Fabrication of a Crack-Free Large Area Photonic Crystal with Colloidal Silica Spheres Modified with Vinyltriethoxysilane

Abstract

Crack-free large area photonic crystals have been fabricated using colloidal silica spheres modified the surface with vinyltriethoxysilane (VTES) and an in situ photo-cross-linking (ISPL) process during the self-assembly of the surface modified spheres (SMS). The VTES has been covalently attached on the surface of the silica spheres by hydrolysis and condensation reactions. The weight ratios of the VTES and the spheres are 1:7 (VTES-A), 2:7 (VTES-B), and 3:7 (VTES-C). The Fourier transform infrared (FTIR) absorption peak attributed to the −OH bond stretching vibration shifts from 3230 to 3480 cm–1 with increasing the amount of VTES. The characteristic absorption peaks of −CH and −CH2 appeared at 2853, 2956, and 3023 cm–1 for VTES-C. The absorption peat at 1409 cm–1 representing the −CH deformation vibration increased with the increase of the amount of VTES. The stop bands are shown at 655, 693, and 708 nm for VTES-A, VTES-B, and VTES-C, respectively. The stop band shift toward longer wavelength is mainly due to the increase of the effective refractive index. The characteristic absorption peak −CH2–CH3 increased drastically after the ISPL process and the washing process due to the stronger absorption intensity of the −CH2–CH3 compared with the absorption intensity of −CH═CH2. Although the photonic crystal constructed with pure silica spheres has cracks between the clusters, the photonic crystal fabricated with SMS with VTES and the ISPL process during the self-assembly of the silica spheres shows no crack in large area. This result provides the fabrication method of a large area and stable photonic crystal without cracks.