A sers substrate of hemispherical hole metal nano composite structure array and a preparation method thereof
By designing a SERS substrate with a hemispherical porous metal nanocomposite structure array and combining local and propagating surface plasmon resonance, the problems of low enhancement effect and unstable composite structure of noble metal SERS substrates were solved, and high sensitivity and stable molecular detection were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA JILIANG UNIV
- Filing Date
- 2023-09-15
- Publication Date
- 2026-05-12
Smart Images
Figure CN117388231B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of surface enhancement of Raman scattering (SERS) technology and analytical detection, and discloses a SERS substrate for a hemispherical porous metal nanocomposite structure array and its preparation method. Background Technology
[0002] Surface-enhanced Raman scattering (SERS) is a spectroscopic technique with single-molecule detection capability. It is simple to operate, highly specific, and has a wide range of applications. Therefore, it is widely used in fields such as food safety, environmental monitoring, and disease diagnosis, and has become a powerful and rapid detection method.
[0003] Surface-enhanced Raman scattering (SERS) refers to the significant enhancement of Raman scattering signals on rough metal surfaces (Au, Ag, Cu, etc.) when molecules are adsorbed. Currently, two main enhancement mechanisms are considered: electromagnetic enhancement and chemical enhancement. The former is primarily related to resonant excitation on the surface of metal nanoparticles, while the latter is related to photoinduced charge transfer between the substrate Fermi level and molecular energy levels. Electromagnetic enhancement is generally considered the main contributor. Because the excitation wavelength of surface plasmons resonates with the plasmon absorption curve of specific nanoparticles, a strong electromagnetic field with evanescent characteristics is generated on the metal surface, significantly enhancing the Raman modes of molecules near the metal surface. Furthermore, when the relevant Raman modes also match the plasmon resonance, the Raman scattered light undergoes a second enhancement. Electromagnetic SERS enhancement is dependent on the fourth power of the incident field amplitude.
[0004] Because electromagnetic enhancement is related to the material, size, and shape of the nanostructure, the SERS substrate is crucial for SERS analysis, amplifying weak Raman scattering signals by several or even tens of orders of magnitude. Noble metal SERS substrates, compared to other types of substrates, have higher SERS enhancement factors, enabling ultrasensitive detection even at the single-molecule level. Among the various types of SERS substrates, they have consistently held a dominant position and are widely used in food safety and environmental pollution control. Rare noble metals in traditional SERS substrates exhibit very significant SERS activity, possessing advantages such as high sensitivity and good stability. However, the SERS enhancement mechanism of single-structure noble metal substrates is simple and the effect is not obvious, while the interface and interactions between different materials in composite SERS substrates may lead to stability issues. Besides noble metal substrates, current research has also found that semiconductors and graphene also possess SERS activity, but the electromagnetic enhancement ability of these two types of SERS substrates is much smaller than that of noble metal nanoparticle substrates, and they generally need to be used in combination with noble metal nanoparticles.
[0005] With the rapid development of nanolithography technologies, such as electron beam lithography, focused ion beam lithography, electrochemical strategies, and wet chemical methods, various metal nanostructures have been precisely designed as SERS substrates. Research has found that SERS substrates with three-dimensional structures can provide a larger specific surface area and more defects, enabling more efficient signal propagation. This improves SERS capability through both electromagnetic field and charge transfer mechanisms. If the three-dimensional space can be designed more rationally, such as by promoting efficient signal propagation paths, it will have a better impact on material properties and enhance the potential for subsequent modification and control. Summary of the Invention
[0006] Noble metal substrates were the first SERS substrates discovered, exhibiting diverse morphologies and good SERS activity. However, the enhancement effect of single SERS structures is usually relatively low. The interfaces and interactions between different materials in composite SERS substrates can lead to instability, potentially resulting in unstable SERS signals. Furthermore, the fabrication process of composite structures is more complex, leading to poor reproducibility of SERS substrates.
[0007] To address the aforementioned problems, in one aspect, this invention proposes a SERS substrate with a hemispherical aperture metal nanocomposite structure array. The SERS substrate includes: a hemispherical aperture array supporting substrate; a metal thin film layer disposed on one side of the substrate; an organic dielectric layer thin film with conical apertures disposed on the side of the metal thin film layer away from the substrate; and metal nanospheres disposed within the conical apertures. The surface of the metal thin film layer can excite propagating surface plasmon resonance (SPR), and the metal nanospheres can excite localized SPR. These localized and propagating SPR effects can couple to enhance the electric field enhancement effect. Furthermore, the unique structure of the hemispherical aperture array and the conical apertures can synergistically enhance the local electric field. Therefore, the electric field enhancement performance of this SERS substrate is significantly improved.
[0008] The hemispherical aperture array supporting substrate has a hemispherical aperture array. Because the hemispherical aperture array increases the surface area of the SERS substrate, it improves the contact area between the sample and the substrate, enabling more effective capture of target molecules and enhancement of their Raman signals. The geometry of the hemispherical aperture array surface increases the morphological complexity, thereby increasing surface energy and giving the SERS substrate surface a higher molecular adsorption capacity. The curvature of the hemispherical aperture array is controllable, and the maximum local electric field enhancement effect can be achieved through precise design and control. Therefore, the hemispherical aperture array of this SERS substrate can enhance the local electric field, significantly improving the electric field enhancement performance.
