High Frequency-Couplers for bERLinPro prove resilient

In synchrotron light sources, an electron accelerator brings electron bunches to almost the speed of light so that they can emit the special “synchrotron light”. The electron bunches get their enormous energy and their special shape from a standing electromagnetic alternating field in so-called cavities. With high electron currents, as required in the bERLinPro project, the power needed for the stable excitation of this high-frequency alternating field is enormous. The coupling of this high power is achieved with special antennas, so-called couplers, and is considered a great scientific and technical challenge. Now, a first measurement campaign with optimised couplers at bERLinPro shows that the goal can be achieved.

Read more on the HZB website

Image: For the measurement campaign, two couplers were mounted in a horizontal test position under a local clean room tent.

Credit: © A. Neumann/HZB

Towards industrial-scale manufacturing of perovskite solar cells

For the production of high-quality metal-halide perovskite thin-films for large area photovoltaic modules often optimized inks are used which contain a mixture of solvents. An HZB team at BESSY II has now analysed the crystallisation processes within such mixtures. A model has also been developed to assess the kinetics of the crystallisation processes for different solvent mixtures. The results are of high importance for the further development of perovskite inks for industrial-scale deposition processes of these semiconductors.

Hybrid organic perovskite semiconductors are a class of materials for solar cells, which promise high efficiencies at low costs. They can be processed from precursor solutions that upon evaporation on a substrate form a polycrystalline thin film. Simple manufacturing processes, such as spin coating a precursor solution, often only lead to good results on a laboratory scale, i.e. for very small samples.

Read more on the HZB website

Image: Schematic illustration: the solvants (ink) are used to produce a thin film of polycrystalline perovskite. 

Credit: © HZB

Graphite electrodes for rechargeable batteries investigated

Rechargeable graphite dual ion batteries are inexpensive and powerful.

A team of the Technical University of Berlin has investigated at the EDDI Beamline of BESSY II how the morphology of the graphite electrodes changes reversibly during cycling (operando).

The 3D X-ray tomography images combined with simultaneous diffraction now allow a precise evaluation of the processes, especially of changes in the volume of the electrodes. This can help to further optimise graphite electrodes.

Read more on the HZB website

Image: The tomogram during the charging process shows the spatially resolved changes in the graphite electrode thickness of a rechargeable aluminium ion battery in a discharged and charged state.

Credit: © HZB

Germanium telluride’s hidden properties revealed

Germanium Telluride is an interesting candidate material for spintronic devices. In a comprehensive study at BESSY II, a Helmholtz-RSF Joint Research Group has now revealed how the spin texture switches by ferroelectric polarization within individual nanodomains.

Germanium telluride (GeTe) is known as a ferrolectric Rashba semiconductor with a number of interesting properties. The crystals consist of nanodomains, whose ferrolectric polarization can be switched by external electric fields. Because of the so-called Rashba effect, this ferroelectricity can also be used to switch electron spins within each domain. Germanium telluride is therefore an interesting material for spintronic devices, which allow data processing with significantly less energy input.

Russian German Cooperation

Now a team from HZB and the Lomonosov Moscow State University, which has established a Helmholtz-RSF Joint Research Group, has provided comprehensive insights into this material at the nanoscale. The group is headed by physical chemist Dr. Lada Yashina (Lomonosov State University) and HZB physicist Dr. Jaime Sánchez-Barriga. “We have examined the material using a variety of state-of-the-art methods to not only determine its atomic structure, but also the internal correlation between its atomic and electronic structure at the nanoscale,” says Lada Yashina, who produced the high-quality crystalline samples in her laboratory.

Read more on the BESSY II website

Image: The Fermi surface of multidomain GeTe (111) bulk single crystal measured with high-resolution angle-resolved photoemission at BESSY II. © HZB

Order in the disorder: density fluctuations in amorphous silicon discovered

For the first time, a team at HZB has identified the atomic substructure of amorphous silicon with a resolution of 0.8 nanometres using X-ray and neutron scattering at BESSY II and BER II. Such a-Si:H thin films have been used for decades in solar cells, TFT displays, and detectors. The results show that three different phases form within the amorphous matrix, which dramatically influences the quality and lifetime of the semiconductor layer. The study was selected for the cover of the actual issue of Physical Review Letters.

Silicon does not have to be crystalline, but can also be produced as an amorphous thin film. In such amorphous films, the atomic structure is disordered like in a liquid or glass. If additional hydrogen is incorporated during the production of these thin layers, so-called a-Si:H layers are formed. “Such a-Si:H thin films have been known for decades and are used for various applications, for example as contact layers in world record tandem solar cells made of perovskite and silicon, recently developed by HZB” explains Prof. Klaus Lips from HZB. “With this study, we show that the a-Si:H is by no means a homogeneously amorphous material. The amorphous matrix is interspersed with nanometre-sized areas of varying local density, from cavities to areas of extremely high order,” the physicist comments.

