Lessons from Oxypnictide Thin Films

TL;DR

This paper reviews the challenges and progress in fabricating oxypnictide F-doped LaFeAsO thin films, highlighting the difficulties in in-situ growth and the success of two-step methods, along with insights into their superconducting properties.

Contribution

It provides a comprehensive analysis of fabrication challenges and demonstrates the effectiveness of two-step processes for high-quality oxypnictide thin films, advancing understanding of their superconductivity.

Findings

In-situ PLD growth is hindered by impurity phases.

Two-step fabrication yields high-quality epitaxial films.

Superconducting properties reveal multiband behavior.

Abstract

First experiments on the growth of oxypnictide F-doped LaFeAsO thin films indicated an incomplete normal-to-superconducting transition and offered a work programme challenging to overcome possible difficulties in their fabrication. In this regard the possibility of an all in-situ epitaxial growth appeared to be a matter of time and growth parameters. The following review clarifies that F-doped oxypnictide thin films are extremely difficult to grow by in-situ PLD due to the formation of very stable impurity phases such as oxyfluorides (LaOF) and oxides (La2O3) and the loss of stoichiometry possibly due to incongruent evaporation of the target or re-evaporation of volatile elements at the substrate surface. However, the review also demonstrates that the employed two-step fabrication process for oxypnictide thin films has been successfully applied in the preparation of clean polycrystalline as well as of epitaxial thin films. Fundamental investigations on the upper critical field, its temperature dependence and its anisotropy contributed to an understanding of multiband superconductivity in oxypnictides.