[0009] A suitable support substrate can not only improve the enhancement effect of noble metal nanoparticles, but also provide conditions for the flat alignment of the particles, thereby ensuring signal repeatability. Preferably, the material forming the support substrate of the hemispherical aperture array can be a silicon-based material, including one or more of single-crystal silicon, polycrystalline silicon, silicon dioxide, or silicon-based composite materials. Silicon-based materials have strong nonlinear optical properties such as the nonlinear Kerr effect, and nonlinear processes such as two-photon absorption, free carrier absorption, and free carrier dispersion determined by the material itself, which have a strong confinement effect on light. The nonlinear effects of silicon-based materials can be used to generate Raman amplifiers and Raman lasers. Silicon-based materials can improve the SERS enhancement effect of metal materials. Using silicon-based materials as a support for metal particles, the interaction between noble metals and silicon-based materials is conducive to the coupling of surface plasmons. Under laser irradiation, the surface plasmon resonance of metal particles on the silicon-based material surface will be excited, thereby promoting the Raman signal. In addition, studies have shown that semiconductor-to-metal electron transfer occurring at the heterojunction interface can also promote the SERS enhancement effect. In summary, the advantages of silicon-based materials, such as low cost, excellent light transmittance, refractive index, and tunability, can further enhance the electric field enhancement effect of this SERS.
[0010] Preferably, the material of the metal thin film layer is one or more of Ag or Au. Au and Ag are two noble metals with low dielectric loss, and the nanospheres prepared from them can generate a strong surface plasmon resonance effect, further enhancing the electric field enhancement effect of the SERS substrate and improving detection sensitivity.
[0011] Preferably, the organic dielectric layer has a thickness of 40-55 nm and includes an organic substrate and a dielectric enhancement material dispersed in the organic substrate. The material forming the organic substrate is one or more of polymethyl methacrylate, polyvinyl alcohol, polystyrene, polypropylene, polyimide, and siloxane. The thickness of the organic dielectric layer can affect the resonant coupling between propagating surface plasmons (SFPs) and localized surface plasmons (LSPs). When the organic dielectric layer is thinner, the locally enhanced electric fields generated between the propagating SFPs and LSPs are closer together, enabling electromagnetic resonance and thus causing a resonant coupling effect. The overlap of the localized electric fields between the propagating SFPs and LSPs induces a stronger locally enhanced electric field. Simultaneously, because they are closer to the metal surface, the LSP modes can concentrate the local electromagnetic field near the sample molecules, improving the signal enhancement effect and thus enhancing the SERS signal. However, when the organic dielectric layer is too thin, it weakens the interaction between the propagating SFPs and LSPs, leading to a decrease in resonant coupling efficiency and a weakening of the SERS signal. Therefore, by carefully optimizing the thickness of the organic dielectric layer, the prepared organic dielectric layer film thickness was 40-55 nm to achieve the best performance of the SERS substrate.
[0012] The SERS enhancement effect of noble metal nanomaterials depends not only on their own composition, morphology, size, and structure, but also on the dielectric constant of the surrounding environment. Preferably, a dielectric enhancement material is used to modulate the dielectric of the organic dielectric layer. This dielectric enhancement material is one or more of alumina, boron nitride, and silicon nitride ceramic materials. Ceramic materials, as dielectric enhancement materials, possess excellent thermal and chemical stability, have high melting points, and are not easily corroded; they also have high dielectric constants, thereby increasing the refractive index of the organic dielectric layer. Therefore, the dielectric constant of the organic dielectric layer can be modulated by the doping amount of the dielectric enhancement material.
[0013] Preferably, the curvature range of the hemispherical aperture array supporting the substrate is 5 × 10⁻⁶. 6 ~10 7 m -1 The curvature corresponds to the degree of bending of the hemispherical aperture. A hemispherical aperture with too little curvature reduces the surface area and local electric field of the substrate, thus lowering the detection limit of the SERS substrate. Conversely, a SERS substrate with excessive curvature has a more complex morphology, resulting in different local electric field enhancement effects at different locations. Consequently, the adsorption positions and mechanisms of molecules are uncertain, leading to poor repeatability of the SERS signal. Therefore, calculations using the finite-domain difference (FDTD) method show that the curvature of the hemispherical aperture within a specific curvature range offers better repeatability and achieves a stronger SERS signal enhancement effect on the substrate, thereby improving the detection limit.
[0014] Preferably, a conical aperture is photolithographically etched on the organic dielectric layer. Thus, when light shines on the surface of the conical aperture, the aperture allows the incident light to be scattered and refracted multiple times within the aperture, increasing the optical path length of the incident light in the medium and playing a crucial role in the anti-reflection properties of the upper surface. The presence of the conical aperture can significantly increase the surface area of the SERS substrate, enabling it to more effectively capture target molecules and enhance their Raman signals. The formation of the conical aperture requires higher surface energy, and the geometry of the conical aperture surface leads to increased surface morphology complexity, thereby increasing surface energy and making it more conducive to molecular adsorption, thus giving the SERS substrate surface a higher molecular adsorption capacity.
[0015] Preferably, the depth of the conical aperture photolithographically formed on the organic dielectric layer is 40-55 nm. The depth of the conical aperture has a certain impact on the SERS effect. When the conical aperture is too deep, the peak width of the SERS signal may increase, which will reduce the resolution and sensitivity of the SERS signal. When the conical aperture is too shallow, the surface area is relatively small, resulting in an insufficient number of adsorption sites, thereby limiting the adsorption capacity of molecules. Therefore, the conical aperture on the organic dielectric layer within this depth range can enhance the surface area of the substrate, which is more conducive to the adsorption of molecules, and at the same time maximize the plasmon effect of the SERS substrate, thereby obtaining a stronger electric field enhancement and improving the detection effect.
