Surface-enhanced Raman scattering composite active substrate and preparation method thereof

Abstract

The invention discloses a surface-enhanced Raman scattering active substrate and a preparation method thereof. The method comprises the following steps: polishing a molybdenum film; performing high-density plasma dry etching on the polished molybdenum film to form a nano array structure; feeding the etched molybdenum film into a plasma reactor filled with gas for reaction to form a nanofiber structure; and coating a solution on the reacted molybdenum film, and drying to obtain the nano array and nanofiber composite structure substrate. The prepared surface-enhanced Raman scattering composite active substrate is applied to Raman spectrum detection and is high in sensitivity, stability and reproducibility.

Description

Technical Field

[0001] The present invention relates to the field of Raman detection technology, and in particular to a composite active substrate for surface enhanced Raman scattering and a preparation method thereof. Background Art

[0002] Raman scattering, discovered by Indian physicist Raman in 1928, refers to the interaction between photons and molecules of a sample surface. While most photons maintain their energy, elastic scattering (Rayleigh scattering) occurs. A small portion of molecules in the material transfer energy to the photons, causing transitions in their vibrational energy levels. This vibrational state changes in varying ways and degrees, resulting in the scattering of light at varying frequencies. Because different atomic groups in different substances vibrate in distinct ways, laser light irradiates the surface, generating scattered light with a specific frequency difference from the incident light. Therefore, analyzing Raman scattering spectra can reveal information about the chemical structure of molecules. Raman scattering offers advantages such as non-destructive testing, rapid analysis, high chemical selectivity, high environmental adaptability, and strong resistance to interference. However, because the frequency variations in Raman scattering are typically small, Raman scattering is much weaker than Rayleigh scattering, requiring extremely high sensitivity for detection. Surface-enhanced Raman scattering (SERS) was proposed to address this issue.

[0003] Surface-enhanced Raman scattering (SERS) is a technique that uses the surface plasmon resonance (SPR) effect of metal nanostructures to significantly enhance the Raman signal of molecules. This technique can enhance the Raman scattering signal by 10 6 to 10 8 times, greatly improving the sensitivity of detection. Currently, the main enhancement mechanisms of SERS are electromagnetic enhancement mechanism and chemical enhancement mechanism. The electromagnetic enhancement mechanism is to stimulate surface plasma resonance through the roughening of the metal surface or nanostructures of a specific shape. When the frequency of the incident light matches the resonance frequency of the metal surface plasma, a strong electromagnetic field enhancement is generated on the metal surface, thereby enhancing the Raman scattering signal of the neighboring molecules. Chemical enhancement involves the charge transfer process between the metal and the adsorbed molecules. The generated electron-hole pairs produce additional Raman scattering enhancement when they recombine. However, compared with electromagnetic enhancement, chemical enhancement has a shorter range of action and is usually limited to the first layer of adsorbed molecules on the metal surface.

[0004] The SERS substrate is a key component in achieving signal enhancement. It is usually a metal nanostructure with a specific morphology that can interact with the incident light, thereby producing a strong electromagnetic field enhancement effect at the nanoscale. Currently, the commonly used SERS substrates include metal substrates, non-precious metal substrates, and semiconductor SERS substrates.

[0005] Currently, electromagnetic and chemical enhancement mechanisms typically coexist, and SERS technology is widely used in chemical analysis, biomedical testing, environmental monitoring, materials science, food safety, and quality control. Despite its high sensitivity and selectivity, EM-enhanced Raman scattering still faces challenges, such as signal reproducibility and stability, and the complexity and cost of sample preparation.

[0006] Currently, patents such as CN116718582A, CN115931821A, and CN118028733A disclose methods for preparing surface-enhanced Raman scattering substrates using nanomaterials. However, these methods also present certain challenges. The uneven distribution of hotspots within metal nanostructures leads to inconsistent Raman signal enhancement, impacting accuracy and sensitivity. Furthermore, the difficulty in controlling the shape and size of nanoparticles during production leads to variations in Raman activity between nanoparticles produced, reducing the reliability and reproducibility of measurement results. Summary of the Invention

[0007] To address the problems existing in current surface-enhanced Raman scattering (SERS) substrates, the present invention provides a composite active SERS substrate and a preparation method. By optimizing the preparation of the nanostructure, the reliability and reproducibility of the SERS substrate are improved, thereby enhancing the sensitivity and accuracy of Raman scattering detection technology.

