Glass surface-enhanced raman substrate and its femtosecond laser preparation method

Abstract

The application discloses a glass surface enhanced Raman substrate and a femtosecond laser preparation method thereof, and belongs to the fields of optics, materials and biology and the like.The femtosecond laser preparation method of the glass surface enhanced Raman substrate disclosed by the application constructs a composite micro-nano structure with a micron skeleton structure, a subwavelength stripe and a nano protrusion through two-stage femtosecond laser processing, realizes high-density and uniform distribution of hot spots, and significantly improves an enhancement factor and a signal-to-noise ratio of the glass surface enhanced Raman substrate.A precious metal plating layer with a thickness difference / gradient is prepared, electromagnetic enhancement effects and local structure optimization of different regions are realized, and sensitivity and stability of the SERS substrate are improved.The consistency and repeatability of batch preparation are ensured by standard Raman probe molecule calibration, selection of optimal laser parameters, film thickness and reconstruction conditions.The Raman signal of the glass substrate itself is very weak, background noise interference is effectively avoided, and reliability and stability of a detection result are improved.

Description

Technical Field

[0001] This invention relates to multiple fields such as optics, materials, and biology, and in particular to a glass surface-enhanced Raman substrate and its femtosecond laser preparation method. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) technology, due to its ultra-high sensitivity and ability to provide molecular "fingerprint" information, has been widely applied in fields such as chemistry, materials science, biomedicine, and environmental monitoring, showing great potential, especially in trace analysis. The enhancement of the SERS effect mainly originates from the huge electromagnetic field enhancement generated by local surface plasmon resonances on the substrate surface. Since the intensity of the enhancement effect is closely related to the surface morphology and the local electromagnetic field density of the material, the enhancement effect of the SERS substrate directly depends on the fine construction of its micro- and nano-structures.

[0003] Currently, the main methods for preparing SERS substrates include chemical synthesis, micro / nano fabrication technology, and self-assembly technology. (1) Chemical synthesis: such as using gold or silver nanoparticle colloids directly as substrates, but the substrate uniformity of this method is poor, the reproducibility is low, and the nanoparticles are easy to aggregate, leading to performance degradation; (2) Micro / nano fabrication technology: such as electron beam lithography, focused ion beam, nanoimprint lithography, etc. These methods can precisely control the morphology and size, but they generally have problems such as expensive equipment, low processing efficiency, high cost, and difficulty in large-area preparation; (3) Self-assembly technology: such as nanosphere-based lithography, although the cost is low, the preparation process is complex and it is difficult to avoid the generation of defects.

[0004] Femtosecond laser (pulse width in 10) -15 Femtosecond lasers possess extremely high peak power and ultra-short interaction times, enabling them to induce the formation of micro- and nano-structures on the surfaces of solid materials such as glass. Femtosecond laser processing exhibits strong nonlinearity, non-thermal equilibrium, and "cold processing" characteristics, allowing for the efficient formation of fine structures on almost any solid material surface, and has become an important technology for fabricating high-performance SERS substrates.

[0005] However, the response of glass surfaces to femtosecond lasers is highly dependent on the deposition of local energy and the laser scanning strategy. Traditional single processing parameters can often only obtain limited rough structures, making it difficult to simultaneously optimize hotspot density, uniformity, and repeatability. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a method for fabricating enhanced Raman substrates by femtosecond laser processing on the surface of transparent dielectric glass through staged femtosecond laser processing to construct multi-scale composite micro-nano structures, and combining this with the controllable reconstruction of noble metal thin films to form nano-interval hot spots. Another objective of the present invention is to provide a glass surface enhanced Raman substrate with high sensitivity, high uniformity, and high batch consistency.

[0007] This invention discloses a femtosecond laser fabrication method for glass surface-enhanced Raman substrates, comprising:

[0008] A glass substrate is provided, and the glass substrate is pretreated to make its surface clean;

[0009] The first stage of femtosecond laser scanning processing forms a micron-sized framework structure on the surface of the glass substrate at a first scanning speed and a first line spacing.

[0010] The second stage of femtosecond laser scanning processing uses a second scanning speed, a second line spacing, and a scanning strategy to form a nanostructure in which subwavelength periodic stripes and nanoprotrusions coexist, giving the surface of the glass substrate a composite micro-nano structure.

