A suspended palladium nanotube material based on metal contact, preparation method and application

Abstract

The present invention belongs to the field of gas sensors, specifically relating to a metal-contact suspended palladium nano-half-tube material, its preparation method, and its application. A metal-contact suspended palladium nano-half-tube material preparation method comprises the following steps: S1: mixing polyvinyl alcohol and a solvent at a mass ratio of 1 to 2:10, stirring uniformly by magnetic stirring, and degassing to obtain a precursor solution. The precursor solution is electrospun and received using a template to obtain polyvinyl alcohol nanofibers; S2: evaporating metal palladium onto the polyvinyl alcohol nanofibers obtained in S1, and simultaneously evaporating tin oxide onto a substrate. The fibers are then transferred to the substrate via a water vapor dissolution method to obtain a suspended palladium nano-half-tube material. This preparation method enables the low-cost and high-efficiency preparation of 10nm-level thin film groove structures, and can be transferred to any substrate, thus possessing a wide range of potential applications.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensors, and in particular relates to a metal contact-based suspended palladium nano-half-tube material, a preparation method and an application thereof. Background Art

[0002] In recent years, hydrogen (H2) has attracted widespread attention in the energy and environmental fields as a highly efficient energy storage method with high energy density, cleanness, and easy distribution. H2 gas is also used in various industrial applications, including petroleum and glass refining, semiconductor and pharmaceutical manufacturing, H2 cooling systems, and metallurgical processes. Although H2 gas can be used in many industrial applications and fuel cells, since the explosion limit of colorless and odorless H2 gas at room temperature is very low, only 4%, it needs to be continuously monitored for its leakage. Therefore, hydrogen sensors with high response, high selectivity, low cost, low power consumption, and high reliability are necessary to ensure hydrogen safety, among which cost and power consumption are the most important considerations for the practical application of sensors.

[0003] Palladium-based chemiresistor sensors are currently attracting significant attention as reliable, efficient, and highly scalable hydrogen sensors, particularly for their ability to selectively detect hydrogen at room temperature. When H₂ gas molecules come into contact with palladium (Pd), they split into hydrogen atoms on the Pd metal surface and enter the Pd lattice, forming PdHx. This phenomenon causes a change in the Pd's electrical resistance. Because this change is so minute, Pd-based sensors typically exhibit excellent gas-sensing performance only when they possess nanoscale structures. Sensors are primarily fabricated using micro- and nanofabrication processes such as photolithography and MEMS. However, these processes are costly, difficult, and complex, limiting the development and application of Pd-based sensors. Therefore, a low-cost, simple, and high-performance Pd-based sensor fabrication method is urgently needed. Furthermore, material contact (metal / metal, metal / metal oxide) can influence the chemical and electronic properties of the oxide within the first few nanometers, leading to changes in the material's chemical reactivity, electrical conductivity, and energy level arrangement. These effects can alter the oxide's ability to perform its intended function. Therefore, creating conditions where other metals or metal oxides can contact Pd thin films holds promise for improving their gas-sensing properties, enabling their application in hydrogen sensing.

[0004] A nanograting-supported suspended palladium nanotube structure for hydrogen sensing is fabricated using electrospinning, electron beam evaporation, and UV nanoimprinting techniques. Compared to other methods (gas phase, liquid phase, template, and hydrothermal), electrospinning (electrospinning) is a simpler method for preparing one-dimensional nanomaterials. Adjusting the parameters of the electrospinning process allows for flexible adjustment of nanofiber diameter, length, and surface morphology. Electrospinning primarily consists of three components: a high-voltage power supply, a spinneret, and a receiving device. In a high-voltage electrostatic field, charged polymer melts or solutions form Taylor cones under the combined action of the electric field and surface tension. When the electric field force is large enough to overcome the surface tension, ejection, stretching, splitting, solidification, or solvent volatilization occurs to form fibrous substances. Electron beam evaporation is a method of bombarding the coating material with accelerated electrons to heat and evaporate it, forming a film. It can deposit high-purity and high-precision thin films. UV nanoimprinting technology can achieve rapid replication and transfer of micro-nanoscale graphic structures, with the advantages of high resolution, high output, and low cost, and can easily produce 3D structures and structures with high aspect ratios.

