Nickel Sulfide Thin Films from Thio- and Dithiobiuret Precursors

The nickel(II) complexes of several 1,1,5,5-tetraalky1-2-thiobiurets (R = methyl (1); methyl, ethyl (2); ethyl (3); isopropyl (4)) and 1,1,5,5-tetraalky1-2,4-dithiobiurets (R = methyl (5); methyl, ethyl (6); ethyl (7)) have been synthesized. The single crystal X-ray structures of complexes (I), (3), (4), (6), and (7) have been determined. Thermogravimetric analysis shows all seven complexes decompose in a single step to one or another form of nickel sulfide. The complexes were used as single-source precursors for the deposition of nickel sulfide thin films by aerosol assisted chemical vapor deposition (AACVD) at temperatures between 320 and 480 degrees C. Complex (1) gave orthorhombic Ni7S6 at all temperatures with spherical tipped wirelike crystallites and plates. Complex (2) gave mixtures of hexagonal Ni17S18 and orthorhombic Ni7S6 with wires and plates. Complex (3) also led to a mixture of hexagonal Ni17S18 and orthorhombic Ni7S6 phases but with platelike crystallites. In contrast complex (4) gave orthorhombic Ni9S8 with flowerlike structures at 320 and 360 degrees C and branched structures at 400 C. Complex (6) gave hexagonal NiS1.03 at 360 and 400 degrees C, and orthorhombic Ni7S6 at 440 and 480 degrees C with wires and rods composed of spherical particles. Complex (7) gave rods composed of hexagonal plates with hexagonal NiS1.03 phase at 360 and 400 degrees C and orthorhombic Ni7S6 at 440 and 480 degrees C. The composition of films deposited from all these complexes was confirmed by EDX analysis. The influence of the precursors on the nature of the deposited films is discussed.