CN112441574A - Method for controllable growth of metallic single-walled carbon nanotube through substrate design - Google Patents

Abstract

The invention relates to the field of controllable preparation of metallic single-walled carbon nanotubes, in particular to a method for controllably growing metallic single-walled carbon nanotubes through substrate design. Using spinel as the substrate, metal oxide nanoclusters with uniform size were prepared by the self-assembly method of block copolymer; the size, structure and high temperature stability of the catalyst nanoparticles were controlled by the solid solution and pinning effect of the spinel substrate. Combined with the effect of spinel substrate on the growth rate of single-walled carbon nanotubes with different conductive properties, the selective growth of metallic single-walled carbon nanotubes is achieved. The prepared metallic single-walled carbon nanotubes have a diameter of 1.1±0.2 nm and a content of 75-85 percent. The invention realizes the direct and controllable growth of metallic single-walled carbon nanotubes with narrow diameter distribution through substrate design and selection, and lays a material foundation for promoting the application of metallic single-walled carbon nanotubes.

Description

A method for controllable growth of metallic single-walled carbon nanotubes through substrate design

technical field

The invention relates to the field of controllable preparation of metallic single-walled carbon nanotubes, in particular to a method for controllably growing metallic single-walled carbon nanotubes through substrate design.

Background technique

Single-walled carbon nanotubes can be metallic or semiconducting due to their different chiral angles and diameters. Metallic single-walled carbon nanotubes have quantum transport effects and can be used as flexible electrode materials and interconnecting wires for future nanoelectronic devices. However, commonly prepared SWCNT samples are a mixture of metallic and semiconducting carbon tubes. How to obtain high-purity metallic single-walled carbon nanotubes is the key to promote their practical application. The content of metallic single-walled carbon nanotubes in common samples is only about 1/3, and its chemical activity is higher than that of semiconducting single-walled carbon nanotubes, so it is more difficult to selectively prepare metallic single-walled carbon nanotubes. At present, representative works on the selective preparation of metallic SWNTs are as follows: (1) Controlling the surface morphology of the catalyst during nucleation to preferentially grow metallic SWNTs (Reference 1: Harutyunyan A.R.; Cheng, G. , Sumanasekera, G.U.et.al.Science, 2009, 326, 116); (2) Hydrogen selective etchant for small-diameter semiconducting carbon nanotubes to prepare metal-enriched single-walled carbon nanotubes (Document 2: Hou, P.X.; Li, W.S.; Liu C. et al. ACS Nano 2013, 8, 7156); (3) Growth of metallic carbon nanotubes by controlling the specific crystal face of the catalyst to match the structure of single-walled carbon nanotubes (Literature 3: Yang , F.; Wang, X.; Li, Y. et al. Nature 2014, 510, 7506); (4) Metallic carbon nanotubes were prepared by controlling the symmetry matching between the catalyst and carbon nanotubes (Literature 4: Zhang, S.C.; Kang, L.X.; Zhang, J. et al. Nature 2017, 543, 7644). (5) Controlling the size and oxygen content of high melting point non-metal oxide catalyst nanoparticles to realize the direct growth of narrow diameter distribution and metallic single-walled carbon nanotubes (Literature 5: Zhang, L.L.; Sun, D.M.; Liu, C. et al. Advanced Materials, 2017, 29, 32).

However, there are still many problems in the preparation of metallic single-walled carbon nanotubes at present: (1) The catalyst has poor thermal stability at high temperature on the surface of the silicon substrate that interacts with it less, resulting in poor uniformity of the diameter of carbon nanotubes; (2) It is difficult to control the crystal plane structure and symmetry of the catalyst, resulting in poor repeatability; (3) The mechanism of controllable growth of metallic SWNTs is still unclear; (4) The substrate directly affects the growth of carbon nanotubes. Thermodynamic and kinetic factors are unclear.

Therefore, the main problem currently facing is: how to expand the difference between the nucleation and growth of metallic and semiconducting single-walled carbon nanotubes on the basis of understanding the controllable growth mechanism, and develop a simple and controllable growth with narrow diameter distribution, A method for metallic single-walled carbon nanotubes.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a simple and controllable method for the controllable growth of metallic single-walled carbon nanotubes through substrate design. The controlled growth has laid a material foundation for promoting the application of metallic single-walled carbon nanotubes.

