Raman spectrum enhanced substrate and femtosecond laser liquid phase ablation preparation method thereof

Abstract

The invention relates to a Raman spectrum enhanced substrate and a femtosecond laser liquid phase ablation preparation method thereof, and belongs to the technical field of femtosecond laser processing. The metal nanoparticles are embedded on the surface of the titanium dioxide nanotube array in a direct writing manner, so that a multi-element plasma nanostructure is formed, and the SERS performance is further improved. Due to the existence of the local surface plasma resonance effect, the multi-metal nanostructure resonates to generate a hot spot, so that an enhanced local electric field is generated, and the SERS signal performance is adjusted. Compared with other processing methods, the method has the advantages of simple and efficient process steps and high controllability and stability.

Description

Technical Field

[0001] The present invention relates to a Raman spectroscopy enhancement substrate and a femtosecond laser liquid-phase ablation preparation method thereof, belonging to the technical field of femtosecond laser processing. Background Art

[0002] Surface-enhanced Raman scattering (SERS) is a powerful trace analysis technique, with the sensitivity of single-molecule detection and providing molecular fingerprint information, having great application value in fields such as trace analysis and interface characterization. Among them, the core functional structure of surface-enhanced Raman scattering of the substrate material has wide applications in fields such as biomedicine, environmental monitoring, and food safety. Compared with traditional single-component plasmonic nanostructures, multi-metal plasmonic nanostructures have resonance coupling enhancement characteristics and unique energy dissipation mechanisms. At present, various preparation methods of single-component plasmonic nanostructures have been developed, such as self-assembly, physical and chemical deposition, photoreduction reaction, electron beam lithography, etc. These traditional methods have all achieved the direct preparation of metal plasmonic nanostructures on the metal surface, but there are still certain defects, such as cumbersome processing technology, poor controllability, long preparation cycle, etc. Since the controllable preparation of multi-metal plasmonic nanostructures requires the modulation of different materials in multiple directions, it greatly increases the complexity of the process and the difficulty of controllable synthesis, and limits the further application of multi-metal plasmonic nanostructures. Therefore, a flexible and stable preparation method of multi-metal plasmonic nanostructures is needed to expand its application range. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: overcoming the deficiencies of the prior art, a Raman spectroscopy enhancement substrate and a femtosecond laser liquid-phase ablation preparation method thereof are proposed. The purpose is to provide a simple method for controllably preparing nanotube-metal particle multi-metal plasmonic nanostructures by femtosecond laser pulse liquid-phase ablation-assisted metal ion reduction. The present invention uses femtosecond laser pulse liquid-phase ablation-assisted metal ion reduction to efficiently and controllably prepare nanotube-metal particle multi-metal plasmonic nanostructures on titanium dioxide nanotubes. This process method has simple steps, low cost, and extremely high controllability and stability.

[0004] The technical solution of the present invention is:

[0005] A Raman spectroscopy enhancement substrate, the structure of the substrate includes a titanium metal substrate, a nanotube array located on the titanium metal substrate, and nanoparticles located at the top of the nanotube array;

[0006] The nanotube is a titanium dioxide nanotube;

[0007] The nanoparticles are two of gold nanoparticles, silver nanoparticles, and platinum nanoparticles.

[0008] A method for preparing a femtosecond laser liquid-phase ablation Raman spectroscopy enhancement substrate, the steps of the method comprising:

[0009] Step 1: Polish the titanium metal substrate on a polishing machine, and then place the polished titanium metal substrate in an ammonium fluoride solution for anodic oxidation for 20 - 40 minutes to obtain a titanium metal substrate with a titanium dioxide nanotube array grown on its surface;

[0010] Step 2: Immerse the titanium metal substrate with a titanium dioxide nanotube array grown on its surface obtained in Step 1 in a mixed solution;

[0011] The mixed solution is a mixture of two of chloroauric acid, chloroplatinic acid, and silver nitrate;

[0012] When the mixed solution is a mixture of chloroauric acid and chloroplatinic acid, the concentrations of both chloroauric acid and chloroplatinic acid are 0.1 mol / L, and the volume ratio of chloroauric acid to chloroplatinic acid is 0.5 - 1.5:1;

[0013] When the mixed solution is a mixture of chloroauric acid and silver nitrate, the concentrations of both chloroauric acid and silver nitrate are 0.1 mol / L, and the volume ratio of chloroauric acid to chloroplatinic acid is 0.5 - 1.5:1;

