The reaction path from aqueous oxohydroxometalate [(CH3)4N]6[H2Ta6O19]·xH2O to Ta2O5 thin film explains observed thin-film morphological characteristics–high density, uniform, pore free, and smooth. Film dehydration and tetramethylammonium thermal decomposition were observed via temperature-programmed desorption. The morphological, structural, and optical properties of the films were examined by X-ray diffraction, X-ray reflectivity, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic ellipsometry. Evolution of (CH3)4N+ reaction products in concert with condensation of the polyoxometalate clusters and structural relaxation led to film densities as high as 95% of single-crystal β-Ta2O5. The process enabled film deposition with single-digit-nanometer thickness.
Ryan H. Mansergh, Lauren B. Fullmer, Deok-Hie Park, May Nyman, and Douglas A. Keszler. Reaction Pathway: Aqueous Hexatantalate Clusters to High-Density Tantalum Oxide Nanofilms, Chemistry of Materials (2016) 28 (5), 1553-1558