Site-selective X-ray absorption fine structure (XAFS) spectroscopy. (1) Design of fluorescence spectrometer and emission spectra

A Rowland-type fluorescence spectrometer was designed to measure site-selective XAFS spectra by utilizing the chemical shift of emission peak for each site. The positions of Johansson-type cylindrically-bent Ge(111) crystal and scintillation counter were controlled independently by five-channel stepping motors, thereby satisfying precise Rowland condition. Thus, measurements of many fluorescence lines over wide ranges of Bragg angle 55.6-83.9 degrees and Rowland radius 127.7-240.9 nlm are made feasible. The Cu K alpha peak shifted by +1.6 eV on going from Cu to CuCl and by -0.6 eV on going from CuCl to CuCl2. The Cr K beta(1) peak shifted by +0.8 eV on going from Cr to Cr2O3 and by -1.6 eV on going from Cr2O3 to K2CrO4. The FWHM of Cn K alpha peaks was as small as 3.0 eV. The major factor to control the energy resolution of this spectrometer was found to be geometrical angle width (slit size). The effects of Rowland radius and X-ray penetration depth into the bent crystal were smaller in the range of slit size in this paper [slit length (horizontal) in front of I-0 ion chamber was 0.5-2.0 mm and two slit lengths (vertical) in Rowland circle were 0.5-5.5 mm].