Method for preparing graphene through chemical vapor deposition

Abstract

The invention provides a method for preparing graphene through chemical vapor deposition, which comprises the following steps of: growing a graphene film on the surface of a substrate through a chemical vapor deposition method by taking a nitrogen-containing organic matter or a composition containing the nitrogen-containing organic matter and an alcohol compound as a carbon source; wherein in the composition, the volume fraction of the alcohol compound is less than or equal to 1%. The nitrogen-containing organic matter disclosed by the invention can be efficiently cracked under a high-temperature and hydrogen-free condition to provide enough carbon active species so as to promote the growth of graphene; the nitrogen-containing organic matter has good volatility and stability, so that the carbon source can effectively participate in the CVD reaction, and the carbon source can continuously and uniformly supply carbon atoms in the whole growth process; furthermore, hydroxyl radicals generated by cracking of the alcohol compounds can effectively remove amorphous carbon, so that the crystallization quality of graphene is improved, and defects are reduced; in addition, hydrogen does not need to be introduced in the preparation process, and potential safety hazards caused by hydrogen are eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene, and particularly to a method for preparing graphene by chemical vapor deposition. Background Art

[0002] Graphene is a two-dimensional material formed by arranging single-layer carbon atoms in a hexagonal honeycomb structure, with excellent electrical, thermal, and mechanical properties. It has been widely used in many cutting-edge fields such as electronic devices, sensors, and energy storage materials. The chemical vapor deposition (CVD) method has become the mainstream technical route for preparing high-quality graphene films due to its strong controllability and suitability for large-area preparation.

[0003] Currently, methane is commonly used as the carbon source in the method of preparing graphene by CVD. Methane has problems such as insufficient activity and low cracking efficiency. To promote the decomposition of the carbon source and inhibit the formation of graphene defects, a certain amount of hydrogen is usually introduced as an auxiliary gas during the growth process.

[0004] For example, Chinese invention patent CN 114804082 A discloses a step-regulated graphene sapphire wafer and its preparation method. In this method, graphene is synthesized on a sapphire substrate by CVD at a very high temperature (such as above 1300 °C), and hydrogen with a flow rate of 300 - 500 sccm is continuously introduced throughout the growth process to improve the crystallization quality of graphene.

[0005] However, hydrogen is a highly flammable and explosive gas, and its large-scale use in a high-temperature environment brings serious industrial safety hazards. Especially in large-scale and continuous industrial production, there are risks of gas leakage, fire, and even explosion. Therefore, how to reduce or avoid the use of hydrogen while ensuring high crystallinity and low defect density of graphene has become one of the important challenges faced by current graphene CVD technology.

[0006] In view of this, the present invention is particularly proposed. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the safety hazards brought by using hydrogen as an auxiliary gas in the prior art and the poor controllability of the carbon source in traditional CVD methods, and provide a method for preparing graphene by chemical vapor deposition, which can successfully prepare graphene with high crystallinity and low defect density even under the condition of no hydrogen, thereby improving the crystallization quality and stability of graphene.

[0008] To this end, the basic concept of the technical solution adopted by the present invention is:

[0009] A method for preparing graphene by chemical vapor deposition, comprising the following steps:

[0010] Using a nitrogen-containing organic compound or a composition containing a nitrogen-containing organic compound and an alcohol compound as a carbon source, growing a graphene film on the surface of a substrate by chemical vapor deposition; wherein, in the composition, the volume fraction of the alcohol compound is less than or equal to 1%.

[0011] The nitrogen-containing organic compound of the present invention can be efficiently cracked under high temperature and hydrogen-free conditions to provide sufficient carbon active species to promote the growth of graphene; and the nitrogen-containing organic compound has good volatility and stability, which not only ensures that the carbon source can effectively participate in the reaction in the CVD process, but also ensures that the carbon source can continuously and uniformly supply carbon atoms throughout the growth process, and will not cause fluctuations in the quality of the graphene film due to incomplete or unstable cracking.

[0012] In addition, the carbon source contains an alcohol compound. The alcohol compound has mild reactivity, high volatility and low by-product generation, can provide a stable carbon source in the CVD preparation process of graphene, and effectively removes amorphous carbon through the hydroxyl radicals generated by cracking, thereby improving the crystallization quality of graphene and reducing defects.

