BESSY II at HZB – Page 3 – Lightsources.org

Small powerhouses for very special light

2024/06/272024/07/03

An international team presents the functional principle of a new source of synchrotron radiation in Nature Communications Physics. Steady-state microbunching (SSMB) allows to build efficient and powerful radiation sources for coherent UV radiation in the future. This is very attractive for applications in basic research as well in the semiconductor industry.

When ultrafast electrons are deflected, they emit light – synchrotron radiation. This is used in so called storage rings in which magnets force the particles onto a closed path. This light is longitudinally incoherent and consists of a broad spectrum of wavelengths. Its high brilliance makes it an excellent tool for materials research. Monochromators can be used to pick out individual wavelengths from the spectrum, but this reduces the radiant power by many orders of magnitude to values of a few watts only.

Size matters

But what if a storage ring were instead to deliver monochromatic, coherent light with outputs of several kilowatts, analogous to a high-power laser? Physicist Alexander Chao and his doctoral student Daniel Ratner found an answer to this challenge in 2010: if the electron bunches orbiting in a storage ring become shorter than the wavelength of the light they emit, the emitted radiation becomes coherent and therefore millions of times more powerful.

Image: Jörg Feikes and PhD student Arnold Kruschinski in the control room of BESSY II and the MLS.

Credit: Ina Helms / HZB

MXenes for energy storage: Chemical imaging more than just surface deep

2024/06/172024/07/03

A new method in spectromicroscopy significantly improves the study of chemical reactions at the nanoscale, both on surfaces and inside layered materials. Scanning X-ray microscopy (SXM) at MAXYMUS beamline of BESSY II enables the investigation of chemical species adsorbed on the top layer (surface) or intercalated within the MXene electrode (bulk) with high chemical sensitivity. The method was developed by a HZB team led by Dr. Tristan Petit. The scientists demonstrated among others first SXM on MXene flakes, a material used as electrode in lithium-ion batteries.

Since their discovery in 2011, MXenes have gathered significant scientific interest due to their versatile tunable properties and diverse applications, from energy storage to electromagnetic shielding. Researchers have been working to decipher the complex chemistry of MXenes at the nanoscale.

The team of Dr. Tristan Petit now made a significant progress in MXene characterization, as described in their recent publication. They utilized SXM to investigate the chemical bonding of Ti₃C₂T_x MXenes, with T_x denoting the terminations (T_x=O, OH, F, Cl), with high spatial and spectral resolution. The novelty in this work is to combine simultaneously two detection modes, transmission and electron yield, enabling different probing depths.

SXM provided detailed insights into the chemical composition and structure of MXenes. According to Faidra Amargianou, first author of the study: “Our findings shed light on the chemical bonding within MXene structure, and with surrounding species, offering new perspective for their utilization across various applications, especially in electrochemical energy storage.”

Image: Scanning X-ray images of a dismounted Li-ion battery with cycled MXene electrode (green), electrolyte/ carbonate species (red) and separator (yellow). The Transmission (bulk-sensitive) image is on the left, the electron yield (surface-sensitive) image on the right.

Credit: HZB

New joint leadership for BESSY II

2024/06/132024/07/29

Andreas Jankowiak as new Technical Director and Facility Spokesperson Antje Vollmer share management responsibilities.

Prof. Andreas Jankowiak has been appointed Technical Director of BESSY II with a term of office of three years as of 1 June 2024 by resolution of the HZB board of directors. Antje Vollmer will start her second term as BESSY II Facility Spokesperson on 1 July 2024. Together, they form the new management duo to coordinate the scientific and technical development of the BESSY II X-ray source on behalf of the HZB management.

They will coordinate with internal stakeholders and external partners, prioritise their requirements, make recommendations to the HZB board of directors and prepare management decisions.

Image: Andreas Jankowiak and Antje Vollmer have been working together on a trusting basis for many years. As the new dual leadership, they are driving forward the technical and scientific development of BESSY II.

Credit: HZB/M.Setzpfandt

Dynamic measurements in liquids now possible in the laboratory

2024/05/232024/05/30

A team of researchers in Berlin has developed a laboratory spectrometer for analysing chemical processes in solution – with a time resolution of 500 ps. This is of interest not only for the study of molecular processes in biology, but also for the development of new catalyst materials. Until now, however, this usually required synchrotron radiation, which is only available at large, modern X-ray sources such as BESSY II. The process now works on a laboratory scale using a plasma light source.

