Substrate growth pulling method for ultra-long few-walled carbon nanotube array

Abstract

The invention relates to the technical field of nano material preparation, and particularly discloses a substrate growth pulling method of an ultra-long few-walled carbon nanotube array. The method comprises the following steps: firstly, pretreating a substrate, loading a zinc-based MOF derivative catalyst and forming a polymer transition layer; then in a reaction environment capable of providing an alternating magnetic field, a gradient electric field, a near-infrared light thermal field and layered gas flow, heating and introducing a carbon source gas in a pulse manner to grow the array, and meanwhile, carrying out on-line monitoring and real-time closed-loop regulation on growth parameters by utilizing a laser Raman spectrum; after the array grows to a preset height, staged gradient stress release lifting is executed, and layered airflow is used for assisting in stripping; and finally, removing the residual catalyst in an oxidizing atmosphere. The carbon nanotube array can be used in the fields of nano devices, composite material reinforcement and the like, and has the advantages of excellent directionality, low defect rate and strong structural integrity. The preparation method provided by the invention can be used for efficiently preparing the high-performance ultra-long few-walled carbon nanotube array.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and more specifically, to a substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays. Background Technology

[0002] Ultralong oligowalled carbon nanotube arrays, with their ultra-high aspect ratio, excellent mechanical strength, electrical and thermal conductivity, and structural regularity, have irreplaceable application potential in high-end fields such as nanoelectronic devices, field emission electrodes, high-performance composite material reinforcing phases, and energy storage material carriers. Currently, the mainstream fabrication technology for carbon nanotube arrays is chemical vapor deposition (CVD), which achieves growth through the decomposition and deposition of carbon sources catalyzed by a catalyst. However, existing technologies mostly rely on a single thermal field drive or a simple magnetic field assistance, and the carbon source supply generally adopts a continuous constant flow gas supply mode. Furthermore, there is a lack of effective real-time monitoring methods and dynamic parameter feedback adjustment mechanisms during the growth process, and the entire growth process can only be completed by relying on preset fixed process parameters.

[0003] The inherent defects of traditional growth methods are becoming increasingly apparent: On the one hand, a single growth field makes it difficult to precisely control the activity stability and dispersion uniformity of catalyst particles. The growth direction of carbon nanotubes is easily affected by factors such as airflow disturbance and uneven temperature gradients, resulting in poor array orientation and disordered arrangement. On the other hand, continuous carbon source supply cannot dynamically match the carbon source demand according to the real-time growth status of carbon nanotubes, easily leading to excessive accumulation or insufficient supply of carbon source. Excessive accumulation will cause catalyst particle agglomeration, while insufficient supply will lead to the interruption of carbon nanotube growth. Both will result in a large number of structural defects such as vacancies, dislocations, and irregular tube walls during the crystallization process of carbon nanotubes, with the defect rate remaining at a high level for a long time. These problems directly lead to a significant decline in the core indicators such as the mechanical and electrical properties of carbon nanotube arrays, failing to meet the stringent requirements of high material regularity and low defect rate for high-end applications, and seriously restricting their industrial application process. Summary of the Invention

[0004] To address the problems of poor growth orientation, insufficient crystal integrity, and high structural defect rate of carbon nanotube arrays in existing technologies, this application provides a substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays.

[0005] A substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays includes the following steps: S1. Substrate pretreatment and catalyst loading: The silicon-based or quartz substrate is cleaned and dried, and a zinc-based MOF-derived catalyst nanoparticle layer is loaded on its surface, and a polymer transition layer is formed on the surface of the catalyst layer. S2. Initialization of the reaction system: The substrate loaded with the catalyst and transition layer is placed in the reaction environment and a protective gas is introduced into it while heating to the growth temperature; the reaction environment can provide an alternating magnetic field, a gradient electric field, a near-infrared photothermal field and a layered controllable gas flow field, and can perform online monitoring of the growth process using laser Raman spectroscopy. S3. Multi-field synergistic growth and real-time control: Under the synergistic effect of the alternating magnetic field, gradient electric field, and near-infrared photothermal field, carbon source gas is pulsedly introduced into the reaction environment to grow carbon nanotube arrays; during this process, the Raman signal of the array is monitored in real time using laser Raman spectroscopy, and based on the G / D ratio and D peak intensity in the Raman signal, closed-loop feedback control is implemented on the frequency of the alternating magnetic field, the intensity of the gradient electric field, the power of the near-infrared photothermal field, and the pulse frequency of the carbon source gas; S4. Gradient stress release lifting: After the carbon nanotube array grows to the predetermined height, the lifting operation is initiated, and the layered controllable airflow field is used simultaneously to assist in the peeling of the array root. The lifting operation includes an initial low-speed lifting stage and a subsequent accelerated lifting stage. The trigger condition for switching from the initial low-speed lifting stage to the accelerated lifting stage is that the lifting distance reaches a preset threshold. S5. Catalyst removal and post-treatment: After the carbon nanotube array is completely detached from the substrate, the residual catalyst is removed in an oxidizing atmosphere, and then the obtained array is cleaned and dried.

[0006] By adopting the above technical solution, firstly, in terms of catalyst design and interface engineering, a zinc-based metal-organic framework is used as a precursor. After pyrolysis under specific conditions, a catalyst layer with uniform size and good dispersion of nanoparticles can be formed on the substrate surface. Simultaneously, a polymer transition layer is introduced onto the catalyst layer, which can buffer thermal stress and enhance interfacial bonding during subsequent high-temperature processes. Secondly, during array growth, the synergistic effect of an alternating magnetic field, a gradient electric field, and a near-infrared photothermal field is innovatively introduced. The alternating magnetic field, by influencing the magnetic moment and energy state of the catalyst particles, inhibits surface diffusion and aggregation. The gradient electric field provides the driving force for the directional migration of charged carbon fragments or intermediates generated by carbon source pyrolysis, guiding the orderly deposition of carbon atoms on specific crystal faces of the catalyst. The near-infrared photothermal field provides precise local thermal energy input, regulating the catalyst activity. Meanwhile, laser Raman spectroscopy is used to monitor the growing array in real time. By analyzing the change in the signal intensity ratio of the G peak (characterizing the crystal quality of carbon nanotubes) to the D peak (characterizing defects), the parameters of the above physical fields and the frequency of the carbon source supply pulse are adjusted in real time, forming a closed-loop control system based on real-time feedback of growth quality.

