Three-dimensional carbon-based micro-nano structure and manufacturing method thereof

Abstract

The application discloses a three-dimensional carbon-based micro-nano structure and a manufacturing method thereof, and makes PAN electrospinning liquid applied with an adsorption threshold voltage pass through micropores and form liquid drops; a collector for receiving the electrospinning liquid is poked into the liquid drops and then removed, so as to initiate ejection; the volume of the liquid drops of the electrospinning liquid is reduced after the initiation of the ejection, and the distance between the collector and the liquid drops is kept within a preset range, so as to form fiber deposition on the collector; the fiber deposition on the surface of the collector is sequentially subjected to thermal stabilization treatment and pyrolysis treatment, so as to form a three-dimensional carbon-based micro-nano structure combined with a carbon fiber array below 10 nanometers and a micron-scale carbon micro column. The application can combine carbon fibers below 10 nanometers in an orderly arranged manner with three-dimensional carbon micro columns, so that the carbon fiber characteristics closely related to semiconductors can be directly combined with traditional semiconductors in a pyrolysis process, and a road is paved for a new generation of multifunctional electronic devices.

Description

Technical Field

[0001] This invention relates to a three-dimensional carbon-based micro / nano structure and its manufacturing method. Background Technology

[0002] In the fabrication of three-dimensional (3D) carbon micropillars, scale and specific surface area have a significant impact on performance. Currently, 3D carbon micropillars have a wide range of applications, including energy storage, high-sensitivity detection, lithium-ion capacitors, battery research, and general electrochemical applications. Carbon nanofiber arrays, arranged on 3D carbon micropillars (3DCMPs), hold promise for highlighting the influence of nanoscale and high specific surface area on performance, thereby developing high-performance multifunctional devices. Researchers have attempted to fabricate such carbon nanofiber arrays using chemical vapor deposition (CVD), but these arrays typically grow on different bulk substrate surfaces, making orderly deposition onto the substrate's microstructure difficult. However, electrospinning and carbonization of polymers such as polyacrylonitrile (PAI) and SU-811 as precursors can prepare carbon fiber arrays on the surface of carbon micropillars, becoming an effective alternative to CVD. The corresponding carbon fiber diameters have increased from the nanometer scale to the submicrometer scale of 100 to 1000 nanometers.

[0003] To reduce the diameter of arrayed carbon fibers to the nanoscale, two conditions must be met: forming finer polymer fibers during near-field electrospinning; and increasing the shrinkage rate of the polymer fibers during pyrolysis to convert them into carbon fibers. To this end, Bisht et al.

[12] used low-voltage near-field electrospinning technology, introducing an extremely high local electric field at an extremely low voltage of 200V using glass microprobe tips (1 to 3 μm in diameter), to reduce the diameter of polyethylene oxide fibers to 16.2 nm. However, polyethylene oxide fibers cannot be converted into carbon fibers through carbonization. For pyrolytic polymers like SU-8, this method would increase the diameter of these polymer fibers to the submicron level, resulting in carbon nanowires with a diameter of approximately 180 nm. Furthermore, to address the high shrinkage rate during fiber conversion, current methods mainly include weakening the radial shrinkage of fibers, mechanically stretching fibers, and thermally inducing fiber shrinkage. However, research related to these methods has been largely limited in its efforts to further increase the shrinkage rate to 90%, thus maintaining the resulting carbon fibers at the micrometer scale. Therefore, a key obstacle to the fabrication of carbon nanofiber arrays on micropillars is the lack of a method for preparing thin, pyrolytic polymer fibers in near-field electrospinning, and for maximizing the radial shrinkage of the fibers during stabilization and pyrolysis. Summary of the Invention

[0004] To overcome the technical problem that it is difficult to form nanoscale fiber arrays of carbon nanofibers, this invention provides a three-dimensional micro / nano carbon structure based on carbon nanofiber arrays (carbon fiber diameter less than 10 nm) and three-dimensional carbon micropillars, and its manufacturing method.

[0005] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:

[0006] A three-dimensional carbon-based micro / nano structure includes a micropillar array formed by multiple carbon micropillars and carbon fibers attached to the micropillar array. The diameter of the carbon fibers on the carbon micropillars is less than 10 nanometers, the diameter of the carbon micropillars is 35 to 50 micrometers, the height is 20 micrometers, and the spacing between each carbon micropillar is 13 to 17 micrometers.

