Observation of selective surface element substitution in FeTe _0.5 Se _0.5 superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy

Abstract

A systematic investigation of oxidation on a superconductive FeTe 0.5 Se 0.5 thin film, which was grown on Nb-doped SrTiO 3 (001) by pulsed laser deposition, has been carried out. The sample was exposed to ambient air for one month for oxidation. Macroscopically, the exposed specimen lost its superconductivity due to oxidation. The specimen was subjected to in situ synchrotron radiation photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS) measurements following cycles of annealing and argon ion etching treatments to unravel what happened in the electronic structure and composition after exposure to air. By the spectroscopic measurements, we found that the as-grown FeTe 0.5 Se 0.5 superconductive thin film experienced an element selective substitution reaction. The oxidation preferentially proceeds through pumping out the Te and forming Fe-O bonds by O substitution of Te. In addition, our results certify that in situ vacuum annealing and low-energy argon ion etching methods combined with spectroscopy are suitable for depth element and valence analysis of layered structure superconductor materials.

Temporal Spinodal Decomposition of the Fe1+yTe1−xSex Crystals and its Impact on Superconducting Properties

“…Using the photoelectron emission spectroscopy and X‐ray absorption spectroscopy, the authors of another study [ 11 ] found the loss of chalcogens by FeTe 0.5 Se 0.5 film, and in the film of 100 nm thickness, the irreversible changes occurred over a period of 1 month. Increasing the temperature can significantly speed up this process.…”