A method for preparing graphene by contactless confined growth

Abstract

The present invention relates to the technical field of graphene materials, and discloses a method for preparing graphene with non-contact confined growth. The graphene preparation method comprises: setting a barrier layer and a cold source in the inner cavity of a CVD furnace, the barrier layer is provided with a restriction structure that runs through its thickness, and the restriction structure is connected to the cold source; placing the growth substrate below the barrier layer, the barrier layer and the growth substrate are spaced apart by a distance, and the orthographic projection area of ​​the restriction structure on the growth substrate is the growth area of ​​the graphene; and using a roll-to-roll CVD process to prepare a graphene sample. The present invention improves the existing graphene preparation method to improve the preparation quality of patterned graphene, and is compatible with the roll-to-roll CVD preparation process. Due to the non-contact regulation, no barrier layer is introduced on the growth substrate, so impurities will not be introduced, and the quality of the graphene film will not be affected.

Description

Technical Field

[0001] The invention relates to the technical field of graphene materials, and in particular to a method for preparing graphene by contactless confined growth. Background Art

[0002] At present, chemical reduction and chemical vapor deposition (CVD) are the two most mature methods for preparing graphene. The chemical reduction preparation process obtains graphene powder. Due to the two treatment stages of oxidation and reduction, the graphene prepared by this process often has many defects and it is difficult to obtain high-quality single-layer graphene; the CVD method can prepare high-quality defect-free single-layer graphene, and the roll-to-roll CVD method is a method that can continuously grow high-quality graphene.

[0003] With the continuous update of transfer technology, the application results of graphene in the field of electronic devices continue to emerge, which also puts forward new requirements for the preparation method of graphene. In the field of electronic devices, graphene with a specific number of layers and specific patterns is often required.

[0004] In the prior art, after a continuous large area of ​​graphene is transferred, the excess part is removed by etching to obtain a specific patterned graphene. The current roll-to-roll CVD preparation process grows a continuous large area of ​​graphene on the growth substrate, but the continuous large area of ​​graphene often suffers from a large amount of loss, introduction of impurities, and low utilization rate during the transfer and etching process. Therefore, the existing graphene preparation method needs to be improved to improve the preparation quality of patterned graphene and be compatible with the roll-to-roll CVD preparation process. Summary of the invention

[0005] The technical problem to be solved by the present invention is to improve the existing graphene preparation method to enhance the preparation quality of patterned graphene and to be compatible with the roll-to-roll CVD preparation process.

[0006] In order to solve the above problems, the present invention provides a method for preparing graphene by contactless confined growth, comprising the following steps:

[0007] A barrier layer and a cold source are arranged in the inner cavity of the CVD furnace, wherein a restriction structure penetrating the thickness of the barrier layer is arranged on the barrier layer, and the restriction structure is connected to the cold source;

[0008] Placing the growth substrate below the barrier layer, with a distance between the barrier layer and the growth substrate, and the orthographic projection area of ​​the confinement structure on the growth substrate being the growth area of ​​the graphene;

[0009] The graphene samples were prepared using a roll-to-roll CVD process.

[0010] Preferably, the step of placing the growth substrate below the barrier layer specifically includes:

[0011] Fixing the growth substrate to a graphite plate to form a growth structure, and placing the growth structure parallel to and below the barrier layer;

[0012] The distance between the growth structure and the barrier layer is adjusted.

[0013] Preferably, the area of ​​the growth substrate is larger than the area of ​​the orthographic projection of the confinement structure on the growth substrate.

[0014] Preferably, the growth substrate is a metal foil, and before the step of placing the growth substrate under the barrier layer, the following steps are also included:

[0015] Soaking the metal foil in a hydrochloric acid aqueous solution;

[0016] Rinse the metal foil after immersion with anhydrous ethanol;

[0017] The rinsed foil was dried using a nitrogen gun.

