Integrated optical waveguide hydrogen sensor based on self-assembled metal nanocavity structure and preparation method thereof

Abstract

The present invention relates to an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure, and its preparation method, within the field of photochemical sensor technology. The sensor comprises a hydrogen sensing unit and a SOI optical waveguide structure. The hydrogen sensing unit is sequentially layered from bottom to top with a base layer, a conductive layer, an insulating layer, a hydrogen-sensitive metal layer, and a self-assembled metal nanocavity structure layer. The self-assembled metal nanocavity structure layer comprises a plurality of metal nanocubes arranged on the surface of the hydrogen-sensitive metal layer through a self-assembly process, with gaps between adjacent metal nanocubes. The SOI optical waveguide structure is etched with a recess for mounting the hydrogen sensing unit, which is attached to the SOI optical waveguide structure. This invention improves the sensor's sensitivity to hydrogen, achieving high sensitivity and good optical signal transmission efficiency. It is widely applicable to fields such as environmental monitoring and industrial safety, providing a novel and efficient solution for hydrogen detection.

Description

Technical Field

[0001] The present invention relates to the technical field of photochemical sensors, and in particular to an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure and a preparation method thereof. Background Art

[0002] With the widespread application of hydrogen energy, the safe detection of hydrogen has become an important research direction. At present, common hydrogen sensors mainly include electrochemical sensors, metal oxide semiconductor sensors and optical sensors. Among them, electrochemical sensors are widely used due to their high sensitivity and good selectivity, but they are sensitive to environmental conditions, easily affected by changes in temperature and humidity, and have a limited service life. Metal oxide semiconductor sensors perform well in high temperature environments, but their sensitivity and selectivity are insufficient. Optical sensors usually have higher sensitivity and response speed, but they are expensive and difficult to miniaturize. Therefore, there is an urgent need to develop a new type of hydrogen sensor to overcome the limitations of existing technologies. Summary of the Invention

[0003] In view of the defects in the prior art, the object of the present invention is to provide an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure and a preparation method thereof.

[0004] According to the present invention, an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure includes a hydrogen sensing unit and an SOI optical waveguide structure;

[0005] The hydrogen sensing unit is sequentially provided with a base layer, a conductive layer, an insulating layer, a hydrogen-sensitive metal layer and a self-assembled metal nanocavity structure layer from bottom to top. The self-assembled metal nanocavity structure layer is composed of a plurality of metal nanocubes arranged on the surface of the hydrogen-sensitive metal layer through a self-assembly process, with gaps between adjacent metal nanocubes.

[0006] The SOI optical waveguide structure is etched with a receiving groove for installing the hydrogen sensing unit, and the hydrogen sensing unit is connected to the SOI optical waveguide structure.

[0007] In some embodiments, the material of the metal nanocubes is silver, and the self-assembly process utilizes the induction effect of the interface between the water phase and n-hexane to arrange the metal nanocubes in an orderly manner at the interface.

[0008] In some embodiments, the size of the metal nanocubes is 50-300 nm, and the distance between adjacent silver nanocubes is 10-100 nm.

[0009] In some embodiments, the conductive layer is made of gold, and the thickness of the conductive layer is 10-20 nm.

[0010] In some embodiments, the insulating layer is made of aluminum oxide, and the thickness of the insulating layer is 3-5 nm.

[0011] In some embodiments, the hydrogen-sensitive metal layer is made of palladium or platinum, and the thickness of the hydrogen-sensitive metal layer is 10-20 nm.

[0012] The present invention also provides a method for preparing an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure, comprising the following steps:

[0013] S1, the silicon wafer is used as the base layer, and the silicon wafer is cleaned and dried;

[0014] S2, sputtering a gold film on the silicon wafer obtained in step S1 by magnetron sputtering to form a conductive layer, wherein the thickness of the conductive layer is 10-20 nm;

[0015] S3, exposing the sample obtained in step S2 alternately to an aluminum source gas and an oxygen source gas, and depositing aluminum oxide layer by layer by atomic layer deposition to form an insulating layer with a thickness of 3-5 mm;

[0016] S4, depositing a palladium film on the insulating layer of the sample obtained in step S3 by magnetron sputtering to form a hydrogen-sensitive metal layer, wherein the thickness of the hydrogen-sensitive metal layer is 10-20 nm;

[0017] S5, mixing a silver nitrate solution with ascorbic acid, using polyvinyl pyrrolidone as a stabilizer to prepare silver nanocubes, and then utilizing the induction effect of the interface between the aqueous phase and n-hexane to orderly arrange the silver nanocubes at the interface and self-assemble them on the hydrogen-sensitive metal layer to form a self-assembled metal nanocube structure layer;

[0018] S6, drying the sample prepared in step S5 to obtain a sensor unit;

[0019] S7, depositing silicon dioxide on a silicon wafer to obtain an SOI optical waveguide structure, forming a receiving groove on the SOI optical waveguide structure through photolithography and dry etching processes, and bonding and fixing the sensor unit obtained in step S9 into the receiving groove of the SOI optical waveguide structure to form an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure.