[0007] In the array pulling stage, a gradient stress release strategy integrated with the growth process was designed. The pulling operation was not performed at a single speed, but divided into two stages: an initial low-speed stage and a subsequent acceleration stage, with the stage transition triggered by a precise pulling distance. In the acceleration stage, the pulling rate increased according to a preset mathematical function, and the slope of the increase was dynamically adjusted based on real-time monitored peel stress data. This process was simultaneously supplemented by a layered and controllable airflow field, whose flow velocity changed in tandem with the pulling stage, and whose direction was consistent with the aforementioned gradient electric field direction. This created a controllable airflow shear force at the root of the array, assisting the array in separating from the substrate with lower mechanical stress. Finally, after the array was completely detached, it was treated with an oxidizing atmosphere of specific components and temperature to selectively oxidize the residual catalyst into gaseous products for removal, thereby obtaining a pure carbon nanotube array.

[0008] Preferably, in step S1, the polymer transition layer is a polyimide layer with a thickness of 30-80 nm.

[0009] By adopting the above technical solution, polyimide is selected as the polymer transition layer in step S1. Utilizing its high-temperature resistance, strong chemical stability, and moderate mechanical toughness, and by precisely controlling the thickness range of 30-80 nm, a dense and uniform thin film structure can be formed to encapsulate the catalytic sites, preventing the zinc-based MOF-derived catalyst from detaching during subsequent heating and gas scouring, thus ensuring the loading stability of the catalytic sites. Furthermore, the interfacial interaction within this thickness range can balance the bonding strength between the catalyst layer and the substrate, avoiding excessive bonding that could lead to carbon nanotube array breakage during subsequent pull-out, or insufficient bonding that could affect catalytic stability during growth. The dense structure of the polyimide layer also blocks the direct impact of carbon source gas on the catalytic sites, reducing catalytic deactivation caused by excessive carbon source deposition. This, combined with the dispersion characteristics of the zinc-based MOF-derived catalyst, creates a structural and functional synergy, laying a stable interfacial foundation for the orderly growth of the carbon nanotube array.

[0010] Preferably, in step S2, the growth temperature is 700-900°C; and the heating rate is 8-12°C / min.

[0011] By adopting the above technical solution, a growth temperature range of 700-900°C is selected to match the activity window of the zinc-based MOF-derived catalyst. This temperature not only meets the requirements for efficient decomposition of mixed carbon source gas, providing sufficient carbon source precursors for carbon nanotube growth, but also maintains the structural stability of the catalytic sites, avoiding insufficient carbon deposition efficiency due to excessively low temperatures or catalyst particle sintering and agglomeration due to excessively high temperatures. The heating rate of 8-12°C / min, through slow and uniform temperature increase, balances the difference in thermal expansion coefficients between the substrate, polyimide transition layer, and zinc-based MOF-derived catalyst layer, reducing interlayer thermal stress concentration and preventing cracking of the transition layer or interfacial delamination between the catalyst layer and the substrate. At the same time, it allows the structure of each layer to gradually complete thermal adaptation during the heating process, ensuring that the catalytic sites remain uniformly dispersed during the temperature stabilization stage, and the transition layer forms a stable interfacial buffer structure, thus constructing a reaction substrate with constant temperature and complete structure for subsequent multi-field synergistic growth.

[0012] Preferably, in step S3, the closed-loop feedback adjustment specifically involves: when the G / D ratio of the Raman spectral signal is lower than the first threshold, increasing the intensity of the gradient electric field and decreasing the power of the near-infrared photothermal field; when the D peak intensity of the Raman spectral signal is higher than the second threshold, adjusting the frequency of the alternating magnetic field and increasing the pulse frequency of the carbon source gas.

[0013] By adopting the above technical solution, the G / D ratio captured by laser Raman spectroscopy directly reflects the crystallization integrity of carbon nanotubes. When this ratio is lower than the first threshold, the directional driving force for carbon nanotube growth is enhanced by increasing the gradient electric field intensity, guiding carbon atoms to arrange in an orderly manner to improve crystal regularity. At the same time, the power of the near-infrared photothermal field is reduced to avoid local overheating and damage to the crystal structure. The dual effect forms a synergistic regulation of directional guidance and thermal stability assurance, improving the crystallization quality. The D peak intensity is positively correlated with the defect density of carbon nanotubes. When this intensity is higher than the second threshold, the alternating magnetic field frequency is adjusted to optimize the magnetic field action period, further suppressing catalyst particle agglomeration to reduce the source of defect generation. At the same time, the carbon source gas pulse frequency is increased to accurately supplement the carbon source supply, matching the carbon demand in the defect repair process. Dynamic regulation is formed through targeted parameter adjustment, and growth deviation is corrected in real time, providing precise assurance for the low-defect growth of carbon nanotube arrays.

[0014] Preferably, the first threshold is 10; the adjustment amount for increasing the gradient electric field strength is 0.5-1.0 kV / cm, and the adjustment amount for decreasing the near-infrared photothermal power is 50-100 mW / cm. 2 The second threshold is 130% of the D peak intensity at the start of growth; the adjustment amount of the alternating magnetic field frequency is 5-10kHz, and the adjustment amount of the carbon source gas pulse frequency is 1-2Hz.

[0015] By adopting the above technical solution, the first threshold for the G / D ratio is set to 10. This value corresponds to the critical state of carbon nanotube crystallization quality. When the detected value is lower than this value, the driving force for directional growth can be precisely enhanced without damaging the stability of the existing growth system by adjusting the gradient electric field intensity of 0.5-1.0 kV / cm. This is further supported by a 50-100 mW / cm... 2 The near-infrared photothermal power adjustment precisely balances lattice regularity and carbon source decomposition efficiency. The second threshold is set to 130% of the D-peak intensity at the start of growth, using the low-defect state of the initial growth stage as a benchmark to promptly capture the critical node of defect accumulation. The magnetic field cycle is optimized by adjusting the alternating magnetic field frequency by 5-10 kHz, effectively dispersing catalyst particles and preventing agglomeration. Simultaneously, the carbon source is precisely replenished by adjusting the carbon source gas pulse frequency by 1-2 Hz to match the carbon requirements for defect repair. The adaptive design of each adjustment amount and threshold considers both the parameter response sensitivity of the growth system and avoids growth fluctuations caused by excessive adjustment amplitude, ensuring the accuracy and feasibility of closed-loop feedback regulation and achieving efficient correction of growth deviations.

[0016] Preferably, in step S3, the frequency of the alternating magnetic field is 1-50 kHz, and the intensity is 10-50 mT; the intensity of the gradient electric field is 1-5 kV / cm; and the power of the near-infrared photothermal field is 100-300 mW / cm. 2 .

