Korean scientists test the brand-new MYSTIIC

Jongwoo and his team from Seoul are “friendly users”. This name is given to scientists who do their experiments on a pristine machine, before it goes into user operation. Back in Korea we called them to hear more about their special beamtime and what it means for their battery research.

Who are you and how did you discover BESSY II?

I am Jongwoo Lim, assistant professor at the department of chemistry at Seoul National University. My research group “Battery and Energy Research Lab” counts many talented young scientists. In 2018 a colleague from the Max Planck Society invited me to give a talk and, on this occasion, I visited BESSY II. Back in Seoul I wanted my team to discover this amazing science environment.

Getting beamtime at BESSY II, how does this work?

The competition for beamtime is very strong, many scientists want to come to BESSY II! We send in a proposal and were rejected several times. Finally, after 2 years we got the green light for some beamtime at MAXYMUS, the beamline of the Max Planck Institute for Intelligent Systems (more below). And on top of that, beamline scientist Markus asked us if we were interested to use and test MYSTIIC (Microscope for x-raY Scanning Transmission In-situ Imaging of Catalysts). This new microscope will go into operation in Spring 2022.

Read more on the HZB blog science site

Image: Jongwoo’s team from Korea at BESSY II

Great minds think alike!

Marion Flatken from BESSY II & Luisa Napolitano from Elettra give advice to those at the start of their careers

Our #LightSourceSelfies campaign features staff and users from 25 light sources across the world. We invited them all to answer a specific set of questions so we could share their insights and advice via this video campaign. Today’s montage features Marion Flatken from BESSY II, in Germany, and Luisa Napolitano from Elettra, in Italy. Both scientists offered the same advice to those starting out on their scientific journeys: “Be curious and stay curious”. Light source experiments can be very challenging and the tough days can lead to demotivation and self-doubts. In these times, it is good to seek out support from colleagues, all of whom will have experienced days like this. Even if you think you can’t succeed with your research goals, try because it is amazing what can be achieved through hard work, tenacity and collaboration.

Liquid crystals for fast switching devices

An international team has investigated a newly synthesized liquid-crystalline material that promises applications in optoelectronics. Simple rod-shaped molecules with a single center of chirality self-assemble into helical structures at room temperature. Using soft X-ray resonant scattering at BESSY II, the scientists have now been able to determine the pitch of the helical structure with high precision. Their results indicate an extremely short pitch at only about 100 nanometres which would enable applications with particularly fast switching processes.

Liquid crystals are not solid, but some of their physical properties are directional – like in a crystal. This is because their molecules can arrange themselves into certain patterns. The best-known applications include flat screens and digital displays. They are based on pixels of liquid crystals whose optical properties can be switched by electric fields.

Some liquid crystals form the so-called cholesteric phases: the molecules self-assemble into helical structures, which are characterised by pitch and rotate either to the right or to the left. “The pitch of the cholesteric spirals determines how quickly they react to an applied electric field,” explains Dr. Alevtina Smekhova, physicist at HZB and first author of the study, which has now been published in Soft Matter.

Read more on the HZB website

Image: The photo shows the cells on the modified sample holder which was used in the real experiment. This modified sample holder is mounted within the ALICE chamber at BESSY II.

Credit: © A. Smekhova/HZB

Green information technologies: Superconductivity meets Spintronics

Superconducting coupling between two regions separated by a one micron wide ferromagnetic compound has been proved by an international team. This macroscopic quantum effect, known as Josephson effect, generates an electrical current within the ferromagnetic compound made of superconducting Cooper-pairs. Magnetic imaging of the ferromagnetic region at BESSY II has contributed to demonstrate that the spin of the electrons forming the Cooper pairs are equal. These results pave the way for low-power consumption superconducting spintronic-applications where spin-polarized currents can be protected by quantum coherence.

When two superconducting regions are separated by a strip of non-superconducting material, a special quantum effect can occur, coupling both regions: The Josephson effect. If the spacer material is a half-metal ferromagnet novel implications for spintronic applications arise. An international team has now for the first time designed a material system that exhibits an unusually long-range Josephson effect: Here, regions of superconducting YBa2Cu3O7 are separated by a region of half-metallic, ferromagnetic manganite (La2/3Sr1/3MnO3) one micron wide.

Read more on the HZB website

Image: Device where the long range Josephson coupling has been demonstrated.  Superconducting YBa2Cu3Oregions (yellow) are separated by a half-metal La2/3Sr1/3MnO3 ferromagnet (green).

Credit: © Nature Materials 2021: 10.1038/s41563-021-01162-5

World changing science

Marion Flatken is a 3rd year PhD student working in the Department Novel Materials and Interfaces for photovoltaic solar cells led by Prof. Dr. Antonio Abate, at HZB.

