Nanometer sieve as well as preparation method and application thereof

Abstract

The invention relates to a nano-sieve and a preparation method and application thereof, the nano-sieve is composed of multiple layers of micro-nano processing stacked structures, the nano-sieve internally comprises a high-density nano-channel array, the cross section of each channel is rectangular, and the width of each channel is determined according to the size of a target separation particle. The preparation method of the nano sieve comprises the following steps: preparing an initial groove; filling and flattening the photoresist; performing film deposition and secondary configuration; constructing a stacking structure; cutting and forming; and removing the photoresist. The method has the advantages of being small in screening scale, high in mechanical strength, high in flux, high in anti-blocking capacity and high in process compatibility.

Description

Technical Field

[0001] This invention relates to the field of micro-nano manufacturing and separation technology, and in particular to a nanosieve, its preparation method and application. Background Technology

[0002] As a key nanoscale separation element, the performance of nanosieves is highly dependent on pore size uniformity, channel aspect ratio, and overall structural strength. Existing nanosieve fabrication technologies mainly include photolithography combined with etching, template methods, and self-assembly. These methods can fabricate fine structures with pore sizes down to several nanometers on thin-layer materials, but they generally face the challenge of simultaneously achieving a good channel aspect ratio and overall mechanical strength of the nanosieve.

[0003] In practical applications, nanosieves need sufficient thickness to maintain mechanical stability, especially in high-throughput filtration or high-pressure operating environments. Excessively thin sieves are prone to cracking or deformation, leading to separation failure. While traditional dry or wet etching techniques used in semiconductor processes can achieve nanoscale pore sizes, the aspect ratio of the pores is typically limited to tens to hundreds. When the etching depth reaches hundreds of micrometers or more, the pore sidewalls are prone to tilting and twisting, making it difficult to achieve high-form-precision pore structures with aspect ratios exceeding 100. Furthermore, high aspect ratio etching faces numerous challenges, including poor etching rate uniformity, insufficient selectivity, and residue within the pores, making it impossible to fabricate nanosieves that simultaneously possess fine pore sizes, steep pore walls, and excellent mechanical properties.

[0004] On the other hand, certain special materials, such as glass, quartz, or high-strength polymers, while possessing excellent mechanical and chemical stability, are difficult to fabricate with large-thickness nanopore arrays using conventional microfabrication methods. For example, low-refractive-index fluorinated glass is inherently brittle and has poor machinability; while high-refractive-index glass, due to its high hardness, has a narrow etching process window, further limiting the fabrication of high aspect ratio nanosieves.

[0005] Therefore, existing technologies lack reliable methods to achieve high aspect ratio and high conformal nanopore structures in materials with good mechanical strength, which restricts the application of nanosieves in separation and detection under high pressure, high flow rate or harsh environments. Summary of the Invention

[0006] The main objective of this invention is to provide a nanosieve with a large aspect ratio and high mechanical strength.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A nanosieve is composed of a multi-layer micro-nano fabricated stacked structure. The interior of the nanosieve contains a high-density array of nanochannels. The cross-section of the channels is rectangular, and the width of the channels is determined according to the size of the target separated particles.

[0008] The nanosieve has an outer edging structure, and the edging material is an organic or inorganic curable slurry.

[0009] The curable slurry is a resin slurry, glass slurry, or metal slurry; the thickness of the edging is 50-200 mm. .

[0010] This invention also provides a method for preparing nanosieves, comprising the following steps: 1) Initial trench fabrication: A trench structure with a preset duty cycle and aspect ratio is fabricated on the surface of an etchable substrate material. The width w of the resulting initial trench satisfies: D samll＋ 2δ<W<D large Among them, D samll D is the hydrodynamic diameter of the small particle to be passed through. large δ is the hydrodynamic diameter of the large particle to be blocked, and δ is the size of the gap on one side; 2) Photoresist filling and planarization: Photoresist is filled into the trenches of the trench structure, and a planarization process is used to make the surface of the photoresist flush with the surface of the initial trench, forming a flat composite plane. 3) Thin film deposition and secondary configuration: A layer of etchable material film is deposited on the surface of the planarized sample. The thickness of the etchable material film is greater than the depth of the initial trench. Then, the trench structure is prepared on the etchable material film using the same process as in step 1), so that the upper and lower trenches are angularly aligned in the length direction. 4) Stacked structure construction: Repeat steps 2) and 3) multiple times to stack layer by layer to form a multi-layered composite structure; 5) Cutting and shaping: The sample is precisely cut or ground along the direction perpendicular to the length of the groove to obtain an independent nanosieve device with a glue structure; 6) Photoresist removal: The nanosieve device is processed using wet or dry photoresist removal processes to remove all photoresist filling the trenches and form a nanochannel array that runs through the entire stacked device. Nanosieves were obtained.

