Double-layer graphene film and method for preparing the same

Abstract

The application discloses a preparation method of a double-layer graphene film, which comprises the following steps: S1, introducing hydrogen and methane into a vapor deposition system to perform a vapor deposition reaction, and growing a graphene core with a double-layer graphene domain on a substrate; S2, introducing oxygen into the vapor deposition system; and S3, increasing the methane partial pressure and continuing to grow. The method for directly growing the double-layer graphene film by the chemical vapor deposition method of the application firstly forms a double-layer graphene small core; then the unstable graphene core is etched and removed by introducing oxygen; finally, the methane partial pressure is increased to promote the growth of the double-layer graphene, so that the double-layer graphene film with a second-layer graphene layer area being similar to a first-layer area is prepared. Moreover, the method of the application can form the double-layer graphene film with an arbitrary twist angle.

Description

Technical Field

[0001] The invention belongs to the field of material preparation, and particularly relates to a method for preparing double-layer graphene and the double-layer graphene prepared by the method. Background Art

[0002] Graphene is composed of carbon atoms connected by sp 2 Quasi-two-dimensional crystalline materials formed by hybridization have excellent electrical, optical and other properties. Double-layer graphene is two separate layers of graphene coupled into a double layer. At present, double-layer graphene is mostly prepared by micromechanical exfoliation and manual stacking methods, which inevitably introduce interlayer contamination during the transfer process. Among the many growth methods, chemical vapor deposition is the most promising direct growth method for high-quality graphene. In 2020, Pan Mengchun et al. disclosed a large-area directly grown twisted double-layer graphene and its preparation method (CN111573658A). They used a single-crystal metal film with carbon solubility as a substrate, and used the CVD method to control the temperature to grow the first layer of graphene on its upper surface. Then, they controlled the cooling rate and used the single-crystal metal film to dissolve carbon and then precipitate the second layer of graphene between the substrate and the first layer of graphene, thereby directly preparing double-layer graphene. Although this method is relatively simple to operate, the area of ​​the second-layer graphene domain prepared is very small and the shape is irregular. The double-layer graphene currently prepared has a significantly reduced area of ​​the second-layer graphene domain, which is very different from the area of ​​the first-layer graphene, which is not conducive to subsequent scientific research and practical applications. Summary of the Invention

[0003] The present invention provides a method for preparing a double-layer graphene film with two layers having similar areas by chemical vapor deposition, and the double-layer graphene film prepared by the method.

[0004] The present invention provides a method for preparing a double-layer graphene film, comprising: S1, introducing hydrogen and methane into a vapor deposition system to carry out a vapor deposition reaction, thereby growing a graphene core having a double-layer graphene domain on a substrate; S2, introducing oxygen into the vapor deposition system; and S3, increasing the methane partial pressure to continue the growth.

[0005] According to one embodiment of the present invention, in step S1, the methane partial pressure is 0.15-0.8 Pa, and the growth time is 3-20 min.

[0006] According to another embodiment of the present invention, the partial pressure of oxygen in steps S2 and S3 is greater than 0 and less than or equal to 5 Pa.

[0007] According to another embodiment of the present invention, the methane partial pressure in step S3 is 6-14 Pa.

[0008] According to another embodiment of the present invention, the partial pressure of methane in step S2 is 0.15-0.8 Pa.

[0009] According to another embodiment of the present invention, the growth temperature of steps S1-S3 is 1020°C-1080°C.

[0010] According to another embodiment of the present invention, the step of heat treating the substrate is further included before step S1.

[0011] According to another embodiment of the present invention, the step of heat treating the substrate is further included before step S1.

[0012] According to another embodiment of the present invention, the substrate is a metal substrate.

[0013] According to another embodiment of the present invention, the substrate is copper or copper-nickel alloy.

[0014] The present invention also provides a double-layer graphene film prepared by the method.

[0015] The present invention provides a method for directly growing a double-layer graphene film using chemical vapor deposition. The method first forms a double-layer graphene core; then, oxygen is introduced to etch away unstable graphene cores; finally, the partial pressure of methane is increased to promote the growth of the double-layer graphene, thereby producing a double-layer graphene film in which the area of ​​the second graphene layer is approximately the same as that of the first layer. Furthermore, the method can form a double-layer graphene film with any twist angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a scanning electron microscope (SEM) photograph of the double-layer graphene film prepared in Example 1.

