Preparation process of palladium nano-film hydrogen sensor

Abstract

The invention discloses a preparation process of a palladium nano-film hydrogen sensor, and belongs to the field of sensor preparation. The preparation process of the palladium nano-film hydrogen sensor comprises the following steps: step 1, pre-treating an aluminum sheet, and flattening to remove a surface oxide layer; 2, carrying out primary oxidation and secondary oxidation; thirdly, the aluminum oxide layer is subjected to chambering operation, and an aluminum-based negative mold is obtained; step 4, carrying out polymerization and demolding; 5, coating the PMMA nano-column array sample through electron beam evaporation equipment to form a palladium alloy nano-film; step 6, preparing and arranging a microelectrode; 7, completing electrical connection and packaging between the microelectrode and an external circuit; the response value and the response speed of the prepared palladium nano-film hydrogen sensor are remarkably improved, and the situation that the sensor is rapidly aged and breaks down due to embrittlement, cracking or stripping caused by substrate limitation and strong lattice stress is avoided.

Description

Technical Field

[0001] This invention relates to the field of sensor fabrication technology, and in particular to a fabrication process for a palladium nanofilm hydrogen sensor, which is suitable for rapid detection of trace amounts of hydrogen in new energy, chemical, and coal mining fields. Background Technology

[0002] Existing methods for preparing palladium nanofilms can be broadly categorized into the following three types: One method is the template-assisted method, which uses template technology to prepare palladium nanopillar array films. First, an appropriate template material is selected to form the desired pores or micro / nano structures. Then, palladium nanopillars or nanostructures are deposited in the template by techniques such as chemical reduction or electrochemical deposition. Finally, the palladium nanopillar array film is obtained by removing the template (e.g., chemical dissolution or mechanical exfoliation). Although this method can better control the shape and size of the palladium nanopillars, the selection of the template and the removal process may affect the quality and uniformity of the final palladium nanofilm.

[0003] The second method is the self-assembly method, which spontaneously assembles palladium nanoparticles or palladium nanowires into an array structure. Chemical reagents such as surfactants or organic ligands are used to guide the arrangement of palladium nanoparticles or nanowires. This method has the advantages of mild preparation conditions and simple operation, but the structural order and consistency of the palladium nanopillar array are affected by the properties of the material itself and the preparation conditions, which may result in poor reproducibility of the preparation.

[0004] The last method is nano-sculpting, which uses nanoscale processing techniques (such as focused ion beam and electron beam etching) to carve palladium materials to form an array of palladium nanopillars. This method can precisely control the size and arrangement of palladium nanopillars, but the processing is complex, time-consuming, and costly.

[0005] Secondly, existing technologies face many challenges. Firstly, the selection and preparation of templates limit the diversity of material types and structures. Removing the template may damage the nanopillar array, reducing product quality. The process may involve hazardous chemicals, posing environmental and safety risks. Large-scale production may be inefficient and relatively costly. The structural order and uniformity of self-assembly methods depend on subtle changes in the self-assembly process, resulting in poor repeatability and controllability. Sometimes, additional chemical treatment steps are needed to stabilize the structure, increasing complexity. The resulting nanopillar distribution is not compact enough, affecting sensor performance. It is also sensitive to environmental conditions, and the preparation process is easily affected by external factors. Nano-engraving methods are expensive due to the involvement of costly specialized equipment and consumables. The processing is complex, requiring specialized technical support and a high level of operational expertise. The slow production speed makes it difficult to meet the demands of large-scale, rapid production, resulting in significant material loss and low effective material utilization. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and to propose a fabrication process for a palladium nanofilm hydrogen sensor.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A fabrication process for a palladium nanofilm hydrogen sensor includes the following steps: Step 1: After pre-treating the aluminum sheet, flatten it and immerse it in NaOH solution to remove the surface oxide layer; Step 2: Perform primary and secondary oxidation; Step 3: Perform a pore-expanding operation on the alumina layer to obtain an aluminum-based negative mold; Step 4: Perform polymerization and demolding; Place the fluorinated glass vial open in a sealed container, add 1H,1H,2H,2H-perfluorodecyltrichlorosilane to the container, let it stand for a period of time, place the aluminum-based negative mold at the bottom of the vial, add a solution of methyl methacrylate mixed with 2% benzoyl peroxide, sonicate the vial for 10 seconds to remove the air from the nanopores of the aluminum-based negative mold, then tighten the cap of the vial and heat it. When the liquid in the vial becomes viscous, immediately remove it and place it in an ice water bath to cool to room temperature. The glass vial was broken to remove the PMMA. After cutting out the edge areas of the PMMA and aluminum sheet, it was immersed in a 10% sodium hydroxide solution to remove the aluminum substrate, thus obtaining a PMMA nanopillar array. Step 5: Deposit a palladium alloy nanofilm by passing the PMMA nanopillar array sample through an electron beam evaporation device; Step Six: Fabrication and layout of microelectrodes; Step 7: Use cold welding technology to transfer the prepared palladium alloy nanofilm onto a substrate with microelectrodes; complete the electrical connection and encapsulation between the microelectrodes and the external circuit.

