Graphene on the way to superconductivity

Scientists at HZB have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance. They probed the bandstructure at BESSY II with extremely high resolution ARPES and could identify a flat area at a surprising location.

Carbon atoms have diverse possibilities to form bonds. Pure carbon can therefore occur in many forms, as diamond, graphite, as nanotubes, football molecules or as a honeycomb-net with hexagonal meshes, graphene. This exotic, strictly two-dimensional material conducts electricity excellently, but is not a superconductor. But perhaps this can be changed.

A complicated option for superconductivity
In April 2018, a group at MIT, USA, showed that it is possible to generate a form of superconductivity in a system of two layers of graphene under very specific conditions: To do this, the two hexagonal nets must be twisted against each other by exactly the magic angle of 1.1°. Under this condition a flat band forms in the electronic structure. The preparation of samples from two layers of graphene with such an exactly adjusted twist is complex, and not suitable for mass production. Nevertheless, the study has attracted a lot of attention among experts.

>Read more on the BESSY II at HZB website

Image: The data show that In the case of the two-layer graphene, a flat part of bandstructure only 200 milli-electron volts below the Fermi energy. Credit: HZB

The search for clean hydrogen fuel

The world is transitioning away from fossil fuels and hydrogen is poised to be the replacement.

Two things are needed if we are to make the transition to a low carbon, “hydrogen economy” they are clean and high yielding sources of hydrogen, as well as efficient means of producing and storing energy using hydrogen.

Hydrogen powered cars are the perfect case study for how a hydrogen-fuelled future would look. While they work and show a great deal of promise, the best examples of hydrogen being used in fuel require very clean sources of hydrogen. If the source of hydrogen is mixed with contaminants like carbon monoxide, the efficiency of the fuel goes down and causes downstream problems in the fuel cell.

A team from KTH led by Jonas Weissenrieder is visiting MAX IV this week to try and solve this exact problem, how can we generate clean hydrogen for fuel cells? The team is working on a process to catalyse the oxidation of carbon monoxide, which adversely affects fuel cell performance, to harmless carbon dioxide. The catalysis reaction must be selective, and not affect the hydrogen gas that could be oxidised to water which is not great for running car engines.

>Read more on the MAX IV Laboratory website

Research gives clues to CO2 trapping underground

CO2 is an environmentally important gas that plays a crucial role in climate change.

It is a compound that is also present in the depth of the Earth but very little information about it is available. What happens to CO2 in the Earth’s mantle? Could it be eventually hosted underground? A new publication in Nature Communications unveils some key findings.

Carbon dioxide is a widespread simple molecule in the Universe. In spite of its simplicity, it has a very complex phase diagram, forming both amorphous and crystalline phases above the pressure of 40 GPa. In the depths of the Earth, CO2 does not appear as we know it in everyday life. Instead of being a gas consisting of molecules, it has a polymeric solid form that structurally resembles quartz (a main mineral of sand) due to the pressure it sustains, which is a million times bigger than that at the surface of the Earth.

Researchers have been long studying what happens to carbonates at high temperature and high pressure, the same conditions as deep inside the Earth. Until now, the majority of experiments had shown that CO2 decomposes, with the formation of diamond and oxygen. These studies were all focused on CO2 at the upper mantle, with a 70 GPa of pressure and 1800-2800 Kelvin of temperature.

>Read more on the European Synchrotron (ESRF) website

Picture: Mohamed Mezouar, scientist in charge of ID27, on the beamline.
Credit: S. Candé. 

One size does not fit all when exploring how carbon in soil affects the climate

Scientists from Stanford University are opening a window into soil organic carbon, a critical component of the global carbon cycle and climate change.

“We have to know what kind of carbon is in soil in order to understand where the carbon comes from and where it will go,” said Hsiao-Tieh Hsu, a PhD student in chemistry at Stanford University and a member of a Kate Maher’s research group.

The natural fluxes of soil organic carbon, the exchange of carbon moving from vegetation to the soil and recycled by microorganisms before being stabilized in the soil or returned to the atmosphere, is 10 to 20 times higher than human emissions. Even the smallest change in the flux of soil organic carbon would have a huge impact on the climate.

Soil organic carbon occurs naturally and is part of the carbon cycle. Through photosynthesis, plants absorb carbon dioxide from the atmosphere. As plants and their roots decompose, they deposit organic carbon in the soil. Microorganisms, decomposing animals, animal feces and minerals also contribute to the organic carbon in the soil. In turn, plants and microorganisms “eat” that carbon, which is an essential nutrient.

All of this results in different “flavours” or compounds within the soil, say Hsu and Maher, who is also a faculty member of the Stanford Center for Carbon Storage.

>Read more on the Canadian Light Source website

Image: Members of the research team at the East River, Colorado, field site (left to right): Hsiao-Tieh Hsu; Grace Rainaldi, Stanford undergraduate; Corey Lawrence, research geologist at United States Geological Survey; Kate Maher; Matthew Winnick, Stanford postdoctoral fellow.
Credit: Kate Maher.