[0018] Preferably, the method of preparing the graphene sample using a roll-to-roll CVD process specifically comprises the following steps:

[0019] At room temperature, 200 sccm of nitrogen gas is introduced into the CVD furnace for washing, and after washing, the nitrogen gas is introduced at a flow rate of 100 sccm;

[0020] Heating to a target temperature at a heating rate of 5°C / min; the target temperature is 850-1000°C;

[0021] Maintain the target temperature for 10-30 minutes to stabilize the target temperature, and introduce hydrogen at a flow rate of 10 sccm until the reaction is completed;

[0022] Under the target temperature environment, introducing ethylene gas at a flow rate of 20-100 sccm for 2-10 minutes;

[0023] Under the target temperature environment, after the ethylene gas is introduced for 20-40 min, the flow rate of the ethylene gas is adjusted to 150-300 sccm, and the flow rate is maintained until the reaction is completed;

[0024] After the reaction is completed, the heating system of the CVD furnace is turned off, the introduction of the ethylene gas and the hydrogen gas is stopped, and after cooling to room temperature, the introduction of the nitrogen gas is stopped.

[0025] Preferably, the barrier layer is a metal grid made of stainless steel.

[0026] Preferably, the restriction structure is a triangle, and the stainless steel pipe is cut into three steel pipes of equal length and welded together to form the restriction structure.

[0027] Preferably, the distance between the growth substrate and the barrier layer is set to 0.5-5 mm.

[0028] Preferably, the thickness of the metal foil is set to 25-200 μm.

[0029] Preferably, the cooling source is a water cooling system of the CVD furnace wall.

[0030] Compared with the prior art, the present invention has at least one of the following beneficial technical effects:

[0031] It is connected to the barrier layer through a water cooling system to form a low temperature domain, and the area where the barrier layer is not connected to the water cooling system is a normal temperature domain. Since the graphene to be prepared is a customized shape, the role of the restriction structure is to hinder the growth substrate where graphene is not needed to grow. The growth substrate is confined in the low temperature domain, and the growth of patterned graphene can be achieved by shaping the restriction structure; and the barrier layer and the growth substrate are separated by a certain distance, so there is no need to construct a patterned barrier boundary on the growth substrate, and impurities will not be introduced during the graphene growth process. There is no need to cut and shape the growth substrate, and it is compatible with the roll-to-roll CVD preparation process. Due to the contactless regulation, this preparation method does not introduce a barrier layer on the growth substrate, so it will not introduce impurities and will not affect the quality of the graphene film. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0033] Figure 1 It is a schematic diagram of the process of preparing graphene by contactless confined growth in an embodiment of the present invention.

[0034] Figure 2 It is a schematic diagram of a sub-process of a method for preparing graphene by contactless confined growth in an embodiment of the present invention.

[0035] Figure 3 Schematic diagram of another sub-process of the method for preparing graphene by contactless confined growth in an embodiment of the present invention.

[0036] Figure 4 It is another sub-process schematic diagram of the method for preparing graphene by contactless confined growth in an embodiment of the present invention.

[0037] Figure 5 Schematic diagram of the results of SEM testing in an embodiment of the present invention.

[0038] Figure 6 This is the Raman spectrum of the non-confined growth area in the embodiment of the present invention.

[0039] Figure 7 This is the Raman spectrum of the confined area in the embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0042] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0043] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0044] The embodiment of the present invention provides a method for preparing graphene with non-contact confined growth. Figures 1 to 7 This application is described in further detail.

[0045] Please refer to Figure 1 The graphene preparation method is compatible with the existing roll-to-roll CVD preparation process and is applied in a CVD furnace. The preparation process can unwind and rewind at the same time to improve work efficiency. The graphene preparation method mainly grows graphene in a specific area of ​​the substrate through temperature regulation to prepare a graphene film with a customized shape.

[0046] The graphene preparation method comprises steps S100-S300:

[0047] Step S100: a barrier layer and a cold source are fixedly arranged in the inner cavity of a CVD furnace, a limiting structure penetrating the thickness of the barrier layer is arranged on the barrier layer, and the limiting structure is connected to the cold source.

[0048] Specifically, the cold source is a water cooling system of the CVD furnace wall, and the water cooling system is connected to the barrier layer to form a low temperature region, and the area where the barrier layer is not connected to the water cooling system is a normal temperature region; the barrier layer uses a stainless steel metal grid, and in other embodiments, the barrier layer can also be made of other materials. Since the graphene to be prepared is a customized shape, the role of the metal grid is to block the growth substrate where the graphene does not need to grow.