[0013] Further, the carbon source is liquid in the temperature range of 20 - 25°C and the pressure condition of 50.663 - 101.325 kPa.

[0014] Selecting a carbon source that is liquid in the temperature range of 20 - 25°C and the pressure of 50.663 - 101.325 kPa can ensure a more stable carbon source supply in the chemical vapor deposition process. The liquid carbon source can be effectively gasified and participate in the reaction during the cracking process, providing a uniform and continuous carbon source to ensure the stable and controllable growth process of the graphene film.

[0015] Further, the nitrogen-containing organic compound includes one or two of acetonitrile and pyridine.

[0016] Acetonitrile and pyridine can be effectively cracked at high temperature to release carbon atoms for the growth of graphene, and have good volatility and cracking efficiency, ensuring a stable carbon source supply. By selecting these two nitrogen-containing organic compounds, the growth process of graphene can be optimized under the condition of no hydrogen participation, obtaining a graphene film with good crystallization quality, while reducing the safety hazards brought by the use of hydrogen and improving the safety and controllability of the production process.

[0017] Further, the alcohol compound includes one or more of methanol, ethanol, propanol, and isopropanol; preferably ethanol.

[0018] The gentle etching effect of ethanol at high temperatures can ensure the orderliness of graphene growth, avoiding the negative impact of overly strong etching on graphene growth. At the same time, its low cost, easy availability, and high safety make it an ideal choice in industrial production.

[0019] Furthermore, the carbon source includes acetonitrile and ethanol, and the volume fraction of ethanol is less than or equal to 1%; preferably 0.8 - 1%.

[0020] When the volume fraction of ethanol is less than or equal to 1%, it can avoid the interference of excessive ethanol on the graphene growth process. Although ethanol can provide hydroxyl radicals and selectively etch amorphous carbon, its too high concentration will lead to overly strong etching, affecting the growth and quality of graphene. By controlling the volume fraction of ethanol, it is ensured that while providing a carbon source and hydroxyl radicals, it will not overly interfere with the orderly growth of graphene.

[0021] As the main carbon source, acetonitrile can provide efficient carbon atom supply and promote graphene crystallization. At the same time, as an auxiliary material, ethanol can effectively remove amorphous carbon through the hydroxyl radicals generated during its cracking process, further improving the crystallization quality of graphene. The design of the liquid carbon source of acetonitrile and ethanol not only ensures the stability and efficient cracking of the carbon source, but also ensures the efficient growth of graphene by controlling the volume fraction of ethanol, while avoiding the negative impact of overly strong etching on the growth process.

[0022] Furthermore, during the chemical vapor deposition process, the input flow rate of the carbon source is 50 - 300 sccm, the growth duration of graphene is 50 - 70 min, the growth pressure is 2000 - 5000 Pa, and the growth temperature is 1350 - 1450 °C.

[0023] Preferably, the input flow rate of the carbon source is 100 sccm, the growth duration of graphene is 60 min, the growth pressure is 3000 Pa, and the growth temperature is 1400 °C.

[0024] Furthermore, the carbon source is transported to the heating furnace by carrier gas through the bubbling method. The heating furnace includes but is not limited to an electromagnetic induction heating furnace, and the input flow rate of the carbon source is the carrier gas flow rate.

[0025] The present invention helps to ensure the uniform supply of the carbon source, optimize the crystallization quality of graphene, reduce the formation of defects, and improve the controllability of the growth process by controlling the input flow rate of the carbon source, the growth duration of graphene, the growth pressure, and the growth temperature.

[0026] Further, during the chemical vapor deposition process, the ambient temperature is raised to the growth temperature of graphene before introducing the carbon source. The process includes a first heating stage with a first heating rate and a second heating stage with a second heating rate, and the first heating rate is greater than the second heating rate.

[0027] Further, the first heating stage includes raising the ambient temperature to 900 - 1000 °C at a first heating rate of 20 - 30 °C / min; the second heating stage includes raising the ambient temperature to the growth temperature of graphene at 1350 - 1450 °C at a second heating rate of 10 - 15 °C / min.

[0028] Preferably, during the chemical vapor deposition process, after the ambient temperature is raised to the growth temperature of graphene, the growth temperature is maintained for 5 - 15 min before introducing the carbon source.

