A tunable micro-nano structure printing device and a printing method thereof

Abstract

A kind of printing device and printing method of tunable micro-nano structure, using the way of directly loading pattern for microstructure projection of projection element, avoid forming oxidation structure in the process of femtosecond laser processing micro-nano structure by medium auxiliary, and structure and component do not change obviously when exposure time is improved;Liquid medium can reduce the generation of air bubbles and / or discharge air bubbles in time, reduce the influence of air bubbles on light, improve the precision of micro-nano structure.

Description

Technical Field

[0001] This invention relates to the field of micro / nano structure processing on material surfaces, and more particularly to a method for printing tunable micro / nano structure patterns using femtosecond laser processing. Background Technology

[0002] With the continuous development of science and technology, the demand for micro- and nano-structures on material surfaces is increasing. Among the many methods for fabricating micro- and nano-structures, laser processing technology has attracted much attention due to its advantages such as high precision, high flexibility, and non-contact operation.

[0003] Traditional laser processing methods often have limitations when fabricating micro- and nano-structures on material surfaces. For example, they have limited processing precision, making it difficult to achieve complex micro-pattern structures; the tunability of the patterns is poor, making it difficult to meet the needs of different application scenarios; and the processing may cause thermal damage to the material, affecting its performance and service life.

[0004] Femtosecond lasers, as ultrashort pulse lasers, possess extremely high peak power and extremely short pulse widths, enabling high-precision material processing. However, femtosecond laser processing alone also faces some challenges, such as relatively low processing efficiency, high requirements for the processing environment, and limited processing methods.

[0005] By utilizing the interaction between lasers and materials to form subwavelength surface fringes, it is possible to achieve precision that breaks through the diffraction limit. This has important applications in the manufacture of high-precision gratings, electromagnetic wave control devices, biosensors, hydrophilic and hydrophobic surfaces, and cell growth regulation.

[0006] Currently, laser-induced periodic surface structures (LIPSS) mainly include low-period LSFLs (period > λ / 2) and high-period HSFLs (period > λ / 2), with HSFLs typically only formed by ultrafast laser induction. Significant technical obstacles remain in forming multi-level ordered and controllable micro / nano patterned structures from HSFLs. On one hand, existing techniques primarily utilize galvanometers and field mirrors for scanning, resulting in poor pattern flexibility. On the other hand, when the laser enters the medium, nonlinear effects limit the spot's focus, leading to low pattern precision.

[0007] Currently, although there has been some research on femtosecond laser processing, research on tunable micro / nanostructure pattern printing is relatively limited. Therefore, developing an efficient, precise, and tunable femtosecond laser projection-induced micro / nanostructure patterning printing method for material surfaces has significant practical implications and application value. Summary of the Invention

[0008] This invention provides a printing device and method for tunable micro / nano structures, enabling the fabrication of submicron-level controllable structures and super-periodic surface structures.

[0009] The tunable micro / nano structure printing device includes an ultrafast laser, an optical switch, an energy adjustment device, a beam shaping device, a lens group, a first mirror, a second mirror, a third mirror, a spatial light modulator, an imaging lens, a laser mirror, an imaging objective lens, a sample, a three-axis displacement stage, an illumination source, a beam splitter, a second mirror, an imaging lens, a detector, and a computer control system.

[0010] During processing, the ultrafast laser 1 emits a beam that passes through an optical switch 2 and an energy adjustment device 3, enters a beam shaping device 4, is expanded by a lens group 5, passes through a first reflecting mirror 6, and then the angle of the incident spatial light modulator 9 is adjusted by a second reflecting mirror 7 and a third reflecting mirror 8. The spatial light modulator loads a pattern, and the beam generates spatial chirp through the spatial light modulator 9 before passing through an imaging lens 10, entering a laser reflecting mirror 11, and then projecting the pattern onto a sample 13 placed on a triaxial displacement stage 14 through an imaging objective lens 12.

[0011] Meanwhile, the light emitted by the illumination source 15 is reflected by the beam splitter 16 and passes through the laser reflector 11 and the imaging objective lens 12 to illuminate the sample 13. The image information reflected from the sample 13 is then collected by the detector 19 through the laser reflector 11, the beam splitter 16, the fourth reflector 17, and the imaging lens 18, and is used to monitor the printed pattern on the sample surface.

[0012] The samples that can be processed are not limited to metal-semiconductor composite thin films; they can be processed on materials such as silicon wafers and metals.

[0013] Furthermore, the beam shaping device 4 is used for beam homogenization.

[0014] Furthermore, the spatial light modulator 9 is a DMD spatial light modulator.

