Graphene film processing method and graphene film obtained by same

Abstract

The invention discloses a treatment method of a graphene film and the graphene film obtained by the treatment method. The treatment method of the graphene film comprises the step of treating the graphene film by adopting ozone. Mild ozone (O3) is adopted to treat the graphene film, and the lattice structure of graphene cannot be changed. Meanwhile, ozonation is extremely high, so that organic impurities and pollutants can be effectively removed, and the chemical property of the surface of the material can be changed. Firstly, oxygen-containing functional groups (such as carboxyl and hydroxyl) can be introduced to the surface of graphene through ozone treatment, the hydrophilicity of the graphene is improved, and the binding capacity with other materials is improved. And secondly, the conductivity of the graphene can be optimized through ozone treatment, and the performance of the graphene in optoelectronic devices or electronic devices is improved, such as the application of the graphene in batteries, capacitors, field effect transistors or Hall elements. The method is simple, convenient and fast, and has a good industrial prospect.

Description

Technical Field

[0001] The present invention belongs to the field of carbon materials, and particularly relates to a method for treating a graphene film and the graphene film obtained by this method. Background Art

[0002] Graphene is a two-dimensional material in which a single layer of carbon atoms is arranged in a hexagonal shape, and has excellent electrical conductivity, thermal conductivity and mechanical strength, and is widely used in fields such as electronic devices and sensors. The chemical vapor deposition (CVD) method can be used to prepare single-layer, double-layer and few-layer graphene films on different substrates such as copper foils, silicon wafers, and sapphires. During the preparation process, many pollutants will be generated on the surface of the graphene film. For example, amorphous carbon generated during the growth process, residual poly(methyl methacrylate) (PMMA) adhesive residues on the graphene surface after the transfer process, and hydrocarbons generated on the surface during the preparation process. These pollutants will make the graphene film hydrophobic. We can perform functional modification on the generally existing graphene film with a non-clean surface to make its hydrophilicity adjustable.

[0003] At present, there are two ways to treat graphene films. The first is the way of destroying the graphene lattice. Research shows that by certain chemical doping (such as elements nitrogen, boron, phosphorus, etc.), the crystal structure of graphene can be changed, thereby improving its electrical conductivity. For example, nitrogen doping can increase the carrier concentration and improve the electrical conductivity. Chemical doping will introduce defects into the graphene lattice, destroying its crystal structure, thereby changing the electrical conductivity of the graphene film. The second is the way of not destroying the lattice. Research shows that using chemical or physical methods to modify the surface of graphene can increase its electrical conductivity, but this way is not environmentally friendly.

[0004] The disadvantages of the prior art are that the crystal structure of graphene will be destroyed on the basis of improving its electrical conductivity, and the modification method that does not destroy the crystal structure is not environmentally friendly and cannot change the hydrophobicity of the graphene film. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present invention is to perform mild treatment on the graphene film without destroying the graphene crystal structure, so as to increase its electrical conductivity and have adjustable hydrophilicity.

[0006] The present invention provides a method for treating a single-layer graphene, including: treating the graphene film with ozone.

[0007] According to an embodiment of the present invention, the ozone is generated by an ultraviolet ozone cleaning machine, the output power of the ultraviolet ozone cleaning machine is less than 20W, and the ozone treatment time is 0 < T ≤ 240 seconds.

[0008] According to another embodiment of the present invention, the graphene film to be treated is obtained by a chemical vapor deposition method.

[0009] According to another embodiment of the present invention, the graphene film to be processed is a graphene film grown by chemical vapor deposition and transferred to a target substrate.

[0010] According to another embodiment of the present invention, the graphene film is a single-layer graphene film or a multi-layer graphene film.

[0011] According to another embodiment of the present invention, the resistance of the graphene film to be treated decreases by 20%-70% after being treated with ozone.

[0012] The present invention also provides a graphene film, which is obtained by processing using the above processing method.

