A method for preparing a high-uniformity graphene film by using a mold to construct a specific confined space

Abstract

The application relates to a method for preparing a high-uniformity graphene film by constructing a specific limited space by using a mold, and relates to a method for preparing a graphene film. The application aims to solve the problems that the graphene prepared by a chemical vapor deposition method needs a transfer step, the graphene film grown on an insulating material substrate is affected by long nucleation time, slow growth rate and more defects, and the application of the graphene is limited. The method comprises the following steps: one, ultrasonic cleaning; two, placing a non-metal substrate cleaned by ultrasonic cleaning into a center groove of a high-temperature mold cleaned by ultrasonic cleaning, and covering a cover piece cleaned by ultrasonic cleaning on the center groove of the high-temperature mold; three, placing a reactor provided with the non-metal substrate at a central position of a high-temperature tube furnace, growing a graphene film on the non-metal substrate by using a chemical vapor deposition method, and obtaining a high-uniformity graphene film. The application can obtain a method for preparing a high-uniformity graphene film by constructing a specific limited space by using a mold.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing a graphene film. BACKGROUND

[0002] Currently, the chemical vapor deposition growth of graphene is mainly based on metals such as Cu and Ni which have catalytic effect on the cracking of methane, and if the graphene is to be transferred to a silicon substrate for the application of a transistor, an additional graphene film transfer step is required. In order to avoid the cumbersome transfer step, the growth of graphene film directly on an insulating material substrate is widely studied. For quartz, silicon wafer, silicon oxide wafer, sapphire and other insulating substrates, their catalytic ability for carbon source decomposition is very limited. Thermal cracking is the main way of carbon source decomposition in the CVD system, and the generation and supply of active carbon species in the gas phase reaction is an important process for the growth of graphene on the surface of the insulating substrate. The growth of graphene directly on the insulating substrate is often affected by long nucleation time, slow growth rate and more defects, because the main place of carbon source thermal cracking is in the furnace tube, and the cracking barrier is high and the efficiency is low, which makes the concentration of carbon active molecules in the reaction system very low, and it is difficult to splice into a continuous graphene film in a short time, which limits the application of graphene. SUMMARY

[0003] The purpose of the present application is to solve the problems of the current chemical vapor deposition growth of graphene which requires a transfer step and the growth of graphene film on an insulating material substrate which is affected by long nucleation time, slow growth rate and more defects, and to provide a method for preparing a high uniformity graphene film by constructing a specific confined space using a mold.

[0004] A method for preparing a high uniformity graphene film by constructing a specific confined space using a mold is completed by the following steps:

[0005] I. Ultrasonic cleaning:

[0006] The non-metallic substrate, the cover sheet and the high-temperature-resistant mold with a recess in the center are ultrasonically cleaned, and then blown dry to obtain the ultrasonically cleaned non-metallic substrate, the cover sheet and the high-temperature-resistant mold with a recess in the center;

[0007] II. The ultrasonically cleaned non-metallic substrate is placed in the center recess of the ultrasonically cleaned high-temperature-resistant mold, and the ultrasonically cleaned cover sheet is then covered on the center recess of the high-temperature-resistant mold, wherein the center of the cover sheet is aligned with the center of the recess, to obtain a reactor containing the non-metallic substrate;

[0008] III. The reactor containing the non-metallic substrate is placed at the center of the high-temperature tube furnace, and a graphene film is grown on the non-metallic substrate by chemical vapor deposition to obtain a high uniformity graphene film;

[0009] The process of the chemical vapor deposition method described in step three is specifically as follows: inert gas and hydrogen are introduced into a high-temperature tube furnace, the flow rate of the inert gas is controlled to be 10-500 mL / min, the flow rate of the hydrogen is controlled to be 1-100 mL / min, the reactor loaded with the nonmetallic substrate is heated to 900-1200 DEG C, and is kept at 900-1200 DEG C for 5-30 min; the flow rates of the inert gas and the hydrogen are kept unchanged, carbon source gas is introduced into the high-temperature tube furnace at 900-1200 DEG C, graphene is grown on the nonmetallic substrate, the growth time is 2-6 h, after the growth is completed, the carbon source gas is turned off, and the graphene thin film with high uniformity is obtained by cooling to room temperature under the protection of the inert gas and the hydrogen.