[0011] Furthermore, it also includes: Edge wrapping treatment: Coat the perimeter of the nanosieve with organic or inorganic curable slurry to form a nanosieve with an edge wrapping structure; the edge wrapping treatment is performed before cutting and shaping in step 5), before cutting and shaping in step 5), or after photoresist removal in step 6).

[0012] The etchable substrate material is monocrystalline silicon, quartz glass, silicon nitride, or silicon carbide. Before etching, the etchable substrate material is cleaned by a standard cleaning process to remove surface contaminants and then dried with nitrogen gas for later use.

[0013] The thickness of the etchable substrate material is 200-500 mm. The thickness of the etchable material film is greater than the depth of the trench by 200-800 nm; the depth of each etched trench is 200-500 nm; and the width of the single-sided gap is 0.5-1 nm. In step 1), a nano-trench array is fabricated on the surface of an etchable substrate material using micro / nano fabrication techniques such as electron beam lithography, ultraviolet lithography, or nanoimprint lithography followed by etching; the initial trench has an aspect ratio of 0.5-1, and the preset duty cycle is 0.2-0.8; after etching, the surface of the etchable substrate material is cleaned using a dry or wet method to remove the photoresist, and then dried with nitrogen. In step 2), after filling the trenches of the trench structure with photoresist, the area is soft-baked at 80-110℃ for 2-8 minutes, and after curing the photoresist, a planarization process is performed. The leveling process includes chemical mechanical polishing or ion beam polishing.

[0014] The thickness of the photoresist layer is 200-500 nm greater than the trench depth; after the photoresist layer has been initially cured, the surface is smoothed by chemical mechanical polishing. The deposition of an etchable thin film material is achieved using chemical vapor deposition or physical vapor deposition techniques, and the etchable thin film material is silicon nitride or silicon dioxide; the deviation of the angle alignment is controlled within ±0.5°. The cutting process uses a diamond wire saw to cut the stack into independent sheet-like devices with a thickness of 0.5 ± 0.05 mm along the direction perpendicular to the groove. Deionized water is used as the coolant during the cutting process. The cut nanosieve devices were immersed in N-methylpyrrolidone solution and cleaned at 50-90°C for 3-7 hours. Then, they were ultrasonically cleaned with acetone, isopropanol and deionized water for 5-20 minutes in sequence. The ultrasonic cleaning power was 100-400W and the frequency was 20-40kHz. The devices were then dried with nitrogen.

[0015] Furthermore, after each layer of etchable material film is deposited, a surface activation treatment is performed, which is an oxygen plasma treatment.

[0016] The present invention also provides an application of the nanosieve described above in biomedical separation, environmental water quality detection, or nanoparticle purification.

[0017] By employing the above technical solution, the present invention has at least the following advantages: 1. Small screening scale: It realizes a large aspect ratio nanochannel structure based on size-precise screening, and the channel width can be precisely designed according to the target particle size to achieve nanoscale precision screening; 2. High mechanical strength: By forming a block structure through multi-layer stacking and combining it with a large aspect ratio design, the device can withstand high-pressure operation, overcoming the problems of easy deformation and brittleness of traditional direct fabrication of ultra-thin screening devices.

[0018] 3. High throughput and strong anti-clogging ability: The large depth-to-width ratio structure provides a large flow volume, allowing for higher operating pressure and improved backflushing efficiency, reducing the risk of clogging.

[0019] 4. Strong process compatibility: The etchable substrate materials can be commonly used micro-nano processing materials such as silicon, quartz glass, and silicon nitride, which have good adaptability and scalability.

[0020] The preparation method of this invention provides a new technical route for the manufacture of high-performance nanosieve devices, and is particularly suitable for applications requiring high-intensity and high-precision sieving, such as biomedical separation, environmental water quality detection, and nanoparticle purification.

