Scientific Highlights

Researchers from the Helmholtz Zentrum Berlin (HZB) and the TOMCAT beamline have achieved a new world record in time-resolved tomography by measuring over 200 tomographies per second during heating of an evolving aluminium metal foam.

The increasingly popular power-to-gas technology for the utilization of hydrogen as a clean energy vector involves the use of electrolyzers to convert water into H₂ and O₂. The oxygen evolution reaction (OER) is the least efficient among these processes, and a catalyst is required to speed up its kinetics at the high potentials (customarily ≥ 1.4 V vs. the reversible hydrogen electrode) at which the reaction takes place. 

Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd₂As₂. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations.

From 17 – 21 June 2019 the Neutron and Muon Division (NUM) and the Photon Science Division (PSD) of PSI hosted 18 Master Degree students of physics, chemistry, materials and interdisciplinary science, as well as nuclear engineering to provide an introduction to the characterization of materials with large scale facilities like SINQ, SμS, SLS and SwissFEL. The course taught a basic understanding of how photons, neutrons and muons interact with matter, and how this knowledge can be used to solve specific problems in materials research.

Details of the program can be found at http://indico.psi.ch/event/PSImasterschool

Lithography‐like writing of conducting regions at the interface between SrTiO₃ and amorphous Si using X‐ray irradiation opens ways for spatially controlled functionalities in oxide heterostructures.

In the week of April 1-5 PSI welcomes 20 PhD students and postdocs taking part in the European HERCULES 2019 school on Neutron and Synchrotron Radiation. They will attend lectures and perform two days of practical courses at several beam lines of the Swiss Light Source.

Lithium ion batteries (LIB) are essential in modern everyday life, with increasing interest in enhancing their performance and lifetime. Secondary particles of Li-rich cathode material were examined with correlated ptychographic X-ray tomography and diffraction microscopy at different stages of cycling to probe the aging mechanism.

Niéli’s paper is accepted in the Journal of Physical Chemistry Letters! We use X-ray absorption spectroscopy and X-ray magnetic circular dichroism to watch directly how the Co and Fe ions in a molecular cube change their oxidation states and turn from diamagnetic into paramagnetic units upon light irradiation.

Additive manufacturing of high-entropy alloys combines the mechanical properties of this novel family of alloys with the geometrical freedom and complexity required by modern designs. An approach to additive manufacturing of high-entropy alloys has been developed based on 3D extrusion of inks containing a blend of oxide nanopowders (Co₃O₄ + Cr₂O₃ + Fe₂O₃ + NiO), followed by co-reduction to metals, inter-diffusion and sintering to near-full density CoCrFeNi in H₂. A complex phase evolution path is observed by in-situ X-ray diffraction in extruded filaments: the oxide phases undergo reduction and the resulting metals inter-diffuse, ultimately forming the desired fcc-CoCrFeNi alloy (see figure). Linked to this phase evolution is a complex micro-structural one, from loosely packed oxide particles to fully-annealed, metallic CoCrFeNi with 99.6 ± 0.1% relative density. CoCrFeNi micro-lattices are created with strut diameters as low as 100 μm and excellent mechanical properties at ambient and cryogenic temperatures.

Abdominal aortic aneurysm, an enlargement of the abdominal aorta, may lead to rupture and thus acute health issues and death. Scanning X-ray imaging enabled new insights in the nano-structure of calcifications associated with abdonimal and popliteal aneurysm and allowed mapping the distribution of nano- and micro-calcifications as well as of collagen, elastin and myofilament as building blocks of connective tissue across samples from human donors.

Scientists have demonstrated in a combined theoretical and experimental effort that the new ligand-field density functional theory method (LF-DFT) can be used to calculate the X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) of lanthanide compounds from purely structural input.

Synchrotron-based X-ray tomographic microscopy of melanophores (skin pigment cells) of an amazingly well preserved 180 million years old ichtyosaur (extinct marine reptile similar to whales) contributed in a multidisciplinary investigation to the new findings published today in Nature.

The reliable electrical detection of magnetic skyrmions is of fundamental importance for the application of such topological magnetic quasi-particles for data storage devices. Researchers in a joint collaboration between the University of Leeds and the PolLux endstation have investigated the electrical detection of isolated magnetic skyrmions in applications-relevant nanostructured devices, observing the presence of a strong skyrmion-dependent contribution to the Hall resistivity.

In March 2018, the nine-week MOOC “Introduction to synchrotrons and x-ray free-electron lasers” (abbreviated to “SYNCHROTRONx”) came online via the edX provider of the École Polytechnique Fédérale de Lausanne (EPFL), created by Phil Willmott of the Swiss Light Source, Paul Scherrer Institute. “MOOC” is an acronym for “massive open online course”, a teaching platform started in the first decade of this century, which has become increasingly popular in the last five to six years. MOOCs have no limits to participation and are free. Some of the most popular MOOCs can attract many tens of thousands of participants. Even the most specialized subjects may have an initial enrollment of over a thousand, more than an order of magnitude larger than that typically found in traditional higher education. There were over 70 million MOOC enrollments covering nearly 10’000 subjects offered by the top five providers in 2017 alone!

In the week of March 18-23 PSI welcomes 20 PhD students and postdocs taking part in the HERCULES 2018 school on Neutron and Synchrotron Radiation. They will attend lectures and perform two days of practical courses at several beam lines of the Swiss Light Source.

Classical theory predicts that supersaturated carbonate solutions consist mostly of ions and ion pairs, with a small number of larger clusters present in the solution. The population of the different sized clusters in a solution is solely defined by the cluster’s size dependent Free Energy. If clusters are large enough they serve as nucleation germs for a new solid phase. The nucleation occurs once the surface free energy barrier posed by the new solid-liquid interface is overcome by the free energy win from bulk phase growth.

Using a unique set of well-defined silica-supported Ni nanoclusters (1–7 nm) and advanced characterization methods it was proved how structure sensitivity influences the mechanism of catalytic CO2 reduction, the nature of which has been long debated.

The unexpected finding that in an ‘artificial spin ice’ magnetostatic energy can be transformed into directed rotation of magnetization provides fresh insights into such nano-patterned magnetic structures — and might enable novel applications in nanoscale devices.

Fluid catalytic cracking catalysts, which are composite particles of hierarchical porosity, were examined using ptychographic X-ray tomography. These particles are essential to the conversion of crude oil into gasoline. Examination of catalysts at decreasing levels of catalytic conversion efficacy allowed the detection of possible deactivation causes.

Current-induced spin-orbit torques hold a great potential for manipulation of magnetization at ultrafast timescales. Researchers at ETH Zürich have demonstrated, using time-resolved STXM imaging at the Swiss Light Source, the influence of spin-orbit torques on the switching behaviour of Pt/Co/AlO_x nanostructured elements.

Highly crystalline thin films of organic semiconductors offer great potential for high-performance, low-cost flexible electronics. Researchers at IMEC Belgium have developed a new double-step thin film fabrication process that offers higher performance devices. Soft X-ray spectro-microscopy at the Swiss Light Source was used to prove that the increased performance comes from larger areas of material sharing the same molecular orientation.

The SPS 2017 Prize in Condensed Matter Physics, sponsored by IBM, has been awarded to Dr. Nan Xu for his excellent work on topological quantum states. Dr. Nan Xu is a joint postdoc of Paul Scherrer Institute (PSI) and the École Polytechnique Fédérale de Lausanne (EPFL).