[0010] Principle of the present application:

[0011] Firstly, the present application increases the controllability of the graphene growth process on the insulating substrate, the present application designs a mold with controllable diffusion distance to adjust the carbon active molecule concentration near the substrate during the graphene growth process, thereby controlling the graphene deposition rate to improve the controllability of the graphene growth, and the present application can prevent dust and other pollutants in the furnace cavity from affecting the cleanliness of the growing graphene by directly covering the mold surface with the upper cover sheet, thereby improving the quality and uniformity of the obtained graphene thin film; the present application uses a high-temperature-resistant mold as a container for the silicon substrate, the uppermost layer is covered with a cover sheet with a side length of Wo, a small reaction container is constructed, and a graphene thin film with high quality and high uniformity is obtained on the silicon substrate, which has the advantages of low cost, simple operation, high uniformity of the obtained graphene thin film, and few defects, and can be used for preparing large-area graphene thin films on insulating substrates.

[0012] Secondly, the present application uses a high-temperature-resistant mold to load the nonmetallic substrate, and provides a confined space for the nonmetallic substrate through the groove in the mold and the upper cover sheet of the mold, so that a graphene thin film with few defects and high uniformity can be obtained, and the use of the mold greatly improves the quality of the obtained graphene. Furthermore, the present application can grow graphene on substrates of different specifications by changing the lengths of Ls, Lt and Wo, which can be extended to the growth of larger size graphene thin films, and is conducive to industrial application.

[0013] Thirdly, the present application has the advantages of simple operation and low cost, and the quality of the obtained graphene thin film is better than that obtained by the traditional growth method, so the present application method can be widely applied to the preparation of large-area high-quality graphene thin films on insulating substrates. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The structure diagram for constructing a specific confined space by using the mold in Example 1 is shown in the figure, wherein 1 is a cover sheet, 2 is a nonmetallic substrate, 3 is a high-temperature-resistant mold with a groove in the center, and 4 is the central groove of the high-temperature-resistant mold.

[0015] Figure 2 Digital photo of non-metallic substrate placed into the groove in the center of the high-temperature-resistant mold in Example 1, and then covered by the cover sheet;

[0016] Figure 3 Digital photo of the graphene film grown on the silicon wafer using the mold in Example 1 and by the chemical vapor deposition method;

[0017] Figure 4 Raman comparison chart of the center and edge area of the graphene film grown on the silicon wafer using the mold in Example 1 and by the chemical vapor deposition method, wherein 1 is the edge area, and 2 is the center area;

[0018] Figure 5 SEM chart of the graphene film grown on the silicon wafer using the mold in Example 1 and by the chemical vapor deposition method;

[0019] Figure 6 SEM chart of the graphene film grown on the silicon wafer without using the high-temperature-resistant mold with the groove in the center and by the same chemical vapor deposition method as in Example 1 in Example 6;

[0020] Figure 7 Digital photo of the graphene film grown on the silicon wafer with the substrate directly contacting the cover sheet in Example 5;

[0021] Figure 8 Raman comparison chart of the center and edge area of the graphene film grown on the silicon wafer with the substrate directly contacting the cover sheet in Example 5, wherein 1 is the edge area, and 2 is the center area;

[0022] Figure 9 Raman spectrum comparison chart of the graphene film grown on the silicon wafer in Example 1 and Example 6, wherein 1 is the graphene film grown on the silicon wafer in Example 6, and 2 is the graphene film grown on the silicon wafer in Example 1;

[0023] Figure 10 Raman spectrum comparison chart of the graphene film grown on the silicon wafer with different Wo lengths. DETAILED DESCRIPTION

[0024] Specific embodiment one: a method for preparing a high-uniformity graphene film by constructing a specific confined space by using a mold, which is completed according to the following steps:

[0025] I. Ultrasonic cleaning

[0026] The non-metallic substrate, the cover sheet, and the high-temperature-resistant mold with the groove in the center are ultrasonically cleaned, and then blown dry to obtain the ultrasonically cleaned non-metallic substrate, the cover sheet, and the high-temperature-resistant mold with the groove in the center;