[0017] Figure 2 This is an industrial microscope (OM) photograph of the double-layer graphene film prepared in Example 2.

[0018] Figure 3 This is a scanning electron microscope (SEM) photograph of the double-layer graphene film prepared in Example 3.

[0019] Figure 4A This is a statistical diagram of the second layer area of ​​different domains of the double-layer graphene film sample prepared in Example 4.

[0020] Figure 4B This is a statistical chart of the ratio of the second layer area to the first layer area in different domains of the double-layer graphene film sample prepared in Example 4.

[0021] Figure 5 This is an industrial microscope (OM) photograph of the double-layer graphene film prepared in Example 5.

[0022] Figure 6 This is an industrial microscope (OM) photograph of the double-layer graphene film prepared in Example 5.

[0023] Figure 7 This is a scanning electron microscope (SEM) photograph of the double-layer graphene film prepared in Comparative Example 1.

[0024] Figure 8 This is an industrial microscope (OM) image of the double-layer graphene film prepared in Comparative Example 2.

[0025] Figure 9 This is an industrial microscope (OM) photograph of the double-layer graphene film prepared in Comparative Example 3.

[0026] Figure 10 This is a scanning electron microscope (SEM) image of the double-layer graphene film prepared in Comparative Example 4.

[0027] Figure 11 This is an industrial microscope (OM) photograph of the double-layer graphene film prepared in Comparative Example 5. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to specific embodiments.

[0029] The method for preparing a double-layer graphene film of the present invention comprises: S1, introducing hydrogen and methane into a vapor deposition system to carry out a vapor deposition reaction, thereby growing a graphene core having a double-layer graphene domain on a substrate; S2, introducing oxygen into the vapor deposition system; and S3, increasing the methane partial pressure to continue the growth.

[0030] In step S1, a graphene core having a double-layer graphene domain is first formed on a substrate. In this step, the methane partial pressure can be 0.15-0.8 Pa, and the growth time is 3-20 minutes. The methane and hydrogen partial pressures in this step can be any value within the aforementioned range, such as, but not limited to, 0.15 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.7 Pa, 0.8 Pa, etc.

[0031] In step S2, oxygen is introduced into the vapor deposition system. Oxygen etches the unstable graphene cores, reducing the density of the graphene domains and facilitating the growth of stable bilayer graphene cores. The methane partial pressure in this step can be 0.15-0.8 Pa. The methane partial pressure in step S2 can be the same.

[0032] Next, in step S3, the partial pressure of methane is increased, that is, the inflow of the carbon source gas is increased to promote the rapid growth of the graphene core. In this step, the partial pressure of methane can be any value within the range of 6-14 Pa, such as, but not limited to, 6 Pa, 7 Pa, 8 Pa, 9 Pa, 10 Pa, 11 Pa, 12 Pa, 13 Pa, 14 Pa, etc. Preferably, oxygen is still introduced in this step. Due to the presence of oxygen, the migration barrier of carbon active species between graphene layers is reduced, making it easier for carbon active species to participate in the growth of the second layer, thereby increasing the growth rate of the second layer of graphene, and then obtaining a double-layer graphene film with two layers of similar area.

[0033] The partial pressures of oxygen introduced in steps S2 and S3 can be the same or different. However, the oxygen partial pressure in both steps is between greater than 0 and less than or equal to 5 Pa. An oxygen partial pressure exceeding 5 Pa can cause oxidation of the substrate and graphene surface, thereby affecting the quality of the produced double-layer graphene. The methane partial pressures in steps S2 and S3 can be the same or different.

[0034] The amount of hydrogen introduced in steps S1-S3 can be any amount suitable for gas phase growth of graphene. The growth temperature in steps S1-S3 can be 1020°C-1080°C.

[0035] Before step S1, a heat treatment step is also included for the substrate to remove dirt and impurities on the surface of the substrate. The heat treatment step can be to place the substrate in the range of 800°C-900°C under a protective atmosphere (such as hydrogen, argon, etc.) for a period of time, and then continue to heat it to 1020°C-1080°C using a protective gas (such as hydrogen, etc.) and maintain it for a period of time to complete the heat treatment. The pressure during the heating and annealing stages can be maintained between 200Pa and 5KPa.

