Method for controlling growth of double-walled carbon nanotube vertical array with high crystallinity and large diameter

Abstract

The invention relates to the field of controllable preparation of ordered macroscopic bodies of carbon nanotubes, in particular to a method for controlling growth of a high-crystallinity and large-diameter double-walled carbon nanotube vertical array. According to the method, catalyst nanoparticles are obtained by designing components of a metal catalyst and regulating and controlling the thickness of the metal catalyst; the method comprises the following steps: pre-dissolving carbon in catalyst nanoparticles through low-temperature hydrocarbon plasma pretreatment; and preparing the double-walled carbon nanotube vertical array with high crystallinity and large diameter at a target temperature. In the growth process of the carbon nanotubes, carbon atoms form a competitive relationship between the carbon nanotubes and amorphous carbon, and the catalyst nanoparticles' pre-dissolved carbon 'shortens the inoculation period of the carbon nanotubes, so that on one hand, the conversion probability of the carbon atoms to the amorphous carbon is reduced, on the other hand, the catalytic activity of the particles is maintained, and the conversion efficiency of the carbon to the carbon nanotubes is improved; the high-crystallinity carbon nanotube vertical array shows excellent heat-conducting property, and has a good application prospect in the aspect of flexible thermal interface materials.

Description

Technical Field

[0001] The invention relates to the field of controllable preparation of ordered macroscopic carbon nanotubes, in particular to a method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter. Background Art

[0002] Double-walled carbon nanotubes are a type of carbon nanostructure composed of two coaxial single-walled carbon nanotubes nested together. They exhibit both the high stability of multi-walled carbon nanotubes and the flexibility of single-walled carbon nanotubes, and have shown advantages in field effect transistors (Reference 1: Shimada, T. et al. Double-wall carbon nanotube field-effect transistors: Ambipolar transport characteristics. Appl. Phys. Lett. 2004, 84, 2412-2414.). Studies have shown that vertical arrays of large-diameter double-walled carbon nanotubes have higher conductivity than vertical arrays of small-diameter single-walled carbon nanotubes (Reference 2: Zhao, B.; et al. Exploring Advantages of Diverse Carbon Nanotube Forests with Tailored Structures Synthesized by Supergrowth from Engineered Catalysts. ACS Nano 2009, 3 (1), 108-114.). The thermal conductivity of vertical arrays of high-crystallinity carbon nanotubes is 5 times higher than that of vertical arrays of low-crystallinity carbon nanotubes (Reference 3: Ivanov, I.; et al. Fastand highly anisotropic thermal transport through vertically aligned carbon nanotube arrays. Appl. Phys. Lett. 2006, 89 (22), 223110.). Therefore, the preparation of vertical arrays of double-walled carbon nanotubes with high crystallinity and large diameter is the key to achieving their excellent performance.

[0003] At present, strategies for directly controlling the preparation of vertical arrays of high crystallinity and controllable structure carbon nanotubes include water-assisted growth (Reference 4: Hata, K.; et al. Water-assisted highly efficient synthesis of impurity-free single-walled carbon nanotubes. Science 2004, 306 (5700), 1362-1364.), catalyst component design (Reference 5: Sugime, H.; et al. Gd-enhanced growth of multi-millimeter-tallforests of single-wall carbon nanotubes. ACS Nano 2019, 13, 13208-13216.) and external field regulation (Reference 6: Kimura, H.; et al. Mutual exclusivity in the synthesis of high crystallinity and high Yield single-walled carbon nanotubes. Journal of the American Chemical Society 2012, 134 (22), 9219-9224.), etc. For example, Yamada et al. prepared 85% selectivity double-walled carbon nanotube vertical arrays by adjusting the thickness of the iron catalyst (Reference 7: Yamada, T., et al. Size-selective growth of double-walled carbon nanotube forests from engineered iron catalysts." Nature Nanotechnology 2006, 1: 131-136.). However, in the vertical arrays of carbon nanotubes prepared by the existing methods, the larger the diameter of the carbon nanotubes, the lower their crystallinity (Reference 8: Chen, G.; et al. Absence of an ideal single-walled carbon nanotube forest structure for thermal and electrical conductivities. ACS Nano 2013, 7 (11), 10218-10224.). Controlling the preparation of vertical arrays of double-walled carbon nanotubes with both high crystallinity and large diameter is an important challenge in the field of carbon nanotube research. Summary of the invention