[0007] A method for fabricating three-dimensional carbon-based micro / nano structures includes the following steps:

[0008] The PAN electrospinning solution, to which an adsorption threshold voltage is applied, is passed through micropores and forms droplets. A collector for receiving the electrospinning solution is then inserted into the droplets and removed, thereby initiating a jet. Simultaneously, after the jet is initiated, the droplet volume of the electrospinning solution is reduced, and the distance between the collector and the droplets is maintained within a preset range, thereby forming fiber deposition on the collector.

[0009] The fiber deposits on the collector surface are subjected to thermal stabilization and pyrolysis treatments in sequence to form a three-dimensional carbon-based micro / nano structure.

[0010] The manufacturing method described herein, adsorption threshold voltage V R for:

[0011]

[0012] Where g0 is the axial distance between the electrospinning solution and the collector, K is the elastic coefficient, ε is the dielectric constant, A is the area of ​​the electrospinning solution opposite to the collector, and y5 is the displacement when the electrostatic force and the elastic force are equal, calculated by the following formula:

[0013]

[0014] Where π is the mathematical constant pi, θ is the arccosine value corresponding to the threshold voltage torque, θ = arccosT, and T represents the threshold voltage torque.

[0015] In the manufacturing method described above, the collector is a roller for collecting PAN jet fibers. The surface of the roller is provided with a micropillar array formed by multiple carbon micropillars, and the roller rotates around its own axis. At the same time, the micropores and the roller maintain relative translational motion, so that the fiber deposition uniformly covers the micropillar array.

[0016] In the manufacturing method described above, the micropillar array is formed on the surface of a silicon wafer by photolithography and pyrolysis. The silicon wafer is placed in a groove on the surface of a roller, and the top of the micropillar array on the silicon wafer is lower than the surface of the roller. The groove is arranged along the axis of the roller itself. The diameter of the carbon micropillars in the micropillar array is 35 to 50 micrometers, the height is 20 micrometers, and the spacing between each carbon micropillar is 13 to 17 micrometers.

[0017] In the manufacturing method described above, the rotation speed of the roller is not less than 800 r / min, and the relative translation speed between the micropores and the roller is 480 micrometers, so that the fibers deposited on the surface of the roller are a uniform linear structure.

[0018] The manufacturing method described above reduces the droplet volume of the electrospinning solution sprayed out of the micropores by placing a water-absorbing material with water-absorbing properties at the micropores, thereby absorbing part of the liquid in the droplets to reduce the droplet volume so that the droplet volume is no more than 100 nanoliters.

[0019] In the manufacturing method described, the distance between the collector and the droplet is maintained between 1.7 mm and 1.8 mm, thereby generating a fiber deposition on the collector with a diameter between 120 nm and 80 nm. The greater the distance between the collector and the droplet, the smaller the diameter of the fiber deposition.

[0020] The manufacturing method described herein involves heat stabilizing the fiber deposition by heating it in air at a rate of 15–18 °C / min, maintaining the temperature at 106–115 °C for 16–18 hours, and then cooling it to room temperature.

[0021] The manufacturing method described above involves pyrolyzing the fiber deposition by first heating it in nitrogen from room temperature to 115°C over a period of 0.8 to 1.2 hours, maintaining it at 115°C for 1 hour, then heating it to 970 to 1050°C at a heating rate of 15 to 18°C / min and maintaining it for 1 to 1.2 hours, and finally cooling it to room temperature at a cooling rate of 2.7 to 5°C / min.

[0022] The technical advantage of this invention lies in providing a carbon fiber array of less than 10 nanometers on a carbon micropillar array, along with a corresponding manufacturing method. This invention not only enables the orderly deposition of nanoscale PAN-based jet fibers onto semiconductor wafers, such as silicon and 3D carbon micropillars, allowing the carbon fiber properties closely related to semiconductors to be directly integrated with traditional semiconductors during pyrolysis, paving the way for next-generation multifunctional electronic devices, but also facilitates the fabrication of 3D carbon-based micro / nanostructures based on nanofibers and carbon micropillars, significantly expanding the range of usable 3D carbon-based micro / nanostructures. This improves the scale-performance effect of 3D carbon-based micro / nanostructures, offering greater potential for applications in high-rate supercapacitors, electromagnetic interference shielding, capacitor deionization, and electrocatalysis. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of low-voltage near-field electrospinning in this invention.