[0005] Currently, a phase-change-suppressed Pd nanowire H2 sensor has been developed. Specifically, a 20nm Al2O3 capping layer is deposited on a Si nanograting using an atomic layer deposition system. A Cu sacrificial shadow mask is formed by two oblique-angle depositions using PVD on the Al2O3-coated Si nanograting substrate. This is followed by a forming gas annealing process at 410°C for 40 minutes in an H2+N2 ambient (1:9 ratio). Pd with a chromium (Cr) adhesion layer is then deposited vertically onto the desired nanowire array area using a boost method with a negative photoresist. After removing the PR and SSP layers using photolithography, electrodes are formed by aluminum DC sputtering using another lift-off process. A measurement device was constructed to detect H2 gas responses at varying concentrations in a nitrogen atmosphere. This method achieves highly linear hydrogen sensing by suppressing the Pd phase change through the nanograting's grooves and aluminum oxide contacts.

[0006] However, this method involves photolithography, boosted pressure deposition, and oblique angle deposition, leading to high costs, complex processes, and low efficiency. Furthermore, the gas-sensing test results show that the sensor has a slow response time. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method for preparing a suspended palladium nano-half-tube material based on metal contact, comprising the following steps:

[0008] S1: mixing polyvinyl alcohol and a solvent in a mass ratio of 1 to 2:10, stirring uniformly by magnetic stirring, degassing to obtain a precursor solution, electrospinning the precursor solution, and receiving it using a template to obtain polyvinyl alcohol nanofibers;

[0009] S2: Vapor-depositing metallic palladium on the polyvinyl alcohol nanofibers obtained in S1, and simultaneously vapor-depositing tin oxide on the substrate, and transferring the fibers to the substrate by water vapor dissolution method to obtain a suspended palladium nano-half-tube material.

[0010] Furthermore, the temperature of magnetic stirring in S1 was 65-85 °C, the stirring time was 12 h, and the stirring rate was 600 r·min -1 , degassing rate is 3000r·min -1 , the degassing time is 3 to 5 minutes.

[0011] Furthermore, the pushing speed during the spinning process in S1 was 0.1-0.2 mm·min -1 , the DC voltage is 16-20 kV, the distance between the needle tip and the receiving template is 15-20 cm, and the spinning time is 5-15 min.

[0012] Furthermore, the temperature of the spinning process in S1 is 40° C. and the humidity is 20-30 RH; the template is a rectangular hollow template, and the hollow size is 100 mm*20 mm.

[0013] Furthermore, the metal palladium in S2 is 10 nm and the coating rate is 0.8 nm / min.

[0014] A suspended palladium nanometer half-tube material based on metal contact, wherein the suspended palladium nanometer half-tube material is a half-tube structure.

[0015] The invention discloses an application of a suspended palladium nanometer half-tube material based on metal contact, wherein the suspended palladium nanometer half-tube material is applied in the preparation of a hydrogen sensor.

[0016] Beneficial effects

[0017] (1) The present invention provides a metal contact-based suspended palladium nanotube material, preparation method and application, using PVA nanofiber as a sacrificial template and proposing a water vapor transfer method to achieve low-cost and high-efficiency preparation of 10nm-level thin film groove structures, which can be transferred to any substrate and has rich potential applications.

[0018] (2) The present invention provides a suspended palladium nano-half-tube material based on metal contact, a preparation method and an application thereof, which utilizes the half-tube and suspension structure to increase the specific surface area of ​​the palladium film, while reducing the inhibition of the base material on the palladium-hydrogen reaction expansion process to increase the response speed.

[0019] (3) The present invention provides a suspended palladium nanotube material based on metal contact, a preparation method and an application thereof. For the first time, metal oxide is used as a base material in contact with a metal semi-tube to influence the chemical and electronic properties in the gas sensing process, thereby causing changes in the chemical reactivity, electrical conductivity and energy level arrangement characteristics of the metal and the metal oxide. These influences can change the gas sensing performance of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following is a brief introduction to the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other relevant drawings can be obtained based on these drawings without creative work.

[0021] In the picture:

[0022] Figure 1 A schematic diagram and process flow chart of the palladium half-tube hydrogen sensor of the present invention;

[0023] Figure 2 This is a process flow chart for preparing the nanowire substrate of the present invention;

[0024] Figure 3 This is the SEM image of the front and back palladium half tubes transferred onto the silicon substrate of the present invention;

[0025] Figure 4 This is an SEM image of a palladium half-tube supported by nanowires of the present invention;

[0026] Figure 5 Graph showing the resistance response of the sensor of the present invention to 1% and 0.1% hydrogen at room temperature. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments 1-3 of the present invention and the attached Figures 1 to 5 The present invention clearly and completely describes the technical solution of the present invention. It is obvious that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] The present invention provides a method for preparing a suspended palladium nano-half-tube material based on metal contact, comprising the following steps:

[0029] S1: First, polyvinyl alcohol and deionized water are mixed and stirred thoroughly with a magnetic stirrer to obtain a precursor solution after degassing. The precursor solution is electrospun and received by a rectangular hollow template to obtain uniform polyvinyl alcohol nanofibers with an oriented structure;

[0030] S2: Palladium is deposited onto the polyvinyl alcohol nanofibers obtained in S1, while tin oxide is simultaneously deposited onto a substrate. The fibers are then transferred to the substrate via a water vapor dissolution method to produce a suspended palladium nanotube material. Due to the directional nature of electron beam evaporation, a semi-tube structure can be formed on the nanofiber surface, resulting in a suspended palladium nanotube material based on metal contacts.

[0031] Example 1

[0032] S1: 1 g of 1788 polyvinyl alcohol was mixed with 10 mL of deionized water and stirred thoroughly with a magnetic stirrer at 65 °C for 12 h at a stirring rate of 600 r / min. -1 , degassing rate is 3000r·min -1 , the degassing time is 3min; the precursor solution is electrospun, and the pushing speed during the spinning process is 0.1mm·min -1 The DC voltage was 16 kV, the distance between the needle tip and the receiving template was 15 cm, the spinning time was 5 min, the temperature was 40 ° C, and the humidity was 20 RH. A rectangular hollow template was used for receiving, and the size of the hollow part of the rectangular hollow template was 100 mm * 20 mm. Uniform polyvinyl alcohol nanofibers with an oriented structure were obtained.

[0033] S2: Evaporate 10nm of metal palladium on the polyvinyl alcohol nanofibers obtained in S1. Before evaporation, reduce the vacuum degree of the cavity to 5*10 -4 Below, the coating rate is 0.8nm / min, and 10nm tin oxide is evaporated on the nanowire substrate. Before evaporation, the vacuum degree of the chamber is reduced to 5*10 -4 Below, the coating rate is 0.5nm / min, and a nanowire substrate with a tin oxide thin film is obtained, and then the fiber is transferred to the substrate by water vapor dissolution method; due to the directionality of electron beam evaporation, a semi-tube structure can be formed on the surface of the nanofiber to obtain a suspended palladium nano-semi-tube material based on metal contact.

[0034] Combine Figure 1In the present invention, nanofibers are placed on different transfer substrates through polyvinyl alcohol, and the sample is placed in a closed space. A burner filled with 50 to 80 ml of deionized water is placed in the space, heated to 80 to 90°C, and allowed to stand for 24 hours. This step uses water vapor to dissolve the polyvinyl alcohol. Since the semi-tube film is only 5 to 15 nm and has a fragile structure, this method can improve the transfer efficiency and yield compared to dripping and spraying water mist. After dissolution, the nanofibers are removed to form a palladium metal film with a semi-tube structure. The method of this step can transfer the semi-tube to any substrate. Specifically, we have achieved transfer on PET, gold film, PI, silicon wafer, ceramic, fabric and nanowire substrates, which fully demonstrates the versatility of the method.

[0035] Combine Figure 2 The present invention utilizes nanowires with a line width / groove width ratio of 200 / 400 or 200 / 600 as a substrate, which is obtained by nanoimprinting. Specifically, a tackifier, isopropyl alcohol, and an organic UV-curable polymer are sequentially spin-coated onto a 2-inch silicon wafer and then heated to solidify. The PET nanowire template is then imprinted onto the silicon wafer via UV embossing, achieving suspended nanotubes.

[0036] from Figure 3 In the figure, we can see the palladium half-tube structure prepared using the PVA sacrificial template. Figure 3 (a) and Figure 3 (b) shows the front and back of a half-tube structure. The half-tube diameter is approximately 200-300 nm, and the wall thickness is 10 nm. The front view clearly shows the semicircular cross-section of the palladium half-tube structure, while the back view also shows a complete, clear groove shape, demonstrating that this method can fabricate palladium half-tube structures. While the 10 nm wall thickness makes the half-tube relatively fragile, the water vapor transfer method allows for the fabrication of large-scale structures.

[0037] from Figure 4 (a) As can be seen in the figure, the palladium half-tube transferred to the nanowire substrate realizes a suspended structure, similar to a "bridge" shape. Figure 4 (b) In the figure, we can see that the half-tube structure is suspended due to the support of the nanowires. The cantilever beam structure beyond the nanowires will collapse, that is, Figure 4 (b) Enlarged view.