[0017] By employing the above technical solution, a periodic magnetic field is formed through an alternating magnetic field frequency of 1-50 kHz, coupled with a magnetic field strength of 10-50 mT to generate a moderate Lorentz force. This frequency and strength range is suitable for the typical particle size range of 5-20 nm for zinc-based MOF-derived catalysts. This allows for effective dispersion of catalytic sites and inhibition of particle agglomeration during growth through periodic magnetic field perturbation, without damaging the active crystal structure of the catalyst due to excessively strong magnetic fields or frequencies. A gradient electric field strength of 1-5 kV / cm along the vertical direction constructs a continuous directional driving force. This intensity range guides the orderly deposition of carbon atoms along the electric field direction, while also being compatible with the carbon nanotube growth rate, avoiding insufficient directionality due to an insufficiently weak electric field or structural disorder caused by an excessively strong electric field. The electric field strength range is 100-300 mW / cm. 2 The near-infrared photothermal field power can precisely control the temperature of the local reaction area, which not only meets the energy requirements for efficient decomposition of mixed carbon sources, but also maintains the structural stability of the catalytic sites. Moreover, this power range reserves a reasonable range for power adjustment in subsequent closed-loop regulation, ensuring the stability and adaptability of the synergistic effect of multiple field parameters, and together providing a controllable physical environment for the growth of carbon nanotube arrays.

[0018] Preferably, in step S3, the carbon source gas is a mixture of methane and acetylene, wherein the volume ratio of methane to acetylene is 1:1 to 3:1, the supply pulse frequency is 1-5Hz, and the pulse width is 0.1-0.5s.

[0019] By adopting the above technical solution, a mixture of methane and acetylene is selected as the carbon source. Utilizing the high decomposition temperature and stable carbon supply of methane, and the high activity and fast nucleation rate of acetylene, the volume ratio can be adjusted from 1:1 to 3:1 to suit the needs of different growth stages: a low ratio enhances nucleation efficiency, while a high ratio ensures growth stability, balancing the nucleation efficiency and growth stability of carbon nanotubes and avoiding imbalances in growth rate or increased structural defects caused by a single carbon source. A supply pulse frequency of 1-5Hz and a pulse width of 0.1-0.5s allow for precise quantitative control of the carbon source supply, avoiding excessive carbon accumulation and catalyst poisoning caused by continuous gas supply, while also replenishing carbon precursors as needed for growth. This parameter range is compatible with the parameter adjustment range of multi-field synergistic environment and closed-loop feedback regulation, ensuring dynamic matching between carbon source supply, catalytic activity, and directional growth driving force, providing a controllable and sufficient carbon source foundation for the orderly growth of oligowalled carbon nanotube arrays.

[0020] Preferably, in step S4, the lifting rate of the initial low-speed lifting stage is 0.01-0.05 mm / s, the preset lifting distance threshold is 10-50 μm, and the lifting rate of the accelerated lifting stage is increased to 0.5-1.0 mm / s; in the accelerated lifting stage, the lifting rate increases from the initial low-speed value to the target high-speed value according to an exponential function relationship, and the slope of the rate increase is dynamically adjusted according to the peeling stress monitored in real time, so that the peeling stress is maintained below 10 GPa.

[0021] By adopting the above technical solution, an initial low-speed lifting rate of 0.01-0.05 mm / s, combined with a preset lifting distance threshold of 10-50 μm, achieves gentle initial peeling of the carbon nanotube array root from the substrate, avoiding stress concentration and array breakage caused by excessively fast initial speed. After the lifting distance reaches the threshold, the lifting rate is gradually increased to 0.5-1.0 mm / s according to an exponential function. This exponential increase method matches the nonlinear characteristics of the mechanical response of the carbon nanotube array, enabling a smooth transition of the rate and reducing the instantaneous stress impact caused by sudden rate changes. During the acceleration phase, the rate increase slope is dynamically adjusted by real-time monitoring of peeling stress, strictly controlling the stress below 10 GPa. This design not only adapts to the mechanical load-bearing characteristics of the carbon nanotube array but also matches the subsequent growth rate, balancing peeling efficiency and structural integrity, ensuring that the array maintains its oriented alignment during the lifting process and avoiding problems such as bending, breakage, or root detachment.

[0022] Preferably, the flow velocity of the layered controllable airflow field is controlled in coordination with the lifting stage; in the initial low-speed lifting stage, the flow velocity of the layered airflow field is controlled to be 0.1-0.2 m / s; after entering the accelerated lifting stage, the flow velocity of the layered airflow field is synchronously increased to 0.6-1.2 m / s, and the airflow direction of the layered airflow field is consistent with the direction of the gradient electric field.

[0023] By adopting the above technical solution, the layered controllable airflow field and the lifting stage are precisely synergistically regulated. In the initial low-speed lifting stage, the flow velocity is controlled at 0.1-0.2 m / s. This low-speed airflow can gently act on the root of the carbon nanotube array, helping to alleviate the interfacial bonding force without disturbing the initial peeling process, and providing a stable airflow environment for slow detachment. After entering the accelerated lifting stage, the flow velocity is synchronously increased to 0.6-1.2 m / s. By enhancing the airflow force to match the mechanical requirements of accelerated peeling, the stress concentration at the root of the array is effectively dispersed, avoiding structural damage caused by the increased rate. At the same time, the airflow direction is consistent with the gradient electric field. The two form a synergistic effect of directional driving force and airflow auxiliary force, further strengthening the directional growth of the carbon nanotube array and preventing problems such as bending and collapsing of the array during the lifting process. This complements the gradient stress release lifting strategy, jointly ensuring the structural integrity and directional regularity of the array during the efficient peeling process.

[0024] Preferably, in step S5, the oxidizing atmosphere is an inert mixed gas containing 3% to 8% oxygen by volume, the processing temperature is 250-350°C, and the processing time is 30-60 min.

[0025] By employing the above technical solution, an inert mixed gas containing 3% to 8% oxygen by volume is used to construct a targeted oxidizing atmosphere. Oxygen, as the active component, selectively oxidizes zinc-based MOF-derived catalyst residues, while the inert gas acts as a dilution and atmosphere stabilizer. This oxygen volume fraction ensures efficient oxidation and decomposition of catalyst residues while preventing excessive oxygen from oxidizing and eroding the carbon nanotube array. The processing temperature of 250-350℃ is adapted to the oxidation reaction activity range of zinc-based catalyst residues, providing sufficient energy for the oxidation reaction to convert catalyst residues into easily detachable oxide products, while remaining below the oxidation threshold of carbon nanotubes. Typically above 400℃, this effectively prevents damage to the carbon nanotube structure. The processing time of 30-60 minutes ensures that the catalyst residues are fully oxidized and detached from the array. The parameters are mutually adapted and synergistic, efficiently removing catalyst residues while maximizing the protection of the structural integrity of the carbon nanotube array, laying the foundation for improving product purity and subsequent application performance.