[0021] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation process of the nanosieve provided in the embodiment of the present invention. Detailed Implementation

[0023] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, structures, features, and effects of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0024] like Figure 1The diagram shows the fabrication process of the nanosieve of the present invention. Initial trenches are prepared on the surface of an etchable substrate material 1. Photoresist is filled into the initial trenches, and a planarization process is used to make the surface of the photoresist flush with the upper surface of the initial trenches, forming a flat composite plane, resulting in a planarized sample 2. An etchable material film is deposited on the surface of the planarized sample 2. Trenches are prepared again on the etchable material film, and the surface is planarized after filling with photoresist. The process of stacking etchable material films, preparing trenches, filling with photoresist, and planarizing the surface is repeated. The above steps are repeated to stack layer by layer to form a multilayer composite structure 3 with a large aspect ratio channel. The multilayer composite structure 3 is cut once to obtain a nanosieve device 4 with a glue structure. The photoresist in the nanosieve device 4 is removed and a second cutting and shaping process is performed to obtain a nanosieve device 5 without a glue structure. The nanosieve device 5 without a glue structure is then coated with an edge and cut to a specific thickness to obtain a nanosieve device 6 with an edge structure.

[0025] This invention provides a nanosieve composed of a multi-layer micro-nano fabricated stacked structure. The interior of the nanosieve contains a high-density array of nanochannels. The cross-section of the channels is rectangular, and the width of the channels is determined according to the size of the target separated particles.

[0026] The nanosieve structure of the present invention is composed of multiple layers of precision grooves stacked together. While maintaining high mechanical strength, the nanosieve structure achieves a large aspect ratio and realizes the purpose of efficient separation of particles of different sizes. The nanosieve has the characteristics of uniform pore size, high aspect ratio and excellent mechanical properties, and can be used for precise separation of nanoparticles under high pressure and high flow rate environments.

[0027] Furthermore, the nanosieve has an outer edging structure, and the edging material is an organic or inorganic curable slurry.

[0028] Preferably, the curable slurry is a resin slurry, glass slurry, or metal slurry; the thickness of the edging is 50-200 mm. .

[0029] The nanosieve of this invention has a surrounding edge, which protects the brittle nanochannel structure inside the nanosieve, prevents damage or deformation of the edge channels during use, and improves the overall strength of the nanosieve. The thickness of the edge is preferably 100 mm. If the edge banding layer is too thin, the protection effect will be insufficient and the edges will be easily damaged; if the edge banding layer is too thick, the device size will be increased, which is not conducive to integrated applications.

[0030] This invention also provides a method for preparing nanosieves, comprising the following steps: 1) Initial Trench Fabrication: Initial trench fabrication involves fabricating a trench structure with a preset duty cycle and aspect ratio on the surface of an etchable substrate material. The width w of the resulting initial trench satisfies: Dsamll＋ 2δ<W<D large The initial trench width w determines the separation selectivity of the nanosieve, where D samll D is the hydrodynamic diameter of the small particle to be passed through. large δ represents the hydrodynamic diameter of the large particle to be blocked, and δ represents the width of the single-sided gap. The width of the single-sided gap refers to the distance from the side of the small particle to be passed through to the inner wall of the trench to the inner wall of the trench. 2) Photoresist filling and planarization: Photoresist is filled into the trenches of the trench structure, and planarization processes such as chemical mechanical polishing and ion beam polishing are used to make the photoresist surface flush with the upper surface of the trench, forming a flat composite plane. 3) Thin film deposition and secondary configuration: A layer of etchable material film is deposited on the surface of the planarized sample. The thickness of the etchable material film needs to be much greater than the depth of the initial trench. Then, the trench structure is prepared on the etchable material film using the same process as in step 1), so that the upper and lower trenches are angularly aligned in the length direction. 4) Construction of stacked structure: Repeat steps 2) and 3) multiple times to stack layer by layer to form a multilayer composite structure with a large aspect ratio channel; the total thickness of the stacked layers is the thickness of the required nanosieve. 5) Photoresist removal: The nanosieve device is processed using wet or dry photoresist removal processes to remove all photoresist filling the trenches and form a nanochannel array that runs through the entire stacked device. Nanosieves were obtained; 6) Edge wrapping: Coat the perimeter of the nanosieve with organic or inorganic curable slurry to form a nanosieve with an edge wrapping structure.