[0027] II. Put the nonmetallic substrate cleaned by ultrasonic into the center groove of the high-temperature mold cleaned by ultrasonic, and then cover the lid piece cleaned by ultrasonic onto the center groove of the high-temperature mold, wherein the center of the lid piece is aligned with the center of the groove, to obtain a reactor containing the nonmetallic substrate;

[0028] III. Put the reactor containing the nonmetallic substrate into the center of the high-temperature tube furnace, and grow a graphene film on the nonmetallic substrate by chemical vapor deposition to obtain a graphene film with high uniformity.

[0029] The process of the chemical vapor deposition method in step III is specifically as follows: inert gas and hydrogen are introduced into the high-temperature tube furnace, the flow rate of the inert gas is controlled to be 10-500 mL / min, the flow rate of the hydrogen is controlled to be 1-100 mL / min, the reactor containing the nonmetallic substrate is heated to 900-1200℃, and is kept at 900-1200℃ for 5-30 min; the flow rates of the inert gas and the hydrogen are kept unchanged, carbon source gas is introduced into the high-temperature tube furnace at 900-1200℃, the graphene grows on the nonmetallic substrate, the growth time is 2-6 h, after the growth is completed, the carbon source gas is turned off, and the temperature is cooled to room temperature under the protection of the inert gas and the hydrogen, to obtain a graphene film with high uniformity.

[0030] Specific implementation method II: The difference between this implementation method and the specific implementation method I is that: the nonmetallic substrate, the lid piece and the high-temperature mold with a center groove are sequentially cleaned by ultrasonic using acetone, isopropyl alcohol and ultrapure water as solvents, and then dried by nitrogen, to obtain the nonmetallic substrate cleaned by ultrasonic and the high-temperature mold with a center groove cleaned by ultrasonic. The other steps are the same as those in the specific implementation method I.

[0031] Specific implementation method III: The difference between this implementation method and the specific implementation method I or II is that: the material of the nonmetallic substrate in step I is a silicon wafer, a quartz wafer, a silicon wafer with a silicon dioxide coating, aluminum oxide or silicon nitride. The other steps are the same as those in the specific implementation method I or II.

[0032] Specific implementation method IV: The difference between this implementation method and any one of the specific implementation methods I to III is that: the size of the nonmetallic substrate in step I is Ls x Ls x d1, wherein 1 cm≤Ls≤5 cm, and 0

[0033] Specific implementation method V: The difference between this implementation method and any one of the specific implementation methods I to IV is that: the material of the lid piece in step I is a silicon wafer, a quartz wafer, a silicon wafer with a silicon dioxide coating, aluminum oxide or silicon nitride. The other steps are the same as those in the specific implementation method I to IV.

[0034] Sixth embodiment: the difference between this embodiment and the first to fifth embodiments is that the size of the cover sheet in step one is Wo x Wo x d3, where Ls < Wo ≤ Lt, 0 < d3 ≤ 0.5 cm. The other steps are the same as the first to fifth embodiments.

[0035] Seventh embodiment: the difference between this embodiment and the first to sixth embodiments is that the material of the high-temperature-resistant mold with a recessed center in step one is quartz, alumina or corundum. The other steps are the same as the first to sixth embodiments.

[0036] Eighth embodiment: the difference between this embodiment and the first to seventh embodiments is that the outer size of the high-temperature-resistant mold with a recessed center in step one is Lt x Lt x d, and the size of the recess is Ls x Ls x d2, where 5 cm ≤ Lt ≤ 10 cm, 0.5 cm ≤ d ≤ 2 cm, d1 < d2 < d. The other steps are the same as the first to seventh embodiments.

[0037] Ninth embodiment: the difference between this embodiment and the first to eighth embodiments is that the inert gas is argon, helium or nitrogen; and the carbon source gas is one or more of methane, ethane, acetylene, ethylene and propane. The other steps are the same as the first to eighth embodiments.

