Stabilization of monodispersed spherical silica particles and their alignment with reduced crack density

Monodispersed spherical silica nanoparticles synthesized by the Stِber process contain large amounts of impurities and adsorbed- and structural water which cause structural and thermal instability of the microspheres. Proper heat treatment was applied to remove the impurities and water endowing the particles with high thermal and structural stability suitable for post-processes. Intrinsic changes of as-prepared silica particles during heat treatment at 550 °C were thoroughly examined by TGA, FT-IR, SAXS, TEM and SEM characterization. The annealed silica particles became much more reliable building blocks for a self-assembled thin film, as evidenced by low crack/defect density in the fabricated film. In this paper, we provide a method of stabilizing silica particles and thereby aligning them into a close packed structure without macroscopic defects. This method is potentially useful for the delicate silica alignment for patterning and fabrication of high-quality photonic crystals adequate for optical switches, wave-guides, lasers and antireflective films for solar cells.