[0031] 7) Cutting and shaping: The sample is precisely cut or ground along the direction perpendicular to the length of the groove to obtain an independent nanosieve device with a cutting thickness of 0.5 ±0.05 mm; The preparation method of this invention is based on a high-strength nanosieve fabrication method combining multilayer stacking and micro / nano fabrication. The resulting nanosieve has an outer rimmed region and an inner nanochannel array structure, with each channel having a rectangular cross-section.

[0032] Preferably, the etchable substrate material is monocrystalline silicon, quartz glass, silicon nitride, or silicon carbide. Before etching, the etchable substrate material is cleaned by a standard cleaning process to remove surface contaminants and then dried with nitrogen gas for later use.

[0033] Preferably, the thickness of the etchable substrate material is 200-500 mm. The thickness of the etchable material film is 200-800 nm greater than the depth of the initial trench; the depth of each etched trench is 200-500 nm; and the width of the single-sided gap is 0.5-1 nm. The etchable substrate material of this invention requires standard cleaning procedures (such as wet chemical cleaning) to remove surface contaminants and is then dried with nitrogen gas before use. Preferably, the thickness of the etchable substrate material is 200-500 μm. If the etchable substrate material is too thin, it is prone to warping or cracking during subsequent multilayer stacking; if the etchable substrate material is too thick, it will affect the heat conduction and structural uniformity of the overall device during the etching process.

[0034] In step 1), a nano-trench array is fabricated on the surface of an etchable substrate material using electron beam lithography, ultraviolet lithography, or nanoimprint lithography followed by etching. The aspect ratio of the initial trench is 0.5-1, typically 1, and the preset duty cycle is 0.2-0.8. After etching, the surface of the etchable substrate material is cleaned using a dry or wet method and then dried with nitrogen.

[0035] This invention sets the aspect ratio between 0.5 and 1, which facilitates control over the screening effect of the nanosieve on particle size and shape, and is also beneficial for the etching of the trench structure, the filling of photoresist, and subsequent planarization. If the aspect ratio is too large, it can easily lead to deformation of the etched structure, and may also result in incomplete photoresist filling or the formation of air bubbles within the filled photoresist. Setting the preset duty cycle between 0.2 and 0.8 ensures that the channel has sufficient sidewall support, avoiding structural collapse due to insufficient mechanical strength.

[0036] Preferably, a negative photoresist (such as the SU-8 series) is spin-coated to fill the trench, and the thickness of the photoresist layer is 200-500 nm higher than the trench depth. After the photoresist layer is initially cured, chemical mechanical polishing (CMP) is used to smooth the surface until the photoresist surface is flush with the upper surface of the trench, forming a stepless composite plane.

[0037] If the adhesive layer is too thin, it may result in incomplete filling or insufficient adhesive layer after planarization; if the adhesive layer is too thick, it will increase the difficulty of planarization and process time. The purpose of planarization is to provide a uniform substrate for subsequent deposition of etchable material films. If the surface is uneven, it will lead to uneven stress distribution in the etchable material film, affecting the interlayer bonding and channel alignment accuracy.

[0038] The deposition of an etchable thin film material is achieved using chemical vapor deposition or physical vapor deposition techniques, and the etchable thin film material is silicon nitride or silicon dioxide; the deviation of the angle alignment is controlled within ±0.5°. This invention limits the thickness of the etchable material film to be 200-800 nm greater than the initial trench depth. If the etchable material film is too thin, the remaining material at the bottom after etching will be insufficient, leading to insufficient support or easy breakdown during etching, resulting in interlayer crosstalk. If the etchable material is too thick, the proportion of nanopores will decrease, reducing screening efficiency, increasing stress, and prolonging process time. Excessive alignment deviation will lead to inconsistent channel opening areas, severely affecting screening consistency.

[0039] The cutting process employs a diamond wire saw to cut the stacked body into individual sheet-like devices with a thickness of 0.5 ± 0.05 mm along a direction perpendicular to the groove. Deionized water is used as the coolant during the cutting process to prevent thermal damage to the structure. If the cutting speed is too fast or the cooling is insufficient, it will lead to thermal stress concentration in the material, causing microcracks or channel deformation.

