Fluorescence-line-selective soft X-ray absorption spectroscopy: a novel approach to element-specific electronic structure analysis

A novel approach to soft X-ray fluorescence-yield absorption spectroscopy is presented using a superconducting tunnel junction (STJ) X-ray detector, a new type of detector for the soft X-ray region. The STJ detector offers superior energy resolution compared with silicon drift detectors and higher detection efficiency than grating-based spectrometers, both of which are widely used in soft X-ray spectroscopy. The STJ detector can simultaneously detect multiple fluorescence lines in a single measurement, even on a bending-magnet beamline, which enables medium-energy-resolution fluorescence detected X-ray absorption spectroscopy (XAS) without the need for large-scale emission spectrometers. Using these characteristics, the Ti Lα/Lℓ XAS and O Kα XAS of SrTiO₃ were measured, where Ti Lℓ XAS are expected to reflect the intrinsic Ti 3d electronic states without being affected by orbital anisotropy, providing a more accurate picture of the transition-metal electronic structure. These results demonstrate that the STJ detector is effective for probing anion electronic states of carbides, nitrides and oxides.