Observation of selective surface element substitution in FeTe<sub>0.5</sub>Se<sub>0.5</sub> superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy

Observation of selective surface element substitution in FeTe_0.5Se_0.5 superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy

Zhang Nian^{1, 2}, Liu Chen¹, Zhao Jia-Li¹, Lei Tao¹, Wang Jia-Ou¹, Qian Hai-Jie¹, Wu Rui¹, Yan Lei³, Guo Hai-Zhong³, Ibrahim Kurash^{1, †,}

(a) Fe-2p PES spectra measured in the order of the specimen treatment process from bottom to top. (b) Schematic of the oxidized thin film and the variation caused by vacuum treatments revealed by PES and XAS results. A quasi-2D Fe₂O₃ layer forms on the fully oxidized surface and a layer that Te is totally substituted by O beneath it. After being etched for 30 min, the O is totally removed from the film, leaving excess iron on the surface caused by the etching process. (c) Fe L_2,3 (2p_3/2 and 2p_1/2 levels) XAS spectra measured in the order of specimen treatment processes from bottom to top. δE = 708.1 – 706.46 = 1.55 eV.