Read more on the BESSY II website

Image: Structural model of highly porous a-Si:H, which was deposited very quickly, calculated based on measurement data. Densely ordered domains (DOD) are drawn in blue and cavities in red. The grey layer represents the disordered a-Si:H matrix. The round sections show the nanostructures enlarged to atomic resolution (below, Si atoms: grey, Si atoms on the surfaces of the voids: red; H: white) © Eike Gericke/HZB

Hope for better batteries – researchers follow the charging and discharging of silicon electrodes live

Using silicon as a material for electrodes in lithium-ion batteries promises a significant increase in battery amp-hour capacity.The shortcoming of this material is that it is easily damaged by the stress caused by charging and discharging.Scientists at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) have now succeeded for the first time in observing this process directly on crystalline silicon electrodes in detail.Operando experiments using the BESSY II synchrotronprovided new insights into how fractures occur in silicon – and also how the material can nevertheless be utilised advantageously.

Whether in smartphones or electric cars – wherever mobile electric power needs to be available, it usually comes from rechargeable lithium-ion batteries. One of the two electrodes inside these batteries consists of graphite in which lithium ions are lodged, thereby storing electrical energy. The disadvantage of this carbon material is that its energy storage capacity is quite small – which makes frequent recharging of the battery necessary. For this reason, researchers worldwide are searching for alternative electrode materials to lengthen the battery charge/discharge cycles.

Read more on the Helmholtz Zentrum Berlin website

Image: The design of the experimental set-up shows how the structure of the silicon electrode periodically changes during charging and discharging on the basis of voltage measurements. © HZB

New substance library to accelerate the search for active compounds

In order to accelerate the systematic development of drugs, the MX team at the Helmholtz-Zentrum Berlin (HZB) and the Drug Design Group at the University of Marburg have established a new substance library. It consists of 1103 organic molecules that could be used as building blocks for new drugs. The MX team has now validated this library in collaboration with the FragMAX group at MAX IV. The substance library of the HZB is available for research worldwide and also plays a role in the search for substances active against SARS-CoV-2.

For drugs to be effective, they usually have to dock to proteins in the organism. Like a key in a lock, part of the drug molecule must fit into recesses or cavities of the target protein. For several years now, the team of the Macromolecular Crystallography Department (MX) at HZB headed by Dr. Manfred Weiss together with the Drug Design Group headed by Prof. Gerhard Klebe (University of Marburg) has therefore been working on building up what are known as fragment libraries. These consist of small organic molecules (fragments) with which the functionally important cavities on the surface of proteins can be probed and mapped. Protein crystals are saturated with the fragments and then analysed using powerful X-ray light. This allows three-dimensional structural information to be obtained at levels of atomic resolution. Among other things, it is possible to find out how well a specific molecule fragment docks to the target protein. The development of these substance libraries took place as part of the joint Frag4Lead research project and was funded by the German Federal Ministry of Education and Research (BMBF).

Read more on the BESSY II website

Image : For the study, the enzyme endothiapepsin (grey) was combined with molecules from the fragment library. The analysis shows that numerous substances are able to dock to the enzyme (blue and orange molecules). Every substance found is a potential starting point for the development of larger molecules. 

Credit: Wollenhaupt/HZB

Formation of a 2D meta-stable oxide in reactive environments

The chemical behaviour of solid material surfaces is an important physical characteristic for applications of catalysis, chemical sensors, fuel cells and electrodes. A research team from the Max Planck Institute for Chemical Energy Conversion has now described an important phenomenon that can occur when metal alloys are exposed to reactive environments at the synchrotron source BESSY II.

In a recent work published in ACS Applied Materials & Interfaces, a researchers’ team led by Dr. Mark Greiner (Surface Structure Analysis, Department of Heterogeneous Reactions) demonstrates an important phenomenon that can occur when metal alloys face reactive environments. They can form meta-stable 2D oxides on their surfaces. Such oxides exhibit chemical and electronic properties that are different from their bulk counterparts. Due to their meta-stability, their existence is also difficult to predict.

Read more on the BESSY II (at HZB) website

Image : Illustration of a CuxOy structure formed on a AgCu alloy in oxidizing environments described in this work. (c) ACS Applied Materials & Interfaces.

