Microscopic analysis of the chemical reaction between Fe(Te,Se) thin films and underlying CaF$_2$

TL;DR

This study uses TEM and EDX to analyze the interdiffusion and chemical reactions at the interface of Fe(Te,Se) superconducting films on various substrates, revealing the influence of fluorine and selenium interdiffusion on superconductivity and lattice parameters.

Contribution

It provides detailed microscopic insights into the chemical interdiffusion processes affecting Fe(Te,Se) films on different substrates, highlighting the role of fluorine and selenium interdiffusion.

Findings

Interdiffusion between fluorine and selenium influences superconductivity.

Chemical substitution of anions determines lattice parameters.

Lattice mismatch is a secondary factor in lattice parameter variation.

Abstract

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