[0016] Preferably, the spacing between the tapered holes etched on the organic dielectric layer is 5-20 nm. The spacing between the tapered holes affects the SERS effect. When the spacing is too small, the distance between adjacent hotspots is also small, causing their electric fields to influence each other, leading to a nonlinear saturation effect in the local electric field. When the spacing is too large, the number of hotspots decreases, and the local electric field intensity of the hotspots decreases, thus weakening the SERS signal. Therefore, within this range, the spacing of the etched tapered holes on the organic dielectric layer can achieve the highest local electric field intensity, thereby improving the detection effect of the SERS substrate.
[0017] The tapered holes etched on the organic dielectric layer have a dielectric constant of 10-20 because the organic dielectric layer is one or more ceramic materials selected from alumina, boron nitride, and silicon nitride ceramic materials as dielectric reinforcement materials. The higher dielectric constant increases the refractive index of the organic dielectric layer, thereby increasing the optical path of incident light in the medium, improving the anti-reflection performance of the upper surface, thereby enhancing the plasmon resonance effect, further improving the electric field enhancement performance of the SERS substrate, and thus improving the detection sensitivity limit.
[0018] Preferably, the metal element forming the metal nanospheres is one or more of Ag or Au, and the diameter of the metal nanospheres is 5-10 nm. The size of the metal nanospheres in the SERS substrate has a significant impact on the SERS signal intensity and stability. When the size of the metal nanospheres is too large: their resonance wavelength may deviate from the excitation wavelength. When the excitation wavelength does not match the resonance wavelength of the metal nanospheres, the resonance effect weakens, leading to a decrease in the SERS enhancement effect. Larger metal nanospheres have a smaller relative specific surface area and a relatively smaller surface charge density, resulting in a relatively stronger van der Waals force. This strengthens the interaction force between nanoparticles, leading to uneven distribution of hotspot regions, affecting the stability and consistency of the local electric field enhancement effect, and thus affecting the reliability and repeatability of the SERS signal. When the size of the metal nanospheres is too small, they usually have higher surface energy and activity, making them more susceptible to oxidation or corrosion, thereby reducing their SERS activity. They also lack sufficient surface area and LSPR resonance peaks, failing to effectively enhance the Raman signal of molecules, which is detrimental to improving the sensitivity of the SERS substrate. Therefore, at this size, the stability and repeatability of the SERS substrate can be enhanced, and lower concentrations of target molecules can be detected, thereby improving the detection effect.
[0019] In another aspect of the present invention, a method for preparing the aforementioned SERS substrate is proposed, comprising the following steps: preparing a support substrate having a hemispherical aperture array by photolithography; preparing a metal thin film on one side of the substrate to form a metal thin film layer; mixing a dielectric enhancement material and an organic substrate, and then preparing an organic dielectric layer on the side of the metal thin film layer away from the substrate by wet chemical method; photolithographically etching a regular conical structure into the organic dielectric layer of the substrate; mixing a metal nanosphere precursor and a composite substrate, and performing post-processing to form metal nanosphere particles within the conical apertures of the organic dielectric layer, thereby forming the SERS substrate. Thus, the SERS substrate prepared by this method possesses all the characteristics and advantages of the aforementioned SERS substrate, which will not be elaborated further here. In summary, this method can easily prepare a SERS substrate simultaneously exhibiting localized surface plasmon resonance and propagating surface plasmon resonance. In this SERS substrate, the hemispherical aperture array enhances light absorption, and the conical apertures improve anti-reflectivity, thereby enhancing the surface plasmon resonance effect and generating high-density hot spots.
[0020] The method for preparing a metal thin film layer further includes: depositing a film using magnetron sputtering at a growth rate of 0.05-0.2 nm / s, resulting in a metal thin film layer with a thickness of 100-200 nm; and then subjecting the metal thin film layer to plasma cleaning after deposition. Therefore, this method can prepare a metal thin film layer, and when the thickness of the metal thin film layer is within the aforementioned range, it can effectively excite surface plasmon polaritons at the interface, thereby increasing the surface plasmon resonance intensity. Furthermore, plasma cleaning of the deposited metal thin film layer can improve its surface activity and enhance the interlayer adhesion between the metal thin film layer and other film layers.
[0021] The organic dielectric layer film comprises an organic substrate and a dielectric reinforcing material dispersed in the organic substrate. The organic substrate is formed by one or more of polymethyl methacrylate, polyvinyl alcohol, polystyrene, polypropylene, polyimide, and siloxane. The dielectric reinforcing material is one or more of alumina, boron nitride, and silicon nitride ceramic materials, with a thickness of 40-55 nm. The organic dielectric layer is prepared by spraying a mixed solution of organic substrate powder and alumina, boron nitride, and silicon nitride ceramic material powder onto the side of the metal film layer away from the substrate using a wet chemical method. Thus, the alumina, boron nitride, and silicon nitride ceramic materials, as dielectric reinforcing materials, possess excellent thermal and chemical stability, and have a high dielectric constant, allowing for flexible control of the dielectric parameters of the organic dielectric layer. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the SERS substrate of the present invention;
[0023] Figure 2 This is a detailed view of the tapered hole in the SERS substrate of the present invention;
[0024] Figure 3 This is a flowchart illustrating the preparation process of the SERS substrate of the present invention;
[0025] Figure 4 This is a schematic diagram of the comparative structure a of the present invention;
[0026] Figure 5 This is a schematic diagram of comparative structure b of the present invention;
[0027] Figure 6 This is a comparison chart of the SERS performance of the present invention with comparative structures a and b;
[0028] Among them, 110 is the hemispherical hole array support substrate, 120 is the metal thin film layer, 130 is the organic dielectric layer, 200 is the conical hole, and 300 is the metal nanosphere particles. Detailed Implementation
[0029] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.
