Switchable Piezoresistive SmS Thin Films on Large Area

Samarium monosulfide (SmS) is a switchable material, showing a pressure-induced semiconductor to metal transition. As such, it can be used in different applications such as piezoresistive sensors and memory devices. In this work, we present how e-beam sublimation of samarium metal in a reactive atmosphere can be used for the deposition of semiconducting SmS thin films on 150 mm diameter silicon wafers. The deposition parameters influencing the composition and properties of the thin films are evaluated, such as the deposition rate of Sm metal, the substrate temperature and the H2S partial pressure. We then present the changes in the optical, structural and electrical properties of this compound after the pressure-induced switching to the metallic state. The back-switching and stability of SmS thin films are studied as a function of temperature and atmosphere via in-situ X-ray diffraction. The thermally induced back switching initiates at 250 °C, while above 500 °C, Sm2O2S is formed. Lastly, we explore the possibility to determine the valence state of the samarium ions by means of X-ray photoelectron spectroscopy.

Исследование зеренной структуры мишеней SmS, полученных при различных условиях

The grains structure of samples of а SmS targets, obtained by pressing methods without and with the use of subsequent high-temperature processing by high- frequency currents (further HFC), under various pressure was investigated. The density of samples obtained under different conditions was determined. The optimal technological conditions for obtaining high-quality targets of a samarium monosulfide are determined: high-frequency annealing with pressing under pressure of 5t/cm 2 is more effective than high-frequency current annealing with pressing under pressure of 4 t/cm 2 . A significant content of unbound metallic samarium in samples obtained by pressing at 5 t/cm 2 but not subjected to high-temperature HFC annealing has been established.

Chemistry and Technology of Samarium Monosulfide

<p class="Pa10">Samarium monosulfide SmS (Fm3m, а = 5.967 Å, ΔЕ = 0.23 V, n = 10²⁰ cm^–1, <em>σ</em><em> </em>= 500 Ω^–1 cm^–1, <em>α</em><em> </em>= 350 μВ/K) is a thermoelectric material (Z&gt;1) and, at the same time, a pressure-sensitive material (K≥40–50). Samarium monosulfide is a daltonide phase with a solid solution whose extent is mostly in the range of cationic vacancies: Sm_1+xS_1-x□_2x (<em>x </em>= 0–0.035; 1750 K). The congruent melting temperature of SmS is 2475 K. In the Sm–S system, Sm₃S₄ crystallizes from melt without change in composition. Samarium monosulfide thermally dissociates to Sm₃S₄ and Sm. Large-scale SmS lots are produced from samarium and sulfur. Synthesis is carried out in sealed-off silica glass ampoules at 500–1350 K followed by heat treatment in tantalum crucibles at 1500–2400 K. The reaction of metal samarium with sulfur results in the formation of sulfide phases that coat the samarium surface in the following order: SmS, Sm₃S₄, Sm₂S₃, and SmS₂. Subsequent annealing at 1500–1800 K provides SmS yields up to 96–97 mol %. Equilibrium minor phases for SmS are Sm₃S₄, Sm₂О₂S, and Sm. X-ray amorphous SmS was prepared by reacting organic samarium compounds with sulfur or H2S. The samarium (+2) oxidation state determines the chemical specifics of SmS. 90–120 μm SmS powders are thermally hydrolyzed starting at 600 K with Н₂ evolution and oxidize starting at 520 K to yield Sm₃S₄ and then Sm₂О₂S phases. A 90–120 μm SmS fraction for film deposition by flash evaporation is prepared by milling annealed SmS samples. Tablets 75 mm in diameter for use in magnetron sputtering are pressed from a &lt;60-μm fraction.</p>