A localized polarization enhanced nonlinear ionization nanolithography system and method

Abstract

The application relates to a local polarization enhanced nonlinear ionization nanolithography system and method, and belongs to the technical field of femtosecond laser processing. The nanolithography method has the capability of large-area processing, can process a large-area nanohole array on a material through a 'flying dotting' mode, can control the distance between adjacent points in the nanohole array by controlling the speed of a high-precision displacement table and the repetition frequency of femtosecond laser pulses, can control the size of the nanohole by controlling the pulse energy, can control the characteristic line width of a nanowire by controlling the pulse energy and the speed of the high-precision displacement table, and can realize the patterning processing of the nanowire by designing a pattern and introducing the high-precision displacement table.

Description

Technical Field

[0001] This invention relates to a locally polarized enhanced nonlinear ionization nanowriting system and method, belonging to the field of femtosecond laser processing technology. Background Technology

[0002] With the increasing integration, multifunctionality, and miniaturization of microelectronic products, higher demands are being placed on micro- and nano-manufacturing technologies. Currently, the main micro- and nano-fabrication technologies in the microelectronics field include photolithography, focused ion beam (FIP), electron beam etching, and nanoimprint lithography. Photolithography is one of the most common technologies in microelectronics processing, capable of achieving nanoscale resolution for structural and patterned fabrication. However, the photolithography process is extremely complex, with high costs for photolithography machines and masks, and it is difficult to achieve cross-scale processing from micrometers to nanometers. Focused ion beam (FIP) achieves precision cutting and etching by focusing a high-energy ion beam onto the surface of a target material. It offers high processing accuracy, adapts to various complex processing needs, and features high flexibility and repeatability. However, FIP requires operation in a high-vacuum environment, resulting in high maintenance costs and relatively low processing efficiency. Electron beam etching is a micro- and nano-fabrication technology that uses an electron beam as a mask to expose photosensitive materials. This technology offers extremely high resolution, eliminates the need to change the mask, and provides high flexibility. However, electron beam etching also requires a high vacuum environment, resulting in high maintenance costs. Compared with other micro-nano fabrication technologies, electron beam etching uses point-by-point scanning, leading to relatively low processing efficiency and difficulty in etching complex patterns. Furthermore, the proximity effect is easily induced during electron beam etching, significantly impacting processing accuracy and quality. Nanoimprint lithography, a template pattern transfer-based processing technology, offers high precision and enables mass production. With precisely designed templates, it can even fabricate quasi-three-dimensional structures. However, nanoimprint lithography requires complex template manufacturing processes and faces challenges in practical applications, including template cost and lifespan, structural consistency, and structural defects. To adapt to the rapid development of the microelectronics field, there is an urgent need to develop a simple, low-cost, and highly adaptable micro-nano fabrication technology.

[0003] Femtosecond laser processing technology is a rapidly developing new nanofabrication method in recent years. With its femtosecond-level pulse duration and ultra-high peak power, it exhibits unparalleled advantages in precision machining, especially suitable for high-precision drilling, cutting, and welding. Compared to traditional micro-nano processing technologies, femtosecond laser processing does not require a high-vacuum environment, possesses "cold processing" characteristics, and has broad material applicability. Furthermore, femtosecond lasers have the unique capability of "true three-dimensional" processing, allowing them to focus on the interior of transparent materials and precisely process the internal structure without damaging the material surface. Despite the many advantages of femtosecond lasers in high-precision machining, the diffraction limit restricts their processing accuracy. A cylindrical vector beam is a type of beam whose polarization state varies along the radial or azimuth direction. When focused by a high numerical aperture (NA) lens, the beam forms a longitudinal field along the propagation direction in the focusing region, creating a more compact spot in space than a scalar light field, and can even break the diffraction limit. Longitudinal light fields possess unique properties, enabling electron acceleration, generating strong localization effects at smaller spatial scales, and more effectively exciting longitudinal dipoles, thus inducing unique optical responses in materials. Currently, the technology of super-resolution processing using vector beams has attracted widespread attention.

[0004] The disadvantages of existing technology are:

[0005] Traditional micro-nano fabrication technologies generally require high vacuum environments, have complex processes, are costly, and lack technical flexibility, making them unable to adapt to the rapid development of the microelectronics field.

[0006] The processing accuracy of traditional femtosecond laser processing technology is limited by the optical diffraction limit, making it difficult to improve the processing accuracy. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and propose a nonlinear ionization nanowriting system and method with enhanced local polarization.