[0014] When the mixed solution is a mixture of chloroplatinic acid and silver nitrate, the concentrations of both chloroplatinic acid and silver nitrate are 0.1 mol / L, and the volume ratio of chloroplatinic acid to silver nitrate is 0.5 - 1.5:1;

[0015] Step 3: Irradiate the titanium dioxide nanotube array grown on the surface of the titanium metal substrate in the mixed solution obtained in Step 2 with femtosecond laser, so that nanoparticles grow at the top of the titanium dioxide nanotube array, and thus a Raman spectroscopy enhancement substrate is obtained;

[0016] The defocus amount during femtosecond laser irradiation is 100 - 300 μm, the repetition frequency of the laser emitting femtosecond laser is set to 85 MHz; the single-pulse energy of the femtosecond laser is 10 nJ - 25 nJ.

[0017] Beneficial effects

[0018] 1. The process method of the femtosecond laser pulse liquid-phase ablation-assisted metal ion reduction for preparing a nanotube-metal particle multi-plasma nanostructure involved in the present invention enhances the formation of a multi-plasma nanostructure by directly writing and embedding metal nanoparticles on the surface of the titanium dioxide nanotube array, thereby enhancing the SERS performance. Due to the existence of the local surface plasmon resonance effect, the multi-metal nanostructure resonates to generate "hot spots", thereby generating an enhanced local electric field to achieve the regulation of SERS signal performance. Compared with other processing methods, this process has simple and efficient steps, and has high controllability and stability.

[0019] 2. The femtosecond laser with time-domain shaping can flexibly control the microscopic morphology of nanotubes-metal nanoparticles by regulating parameters such as pulse energy, pulse delay of the pulse train, and scanning speed. Compared with traditional chemical methods and deposition methods, femtosecond laser ablation in liquid assisted plasma reduction can achieve the embedding of metal nanoparticles on the surface of nanotubes and can realize flexible patterning preparation.

[0020] 3. Rhodamine (R6G) was used to evaluate the SERS performance of the nanotube-metal particle multi-plasma nanostructure. The results show that the prepared multi-structure has significantly enhanced SERS performance and can detect R6G with a minimum concentration of 1×10 -12 M, and the enhancement factor reaches 1.27×10 8 . In addition, the maximum relative standard deviation is 3.02% after being exposed to air for two months. The experimental results prove the physicochemical stability of this structure.

[0021] 4. One-step preparation process. The present invention combines femtosecond laser ablation in liquid and metal ion reduction technology to directly generate a metal particle composite structure on the surface of titanium dioxide nanotubes, optimizing the traditional multi-step process to achieve high-efficiency, low-cost, and pollution-free preparation.

[0022] 5. Adjustable structural parameters. The present invention precisely controls the nanotube pore size, metal particle size and distribution density by regulating femtosecond laser energy, pulse frequency and metal ion concentration, optimizes the multi-plasma resonance effect, and improves the SERS enhancement factor and signal repeatability.

[0023] 6. Interface coupling enhances stability. The present invention forms a strong interface coupling between nanotubes and metal particles to inhibit the aggregation and oxidation of metal particles, so that the substrate still maintains stable SERS performance during long-term use and in extreme environments.

[0024] 7. Realize process simplification and efficiency improvement. Traditional multi-plasma nanostructures require multi-step preparation, with complex processes and long cycles, and are prone to introducing chemical pollution. The present invention realizes high-efficiency and green preparation through in-situ synthesis by one-step femtosecond laser ablation in liquid and metal ion reduction.

[0025] 8. Realize precise regulation of multi-structure parameters. The controllability of the size and distribution of the multi-structure of materials prepared by traditional methods is poor. The present invention significantly improves the SERS enhancement factor (EF) and signal repeatability by optimizing plasma resonance coupling.