[0038] Tenth embodiment: the difference between this embodiment and the first to ninth embodiments is that the flow ratio of the carbon source gas to the inert gas is (0.001-5): 1. The other steps are the same as the first to ninth embodiments.

[0039] The following examples are used to verify the beneficial effects of the present application:

[0040] Example 1: A method for preparing a high-uniformity graphene film using a mold to construct a specific confined space, which is completed according to the following steps:

[0041] I. Ultrasonic cleaning:

[0042] The non-metallic substrate, cover sheet and high-temperature-resistant mold with a recessed center are sequentially ultrasonically cleaned using acetone, isopropyl alcohol and ultrapure water as solvents, and then dried with nitrogen to obtain the ultrasonically cleaned non-metallic substrate, cover sheet and high-temperature-resistant mold with a recessed center.

[0043] The material of the non-metallic substrate in step one is a silicon wafer;

[0044] The size of the non-metallic substrate in step one is Ls x Ls x d1, where Ls = 1.5 cm and d1 = 0.06 cm;

[0045] The material of the cover sheet in step one is a silicon wafer;

[0046] The size of the cover piece in step one is Wo x Wo x d3, wherein Wo = 3 cm and d3 = 0.06 cm;

[0047] The material of the high-temperature-resistant mold with a recess in the center in step one is corundum;

[0048] The outer size of the high-temperature-resistant mold with a recess in the center in step one is Lt x Lt x d, and the size of the recess is Ls x Ls x d2, wherein Ls = 1.5 cm, Lt = 5 cm, d = 0.5 cm, and d2 = 0.1 cm;

[0049] II. The nonmetallic substrate cleaned by ultrasonic cleaning is placed in the recess in the center of the high-temperature-resistant mold cleaned by ultrasonic cleaning, and the cover piece cleaned by ultrasonic cleaning is used to cover the recess in the center of the high-temperature-resistant mold, wherein the center of the cover piece is aligned with the center of the recess, thereby obtaining a reactor containing the nonmetallic substrate;

[0050] III. The reactor containing the nonmetallic substrate is placed at the center of the high-temperature tube furnace, and a graphene film with high uniformity is grown on the nonmetallic substrate by chemical vapor deposition, thereby obtaining the graphene film with high uniformity;

[0051] The process of the chemical vapor deposition in step III is specifically as follows: inert gas and hydrogen are introduced into the high-temperature tube furnace, the flow rate of the inert gas is controlled to be 120 mL / min, the flow rate of the hydrogen is controlled to be 30 mL / min, the reactor containing the nonmetallic substrate is heated to 1180℃, and is kept at 1180℃ for 10 min; the flow rates of the inert gas and the hydrogen are kept unchanged, carbon source gas is introduced into the high-temperature tube furnace at 1180℃, the graphene is grown on the nonmetallic substrate, the growth time is 3 h, after the growth is completed, the carbon source gas is turned off, and the inert gas and the hydrogen are used for protection to cool to room temperature, thereby obtaining the graphene film with high uniformity;

[0052] The inert gas is argon;

[0053] The carbon source gas is methane, and the flow rate of the methane is controlled to be 1.5 mL / min.

[0054] The flow rate ratio of the carbon source gas, the hydrogen, and the inert gas is 1.5:30:120.

[0055] Example 2: The difference between this example and Example 1 is that Wo = 2 cm in step one. The others are the same as those in Example 1.

[0056] Example 3: The difference between this example and Example 1 is that Wo = 4 cm in step one. The others are the same as those in Example 1.

[0057] Example 4: The difference between this example and Example 1 is that Wo = 5cm in step one. Everything else is the same as in Example 1.

[0058] Example 5: The difference between this example and Example 1 is that d1 = 0.1 cm in step one (i.e., the substrate and the cover plate are in direct contact). Everything else is the same as in Example 1.

[0059] Example 6: The method for growing graphene directly on a silicon wafer without using a high-temperature resistant mold with a central groove is completed according to the following steps:

[0060] 1. The silicon wafer is ultrasonically cleaned by sequentially using acetone, isopropanol and ultrapure water as solvents, and then dried with nitrogen gas to obtain the ultrasonically cleaned silicon wafer.

