Preparation method of micro-bubble assisted femtosecond laser direct writing silver nanowires

Abstract

The application discloses a kind of microbubble assisted femtosecond laser direct writing silver nanowire preparation method, belong to micro-nano processing technical field.The application is by after pretreatment substrate is placed in silver precursor solution, make the laser focus point of femtosecond laser after objective focusing at substrate and precursor solution interface, open femtosecond laser and induce to form stable microbubble at focus point, and control three-dimensional precision displacement platform to drive substrate and microbubble moving with substrate relative to fixed laser focus point moves, make laser focus point relatively move in microbubble along preset track, utilize the microlens effect of microbubble converging light field, heat limiting effect inhibits heat diffusion and the LSPR effect of silver nanoparticles localizes light field energy in nanometer scale space range, solve the resolution of prior art processing is limited by diffraction limit, bubble is not effectively utilized and the problem of insufficient resolution of bubble assisted processing, realize the controllable direct writing preparation of silver nanowire far less than optical diffraction limit.

Description

Technical Field

[0001] This invention relates to the field of micro-nano fabrication technology, and in particular to a method for preparing silver nanowires by microbubble-assisted femtosecond laser direct writing. Background Technology

[0002] Femtosecond laser multiphoton reduction technology is an important additive manufacturing method for metal micro and nanostructures. It utilizes ultrafast lasers to directly reduce metal ions in precursor solutions, and has the advantage of high spatial resolution that breaks through the optical diffraction limit. It has broad application prospects in fields such as flexible transparent conductive materials, metasurfaces, plasmon integrated optoelectronic devices, and surface-enhanced Raman scattering.

[0003] However, this technology still faces many insurmountable technical bottlenecks in practical applications. On the one hand, during femtosecond laser multiphoton reduction processing, silver nanoparticles can only grow randomly and deposit disorderly in the laser focal region. The growth state of the particles cannot be precisely controlled, and the linewidth of the final prepared silver nanowires is not only limited by the inherent optical diffraction limit, but also further expanded in size due to the uncontrolled growth of nanoparticles. This makes it difficult to achieve the fabrication of microstructures beyond the diffraction limit, greatly restricting the miniaturization and high-precision development of micro-nano devices. On the other hand, in liquid-phase femtosecond laser processing systems, cavitation bubbles induced by laser irradiation have long been considered a harmful factor in processing. Existing research generally focuses on suppressing bubble formation and eliminating the influence of bubbles, completely ignoring the utilization value of microbubbles and failing to explore their role in assisting high-precision processing. At the same time, the few reported bubble-assisted micro-nano processing technologies suffer from insufficient processing resolution, failing to meet the requirements for direct writing of ultra-small silver nanostructures, and making it difficult to overcome the precision barrier of existing femtosecond laser multiphoton reduction technology. Therefore, there is an urgent need to develop a microbubble-assisted femtosecond laser direct writing method for silver nanowires, which can effectively leverage the auxiliary processing efficiency of laser-induced microbubbles, break through the optical diffraction limit, and solve the industry pain points of difficulty in finely reducing the size of silver nanostructures and insufficient processing resolution. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating silver nanowires by direct writing with microbubbles-assisted femtosecond lasers. This method overcomes the problems in traditional fabrication processes, such as the processing resolution being limited by the optical diffraction limit, the laser-induced cavitation bubbles being simply considered a harmful factor, and the lack of exploration and effective utilization of their auxiliary processing potential. At the same time, it makes up for the shortcomings of insufficient resolution in existing bubble-assisted micro-nano fabrication technologies, breaks through the precision barrier of traditional fabrication processes, and ultimately achieves the direct writing fabrication of high-precision silver nanostructures with feature sizes much smaller than the optical diffraction limit, meeting the fabrication needs of miniaturized and refined micro-nano optoelectronic devices.