[0008] The technical solution of this invention is:

[0009] A locally polarized enhanced nonlinear ionization nanowriting system includes a Ti:sapphire femtosecond laser 1, an energy control module 2, a radial polarization converter 3, a frequency doubling module 4, a conical lens 5, a first dichroic mirror 6, a plano-convex lens 7, a ring phase filter 8, a focusing objective lens 9, a culture dish 10, a high-precision displacement stage 11, a second dichroic mirror 12, an illumination source 13, and a CCD imaging unit 14.

[0010] The Ti:sapphire femtosecond laser 1 is used to emit femtosecond laser to the energy control module 2. The femtosecond laser is a horizontally polarized femtosecond laser with a Gaussian distribution of light intensity in space and a wavelength of 800nm.

[0011] The energy control module 2 is used to adjust the pulse energy of the femtosecond laser and transmit the femtosecond laser after pulse energy adjustment to the radial polarization converter 3.

[0012] The radial polarization converter 3 is used to receive the femtosecond laser after pulse energy adjustment, and convert the received femtosecond laser into radially polarized femtosecond laser before transmitting it to the frequency doubling module 4;

[0013] The frequency doubling module 4 is used to receive radially polarized femtosecond laser light, and convert the received radially polarized femtosecond laser light into frequency-doubled light with a wavelength of 400nm before transmitting it to the conical lens 5.

[0014] The conical lens 5 is used to receive frequency-doubled light with a wavelength of 400nm. The received frequency-doubled light with a wavelength of 400nm is spatially shaped into a primary Bessel-Gaussian beam and then sequentially transmitted to the first dichroic mirror 6 for reflection, the plano-convex lens 7 for transmission, the annular phase filter 8 for filtering, and the focusing objective lens 9 for focusing to obtain a focused beam. The full width at half maximum (FWHM) of the focused beam is much lower than the diffraction limit. The focused beam irradiates the quartz sample fixed in the culture dish 10 and performs nano-writing operation on the quartz sample in an oil immersion environment.

[0015] The illumination light emitted by the illumination source 13 passes sequentially through the second dichroic mirror 12, the first dichroic mirror 6, the plano-convex lens 7, the annular phase filter 8, and the focusing objective lens 9 before illuminating the quartz sample. After being reflected by the surface of the quartz sample, the light returns along the original path and is reflected by the second dichroic mirror 12 into the CCD imaging unit 14, so as to dynamically monitor the entire processing process.

[0016] The high-precision displacement stage 11 can translate at high speed in the XYZ direction, driving the quartz sample to move along a set trajectory.

[0017] The femtosecond laser emitted by the Ti:sapphire femtosecond laser 1, after having its pulse energy adjusted by the energy control module 2, is fed into the radial polarization converter 3. The radial polarization converter 3 converts the horizontally linearly polarized femtosecond laser into radially polarized light. The radially polarized femtosecond laser is then fed into the frequency doubling module 4, becoming frequency-doubled light with a wavelength of 400 nm. The 400 nm frequency-doubled light is then fed into the conical lens 5, which spatially shapes the Gaussian-distributed femtosecond laser into a primary Bessel-Gaussian beam. This primary Bessel-Gaussian beam is reflected by the first dichroic mirror 6 and fed into a 4f beam-constriction system consisting of a plano-convex lens 7 and a focusing objective 9 to obtain a secondary Bessel-Gaussian beam. A ring phase filter 8 placed in front of the focusing objective 9 modulates the phase of the incident light, ultimately resulting in a focused beam behind the focusing objective 9. The full width at half maximum (FWHM) of this focused beam is far below the diffraction limit. The focused beam irradiates a quartz sample fixed in a culture dish 10, performing nano-writing operations on the quartz sample in an oil-immersion environment. The illumination light emitted by the illumination source 13 passes through the second dichroic mirror 12, the first dichroic mirror 6, the plano-convex lens 7, the annular phase filter 8, and the focusing objective lens 9 before illuminating the quartz. After reflection from the quartz surface, the light returns along its original path and is reflected again by the second dichroic mirror 12 to the CCD imaging unit 14, enabling dynamic monitoring of the entire processing. This invention utilizes a sub-diffraction-limited focused beam created by a locally polarized enhanced nonlinear ionization controllable nano-writing system to perform nano-writing on materials.

[0018] The titanium sapphire femtosecond laser emits a laser with a center wavelength of 800 nm, a pulse width of 50 fs, an adjustable repetition frequency of 1 kHz, a maximum single-pulse energy of 3 mJ, and a Gaussian spatial distribution of light intensity with horizontal linear polarization.

[0019] The energy control module consists of a half-wave plate and a polarizer. By rotating the half-wave plate or the polarizer, the relative angle between the half-wave plate and the polarizer is changed to adjust the pulse energy of the incident femtosecond laser.

