CN104787749B - A kind of preparation method of aligned carbon nanotube - Google Patents

Abstract

The invention discloses a method for preparing oriented carbon nanotubes. The method comprises the following steps: 1. Clean the silicon chip with ethanol and dry it, and then use a coating machine to coat the surface of the dried silicon chip. The coating material is iron nickel Alloy powder; 2. Place the coated silicon wafer in an oxidation furnace, and oxidize it in an oxidizing atmosphere for 30-60 minutes; When the temperature of the furnace rises to 600°C-800°C, replace the nitrogen gas with a mixed gas of hydrogen, acetylene and hydrogen fluoride, and apply a pulsed magnetic field to both sides of the tube furnace under heat preservation conditions, stop the ventilation and heating after 10min-30min, and at the same time Turn off the pulsed magnetic field, take out the silicon wafer after cooling with the furnace, and obtain aligned carbon nanotubes on the surface of the silicon wafer. The carbon nanotube prepared by the method of the invention has good orientation, fast preparation speed and high yield.

Description

A kind of preparation method of aligned carbon nanotube

technical field

The invention belongs to the technical field of carbon nanotube preparation, and in particular relates to a preparation method of an aligned carbon nanotube.

Background technique

Carbon nanotubes are formed by curling single-layer or multi-layer graphite sheets. The diameter is generally tens of nanometers, and the length is several to tens of microns. The unique microstructure determines its good electrical properties, excellent thermal conductivity and super strength. Comprehensive mechanical properties. These excellent properties make carbon nanotubes have many potential uses. Carbon nanotubes can be applied to the reinforcement of composite materials due to their high specific strength and high aspect ratio. Good electrical conductivity makes them a good material for probes of atomic force microscopes and scanning tunneling microscopes. Good semiconductor properties make carbon nanotubes Tubes can be used to make diodes, triodes, single-molecule switches, memory cells, and wires for molecular circuits; light-weight, cheap, and efficient solar cells can also be made by using the photoelectric conversion properties of carbon nanotubes. The strong electron emission characteristics of carbon nanotubes make them suitable for manufacturing large-screen, ultra-thin, high-definition, high-brightness, energy-saving, long-life and flexible display screens. However, the carbon nanotubes prepared by the commonly used preparation methods are arranged in disorder and intertwined with each other, which affects the in-depth development and improvement of carbon nanotubes in the above application fields. Therefore, aligning carbon nanotubes is an important prerequisite for their practical application, and it is also a major problem in their practical application.

At present, the preparation methods of aligned carbon nanotube bundles and arrays are basically divided into two categories: one is the growth control method, which refers to the physical influence of controlling the distribution of catalysts and using templates to make the growth of carbon tubes during the preparation and growth process. Growth is directional. Another type of method is the subsequent conversion method, which is to reorient the prepared carbon nanotubes in the physical field (liquid or gas flow field, force field, strong magnetic field, electric field). In the precursor, the carbon nanotubes have been entangled with each other during the preparation process, so the post-processing method has a very limited effect on the unwinding and reorientation of the carbon nanotubes, especially for carbon nanotubes with a large length-diameter ratio. The effect of the tube is weaker. Therefore, the method for preparing aligned carbon nanotubes is still based on the growth control method.

At present, there are several different methods for achieving directional growth of carbon nanotubes: thermal CVD (ThermalCVD), microwave plasma enhanced MPECVD (MicrowavePlasma-enhancedCVD), negative bias enhanced thermal filament NBECVD (NegativeBias-enhancedCVD) and electron cyclotron Resonance ERCCVD (ElectronCyclotronResonanceCVD). These preparation methods still have certain defects. First, the orientation of carbon nanotubes prepared by thermal CVD and MPECVD is not particularly obvious, and the prepared samples still have obvious winding phenomenon, while the orientation of NBECVD and ECRCVD is better, but the preparation speed Slower and less productive.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing aligned carbon nanotubes in view of the above-mentioned deficiencies in the prior art. In this method, a silicon chip is used as a supporting carrier, and iron-nickel alloy powder is used as a coating material to coat a film on the surface of the silicon chip, and the coated silicon chip is oxidized, so that most of the iron on the surface of the silicon chip is oxidized into ferromagnetic iron tetroxide. Thereby improving the ability to receive the pulsed magnetic field, the nickel in the iron-nickel alloy powder can be used as a catalyst to decompose the acetylene passed into the tube furnace, and provide a carbon source for the growth of carbon nanotubes; feed hydrogen, acetylene and hydrogen fluoride into the tube furnace Due to the strong electronegativity of the fluorine atom, it can form a ligand with ferric oxide, form a steric hindrance on the surface of the nickel catalyst, and limit the growth direction of carbon nanotubes; Applying a pulsed magnetic field can prevent the random diffusion and growth of carbon, thereby ensuring the directional growth of carbon nanotubes and uniform tube diameter.

