Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals

A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle θ and adjusting the azimuthal angle φ, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)₂CuO₄ thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO₆ octahedron) in (La,Sr)₂CuO₄ thin films grown on LaSrAlO₄ and SrTiO₃ substrates is uniaxially distorted changing the tetragonality by ∼5 × 10⁻³ in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.