Reaction Pathway: Aqueous Hexatantalate Clusters to High-Density Tantalum Oxide Nanofilms

The reaction path from aqueous oxohydroxometalate [(CH 3 ) 4 N] 6 [H 2 Ta 6 O 19 ]· x H 2 O to Ta 2 O 5 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 (CH 3 ) 4 N + 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-Ta 2 O 5 . The process enabled film deposition with single-digit-nanometer thickness.