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is: a preparation method of aligned carbon nanotubes, characterized in that, comprising the following steps:

Step 1. Clean the silicon wafer with ethanol and dry it, and then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The coating temperature is 1000 ° C ~ 1200 ° C, and the coating pressure is 0.000001Pa～0.001Pa, the coating time is 10min～30min;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 30 minutes to 60 minutes under the conditions of an oxidation atmosphere at a temperature of 300° C. to 400° C. and a pressure of 1 Pa to 5 Pa; the oxidation atmosphere is A mixed gas of oxygen and nitrogen, wherein the volume percentage of oxygen is 2% to 5%;

Step 3. Place the oxidized silicon wafer in step 2 in a tube furnace, feed nitrogen into the tube furnace and heat up the tube furnace until the furnace temperature of the tube furnace rises to 600 When the temperature ranges from ℃ to 800 ℃, the nitrogen gas is replaced by a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After the furnace is cooled, the silicon wafer is taken out, and aligned carbon nanotubes are obtained on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 50% to 80%, and the volume percentage of hydrogen fluoride is 0.5% ~1%.

The above method for preparing aligned carbon nanotubes is characterized in that the mass percentage of nickel in the iron-nickel alloy powder in step 1 is 33.5%-41%.

The above method for preparing aligned carbon nanotubes is characterized in that the heating rate in step 3 is 5°C/min-10°C/min.

The above-mentioned preparation method of aligned carbon nanotubes is characterized in that the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride described in step 3 is 60% to 70%, and the volume percentage of hydrogen fluoride is 0.5% to 1%.

The above method for preparing aligned carbon nanotubes is characterized in that the magnetic field strength of the pulsed magnetic field in Step 3 is 1.5T-2.5T, and the pulse frequency is 10Hz-1000Hz.

Compared with the prior art, the present invention has the following advantages:

1. The present invention adopts a silicon chip as a supporting carrier, uses iron-nickel alloy powder as a coating material to coat a film on the surface of a silicon chip, and oxidizes the silicon chip after coating, so that most of the iron on the surface of the silicon chip is oxidized into strong magnetic trioxide Iron, so as to improve the ability to receive the pulsed magnetic field, the nickel in the iron-nickel alloy powder can be used as a catalyst to decompose the acetylene passed into the tube furnace, and provide a carbon source for the growth of carbon nanotubes.

2. The present invention feeds the mixed gas of hydrogen, acetylene and hydrogen fluoride into the tube furnace. Because the fluorine atom has strong electronegativity, it can form a ligand with ferroferric oxide and form a steric hindrance on the surface of the nickel catalyst. , to limit the growth direction of carbon nanotubes; at the same time, applying a pulsed magnetic field to both sides of the tube furnace can prevent the random diffusion and growth of carbon, thereby ensuring the directional growth of carbon nanotubes and uniform tube diameter.

3. The carbon nanotubes prepared by the method of the present invention have good orientation, fast preparation speed and high yield.

The technical solutions of the present invention will be further described in detail below through examples.

Description of drawings

FIG. 1 is an SEM image of aligned carbon nanotubes prepared in Example 1 of the present invention.

Fig. 2 is a SEM image of carbon nanotubes prepared by a conventional method.

detailed description

Example 1

The preparation method of the present embodiment comprises the following steps:

Step 1. Clean the silicon wafer with ethanol and dry it, then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The temperature of the coating is 1000°C, and the pressure of the coating is 0.000001Pa. The coating time is 30min; the mass percentage of nickel in the iron-nickel alloy powder is 33.5%;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 30 minutes under the conditions of 300° C. and 1 Pa in an oxidizing atmosphere; the oxidizing atmosphere is a mixed gas of oxygen and nitrogen, Wherein the volume percentage of oxygen is 2%;

Step 3, place the silicon wafer after the oxidation treatment in step 2 in a tube furnace, feed nitrogen into the tube furnace and heat up the tube furnace at a rate of 5°C/min. When the furnace temperature of the tube furnace rises to 600°C, the nitrogen gas is replaced with a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After 10 minutes, the ventilation and heating are stopped, and at the same time, the pulsed magnetic field, take out the silicon wafer after cooling with the furnace, and obtain oriented carbon nanotubes on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 50%, and the volume percentage of hydrogen fluoride is 0.5% %, the balance is acetylene; the magnetic field strength of the pulsed magnetic field is 1.5T, and the pulse frequency is 10Hz.

