Powders and dense thin films of late transition metal oxide nanocomposites from structurally characterized single-source precursors

A new class of heterometallic heteroleptic alkoxides, (M2Ta2)-Ta-II(acac)(2)(OEt)(12), M-II=Co, Ni, has been used as single-source precursors in order to obtain nanophase powders and films. (M2Ta2)-Ta-II(acac)(2)(OEt)(12) was prepared via interaction of M-II(acac)(2), M-II=Co, Ni, with Ta(OEt)(5), in toluene and characterized structurally by single-crystal X-ray diffraction, IR and NMR spectroscopy. Oxide films were deposited by spin coating on Si- and SiO2-substrates. Multiple layers, with intermittent heat treatment, were applied to increase the thickness. After annealing at different temperatures and time, the films were characterized by powder X-ray diffraction and SEM. The films were homogeneous and the thickness could be varied between 0.14 mum and 0.67 mum, depending on solution concentration (0.20 - 0.28 M) and number of layers ( 3 - 6). The nanophase powders were also studied at different annealing temperatures. Powder X-ray diffraction of the films coated on Si- substrate and the nanophase powders revealed the presence of CoTa2O6 and Co3O4 phases for the cobalt-tantalum precursor. NiTa2O6 and NiO phases were detected by powder X-ray diffraction with the nickel-tantalum precursor. Atomic force microscopy revealed the oxide films on the Si- substrate to be very smooth and the root mean square roughness was 2.4 nm for a three-layer oxide film with a thickness of 0.50 mum.