[0020] The radial polarization converter can convert linearly polarized femtosecond lasers into radially polarized femtosecond lasers.

[0021] The frequency doubling module consists of a BBO crystal and a filter, which can double the frequency of an 800nm ​​femtosecond laser to a 400nm femtosecond laser.

[0022] The cone lens has a cone base angle of 1°, the plano-convex lens has a focal length of f = 175 mm, and the focusing objective is a 100x oil-immersion objective (NA = 1.4).

[0023] The annular phase filter is a 5-ring phase filter, consisting of 5 concentric rings with radii of r1 = 75 μm, r2 = 117 μm, r3 = 214 μm, r4 = 238 μm, and r5 = 250 μm from the inside to the outside. The annular phase filter is made of fused silica with a thickness of 500 μm. The concentric ring structure is fabricated using photolithography. The areas requiring etching are the annular regions between r1-r2 and r3-r4, fabricated using a three-stage photolithography process, with each step d having a height of 106 nm.

[0024] The sample was fixed in a petri dish containing oil and placed on a high-precision displacement stage.

[0025] The intensity distribution of the focused beam in the focusing region is determined by the Richards–Wolf vector diffraction theory, and its expression in cylindrical coordinates is shown in (1):

[0026]

[0027] Among them, E r and E z These represent the radial and longitudinal components of the total light intensity, respectively; B is the amplitude constant, which can be set to 1; and α is the maximum convergence angle determined by the objective lens numerical aperture NA. J is the apodization function of the focusing objective. i Let θ1 and θ2 be the incident angle before the oil-immersed quartz interface and the refraction angle after the oil-immersed quartz interface, respectively. The relationship between the two angles can be calculated using Snell's law, as follows:

[0028] n1sin(θ1)=n2sin(θ2))(2

[0029] Where n1 and n2 are the refractive indices of oil-impregnated silica and quartz, respectively.

[0030] t p The Fresnel coefficient at the oil-quartz interface is represented by the following formula:

[0031]

[0032] l0(θ1) is the expression for the light field of a primary Bessel-Gaussian beam, as follows:

[0033]

[0034] Wherein, β0 is the truncation parameter, representing the ratio of the pupil radius to the beam waist radius.

[0035] T(θ1) is the transmittance function of the ring phase filter, expressed as:

[0036]

[0037] Where, φ i The angle between the edge of each ring of the ring phase filter and the optical axis can be represented by r. i =sinφ i / NA confirmed, r i Let be the radius of each ring band of the ring phase filter.

[0038] k0, k1, and k2 are the wave vectors of the focused beam in vacuum, oil immersion, and quartz, respectively, denoted as:

[0039]

[0040] λ is the wavelength of the light beam incident on the focusing objective.

[0041] ψ represents the aberration function caused by refractive index mismatch, defined as:

[0042] ψ=d(n2cosθ2-n1cosθ1)(7)

[0043] This invention also provides a locally polarization-enhanced nonlinear ionization nanowriting method based on the above system. This nanowriting method has two processing modes, as detailed below:

[0044] Mode 1: One-dimensional fabrication mode, specifically nanopore fabrication mode, which includes the following steps:

[0045] Step 1: Clean the quartz with ethanol and deionized water for ten minutes each under ultrasonic conditions, then dry it.

[0046] Step 2: Use a locally polarized enhanced nonlinear ionization controllable nano-writing system to create a sub-diffraction-limited focused beam, focus the beam on the quartz surface, adjust the output mode of the Ti:sapphire femtosecond laser 1 to single pulse mode, and adjust the energy control module 2 to adjust the energy of the incident femtosecond laser pulse.

[0047] Step 3: In single-pulse light output mode, the strong longitudinal field of the created sub-diffraction-limited focused beam is used to induce local polarization in the quartz to trigger the redistribution of the electric dipole moment inside the material, thereby enhancing and controlling the nonlinear ionization process of the material, and then processing nanoporous structures on the sample surface.

[0048] Step 4: Immerse the femtosecond laser-processed quartz in a 5% hydrofluoric acid solution for chemical etching post-treatment. After immersion for three minutes, remove it and clean it with ethanol and deionized water for ten minutes each to remove the sputterings and recast layer from the femtosecond laser processing, resulting in a clean surface and a clear nanoporous structure.

[0049] Mode 2: Two-dimensional fabrication mode, specifically nanowire fabrication mode, which has the following steps:

[0050] Step 1: Clean the quartz with ethanol and deionized water for ten minutes each under ultrasonic conditions, and then dry it.

