To transfer graphene from copper, there are several methods that can be used:
1. Chemical Etching: One method involves applying a supporting polymer layer, such as polymethyl methacrylate (PMMA), on top of the graphene. The PMMA-coated graphene is then baked at a specific temperature for solvent evaporation. A copper (or other catalytic metal) etchant is then used to remove the copper substrate, leaving behind the graphene/PMMA film. The film is then cleaned with deionized water and transferred onto the desired substrate. Finally, acetone is used to remove the PMMA after the water vapor evaporates, leaving only the graphene film on the target substrate.
2. Electrochemical Delamination: Another method involves electrochemically delaminating the graphene film from the copper substrate. This can be done by intercalating a layer of copper oxide between the graphene and the copper substrate during the chemical vapor deposition (CVD) process. The copper oxide layer acts as a weak barrier that reduces the hydrostatic compression between the graphene and the copper substrate, allowing for easier removal of the graphene film.
3. Dissolved Substrate Transfer: This transfer method involves dissolving the substrate with an etchant to separate the graphene film. This can be done by using a catalytic metal substrate, such as copper, and dissolving it with a suitable etchant, leaving behind the graphene film. The dissolved substrate transfer method is cost-effective because the substrate can be reused.
4. Separated Substrate Transfer: This transfer method involves mechanically or electrochemically separating the graphene film from the substrate. It can be done by applying a carrier film on top of the graphene and then mechanically peeling it off from the substrate. Alternatively, electrochemical methods can be used to separate the graphene film from the substrate. Separated substrate transfer is also cost-effective because the substrate can be reused.
In addition to these methods, scientists are continuously researching and developing new techniques to improve the transfer process and create higher-quality graphene. For example, treating the copper substrate before the graphene growth process can help reduce catalytic activity and improve the surface morphology, resulting in graphene flakes with fewer imperfections.
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