A method and system for femtosecond laser preparation of micro-nano composite structure

Abstract

This invention relates to the field of micro / nano functional materials and laser processing technology, and discloses a femtosecond laser fabrication method for micro / nano composite structures, comprising the following steps: Step S1, cleaning and drying a rigid substrate and a shape memory polymer film respectively to remove surface contaminants and residual moisture; Step S2, attaching the pretreated shape memory polymer film to a pretreated rigid substrate, and then depositing a metal film on the surface of the shape memory polymer film to form a composite sample. This invention constructs a three-layer composite system of "rigid substrate - shape memory polymer film - metal film," utilizing the local thermal effect of a femtosecond laser to trigger directional volume expansion of SMPs, while simultaneously driving the surface metal film to undergo plastic buckling. Nano-folds are formed synchronously during the self-growth of the micropillars, achieving a one-step integrated molding process for micropillar growth and nano-fold formation, simplifying the process flow.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano functional materials and laser processing, specifically a femtosecond laser preparation method and system for micro-nano composite structures. Background Technology

[0002] Micro-nano composite structures possess core application value in fields such as optical sensing, surface wettability control, surface-enhanced Raman scattering (SERS) substrates, and micro-nano device fabrication due to their combination of the mechanical support properties of micron-scale three-dimensional structures and the functional properties of nanoscale wrinkles. Currently, related fabrication technologies are mainly developing in three directions: polymer micropillar preparation, metal film wrinkle formation, and micro-nano composite structure construction.

[0003] In the field of polymer micropillar fabrication technology, the method of femtosecond laser-induced self-growth of shape memory polymers (SMPs) has attracted widespread attention in recent years. A collaborative study published in *Advanced Materials* (2018, 1803072) by Zhang Yachao et al. from the University of Science and Technology of China and Professor Qiu Chengwei from the National University of Singapore demonstrated that by scanning the surface of a pre-stretched shape memory polymer with a femtosecond laser, microstructures can be triggered to "self-grow" from the surface using local laser heating and ablation effects. An asymmetric laser scanning strategy can be used to further control the resulting structure. This method shows potential applications in information encryption / decryption and micro-object capture / release. However, this technique can only obtain micropillar structures with a single smooth surface, lacking nano-wrinkle modification, resulting in limited functional properties, and it is difficult to meet the electromagnetic field "hotspot" requirements of high-value-added applications such as SERS substrates.

[0004] In the field of metal film wrinkle formation technology, studies have shown that periodic micro- and nanostructures can be formed by depositing metal thin films on substrates using laser induction or thermal stress. Liu Qi, Zhang Nan, Yang Jianjun, et al., published an article titled "The Influence of Different Atmospheric Pressure Environments on Periodic Stripe Structures Induced by Femtosecond Lasers on Chromium Film Surfaces" in *Acta Photonica Sinica* (2018, 47(7): 0714001), which systematically studied the formation law of subwavelength periodic stripe structures induced by femtosecond lasers on the surface of metallic chromium films. The results showed that a vacuum environment can effectively improve the formation quality of stripe structures, and the stripe period is modulated by the laser energy flux density and scanning speed. However, this type of technology mainly focuses on the formation of stripe structures on two-dimensional planes, making it difficult to achieve synchronous integrated fabrication with micron-scale polymer micropillars. A separate structure induction process is required, which is complex.

[0005] In the field of micro / nano composite structure fabrication technology, existing technologies are mostly step-by-step fabrication processes. For example, ShiboXu et al. published a paper titled "Research on Multi-Process Collaborative Fabrication and Characterization Method of Micro / Nano Composite Layered Structures" in *Nanomaterials* (2025, 15(22): 1716), proposing to fabricate silicon-based micro / nano composite layered structures composed of micron-scale platforms and nanopillars by integrating multiple processes such as electron beam lithography, inductively coupled plasma etching, and ultraviolet nanoimprint lithography. Although this method can achieve high-precision fabrication of complex structures, multi-step processes are prone to problems such as alignment errors and material mismatches, and the process flow is complex and costly. In addition, problems such as poor film layer bonding, uneven wrinkle distribution, and low structural consistency in step-by-step processes still need to be solved.