[0051] Step 2: Adjust the output mode of the Ti:sapphire femtosecond laser to multi-pulse mode, and use the sub-diffraction-limited focused beam created by the locally polarized enhanced nonlinear ionization controllable nano-writing system to process nanopore structures on quartz.

[0052] Step 3: Using the nanopores processed in Step 2 as the initial nanocavity, the subsequently incident focused beam interferes with the nanocavity and forms a local enhancement field at the edge of the nanocavity. The local enhancement field causes the distribution of electric dipole moments inside the material to concentrate at the edge of the nanocavity, resulting in enhanced optical response in the vicinity of the nanocavity. By moving the position of the high-precision displacement stage and injecting energy below the threshold, the nanocavity will gradually expand into a nanowire structure on the two-dimensional plane. The formation direction of the nanowire is controlled by controlling the moving direction of the high-precision displacement stage 11.

[0053] Step 4: Immerse the femtosecond laser-processed quartz in a 5% hydrofluoric acid solution for chemical etching post-treatment. After immersion for three minutes, remove it and clean it with ethanol and deionized water for ten minutes each to remove the sputtering material and recast layer from the femtosecond laser processing, thus obtaining the nanowire structure.

[0054] Beneficial effects

[0055] 1. The micro-nano fabrication technology proposed in this invention does not require a vacuum environment, is simple to operate, does not require complicated process steps, has low cost, and the method has strong stability and wide material applicability, enabling ultra-high precision nano-writing on a variety of hard, brittle and transparent materials.

[0056] 2. The locally polarized enhanced nonlinear ionization controllable nanowriting method of the present invention has two writing modes, namely one-dimensional (nanopore) and two-dimensional (nanowire) processing modes, and the processing accuracy of both modes reaches the sub-5nm scale.

[0057] 3. The nano-writing method of this invention utilizes the local polarization effect induced by the strong longitudinal field of a sub-diffraction-limited focused beam to induce a redistribution of the electric dipole moments within the material, thereby enhancing and controlling the nonlinear ionization process of the material and achieving ultra-high precision machining. Furthermore, the two-dimensional machining mode is based on the redistribution of the electric dipole moments within the material induced by the local enhanced field of a radially polarized beam. The formation of this local enhanced field is independent of the polarization direction, depending only on the scanning direction. This characteristic gives the two-dimensional machining mode higher machining freedom, enabling the creation of nanowire structures of arbitrary length in any direction within a two-dimensional plane. In addition, the radially polarized beam, due to its symmetrical polarization and intensity distribution characteristics, effectively avoids the phenomenon of uneven energy deposition of the beam during material removal, which is beneficial for the fabrication of high-quality nanostructures.

[0058] 4. The focused beam created by the locally polarized enhanced nonlinear ionization nanowriting system has a full width at half maximum (FWHM) of only 0.28λ inside the material, which is far below the Abbe diffraction limit (0.5λ / NA). The energy distribution of the beam is more concentrated, which restricts the nonlinear interaction region between the femtosecond laser and the material to a very small spatial range, thereby making the physical processes of nonlinear ionization, lattice heat transfer, and phase transition of the material spatially controllable.

[0059] 5. The nano-writing method of this invention has the capability of large-area processing. Through the "flying dot-mapping" method, it is possible to process large-area nanopore arrays on materials. By controlling the speed of the high-precision displacement stage and the repetition frequency of the femtosecond laser pulse, the distance between adjacent points in the nanopore array can be controlled. By controlling the pulse energy, the size of the nanopores can be controlled. By controlling the pulse energy and the speed of the high-precision displacement stage, the feature linewidth of the nanowires can be controlled. By designing patterns and importing them into the high-precision displacement stage, the patterned processing of nanowires can be realized. Attached Figure Description

[0060] Figure 1 A schematic diagram of the optical path of a nonlinear ionization nanowriting system with enhanced local polarization;

[0061] Figure 2 This is a schematic diagram of a ring-phase filter and a schematic diagram of the steps generated when the ring-phase filter ring structure is fabricated using photolithography.

[0062] Figure 3 The sub-diffraction-limited focused beam created for a locally polarized enhanced nonlinear ionization nanowriting system in the xy plane ( Figure 3 a) and yz plane ( Figure 3 b) Intensity distribution;

[0063] Figure 4 A schematic diagram of a sample being chemically etched for focused beam processing;

[0064] Figure 5 Scanning electron microscope (SEM) images of nanopore structures obtained on quartz in one-dimensional fabrication mode using a locally polarized enhanced nonlinear ionization controllable nanowriting method, and scanning electron microscope (SEM) images of nanopore arrays obtained on quartz using a "flying dotting" method.