“Our laboratory setup now makes this measurement method available to a wider community,” says HZB physicist Dr. Ioanna Mantouvalou, who drove the development together with partners from the Technische Universität Berlin, the Max Born Institute, the Physikalisch-Technische Bundesanstalt and the company Nano Optics Berlin. “In a first step, the laboratory measurements can also more precisely define where further analyses at synchrotron sources are useful and promising. This allows us to make better use of scarce resources,” says Mantouvalou.

Time-resolved soft X-ray spectroscopy provides access to the properties of organic materials and is therefore ideal for studying dynamic changes in the electronic structure of individual elements in disordered systems. However, measurements of liquid solutions in which these molecules or complexes are dissolved are particularly challenging. They require a high photon flux and extremely low noise. Therefore, these experiments require usually large-scale facilities such as modern synchrotron light sources.

Image: The dashed black lines mark the first thin liquid ‘sheet’ in which the molecules are dissolved. There are two nozzles in the upper part and a collecting vessel in the lower part (left image). Transmission image of the flat jet (centre image). X-ray spectrum of the solution on the CCD detector (right image).

Credit: © HZB

Key role of nickel ions in the Simons process discovered

2024/05/212024/05/30

Researchers at the Federal Institute for Materials Research and Testing (BAM) and Freie Universität Berlin have discovered the exact mechanism of the Simons process for the first time. The interdisciplinary research team used the BESSY II light source at the Helmholtz Zentrum Berlin for this study.

The Simons process is of great importance for the production of fluoroorganic compounds and is used in the pharmaceutical, agrochemical, plastics production and electronics industries, among others. The process is named after its inventor, the American chemist Joseph H. Simons, and utilises an electrochemical process to synthesise fluoroorganic compounds. By passing a current through an electrolyte solution containing hydrogen fluoride at an anode and a cathode, fluorine-containing ions are formed which react with other ions or molecules in the solution to form the desired fluorine-containing compounds.

Although this process has been used for over 70 years, the exact mechanism of the Simons process has so far remained a mystery. All that was known was that a black film forms on the nickel anode during the electrolysis process. In order to be able to analyse this film more precisely, the interdisciplinary research team used the synchrotron source BESSY II at the Helmholtz-Zentrum Berlin for the first time. With the help of a specially developed measuring cell, it was possible to carry out in-situ measurements on the anode, which even allowed individual atoms to be observed during electrofluorination. The investigations revealed that centres of highly valent nickel ions are formed in the black layer during the Simons process, which are crucial for the success of electrofluorination.

Image: Accumulations of nickel ions form a dark film on an anode.

Credit: © BAM

IRIS beamline at BESSY II extended with nanomicroscopy

2024/04/252024/05/01

The IRIS infrared beamline at the BESSY II storage ring now offers a fourth option for characterising materials, cells and even molecules on different length scales. The team has extended the IRIS beamline with an end station for nanospectroscopy and nanoimaging that enables spatial resolutions down to below 30 nanometres. The instrument is also available to external user groups.

The infrared beamline IRIS at the BESSY II storage ring is the only infrared beamline in Germany that is also available to external user groups and is therefore in great demand. Dr Ulrich Schade, in charge of the beamline, and his team continue to develop the instruments to enable unique, state-of-the-art experimental techniques in IR spectroscopy.

Image: Infrared image of the nucleolus in the nucleus of a fibroblast cell. The scale bar corresponds to 500 nanometres.

Credit: HZB

A simpler way to inorganic perovskite solar cells

2024/04/172024/04/24

Inorganic perovskite solar cells made of CsPbI₃ are stable over the long term and achieve good efficiencies. A team led by Prof. Antonio Abate has now analysed surfaces and interfaces of CsPbI₃films, produced under different conditions, at BESSY II. The results show that annealing in ambient air does not have an adverse effect on the optoelectronic properties of the semiconductor film, but actually results in fewer defects. This could further simplify the mass production of inorganic perovskite solar cells.

Metal halide perovskites have optoelectronic properties that are ideally suited for photovoltaics and optoelectronics. When they were discovered in 2009, halide perovskites in solar cells achieved an efficiency of 3.9 per cent, which then increased extremely fast. Today, the best perovskite solar cells achieve efficiencies of more than 26 per cent. However, the best perovskite semiconductors contain organic cations such as methylammonium, which cannot tolerate high temperatures and humidity, so their long-term stability is still a challenge. However, methylammonium can be replaced by inorganic cations such as Cesium (Cs). Inorganic halide perovskites with the molecular formula CsPbX₃ (where X stands for a halide such as chloride, bromide and iodide) remain stable even at temperatures above 300 °C. CsPbI₃ has the best optical properties for photovoltaics (band gap ∼1.7 eV).

