A new apparatus for polarized X-ray absorption fine structure using grazing-incidence fluorescence excitation

A new apparatus is described for surface-sensitive X-ray absorption fine structure (XAFS) at the 27-pole wiggler beamline BL13B at the Photon Factory. The apparatus is designed for polarized XAFS experiments at low temperature. A closed-cycle helium cryostat is rotated around the omega axis of a vertically mounted high-precision goniometer. The apparatus can be used for XAFS and X-ray standing-wave experiments, sharing a 19-element pure-Ge detector array as a fluorescence detector. The available temperature range is 15-300 K. The performance is demonstrated by in-plane polarized Cu K-EXAFS for a YBa2Cu3O7 thin film (similar to 1000 Angstrom) epitaxically grown on an SrTiO3 single crystal. An in-situ study of amorphous selenium under optical excitation revealed that neutral defect pairs (C-0(3)-C-0(3)) are formed by photoexcitation of lone pairs. This indicates that grazing-incidence fluorescence excitation is advantageous for 'pump-and-probe' experiments which can minimize the mismatch in the probing depth between X-ray and optical excitation.