IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Tuesday Sessions
       Session TF-TuM

Paper TF-TuM10
Effect of Cation Charge State and Site Occupancy on the Dielectric Response of ITCO Spinel Films

Tuesday, October 30, 2001, 11:20 am, Room 123

Session: Optical Thin Films
Presenter: C.F. Windisch Jr., Pacific Northwest National Laboratory
Authors: C.F. Windisch Jr., Pacific Northwest National Laboratory
K.F. Ferris, Pacific Northwest National Laboratory
G.J. Exarhos, Pacific Northwest National Laboratory
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Cobalt-nickel oxide thin films have recently showed promise as infrared transparent conducting oxide (ITCO) materials. In this work, nominal 100 nm thick films with electrical resistivity on the order of 10@super -3@ ohm cm were prepared using both solution and rf magnetron sputter deposition techniques with subsequent post-deposition annealing in air. A combination of XRD, XPS, UV/Vis, Raman spectroscopy, Hall and Seebeck measurements confirmed that a spinel oxide is the primary conducting component of these films and that the conductivity is maximum at or near the NiCo@sub 2@O@sub 4@ stoichiometry, where x = Co/(Co + Ni) = 0.67. Between x = 0.67 and 1.0, i.e. Co@sub 3@O@sub 4@, the conductivity decreases by many orders of magnitude. As x decreases (higher nickel content), conductivity improves somewhat until phase instability drives precipitation of nickel oxide with concomitant loss in conductivity. The reason for this variation has been the subject of much debate in the literature with important questions still unresolved. In this paper, we show, by careful analysis of the XPS and Raman spectra, that the charge state and site occupancy distribution of the Ni cations, as well as the defect structure involving singly charged oxygen anions, vary predictably with composition and conductivity. Electronic structure modeling studies performed in conjunction with the spectroscopy experiments provide a fundamental perspective on the relationship between the optical response and attendant conductivity for this important new class of TCO materials that are being investigated for prospective use in optical limiting and switching applications. This work was conducted under the "Electroactive Coatings and Shutters for Protection of Sensors" Program funded through DARPA contract DAAD19-99-1-0003. Pacific Northwest National Laboratory (PNNL) is operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.