fields 114 are separated only by the incomplete closure of the contact points, that is, all the wall fields 114 are interconnected, and the gas molecules to be detected can enter the wall field 114 deep in the sensing layer 111 after passing through multiple sealing frames from the wall field 114 on the surface and generate a sensing reaction with the sensor particles 113. By forming a wall field 114 between the sensing particles 113 for the gas molecules to be detected to enter, the parts of the sensing layer 111 that can contact the gas molecules to be detected are not limited to the surface of the sensing layer 111. The sensing particles 113 near the inner wall of the double-pass AAO nanotubes 115 can also contact the gas molecules to be detected and produce a sensing reaction, thereby improving the utilization rate of the sensing particles 113 in the sensing layer 111.

[0046] According to a preferred embodiment, when the sensing particles 113 sense the gas molecules to be detected that have entered the nanotubes, the sensing particles 113 on the surface of the sensing layer 111 are more likely to contact and sense the gas molecules to be detected than the sensing particles 113 deep in the sensing layer 111. However, a small number of gas molecules to be detected can still pass through the wall field 114 in the sensing layer 111 and enter the deep part of the sensing layer 111. In the absence of the catalytic conditions of the catalyst layer 112, it is difficult for the gas molecules to be detected deep in the sensing layer 111 to react quickly with the sensing particles 113 and be detected. Preferably, the catalyst particles 108 constituting the catalyst layer 112 can be arranged in the double-pass AAO nanotubes 115 in a manner such that part of them are completely embedded in the sensing layer 111 and part of them are deposited on the surface of the sensing layer 111, so that the sensing particles 113 deep in the sensing layer 111 can also effectively sense the gas molecules to be detected. More preferably, the arrangement density of the catalyst particles 108 may decrease linearly as the distance between the sensor particles 113 and the surface of the sensing layer 111 increases.

[0047] According to a preferred embodiment, Figure 5, any single nanotube of the double-pass AAO nanotube 115 is provided with an incompletely closed blocking layer 116 near the tube mouth at at least one end. The blocking layer 116 is formed by re-depositing the sensing particles 113 of the same material as the sensing layer 111. When the two ends of the double-pass AAO nanotube 115 are connected, only the gas molecules near the tube wall of the gas molecules entering the nanotube can contact the sensing layer 111 and undergo a sensing reaction. The rest will pass through the nanotube under the action of its own thermal molecular motion. When the concentration of the gas molecules to be detected is low, the number of gas molecules to be detected that can be adsorbed on the nanotube wall is small, the degree to which the sensing layer 111 adsorbs and undergoes a sensing reaction with the gas molecules to be detected is low, the amplitude of the change in the current passing through the sensing layer 111 is low, and the accuracy of judging whether the gas molecules to be detected are detected based on the voltage drop range of the resistor 104 is low. That is, when gas molecules with a relatively low concentration enter the double-pass AAO nanotube 115, only a small number of gas molecules to be detected close to the nanotube wall can be adsorbed and react with the sensing layer 111, and the remaining majority of gas molecules pass through the double-pass AAO nanotube 115 without reacting with the sensing layer 111. Figure 6 As shown, the blocking layer 116 deposited at the mouth of the double-pass AAO nanotube 115 can, to a certain extent, block some of the gas molecules to be detected between the blocking layer 116 and the inner wall of the nanotube in an incompletely blocking manner when the gas to be detected is about to pass through the mouth of the nanotube, forming a vortex 117. The gas molecules to be detected in the vortex 117 can circulate back and forth near the blocking layer 116, thereby increasing the contact probability between the gas molecules to be detected and the sensing layer 111. The gas molecules to be detected in the vortex 117 are more likely to contact the sensing layer 111 to produce a sensing reaction. When the sensing layer 111 contacts and adsorbs as many gas molecules to be detected as possible, it can change the resistance value of the sensing layer 111 based on the number of molecules to be detected, further changing the voltage drop across the resistor 104 connected in series with the sensing layer 111.