[0015] Optionally, the sample is placed in a liquid medium, which the laser must pass through when projected onto the sample. The liquid medium has a high boiling point, making it less likely to generate too many bubbles during laser ablation. Secondly, the surface tension of the liquid medium should be low, so that small bubbles do not easily collide and aggregate to form large bubbles during laser ablation. The liquid medium is water, isopropanol, or propylene glycol methyl ether acetate (PGMEA).

[0016] Optionally, a liquid medium of a set thickness is loaded through a container, which is a surface dish; the manufacturing process is carried out in a surface dish to ensure the supply of liquid medium, ensuring that there is enough liquid medium to control the bubbles generated during the manufacturing process, allowing the bubbles to flow away and reducing the impact of the bubbles on light.

[0017] Optionally, a coverslip is placed on the sample, and the liquid medium is added between the coverslip and the sample. The liquid medium is loaded to a set thickness using a liquid level thickness adjustment device. By covering the liquid medium with the coverslip, the evaporation rate of the liquid medium is reduced, which can ensure the stability of the medium during the efficient large-area manufacturing process. The aforementioned set thickness of the liquid medium loading is to ensure the thickness of the liquid medium above the sample surface.

[0018] Optionally, the liquid medium is loaded into the liquid from one side between the coverslip and the liquid via a peristaltic pump, and flows out from the other side into the waste liquid collection cycle, thereby achieving the flow loading of a medium of fixed thickness; thus continuously providing a stable flow of medium, reducing the impact of bubbles and nanoparticles formed by ablation, and improving manufacturing efficiency.

[0019] Based on the above printing apparatus, a method for printing tunable micro / nano structures is proposed, comprising:

[0020] Step 1: Place the sample on the triaxial displacement stage 14, cover the sample with a coverslip, and there is a liquid medium between the coverslip and the sample;

[0021] Step 2: The ultrafast laser 1 emits a beam to the optical switch 2. After being regulated by the energy adjustment device, the beam enters the beam shaping device for homogenization. The homogenized beam is then expanded by the lens group 5. After expansion, it is reflected by the first reflecting mirror 6, passes through the second reflecting mirror 7 and the third reflecting mirror 8, and then enters the spatial light modulator 9. The first reflecting mirror 6, the first reflecting mirror group 7, and the second reflecting mirror group 8 are used to adjust the incident angle of the beam entering the spatial light modulator 9. After the spatial light modulator loads the pattern to be processed, it performs time-varying on the incoming beam to make it carry the pattern information. The pattern is formed spontaneously by light and matter to form nanoscale stripes. Then, it passes through the imaging lens 10, enters the laser reflecting mirror 11, and is projected onto the sample 13 by the imaging objective lens 12, ablation of the sample surface to form micro-nano structures.

[0022] The orientation of the spontaneously formed nanoscale stripes in the pattern changes with the laser polarization direction.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. Most existing technologies form patterns by scanning point by point, which requires complex trajectory programming. This paper proposes a method for microstructure projection by directly loading patterns using projection elements, which can realize a complex pattern projection etching method without trajectory programming.

[0025] 2. Existing projection methods using projection units face challenges such as uneven light spots and oxidation of material surfaces in air, leading to changes in both the structure and composition of the sample. The medium-assisted method proposed in this work, however, isolates the sample from air in a liquid medium environment, preventing the formation of oxidized structures. Furthermore, it ensures that the nanostructure and composition remain largely unchanged even with extended exposure times. Simultaneously, the liquid medium reduces bubble formation and / or facilitates timely bubble removal, minimizing the impact of bubbles on light and improving the precision of the micro / nano structures.

[0026] 3. The device provided in this paper utilizes a spatial light modulator to disperse the laser during manufacturing, achieving spatiotemporal focusing and reducing peak power in areas outside the focal point. This enables the formation of HSFL structures within a constrained, high-precision structure. Ultimately, it allows for the formation of nanoscale stripes within submicron-level structures. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the tunable micro / nano structure printing device provided by the present invention;

[0028] Figure 2 This is one method of bearing the processed sample of the present invention;

[0029] Figure 3 This is the second method of bearing the processed sample of the present invention;

[0030] Figure 4 This is the third way of bearing the processed sample in this invention;

[0031] Figure 5 This is a schematic diagram of the ablation results of the processed sample in different media environments. Detailed Implementation

[0032] To better illustrate the objectives and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples. It should be noted that the implementation of the present invention is not limited to the following embodiments, and any modifications or alterations made to the present invention will fall within the scope of protection of the present invention.

[0033] A tunable micro / nano structure printing device includes an ultrafast laser, an optical switch, an energy regulation device, a beam shaping device, a lens group, a first mirror, a second mirror, a third mirror, a spatial light modulator, an imaging lens, a laser mirror, an imaging objective lens, a sample, a triaxial displacement stage, an illumination source, a beam splitter, a second mirror, an imaging lens, a detector, and a computer control system.