[0036] The substrate used in the vapor deposition system can be any suitable substrate, such as a metal substrate, but not limited to, copper, copper-nickel alloy, etc.

[0037] The double-layer graphene film prepared by the preparation method of the present invention has an area difference between the upper and lower layers and can have an arbitrary twist angle, and can be widely used in scientific research and practical applications.

[0038] The present invention is further described below by way of specific examples. However, these examples are merely exemplary and do not limit the scope of the present invention in any way. In the following examples and comparative examples, all reagents, materials, and instruments used are commercially available unless otherwise specified. The flow rates described in the following examples and comparative examples refer to volume flow rates.

[0039] Example 1

[0040] A Cu foil was used as the substrate for chemical vapor deposition (CVD) of graphene and placed in a CVD furnace. The air inside the CVD furnace (a tubular furnace) was evacuated to near-vacuum (<8 Pa). A certain amount of protective gas (1000 sccm of argon) was introduced into the tubular furnace and the furnace temperature was raised to 850°C at the center, where it was held for 5 minutes. The temperature was then raised to 1070°C using a protective gas (1000 sccm of hydrogen) and held for 40 minutes to complete the substrate processing. The pressure was maintained at 1 kPa during the heating and annealing stages.

[0041] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen and methane into the tubular furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 999.5Pa), and the flow rate of methane is 0.5sccm (partial pressure is about 0.499Pa), and grow at a temperature of 1070℃ for 10 minutes (step S1).

[0042] Then, the flow rates of hydrogen and methane are kept constant, oxygen is introduced (the oxygen partial pressure is kept at 3 Pa), and the growth temperature is maintained at 1070°C (step S2).

[0043] Next, while maintaining the hydrogen flow rate constant, the methane flow rate was increased to 1.1 sccm (partial pressure approximately 13.604 Pa), maintaining a growth temperature of 1070°C. Oxygen was also introduced (maintaining an oxygen partial pressure of 3 Pa) to maintain the growth temperature at 1070°C. During this step, the pressure in the chemical vapor deposition furnace was controlled at 13 kPa (step S3), and the growth period lasted for 150 minutes.

[0044] Figure 1 The prepared double-layer graphene film is shown in Figure 1. The left and right figures are SEM images of different parts of the same double-layer film. As can be seen from both figures, the double-layer graphene film prepared in Example 1 has a twist angle, and the areas of the two layers are comparable.

[0045] Example 2

[0046] The heat treatment process of the metal Cu foil is the same as that in Example 1.

[0047] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen and methane into the tube furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 999.7Pa), and the flow rate of methane is 0.3sccm (partial pressure is about 0.2999Pa), and grow at a temperature of 1070℃ for 15min (step S1).

[0048] Next, while maintaining the flow rates of hydrogen and methane, oxygen is introduced (maintaining an oxygen partial pressure of 3 Pa), maintaining a growth temperature of 1070°C (step S2). Next, while maintaining the flow rate of hydrogen, the methane flow rate is increased to 1.1 sccm (partial pressure of approximately 13.604 Pa), maintaining a growth temperature of 1070°C. Simultaneously, oxygen is continued to be introduced (maintaining an oxygen partial pressure of 3 Pa), maintaining a growth temperature of 1070°C. This step controls the pressure in the chemical vapor deposition furnace at 13 kPa (step S3), and the growth process continues for 150 minutes.

[0049] Figure 2 The prepared double-layer graphene film is shown. It can be seen that the two layers have a certain twist angle and the two layers are of similar size.

[0050] Example 3

[0051] The heat treatment process of the metal Cu foil is the same as that in Example 1.

[0052] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen and methane into the tubular furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 999.3Pa), and the flow rate of methane is 0.7sccm (partial pressure is about 0.69951Pa), and grow at a temperature of 1070℃ for 5min (step S1).