[0020] In some embodiments, the specific steps of preparing silver nanocubes and arranging them on the hydrogen-sensitive metal layer using a self-assembly process in step S5 include:

[0021] S5-1, adding 0.1 wt% polyvinyl pyrrolidone solution to 50 mL of 0.1 M silver nitrate solution and stirring uniformly, then slowly adding 5 mL of 0.1 M ascorbic acid solution while stirring to carry out mixing reaction. After the mixing reaction lasts for 30-60 minutes, the reaction mixture is placed in an ice bath, and then the synthesized silver nanocube solution is centrifuged and washed with deionized water to remove unreacted raw materials and by-products. The washed silver nanocubes are then suspended in deionized water to obtain a silver nanocube suspension of a predetermined concentration;

[0022] S5-2, placing the silver nanocube suspension prepared in step S5 in an ultrasonic bath for uniform dispersion treatment, then adding polyvinyl pyrrolidone to the silver nanocube suspension and stirring evenly, wherein the mass of the added polyvinyl pyrrolidone is 1-5% of the mass of the silver nanocubes;

[0023] S5-3, pouring a predetermined amount of n-hexane into the solution prepared in step S6 to form an interface between the aqueous phase and the n-hexane phase, and inducing self-assembly of the silver nanocubes at the interface between the two phases;

[0024] S5-4, placing the sample prepared in step S4 into the aqueous liquid containing silver nanocubes prepared in step S7 from the side with the palladium film facing upward, and then scooping up the sample prepared in step S4 by clamping one end. During the scooping process, the silver nanocubes will be supported by the surface tension of water on the surface of the palladium film to form a self-assembled metal nanocavity structure layer.

[0025] In some embodiments, the size of the metal nanocubes is 50-300 nm, and the distance between adjacent silver nanocubes is 10-100 nm.

[0026] In some implementations, in step S7, the sensor unit is bonded to the receiving groove of the SOI optical waveguide structure using a polyvinyl alcohol solution as an adhesive.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The self-assembled metal nanocavity structure of the integrated optical waveguide hydrogen sensor fabricated by this invention utilizes the adsorption and dissociation reaction of hydrogen by a palladium metal film, combined with the metal nanocavity formed by silver nanocubes. The gaps between the silver nanocubes excite the surface plasmon effect, utilizing the principle of gapped surface plasmons (GAP-SPP). This enhances the local electric field and improves the response of hydrogen molecules. The hydrogen sensor is also integrated into the optical waveguide using a SOI optical waveguide structure. The total internal reflection principle of the SOI optical waveguide effectively controls the propagation path of the optical signal, improving signal transmission efficiency. The optical signal is guided to the sensing area, and changes in the optical signal are monitored to accurately detect hydrogen concentration. This improves the sensor's sensitivity to hydrogen. The sensor boasts high sensitivity and excellent optical signal transmission efficiency, making it widely applicable to fields such as environmental monitoring and industrial safety, providing a novel and efficient solution for hydrogen detection.

[0029] 2. In the self-assembled metal nanocavity structure of the integrated optical waveguide hydrogen sensor fabricated by this invention, the size and spacing of the metal nanocubes significantly influence performance. The size of the metal nanocubes determines the sensor's response range to light signals of a specific wavelength. Larger cubes excite surface plasmons with longer wavelengths, helping to match the desired wavelength. The spacing between nanocubes directly influences sensitivity: smaller spacing enhances the local electric field, improving hydrogen molecule detection sensitivity, while smaller spacing reduces sensitivity. By optimizing the size and spacing of the metal nanocubes, the sensor can precisely adjust its wavelength range and sensitivity to meet diverse application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0031] Figure 1 Schematic diagram of a hydrogen sensing unit of the present invention, wherein a gold film is magnetron sputtered on a silicon wafer;

[0032] Figure 2 Yes Figure 1 Schematic diagram of atomically deposited aluminum oxide film;

[0033] Figure 3 Yes Figure 2 Schematic diagram of magnetron sputtering of palladium metal film;

[0034] Figure 4 1 is a schematic top view of the hydrogen sensing unit of the present invention;

[0035] Figure 5 is a cross-sectional schematic diagram of a hydrogen sensing unit of the present invention;

