Graphene preparation technology has developed rapidly. The excellent performance and wide application prospect of graphene greatly promote the rapid development of graphene preparation technology. Since Geim et al. first prepared graphene by micromechanical stripping in 2004, researchers have developed numerous methods for preparing graphene. Among the more mainstream methods are epitaxial growth method, chemical vapor deposition CVD method and graphite oxide reduction method.
Existing methods cannot meet the requirements of graphene industrialization. Numerous preparation methods including micro mechanical peeling, epitaxial growth, chemical vapor deposition CVD and graphite oxide reduction are still unable to meet the requirements of industrialization. In particular, industrialization requires graphene preparation technology to produce graphene with large area and high purity at a stable and low cost. This technical problem has not yet been solved.
Micromechanical stripping
Graphene is first produced by micromechanical stripping. The micro-mechanical stripping method is to press the highly oriented pyrolytic graphite sheet onto other surfaces with a transparent tape to perform multiple peeling, and finally obtain a single layer or several layers of graphene. In 2004, Geim, Novoselov, etc. obtained the first single layer of graphene in the world by this method, which proved that the two-dimensional crystal structure can exist at normal temperature.
The micro-mechanical stripping method is simple in operation and high in sample quality, and is currently the main method for preparing single-layer high-quality graphene. However, its controllability is poor, and the produced graphene is small in size and has great uncertainty, while being low in efficiency and high in cost, and is not suitable for mass production.
Epitaxial growth method
The epitaxial growth method includes a silicon carbide epitaxial growth method and a metal catalytic epitaxial growth method. The silicon carbide epitaxial growth method refers to heating a SiC single crystal at a high temperature such that Si atoms on the surface of the SiC are evaporated to escape from the surface, and the remaining C atoms are reconstructed by an autonomous form to obtain a graphene based on a SiC substrate.
The metal-catalyzed epitaxial growth method is to introduce a hydrocarbon into a catalytically active transition metal substrate such as Pt, Ir, Ru, Cu, etc. under ultra-high vacuum conditions, and catalytically dehydrogenate the adsorbed gas by heating to obtain graphene. . The gas can grow over the entire metal substrate during the adsorption process, and the growth process is a self-limiting process, that is, the substrate does not repeatedly absorb after adsorbing the gas. Therefore, the prepared graphene is mostly a single layer, and can be widely used. Uniform graphene was prepared.
Chemical vapor deposition CVD: the most promising large-scale production method
The CVD method is considered to be the most promising preparation of high-quality, large-area graphene, and is the most promising method for industrial production of graphene films. The specific process of the chemical vapor deposition CVD method is: introducing hydrocarbon methane, ethanol, etc. into the surface of the high-temperature heated metal substrate Cu, Ni, and cooling after a certain period of time, and several layers are formed on the surface of the substrate during the cooling process or Single-layer graphene, in which carbon atoms are dissolved and diffused on the substrate. The method is similar to the metal catalytic epitaxial growth method, and has the advantages that it can be carried out at a lower temperature, thereby reducing the energy consumption in the preparation process, and the graphene and the substrate can be easily separated by the chemical corrosion metal method, which is advantageous for The graphene is processed later.
In this way, Samsung obtained a single-layer graphene with a diagonal length of 30 inches, showing the great potential of this method as an industrial production method. However, the thickness of graphene prepared by this process is difficult to control. Only a small amount of available carbon is converted into graphene during the precipitation process, and the transfer process of graphene is complicated.
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