[0038] from Figure 5As can be seen in the gas-sensing test graph, the material's resistance response to 1% and 0.1% hydrogen gas is tested. The material maintains a stable resistance change over dozens of cycles, with a large response value of approximately 12% and a response time of less than 100 seconds. Hydrogen concentrations above 4% pose an explosion risk. The US Department of Energy's performance targets for stationary and automotive hydrogen safety sensors require a concentration detection capability below 4%, with a detection limit of 0.1%. Our material's performance meets these targets, and its simple preparation makes it promising for research and application.

[0039] The suspended palladium nanometer half-tube material obtained by the present invention can be evaporated on a nanowire substrate with 10nm of tin oxide (SnO2) material. Electron exchange and potential barrier changes will occur at the contact interface between palladium and tin dioxide, forming a Schottky junction, which helps to improve gas sensing performance. In the experiment, tin oxide was evaporated on the substrate. Because the substrate is a nanowire, only the tin oxide on the linear portion can contact the palladium half-tube, which will form a structure similar to a parallel circuit, with the palladium half-tube being compared to a wire and the tin oxide nanowire portion being compared to a resistor. Here, the tin oxide is also 10nm tin oxide evaporated using an electron beam. This enhances the complexity of the structure and the contact interface of different substances. At the contact interface, there will be electron movement caused by the difference in potential barrier energy levels, that is, a heterogeneous structure, which helps to improve gas sensing performance.

[0040] The present invention uses a water vapor dissolution method to transfer a palladium half-tube fiber network with an oriented structure onto a nanowire substrate. The two structures are in a cross shape, and conductive silver paste is applied to both ends of the sample (suspended palladium half-tube structure) to form electrodes, which can be made into a hydrogen sensor.

[0041] As for the microstructure, the microstructure of the suspended palladium nanotube material is mainly a palladium half-tube structure film with a thickness of about 10nm placed on a nanowire substrate with a width of 200nm and a gap of 400nm. In the present invention, tin dioxide is evaporated on the substrate. This material has an electronic modulation effect when in contact with the palladium half-tube, which is also helpful for enhancing the gas sensing performance. The half-tube structure is Figure 1 and Figure 3 As can be seen in the image above, the cross-section is a semicircle with a diameter between 200 and 300 nm. This semicircular structure and the 10 nm membrane thickness give it a very high specific surface area. Furthermore, unlike planar structures, the addition of a suspended portion to the nanowire substrate increases the specific surface area and reduces substrate constraints on the semi-tube structure. During gas testing, palladium absorbs hydrogen and expands, reducing substrate constraints and improving gas sensing performance.

[0042] Example 2

[0043] S1: 2 g of 1788 polyvinyl alcohol was mixed with 10 mL of deionized water and stirred thoroughly with a magnetic stirrer at a temperature of 85 ° C, a stirring time of 12 h, and a stirring rate of 600 r min. -1 , degassing rate is 3000r·min -1 , the degassing time is 5min; the precursor solution is electrospun, and the spinning process is carried out at a pushing speed of 0.2mm·min -1 The DC voltage was 20 kV, the distance between the needle tip and the receiving template was 20 cm, the spinning time was 15 min, the temperature was 40 ° C, and the humidity was 30 RH. A rectangular hollow template was used for receiving, and the size of the hollow part of the rectangular hollow template was 100 mm * 20 mm. Uniform polyvinyl alcohol nanofibers with an oriented structure were obtained.

[0044] S2: Evaporate 10nm of metal palladium on the polyvinyl alcohol nanofibers obtained in S1. Before evaporation, reduce the vacuum degree of the cavity to 5*10 -4 Below, the coating rate is 0.8nm / min, and 10nm tin oxide is evaporated on the nanowire substrate. Before evaporation, the vacuum degree of the chamber is reduced to 5*10 -4 Below, the coating rate is 0.5nm / min, and a nanowire substrate with a tin oxide thin film is obtained, and then the fiber is transferred to the substrate by water vapor dissolution method; due to the directionality of electron beam evaporation, a semi-tube structure can be formed on the surface of the nanofiber to obtain a suspended palladium nano-semi-tube material based on metal contact.

[0045] Example 3

[0046] S1: 1.5 g of 1788 polyvinyl alcohol was mixed with 10 mL of deionized water and stirred thoroughly with a magnetic stirrer at a temperature of 70 ° C, a stirring time of 12 h, and a stirring rate of 600 r min. -1 , degassing rate is 3000r·min -1 , the degassing time is 5min; the precursor solution is electrospun, and the spinning process is carried out at a pushing speed of 0.15mm·min -1 The DC voltage was 18 kV, the distance between the needle tip and the receiving template was 17 cm, the spinning time was 10 min, the temperature was 40 ° C, and the humidity was 25 RH. A rectangular hollow template was used for receiving, and the size of the hollow part of the rectangular hollow template was 100 mm * 20 mm. Uniform polyvinyl alcohol nanofibers with an oriented structure were obtained.

