AVS 47th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThA

Paper TF-ThA8
Synthesis and Characterization of TCO Cobalt-Nickel Spinel Films

Thursday, October 5, 2000, 4:20 pm, Room 203

Session: Transparent Optical Coatings
Presenter: C.F. Windisch, Jr., Pacific Northwest National Laboratory
Authors: C.F. Windisch, Jr., Pacific Northwest National Laboratory
K. Ferris, Pacific Northwest National Laboratory
G.J. Exarhos, Pacific Northwest National Laboratory
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Cobalt-nickel oxide films of nominal 100 nm thickness, and resistivities on the order of 0.01 ohm-cm have been prepared by spin-casting from both aqueous and organic precursor solutions followed by annealing at 450 C in air. Films deposited on sapphire substrates exhibit a refractive index of about 1.7 and are relatively transparent in the wavelength region from 600 to 8000 nm. They are also magnetic. The electrical and spectroscopic properties of the oxides have been studied as a function of Co/Ni ratio. An increase in film resistivity was found upon substitution of other cations (Zn@super 2+@, Al@super 3+@) for Ni in the spinel structure. However, some improvement in the mechanical properties of the films resulted. Conducting films also have been prepared upon substitution of cobalt by palladium. A combination of XRD, XPS, UV/Vis and Raman spectroscopy indicated that NiCo@sub 2@O@sub 4@ is the primary conducting component and that the conductivity is maximum at this stoichiometry. When Co/Ni < 2, NiO forms leading to an increase in resistivity; when Co/Ni > 2, the oxide was all spinel but the increased Co content lowered the conductivity. The influence of cation charge state and site occupancy in the spinel structure markedly affects calculated electron band structures and likely influences an anomalous switch of p-type conductivity to n-type conductivity seen at a Co/Ni ratio of 2. Electronic structure modeling studies also suggest the important role of the Ni@super +3@ cation in the conductivity mechanism. Finally, Raman spectra of the films were relatively easy to obtain and therefore were useful as a routine tool for identifying composition and optimizing conductivity.