Electrochromism of fluorinated and electron-bombarded tungsten oxide films

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Abstract
Reactive dc magnetron sputtering of W was performed in a plasma of Ar+O2 with and without CF4 addition and substrate bias. Structural studies by atomic force microscopy, X‐ray diffraction, infrared reflectance spectroscopy, and Raman spectroscopy indicated that the electron e bombardment associated with a positive substrate bias led to grain growth and partial crystallization while maintaining a high density of W=O double bonds presumably on internal surfaces. Electrochemical measurements showed that the durability under extended Li+ intercalation/ deintercalation was excellent for e‐bombarded oxide films and poor for oxyfluoride films. Spectrophotometric studies of the electrochromism yielded that the color/bleach dynamics was slow for the e‐bombarded oxide but fast for the oxyfluoride. The range of optical modulation was large. Tandem films, with a thin protective layer of e‐bombarded oxide covering a thicker oxyfluoride layer, were able to combine rapid dynamics with good durability.