[0006] A review of femtosecond laser direct writing technology points out that although the technology can achieve submicron resolution and true three-dimensional free manufacturing, the traditional processing mode is still mainly based on single-point scanning, which has limitations in the integrated molding of multifunctional structures.

[0007] In summary, existing technologies have not yet solved the integrated fabrication problem of SMP micropillar self-growth and conformal metal film wrinkle formation. They lack dedicated material systems and molding mechanisms, making it difficult to fabricate micro / nano composite structures with both supporting and functional properties through simple processes. This application addresses this issue by constructing a three-layer composite system of "rigid substrate-shape memory polymer film-metal film," utilizing the local thermal effect of a femtosecond laser to trigger directional volume expansion of SMPs, simultaneously driving the surface metal film to undergo plastic buckling. This allows for the synchronous formation of nano-wrinkles during the micropillar self-growth process, achieving integrated and controllable fabrication of micro / nano composite structures. Summary of the Invention

[0008] This invention aims to solve at least one of the technical problems existing in the prior art; Therefore, this invention proposes a method and system for fabricating femtosecond lasers of micro-nano composite structures.

[0009] A method for fabricating femtosecond laser-based micro / nano composite structures includes the following steps: Step S1: The rigid substrate and the shape memory polymer film are cleaned and dried respectively to remove surface contaminants and residual moisture. Step S2: The pretreated shape memory polymer film is attached to the pretreated rigid substrate, and then a metal film is deposited on the surface of the shape memory polymer film to form a composite sample; Step S3: The composite sample is scanned using a femtosecond laser, with the laser focus acting on the surface of the metal film. Through the local thermal effect of the femtosecond laser, the shape memory polymer film in the scanned area is triggered to undergo directional volume expansion. At the same time, the metal film attached to its surface undergoes plastic buckling under thermal stress and expansion drive. Step S4: During the process of the shape memory polymer film growing to form a micron-scale micropillar body, the metal film is simultaneously driven to form nanoscale wrinkles in situ on the surface of the micropillar, thereby obtaining a metal micropillar array micro-nano composite structure with nano-wrinkles on the surface.

[0010] Furthermore, in step S1, the cleaning process uses anhydrous ethanol for ultrasonic cleaning; the drying process uses a vacuum drying oven to ensure that there is no moisture residue on the surface.

[0011] Furthermore, in step S2: The rigid substrate is a glass slide, a quartz sheet, or a silicon wafer; The shape memory polymer film is a polystyrene film with a thickness of 300 μm or other thicknesses can be selected according to the height requirements of the micropillars; The method of attaching the shape memory polymer film is by adhesive bonding or by clamping and fixing with a fixture; The metal film is a silver film, gold film, platinum film, copper film, or aluminum film; The method for attaching the metal thin film is magnetron sputtering, electron beam evaporation, or thermal evaporation.

[0012] Furthermore, in step S2, an adhesion layer is provided between the metal film and the shape memory polymer film; the adhesion layer is a titanium film or a chromium film, used to enhance the bonding force between the metal film and the shape memory polymer film.

[0013] Furthermore, in step S3, the processing parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, repetition frequency 2.5kHz, scanning speed 50mm / s, and scanning power 70mW.

[0014] Furthermore, in step S3, the height of the micropillar and the surface nano-wrinkle morphology are controlled by adjusting the number of scans of the femtosecond laser; the number of scans is 10-50 times, and as the number of scans increases, the wrinkle morphology evolves from sparse to dense gradient.

[0015] Furthermore, when the number of scans reaches 40 or more, a continuous, dense and regular nano-wrinkled structure is formed on the surface of the micropillar.

[0016] Furthermore, in step S3, the scanning path of the femtosecond laser is an array of circles with a diameter of 0.14 mm and a center-to-center distance of 0.2 mm.