[0036] Figure 6 Yes Figure 5 Schematic diagram of the cross section after transfer to the optical waveguide structure. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0038] This embodiment provides an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure. The sensor primarily comprises an SOI optical waveguide structure 2 and a hydrogen sensing unit 1 connected to the SOI optical waveguide structure 2. The hydrogen sensing unit 1 utilizes a silicon wafer as a base layer 11, upon which a conductive layer 12, an insulating layer 13, a hydrogen-sensitive metal layer 14, and a metal nanocavity structure layer 15 are sequentially layered. The SOI optical waveguide structure 2 utilizes a silicon (Si) substrate with a silicon dioxide layer formed thereon. The method for fabricating the sensor is as follows:

[0039] S1. Select a high-purity silicon wafer as the substrate 11 of the hydrogen sensor unit 1. Ultrasonic cleaning is performed on the silicon wafer, followed by treatment with acetone, ethanol, and deionized water to remove surface contaminants and grease. After cleaning, the wafer is dried with nitrogen to ensure smoothness and cleanliness.

[0040] S2, on the cleaned silicon wafer, a gold film is deposited on the base layer 11 by magnetron sputtering method, with a sputtering current of 40mA, a power of 20W, and a rate of 10nm / min, to form a conductive layer 12 with a thickness of between 10-20nm. The gold film as the conductive layer 12 not only provides excellent conductivity, but also provides good adhesion for subsequent layers, such as Figure 1 shown.

[0041] S3, by atomic layer deposition method, the gold film is alternately exposed to aluminum source gas and oxygen source gas, and aluminum oxide thin film is deposited layer by layer to form an insulating layer 13, and the thickness of the insulating layer 13 is controlled to be 3-5nm, such as Figure 2 As shown, the insulating layer 13 serves as an insulating material and can effectively isolate the gold film and the subsequent palladium metal film to prevent unnecessary electrochemical reactions.

[0042] S4, depositing a palladium metal film on the insulating layer 13 by magnetron sputtering method, with a sputtering current of 20mA, a power of 12W, and a rate of 6nm / min, to form a hydrogen-sensitive metal layer 14 with a thickness of 10-20nm, such as Figure 3 shown.

[0043] S5, mixing the silver nitrate solution with ascorbic acid, using polyvinyl pyrrolidone (PVP) as a stabilizer to prepare silver nanocubes, and then utilizing the induction effect of the interface between the aqueous phase and n-hexane to orderly arrange the silver nanocubes at the interface and self-assemble them on the hydrogen-sensitive metal layer 14 to form a metal nanocube structure layer 15. The specific steps are as follows:

[0044] S5-1: Add 50 mL of 0.1 M silver nitrate solution to the reaction vessel, followed by 5 mL of 0.1 wt% polyvinylpyrrolidone (PVP) solution, and stir thoroughly. While stirring, slowly add 5 mL of 0.1 M ascorbic acid solution and continue stirring the reaction mixture. The reaction time is generally 30-60 minutes to ensure the complete formation of silver nanocubes 150. The resulting silver nanocubes 150 have a structural size of 50-300 nm. Place the reaction mixture in an ice bath to lower the temperature and terminate the reaction. Centrifuge the synthesized silver nanocube solution and wash it multiple times with deionized water to remove unreacted starting materials and byproducts. Finally, resuspend the washed silver nanocubes in an appropriate amount of deionized water to obtain a silver nanocube suspension of the desired concentration.

[0045] In step S5-2, place the synthesized silver nanocube suspension in an ultrasonic bath and gently shake it to ensure uniform dispersion. Add an appropriate amount of polyvinylpyrrolidone (PVP) to the silver nanocube suspension, ranging from 1-5% by mass to the silver nanocubes, and stir thoroughly. The addition of PVP can reduce the positive surface charge of the nanoparticles, reduce mutual repulsion between the nanoparticles, and promote self-assembly.

[0046] S5-3, pouring an appropriate amount of n-hexane into the aqueous phase containing the silver nanocubes to form a two-phase interface. At the interface between the aqueous phase and the n-hexane phase, ethanol is used as an inducer to promote the self-assembly of the silver nanocubes at the water-n-hexane interface.

[0047] S5-4, place the structure obtained in step S4 with the palladium metal film facing up into the solution of step S5-3 on the water surface. Use tweezers or a gripper to gently grasp one end of the structure obtained in step S4 and slowly pick it up. During the picking process, the silver nanocubes are supported on the surface of the palladium metal film by the surface tension of the water. The tiny gaps between the silver nanocubes form metal nanocavities, thereby obtaining a self-assembled metal nanocavity structure layer 15. Figure 4 In the metal nanocavity structure layer 15 , the spacing between the nanocubes 150 is controlled to be between 10-100 nm.