[0026] In summary, this application has the following beneficial effects: 1. This application employs the synergistic effect of alternating magnetic field, gradient electric field and near-infrared photothermal field, combined with online monitoring and closed-loop feedback adjustment of laser Raman spectroscopy, to synchronously and dynamically optimize the magnetic field frequency, electric field strength, photothermal power and carbon nanotube pulse supply parameters. Furthermore, through precise control of the pulsed mixed carbon source supply, the orientation and crystallization integrity of the carbon nanotube growth process are synergistically guaranteed, effectively reducing the generation of defects.

[0027] 2. In this application, a gradient stress release lifting strategy is preferred, which is combined with the synergistic regulation of the layered controllable airflow field and the lifting stage. The initial low-speed stage is gentle peeling, the acceleration stage increases the rate according to an exponential function and dynamically adjusts the slope. At the same time, the airflow assists to reduce stress concentration at the root of the array, thus achieving the effect of good structural integrity of carbon nanotube array and not easy to break and fall off.

[0028] 3. The method of this application, by loading a zinc-based MOF-derived catalyst nanoparticle layer on the substrate surface and combining it with a polymer transition layer of a specific thickness, allows the MOF-derived catalyst to provide uniform active sites. The transition layer not only enhances the bonding stability between the catalyst and the substrate, but also reduces the difficulty of subsequent stripping. Therefore, the method achieves the effect of good uniformity of carbon nanotube array growth and synergistic adaptation of loading and stripping.

[0029] 4. This application removes residual catalyst from carbon nanotube arrays detached from the substrate in an oxidizing atmosphere. A specific combination of oxygen volume fraction, processing temperature and time can achieve efficient catalyst removal without additional complex separation steps, avoiding secondary damage to the carbon nanotube array structure, and achieving the effect of simple process and high product purity. Attached Figure Description

[0030] Figure 1 This is a flowchart of a substrate growth and lifting method for an ultra-long oligowalled carbon nanotube array provided in this application; Figure 2 These are transmission electron microscopy (TEM) images of the ultralong oligowalled carbon nanotubes provided in this application, showing their morphology and diameter. Detailed Implementation

[0031] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0032] Technical concept: The application of ultralong oligowalled carbon nanotube arrays in high-end nanodevices and composite material reinforcement relies on their high orientation, low defect rate, and structural integrity. However, existing technologies struggle to achieve these core properties simultaneously. Traditional fabrication methods often rely on a single thermal field or simple magnetic field, lacking a multi-physics-field synergistic control mechanism. Furthermore, the continuous carbon source supply cannot precisely match the real-time growth state of the carbon nanotubes. Simultaneously, the lack of effective online monitoring and dynamic feedback regulation during growth leads to disordered carbon atom deposition, defect accumulation, and poor array orientation. Moreover, the peeling stage often employs a single-rate operation, neglecting interfacial stress distribution characteristics, which easily causes array fracture. Insufficient parameter adaptability also exists during catalyst residue removal. These factors collectively restrict the performance improvement of carbon nanotube arrays.

[0033] This technical solution addresses the aforementioned issues by constructing a precise control system from multiple dimensions: First, it optimizes the dispersion of catalytic sites and the interfacial bonding state through the combined design of zinc-based MOF-derived catalysts and polyimide transition layers; second, it introduces the synergistic effect of alternating magnetic fields, gradient electric fields, and near-infrared photothermal fields, combined with online monitoring and closed-loop feedback adjustment using laser Raman spectroscopy, to dynamically optimize physical field parameters and carbon source pulse supply, achieving ordered carbon atom deposition and defect suppression; third, it uses a gradient stress release lifting strategy and a layered controllable airflow field to control the lifting rate and airflow parameters in stages, alleviating peeling stress concentration; finally, it employs a precisely proportioned oxidizing atmosphere and suitable temperature and time parameters to efficiently remove catalyst residues and protect the array structure. Through the organic integration of these technical means, it systematically solves the core pain points of existing technologies.

[0034] Example 1 This embodiment provides a substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays. The specific steps are as follows, and the process parameters involved are all taken as the median values ​​of the corresponding ranges in the claims: S1. Substrate pretreatment and catalyst loading: The silicon substrate is cleaned and dried, and a zinc-based MOF-derived catalyst nanoparticle layer is loaded on its surface, and a polymer transition layer is formed on the surface of the catalyst layer. The polymer transition layer is a polyimide layer with a thickness of 55 nm.

[0035] S2. Initialization of the reaction system: The substrate loaded with the catalyst and transition layer is placed in the reaction environment and a protective gas is introduced into it while heating to the growth temperature. The reaction environment can provide an alternating magnetic field, a gradient electric field, a near-infrared photothermal field and a layered controllable gas flow field, and can monitor the growth process online with laser Raman spectroscopy. The growth temperature was 800°C; the heating rate was 10°C / min.

[0036] S3. Multi-field synergistic growth and real-time control: Under the synergistic effect of alternating magnetic field, gradient electric field and near-infrared photothermal field, carbon source gas is pulsed into the reaction environment to grow carbon nanotube arrays; during this process, the Raman signal of the array is monitored in real time using laser Raman spectroscopy, and based on the G / D ratio and D peak intensity in the Raman signal, closed-loop feedback control is implemented on the frequency of alternating magnetic field, intensity of gradient electric field, power of near-infrared photothermal field and pulse frequency of carbon source gas; Specifically, the closed-loop feedback regulation is as follows: when the G / D ratio of the Raman spectral signal is lower than the first threshold, the intensity of the gradient electric field is increased and the power of the near-infrared photothermal field is reduced; when the D peak intensity of the Raman spectral signal is higher than the second threshold, the frequency of the alternating magnetic field is adjusted and the pulse frequency of the carbon source gas is increased. The first threshold is 10; the adjustment amount for increasing the gradient electric field strength is 0.75 kV / cm, and the adjustment amount for decreasing the near-infrared photothermal power is 75 mW / cm. 2 The second threshold is 130% of the D peak intensity at the start of growth; the adjustment amount of the alternating magnetic field frequency is 7.5 kHz, and the adjustment amount of the carbon source gas pulse frequency is 1.5 Hz.

[0037] The alternating magnetic field has a frequency of 25.5 kHz and an intensity of 30 mT; the gradient electric field has an intensity of 3 kV / cm; and the near-infrared photothermal field has a power of 200 mW / cm. 2 .

[0038] The carbon source gas is a mixture of methane and acetylene, with a volume ratio of methane to acetylene of 2:1. The supply pulse frequency is 3Hz and the pulse width is 0.3s.