[0013] The present invention uses mild ozone (O3) to treat the graphene film, which will not change the graphene lattice structure. At the same time, due to the strong oxidizing property of ozone, it can effectively remove organic impurities and pollutants, and can also change the chemical properties of the material surface. First, oxygen-containing functional groups (such as carboxyl, hydroxyl, etc.) can be introduced on the graphene surface through ozone treatment to improve its hydrophilicity and increase its ability to bind with other materials. Secondly, ozone treatment can optimize the conductivity of graphene and improve its performance in optoelectronic devices or electronic devices, such as applications in batteries, capacitors, field effect transistors or Hall elements. The method of the present invention is simple and fast, and has good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 These are Raman spectra of the graphene films on different substrates before and after treatment in Example 1 and Comparative Example 1, wherein (a) is a Raman spectrum on a copper substrate, and (b) is a Raman spectrum on a silicon wafer substrate.

[0015] Figure 2 The graphs are contact angle change diagrams of the graphene films on different substrates before and after treatment in Example 1 and the comparative example, wherein (a) is a contact angle change diagram on a copper substrate, and (b) is a contact angle change diagram on a silicon wafer substrate.

[0016] Figure 3 It is a curve diagram showing the change of the surface resistance of the graphene film before and after treatment with ozone treatment time in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with specific implementation modes.

[0018] The method for treating a graphene film of the present invention includes treating the graphene film with ozone. In the present invention, ozone is used to treat the graphene film. Since ozone is a strong oxidant, it can perform functional modification on the hydrocarbon contamination points on the graphene film, increasing its conductivity and making its hydrophilicity adjustable. Moreover, treating the graphene film with relatively mild ozone will not damage the crystal structure of graphene.

[0019] In an optional embodiment, the ozone is generated by an ultraviolet ozone cleaner. The output power of the ultraviolet ozone cleaner is less than 20 W, and the treatment time is 0 < T ≤ 240 seconds. Through experiments, it is found that when treating the graphene film with ozone generated by the ultraviolet ozone machine with the above power, the conductivity of the graphene film decreases when the treatment time exceeds 240 seconds. Therefore, the treatment time of ozone is preferably below 240 seconds. The specific treatment time can be reasonably selected according to the required conductivity and hydrophilicity of the graphene film to be obtained, such as but not limited to 10 seconds, 20 seconds, 30 seconds, 50 seconds, 60 seconds, 100 seconds, 120 seconds, 150 seconds, 180 seconds, 200 seconds, 210 seconds, 240 seconds, etc.

[0020] In an optional embodiment, the graphene film to be treated can be obtained by chemical vapor deposition (CVD). Alternatively, it can also be a graphene film obtained by transferring a graphene film grown by chemical vapor deposition to a target substrate. The graphene film grown on the surface of a substrate (such as copper foil, etc.) by the CVD method has impurities such as amorphous carbon on its surface, which affects the conductivity of the graphene film and makes the graphene hydrophobic. For the graphene film prepared by chemical vapor deposition and transferred using a transfer medium (such as PMMA), in addition to amorphous carbon, there may also be residual glue on its surface. Since the contaminants present on the surface of the graphene film make the conductivity of the graphene film far lower than its intrinsic conductivity, after ozone treatment, the contaminants present on the surface of the graphene film are surface-modified and the crystal structure of graphene is not damaged. Therefore, the conductivity can be increased. At the same time, oxygen-containing functional groups (such as carboxyl groups, hydroxyl groups, etc.) will be formed on the surface of the graphene film during the oxidation treatment process, which can improve the hydrophilicity. Moreover, ozone decomposes into oxygen in the air and will not cause environmental pollution.

[0021] Compared with the graphene film to be treated (i.e., the graphene film before treatment), the sheet resistance of the graphene film obtained by the above treatment method has decreased by 20% - 70%.

[0022] The graphene film of the present invention has high conductivity and hydrophilicity and can be used in optoelectronic devices or electronic components, such as batteries, capacitors, field effect transistors, Hall elements, etc. Of course, the graphene film of the present invention can also be used in any other fields where graphene films can be applied except for optoelectronic devices and electronic devices.