[0053] Next, while maintaining the flow rates of hydrogen and methane, oxygen is introduced (maintaining an oxygen partial pressure of 3 Pa), maintaining a growth temperature of 1070°C (step S2). Next, while maintaining the flow rate of hydrogen, the methane flow rate is increased to 1.1 sccm (partial pressure of approximately 13.604), maintaining a growth temperature of 1070°C. Simultaneously, a certain amount of oxygen (maintaining an oxygen partial pressure of 3 Pa) is introduced to continue growth, maintaining a growth temperature of 1070°C. This step controls the pressure in the chemical vapor deposition furnace at 13 kPa (step S3), and the growth process continues for 150 minutes.

[0054] Figure 3 The prepared double-layer graphene film is shown. It can be seen that the two layers have a certain twist angle and the two layers are of similar size.

[0055] Example 4

[0056] The reaction conditions were the same as those in Example 1 except that the partial pressure of oxygen in step S3 was 0, 1.5 Pa, and 5 Pa, respectively. A double-layer graphene film sample was obtained. The area of ​​the second layer was measured at different domains of the sample and the area ratio of the second layer to the first layer was calculated. The measurement results are shown in FIG. Figure 4A and Figure 4B As shown in the figure, the measurement results of different domains were obtained at different partial pressures at each point. As can be seen from the figure, as the oxygen partial pressure increases in step S3, the promotion effect on the growth of the second layer is enhanced.

[0057] Example 5

[0058] A Cu foil was used as the substrate for chemical vapor deposition (CVD) of graphene and placed in a CVD furnace. The air inside the CVD furnace (a tubular furnace) was evacuated to near-vacuum (<8 Pa). A certain amount of protective gas (1000 sccm of argon) was introduced into the tubular furnace and the furnace temperature was raised to 850°C at the center, where it was held for 5 minutes. The temperature was then raised to 1070°C using a protective gas (1000 sccm of hydrogen) and held for 40 minutes to complete the substrate processing. The pressure was maintained at 1 kPa during the heating and annealing stages.

[0059] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen and methane into the tubular furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 999.5Pa), and the flow rate of methane is 0.3sccm (partial pressure is about 0.2999Pa), and grow at a temperature of 1070℃ for 20min (step S1).

[0060] Then, the flow rates of hydrogen and methane are kept constant, oxygen is introduced (the oxygen partial pressure is kept at 1.27 Pa), and the growth temperature is maintained at 1070°C (step S2).

[0061] Next, while maintaining the hydrogen flow rate constant, the methane flow rate was increased to 0.6 sccm (partial pressure approximately 7.64 Pa), maintaining a growth temperature of 1070°C. Oxygen was also introduced (at a partial pressure of 1.27 Pa), maintaining a growth temperature of 1070°C. During this step, the pressure in the chemical vapor deposition furnace was controlled at 13 kPa (step S3), and the growth period lasted for 100 minutes.

[0062] Figure 5 The prepared double-layer graphene film is shown. It can be seen that the two layers have a certain twist angle and the two layers are of similar size.

[0063] Example 6

[0064] A Cu foil was used as the substrate for chemical vapor deposition (CVD) of graphene and placed in a CVD furnace. The air inside the CVD furnace (a tubular furnace) was evacuated to near-vacuum (<8 Pa). A certain amount of protective gas (1000 sccm of argon) was introduced into the tubular furnace and the furnace temperature was raised to 850°C at the center, where it was held for 5 minutes. The temperature was then raised to 1070°C using a protective gas (1000 sccm of hydrogen) and held for 40 minutes to complete the substrate processing. The pressure was maintained at 1 kPa during the heating and annealing stages.

[0065] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen and methane into the tubular furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 999.5Pa), and the flow rate of methane is 0.4sccm (partial pressure is about 0.3998Pa), and grow at a temperature of 1070℃ for 15min (step S1).

[0066] Then, the flow rates of hydrogen and methane are kept constant, oxygen is introduced (the oxygen partial pressure is kept at 3 Pa), and the growth temperature is maintained at 1070°C (step S2).

[0067] Next, while maintaining the hydrogen flow rate constant, the methane flow rate was increased to 0.9 sccm (partial pressure approximately 11.133 Pa), maintaining a growth temperature of 1070°C. Oxygen was also introduced (maintaining an oxygen partial pressure of 3 Pa) to maintain the growth temperature at 1070°C. During this step, the pressure in the chemical vapor deposition furnace was controlled at 13 kPa (step S3), and the growth period lasted 220 minutes.

