Amorphous and crystalline copper sulfides, CuS

Copper sulfides CuS have been synthesized by a reaction between [Cu(en)(2)](2+) (en = ethylenediamine) and thiourea in alkaline solutions at different temperatures. The product obtained at 10 degrees C (CuS-10) was amorphous and showed semiconductive properties with an electrical conductivity of 0.1 S cm(-1) at 298 K and 3.6 x 10(-3) 8 cm(-1) at 108 K, whereas the product at 30 degrees C (CuS-30) was a crystalline CuS (covellite) that exhibited a metal-hire temperature dependence with a conductivity of 92 S cm(-1) at 304 K and 101 S cm(-1) at 101 K. CuS-10 was changed to a crystalline CuS when annealed at 100-150 degrees C. The resulting CuS had a higher crystallinity than that of CuS-30, and the electrical conductivity showed a metal-like temperature dependence: 27 S cm(-1) at 299 K and 31 S cm(-1) at 98 K. When the reactions were conducted with an immersed polymer film in the solution, CuS films were formed on the substrate surface. The CuS-30 film and the annealed CuS-10 film were electroconductive and transparent in the visible spectral region. The synthesis of amorphous CuS followed by thermal treatment is a new method for the fabrication of metal sulfide films of high quality.