[0048] According to a preferred embodiment, a blocking layer 116 is formed by depositing particles made of the same material as the sensing layer 111. This increases the number and area of ​​the sensing particles 113 capable of detecting the gas molecules to be detected in the lateral direction. This allows the gas to be detected, which is blocked by the blocking layer 116 and cannot enter the double-layer AAO nanotubes for detection, to undergo a sensing reaction with the sensing particles 113 on the blocking layer 116 during the process of contacting and being blocked by the blocking layer 116. The sensing current of the sensing layer 111 also changes when the blocking layer 116 undergoes a sensing reaction, thus resolving the problem that the sensing reaction and detection can only occur within the AAO nanotubes, and further improving the detection sensitivity of the layered structure 100 for gas-sensitive detection.

[0049] According to a preferred embodiment, the blocking layer 116, located at both ends of the double-pass AAO nanotube 115, provides a certain degree of sealing for the nanotube. When heat from the heating layer 107 is transferred to the double-pass AAO nanotube 115 through the heat-conducting layer 106, the heat in the longitudinal direction of the double-pass AAO nanotube 115 does not immediately flow out of the tube orifice and dissipate. The temperature environment within the double-pass AAO nanotube 115 can more quickly reach the temperature conditions required for the sensing reaction. The blocking layer 116 can reduce heat loss within the tube during the sensing reaction, thereby reducing heat loss during the sensing detection process.

[0050] According to a preferred embodiment, the layered structure device 101 is configured to detect the presence of one or more gases in a space, wherein the gases to be detected can be ammonia, methane, carbon monoxide, carbon dioxide, or volatile organic compounds. Due to the microstructure of the gas-sensitive detection layer structure 100, the device can be configured to detect gases in various applications based on the shape of the object being carried: home kitchens, smart devices, automobile exhaust systems, electronic equipment manufacturing workshops, gas stations, gas storage rooms, and any other application that a person skilled in the art can imagine requiring gas detection.

[0051] According to a preferred embodiment, Figure 1 and Figure 2 , the second power supply 103 applies a voltage to the temperature-elevating layer 107. In response to the voltage, the temperature-elevating layer 107 is heated to a temperature that at least matches the resistance of the second power supply 103 and the temperature-elevating layer 107. The temperature generated by the temperature-elevating layer 107 is uniformly conducted through the heat-conducting layer 106 and then transferred to the sensing layer 111 on the double-pass AAO nanotubes 115. During the heating period, the sensing layer 111 is heated by the temperature-elevating layer 107 to a sensing temperature. The sensing temperature is based on at least the properties of the gas to be detected, the sensing temperature of the sensing layer 111, and the temperature at the location of the gas-sensitive detection layer structure 100. For example, the sensing temperature range is 200-300°C. Since the thickness of the sensing layer 111 is at the nanometer level, its distance from the temperature-elevating layer 107 is negligible on a macroscopic basis, even with the presence of the heat-conducting layer 106. Therefore, the temperature-elevating layer 107 can essentially instantly heat the sensing layer 111 to the sensing temperature. Preferably, to achieve the effect of heating a small area, this embodiment provides a folded heating resistance wire. The heating electrode is preferably rectangular. Because the folded heating resistor wire is longer than the heating electrode and much narrower, the heat generated by the heating layer 107 is primarily concentrated on the folded heating resistor wire. This allows for heating of a small area. Since the double-pass AAO nanotubes 115 are porous, their longitudinal thermal conductivity is greater than their transverse thermal conductivity, resulting in less transverse heat loss and higher heating efficiency in the longitudinal direction.

[0052] After the sensing layer 111 is heated to the sensing temperature, the voltage from the first power supply 102 establishes a current through the first conductive plate 109, the sensing layer 111, the second conductive plate 110, and the resistor 104. The value of this current is based on at least the combined resistance of the first conductive plate 109, the sensing layer 111, the second conductive plate 110, and the resistor 104. Since the first conductive plate 109, the sensing layer 111, the second conductive plate 110, and the resistor 104 are connected in series, the currents passing through them are equal. When the gas-sensitive detection layer structure 100 is placed in a space containing or not containing the gas to be detected, the layer structure device 101 and the resistor 104 form a voltage divider circuit, and the voltage drop across the resistor 104 is detected to determine whether the space contains the gas to be detected. Specifically, if the gas to be detected is a reducing gas, as the gas enters and is adsorbed and bound to the sensing layer 111, the resistance of the sensing layer 111 decreases, and the current flowing through it increases. If the gas to be detected is an oxidizing gas, as the gas enters and is adsorbed and bound to the sensing layer 111, the resistance of the sensing layer 111 increases, and the current flowing through it decreases. The current change is monitored by the voltage variation trend across the external circuit detection resistor 104.