[0048] Due to its excellent optical properties, the self-assembled metal nanocavity structure can effectively enhance the interaction between light and matter, improve the sensitivity and response speed of the sensor, and the self-assembly process is simple and controllable, making the construction of nanocavity an efficient method.

[0049] S6, drying the intermediate product prepared in step S5 naturally in air or slightly heating and drying it in a low-temperature oven to enhance the adhesion of the nanocubes, thereby obtaining a hydrogen sensing unit 1, such as Figure 5 shown.

[0050] In step S7, the silicon wafer serving as the substrate is first ultrasonically cleaned using deionized water, acetone, and ethanol. After cleaning, it is dried with nitrogen to ensure that the silicon wafer surface is free of contaminants. Next, a silicon dioxide layer is formed using chemical vapor deposition or magnetron sputtering on the silicon wafer to complete the fabrication of the SOI (Silicon On Insulator) optical waveguide structure 2. This SOI (Silicon On Insulator) optical waveguide structure formed on the silicon wafer enables the sensor to efficiently guide optical signals, achieving highly sensitive hydrogen detection. Photolithography and dry etching (e.g., plasma etching) are used to etch a deep receiving groove on the upper surface of the silicon dioxide layer of the fabricated SOI optical waveguide structure 2. The hydrogen sensor unit 1 fabricated in step S6 is then aligned with the etched groove of the SOI optical waveguide structure 2, ensuring good contact between the bottom layer of the sensor unit 1 and the groove. Polyvinyl alcohol (PVA) is used as an adhesive to secure the hydrogen sensor unit 1 within the groove, ensuring stability and adhesion. The structure is placed at room temperature to dry naturally or slightly heated in a low-temperature oven to enhance adhesion. After drying, an integrated optical waveguide hydrogen sensor with a self-assembled metal nanocavity structure is obtained, such as Figure 6 shown.

[0051] The self-assembled metal nanocavity structure integrated optical waveguide hydrogen sensor fabricated by the present invention operates as follows: the sensor unit utilizes the adsorption and dissociation reaction of hydrogen by a palladium metal film, combined with the metal nanocavity formed by silver nanocubes. The gaps between the silver nanocubes excite the surface plasmon effect, enhancing the local electric field and thus improving the response of hydrogen molecules. Furthermore, the hydrogen sensor is integrated into the optical waveguide using a SOI optical waveguide structure. The total internal reflection principle of the SOI optical waveguide effectively controls the propagation path of the optical signal, improving signal transmission efficiency. The optical signal is guided to the sensing area, and accurate hydrogen concentration detection is achieved by monitoring changes in the optical signal. This not only improves the sensor's sensitivity to hydrogen, but also offers high sensitivity and excellent optical signal transmission efficiency. It is widely applicable in fields such as environmental monitoring and industrial safety, providing a novel and efficient solution for hydrogen detection. Furthermore, the size and spacing of the metal nanocubes significantly influence the sensor's performance. The size of the metal nanocubes determines the sensor's response range to optical signals of a specific wavelength. Larger cubes excite surface plasmons of longer wavelengths, helping to match the desired wavelength. The spacing between nanocubes directly affects sensitivity: smaller spacing enhances the local electric field, increasing hydrogen molecule detection sensitivity, while larger spacing reduces sensitivity. By optimizing the size and spacing of the metal nanocubes, the sensor can precisely adjust the optical wavelength range and sensitivity to meet the needs of different applications.

[0052] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0053] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. An integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure, characterized in that: It includes a hydrogen sensing unit (1) and an SOI optical waveguide structure (2); The hydrogen sensing unit (1) is provided with a base layer (11), a conductive layer (12), an insulating layer (13), a hydrogen-sensitive metal layer (14), and a self-assembled metal nanocavity structure layer (15) in order from bottom to top. The self-assembled metal nanocavity structure layer (15) is composed of a plurality of metal nanocubes (150) arranged on the surface of the hydrogen-sensitive metal layer (14) through a self-assembly process, and gaps are provided between adjacent metal nanocubes (150); The SOI optical waveguide structure (2) is etched with a receiving groove for installing the hydrogen sensing unit (1), and the hydrogen sensing unit (1) is connected to the SOI optical waveguide structure (2); Mixing silver nitrate solution with ascorbic acid, using polyvinyl pyrrolidone (PVP) as a stabilizer to prepare metal nanocubes, and then utilizing the induction effect of the interface between the aqueous phase and n-hexane to orderly arrange the metal nanocubes at the interface and self-assemble them on the hydrogen-sensitive metal layer (14) to form a metal nanocube structure layer (15); The size of the metal nanocube (150) is 50-300 nm, and the spacing between adjacent metal nanocubes is 10-100 nm; The material of the hydrogen-sensitive metal layer (14) is palladium or platinum, and the thickness of the hydrogen-sensitive metal layer (14) is 10-20 nm.

