Jul 17, 2019 | Updated: 08:57 AM EDT

How Hydrogen Atoms Chemically Bind to Graphene in One of the Fastest Reactions Ever Studied

May 03, 2019 10:03 PM EDT

How Hydrogen Atoms Chemically Bind to Graphene in One of the Fastest Reactions Ever Studied
(Photo : Oliver Bünermann / Max Planck Institute for Biophysical Chemistry & University of Göttingen)

An extraordinary material celebrated across many platforms if graphene. It consists of pure carbon, only a single atomic layer thick. However, graphene is exceptionally stable, durable, and even conductive. For electronics, graphene still has critical disadvantages. It is not possible to use it as a semiconductor since it has no bandgap. Such a bandgap can be formed through sticking hydrogen atoms to graphene.

Recently, a group of researchers from Gottingen and Pasadena (USA) has produced an "atomic scale movie" showing how hydrogen atoms chemically bind to graphene in one of the fastest reactions ever studied.

The team of researchers bombarded graphene with hydrogen atoms. Alec Wodtke who is the head of the Department of Dynamics at Surfaces at the Max Planck Institute (MPI), said that the hydrogen atom behaved quite differently than they expected. Instead of immediately flying away, the hydrogen atoms 'stick' briefly to the carbon atoms and then bounce off the surface. They form a transient chemical bond. And something else amazed the scientists. They saw that the hydrogen atoms have a lot of power before they hit the graphene, but not much left when they fly away. Hydrogen atoms lose most of their energy on collision but where does it go.

The explanation of these fantastic experimental observations prompted Alexander Kandratsenka, a researcher at the Gottingen MPI and his colleagues at the California Institute of Technology to develop theoretical methods which they simulated on the computer and then compared to their experiments. With these theoretical simulations which agree well with the experimental observations, the researchers were able to reproduce the ultra-fast movements of atoms forming the transient chemical bond. Kandratsenka further explained that this bond lasts for only about ten femtoseconds, ten quadrillionths of a second. This outcome makes it one of the fastest chemical reactions ever observed directly.

In the course of these ten femtoseconds, the hydrogen atom can transfer almost all its energy to the carbon atoms of the graphene, and it triggers a sound wave that propagates outward from the point of the hydrogen atom impact over the graphene surface, much like a stone that falls into the water and unleashes a wave. The sound wave contributes to the fact that the hydrogen atom can bind more quickly to the carbon atom than the scientists had expected and previous models had predicted.

The outcomes of the research team offer fundamentally new insight into chemical bonding. Also, these results are of great interest to industry. There will be a bandgap with sticking hydrogen atoms to graphene which will make it a useful semiconductor and much more versatile in electronics.

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