The technical scheme of the present invention is:

A method for controllable growth of metallic single-walled carbon nanotubes through substrate design, selects the magnesium-aluminum spinel single crystal that generates lattice thermal vibration at high temperature and uses phonons as the main heat conduction mode as the substrate, and utilizes the substrate and catalyst. The strong interaction of the catalyst can control the size, structure and high temperature stability of the catalyst; the energy fluctuation caused by the lattice thermal vibration of the substrate at high temperature can be used to control the energy supply required for the growth of carbon nanotubes, and realize the metal single-walled carbon nanotubes and carbon nanotubes. Maximizing the difference in growth rate of semiconducting single-wall carbon nanotubes, selectively growing metallic single-wall carbon nanotubes.

In the method for the controllable growth of metallic single-walled carbon nanotubes through substrate design, the substrate needs to be heat-treated in oxidizing and reducing atmospheres to improve its crystallinity and obtain atomic steps suitable for the growth of carbon nanotubes; oxygen plasma is applied to the substrate. body treatment to improve the wettability between the catalyst precursor solution and the substrate surface.

In the method for the controllable growth of metallic single-walled carbon nanotubes through substrate design, the catalyst is a mixture of block copolymer micelles chemically adsorbed cations prepared by self-assembly of block copolymers, which is uniformly covered by spin coating to form a film. The surface of the substrate is treated with oxygen plasma to remove the block copolymer on the surface to obtain monodisperse metal oxide nanoclusters.

In the method for the controllable growth of metallic single-walled carbon nanotubes through substrate design, the metal oxide nanoclusters are sequentially subjected to high-temperature oxidative heat treatment at 400-600° C. for 1-5 minutes in an air atmosphere, and 700° C. in a hydrogen/argon mixed atmosphere. ～850℃ reduction heat treatment for 1～6min, obtain metal nanoparticles with a diameter distribution of 1～3nm; by adjusting the reduction temperature of heat treatment, the solid solution of the catalyst and the substrate is effectively achieved, the high temperature thermal stability of the catalyst is improved, and the metal nanoparticles are Pinning on the spinel surface improves the thermal stability of metal nanoparticle catalysts.

In the method for controllable growth of metallic single-walled carbon nanotubes through substrate design, in a hydrogen/argon mixed atmosphere, the flow rate of hydrogen gas is 5-10 sccm, and the flow rate of argon gas is 50-100 sccm.

The described method for controllable growth of metallic single-walled carbon nanotubes through substrate design, under the condition of chemical vapor deposition of critical nucleation growth, through the regulation of the lattice thermal vibration and phonon thermal conductivity of the substrate, to expand different electrical conductivity The difference in the energy required for the growth of the property carbon nanotubes makes the average length of the grown metallic carbon nanotubes much larger than that of the semiconducting carbon nanotubes, thereby realizing the controllable growth of metallic single-walled carbon nanotubes.

In the method for the controllable growth of metallic single-walled carbon nanotubes through substrate design, the chemical vapor deposition conditions are: growth temperature of 755-775° C., carbon source flow rate of 5-20 sccm, hydrogen flow rate of 0.5-5 sccm, and argon carrier gas flow rate 40～100sccm, the total gas flow is 50～125sccm, and the growth time is 5～15min.

In the method for controllable growth of metallic single-walled carbon nanotubes through substrate design, the length of the grown metallic single-walled carbon nanotubes is 2-10 μm, the diameter is concentrated at 1.1±0.2 nm, and the number and content of metallic single-walled carbon nanotubes are 75 to 85%.

