Surface morphological, microstructural, and electrochromic properties of short-range ordered and crystalline nickel oxide thin films

The electrochromic (EC) properties between short-range ordered and polycrystalline nickel oxides grown by reactive radio frequency (rf) sputtering were compared using X-ray diffraction (XRD), atomic force microscopy (AFM), as well as electrochemical methods including potential cycling and potentiostatic pulse wave, X-ray photoelectron spectroscopy (XPS) and transmittance spectra. Based on the results of XRD, AFM, potential cycling, and XPS, the amount of amorphous Ni(OH)2 produced during the bleaching process and the electrochromic reaction during potential cycling were considerably more significant for the case of amorphous sputtered nickel oxide. The time response for current densities by the potentiostatic pulse wave measurement showed that the intercalation of protons from the EC nickel oxide was easier than the deintercalation of protons. In particular, the proton intercalation for the polycrystalline sputtered nickel oxide was very difficult. The transmittance differences were 41.3 and 3.43% at 550 nm for the potential-cycled amorphous and polycrystalline sputtered nickel oxides, respectively. This is related to the microstructure, surface morphology and roughness, as well as the electrochemical properties of the sputtered nickel oxide films.