Under cover of graphene
Phoenex-Apparatus
© HZB
Researchers at Helmholtz-Zentrum Berlin have developed a method to conserve electronic surface states using graphene.
Scientists at Helmholtz-Zentrum Berlin (HZB), together with colleagues from Dresden and Jülich, have succeeded in making the electronic surface-state of a metal extra-durable. To this end, they seal the surface of the metal iridium with a layer of carbon that has the thickness of a single atom. This modification of carbon known as graphene proves to be an efficient shield against outside influences. This ability to preserve the electronic surface-state is of paramount interest for spintronics. The HZB scientists have published their findings today in the journal "Physical Review Letters" (DOI: 10.1103/PhysRevLett.108.066804).
Spintronics employs the magnetic moment - the spin - of electrons in order to process information. Surfaces are particularly well suited for distinguishing electrons with different spin, due to what physicists call a "broken symmetry". The electrons at the surface, on the other hand, are extremely active and easily form a chemical bond, with oxygen for example. Therefore, it has only been possible to preserve a particular spin state under extreme conditions, e.g. ultrahigh vacuum.
In their successful experiments to conserve the electronic surface structure, HZB researchers tested the metal iridium. "We treated the metal catalytically with propylene gas, a hydrocarbon" says project leader Dr. Andrei Varykhalov from the HZB department for magnetization dynamics. The surface allows for two competing reactions, explains Varykhalov, of which the graphenization wins out. "In this way, a single layer of carbon atoms forms on the iridium."
HZB researchers studied this graphene layer as well as the spin states of the top layer of the metal with sophisticated analytical methods at the electron storage ring BESSY II. Their instrument contains an apparatus from particle physics, a so-called spin detector.
"At first, we were able to demonstrate that the spin states of the iridium do not change under the gaphene layer. This was in agreement with model calculations made by researchers in Jülich" Varykhalov explains. "In a second step we found that they also persist in the air". This is considered an important progress for spintronics. Varykhalov: "Our graphene-covered iridium is still a model system for research. If we succeed with graphene to also conserve the spin states of an insulator, we can bring realistic applications for spintronics within reach."
- MXene for energy storage: More versatile than expectedMXene materials are promising candidates for a new energy storage technology. However, the processes by which the charge storage takes place were not yet fully understood. A team at HZB has examined, for the first time, individual MXene flakes to explore these processes in detail. Using the in situ Scanning transmission X-ray microscope 'MYSTIIC' at BESSY II, the scientists mapped the chemical states of Titanium atoms on the MXene flake surfaces. The results revealed two distinct redox reactions, depending on the electrolyte. This lays the groundwork for understanding charge transfer processes at the nanoscale and provides a basis for future research aimed at optimising pseudocapacitive energy storage devices.
- AI re-examines dinosaur footprintsFor decades, paleontologists have pondered over mysterious three-toed dinosaur footprints. Were they left by fierce carnivores, gentle plant-eaters, or even early birds? Now, an international team has used artificial intelligence to tackle the problem—creating a free app that readily lets anyone decipher the past.
- Compact electron accelerator for treating PFAS-contaminated waterSo-called forever chemicals or PFAS compounds are a growing environmental problem. An innovative approach to treating PFAS-contaminated water and soil now comes from accelerator physics: high-energy electrons can break down PFAS molecules into harmless components through a process called radiolysis. A recent study published in PLOS One shows that an accelerator developed at HZB, based on a SRF photoinjector, can provide the necessary electron beam.