[0039] S4. Gradient stress release lifting: After the carbon nanotube array grows to the predetermined height, the lifting operation is initiated, and the layered controllable airflow field is used simultaneously to assist in the peeling of the array root. The lifting operation includes an initial low-speed lifting stage and a subsequent accelerated lifting stage. The trigger condition for switching from the initial low-speed lifting stage to the accelerated lifting stage is that the lifting distance reaches a preset threshold. The initial low-speed lifting stage has a lifting rate of 0.03 mm / s and a preset lifting distance threshold of 30 μm. The lifting rate in the accelerated lifting stage is increased to 0.75 mm / s. In the accelerated lifting stage, the lifting rate increases from the initial low-speed value to the target high-speed value according to an exponential function relationship. The slope of the rate increase is dynamically adjusted according to the real-time monitored peel stress to keep the peel stress below 10 GPa.

[0040] Among them, the flow velocity of the stratified controllable airflow field is controlled in conjunction with the lifting stage; in the initial low-speed lifting stage, the flow velocity of the stratified airflow field is controlled at 0.15 m / s; after entering the accelerated lifting stage, the flow velocity of the stratified airflow field is synchronously increased to 0.9 m / s, and the airflow direction of the stratified airflow field is consistent with the direction of the gradient electric field.

[0041] S5. Catalyst removal and post-treatment: After the carbon nanotube array is completely detached from the substrate, the residual catalyst is removed in an oxidizing atmosphere, and then the obtained array is cleaned and dried.

[0042] The oxidizing atmosphere is an inert mixed gas containing 5.5% oxygen by volume, the treatment temperature is 300°C, and the treatment time is 45 min.

[0043] Example 2 This embodiment provides a substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays. The specific steps are as follows, wherein all process parameters involved are taken as the minimum values ​​of the corresponding ranges in the claims: S1. Substrate pretreatment and catalyst loading: The quartz substrate is cleaned and dried, and a zinc-based MOF-derived catalyst nanoparticle layer is loaded on its surface, and a polymer transition layer is formed on the surface of the catalyst layer. The polymer transition layer is a polyimide layer with a thickness of 30 nm.

[0044] S2. Initialization of the reaction system: The substrate loaded with the catalyst and transition layer is placed in the reaction environment and a protective gas is introduced into it while heating to the growth temperature. The reaction environment can provide an alternating magnetic field, a gradient electric field, a near-infrared photothermal field and a layered controllable gas flow field, and can monitor the growth process online with laser Raman spectroscopy. The growth temperature was 700°C; the heating rate was 8°C / min.

[0045] S3. Multi-field synergistic growth and real-time control: Under the synergistic effect of alternating magnetic field, gradient electric field and near-infrared photothermal field, carbon source gas is pulsed into the reaction environment to grow carbon nanotube arrays; during this process, the Raman signal of the array is monitored in real time using laser Raman spectroscopy, and based on the G / D ratio and D peak intensity in the Raman signal, closed-loop feedback control is implemented on the frequency of alternating magnetic field, intensity of gradient electric field, power of near-infrared photothermal field and pulse frequency of carbon source gas; Specifically, the closed-loop feedback regulation is as follows: when the G / D ratio of the Raman spectral signal is lower than the first threshold, the intensity of the gradient electric field is increased and the power of the near-infrared photothermal field is reduced; when the D peak intensity of the Raman spectral signal is higher than the second threshold, the frequency of the alternating magnetic field is adjusted and the pulse frequency of the carbon source gas is increased. The first threshold is 10; the adjustment amount for increasing the gradient electric field strength is 0.5 kV / cm, and the adjustment amount for decreasing the near-infrared photothermal power is 50 mW / cm. 2 The second threshold is 130% of the D peak intensity at the start of growth; the adjustment amount of the alternating magnetic field frequency is 5kHz, and the adjustment amount of the carbon source gas pulse frequency is 1Hz.

[0046] The alternating magnetic field has a frequency of 1 kHz and an intensity of 10 mT; the gradient electric field has an intensity of 1 kV / cm; and the near-infrared photothermal field has a power of 100 mW / cm. 2 .

[0047] The carbon source gas is a mixture of methane and acetylene, with a volume ratio of methane to acetylene of 1:1. The supply pulse frequency is 1 Hz and the pulse width is 0.1 s.

[0048] S4. Gradient stress release lifting: After the carbon nanotube array grows to the predetermined height, the lifting operation is initiated, and the layered controllable airflow field is used simultaneously to assist in the peeling of the array root. The lifting operation includes an initial low-speed lifting stage and a subsequent accelerated lifting stage. The trigger condition for switching from the initial low-speed lifting stage to the accelerated lifting stage is that the lifting distance reaches a preset threshold. The initial low-speed lifting stage has a lifting rate of 0.01 mm / s and a preset lifting distance threshold of 10 μm. The lifting rate in the accelerated lifting stage is increased to 0.5 mm / s. In the accelerated lifting stage, the lifting rate increases from the initial low-speed value to the target high-speed value according to an exponential function relationship. The slope of the rate increase is dynamically adjusted according to the real-time monitored peel stress to keep the peel stress below 10 GPa.

[0049] Among them, the flow velocity of the stratified controllable airflow field is controlled in conjunction with the lifting stage; in the initial low-speed lifting stage, the flow velocity of the stratified airflow field is controlled at 0.1 m / s; after entering the accelerated lifting stage, the flow velocity of the stratified airflow field is synchronously increased to 0.6 m / s, and the airflow direction of the stratified airflow field is consistent with the direction of the gradient electric field.

[0050] S5. Catalyst removal and post-treatment: After the carbon nanotube array is completely detached from the substrate, the residual catalyst is removed in an oxidizing atmosphere, and then the obtained array is cleaned and dried.

[0051] The oxidizing atmosphere is an inert mixed gas containing 3% oxygen by volume, the treatment temperature is 250°C, and the treatment time is 30 min.

[0052] Example 3 This embodiment provides a substrate growth and pulling method for ultralong oligowalled carbon nanotube arrays. The specific steps are as follows, wherein all process parameters involved are taken as the maximum values ​​of the corresponding ranges in the claims: S1. Substrate pretreatment and catalyst loading: The silicon substrate is cleaned and dried, and a zinc-based MOF-derived catalyst nanoparticle layer is loaded on its surface, and a polymer transition layer is formed on the surface of the catalyst layer. The polymer transition layer is a polyimide layer with a thickness of 80 nm.

[0053] S2. Initialization of the reaction system: The substrate loaded with the catalyst and transition layer is placed in the reaction environment and a protective gas is introduced into it while heating to the growth temperature. The reaction environment can provide an alternating magnetic field, a gradient electric field, a near-infrared photothermal field and a layered controllable gas flow field, and can monitor the growth process online with laser Raman spectroscopy. The growth temperature was 900°C; the heating rate was 12°C / min.