The design idea of the present invention is:

The present invention proposes to select spinel with a melting point of 2130° C., a face-centered cubic Fd3m structure, and a magnesium-aluminum structure characteristic of lattice thermal vibration and cation exchange at high temperature as the substrate for carbon nanotube growth, and using spinel single crystal The strong interaction between the solid solution and pinning of the substrate and the catalyst nanoparticles can effectively avoid the high temperature agglomeration of the catalyst, thereby controlling the catalyst size, structure and high temperature stability; at the same time, using the lattice thermal vibration of the spinel substrate at high temperature. The energy fluctuation is used to regulate the energy supply required for the growth of carbon nanotubes, to maximize the difference in the growth rate of metallic SWNTs and semiconducting SWNTs, which in turn affects the growth of SWNTs with different conductivity properties. Under the critical nucleation growth conditions, the growth of metallic single-walled carbon nanotubes is regulated, and finally the narrow diameter distribution and high-quality metallic single-walled carbon nanotubes are obtained.

The advantages and beneficial effects of the present invention are:

(1) The present invention realizes the control of nanoparticle size, structure, chemical state and high temperature thermal stability through the strong interaction between the substrate and the catalyst, and solves the problem of high temperature agglomeration of the catalyst;

(2) The present invention generates energy fluctuations on the surface of the substrate through the high-temperature lattice thermal vibration of the substrate, which affects the energy supply required for the growth of carbon nanotubes, thereby increasing metallic single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes. difference in growth rate;

(3) The present invention utilizes a simple and universal method to directly grow high-purity metallic-enriched single-walled carbon nanotubes by using cobalt for efficiently growing carbon nanotubes as a catalyst;

(4) the present invention realizes the diameter control of metallic single-walled carbon nanotubes;

(5) The present invention clarifies the main factors affecting the growth of metallic single-walled carbon nanotubes, and provides a new idea for regulating the growth of carbon nanotubes.

Description of drawings

Figure 1. Flow chart of the self-assembly of block copolymers to prepare catalyst nanoparticles.

Figure 2. Schematic diagram of the principle of growing narrow-diameter distribution metallic single-walled carbon nanotubes on cobalt-spinel-based structures.

Fig. 3. Surface AFM photo of (110) spinel substrate after heat treatment (a) and its atomic step height statistics (b).

Fig. 4. Raman characteristic peaks of (110) surface spinel substrate with different heat treatments, 2～4h at 400～500℃, 2～4h at 600～700℃, and 2～4h at 800～900℃.

Figure 5. The (110) face of spinel: (a) TEM image of catalyst nanoparticle morphology, (b) particle size statistical distribution of nanoparticle, (c) scanning transmission electron imaging image of nanoparticle.

Figure 6. Growth temperature of 765 °C, carbon nanotubes on spinel (110) surface: (a) SEM photo; (b) TEM photo; (c) diameter statistics, the abscissa Diameter represents the diameter (nm ), and the ordinate Counts represents counts.

Figure 7. Raman characterization of carbon nanotubes on spinel (110) surface at a growth temperature of 765°C: (a) breathing mode excited by 633 nm laser; (b) breathing mode excited by 532 nm laser; (c) 785 nm Breathing modes excited by wavelength laser; (d) D and G modes excited by 633 nm laser.

Figure 8. Statistics of chirality and growth rate of carbon nanotubes grown on spinel (110) surface at a growth temperature of 765°C: (a) Raman laser scan at 633 nm wavelength; (b) Raman laser scan at 532 nm wavelength ; (c) Statistics of the corresponding growth lengths of carbon nanotubes with different conductivity properties.

Figure 9. Morphology and structural characterization of cobalt catalyst particles prepared on the surface of silicon wafers. (a) AFM photo of nanoparticles; (b) TEM photo of nanoparticles; (c) TEM statistical particle size distribution histogram; (d) SEM image of single-walled carbon nanotubes grown on the surface of silicon wafers photo.

Figure 10. Radial breathing modes of multi-wavelength Raman spectra of single-walled carbon nanotubes grown on silicon wafers: (a) 532 nm wavelength laser; (b) 633 nm wavelength laser; (c) 785 nm wavelength laser; (d) 633 nm laser Excited D and G modes.

Fig. 11. SEM images of single-walled carbon nanotubes grown on spinel (110) surfaces at a growth temperature of 825°C and the corresponding radial breathing modes of multi-wavelength Raman spectroscopy: (a) SEM images; (b) 532nm wavelength laser; (c) 633nm wavelength laser.