[0008] Preferably, in step one, the aluminum sheet pretreatment operation first uses detergent to clean the surface, removes larger grease and dust impurities, rinses it with tap water, then rinses it with Milli-Q water, and then places it in solutions such as Milli-Q water, alcohol and acetone in sequence for 15-20 minutes each, followed by rinsing it with Milli-Q water and drying it with nitrogen. The pretreated aluminum sheet is flattened using a tablet press, and then placed in a 1M NaOH solution at room temperature for 14-20 minutes to remove the surface oxide layer.

[0009] Further, in step one, after the aluminum sheet placed in the NaOH solution at room temperature is taken out, it is rinsed with Milli-Q water and dried again with nitrogen gas before the aluminum sheet polishing work can be carried out; the polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate, the electrode spacing is 4-6cm, the polishing voltage is 16-25V, and the polishing time is 30-40min.

[0010] Preferably, in step two, before the first oxidation, a pre-oxidation of 2-5 minutes is required. Then, a thicker masking layer is applied to the back of the aluminum sheet that does not need to be oxidized and the part of the aluminum sheet that is in contact with air. The sheet is then placed in a 60°C oven and dried for 15-20 minutes. The acidic electrolyte used in the first oxidation is a 0.3M oxalic acid solution, and the oxidation voltage is 36-45V. The oxidation temperature is controlled at 15±2°C using cooling circulating water, and the first oxidation time is 11.5-12.5 hours.

[0011] Furthermore, in step two, after the first oxidation, the aluminum oxide layer formed on the surface of the aluminum sheet will be removed. At this time, a regular groove will be left on the surface of the aluminum sheet. Based on this, a second oxidation will be carried out to obtain a regular porous aluminum oxide layer. The method for removing the primary oxide layer is as follows: Place the aluminum sheet after primary oxidation into a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:1 between phosphoric acid and chromic acid. The reaction temperature is 63℃-68℃, and the reaction time is 6-12 hours, until there is no brown oxide layer residue on the surface of the aluminum sheet and a uniform metallic luster is present. The steps and parameters for the secondary oxidation are the same as those for the primary oxidation.

[0012] Furthermore, in step three, the solution selected for pore expansion is a 5% phosphoric acid solution, and the pore expansion temperature is 32℃-35℃.

[0013] Preferably, in step four, the standing time is 30-40 minutes, the added methyl methacrylate (MMA) solution completely immerses the aluminum-based negative mold, the heating operation is carried out in a water bath at 90°C for 15-20 minutes, after cooling to room temperature, the vial needs to be transferred to a constant temperature oven at 60°C for low-temperature polymerization for 8-12 hours, and then taken out and heated at 100°C for an additional hour to ensure complete polymerization before the PMMA can be taken out.

[0014] Preferably, in step five, the coating chamber of the electron beam evaporation equipment is first cleaned to ensure that there is no dust or impurities before the coating operation begins. During coating, the coating chamber is evacuated to the required working pressure, the electron beam gun is preheated to a suitable temperature, the palladium alloy material is loaded into the crucible for electron beam evaporation, the focal length and energy of the electron beam gun are adjusted, and the palladium alloy material in the crucible is aimed. When the material reaches the evaporation temperature, the electron beam will cause the palladium alloy to gradually evaporate. When the coating reaches the required thickness, the electron beam gun is turned off, the coating chamber is restored to normal pressure, and the sample is removed without damaging it. Specifically, the palladium alloy can be any one of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, or palladium-silver alloy, and the required coating thickness is 10-300nm.

[0015] Preferably, in step six, microelectrodes are fabricated on a silicon substrate using photolithography, and the electrode material is either platinum or gold.

[0016] Preferably, in step seven, the prepared palladium alloy nanofilm is transferred onto a substrate with microelectrodes, and the microelectrodes and the metal wire connection parts are encapsulated with epoxy resin.

[0017] Compared with the prior art, the present invention provides a fabrication process for a palladium nanofilm hydrogen sensor, which has the following beneficial effects: 1. The fabrication process of this palladium nanofilm hydrogen sensor utilizes an anodic aluminum oxide template to provide highly consistent periodic nanopores, enabling the PMMA nanopillar array to have uniform size and spacing, thereby producing palladium nanofilms with consistent dimensions. This represents a significant improvement over the precision that is difficult to achieve with traditional fabrication methods. By adjusting the fabrication conditions of the anodic aluminum oxide, such as voltage, temperature, and electrolyte composition, the diameter, depth, and density of the pores can be precisely controlled, thereby achieving precise control over the PMMA nanopillar array and the final palladium film nanostructure.