[0005] To achieve the above objectives, this invention provides a method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires, comprising the following steps: S1. The substrate is ultrasonically cleaned and dried to obtain the pretreated substrate. S2. Mix the silver source with water, stir for the first time, add ammonia water to obtain a diammine silver ion solution; dissolve the surfactant in water, stir for the second time to obtain a surfactant solution; mix the surfactant solution with the diammine silver ion solution, stir for the third time to obtain a precursor solution containing silver ions; S3. Fix the pretreated substrate on a three-dimensional precision displacement platform, drop a precursor solution containing silver ions onto the substrate surface, seal it with a coverslip, and drop immersion oil onto the coverslip surface. Adjust the three-dimensional precision displacement platform so that the laser focus of the femtosecond laser direct writing system's light source beam, after being focused by the objective lens, is located at the interface between the substrate and the precursor solution containing silver ions. Turn on the light source, and stable microbubbles are induced at the laser focus. Adjust the three-dimensional precision displacement platform to move the substrate and microbubbles relative to the laser focus, so that the laser focus moves relative to the microbubbles along a preset trajectory within the microbubbles. Clean and dry to obtain silver nanowires. The femtosecond laser direct writing system uses a femtosecond laser as the light source. A shutter, a half-wave plate, a polarization beam splitter, and a mirror are sequentially arranged in the output optical path. After being reflected by the mirror, the laser is introduced into an inverted microscope and focused onto a precursor solution containing silver ions through the objective lens.

[0006] Preferably, in S1, the substrate includes glass, transparent crystal, silicon wafer or PET flexible material; the drying temperature is 80-100℃ and the drying time is 20-30min.

[0007] Preferably, in S2, the silver source includes one of silver nitrate, silver chloride, or silver sulfate; the surfactant includes anionic surfactants containing amide bonds or polyvinylpyrrolidone, and the anionic surfactants containing amide bonds include one of N-acylglycinate, N-decanoic acid sodium salt, N-acylglutamate, N-acylalanine, N-acyl-N-methyl-β-alanine, acylglycinate, acylglutamate, acylalanine, acylmethylalanine, acyltaurate, and amide betaine.

[0008] Preferably, in S2, the mass-to-volume ratio of silver source, water, and ammonia is 0.034g:1.8mL:0.2mL, and the mass fraction of ammonia is 25%; the mass-to-volume ratio of surfactant and water is 0.0525g:1mL; and the volume ratio of surfactant solution to diammonium silver ion solution is 1:1.

[0009] Preferably, in S2, the concentration of silver ions in the precursor solution containing silver ions is 0.005-0.15M, and the concentration of surfactant is 0.005-0.2M.

[0010] Furthermore, the concentration of silver ions in the precursor solution containing silver ions was 0.05 M, and the concentration of the surfactant was 0.099 M.

[0011] Preferably, in S2, the first stirring time is 5 minutes, the second stirring time is 10 minutes, and the third stirring time is 10 minutes.

[0012] Preferably, in S3, the volume ratio of the silver ion precursor solution to the substrate surface area is 40 μL: 225 mm². 2 The objective lens is an oil immersion objective lens with a magnification of 40-100X and a numerical aperture of 1.2-1.49.

[0013] Preferably, in S3, the diameter of the microbubble is 500nm-50μm, and the speed at which the three-dimensional precision displacement platform moves the substrate and the microbubble relative to the laser focus is 1-20μm / s, with the preset trajectory being a straight line.

[0014] Furthermore, the three-dimensional precision displacement platform drives the substrate and microbubbles to move at a speed of 1-10 μm / s relative to the laser focus.

[0015] Preferably, the femtosecond laser includes a Ti:sapphire femtosecond laser, the output pulse width of which is 3.7-200 fs, the center wavelength is 700-900 nm, the repetition frequency is 1 MHz-1 GHz, and the power is 0.1-20 mW.

[0016] Furthermore, the power of the femtosecond laser is 1.0-5.0mW.