[0053] According to a preferred embodiment, the double-pass AAO nanotubes 115 can also be a double-pass honeycomb structure. The preparation method of the double-pass AAO nanotubes 115 is as follows (for details, please refer to CN201710321598.8):

[0054] S1: Select an aluminum sheet with a purity of 5N, cut it into rectangles, and then wash it with deionized water and electrochemically polish it.

[0055] S2: performing secondary anodization on the aluminum sheet after completing step S1;

[0056] S3: After the secondary anodized aluminum sheet is cut again, a gold layer is sprayed on the A side of the aluminum sheet, a circular hole is opened in the plastic film, and then the A side of the aluminum sheet is laminated with aluminum foil and double-sided plasticized using a laminator. The aluminum sheet is fully plasticized, but the aluminum foil is not fully plasticized. The B side of the aluminum sheet is facing the hole in the plastic film, so that the B side is not completely covered by the plastic film, that is, there is a circular hole on the B side that is not plasticized after the plasticization.

[0057] S4: The aluminum oxide layer on the unmolded area of ​​the aluminum sheet B surface after molding is removed with a sodium hydroxide solution, and then the aluminum substrate is removed with a saturated copper chloride solution. The surface of the template with the aluminum substrate removed is then treated with phosphoric acid to remove the barrier layer and expand the pores. Finally, the template is washed with deionized water and dried to obtain a double-pass AAO template.

[0058] S5: HAuCl solution was prepared, and Au nanowires were electrodeposited in a three-electrode system using a platinum electrode as the auxiliary electrode, a calomel electrode as the reference electrode, and the double-pass AAO template prepared in S4 as the working electrode.

[0059] A method for preparing a gas sensitive detection layer structure. The steps are as follows:

[0060] Step 1: The double-pass AAO nanotube 115 is subjected to a "roughening" treatment, and the double-pass AAO nanotube 115 is treated by etching or impact grinding, so that irregular grooves or dents appear on the tube wall of the double-pass AAO nanotube 115.

[0061] Step 2: Deposit nanoscale sensing particles 113 on the inner wall of the double-pass AAO nanotube 115 to form the sensing layer 111. When SnO2 is selected as the sensing particle 113, the specific deposition method is as follows: using tetrakis(dimethylamino)tin as the tin source, open the ALD tin source valve for 300ms, close the tin source pump valve, allow the tin source to remain in the chamber for 30s, and open the ammonia pump valve to purge the chamber for 30s; open the ALD gaseous water source valve for 30ms, close the gaseous water source pump valve, allow the gaseous water to remain in the chamber for 30s, and open the ammonia pump valve to purge the chamber for 5s. In this cycle, the thickness of SnO2 deposited on the inner wall of the double-pass AAO nanotube 115 is 0.1nm. After multiple deposition cycles, a sensing layer 111 film suitable for the diameter of the double-pass AAO nanotube 115 is obtained, and then high-temperature calcination and curing is performed in air.

[0062] Step 3: Distribute catalytic particles 108 on the surface of the sensing layer 111. Preferably, the catalytic particles 108 forming the catalyst layer 112 can be platinum nanoparticles. The specific distribution method is as follows: Immerse the double-pass AAO nanotube 115, on which the sensing layer 111 has been deposited, in a solution containing the catalytic particles 108. Rotate or otherwise move the double-pass AAO nanotube 115 to encourage the catalytic particles 108 to penetrate the inner wall of the double-pass AAO nanotube 115.

[0063] Step 4: Place the double-pass AAO nanotube 115, on which the catalyst layer 112 has been deposited, close to and contact the tetradimethylaminotin solution with its axis perpendicular to the horizontal plane of the tetradimethylaminotin, and use an ammonia pump valve to rinse the contact portion; open the ALD gaseous water source valve for 30ms, close the gaseous water source pump valve, allow the gaseous water to remain at the deposition site at the tube orifice for 30s, and then open the ammonia pump valve to clean the tube orifice for 5s. This cycle can deposit SnO2 with a thickness of 0.1nm at the tube orifice of the double-pass AAO nanotube 115. After multiple cycles, a plugging layer 116 of any target thickness desired by those skilled in the art can be deposited at the tube orifices of the double-pass AAO nanotube 115.