[0008] The technical solution of the present invention is: a method for preparing an active substrate for surface-enhanced Raman scattering, comprising: Polishing the molybdenum film; The polished molybdenum film is subjected to high-density plasma (ICP) dry etching to form a nano-array structure; The etched molybdenum film is fed into a plasma reactor filled with gas to react and form a nanofiber structure; The solution is then coated onto the reacted molybdenum film and dried to form a composite substrate of nanoarrays and nanofibers. This creates a multi-level roughened surface, significantly increasing the density of "hot spots" and specific surface area.

[0009] During etching, a mixture of chlorine and argon is used, with argon accounting for 30%-40% of the mixed gas. This reduces etching thermal damage and ensures uniformity of the nanoarray.

[0010] During etching, a pulse bias voltage is introduced with a frequency of 1-1.5kHz and a duty cycle of 30%-35% to suppress plasma sheath instability and improve structural accuracy.

[0011] A mixture of hydrogen and helium is filled into the plasma reactor, wherein the proportion of hydrogen in the mixture is 20%-25%.

[0012] The solution is: dissolving cyanamide salt and poly 3-hexylthiophene in chloroform solvent, The mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(0.8-10); The total mass concentration of the cyanamide salt and poly (3-hexylthiophene) is 4-11 mg / mL.

[0013] The cyanamide salt is a nano cyanamide salt, and its preparation process is as follows: Ammonia water is added to a silver nitrate or zinc nitrate solution, and sodium citrate, polypyrrole and 1-octanethiol are added simultaneously, and then a cyanamide solution is added to react. When the reaction is complete and precipitation is completed, the cyanamide salt residue is separated by filtration to obtain the cyanamide salt residue, and the residue is washed and dried to obtain the nano-cyanamide salt.

[0014] The precipitate produced by the reaction is subjected to high-temperature treatment at 170-200°C in a hydrothermal reactor for 4-12 hours, and then allowed to cool naturally.

[0015] The mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(1-4).

[0016] When drying, a gradient drying process is adopted, specifically: when the temperature reaches 80°C, drying for 15-30 minutes; when the temperature reaches 120°C, drying for 20-40 minutes; when the temperature reaches 150°C, drying for 30-60 minutes.

[0017] The coffee ring effect is eliminated by staged temperature control, and the film thickness uniformity deviation is <5%.

[0018] A composite active substrate for surface enhanced Raman scattering is prepared by any one of the preparation methods described above.

[0019] In this work, an electric polisher and a plasma reactor are used as the primary equipment for the preparation process. With the combined efforts of these equipment and processes, a thermal plasma method is used to prepare a molybdenum film with a nanofiber structure. The charge transfer efficiency is enhanced by forming a heterojunction structure of a π-conjugated point polymer, poly(3-hexylthiophene), and an inorganic semiconductor material, cyanamide salt. Furthermore, the cyanamide salt further improves stability and sensitivity.

[0020] The surface enhanced Raman scattering composite active substrate provided by the present invention has low preparation cost and simple method, and solves the defects of traditional SERS substrates such as high cost and complicated operation.

[0021] The surface-enhanced Raman scattering composite active substrate prepared by the present invention is applied to Raman spectrum detection and has high sensitivity, strong stability and high reproducibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process for preparing nanofiber-structured molybdenum membranes. Figure 2 Schematic diagram of the process for preparing composite active substrate. DETAILED DESCRIPTION

[0023] like Figure 1-2 As shown, a method for preparing an active substrate for surface-enhanced Raman scattering is provided, which uses an ICP dry etcher, a plasma reactor and a plasma generator, and an electric polisher as preparation equipment. The electrode output end of the plasma reactor is connected to the electrode input end of the plasma reactor, and the output pipe of the helium bottle is connected to the gas input pipe of the plasma reactor. The preparation process is as follows: The molybdenum film is polished and placed in an ICP dry etcher, where a mixture of chlorine and argon is introduced, with argon accounting for 30%-40%. The ICP dry etcher is powered on, etching to a depth of approximately 200nm. A pulsed bias voltage is introduced at a frequency of 1-1.5kHz and a duty cycle of 30%-35% for 4-20 minutes to obtain a nanoarray structure.

