Nanocrystalline NiGa2O4 films were deposited on silicon substrates by the CVD of a new heterometal alkoxide, [NiGa2(OtBu)8]. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) showed a single-step decomposition behavior for the molecular precursor at low temperature (240°C), suitable for a CVD process. [NiGa2(OtBu)8] is monomeric in solid state with a tetrahedral Ni2+ center coordinated by two monoanionic {Ga(OtBu)4}-moieties. Despite an adequate vapor pressure, the gas-phase transport of [NiGa2(OtBu)8] is susceptible to the distance and geometry of the effective diffusion path. Investigations on CVD deposits obtained using different transport pathways (reservoir –> substrate) show that gas-phase travel through a long (39 cm) and angular reactor tube induces fragmentation of the heterometal compound, which yields minor amounts of Ni, NiO, and Ga2O3 (amorphous), besides the target (NiGa2O4) composition. Shortened reservoir –> substrate path length (13 cm) produced stoichiometric NiGa2O4 films, apparently due to reduced collision probabilities and a laminar flow. In both cases, the chemical composition was determined using energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS), whilst the structure was evaluated using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). From these, the advantages and limitations of the single molecular source in the growth of NiGa2O4 films could be determined.
Chemical Vapor Deposition , 2005, 11 (1), 11-16.