Fondements de la nature

Researchers from the SwissFEL laser group have succeeded in using intense Terahertz radiation to dramatically change the optical properties of a semiconductor on a sub-cycle timescale. In their experiment the material Gallium Phosphide (GaP) was illuminated by an extremely strong THz electric field with up to 50 MV/cm in strength.

Sr₂CuTeO₆ presents an opportunity for exploring low-dimensional magnetism on a square lattice of S=1/2  Cu²⁺ ions. We employ ab initio multireference configuration interaction calculations to unravel the Cu²⁺ electronic structure and to evaluate exchange interactions in Sr₂CuTeO₆.

The influence of different background gases and substrate heating on the plasma plume dynamics from silver ablation is investigated by species selected time and space resolved imaging. The results provide a time-resolved understanding on how those process parameters affect the expansion: from a free expansion in vacuum with velocities exceeding 20'000 m/s to a very slow expansion in Ar at 1 × 10⁻¹ mbar with arrival velocities of 280 m/s.

Lattice vibrations (phonons) in crystals are typically weakly interacting with the electronic and magnetic degrees of freedom, such as charge and spin fluctuations. Researchers of PSI together with collaborators from EPF Lausanne, Japan and USA discovered an unexpectedly strong coupling between lattice vibrations and spin fluctuations in the quantum magnet LiCrO₂. The observed magnetoelastic waves or electromagnons carry both electric and magnetic dipole moment.

Highly active phases in carbon monoxide oxidation are known, however they are transient in nature. Here, we determined for the first time the structure of such a highly active phase on platinum nanoparticles in an actual reactor.

Here we present a study of magnetism in Co_0.05Ti_0.95O_2−δ anatase films grown by pulsed laser deposition under a variety of oxygen partial pressures and deposition rates. Energy-dispersive spectrometry and transmission electron microscopy analyses indicate that a high deposition rate leads to a homogeneous microstructure, while a very low rate or postannealing results in cobalt clustering.

By means of magnetization, specific heat, and muon-spin relaxation measurements, we investigate newly synthesized high-pressure oxidized Cu_0.75Mo_0.25Sr₂YCu₂O_7.54, in which overdoping is achieved up to p ˜ 0.46 hole/Cu, well beyond the T_c-p superconducting dome of cuprates, where Fermi-liquid behavior is expected.

The deuteron — one of the simplest atomic nuclei, consisting of just one proton and one neutron — is considerably smaller than previously thought. This finding was arrived at by an international research group that carried out experiments at the Paul Scherrer Institute, PSI. The new result is consistent with a 2010 study by the same group, in which the researchers measured the proton and found a significantly smaller value than previous research using different experimental methods.

Single holmium atoms adsorbed on few monolayers of magnesium oxide are extraordinarily stable magnets. They retain a significant fraction of their magnetization when the external magnetic field is switched off. This has been shown recently in a study combining x-ray magnetic circular dichroism performed at the Swiss Light Source (SLS) and at the European Synchrotron Radiation Facility (ESRF) as well as scanning tunneling microscopy. The results open perspectives of storing and processing information at ultrahigh density.

Radio-frequency structures at X-band frequencies (~ 12 GHZ) are being considered for applications in compact Free Electron Lasers, medical linacs, a future linear collider (CLIC project) and as a diagnostic for measuring ultra-short (femtosecond) electron pulses in FELs. A first prototype of such a structure has been built at PSI employing the realization procedures that have been developed for the C-Band (6 GHz) structures of the SwissFEL linac.

Epitaxial thin films of the proton-conducting perovskite BaZr_0.53In_0.47O_3−δH_0.47−2δ, grown by pulsed laser deposition, were investigated in their hydrated and dehydrated conditions through a multitechnique approach with the aim to study the structure and proton concentration depth profile and their relationship to proton conductivity.

The false coincidence background has so far limited the analytical application of PEPICO, photoelectron photoion coincidence. A new photoioin rastering technique has been developed to separate the wheat from the chaff and identify true coincidences based on the ion hit time and position. This expands the dynamic range of the experiment by at least two orders of magnitude, allowing for novel applications to look for reactive intermediates and short lived species in reaction environments.

The European Cluster of Advanced Laser Light sources (EUCALL), a European Union-funded project that aims to foster links between accelerator- and laser-driven X-ray facilities, has completed the first year of its three year project period. The project successfully met all twenty of its milestones for the year, producing a new open-source tool for experiment simulations and developing specifications for several pieces of new scientific equipment.

The recent developments in scientific complementary metal oxide semiconductor (sCMOS) detector technology allow for imaging of relevant processes with very high temporal resolution with practically negligible readout time. However, it is neutron intensity that limits the high temporal resolution neutron imaging. In order to partially overcome the neutron intensity problem for the high temporal resolution imaging, a parabolic neutron focussing guide was utilized in the test arrangement and placed upstream the detector in such a manner that the focal point of the guide was positioned slightly behind the scintillator screen. In such a test arrangement, the neutron flux can be increased locally by about one order of magnitude, albeit with the reduced spatial resolution due to the increased divergence of the neutron beam. In a pilot test application, an in-situ titration system allowing for a remote delivery of well-defined volumes of liquids onto the sample stage was utilized. The process of droplets of water (H₂O) falling into the container filled with heavy water (D₂O) and the subsequent process of the interaction and mixing of the two liquids were imaged with temporal resolution of 0.01 s.

The recent improvement on the capability of neutron imaging that allows acquiring neutron images with isotropic spatial resolution of about 5 micrometres is demonstrated. This is achieve by combining the tailor-made high-numerical aperture magnifying optics together with a thin isotopically-enriched ¹⁵⁷Gd₂O₂S:Tb scintillator screens (see Trtik & Lehmann, NIM-A 788 (2015) 67-70). The newly achieved level of the spatial resolution represents about 30% enhancement compared to the first prototype (see Trtik et al, Physics Procedia 69 (2015) 169-176) and approximately six-fold enhancement in the spatial resolution capabilities available for the general users community at PSI before the start of the Neutron Microscope project.

JUNGFRAU is a charge-integrating, two-dimensional pixel detector developed at the Paul Scherrer Institut for use at free-electron lasers, in particular SwissFEL, and synchrotron light sources. On the 10th October, the first protein crystallography experiment using the JUNGFRAU detector, was performed at the beamline X06SA (PXI) of the Swiss Light Source by the members of the Protein Crystallography and Detectors groups at PSI.

The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. This work shows that isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C–H or H–H activation via a 1,2 addition across a Co–O bond.

JUNGFRAU is a charge-integrating, two-dimensional pixel detector developed at the Paul Scherrer Institut for use at free-electron lasers, in particular SwissFEL, and synchrotron light sources. On the 10th October, the first protein crystallography experiment using the JUNGFRAU detector, was performed at the beamline X06SA (PXI) of the Swiss Light Source by the members of the Protein Crystallography and Detectors groups at PSI.