Production in glove boxes

Perovskite semiconductors are produced by spin coating or printing from a solution onto a substrate and are typically processed in glove boxes under a controlled atmosphere: There, the solvent is evaporated by heating, after which a thin layer of perovskite crystallizes. This ‘controlled environment’ significantly increases the cost and complexity of production.

…or ambient conditions

In fact, CsPbI₃ layers can also be annealed under ambient conditions without loss or even with an increase in efficiency of up to 19.8 per cent, which is even better than samples annealed under controlled conditions.

What happens at the interfaces?

“We investigated the interfaces between CsPbI₃ and the adjacent material in detail using a range of methods, from scanning electron microscopy to photoluminescence techniques and photoemission spectroscopy at BESSY II,” says Dr. Zafar Iqbal, first author and postdoctoral researcher in Antonio Abate’s team.

Image: Under the scanning electron microscope, the CsPbI₃ layer (large blocks in the upper part of the image) on the FTO substrate looks almost exactly the same after annealing in ambient air as after annealing under controlled conditions.

Credit: HZB

Spintronics: A new path to room temperature swirling spin textures

2024/04/162024/04/25

A team at HZB has investigated a new, simple method at BESSY II that can be used to create stable radial magnetic vortices in magnetic thin films.

In some materials, spins form complex magnetic structures within the nanometre and micrometre scale in which the magnetization direction twists and curls along specific directions. Examples of such structures are magnetic bubbles, skyrmions, and magnetic vortices. Spintronics aims to make use of such tiny magnetic structures to store data or perform logic operations with very low power consumption, compared to today’s dominant microelectronic components. However, the generation and stabilization of most of these magnetic textures is restricted to a few materials and achievable under very specific conditions (temperature, magnetic field…).

A new approach

An international collaboration led by HZB physicist Dr Sergio Valencia has now investigated a new approach that can be used to create and stabilize complex spin textures, such as radial vortices, in a variety of compounds. In a radial vortex, the magnetization points towards or away from the center of the structure. This type of magnetic configuration is usually highly unstable. Within this novel approach radial vortices are created with the help of superconducting structures while their stabilization is achieved by the presence of surface defects.

Superconducting YBCO-islands

Samples consist of micrometer size islands made of the high-temperature superconductor YBCO on which a ferromagnetic compound is deposited. On cooling the sample below 92 Kelvin (-181 °C), YBCO enters the superconducting state. In this state, an external magnetic field is applied and immediately removed. This process allows the penetration and pinning of magnetic flux quanta, which in turn creates a magnetic stray field. It is this stray field which produces new magnetic microstructures in the overlying ferromagnetic layer: spins emanate radially from the structure centre, as in a radial vortex.

BESSY II: How pulsed charging enhances the service time of batteries

2024/04/082024/04/24

An improved charging protocol might help lithium-ion batteries to last much longer. Charging with a high-frequency pulsed current reduces ageing effects, an international team demonstrated. The study was led by Philipp Adelhelm (HZB and Humboldt University) in collaboration with teams from the Technical University of Berlin and Aalborg University in Denmark. Experiments at the X-ray source BESSY II were particularly revealing.

Ageing effects analysed

Lithium-ion batteries are powerful, and they are used everywhere, from electric vehicles to electronic devices. However, their capacity gradually decreases over the course of hundreds of charging cycles. The best commercial lithium-ion batteries with electrodes made of so-called NMC532 (molecular formula: LiNi_0.5Mn_0.3Co_0.2O₂) and graphite have a service life of up to eight years. Batteries are usually charged with a constant current flow. But is this really the most favourable method? A new study by Prof Philipp Adelhelm’s group at HZB and Humboldt-University Berlin answers this question clearly with no. The study in the journal Advanced Energy Materials analyses the effect of the charging protocol on the service time of the battery.

Part of the battery tests were carried out at Aalborg University. The batteries were either charged conventionally with constant current (CC) or with a new charging protocol with pulsed current (PC). Post-mortem analyses revealed clear differences after several charging cycles: In the CC samples, the solid electrolyte interface (SEI) at the anode was significantly thicker, which impaired the capacity. The team also found more cracks in the structure of the NMC532 and graphite electrodes, which also contributed to the loss of capacity. In contrast, PC-charging led to a thinner SEI interface and fewer structural changes in the electrode materials.