[0018] 2. The fabrication process of this palladium nanofilm hydrogen sensor utilizes a palladium nanofilm as the active layer of the hydrogen sensor. The larger the surface area of ​​the palladium nanofilm, the stronger its adsorption capacity for hydrogen and the higher the sensitivity of the sensor. By using nanopore template technology, the surface area of ​​the palladium film can be significantly increased, thereby improving the performance of the hydrogen sensor. Electron beam evaporation coating technology can precisely control the coating thickness and uniformity, reducing material waste. Compared with traditional physical vapor deposition, it has a higher material utilization rate. The combination of anodic aluminum oxide template and electron beam evaporation coating can produce nanofilms at lower temperatures, which can significantly reduce energy consumption and costs compared with traditional methods that require high-temperature processing.

[0019] 3. The fabrication process of this palladium nanofilm hydrogen sensor: The palladium nanofilm can significantly increase the specific surface area of ​​the film, making it easier to detect low concentrations of hydrogen. The response time is shorter and the sensitivity is higher than that of continuous films. However, while the palladium nanofilm possesses excellent properties, it also brings problems such as more difficult processing, poorer consistency, and lower yield. This solution proposes using a periodic nanoporous structure of anodic aluminum oxide as a mold to prepare a PMMA nanopillar array, combined with electron beam evaporation coating technology, to obtain a palladium film with a nanostructure. The palladium nanofilm hydrogen sensor prepared in this way shows a significant improvement in both response value and response speed, an increased detection range, and higher sensitivity to hydrogen. Compared to continuous palladium thin film hydrogen sensors, a significant advantage of the palladium nanostructure is that the intense lattice expansion caused by high concentrations of hydrogen will not adversely affect the sensor performance. That is, it will not become brittle, crack, or peel off due to substrate limitations and strong lattice stress, leading to rapid aging and failure of the sensor. Attached Figure Description

[0020] Figure 1 This is a TEM image showing the morphology of the porous alumina layer after pore expansion in the fabrication process of a palladium nanofilm hydrogen sensor proposed in this invention. Figure 2 TEM images of PMMA nanopillar arrays of different lengths used in the fabrication process of a palladium nanofilm hydrogen sensor proposed in this invention. Figure 3 This is a flowchart illustrating the fabrication process of a palladium nanofilm hydrogen sensor proposed in this invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] Example 1: Refer to Figures 1-3 A fabrication process for a palladium nanofilm hydrogen sensor includes the following steps: Step 1: After pre-treating the aluminum sheet, flatten it and immerse it in NaOH solution to remove the surface oxide layer; Specifically, the aluminum sheet pretreatment operation first uses detergent to clean the surface, removing larger grease and dust impurities. After rinsing with tap water, it is rinsed with Milli-Q water. Then, it is placed in solutions of Milli-Q water, alcohol, and acetone, and sonicated for 15 minutes each. After that, it is rinsed with Milli-Q water and dried with nitrogen. The pretreated aluminum sheet is flattened using a sheet press to ensure surface flatness, which is beneficial for subsequent processing operations. Then it is placed in a 1M NaOH solution and left at room temperature for 14 minutes until the oxide layer is removed. The phenomenon of oxide layer removal is the appearance of uniform bubbles, which activates the surface of the aluminum sheet.

[0024] It should be noted that in the initial state, the surface of aluminum sheets often has a large amount of grease and dust and other impurities attached to it. By cleaning with detergent, the surfactants in the detergent can emulsify and disperse the grease in the water, while the rinsing action of the water flow removes the dust and other impurities. This provides a relatively clean surface base for subsequent fine processing and ensures the stability of the entire manufacturing process and the consistency of product performance.

[0025] Milli-Q water is ultrapure water produced by the Milli-Q ultrapure water system. Rinsing with Milli-Q water thoroughly removes residual trace impurities, ensuring the aluminum sheet surface is in a high-purity, contamination-free state, preparing it for subsequent more precise processing steps. Ultrasonic treatment further enhances the cleaning effect, removing stubborn stains, surface organic matter, and improving surface activity. After ultrasonic treatment, the aluminum sheet surface may retain Milli-Q water, alcohol, acetone, and other solutions. If not rinsed thoroughly, these residual solutions may form on the aluminum sheet surface during subsequent processes. Residues can form on the aluminum sheet, affecting the quality of subsequent surface treatments or forming processes. Nitrogen is an inert gas, stable and drying. Using nitrogen to dry aluminum sheets can quickly remove residual moisture from the surface, preventing the re-adsorption of impurities due to water residue or prolonged contact with air during natural drying. Furthermore, compared to drying methods using hot air, nitrogen drying does not introduce reactive gases such as oxygen that may chemically react with the aluminum sheet, preventing unnecessary oxidation and ensuring the aluminum sheet maintains a good pre-treatment condition for subsequent processing.