[0029] By rapidly heating to 900 °C - 1000 °C, the present invention can quickly heat the reaction chamber to a temperature close to that required for graphene growth. Subsequently, by reducing the heating rate, the change in temperature can be further precisely controlled, avoiding unstable factors that may be caused by too rapid temperature increase.

[0030] After the present invention raises the temperature to the growth temperature of graphene and maintains the growth temperature for a certain period of time before introducing the carbon source, it helps to further refine and control the growth environment, ensuring that the layers and quality of graphene are consistent, which is particularly important in industrial applications that require high-purity and high-crystalline-quality graphene.

[0031] The technical solution of the present invention has the following advantages:

[0032] The nitrogen-containing organic compound of the present invention can be efficiently cracked under high temperature and hydrogen-free conditions to provide sufficient carbon active species to promote the growth of graphene; and the nitrogen-containing organic compound has good volatility and stability, which not only ensures that the carbon source can effectively participate in the reactions in the CVD process, but also ensures that the carbon source can continuously and uniformly supply carbon atoms throughout the growth process, without causing fluctuations in the quality of the graphene film due to incomplete or unstable cracking; in addition, no hydrogen needs to be introduced during the preparation process of the present invention, eliminating the safety hazards brought by hydrogen.

[0033] The carbon source of the present invention contains alcohol compounds. Alcohol compounds have mild reactivity, high volatility, and low by-product generation, and can provide a stable carbon source during the CVD preparation of graphene. The hydroxyl radicals generated by cracking can effectively remove amorphous carbon, thereby improving the crystalline quality of graphene and reducing defects.

[0034] By optimizing the carbon source design, the prepared graphene in the present invention has excellent crystallization quality and stability, significantly improving the electrical, thermal and mechanical properties of graphene, providing a more reliable material basis for its wide use in high-end electronic devices and other application fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is the temperature-time curve graph of the rapid cold-wall electromagnetic induction heating furnace corresponding to Embodiment 1 of the present invention; (a is the first-stage heating process, b is the second-stage heating process, c is the annealing process, d is the graphene growth process, e is the cooling process);

[0037] Figure 2 It is the Raman spectra corresponding to Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following embodiments are provided to better further understand the present invention. It is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0039] For those embodiments where specific experimental steps or conditions are not specified, the operations or conditions of the conventional experimental steps described in the literature in the art can be followed. For reagents or instruments where the manufacturer is not specified, they are all conventional reagent products that can be obtained through commercial purchase.

[0040] Embodiment 1

[0041] This embodiment provides a method for preparing graphene, which specifically includes the following steps:

[0042] (1) Substrate preparation: Immerse the sapphire substrate in acetone, ethanol and deionized water in sequence for ultrasonic cleaning, and each cleaning lasts for 10 minutes; after cleaning, use high-purity nitrogen to dry the substrate for later use;

[0043] (2) Reaction chamber cleaning: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction chamber of the rapid cold-wall electromagnetic induction heating furnace to remove the particles and impurities inside the reaction chamber;

[0044] (3) Purification of the reaction chamber atmosphere: Continuously introduce argon with a flow rate of 300 sccm into the reaction chamber and purge for 15 minutes to thoroughly remove the residual air and impurity gases in the reaction chamber, ensuring the purity of the reaction chamber atmosphere;

[0045] (4) Placement of the substrate: Place the sapphire substrate cleaned in step (1) in a graphite carrier, and accurately place the graphite carrier at the center of the reaction chamber of the rapid-cooling wall electromagnetic induction heating furnace to ensure symmetrical position. Then close the furnace door;

[0046] (5) Start the vacuum system: Pump the pressure in the reaction chamber to below 5 Pa. After confirming good airtightness of the reaction chamber, slowly backfill with argon with a flow rate of 500 sccm to 3000 Pa;

[0047] (6) Temperature control: Start the temperature control system, set the heating program, and raise the temperature from room temperature to the growth temperature of graphene, 1400 °C. The heating method is staged heating, including a first heating stage with a first heating rate and a second heating stage with a second heating rate, and the first heating rate is greater than the second heating rate; Specifically, as Figure 1 shown, section a is the first heating process, raising the ambient temperature from room temperature of 20 °C to 1000 °C with a heating rate of 25 °C / min; section b is the second heating process, raising the ambient temperature from 1000 °C to 1400 °C with a heating rate of 10 °C / min, ensuring stable temperature control and uniform thermal field;