[0040] In this invention, the channels in the nanosieve maintain a consistent height and the sidewalls are steep. Since the mechanical strength of the nanosieve is directly proportional to its aspect ratio and positively correlated with the fluid flux, the larger the aspect ratio, the higher the strength and the greater the fluid flux. Therefore, the preferred cutting thickness of the nanosieve is 0.5 mm to ensure high mechanical strength and high flux characteristics.

[0041] Furthermore, the cut nanosieve devices are immersed in a pure N-methylpyrrolidone solution (NMP) and allowed to stand at 50-90°C for 3-7 hours. Afterward, they are ultrasonically cleaned sequentially with acetone, isopropanol, and deionized water for 5-20 minutes at an ultrasonic power of 100-400W and a frequency of 20-40kHz, and then dried with nitrogen. Incomplete removal of the adhesive can clog channels, reduce throughput, or even cause device failure; incomplete cleaning may introduce contaminants, affecting separation performance.

[0042] Preferably, a surface activation treatment is performed after each deposition of an etchable material film, wherein the surface activation treatment is an oxygen plasma treatment.

[0043] Each layer requires surface activation treatment, such as oxygen plasma treatment, to enhance interlayer adhesion. Without surface activation treatment, the interlayer adhesion is weak, and delamination is likely to occur during cutting or use.

[0044] This invention significantly improves the aspect ratio and overall strength of the sieve body while maintaining nanoscale pore size precision, thereby meeting the application requirements of high-end nanoparticle separation devices. It is particularly suitable for biomedical separation, environmental water quality detection, or nanoparticle purification.

[0045] The present invention will be further described below through specific embodiments: Example 1 This embodiment provides a method for preparing a high aspect ratio nanosieve for separating 250 nm gold nanoparticles and 400 nm polystyrene (PS) microspheres. The specific process is as follows: 1) Select a thickness of 300 A 4-inch diameter N-type single-crystal silicon wafer is used as the substrate. Surface contaminants are removed by wet chemical cleaning, and then the wafer is dried with nitrogen.

[0046] 2) Electron beam lithography was used with an accelerating voltage of 100 kV and a beam current of 500 pA to define a photoresist pattern with a linewidth of 300 nm and a period of 600 nm on the silicon surface, with a single-sided gap width of 0.7 nm.

[0047] 3) Using photoresist as a mask, plasma etching (ICP) was performed on the silicon substrate at a power of 800 W with SF6 / C4F8 gas to form an initial trench with a depth of 300 nm. The preset duty cycle was 0.5. After etching, a plasma dry resist remover was used for cleaning and removal. The removal temperature was 60℃, the power was 600W, and the time was 30 minutes.

[0048] 4) Spin-coat SU-8 2002 photoresist to fill the initial trench. The thickness of the photoresist layer is 300 nm higher than the trench depth. Soft bake at 95°C for 5 minutes. After the photoresist is cured, perform CMP polishing until the surface roughness Ra < 1 nm. The photoresist surface is flush with the upper surface of the initial trench to obtain a flattened sample.

[0049] 5) A 1000 nm thick silicon nitride film was grown on the planarized sample surface using low-pressure chemical vapor deposition (LPCVD). The surface of the silicon nitride film was then treated with oxygen plasma. Trench structures were then fabricated on the silicon nitride film using the same process as in steps 2)-3), ensuring that the upper and lower trenches were angularly aligned along their length. 6) Repeat steps 4)-5), etching trenches to a depth of 300 nm for each layer, forming through-holes with a trench width of 300 nm and a depth of 300 nm after each etching layer; after the final stacking of the silicon nitride film, no more trenches are etched, completing 400 stackings, with a stacked structure thickness of approximately 400 nm. The total thickness is approximately 0.7 mm, resulting in a stacked structure.

[0050] 7) The stacked structure was immersed in 80°C NMP solution for 4 hours to remove the photoresist, and then ultrasonically cleaned in acetone, isopropanol and deionized water for 5 minutes in sequence. The ultrasonic cleaning power was 300W and the frequency was 30kHz. The structure was then dried with nitrogen.