[0030] In one aspect, the present invention provides a SERS substrate for a hemispherical aperture metal composite structure array. According to an embodiment of the invention, reference is made to... Figure 1 The SERS substrate includes: a hemispherical aperture array support substrate 110; a metal thin film layer 120 disposed on one side of the hemispherical aperture array support substrate 110; an organic dielectric layer 130 having a conical aperture 200 disposed on the side of the metal thin film layer 120 away from the substrate; and metal nanospheres 300 disposed in the conical aperture 200. The surface of the metal thin film layer 120 can excite a propagating surface plasmon resonance effect, and the metal nanospheres 300 can excite a localized surface plasmon resonance effect. The localized surface plasmon resonance effect and the propagating surface plasmon resonance effect can couple to enhance the electric field enhancement effect. Simultaneously, the special structure of the hemispherical aperture array and the conical aperture can further synergistically enhance the local electric field. Therefore, the electric field enhancement performance of this SERS substrate is significantly improved. Figure 2 This is a detailed view of the tapered hole in the SERS substrate.
[0031] In this application, the surface of the metal thin film layer 120 can excite a propagating surface plasmon resonance effect, and the metal nanosphere particles 300 can excite a localized surface plasmon resonance effect. The localized surface plasmon resonance effect and the propagating surface plasmon resonance effect can couple with each other to enhance the electric field enhancement effect. At the same time, the special structure of the hemispherical aperture array and the conical aperture can further synergistically enhance the local electric field. Furthermore, according to the wavelength of the incident light, parameters such as the thickness of the metal thin film layer 120, the dielectric constant of the organic dielectric layer 130, the curvature of the hemispherical aperture array, the depth of the conical aperture 200, and the size of the metal nanosphere particles 300 in the SERS substrate can be adjusted to match the wavelength of the incident light, so as to achieve the strongest electric field intensity and further improve the detection limit of the SERS substrate.
[0032] According to an embodiment of the present invention, the material forming the hemispherical aperture array support substrate 110 can be silicon dioxide, which can improve the SERS enhancement effect of the metal material. Using silicon dioxide as a support for the metal particles, the interaction between the noble metal and the silicon-based material is conducive to the coupling of surface plasmons. Under laser irradiation, the surface plasmon resonance of the metal particles on the surface of the silicon-based material will be excited, thereby promoting the Raman signal.
[0033] According to an embodiment of the present invention, the material forming the metal thin film layer 120 can be gold. Therefore, the metal thin film layer 120 can generate a surface plasmon resonance effect at the interface, and this surface plasmon resonance effect can couple with the localized surface plasmon resonance generated by the metal nanosphere particles 300, thereby improving the electric field enhancement performance of the SERS substrate. Specifically, refer to... Figure 1 The metal thin film layer 120 has a thickness of 150 nm, which can effectively excite surface plasmon polaritons at the interface and improve the resonant response intensity to incident light.
[0034] According to an embodiment of the present invention, the organic dielectric layer 130 includes an organic substrate and a dielectric reinforcing material (not shown in the figure) dispersed in the organic substrate. Specifically, the material forming the organic substrate may be polymethyl methacrylate (PMMA), and the dielectric reinforcing material may be boron nitride ceramic material. Thus, by controlling the amount of dielectric reinforcing material added to the organic substrate (PMMA), the dielectric constant of the organic dielectric layer 130 can be easily adjusted. On the one hand, this facilitates the adjustment of the dielectric environment of the metal nanospheres 300, enabling the metal nanospheres 300 to generate localized surface plasmon resonance at a certain incident light wavelength. On the other hand, it facilitates the matching of the dielectric constant of the organic dielectric layer 130 with parameters such as the thickness of the metal thin film layer 120, the size of the metal nanospheres 300, and their spacing, achieving the strongest resonance intensity at a certain incident light wavelength, further improving the electric field enhancement performance of the SERS substrate.
[0035] According to an embodiment of the present invention, a conical aperture 200 is located on an organic dielectric layer 130. The depth of the conical aperture can be 50 nm. The depth of the conical aperture has a certain influence on the SERS effect. When the conical aperture is too deep, the distance between the nanoparticles and the laser increases, thus weakening the interaction. When the conical aperture is too shallow, the surface area is relatively small, resulting in a stronger electric field enhancement for the number of adsorption sites provided, thereby improving the detection effect. Specifically, under a certain incident light wavelength, the depth and spacing of the conical aperture 200 can be simulated using FDTD simulation calculations to optimize the surface plasmon effect of the composite structure and improve the electric field enhancement effect of the SERS substrate.