[0004] The purpose of the present invention is to provide a method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter. Through the design of metal catalyst components and the "pre-dissolved carbon" strategy, the vertical array of double-walled carbon nanotubes with high crystallinity and large diameter can be controlled to grow.

[0005] The technical solution of the present invention is:

[0006] A method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter. The method deposits a metal catalyst film on a substrate by designing the composition of a metal catalyst and regulating its thickness; pretreats the metal catalyst film to obtain catalyst nanoparticles; and "predissolves carbon" in the catalyst nanoparticles through low-temperature carbon hydrogen plasma pretreatment. At a target temperature, a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter is prepared.

[0007] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter deposits a 5-15 nm thick aluminum oxide film on a substrate as a barrier layer to inhibit the aggregation of catalysts and diffusion to the substrate at high temperatures.

[0008] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter adopts a physical deposition method to prepare a metal catalyst film on a substrate, and the substrate is made of a high-temperature resistant substrate material.

[0009] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter is characterized in that the physical deposition method is ion beam coating, magnetron sputtering or atomic deposition, and the substrate is copper, sapphire, quartz or silicon wafer.

[0010] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter, wherein the metal catalyst includes a main catalyst component and other catalyst components, wherein: the main catalyst component is iron, and the thickness of the metal catalyst is adjustable within the range of 1.0 to 2.5 nm; the other catalyst components are one or more of cobalt, nickel, molybdenum, rhodium, and chromium, and the thickness of the metal catalyst is 0 to 0.3 nm.

[0011] The method for controlling the growth of a vertical array of high-crystallinity, large-diameter double-walled carbon nanotubes is as follows: the pretreatment conditions of the metal catalyst film are: heating from room temperature to a hydrocarbon plasma pretreatment temperature, and during the heating process, 100 to 1000 sccm of hydrogen is introduced to form catalyst nanoparticles.

[0012] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter comprises a carbon hydrogen plasma pretreatment temperature of 300 to 500° C., introducing 100 to 500 sccm of hydrogen and 2 to 50 sccm of carbon hydrogen gas, and carbon hydrogen plasma pretreatment of catalyst nanoparticles for a treatment time of 1 to 20 seconds.

[0013] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter is as follows: the growth temperature of the vertical array of double-walled carbon nanotubes is 750-850°C, 100-500sccm of hydrogen is used as a carrier gas, 2-50sccm of hydrocarbon gas is introduced, and the growth time is 1-120min.

[0014] In the method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter, the hydrocarbon gas is ethylene, acetylene or methane.

[0015] The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter, wherein the height of the vertical array of double-walled carbon nanotubes is 1 to 1000 μm, G / I D (Crystallinity) ranges from 1 to 25, diameter distribution ranges from 4 to 10 nm, and density distribution ranges from 17 to 70 kg / m 3 ; The vertical array of double-walled carbon nanotubes was tested by a laser thermal conductivity meter, and its thermal diffusion coefficient was 50-200 mm 2 / s.

[0016] The design concept of the present invention is:

[0017] The present invention obtains catalyst nanoparticles by designing the composition of the catalyst and regulating its thickness and reduction conditions; the catalyst nanoparticles are pretreated by low-temperature hydrocarbon plasma to pre-dissolve carbon into the catalyst nanoparticles, shorten the incubation period of carbon nanotubes, reduce the generation of carbon disordered structures, and significantly improve the crystallinity of the vertical array of carbon nanotubes; during the growth of carbon nanotubes, carbon atoms compete with amorphous carbon in the formation of carbon nanotubes, and the "pre-dissolved carbon" of the catalyst nanoparticles shortens the incubation period of carbon nanotubes, reduces the conversion probability of carbon atoms to amorphous carbon, and maintains the catalytic activity of the particles, improves the conversion efficiency of carbon to carbon nanotubes, and obtains a vertical array of high-crystallinity carbon nanotubes. The present invention combines the catalyst component design with the "pre-dissolved carbon" strategy to prepare a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter.