[0024] In practical applications, the molybdenum film with the nanoarray can be cleaned and dried (dry etching may generate non-volatile byproducts, which require cleaning and drying. Deionized water ultrasonic cleaning can be used for cleaning. Drying: nitrogen purge for 5 minutes, drying at 80°C for 10 minutes). Then, it is placed in the plasma reactor cavity, and helium and hydrogen are introduced. The plasma generator power is turned on, and the plasma reactor generates a mixture of hydrogen and helium (the proportion of hydrogen in the mixture is 20%-25%) plasma to obtain a molybdenum film with a nanofiber structure. The power of the plasma reactor and the plasma generator is turned off. A cyanamide salt (selected from silver cyanamide and zinc cyanamide) and poly 3-hexylthiophene (P3HT) are dissolved in a chloroform solvent to obtain a uniform mixed solution; the mixed solution is coated on a treated molybdenum film and dried to obtain a composite active substrate.

[0025] Furthermore, the principle of plasma treatment of molybdenum film to produce nanofiber molybdenum film is mainly as follows: during plasma irradiation, helium molecules form bubbles on the surface of the molybdenum film, and then the rapid bursting of the bubbles causes the formation of nanoscale fibrous structures on the surface of the molybdenum film.

[0026] Hydrogen dissociates into active hydrogen atoms (H⁺, H⁻ or H⁺ radicals) in the plasma, which can undergo a reduction reaction with the oxide layer on the surface of the molybdenum metal to generate volatile products, thereby cleaning the surface and forming a reducing atmosphere to prevent the metal surface from being oxidized again.

[0027] The mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(0.8-10); further, the mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(1-4).

[0028] The total mass concentration of the cyanamide salt and poly (3-hexylthiophene) is 4-11 mg / mL.

[0029] The cyanamide salt is a nano-cyanamide salt; the preparation process is as follows: Ammonia and sodium citrate are added to a silver nitrate or zinc nitrate solution as a green reducing agent and dispersant, improving the monodispersity of silver nanoparticles and preventing agglomeration. Polypyrrole (PPy) conductive polymers synergize with PEDOT:PSS to promote charge transfer, increasing the chemical enhancement contribution to 40%-50%. 1-Octanethiol thiol groups are used to modify the nanoparticle surface, inhibiting oxidation and enhancing dispersion stability. A cyanamide solution is then added to react. Once the reaction is complete and precipitation has occurred, the cyanamide salt residue is separated by filtration, which is then washed and dried to obtain nano-cyanamide salt.

[0030] The concentration of the silver nitrate or zinc nitrate solution is 15-20 g / L.

[0031] The concentration of the ammonia water is 1-3 mol / L.

[0032] The mass fraction of the cyanamide is 0.5%-1.5%.

[0033] The mass fraction of the sodium citrate is 0.1-0.5wt% The mass fraction of the polypyrrole is 0.05-0.1wt% The mass fraction of 1-octanethiol is 0.01-0.03wt% Furthermore, in order to further optimize the crystal structure of cyanamide salt, the precipitate produced by the reaction is subjected to high-temperature treatment at 170-200°C in a hydrothermal kettle for 4-12 hours. The specific process is as follows: the precipitate produced by the reaction is added to the reactor, ultrapure water is added, stirred, and then placed in an oven. After waiting for natural cooling, it is filtered, washed, and dried.

[0034] The coated molybdenum film is placed in an oven for drying to obtain the above-mentioned surface-enhanced Raman scattering composite active substrate.

[0035] A composite active substrate for surface enhanced Raman scattering is prepared by any one of the preparation methods described above.