[0036] According to an embodiment of the present invention, tapered holes 200 are disposed on an organic dielectric layer 130. The spacing between the tapered holes can be 10 nm. The spacing between the tapered holes affects the SERS effect. When the spacing between the tapered holes is too small, the distance between adjacent hot spots is also very small, and their electric fields will affect each other, leading to a nonlinear saturation effect in the local electric field. When the spacing between the tapered holes is too large, the number of hot spots decreases, and the local electric field intensity of the hot spots decreases, thereby weakening the SERS signal. Therefore, within this range, the spacing of the etched tapered holes on the organic dielectric layer can obtain the highest local electric field intensity, thereby improving the detection effect of the SERS substrate.
[0037] According to an embodiment of the present invention, the metal element forming the metal nanospheres 300 can be Ag, specifically, see reference. Figure 2 The metal nanospheres 300 have a particle size of 8 nm, which can generate local surface plasmon resonance well. Furthermore, the particle size of the metal nanospheres 300 can be adjusted within the above range so that the particle size and spacing of the metal nanospheres 300, the thickness of the metal thin film layer 120, the dielectric constant of the organic dielectric layer 130, and other parameters are matched to achieve the strongest resonance intensity at a certain incident light wavelength, thereby further improving the electric field enhancement performance of the SERS substrate.
[0038] Specifically, under a certain incident light wavelength, the particle size of the metal nanospheres 300 can be simulated using FDTD simulation calculations in order to optimize the local surface plasmon effect of the metal nanospheres and maximize the resonance response intensity of the metal nanospheres 300.
[0039] In another aspect of the invention, a method for preparing the aforementioned SERS substrate is proposed. Figure 3 This is a flowchart illustrating the fabrication process of the SERS structure of this invention. It mainly includes five steps: providing a hemispherical aperture array support substrate S110, forming a metal thin film layer S120, forming an organic dielectric layer S130, photolithographically forming conical apertures S140, and fabricating metal nanospheres S150. Therefore, the SERS substrate prepared by this method possesses all the characteristics and advantages of the SERS substrate described above, which will not be repeated here. In summary, this method can easily prepare a SERS substrate simultaneously possessing localized surface plasmon resonance and surface plasmon polaritons. In this SERS substrate, the special structure of the hemispherical aperture array and conical apertures can enhance the local electric field effect, and the localized surface plasmon resonance and surface plasmon resonance can couple with each other, significantly improving the electric field enhancement performance of the SERS substrate. Furthermore, the thickness of each film layer, the depth and spacing of the conical apertures, and the particle size of the metal nanospheres are precisely controllable in this fabrication method, further improving the electric field enhancement performance of the prepared SERS substrate.
[0040] According to an embodiment of the present invention, the method includes:
[0041] S110: Substrate providing a hemispherical aperture array
[0042] In this step, a hemispherical aperture array is photolithographically formed on a support substrate, providing a hemispherical aperture array support substrate. According to embodiments of the present invention, the substrate can be the substrate described above, for example, the material forming the hemispherical aperture array support substrate is silicon dioxide, which has the following advantages: silicon dioxide acts as a support for metal particles; the interaction between the noble metal and silicon dioxide facilitates the coupling of surface plasmons; under laser irradiation, the surface plasmon resonance of the metal particles on the silicon dioxide surface is excited, thereby promoting Raman signals; silicon dioxide has high transmittance and low absorptivity, enabling it to transmit light and reduce energy loss; the refractive index of silicon dioxide is similar to that of air, thus exhibiting excellent transparency and optical uniformity; the optical properties of silicon dioxide can be adjusted by controlling its thickness and lattice structure. The advantages of silicon dioxide—low cost, excellent transmittance, refractive index, and tunability—further enhance the electric field enhancement effect of the SERS substrate.
[0043] S120: Formation of a thin metal film layer 120
[0044] In this step, a metal thin film layer 120 is prepared on one side of the substrate described in the previous step. According to an embodiment of the invention, the metal can be gold, and the material forming the gold thin film layer can be the same as described above, further including the following steps:
[0045] S121: Coating under vacuum conditions using magnetron sputtering equipment
[0046] In this step, film deposition is performed under vacuum conditions using magnetron sputtering equipment. Specifically, a gold target is selected, and the vacuum level can be 5 × 10⁻⁶. -4 The film growth rate can be approximately 0.05-0.2 nm / s, for example, 0.08 nm / s, 0.1 nm / s, or 0.15 nm / s. Therefore, when the film production rate is within the above range, a gold thin film with good uniformity can be obtained. Specifically, the thickness of the formed gold thin film can be 150 nm, which can effectively excite surface plasmon polaritons at the interface and improve the resonant response intensity to incident light.
[0047] S122: Plasma cleaning treatment of the gold thin film layer
[0048] In this step, the gold thin film layer formed by the previous deposition process undergoes plasma cleaning. Specifically, a plasma cleaner can be used to treat the gold thin film after magnetron sputtering deposition. Oxygen plasma is used for cleaning, with oxygen (O2) as the discharge gas. The pressure inside the cleaning chamber is between 50-200 Pa. Plasma is generated by applying a radio frequency (RF) voltage between 200-1000 V, and the cleaning time is between 5-10 minutes. This improves the surface activity of the gold thin film layer and enhances the interlayer adhesion between the gold thin film layer and the organic dielectric layer prepared by subsequent methods. Specifically, in this method, the substrate can also be pre-treated with plasma before magnetron sputtering deposition, thereby improving the adhesion between the substrate and the metal coating layer.