[0024] Figure 2 This is a schematic diagram of the electrostatic jet initiation process in near-field electrospinning of the present invention. (a) shows the jet initiation scheme design. (bf) shows the evolution of the electrospinning solution into the jet. By reducing the needle spacing as shown in (b)-(c), inserting a rotating roller into the droplet at the tip of the dispensing needle as shown in (d), and initiating the jet as shown in (e) at a 500V adsorption threshold voltage, a continuous jet as shown in (f) is formed, realizing the evolution of the electrospinning solution into the jet. (g) is a scanning electron microscope image of the PAN-based jet fiber.

[0025] Figure 3 This describes the formation process from submicron-sized fibers to nano-sized PAN fibers in this invention. Wherein (a) is based on... Figure 2 (a) Nanofabrication design of PAN-based submicron jetting. (b) Continuous deposition of PAN-based submicron fibers onto a silicon substrate on a roller surface at an adsorption threshold voltage of 500 V. (c) Reduction of applied voltage evolution by decreasing the liquid volume at the tip of the needle. (d) Variation of PAN-based jet fiber diameter with applied voltage. (e) Dependence of PAN fiber diameter on needle-roller distance.

[0026] Figure 4 This invention illustrates the point-to-line structure transformation in the PAN-based jet fiber array. Specifically, (ac) shows the PAN fiber array formed at a rotational speed of 400 r / min and moving speeds of 80 μm / s, 240 μm / s, and 480 μm / s. (d) shows the line-based fiber array formed at a moving speed of 480 μm / s and a rotational speed of 800 r / min.

[0027] Figure 5This invention describes the ring-to-line structure transformation process in the PAN-based jet fiber array. Specifically, (ac) a PAN fiber array is formed under conditions of a rotation speed of 400 r / min and dispensing needle-roller distances of 1.48 mm, 0.95 mm, and 0.16 mm, respectively. (d) A line-structured fiber array is formed under conditions of a dispensing needle-roller distance of 0.16 mm and a rotation speed of 900 r / min.

[0028] Figure 6 This invention presents the micro / nano structure of PAN nanofibers-3D carbon micropillars. (a) PAN nanofiber array. (bc) Relationship between fiber spacing in the polymer nanofiber array and roller rotation speed and dispensing needle movement speed. (d) Distribution of the maximum electric field intensity on the surface of the three-dimensional carbon micropillar array. (e) PAN nanofiber array on the surface of the three-dimensional carbon micropillar array. (f) Micro / nano structure based on the PAN fiber array-three-dimensional carbon micropillar array.

[0029] Figure 7 This invention presents a carbon-based micro / nanostructure composed of a carbon nanofiber array and 3D carbon micropillars. (ac) The carbon-based micro / nanostructure is prepared by inducing the transformation of PAN fibers into carbon fibers through thermal stabilization at 115℃ and pyrolysis at 1000℃. (df) The shrinkage of the PAN-based fibers into carbon fibers depends on the micropillar spacing, thermal stabilization temperature, and carbonization rate. (g) The correlation between the diameter of the suspended carbon fibers between the carbon micropillars and the near-field electrospinning voltage. Detailed Implementation

[0030] This embodiment provides a three-dimensional carbon-based micro / nano structure, including a micropillar array formed by multiple carbon micropillars and carbon fibers attached to the micropillar array. The diameter of the carbon fibers on the carbon micropillars is less than 10 nanometers, the diameter of the carbon micropillars is 35 to 50 micrometers, the height is 20 micrometers, and the spacing between each carbon micropillar is 13 to 17 micrometers.

[0031] This embodiment also provides a method for manufacturing three-dimensional carbon-based micro / nano structures, including the following steps:

[0032] An adsorption threshold voltage is applied to a PAN (polyacrylonitrile) electrospinning solution, which is then passed through micropores to form droplets. A collector for receiving the electrospinning solution is then inserted into the droplets and removed, initiating jetting. Simultaneously, the droplet volume of the electrospinning solution is reduced after jetting, and the distance between the collector and the droplets is maintained within a preset range, thereby forming fiber deposition on the collector. The fiber deposition on the collector surface is then subjected to sequential thermal stabilization and pyrolysis treatments to form a three-dimensional carbon-based micro / nano structure.