Detailed ways

In the specific implementation process, the present invention uses spinel as the substrate, and adopts the block copolymer self-assembly method to prepare small and uniform metal oxide nanoclusters; The size, structure and high temperature stability are regulated by pinning. Combined with the effect of spinel substrate on the growth rate of single-wall carbon nanotubes with different conductive properties, chemical vapor deposition method is used to achieve selective growth of metallic single-wall carbon nanotubes.

As shown in Figure 2, the controllable growth mechanism of metallic single-walled carbon nanotubes, the spinel substrate has strong interactions with the catalyst cobalt due to the atomic steps and surface exposed atoms on the substrate surface, which can effectively inhibit catalyst agglomeration, high temperature Oswald Maturation, high temperature melting of nanoparticles, etc., so as to stabilize the size of the carbon cap in the nucleation stage and control the diameter of the grown single-walled carbon nanotubes. According to the ensemble theory of statistical thermodynamics, the substrate can be regarded as an ideal heat source, which can exchange energy with nanoparticles, molecules containing hydrocarbons, and carbon nanotubes, which can be idealized as a canonical ensemble. Due to the lattice thermal vibration of the substrate and the heat conduction of phonons on the substrate surface, there are energy fluctuations. The energy fluctuation of the canonical ensemble is shown in formula (1). The magnitude of energy fluctuation is inversely proportional to the number of particles. Therefore, the critical nucleation growth conditions of low temperature, low carbon source, low hydrogen and low flow rate are used. The difference in energy supply enables the carbon nanotubes with specific chirality to overcome the potential barrier and take the lead to nucleate into carbon caps;

为系统能量在一切可能微观状态上的平均值，单位J；E为系统具体在某一个状态的能量，单位为J；E与

的相对偏差为

偏差的平方的平均值

称为能量涨落，其开方后与平均能量的比值

为能量的相对涨落；N为系统的总粒子数，单位为mol。in,

is the average value of the system energy in all possible microstates, in J; E is the energy of the system in a specific state, in J; E and

The relative deviation of

mean of squared deviations

called the energy fluctuation, the ratio of its square root to the average energy

is the relative fluctuation of energy; N is the total number of particles in the system, the unit is mol.

In terms of kinetics, on the basis of obtaining uniform carbon caps, combined with the thermal vibration of the substrate lattice, growth energy and carbon source replenishment differences, the difference in growth rates of metallic and semiconducting single-walled carbon nanotubes is maximized. The carbon atoms are slowly diffused and assembled on the catalyst surface under critical conditions, and finally the length difference between the metallic carbon nanotubes and the semiconducting carbon nanotubes is realized by controlling the growth time. Since the generation, propagation and absorption of energy are all quantized, the energy perturbation of carbon nanotubes during nucleation and growth under critical conditions is beneficial to amplify the difference in growth rates of different chiral single-walled carbon nanotubes, making carbon nanotubes with specific structures. Preferential growth of nanotubes.

The specific preparation steps of the method are as follows:

(1) Pretreatment of spinel substrate:

The (110) face magnesium-aluminum spinel single crystal substrate was ultrasonically cleaned in ethanol for 5-10 minutes, dried with a nitrogen gun, placed in a closed ceramic boat, placed in a muffle furnace, and heat-treated at 400-500 °C for 30 minutes- For 4h, atomic steps with high crystallinity and suitable for carbon nanotube growth were obtained. The atomic force characterization of the atomic steps and the height of the steps are shown in Figure 3. It can be seen that the average height of the steps on the (110) plane is 0.8-1 nm, and the surface roughness and the fluctuation of the steps are relatively small, which is suitable for carbon nanotubes to complete the atomic-scale self-assembly growth. The atomic steps formed on the spinel surface also reflect the lattice thermal vibration of the crystal itself at high temperature. Figure 4 shows the Raman spectra of the (110) plane substrate after heat treatment at 400-500℃, 600-700℃, and 800-900℃ for 2-4h, according to its Raman characteristic vibration mode Fd3m=A _1g +E _g + T _1g +3T _2g +2A _2u +2E _u +4T _1u +2T _2u are summarized as follows: heat treatment below 500℃, the Raman characteristic peak of the substrate Eg=398cm ^-1 is relatively sharp, lattice order, crystallinity and symmetry With the increase of heat treatment temperature, the width at half maximum of Eg broadened significantly, and the symmetry decreased significantly, indicating that the thermal vibration of the lattice intensified with the increase of heat treatment temperature, and the characteristic breathing mode of AlO ₄ (A _1g = 717 cm ^-1 ) increases with increasing temperature, which can be attributed to the cation exchange and disorder transition of magnesium ions in regular tetrahedral interstitials with Al ions in regular octahedral interstitials.