In her #LightSourceSelfie, Marion describes the perovskite solar cell research she is undertaking and reflects on the opportunity light sources present to scientists.  She says,

“We are really having the chance to work in a unique environment and to use the knowledge and the facilities and the resources that we have to really change the world literally.”

Marion Flatken’s #LightSourceSelfie

Beamline filming location: HZB ASAXS-Instrument, FCM-beamline at PTB laboratory (Physikalisch-Technische Bundesanstalt), BESSYII

“Green” chemistry

In mechanochemistry, reagents are finely ground and mixed so that they combine to form the desired product, even without need for solvent. By eliminating solvent, this technology promises to contribute significantly towards ‘green’ and environmentally benign chemical manufacture in the future. However, there are still major gaps in understanding the key processes that occur during mechanical treatment and reaction. A team led by the Federal Institute for Materials Research (BAM) has now developed a method at BESSY II to observe these processes in situ with X-ray scattering.

Chemical reactions are often based on the use of solvents that pollute the environment. Yet, many reactions can also work without solvent. This is the approach known as mechanochemistry, in which reagents are very finely ground and mixed together so that they react with each other to form the desired product.  The mechanochemical approach is not only more environmentally friendly, but even potentially cheaper than classical synthesis methods. The International Union of Pure and Applied Chemistry (IUPAC) therefore ranks mechanochemistry among the 10 chemical innovations that will change our world. However, the full potential of this technology cannot be realized until the processes during mechanical treatment are understood in more detail, so that it is possible to precisely direct and control them.

Read more on the HZB website

Image: Finely ground powders can also react with each other without solvents to form the desired product. This is the approach of mechanochemistry.

Credit: © F. Emmerling/BAM

Spintronics: Exotic ferromagnetic order in two-dimensions

An international team has detected at HZB’s vector magnet facility VEKMAG an unusual ferromagnetic property in a two-dimensional system, known as “easy-plane anisotropy”. This could foster new energy efficient information technologies based on spintronics for data storage, among other things. The team has published its results in the renowned journal Science.

The thinnest materials in the world are only a single atom thick. These kinds of two-dimensional or 2D materials – such as graphene, well-known as consisting of a single layer of carbon atoms – are causing a great deal of excitement among research teams worldwide. This is because these materials promise unusual properties that cannot be obtained using three-dimensional materials. As a result, 2D materials are opening the door to new applications in fields such as information and display technology, as well as for critical components in extremely sensitive sensors.

Read more on the HZB website

Image: STM topography of a monolayer CrCl3 grown on Graphene/6H-SiC(0001). Inset, a magnified topography image, which reveals the grain boundaries.

Credit: HZB

Ultrafast magnetism: heating magnets, freezing time

Magnetic solids can be demagnetized quickly with a short laser pulse, and there are already so-called HAMR (Heat Assisted Magnetic Recording) memories on the market that function according to this principle. However, the microscopic mechanisms of ultrafast demagnetization remain unclear. Now, a team at HZB has developed a new method at BESSY II to quantify one of these mechanisms and applied it to the rare-earth element Gadolinium, whose magnetic properties are caused by electrons on both the 4f and the 5d shells. This study is completing a series of experiments done by the team on Nickel, Iron-Nickel Alloys. Understanding these mechanisms is useful for developing ultrafast data storage devices.

New materials should make information processing more efficient, for example, through ultrafast spintronic devices that store data with less energy input. But to date, the microscopic mechanisms of ultrafast demagnetization are not fully understood. Typically, the process of demagnetization is studied by sending an ultrashort laser pulse to the sample, thereby heating it up, and then analyzing how the system evolves in the first picoseconds afterward.

Read more on the HZB website.

Image: The picture shows the glowing filament which keeps the sample at constant temperatures during the measurements.

Credit: © HZB

Beam diagnostics for future laser wakefield accelerators

For decades, particle accelerators have been getting bigger and bigger. In the meantime, ring accelerators with circumferences of many kilometres have reached a practical limit. Linear accelerators in the GHz range also require very long construction lengths. For some years now, however, an alternative is explored: “tabletop particle accelerators” based on the laser excitation of charge waves in plasmas (laser wakefield). Such compact particle accelerators would be particularly interesting for future accelerator-driven light sources, but are also being investigated for high-energy physics. A team from Helmholtz-Zentrum Berlin (HZB) and the Physikalisch-Technische Bundesanstalt (PTB) has developed a method to precisely measure the cross-section of electron bunches accelerated in this way.  This brings applications of these new accelerator technologies for medicine and research closer.