[0033] See Figure 1In this embodiment, an adsorption threshold voltage is applied to the PAN electrospinning solution, and an artificial instability is introduced at the droplet-air interface, i.e., the collector is inserted into the droplet and then removed, as mentioned above, thereby initiating the process. Figure 1 Low-voltage near-field electrospinning is used. During this process, the adsorption threshold voltage becomes sufficiently small, allowing for a greater reduction in the diameter of the polymer fibers. The calculation method for the adsorption threshold voltage in this embodiment is given below:

[0034] Assuming the main forces acting on the electrospun liquid are electrostatic and elastic forces, the governing equation for the applied voltage V related to its adsorption threshold voltage is as follows:

[0035]

[0036] In the formula: F ele For electrostatic force, F K Let m be the elastic force, m be the mass of the electrospinning solution, and y be the elastic force. Figure 1 The axial displacement of the electrospinning solution, ε is the dielectric constant, A is the area of ​​the electrospinning solution opposite the collector, g0 is the axial distance between the electrospinning solution and the collector, K is the elastic coefficient, E is the elastic modulus, and b is... Figure 1 The width of the electrospinning solution, h is Figure 1 The thickness of the electrospinning solution, a is Figure 1 The length of the electrospinning solution, E is the strength of the electrostatic field.

[0037] Considering the critical condition of the adsorption threshold voltage during the adsorption of the electrospinning solution onto the collector surface, d should be satisfied. 2 y / dt 2 =0. (The last part, "d", appears to be a typo and can be left as is.) 2 y / dt 2 Substituting into equation (1), we can obtain the displacement as follows:

[0038]

[0039] Where y1, y2, y3, y4, y5, and y6 are the displacements when the electrostatic force and elastic force are equal, π is pi, θ is the inverse cosine value corresponding to the threshold voltage torque, and T represents the threshold voltage torque. In equation (2), y3>g0 and y6>g0 do not conform to the actual situation, so y3 and y6 are not considered. The remaining displacement and d in equation (2) are then considered. 2 y / dt 2 Substituting 0 into equation (1), we obtain the following voltage:

[0040]

[0041] From equation (3), we can see that V P >V R This indicates that V RThis is the adsorption threshold voltage of the electrospinning solution. Based on the law of conservation of energy for the electrospinning solution adsorbed onto the collector surface at the adsorption threshold voltage, the critical equation is derived as follows:

[0042]

[0043] Combining equations (3) and (4), the electrospinning solution V is obtained. R The adsorption threshold voltage is:

[0044]

[0045] Artificial instabilities are introduced at the adsorption threshold voltage to overcome the surface tension at the droplet-air interface, thereby initiating a polymer jet and forming jet fibers, and obtaining the radius r of the jet fiber cross-section. 17 :

[0046]

[0047] Where E1 is the electric field strength, K1 is the conductivity of the electrospinning solution, I is the total current of the electrojet, Q is the volumetric flow rate, β is the dimensionless conductivity of the electrospinning solution, and C1 is a constant.

[0048] In this embodiment, the collector is a roller for collecting PAN jet fibers. The roller surface is provided with a micropillar array formed by multiple carbon micropillars, and the roller rotates around its own axis. Simultaneously, the micropores and the roller maintain relative translational motion, thereby ensuring uniform fiber deposition covering the micropillar array. The micropillar array is formed on the silicon wafer surface through photolithography and pyrolysis. The silicon wafer is placed within a groove on the roller surface, with the top of the micropillar array on the silicon wafer lower than the roller surface. This is to avoid the problem of introducing additional tensile force between the silicon wafer and the roller if the silicon wafer is directly placed on the roller surface and the micropillar array is formed, which would lead to uneven diameter of the jet fibers deposited on the silicon wafer surface. In this embodiment, the groove is arranged along the roller's own axis, and the diameter of the carbon micropillars in the micropillar array is 35 to 50 micrometers, the height is 20 micrometers, and the spacing between each carbon micropillar is 13 to 17 micrometers.

[0049] Furthermore, based on the relationship between electric field strength and voltage, the electric field strength can be expressed as E1 = V. R / (g0-y). By passing E1=V R Combining / (g0-y) with equations (5) and (6), the diameter of the polymer fiber in near-field electrospinning is obtained:

[0050]

[0051] The effect of voltage on polymer fiber diameter was studied using equation (7), and it was found that the effect of voltage on diameter showed a decreasing trend. As in previous studies, this trend well explains why reducing the near-field electrospinning voltage can reduce the polymer fiber thickness to the nanoscale. According to the relationship between the electrospinning solution thickness and the adsorption threshold voltage in equation (7), reducing the near-field electrospinning voltage... Figure 1 With a thickness of h, the voltage at which the electrospinning solution at the top of the droplet adsorbs onto the collector surface decreases. After further forming the jet fiber, according to the analysis of equation (7), the diameter of the jet fiber can be effectively reduced by decreasing the thickness of the electrospinning solution at the top of the droplet under low voltage and low volumetric flow rate.