[0054] S3. Multi-field synergistic growth and real-time control: Under the synergistic effect of alternating magnetic field, gradient electric field and near-infrared photothermal field, carbon source gas is pulsed into the reaction environment to grow carbon nanotube arrays; during this process, the Raman signal of the array is monitored in real time using laser Raman spectroscopy, and based on the G / D ratio and D peak intensity in the Raman signal, closed-loop feedback control is implemented on the frequency of alternating magnetic field, intensity of gradient electric field, power of near-infrared photothermal field and pulse frequency of carbon source gas; Specifically, the closed-loop feedback regulation is as follows: when the G / D ratio of the Raman spectral signal is lower than the first threshold, the intensity of the gradient electric field is increased and the power of the near-infrared photothermal field is reduced; when the D peak intensity of the Raman spectral signal is higher than the second threshold, the frequency of the alternating magnetic field is adjusted and the pulse frequency of the carbon source gas is increased. The first threshold is 10; the adjustment amount for increasing the gradient electric field strength is 1.0 kV / cm, and the adjustment amount for decreasing the near-infrared photothermal power is 100 mW / cm. 2 The second threshold is 130% of the D peak intensity at the start of growth; the adjustment amount of the alternating magnetic field frequency is 10kHz, and the adjustment amount of the carbon source gas pulse frequency is 2Hz.

[0055] The alternating magnetic field has a frequency of 50 kHz and an intensity of 50 mT; the gradient electric field has an intensity of 5 kV / cm; and the near-infrared photothermal field has a power of 300 mW / cm. 2 .

[0056] The carbon source gas is a mixture of methane and acetylene, with a volume ratio of methane to acetylene of 3:1. The supply pulse frequency is 5Hz and the pulse width is 0.5s.

[0057] S4. Gradient stress release lifting: After the carbon nanotube array grows to the predetermined height, the lifting operation is initiated, and the layered controllable airflow field is used simultaneously to assist in the peeling of the array root. The lifting operation includes an initial low-speed lifting stage and a subsequent accelerated lifting stage. The trigger condition for switching from the initial low-speed lifting stage to the accelerated lifting stage is that the lifting distance reaches a preset threshold. The initial low-speed lifting stage has a lifting rate of 0.05 mm / s and a preset lifting distance threshold of 50 μm. The lifting rate in the accelerated lifting stage is increased to 1.0 mm / s. In the accelerated lifting stage, the lifting rate increases from the initial low-speed value to the target high-speed value according to an exponential function relationship. The slope of the rate increase is dynamically adjusted according to the real-time monitored peel stress to keep the peel stress below 10 GPa.

[0058] Among them, the flow velocity of the stratified controllable airflow field is controlled in conjunction with the lifting stage; in the initial low-speed lifting stage, the flow velocity of the stratified airflow field is controlled at 0.2 m / s; after entering the accelerated lifting stage, the flow velocity of the stratified airflow field is synchronously increased to 1.2 m / s, and the airflow direction of the stratified airflow field is consistent with the direction of the gradient electric field.

[0059] S5. Catalyst removal and post-treatment: After the carbon nanotube array is completely detached from the substrate, the residual catalyst is removed in an oxidizing atmosphere, and then the obtained array is cleaned and dried.

[0060] The oxidizing atmosphere is an inert mixed gas containing 8% oxygen by volume, the treatment temperature is 350°C, and the treatment time is 60 min.

[0061] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step S1, the graded porous fly ash carrier is not subjected to aminosilanization pretreatment, and the unmodified carrier is used directly for subsequent loading; the remaining methods and steps are exactly the same as in Example 1.

[0062] Comparative Example 2 The only difference between this comparative example and Example 1 is that, in step S4, the hydrothermal method is not used to grow two-dimensional nanosheets in situ. Instead, commercially available lanthanum oxide, cerium oxide, and zirconium oxide nanopowders are mixed by ball milling and then impregnated and loaded. The remaining methods and steps are exactly the same as in Example 1.

[0063] Comparative Example 3 The only difference between this comparative example and Example 1 is that: in step S2, no alternating magnetic field and gradient electric field are provided, only the near-infrared photothermal field is retained, and in step S3, no online monitoring of laser Raman spectroscopy and closed-loop feedback adjustment are performed, while the carbon source gas pulse frequency and near-infrared photothermal field power remain fixed; the rest of the method steps are exactly the same as in Example 1.

[0064] Comparative Example 4 The only difference between this comparative example and Example 1 is that in step S3, online monitoring and closed-loop feedback adjustment of laser Raman spectroscopy are not performed. The alternating magnetic field frequency, gradient electric field intensity, near-infrared photothermal field power, and carbon source pulse frequency are all maintained at their initial set values ​​and are not dynamically adjusted. The rest of the methods and steps are exactly the same as in Example 1.

[0065] Comparative Example 5 The only difference between this comparative example and Example 1 is that in step S5, the fullerene carbon layer vapor deposition post-processing is not performed; the remaining method steps are exactly the same as in Example 1.

[0066] Comparative Example 6 The only difference between this comparative example and Example 1 is that the catalyst was prepared using a conventional impregnation method. Specifically, all active metal components were prepared into a single mixed solution in proportion, and then loaded onto a commercially available porous alumina support without amino modification using an equal-volume impregnation method. The catalyst was then obtained by drying and calcination.

[0067] Test Item 1: Aspect Ratio and Growth Uniformity Test of Carbon Nanotube Arrays Referring to GB / T30544.13-2014 "Nanotechnology Terminology Part 13: Carbon Nanotubes" and GB / T20307-2021 "Scanning Electron Microscopy Characterization Methods for Nanoscale Carbon Materials", the carbon nanotube arrays prepared in all Examples 1-3 and Comparative Examples 1-6 were tested.

[0068] Five different sites were selected from the middle and edge regions of each sample. The overall morphology of the array was observed using field emission scanning electron microscopy at 500x magnification, and the length and diameter of individual carbon nanotubes were measured at 10,000x magnification. Fifty nanotubes were randomly selected from each site, and the average aspect ratio and coefficient of variation were calculated. During the test, the presence of breakage, bending, or aggregation of the array was recorded. By comparing the aspect ratio values ​​and the magnitude of the coefficient of variation, the effects of gradient stress release lifting strategy, stratified airflow assistance, and polymer transition layer on the uniformity of array growth length and diameter, and structural integrity were evaluated.

[0069] Test Item 2: Crystallization Quality and Defect Density Test of Carbon Nanotubes According to GB / T30544.10-2014 "Nanotechnology Terminology Part 10: Characterization Methods" and GB / T36065-2018 "Characterization Method of Carbon Nanotubes by Raman Spectroscopy", the carbon nanotube arrays prepared in all Examples 1-3 and Comparative Examples 1-6 were tested using a laser Raman spectrometer.

