Ultralow-n SiO₂Thin Films Synthesized Using Organic Nanoparticles Template

Abstract

In an original effort, this lab attempted to employ polystyrene nanoparticles as a template for the synthesis of ordered and highly porous macroporous SiO2 thin films, utilizing their high combustion temperature and narrow size distribution. However, polystyrene nanoparticle thin films were not obtained due to the low interaction between individual particles and between the particle and silicon substrate. However, polystyrene-polyacrylic acid (PS-AA) colloidal particles of a core-shell structure were synthesized by a one-pot miniemulsion polymerization approach, with hydrophilic polyacrylic acid tails on the particle surface that improved interaction between individual particles and between the particle and silicon substrate. The PS-AA thin films were spin-coated in the thickness ranges from monolayer to approximately 1.0 µm. Using the PS-AA thin films as sacrificial templates, macroporous SiO2 thin films were successfully synthesized by vapor deposition or conventional solution sol-gel infiltration methods. Inspection with field emission scanning electron microscopy (FE-SEM) showed that the macroporous SiO2 thin films consist of interconnected air balls (~100 nm). Typical macroporous SiO2 thin films showed ultralow refractive indices ranging from 1.098 to 1.138 at 633 nm, according to the infiltration conditions, which were confirmed by spectroscopy ellipsometry (SE) measurements. This research shows how the synthetic control of the macromolecule such as hydrophilic polystyrene nanopaticles and silicate sol precursors innovates the optical properties and processabilities for actual applications.Key Words: Ultralow-n, Macroporous, SiO 2 , Polystyrene nanoparticles, Template thin films The reflection and refraction of light at the interface between medium 1 and 2. φ1, φ2, n1, n2, Ep, and Es are incident angle, refraction angle, refractive indices of medium 1 and medium 2, amplitudes of electric field waves parallel or perpendicular to plane of incidence, respectively. The plane of incidence refers to the plane containing incoming light, reflecting light and lying perpendicular to the interface.