[0011] Remove the debris redeposited on the surface of the glass substrate;

[0012] A noble metal coating is deposited on the surface of the glass substrate, wherein the equivalent thickness of the noble metal coating in the top region of the micron skeleton is different from the equivalent thickness in the region inside the trench / pit, so as to form a thickness difference or thickness gradient.

[0013] The noble metal coating is subjected to controlled reconstruction to form nanoparticles, island structures and nano gaps, thereby obtaining a glass surface-enhanced Raman substrate.

[0014] The performance of the glass surface-enhanced Raman substrate was calibrated using standard Raman probe molecules, and the optimal parameter combination was selected for batch preparation of glass surface-enhanced Raman substrates.

[0015] In surface-enhanced Raman scattering (SERS) technology, hotspots refer to tiny regions on the substrate that can generate extremely strong electromagnetic field enhancements, typically the tips, gaps, or narrow gaps between two nanoparticles of a nanostructure.

[0016] This invention also discloses a glass surface-enhanced Raman substrate, which is prepared using the femtosecond laser fabrication method described above. The surface of the glass surface-enhanced Raman substrate has a composite micro / nano structure composed of a micron-scale framework, subwavelength stripes, and nano-protrusions. The surface of the composite micro / nano structure is covered with a noble metal coating, and the noble metal coating is controlled to form granular and island-like structures and nano-interstic gaps. The average size of the nano-interstic gaps is 1-30 nm. The noble metal coating has different equivalent thicknesses or thickness gradients in the top region of the micron-scale framework and the inner region of the trenches / pits.

[0017] This invention discloses a femtosecond laser fabrication method for glass surface-enhanced Raman (SERS) substrates. Through two-stage femtosecond laser processing, a composite micro / nano structure with a micron-scale framework, subwavelength stripes, and nanoprotrusions is constructed, achieving a high-density and uniform distribution of hot spots, significantly improving the enhancement factor and signal-to-noise ratio of the glass surface-enhanced Raman substrate. The fabrication of a noble metal coating with thickness differences / gradients realizes electromagnetic enhancement effects and local structural optimization in different regions, improving the sensitivity and stability of the SERS substrate. Standard Raman probe molecular calibration is used to select optimal laser parameters, film thickness, and reconstruction conditions, ensuring consistency and repeatability in batch fabrication. The Raman signal of the glass substrate itself is very weak, effectively avoiding interference from background noise and improving the reliability and stability of the detection results. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a femtosecond laser fabrication method for a glass surface-enhanced Raman substrate provided in an embodiment of the present invention;

[0019] Figure 2 This is a scanning electron microscope image of a glass surface-enhanced Raman substrate obtained in Embodiment 1 of the present invention;

[0020] Figure 3 for Figure 2 A magnified view of a portion of the image;

[0021] Figure 4 Raman spectra of Rhodamine 6G at different concentration gradients were obtained by sputtering gold onto a smooth quartz glass substrate for comparison.

[0022] Figure 5 Comparison of Rhodamine 6G Raman spectra obtained from the glass surface-enhanced Raman substrate in Example 1 and the comparative smooth quartz glass substrate after gold sputtering.

[0023] Figure 6 For different Au coating thicknesses in the glass surface-enhanced Raman substrate obtained in Example 1, Rhodamine 6G (10 -4 mol / L) at 1312 cm -1 The curve showing the variation of SERS peak intensity at a given location. Detailed Implementation

[0024] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Please see below. Figure 1 , Figure 1 The flowchart of a femtosecond laser fabrication method for a glass surface enhanced Raman substrate provided in an embodiment of the present invention specifically includes steps S10-S70.

[0026] S10. Provide a glass substrate and perform pretreatment on the glass substrate to make its surface clean;

[0027] S20, First-stage femtosecond laser scanning processing, forming a micron-sized skeleton structure on the surface of the glass substrate at a first scanning speed and a first line spacing;

[0028] S30, the second stage of femtosecond laser scanning processing, with a second scanning speed, a second line spacing and a scanning strategy, forms a nanostructure in which subwavelength periodic stripes and nanoprotrusions coexist, so that the surface of the glass substrate has a composite micro-nano structure.

