Nanoporous organosilicate films as antireflection coatings

Abstract

Nanoporous poly(methylsilsesquioxane) (PMSSQ) films prepared by the sacrificial-porogen (pore generator) approach have been demonstrated as potential antireflection coatings. The simplicity of film preparation, tunability of the refractive index and excellent control of thickness make the nanoporous film a good candidate material. The nanoporous structures were generated by removing organic sacrificial polymer from hybrid films of PMSSQ and organic polymer. In the hybrid films, the organic polymer is phase separated from and entrapped in the crosslinked PMSSQ matrix. The optical thickness (refractive index × film thickness) was controlled simply by varying the amount of organic polymer (% loading) that controls porosity (thus refractive index), and the solid content of the solution and spin casting speed that determine the final film thickness. Film thicknesses ranging from about 10 nm to 1 μm have been achieved with refractive indices ranging from 1.18 to 1.44. The reflectivity of glass slides coated with the porous films is in good agreement with theoretical calculations using basic optical equations. Light transmissions of greater than 99% were observed at certain wavelengths. © 2006 Elsevier B.V. All rights reserved.