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S. Mathur, S. Barth, H. Shen:
"Vapor Growth of NiGa₂O₄ Films: Advantages and Limitations of Single Molecular Source";
Chemical Vapor Deposition, 11 (2005), 1; 11 - 16.

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.

Alkoxide precursors; Metal-organic CVD; Nanocrystals; Thin film

http://dx.doi.org/10.1002/cvde.200306314