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 (CaF 2 ).Electrical resistivity measurements indicated that none of all the films exhibited superconductivity. Although an electric double-layer transistor 2 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.

Stabilizing hidden room-temperature ferroelectricity via a metastable atomic distortion pattern

“…We fabricate high-quality CaTiO 3 films on an LaAlO 3 (111) substrate using a pulsed laser deposition (PLD) technique (see “Methods”). As a nonequilibrium growth method 19 , PLD could assist in achieving the metastable a – a – a – OOR pattern in CaTiO 3 films. Atomic force microscopy (Supplementary Fig.…”

Preface to the special issue ‘Focus on 10 Years of Iron-Based Superconductors’

“…Soon after the discovery of unconventional high-temperature superconductivity in iron-based compounds, the richness of possibilities to synthesize such compounds became apparent. Different families of iron-based superconductors are represented in this focus issue, both the most commonly studied ones, such as 122 chalcogenides [69] and pnictides [59][60][61][62]67], 1111 oxypnictides [66,70] and 11 chalcogenides [64,67,71], as well as the less-studied 21311 pnictides [72].…”

“…A decade since the seminal work by the Hideo Hosono group, the technology is maturing in the fabrication of different kinds of samples, all of which are considered in this focus issue, namely thin films [58,59,66,70,71], coated conductors [64], single crystals [61,67,69], polycrystals [60,72] and tapes [62].…”

“…In such samples, T c 's up to ~43 K and high upper critical fields with low anisotropy (γ < 2.25 at low temperature) were obtained. Regarding the use of non-equilibrium film growth techniques to stabilize metastable phases, tetragonal iron sulfide (FeS) films were deposited by Hanzawa and coworkers on different substrates and characterized in terms of structural and transport properties under high-density carrier doping by ionic liquid gating [71]. Regarding the strategies to improve pinning properties, Miura et al demonstrated further enhancement of J c , decreased J c anisotropy, and limited creep rates by incoherent BaZrO 3 nanoparticles with tunable density and size in BaFe 2 (As 0.66 P 0.33 ) 2 films over a wide range of temperatures and magnetic field.…”

Emergence of exchange bias field in FeS superconductor with cobalt-doping

“…One is using Fe powder and Na 2 S 9 • H 2 O as raw materials [5], and the other is using K x Fe 2−y S 2 as the precursor [23]. t-FeS behaves as a paramagnetic metal in the normal state and transforms to hexagonal structure above 400 • C [24]. In addition, it has strong anisotropy [23,25], a lower upper critical field [26], and a large electronic correlation [27].…”