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Graphene is celebrated as an extraordinary material. It consists of pure carbon, only one atomic layer of thickness. Nevertheless, it is extremely stable, powerful and even driver. For the electronics, however, graphene still has crucial disadvantages. It can not be used as a semiconductor because it does not have a bandgap. By bonding hydrogen atoms on graphene, such a band gap can be formed. Researchers from Göttingen and Pasadena (USA) have produced an "atomic scale film" showing how hydrogen atoms chemically bond to graphene in one of the fastest reactions ever studied.
The international research team bombed graphene with hydrogen atoms. "The hydrogen atom has behaved differently than expected," said Alec Wodtke, head of the Surface Dynamics Department at the Max Planck Institute (MPI) of Biophysical Chemistry and Professor at the Institute of Physical Chemistry of the University of Göttingen. "Instead of flying away immediately, the hydrogen atoms" stick "briefly to the carbon atoms, then bounce off the surface, forming a transient chemical bond," says Wodtke. And something else has surprised scientists: the hydrogen atoms have a lot of energy before reaching graphene, but there is not much left when they fly away. Hydrogen atoms lose most of their energy during a collision, but where is it going?
To explain these surprising experimental observations, Alexander Kandratsenka, MPI researcher at Göttingen, developed, in collaboration with colleagues at the California Institute of Technology, theoretical methods, which they simulated on a computer and then compared to their experiments. Thanks to these theoretical simulations, in agreement with the experimental observations, the researchers were able to reproduce the ultra-fast movements of atoms forming the transient chemical bond. "This link lasts only ten femtoseconds, or ten quadrillion seconds, making it one of the fastest chemical reactions ever observed directly," says Kandratsenka.
During these ten femtoseconds, the hydrogen atom can transfer almost all of its energy to the carbon atoms of graphene and triggers a sound wave that propagates from the point of strike of the hydrogen atom to the graphene surface, in in the water and sets off a wave, "said Kandratsenka. The sound wave contributes to the fact that the hydrogen atom can bind more easily to the carbon atom than predicted scientists and previous models.
The results of the research team provide fundamentally new information on chemical binding. In addition, they are of great interest to the industry. Glueing hydrogen atoms into graphene can produce a band gap, making it a useful and much more versatile semiconductor in electronics.
Oliver Bünermann, head of the project group at the University of Göttingen, said the efforts to organize and conduct these experiments were considerable. "We had to make them under ultra-vacuum to keep the graphene surface perfectly clean." Scientists also had to use a large number of laser systems to prepare the hydrogen atoms before the experiment and to detect them after the collision. According to Bünermann, the excellent technical staff of the workshops of the MPI of Biophysical Chemistry and the University of Göttingen was essential to the success of the project.
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Material provided by University of Göttingen. Note: Content can be changed for style and length.
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