Transition énergétique

Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high-frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower-frequency lattice modulations.

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.

In order to achieve high-brillance and ultra-short FEL pulses, a flat current profile of the electron bunch is required. We achieve this by temporal shaping of the photo-cathode laser. From a femtosecond Gaussian pulse, we produce a picosecond long, flat-top laser pulse. At low charge, the photo-cathode laser pulse temporal profile is directly transferred into the electron bunch temporal profile.

Magnetically coupled nanomagnets have multiple applications in nonvolatile memories, logic gates, and sensors. The most effective couplings have been found to occur between the magnetic layers in a vertical stack. We achieved strong coupling of laterally adjacent nanomagnets using the interfacial Dzyaloshinskii-Moriya interaction. This coupling is mediated by chiral domain walls between out-of-plane and in-plane magnetic regions and dominates the behavior of nanomagnets below a critical size.

LNO has just installed a new CEP-capable mid-IR source for SiwssFEL experiments. The new source will enable a new class of experiments focused on understanding the unique properties of nonequilibrium driven states.

The Einstein–de Haas effect, first demonstrated more than a century ago, provides an intriguing link between magnetism and rotation in ferromagnetic materials. An international team led by ETH physicist Steven Johnson now established that the effect has also a central role in ultrafast processes that happen at the sub-picosecond timescale — and thus deliver fresh insight into materials that might form the basis for novel devices.

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.

To date the electrochemical activity of battery materials was always relying in the oxidation/reduction of cationic redox (change of oxidation state of transition metals generally). However, recently, it was established in new cathode materials (so call Li-rich cathode) that the oxygen from the crystal lattice might also play the role of anionic redox center leading to enhance then the specific charge of battery materials.

Light alkanes are abundantly available and cheap resources that are often burned at oil wells because of the missing infrastructure for valorization. Novel technologies are needed for their selective functionalization to use natural gas as an energy vector in the transition between the oil and the renewables era. Catalytic oxyhalogenation may unlock the transformation of cheap and abundant alkanes into commodities. When chlorine-based reactions are compared with bromine, improved selectivities above an iron catalyst arise from surface-confinement of the reaction mechanism in the case of chlorine as halogen.

A new compact von Hamos spectrometer for tender x-rays (current energy range 2.25-4.5 keV), is now available for emission spectroscopy. This spectrometer allows analyzing the energetic composition of fluorescent light from the sample. It provides research opportunities for emission spectroscopy, and RIXS on the K (P-Sc), L (Zr-Cs) and M (Ir-Fr) absorption edges.

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.

In recent years, electronic data processing has been evolving in one direction only: The industry has downsized its components to the nanometer range. But this process is now reaching its physical limits. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Paul Scherrer Institut (PSI) are therefore exploring spin waves or so-called magnons – a promising alternative for transporting information in more compact microchips. Cooperating with international partners, they have successfully generated and controlled extremely short-wavelength spin waves. The physicists achieved this feat by harnessing a natural magnetic phenomenon, as they explain in the journal Nature Nanotechnology.

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.

The high brilliance of new X-ray sources such as X-ray Free Electron Laser opens the way to non-linear spectroscopies. These techniques can probe ultrafast matter dynamics that would otherwise be inaccessible. One of these techniques, Transient Grating, involves the creation of a transient excitation grating by crossing X-ray beams on the sample. Scientists at PSI have realized a demonstration of such crossing by using an innovative approach well suited for the hard X-ray regime.