[0029] S40. Remove the debris redeposited on the surface of the glass substrate;

[0030] S50. Deposit a noble metal coating on the surface of the glass substrate, wherein the equivalent thickness of the noble metal coating in the top region of the micron skeleton is different from the equivalent thickness in the region inside the trench / pit, so as to form a thickness difference or thickness gradient.

[0031] S60. The noble metal coating is subjected to controlled reconstruction treatment to form nanoparticles, island structures and nano gaps to obtain a glass surface enhanced Raman substrate.

[0032] S70. The performance of the glass surface-enhanced Raman substrate is calibrated using standard Raman probe molecules, and the optimal parameter combination is selected for batch preparation of glass surface-enhanced Raman substrates.

[0033] In step S10, the glass substrate is selected from any one of quartz glass, borosilicate glass, and soda-lime glass.

[0034] The pretreatment of the glass substrate to clean its surface includes ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence, followed by drying.

[0035] In one embodiment, in step S20, the first scanning speed is 100-600 mm / s, the first line spacing is 5-30 μm, the micron skeleton structure includes at least one of a trench array, a pit array, and a corrugated array, the depth of the micron skeleton structure is 0.2-6 μm, and the feature scale period is 10-100 μm.

[0036] The micron-scale framework is used to provide multiple scattering and macroscopic light harvesting.

[0037] In one embodiment, in step S30, the second scanning speed is 50-800 mm / s, and the second line spacing is 0.5-15 μm; the scanning strategy includes at least one of cross scanning, polarization rotation scanning, secondary refinement scanning with different energy densities, and dual-pulse time-series scanning; the nanostructure with the coexistence of subwavelength periodic stripes and nanoprotrusions is a subwavelength stripe structure with a period of 100-900 nm accompanied by a nanoprotrusion structure with a height of 10-300 nm.

[0038] For example, the center wavelength of the femtosecond laser is 343-355nm, 515-532nm or 1030-1064nm; the pulse width is 100-600fs; and the repetition frequency is 1kHz-1MHz.

[0039] The preferred center wavelength is 343nm, the pulse width is 150fs, and the repetition frequency is 200kHz.

[0040] More specifically, polarization rotation scanning or cross scanning is used to make the polarization direction difference between adjacent scanning tracks 30°-90°; or dual-pulse timing scanning is used with a dual-pulse delay of 0–5000 fs.

[0041] More specifically, the composite micro / nano structure includes a trench array and a pit array, or a trench array and a corrugated array, within the same active region, and the density of nanostripes and nanoprotrusions at the edges, intersections, or curvature abrupt regions of the micron skeleton is higher than that in flat regions.

[0042] The density of nanostripes and nanoprotrusions is higher at the edges, intersections, or curvature abrupt changes of the micron skeleton than in flat areas, thus causing electromagnetic hotspots to be preferentially distributed at the edges, tips, and structural intersections of the micron skeleton.

[0043] In one embodiment, step S40, the step of removing the debris redeposited on the glass substrate surface, includes:

[0044] The glass substrate is ultrasonically cleaned with deionized water or anhydrous ethanol to remove redeposited debris. After drying, the surface of the glass substrate is activated with ultraviolet light, ozone, or oxygen plasma.

[0045] The surface of the glass substrate is activated by ultraviolet light, ozone, or oxygen plasma to enhance the adhesion and uniformity of subsequently deposited noble metal coatings.

[0046] In one embodiment, in step S50, the noble metal coating includes one of a single-layer noble metal film and a heterogeneous multilayer film; by tilting deposition or rotating and segmented deposition, the equivalent thickness of the noble metal coating in the top region of the micron skeleton is different from the equivalent thickness in the region inside the trench / pit.

[0047] Noble metal thin films are obtained by physical vapor deposition, which includes magnetron sputtering or electron beam evaporation.

[0048] By creating an equivalent thickness difference or thickness gradient between the top region of the micro-skeleton and the interior region of the trench / pit, the reconstructed nano-gap hotspots are transformed from a random distribution to an enriched distribution at the edges and intersections of the micro-skeleton, thereby significantly improving the SERS signal intensity and uniformity.