[0049] More specifically, the limiting structure is used to form the shape of the graphene film, and its shape can be a triangle or other graphics, but it is not limited to this. In the present embodiment, the limiting structure is a triangle as an example. The inner diameter and outer diameter of the stainless steel hollow steel pipe are selected from 1-5mm, such as 1mm, 3mm and 5mm, and the wall thickness is selected from 0.5-4.5mm, such as 0.5mm, 2.5mm and 4.5mm. The inner diameter, outer diameter and wall thickness of the stainless steel hollow steel pipe can be arbitrarily combined. The stainless steel hollow steel pipe is cut into three equal lengths and welded into a limiting structure, which can be used to prepare a triangular graphene film; because the different sizes of the metal grid affect the shape of the graphene film grown subsequently, in other embodiments, stainless steel pipes of other sizes can also be selected according to actual needs.

[0050] Step S200: placing a growth substrate below the barrier layer, with a distance between the barrier layer and the growth substrate, and the orthographic projection area of ​​the restriction structure on the growth substrate is the growth area of ​​the graphene.

[0051] Specifically, a low-temperature domain is manufactured on the growth substrate through a metal gate, and the boundary of the positive projection area of ​​the restriction structure on the growth substrate is the low-temperature domain. The low-temperature domain is used to perform confined growth on the growth substrate, and the growth of patterned graphene can be achieved by shaping the restriction structure of the metal gate; and there is a certain distance between the barrier layer and the growth substrate, so there is no need to construct a patterned barrier boundary on the growth substrate, thereby preventing impurities from being introduced during the graphene growth process.

[0052] Step S300: Prepare a graphene sample using a roll-to-roll CVD process. For this, there is no need to cut and shape the growth substrate, and the roll-to-roll CVD preparation process is compatible.

[0053] Here, the barrier layer is connected to the water cooling system to form a low temperature domain, and the area where the barrier layer is not connected to the water cooling system is a normal temperature domain. Since the graphene to be prepared is a customized shape, the role of the restriction structure is to hinder the growth substrate where the graphene is not needed to grow. Due to the contactless regulation, the preparation method does not introduce a barrier layer on the growth substrate, so it will not introduce impurities and will not affect the quality of the graphene film.

[0054] It is understood that in the description of the following embodiments, the growth substrate is a metal foil. In some embodiments, the metal foil is copper foil as an example.

[0055] Please refer to Figure 2 In a specific embodiment, before “placing the growth substrate under the barrier layer” in step S200, the following sub-steps are also included:

[0056] S201, soaking the metal foil with a hydrochloric acid aqueous solution;

[0057] S202, rinsing the immersed metal foil with anhydrous ethanol;

[0058] S203, using a nitrogen gun to dry the rinsed metal foil.

[0059] Specifically, in the above step S201, in the actual production process, a hydrochloric acid aqueous solution with a concentration range of 0.1-1M, such as 0.1M, 0.5M and 1M, etc., can be selected; wherein M is the molar concentration of the substance, and the unit is mol / L, so 1M hydrochloric acid is 1 mol / L hydrochloric acid; at the same time, the hydrochloric acid aqueous solution soaks the metal foil for 1-20 minutes, such as 1min, 10min and 20min, etc. By soaking the metal foil in hydrochloric acid water, the micro-protrusions and burrs on the surface of the metal foil can be effectively removed, making the surface of the metal foil smoother, and removing the surface oxide layer.

[0060] In addition, in the aforementioned step S203, nitrogen is used as an inert gas, which mainly plays the role of accelerating the evaporation of moisture on the surface of the metal foil.

[0061] Please refer to Figure 3 In a specific embodiment, the aforementioned step S200 of “placing the growth substrate below the barrier layer” specifically includes the following sub-steps:

[0062] S210, fixing the growth substrate to the graphite plate to form a growth structure, and disposing the growth structure in parallel below the barrier layer;

[0063] S220, adjusting the distance between the growth structure and the barrier layer.

[0064] Specifically, in the aforementioned step S210, a flat graphite plate is used to support the growth substrate. Since the barrier layer is fixed in position, the distance between the barrier layer and the growth substrate is controlled by adjusting the height of the graphite plate. Since the barrier layer is close to the growth substrate, the low temperature domain can divide the metal foil into different regions, and the energy of the pyrolyzed heat source gas molecules disappears quickly in the low temperature domain, and continuous growth cannot be achieved at the metal foil substrate position corresponding to the low temperature domain, thereby achieving the purpose of contactless confined growth regulation to obtain customized patterned graphene.