[0034] The samples that can be processed are not limited to metal-semiconductor composite thin films; they can be processed on materials such as silicon wafers and metals.

[0035] The sample is in a liquid medium, and the light beam must pass through this liquid medium when it is projected onto the sample; the liquid medium is water or propylene glycol methyl ether acetate (PGMEA); a quantitative amount of liquid medium can be loaded through a container, such as a watch glass, thereby controlling the bubbles generated during the manufacturing process, allowing the bubbles to flow away, and reducing the impact of the bubbles on the light.

[0036] Optionally, a coverslip is placed over the sample, and a liquid medium is loaded between the coverslip and the sample. By covering the liquid medium with the coverslip, the evaporation rate of the liquid medium is reduced, ensuring the stability of the medium during the efficient large-area manufacturing process. A fixed thickness of the liquid medium between the coverslip and the sample can be loaded using a liquid level adjustment device. Alternatively, a peristaltic pump can be used to load the liquid medium from one side between the coverslip and the liquid, and the liquid medium flows out from the other side and enters the waste liquid collection and circulation, achieving a fixed thickness of medium loading. This continuous supply of a stable flowing medium reduces the impact of bubbles and nanoparticles formed by ablation, improving manufacturing efficiency.

[0037] The optical path during processing is as follows: the ultrafast laser 1 emits a beam that passes through the optical switch 2 and the energy adjustment device 3, enters the beam shaping device 4 (for beam homogenization), is expanded by the lens group 5, passes through the first reflecting mirror 6, and then the angle of the incident spatial light modulator 9 is adjusted by the second reflecting mirror 7 and the third reflecting mirror 8. After the beam is time-controlled by the DMD spatial light modulator 9, it passes through the imaging lens 10, enters the laser reflecting mirror 11, and is projected onto the sample 13 placed on the triaxial displacement stage 14 by the imaging objective lens 12.

[0038] Meanwhile, the light emitted by the illumination source 15 is reflected by the beam splitter 16 and passes through the laser reflector 11 and the imaging objective lens 12 to illuminate the sample 13.

[0039] The reflected image information is collected by detector 19 after passing through laser reflector 11, beam splitter 16, fourth reflector 17, and imaging lens 18.

[0040] Based on the above printing apparatus, a method for printing tunable micro / nano structures is proposed, comprising:

[0041] Step 1: Place the sample on the triaxial displacement stage 14, cover the sample with a coverslip, and there is a liquid medium between the coverslip and the sample;

[0042] Step 2: The ultrafast laser 1 emits a beam to the optical switch 2. After passing through the energy adjustment device, the beam is homogenized by the beam shaping device. The homogenized beam is then expanded by the lens group 5. After expansion, it is reflected by the first reflecting mirror 6 and passes through the second reflecting mirror 7 and the third reflecting mirror 8 before entering the spatial light modulator 9. The first reflecting mirror 6, the first reflecting mirror group 7, and the second reflecting mirror group 8 are used to adjust the incident angle of the beam entering the spatial light modulator 9. The beam is time-controlled by the spatial light modulator 9 to form a micron-scale pattern (the spatial light modulator loads the pattern to be processed and then time-controlled the incoming beam to form a micron-scale pattern). The pattern contains nanoscale stripes spontaneously formed by light and matter. After passing through the imaging lens 10, the beam enters the laser reflecting mirror 11 and is projected onto the sample 13 by the imaging objective lens 12, ablating the sample surface to form micro- and nano-structures. The direction of the spontaneously formed nanoscale stripes in the pattern changes with the laser polarization direction.

[0043] Laser parameters of 1 kHz, 120 fs, center wavelength 798 nm, ablation results in air, water, and PGMEA materials at the same power are as follows: Figure 5 As shown. Experiments revealed that:

[0044] Patterning in air presents two main challenges. First, the uniformity of the light spot significantly leads to structural inhomogeneity. While increasing the exposure time can, to some extent, keep the entire structure in an ablation state, excessively long exposure times in air result in strongly ablated areas forming nanoscale LIPSS and micrometer-scale disordered structures. Weakly ablated structures, on the other hand, form LIPSS, further contributing to overall texture inhomogeneity. Second, when the exposure time is too long, EDS imaging of local structures reveals the introduction of oxygen into the structure, altering its composition.

[0045] In a liquid environment, lasers can lower the damage threshold, increase the direct-write window, and promote uniformity. They can also improve oxygen isolation from the air, inhibiting the formation of oxidized structures. While laser-induced filtration (FPL) in water controls the reduction of the damage threshold, it induces the formation of viscous bubbles. These bubbles adhere to the structure surface, are difficult to break, and aggregate during the manufacturing process. Under high-energy conditions, these bubbles can locally form, leading to the superposition of LSFLs on top of HSFLs, resulting in hybrid micro / nano structures. In PGMEA, although bubbles also form, their better fluidity and unstable state allow new bubbles to break or push away existing ones, ensuring overall uniformity. Therefore, the uniformity of PGMEA formation is stronger than that in air and water, and the microstructure is also more uniform.