[0026] 9. Achieve breakthroughs in stability and applicability. Traditional metal substrates are prone to oxidation and are difficult to be applied in complex and extreme environments. The present invention extends the substrate life to more than 10 times that of traditional methods through strong interface coupling between nanotubes and metal particles, and is suitable for applications in complex environments. Description of the Drawings

[0027] Figure 1 Schematic diagram of the preparation process of the Raman spectroscopy enhancement substrate of the present invention;

[0028] Figure 2 Scanning electron microscope images of the microscopic morphology of nanotube-metal particle multi-plasma nanostructures under different laser parameters;

[0029] Figure 3 Elemental analysis of the prepared patterned multi-SERS substrate under elemental analysis scanning characterization, where (a) scanning electron microscope image; (b) titanium elemental surface distribution; (c) oxygen elemental surface distribution; (d) platinum elemental surface distribution;

[0030] Figure 4 Transmission electron microscope images of metal nanoparticles embedded in nanotubes; where (a) morphology of titanium dioxide nanotubes; (b) morphology of nanoparticles; (c) electron diffraction pattern;

[0031] Figure 5 Actual Raman performance test of the prepared multi-plasma nanostructure;

[0032] Figure 6 Performance characterization of the prepared nanotube-metal particle multi-plasma nanostructure SERS substrate after 2 months. Detailed implementation manners

[0033] In order to make the technical means, creative features, achieved purposes and effects realized by the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments and illustrations.

[0034] Example 1

[0035] The parameters of the femtosecond laser used are as follows: The femtosecond laser system uses a laser produced by Newport Corporation, the central wavelength of the laser is 800 nm, the pulse width is 35 fs, the repetition frequency is 85 MHz, the maximum energy of a single pulse is 25 nJ, the intensity distribution is Gaussian, and the polarization is linear;

[0036] A Raman spectroscopy enhancement substrate, the structure of the substrate includes a titanium metal substrate, a nanotube array located on the titanium metal substrate, and nanoparticles located at the top of the nanotube array;

[0037] The nanotube is a titanium dioxide nanotube;

[0038] The nanoparticles are gold nanoparticles and platinum nanoparticles.

[0039] As Figure 1 shown, a femtosecond laser liquid-phase ablation preparation method for a Raman spectroscopy enhancement substrate, the steps of the method include:

[0040] Step 1: Polish the titanium metal substrate on a polishing machine, then place the polished titanium substrate in an ammonium fluoride solution for anodic oxidation for 30 minutes to obtain a titanium dioxide nanotube array, and finally fix the sample on the surface of a high-precision displacement stage.

[0041] Step 2: Immerse the sample with a titanium dioxide nanotube array on its surface in a mixed solution of chloroauric acid and chloroplatinic acid. The concentrations of both solutions are 0.1 mol / L and they are mixed in a ratio of 1:1.

[0042] Step 3: Set the repetition frequency of the titanium sapphire femtosecond laser to 85 MHz, set the defocus amount to 200 μm, and the single pulse energy of the femtosecond laser to 20 nJ. Irradiate the titanium dioxide nanotube array grown on the surface of the titanium metal substrate in the mixed solution obtained in Step 2 with the femtosecond laser to grow nanoparticles at the top of the titanium dioxide nanotube array, obtaining a Raman spectroscopy enhanced substrate, that is, a titanium dioxide nanotube - platinum - gold SERS structure substrate, as Figure 2 shown; perform elemental analysis on the prepared patterned multi - element SERS substrate, and its elemental composition is as Figure 3 shown; use a transmission electron microscope to characterize the lattice structure of the metal nanoparticles embedded in the nanotubes, as Figure 4 shown.

[0043] Step 4: For the titanium dioxide nanotube - platinum - gold SERS structure substrate obtained in Step 3, perform SERS signal characterization using a Raman spectrometer, and the results obtained are as Figure 5 shown. The signal intensity of the titanium dioxide nanotube - platinum - gold substrate is much higher than that of single - metal (titanium dioxide - gold, titanium dioxide - platinum) samples, which confirms that the prepared titanium dioxide nanotube - platinum - gold SERS structure substrate has more excellent Raman enhancement performance.

[0044] The stability of the titanium dioxide nanotube - platinum - gold SERS substrate structure and the repeatability of signal measurement are key indicators for measuring the performance of the SERS substrate.

[0045] Figure 6 They are respectively the initial test results and the SERS signal tests after being placed in air for one month and two months. From Figure 6 it can be seen that these three curves almost coincide. Calculate the standard deviation (SD) and the average value (Mean) of the peak intensity values of multiple measurements, and calculate the percentage of the standard deviation to the average value. The relative standard deviation of the Raman signal at the peak of 1360 cm -1 is 3.02%, indicating that the prepared titanium dioxide nanotube - platinum - gold SERS structure substrate has good chemical stability and repeatability.