[0064] Step 5: Evaporate the first conductive plate 109 on the upper surface of the double-pass AAO nanotube 115, and evaporate the second conductive plate 110 on the lower surface of the double-pass AAO nanotube 115; the first conductive plate 109 and the second conductive plate 110 have upper and lower vertically opposite parts, and the upper and lower vertically opposite parts are marked as overlapping parts.

[0065] Step 6: Deposit a heat conducting layer 106 on the lower surface of the second conductive plate 110, and ensure that the area of ​​the heat conducting layer 106 matches the area of ​​the temperature rising layer 107. Preferably, the material of the heat conducting layer 106 can be SiO2.

[0066] Step 7: A temperature-raising layer 107 is deposited on the lower surface of heat-conducting layer 106. Temperature-raising layer 107 includes a heater electrode and a resistance wire electrically connected to the heater electrode, with the resistance wire perpendicularly positioned above and below the overlapping portion. Specifically, a metal layer or metal deposit is deposited on the lower surface of heat-conducting layer 106 using thermal evaporation or electron beam evaporation techniques in a high vacuum environment.

[0067] Step 8: Deposit a strengthening layer 105 on the lower surface of the temperature-elevating layer 107. The strengthening layer 105 is used to increase the physical strength of the gas-sensitive detection layer structure 100. Preferably, the strengthening layer 105 can be made of SiO2.

[0068] Step 9: Encapsulating the gas-sensitive detection layer structure 100. Preferably, after the AAO device is cut into any size suitable for its purpose, the AAO device is encapsulated in a ceramic tube using conductive glue.

[0069] According to a preferred embodiment, the double-pass AAO nanotube 115 is different from the traditional AAO nanotube. Both ends of the double-pass AAO nanotube 115 can accommodate the gas to be detected to enter for detection. When the traditional double-pass AAO nanotube is detecting the gas to be detected, there is some ambient gas deposited inside the nanotube itself. When detecting the gas to be detected, it can only rely on the random movement of the gas molecules to be detected to squeeze out the original gas molecules in the nanotube and then enter the inner wall of the nanotube to contact the sensing layer 111. As a result, the rate of the gas molecules to be detected entering the nanotube is relatively low, and the time required for the sensing layer 111 to contact and have a sensing reaction with the gas molecules to be detected is relatively long. At the same time, most of the gas molecules to be detected are adsorbed near the tube orifice of the nanotube, causing the gas molecules to be detected to accumulate at the tube orifice. The sensing layer 111 deposited deep in the nanotube can only adsorb a small amount or cannot adsorb the gas to be detected for sensing reaction. This phenomenon greatly reduces the detection sensitivity of the layer structure 100 for gas sensitive detection. Both ends of the double-pass AAO nanotube 115 can accommodate the gas to be detected to enter, and the gas flow in the nanotube is strong, making it easier for the gas molecules to be detected to enter the nanotube and adsorb and react with the sensing layer 111. The two ends of the double-pass AAO nanotube 115 are connected, and there is no dead end where gas molecule flow is difficult. The gas molecules to be detected can fully contact the sensing layer 111 on the nanotube and perform a sensing reaction.

[0070] According to a preferred embodiment, as Figure 5 , the thickness of the incompletely closed plugging layer 116 is limited by the ratio of the number of gas molecules to be detected that can be accommodated by the eddy current 117 generated under its influence to enter and circulate to the number of gas molecules to be detected that cannot enter the nanotube for detection under the influence of the incompletely closed plugging layer. That is, when the thickness h of the plugging layer 116 reaches the radial radius R of the double-pass AAO nanotube 115, the gas to be detected in the external environment cannot enter the double-pass AAO nanotube 115 for detection. When the thickness of the plugging layer 116 is negligible, it cannot generate an eddy current 117 with sufficient ability to block as many gas molecules to be detected as possible back into the nanotube for detection. Preferably, the thickness of the plugging layer 116 can be set as: R / 10 < h < R / 2; more preferably: the thickness of the plugging layer 116 can be set as: R / 4 < h < R / 3.

[0071] According to a preferred embodiment, in steps two and three, a method of co-depositing catalyst particles 108 with a linearly increasing number of particles added to the tin source solution on the inner wall of the double-pass AAO nanotube 115 in batches can be adopted to form a deposition layer on the inner wall of the double-pass AAO nanotube 115 with a linearly increasing arrangement density of catalyst particles 108 from the deep part near the tube wall to the surface.