[0046] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A printing device for tunable micro / nano structures, characterized in that: The system includes an ultrafast laser, an optical switch, an energy adjustment device, a beam shaping device, a lens group, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a spatial light modulator, an imaging lens, a laser reflecting mirror, an imaging objective, a sample, a liquid medium, a liquid level thickness adjustment device, a three-axis displacement stage, and a computer control system for controlling the above components. During processing, the ultrafast laser beam passes through the optical switch and the energy adjustment device, is expanded by the lens group, and then passes through the first reflecting mirror. The angle of the beam incident on the spatial light modulator is then adjusted by the second and third reflecting mirrors. The spatial light modulator loads a pattern, and the beam, after generating spatial chirp through the spatial light modulator, passes through the imaging lens, enters the laser reflecting mirror, and is projected onto the sample placed on the three-axis displacement stage by the imaging objective. The sample is surrounded by a liquid medium, which is propylene glycol methyl ether acetate (PGMEA). A cover glass is placed on the sample and a liquid medium is added between the cover glass and the sample. The liquid medium is loaded to a set thickness by adjusting the liquid level thickness using a liquid thickness adjustment device. It also includes an illumination source, a beam splitter, a fourth reflecting mirror, an imaging lens, and a detector; the light emitted by the illumination source passes through the beam splitter, the laser reflecting mirror, and the imaging objective lens to illuminate the sample, thus reflecting the image information on the sample, which is then collected by the detector after passing through the laser reflecting mirror, the beam splitter, the fourth reflecting mirror, and the imaging lens. A beam shaping device is also provided between the energy adjustment device and the lens group to homogenize the beam.

2. The printing apparatus according to claim 1, characterized in that: The spatial light modulator is a DMD spatial light modulator.

3. A printing device for tunable micro / nano structures, characterized in that: The system includes an ultrafast laser, an optical switch, an energy adjustment device, a beam shaping device, a lens group, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a spatial light modulator, an imaging lens, a laser reflector, an imaging objective, a sample, a liquid medium, a peristaltic pump, a three-axis displacement stage, and a computer control system for controlling the above components. During processing, the ultrafast laser beam passes through the optical switch and the energy adjustment device, is expanded by the lens group, and then passes through the first reflecting mirror. The angle of the beam incident on the spatial light modulator is then adjusted by the second and third reflecting mirrors. The spatial light modulator loads a pattern, and the beam, after generating spatial chirp through the spatial light modulator, passes through the imaging lens, enters the laser reflector, and is projected onto the sample placed on the three-axis displacement stage by the imaging objective. The sample is surrounded by a liquid medium, which is propylene glycol methyl ether acetate (PGMEA). A cover glass is placed on the sample and a liquid medium is added between the cover glass and the sample. The liquid medium is loaded into the sample from one side between the cover glass and the liquid by a peristaltic pump and flows out from the other side into the waste liquid collection and circulation, so as to realize the flow loading of a medium with a fixed thickness. It also includes an illumination source, a beam splitter, a fourth reflecting mirror, an imaging lens, and a detector; the light emitted by the illumination source passes through the beam splitter, the laser reflecting mirror, and the imaging objective lens to illuminate the sample, thus reflecting the image information on the sample, which is then collected by the detector after passing through the laser reflecting mirror, the beam splitter, the fourth reflecting mirror, and the imaging lens. A beam shaping device is also provided between the energy adjustment device and the lens group to homogenize the beam.

4. The printing apparatus according to claim 3, characterized in that: The spatial light modulator is a DMD spatial light modulator.

5. A method for printing tunable micro / nano structures, using a printing apparatus for tunable micro / nano structures as described in any one of claims 1-4, comprising: Step 1: Place the sample on a triaxial displacement stage, cover the sample with a coverslip, and place a liquid medium between the coverslip and the sample; Step 2: The ultrafast laser emits a beam to an optical switch. After being regulated by an energy adjustment device, the beam enters a beam shaping device for homogenization. The homogenized beam is then expanded by a lens group. After expansion, it is reflected by a first mirror and then passes through a second and third mirror before entering a spatial light modulator. The first mirror, the first mirror group, and the second mirror group are used to adjust the incident angle of the beam entering the spatial light modulator. The spatial light modulator loads the pattern to be processed and then performs time-varying on the incoming beam to carry the pattern information. The pattern is formed spontaneously by light and matter to create nanoscale stripes. After passing through an imaging lens, the beam enters a laser mirror and is projected onto the sample by an imaging objective lens, ablating the sample surface to form micro- and nano-structures.

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