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    Straightforward prediction of the Ni1-xO layers stoichiometry by using optical and electrochemical measurements

    Year: 2017

    Journal: J. Phys. D-Appl. Phys., Volume 50, JUN 7

    Authors: Manceriu, Laura Maria; Colson, Pierre; Maho, Anthony; Eppe, Gauthier; Ngoc Duy Nguyen; Labrugere, Christine; Rougier, Aline; Cloots, Rudi; Henrist, Catherine

    Organizations: Walloon Region of Belgium [1117339]; Walloon Region; AGC Flatglass [7428]; 'Fonds de la Recherche Scientifique' (FNRS) [FC 86864]

    Keywords: nickel oxide; thin films; stoichiometry evaluation; impedance spectroscopy; optical properties

    In this study, we propose a straightforward method for x determination in sub-stoichiometric nickel oxide (Ni1-xO) films prepared by ultrasonic spray pyrolysis on fluor-tin oxide (FTO) substrates by varying the post-deposition thermal treatment. The Ni3+ concentration, the flat band potential (Phi(fb)) and the open circuit potential (V-oc) were determined by electrochemical impedance analysis in aqueous media and correlated to the transmission of Ni1-xO films. An x-ray photoelectron spectroscopy study was also performed to quantify the amount of Ni3+ in the films and compare it with the one determined by electrochemical analysis. The electrochromic behavior of the Ni1-xO films in non-aqueous electrolyte was investigated as well. With increasing Ni3+ concentration the films became more brownish and more conductive, both V-oc and Phi(fb) values increased. Calibration curves of transmission at 550 nm or open circuit potential versus carrier concentration were plotted and allowed the prediction of x in an unknown Ni1-xO sample. The Ni1-xO films characterized by the highest Ni3+ concentration have a darker colored state but lower transmission modulation, due to their reduced specific surface and increased crystallinity.
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