[0049] The thickness gradient structure enables the formation of a continuous thickness parameter library on the same sample. Combined with standard probe molecular calibration, the optimal thickness range can be quickly locked, which can be used to solidify the process window during large-scale preparation and significantly reduce batch differences.

[0050] The principle behind the effect of thickness gradient is primarily that thickness determines the morphological path of dewetting reconstruction. Thinner noble metal films with a thickness of 10-12 nm are more prone to fracturing into discrete islands, but the gaps between islands may be relatively large, resulting in strong but few hot spots, and the overall signal has not yet taken hold. Noble metal films with a moderate thickness of 14-16 nm can form both high-density particles or island structures and generate a large number of effective gaps of 1-30 nm, with both the number and intensity of hot spots entering the optimal range, thus resulting in a peak signal. Excessively thick noble metal films with a thickness ≥18-24 nm tend to be continuous or form coarse island clusters or coalesce, the nano-gaps are filled, the number of gaps decreases, hot spots attenuate, and the signal declines.

[0051] Secondly, thickness differences or thickness gradients "push" the reconstruction towards the edges, increasing the effective proportion of hotspots. Because the local curvature, temperature field, and material migration path differ between the top and valley of the micron-scale framework structure, reconstruction is often random without thickness differences. With continuity and a thickness gradient, the driving force of material migration and film stability are redistributed. Thicker films at the valley bottoms make it easier to form islands and small gaps and retain their quantity, while thinner films at the top avoid forming large continuous films, reducing the phenomenon of "hotspot flooding." Reconstruction with films having thickness differences ultimately concentrates hotspots at the edges and intersections, effectively increasing the proportion of hotspots.

[0052] Finally, the thickness gradient is essentially a "built-in tolerance design," improving repeatability. Actual processing inevitably involves minor fluctuations (energy, focus, cleaning residue), and the thickness gradient ensures that there's always a section on the same sheet with a thickness within the optimal range. This makes it easier to calibrate and screen out qualified areas during mass production, improving consistency.

[0053] In one embodiment, in step S50, before depositing a noble metal coating on the surface of the glass substrate, an adhesion layer or a wetting control layer is deposited first; the thickness of the adhesion layer or the wetting control layer is 1-5 nm; the adhesion layer is selected from at least one of Ti, Cr, Ta, Al2O3, and SiO2; the thickness of the noble metal coating is 5-60 nm; the noble metal coating is selected from at least one of Au, Ag, and Pt.

[0054] Before depositing the noble metal thin film, an adhesion layer of 1-5 nm is first deposited to increase the adhesion of the noble metal thin film.

[0055] More specifically, the heterogeneous multilayer film includes one of the following: a stack of Ag and Au layers, a stack of Au and Ag layers, a stack of metal layer-dielectric layer-metal layer, an Ag-Ag alloy layer, and an Ag-Pt alloy layer; in the Ag and Au layer stack, the thickness of the Ag layer is 10-60 nm, and the thickness of the Au layer is 1-15 nm; in the Au and Ag layer stack, the thickness of the Au layer is 5-50 nm, and the thickness of the Ag layer is 5-40 nm; in the metal layer-dielectric layer-metal layer stack, the dielectric layer is SiO2 or Al2O3, and the thickness is 1-10 nm; in the Au and Ag alloy layer or the Ag and Pt alloy layer, the atomic ratio of Au to Ag or Ag to Pt is 1:9-9:1.

[0056] Heterogeneous stacked films can control the particle size and nano-gap distribution after dewetting and reconstruction, so that the nano-gap preferentially appears at the edge of the micron skeleton and the intersection of the nano-stripes.

[0057] In one embodiment, in step S60, the controlled reconstruction process includes heat treatment or femtosecond laser shaping to trigger thin film dewetting reconstruction, so that the noble metal is transformed into particles and island structures at the structural tips and gaps and forms nano-gap hot spots.

[0058] For example, the heat treatment is performed under an inert atmosphere or vacuum, at a temperature of 150-500℃, and for a holding time of 5-120 minutes. The line energy of the femtosecond laser shaping process is lower than that in step S20, allowing the noble metal coating to undergo dewetting and reconstruction without damaging the micron-scale framework structure.