[0026] Specifically, after removing the aluminum sheet from the NaOH solution at room temperature, rinse it with Milli-Q water and dry it again with nitrogen to prevent residue from forming on the surface. Then, the aluminum sheet can be polished. The polishing solution is a mixture of perchloric acid and ethanol. The mixture can quickly and effectively remove unevenness, micro-scratches, and oxidation marks on the surface of the aluminum sheet, thereby obtaining a smooth and flat surface and achieving the ideal chemical polishing effect. The polishing temperature is 15±2℃, with temperature control using circulating cooling water. The polishing cathode is a stainless steel plate with a plate spacing of 5cm. The polishing voltage is 20V, and the polishing time is 35min.

[0027] Step 2: Perform primary and secondary oxidation; Specifically, a 3-minute pre-oxidation is required before the first oxidation step to ensure a stronger adhesion of the masking layer applied later. The masking layer is mainly composed of one or more of the following: nitrocellulose, acrylic resin, epoxy resin, and phenolic resin. A thicker masking layer is then applied to the back of the aluminum sheet that does not require oxidation and to the parts of the aluminum sheet that are in contact with air. The sheet is then placed in a 60°C oven and dried for 15 minutes. The acidic electrolyte used in the first oxidation step is a 0.3M oxalic acid solution, which is prepared fresh for use. The oxidation voltage is 40V. The oxidation temperature is controlled at 15±2°C using cooling circulating water. The first oxidation step takes 12 hours. After the first oxidation, a porous alumina layer tens of micrometers thick is formed. This porous alumina layer is removed as a sacrificial layer, leaving regular grooves on the surface of the aluminum sheet. Based on this, a second oxidation is performed to obtain a regular porous alumina layer.

[0028] The method for removing the primary oxide layer is as follows: the aluminum sheet after primary oxidation is placed in a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:1 between phosphoric acid and chromic acid. The reaction temperature is 65℃ and the reaction time is 10h until a bright aluminum sheet layer is obtained. The steps and parameters for the secondary oxidation are the same as those for the primary oxidation: first, a protective layer is applied, and then the secondary oxidation is performed.

[0029] Step 3: Perform a pore-expanding operation on the alumina layer to obtain an aluminum-based negative mold; The well-formed porous alumina layer after secondary oxidation often has pore sizes that do not meet experimental requirements, necessitating pore enlargement experiments. Specifically, a 5% (w / w) phosphoric acid solution was used for pore enlargement at 34°C. An aluminum-based negative mold was then obtained. TEM images of the morphology of the porous alumina layer after pore enlargement are shown below. Figure 1 As shown.

[0030] Step 4: Perform polymerization and demolding; After obtaining the aluminum-based negative mold, the polymer can be molded. The fluorinated glass vial is placed open in a sealed container, and tens of microliters of 1H,1H,2H,2H-perfluorodecyltrichlorosilane are added dropwise to the container. The total amount added depends on the number of vials being modified at the same time. After standing for about half an hour, the vial is taken out. The inner wall of the vial turns into a foggy white color, but this does not affect the polymerization process. The foggy white color will disappear during the heating process of polymerization. Then, an aluminum-based negative mold was placed at the bottom of the vial, and a methyl methacrylate solution containing 2% benzoyl peroxide was added dropwise. Benzoyl peroxide acted as a thermal initiator to generate free radicals. The vial was sonicated for 10 seconds to expel air from the nanopores of the aluminum-based negative mold. The vial was then capped and heated. When the liquid inside the vial became viscous, it was immediately removed and placed in an ice-water bath to cool to room temperature. The glass vial was then broken to remove the PMMA. After cutting out the edge regions of the PMMA and aluminum sheet, the vial was immersed in a 10% sodium hydroxide solution to remove the aluminum substrate, yielding a PMMA nanopillar array. TEM images of PMMA nanopillar arrays of different lengths are shown below. Figure 2 As shown.

[0031] The settling time is 35 minutes. The added methyl methacrylate solution completely submerges the aluminum-based negative mold. The heating operation is carried out in a 90°C water bath for 15 minutes. After cooling to room temperature, the vial needs to be transferred to a 60°C constant temperature oven for low-temperature polymerization for 10 hours. Then, it is taken out and heated at 100°C for an additional hour to ensure complete polymerization before the PMMA can be removed.