[0051] 8) Vertically cut the structure obtained in step 7) after removing the photoresist into blocks with dimensions of 5 mm × 0.7 mm × 50 mm. Then, use a low-temperature glass paste to edge-band the four sides except the end faces, with an edge thickness of approximately 150 mm. This results in a stacked volume.

[0052] 9) Use a diamond wire saw to cut the stack into devices with dimensions of 5 mm × 0.7 mm × 0.5 mm.

[0053] Scanning electron microscopy (SEM) characterization revealed that the nanochannels had a width of (300±5) nm, a depth of 0.5 mm, and an aspect ratio of 1667:1. Using this nanosieve, a mixed particle sample (250 nm gold particles and 400 nm PS microspheres) was filtered. Under a pressure difference of 0.1 MPa, the gold particle throughput reached 98%, the PS microsphere rejection rate exceeded 99%, and the throughput reached 3.5 L / (cm²·h·bar). After 20 hours of continuous operation, the structure showed no breakage or significant blockage, demonstrating good stability.

[0054] Example 2 This embodiment provides a method for preparing a high aspect ratio nanosieve for separating 400 nm silica nanoparticles and 800 nm cerium oxide microspheres. The specific process is as follows: 1) Select a thickness of 500 A 4-inch diameter silicon nitride substrate is used, and surface contaminants are removed by wet chemical cleaning, followed by drying with nitrogen gas.

[0055] 2) Ultraviolet exposure technology was used, with an exposure dose of 100 mJ / cm². 2 The exposure time is 25s, and a photoresist pattern with a linewidth of 2400 nm and a period of 3000 nm is defined on the silicon nitride surface, with a single-sided gap width of 0.5 nm.

[0056] 3) Using photoresist as a mask, plasma (ICP) etching was performed with SF6 / C4F8 gas at a power of 600 W to etch the silicon nitride substrate, forming an initial trench with a depth of 450 nm. The preset duty cycle was 0.2. After etching, a plasma dry resist remover was used for cleaning and removing the resist at a temperature of 70°C, a power of 500 W, and a time of 25 min.

[0057] 4) Spin-coat SU-8 2002 photoresist to fill the initial trench. The thickness of the photoresist layer is 400 nm higher than the trench depth. Soft bake at 110℃ for 2 minutes. After the photoresist is cured, perform CMP polishing to a surface roughness Ra=0.7 nm. The photoresist surface is flush with the upper surface of the initial trench to obtain a smoothed sample.

[0058] 5) An 800 nm thick silica film was grown on the planarized sample surface using low-pressure chemical vapor deposition (LPCVD). Trench structures were then fabricated on the silica film using the same process as in steps 2)-3), ensuring that the upper and lower trench layers were angularly aligned along their length. 6) Repeat steps 4)-5), etching trenches to a depth of 450 nm for each layer, creating through-holes with a width of 600 nm and a depth of 450 nm after each etching layer; after the final stacking of the silicon dioxide film, no further trenches are etched, completing 500 stacking operations with a stacked structure thickness of approximately 400 nm. The total thickness is approximately 0.9 mm, resulting in a stacked structure.

[0059] 7) The stacked structure was immersed in NMP solution at 50℃ for 6 hours to remove the photoresist, and then ultrasonically cleaned in acetone, isopropanol and deionized water for 10 minutes in sequence. The ultrasonic cleaning power was 100W and the frequency was 40kHz. The structure was then dried with nitrogen.

[0060] 8) Vertically cut the structure obtained in step 7) after removing the photoresist into blocks with dimensions of 8mm × 0.9mm × 60mm. Then, use paraffin wax paste to edge-wrap the four sides except the end faces, with an edge-wrap thickness of approximately 200mm. This results in a stacked volume.

[0061] 9) Use a diamond wire saw to cut the stack into devices with dimensions of 8mm × 0.9mm × 0.55mm.

[0062] Scanning electron microscopy (SEM) characterization revealed that the nanochannels had a width of (600±3) nm, a depth of 0.55 mm, and an aspect ratio of 916:1. Using this nanosieve to filter a mixed particle sample (400 nm silica nanoparticles and 500 nm cerium oxide microspheres), under a pressure difference of 0.1 MPa, the silica particle throughput reached 97%, while the cerium oxide microspheres exhibited a rejection rate exceeding 99%, resulting in a throughput of 2.9 L / (cm²·h·bar). After 20 hours of continuous operation, the structure showed no signs of breakage or significant blockage, demonstrating excellent stability.

