Graphene surface cleaning method

Abstract

The invention discloses a method for cleaning a graphene surface. The graphene surface is cleaned by electron beam irradiation. By means of the method, in-situ cleaning of pollutants on the surface of the graphene film can be achieved, and the lattice structure of graphene cannot be damaged. The method is easy to operate, high in cleaning speed, capable of achieving fixed-point removal of pollutants, good in cleaning effect on different kinds of pollutants and high in universality, and has important significance in further achieving and expanding high-end application of preparation of graphene through a CVD method.

Description

Technical Field

[0001] The invention relates to the field of graphene materials, and in particular to a surface cleaning method of a graphene film material. Background Art

[0002] Graphene is a two-dimensional atomic crystal with a hexagonal lattice honeycomb composed of a single layer of carbon atoms. It has optical, electrical, magnetic, mechanical, thermal and other properties that are difficult to match with other materials and has broad application prospects. The chemical vapor deposition (CVD) method is the most commonly used technical means to prepare high-quality graphene films. However, amorphous carbon byproducts are formed during the high-temperature synthesis of graphene, causing intrinsic pollution. In addition, polymer contamination will also exist in the process of transferring the CVD-grown graphene film to the desired substrate. The presence of these pollutants will reduce the transmittance of graphene, shift the Dirac point, reduce the mobility, increase the surface resistance and contact resistance, and change the hydrophilicity and hydrophobicity, which seriously restricts the excellent performance of graphene and subsequent device applications.

[0003] Existing methods for cleaning graphene surfaces have the following disadvantages: 1) the operation is complicated and tedious, and the cleaning time is long; 2) it causes certain damage to the graphene lattice structure; 3) it is impossible to achieve targeted cleaning of micro-areas, and the cleaning effect is poor; and 4) it is difficult to remove different types of pollutants, and the universality is low.

[0004] Therefore, effectively removing various pollutants on the surface of graphene films during CVD preparation and transfer without damaging the graphene lattice structure is an urgent problem to be solved in this field. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for cleaning the surface of graphene.

[0006] The method for cleaning the graphene surface of the present invention adopts electron beam irradiation to clean the graphene surface.

[0007] According to one embodiment of the present invention, the conditions for the electron beam irradiation are: the irradiation voltage is not higher than 83 kV, and the electron beam current dose is 5 to 20 nA.

[0008] According to another embodiment of the present invention, the electron beam irradiation is performed in a transmission electron microscope.

[0009] According to another embodiment of the present invention, the electron beam irradiation treatment time is 5 to 2000 s, and the magnification is 100 to 300 kx.

[0010] The present invention provides a method for cleaning the surface of graphene by electron beam irradiation, which can realize in-situ cleaning of pollutants on the surface of graphene film without destroying the graphene lattice structure. The method of the present invention is simple to operate, has a fast cleaning rate, can realize point-to-point removal of pollutants, and has a good cleaning effect for different types of pollutants. The method has high universality and is of great significance for further realizing and expanding the high-end application of preparing graphene by CVD method. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of in-situ cleaning of graphene surface by electron beam irradiation of the present invention.

[0012] Figure 2 TEM images of graphene before and after treatment according to Example 1 of the present invention.

[0013] Figure 3 This is a TEM image of graphene after being processed according to Example 2 of the present invention.

[0014] Figure 4 TEM images of graphene before and after treatment according to Example 3 of the present invention. DETAILED DESCRIPTION

[0015] The present invention is described in detail below in conjunction with specific implementation modes.

[0016] The method for cleaning the graphene surface of the present invention uses electron beam irradiation to clean the graphene surface. Figure 1 As shown, the in-situ cleaning of the pollutants on the surface of the graphene film can be achieved by electron beam irradiation without destroying the graphene lattice structure. The method is simple to operate, has a fast cleaning rate, can achieve targeted removal of pollutants, and has a good cleaning effect on different types of pollutants. The method is highly universal and has important significance for further realizing and expanding the high-end application of CVD method for preparing graphene.