[0046] Example 2

[0047] The parameters of the femtosecond laser used are as follows: The femtosecond laser system uses a laser produced by Newport Corporation of the United States. The central wavelength of the laser is 800 nm, the pulse width is 35 fs, the repetition frequency is 85 MHz, the maximum energy of a single pulse is 25 nJ, the intensity distribution is Gaussian, and it is linearly polarized.

[0048] A Raman spectroscopy enhancement substrate, the structure of which includes a titanium metal substrate, a nanotube array located on the titanium metal substrate, and nanoparticles located at the top of the nanotube array.

[0049] The nanotubes are titanium dioxide nanotubes.

[0050] The nanoparticles are gold nanoparticles and silver nanoparticles.

[0051] A femtosecond laser liquid-phase ablation preparation method for a Raman spectroscopy enhancement substrate, the steps of which include:

[0052] Step 1: Polish the titanium metal substrate on a polishing machine, then place the polished titanium substrate in an ammonium fluoride solution for anodic oxidation for 30 minutes to obtain a titanium dioxide nanotube array, and finally fix the sample on the surface of a high-precision displacement stage.

[0053] Step 2: Immerse the sample with a titanium dioxide nanotube array on its surface in a mixed solution of chloroauric acid and silver nitrate, and the concentrations of both solutions are 0.1 mol / L. Chloroauric acid and silver nitrate are mixed in a ratio of 1:1.

[0054] Step 3: Set the repetition frequency of the titanium sapphire femtosecond laser to 85 MHz, set the defocus amount to 200 μm, and the single pulse energy of the femtosecond laser to 25 nJ. Use the femtosecond laser direct writing method to process a large-area controllable titanium dioxide nanotube-metal nanoparticle multi-component plasma nanostructure on the titanium dioxide nanotube substrate to obtain a titanium dioxide nanotube-silver-gold SERS structure substrate.

[0055] Step 4: For the titanium dioxide nanotube-silver-gold SERS structure substrate obtained in Step 3, use a Raman spectrometer to perform SERS signal characterization. The measurement results also show that the signal intensity of the titanium dioxide nanotube-silver-gold substrate is much higher than that of single-metal (titanium dioxide-gold, titanium dioxide-silver) samples, which confirms that the prepared multi-component plasma nanostructure has more excellent Raman enhancement performance.

[0056] Step 5: The stability of the titanium dioxide nanotube-silver-gold SERS substrate structure and the repeatability of signal measurement are key indicators for measuring the performance of the SERS substrate. Perform SERS signal tests on the sample after it has been placed in the air for one month and two months. The tests show that the prepared multi-metal plasma resonance nanostructure has good chemical stability and repeatability.

[0057] Example 3

[0058] The parameters of the femtosecond laser used are as follows: The femtosecond laser system uses a laser produced by Newport Corporation. The central wavelength of the laser is 800 nm, the pulse width is 35 fs, the repetition rate is 85 MHz, the maximum energy of a single pulse is 25 nJ, the intensity distribution is Gaussian, and it is linearly polarized;

[0059] A Raman spectroscopy enhanced substrate, the structure of which includes a titanium metal substrate, a nanotube array located on the titanium metal substrate, and nanoparticles located at the top of the nanotube array;

[0060] The nanotubes are titanium dioxide nanotubes;

[0061] The nanoparticles are silver nanoparticles and platinum nanoparticles.

[0062] A femtosecond laser liquid-phase ablation preparation method for a Raman spectroscopy enhanced substrate, the steps of which include:

[0063] Step 1: Polish the titanium metal substrate on a polishing machine, then place the polished titanium substrate in an ammonium fluoride solution for anodic oxidation for 30 minutes to obtain a titanium dioxide nanotube array, and finally fix the sample on the surface of a high-precision displacement stage.

[0064] Step 2: Immerse the sample with a titanium dioxide nanotube array on its surface in a mixed solution of chloroplatinic acid and silver nitrate. The concentrations of both solutions are 0.1 mol / L, and the ratio of chloroplatinic acid to silver nitrate is 1:1.