[0068] Figure 6 The prepared double-layer graphene film is shown. It can be seen that the two layers have a certain twist angle and the two layers are of similar size.

[0069] Comparative Example 1

[0070] Continue to maintain the pressure at 1KPa, and introduce a certain amount of hydrogen, methane and a small amount of oxygen (3Pa) into the tube furnace, where the flow rate of hydrogen is 1000sccm (partial pressure is about 951.9276Pa), the flow rate of methane is 0.5sccm (partial pressure is about 0.47596Pa), and the growth is carried out at a temperature of 1070℃ for 10 minutes (step S1).

[0071] Next, the hydrogen and methane flow rates were maintained constant, while oxygen was continuously introduced (maintaining an oxygen partial pressure of 3 Pa), maintaining a growth temperature of 1070°C (step S2). Next, while maintaining the hydrogen and oxygen flow rates constant, the methane flow rate was increased to 1.1 sccm, maintaining a growth temperature of 1070°C. This step controlled the pressure in the chemical vapor deposition furnace to 13 kPa (step S3), and the growth process continued for 150 minutes.

[0072] Figure 7 The prepared double-layer graphene film is shown. It can be seen that the two layers present AB stacking and the two layers are of comparable size.

[0073] Comparing Example 1 with Comparative Example 1, it can be seen that when a small amount of oxygen is also introduced in step S1, a double-layer graphene layer with arbitrary twist angles cannot be formed. However, two double-layer graphene films with roughly equal areas can be formed.

[0074] Comparative Example 2

[0075] Except that oxygen was not introduced in step S3, other conditions were the same as those in Example 1.

[0076] The obtained double-layer graphene film is Figure 8 As shown. Figure 8 It can be seen that the area of ​​the first domain is much larger than that of the second domain. Comparing Example 1 and Comparative Example 2, it can be seen that when no oxygen is introduced in step S3, the areas of the two layers of the double-layer graphene film are quite different.

[0077] Comparative Example 3

[0078] Except that the oxygen partial pressure in step S3 is 6 Pa, other conditions are the same as those in Example 1. The obtained double-layer graphene film is as follows Figure 9 As shown. Figure 9 It can be seen that the substrate surface is severely oxidized and the edge of graphene is also oxidized.

[0079] Comparative Example 4

[0080] Except that the methane flow rate in step S1 is 2 sccm (partial pressure is about 1.996 Pa), other conditions are the same as those in Example 1. The obtained double-layer graphene film is as follows Figure 8 As shown. Figure 10 It can be seen that graphene is mainly composed of multi-layer inverted pyramids.

[0081] Comparative Example 5

[0082] The methane flow rate in step S3 is 0.5 sccm (partial pressure is about 6.187 Pa), the growth time of S3 is 20 min, and the other conditions are the same as those in Example 1.

[0083] The obtained double-layer graphene film is Figure 11 As shown. Figure 11 It can be seen that the graphene growth domain is small.

[0084] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a double-layer graphene film, characterized in that: include: S1, introducing hydrogen and methane into the vapor deposition system to perform a vapor deposition reaction, thereby growing a graphene core having a double-layer graphene domain on a substrate; S2, introducing oxygen into the vapor deposition system; as well as S3, increasing the methane partial pressure and continuing the growth, and oxygen is still introduced in this step; In the step S1, the methane partial pressure is 0.15-0.8 Pa, and the growth time is 3-20 min; The partial pressure of methane in the step S2 is 0.15-0.8 Pa; The methane partial pressure in the step S3 is 6-14 Pa; The partial pressure of oxygen in steps S2 and S3 is greater than 0 and less than or equal to 5 Pa.

2. The preparation method according to claim 1, characterized in that The growth temperature of the steps S1-S3 is 1020°C-1080°C.

3. The preparation method according to claim 1, characterized in that Before step S1, a heat treatment step is further included for the substrate.

4. The preparation method according to claim 1, characterized in that The substrate is a metal substrate.

5. The preparation method according to claim 4, characterized in that The substrate is copper or copper-nickel alloy.

6. A double-layer graphene film, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

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