Traditionally the activities of the High Resolution and Resonance Scattering Group cover a wide scientific and methodological range from a better understanding of basic phenomena to applications and new developments. The main fields are investigations of electric and magnetic properties as well as structural dynamics, with an emphasis on extreme conditions such as high pressure, high and low temperature, external magnetic fields, and confined geometry. This section presents a broad set of examples and is structured according to basic phenomena, applications, and new developments.

A single photon can ionise only one electron of an atom, that is what we learn from the textbook. Double photoionisation with a single photon cannot occur directly but only by interaction of the electrons with each other within an atom. Such discoveries already date back a couple of years. Today, Huotari et al. present a systematic study of 3d transition metals in comparison with theory. Their study suggests that near threshold the excitation is a quasi-classical knock-out rather than a quantum-mechanical shake-off effect, and they found a universal scaling law for the double photoionisation energy evolution.

Hydrogen bonds are of paramount importance in many disciplines of natural sciences. Even in a chemically simple system such as water, and despite decades of intense research efforts, new insights are still being gained today. Tse et al. carried out X-ray Raman measurements on the solid and liquid phases of water in order to characterise the nature of the distinct pre-edge of the oxygen K-edge. Winkler et al. studied the dispersion of OH-stretching modes in diaspore (AlOOH), exploiting the unique possibility of inelastic X-ray scattering to study these high-energy excitations with a resolution of 6 meV.

The structures of some simple elements may change at high pressure becoming rather complex. Rb-IV (others include Na, Ka, Ba) belongs to the class of incommensurate host-guest systems, whose crystal structures have been studied in great detail. Loa et al. investigated the pressure dependence of the longitudinal acoustic phonon dispersion, and found that the guest lattice vibrations closely resemble a mono-atomic linear chain, indicating very weak coupling between the host and the guest structure.

Applications are going towards nanocrystalline material and catalysts. Stankov et al. were surprised that atomic vibrations in nanocrystalline grains are actually identical to those in the bulk even for extremely small grain sizes and that the anomalous dynamics of nanocrystalline material arises in fact from the atomic vibrations in the disordered interfaces.

Spectroscopic studies of catalytic reactions have received considerable public attention with the Noble Prize for Gerhard Ertl in 2007. The hard X-ray probe at the ESRF is ideally suited to the investigation of catalytic reactions on real catalysts under working conditions. This is crucial to advance the understanding of the chemistry. Two examples from ID26 are presented. The first concerns the oxidation of carbon monoxide that is relevant for the purification of feed gas for fuel cells and automotive exhaust gas. The second contribution presents the visualisation of a catalytic reaction in space and in time by means of the ESRF FReLoN camera.

New developments continued to play an important role. The demand to access high-energy Mössbauer transitions is continuously growing. After last year’s presentation of the nickel case, we continued to exploit this element utilising synchrotron radiation based perturbed angular correlation spectroscopy (SRPAC) [1]. In this issue antimony (37.1 keV) and the first tellurium (35.5 keV) results are presented. In the spotlight are skutterudites, a thermoelectric and ferromagnetic material, as well as phase change materials used in rewritable optical data storage.

Finally, Bosak et al. utilised thermal diffuse scattering (TDS) to visualise portions of the Fermi surface in three dimensions via intensity modulations which arise from Kohn anomalies in the phonon dispersion. The experiment on Zn was performed on the Swiss-Norwegian beamlines BM01, and gives a flavour of the great potential if an undulator based beamline and a state-of-the-art detector system could be utilised.

R. Rüffer



[1] I. Sergueev et al., PRB 78, 214436 (2008).