BM31

Station Bending Magnet 31 (BM31)

BM31 is specialized X-ray Absorption Spectroscopy (XAS) and High Resolution Powder
Diffraction (HRPD) beamline.
The beamline is designed in a flexible way to measure XAS and HRPD or even combination
of both techniques on the samples under different experimental conditions
(heating, cooling, in situ catalytic conditions etc).

X-ray Absorption Spectroscopy

X-ray Absorption Spectroscopy (XAS) is a powerful structural technique to investigate the short-range
environment around selected atomic species in condensed matter. XAS is applicable for the
fundamental studies of structural properties in materials like:

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

Schematic layout of the Swiss-Norwegian beamline BM31

Beamline characteristics

BM31 is designed to perform experiments, which require the capabilities of most second-generation

synchrotron sources. The main characteristics are the following:

• Incident energy range with the reasonable flux from 4.9 to 70 keV.
• 13 element Ge detector with fast digital multi channel analyser electronics.
• Step-by-step data collection with the reasonable acquisition time of 1s for optimised samples.
• Quick monochromator scans with 'on-the-fly' date collection for fast XANES measurements
  (available Jan2008).
• Feedback on the second crystal of the monochromator to minimize the glitches
• Fast switching between 111 and 311 (~ several minutes)


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Optics

Flux factor of 3 less for Si [311] compared to Si [111]

Detectors

The following options are available:

• Three ionisation chambers, 30 cm long for transmission experiments
• 13-element Germanium Detector for XAS measurements at low concentrations.

Software

We use standard ESRF spec software and have full support of BLISS group.

Sample Environment

• Low temperature measurements down to 5K can be performed using specially designed cryostat
  with the sample in He atmosphere. Kapton windows allow measuring the samples in transmission
  and fluorescence modes. Several samples can be mounted simultaneously on the sample holder
  and measured one after the other using linear translation stage.
• Gas blower to heat the samples inside the capillary up to 750 C
• Some cells for catalysis experiments are available

Recommendations to Users

When submitting beam time proposals, please be as clear and accurate as possible in terms of the
concentration of the absorber in your sample. This determines the type of detection system to be
used and permits a much better estimation of the necessary number of shifts to perform the experiment.
The information about the sample environment (temperature, gases etc) is also very important
to plan the experiment in advance.

Mass Spectrometer calibration.

High Resolution Powder Diffraction.

    The SNB Diffractometer   

A robust 2-circle diffractometer is available for High Resolution Powder Diffraction measurements.
Each circle has a high precision encoder mounted directly on the rotary axis.
The diffractometer is currently equipped with 6 counting chains, meaning that 6 complete patterns
are collected simultaneously, with an offset in 2-theta. The angular offset between the detectors has
been kept to very small (~1.1 deg) in order to keep the total data collection time to a minimum.
An Si-111 analyser crystal is mounted in front of each detector (Na-I scintillation counter), resulting
in an intrinsic resolution (FWHM) of approx. 0.01 deg at a wavelength of 1 A. The available wavelength
range for the instrument is 0.4 to 1.2 A.

Sample environment

Transmission (capillary) measurements can be perfomed between 5 and 1023 K. A flat plate sample
spinner as well as a texture attachment can be mounted. Avalable on the beamline are thus a cryostat
for temperatures between 4 and 298 K.
The environment in the furnace can be controlled with both oxidizing and inert atmospheres.