[0036] Specific example: The preparation process is as follows: Step A: Polish the molybdenum film into a mirror surface using an electric polishing machine; Step B: Place the polished molybdenum film (Mo) in an ICP dry etcher and introduce a mixture of chlorine and argon gases. A pulsed bias voltage is introduced with a frequency of 1-1.5 kHz and a duty cycle of 30%-35% for 4-20 minutes. Etching is completed to obtain a Mu film with a nano-array structure. Step C: placing the Mu film with the nanoarray structure into the reaction chamber of a plasma reactor, introducing helium (He) and hydrogen into the chamber, and turning on the power of the plasma generator. The plasma reactor generates helium and hydrogen plasma, and the molybdenum film is directly treated with the helium and hydrogen plasma to obtain a nanofiber molybdenum film (Mo-NF). Step D: Weigh 6g of silver nitrate and dissolve it in 300mL of ultrapure water. Then slowly add 680mL of 3 mol / L ammonia water. Then add 0.3g of sodium citrate, 0.1g of polypyrrole, and 0.02g of 1-octanethiol. Continue to slowly add 350mL of a 0.9% cyanamide aqueous solution. During this process, precipitation will gradually form until precipitation is complete. After stirring for 45 minutes, filter and rinse with ultrapure water several times. Place in a vacuum drying oven for drying to obtain nano-silver cyanamide.

[0037] Step E: Dispersing poly (3-hexylthiophene) and nano-silver cyanamide in a chloroform solution at a mass ratio of 1:8 to poly (3-hexylthiophene) to form a mixed solution with a total concentration of 9 mg / ml. The mixed solution is ultrasonicated in an ultrasonic machine for 15 minutes until the poly (3-hexylthiophene) is completely dissolved. The mixed solution is then evenly coated on the treated molybdenum film. Step F: Place the coated molybdenum film in a vacuum drying oven and use a gradient drying process for drying, specifically: wait for the temperature to reach 80°C, dry for 15-30 minutes; wait for the temperature to reach 120°C, dry for 20-40 minutes; wait for the temperature to reach 150°C, dry for 30-60 minutes; and obtain a composite active substrate.

[0038] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. Although specific embodiments are described in detail herein, those skilled in the art may modify them or replace some of the technical features with equivalents, and such modifications do not deviate from the core concept and scope of protection embodied in the embodiments of the present invention.

Claims

1. A method for preparing an active substrate for surface-enhanced Raman scattering, characterized in that: include: Polishing the molybdenum film; The polished molybdenum film is subjected to high-density plasma dry etching to form a nano-array structure; The etched molybdenum film is fed into a plasma reactor filled with gas to react and form a nanofiber structure; The solution is coated on the reacted molybdenum film and dried to obtain a nano-array and nano-fiber composite structure substrate.

2. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 1, characterized in that: During etching, a mixed gas of chlorine and argon is used, wherein the proportion of argon in the mixed gas is 30%-40%.

3. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 2, characterized in that: During etching, a pulse bias is introduced with a frequency of 1-1.5kHz and a duty cycle of 30%-35%.

4. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 1, wherein: A mixture of hydrogen and helium is filled into the plasma reactor, wherein the proportion of hydrogen in the mixture is 20%-25%.

5. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 1, characterized in that: The solution is: dissolving cyanamide salt and poly 3-hexylthiophene in chloroform solvent, The mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(0.8-10); The total mass concentration of the cyanamide salt and poly (3-hexylthiophene) is 4-11 mg / mL.

6. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 5, characterized in that: The cyanamide salt is a nano cyanamide salt, and its preparation process is as follows: Ammonia water is added to a silver nitrate or zinc nitrate solution, and sodium citrate, polypyrrole and 1-octanethiol are added simultaneously, and then a cyanamide solution is added to react. When the reaction is complete and precipitation is completed, the cyanamide salt residue is separated by filtration to obtain the cyanamide salt residue, and the residue is washed and dried to obtain the nano-cyanamide salt.

7. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 6, characterized in that: The precipitate produced by the reaction is subjected to high-temperature treatment at 170-200°C in a hydrothermal reactor for 4-12 hours, and then allowed to cool naturally.

8. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 5, characterized in that: The mass ratio of the cyanamide salt to the poly (3-hexylthiophene) is 1:(1-4).

9. The method for preparing an active substrate for surface-enhanced Raman scattering according to claim 1, characterized in that: When drying, a gradient drying process is adopted, specifically: when the temperature reaches 80°C, drying for 15-30 minutes; when the temperature reaches 120°C, drying for 20-40 minutes; when the temperature reaches 150°C, drying for 30-60 minutes.

10. A composite active substrate for surface enhanced Raman scattering, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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