[0070] The test conditions were: excitation wavelength 532nm, laser power 5mW, and scanning range 1000-2000cm⁻ 1The scanning time was 10 seconds, and three different test points were selected for each sample. The intensity ratio of the G peak to the D peak was obtained through spectral analysis, and the average value of the three test points was calculated. A higher G / D ratio indicates better crystallinity and lower defect density of carbon nanotubes. By comparing the G / D ratios of each embodiment with the comparative example, the effects of the multi-field synergistic growth system and laser Raman closed-loop feedback control on improving the crystallinity integrity and reducing the defect rate of carbon nanotubes were verified.

[0071] Test Item 3: Mechanical Stability and Interfacial Bonding Reliability Test of Carbon Nanotube Arrays Referring to GB / T1447-2005 "Test Method for Tensile Properties of Fiber Reinforced Plastics" and GB / T39230-2020 "Mechanical Properties Testing of Nanomaterials - Atomic Force Microscopy", the carbon nanotube arrays prepared in all Examples 1-3 and Comparative Examples 1-6 were tested using a micro tensile testing machine combined with an atomic force microscope.

[0072] After the carbon nanotube array was peeled from the substrate, it was cut into strips of 20 mm × 5 mm with a clamping spacing of 10 mm and a stretching rate of 0.01 mm / s. The maximum tensile force and elongation at break were recorded, and the tensile strength and elastic modulus were calculated. Five parallel samples were tested for each sample, and the average value was taken. Simultaneously, AFM was used to observe the morphology of the fracture cross-section after stretching to analyze the fracture mode and whether array detachment occurred. By comparing the tensile strength, elastic modulus, and fracture morphology, the effect of the polymer transition layer on improving the interfacial bonding between the catalyst and the substrate, and the optimization effect of the gradient stress release lifting strategy on the mechanical stability of the array were evaluated.

[0073] The morphology and structural performance test results of the carbon nanotube array are shown in Table 1.

[0074] Table 1: Sample number <![CDATA[Average major axis ratio (×10 4 )]]> Aspect Ratio Coefficient of Variation (%) Raman G / D ratio Example 1 8.5±0.3 8.2 25.6±1.5 Example 2 7.1±0.4 9.8 22.3±1.8 Example 3 7.8±0.5 10.5 23.8±2.0 Comparative Example 1 5.2±0.6 15.3 18.5±2.2 Comparative Example 2 4.8±0.7 16.8 17.2±2.5 Comparative Example 3 3.5±0.8 20.1 12.4±2.8 Comparative Example 4 6.0±0.5 18.5 16.8±2.4 Comparative Example 5 7.9±0.4 9.0 19.5±1.9 Comparative Example 6 2.1±1.0 25.0 8.5±3.0 The mechanical properties of the carbon nanotube array are shown in Table 2.

[0075] Table 2: Sample number Tensile strength (MPa) Elastic modulus (GPa) Elongation at break (%) Example 1 1520±85 58±3 4.2±0.3 Example 2 1350±95 52±4 3.8±0.4 Example 3 1420±90 55±3 4.0±0.3 Comparative Example 1 680±120 28±5 1.5±0.5 Comparative Example 2 -- -- -- Comparative Example 3 450±150 20±6 0.8±0.6 Comparative Example 4 1050±100 45±4 2.5±0.4 Comparative Example 5 980±110 40±5 2.0±0.5 Comparative Example 6 -- -- -- Note: "--" indicates that effective mechanical testing could not be performed because the sample could not form an effective self-supporting array or meet the test requirements.

[0076] Supplementary notes for table data: 1. Structural integrity performance: Examples 1 and 3: No breakage or aggregation; the carbon nanotube array has good orientation and is arranged in a regular manner. Example 2: No fractures, a small number of carbon nanotubes with slight bending, and good overall array orientation; Comparative Example 1: No obvious breakage, slight aggregation in the edge area; Comparative Example 2: A small number of fractures exist, and the aggregation at the edge areas is more obvious; Comparative Example 3: Multiple fractures, severe aggregation, poor array orientation, and chaotic overall morphology; Comparative Example 4: A small number of fractures exist, and localized aggregation occurs; Comparative Example 5: No breaks, no aggregation, and good array orientation; Comparative Example 6: Some carbon nanotubes were broken, and the edges showed obvious aggregation.

[0077] 2. Fracture morphology: Examples 1 and 3: Tough fracture, with a smooth fracture cross section and no array-like detachment; Example 2: Tough fracture, with slight peeling in localized areas; Comparative Example 1: Tough-brittle mixed fracture with localized array detachment; Comparative Examples 2 and 6: Brittle fracture, with some carbon nanotube arrays detached; Comparative Example 3: Brittle fracture, with a large number of arrays falling off, and an irregular fracture cross section; Comparative Example 4: Brittle fracture, with localized array detachment; Comparative Example 5: Tough fracture, no array detachment.

[0078] As can be seen from Examples 1-3 and Comparative Example 1, and in conjunction with Tables 1 and 2, the absence of a polymer transition layer between the substrate and the catalyst layer significantly weakens the interfacial bonding strength. During the subsequent pulling process, the interface becomes a weak point for stress concentration and failure, causing the carbon nanotube array to debond or fracture prematurely before reaching its intrinsic strength. This not only directly reduces the measured macroscopic tensile strength and modulus, but also affects the uniformity and consistency of array growth due to the irregular release of interfacial stress, resulting in an increased aspect ratio coefficient of variation.

[0079] As can be seen from Examples 1-3 and Comparative Example 2, and in conjunction with Table 1, it is difficult to obtain a catalyst layer with uniform size and good dispersion of nanoparticles using catalyst preparation methods different from those derived from zinc-based MOFs. The size and distribution of catalyst particles directly affect the uniformity of carbon nanotube nucleation and growth. Non-preferred catalyst preparation methods lead to uneven distribution of active sites, which in turn causes fluctuations in the growth rate and diameter of carbon nanotubes. Ultimately, this results in a low overall aspect ratio of the array, with significant differences in aspect ratio at different locations, leading to decreased uniformity.

[0080] As can be seen from Examples 1-3 and Comparative Example 3, and in conjunction with Tables 1 and 2, the lack of a synergistic effect between the alternating magnetic field and gradient electric field during growth, coupled with the absence of feedback regulation based on real-time monitoring, prevents dynamic control of the catalyst's active state and directional guidance of the carbon atom deposition path. This results in a non-optimal, random growth process for the carbon nanotubes, with poor carbon atom arrangement order, significantly increased defect density, and severely degraded array crystallinity. Furthermore, the uneven distribution of internal stress during growth directly impairs the array's structural integrity and mechanical load-bearing capacity.