[0047] S2: Evaporate 10nm of metal palladium on the polyvinyl alcohol nanofibers obtained in S1. Before evaporation, reduce the vacuum degree of the cavity to 5*10 -4Below, the coating rate is 0.8nm / min, and 10nm tin oxide is evaporated on the nanowire substrate. Before evaporation, the vacuum degree of the chamber is reduced to 5*10 -4 Below, the coating rate is 0.5nm / min, and a nanowire substrate with a tin oxide thin film is obtained, and then the fiber is transferred to the substrate by water vapor dissolution method; due to the directionality of electron beam evaporation, a semi-tube structure can be formed on the surface of the nanofiber to obtain a suspended palladium nano-semi-tube material based on metal contact.

[0048] The present invention provides a suspended palladium nanotube material based on metal contact. The unique structural design of the suspended palladium nanotubes significantly increases the specific surface area. By utilizing the semi-tubes and suspended structure, the contact area with gas molecules is effectively increased, thereby enhancing the reaction rate and further improving sensor performance. By reducing the inhibitory effect of the substrate material on the palladium film, the present invention can increase the expansion response speed of the palladium film during the hydrogen reaction. This improvement enables the sensor to quickly respond to changes in dynamic environments, making it suitable for real-time monitoring and control.

[0049] The present invention provides a method for preparing a suspended palladium nano-half-tube material based on metal contact. The preparation method uses metal oxide as a base material in contact with the palladium half-tube. By adjusting the interface properties of the metal and the metal oxide, the chemical reactivity and conductivity of the sensor can be effectively changed. This design not only improves the sensitivity of the gas sensor, but also improves the response speed, especially in the detection of low-concentration gases. The water vapor transfer method is combined with PVA nanofibers as a sacrificial template to achieve low-cost and high-efficiency preparation of 10nm-level thin film groove structures. This method not only reduces the production steps, but also reduces material consumption, and has good industrialization prospects. Through the contact between the metal and the metal oxide, the energy level arrangement characteristics of the material can be adjusted, and the transmission characteristics of the charge carriers at the interface can be optimized. This change helps to improve the efficiency of electronic devices and provides new ideas for subsequent integrated circuit and sensor designs.

[0050] The present invention provides an application of a suspended palladium nanotube material based on metal contact. This suspended palladium nanotube material can be transferred to a variety of substrates, making it have broad application potential in fields such as sensors and catalysts, especially in gas detection, environmental monitoring, and safety protection.

Claims

1. A method for preparing a suspended palladium nanotube material based on metal contact, characterized in that: The following steps are involved: S1: PVA and solvent are mixed at a mass ratio of 1 to 2:10, stirred evenly by magnetic stirring, and degassed to obtain a precursor solution, which is then electrospun onto a hollow template with a size of 100 mm*20 mm to obtain PVA nanofibers. S2: 10nm of metallic palladium was evaporated on the polyvinyl alcohol nanofibers obtained in S1, and 10nm of tin oxide was evaporated on the nanowire substrate to form a Schottky junction interface. The fibers were transferred to the nanowire substrate by water vapor dissolution to obtain a suspended palladium nano-half-tube material; the coating rate was 0.8nm / min.

2. The method for preparing a suspended palladium nano-half-tube material based on metal contact according to claim 1, characterized in that: The magnetic stirring temperature in S1 was 65-85 °C, the stirring time was 12 h, and the stirring rate was 600 r·min -1 , degassing rate is 3000r·min -1 , the degassing time is 3 to 5 minutes.

3. The method for preparing a suspended palladium nano-half-tube material based on metal contact according to claim 1, characterized in that: The pushing speed during the spinning process in S1 is 0.1-0.2 mm·min -1 , the DC voltage is 16-20 kV, the distance between the needle tip and the receiving template is 15-20 cm, and the spinning time is 5-15 min.

4. The method for preparing a suspended palladium nano-half-tube material based on metal contact according to claim 1, characterized in that: The temperature of the spinning process in S1 was 40°C and the humidity was 20-30RH.

5. A metal contact-based suspended palladium nano-half-tube material obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The suspended palladium nanometer half-tube material is a half-tube structure.

6. The use of a metal contact-based suspended palladium nano-half-tube material according to claim 5, characterized in that: The suspended palladium nano-half-tube material is used in preparing a hydrogen sensor.

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