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Nickel vacancy behavior in electrical conductance is systematically investigated using various analysis methods on nickel oxide films deposited at different oxygen partial pressures. The results of Rutherford backscattering, x-ray diffraction, and Auger electron spectroscopy analyses demonstrate that the sputtered nickel oxide films are nickel-deficient. Through the deconvolution of Ni2p and O1s spectra in the x-ray photoelectron spectroscopy data, the number of Ni3+ ions is found to increase with the O2 ratio during the deposition. According to the vacancy model, nickel vacancies created from the non-stoichiometry are concluded to produce Ni3+ ions which lead to an increment of the conductivity of the nickel oxide films due to the increase of the hole concentration.
Kim et al. (Wed,) studied this question.