[0061] 2. After ultrasonic cleaning, the silicon wafer is placed in the center of a high-temperature tube furnace, and a graphene film is grown on the silicon wafer using chemical vapor deposition to obtain a highly uniform graphene film.

[0062] The specific process of chemical vapor deposition described in step three is as follows: Inert gas and hydrogen are introduced into a high-temperature tube furnace, with the flow rate of inert gas controlled at 120 mL / min and the flow rate of hydrogen controlled at 30 mL / min. The reactor containing the non-metallic substrate is heated to 1180°C and held at 1180°C for 10 min. While keeping the flow rates of inert gas and hydrogen constant, carbon source gas is introduced into the high-temperature tube furnace at 1180°C. Graphene grows on the silicon wafer for 3 h. After growth, the carbon source gas is turned off, and the furnace is cooled to room temperature under the protection of inert gas and hydrogen to obtain a highly uniform graphene film.

[0063] The inert gas mentioned is argon;

[0064] The carbon source gas is methane, and the flow rate of methane is controlled at 1.5 mL / min;

[0065] The flow rate ratio of the carbon source gas, hydrogen, and inert gas is 1.5:30:120.

[0066] Figure 1 This is a schematic diagram of the structure of a specific confined space constructed using a mold in Example 1. In the figure, 1 is a cover plate, 2 is a non-metallic substrate, 3 is a high-temperature resistant mold with a groove in the center, and 4 is the central groove of the high-temperature resistant mold.

[0067] from Figure 1 It is known that the present invention can regulate the growth quality of graphene by changing the length Wo of the cover sheet.

[0068] Figure 2 This is a digital photograph of the non-metallic substrate placed in the groove in the center of the high-temperature mold in Example 1, and then covered with a cover sheet.

[0069] Figure 3 This is a digital photograph of the graphene film grown on a silicon wafer using a mold and chemical vapor deposition in Example 1.

[0070] Figure 4 The image shows a Raman comparison of the center and edge regions of graphene films grown on silicon wafers using a mold and chemical vapor deposition in Example 1. In the image, 1 represents the edge region and 2 represents the center region.

[0071] from Figure 4 It can be seen that the Raman curves at the two locations have similar shapes. The intensity ratio of the 2D peak to the G peak, I2D / IG, is an important parameter for characterizing the thickness of the graphene film. The larger the ratio I2D / IG, the thinner the graphene film. The I2D / IG value in the central region is 1.15, which is very close to the I2D / IG value of 1.17 in the edge region, indicating that the graphene film thickness distribution in the central and edge regions is uniform.

[0072] Figure 5 SEM images of graphene films grown on silicon wafers using a mold and chemical vapor deposition in Example 1;

[0073] from Figure 5 It can be seen that the graphene film obtained under this condition has a lower defect rate and better flatness.

[0074] Figure 6 SEM images of graphene films grown on silicon wafers in Example 6 without using a high-temperature mold with a central groove and using the same chemical vapor deposition method as in Example 1;

[0075] from Figure 6 It can be seen that the graphene film obtained under this condition has a high defect density and poor flatness.

[0076] Figure 7 This is a digital photograph of a graphene film grown on a silicon wafer in Example 5, where the substrate and cover plate are in direct contact.

[0077] from Figure 7 It can be seen that the graphene film obtained under this condition is not uniformly distributed on the substrate surface, and the central region and the edge region show obvious color contrast.

[0078] Figure 8 This is a Raman comparison image of the center and edge regions of the graphene film grown on the silicon wafer in Example 5 where the substrate and cover sheet are in direct contact. In the image, 1 represents the edge region and 2 represents the center region.

[0079] from Figure 8It can be seen that the Raman curve shapes of the two regions have obvious differences, and the intensity ratio of the 2D peak to the G peak I2D / IG is an important parameter for representing the thickness of the graphene film. The I2D / IG value of the central region is 1.21, and the I2D / IG value of the edge region is 0.89, which indicates that the thickness distribution of the graphene film in the central region is different from that in the edge region.

