| AVS 59th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Thursday Sessions |
| Session GR-ThP |
| Session: | Graphene and Related Materials Poster Session |
| Presenter: | A. Nefedov, Karlsruhe Institute of Technology, Germany |
| Authors: | A. Nefedov, Karlsruhe Institute of Technology, Germany A. Paris, Interdisciplinary Laboratory for Computational Science, FBK-CMM, Italy N. Verbitsky, Moscow State University, Russia Y. Wang, Nagoya University, Japan A. Fedorov, IFW Dresden, Germany D. Haberer, IFW Dresden, Germany M. Oehzelt, Helmholtz-Zentrum Berlin für Materialien und Energie, Germany L. Petaccia, Elletra Synchrotron Light Laboratory, Italy D. Usachov, St. Petersburg State University, Russia D. Vyalikh, Technical University Dresden, Germany H. Sachdev, Max-Planck-Institute for Polymer Research, Germany Ch. Wöll, Karlsruhe Institute of Technology, Germany M. Knupfer, IFW Dresden, Germany B. Buechner, IFW Dresden, Germany L. Calliari, Interdisciplinary Laboratory for Computational Science, FBK-CMM, Italy L. Yashina, Moscow State University, Russia S. Irle, Nagoya University, Japan A. Grueneis, University of Vienna, Austria |
| Correspondent: | Click to Email |
Kinetic isotope effects (KIE) are important phenomena in physical chemistry and have been investigated for a long time in relation to activation and rate of chemical reactions. KIE are easily observable for the hydrogen isotopes due to the large relative mass difference and have been studied for example in hydrogen transfer in organic chemistry such as acid and base catalysis, enzyme reactions and catalytic decomposition.
Here we present results of time-dependent x-ray photoemission spectroscopy (XPS) in order to investigate the kinetics of the hydrogenation/deuteration reaction of graphene. A pristine monolayer graphene was prepared under ultrahigh vacuum conditions by chemical vapor deposition on Ni(111) thin films epitaxial grown on W(110). Then a monolayer of Au was intercalated into the interface between Ni and graphene, making the latter quasi free-standing. The graphene layer was then exposed to hydrogen or deuterium atomic gas beams, obtained by thermal cracking in a tungsten capillary at T=3000 K. The maximum surface coverage was obtained after several hydrogenation or deuteration steps of different time. After each step XPS of the C1s line was performed in order to measure H/C and D/C ratios. After reaching saturation, the electronic structure of the hydrogenated and deuterated layer was analyzed by near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy at the carbon K-edge.
We have observed a strong inverse KIE for the hydrogenation/deuteration reaction leading to substantially faster adsorption and higher maximum D/C ratios as compared to H/C (D/C~35% vs. H/C~25%). These results can be understood by the fact that atomic D has a lower chemisorption barrier and a higher desorption barrier. Quantum chemical calculations and molecular dynamics simulations can reproduce the experimental trends and reveal the contribution of the constituent chemisorption, reaction and associative desorption processes of H(D) atoms onto graphene. The reported case of a strong inverse KIE is an extremely unusual case and is important for isotope specific chemical reactivity in organic molecules and functionalized graphene.