[0017] The present invention also proposes a processing system for the method, comprising: A femtosecond laser is used to generate pulsed lasers with an output laser center wavelength of 1030 nm, a pulse width of 290 fs, and a repetition frequency of 2.5 kHz. The optical path transmission and control unit includes multiple mirrors, apertures, half-wave plates, and Glan Taylor prisms arranged sequentially along the optical path; the mirrors are used to change the laser propagation direction, the apertures are used for beam shaping and aperture limiting, and the half-wave plates and Glan Taylor prisms work together to achieve precise control of the laser polarization state and energy filtering. A scanning galvanometer, positioned after the optical path transmission and control unit, is used to receive the controlled laser and achieve high-speed deflection and focusing. The stage is used to support and fix the composite sample, and can move in three dimensions; A control computer, connected to the femtosecond laser and scanning galvanometer, is used to control the laser parameters and scanning path.

[0018] This invention proposes a micro-nano composite structure, which is prepared by the method described above.

[0019] Compared with the prior art, the beneficial effects of the present invention are: This invention constructs a three-layer composite system of "rigid substrate-shape memory polymer film-metal film," utilizing the local thermal effect of femtosecond laser to trigger directional volume expansion of SMPs, simultaneously driving the surface metal film to undergo plastic buckling, thus forming nanofolds during the self-growth of micropillars. Compared with existing stepwise fabrication processes, this invention achieves a one-step integrated molding process for micropillar growth and nanofold formation, simplifying the process flow and improving structural consistency and film adhesion.

[0020] This invention is based on the principle of thermal stress mismatch. The thermal expansion of SMPs provides an upward driving force, while the rigid metal membrane undergoes plastic buckling due to constraint. This mechanism differs from the self-growth method of SMPs that relies solely on contraction in existing technologies, and also from the simple thermal stress buckling of the metal membrane. Instead, it couples the two, achieving an integrated structure-function construction.

[0021] This invention enables dual control over the height of micropillars and the surface nano-wrinkle morphology by adjusting the number of femtosecond laser scans. When the number of scans reaches 40 or more, a continuous, dense, and regular nano-wrinkle structure can be formed on the surface of the micropillars, providing abundant electromagnetic field "hot spots" for applications such as SERS substrates.

[0022] The micro-nano composite structure prepared by this invention has both high specific surface area and abundant electromagnetic field "hot spots", which is suitable for multiple cutting-edge fields such as surface-enhanced Raman scattering substrates, superhydrophobic surfaces, micromixers in microfluidic chips, and biological cell culture scaffolds, providing a new technical path for the controllable preparation of high-performance micro-nano functional devices. Attached Figure Description

[0023] Figure 1 This is a flowchart of the preparation method of the micro-nano composite structure in Example 1 of the present invention; Figure 2 This is a schematic diagram of the processing flow using magnetron sputtering Ag and femtosecond laser in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the femtosecond laser micro / nano fabrication system in Embodiment 1 of the present invention; Figure 4 The diagram shows the structure of the micropillars formed by femtosecond laser-induced self-growth after 10, 20, and 30 scans in Example 1 of this invention (scale bar: 10 μm). Figure 5 The structure diagram of the micropillars formed by femtosecond laser-induced self-growth after 40 and 50 scans in Example 1 of the present invention (scale bar: 10 μm). Figure 6 This is an electron microscope schematic diagram showing the wrinkled morphology at the top of the micropillar formed under different scan numbers in Embodiment 1 of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0026] Example 1

[0027] This embodiment provides a femtosecond laser fabrication method for micro / nano composite structures, which will be described below in conjunction with... Figures 1 to 6 The technical solution of this embodiment will be described in detail.

[0028] I. Material Preparation and Composite Sample Preparation First, material preparation is carried out. In this embodiment, a glass slide is selected as the rigid substrate, a 300μm thick polystyrene film is selected as the shape memory polymer film, and a silver target is selected as the sputtering material for the metal film.