[0065] Figure 6 Scanning electron microscope (SEM) images and optical microscope (OEM) images of the surface morphology of nanoporous structures fabricated on quartz in a one-dimensional fabrication mode using a locally polarized enhanced nonlinear ionization controllable nanowriting method.

[0066] Figure 7 A schematic diagram of the local enhancement field formed by the focused beam at the edge of the quartz nanopore in the two-dimensional processing mode of the simulated locally polarized enhanced nonlinear ionization controllable nanowriting method;

[0067] Figure 8 Scanning electron microscope image of nanowire structures fabricated on quartz in a two-dimensional fabrication mode using a locally polarized enhanced nonlinear ionization controllable nanowriting method;

[0068] Figure 9 The image shows a scanning electron microscope (SEM) image of a patterned nanowire structure fabricated on quartz in a two-dimensional fabrication mode using a locally polarized enhanced nonlinear ionization controllable nanowriting method. The inset is an optical microscope image of the patterned nanowire structure.

[0069] Figure 10 Scanning electron microscope (SEM) images of nanopores and nanowire structures created on sapphire, YAG, and LiNbO3 using a locally polarized enhanced nonlinear ionization controllable nanowriting method. The scale bars in the images are all 200 nm.

[0070] Among them, 1-Titanium sapphire femtosecond laser, 2-energy control module, 3-radial polarization converter, 4-frequency doubling module, 5-conical lens, 6-first dichroic mirror, 7-plano-convex lens, 8-ring phase filter, 9-focusing objective lens, 10-culture dish, 11-high-precision displacement stage, 12-second dichroic mirror, 13-illumination source, 14-CCD imaging unit. Detailed Implementation

[0071] To make the technical means, creative features, objectives and effects of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0072] This invention provides a locally polarized enhanced nonlinear ionization controllable nanowriting system and method. The system and method utilize a ring phase filter to phase modulate a tightly focused radially polarized Bessel-Gaussian beam, shaping a conventional Gaussian-distributed femtosecond laser into a sub-diffraction-limited focused beam with a high-purity longitudinal component. The full width at half maximum (FWHM) of the focused beam is only 0.28λ, far smaller than the optical diffraction limit (Abbe diffraction limit: 0.5λ / NA). Utilizing the local polarization effect of the strong longitudinal field of the sub-diffraction-limited focused beam, a redistribution of the electric dipole moments within the material is induced, significantly enhancing and controlling the nonlinear interaction between the femtosecond laser and the material, thereby achieving high-precision processing. In two-dimensional processing mode, the initial nanocavity prepared by the focused beam interferes with the subsequent incident beam, causing a redistribution of the optical field intensity near the nanocavity and forming a locally enhanced field. This locally enhanced field causes the electric dipole moments in the material to concentrate at the edge of the nanocavity, resulting in enhanced optical response in the edge region of the nanocavity. In this process, by moving the position of a high-precision displacement stage and injecting energy below a threshold into the material, the nanocavity will gradually expand into a nanowire structure on a two-dimensional plane.

[0073] refer to Figure 1As shown, the locally polarized enhanced nonlinear ionization controllable nanowriting system provided by the present invention includes a Ti:sapphire femtosecond laser 1, an energy control module 2, a radial polarization converter 3, a frequency doubling module 4, a conical lens 5, a first dichroic mirror 6, a plano-convex lens 7, a ring phase filter 8, a focusing objective lens 9, a culture dish 10, a high-precision displacement stage 11, a second dichroic mirror 12, an illumination source 13, and a CCD imaging unit 14. The femtosecond laser emitted by the Ti:sapphire femtosecond laser 1, after having its pulse energy adjusted by the energy control module 2, is fed into the radial polarization converter 3. The radial polarization converter 3 converts the horizontally linearly polarized femtosecond laser into a radially polarized femtosecond laser. This radially polarized femtosecond laser is then fed into the frequency doubling module 4, becoming frequency-doubled light with a wavelength of 400 nm. The 400 nm frequency-doubled light is then fed into the conical lens 5, which spatially shapes the Gaussian-distributed femtosecond laser into a primary Bessel-Gaussian beam. This primary Bessel-Gaussian beam is reflected by the first dichroic mirror 6 and then fed into a 4f beam-constriction system consisting of a plano-convex lens 7 and a focusing objective lens 9 to obtain a secondary Bessel-Gaussian beam. A ring phase filter 8 placed in front of the focusing objective lens 9 modulates the phase of the beam incident on the focusing objective lens 9, ultimately resulting in a focused beam behind the focusing objective lens 9. This focused beam irradiates a quartz sample fixed in a culture dish 10, performing nano-writing operations on the quartz sample in an oil-immersion environment. The illumination light emitted by the illumination source 13 passes through the second dichroic mirror 12, the first dichroic mirror 6, the plano-convex lens 7, the annular phase filter 8, and the focusing objective lens 9 before illuminating the quartz. After reflection from the quartz surface, the light returns along its original path and is reflected again by the second dichroic mirror 12 to the CCD imaging unit 14, enabling dynamic monitoring of the entire processing. This invention utilizes a sub-diffraction-limited focused beam created by a locally polarized enhanced nonlinear ionization controllable nano-writing system to perform nano-writing on the sample.