[0017] The mechanism of the present invention, such as Figure 1 As shown: A femtosecond laser is used to generate femtosecond pulsed laser light, which is focused into a precursor solution through a high numerical aperture objective lens. By setting appropriate power, pulse width, repetition frequency, center wavelength, and focusing position in the precursor solution, the femtosecond laser can induce the formation of microbubbles in a silver ion-containing precursor solution, causing the silver ions in the precursor solution to be reduced to silver nanoparticles through multiphoton absorption. By controlling the scanning of the femtosecond laser beam relative to the substrate, the laser focus moves within the microbubbles. The microbubble microlens effect converges the light field, the thermal confinement effect suppresses thermal diffusion, and the near-field enhancement effect of localized surface plasmon resonance (LSPR) of the silver nanoparticles localizes the light field energy within a nanoscale spatial range. Silver nanoparticles are deposited at the interface between the microbubbles and the substrate to form silver nanowires. The characteristic size of the formed silver nanowires is much smaller than the diffraction limit of the femtosecond laser.

[0018] Therefore, the present invention employs the above-mentioned method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires, which has the following beneficial effects: (1) This invention is the first to synergistically apply the microlens effect and thermal confinement effect of femtosecond laser-induced microbubbles and the LSPR near-field enhancement effect of silver nanoparticles to the multiphoton reduction direct writing process of metal ions. The synergistic effect of the three effects highly localizes the light field energy within the nanoscale spatial range, and realizes that the feature size of silver nanowires processed inside the bubble is about 1 / 6 of the feature size of silver nanowires processed outside the bubble.

[0019] (2) This invention overcomes the technical bias of viewing laser-induced microbubbles as processing defects in the prior art, and transforms microbubbles from a processing interference factor into a core tool for achieving super-diffraction limit processing.

[0020] (3) The present invention does not require complex mask and etching processes and can be implemented in a conventional femtosecond laser direct writing system.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the mechanism of a microbubble-assisted femtosecond laser direct writing method for silver nanowires according to the present invention; Figure 2 This is an optical microscope image of microbubbles induced by femtosecond laser in Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the silver nanowires prepared in Example 1 of this invention; Figure 4 These are scanning electron microscope images and energy dispersive spectroscopy (EDS) analysis spectra of the silver nanowires prepared in Example 1 of this invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0025] In this invention, AgNO3 and ammonia water were purchased from Sinopharm Chemical Reagent Co., Ltd., and sodium N-decanoylamino acid (NDSS, CAS: 30377-07-2) was purchased from Tokyo Chemical Industry Co., Ltd., Japan. Other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0026] Example 1 A method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires includes the following steps: S1. Sodium-calcium silicate glass (substrate, 15mm×15mm) was ultrasonically cleaned for 5 minutes under five conditions: cleaning agent with deionized water, deionized water, ethanol, acetone and deionized water. It was then dried in an oven at 90℃ for 25 minutes and cleaned by oxygen plasma to obtain the pretreated substrate. S2. Mix 0.034g AgNO3 (silver source) with 1.8mL deionized water, stir magnetically for 5min, and add 0.2mL of 25% ammonia solution to obtain a diammine silver ion solution; dissolve 0.0525g of N-decanoic acid sodium salt (surfactant) in 1mL deionized water, stir magnetically for 10min to obtain a surfactant solution; mix 1mL of surfactant solution with 1mL of diammine silver ion solution, stir magnetically for 10min to obtain a precursor solution containing silver ions (silver ion concentration is 0.05M, surfactant concentration is 0.099M). S3. A Ti:sapphire femtosecond laser is used as the light source. The center wavelength of the output laser is 800nm, the pulse width is 47fs, and the repetition frequency is 80MHz. A shutter, a half-wave plate, a polarization beam splitter and a mirror are arranged in sequence on the output optical path of the femtosecond laser. After the laser is reflected by the mirror, it is introduced into an inverted microscope and focused through an oil immersion objective lens (100X) with a numerical aperture of 1.3. The pretreated substrate was fixed on a three-dimensional precision displacement platform. 40 μL of a precursor solution containing silver ions was dropped onto the substrate surface using a pipette. The substrate was then sealed with a 15 mm × 15 mm coverslip, and immersion oil was added to the coverslip. The three-dimensional precision displacement platform was adjusted so that the laser focus of the femtosecond laser direct writing system, after being focused by the objective lens, was located at the interface between the substrate and the silver ion-containing precursor solution. The laser power was set to 2.88 mW, and the Ti:sapphire femtosecond laser was turned on. Stable microbubbles (15 μm in diameter) were induced at the laser focus. The three-dimensional precision displacement platform was adjusted to move the substrate and microbubbles relative to the laser focus at a speed of 2 μm / s, so that the laser focus moved relative to the microbubbles along a preset straight trajectory to form a silver nanowire sample on the substrate. The sample was immersed in an ethanol solution with a mass concentration ≥99.5% for 10 min. The residual silver ion precursor solution on the substrate surface was removed, and deionized water was slowly added from the coverslip interface using a pipette. The coverslip was then separated, washed, and dried to obtain silver nanowires.

