Microscopic analysis of the chemical reaction between Fe(Te, Se) thin films and underlying CaF₂

Abstract

To understand the chemical reaction at the interface of materials, we\nperformed a transmission electron microscopy (TEM) observation in four types of\nFe(Te,Se) superconducting thin films prepared on different types of substrates:\nCaF2 substrate, CaF2 substrate with a CaF2 buffer layer, CaF2 substrate with a\nFeSe buffer layer, and a LaAlO3 substrate with a CaF2 buffer layer. Based on\nthe energy-dispersive X-ray spectrometer (EDX) analysis, we found possible\ninterdiffusion between fluorine and selenium that has a strong influence on the\nsuperconductivity in Fe(Te,Se) films. The chemical interdiffusion also plays a\nsignificant role in the variation of the lattice parameters. The lattice\nparameters of the Fe(Te,Se) thin films are primarily determined by the chemical\nsubstitution of anions, and the lattice mismatch only plays a secondary role.\n