[0052] During fiber deposition, the fiber deposition rate and the roller linear velocity are related. 18 The interaction of relative velocities leads to various defects such as bending and beading. The fiber velocity depends on the jet velocity from the nozzle, calculated using the following formula:

[0053]

[0054] Where v is the velocity of the fiber. Combining equation (8), the tensile stress of the fiber is derived:

[0055]

[0056] Where F is the tensile stress of the jet fiber, v1 is the linear velocity of the collector, m1 is the mass of the jet fiber, and Δt is the time it takes for the jet fiber to deposit on the collector surface.

[0057] In this embodiment, these deposition defects are eliminated by increasing the tensile stress in equation (9). During changes in volumetric flow rate, Figure 1 The changes in the length, width, and thickness of the droplet tip demonstrate that increasing tensile stress by controlling these factors is extremely difficult. To eliminate these shortcomings, simultaneously increasing the collector linear velocity and reducing the fiber deposition time (Δt) to effectively increase the tensile stress in equation (9) becomes a feasible option.

[0058] During the deposition of jet fibers onto the microstructures on the collector surface, the deposition location is primarily determined by the electric field intensity distribution on the microstructure surface. Based on the principle of potential superposition, we obtain... Figure 1 The electric field intensity at any point in the xz plane on the surface of the medium-carbon micropillar is as follows:

[0059]

[0060] In the formula: E P Let λ be the electric field strength, λ be the electric field linear density between the carbon micropillars, ε0 be the vacuum permittivity, and L be the electric field strength. C Let be the radius of the carbon micropillar.

[0061] Analysis of equation (10) shows that x = ±0.84z is the critical condition for the electric field intensity on the surface of the carbon micropillar to reach its maximum value. Sprayed fibers tend to be deposited at the position x = ±0.84z on the surface of the carbon micropillar.

[0062] Analysis based on equations (5) and (7) shows that reducing the droplet thickness and the distance between the syringe and the droplet is beneficial to lowering the adsorption threshold voltage, thereby producing finer polymer fibers. Figure 2 As shown in (a), porous absorbent paper is introduced and placed on top of the dispensing electrode needle to absorb some of the liquid, thereby reducing the droplet thickness. By reducing the distance between the needle and the roller, a portion of the liquid in the droplet is adsorbed onto the roller surface and carried away from the droplet at the needle tip, further reducing the droplet thickness. Furthermore, to initiate the spraying, the piercing action introduces artificial instability at the droplet-roller interface, generating a very high local electric field, thus producing sufficiently large electrical stress. 16 These are for Figure 2 (a) The design of thin, pyrolytic PAN-based polymer fibers offers the possibility.

[0063] Based on the above theoretical analysis, this embodiment is designed as follows: Figure 2 (a) The electrostatic jet initiation process based on near-field electrospinning was described, and the following was implemented: Figure 2 The jet spraying process is shown in (b)-(f). This is achieved by using porous absorbent paper and reducing the needle-roller distance. Figure 2 (b)-(c)) and the droplet inserted into the tip of the dispensing needle by pressing the roller ( Figure 2 (d) The volume of the droplet at the tip of the needle decreases sharply. Figure 2 (e)) thus achieving jet initiation at a lower adsorption threshold voltage (500V). Figure 2 (e)-(f)). Under jet-initiated conditions, the jet moves toward the drum and, accompanied by partial solvent evaporation, forms PAN-based polymer fibers on the silicon wafer surface on the drum. In this embodiment, these fibers were characterized using scanning electron microscopy, and their diameter was ~240 nm. Figure 2 (g) This indicates that the preliminary manufacturing design based on theoretical analysis can ensure continuous spraying at a low adsorption threshold voltage (500V) and produce submicron-sized pyrolytic PAN-based polymer fibers.

