Monolayer of Mie-Resonant Silicon Nanospheres for Structural Coloration

Abstract

Structural coloration of a monolayer of Mie-resonant silicon (Si) nanospheres (NSs) produced by a solution-based process is studied. It is shown by simulation that a monolayer of hexagonal close-packed Si NSs exhibits size-dependent structural color with a peak reflectance of ∼50%. The peak reflectance can be increased to over 90% by introducing spaces between the Si NSs. The high reflectance despite the small coverage is due to the very high scattering efficiency of Mie-resonant Si NSs. Monolayers of densely packed Si NSs are produced from Si NS suspensions by the Langmuir-Blodgett method. The monolayers exhibit size-dependent structural color with a peak reflectance of 30-50%. The color is very insensitive to the viewing angle, and the angle dependence of the reflectance spectra is very small. The peak reflectance is increased by increasing the distance between the NSs by partially oxidizing the layers. The results demonstrate that iridescence-free structural coloration of a substance is possible by a layer of Si NSs much thinner than the monolayer, i.e., by sparsely scattered Si NSs.