The beamlines of the Electronic Structure, Magnetism and Dynamics (EMD) Group were fully dedicated to user operation in 2016. We are grateful to the many users who agreed to give presentations at the spectroscopy meetings during their visits to the ESRF. The scientist in the EMD group working on theoretical spectroscopy, M. Retegan, released (via GitHub) his program Crispy that provides a graphical user interface (written in Python) for the code Quanty written by M. Haverkort (University of Heidelberg) to perform calculations of core-level spectra. Crispy is a user-friendly tool to model X-ray spectra that is particularly powerful when intra-atomic electron-electron interactions strongly influence the spectral shape. Future developments will include interfaces to density functional calculations thus broadening the range of applications. Crispy has a modular design open to contributions from the user community; it runs on Windows, macOS and Linux. This important software development, made in collaboration with a growing number of external groups, will help the ESRF users applying spectroscopy to extract more information from their experimental data.

This highlight chapter presents some of the outstanding research that was performed on the beamlines of the EMD group (ID12, ID20, ID26, ID28, ID32) as well as the CRG beamlines BM01 and BM08.

ID12 is a unique instrument worldwide devoted to X-ray spectroscopy with extreme sensitivity using polarised synchrotron radiation in the energy range from 2 to 15 keV. Its outstanding performance is illustrated with the detection of the influence of an external electric field on X-ray absorption spectra (Ney et al.). It became possible to detect the spectral changes thanks to remarkable reproducibility of the energy scale at the level of 10-7. The magnetism community benefits from an experimental station dedicated to X-ray magnetic circular dichroism spectroscopy at low temperatures (down to 2 K) and high magnetic field (up to 17 Tesla). This technique is becoming increasingly popular amongst chemists, which is illustrated by the results obtained on iridium based molecular complexes (Pedersen et al.). Moreover, an end station at ID12 dedicated to XMCD studies under high pressure was upgraded in autumn 2016. Users can now perform measurements in a magnetic field of 8 Tesla and temperatures below 3 K.

ID20 provides multiple X-ray spectroscopic techniques for the investigation of the electronic structure of materials, including resonant and non-resonant inelastic X-ray scattering. The research activity at ID20 in 2016 was largely focused on hard condensed matter, chemistry, material science and environmental science. One highlight (Donner et al.) describes the study of magnetic excitations in a prototypical pyrochlore iridate. A very interesting application of X-ray Raman spectroscopy is shown by Sahle et al. who followed the evolution of the hydrogen storage material Mg(BH4)2 under in situ conditions. Recent technical developments concerned the installation of a chamber that hosts a pair of phase plates and of an additional end station in the first experimental hutch. This new end station facilitates studies that require a reduced beam divergence (~10 µrad) and can host experiments with unconventional setups that do not require the instruments for inelastic X-ray scattering located in the other experimental hutches.

ID26 is a user-friendly beamline for X-ray absorption and emission spectroscopy that many researchers visit for in situ studies and dilute and radiation sensitive samples. The power of combining X-ray spectroscopy with diffraction is demonstrated in the highlight by Lezcan-González et al. where the authors studied Mo species during the catalytic conversion of methane. In the highlight by Butorin et al., the authors exploit resonant inelastic X-ray scattering (RIXS) at the M-edges of actinides to directly probe the crystal field splitting. This work anticipates the advent of a new spectrometer for X-ray emission spectroscopy in the energy range 1.5 – 5 keV thus extending the existing capacities on ID26 to lower energies. The instrument that is being realised in collaboration with the Université Grenoble Alpes (ANR - EcoX Equipex) will be installed starting in spring 2017 and commissioned after the summer. Besides the M emission lines of actinides, the energy range covers the L emission lines of 4d transition metals and the K emission lines of Al, Si, P, S, Cl and K.

ID28 pursued its traditional activity in the study of lattice dynamics in strongly correlated systems and ferroelectrics and observed an increased interest in thermoelectrics and a revival of activity in biological systems. The detectors in the inelastic X-ray scattering spectrometer now employ a new, sustainable sensor material based on CdTe. It has been in operation for nearly one year with very good performance. The main milestone that was achieved in 2016 was the end of the construction and commissioning of a new side station that operates in parallel with the main branch spectrometer and is devoted to diffuse scattering studies. The use of roadmaps obtained by diffuse scattering for the inelastic scattering experiments is expected to significantly increase the efficiency of the beamline. First users will benefit from its tandem operation starting in March 2017. The side station has been commissioned for wavelengths ranging from 0.52 Å to 0.98 Å, providing flux in the order of 1012 photons/second with a focal spot size below 50 µm. Temperatures between 85 and 1000 K are available as well as diamond anvil cells for high pressure studies. Test experiments on a variety of systems, including ferroelectrics, high-temperature superconductors, oxygen conductors, zeolites, quasicrystals, disordered alloys, show very good performance owing in part to the use of a photon counting pixel array detector and stable, versatile goniometry.

The emphasis of the soft X-ray beamline, ID32, in 2016 has been on developing the user programme for the very high energy resolution RIXS branch. The branch is running full time and many experiments have been carried out that will certainly contribute to the Highlights in the coming years. The soft X-ray dichroism branch (XMCD) has continued its successful operation, examples of which are given by Donati et al. and Candini et al. The surface science complex for preparing samples in situ [1] is proving to be very effective and allows unique samples to be fabricated and measured at the beamline. Consequently, the prospects for many interesting results in 2017 look very promising.

P. Glatzel

 

 

References

[1] K. Kummer et al., J. Synchrotron Rad. 23, 464-473 (2016).