[0017] In an optional embodiment, the conditions for electron beam irradiation are: the irradiation voltage is not higher than 83 kV, and the electron beam current dose is 5 to 20 nA.

[0018] In an optional embodiment, the electron beam irradiation is performed in a transmission electron microscope. The treatment time can be selected to be 5 to 2000 s. When the treatment time is less than 5 s, the treatment effect is not obvious. When the treatment time is greater than 2000 s, the treatment effect does not change much. An appropriate treatment time can be selected according to the amount of pollutants on the graphene surface, such as 10 s, 100 s, 500 s, 800 s, 1000 s, 1500 s, etc. When the electron beam irradiation treatment is performed in a transmission electron microscope, the magnification can be selected to be 100 to 300 kx.

[0019] 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.

[0020] Example 1

[0021] Using the CVD method, a graphene film was grown on a copper foil, which was covered with amorphous carbon contaminants. Then, the graphene film grown on the copper foil surface was transferred to a porous carbon film using a polymer-assisted transfer method for TEM characterization (FEI TITAN TEM G2), as shown in Figure 2. Figure 2 As shown in the photo on the left, a non-clean graphene film sample with amorphous carbon contaminants covering an area of ​​up to 73.4% was obtained. It can be determined that the graphene surface transferred to the porous carbon is covered with amorphous carbon contaminants and polymer contaminants. Then, in the bright field (BF) mode of the TEM, the irradiation voltage was set to 80kV, the magnification was 165kx, the electron beam current dose was controlled to 15nA, and the processing time was 300s. The graphene cleaned by electron beam irradiation was obtained, and the characterization photo is as follows Figure 2 The photo on the right shows that after the above treatment, the number and area ratio of pollutants on the graphene surface are significantly reduced. This proves that the above electron beam irradiation treatment can effectively remove amorphous carbon pollutants and polymer pollutants on the graphene surface, while the lattice structure of graphene remains intact.

[0022] Example 2

[0023] The difference from Example 1 is that a glue-free clean transfer method is used to transfer the graphene film from the copper foil substrate to the TEM grid, and the other conditions are the same as in Example 1. TEM characterization of the transferred graphene shows that the contaminant coverage on the transferred graphene surface is about 55%. Since it is a glue-free clean transfer, the contaminants on the graphene surface are basically all amorphous carbon contaminants during the growth process. Subsequently, in a transmission electron microscope, the magnification was adjusted to 265kx, the electron beam dose was controlled to 10nA, and the processing time was set to 50s, 350s, and 550s, respectively. The rest of the TEM working modes and irradiation voltage values ​​are the same as in Example 1. TEM characterization photos of different processing times are shown in Figure 1. Figure 3 As shown in . Figure 3 From the three photos in Figure 1, it can be seen that the contaminants on the graphene surface can be effectively removed by electron beam treatment, and the graphene lattice structure is not destroyed. As the electron beam irradiation time increases, the number and area ratio of contaminants continue to decrease.

[0024] Example 3

[0025] The difference between this embodiment and embodiment 2 is that the surface contaminant coverage of the initial sample to be cleaned is 19.6%. The magnification is adjusted to 265kx, the electron beam current dose is controlled to 5nA, and the processing time is set to: 1000s. The rest of the TEM working mode and irradiation voltage value are the same as in embodiment 1. The TEM characterization results before and after the treatment are shown in FIG. Figure 4 As shown. Figure 4 It can be seen from the two photos that after electron beam irradiation treatment, the number and area ratio of pollutants on the graphene surface are reduced, and the graphene lattice structure is not destroyed.

[0026] 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 cleaning a graphene surface, characterized in that: The graphene surface was cleaned by electron beam irradiation.

2. The method according to claim 1, characterized in that The conditions of the electron beam irradiation are: the irradiation voltage is not higher than 83 kV, and the electron beam current dose is 5 to 20 nA.

3. The method according to claim 1, characterized in that The electron beam irradiation is performed in a transmission electron microscope.

4. The method according to claim 3, characterized in that The processing time of the electron beam irradiation is 5 to 2000 seconds, and the magnification is 100 to 300 kx.

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