Speaker: Siegfried Eigler
Affiliation: Friedrich Alexander University, Germany
Abstract Details: The bulk chemistry of graphene is based on the oxidation of graphite, with a tradition of more than 150 years. It turned out that all developed oxidation methods resulted in functionalized layers of graphene with plenty of defects within the carbon framework. Thereby the procedures are accompanied by over-oxidation leading to more amorphous structures with manifold functional groups. This over-oxidation can even lead to disintegration of flakes and the generation of oxidative debrides. Thus, chemical functionalization of graphene oxide is dominated by reactivity of edge-groups of defects. Approximately one missing carbon atom was determined in graphene oxide on about 25 lattice atoms using a conventional synthetic protocol. Thus, chemistry was predominantly driven by the functionalization of defects. We optimized the oxidative procedure to avoid the formation of defects and now a residual average density of defects of about 0.05% was reached. Statistical Raman microscopy is now available to monitor the impact of reaction on the integrity of the carbon lattice. With such materials, the chemistry of graphene can be explored while defects play a minor role. We used oxo-functionalized graphene with organosulfate groups to prepare a composite that can be used as charge storing layer in floating gate memory devices operating at 3V. This goal was only reached by controlled chemistry. In another recent study we used graphite sulfate, which is a long known intercalation compound that bears a C24 subunit with one positive charge. This charge can be used for chemical functionalization and an oxo-functionalized graphene derivative with an idealized subunit of C24(OH)(H2O)2 is yielded. Chemical reduction and statistical Raman analysis reveals that the best average quality of graphene can be prepared from this novel derivative of graphene. Overcoming performance limits, as determined for graphene oxide, is in reach using controlled chemistry of oxo-functionalized graphene.
 S. Eigler, A. Hirsch, Angew. Chem. Int. Ed. 2014, 53, 7720.
 S. Eigler, M. Enzelberger-Heim, S. Grimm, P. Hofmann, W. Kroener, A. Geworski, C. Dotzer, M. Rockert, J. Xiao, C. Papp, O. Lytken, H. P. SteinrÃ¼ck, P. MÃ¼ller, A. Hirsch, Adv. Mater. 2013, 25, 3583.
 S. Eigler, F. Hof, M. Enzelberger-Heim, S. Grimm, P. MÃ¼ller, A. Hirsch, J. Phys. Chem. C 2014, 118, 7698.
 Z. Wang, S. Eigler, Y. Ishii, Y. Hu, C. Papp, O. Lytken, H.-P. SteinrÃ¼ck, M. Halik, J. Mater. Chem. C 2015, 3, 8595.
 S. Eigler, Chem. Commun. 2015, 51, 3162."
Speaker: Siegfried Eigler