(2) Preparation of cobalt metal catalyst on spinel substrate: As shown in Figure 1, the spinel substrate exposed on the (110) surface was placed in a cavity with a power of 17-32 W and a vacuum of 0.5-0.8 Torr. Oxygen plasma treatment for 3 to 5 min; using nitrogen-nitrogen dimethylacetamide (DMF) as solvent to prepare block copolymers with a concentration of 0.005 to 0.015 wt% PS ₂₀₃₃ -b-P4VP ₁₃₃ and a concentration of 0.05 to 0.1 mM CoCl _2. The mixed solution of 6H ₂ O is heated and stirred in an oil bath at 80 to 95 °C for 1 to 2 h to form a uniform mixture of block copolymer micelles chemisorbing cations; the mixture is spin-coated at 1500 to 2000rpm on hydrophilic The surface of the treated spinel substrate is treated with oxygen plasma for 3 to 5 minutes to remove the block copolymer on the surface to obtain metal oxide nanoclusters; the substrate with the metal oxide nanoclusters dispersed on the surface is placed on a quartz boat And push it into the tube furnace, heat treatment in the air at 400 ~ 600 ℃ for 1 ~ 5min, and then cool to room temperature; pass 500 ~ 800sccm argon into the tube furnace for 4min, and then switch to 50 ~ 100sccm Ar and 5 ~ 10sccm A mixed gas of H ₂ was used, and the substrate was pushed into a constant temperature zone of 700-850 °C for reduction for 1-6 min to prepare metal nanoparticles.

(3) Growth of metallic single-walled carbon nanotubes on the basal surface of spinel: the cobalt particles carried on the crystal surface of the spinel (110) prepared in step (2) are used as catalysts, and the temperature is 755°C to 775°C. At the same temperature, 5-20 sccm argon was loaded into ethanol (in an ice-water bath at 0°C) as a carbon source, and 0.5-5 sccm H ₂ was used as an etchant for reducing and adjusting the growth rate of carbon nanotubes by nanoparticles, while feeding 40-100 sccm of argon adjusts the gas flow rate, carbon source and hydrogen concentration, the total gas flow is maintained at 50-125 sccm, and the carbon nanotubes are grown, and the growth time is 5-15 min.

Hereinafter, the present invention will be described in further detail through embodiments and accompanying drawings.

Example 1

In this embodiment, the spinel containing the (110) crystal plane treated in the above step (1) is heat-treated at 450° C. for 3 hours in the air.

Using step (2), the cobalt particles are supported on the spinel (110) surface and subjected to oxidation and reduction treatment. The oxidation conditions are 450°C for 3min; the reduction conditions are 765°C, 90sccmAr+4sccmH ₂ , 3min. The morphology of the cobalt particles prepared in step (2) was characterized by transmission electron microscopy (Fig. 5a), and it was found that the particle size was small and uniform; 3 nm; scanning transmission electron imaging of Figure 5c further demonstrates the compositional homogeneity of the cobalt particles. The surface of the substrate was sputtered by X-ray photoelectron spectroscopy and secondary ion mass spectrometry, respectively. The results showed that the cobalt element was dissolved into the spinel substrate and showed a gradient decreasing distribution with depth, and the cobalt 2p3/2 peak on the surface The cobalt 2p3/2 peak position (775 eV) inside the substrate is in the oxidized state (+3 and +2 valence). The above results indicate that the substrate and the catalyst form bonds, resulting in strong pinning and confinement effects, and when the substrate undergoes disordered transition of magnesium ions and aluminum ions, the catalyst atoms are dissolved and cation exchange is achieved. The high-resolution TEM images of cobalt nanoparticles showed good crystallinity, with a typical face-centered cubic structure. The lattice fringe spacing of the 50 particles was concentrated in 0.2-0.22 nm, indicating that the substrate has a significant role in stabilizing the catalyst structure.