[0048] (7) Introduction of carbon source: As shown in section c of Figure 1 , when the temperature reaches 1400 °C, control to keep the temperature constant at 1400 °C for 15 minutes; Subsequently, the mixed liquid carbon source of acetonitrile and ethanol is delivered into the reaction chamber by the bubbling method. The volume fraction of ethanol in the mixed liquid carbon source is 1%, the bubbling carrier gas is argon, and the flow rate is set to 100 sccm. Graphene is continuously grown at 1400 °C for 1 hour, corresponding to section d of Figure 1 ;

[0049] (8) Cooling: After the growth is completed, immediately close the bubbling carrier gas, stop introducing the carbon source, and turn off the heating power supply to allow the temperature in the reaction chamber to naturally cool from 1400 °C to room temperature of 20 °C, corresponding to section e of Figure 1 . During this process, continuously introduce argon to prevent residual reaction of the carbon source; When the temperature in the reaction chamber drops below 100 °C, turn off the vacuum system, backfill with argon to atmospheric pressure, open the furnace door, and take out the sample.

[0050] Example 2

[0051] The difference between this example and Example 1 is that: ethanol is not added to the liquid carbon source in step (7), and the liquid carbon source is only acetonitrile.

[0052] Example 3

[0053] The types of nitrogen-containing organic compounds in the liquid carbon source of this example are different from those in Example 1; that is, the difference between this example and Example 1 lies in that the nitrogen-containing organic compound in the liquid carbon source in step (7) is pyridine, not acetonitrile.

[0054] Example 4

[0055] The addition amount of alcohol compounds in the liquid carbon source of this example is different from that in Example 1; that is, the difference between this example and Example 1 lies in that the volume fraction of ethanol in the liquid carbon source in step (7) is 0.9%, which is lower than 1%.

[0056] Example 5

[0057] This example provides a method for preparing graphene, which specifically includes the following steps:

[0058] (1) Substrate preparation: Immerse the sapphire substrate in acetone, ethanol, and deionized water in sequence for ultrasonic cleaning, with each cleaning lasting for 8 minutes; after cleaning, dry the substrate with high-purity nitrogen for later use;

[0059] (2) Reaction chamber cleaning: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction chamber of the rapid cold-wall electromagnetic induction heating furnace to remove the particles and impurities inside the reaction chamber;

[0060] (3) Reaction chamber atmosphere purification: Continuously introduce argon with a flow rate of 310 sccm into the reaction chamber and purge for 15 minutes to thoroughly remove the residual air and impurity gases in the reaction chamber and ensure the purity of the reaction chamber atmosphere;

[0061] (4) Placing the substrate: Place the sapphire substrate cleaned in step (1) in a graphite carrier, and accurately place the graphite carrier at the center of the reaction chamber of the rapid cold-wall electromagnetic induction heating furnace to ensure symmetrical position, and then close the furnace door;

[0062] (5) Starting the vacuum system: Pump the pressure in the reaction chamber to below 10 Pa, and after confirming good airtightness of the reaction chamber, slowly backfill with argon with a flow rate of 500 sccm to 2000 Pa;

[0063] (6) Temperature control: Start the temperature control system, set the heating program, and raise the temperature from room temperature to the growth temperature of graphene, 1450 °C. The heating method is staged heating, including a first heating stage with the first heating rate and a second heating stage with the second heating rate, and the first heating rate is greater than the second heating rate; specifically, in the first stage of heating, the ambient temperature is raised from room temperature of 20 °C to 1000 °C at a heating rate of 20 °C / min; in the second stage of heating, the ambient temperature is raised from 1000 °C to 1450 °C at a heating rate of 10 °C / min to ensure stable temperature control and uniform thermal field.

[0064] (7) Carbon source introduction: When the temperature reaches 1450 °C, control the temperature to be kept at 1450 °C for 5 minutes; then, the mixed liquid carbon source of pyridine and isopropanol is delivered into the reaction cavity by the bubbling method. The volume fraction of isopropanol in the mixed liquid carbon source is 0.9%, the bubbling carrier gas is argon, and the flow rate is set at 50 sccm, and graphene is continuously grown for 70 min.

