The Development of Methods and Instruments for Synchrotron X-Ray Scattering
High Energy Synchrotron X-ray Scattering
High energy synchrotron radiation with photon energies of around 100 keV interacts with matter in a significantly weaker way than conventional 10 keV x-rays. Even in metals, the penetration depth reaches several millimetres, extinction is usually negligible, and momentum space resolution ΔQ/Q easily reaches 10-5 at a flux of approximately 1011 photons per second. We have pioneered the study of magnetic materials using high energy X-rays up to energies of 500 keV. At the Advanced Photon Source APS, a research facility within the Argonne National Laboratory, near Chicago, Illinois, we have built a station for high energy X-ray scattering at the undulator line used by the MuCAT collaboration. The station is equipped with a single crystal diffractometer and an area detector. Typical applications range from single crystal studies of short range correlations, through to spin, charge and orbital order as well as lattice distortions, PDF (pair distribution function) studies of both powder and nanocrystalline materials along with the determination of short range order in levitated metallic melts.
A New Portable UHV Goniometer for Resonant Soft X-ray Scattering (RSXS)
Most of the soft x-ray scattering chambers available today host two-circle diffractometers. This geometry leads to severe restrictions for sample rotations around the surface normal (φ-circle) and sample tilting (χ-circle). To overcome these limitations, a new portable goniometer has been built, making it feasible to adjust samples along χ (±2.5°, even at temperatures down to 10 K) and φ (360°, above 220 K). This miniature goniometer thus dramatically improves the efficiency of soft x-ray scattering chambers and can be used to unravel the ordering phenomena of lattice, charge, orbital and spin degrees of freedom in complex oxides by the RSXS technique.
Resonant X-ray Scattering with Polarization Analysis
A significant resonant enhancement of scattering signals can often be observed when X-ray energies are tuned to the vicinity of the absorption edge of an element. This resonant effect has been found highly sensitive to local symmetry, chemical and electronic states of resonant atoms. Nowadays, resonant X-ray scattering has emerged as a very powerful technique to obtain information about charge, orbital and magnetic degrees of freedom in complex materials, by combining a spatial modulation resolved diffraction method and an electronic structure-resolved spectroscopic approach. An important aspect of resonant scattering is that it strongly depends on the polarization of both incident and scattered X-rays. This is due to the tensorial character of atomic scattering factors near the absorption edge. We have employed this technique to investigate complex charge, orbital and magnetic ordering phenomena in highly correlated electron systems such as La1-xSrxMnO3 and Fe3O4.