[0018] The advantages and beneficial effects of the present invention are:

[0019] 1. The present invention provides a controlled growth method combining catalyst component design with pre-dissolved carbon to obtain a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter.

[0020] 2. Thermal diffusion coefficient of the vertical array of double-walled carbon nanotubes prepared by the present invention (157 mm 2 / s) is better than copper (111mm 2 / s) and graphite (100mm 2 / s), and is expected to be used as a flexible thermal interface material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 . Schematic diagram of the process of preparing vertical arrays of highly crystalline carbon nanotubes using catalyst "pre-dissolved carbon".

[0022] Figure 2 .(a) Raman spectrum, (b) transmission electron microscope image and (c) diameter distribution diagram of vertical arrays of carbon nanotubes grown on 0.1nm Mo / 0.1nm Ni / 1.4nm Fe / 10nm Al2O3 catalyst before and after "pre-dissolved carbon".

[0023] Figure 3 . Laser thermal conductivity meter test results of vertical arrays of carbon nanotubes grown using “pre-dissolved carbon” as a catalyst of 0.1nm molybdenum / 0.1nm nickel / 1.4nm iron / 10nm alumina. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, in the specific implementation process, the process of preparing a vertical array of high-crystallinity carbon nanotubes by using a catalyst "pre-dissolved carbon" is as follows: first, design the composition of the metal catalyst and adjust its thickness, and deposit a metal catalyst film on a substrate; second, heat the temperature from room temperature to a carbon-hydrogen plasma pretreatment temperature (e.g., 400°C), and during the heating process, introduce 500sccm of hydrogen to obtain metal catalyst nanoparticles; then, in a plasma-enhanced chemical vapor deposition device, pretreat the metal catalyst with carbon-hydrogen plasma (e.g., acetylene) at about 400°C to dissolve carbon atoms in the metal catalyst, and obtain metal catalyst nanoparticles after pre-dissolving carbon; finally, heat the temperature to a target temperature (e.g., 800°C) to prepare a vertical array of double-walled carbon nanotubes with high crystallinity, large diameter, and high purity.

[0025] The present invention is further described in detail below through examples and drawings.

[0026] Example 1

[0027] like Figure 1 As shown, the method for controlling the growth of vertical arrays of double-walled carbon nanotubes with high crystallinity and large diameter is as follows:

[0028] First, an ion beam coating apparatus was used to deposit a 10 nm aluminum oxide film as a buffer layer on the surface of a silicon wafer, and then 0.1 nm molybdenum, 0.1 nm nickel, and 1.4 nm iron were deposited in sequence to form a catalyst array film. Secondly, the catalyst array film sample was placed in a plasma enhanced chemical vapor deposition furnace and heated from room temperature to 400°C. During the heating process, 500 sccm of hydrogen was introduced to obtain catalyst nanoparticles. Then, 500 sccm of hydrogen was used as a carrier gas, the temperature was quickly raised to 800°C, 10 sccm of acetylene was introduced, and the growth time was set to 20 min. A low crystallinity (I G / I D =6), a double-walled carbon nanotube vertical array with a smaller diameter (d=4.8nm) and lower purity (the proportion of double-walled carbon nanotube walls is 36%). In this embodiment, since the metal catalyst "pre-dissolved carbon" was not used, the proportion of double-walled tubes, crystallinity, diameter and height in the prepared carbon nanotube vertical array were all low. Since the height of the array was only 29μm, it was difficult to transfer without loss, and the thermal diffusion coefficient test could not be performed, which was not suitable for thermal conductivity applications.

