Reflective properties of nanoparticle-arrayed surfaces

The reflective properties of nanostructured surfaces, fabricated by laying nanoparticles in a square arrangement on the substrate, were investigated theoretically. Maxwell's equations relating to the subwavelength structure were solved by a rigorous coupled-wave analysis (RCWA), and the results were compared with those of two approximation methods, i.e., the effective medium theory (EMT) and the effective single-layer model (ESL), which have been used extensively in the prior literature. The study presents an analysis of the reflectance characteristics subject to the influences of the size of the nanoparticles, their refractive index, and the surface nanoparticle density. The calculated results revealed that, disregarding variations in the refractive index of the nanoparticles and the surface nanoparticle density, a nanostructured surface with particles of ∼ 120 nm in diameter yields the optimal performance for antireflection with respect to the visible-light region. It was found that, for large particle sizes and refractive indices of the nanoparticles, the results calculated by EMT and ESL may result in considerable deviations relative to those calculated by RCWA and that regarding the nanoparticle-arrayed structure as a gradient refractive-index layer or as a homogeneous layer is inappropriate.