[0065] (8) Cooling: After the growth is completed, immediately close the bubbling carrier gas, stop introducing the carbon source, and turn off the heating power supply to allow the temperature in the reaction cavity to cool naturally from 1450 °C to room temperature of 20 °C, while continuing to introduce argon to prevent residual reaction of the carbon source; when the temperature of the reaction cavity drops below 100 °C, turn off the vacuum system, backfill with argon to atmospheric pressure, open the furnace door, and take out the sample.

[0066] Example 6

[0067] This example provides a method for preparing graphene, which specifically includes the following steps:

[0068] (1) Substrate preparation: Immerse the sapphire substrate in acetone, ethanol, and deionized water in sequence for ultrasonic cleaning, with each cleaning lasting for 11 minutes; after cleaning, dry the substrate with high-purity nitrogen for standby.

[0069] (2) Reaction cavity cleaning: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction cavity of the rapid-cooling wall electromagnetic induction heating furnace to remove the microparticles and impurities inside the reaction cavity.

[0070] (3) Reaction cavity atmosphere purification: Continuously introduce argon with a flow rate of 290 sccm into the reaction cavity and purge for 15 minutes to thoroughly remove the residual air and impurity gases in the reaction cavity and ensure the purity of the reaction cavity atmosphere.

[0071] (4) Placing the substrate: Place the sapphire substrate cleaned in step (1) in the graphite carrier, and accurately place the graphite carrier at the center of the reaction cavity of the rapid-cooling wall electromagnetic induction heating furnace to ensure symmetrical position, and then close the furnace door.

[0072] (5) Start the vacuum system: Pump the pressure in the reaction chamber to below 5 Pa. After confirming that the airtightness of the reaction chamber is good, introduce argon with a flow rate of 500 sccm and slowly backfill to 5000 Pa.

[0073] (6) Temperature control: Start the temperature control system, set the heating program, and raise the temperature from room temperature to the growth temperature of graphene, 1350 °C. The heating method is staged heating, including a first heating stage with a first heating rate and a second heating stage with a second heating rate, and the first heating rate is greater than the second heating rate. Specifically, in the first stage of heating, raise the ambient temperature from room temperature of 20 °C to 1000 °C at a heating rate of 30 °C / min. In the second stage of heating, raise the ambient temperature from 1000 °C to 1350 °C at a heating rate of 15 °C / min to ensure stable temperature control and uniform heat field.

[0074] (7) Introduction of carbon source: When the temperature reaches 1350 °C, control the temperature to remain constant at 1350 °C for 10 minutes. Subsequently, use the bubbling method to transport the mixed liquid carbon source of pyridine and methanol into the reaction chamber. The volume fraction of methanol in the mixed liquid carbon source is 0.8%, the bubbling carrier gas is argon, and the flow rate is set to 300 sccm, and grow graphene continuously for 50 min.

[0075] (8) Cooling: After the growth is completed, immediately turn off the bubbling carrier gas, stop introducing the carbon source, and turn off the heating power supply to allow the temperature in the reaction chamber to cool naturally from 1350 °C to room temperature of 20 °C. During this process, continuously introduce argon to prevent residual reaction of the carbon source. When the temperature in the reaction chamber drops below 100 °C, turn off the vacuum system, backfill with argon to atmospheric pressure, open the furnace door, and take out the sample.

[0076] Example 7

[0077] This example provides a method for preparing graphene, which specifically includes the following steps:

[0078] (1) Substrate preparation: Immerse the sapphire substrate in acetone, ethanol, and deionized water in sequence for ultrasonic cleaning, with each cleaning lasting for 10 minutes. After cleaning, use high-purity nitrogen to dry the substrate for standby.

[0079] (2) Cleaning of the reaction chamber: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction chamber of the rapid-cooling wall electromagnetic induction heating furnace to remove the microparticles and impurities inside the reaction chamber.

[0080] (3) Purification of the reaction chamber atmosphere: Continuously introduce argon with a flow rate of 300 sccm into the reaction chamber and purge for 15 minutes to thoroughly remove the residual air and impurity gases in the reaction chamber and ensure the purity of the chamber atmosphere.