[0059] After controlled reconstruction treatment, the noble metal coating forms nanoparticles or island structures at the edges of the micron framework and at the nanostructure, and generates nano gaps. These nano gaps are the main contributing regions for SERS enhancement hotspots.

[0060] In step S70, the standard Raman probe molecule includes any one of 4-mercaptobenzoic acid, rhodamine 6G, or crystal violet; in the step of screening for the optimal parameter combination, the screening indicators include characteristic peak intensity, peak position stability, and uniformity.

[0061] The uniformity index is defined as a relative standard deviation (RSD) of peak intensity obtained by multi-point or surface scanning within the active region not exceeding 15%, and a peak position drift not exceeding 2 cm. -1 .

[0062] This invention also discloses a glass surface-enhanced Raman substrate, which is prepared using the femtosecond laser fabrication method described in any of the above embodiments. The surface of the glass surface-enhanced Raman substrate has a composite micro / nano structure composed of a micron-scale framework, subwavelength stripes, and nano-protrusions. The surface of the composite micro / nano structure is covered with a noble metal coating, and the noble metal coating is controlled to form particles and island structures and nano-interstic gaps. The average size of the nano-interstic gaps is 1-30 nm. The noble metal coating has different equivalent thicknesses or thickness gradients in the top region of the micron-scale framework and the inner region of the trenches / pits.

[0063] The femtosecond laser-processed glass surface enhanced Raman substrate provided in this invention can be used for trace Raman spectroscopy detection of organic dye molecules, pesticide residues, or biomarkers.

[0064] The specific detection steps include: using a pipette to drop the test solution onto a glass surface Raman-enhanced substrate; after the solvent evaporates or adsorption reaches equilibrium, using a Raman spectrometer to irradiate the substrate surface with a laser and collect Raman signals; and analyzing the composition and concentration of the analyte based on the intensity and shift of the Raman characteristic peaks.

[0065] Specific preparation examples are as follows:

[0066] Example 1

[0067] (1) Take a fused silica glass plate with a size of 20mm×20mm×1mm and place it in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning in sequence, each step lasting 10-15 minutes. After cleaning, dry it with high-purity nitrogen or compressed air and store it in a clean environment for later use.

[0068] (2) The cleaned glass substrate was fixed on a three-dimensional precision displacement platform, and a femtosecond laser direct writing system was used for staged scanning processing. The operating parameters of the femtosecond laser were set to a center wavelength of 343 nm, a pulse width of 150 fs, and a repetition frequency of 200 kHz. First stage: The surface of the glass substrate was scanned at a high scanning speed (400 mm / s) and a large line spacing (9 μm) to form a micron-scale skeleton structure. The micron-scale skeleton structure was a trench array with a trench depth of 0.5–5 μm. The laser energy density of the first stage was set to 3.33 μJ, and the spot diameter was 11 μm. The roughness and multiple scattering characteristics at the micron scale were controlled by the scanning speed and line spacing.

[0069] (3) Second stage: The edges, sidewalls and bottom regions of the micron skeleton structure formed in the first stage are finely processed at a low scanning speed (200 mm / s) and a small line spacing (5 μm). Through cross scanning and polarization rotation scanning, the laser action area produces a nano-substructure with periodic stripes and nano-protrusions coexisting. The stripe period is 100-300 nm and the protrusion height is 50-150 nm.

[0070] (4) The processed glass substrate is ultrasonically cleaned with deionized water or anhydrous ethanol for 3-5 minutes to remove the redeposited debris on the surface. After cleaning, the substrate is placed in a clean environment to dry, and optionally subjected to ultraviolet ozone treatment for 5-10 minutes to enhance the adhesion and uniformity of the coating.

[0071] (5) A single-layer Au film with a thickness of 20-40 nm was deposited on the surface of the treated composite micro / nano structure using magnetron sputtering deposition. Before deposition, an adhesion layer of 1-5 nm, such as Ti, Cr, or Ta, was deposited to increase the adhesion of the film. During the deposition process, tilting deposition and substrate rotation were used to make the Au film form different equivalent thicknesses at the top of the micron skeleton and in the trench / pit region.

