Fabrication of powders and thin films of various nickel sulfides by soft solution-processing routes

We have demonstrated a soft solution-processing route for selective synthesis of various phases of nickel sulfides, in which a novel liquid-solid interfacial reaction between a nickel substrate and sulfur is involved, and the reaction of the Ni²⁺ ion with sulfur in different solvents at low temperatures (≤ 200 °C). Nanostructured Ni₃S₂ thin films, NiS (millerite) nanowhiskers, and NiS₂ single crystals with dodecahedron (101) unit polytype shape were directly synthesized in ethylenediamine. Similar reactions in other solvents were also investigated. In addition, a new molecular precursor Ni(en)_xS_y (where (en) is the ethylenediamine ligand) with the composition Ni(en)₃S₄ derived in ethylenediamine was found to be an excellent precursor for synthesis of nickel sulfide nanoparticles. The reaction mechanism, phase formation, and transformation process are proposed. Nickel sulfide materials with different phases and special shapes could find applications in catalysis, semiconductors, and magnetic devices.