[0081] (4) Substrate placement: Place the sapphire substrate cleaned in step (1) in a graphite carrier, and accurately place the graphite carrier at the center of the reaction cavity of the rapid cold-wall electromagnetic induction heating furnace, ensuring symmetric placement. Then close the furnace door;

[0082] (5) Start the vacuum system: Pump the pressure in the reaction cavity to below 5 Pa. After confirming good airtightness of the reaction cavity, slowly backfill with argon at a flow rate of 500 sccm to 3500 Pa;

[0083] (6) Temperature control: Start the temperature control system, set the heating program, and raise the temperature from room temperature of 20 °C to 1350 °C. The heating method is staged heating, including a first heating stage with the first heating rate and a second heating stage with the second heating rate, and the first heating rate is greater than the second heating rate; specifically, in the first heating process, raise the ambient temperature from room temperature of 20 °C to 950 °C at a heating rate of 20 °C / min; in the second heating process, raise the ambient temperature from 950 °C to 1350 °C at a heating rate of 12 °C / min, ensuring stable temperature control and uniform heat field;

[0084] (7) Carbon source introduction: When the temperature reaches 1350 °C, control the temperature to remain constant at 1350 °C for 13 minutes; then, through the bubbling method, transport the mixed liquid carbon source of acetonitrile and propanol into the reaction cavity. The volume fraction of propanol in the mixed liquid carbon source is 0.9%, the bubbling carrier gas is argon, and the flow rate is set to 50 sccm, and grow graphene continuously for 70 min;

[0085] (8) Cooling: After the growth is completed, immediately close the bubbling carrier gas, stop introducing the carbon source, and turn off the heating power supply to allow the temperature in the reaction cavity to cool naturally from 1350 °C to room temperature of 20 °C. At the same time, continue to introduce argon to prevent residual reaction of the carbon source; when the temperature of the reaction cavity drops below 100 °C, turn off the vacuum system, backfill with argon to atmospheric pressure, open the furnace door, and take out the sample.

[0086] Example 8

[0087] This example provides a method for preparing graphene, which specifically includes the following steps:

[0088] (1) Substrate preparation: Immerse the sapphire substrate in acetone, ethanol, and deionized water in sequence for ultrasonic cleaning, with each cleaning lasting for 10 minutes; after cleaning, dry the substrate with high-purity nitrogen for standby;

[0089] (2) Reaction cavity cleaning: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction cavity of the rapid cold-wall electromagnetic induction heating furnace to remove particles and impurities inside the reaction cavity;

[0090] (3) Purification of the reaction chamber atmosphere: Continuously introduce argon with a flow rate of 300 sccm into the reaction chamber and purge for 15 minutes to thoroughly remove the residual air and impurity gases in the reaction chamber, ensuring the purity of the chamber atmosphere;

[0091] (4) Placement of the substrate: Place the sapphire substrate cleaned in step (1) in a graphite carrier, and accurately place the graphite carrier at the center of the reaction chamber of the rapid-cooling wall electromagnetic induction heating furnace to ensure symmetrical position. Then close the furnace door;

[0092] (5) Start the vacuum system: Pump the pressure in the reaction chamber to below 5 Pa. After confirming good airtightness of the reaction chamber, slowly backfill with argon with a flow rate of 500 sccm to 4000 Pa;

[0093] (6) Temperature control: Start the temperature control system, set the heating program, and raise the temperature from room temperature to 1450 °C. The heating method is staged heating, including a first heating stage with the first heating rate and a second heating stage with the second heating rate, and the first heating rate is greater than the second heating rate; Specifically, in the first stage of heating, raise the ambient temperature from room temperature of 20 °C to 900 °C with a heating rate of 30 °C / min; in the second stage of heating, raise the ambient temperature from 900 °C to 1450 °C with a heating rate of 15 °C / min to ensure stable temperature control and uniform heat field;

[0094] (7) Introduction of the carbon source: When the temperature reaches 1450 °C, control the temperature to remain constant at 1450 °C for 15 minutes; Subsequently, transport the mixed liquid carbon source of acetonitrile and ethanol into the reaction chamber by the bubbling method. The volume fraction of ethanol in the mixed liquid carbon source is 0.8%, the bubbling carrier gas is argon, the flow rate is set to 300 sccm, and grow graphene for 50 min;

[0095] (8) Cooling: After the growth is completed, immediately close the bubbling carrier gas, stop introducing the carbon source, and turn off the heating power supply to allow the temperature in the reaction chamber to naturally cool from 1450 °C to room temperature of 20 °C. During this process, continuously introduce argon to prevent residual reaction of the carbon source; When the temperature in the reaction chamber drops below 100 °C, turn off the vacuum system, backfill with argon to atmospheric pressure, open the furnace door, and take out the sample.