[0049] S130: Forming an organic dielectric layer 130 to form a composite substrate.
[0050] In this step, the dielectric reinforcing material and the organic substrate are mixed and then sprayed onto the side of the metal thin film layer 120 prepared in the previous step away from the substrate to form the organic dielectric layer 130, thereby forming a composite substrate in which the substrate, the metal thin film layer, and the organic dielectric layer are sequentially stacked. According to embodiments of the present invention, the specific types of materials forming the organic substrate and the dielectric reinforcing material can be the same as described above. The material forming the organic substrate can be polymethyl methacrylate, and the dielectric reinforcing material can be BNNSs (boron nitride) ceramic material. Specifically, refer to... Figure 4 The organic dielectric layer 130 can be prepared by the following method:
[0051] Wet chemical synthesis method:
[0052] S131: Formation of the first dispersion
[0053] In this step, boron nitride ceramic material powder is dispersed in a first solvent and stirred to form a first dispersion. Specifically, the first solvent can be N,N-dimethylformamide (DMF), and the method can specifically include: (1) adding boron nitride ceramic material powder to DMF and ultrasonically peeling it with an ultrasonic cleaner until it is completely dispersed; (2) centrifuging the ultrasonically dispersed first dispersion at low speed, for example, centrifuging at 2000 r / min for 20 min, and then extracting the supernatant; (3) concentrating the extracted supernatant while stirring and heating (for example, heating to 40°C) to prepare a BNNSs / DMF first dispersion of a certain concentration, while keeping the mixture stirred. Thus, a first dispersion of a certain concentration can be obtained, which is convenient for the preparation of subsequent steps.
[0054] S132: Add the organic substrate powder to the first dispersion to form the second dispersion.
[0055] In this step, an organic base powder (e.g., polymethyl methacrylate powder) is added to the first dispersion prepared in the previous step and stirred to form a second dispersion. Specifically, the organic base powder (e.g., polymethyl methacrylate powder) can be slowly added to the first dispersion in increments, dissolving as it is added. Furthermore, the second dispersion can be stirred to form a uniformly dispersed second dispersion.
[0056] S133: Spray the prepared polymer solution onto the substrate.
[0057] The pressure was set to 30 PSI, and a 0.5 mm nozzle was used to achieve a speed of 3 ml / s per minute. The mixture was then placed in an environment of 80°C for 24 hours to cure, forming a uniform thin film and an organic dielectric layer.
[0058] Therefore, the above method can easily prepare the organic dielectric layer 130, and the dielectric constant of the organic dielectric layer 130 is easily adjustable. For example, the dielectric constant of the final organic dielectric layer can be easily adjusted by adjusting the content of ceramic material (e.g., BNNSs) in the first dispersion. This facilitates the matching of the dielectric constant of the organic dielectric layer with parameters such as the thickness of the metal thin film layer prepared in the previous steps, the size and spacing of the metal nanospheres prepared in the subsequent steps, etc., so as to achieve the strongest resonance intensity at a certain incident light wavelength, further improving the electric field enhancement performance of the SERS substrate prepared by this method.
[0059] S140: A tapered hole 200 is formed on the organic dielectric layer 130 by photolithography.
[0060] S141: Photoresist coating
[0061] For spin coating of photoresist, the optimal spin speed is 2000–4000 rpm.
[0062] S142: Pre-baking
[0063] The purpose of pre-baking is to evaporate the organic solvents in the photoresist through temperature, allowing the photoresist on the wafer surface to solidify. Pre-baking can be performed on a hot plate or in an oven, with a temperature between 80-120℃ and a pre-baking time of 60 seconds. After pre-baking, the photoresist must be allowed to cool to room temperature before proceeding to the next process.
[0064] S143: Exposure
[0065] Specific wavelengths of light are used to selectively irradiate the photoresist covering the substrate. The photosensitizer in the photoresist undergoes a photochemical reaction, causing changes in the chemical composition of the irradiated areas (photosensitive areas) of the positive photoresist and the unirradiated areas (non-photosensitive areas) of the negative photoresist. These areas with altered chemical compositions become soluble in a specific developing solution in the next step. After irradiation, the photosensitizer DQ in the positive photoresist undergoes a photochemical reaction, transforming into ketene, which further hydrolyzes into indene-carboxylic acid (CA). The solubility of carboxylic acid in alkaline solvents is approximately 100 times higher than that of the unexposed photoresist, and the generated carboxylic acid also promotes the dissolution of phenolic resin. By utilizing the different solubilities of the photosensitive and unexposed photoresists in alkaline solvents, mask patterns can be transferred.
[0066] S144: Development
[0067] After the exposure process is complete, a developer is added, which dissolves the photosensitive areas of the positive photoresist and the non-photosensitive areas of the negative photoresist. Once this step is finished, the pattern in the photoresist layer can be revealed.
[0068] S145: Hard membrane
[0069] After photoresist development, the pattern is essentially determined, and hard baking further stabilizes the photoresist's properties. During this process, high-temperature treatment removes residual solvents from the photoresist, enhances its adhesion to the silicon wafer surface, and improves its resistance to subsequent etching and ion implantation. Additionally, the high temperature softens the photoresist, creating a molten state similar to glass at high temperatures. This smooths the photoresist surface under surface tension and reduces defects (such as pinholes) in the photoresist layer, thus correcting the edge contours of the photoresist pattern. Finally, before etching or coating, hard baking is required to remove residual developer and water, and annealing improves interfacial bonding caused by penetration and expansion during development. This also increases the hardness and etching resistance of the photoresist. Hard baking temperatures are typically above 120°C, and the time is around 20 minutes. The main limitation is that excessively high temperatures can worsen the pattern edges and make it difficult to remove after etching.
