Hydrophobic surface modified HfO antireflective coatings.

A multifunctional antireflective (AR) thin film is always a prerequisite for growing high-tech applications. Herein we proposed a surface modification technique to transform the hydrophilic behaviour of HfO AR nanofilms into hydrophobic without influencing the nanostructure, morphology, refractive index (η) or AR efficacy of HfO nanofilms. Our experimental results demonstrate that the fabricated HfO AR nanofilms retain its AR efficiency after surface modification to <1% in the visible wavelength range (450-700 nm) on FTO and sapphire. HfO AR nanofilms show hydrophilic behaviour before surface modification with a water contact angle (WCA) of 29° on FTO and 22° on sapphire. However, after surface treatment, they display hydrophobic nature θ  > θ > 90° with a contact angle of (127°-130°). The experimental result demonstrates that the η of the thin layers fabricated at deposition angle 0°, 80°, and 88° before and after modification remains almost the same. HfO AR nanofilms exhibit long term AR permanency as AR efficiency measured within a year practically displays the equivalent reflectance curves similar to as deposit AR thin films, i.e. <1% in the wavelength range of 450-700 nm. We proposed a cost-effective procedure to make hydrophilic AR films to show non-wetting behaviour for its long-term exposure in a moist, damp environment without affecting the refractive index of AR thin film.