[0080] Figure 9 For the Raman spectrum comparison of the graphene films grown on the silicon wafer in Example 1 and Example 6, Figure 1 is the graphene film grown on the silicon wafer in Example 6, and Figure 2 is the graphene film grown on the silicon wafer in Example 1.

[0081] From Figure 9 It can be seen that the Raman curve shapes of the graphene films obtained in the two cases have great differences. The ratio of the D peak intensity to the G peak intensity ID / IG is usually used to determine the defect content of graphene. The greater the ratio ID / IG, the higher the defect density of the graphene film. In Example 1, ID / IG is 1.07, and I2D / IG is 0.72. In Example 6, ID / IG is 0.51, and I2D / IG is 1.91, which indicates that the graphene film grown using the mold has a lower defect density and fewer layers.

[0082] Figure 10 For the Raman spectrum comparison of the graphene films grown on the silicon wafer in Example 1 and Example 6, Figure 1 is the graphene film grown on the silicon wafer in Example 6, and Figure 2 is the graphene film grown on the silicon wafer in Example 1.

[0083] From Figure 10 It can be seen that the Raman curve shapes of the graphene films obtained in the two cases have great differences. The ratio of the D peak intensity to the G peak intensity ID / IG is usually used to determine the defect content of graphene. The greater the ratio ID / IG, the higher the defect density of the graphene film. In Example 1, ID / IG is 1.07, and I2D / IG is 0.72. In Example 6, ID / IG is 0.51, and I2D / IG is 1.91, which indicates that the graphene film grown using the mold has a lower defect density and fewer layers.

Claims

1. A method for fabricating a high uniformity graphene film using a mold to construct a specific confined space, characterized in that The method is specifically completed by the following steps: I. Ultrasonic cleaning: The non-metallic substrate, cover sheet and center recessed high-temperature mold are sequentially subjected to ultrasonic cleaning using acetone, isopropyl alcohol and ultrapure water as solvents, and then dried using nitrogen to obtain the non-metallic substrate, cover sheet and center recessed high-temperature mold after ultrasonic cleaning; The material of the non-metallic substrate in step one is a silicon wafer; The size of the non-metallic substrate in step one is Ls x Ls x d1, wherein Ls = 1.5 cm and d1 = 0.06 cm; The material of the cover sheet in step one is a silicon wafer; The size of the cover sheet in step one is Wo x Wo x d3, wherein Wo = 3 cm and d3 = 0.06 cm; The material of the center recessed high-temperature mold in step one is corundum; The outer size of the center recessed high-temperature mold in step one is Lt x Lt x d, and the size of the recess is Ls x Ls x d2, wherein Ls = 1.5 cm, Lt = 5 cm, d = 0.5 cm and d2 = 0.1 cm; II. The non-metallic substrate after ultrasonic cleaning is placed in the center recess of the high-temperature mold after ultrasonic cleaning, and the cover sheet after ultrasonic cleaning is covered on the center recess of the high-temperature mold, wherein the center of the cover sheet is aligned with the center of the recess, to obtain a reactor containing a non-metallic substrate; III. The reactor containing a non-metallic substrate is placed at the center of a high-temperature tube furnace, and a graphene film is grown on the non-metallic substrate by chemical vapor deposition to obtain a high-uniformity graphene film; The process of the chemical vapor deposition method in step III is specifically as follows: inert gas and hydrogen are introduced into the high-temperature tube furnace, the flow rate of the inert gas is controlled to be 120 mL / min, the flow rate of the hydrogen is controlled to be 30 mL / min, the reactor containing a non-metallic substrate is heated to 1180℃, and maintained at 1180℃ for 10 min; the flow rates of the inert gas and the hydrogen are kept unchanged, carbon source gas is introduced into the high-temperature tube furnace at 1180℃, graphene is grown on the non-metallic substrate, the growth time is 3 h, after the growth is completed, the carbon source gas is turned off, and the temperature is cooled to room temperature under the protection of the inert gas and the hydrogen to obtain a high-uniformity graphene film; The inert gas is argon; The carbon source gas is methane, and the flow rate of the methane is controlled to be 1.5 mL / min; The flow rate ratio of the carbon source gas, hydrogen and inert gas is 1.5:30:120.

Images