[0027] Example 1: Optical microscope image of microbubbles induced by femtosecond laser as shown in the figure. Figure 2 As shown, where Figure 2 Image (a) is an optical microscope image of the microbubbles just after they have been induced. Figure 2 Image (b) shows an optical microscope image of the microbubbles as they gradually increase in size and stabilize with the accumulation of laser exposure time. Figure 2 Image (c) is an optical microscope image of induced bubbles in the processing area of ​​Example 1. Figure 2 (d) is an optical microscope image of the silver nanowire fabrication process in microbubbles in Example 1.

[0028] from Figure 2 As can be seen, with the accumulation of laser exposure time, the induced bubbles gradually increase in size and tend to stabilize. In the femtosecond laser processing, the laser is focused inside the bubble, and the laser is scanned inside the bubble by the movement of the displacement platform, thereby processing silver nanowires inside the bubble.

[0029] The morphology of the silver nanowires prepared in Example 1 was characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown, where Figure 3 Image (a) is a SEM image of the silver nanowires prepared in Example 1, with the area within the frame representing the processing region inside the bubble. Figure 3 Image (b) shows SEM images of the silver nanowires prepared in Example 1, showing the internal and external processing of the bubbles. Figure 3 As can be seen, the feature size of silver nanowires processed inside the bubble (linewidths of 266 nm, 318 nm, and 422 nm) is about 1 / 6 of the feature size of silver nanowires processed outside the bubble (linewidth of 2820 nm), resulting in a significant improvement in resolution. Furthermore, the feature size of silver nanowires processed inside the bubble is much smaller than the diffraction limit of the femtosecond laser (307 nm).

[0030] The composition of silver nanowires was analyzed using energy-dispersive X-ray spectroscopy (EDS), and the results are as follows: Figure 4 As shown, where Figure 4 Image (a) is a SEM image of the silver nanowires prepared in Example 1. Figure 4 Image (b) is a SEM EDS distribution map of silver elements in silver nanowires prepared in Example 1. Figure 4 As can be seen, the distribution of silver elements is basically consistent with the distribution of the prepared nanowires, confirming that the nanowires were prepared by the photochemical reduction reaction of silver ions.