[0065] Step 3: Set the repetition rate of the titanium sapphire femtosecond laser to 85 MHz, set the defocus amount to 240 μm, and the single pulse energy of the femtosecond laser to 25 nJ. Use the femtosecond laser direct writing method to process a large-area controllable titanium dioxide nanotube-metal nanoparticle multi-plasma nanostructure on the titanium dioxide nanotube substrate to obtain a titanium dioxide nanotube-silver-gold SERS structure substrate;

[0066] Step 4: For the titanium dioxide nanotube-platinum-silver SERS structure substrate obtained in Step 3, use a Raman spectrometer to perform SERS signal characterization. The results show that the signal intensity of the titanium dioxide nanotube-platinum-silver substrate is much higher than that of single-metal (titanium dioxide-platinum, titanium dioxide-silver) samples, which confirms that the prepared multi-plasma nanostructure has more excellent Raman enhancement performance.

[0067] Step 5: The stability of the titanium dioxide nanotube-platinum-silver SERS substrate structure and the repeatability of signal measurement are key indicators for measuring the performance of the SERS substrate. The SERS signal tests were carried out after the samples were placed in the air for one month and two months. The tests show that the multi-metal plasmon resonance nanostructures prepared in this paper have good chemical stability and repeatability.

[0068] In summary, the above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A Raman spectroscopy enhancement substrate, characterized in that: The structure of the substrate includes a titanium metal substrate, a nanotube array located on the titanium metal substrate, and nanoparticles located at the top of the nanotube array; The nanoparticles are two of gold nanoparticles, silver nanoparticles, and platinum nanoparticles.

2. The Raman spectroscopy enhancement substrate according to claim 1, characterized in that: The nanotubes are titanium dioxide nanotubes.

3. A femtosecond laser liquid-phase ablation preparation method for a Raman spectroscopy enhancement substrate, characterized in that The steps of this method include: Step 1, polish the titanium metal substrate on a polishing machine, and then place the polished titanium metal substrate in an ammonium fluoride solution for anodic oxidation to obtain a titanium metal substrate with a titanium dioxide nanotube array grown on its surface; Step 2, immerse the titanium metal substrate with the titanium dioxide nanotube array grown on its surface obtained in Step 1 in a mixed solution, and the mixed solution is a mixture of two of chloroauric acid, chloroplatinic acid, and silver nitrate; Step 3, irradiate the titanium dioxide nanotube array grown on the surface of the titanium metal substrate in the mixed solution obtained in Step 2 with femtosecond laser to grow nanoparticles at the top of the titanium dioxide nanotube array, and obtain a Raman spectroscopy enhancement substrate.

4. The femtosecond laser liquid-phase ablation preparation method of the Raman spectroscopy enhancement substrate according to claim 3, characterized in that: In Step 1, the anodic oxidation time is 20 - 40 min.

5. The femtosecond laser liquid-phase ablation preparation method of the Raman spectroscopy enhancement substrate according to claim 3, characterized in that: In Step 2, the mixed solution is a mixture of chloroauric acid and chloroplatinic acid, the concentrations of chloroauric acid and chloroplatinic acid are both 0.1 mol / L, and the volume ratio of chloroauric acid to chloroplatinic acid is 0.5 - 1.5:

1.

6. The femtosecond laser liquid-phase ablation preparation method of the Raman spectroscopy enhancement substrate according to claim 3, characterized in that: In Step 2, the mixed solution is a mixture of chloroauric acid and silver nitrate, the concentrations of chloroauric acid and silver nitrate are both 0.1 mol / L, and the volume ratio of chloroauric acid to chloroplatinic acid is 0.5 - 1.5:

1.

7. The femtosecond laser liquid-phase ablation preparation method of the Raman spectroscopy enhancement substrate according to claim 3, characterized in that: In Step 2, the mixed solution is a mixture of chloroplatinic acid and silver nitrate, the concentrations of chloroplatinic acid and silver nitrate are both 0.1 mol / L, and the volume ratio of chloroplatinic acid to silver nitrate is 0.5 - 1.5:

1.

8. The femtosecond laser liquid-phase ablation preparation method of the Raman spectroscopy enhancement substrate according to claim 3, characterized in that: In Step 2, the defocus amount during the femtosecond laser irradiation is 100 - 300 μm, the repetition frequency of the laser emitting the femtosecond laser is set to 85 MHz; the single-pulse energy of the femtosecond laser is 10 nJ - 25 nJ.

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