[0063] Example 3 This embodiment provides a method for preparing a high aspect ratio nanosieve for separating 200 nm graphene particles and 600 nm polyethylene glycol nanoparticles. The specific process is as follows: 1) Select a thickness of 400 A 4-inch diameter quartz glass substrate is used, and surface contaminants are removed by wet chemical cleaning, followed by drying with nitrogen.

[0064] 2) Nanoimprint technology is used, with a pressure of 9 bar, a curing time of 30 seconds, and an ultraviolet light intensity of 105 mW / cm². 2 A photoresist pattern with a linewidth of 100 nm and a period of 500 nm was defined on the surface of quartz glass, with a single-sided gap width of 0.7 nm.

[0065] 3) Using photoresist as a mask, plasma (ICP) etching was performed with SF6 / C4F8 gas at a power of 800 W to etch a quartz glass substrate, forming an initial trench with a depth of 500 nm. The preset duty cycle was 0.8. After etching, a plasma dry resist remover was used for cleaning and removal. The remover removal temperature was 60℃, the power was 600 W, and the time was 35 min.

[0066] 4) Spin-coat SU-8 2002 photoresist to fill the initial trench. The thickness of the photoresist layer is 200 nm higher than the trench depth. Soft bake at 80°C for 8 minutes. After the photoresist is cured, perform CMP polishing to a surface roughness Ra=0.8 nm. The photoresist surface is flush with the upper surface of the initial trench to obtain a flattened sample.

[0067] 5) A 1050 nm thick silicon nitride film was grown on the planarized sample surface using low-pressure chemical vapor deposition (LPCVD). Trench structures were then fabricated on the silicon nitride film using the same process as in steps 2)-3), ensuring that the upper and lower trench layers were angularly aligned along their length. 6) Repeat steps 4)-5), etching trenches to a depth of 250 nm for each layer, forming through-holes with a width of 400 nm and a depth of 250 nm after each etching layer; after the final stacking of the silicon nitride film, no more trenches are etched, completing 300 stackings, with a stacked structure thickness of approximately 315 nm. The total thickness is approximately 0.715 mm, resulting in a stacked structure.

[0068] 7) The stacked structure was immersed in 90℃ NMP solution for 7 hours to remove the photoresist, and then ultrasonically cleaned in acetone, isopropanol and deionized water for 15 minutes in sequence. The ultrasonic cleaning power was 400W and the frequency was 20kHz. The structure was then dried with nitrogen.

[0069] 8) Vertically cut the structure obtained in step 7) after removing the photoresist into blocks with dimensions of 10mm × 0.715mm × 80mm. Then, wrap the edges of all four sides except the end faces with epoxy resin, with a wrapping thickness of approximately 100mm. This results in a stacked volume.

[0070] 9) Use a diamond wire saw to cut the stack into devices with dimensions of 10mm × 0.715mm × 0.45mm.

[0071] Scanning electron microscopy (SEM) characterization revealed that the nanochannels had a width of (400±10) nm, a depth of 0.45 mm, and an aspect ratio of 1125:1. Using this nanosieve, a filtration test was conducted on a mixed particle sample (200 nm graphene particles and 600 nm polyethylene glycol particles). Under a pressure difference of 0.2 MPa, the throughput of silica particles reached 99%, the cerium oxide microspheres exhibited a blocking rate exceeding 98%, and the flux reached 4.3 L / (cm²·h·bar). After 20 hours of continuous operation, no structural breakage or significant blockage occurred, demonstrating good stability.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A nanosieve, characterized in that: Composed of a multi-layered micro-nano fabricated stacked structure, the nanosieve contains a high-density array of nanochannels, the cross-section of which is rectangular, and the width of which is determined according to the size of the target separated particles.

2. The nanosieve according to claim 1, characterized in that, The nanosieve has an outer edging structure, and the edging material is an organic or inorganic curable slurry.

3. The nanosieve according to claim 2, characterized in that, The curable slurry is a resin slurry, glass slurry, or metal slurry; the thickness of the edging is 50-200 mm. .

