Electric-Field Tuning of the Bragg Peak in Large-Pore TiO₂ Inverse Shell Opals

Inverse opals with large connection pores were fabricated by infiltrating sintered polystyrene opal templates using low-temperature atomic layer deposition of TiO2 and subsequently dissolving the polystyrene in toluene. The dielectric lattice, consisting of overlapping air spheres in a TiO2 matrix, was then infiltrated with nematic liquid crystal, with some samples having received a prior hydrophobic surface treatment. The specular reflectance is shown to depend not only on electric-field amplitude, but also on film structure. In the hydrophobic-treated sample, a 20 nm shift of the Bragg peak was observed for an applied electric field of 50 kV∕cm.