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

Abstract

A new class of heterometallic heteroleptic alkoxides, MII₂Ta₂(acac)₂(OEt)₁₂, MIICo, Ni, has been used as single-source precursors in order to obtain nanophase powders and films. M^II₂Ta₂(acac)₂(OEt)₁₂ was prepared via interaction of M^II(acac)₂, M^IICo, 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 µm and 0.67 µm, 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 µm.