[0032] Step 5: Deposit a palladium alloy nanofilm by passing the PMMA nanopillar array sample through an electron beam evaporation device; Clean the coating chamber of the electron beam evaporation equipment to ensure it is free of dust and impurities to avoid degrading the coating quality. Fix the PPMMA microsphere array sample on the sample stage of the electron beam evaporation equipment. Start the electron beam evaporation equipment and evacuate the coating chamber to the required working pressure to reduce the influence of gas molecules. Preheat the electron beam gun to the appropriate temperature so that the electron beam can be emitted stably. Load the palladium alloy material into the crucible for electron beam evaporation. Adjust the focus and energy of the electron beam gun and aim it at the palladium alloy material in the crucible. When the material reaches the evaporation temperature, the electron beam will gradually evaporate the palladium alloy. Use a coating thickness monitoring device to monitor the coating process in real time to ensure that the palladium alloy layer reaches the preset thickness. When the coating reaches the required thickness, turn off the electron beam gun, restore the coating chamber to atmospheric pressure, and remove the sample without damaging it. Specifically, the palladium alloy can be any one of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, or palladium-silver alloy, and the required coating thickness is 10-300nm. In this embodiment, the palladium alloy is specifically a palladium-nickel alloy, and the coating thickness is 100nm.

[0033] Step Six: Fabrication and layout of microelectrodes; First, microelectrodes are fabricated on a suitable silicon substrate using photolithography. Platinum is used as the electrode material, as both platinum and gold have good chemical stability and electrical conductivity. The electrode layout is designed to optimize the hydrogen response characteristics of the palladium alloy thin film, generally using an interlaced microelectrode structure to increase the contact area between the gas and the sensing film.

[0034] Step 7: Use cold welding technology to transfer the prepared palladium alloy nanofilm onto a substrate with microelectrodes; complete the electrical connection and encapsulation between the microelectrodes and the external circuit.

[0035] This step requires ensuring good electrical contact between the palladium alloy film and the microelectrode; then, using fine platinum wires and micro-welding technology, the microelectrode is connected to the external circuit to complete the electrical connection; and epoxy resin is used to encapsulate the microelectrode and the wire connection to protect them from external influences, while ensuring that the sensitive areas of the palladium alloy nanofilm are exposed to fully contact hydrogen gas.

[0036] Example 2: Refer to Figures 1-3 A fabrication process for a palladium nanofilm hydrogen sensor includes the following steps: Step 1: After pre-treating the aluminum sheet, flatten it and immerse it in NaOH solution to remove the surface oxide layer; Step 2: Perform primary and secondary oxidation; Step 3: Perform a pore-expanding operation on the alumina layer to obtain an aluminum-based negative mold; Step 4: Perform polymerization and demolding; Place the fluorinated glass vial open in a sealed container, add 1H,1H,2H,2H-perfluorodecyltrichlorosilane to the container, let it stand for a period of time, place the aluminum-based negative mold at the bottom of the vial, add a solution of methyl methacrylate mixed with 2% benzoyl peroxide, sonicate the vial for 10 seconds to remove the air from the nanopores of the aluminum-based negative mold, then tighten the cap of the vial and heat it. When the liquid in the vial becomes viscous, immediately remove it and place it in an ice water bath to cool to room temperature. The glass vial was broken to remove the PMMA. After cutting out the edge areas of the PMMA and aluminum sheet, it was immersed in a 10% sodium hydroxide solution to remove the aluminum substrate, thus obtaining a PMMA nanopillar array. Step 5: Deposit a palladium alloy nanofilm by passing the PMMA nanopillar array sample through an electron beam evaporation device; Step Six: Fabrication and layout of microelectrodes; Step 7: Use cold welding technology to transfer the prepared palladium alloy nanofilm onto a substrate with microelectrodes; complete the electrical connection and encapsulation between the microelectrodes and the external circuit.

[0037] In step one, the aluminum sheet pretreatment operation first uses detergent to clean the surface, removing larger grease and dust impurities. After rinsing with tap water, it is rinsed with Milli-Q water. Then, it is placed in solutions of Milli-Q water, alcohol, and acetone in sequence and sonicated for 20 minutes each. After that, it is rinsed with Milli-Q water and dried with nitrogen. The pretreated aluminum sheet was flattened using a tablet press and then placed in a 1M NaOH solution at room temperature for 20 minutes to remove the surface oxide layer.

[0038] After removing the aluminum sheet from the NaOH solution at room temperature, rinse it with Milli-Q water and dry it again with nitrogen gas before polishing. The polishing solution is a mixture of perchloric acid and ethanol. The polishing temperature is 15±2℃. The polishing cathode is a stainless steel plate with a plate spacing of 6cm. The polishing voltage is 20V and the polishing time is 40min.

[0039] In step two, a 3-minute pre-oxidation is required before the primary oxidation. Then, a thicker masking layer is applied to the back of the aluminum sheet that does not need to be oxidized and the parts of the aluminum sheet that are in contact with air. The sheet is then placed in a 60°C oven to dry for 20 minutes. The acidic electrolyte used in the primary oxidation is a 0.3M oxalic acid solution, and the oxidation voltage is 40V. The oxidation temperature is controlled at 15±2°C using cooling circulating water, and the primary oxidation time is 12.5 hours.

