We have demonstrated the utility of hollow silica nanoparticles in fabricating conformal thin film nanoporous antireflection (AR) coatings on both poly(methyl methacrylate) (PMMA) and glass substrates. Layer-by-layer (LbL) assembly was successfully used to produce ultrathin AR coatings on planar and textured surfaces. Hollow silica nanoparticles were synthesized to extend the range of apparent refractive indices possible in an AR coating, enabling the design of both single index and graded index AR coatings on PMMA substrates. The diameter and shell thickness of the silica nanoparticles are the two independent, controllable parameters that we manipulated to tune the refractive index of the coating. The AR coatings reduced the minimum reflection of PMMA from 7% to 0.5%, while the maximum transmission increased from 92% to 98% at the optimized wavelength region that could be adjusted from the near UV into the visible. Cross sectional SEM showed that conformal coatings can be achieved on grooved PMMA Fresnel lenses. AFM was used to study surface topography on flat substrates.
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