Comparing Figure 1 and Figure 2, it can be seen that the growth direction of carbon nanotubes prepared by conventional methods is disordered and intertwined. However, the carbon nanotubes prepared by the method of this embodiment have good directional growth and no obvious entanglement with each other. The average length of the carbon nanotubes prepared in this example is 3.5 μm, and the entanglement rate is 7.5%.

Example 2

The preparation method of the present embodiment comprises the following steps:

Step 1: Clean the silicon wafer with ethanol and dry it, then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The temperature of the coating is 1050°C, and the pressure of the coating is 0.00001Pa. The coating time is 25min; the mass percentage of nickel in the iron-nickel alloy powder is 35%;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 35 minutes under the conditions of 320° C. and 2 Pa in an oxidizing atmosphere; the oxidizing atmosphere is a mixed gas of oxygen and nitrogen, Wherein the volume percentage of oxygen is 2%;

Step 3. Place the oxidized silicon wafer in step 2 in a tube furnace, feed nitrogen gas into the tube furnace and raise the temperature of the tube furnace at a rate of 10°C/min. When the furnace temperature of the tube furnace rises to 650°C, the nitrogen gas is replaced by a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After 15 minutes, the ventilation and heating are stopped, and at the same time, the Pulse magnetic field, take out the silicon wafer after cooling with the furnace, and obtain oriented carbon nanotubes on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 60%, and the volume percentage of hydrogen fluoride is 0.5% %; the magnetic field strength of the pulsed magnetic field is 1.7T, and the pulse frequency is 100Hz.

The average length of the carbon nanotubes prepared in this example is 4.7 μm, and the entanglement rate is 8.5%.

Example 3

The preparation method of the present embodiment comprises the following steps:

Step 1. Clean the silicon wafer with ethanol and dry it, and then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The temperature of the coating is 1100°C, and the pressure of the coating is 0.0001Pa. The coating time is 20min; the mass percentage of nickel in the iron-nickel alloy powder is 39%;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 60 minutes under the conditions of 360° C. and 1 Pa in an oxidizing atmosphere; the oxidizing atmosphere is a mixed gas of oxygen and nitrogen, Wherein the volume percentage of oxygen is 2%;

Step 3. Place the silicon wafer after the oxidation treatment in step 2 in a tube furnace, feed nitrogen into the tube furnace and heat up the tube furnace at a rate of 8°C/min. When the furnace temperature of the tube furnace rises to 700°C, the nitrogen gas is replaced by a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After 25 minutes, the aeration and heating are stopped, and at the same time, the Pulse magnetic field, take out the silicon wafer after cooling with the furnace, and obtain aligned carbon nanotubes on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 80%, and the volume percentage of hydrogen fluoride is 1 %; the magnetic field strength of the pulsed magnetic field is 1.8T, and the pulse frequency is 200Hz.

The average length of the carbon nanotubes prepared in this example is 5.5 μm, and the entanglement rate is 8.1%.

Example 4

The preparation method of the present embodiment comprises the following steps:

Step 1. Clean the silicon wafer with ethanol and dry it, and then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The temperature of the coating is 1150°C, and the pressure of the coating is 0.001Pa. The coating time is 15 minutes; the mass percentage of nickel in the iron-nickel alloy powder is 41%;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 45 minutes under an oxidation atmosphere at a temperature of 380° C. and a pressure of 4 Pa; the oxidation atmosphere is a mixed gas of oxygen and nitrogen, Wherein the volume percentage of oxygen is 4%;

Step 3. Put the oxidized silicon wafer in step 2 in a tube furnace, feed nitrogen into the tube furnace and raise the temperature of the tube furnace at a rate of 6° C./min. When the furnace temperature of the tube furnace rises to 750°C, the nitrogen gas is replaced with a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After 28 minutes, the ventilation and heating are stopped, and at the same time, it is closed Pulse magnetic field, take out the silicon wafer after cooling with the furnace, and obtain oriented carbon nanotubes on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 70%, and the volume percentage of hydrogen fluoride is 1 %; the magnetic field strength of the pulsed magnetic field is 2.0T, and the pulse frequency is 500Hz.