[0029] Example 2

[0030] like Figure 1 As shown, the method for controlling the growth of vertical arrays of double-walled carbon nanotubes with high crystallinity and large diameter is as follows:

[0031] First, an ion beam coater was used to deposit a 10nm aluminum oxide film on the surface of a silicon wafer as a buffer layer, and then 0.1nm molybdenum, 0.1nm nickel and 1.4nm iron were deposited in sequence to form a catalyst array film. Secondly, the catalyst array film sample was placed in a plasma enhanced chemical vapor deposition furnace and heated from room temperature to 400°C. During the heating process, 500sccm of hydrogen was introduced to obtain metal catalyst nanoparticles. Then, 150sccm of hydrogen and 15sccm of acetylene were introduced, and the catalyst was pretreated with acetylene / hydrogen plasma. The time was set to 5s to obtain metal catalyst nanoparticles after pre-dissolving carbon. Finally, the temperature was quickly raised to 800°C, 500sccm of hydrogen and 10sccm of acetylene were introduced, and the growth time was 20min to prepare a high crystallinity (I G / I D =12), large diameter (d=6.4nm) and high purity (86% of double-walled carbon nanotube wall number ratio) double-walled carbon nanotube vertical array, the height of the double-walled carbon nanotube vertical array is 199μm, the density is 43kg / m 3 , thermal diffusivity is 157mm 2 / s.

[0032] like Figure 2As shown in (a), the Raman spectra of the vertical array of carbon nanotubes grown by 0.1nm Mo / 0.1nm Ni / 1.4nm Fe / 10nm Al2O3 catalyst before and after "pre-dissolved carbon" are shown. Compared with the sample without pre-dissolved carbon, the Raman D mode of the vertical array of carbon nanotubes grown by the metal catalyst pre-dissolved carbon is significantly reduced. G / I D The increase from 6 to 12 indicates that the metal catalyst "pre-dissolved carbon" can grow vertical arrays of carbon nanotubes with high crystallinity.

[0033] like Figure 2 (b) shows a transmission electron microscope photograph of a vertical array of carbon nanotubes grown by the "pre-dissolved carbon" of a 0.1nm molybdenum / 0.1nm nickel / 1.4nm iron / 10nm alumina catalyst. It can be seen that a vertical array of double-walled carbon nanotubes with large diameter and high crystallinity was obtained by using this catalyst.

[0034] like Figure 2 (c) shows the diameter distribution of the vertical array of carbon nanotubes grown by the "pre-dissolved carbon" of 0.1nm molybdenum / 0.1nm nickel / 1.4nm iron / 10nm alumina catalyst. As shown in the figure, after using Gatan's Digital Micrograph software to count the diameter and number of tube walls of the vertical array of carbon nanotubes, it was found that the proportion of double-walled carbon nanotubes in this sample was 86%, and the average diameter was 6.4nm.

[0035] To sum up, a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter was prepared by "pre-dissolving carbon" of 0.1nm molybdenum / 0.1nm nickel / 1.4nm iron / 10nm alumina catalyst.

[0036] like Figure 3 As shown, the thermal diffusion coefficient of the double-walled carbon nanotube vertical array was tested by a laser thermal conductivity meter. The thermal diffusion coefficient of the carbon nanotube vertical array grown by the "pre-dissolved carbon" catalyst of 0.1nm molybdenum / 0.1nm nickel / 1.4nm iron / 10nm alumina is about 157mm 2 / s, the thermal diffusion coefficient is much higher than that of oriented graphite (100mm 2 / s) and copper (111mm 2 / s), indicating that the prepared double-walled carbon nanotube vertical array has excellent thermal conductivity.