[0074] The ring phase filter 8 is a 5-ring phase filter, consisting of 5 concentric rings. From the inside out, the concentric rings are r1 = 75 μm, r2 = 117 μm, r3 = 214 μm, r4 = 238 μm, r5 = 250 μm, and r6 = 250 μm respectively. Figure 2 a). The ring phase filter is made of fused silica with a thickness of 500 μm. The concentric circular structure on the ring phase filter is fabricated by photolithography. The areas to be etched are the ring-shaped regions between r1-r2 and r3-r4, which are fabricated using a three-stage photolithography process. The height of each step d is 106 nm. Figure 2 b).

[0075] Supported by the aforementioned locally polarized enhanced nonlinear ionization controllable nanowriting system, this invention also proposes a locally polarized enhanced nonlinear ionization controllable nanowriting method, which has both one-dimensional and two-dimensional processing modes, as detailed below:

[0076] One-dimensional processing mode: obtaining a sub-diffraction-limited focused beam through a locally polarized enhanced nonlinear ionization controllable nano-writing system. Figure 3 This beam possesses an extremely high purity longitudinal field, with a full width at half maximum (FWHM) of only 0.28λ within the material. After the focused beam irradiates the sample surface, the strong longitudinal field of the beam induces local polarization in the sample, thereby causing a rearrangement of the electric dipole moments within the material. This enhances and modulates the nonlinear ionization process of the material, allowing for the fabrication of nanoporous structures on the sample using this mechanism.

[0077] Two-dimensional fabrication mode: The nanopore fabricated by the sub-diffraction-limited focused beam is used as the initial nanocavity. The subsequent incident focused beam interferes with the nanocavity and forms a local enhancement field at the edge of the nanocavity. Figure 7 The local enhancement field enhances and modulates the electric dipole moment distribution density at the edge of the nanocavity. By moving the position of the high-precision displacement stage and injecting energy below the threshold into the material, the nanopores gradually expand on the two-dimensional plane and form a nanowire structure.

[0078] Example 1

[0079] A method for controllably preparing quartz nanopores by locally polarized enhanced nonlinear ionization, comprising the following steps:

[0080] Step 1: Clean the quartz with ethanol and deionized water for ten minutes under ultrasonic conditions, then dry the sample and place it in a petri dish containing oil.

[0081] Step 2: Adjust the collimation of the optical path of the locally polarized enhanced nonlinear ionization controllable nanowriting system to create a sub-diffraction-limited focused beam. The parameters of the Ti:sapphire femtosecond laser used in the experiment are as follows: The femtosecond laser system uses a laser manufactured by Spectrophysic, Inc., with a laser center wavelength of 800 nm, a pulse width of 50 fs, an adjustable repetition frequency of 1 kHz, a maximum single-pulse energy of 3 mJ, and a Gaussian spatial intensity distribution with linear polarization. The sample to be processed in the experiment is a Z-cut quartz crystal with dimensions of 10 mm × 10 mm × 0.5 mm.

[0082] Step 3: Adjust the position of the high-precision displacement stage 11 so that the image formed by the quartz in the CCD imaging unit 14 is clearly visible;

[0083] Step 4: Change the output mode of the Ti:sapphire femtosecond laser 1 to single-pulse output mode. Adjust the pulse incident energy of the femtosecond laser through the energy control module 2. Process a nanopore structure on the quartz sample. Control the pore size of the nanopore by adjusting the incident pulse energy until the pore size meets the requirements.

[0084] Step 5: Clean the femtosecond laser-processed quartz sample with ethanol and deionized water for ten minutes each under ultrasonic conditions, dry it, and then place it in a 5% hydrofluoric acid solution for chemical etching post-treatment. Etch at room temperature for three minutes. Figure 4 Remove the quartz and clean it with ethanol and deionized water for ten minutes each under ultrasonic conditions, then dry it.

[0085] Step 6: Characterize the nanopores fabricated by the focused beam using a scanning electron microscope, and characterize the depth of the nanopores using an optical microscope. Figure 5 a shows the surface morphology of a nanoporous structure with a diameter of 4.83 nm. Figure 6 a shows the surface morphology of a nanopore with a diameter of 13.6 nm. Figure 6 b shows the corresponding depth of the nanopore (3.3 μm), and the calculated depth-to-diameter ratio of the nanopore is 243:1.