[0031] Therefore, this invention places the pretreated substrate in a silver precursor solution, and positions the laser focal point of the femtosecond laser, after being focused by the objective lens, at the interface between the substrate and the precursor solution. The femtosecond laser is then activated to induce the formation of stable microbubbles at the focal point. A three-dimensional precision displacement platform is controlled to move the substrate and the microbubbles that move with the substrate relative to the fixed laser focal point. This allows the laser focal point to move relative to the microbubbles along a preset trajectory. By utilizing the microlens effect of the microbubbles to converge the light field, the thermal confinement effect to suppress thermal diffusion, and the LSPR effect of the silver nanoparticles, the light field energy is localized within the nanoscale spatial range. This solves the problems of the existing technology, such as the processing resolution being limited by the diffraction limit, the ineffective utilization of bubbles, and the insufficient resolution of bubble-assisted processing. It achieves the controllable direct writing fabrication of silver nanowires with a resolution far below the optical diffraction limit.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing silver nanowires by microbubble-assisted femtosecond laser direct writing, characterized in that: Includes the following steps: S1. The substrate is ultrasonically cleaned and dried to obtain the pretreated substrate. S2. Mix the silver source with water, stir for the first time, add ammonia water to obtain a diammine silver ion solution; dissolve the surfactant in water, stir for the second time to obtain a surfactant solution; mix the surfactant solution with the diammine silver ion solution, stir for the third time to obtain a precursor solution containing silver ions; S3. Fix the pretreated substrate on a three-dimensional precision displacement platform, drop a precursor solution containing silver ions onto the substrate surface, seal it with a coverslip, and drop immersion oil onto the coverslip surface. Adjust the three-dimensional precision displacement platform so that the laser focus of the femtosecond laser direct writing system's light source beam, after being focused by the objective lens, is located at the interface between the substrate and the precursor solution containing silver ions. Turn on the light source, and stable microbubbles are induced at the laser focus. Adjust the three-dimensional precision displacement platform to move the substrate and microbubbles relative to the laser focus, so that the laser focus moves relative to the microbubbles along a preset trajectory within the microbubbles. Clean and dry to obtain silver nanowires. The femtosecond laser direct writing system uses a femtosecond laser as the light source. A shutter, a half-wave plate, a polarization beam splitter, and a mirror are sequentially arranged in the output optical path. After being reflected by the mirror, the laser is introduced into an inverted microscope and focused onto a precursor solution containing silver ions through the objective lens.

2. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S1, the substrate includes glass, transparent crystal, silicon wafer or PET flexible material; the drying temperature is 80-100℃ and the drying time is 20-30min.

3. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S2, the silver source includes one of silver nitrate, silver chloride, or silver sulfate; the surfactant includes anionic surfactants containing amide bonds or polyvinylpyrrolidone, and the anionic surfactants containing amide bonds include one of N-acylglycinate, N-decanoylaminoacetic acid sodium salt, N-acylglutamate, N-acylalanine, N-acyl-N-methyl-β-alanine, acylglycinate, acylglutamate, acylalanine, acylmethylalanine, acyltaurate, and amide betaine.

4. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S2, the mass-to-volume ratio of silver source, water, and ammonia is 0.034 g: 1.8 mL: 0.2 mL, and the mass fraction of ammonia is 25%; the mass-to-volume ratio of surfactant and water is 0.0525 g: 1 mL; and the volume ratio of surfactant solution to diammonium silver ion solution is 1:

1.

5. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S2, the concentration of silver ions in the precursor solution containing silver ions is 0.005-0.15M, and the concentration of surfactant is 0.005-0.2M.

6. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S2, the first stirring time is 5 minutes, the second stirring time is 10 minutes, and the third stirring time is 10 minutes.

7. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S3, the volume ratio of the silver ion precursor solution to the substrate surface area is 40 μL: 225 mm². 2 The objective lens is an oil immersion objective lens with a magnification of 40-100X and a numerical aperture of 1.2-1.

49.

8. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: In S3, the diameter of the microbubble is 500nm-50μm, and the three-dimensional precision displacement platform drives the substrate and microbubble to move at a speed of 1-20μm / s relative to the laser focus, with the preset trajectory being a straight line.

9. The method for preparing microbubble-assisted femtosecond laser direct writing silver nanowires according to claim 1, characterized in that: Femtosecond lasers include Ti:sapphire femtosecond lasers. The output pulse width of femtosecond lasers is 3.7-200 fs, the center wavelength is 700-900 nm, the repetition frequency is 1 MHz-1 GHz, and the power is 0.1-20 mW.

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