[0040] After the first oxidation, the aluminum oxide layer formed on the surface of the aluminum sheet is removed, leaving regular grooves on the surface of the aluminum sheet. Based on this, a second oxidation is carried out to obtain a regular porous aluminum oxide layer. The method for removing the primary oxide layer is as follows: the aluminum sheet after primary oxidation is placed in a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:1 between phosphoric acid and chromic acid. The reaction temperature is 65℃ and the reaction time is 12h until a bright aluminum sheet layer is obtained. The steps and parameters for the secondary oxidation are the same as those for the primary oxidation.

[0041] In step three, the solution selected for pore enlargement is a 5% phosphoric acid solution, and the pore enlargement temperature is 34℃.

[0042] In step four, the settling time is 40 minutes. The added methyl methacrylate solution completely submerges the aluminum-based negative mold. The heating operation is carried out in a 90°C water bath for 20 minutes. After cooling to room temperature, the vial needs to be transferred to a 60°C constant temperature oven for low-temperature polymerization for 10 hours. Then, it is taken out and heated at 100°C for an additional hour to ensure complete polymerization before the PMMA can be removed.

[0043] In step five, first clean the coating chamber of the electron beam evaporation equipment to ensure that there is no dust or impurities before starting the coating operation. During coating, the coating chamber is evacuated to the required working pressure, the electron beam gun is preheated to the appropriate temperature, the palladium alloy material is loaded into the crucible for electron beam evaporation, the focus and energy of the electron beam gun are adjusted, and the palladium alloy material in the crucible is aimed. When the material reaches the evaporation temperature, the electron beam will cause the palladium alloy to gradually evaporate. When the coating reaches the required thickness, the electron beam gun is turned off, the coating chamber is restored to normal pressure, and the sample is removed without damaging it. Specifically, the palladium alloy can be any one of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, or palladium-silver alloy, and the required coating thickness is 10-300nm. In this embodiment, the palladium alloy is specifically a palladium-nickel alloy, and the coating thickness is 200nm.

[0044] In step six, microelectrodes are fabricated on a silicon substrate using photolithography, with platinum as the electrode material.

[0045] In step seven, the prepared palladium alloy nanofilm is transferred onto a substrate with microelectrodes, and the microelectrodes and the metal wire connection parts are encapsulated with epoxy resin.

[0046] Example 3: Refer to Figures 1-3 A fabrication process for a palladium nanofilm hydrogen sensor includes the following steps: Step 1: After pre-treating the aluminum sheet, flatten it and immerse it in NaOH solution to remove the surface oxide layer; Step 2: Perform primary and secondary oxidation; Step 3: Perform a pore-expanding operation on the alumina layer to obtain an aluminum-based negative mold; Step 4: Perform polymerization and demolding; Place the fluorinated glass vial open in a sealed container, add 1H,1H,2H,2H-perfluorodecyltrichlorosilane to the container, let it stand for a period of time, place the aluminum-based negative mold at the bottom of the vial, add a solution of methyl methacrylate mixed with 2% benzoyl peroxide, sonicate the vial for 10 seconds to remove the air from the nanopores of the aluminum-based negative mold, then tighten the cap of the vial and heat it. When the liquid in the vial becomes viscous, immediately remove it and place it in an ice water bath to cool to room temperature. The glass vial was broken to remove the PMMA. After cutting out the edge areas of the PMMA and aluminum sheet, it was immersed in a 10% sodium hydroxide solution to remove the aluminum substrate, thus obtaining a PMMA nanopillar array. Step 5: Deposit a palladium alloy nanofilm by passing the PMMA nanopillar array sample through an electron beam evaporation device; Step Six: Fabrication and layout of microelectrodes; Step 7: Use cold welding technology to transfer the prepared palladium alloy nanofilm onto a substrate with microelectrodes; complete the electrical connection and encapsulation between the microelectrodes and the external circuit.

[0047] In step one, the aluminum sheet pretreatment operation first uses detergent to clean the surface, removing larger grease and dust impurities. After rinsing with tap water, it is rinsed with Milli-Q water. Then, it is placed in solutions of Milli-Q water, alcohol, and acetone, and sonicated for 18 minutes each. After that, it is rinsed with Milli-Q water and dried with nitrogen. The pretreated aluminum sheet was flattened using a tablet press and then placed in a 1M NaOH solution at room temperature for 18 minutes to remove the surface oxide layer.

[0048] In step one, after the aluminum sheet placed in the NaOH solution at room temperature is taken out, it is rinsed with Milli-Q water and dried again with nitrogen gas before the aluminum sheet polishing work can be carried out. The polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate with a plate spacing of 4cm, the polishing voltage is 20V, and the polishing time is 30min.