[0070] S146: Electron beam etching
[0071] In this step, the electron beam energy is 500-5000eV, the electron beam current is 10-100mA, the scanning speed is 1-100mm / s, the etching gas is oxygen (O2), the gas flow rate is between 10 standard cubic centimeters per minute (sccm) and 1000 sccm, and the substrate temperature is set at 25-300℃.
[0072] S147: Remove photoresist
[0073] Therefore, the above method can fabricate conical holes on an organic dielectric layer, and the depth and spacing of these conical holes are easily adjustable. For example, the spacing of the conical holes can be controlled by adjusting the irradiation interval, and the depth of the conical holes can be controlled by adjusting the etching time. This facilitates the matching of the depth and spacing of the conical holes in the organic dielectric layer with parameters such as the thickness of the metal thin film layer prepared in the preceding steps, the thickness of the organic dielectric layer, and the size of the metal nanospheres prepared in subsequent steps, achieving the strongest resonance intensity at a certain incident light wavelength, and further improving the electric field enhancement performance of the SERS substrate prepared by this method.
[0074] S150: Formation of 300 metal nanospheres
[0075] In this step, the metal nanosphere precursor is mixed with the composite substrate prepared in the previous step, which consists of a hemispherical hole array support substrate, a metal thin film layer, and an organic dielectric layer, and then post-processed to form silver nanospheres in the conical holes of the organic dielectric layer. According to embodiments of the present invention, the metal can be silver, and the metal nanosphere precursor can include AgNO3. Specifically, the method further includes:
[0076] S151: Precursor solution for forming silver nanospheres
[0077] In this step, the silver nanosphere precursor and the second solvent are mixed to form a silver nanosphere precursor solution. Specifically, the silver nanosphere precursor is AgNO3; the second solvent can be deionized water. The concentration of the silver nanosphere precursor solution can be (0.01-20) g / L, for example, 0.05 g / L, 0.1 g / L, 1 g / L, 5 g / L, 10 g / L, 12 g / L, 15 g / L, etc. When the concentration of the silver nanosphere precursor solution is within the above range, it facilitates the preparation of silver nanospheres with particle size and spacing within a certain range through subsequent steps, and the prepared silver nanospheres exhibit good localized surface plasmon resonance effect. When the concentration of the silver nanosphere precursor solution is too high (e.g., greater than 20 g / L), the prepared silver nanospheres have too large a particle size and too small a spacing, resulting in poor local surface plasmon resonance effect. When the concentration of the silver nanosphere precursor solution is too low (e.g., less than 0.01 g / L), the prepared silver nanospheres have too small a particle size and too large a spacing, resulting in poor local surface plasmon resonance effect.
[0078] S152: Pre-fabricated silver nanospheres
[0079] In this step, the composite substrate prepared in the previous step is placed in a silver nanosphere precursor solution (AgNO3), ammonia is added, and the mixture is stirred to form silver nanospheres within the conical pores of the organic dielectric layer. Specifically, the concentration of the added ammonia can be (0.01-10) mol / L, for example, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 5 mol / L, 7 mol / L, etc. Therefore, when the ammonia concentration is within the above range, it facilitates the reaction between the silver nanosphere precursor and the ammonia in the previous step, forming a nanoparticle prefabricated layer within the conical pores on the surface of the organic dielectric layer. When the concentration of ammonia is too high (e.g., greater than 10 mol / L), the particle size of the prepared silver nanospheres is too large, which will affect the local surface plasmon resonance effect of the silver nanospheres. In addition, the high concentration of ammonia will also prevent the silver nanospheres from being well loaded on the surface of the silver film layer. When the concentration of ammonia is too low (e.g., less than 0.01 mol / L), the particle size of the prepared silver nanospheres is too small, which will affect the local surface plasmon resonance effect of the silver nanospheres and easily lead to problems such as excessively long operation time and low preparation efficiency.
[0080] S153: Perform plasma discharge treatment to form silver nanospheres.
[0081] In this step, the composite substrate with pre-formed silver nanospheres from the previous step is subjected to plasma discharge treatment to form silver nanospheres. Specifically, the composite substrate with pre-formed silver nanospheres is placed in a plasma discharge device, using hydrogen as the working gas. First, hydrogen is introduced into the reactor for 1-2 minutes to purge the air from the reactor. Then, the plasma power supply is turned on to perform dielectric barrier discharge treatment at room temperature and pressure. The discharge time can be 20-40 seconds, and the plasma discharge parameters can be: power 75-95W, frequency 10-20kHz, to form silver nanospheres.
[0082] Therefore, this method can easily prepare metal nanospheres 300 with localized surface plasmon resonance effect, and can also achieve precise and controllable loading of the metal nanospheres 300 on the composite substrate in terms of size and spacing. Furthermore, when the concentrations of the metal nanosphere precursor solution and the ammonia solution are within the aforementioned ranges, it is easy to control the particle size of the formed metal nanospheres 300, ensuring that the particle size matches the previously mentioned organic dielectric layer 130, metal thin film layer 120, etc., achieving the strongest resonance intensity at a certain incident light wavelength, further improving the electric field enhancement performance of the SERS substrate prepared by this method.
