Graphene on Nickel: Electrons behave like light
In a graphene sheet on nickel, every other
carbon atom is strongly bonded to the nickel atom
which it sits on top of while its neighboring
carbon atoms do not face nickel atoms.
This atomic arrangement breaks the original
lattice symmetry. © STM, A. Varykhalov, HZB
Dr. Andrei Varykhalov and his colleagues in the group of Prof. Dr. Oliver Rader investigated at BESSY II the electronic properties of nickel coated with graphene and achieved an astonishing result. They could show that the conduction electrons of the graphene behave rather as light than as particles. Physicists had originally expected such behavior only for freestanding graphene layers which show a perfect honeycomb structure and not for graphene on nickel which disturbs the perfect hexagonal symmetry. Their results are supported by calculations of two theoretical groups using novel concepts. Their report was published in the open access journal, Phys. Rev. X, the new top journal of the Physical Review.
Employing photoelectron spectroscopy at BESSY II, the physicists were able to establish so-called Dirac cones of massless fermions, which prove the light-like behavior. After their experiments, they could enlist two theoretical groups for supporting their results by contributing new explanations to today's publication. “These results are surprising” says Varykhalov, the reason being that the nickel atoms interact in two different and mutually compensating ways with the carbon atoms of the graphene. On the one hand, they destroy the perfect hexagonal symmetry of the graphene lattice. On the other hand they provide the graphene layer with extra electrons - which compensates for the “damage” inflicted upon the graphene by disturbing the lattice. “We uncovered a fundamental mechanism that is interesting for possible applications” says Varykhalov adding that graphene is usually supported by such a substrate and that the extra electrons for “healing” could as well be supplied by an electrical voltage.
http://prx.aps.org/
A. Varykhalov et al. , Phys. Rev. X 2, 041017
- Porous Radical Organic framework improves lithium-sulphur batteriesA team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.
- Metallic nanocatalysts: what really happens during catalysisUsing a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY's NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This configuration allows a better understanding of structural changes in, for example, rhodium-platinum catalysts for emission control. The results show that under typical catalytic conditions, some of the rhodium in the shell can diffuse into the interior of the nanoparticles. However, most of it remains on the surface and oxidises. This process is strongly dependent on the surface orientation of the nanoparticle facets.
- Key technology for a future without fossil fuelsIn June and July 2025, catalyst researcher Nico Fischer spent some time at HZB. It was his sabbatical, he was relieved of his duties as Director of the Catalysis Institute in Cape Town for several months and was able to focus on research only. His institute is collaborating with HZB on two projects that aim to develop environmentally friendly alternatives using innovative catalyst technologies. The questions were asked by Antonia Rötger, HZB.