[0065] More specifically, in some embodiments, the area of ​​the growth substrate is larger than the area of ​​the orthographic projection of the confinement structure on the growth substrate. Since the metal foil has a catalytic effect on the growth of graphene, only when the area of ​​the metal foil is larger than the metal grid can the part of the metal foil that does not need to grow graphene be blocked, which is more conducive to the growth of graphene through the CVD process.

[0066] More specifically, in some embodiments, a spacing is set to ensure that the metal grid and the metal foil substrate are not in contact. The distance between the metal grid and the metal foil substrate is set to 0.5-5 mm, for example, 0.5 mm, 2.5 mm, and 5 mm. This spacing can ensure that the pyrolysis carbon source particles lose energy when they are in contact with the metal grid area, so that they cannot obtain sufficient energy when they settle on the surface of the metal foil. At the same time, the thickness of the metal foil is set to 25-200 μm, for example, 25 μm, 100 μm, 150 μm, and 200 μm. The metal foil has good ductility within this thickness range. If the metal foil is too thin, it is easy to be damaged and wrinkled, while if the metal foil is too thick, it lacks ductility and is not conducive to liquid phase transfer application.

[0067] Please refer to Figure 4 In a specific embodiment, the aforementioned step S300 of “placing the growth substrate under the barrier layer” specifically includes the following sub-steps S310-S360:

[0068] S310, machine washing stage. At room temperature, 200 sccm of nitrogen is introduced into the CVD furnace for machine washing. After washing, 100 sccm of nitrogen is introduced. The purpose of introducing nitrogen is to remove the oxide layer on the surface of the metal foil. Among them, sccm is a mass flow unit, representing standard milliliters per minute.

[0069] S320, heating stage. The temperature in the CVD furnace is raised to the target temperature at a heating rate of 5°C / min; wherein the target temperature is 850-1000°C. More specifically, during the production process, the target temperature can be set to 920°C. Since the temperature for preparing graphene by CVD should be around 1000°C, by setting the target temperature to 920°C, graphene can grow relatively gently under this temperature condition to avoid the problem of excessive nucleation and excessive number of crystal domains. At the same time, it can also ensure the effective energy absorption of the pyrolytic carbon source particles by the metal gate area, so as to achieve the purpose of contactless barrier growth. If the target temperature is too high, the barrier effect of the metal gate will be weakened or even lose the barrier growth effect, resulting in the inability to achieve contactless barrier growth.

[0070] S330, temperature stabilization stage. Maintain the target temperature for 10-30 minutes to stabilize the target temperature, and introduce hydrogen at a flow rate of 10 sccm until the reaction is completed. The role of hydrogen in the temperature stabilization stage is to clean the copper foil to remove the oxide layer on the surface of the copper foil; at the same time, in the subsequent nucleation and growth stages, since hydrogen has a reducing property, the carbon source gas is prone to lose energy oxidation after pyrolysis, and hydrogen can also maintain its high energy state to keep the reactants active during the reaction.

[0071] S340, nucleation stage. In the target temperature environment, ethylene gas is introduced at a flow rate of 20-100 sccm for 2-10 minutes. The purpose of introducing ethylene gas is to form nuclei on the metal foil.

[0072] S350, growth stage. Under the target temperature environment, after ethylene gas is introduced for 20-40 min, the ethylene gas flow rate is adjusted to 150-300 sccm, and the flow rate is maintained until the reaction is completed. In this embodiment, the "reaction is completed" in the aforementioned steps S330 and S350 refers to the entire CVD process graphene growth reaction, that is, the hydrogen and ethylene gases are introduced until the cooling stage of the following step S360 before being turned off.

[0073] S360, cooling stage. After the reaction is completed, the heating system of the CVD furnace is turned off, and the introduction of ethylene gas and hydrogen is stopped. After cooling to room temperature, the introduction of nitrogen is stopped.

[0074] In a specific embodiment, after "placing the growth substrate under the barrier layer" in step S300, the step further includes: S400, taking out the graphene sample for testing, taking different positions on the copper foil for SEM and Raman testing to determine whether there is graphene growth on the copper foil.

[0075] Please refer to Figures 5 to 7Among them, the SEM test can directly observe the growth shape of graphene. The growth shape of graphene on the copper foil can be clearly observed through the SEM test image, for example, the growth shape of graphene in this embodiment is wrinkled; graphene samples at different positions are taken for Raman testing. There is no graphene response peak in the metal gate confined area, and there are graphene response peaks in other areas. From the test results, it can be seen that the metal gate connected to the cold source can achieve low-temperature confined growth.

