Selective Deposition of Cobalt Sulfide Nanostructured Thin Films from Single-Source Precursors

The cobalt(III) complexes of 1,1,5,5-tetramethyl- and 1,1,5,5-tetraethyl-2,4-dithiobiuret and the cobalt(II) complex of 1,1,5,5-tetra-iso-propyl-2-thiobiuret have been synthesized. The single-crystal X-ray structure of the thiocyanide (1) and cobalt tetrachlorate (2) salts of the parent cyclized ligand, together with complexes [Co{N(SCNMe2)2}3] (3), [Co{N(SCNEt2)2}3] (4) and [Co{N(SOCNiPr2)2}2] (5) have been determined. The thermal decomposition of 3, 4, and 5 was studied. The complexes were used as single source precursors for the deposition of cobalt sulfide thin films by aerosol assisted chemical vapor deposition (AACVD). The X-ray diffraction (XRD) of the deposited films showed hexagonal Co1−xS from complexes (3) and (4) whereas complex (5) gave a mixture of cubic and hexagonal Co4S3. The morphology of films was characterized by scanning electron microscope (SEM) and showed rod like crystallites from 3, granular crystallites from 4 and stalagmitic structures from 5. Transmission electron microscopy (TEM) of the samples obtained from thin films from 3 and 4 show that the films are composed of hexagonal nanoplates with nanocubes from 5. Magnetic measurements showed the para or ferro-magnetic behavior from crystallites. The mechanism for decomposition of precursors to the cobalt sulfide was studied by pyrolysis gas chromatography (Py-GC-MS).