[0096] Comparative Example 1

[0097] The type of carbon source in this comparative example is different from that in Example 1; that is, the difference between this comparative example and Example 1 is that: the carbon source in step (7) is methane, that is, introduce methane into the reaction chamber, the methane flow rate is 60 sccm, and the introduction duration is 1 h.

[0098] Comparative Example 2

[0099] The addition amount of alcohol compounds in the liquid carbon source of this comparative example is different from that in Example 1; that is, the difference between this example and Example 1 is that the volume fraction of ethanol in the liquid carbon source in step (7) is 2%, which is higher than 1%.

[0100] Experimental Example 1

[0101] To verify the influence of different carbon source types on the preparation of graphene, Raman spectra of the products of Example 1, Example 2, and Comparative Example 1 were obtained in this experimental example, specifically as Figure 2 shown, where curve a represents the Raman spectrum of graphene in Example 1, curve b represents the Raman spectrum of graphene in Example 2, and curve c represents the Raman spectrum of graphene in Comparative Example 1.

[0102] The D peak in the Raman spectrum represents the defect peak. The greater the intensity of the D peak, the more defects it means; the G peak represents the image peak, which is a peak related to the sp 2 hybrid vibration between carbon atoms and reflects the lattice order of the material. When the intensity of the G peak is relatively high, it usually means that the material has a high degree of crystallinity and fewer defects. According to Figure 2 the Raman spectra, the corresponding ID D / IG G values were calculated for each example and comparative example. ID D is the intensity of the D peak, IG G is the intensity of the G peak. The lower the ID D / IG G value, the better the quality of graphene, the fewer defects, and the more ordered the structure. The specific details are shown in Table 1 below:

[0103] Table 1:

[0104] Group Carbon source composition <![CDATA[I D / I G value]]> Example 1 Acetonitrile + Ethanol 0.46 Example 2 Acetonitrile 0.85 Comparative Example 1 Methane 1.73

[0105] As can be seen from the above table, the liquid carbon source in Example 1 is a mixture of acetonitrile and ethanol, and its corresponding ID D / IG G value is the smallest, and the corresponding G peak is the sharpest. The smaller the ID D / IG G value, the lower the defect density in graphene and the better the crystallization quality. It can be seen that the mixture of acetonitrile and ethanol as a carbon source can provide a stable carbon source. At the same time, the hydroxyl radicals generated during the cracking process of ethanol can effectively remove amorphous carbon and inhibit the formation of defects. Therefore, the crystallinity of graphene has been significantly improved and the defect density has been effectively reduced. And the G peak corresponding to Example 1 is the sharpest, indicating that the arrangement of carbon atoms in the graphene of Example 1 is very regular and the crystallinity is good.

[0106] Comparing Example 1 and Example 2, it can be seen that in Example 2, ethanol is not added to the liquid carbon source, and only acetonitrile is used as the carbon source. The obtained graphene IDD / I G The value is relatively large, which means that the defect density in graphene is relatively high and the crystallization quality is poor. Without the assistance of ethanol, the effect of removing amorphous carbon is not as obvious as when ethanol is added, resulting in the ineffective suppression of the generation of defects; more defects appear in the graphene film, affecting the overall quality of graphene.

[0107] Moreover, the G peak corresponding to the graphene in Example 2 is relatively wide, and its crystallinity is not as good as that of the sample in Example 1. That is, without the participation of ethanol, the removal mechanism of amorphous carbon is lacking during the growth process of graphene, resulting in a decline in crystallization quality.

[0108] In Comparative Example 1, methane was used alone as the carbon source and hydrogen was not introduced, and the prepared graphene I D / I G value is significantly greater than the I D / I G value corresponding to the graphene prepared in Example 1 and Example 2; it can be seen that the defect density of the graphene prepared by using methane alone as the carbon source is very high and the crystallinity is poor; when methane is used as the carbon source and without the assistance of hydrogen, its cracking efficiency is relatively low, resulting in poor quality and many defects of graphene. Especially without the assistance of hydrogen, the growth process of graphene lacks regulation, which will lead to the generation of a large number of defects.