4. A method for preparing the nanosieve according to any one of claims 1-3, characterized in that: Includes the following steps: 1) Initial trench fabrication: A trench structure with a preset duty cycle and aspect ratio is fabricated on the surface of an etchable substrate material. The width w of the resulting initial trench satisfies: D samll＋ 2δ<W<D large Among them, D samll D is the hydrodynamic diameter of the small particle to be passed through. large δ is the hydrodynamic diameter of the large particle to be blocked, and δ is the size of the single-sided gap; 2) Photoresist filling and planarization: Photoresist is filled into the trenches of the trench structure, and a planarization process is used to make the surface of the photoresist flush with the surface of the initial trench, forming a flat composite plane. 3) Thin film deposition and secondary configuration: A layer of etchable material film is deposited on the surface of the planarized sample. The thickness of the etchable material film is greater than the depth of the initial trench. Then, the trench structure is prepared on the etchable material film using the same process as in step 1), so that the upper and lower trenches are angularly aligned in the length direction. 4) Stacked structure construction: Repeat steps 2) and 3) multiple times to stack layer by layer to form a multi-layered composite structure; 5) Cutting and shaping: The sample is precisely cut or ground along the direction perpendicular to the length of the groove to obtain an independent nanosieve device with a glue structure; 6) Photoresist removal: The nanosieve device is processed using wet or dry photoresist removal processes to remove all photoresist filling the trenches and form a nanochannel array that runs through the entire stacked device. Nanosieves were obtained.

5. The preparation method according to claim 4, characterized in that, Also includes: Edge wrapping treatment: Coat the perimeter of the nanosieve with organic or inorganic curable slurry to form a nanosieve with an edge wrapping structure; the edge wrapping treatment is performed before cutting and shaping in step 5), before cutting and shaping in step 5), or after photoresist removal in step 6).

6. The preparation method according to claim 5, characterized in that, The etchable substrate material is monocrystalline silicon, quartz glass, silicon nitride, or silicon carbide. Before etching, the etchable substrate material is cleaned by a standard cleaning process to remove surface contaminants and then dried with nitrogen gas for later use.

7. The preparation method according to claim 6, characterized in that, The thickness of the etchable substrate material is 200-500 mm. The thickness of the etchable material film is greater than the depth of the trench by 200-800 nm; the depth of each etched trench is 200-500 nm; and the width of the single-sided gap is 0.5-1 nm. In step 1), a nano-groove array is fabricated on the surface of an etchable substrate material using electron beam lithography, ultraviolet lithography, or nanoimprint lithography followed by etching micro-nano fabrication techniques. The initial trench has a depth-to-width ratio of 0.5-1, and the preset duty cycle is 0.2-0.8; After etching, the surface of the etchable substrate material is cleaned using a dry or wet method to remove the photoresist, and then dried with nitrogen. In step 2), after filling the trenches of the trench structure with photoresist, the area is soft-baked at 80-110℃ for 2-8 minutes, and after curing the photoresist, a planarization process is performed. The leveling process includes chemical mechanical polishing or ion beam polishing.

8. The preparation method according to claim 7, characterized in that, The thickness of the photoresist layer is 200-500 nm greater than the trench depth; after the photoresist layer has been initially cured, the surface is smoothed by chemical mechanical polishing. The deposition of an etchable thin film material is achieved using chemical vapor deposition or physical vapor deposition techniques, and the etchable thin film material is silicon nitride or silicon dioxide; the deviation of the angle alignment is controlled within ±0.5°. The cutting process uses a diamond wire saw to cut the stack into independent sheet-like devices with a thickness of 0.5 ± 0.05 mm along the direction perpendicular to the groove. Deionized water is used as the coolant during the cutting process. The cut nanosieve devices were immersed in N-methylpyrrolidone solution and cleaned at 50-90°C for 3-7 hours. Then, they were ultrasonically cleaned with acetone, isopropanol and deionized water for 5-20 minutes in sequence. The ultrasonic cleaning power was 100-400W and the frequency was 20-40kHz. The devices were then dried with nitrogen.

9. The preparation method according to any one of claims 4-8, characterized in that, After each layer of etchable material film is deposited, a surface activation treatment is performed, which is an oxygen plasma treatment.

10. The application of the nanosieve according to any one of claims 1-3 in biomedical separation, environmental water quality detection, or nanoparticle purification.

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