The average length of the carbon nanotubes prepared in this example is 7.8 μm, and the entanglement rate is 8.5%.

Example 5

The preparation method of the present embodiment comprises the following steps:

Step 1. Clean the silicon wafer with ethanol and dry it, and then use a coating machine to coat the surface of the dried silicon wafer. The coating material is iron-nickel alloy powder. The temperature of the coating is 1200°C, and the pressure of the coating is 0.001Pa. The coating time is 10 minutes; the mass percentage of nickel in the iron-nickel alloy powder is 35%;

Step 2. Place the silicon wafer coated in step 1 in an oxidation furnace, and oxidize it for 30 minutes under the conditions of 400° C. and 5 Pa in an oxidizing atmosphere; the oxidizing atmosphere is a mixed gas of oxygen and nitrogen, Wherein the volume percentage of oxygen is 5%;

Step 3. Place the oxidized silicon wafer in step 2 in a tube furnace, feed nitrogen gas into the tube furnace and raise the temperature of the tube furnace at a rate of 10°C/min. When the furnace temperature of the tube furnace rises to 800°C, the nitrogen gas is replaced with a mixed gas of hydrogen, acetylene and hydrogen fluoride, and a pulsed magnetic field is applied to both sides of the tube furnace under heat preservation conditions. After 30 minutes, the ventilation and heating are stopped, and at the same time, the Pulse magnetic field, take out the silicon wafer after cooling with the furnace, and obtain oriented carbon nanotubes on the surface of the silicon wafer; the volume percentage of hydrogen in the mixed gas of hydrogen, acetylene and hydrogen fluoride is 65%, and the volume percentage of hydrogen fluoride is 0.8 %; the magnetic field strength of the pulsed magnetic field is 2.5T, and the pulse frequency is 1000Hz.

The average length of the carbon nanotubes prepared in this example is 11.8 μm, and the entanglement rate is 10.7%.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any way. All simple modifications, changes and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still belong to the technical aspects of the present invention. within the scope of protection of the scheme.

Claims (5)

1. the preparation method of an aligned carbon nanotube, it is characterised in that comprise the following steps:

Step one, by clean for silicon chip ethanol purge post-drying, then adopting coater silicon chip surface plated film after the drying, Coating Materials is FeNi powders, and the temperature of plated film is 1000 DEG C～1200 DEG C, the pressure of plated film is 0.000001Pa～0.001Pa, and the time of plated film is 10min～30min；

Step 2, being placed in oxidation furnace by the silicon chip after plated film in step one, under oxidizing atmosphere, temperature is 300 DEG C～400 DEG C, oxidation processes 30min～60min when pressure is 1Pa～5Pa；Described oxidizing atmosphere is the mixing gas of oxygen and nitrogen, and wherein the volumn concentration of oxygen is 2%～5%；

Step 3, the silicon chip after oxidation processes in step 2 is placed in tube furnace, in described tube furnace, pass into nitrogen and tube furnace is heated up, when the furnace temperature of described tube furnace rises to 600 DEG C～800 DEG C, nitrogen is changed into hydrogen, acetylene and hydrofluoric mixing gas, and under heat-retaining condition, pulsed magnetic field is applied to described tube furnace both sides, ventilation and heating is stopped after 10min～30min, simultaneously close off pulsed magnetic field, take out silicon chip after furnace cooling, obtain aligned carbon nanotube at silicon chip surface；In described hydrogen, acetylene and hydrofluoric mixing gas, the volumn concentration of hydrogen is 50%～80%, and hydrofluoric volumn concentration is 0.5%～1%.

2. the preparation method of a kind of aligned carbon nanotube according to claim 1, it is characterised in that in FeNi powders described in step one, the weight/mass percentage composition of nickel is 33.5%～41%.

3. the preparation method of a kind of aligned carbon nanotube according to claim 1, it is characterised in that the speed heated up described in step 3 is 5 DEG C/min～10 DEG C/min.

4. the preparation method of a kind of aligned carbon nanotube according to claim 1, it is characterized in that, in hydrogen described in step 3, acetylene and hydrofluoric mixing gas, the volumn concentration of hydrogen is 60%～70%, and hydrofluoric volumn concentration is 0.5%～1%.

5. the preparation method of a kind of aligned carbon nanotube according to claim 1, it is characterised in that the magnetic field intensity of pulsed magnetic field described in step 3 is 1.5T～2.5T, pulse frequency is 10Hz～1000Hz.