[0029] Step S1, Preparation of the composite sample: The glass slide and the 300 μm thick polystyrene film were ultrasonically cleaned with anhydrous ethanol for 10-15 minutes to remove oil, dust, and other impurities from their surfaces. After cleaning, both were placed in a vacuum drying oven at 40°C for 30 minutes to ensure no moisture residue remained on the surface. After drying, the polystyrene film was tightly adhered to the surface of the glass slide, forming a bubble-free and misaligned "glass slide-polystyrene film" composite layer, providing stable support for subsequent metal film deposition.

[0030] Secure the glass slide with the attached polystyrene film onto the sample holder of the magnetron sputtering instrument. Close the sputtering chamber and evacuate to a background vacuum level better than 5 × 10⁻⁶. -4 At Pa, the sputtering current was set to 30 mA and the sputtering time to 60 seconds. The magnetron sputtering instrument was started, and a uniform silver film with a thickness of approximately 50 nm was deposited on the surface of the polystyrene film. This yielded a three-layer composite sample of "glass slide-polystyrene film-silver film," completing the substrate preparation before laser processing.

[0031] II. Femtosecond Laser Micro / Nano Fabrication System The femtosecond laser micro / nano fabrication system used in this embodiment is as follows: Figure 3 As shown, it includes a femtosecond laser, an optical path transmission and control unit, a scanning galvanometer, a stage, and a control computer.

[0032] The femtosecond laser uses a Ti:sapphire femtosecond laser with an output laser center wavelength of 1030nm, a pulse width of 290fs, and a repetition frequency of 2.5kHz.

[0033] The optical path transmission and control unit comprises multiple mirrors, apertures, half-wave plates, and GlanTylene prisms arranged sequentially along the optical path. Its workflow is as follows: After the pulsed laser is emitted from the femtosecond laser, it is vertically redirected by the first mirror and then passes through the aperture for beam shaping and aperture limitation to optimize beam quality. The shaped laser is then horizontally transmitted through the second mirror, passing sequentially through the half-wave plate and the GlanTylene prism to achieve precise control of the laser polarization state and energy filtering. The polarization-controlled laser then passes through the aperture again to further suppress stray light and improve energy concentration. Subsequently, the laser is redirected by two mirrors and enters the scanning galvanometer.

[0034] The scanning galvanometer is used to receive the controlled laser and achieve high-speed deflection and focusing. Through high-speed deflection, precise focusing is achieved, which ultimately acts on the surface of the sample to be processed placed on the stage.

[0035] The stage can achieve precise displacement in the X, Y, and Z axes, and in conjunction with the high-speed scanning of the scanning galvanometer, it can complete the processing of large areas and complex shapes. The movement accuracy of the stage can reach 1μm.

[0036] The control computer is connected to the femtosecond laser and scanning galvanometer, and is equipped with SAMLight processing software to control laser parameters and scanning path.

[0037] III. Femtosecond Laser Processing Parameter Setting and Path Design Step S2, Femtosecond laser processing: Place the three-layer composite sample prepared in step S1 on the stage of the femtosecond laser processing system, and manually adjust the X, Y, and Z axes of the stage so that the processing focus of the femtosecond laser is precisely aligned with the silver film layer on the sample surface.

[0038] Launch the SAMLight processing software on the femtosecond laser control computer. Based on the micropillar array design requirements, draw a self-growing circular pattern with a diameter of 0.14 mm. Set the scanning center distance to 0.2 mm to generate the laser scanning path for the micropillar array. The scanning path is a circular array arrangement, such as... Figure 2 As shown.

[0039] The laser scanning speed and number of scans are adjusted using the SAMLight processing software, and the laser scanning power is adjusted by moving the attenuator in the optical path system. In this embodiment, the laser processing parameters are set as follows: scanning speed 50 mm / s, scanning power 70 mW.

[0040] To investigate the effect of the number of scans on the formation of micropillars and wrinkles, this embodiment designed five sets of scan number parameters: 10, 20, 30, 40 and 50 scans.

[0041] IV. Femtosecond laser-induced integrated self-growing molding: Step S3, Integrated self-growing molding: After completing all parameter and path settings, click the "Mark" button in the software to perform femtosecond laser scanning on the processing area of ​​the composite sample.