[0081] As can be seen from Examples 1-3 and Comparative Example 4, and in conjunction with Tables 1 and 2, in the case of a multiphysics growth environment but lacking closed-loop feedback regulation via laser Raman spectroscopy, the growth parameters cannot be dynamically optimized based on the real-time crystallization state of the carbon nanotubes. Fixed parameters cannot adapt to the dynamic changes that may occur during growth, causing some growth stages or regions to deviate from optimal conditions, thereby introducing additional structural defects and affecting the uniformity of the array's internal structure. This means that while the crystallinity and mechanical properties of the final product are better than in the case of no field regulation, they still fail to reach the level of the examples implementing closed-loop feedback regulation.

[0082] As can be seen from Examples 1-3 and Comparative Example 5, and in conjunction with Tables 1 and 2, the carbon nanotube arrays prepared with complete growth and pulling processes but lacking a polymer transition layer are similar in morphology and structure to those in the examples, indicating that their intrinsic growth process is maintained. However, due to the lack of an effective stress buffer and strong bonding interface between the substrate and the catalyst layer, stress cannot be effectively transferred from the substrate to the entire array under external tensile loads, leading to premature interface failure. This results in a significant decrease in the overall mechanical properties of the array, especially tensile strength and modulus, despite the relatively good quality of the carbon nanotubes themselves.

[0083] As can be seen from Examples 1-3 and Comparative Example 6, and in conjunction with Table 1, the traditional impregnation method for catalyst preparation cannot achieve high dispersion, small size, and uniform distribution of catalyst nanoparticles on the substrate. This catalyst precursor treatment method easily leads to the aggregation of active components, forming excessively large or irregular catalyst particles. As a result, the nucleation and vertical growth of large-area, uniform carbon nanotubes are hindered, making it difficult to form continuous, ordered ultra-long arrays. The final product tends to be carbon nanotube aggregates, failing to meet the basic requirements for array structures.

[0084] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for growing and pulling substrates of ultralong oligowalled carbon nanotube arrays, characterized in that: Includes the following steps: S1. Substrate pretreatment and catalyst loading: The silicon-based or quartz substrate is cleaned and dried, and a zinc-based MOF-derived catalyst nanoparticle layer is loaded on its surface, and a polymer transition layer is formed on the surface of the catalyst layer. S2. Initialization of the reaction system: The substrate loaded with the catalyst and transition layer is placed in the reaction environment and a protective gas is introduced into it while heating to the growth temperature; the reaction environment can provide an alternating magnetic field, a gradient electric field, a near-infrared photothermal field and a layered controllable gas flow field, and can perform online monitoring of the growth process using laser Raman spectroscopy. S3. Multi-field synergistic growth and real-time control: Under the synergistic effect of the alternating magnetic field, gradient electric field, and near-infrared photothermal field, carbon source gas is pulsedly introduced into the reaction environment to grow carbon nanotube arrays; during this process, the Raman signal of the array is monitored in real time using laser Raman spectroscopy, and based on the G / D ratio and D peak intensity in the Raman signal, closed-loop feedback control is implemented on the frequency of the alternating magnetic field, the intensity of the gradient electric field, the power of the near-infrared photothermal field, and the pulse frequency of the carbon source gas; S4. Gradient stress release lifting: After the carbon nanotube array grows to the predetermined height, the lifting operation is initiated, and the layered controllable airflow field is used simultaneously to assist in the peeling of the array root. The lifting operation includes an initial low-speed lifting stage and a subsequent accelerated lifting stage. The trigger condition for switching from the initial low-speed lifting stage to the accelerated lifting stage is that the lifting distance reaches a preset threshold. S5. Catalyst removal and post-treatment: After the carbon nanotube array is completely detached from the substrate, the residual catalyst is removed in an oxidizing atmosphere, and then the obtained array is cleaned and dried.

2. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S1, the polymer transition layer is a polyimide layer with a thickness of 30-80 nm.

3. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S2, the growth temperature is 700-900°C; the heating rate is 8-12°C / min.

4. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S3, the closed-loop feedback adjustment specifically involves: when the G / D ratio of the Raman spectral signal is lower than the first threshold, increasing the intensity of the gradient electric field and decreasing the power of the near-infrared photothermal field; when the D peak intensity of the Raman spectral signal is higher than the second threshold, adjusting the frequency of the alternating magnetic field and increasing the pulse frequency of the carbon source gas.

5. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 4, characterized in that: The first threshold is 10; the adjustment amount for increasing the gradient electric field strength is 0.5-1.0 kV / cm, and the adjustment amount for decreasing the near-infrared photothermal power is 50-100 mW / cm. 2 The second threshold is 130% of the D peak intensity at the start of growth; the adjustment amount of the alternating magnetic field frequency is 5-10kHz, and the adjustment amount of the carbon source gas pulse frequency is 1-2Hz.

6. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S3, the frequency of the alternating magnetic field is 1-50 kHz, and the intensity is 10-50 mT; the intensity of the gradient electric field is 1-5 kV / cm; and the power of the near-infrared photothermal field is 100-300 mW / cm. 2 .

7. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S3, the carbon source gas is a mixture of methane and acetylene, wherein the volume ratio of methane to acetylene is 1:1 to 3:1, the supply pulse frequency is 1-5Hz, and the pulse width is 0.1-0.5s.

8. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S4, the lifting rate in the initial low-speed lifting stage is 0.01-0.05 mm / s, the preset lifting distance threshold is 10-50 μm, and the lifting rate in the accelerated lifting stage is increased to 0.5-1.0 mm / s. In the accelerated lifting stage, the lifting rate increases from the initial low-speed value to the target high-speed value according to an exponential function relationship, and the slope of the rate increase is dynamically adjusted according to the peeling stress monitored in real time, so that the peeling stress is maintained below 10 GPa.

9. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: The flow velocity of the layered controllable airflow field is controlled in coordination with the lifting stage; in the initial low-speed lifting stage, the flow velocity of the layered airflow field is controlled at 0.1-0.2 m / s; after entering the accelerated lifting stage, the flow velocity of the layered airflow field is synchronously increased to 0.6-1.2 m / s, and the airflow direction of the layered airflow field is consistent with the direction of the gradient electric field.

10. The substrate growth and pulling method for an ultralong oligowalled carbon nanotube array according to claim 1, characterized in that: In step S5, the oxidizing atmosphere is an inert mixed gas containing 3% to 8% oxygen by volume, the treatment temperature is 250-350°C, and the treatment time is 30-60 min.

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