[0023] The present invention is further described below by specific examples. However, these examples are merely exemplary and do not constitute any limitation to the scope of the present invention. In the following examples and comparative examples, the reagents, materials and instruments used are all commercially available unless otherwise specified.

[0024] Example 1

[0025] Graphene was grown on copper foil using the CVD method. First, a 25-micron-thick copper foil was annealed in a reducing atmosphere of hydrogen for 30 minutes to flatten its surface and eliminate organic contamination. Subsequently, hydrogen and methane were introduced into the chamber to induce the growth of graphene film for 10 to 60 minutes. After the growth was completed, the CVD system was cooled under the same gas supply conditions. PMMA was used to transfer it to a silicon wafer substrate. First, PMMA was spin-coated onto the graphene / copper sample and then heated at 170°C for 5 minutes. 1 mol·L -1 The copper substrate was etched with sodium persulfate solution to obtain a self-supporting PMMA / graphene film. After rinsing with deionized water, the PMMA / graphene film was then transferred to a silicon wafer substrate. Finally, acetone was used to remove the PMMA on the graphene surface. At room temperature, the prepared single-layer graphene film was placed in an ultraviolet / ozone cleaning machine (model: UVC-1014, average input power 20W), and the cleaning machine was turned on to treat the prepared single-layer graphene film. The treatment time was 10 seconds, 30 seconds, 40 seconds, 120 seconds, 140 seconds, 170 seconds and 240 seconds, respectively, to obtain a treated single-layer graphene film.

[0026] Comparative Example 1

[0027] The single-layer graphene film obtained by the same preparation method and transfer method as in Example 1 was not subjected to ozone treatment.

[0028] The single-layer graphene film obtained in Example 1 and Comparative Example 1 was subjected to Raman, contact angle and electrical tests, respectively, to observe the changes before and after the treatment. The contact angle test was conducted in the air at room temperature using a static contact angle tester, with a water droplet diameter in the range of 2-5 mm. Electrical test steps: First, a micron-sized field effect transistor device was processed, and then tested based on the four-probe principle.

[0029] The Raman spectra, contact angle comparison and surface resistance change diagram before and after treatment are shown in Figure 2. Figure 1-3 As shown. Figure 1 Figure (a) shows the Raman spectrum of graphene on a copper substrate, and Figure (b) shows the Raman spectrum of graphene on a silicon wafer substrate. Comparing the two figures, it can be seen that no D peak appears in the Raman spectrum of graphene on different substrates before and after treatment, indicating that no defects are generated, indicating that the crystal structure of graphene is not destroyed by treatment.

[0030] Figure 2 Figure (a) shows the contact angle change of graphene on a copper substrate, and Figure (b) shows the contact angle change of graphene on a silicon wafer substrate. It can be seen that on different substrates, the contact angle of the graphene surface does not gradually decrease with the increase of processing time.

[0031] Figure 3 This means that as the ozone treatment time increases, the surface resistance of graphene gradually decreases, indicating that its conductivity gradually increases. From the data in the figure, it can be seen that the surface resistance of the graphene film after ozone treatment is reduced by 20%-70% compared with the untreated one.

[0032] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for processing a graphene film, characterized in that: Including: Treating the graphene film with ozone.

2. The processing method according to claim 1, characterized in that: The ozone is generated by an ultraviolet ozone cleaner, the output power of the ultraviolet ozone cleaner is less than 20 W, and the ozone treatment time is 0 < T ≤ 240 seconds.

3. The processing method according to claim 1, characterized in that: The graphene film to be treated is obtained by chemical vapor deposition.

4. The processing method according to claim 1, characterized in that: The graphene film to be treated is a graphene film obtained by transferring the graphene film grown by chemical vapor deposition to a target substrate.

5. The processing method according to claim 1, characterized in that: The graphene film is a single-layer graphene film or a multi-layer graphene film.

6. The processing method according to any one of claims 1 to 5, characterized in that: The sheet resistance of the graphene film to be treated decreases by 20% - 70% after ozone treatment.

7. A graphene film, characterized in that: The graphene film is obtained by the treatment method described in any one of claims 1 - 6.

Images