[0042] During processing, the localized thermal effect of the femtosecond laser triggers directional volume expansion of the polystyrene film in the scanned area. Upon heating, the polystyrene film rapidly rises above its glass transition temperature (approximately 107°C), resulting in a significant volume expansion effect. Simultaneously, the silver film attached to its surface undergoes plastic buckling under thermal stress and expansion.

[0043] The specific mechanism is as follows: the local thermal effect of the femtosecond laser causes the polystyrene film to expand thermally, forming non-uniform thermal stress between the film layers. The expansion of the polystyrene film is constrained by the upper rigid silver film. The stress mismatch generated between the film layers exceeds the yield strength of the silver film, driving the silver film to undergo plastic buckling while the micropillars grow upward, spontaneously forming nanofolds.

[0044] During the self-growth of polystyrene film into micron-sized micropillars, a silver film is simultaneously driven to form nanoscale wrinkles on the surface of the micropillars in situ. This process achieves simultaneous and integrated molding of micropillar growth and wrinkle formation, without the need for additional processing steps.

[0045] After processing, a silver micropillar array micro-nano composite structure with nanofolds on the surface is obtained.

[0046] V. Structural Characterization and Detection After processing, the fabricated micropillar array was observed in three dimensions using a 3D laser measurement microscope, and geometric parameters such as the height and diameter of the micropillars were measured. Electron microscopy was used to observe the morphology, distribution, density, and regularity of the nanofolds on the micropillar surface, and structural characterization data were recorded at different scan counts.

[0047] Figure 4 and Figure 5 The structures of micropillars formed by femtosecond laser-induced self-growth under different scan numbers are shown. It can be seen that with the increase of the number of femtosecond laser scans, the height of the micropillars shows a significant gradient growth trend, and the development degree of nanofolds on the surface of the micropillars increases synchronously.

[0048] When the number of scans is 10, the micropillar height is low, and the surface wrinkles are sparse and shallow. When the number of scans increases to 20 and 30, the micropillar height gradually increases, and the surface wrinkles gradually become denser and deeper. When the number of scans reaches 40 or more, a continuous, dense, and regular nano-wrinkled structure forms on the surface of the micropillar. This pattern verifies that the height of the micropillar and the morphology of the surface nano-wrinkles can be controlled by adjusting the number of scans. As the number of scans increases, the wrinkle morphology evolves from sparse to dense.

[0049] Figure 6 This paper presents electron microscope (EM) images showing the wrinkled morphology formed at the top of the micropillars after different scan counts. The top row shows the EEM images of the top of the micropillars after 10, 20, 30, 40, and 50 scans (scale bar: 10 μm), and the bottom row shows magnified views of the corresponding locations (scale bar: 1 μm). Figure 5 The study clearly demonstrates the evolution of nanofolds from nothing to something, from sparse to dense, and from shallow to deep, intuitively reflecting the precise control effect of the number of laser scans on the fold morphology.

[0050] This phenomenon is attributed to the cumulative effect of local thermal effects of femtosecond lasers: the increase in the number of scans makes the polystyrene film more thermally stimulated, the degree of volume expansion gradually increases, and the driving force on the upper silver film is continuously enhanced. This not only promotes the continuous growth of micropillars in the vertical direction, but also makes the plastic buckling deformation of the silver film more significant, ultimately achieving the dual effect of increasing the height of micropillars and the gradual development of wrinkled structures.

[0051] The gradient increase in the height of the micropillars reflects the controllability of the number of laser scans on the three-dimensional morphology of the microstructure, while the synchronous improvement in the degree of wrinkle development reflects the regulatory effect of thermal stress accumulation on the nanoscale surface texture.

[0052] VI. Post-processing After processing, the target sample can be ultrasonically cleaned in anhydrous ethanol for 10-15 minutes to remove any possible residual surface impurities, and then dried with cold air to obtain a clean micro-nano composite structure sample.

