Origin of lattice compression of FeSe1-xTex thin films on CaF2 substrates

I Tsukada,A Ichinose,A Maeda,F Nabeshima,Y Imai

doi:10.1063/1.4963646

Abstract

Microstructure of FeSe1-xTex thin films near the interface to CaF2 is investigated by means of transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). TEM observation at the initial crystal-growth stage reveals that marked lattice compression occurs along the in-plane direction in the films with Se-rich composition, while the a-axis length of FeTe remains as its original value of bulk crystal. Subsequent EDX analysis demonstrates substantial diffusion of Se into the CaF2 substrate. Such diffusion is not prominent for Te. Thus, the formation of Se-deficient layer at the initial growth stage on CaF2 is concluded to be the main reason of the lattice compression in FeSe1-xTex thin films.

Highlights

More than seven years have passed since the discovery of iron-based superconductors.1,2 For the practical use, it is important to establish thin-film fabrication techniques, which we can utilize for producing low-power electric devices such as Josephson devices and high-power electric cables constructed from coated conductors
We proposed to use cubic CaF2 (a0 = 0.5463 nm) as a substrate instead of oxide substrates, and found that FeSe1-xTex films exhibit higher T C than bulk crystals and associated lattice compression along the in-plane direction, which shows a clear contrast to lattice expansion on many oxide substrates
We have studied the interface between CaF2 and FeSe1-xTex thin films with respect to transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDX)

Summary

Introduction

More than seven years have passed since the discovery of iron-based superconductors.1,2 For the practical use, it is important to establish thin-film fabrication techniques, which we can utilize for producing low-power electric devices such as Josephson devices and high-power electric cables constructed from coated conductors.

Results

Conclusion