Researchers from Freie Universität Berlin, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Universität Ulm have defined the mechanism on which the wet chemical synthesis of graphene from graphite is based. They succeeded in solving the basic problem of how to separate an individual layer of graphene from a graphite crystal.
The team was able to successfully stabilize individual layers of carbon from graphite using chemical functionalization. By using computer simulations, the group was able to prove the mechanism. They succeeded in making the structure of the graphene manufactured using wet chemical methods visible at the atomic level with the help of electron beam microscopy.
The challenge faced when developing electronics based on graphene is to obtain sufficiently large quantities of the material, as it is very challenging to isolate graphene from graphite without damaging it. It is known that the space between the individual layers of graphene in graphite can be increased, but it is still difficult to separate the graphene layers in large quantities and stabilize the individual layers in solvent without destroying them in the process. Without stabilization, individual layers of graphene would merge to form graphite or undefined carbon particles. The excellent properties of graphene would be lost as a result.
The researchers were able to prove that highly crystalline graphite with a well-defined order of layers is particularly well suited for being transferred to an intercalation compound in which molecules and ions are stored between the carbon layers. This is particularly successful if the layers of graphene are partially electronically oxidized, in other words positively charged.
Molecule dynamic simulations show that the order of the graphene layers in the graphite together with electronic oxidation drastically reduce the friction of the molecules between the layers. Conversely, this means that a high level of friction of molecules in the layered material can restrict their movement, preventing graphite from being activated. Activation allows water molecules to react in the next step with the activated graphite. Alcohol groups are attached to the surface of the graphene, making it possible to separate individual layers of graphene and stabilize them in water. It was then possible to transfer this separated polar graphene to surfaces and reduce it to uncharged graphene.