Fabrication of antireflective films composed of high and low refractive index layers using layer-by-layer self-assembly method

We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of multilayer films based on layer-by-layer (LbL) self-assembly (SA) method. For the fabrication of these films, blend (i.e., mixed) layers containing both polyanions (i.e., titanium precursor (TALH) and poly(sodium 4-styrenesulfonate) (PSS)) were assembled with polycation (i.e., poly(diallyldimethylammonium chloride) (PDAD)) for the formation of the high refractive index multilayers and on the other hand, the negatively charged silica particles with the diameter of about 100 nm were employed for low refractive index layer. The refractive index of TALH:PSS/PDAD multilayer was controlled by blending ratio and annealing temperature as TALH has the relatively high refractive index (n = 1.68) in comparison with that (n = 1.46) of conventional polyelectrolytes (PEs) at room temperature and furthermore these titanium precursors are partially changed into TiO₂ with relatively high refractive indices (n = 1.50 - 1.81) at annealing temperature of 250 °C. In the case of silica particle layer used for low refractive index layer, the calculated refractive index was about 1.35 due to much vacancy among the adsorbed silica colloids although the inherent refractive index of silica material is about 1.45. As a result, the films composed of TALH:PSS/PDAD multilayers with tunable refractive index and silica colloidal layer can easily modulate the optical properties of multilayer films by blending ratio and heat treatment.