TOWARD EFFICIENT ELECTROCHROMIC NIOX FILMS - A STUDY OF MICROSTRUCTURE, MORPHOLOGY, AND STOICHIOMETRY OF RADIO-FREQUENCY SPUTTERED FILMS

In this work, NiOx films were deposited by reactive radio frequency sp uttering, varying either the oxygen flow or the power during depositio n. The morphology was studied by atomic force microscopy. The Ni/O and Ni/H ratios were determined by Rutherford backscattering spectroscopy and forward recoil spectroscopy. The microstructure of pristine and c olored or bleached films were investigated by means of X-ray diffracti on. The electrochromic and mechanical behavior in aqueous alkaline ele ctrolyte were investigated in situ. Samples deposited at low oxygen fl ow (or high power) are transparent, and have the highest Ni/O ratio an d the lowest Ni/H ratio. The effective area is also greater for these samples. Samples deposited at high oxygen flow (or low power) are dark brown and present the lowest Ni/O ratio and the highest Ni/H ratio. F or all samples, the Ni/O ratio is lower than 1. All films were cubic N iO, with preferred orientation in the (111) direction. Lattice paramet ers and crystalline grain size increase with the increase of oxygen fl ow (or decrease of power) during deposition. The highest optical contr ast and lowest stress changes upon intercalation were obtained for sam ples deposited at law oxygen flow Nonintentional, low-size dopants, Li ke H, favor the mechanical stability of the films.