[0072] (6) The deposited Au film is reconstructed in a controlled manner by heat treatment or low-energy femtosecond laser shaping. Heat treatment is carried out in an inert atmosphere at a temperature of 250-450℃ for 20-60 minutes. During femtosecond laser shaping, the laser energy density is low (lower than the laser energy in the first stage). The pulse energy of the femtosecond laser guides the Au film to undergo dewetting, causing the noble metal Au to form nanoparticles and island structures at the tips and gaps of the structure, and generating nano-gap hot spots. After reconstruction, a glass surface-enhanced Raman substrate is obtained.

[0073] (7) Rhodamine 6G (R6G), a standard Raman probe molecule, was used to calibrate surface-enhanced Raman spectroscopy (SERS) substrates with different structural parameters and thicknesses. The parameter combination with the highest peak intensity, best peak position stability, and optimal uniformity was selected. Based on this calibration parameter combination, batch preparation was carried out to ensure the consistency and high performance of SERS substrates in large-scale production.

[0074] The obtained glass surface-enhanced Raman substrate was subjected to scanning electron microscopy (SEM) testing, and the resulting structure is shown below. Figures 2-3 As shown, the surface of the glass surface-enhanced Raman spectroscopy substrate has a micron-scale framework structure (the micron-scale framework structure is a trench array), a nanoscale substructure in which periodic stripes and nanoprotrusions coexist, and a composite micro / nano structure of "micron-scale framework-nano stripes-nano protrusions" is obtained, which also has nanoparticles, island structures and nano gaps.

[0075] Example 2

[0076] (1) The glass substrate was cleaned and dried using the same method as in Example 1 to ensure that its surface was free of contaminants.

[0077] (2) Using the same femtosecond laser as in Example 1, different processing modes were applied to the glass substrate. First stage: A microgroove array or micropit array was formed on the substrate surface using a low scanning speed (200 mm / s) and a large line spacing (10 μm) to control the processing depth (0.5-8 μm) and ensure the uniformity of the grooves / pits.

[0078] (3) Second stage: At the intersection, edge or bottom area of ​​the micro-groove or micro-pit structure, cross scanning or polarization rotation is used for fine finishing to form subwavelength periodic stripes and nano-protrusions. The stripe period is 100-500nm and the protrusion height is 50-300nm, ensuring that the hot spot is concentrated in the intersection area of ​​the micro-groove.

[0079] (4) Use deionized water for ultrasonic cleaning and perform ultraviolet ozone treatment for 5–10 minutes to enhance the adhesion of the coating.

[0080] (5) On the treated substrate, a gold-silver alloy thin film is deposited using magnetron sputtering. The film thickness is 20-40 nm, and a two-step deposition method is preferred: first, a thinner gold layer (10-15 nm) is deposited, and then a thicker silver layer (10-30 nm) is deposited. During the deposition process, substrate rotation and tilting deposition techniques are used to create different equivalent thicknesses of the alloy film at the top of the micron framework and inside the trenches / pits.

[0081] (6) The gold-silver alloy film is dewetting by heat treatment (holding at 450℃ for 30 minutes), forming nanoparticles and island structures, and forming nano gaps at the tips of the structures and the intersection of grooves / pits, thus obtaining a glass surface reinforced Raman substrate.

[0082] (7) The performance of the obtained glass surface-enhanced Raman substrate was calibrated using the standard probe molecule R6G to ensure the consistency of the glass surface-enhanced Raman substrate in different batches of production. The laser parameters, coating thickness and reconstruction conditions with the best performance were selected for large-scale production.

[0083] Example 3

[0084] Steps (1) to (4) are performed using the same methods as in Example 1.

[0085] (5) Using a bimetallic stacked thin film structure (such as Ag / Au stack or Au / Ag stack), a silver layer (10–30 nm) is first deposited, followed by a gold layer (2–10 nm). By controlling the deposition order and thickness, the thickness difference of the metal layer in different regions can be achieved.

[0086] (6) Low-energy femtosecond laser is used to shape the thin film, so that the silver metal undergoes dewetting reconstruction at the tip and gap of the micro-nano structure, forming nanoparticles and island structures and forming nano gap hot spots, thus obtaining a glass surface enhanced Raman substrate.