Credit: © (2020) ACS Publishing

Experiment shows for the first time in detail how electrolytes become metallic

An international team has developed a sophisticated experimental technique at BESSY II to observe the formation of a metallic conduction band in electrolytes.

To accomplish this, the team first prepared cryogenic solutions of liquid ammonia containing different concentrations of alkali metals. The colour of the solutions changes with concentration from blue to golden as the individual atoms of metal in solution transition to a metallic compound. The team then examined these liquid jets using soft X-rays at BESSY II and subsequently has been able to analyse this process in detail from the data they acquired combined with theoretical predictions. The work has been published in Science and appears even on the cover.

What distinguishes metals from other materials is generally well understood. In a metal, some of the atoms’ outer electrons move through the crystalline lattice in what is called a conduction band. This is how metals conduct electric current. In contrast to metals, the ions in electrolytes are disordered and electrical conductivity even decreases with increasing ion concentration. So how does metallic behaviour arise from the many individual metal atoms dissolved in the electrolyte? At what concentration and exactly how does a conduction band form, and how do the electron orbitals behave during this process?

>Read more on the Bessy II (at HZB) website

Image: The theorists in the team have elaborately simulated the structure of the solvated electron in liquid ammonia.

Credit : Charles Universität Prag/O. Maršálek & T. Martinek

Insights into the visual perception of plants

Plants use light not only for photosynthesis. Although the plant cell does not have eyes, it can still perceive light and thus its environment. Phytochromes, certain turquoise proteins, play the central role in this process. How exactly they function is still unclear. Now a team led by plant physiologist Jon Hughes (Justus Liebig University Gießen) has been able to decipher the three-dimensional architecture of various plant phytochrome molecules at BESSY II. Their results demonstrate how light alters the structure of the phytochrome so that the cell transmits a signal to control the development of the plant accordingly.

Plants use light to live, via a process called photosynthesis. Yet, they do use light also by so called phytochromes – special molecules that give plants a kind of sight and can thus control the biochemistry of the cell and the development of the plant. It is now known that phytochromes regulate almost a quarter of the plant genome.

Read more on the BESSY II (at HZB) website

Image : Inside the 3D-structure of a phytochrome a bilin pigment absorbs the photon and rotates, which triggers a signal

Credit: Jon Hughes

How new materials increase the efficiency of direct ethanol fuel cells

A group from Brazil and an HZB team have investigated a novel composite membrane for ethanol fuel cells. It consists of the polymer Nafion, in which nanoparticles of a titanium compound are embedded by the rarely explored melt extrusion process. At BESSY II they were able to observe in detail, how the nanoparticles in the Nafion matrix are distributed and how they contribute to increase proton conductivity.

Ethanol has five times higher volumetric energy density (6.7 kWh/L) than hydrogen (1.3 kWh/L) and can be used safely in fuel cells for power generation. In Brazil in particular there is great interest in better fuel cells for ethanol as all the country distributes low-cost ethanol produced in a renewable way from sugar cane. Theoretically, the efficiency of an ethanol fuel cell should be 96 percent, but in practice at the highest power density it is only 30 percent, due to a variety of reasons. So there is great room for improvements.

Nafion with nanoparticles

A team led by Dr. Bruno Matos from the Brazilian research institute IPEN is therefore investigating novel composite membranes for direct ethanol fuel cells. A promising solution is tailoring new polymer-based composite electrolyte materials to replace the state-of-the-art polymer electrolyte such as Nafion. Matos and his team use melt extrusion process to produce composite membranes based on Nafion with additional titanate nanoparticles, which have been functionalized with sulfonic acid groups.

Read more on BESSY II (at HZB) website

Image: The material consists of Nafion with embedded nanoparticles.

Credit: © B.Matos/IPEN

New interaction between light and matter discovered at BESSY II

A German-Chinese team led by Gisela Schütz from the MPI for Intelligent Systems has discovered a new interaction between light and matter at BESSY II.

They succeeded in creating nanometer-fine magnetic vortices in a magnetic layer. These are so-called skyrmions, and candidates for future information technologies.
Skyrmions are 100 nanometre small three-dimensional structures that occur in magnetic materials. They resemble small coils: atomic elementary magnets – so-called spins – which are arranged in closed vortex structures. Skyrmions are topologically protected, i.e. their shape is unchangeable, and are therefore considered energy-efficient data storage devices.

Soft x-rays at BESSY II

In a series of experiments on the MAXYMUS beamline of BESSY II, the researchers have now shown that a bundled soft X-ray beam with a diameter of less than 50 nanometres can generate a magnetic vortex of 100 nanometres. In order to make the skyrmions visible, the researchers use the MAXYMUS scanning transmission X-ray microscope. This is a high-resolution X-ray microscope, weighing 1.8 tons, located at BESSY II.

