54 Experimental Methods
Figure 3.7: X-ray Absorption Spectrum for the Mn K-edge, exemplifying the two
main regions of XAS analysis. Here the normalised absorption is plotted against the
incoming photon energy. The XANES region is comprised of the pre-edge and rising
edge area, whereas the EXAFS region is after the main edge.
a measure of the entire edge shift based on the range of energy dened by Ei
and Ef . An edge energy can then be calculated from:
E0 = 2Ew �� Ef (3.6)
For a small set of samples X-ray Absorption Spectroscopy, XAS, measurements
were carried out to investigate the oxidation state of Mn. These experiments
were performed at the 6-2 ES2 beamline at Stanford Synchrotron Radiation
Lightsource, SSRL SLAC. Beamline scientists Tsu-Chien Weng, Dimosthenis
Sokaras and Dennis Nordlund set up all the equipment and helped with the data
acquisition. High energy resolution uorescence detection was used to measure
the absorption edges. The sample setup comprised a glass cell with a small and
thin glassy carbon wafer attached with epoxy on one side and inlets for counter
and reference electrodes. The catalytically active lms were deposited on the
carbon wafers and could therefore be in contact with the electrolyte while being
exposed to synchrotron radiation from the back. An image of this cell can be
seen in gure 3.8, together with a schematic of the beam and signal pathways.