[0053] Example 2

[0054] This embodiment is basically the same as Embodiment 1, except that in step S1, before depositing the silver film, an extremely thin titanium film is deposited as an adhesion layer.

[0055] Specifically, the glass slide with the polystyrene film attached is fixed onto the sample holder of the magnetron sputtering instrument. The sputtering chamber is closed and a vacuum is evacuated to a background vacuum level better than 5 × 10⁻⁶. -4 First, the sputtering current of the titanium target was set to 10 mA and the sputtering time to 30 seconds, depositing a titanium film with a thickness of approximately 10 nm on the surface of the polystyrene film. Then, the target was switched to a silver target, and the sputtering current was set to 30 mA and the sputtering time to 60 seconds, depositing a uniform silver film with a thickness of approximately 50 nm on the titanium film surface. The introduction of the titanium film enhanced the adhesion between the silver film and the polystyrene film, effectively preventing film detachment during subsequent processing and further improving the stability of the composite structure.

[0056] The other steps are the same as in Example 1.

[0057] Example 3

[0058] This embodiment is basically the same as Embodiment 1, except that in step S1, the polystyrene film is clamped and fixed using a fixture instead of being pasted to the glass slide, ensuring only the flatness and stability of the polystyrene film during processing. The other steps are the same as in Embodiment 1.

[0059] Example 4

[0060] This embodiment is basically the same as Embodiment 1, except that in step S1, a gold film is used instead of a silver film, and a chromium film is used as the adhesion layer. Specifically, a chromium film is deposited by sputtering using a chromium target as the adhesion layer, followed by magnetron sputtering deposition of a gold film using a gold target. The sputtering current for the chromium film is 10 mA, and the sputtering time is 30 seconds; the sputtering current for the gold film is 15 mA, and the sputtering time is 150 seconds. The other steps are the same as in Embodiment 1.

[0061] Example 5

[0062] This embodiment is basically the same as Embodiment 1, except that in step S1, a quartz plate is used instead of a glass slide for the rigid substrate. The other steps are the same as in Embodiment 1.

[0063] Example 6

[0064] This embodiment provides a micro-nano composite structure prepared by the method described in any one of Examples 1 to 5. The structure comprises a micrometer-scale polymer micropillar body and a nanometer-scale metal wrinkled layer located on the surface of the micropillar, with the micropillar and the wrinkled layer integrally formed.

[0065] Comparative Example 1 This comparative example is basically the same as Example 1, except that in step S1, no metallic silver film is deposited; instead, a femtosecond laser processing is performed using a "glass slide-polystyrene film" double-layer structure. The results show that only smooth micropillar structures can be formed on the surface of the polystyrene film, and nanoscale wrinkles cannot be formed on the surface of the micropillars.

[0066] Comparative Example 2 This comparative example is basically the same as Example 1, except that in step S2, the femtosecond laser scanning power is set to 30mW, which is lower than the preferred power range of the present invention. The results show that the polystyrene film does not expand sufficiently due to thermal expansion, the micropillar height is low, and only sparse, discontinuous wrinkled structures can be formed on the surface of the silver film.

[0067] Comparative Example 3 This comparative example is basically the same as Example 1, except that in step S2, the number of femtosecond laser scans was set to 5. The results show that the height of the micropillar is only about 30% of that of Example 1, and almost no nano-wrinkles are observed on the surface of the silver film.

[0068] Comparative Example 4 This comparative example is basically the same as Example 2, except that a titanium adhesion layer is not deposited in step S1, only a silver film is deposited. The prepared composite sample was subjected to ultrasonic cleaning (100W power, 5 minutes), and then the film bonding was observed. The results showed that the sample without an adhesion layer showed local silver film detachment after ultrasonic cleaning, while the sample with a titanium adhesion layer in Example 2 had an intact film after the same ultrasonic cleaning treatment, verifying the significant effect of the adhesion layer on enhancing the bonding force between the metal film and the polymer layer.

