Fabry–Pérot fringes of hydrogen-bonded assembly films

Thin films were fabricated from poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) based on hydrogen bonding layer-by-layer (LBL) assembly process. Due to light interference, PVPON/PAA films present Fabry–Pérot fringes in the UV–Vis–NIR spectrum. LBL assembly constructed the film on both sides of substrate (double-side film), which are different to traditional vacuum deposition that forms the film only on one side of substrate (single-side film). The light interference processes of the double-and single-side films were fully analyzed. Using the peak positions and amplitude of the Fabry–Pérot fringes, the refractive index and thickness of the film can be evaluated. Furthermore, Fabry–Pérot fringes can be utilized to monitor the film's growth and water content variation in the film.