[0086] Example 2

[0087] Similar to Example 1, the difference lies in step four, where the repetition frequency of the Ti:sapphire femtosecond laser 1 is adjusted to 100Hz, and the movement speed of the high-precision displacement stage 11 is adjusted to 600μm / s. A nanopore array structure is fabricated on the quartz using a "flying dot-mapping" method, and the femtosecond laser-fabricated nanopore array is characterized using a scanning electron microscope. Figure 5 Figure b shows the surface morphology of the nanopore array, with a distance of 6 μm between two adjacent nanopores.

[0088] Example 3

[0089] A method for fabricating quartz nanowires with locally polarized enhanced nonlinear ionization controllable process, comprising the following steps:

[0090] Step 1: Clean the quartz with ethanol and deionized water for ten minutes under ultrasonic conditions. After drying the sample, place it in a petri dish containing oil. The sample to be processed is a Z-cut quartz crystal with dimensions of 10mm×10mm×0.5mm.

[0091] Step 2: Adjust the optical path collimation of the locally polarized enhanced nonlinear ionization controllable nanowriting system to create a sub-diffraction-limited focused beam. Adjust the repetition frequency of the Ti:sapphire femtosecond laser 1 to 1kHz. Use the energy control module 2 to adjust the incident laser pulse energy. Set the speed of the high-precision displacement stage 11 to 100μm / s. Use the high-precision displacement stage 11 to drive the quartz sample to move in an directional manner.

[0092] Step 3: Using a sub-diffraction-limited focused beam, an initial nanocavity is fabricated on the quartz. Subsequent focused beams incident on the edge of the nanocavity form a focal plane around the nanocavity. Figure 7The local enhancement field shown is used to fabricate a single nanowire structure on quartz by moving the position of the high-precision displacement stage 11.

[0093] Step 4: Clean the quartz sample processed by the focused beam with ethanol and deionized water for ten minutes each in an ultrasonic environment, dry it, and then place it in a 5% hydrofluoric acid solution for chemical etching post-treatment. After etching at room temperature for three minutes, take out the quartz and clean it with ethanol and deionized water for ten minutes each in an ultrasonic environment, and then dry it.

[0094] Step 5: The single nanowire structure prepared by the focused beam is characterized using a scanning electron microscope. Figure 8 The surface morphology of a single nanowire structure with a linewidth of 4.86 nm is shown.

[0095] Example 4

[0096] Similar to Example 3, the difference lies in step three, where a trajectory is set in the high-precision displacement stage 11, patterned nanowire structures are fabricated on quartz, and the fabricated patterned nanowire structures are characterized using scanning electron microscopy and optical microscopy. Figure 9 The surface morphology of the patterned nanowire structure was shown. Figure 9 The illustration shows an optical microscope image of a patterned nanowire structure.

[0097] Example 5

[0098] Similar to Example 1, except that the processed samples in Example 1 were replaced with sapphire, YAG, and LiNbO3, respectively. Nanopores were fabricated on the material surface using a locally polarized enhanced nonlinear ionization controllable nanowriting system. The fabricated nanopore structures were characterized using scanning electron microscopy. Figure 10 a, 10b, and 10c are scanning electron microscope images of nanoporous structures prepared on sapphire, YAG, and LiNbO3 by a focused beam, respectively.

[0099] Example 6

[0100] Similar to Example 3, except that the processed samples in Example 3 were replaced with sapphire, YAG, and LiNbO3, respectively. Nanowires were fabricated on the material surface using a locally polarized enhanced nonlinear ionization controllable nanowriting system, and the fabricated nanowire structures were characterized using scanning electron microscopy. Figure 10 d, 10e, and 10f are scanning electron microscope images of nanowire structures prepared on sapphire, YAG, and LiNbO3 by a focused beam, respectively.