Fuel Cells: Oxidation processes of phosphoric acid

2024/04/032024/04/08

Hydrogen fuel cells convert chemical energy from hydrogen into electrical energy through separate reactions of hydrogen fuels and oxidizing agents (oxygen). Among hydrogen fuel cells, high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are attractive for micro-stationary electricity sources. One disadvantage of these HT-PEMFCs is that the phosphoric acid (H₃PO₄) proton conductor leaches out of the H₃PO₄-doped polybenzimidazole membrane and poisons the platinum catalyst. Recent studies show further complications during the operation of the HT-PEMFC, where some of H₃PO₄ might be reduced to H₃PO₃, which may further poison the platinum catalysts, leading to a significant loss of performance.

An earlier study by Prof. Dr Marcus Bär’s team showed that opposite processes also take place at the interface between Pt and aqueous H₃PO₃ and that the interactions between the platinum catalyst and the H₃PO₃/H₃PO₄ are very complex: while H₃PO₃ can lead to poisoning of the platinum catalyst, at the same time platinum might catalyzes the oxidation of H₃PO₃back to H₃PO₄.

In order to investigate the oxidation behaviour of aqueous H₃PO₃ under conditions close to HT-PEMFCs working conditions, Bär’s team has now analysed the chemical processes using an in-housed designed heatable electrochemical cell compatible for in situ tender X-ray studies at the OÆSE end-station recently set up in the Energy Materials In-situ Laboratory Berlin (EMIL). They used intense X-ray light in the tender X-ray energy range (2 keV – 5 keV), which is provided by the EMIL beamline at the X-ray source BESSY II. In this energy range, X-ray absorption near-edge structure spectroscopy (XANES) at the P K-edge is used to monitor oxidation processes from H₃PO₃ to H₃PO₄.

Image: The illustration shows four different oxidation pathways (1-4) of aqueous phosphoric acid (H₃PO₃), which could be elucidated by XANES at BESSY II. All these reactions depend on the humidity present.

Credit: HZB

Fertilisation under the X-ray beam

2024/03/192024/04/08

After the egg has been fertilized by a sperm, the surrounding egg coat tightens, mechanically preventing the entry of additional sperm and the ensuing death of the embryo. A team from the Karolinska Institutet has now gained this new insight through measurements at the X-ray light sources BESSY II, DLS and ESRF.

Fertilization in mammals begins when a sperm attaches to the egg coat, a filamentous extracellular envelope that sperm must penetrate in order to fuse with the egg. Now an international team of researchers has mapped in detail the structure and function of the protein ZP2, an egg coat filament component that plays a key role in regulating how egg and sperm interact with each other at fertilization.

“It was known that ZP2 is cleaved after the first sperm has entered the egg, and we explain how this event makes the egg coat harder and impermeable to other sperm,” says Luca Jovine, Professor at the Department of Biosciences and Nutrition, Karolinska Institutet, who led the study. “This prevents polyspermy – the fusion of multiple sperm with a single egg – which is a fatal condition for the embryo.”

The changes in the egg coat after fertilization are also crucial to female fertility by ensuring the protection of the developing embryo until this implants in the uterus. The new knowledge may therefore have implications for the development of non-hormonal contraceptives that interfere with the formation of the egg coat. Moreover, the study explains egg coat-associated forms of female infertility.

“Mutations in the genes encoding egg coat proteins can cause female infertility, and more and more such mutations are being discovered,” explains Luca Jovine. “We hope that our study will contribute to the diagnosis of female infertility and, possibly, the prevention of unwanted pregnancies.”

The future of BESSY

2024/03/072024/04/08

In autumn 2023, HZB celebrated 25 years of research at the BESSY II light source in Berlin-Adlershof. To continue offering scientists from all over the world the best research opportunities in the coming decades, it is important to have a vision for BESSY II. In addition, many light sources around the world are currently being modernised or even newly built to keep up with the latest research questions and contribute with state-of-the art research infrastructures.

The article “Material Discovery at BESSY” shows the relevance of BESSY light source for the research questions of the future. The HZB team describes the goals of the BESSY II+ upgrade programme. Among other things, the programme aims to expand operando techniques that are of great benefit in developing materials for the energy transition.

Image: This is what the successor source BESSY III could look like in the future.

Credit: HZB

Sodium-ion batteries: How doping works

2024/02/202024/02/22

Sodium-ion batteries still have a number of weaknesses that could be remedied by optimising the battery materials. One possibility is to dope the cathode material with foreign elements. A team from HZB and Humboldt-Universität zu Berlin has now investigated the effects of doping with Scandium and Magnesium. The scientists collected data at the X-ray sources BESSY II, PETRA III, and SOLARIS to get a complete picture and uncovered two competing mechanisms that determine the stability of the cathodes.