[0037] Example 3

[0038] like Figure 1 As shown, the method for controlling the growth of vertical arrays of double-walled carbon nanotubes with high crystallinity and large diameter is as follows:

[0039] First, an ion beam coater was used to deposit a 10nm aluminum oxide film on the surface of the silicon wafer as a buffer layer, and then 0.1nm molybdenum and 1.8nm iron were deposited in sequence to form a catalyst array film. Secondly, the catalyst array film sample was placed in a plasma enhanced chemical vapor deposition furnace and heated from room temperature to 400°C. During the heating process, 500sccm of hydrogen was introduced to obtain metal catalyst nanoparticles. Then, 150sccm of hydrogen and 15sccm of acetylene were introduced, and the catalyst was pretreated with acetylene / hydrogen plasma. The time was set to 5s to obtain metal catalyst nanoparticles after pre-dissolving carbon. Finally, the temperature was quickly raised to 800°C, 500sccm of hydrogen and 10sccm of acetylene were introduced, and the growth time was 20min to prepare a high crystallinity (I G / I D =6), a double-walled carbon nanotube vertical array with large diameter (d=6.7nm) and high purity (the proportion of double-walled carbon nanotube wall is 87%), the height of the double-walled carbon nanotube vertical array is 166μm, and the density is 29kg / m 3 , thermal diffusivity is 116mm 2 / s.

[0040] The implementation results show that the vertical array of double-walled carbon nanotubes prepared based on the present invention exhibits excellent thermal conductivity and has good application prospects in flexible thermal interface materials.

Claims

1. A method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter, characterized in that: The method deposits a metal catalyst thin film on a substrate by designing the composition of the metal catalyst and regulating its thickness; Pre-treat the metal catalyst film to obtain catalyst nanoparticles; pre-dissolve carbon in the catalyst nanoparticles through low-temperature carbon-hydrogen plasma pretreatment; and prepare vertical arrays of double-walled carbon nanotubes with high crystallinity and large diameter at the target temperature.

2. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: A 5-15 nm thick aluminum oxide film is deposited on the substrate as a barrier layer to inhibit the catalyst from agglomerating and diffusing to the substrate at high temperatures.

3. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1 or 2, characterized in that: The metal catalyst film is prepared on the substrate by a physical deposition method, and the substrate is made of a high temperature resistant substrate material.

4. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 3, characterized in that: The physical deposition method is ion beam plating, magnetron sputtering or atomic deposition, and the substrate is copper, sapphire, quartz or silicon wafer.

5. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: The metal catalyst includes a main catalyst component and other catalyst components, wherein: the main catalyst component is iron, and the thickness of the metal catalyst is adjustable within the range of 1.0 to 2.5 nm; the other catalyst components are one or more of cobalt, nickel, molybdenum, rhodium, and chromium, and the thickness of the metal catalyst is 0 to 0.3 nm.

6. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: The pretreatment conditions of the metal catalyst film are: heating from room temperature to the carbon hydrogen plasma pretreatment temperature, and during the heating process, 100 to 1000 sccm of hydrogen is introduced to form catalyst nanoparticles.

7. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: The carbon-hydrogen plasma pretreatment temperature is 300-500° C., 100-500 sccm of hydrogen and 2-50 sccm of carbon-hydrogen gas are introduced, and the carbon-hydrogen plasma pretreatment catalyst nanoparticles have a treatment time of 1-20 seconds.

8. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: The growth temperature of the double-walled carbon nanotube vertical array is 750-850° C., 100-500 sccm of hydrogen is used as a carrier gas, 2-50 sccm of hydrocarbon gas is introduced, and the growth time is 1-120 minutes.

9. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 7 or 8, characterized in that: The hydrocarbon gas is ethylene, acetylene or methane.

10. The method for controlling the growth of a vertical array of double-walled carbon nanotubes with high crystallinity and large diameter according to claim 1, characterized in that: The height of the double-walled carbon nanotube vertical array is 1 to 1000 μm. G / I D (Crystallinity) ranges from 1 to 25, diameter distribution ranges from 4 to 10 nm, and density distribution ranges from 17 to 70 kg / m 3 ; The vertical array of double-walled carbon nanotubes was tested by a laser thermal conductivity meter, and its thermal diffusion coefficient was 50-200 mm 2 / s.

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