The miracle material graphene: convex as a chesterfield
Scanning Tunneling Microscopy shows the regular corrugation pattern of graphene over clusters of gold. © HZB
A typical Chesterfield pattern. ( © mit freundlicher Genehmigung von Petr Kratochvil
Graphene possesses extreme properties and can be utilised in many ways. Even the spins of graphene can be controlled through use of a trick. This had already been demonstrated by a HZB team some time ago: the physicists applied a layer of graphene onto a nickel substrate and introduced atoms of gold in between (intercalation). The scientists now show why this has such a dramatic influence on the spins in a paper published in 2D Materials. As a result, graphene can also be considered as a material for future information technologies that are based on processing spins as units of information.
Graphene is probably the most exotic form of carbon: all of the atoms are bound to one another solely in a plane (monolayer), forming a matrix of hexagons like a honeycomb. Graphene is strictly two-dimensional, therefore infinitely thin, extremely conductive, perfectly transparent, and quite strong. In addition, this miracle material possesses other interesting properties related to its structure.
For example, the spins (tiny magnetic moments) of the conduction electrons surprisingly can be extremely well controlled. If you apply a layer of graphene to a nickel substrate and shove atoms of gold in between, then what is known as the spin-orbit interaction dramatically rises by a factor of 10,000, allowing the orientation of the spins to be influenced by external fields.
Physicists working with Dr. Andrei Varykhalov at the HZB had already demonstrated several times that this works. However, it was not clear why the presence of the atoms of gold has such a strong effect on the spin splitting behaviour in graphene.
“We wanted to discover how it happens that the high spin-orbit interaction, which is characteristic of gold, is transferred over to graphene”, says Varykhalov. The physicists show in the work recently published that the atoms of gold are not distributed completely uniformly in the interlayer, but instead are located on the nickel substrate in small groups or clusters. These gold clusters in turn form a regular pattern beneath the graphene. Between these clusters nickel atoms remain uncovered by gold. Graphene binds strongly to the nickel, arching over the gold clusters. “It looks almost like a bolster of material on a chesterfield sofa”, explains Varykhalov. “At the points where the gold and carbon come into close contact, we observed an extremely strong spin-orbit interaction arise. This result was supported by scanning tunnelling microscopy, and analyses using density functional theory.”
To the publication:
2D Materials, Vol.4, Nr3 (2017): "Nanostructural origin of giant Rashba effect in intercalated graphene". M Krivenkov, E Golias, D Marchenko, J Sánchez-Barriga, G Bihlmayer, O Rader and A Varykhalov.
Doi: 10.1088/2053-1583/aa7ad8
- Energy of charge carrier pairs in cuprate compoundsHigh-temperature superconductivity is still not fully understood. Now, an international research team at BESSY II has measured the energy of charge carrier pairs in undoped La₂CuO₄. Their findings revealed that the interaction energies within the potentially superconducting copper oxide layers are significantly lower than those in the insulating lanthanum oxide layers. These results contribute to a better understanding of high-temperature superconductivity and could also be relevant for research into other functional materials.
- Electrocatalysis with dual functionality – an overviewHybrid electrocatalysts can produce green hydrogen, for example, and valuable organic compounds simultaneously. This promises economically viable applications. However, the complex catalytic reactions involved in producing organic compounds are not yet fully understood. Modern X-ray methods at synchrotron sources such as BESSY II, enable catalyst materials and the reactions occurring on their surfaces to be analysed in real time, in situ and under real operating conditions. This provides insights that can be used for targeted optimisation. A team has now published an overview of the current state of knowledge in Nature Reviews Chemistry.
- Successful master's degree in IR thermography on solar facadesWe are delighted to congratulate our student employee Luca Raschke on successfully completing her Master's degree in Renewable Energies at the Hochschule für Technik und Wirtschaft Berlin - and with distinction!