2. The integrated optical waveguide hydrogen sensor based on the self-assembled metal nanocavity structure according to claim 1, characterized in that: The conductive layer (12) is made of gold, and has a thickness of 10-20 nm.

3. The integrated optical waveguide hydrogen sensor based on the self-assembled metal nanocavity structure according to claim 1, characterized in that: The material of the insulating layer (13) is aluminum oxide, and the thickness of the insulating layer (13) is 3-5 nm.

4. A method for preparing an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure, characterized in that: The steps include: S1, a silicon wafer is used as a base layer (11), and the silicon wafer is cleaned and dried; S2, sputtering a gold film on the silicon wafer obtained in step S1 by magnetron sputtering to form a conductive layer (12), wherein the thickness of the conductive layer (12) is 10-20 nm; S3, exposing the sample obtained in step S2 alternately to an aluminum source gas and an oxygen source gas, and depositing aluminum oxide layer by layer by atomic layer deposition to form an insulating layer (13), wherein the thickness of the insulating layer is 3-5 mm; S4, depositing a palladium film on the insulating layer (13) of the sample obtained in step S3 by magnetron sputtering to form a hydrogen-sensitive metal layer (14), wherein the thickness of the hydrogen-sensitive metal layer (14) is 10-20 nm; S5, mixing silver nitrate solution with ascorbic acid, using polyvinyl pyrrolidone (PVP) as a stabilizer to prepare silver nanocubes, and then utilizing the induction effect of the interface between the aqueous phase and n-hexane to orderly arrange the silver nanocubes at the interface and self-assemble on the hydrogen-sensitive metal layer (14) to form a self-assembled metal nanocube structure layer (15); S6, drying the sample prepared in step S5 to obtain a sensor unit (1); S7, depositing silicon dioxide on a silicon wafer to obtain an SOI optical waveguide structure (2), forming a receiving groove on the SOI optical waveguide structure through photolithography and dry etching processes, and bonding and fixing the sensor unit obtained in step S9 into the receiving groove of the SOI optical waveguide structure to form an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure.

5. The method for preparing an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure according to claim 4, characterized in that: The specific steps of preparing silver nanocubes and arranging them on the hydrogen-sensitive metal layer (14) using a self-assembly process in step S5 include: S5-1, adding 0.1 wt% polyvinylpyrrolidone (PVP) solution to 50 mL of 0.1 M silver nitrate solution and stirring uniformly, then slowly adding 5 mL of 0.1 M ascorbic acid solution while stirring to carry out mixing reaction. After the mixing reaction lasts for 30-60 minutes, the reaction mixture is placed in an ice bath, and then the synthesized silver nanocube solution is centrifuged and washed with deionized water to remove unreacted raw materials and by-products. The washed silver nanocubes are then suspended in deionized water to obtain a silver nanocube suspension of a predetermined concentration; S5-2, placing the silver nanocube suspension prepared in step S5 in an ultrasonic bath for uniform dispersion treatment, then adding polyvinyl pyrrolidone (PVP) to the silver nanocube suspension and stirring uniformly, wherein the mass of the added polyvinyl pyrrolidone (PVP) is 1-5% of the mass of the silver nanocubes; S5-3, pouring a predetermined amount of n-hexane into the solution prepared in step S6 to form an interface between the aqueous phase and the n-hexane phase, and inducing self-assembly of the silver nanocubes at the interface between the two phases; S5-4, the sample prepared in step S4 is placed from the side into the aqueous liquid containing silver nanocubes prepared in step S7 with the palladium film facing upward, and then picked up by clamping one end of the sample prepared in step S4. During the picking up process, the silver nanocubes are supported on the surface of the palladium film by the surface tension of water to form a self-assembled metal nanocavity structure layer (15).

6. The method for preparing an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure according to claim 5, characterized in that: The size of the metal nanocube (150) is 50-300 nm, and the distance between adjacent silver nanocubes is 10-100 nm.

7. The method for preparing an integrated optical waveguide hydrogen sensor based on a self-assembled metal nanocavity structure according to claim 4, characterized in that: In step S7 , the sensor unit is bonded to the receiving groove of the SOI optical waveguide structure by using a polyvinyl alcohol solution as an adhesive.

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