[0101] 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 locally polarized enhanced nonlinear ionization nanowriting system, characterized in that: The writing system includes a Ti:sapphire femtosecond laser, an energy control module, a radial polarization converter, a frequency doubling module, a conical lens, a first dichroic mirror, a plano-convex lens, a ring phase filter, a focusing objective, a culture dish, a high-precision displacement stage, a second dichroic mirror, an illumination source, and a CCD imaging unit. The Ti:sapphire femtosecond laser is used to emit femtosecond laser light to the energy control module. The femtosecond laser is a horizontally polarized femtosecond laser with a Gaussian distribution of light intensity in space and a wavelength of 800 nm. The energy control module is used to adjust the pulse energy of the femtosecond laser and transmit the femtosecond laser with adjusted pulse energy to the radial polarization converter. The radial polarization converter is used to receive femtosecond laser with pulse energy adjustment, and convert the received femtosecond laser into radially polarized femtosecond laser before transmitting it to the frequency doubling module; The frequency doubling module is used to receive radially polarized femtosecond laser light, and convert the received radially polarized femtosecond laser light into frequency-doubled light with a wavelength of 400nm before transmitting it to the conical lens. The conical lens is used to receive frequency-doubled light with a wavelength of 400nm. The received frequency-doubled light with a wavelength of 400nm is spatially shaped into a primary Bessel-Gaussian beam and then sequentially transmitted to the first dichroic mirror for reflection, the plano-convex lens for transmission, the annular phase filter for filtering, and the focusing objective lens for focusing to obtain a focused beam. The focused beam irradiates the quartz sample fixed in the petri dish and performs nano-writing operation on the quartz sample in an oil immersion environment. The illumination light emitted by the illumination source passes sequentially through the second dichroic mirror, the first dichroic mirror, the plano-convex lens, the ring phase filter, and the focusing objective lens before illuminating the quartz sample. After being reflected by the surface of the quartz sample, the light returns along the original path and is reflected by the second dichroic mirror into the CCD imaging unit, enabling dynamic monitoring of the entire processing process.

2. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The high-precision displacement stage can translate at high speed in the XYZ directions, driving the quartz sample to move along a set trajectory.

3. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The titanium sapphire femtosecond laser emits a laser with a center wavelength of 800 nm, a pulse width of 50 fs, an adjustable repetition frequency of 1 kHz, a maximum single-pulse energy of 3 mJ, and a Gaussian spatial distribution of light intensity with horizontal linear polarization.

4. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The energy control module consists of a half-wave plate and a polarizer. By rotating the half-wave plate or the polarizer, the relative angle between the half-wave plate and the polarizer is changed to adjust the pulse energy of the incident femtosecond laser.

5. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The radial polarization converter is used to convert linearly polarized femtosecond laser into radially polarized femtosecond laser.

6. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The frequency doubling module consists of a BBO crystal and a filter, and is used to double the frequency of an 800nm ​​femtosecond laser to a 400nm femtosecond laser.

7. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The cone lens has a cone base angle of 1°, the plano-convex lens 7 has a focal length of f = 175 mm, the focusing objective is a 100x oil-immersion objective, and NA = 1.

4.

8. The locally polarized enhanced nonlinear ionization nanowriting system according to claim 1, characterized in that: The annular phase filter is a 5-ring phase filter, consisting of 5 concentric rings with radii of r1 = 75 μm, r2 = 117 μm, r3 = 214 μm, r4 = 238 μm, and r5 = 250 μm from the inside to the outside. The annular phase filter is made of fused silica with a thickness of 500 μm. The concentric ring structure is fabricated by photolithography. The areas to be etched are the annular regions between r1-r2 and r3-r4, which are fabricated using a three-stage photolithography process. The height of each step d is 106 nm.

9. A locally polarized enhanced nonlinear ionization nanowriting method, characterized in that: Step 1: Clean the quartz sample with ethanol and deionized water under ultrasonic conditions and then dry it. Step 2: Use the nano-writing system described in claim 1 to create a sub-diffraction-limited focused beam, focus the beam on the quartz surface, adjust the output mode of the Ti:sapphire femtosecond laser to single pulse mode, and adjust the energy control module to adjust the energy of the incident femtosecond laser pulse. Step 3: In single-pulse light output mode, the strong longitudinal field of the created sub-diffraction-limited focused beam is used to process nanoporous structures on the quartz surface. Step four involves chemically etching and cleaning the femtosecond laser-processed quartz to obtain a nanoporous structure.

10. A locally polarized enhanced nonlinear ionization nanowriting method, characterized in that: Step 1: Clean the quartz with ethanol and deionized water under ultrasonic conditions and then dry it. Step 2: Adjust the output mode of the Ti:sapphire femtosecond laser to a multi-pulse mode, and use the writing system described in claim 1 to create a sub-diffraction-limited focused beam to process nanopore structures on quartz. Step 3: Using the nanopores processed in Step 2 as the initial nanocavities, the nanocavities gradually expand into nanowire structures on a two-dimensional plane by moving the position of the high-precision displacement stage and injecting energy below the threshold. The formation direction of the nanowires is controlled by controlling the movement direction of the high-precision displacement stage. Step four involves chemically etching and cleaning the femtosecond laser-processed quartz to obtain a nanowire structure.

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