Using step (3) to grow single-walled carbon nanotubes, the growth temperature is 765°C, the flow rate of argon loaded with ethanol is 15sccm, the flow rate of hydrogen gas is 0.5sccm, the flow rate of argon carrier gas is 80sccm, and the growth time is 5min. The morphology of the single-walled carbon nanotubes grown in step (3) was characterized by scanning electron microscopy (Fig. 6a). Transmission electron microscopy (Fig. 6b) shows that the wall of the single-walled carbon nanotubes is straight and clear, indicating that they have good crystallinity. The diameters of 150 carbon nanotubes were randomly counted under the transmission electron microscope (Fig. 6c), which had a very narrow diameter distribution, mainly concentrated in 0.9-1.3 nm. The breathing modes of the multi-wavelength (532nm, 633nm, 785nm) laser Raman spectra are shown in Figure 7(a-c). According to the Katarula plots, most of the excited SWNTs are located in the metallic carbon tube region, and the G mode ( Figure 7d) is a typical metallic BWF-type peak. According to the Katarula plots and the number of breathing mode peaks in the corresponding interval, it is estimated that the content of metallic single-walled carbon nanotubes is about 85%. The carbon nanotubes grown in step (3) are scanned with 633nm and 532nm wavelength lasers. The results are shown in Figure 8. It can be seen that the length of the metallic carbon nanotubes is longer (5-10 μm), and the length of the semiconducting carbon nanotubes is shorter. (1 to 6 μm).

Example 2:

In this embodiment, step (1) is the same as step (1) of the embodiment, and the temperature and time of heat treatment in air are 500° C. and 2h, respectively.

Step (2) is the same as step (2) of the embodiment, the oxidation temperature and time are respectively 600°C and 1min, the reduction temperature and time are respectively 850°C and 1min, and the reducing atmosphere is 100sccmAr+3sccmH ₂ . The size and morphology of the Co particles were characterized by transmission electron microscopy. The lattice fringe spacing of the 50 particles is centered at 0.2-0.22 nm, indicating that the substrate has a significant role in stabilizing the catalyst structure.

Step (3) is the same as the step (3) of the embodiment, the growth temperature and time of single-walled carbon nanotubes are respectively 775 ° C and 7min, the argon flow rate loaded with ethanol is 17sccm, the hydrogen flow rate is 1sccm, and the argon carrier gas flow rate is 90sccm. Scanning electron microscope results show that single-walled carbon nanotubes grow directionally and the length is 3-7 μm; transmission electron microscopy shows that the wall of single-walled carbon nanotubes is straight and clear, indicating that they have good crystallinity; 150 carbon nanotubes were randomly counted under transmission electron microscopy. The diameter of the tube, the diameter is mainly concentrated in 1.0 ~ 1.3nm; the breathing mode of the multi-wavelength (532nm, 633nm, 785nm) laser Raman spectrum shows that most of the excited single-walled carbon nanotubes are located in the metallic carbon tube range, according to Katarula plots The figure estimates that the metallic SWNT content is about 78%.

Example 3:

In this embodiment, step (1) is the same as step (1) of the embodiment, and the temperature and time of heat treatment in air are 400° C. and 3h, respectively.

Step (2) is the same as step (2) in the embodiment, the oxidation temperature and time are 400°C and 5min respectively, the reduction temperature and time are 700°C and 5min respectively, and the reducing atmosphere is 80sccmAr+5sccmH ₂ . The size and morphology of the Co particles were characterized by transmission electron microscopy. The lattice fringe spacing of the 50 particles is centered at 0.2-0.22 nm, indicating that the substrate has a significant role in stabilizing the catalyst structure.

