BM29 Users Guide

Contact Tel: +33(0)47688 +ext Sakura PASCARELLI, Scientist in charge 2147 Olivier MATHON, Beamline Operation Manager 2561 BM29 Control Cabin 2628

Within the ESRF upgrade programme, one of the first upgrade projects concerns the renewal of the XAS beamline BM29.

The shutdown of the beamline is foreseen to start on May 26th, 2010 for relocation on BM23 port.

We plan to reopen the renewel beamline at the beginning of 2011.

Synopsis

BM29 is the general purpose X-ray absorption spectroscopy beamline at the ESRF. It aims to meet the needs of the member countries in the area of conventional X-ray absorption spectroscopy. Principally, BM29 is designed to perform experiments which have requirements that fall beyond the capabilities of most second generation synchrotron sources, but which do not require the specialist characteristics of the other ESRF X-ray absorption instruments. The strengths to which BM29 operates arise from the intrinsic properties of the ESRF synchrotron, coupled with a bending magnet source and the high quality performance of the beamline's principle optical element, its monochromator. These strengths can be summarised as:

• a very large operational energy range with reasonable X-ray flux: 4 keV to 74 keV;
• high energy resolution: typically a factor 3 to 5 better than the intrinsic spectral broadening at any K or L absorption edge.;
• high spectral signal to noise ratio: above 7.0 * 10ˆ4 for well prepared samples;
• high beam stability: compatible with the demands of extreme sample environments such as pressure cells, where beam dimensions of 1.0 mm * 0.2 mm are required;
• a high level of automation which allows the user to perform non-conventional scanning measurements, like single energy temperature scan and energy scanning x-ray diffraction.

Scientific Applications

X-ray Absorption Spectroscopy (XAS) is a powerful structural technique to investigate the short-range environment around selected atomic species in condensed matter. While scanning the x-ray energy impinging onto the sample, a core level photoelectron is generated. This is scattered by the surroundings matter producing interference effects visible in the absorption cross-section and usually referred to as x-ray absorption fine structure (XAFS). The process itself is general and therefore fundamental to study structural properties in materials like:

• liquids, molecular solutions, liquid crystals;
• single- and poly-crystalline materials;
• amorphous and highly disordered solids;
• molecules and macromolecules containing metallic atoms or partially substituted with heavy atoms.

The energy range 4.5 keV < E < 74 keV is sufficient for K-edge studies of elements in the range 22 < Z < 76. For Z > 76 one must probe L-edges instead. The sample thicknesses for experiments are in the µm range for transmission experiments. However, thin film and/or dilute systems studies are still possible in fluorescence mode.

Techniques Available

X-ray Absorption Spectroscopy (XAS, XANES and XAFS)

The fundamental capability of this experimental station is of course associated with the possibility of scanning the monochromator energy while simultaneously keeping fixed beam position and detuning fraction. The scans can be performed in the "quick-EXAFS" mode (ideal for collecting complete spectra within few seconds), or in the "step-by-step" method for extremely low noise measurements and wide energy ranges.

Energy Scanning X-ray Diffraction (ESXD)

The principle of ESXD is based on the idea of exploiting the performances of a high precision goniometer (the monochromator) to collect high-resolution diffraction patterns at fixed angle with the incoming beam. The possibility to add up to 8 different detector collimators largely decreases the total energy range to be scanned.

Single Energy X-ray Absorption Temperature Scan

Evidence for sample transformations occurring as a function of temperature and their reproducibility can be obtained from this technique. By selecting an appropriate monochromator energy it is possible to enhance the sensitivity to structural or electronic properties.

Complementary Information

BM29 reference articles:

• An Experimental Station for Advanced Research on Condensed Matter Under Extreme Conditions at the European Synchrotron Radiation Facility - BM29 Beamline,

  A. Filipponi, M. Borowski, D. T. Bowron, S. Ansell, S. De Panfilis, A. Di Cicco, and J.-P. Itie, Rev. Sci. Instruments, 71(6), 2422-2432 (2000).

• A multi-channel detector-collimator for powder diffraction measurements at energy scanning x-ray absorption spectroscopy synchrotron radiation beamlines for high-pressure and high-temperature applications,

  A. Filipponi, V.M. Giordano, S. De Panfilis, A. Di Cicco, E. Principi, A. Trapananti, M. Borowski and J.-P. Itie, Rev. Sci. Instruments, 74(5), 2654-2663 (2003).