Fabrication of tetragonal FeSe - FeS alloy films with high sulfur contents by alternate deposition

TL;DR

This study successfully synthesizes tetragonal FeS_xSe_{1-x} alloy films with high sulfur content using alternate pulsed-laser deposition, revealing enhanced sulfur solubility compared to bulk materials.

Contribution

It introduces an alternate deposition method to produce high sulfur content tetragonal FeS_xSe_{1-x} films with homogeneous alloying, surpassing bulk solubility limits.

Findings

Sulfur solubility in films reaches x=0.78, higher than bulk.

Lattice parameter follows Vegard's law, indicating homogeneous alloying.

Films are synthesized with controlled composition via layer thickness ratio.

Abstract

We report the synthesis of tetragonal $\mathrm{FeS}_x\mathrm{Se}_{1-x}$ films ($x \leq 0.78$) by pulsed-laser deposition. To fabricate the tetragonal alloy films with tetragonal FeSe and hexagonal FeS targets, we adopted an alternate deposition technique with FeSe buffer layer on MgO(001). The overall film composition is controlled by the thickness ratio of FeS / FeSe layers. The out-of-plane lattice parameter of the films follows Vegard's law, demonstrating homogeneous alloying by inter-diffusion. The sulfur solid solubility reaches $x = 0.78$ in the $\mathrm{FeS}_x\mathrm{Se}_{1-x}$ films, which is by far larger than $x \approx 0.40$ in bulk governed by the tetragonal phase instability.