[0076] More specifically, in some embodiments, the graphene sample grown in step S300 is taken out and placed on a flat heater. When the air temperature rises to 80°C, it is found that there is an obvious purple-red line on the copper foil at the position corresponding to the metal grid, with a width of about 4.5 mm. This is because the place where the graphene grows protects the copper foil and the copper foil will not be oxidized; otherwise, the copper foil will oxidize to purple-red due to high temperature.

[0077] Heating is the most direct way to verify whether complete graphene has grown on copper foil. In the location where graphene has grown, the complete long-range ordered six-membered ring structure of graphene can hinder the penetration of oxygen molecules and react with copper atoms, so there will be no color change and the color will remain the original color of the copper foil. In the location where no graphene has grown, air can be in direct contact with the copper foil. At a certain temperature, copper atoms react with oxygen in the air, and the color will deepen and turn purple-red.

[0078] In addition, in a specific embodiment, the limiting structure of the metal grid in the aforementioned step S100 can be formed by welding hollow steel pipes, or can be replaced by solid stainless steel bars. Other steps remain unchanged and will not be described in detail.

[0079] The results show that when the length of the metal grid is greater than 50 cm, the copper foil does not change color at the position corresponding to the metal grid when the air temperature rises to 80°C, indicating that complete graphene grows in the middle position of the copper foil corresponding to the metal grid; when the air temperature rises to 80°C, the copper foil at the position corresponding to the metal grid oxidizes into purple-red due to high temperature, indicating that there is still a confined growth effect near the two ends of the cold source.

[0080] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing graphene by contactless confined growth, characterized in that: The following steps are involved: A barrier layer and a cold source are arranged in the inner cavity of the CVD furnace, wherein a restriction structure penetrating the thickness of the barrier layer is arranged on the barrier layer, and the restriction structure is connected to the cold source; soaking the growth substrate with an aqueous hydrochloric acid solution; Rinse the soaked growth substrate with anhydrous ethanol; Drying the rinsed growth substrate using a nitrogen gun; Placing the growth substrate below the barrier layer, with a distance between the barrier layer and the growth substrate, and the orthographic projection area of ​​the confinement structure on the growth substrate being the growth area of ​​the graphene; Graphene samples were prepared using a roll-to-roll CVD process; At room temperature, 200 sccm of nitrogen gas is introduced into the CVD furnace for washing, and after washing, 100 sccm of nitrogen gas is introduced instead; Heating to a target temperature at a heating rate of 5°C / min; the target temperature is 850-1000°C; Maintain the target temperature for 10-30 minutes to stabilize the target temperature, and introduce hydrogen at a flow rate of 10 sccm until the reaction is completed; Under the target temperature environment, introducing ethylene gas at a flow rate of 20-100 sccm for 2-10 minutes; Under the target temperature environment, after the ethylene gas is introduced for 20-40 min, the flow rate of the ethylene gas is adjusted to 150-300 sccm, and the flow rate is maintained until the reaction is completed; After the reaction is completed, the heating system of the CVD furnace is turned off, the introduction of the ethylene gas and the hydrogen gas is stopped, and after cooling to room temperature, the introduction of the nitrogen gas is stopped.

2. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The step of placing the growth substrate below the barrier layer specifically includes: Fixing the growth substrate to a graphite plate to form a growth structure, and placing the growth structure parallel to and below the barrier layer; The distance between the growth structure and the barrier layer is adjusted.

3. A method for preparing graphene by contactless confined growth according to claim 1 or 2, characterized in that: An area of ​​the growth substrate is larger than an area of ​​an orthographic projection of the confinement structure on the growth substrate.

4. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The barrier layer is a metal grid made of stainless steel.

5. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The limiting structure is in the shape of a triangle, and the stainless steel pipe is cut into three steel pipes of equal length and welded together to form the limiting structure.

6. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The distance between the growth substrate and the barrier layer is set to 0.5-5 mm.

7. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The thickness of the growth substrate is set to 25-200 μm.

8. The method for preparing graphene by contactless confined growth according to claim 1, characterized in that: The cold source is a water cooling system of the CVD furnace wall.

Images