# Stabilization and heteroepitaxial growth of metastable tetragonal FeS thin films by pulsed laser deposition

## TL;DR

This study demonstrates the stabilization of metastable tetragonal FeS thin films via pulsed laser deposition, identifying key growth parameters, but finds no superconductivity despite high-density carrier doping attempts.

## Contribution

It introduces a method to stabilize tetragonal FeS thin films using pulsed laser deposition and details the optimal growth conditions for heteroepitaxial film formation.

## Key findings

- Successful stabilization of tetragonal FeS thin films.
- No superconductivity observed in the films.
- High-density carrier doping did not induce phase transition.

## Abstract

Pulsed laser deposition, a non-equilibrium thin-film growth technique, was used to stabilize metastable tetragonal iron sulfide (FeS), the bulk state of which is known as a superconductor with a critical temperature of 4 K. Comprehensive experiments revealed four important factors to stabilize tetragonal FeS epitaxial thin films: (i) an optimum growth temperature of 300 {\deg}C followed by thermal quenching, (ii) an optimum growth rate of ~7 nm/min, (iii) use of a high-purity bulk target, and (iv) use of a single-crystal substrate with small in-plane lattice mismatch (CaF2). Electrical resistivity measurements indicated that none of all the films exhibited superconductivity. Although an electric double-layer transistor structure was fabricated using the tetragonal FeS epitaxial film as a channel layer to achieve high-density carrier doping, no phase transition was observed. Possible reasons for the lack of superconductivity include lattice strain, off-stoichiometry of the film, electrochemical etching by the ionic liquid under gate bias, and surface degradation during device fabrication.

---
Source: https://tomesphere.com/paper/1903.08820