[0083] Prepare three types of SERS substrates:
[0084] (a) A schematic diagram of the comparative structure a of the present invention, as shown. Figure 4 A planar support substrate; a metal thin film layer disposed on one side of the substrate; an organic dielectric thin film disposed on the side of the metal thin film layer away from the substrate; and metal nanospheres disposed on the organic dielectric layer.
[0085] (b) A schematic diagram of the comparative structure b of the present invention, as shown. Figure 5 A hemispherical hole array supports the substrate; a metal thin film layer is disposed on one side of the substrate; an organic dielectric thin film is disposed on the side of the metal thin film layer away from the substrate; and metal nanospheres are disposed on the organic dielectric layer.
[0086] (c) A hemispherical aperture array supporting substrate; a metal thin film layer disposed on one side of the substrate; an organic dielectric thin film with tapered apertures disposed on the side of the metal thin film layer away from the substrate; and metal nanospheres disposed in the tapered apertures, which is the SERS substrate described in this invention;
[0087] The detection method is as follows:
[0088] S210: Prepare the wastewater sample to be tested; the selectable concentration is 10. -9 M in an aqueous solution of an organophosphorus compound;
[0089] S220: Set the concentration to 10 -9 An aqueous solution of organic nitrogen compound M was drop-coated onto the SERS substrate of the present invention and then dried.
[0090] S230: Turn on the Raman spectrometer and irradiate the above SERS substrate with a laser light source to obtain the SERS spectrum;
[0091] S240: Reconstruction of the absorption spectrum. The absorption spectrum is decomposed into multiple Gaussian functions through Gaussian decomposition, and the decomposed Gaussian functions are superimposed to reconstruct the absorption spectrum.
[0092] S250: The split Gaussian functions are sorted, classified and analyzed to obtain the predicted components and their corresponding concentrations in the water sample.
[0093] The SERS spectra of the three composite SERS substrates described above were obtained using the aforementioned detection methods, as shown below. Figure 6 .pass Figure 6 Analysis shows that the SERS substrate of this invention, which has both a hemispherical aperture array and a conical aperture, has the best detection performance, indicating that the SERS substrate of this invention has strong usability and the highest detection sensitivity.
[0094] Therefore, this detection device possesses all the features and advantages of the SERS substrate described above, which will not be repeated here. In summary, this wastewater detection device performs well. The SERS substrate exhibits good electric field enhancement properties, which can improve the detection limit of the wastewater detection device.
[0095] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.
[0096] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.
[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A SERS substrate for a hemispherical porous metal nanocomposite structure array, characterized in that, The substrate includes: Hemispherical aperture array supports the substrate; A metal thin film layer is disposed on one side of the substrate; An organic dielectric layer with tapered holes is disposed on the side of the metal thin film layer away from the substrate; and Metal nanospheres set inside a conical pore; The surface of the metal thin film layer excites and propagates surface plasmon resonance, while the metal nanospheres excite local surface plasmon resonance. The local surface plasmon resonance and the propagating surface plasmon resonance are coupled to enhance the electric field. At the same time, the structure of the hemispherical hole array and the conical hole further enhances the local electric field in a synergistic manner.
2. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The material of the hemispherical aperture array support substrate is a silicon-based material, including one or more of monocrystalline silicon, polycrystalline silicon, silicon dioxide, or silicon-based composite materials.
3. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The curvature range of the hemispherical aperture array supporting the substrate is (5×10). 6 ~5×10 7 )m -1 .
4. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The material of the metal thin film layer is one or more of Ag or Au.
5. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The organic dielectric layer has a thickness of 40-55 nm and includes an organic substrate and a dielectric reinforcing material dispersed in the organic substrate. The organic substrate is made of one or more of polymethyl methacrylate, polyvinyl alcohol, polystyrene, polypropylene, polyimide, and siloxane. The dielectric reinforcing material is made of one or more of alumina, boron nitride, and silicon nitride ceramic materials.
6. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The height of the tapered hole on the organic dielectric layer is 40-55 nm.
7. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 1, characterized in that, The metal nanospheres are composed of one or more of Ag or Au, and the diameter of the metal nanospheres is 5-10 nm.
8. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: A hemispherical aperture array is fabricated on a substrate using electron beam lithography, and a substrate is provided to support the hemispherical aperture array. A metal thin film layer is prepared on one side of the hemispherical hole array support substrate; After mixing the dielectric enhancement material and the organic substrate, the mixture is sprayed onto the side of the metal thin film layer away from the hemispherical hole array support substrate to form an organic dielectric layer. A tapered hole is formed in the organic dielectric layer using photolithography; The metal nanosphere precursor is mixed with a composite substrate consisting of a hemispherical hole array support substrate, a metal thin film layer and an organic dielectric layer, and then post-processed to form metal nanospheres in the conical holes on the side of the organic dielectric layer away from the metal thin film layer, thus forming the SERS substrate.
9. The SERS substrate for the hemispherical porous metal nanocomposite structure array according to claim 8, characterized in that, The formation of the metal thin film layer further includes: depositing a metal thin film on a hemispherical hole array support substrate by magnetron sputtering at a growth rate of 0.05-0.2 nm / s, and forming a metal thin film layer with a thickness of 100-200 nm; after the deposition, the metal thin film layer is subjected to plasma cleaning treatment.