[0072] It should be noted that the above-described specific embodiments are illustrative only. Those skilled in the art may devise various solutions based on the disclosure of the present invention, and such solutions fall within the scope of the present invention and are intended to be protected by the present invention. Those skilled in the art should understand that the present description and its accompanying drawings are intended to be illustrative only and are not intended to limit the scope of the claims. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A layer structure for gas sensitive detection, comprising: A sensing layer (111) capable of changing its own electrical properties based on contact and sensing reaction of the gas to be detected; A catalyst layer (112) is used to accelerate the process of changing the electrical properties of the sensing layer (111) when a sensing reaction occurs; Double-pass AAO nanotubes (115) are used to provide carriers required for the deposition of the sensing layer (111) and the catalyst layer (112) and to transfer electrical parameters of the sensing layer (111); The invention is characterized in that the sensing layer (111) and the catalyst layer (112) are sequentially deposited on the inner wall of the double-pass AAO nanotube (115) with the blocking layer (116) deposited at both ends of the tube mouth in an incompletely closed manner, so that some gas molecules to be detected can be circulated and detected at the tube mouth of the double-pass AAO nanotube (115) in a manner that a vortex (117) is formed in the tube near the tube mouth of the double-pass AAO nanotube (115), wherein some catalyst particles (108) with a linearly increasing number of particles made of the same material as the catalyst layer (112) are embedded in the sensing layer (111) by adding a solution of sensing particles (113) and deposited together on the inner wall of the double-pass AAO nanotube (115) in batches in a manner that the arrangement density changes linearly based on the depth of the sensing layer (111).

2. The layer structure according to claim 1, characterized in that Before depositing the sensing layer (111) and the catalyst particles (108) on the inner wall of the double-pass AAO nanotube (115), the double-pass AAO nanotube (115) is roughened to encourage the sensing layer (111) to be deposited and integrated on the inner wall of the double-pass AAO nanotube (115) in a non-matching manner.

3. The layer structure according to claim 2, characterized in that The catalyst particles (108) and the sensing particles (113) constituting the sensing layer (111) are deposited in a mismatched manner; the sensing particles (113) and the catalyst particles (108) have at least one contact point with another particle on their defined particle boundaries, and the contact points form a wall field (114) capable of accommodating gas molecules to be detected.

4. The layer structure according to claim 1, characterized in that The two ends of the double-pass AAO nanotubes (115) are connected, and the nanotubes are arranged in a uniform array without gaps between them.

5. The layer structure according to claim 1, characterized in that A first conductive plate (109) and a second conductive plate (110) are respectively provided at two ends of the double-pass AAO nanotube (115) in the third direction, and the first conductive plate (109) and the second conductive plate (110) are arranged opposite to each other.

6. The layer structure according to claim 5, characterized in that A heat conduction layer (106) is provided in a direction opposite to the third direction of the second conductive plate (110), and a temperature rising layer (107) is provided in a direction opposite to the third direction of the heat conduction layer (106). The heat conduction layer (106) can transfer heat generated by the temperature rising layer (107) to the double-pass AAO nanotube (115) in a uniform conduction manner.

7. The layer structure according to claim 6, characterized in that A strengthening layer (105) capable of enhancing the physical strength of the gas sensitive detection layer structure (100) is provided in a direction opposite to the third direction of the temperature raising layer (107).

8. The layer structure according to claim 1, characterized in that The thickness h of the blocking layer (116) matches the diameter R of the double-pass AAO nanotube (115).

9. The layer structure according to claim 8, characterized in that The thickness h of the blocking layer (116) is set to: R / 10 <h<R / 2。 10. The layer structure according to claim 9, characterized in that The thickness h of the blocking layer (116) is set to: R / 4 <h<R / 3。 11. A method for preparing a gas sensitive detection layer structure, characterized in that: Based on the layer structure described in claim 1, a sensing layer (111) and a catalyst layer (112) with catalyst particles (108) are sequentially deposited on the inner wall of the roughened double-pass AAO nanotube (115), wherein the arrangement density of the catalyst particles (108) changes linearly as the depth of the sensing layer (111) increases.

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