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

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 °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.

References in corpus (7)

• Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure
• Iron-Based Superconductors: current status of materials and pairing mechanism
• Exploration of new superconductors and functional materials and fabrication of superconducting tapes and wires of iron pnictides
• Effects of strain on the electronic structure, superconductivity, and nematicity in FeSe studied by angle-resolved photoemission spectroscopy
• Pressure-dependent magnetization and magnetoresistivity studies on the tetragonal FeS (mackinawite): revealing its intrinsic metallic character
• Fabrication of tetragonal FeSe - FeS alloy films with high sulfur contents by alternate deposition
• Insulator-like behavior coexisting with metallic electronic structure in strained FeSe thin films grown by molecular beam epitaxy