Date and Time: Tuseday, 25 February, 15:00～16:00
Place: IMRAM Administration Building, 2nd Floor, Main conference room, Katahira Campus,
Tohoku University

Wet-Chemically Prepared Graphene – Chemistry and Device Fabrication
Prof. Siegfried Eigler, Professor
（Institute for Chemistry and Biochemistry, Freie Universität Berlin）

Outline：The wet-chemically synthesis of graphene and the controlled chemical functionalization is an ongoing challenge. Complete delamination of the layers of graphite, without destroying the honeycomb lattice, is mandatory to control the chemical functionalization. Chemically versatile is the oxidative functionalization of graphite, allowing delamination to functionalized graphene, which is stabilized by the covalent C-O functionalities. A subsequent post-functionalization or conversion to graphene are possible. However, overall the chemical toolbox must be improved to give control over the surface chemistry of graphene to enable applications, such as specific sensing.
We made rapid progress in the last five years and demonstrated that graphene can indeed be yielded by oxo-functionalization of activate graphite. The respective graphene possesses mobility values of charge carriers exceeding 1000 cm2/Vs. However, the quality of graphene is statistically distributed from flake to flake. Mechanistic insights into the oxidation process is presented, helping to understand the intercalation of graphite (Figure 1). Now, we can produce graphene with a narrow distribution of the quality with the remaining density of defects of about 0.02% in average. Moreover, the nature of defects was revealed at atomic resolution (Figure 2). With this knowledge, it is possible to benefit from specific defects, such as vacancies, to further manipulate those. Accordingly, defects can be seen as a structural motif for post-functionalization. In a recent study we demonstrated that radical functionalization is selectively possible in close proximity to defect-sites, if the concentration of organic radicals is well-controlled.
Recently, we started fabricating field-effect transistor devices and investigate the properties of differently prepared and processed oxo-functionalized graphene derivatives and related graphene materials. In particular, the fabrication of hetero-stacks is in the current focus to enhance sensing devices.