Nickel Sulfide Thin Films from Thio- and Dithiobiuret Precursors

The nickel(II) complexes of several 1,1,5,5-tetraalkyl-2-thiobiurets (R = methyl (<b>1</b>); methyl, ethyl (<b>2</b>); ethyl (<b>3</b>); isopropyl (<b>4</b>)) and 1,1,5,5-tetraalkyl-2,4-dithiobiurets (R = methyl (<b>5</b>); methyl, ethyl (<b>6</b>); ethyl (<b>7</b>)) have been synthesized. The single crystal X-ray structures of complexes (<b>1</b>), (<b>3</b>), (<b>4</b>), (<b>6</b>), and (<b>7</b>) 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 °C. Complex (<b>1</b>) gave orthorhombic Ni₇S₆ at all temperatures with spherical tipped wirelike crystallites and plates. Complex (<b>2</b>) gave mixtures of hexagonal Ni₁₇S₁₈ and orthorhombic Ni₇S₆ with wires and plates. Complex (<b>3</b>) also led to a mixture of hexagonal Ni₁₇S₁₈ and orthorhombic Ni₇S₆ phases but with platelike crystallites. In contrast complex (<b>4</b>) gave orthorhombic Ni₉S₈ with flowerlike structures at 320 and 360 °C and branched structures at 400 °C. Complex (<b>6</b>) gave hexagonal NiS_1.03 at 360 and 400 °C, and orthorhombic Ni₇S₆ at 440 and 480 °C with wires and rods composed of spherical particles. Complex (<b>7</b>) gave rods composed of hexagonal plates with hexagonal NiS_1.03 phase at 360 and 400 °C and orthorhombic Ni₇S₆ at 440 and 480 °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.