Step (3) is the same as the step (3) of the embodiment, the growth temperature and time of the single-walled carbon nanotubes are respectively 765 ° C and 10min, the argon flow rate loaded with ethanol is 20sccm, the hydrogen flow rate is 3sccm, and the argon carrier gas flow rate is 100sccm. Scanning electron microscope results show that single-walled carbon nanotubes grow directionally, and the length is 4-8 μm; transmission electron microscopy shows that the wall of single-walled carbon nanotubes is straight and clear, indicating that they have good crystallinity; 150 carbon nanotubes were randomly counted under transmission electron microscopy. The diameter of the tube, the diameter is mainly concentrated in 0.9 ~ 1.3nm; the breathing mode of the multi-wavelength (532nm, 633nm, 785nm) laser Raman spectrum shows that most of the excited single-walled carbon nanotubes are located in the metallic carbon tube range, according to Katarula plots The figure estimates that the metallic SWNT content is about 80%.

Comparative Example 1: Control of Thermodynamic and Kinetic Conditions - Preparation of Catalyst and Growth of Single-Walled Carbon Nanotubes on the Surface of a Silicon Substrate.

A silicon wafer with a melting point of 1410 °C and a surface oxide layer thickness of 300 nm of amorphous silicon oxide was used as the substrate, and the same catalyst preparation and treatment method as in Example (1) was used. The morphology and size of the obtained catalyst cobalt particles are shown in Figure 9a- b, it can be seen that the particle size distribution is uneven. The diameter distribution of 150 Co particles was counted under transmission electron microscope (Fig. 9c), and it was found that the diameter distribution of Co particles was in the range of 1.5-5.5 nm, which was larger than the average size of the particles prepared in Example (1) and wider in diameter distribution. , indicating that the interaction between the silicon substrate and the cobalt catalyst is relatively weak.

Single-walled carbon nanotubes were prepared using the same chemical vapor deposition conditions as in step (3) in Example (1) using the Co nanoparticles prepared from the above silicon substrate as catalysts. The scanning electron microscope of the grown carbon nanotubes is shown in Figure 9d. It can be seen that a long and dense carbon nanotube network has grown on the surface of the silicon wafer, and the silicon wafer has no control effect on the orientation and growth rate of carbon nanotubes. Raman spectroscopy (Fig. 10) analyzes its conductive properties, and it is found that the diameter distribution of carbon nanotubes is wide, and the content of metallic carbon nanotubes is about 35%. From the D and G modes, the selectivity of its non-conductive properties can be seen. The key role of spinel substrate for the controlled growth of metallic carbon nanotubes is verified.

By heat treatment at 500°C, 700°C, and 900°C for 2 to 4 hours on the silicon wafer substrate, the Raman characteristic peak width at half maximum of the silicon wafer did not change significantly, and the symmetry was strong, indicating that the lattice thermal vibration of the silicon wafer substrate Compared with the weaker spinel, the silicon wafer has less influence on the growth of carbon nanotubes due to the thermal vibration of the substrate lattice.

Comparative Example 2: Kinetic Condition Control - Temperature

Take spinel as base, select and prepare and process Co nano-particles with exactly the same steps as in Example (1); take it as a catalyst, select the same chemical vapor deposition conditions as in Example (1), just select higher Growth temperature (825°C) to grow single-walled carbon nanotubes. Scanning electron microscope pictures showed (Fig. 11a) that the density and length of carbon nanotubes were significantly improved, indicating that the growth efficiency and rate of carbon nanotubes changed with temperature. The multi-wavelength Raman spectroscopy (Fig. 11b-c) shows a broadened distribution of the diameter and conductive properties of the carbon nanotubes. The above comparative example shows that under the condition of critical nucleation growth at low temperature, the lattice thermal vibration and energy fluctuation of the substrate are conducive to the differential supply of energy, thereby maximizing the growth rate difference between metallic carbon nanotubes and semiconducting carbon nanotubes; At high temperature, the temperature of the reaction system is sufficient to meet the energy supply for the growth of carbon nanotubes with different properties, and the effect of the substrate on the growth of carbon nanotubes will be weakened.