[0087] (7) The performance of the obtained glass surface-enhanced Raman substrate was calibrated using the standard probe molecule R6G to ensure the consistency of the glass surface-enhanced Raman substrate in different batches of production. The laser parameters, coating thickness and reconstruction conditions with the best performance were selected for large-scale production.

[0088] Comparative Example

[0089] It uses a smooth quartz glass base with a gold-plated surface.

[0090] Raman spectra of different concentrations of the standard Raman probe molecule rhodamine 6G were tested on a smooth quartz glass substrate as a comparative example. The test results are as follows: Figure 4 As shown. When the concentration of Rhodamine 6G is 10... -8 At mol / L, using a comparative smooth quartz glass substrate, it was not possible to obtain an effective Raman spectrum.

[0091] The glass surface-enhanced Raman substrate prepared in Example 1 was tested at a concentration of 10. -8 The Raman spectrum obtained from a mol / L rhodamine 6G solution is as follows: Figure 5 As shown.

[0092] like Figure 5As shown, the Raman spectrum obtained using the glass surface-enhanced Raman substrate obtained in Example 1 clearly shows multiple characteristic Raman peaks of the R6G molecule, such as 612, 775, 1183, 1360, 1509, and 1649 cm⁻¹. -1 The signal strength is extremely high and the background is clean. Comparison with the Raman spectrum obtained on a flat gold-plated quartz plate in the comparative example shows that the glass surface-enhanced Raman substrate obtained in Example 1 achieves a signal enhancement factor of 3.87 × 10⁻⁶ for R6G. 6 At least 10 - 8 The mol / L concentration was effectively detected.

[0093] Tests were conducted on R6G (10) at different Au coating thicknesses. -4 mol / L) at 1312 cm -1 The SERS peak intensity at the location is as follows: Figure 6 As shown.

[0094] like Figure 6 As shown, the effect of Au coating thickness on performance exhibits a pattern of first increasing and then decreasing. When the equivalent Au thickness increases from 10 nm to 16 nm, R6G at 1312 cm⁻¹... -1 The peak intensity increased significantly; when the thickness was further increased to 18-24 nm, the peak intensity decreased, indicating that the thickness gradient and reconstruction jointly determine the effective formation probability and coupling efficiency of hotspots. The Raman peak intensity showed a characteristic of first increasing and then decreasing with the increase of Au thickness, reaching a maximum value at about 16 nm, proving that the thickness of the noble metal coating has a decisive influence on the formation of nano-gap hotspots after dewetting and reconstruction.

[0095] By introducing an equivalent thickness difference or thickness gradient between the top of the micron skeleton and the inside of the grooves / pits, the hot spots in the reconstructed nano gaps are transformed from a random distribution to an enriched distribution in the edge / intersection region, thereby significantly improving the SERS signal intensity and uniformity.

[0096] The thickness gradient structure enables the formation of a continuous thickness parameter library on the same glass surface-enhanced Raman substrate. Combined with standard probe molecular calibration, the optimal thickness range can be quickly locked, which can be used for process window curing during large-scale preparation and significantly reduce batch differences.

[0097] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for fabricating a femtosecond laser on a glass surface-enhanced Raman substrate, characterized in that, include: A glass substrate is provided, and the glass substrate is pretreated to make its surface clean; The first stage of femtosecond laser scanning processing forms a micron-sized framework structure on the surface of the glass substrate at a first scanning speed and a first line spacing. The second stage of femtosecond laser scanning processing uses a second scanning speed, a second line spacing, and a scanning strategy to form a nanostructure in which subwavelength periodic stripes and nanoprotrusions coexist, giving the surface of the glass substrate a composite micro-nano structure. Remove the debris redeposited on the surface of the glass substrate; A noble metal coating is deposited on the surface of the glass substrate, wherein the equivalent thickness of the noble metal coating in the top region of the micron skeleton is different from the equivalent thickness in the region inside the trench / pit, so as to form a thickness difference or thickness gradient. The noble metal coating is subjected to controlled reconstruction to form nanoparticles, island structures and nano gaps, thereby obtaining a glass surface-enhanced Raman substrate. The performance of the glass surface-enhanced Raman substrate was calibrated using standard Raman probe molecules, and the optimal parameter combination was selected for mass production of glass surface-enhanced Raman substrates.

2. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 1, characterized in that, The first scanning speed is 100-600 mm / s, and the first line spacing is 5-30 μm; the micron skeleton structure includes at least one of a groove array, a pit array, and a corrugated array; the depth of the micron skeleton structure is 0.2-6 μm, and the feature scale period is 10-100 μm.

3. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 2, characterized in that, The second scanning speed is 50-800 mm / s, and the second line spacing is 0.5-15 μm; the scanning strategy includes at least one of cross scanning, polarization rotation scanning, secondary refinement scanning with different energy densities, and dual-pulse time-series scanning; the nanostructure with the coexistence of subwavelength periodic stripes and nanoprotrusions is a subwavelength stripe structure with a period of 100-900 nm and accompanied by a nanoprotrusion structure with a height of 10-300 nm.

4. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 1, characterized in that, The composite micro / nano structure includes a trench array and a pit array, or a trench array and a corrugated array, within the same active region, and the density of nanostripes and nanoprotrusions at the edges, intersections, or curvature abrupt regions of the micron skeleton is higher than that in flat regions.

5. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 1, characterized in that, The step of removing the debris redeposited on the surface of the glass substrate includes: The glass substrate is ultrasonically cleaned with deionized water or anhydrous ethanol to remove redeposited debris. After drying, the surface of the glass substrate is activated with ultraviolet light, ozone, or oxygen plasma.

6. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 1, characterized in that, The noble metal coating includes one of a single-layer noble metal film and a heterogeneous multilayer film; by tilting deposition or rotating and segmented deposition, the equivalent thickness of the noble metal coating in the top region of the micron skeleton is different from the equivalent thickness in the region inside the trench / pit.

7. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 6, characterized in that, Before depositing a noble metal coating on the surface of the glass substrate, an adhesion layer or a wetting control layer is deposited first; the thickness of the adhesion layer or the wetting control layer is 1-5 nm; the adhesion layer is selected from at least one of Ti, Cr, Ta, Al2O3, and SiO2; the thickness of the noble metal coating is 5-60 nm; the noble metal coating is selected from at least one of Au, Ag, and Pt.

8. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 6, characterized in that, The heterogeneous multilayer thin film includes one of the following: a stack of Ag and Au layers, a stack of Au and Ag layers, a metal-dielectric-metal layer stack, an Au and Ag alloy layer, and an Ag and Pt alloy layer; in the Ag and Au layer stack, the thickness of the Ag layer is 10-60 nm and the thickness of the Au layer is 1-15 nm; in the Au and Ag layer stack, the thickness of the Au layer is 5-50 nm and the thickness of the Ag layer is 5-40 nm; in the metal-dielectric-metal layer stack, the dielectric layer is SiO2 or Al2O3 with a thickness of 1-10 nm; in the Au and Ag alloy layer or the Ag and Pt alloy layer, the atomic ratio of Au to Ag or Ag to Pt is 1:9-9:

1.

9. The femtosecond laser fabrication method for glass surface-enhanced Raman substrates according to claim 1, characterized in that, The controlled reconstruction process includes thermal treatment or femtosecond laser shaping to trigger thin film dewetting reconstruction, so that the noble metal is transformed into a particle / island structure at the structural tip and gap and forms a nano gap hot spot; the standard Raman probe molecule includes any one of 4-mercaptobenzoic acid, rhodamine 6G or crystal violet; in the step of screening the optimal parameter combination, the screening index includes characteristic peak intensity, peak position stability and uniformity index.

10. A glass surface-reinforced Raman substrate, characterized in that, The glass surface-enhanced Raman substrate, prepared by the femtosecond laser fabrication method as described in any one of claims 1-9, has a composite micro / nano structure consisting of a micron-scale framework, subwavelength stripes, and nano-protrusions. The surface of the composite micro / nano structure is covered with a noble metal coating, which is controlled to reconstruct particles and islands to form nano-gap structures. The average size of the nano-gap is 1-30 nm. The noble metal coating has different equivalent thicknesses or thickness gradients in the top region of the micron-scale framework and the interior region of the trenches / pits.

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