The principle of laser wakefield accelerators: A high-power laser excites a charge wave in a plasma, which propagates at the speed of the laser pulse and pulls electrons behind it in its “wake”, thus accelerating them. Electron energies in the GeV range have been achievable with this technique for some time. However, the electron bunches produced in this way have so far been too small and too poorly focused to use the synchrotron radiation they emit, an intense, coherent light that is used for research in many different disciplines.

Read more on the HZB website

Image: Information on beam quality can be extracted via the interference patterns at different focal lengths and photon intensities.

Credit: © http://www.nature.com/articles/s42005-021-00717-x

X-ray microscopy with 1000 tomograms per second

Tomoscopy is an imaging method in which three-dimensional images of the inside of materials are reconstructed in rapid succession. A new world record has now been set at the Swiss Light Source at the Paul Scherrer Institute: with 1000 tomograms per second, it is now possible to non-destructively capture very fast processes and structural changes in materials on the micrometre scale, such as the burning of a sparkler or the foaming of a metal alloy for the production of stable lightweight materials. 

Most people are familiar with computed tomography from medicine: a part of the body is X-rayed from all sides and a three-dimensional image is then calculated, from which any sectional images can be created for diagnosis.

This method is also very useful for material analysis, non-destructive quality testing or in the development of new functional materials. However, to examine such materials with high spatial resolution and in the shortest possible time, the particularly intense X-ray light of a synchrotron light source is required. In the synchrotron light, even rapid changes and processes in material samples can be visualised if it is possible to capture 3-dimensional images in a very short time sequence.

A team led by Francisco García Moreno from the Helmholtz Centre Berlin is working on this, together with researchers from the Swiss Light Source SLS at the Paul Scherrer Institute (PSI). Two years ago, they managed a record 200 tomograms per second, calling the method of fast imaging “tomoscopy”. Now the team has achieved a new world record: with 1000 tomograms per second, they can now record even faster processes in materials or during the manufacturing process. This is achieved without any major compromises in the other parameters: the spatial resolution is still very good at several micrometres, the field of view is several square millimetres and continuous recording periods of up to several minutes are possible.

Read more on the PSI website

Also on the HZB website

Image: Christian Schlepütz at the Tomcat beamline of the Swiss Light Source SLS, where a team of scientists have developed a 3D imaging method capable of recording 1,000 tomograms per second.

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Sharper insights into thin-film systems

Interfaces in semiconductor components or solar cells play a crucial role for functionality. Nevertheless, until now it has often been difficult to investigate adjacent thin films separately using spectroscopic methods. An HZB team at BESSY II has combined two different spectroscopic methods and used a model system to demonstrate how well they can be distinguished.

Photoelectron spectroscopy (PES) enables the chemical analysis of surfaces and semiconductor layers. In this process, an X-ray pulse (photons) hits the sample and excites electrons to leave the sample. With special detectors, it is then possible to measure the direction and binding energy of these electrons and thus obtain information about electronic structures and the chemical environment of the atoms in the material. However, if the binding energies are close to each other in adjacent layers, then it is hardly possible to distinguish these layers from each other with PES.

 A team at HZB has now shown how precise assignments can nevertheless be achieved: they combined photoelectron spectroscopy with a second spectroscopic method: Auger electron spectroscopy. Here, photoelectrons and Auger electrons are measured simultaneously, which gives the resulting method its name: APECS for Auger electron photoelectron coincidence spectroscopy (APECS). 

Read more on the HZB website

Image: The illustration shows how the APECS measurement works on a nickel single crystal with an oxidised surface. An X-ray beam ionises atoms, either in the nickel crystal or on the surface. The excited photoelectrons from the surface and from the crystal have slightly different binding energies. The Auger electrons make it possible to determine the origin of the photoelectrons. 

Credit: © Martin Künsting /HZB

Disorder brings out quantum physical talents

Quantum effects are most noticeable at extremely low temperatures, which limits their usefulness for technical applications. Thin films of MnSb2Te4, however, show new talents due to a small excess of manganese. Apparently, the resulting disorder provides spectacular properties: The material proves to be a topological insulator and is ferromagnetic up to comparatively high temperatures of 50 Kelvin, measurements at BESSY II show.  This makes this class of material suitable for quantum bits, but also for spintronics in general or applications in high-precision metrology.

Quantum effects such as the anomalous quantum Hall effect enable sensors of highest sensitivity, are the basis for spintronic components in future information technologies and also for qubits in quantum computers of the future. However, as a rule, the quantum effects relevant for this only show up clearly enough to make use of them at very low temperatures near absolute zero and in special material systems.

Read more on the HZB website

Image: The Dirac cone is typical for topological insulators and is practically unchanged on all 6 images (ARPES measurements at BESSY II). The blue arrow additionally shows the valence electrons in the volume. The synchrotron light probes both and can thus distinguish the Dirac cone at the surface (electrically conducting) from the three-dimensional volume (insulating).