The above examples and comparative examples show that spinel can effectively solid solution and pin metal nanoparticles compared with the commonly used silicon substrate, which solves the problems of catalyst agglomeration and Oswald ripening, and improves the high temperature of the catalyst. Thermal stability; and under the critical nucleation growth conditions of low temperature and low carbon source, due to the severe lattice thermal vibration of spinel, the energy differential supply of metal and semiconducting carbon nanotubes is realized, and the growth length is 5~ 10μm, narrow diameter distribution (0.9-1.3nm), single-walled carbon nanotubes with a metallic content of 75-85% are more than 2 times that of ordinary samples; this method is simple and has strong applicability; it clarifies the influence of metallicity The main factors of carbon nanotube growth and its growth mechanism provide novel methods and ideas for the controllable growth of carbon nanotubes. The present invention is not limited to the above-mentioned embodiments and comparative examples, and relates to various modifications and improvements of the single crystal substrate made by engineers and technicians in the field under the idea of the present invention, which shall belong to the claims of the present invention. Protect.

Claims (8)

1. a method for controllable growth of metallic single-walled carbon nanotubes by substrate design, is characterized in that, selecting to produce lattice thermal vibration at high temperature and taking phonon as the main heat conduction mode of magnesium-aluminum spinel single crystal as substrate , using the strong interaction between the substrate and the catalyst to control the size, structure and high temperature stability of the catalyst; using the energy fluctuation caused by the lattice thermal vibration of the substrate at high temperature to control the energy supply required for the growth of carbon nanotubes to achieve metallicity Maximizing the difference in growth rates between single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes, selectively growing metallic single-walled carbon nanotubes. 2. according to the method for the controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 1, it is characterized in that, the substrate needs to be heat treated in oxidizing and reducing atmospheres respectively to improve its crystallinity to obtain suitable carbon nanotubes Atomic steps for growth; oxygen plasma treatment of the substrate to improve the wettability of the catalyst precursor solution with the substrate surface. 3. according to the method for the controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 1, it is characterized in that, catalyzer is the block copolymer micelle chemical adsorption cation that adopts the block copolymer self-assembly preparation of block copolymer The mixture is uniformly covered on the surface of the substrate by spin coating, and the block copolymer on the surface is removed by oxygen plasma treatment to obtain monodisperse metal oxide nanoclusters. 4 . The method for controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 3 , wherein the metal oxide nanoclusters are sequentially subjected to high-temperature oxidation heat treatment at 400-600° C. in an air atmosphere for 1- 5min, hydrogen/argon mixed atmosphere at 700～850℃ for 1～6min reduction heat treatment to obtain metal nanoparticles with a diameter distribution of 1～3nm; by adjusting the reduction temperature of heat treatment, the solid solution of the catalyst and the substrate can be effectively achieved, and the catalyst performance can be improved. High temperature thermal stability, so that the metal nanoparticles are pinned on the surface of spinel, and the thermal stability of the metal nanoparticle catalyst is improved. 5. The method for controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 4, wherein, in the hydrogen/argon mixed atmosphere, the hydrogen flow rate is 5～10 sccm, and the argon gas flow rate is 50～10 sccm. 100sccm. 6. The method for controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 1, characterized in that, under the chemical vapor deposition conditions of critical nucleation growth, by thermal vibration of the lattice of the substrate and The regulation of phonon thermal conductivity expands the difference in the energy required for the growth of carbon nanotubes with different conductive properties, so that the average length of the grown metallic carbon nanotubes is much larger than that of the semiconducting carbon nanotubes, thereby realizing the growth of metallic single-walled carbon nanotubes. controlled growth. 7. The method for controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 6, wherein the chemical vapor deposition conditions are: growth temperature 755-775 ℃, carbon source flow 5-20 sccm, hydrogen gas The flow rate is 0.5-5 sccm, the argon carrier gas flow is 40-100 sccm, the total gas flow is 50-125 sccm, and the growth time is 5-15 min. 8 . The method for controllable growth of metallic single-walled carbon nanotubes by substrate design according to claim 1 , wherein the grown metallic single-walled carbon nanotubes have a length of 2-10 μm and a diameter of 1.1±0.2 μm. 9 . nm, and the number content of metallic carbon nanotubes is 75-85%.

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