[0064] Based on theoretical analysis of equations (5) and (7), this embodiment designs as follows: Figure 3 (a) Submicro / nano forming process of the PAN-based fibers. According to this design, electrostatic emission is initiated from near-field electrospinning and along... Figure 3(b) The dispensing electrode needle moves along the x-axis, and PAN-based jet fibers are continuously deposited on the silicon substrate surface on the groove of the roller, forming an array of submicron-sized PAN-based fibers. During the fiber deposition process, the effect of the electrospinning liquid volume on the minimum voltage was experimentally investigated, and findings were made such as... Figure 3 (c) shows the voltage variation with liquid volume: reducing the liquid volume during electrospinning can lower the voltage from 1200V to 35V. The jet fibers at different voltages were characterized using scanning electron microscopy, and the results are as follows: Figure 3 (d) shows the diameter dimension. Figure 3 The relationship between voltage and jet fiber diameter in (d) shows that reducing the applied voltage can reduce the average diameter of the jet fiber to ~120 nm. The relationship between the diameter and the volume of the electrospinning liquid at the top of the droplet and the voltage on the needle-roller is consistent with the results obtained from the analysis of equation (7), which provides the possibility for the preparation of near-nanoscale PAN fibers.

[0065] Based on this, and according to the analysis of equation (7), the fiber diameter can be further reduced by controlling the distance between the needle and the roller. Further experimental research reveals that... Figure 3 (e) shows the effect of needle-drum distance on PAN fiber diameter: under different voltages (including 35V, 100V, and 300V), the jet fiber diameter decreases as the needle-drum distance decreases. When the needle-drum distance increases to 1.8mm, the PAN fiber diameter decreases to ~80nm, which achieves near-field electrospinning nanoforming of PAN-based jet fibers. The greater the distance between the collector and the droplet, the smaller the diameter of the deposited fiber.

[0066] In near-field electrospinning, a nanoforming method was developed using mathematical models of the sprayed fiber diameter and tensile stress. This method enabled the fabrication of pyrolytic nanoscale PAN-based fibers, establishing a PAN-based sprayed fiber nanoforming process. This process overcomes the difficulty of reducing the diameter of PAN-based fibers to the nanoscale, exhibiting advantages in manufacturing pyrolytic nanoscale PAN-based fibers. The key to PAN-based fiber nanoforming lies in the process design: inserting a roller into the droplet at the tip of the needle during electrospinning initiation, and simultaneously reducing the liquid volume at the tip and the needle-roller distance during continuous spraying.

[0067] According to the analysis in equation (9), in the fiber deposition process of low-voltage near-field electrospinning, the introduction of a rotating roller increases the linear velocity of the collector and reduces the fiber deposition time (Δt), which provides the possibility of increasing tensile stress to eliminate deposition defects. When the roller speed is 400 r / min, the following is formed: Figure 4 The PAN-based fiber arrays shown in (a)-(d) are illustrated. When the dispensing electrode needle moves at a speed of 80 μm / s, the following phenomena occur: Figure 4(a) shows the dotted line structure. When the moving speed increases from 80 μm / s to 240 μm / s, due to the increase in tensile stress of the jet fiber, such as Figure 4 The dot-line structure shown in (a)-(b) transforms into a multi-point-line structure. As the moving speed increases from 240 μm / s to 2400 μm / s, the tensile stress of the jet fiber further increases, but... Figure 4 The multi-point line structure in (b)-(c) remains unchanged. Under this condition, when the drum speed is increased from 400 r / min to 800 r / min or greater, such as Figure 4 The multi-point-line structure shown in (c) transforms into, as... Figure 4 (d) shows the elimination of defects such as line structures, point-line structures, and multi-point-line structures. As analyzed in equation (9), the effect of rotational speed on tensile stress is the reason for the elimination of defects.

[0068] A larger dispensing needle-roller gap is beneficial for jet fiber nanoforming, but it also comes with challenges such as... Figure 5 The ring-line structure shown is formed. When the dispensing needle-roller distance decreases from 1.48 mm to 0.16 mm, the tensile stress in equation (9) increases, as... Figure 5 The loop-line structure shown in (a) first transforms into the following: Figure 5 The point-line structure shown in (b) then transforms into the following: Figure 5 (c) shows a curved-straight structure. Further reducing the dispensing needle-roller distance makes it difficult to overcome fiber bending in the curved-straight structure, which becomes a major drawback of the jet fiber array. In this case, increasing the control speed from 400 r / min to 900 r / min can achieve the following... Figure 5 The transformation from a curved-straight structure to a linear structure shown in (c)-(d) is an effective way to overcome deposition defects by increasing the tensile stress in equation (9).

[0069] By controlling the moving speed, rotating speed, and syringe spacing, the dispensing needle moves linearly along the x-axis in near-field electrospinning, achieving defect-free directional alignment of PAN nanofibers, thus forming a... Figure 6 (a) shows the PAN nanofiber array. Figure 6 As shown in (b)-(c), by maximizing the rotational speed of the roller and minimizing the moving speed of the dispensing needle, the array spacing between PAN nanofibers can be reduced to ~8 μm.