Credit: © HZB

Review of X-ray scattering methods with synchrotron radiation

Synchrotron light sources provide brilliant light with a focus on the X-ray region and have enormously expanded the possibilities for characterising materials. In the Reviews of Modern Physics, an international team now gives an overview of elastic and inelastic X-ray scattering processes, explains the theoretical background and sheds light on what insights these methods provide in physics, chemistry as well as bio- and energy related themes.

“X-ray scattering can be used to investigate and resolve a wide variety of issues from the properties and excitations of fuctional solids, to homogeneous and heterogeneous chemical processes and reactions or even the proton pathway during the splitting of water,” explains Prof. Dr. Alexander Föhlisch, who heads the Institute Methods and Instrumentation for Research with Synchrotron Radiation at HZB.

Read more on the HZB website

Image: Resonant X-ray excitation (purple) core excites the oxygen atom within a H2O molecule. This causes ultrafast proton dynamics. The electronic ground state potential surface (bottom) and the bond dynamics is captured by distinct spectral features in resonant inelastic X-ray scattering (right).

Credit: © Martin Künsting /HZB

Green hydrogen: Why do certain catalysts improve in operation?

Crystalline cobalt arsenide is a catalyst that generates oxygen during electrolytic water splitting in the production of hydrogen. The material is considered to be a model system for an important group of catalysts whose performance increases under certain conditions in the course of electrolysis. Now a HZB-team headed by Marcel Risch has observed at BESSY II how two simultaneous mechanisms are responsible for this. The catalytic activity of the individual catalysis centres decreases in the course of electrolysis, but at the same time the morphology of the catalyst layer also changes. Under favourable conditions, considerably more catalysis centres come into contact with the electrolyte as a result, so that the overall performance of the catalyst increases.

As a rule, most catalyst materials deteriorate during repeated catalytic cycles – they age. But there are also compounds that increase their performance over the course of catalysis. One example is the mineral erythrite, a mineral compound comprising cobalt and arsenic oxides with a molecular formula of (Co3(AsO4)2∙8H2O). The mineral stands out because of its purple colour. Erythrite lends itself to accelerating oxygen generation at the anode during electrolytic splitting of water into hydrogen and oxygen.

Read more in the HZB website

Image: Schematic of the electrochemical restructuring of erythrite. The fine needle-like structure melts during the conversion from a crystalline material to an amorphous one, which is porous like a Swiss cheese.

Credit: © HZB

When vibrations increase on cooling: Anti-freezing observed

An international team has observed an amazing phenomenon in a nickel oxide material during cooling: Instead of freezing, certain fluctuations actually increase as the temperature drops. Nickel oxide is a model system that is structurally similar to high-temperature superconductors. The experiment, which was carried out at the Advanced Light Source (ALS) in California, shows once again that the behaviour of this class of materials still holds surprises.

In virtually all matter, lower temperatures mean less movement of its microscopic components. The less heat energy is available, the less often atoms change their location or magnetic moments their direction: they freeze. An international team led by scientists from HZB and DESY has now observed for the first time the opposite behaviour in a nickel oxide material closely related to high-temperature superconductors. Fluctuations in this nickelate do not freeze on cooling, but become faster.

Read more on the HZB website

Image: The development of this speckle pattern over time reveals microsocopic fluctuations in the material.

Credit: © 10.1103/PhysRevLett.127.057001

Water as a metal

Under normal conditions, pure water is an almost perfect insulator. Water only develops metallic properties under extreme pressure, such as exists deep inside of large planets. Now, an international collaboration has used a completely different approach to produce metallic water and documented the phase transition at BESSY II. The study is published now in Nature.

Every child knows that water conducts electricity – but this refers to “normal” everyday water that contains salts. Pure, distilled water, on the other hand, is an almost perfect insulator. It consists of H2O molecules that are loosely linked to one another via hydrogen bonds. The valence electrons remain bound and are not mobile. To create a conduction band with freely moving electrons, water would have to be pressurised to such an extent that the orbitals of the outer electrons overlap. However, a calculation shows that this pressure is only present in the core of large planets such as Jupiter.

Providing electrons

An international collaboration of 15 scientists from eleven research institutions has now used a completely different approach to produce a aqueous solution with metallic properties for the first time and documented this phase transition at BESSY II. To do this, they experimented with alkali metals, which release their outer electron very easily.

Read more on the HZB website

Image: The picture on the top left shows an NaK drop in a vacuum without water vapour. The other pictures show the development of this drop over time when water vapour is present. Thus, a gold-coloured layer of metallic water forms first, followed by white spots of alkali hydroxide. After about 10 seconds, the drop falls.

Credit: © HZB/Nature