>Read more on the BESSY II at HZB website

Image: bundled soft X-ray beam with a diameter of less than 50 nanometers writes numerous magnetic vortices, which together form the term “MPI-IS”. Credit: Alejandro Posada, Felix Groß/MPI-IS

Ultra-fast switching of helicity of circularly polarized light pulses

At the BESSY II storage ring, a joint team of accelerator physicists, undulator experts and experimenters has shown how the helicity of circularly polarized synchrotron radiation can be switched faster – up to a million times faster than before.

They used an elliptical double-undulator developed at HZB and operated the storage ring in the so-called two-orbit mode. This is a special mode of operation that was only recently developed at BESSY II and provides the basis for fast switching. The ultra-fast change of light helicity is particularly interesting to observe processes in magnetic materials and has long been expected by a large user community.
In synchrotron radiation sources such as BESSY II, electron bunches orbit the storage ring at almost the speed of light. They are forced to emit extremely bright light pulses with special properties by periodic magnetic structures (undulators).

Experiments with polarized light pulses

Elliptical undulators can be used to generate also circularly polarized light pulses, which display a feature called helicity: the polarisation goes either clockwise or counterclockwise. Magnetic structures in materials react differently to circularly polarized light: Depending on the helicity of the X-ray pulses, they more or less absorb this radiation.

>Read more on the BESSY II (HZB) website

Image: This picture shows an X-ray image of the electron beam in TRIB-mode where two orbits co-exist: the regular orbit and the second one winding around it closing only after three revolutions.
Credit: F. Armborst/K. Holldack

New detector accelerates protein crystallography

In Feburary a new detector was installed at one of the three MX beamlines at HZB.

Compared to the old detector the new one is better, faster and more sensitive. It allows to acquire complete data sets of complex proteins within a very short time.

Proteins consist of thousands of building blocks that can form complex architectures with folded or entangled regions. However, their shape plays a decisive role in the function of the protein in the organism. Using macromolecular crystallography at BESSY II, it is possible to decipher the architecture of protein molecules. For this purpose, tiny protein crystals are irradiated with X-ray light from the synchrotron source BESSY II. From the obtained diffraction patterns, the morphology of the molecules can be calculated.

>Read more on the BESSY II at HZB website

Image: 60s on the new detector were sufficient to obtain the electron density of the PETase enzyme.
Credit: HZB

X-ray microscopy at BESSY II: Nanoparticles can change cells

Nanoparticles easily enter into cells. New insights about how they are distributed and what they do there are shown for the first time by high-resolution 3D microscopy images from BESSY II.

For example, certain nanoparticles accumulate preferentially in certain organelles of the cell. This can increase the energy costs in the cell. “The cell looks like it has just run a marathon, apparently, the cell requires energy to absorb such nanoparticles” says lead author James McNally.
Today, nanoparticles are not only in cosmetic products, but everywhere, in the air, in water, in the soil and in food. Because they are so tiny, they easily enter into the cells in our body. This is also of interest for medical applications: Nanoparticles coated with active ingredients could be specifically introduced into cells, for example to destroy cancer cells. However, there is still much to be learned about how nanoparticles are distributed in the cells, what they do there, and how these effects depend on their size and coating.

>Read more on the BESSY II at Helmholtz-Zentrum Berlin website

Image: 3D architecture of the cell with different organelles:  mitochondria (green), lysosomes (purple), multivesicular bodies (red), endoplasmic reticulum (cream).
Credit: Burcu Kepsutlu/HZB

Watching complex molecules at work

A new method of infrared spectroscopy developed at BESSY II makes single-measurement observation and analysis of very fast as well as irreversible reaction mechanisms in molecules feasible for the first time.

Previously, thousands of such reactions have had to be run and measured for this purpose. The research team has now used the new device to investigate how rhodopsin molecules change after activation by light – a process that is the basis of how we see.

Time-resolved infrared spectroscopy in the sub-millisecond range is an important method for studying the relationship between function and structure in biological molecules. However, the method only works if the reaction can be repeated many thousands of times. This is not the case for a large number of biological processes, though, because they often are based on very rapid and irreversible reactions, for example in vision. Individual light quanta entering the rods of the retina activate the rhodopsin protein molecules, which then decay after fulfilling their phototransductionfunction.

>Read more on the BESSY II at HZB website

Image: Rhodopsin before (left) and after activation by light (right): The activation causes changes in functional groups inside the molecule (magnifying glass), which affect the entire molecule.
Credit: E. Ritter/HZB