[0069] In summary, the performance of the micro / nano composite structures prepared in Examples 1 and 2 was tested. The results show that, due to the high specific surface area and abundant electromagnetic field enhancement effect provided by the nano-wrinkled structure, this structure is suitable as a surface-enhanced Raman scattering substrate. Furthermore, the hierarchical rough surface formed by the micro-pillar structure and the nano-wrinkled structure endows it with excellent hydrophobic properties.

[0070] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for femtosecond laser fabrication of micro-nano composite structure, characterized in that, Includes the following steps: Step S1: The rigid substrate and the shape memory polymer film are cleaned and dried respectively to remove surface contaminants and residual moisture. Step S2: The pretreated shape memory polymer film is attached to the pretreated rigid substrate, and then a metal film is deposited on the surface of the shape memory polymer film to form a composite sample; Step S3: The composite sample is scanned using a femtosecond laser, with the laser focus acting on the surface of the metal film. Through the local thermal effect of the femtosecond laser, the shape memory polymer film in the scanned area is triggered to undergo directional volume expansion. At the same time, the metal film attached to its surface undergoes plastic buckling under thermal stress and expansion drive. Step S4: During the process of the shape memory polymer film growing to form a micron-scale micropillar body, the metal film is simultaneously driven to form nanoscale wrinkles in situ on the surface of the micropillar, thereby obtaining a metal micropillar array micro-nano composite structure with nano-wrinkles on the surface.

2. The production method according to claim 1, characterized by, In step S1, the cleaning process uses anhydrous ethanol for ultrasonic cleaning; the drying process uses a vacuum drying oven to ensure that there is no moisture residue on the surface.

3. The preparation method according to claim 1, characterized in that, In step S2: The rigid substrate is a glass slide, a quartz sheet, or a silicon wafer; The shape memory polymer film is a polystyrene film with a thickness of 300 μm or other thicknesses can be selected according to the height requirements of the micropillars; The method of attaching the shape memory polymer film is by adhesive bonding or clamping and fixing. The metal film is a silver film, gold film, platinum film, copper film, or aluminum film; The method for attaching the metal thin film is magnetron sputtering, electron beam evaporation, or thermal evaporation.

4. The preparation method according to claim 3, characterized in that, In step S2, an adhesion layer is further provided between the metal film and the shape memory polymer film; the adhesion layer is a titanium film or a chromium film, used to enhance the bonding force between the metal film and the shape memory polymer film.

5. The preparation method according to claim 1, characterized in that, In step S3, the processing parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, repetition frequency 2.5kHz, scanning speed 50mm / s, and scanning power 70mW.

6. The preparation method according to claim 5, characterized in that, In step S3, the height of the micropillar and the surface nano-wrinkle morphology are controlled by adjusting the number of scans of the femtosecond laser; the number of scans is 10-50 times, and as the number of scans increases, the wrinkle morphology evolves from sparse to dense gradient.

7. The preparation method according to claim 6, characterized in that, When the number of scans reaches 40 or more, a continuous, dense and regular nano-wrinkled structure is formed on the surface of the micropillar.

8. The preparation method according to claim 1, characterized in that, In step S3, the scanning path of the femtosecond laser is a circular array with a diameter of 0.14 mm and a center-to-center distance of 0.2 mm.

9. A processing system for implementing the method of any one of claims 1-8, characterized in that, include: A femtosecond laser is used to generate pulsed lasers with an output laser center wavelength of 1030 nm, a pulse width of 290 fs, and a repetition frequency of 2.5 kHz. The optical path transmission and control unit includes multiple mirrors, apertures, half-wave plates, and Glan Taylor prisms arranged sequentially along the optical path; the mirrors are used to change the laser propagation direction, the apertures are used for beam shaping and aperture limiting, and the half-wave plates and Glan Taylor prisms work together to achieve precise control of the laser polarization state and energy filtering. A scanning galvanometer, positioned after the optical path transmission and control unit, is used to receive the controlled laser and achieve high-speed deflection and focusing. The stage is used to support and fix the composite sample, and can move in three dimensions; A control computer, connected to the femtosecond laser and scanning mirror, is used to control the laser parameters and scanning path.

10. A micro / nano composite structure, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

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