[0049] In step two, a 3-minute pre-oxidation is required before the primary oxidation. Then, a thicker masking layer is applied to the back of the aluminum sheet that does not need to be oxidized and the parts of the aluminum sheet that are in contact with air. The sheet is then placed in a 60°C oven and dried for 15 minutes. The acidic electrolyte used in the primary oxidation is a 0.3M oxalic acid solution, and the oxidation voltage is 40V. The oxidation temperature is controlled at 15±2°C using cooling circulating water, and the primary oxidation time is 11.5 hours.

[0050] In step two, after the first oxidation, the aluminum oxide layer formed on the surface of the aluminum sheet will be removed. At this time, a regular groove will be left on the surface of the aluminum sheet. Based on this, a second oxidation will be carried out to obtain a regular porous aluminum oxide layer. The method for removing the primary oxide layer is as follows: the aluminum sheet after primary oxidation is placed in a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:1 between phosphoric acid and chromic acid. The reaction temperature is 65℃ and the reaction time is 6h until a bright aluminum sheet layer is obtained. The steps and parameters for the secondary oxidation are the same as those for the primary oxidation.

[0051] In step three, the solution selected for pore enlargement is a 5% phosphoric acid solution, and the pore enlargement temperature is 34℃.

[0052] In step four, the settling time is 30 minutes. The added methyl methacrylate solution completely immerses the aluminum-based negative mold. The heating operation is carried out in a 90°C water bath for 15-20 minutes. After cooling to room temperature, the vial needs to be transferred to a 60°C constant temperature oven for low-temperature polymerization for 10 hours. Then, it is taken out and heated at 100°C for an additional hour to ensure complete polymerization before the PMMA can be removed.

[0053] In step five, first clean the coating chamber of the electron beam evaporation equipment to ensure that there is no dust or impurities before starting the coating operation. During coating, the coating chamber is evacuated to the required working pressure, the electron beam gun is preheated to the appropriate temperature, the palladium alloy material is loaded into the crucible for electron beam evaporation, the focus and energy of the electron beam gun are adjusted, and the palladium alloy material in the crucible is aimed. When the material reaches the evaporation temperature, the electron beam will cause the palladium alloy to gradually evaporate. When the coating reaches the required thickness, the electron beam gun is turned off, the coating chamber is restored to normal pressure, and the sample is removed without damaging it. Specifically, the palladium alloy can be any one of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, or palladium-silver alloy, and the required coating thickness is 10-300nm. In this embodiment, the palladium alloy is specifically a palladium-nickel alloy, and the coating thickness is 50nm.

[0054] In step six, microelectrodes are fabricated on a silicon substrate using photolithography, with gold as the electrode material.

[0055] In step seven, the prepared palladium alloy nanofilm is transferred onto a substrate with microelectrodes, and the microelectrodes and the metal wire connection parts are encapsulated with epoxy resin.

[0056] In summary, the performance of the prepared palladium nanofilm hydrogen sensor is significantly improved in all three examples, with the effect in Example 1 being the most significant. The required coating thickness is 10-300 nm, with 50-150 nm being the optimal thickness for the best results.

[0057] This invention features a highly ordered nanostructure: the anodic aluminum oxide template has a periodic pore structure, enabling the production of highly ordered PMMA nanopillar arrays, a level of order that is often difficult to achieve with similar technologies; it also features controllable structural dimensions: by precisely controlling the parameters of anodizing, such as voltage, time, and electrolyte type, the size of the nanopores can be adjusted, thereby achieving precise control over the diameter and spacing of the PMMA nanopillar array; furthermore, due to the perfection of the template and the precision of the electron beam evaporation coating technology, this technology has high reproducibility and can mass-produce palladium films with uniform nanostructures.

[0058] Electron beam evaporation coating technology can precisely control the thickness of palladium alloy films, significantly improving material utilization efficiency. Compared with traditional physical vapor deposition and other technologies, it can significantly reduce material loss. Electron beam evaporation technology can be carried out at relatively low temperatures, which helps protect heat-sensitive materials from damage. This is gentler than similar technologies that require high-temperature conditions.

[0059] This invention prepares a PMMA nanopillar array using an aluminum-based negative mold, and combines electron beam evaporation coating with cold welding transfer to produce a palladium nanofilm hydrogen sensor with a response time of 6-12s in 1-1000ppm H2. It does not exhibit embrittlement or cracking under high concentrations of H2, solving the problems of slow response and poor stability of traditional sensors. It is suitable for hydrogen detection in the fields of new energy and chemical industry.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fabrication process for a palladium nanofilm hydrogen sensor, characterized in that, Includes the following steps, Step 1: After pre-treating the aluminum sheet, flatten it and immerse it in NaOH solution to remove the surface oxide layer; Step 2: Perform primary and secondary oxidation; Step 3: Perform a pore-expanding operation on the alumina layer to obtain an aluminum-based negative mold; Step 4: Perform polymerization and demolding; Place the fluorinated glass vial open in a sealed container, add 1H,1H,2H,2H-perfluorodecyltrichlorosilane to the container, let it stand for a period of time, place the aluminum-based negative mold at the bottom of the vial, add a solution of methyl methacrylate mixed with 2% benzoyl peroxide, sonicate the vial for 10 seconds to remove the air from the nanopores of the aluminum-based negative mold, then tighten the cap of the vial and heat it. When the liquid in the vial becomes viscous, immediately remove it and place it in an ice water bath to cool to room temperature. The glass vial was broken to remove the PMMA. After cutting out the edge areas of the PMMA and aluminum sheet, it was immersed in a 10% sodium hydroxide solution to remove the aluminum substrate, thus obtaining a PMMA nanopillar array. Step 5: Deposit a palladium alloy nanofilm by passing the PMMA nanopillar array sample through an electron beam evaporation device; Step Six: Fabrication and layout of microelectrodes; Step 7: Use cold welding technology to transfer the prepared palladium alloy nanofilm onto a substrate with microelectrodes; complete the electrical connection and encapsulation between the microelectrodes and the external circuit.

2. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step one, the aluminum sheet pretreatment operation first uses detergent to clean the surface, removing larger grease and dust impurities. After rinsing with tap water, it is rinsed with Milli-Q water. Then, it is placed in solutions of Milli-Q water, alcohol, and acetone in sequence and sonicated for 15-20 minutes each. After that, it is rinsed with Milli-Q water and dried with nitrogen. The pretreated aluminum sheet is flattened using a tablet press, and then placed in a 1M NaOH solution at room temperature for 14-20 minutes to remove the surface oxide layer.

3. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 2, characterized in that, In step one, after the aluminum sheet placed in the NaOH solution at room temperature is taken out, it is rinsed with Milli-Q water and dried again with nitrogen gas before the aluminum sheet polishing work can be carried out. The polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate, the electrode spacing is 4-6cm, the polishing voltage is 16-25V, and the polishing time is 30-40min.

4. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step two, before the first oxidation, a pre-oxidation of 2-5 minutes is required. Then, a thicker masking layer is applied to the back of the aluminum sheet that does not need to be oxidized and the part of the aluminum sheet that is in contact with air. The sheet is then placed in a 60℃ oven to dry for 15-20 minutes. The acidic electrolyte used in the first oxidation is a 0.3M oxalic acid solution, and the oxidation voltage is 36-45V. The oxidation temperature is controlled at 15±2℃ using cooling circulating water, and the first oxidation time is 11.5-12.5 hours.

5. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 4, characterized in that, In step two, after the first oxidation, the aluminum oxide layer formed on the surface of the aluminum sheet will be removed. At this time, a regular groove will be left on the surface of the aluminum sheet. Based on this, a second oxidation will be carried out to obtain a regular porous aluminum oxide layer. The method for removing the primary oxide layer is as follows: Place the aluminum sheet after primary oxidation into a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:1 between phosphoric acid and chromic acid. The reaction temperature is 63℃-68℃, and the reaction time is 6-12 hours, until there is no brown oxide layer residue on the surface of the aluminum sheet and a uniform metallic luster is present. The steps and parameters for the secondary oxidation are the same as those for the primary oxidation.

6. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 5, characterized in that, In step three, the solution selected for pore expansion is a 5% phosphoric acid solution, and the pore expansion temperature is 32℃-35℃.

7. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step four, the settling time is 30-40 minutes. The added methyl methacrylate solution completely immerses the aluminum-based negative mold. The heating operation is carried out in a 90°C water bath for 15-20 minutes. After cooling to room temperature, the vial needs to be transferred to a 60°C constant temperature oven for low-temperature polymerization for 8-12 hours. Then, it is taken out and heated at 100°C for an additional hour to ensure complete polymerization before the PMMA can be removed.

8. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step five, first clean the coating chamber of the electron beam evaporation equipment to ensure that there is no dust or impurities before starting the coating operation. During coating, the coating chamber is evacuated to the required working pressure, the electron beam gun is preheated to the appropriate temperature, the palladium alloy material is loaded into the crucible for electron beam evaporation, the focus and energy of the electron beam gun are adjusted, and the palladium alloy material in the crucible is aimed. When the material reaches the evaporation temperature, the electron beam will cause the palladium alloy to gradually evaporate. When the coating reaches the required thickness, the electron beam gun is turned off, the coating chamber is restored to normal pressure, and the sample is removed without damaging it. Specifically, the palladium alloy can be any one of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, or palladium-silver alloy, and the required coating thickness is 10-300nm.

9. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 8, characterized in that, In step six, microelectrodes are fabricated on a silicon substrate using photolithography, with the electrode material being either platinum or gold.

10. The fabrication process of a palladium nanofilm hydrogen sensor according to claim 9, characterized in that, In step seven, the prepared palladium alloy nanofilm is transferred onto a substrate with microelectrodes, and the microelectrodes and the metal wire connection parts are encapsulated with epoxy resin.

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