[0109] In summary, acetonitrile as the main carbon source can provide efficient carbon atom supply and promote the crystallization of graphene. At the same time, ethanol as an auxiliary material, through the hydroxyl radicals generated during its cracking process, can effectively remove amorphous carbon and further improve the crystallization quality of graphene.

[0110] Experimental Example 2

[0111] In order to verify the influence of the addition amount of ethanol in the carbon source on the preparation of graphene, the Raman spectrum of the graphene in Comparative Example 2 was further obtained in this experimental example (as shown by the d curve in Figure 2 ), and Example 1 was compared with Comparative Example 2, and the results are shown in Table 2 below:

[0112] Table 2:

[0113] Group Carbon source composition Volume fraction of ethanol <![CDATA[I D / I G value]]> Example 1 Acetonitrile + Ethanol 1.00％ 0.46 Comparative Example 2 Acetonitrile + Ethanol 2.00％ No G peak and 2D peak appeared

[0114] It can be seen that the G peak and 2D peak cannot be observed in the Raman spectrum of Comparative Example 2, indicating that the crystallinity of graphene is poor and there are many defects. Thus, it can be seen that when the volume fraction of ethanol is too high, the too strong etching effect will have a negative impact on the growth and quality of graphene, and even the graphene film cannot be formed. Therefore, the volume fraction of ethanol in the liquid carbon source of the present invention is less than or equal to 1%, which can ensure that while providing the carbon source and hydroxyl radicals, it will not overly interfere with the orderly growth of graphene.

[0115] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing graphene by chemical vapor deposition, characterized in that: It includes the following steps: Using a nitrogen-containing organic compound or a composition containing a nitrogen-containing organic compound and an alcohol compound as a carbon source, growing a graphene film on the surface of a substrate by chemical vapor deposition; wherein, in the composition, the volume fraction of the alcohol compound is less than or equal to 1%.

2. The method for preparing graphene by chemical vapor deposition according to claim 1, characterized in that: The carbon source is in a liquid state under the temperature range of 20 - 25 °C and the pressure condition of 50.663 - 101.325 kPa.

3. A method for preparing graphene by chemical vapor deposition according to claim 1 or 2, characterized in that: The nitrogen-containing organic compound includes one or two of acetonitrile and pyridine.

4. A method for preparing graphene by chemical vapor deposition according to any one of claims 1-3, characterized in that: The alcohol compound includes one or more of methanol, ethanol, propanol, and isopropanol.

5. A method for preparing graphene by chemical vapor deposition according to any one of claims 1-4, characterized in that: The carbon source includes acetonitrile and ethanol, and the volume fraction of ethanol is less than or equal to 1%.

6. The method for preparing graphene by chemical vapor deposition according to claim 5, wherein: The volume fraction of ethanol in the carbon source is 0.8 - 1%.

7. A method for preparing graphene by chemical vapor deposition according to any one of claims 1-6, characterized in that: During the chemical vapor deposition process, the input flow rate of the carbon source is 50 - 300 sccm, the growth duration of graphene is 50 - 70 min, the growth pressure is 2000 - 5000 Pa, and the growth temperature is 1350 - 1450 °C.

8. A method for preparing graphene by chemical vapor deposition according to any one of claims 1 - 7, characterized in that: During the chemical vapor deposition process, before inputting the carbon source, the ambient temperature is raised to the growth temperature of graphene, which includes a first heating stage of heating at a first heating rate and a second heating stage of heating at a second heating rate, and the first heating rate is greater than the second heating rate.

9. A method for preparing graphene by chemical vapor deposition according to claim 8, characterized in that: The first heating stage includes heating the ambient temperature to 900 - 1000 °C at a first heating rate of 20 - 30 °C / min; the second heating stage includes heating the ambient temperature to the graphene growth temperature of 1350 - 1450 °C at a second heating rate of 10 - 15 °C / min.

10. A method for preparing graphene by chemical vapor deposition according to any one of claims 1-9, characterized in that: During the chemical vapor deposition process, after the ambient temperature is raised to the graphene growth temperature, the growth temperature is maintained for 5 - 15 min, and then the carbon source is input.

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