[0070] For the micro / nano structures of PAN-based nanofibers, the carbon-MEMS method was employed. 20 Pyrolysis of high aspect ratio and patterned SU-8 structures to prepare materials such as Figure 6(d) shows the 3DCMP array. This embodiment plots the location of the maximum electric field intensity on the 3DCMP surface based on the calculation of equation (10), thus obtaining a distribution map of the maximum electric field intensity. The effect of the electric field intensity on the jet fiber deposition causes the jet fibers to be deposited at the location of the maximum electric field intensity, thereby forming a pattern on the 3DCMPs on the silicon substrate surface as shown in (d). Figure 6 (e) shows the PAN nanofiber array. With... Figure 6 (e) The silicon substrate with PAN nanofibers and 3DCMPs structure is rotated 90°, and the nanofiber array is deposited again onto the 3DCMPs on the surface of the silicon substrate, forming a structure like... Figure 6 (f) shows the PAN nanofiber-3DCMPs micro / nano structure.

[0071] Using a mathematical model of the surface electric field intensity of carbon micropillars, PAN nanofiber arrays were fabricated on 3DCMPs, achieving a nanodeposition step of PAN-based jet fibers in near-field electrospinning. The deposition and alignment of PAN nanofibers on 3DCMPs, and the bonding of PAN nanofibers to the 3DCMP surface, highlight the sophistication of the nanodeposition design. This allows the transformation from PAN fibers to carbon fibers to occur at specific locations on the 3DCMP surface, paving the way for the formation of carbon nanofiber structures on 3DCMPs.

[0072] The conversion of PAN-based jet fibers into carbon fibers typically relies on thermal stabilization treatment in air at 200-300°C, followed by carbonization treatment in an inert atmosphere at 1000-1500°C. This usually produces carbon fibers with a diameter of 150-500 nm. 21 This embodiment will Figure 7 The micro-nanostructure of PAN nanofiber-3D carbon micropillars in (a) was placed in a furnace for further processing. Figure 7 The 115℃ heat stabilization treatment and 1000℃ pyrolysis treatment are shown in (a)-(c). Figure 7 (b) During the thermal stabilization process, a stepped structure consisting of an acridinium ring (40%), a naphthidine ring (30%), and a hydronaphthidine ring (20%) is formed through cyclization and partial dehydrogenation reactions. This enables the polymer fiber to withstand high temperatures during pyrolysis. Further processes such as... Figure 7 (c) shows the pyrolysis process in which polymer fibers with a stepped structure are transformed into carbon fibers with a diameter of ~4 nm.

[0073] In this embodiment, the heat stabilization treatment of the fiber deposition is carried out in air at a heating rate of 15-18°C / min, with the temperature maintained between 106-115°C after heating, and the heating time being 16-18 hours, before cooling to room temperature.

[0074] When pyrolyzing fiber deposition, the process involves first heating the material in nitrogen from room temperature to 115°C over a period of 0.8–1.2 hours, maintaining the temperature at 115°C for 1 hour, then heating it to 970–1050°C at a heating rate of 15–18°C / min and maintaining the temperature for 1–1.2 hours, and finally cooling it to room temperature at a cooling rate of 2.7–5°C / min.

[0075] Through the above theoretical derivation and implementation process, this embodiment can fabricate a micro / nano structure based on carbon nanofiber arrays—3D carbon micropillars—and reduce the diameter of the carbon fibers suspended between the 3D carbon micropillars to below 10 nm. The protocol consists of two parts: using near-field electrospinning to suspend PAN nanofibers between the carbon micropillars to reduce the limiting effect of the micropillars on the radial shrinkage of the fibers during stabilization and pyrolysis; and the adhesion between the fibers and the surface of the carbon micropillars to limit the axial shrinkage of the suspended fibers, which lays the foundation for achieving the tensile stress on the suspended fibers during thermal stabilization and pyrolysis. The diameter of the carbon nanofibers on the surface of the carbon micropillars (( Figure 7 (c) 25nm) is larger than the diameter of the carbon nanofibers suspended between the carbon micropillars. Figure 7 (c) 4nm) indicates that this protocol is crucial for the formation of carbon nanofiber arrays with a diameter of less than 10nm.