Lithium-ion batteries (LIB) have the highest possible energy density per kilogramme, but lithium resources are limited. Sodium, on the other hand, has a virtually unlimited supply and is the second-best option in terms of energy density. Sodium-ion batteries (SIBs) would therefore be a good alternative, especially if the weight of the batteries is not a major concern, for example in stationary energy storage systems.

However, experts are convinced that the capacity of these batteries could be significantly increased by a targeted material design of the cathodes. Cathode materials made of layered transition metal oxides with the elements nickel and manganese (NMO cathodes) are particularly promising. They form host structures in which the sodium ions are stored during discharge and released again during charging. However, there is a risk of chemical reactions which may initially improve the capacity, but ultimately degrade the cathode material through local structural changes. This has the consequence of reducing the lifetime of the sodium-ion batteries.

Image: The schematic illustration shows a sodium ion battery: The positive electrode or cathode (left) consists of layered transition metal oxides which form a host structure for sodium ions. The transition metal nickel can be replaced either by magnesium or scandium ions.

Credit: HZB

Molecular orbitals determine stability

2024/02/072024/02/20

Carboxylic acid dianions (fumarate, maleate and succinate) play a role in coordination chemistry and to some extent also in the biochemistry of body cells. An HZB team at BESSY II has now analysed their electronic structures using RIXS in combination with DFT simulations. The results provide information not only on electronic structures but also on the relative stability of these molecules which can influence an industry’s choice of carboxylate dianions, optimizing both the stability and geometry of coordination polymers.

Now, a team at HZB led by Prof. Alexander Föhlisch has elucidated the influence of the electronic structure on the stability of fumarate, maleate and succinate dianions. “We analysed these compounds at BESSY II with two different, very powerful methods,” says Dr Viktoriia Savchenko, first author of the study. X-ray absorption spectroscopy (XAS) can be used to investigate the unoccupied electronic states of a system, while resonant inelastic X-ray scattering (RIXS) provides information about the occupied highest orbitals and about interactions between the HOMO-LUMO orbitals. The results can be related to macroscopic properties, especially stability.

Image: Molecular geometry structures of the trans- and cis-isomers fumarate and maleate (above, left to right) together with their hydrogenated molecule, succinate dianions (below).

Credit: HZB

Local variations in the structure of High-Entropy Alloys

2024/01/302024/02/20

High-entropy alloys can withstand extreme heat and stress, making them suitable for a variety of specific applications. A new study at the X-ray synchrotron radiation source BESSY II has now provided deeper insights into the ordering processes and diffusion phenomena in these materials. The study involved teams from HZB, the Federal Institute for Materials Research and Testing, the University of Latvia and the University of Münster.

The team analysed samples of a so-called Cantor alloy, which consists of five 3d elements: chromium, manganese, iron, cobalt and nickel. The samples of crystalline structures (face-centred cubic, fcc) were annealed at two different temperatures and then shock frozen.

Image: The analysis of the EXAFS data showed different local environments around the elements of the Cantor alloy depending on the annealing temperature, which indicate different ordering and diffusion processes. Manganese diffuses fastest in the high-temperature state, nickel in the low-temperature state.

Credit: HZB

Green hydrogen: Perovskite oxide catalysts analysed in an X-ray beam

2024/01/092024/01/09

The production of green hydrogen requires catalysts that control the process of splitting water into oxygen and hydrogen. However, the structure of the catalyst changes under electrical tension, which also influences the catalytic activity. A team from the universities of Duisburg-Essen and Twente has investigated at BESSY II and elsewhere how the transformation of surfaces in perovskite oxide catalysts controls the activity of the oxygen evolution reaction.

In a climate-neutral energy system of the future, the sun and wind will be the main sources of electricity. Some of the “green” electricity can be used for the electrolytic splitting of water to produce “green” hydrogen. Hydrogen is an efficient energy storage medium and a valuable raw material for industry. Catalysts are used in electrolysis to accelerate the desired reaction and make the process more efficient. Different catalysts are used for hydrogen separation than for oxygen evolution, but both are necessary.

Perovskite oxide catalysts: inexpensive and with great potential

An interdisciplinary and international group of scientists from the University of Essen-Duisburg, the University of Twente, Forschungszentrum Jülich and HZB has now investigated the class of perovskite oxide catalysts for the oxygen evolution reaction in detail. Perovskite oxide catalysts have been significantly further developed in recent years, they are inexpensive and have the potential for further increases in catalytic efficiency. However, within a short time, changes appear on the surfaces of these materials which reduce the catalytic effect.

Image: Schematic side view of the transformed layer (light grey) on top of the perovskite film (green) grown on a substate (brown). (right) zoom-in of the side view of the transfromed layer together with spin density at the Ni sites from the density functional theory calculations.