[0076] Based on this protocol, this embodiment introduces methods for controlling shrinkage and diameter by further studying the effects of micropillar spacing, stabilization temperature, and carbonization rate on shrinkage during stabilization and pyrolysis, as well as the correlation between carbon fiber diameter and voltage. A micropillar spacing of 15 μm, a stabilization temperature of 15 °C, and a carbonization rate of 15 °C / min are selected. Figure 7 The fiber shrinkage rate shown in (dg) is as high as 96%, demonstrating a method for controlling the increase in fiber shrinkage during the conversion of PAN fibers to carbon fibers. Based on the high fiber shrinkage rate controlled by this method, reducing the voltage to 35V can reduce the carbon fiber diameter to below 10nm, thereby obtaining an array of carbon fibers below 10nm on three-dimensional carbon micropillars.

Claims

1. A method for manufacturing three-dimensional carbon-based micro / nano structures, characterized in that, Includes the following steps: The PAN electrospinning solution, to which an adsorption threshold voltage is applied, is passed through a micropore and forms a droplet. A collector for receiving the electrospinning solution is then inserted into the droplet and removed, thereby initiating a jet. Simultaneously, after the jet is initiated, the droplet volume of the electrospinning solution is reduced, and the distance between the collector and the droplet is maintained within a preset range, thereby forming a fiber deposition on the collector. The fiber deposits on the collector surface are subjected to thermal stabilization and pyrolysis treatments in sequence to form a three-dimensional carbon-based micro / nano structure.

2. The manufacturing method according to claim 1, characterized in that, Adsorption threshold voltage V R for: Where g0 is the axial distance between the electrospinning solution and the collector, K is the elastic coefficient, ε is the dielectric constant, A is the area of ​​the electrospinning solution opposite to the collector, and y5 is the displacement when the electrostatic force and the elastic force are equal, calculated by the following formula: Where π is the mathematical constant pi, θ is the arccosine value corresponding to the threshold voltage torque, θ = arccosT, and T represents the threshold voltage torque.

3. The manufacturing method according to claim 1, characterized in that, The collector is a roller for collecting PAN jet fibers. The surface of the roller is provided with a micropillar array formed by multiple carbon micropillars, and the roller rotates around its own axis. At the same time, the micropores and the roller maintain relative translational motion, so that the fiber deposition uniformly covers the micropillar array.

4. The manufacturing method according to claim 3, characterized in that, The micropillar array is formed on the surface of a silicon wafer by photolithography and pyrolysis. The silicon wafer is placed in a groove on the surface of a roller, and the top of the micropillar array on the silicon wafer is lower than the surface of the roller. The groove is arranged along the axis of the roller itself. The carbon micropillars in the micropillar array have a diameter of 35 to 50 micrometers, a height of 20 micrometers, and a spacing of 13 to 17 micrometers between each carbon micropillar.

5. The manufacturing method according to claim 3, characterized in that, The rotational speed of the roller is not less than 800 r / min, and the relative translational speed between the micropores and the roller is 480 micrometers, so that the fibers deposited on the surface of the roller are a uniform linear structure.

6. The manufacturing method according to claim 1, characterized in that, The volume of the electrospinning solution ejected from the micropores is reduced by placing a water-absorbing material with water-absorbing properties at the micropores, thereby absorbing part of the liquid in the droplets and reducing the droplet volume to no more than 100 nanoliters.

7. The manufacturing method according to claim 1, characterized in that, The distance between the collector and the droplet is maintained between 1.7 mm and 1.8 mm, thereby producing fiber depositions on the collector with diameters between 120 nm and 80 nm. The greater the distance between the collector and the droplet, the smaller the diameter of the fiber deposition.

8. The manufacturing method according to claim 1, characterized in that, When performing thermal stabilization treatment on fiber deposition, the treatment is carried out in air at a heating rate of 15-18°C / min, with the temperature maintained between 106-115°C after heating, and the heating time being 16-18 hours, before cooling to room temperature.

9. The manufacturing method according to claim 8, characterized in that, When performing pyrolysis treatment on fiber deposition, the temperature is first raised to 115°C in nitrogen from room temperature over a period of 0.8 to 1.2 hours, and maintained at 115°C for 1 hour. Then, the temperature is raised to 970 to 1050°C at a heating rate of 15 to 18°C / min and maintained for 1 to 1.2 hours. Finally, the temperature is cooled to room temperature at a cooling rate of 2.7 to 5°C / min to obtain carbon fibers with a diameter of less than 10 nanometers.

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