Subglobular Structure of Photonic Crystal Nanospheres Grown Based on Amorphous Silica at Different Water/TEOS Molar Ratios in the Initial Mixtures

Photonic crystals obtained by the modified Stöber method with the natural sedimentation of nanospheres is investigated. The surfaces of the silica nanospheres are investigated using atomic-force microscopy. The surfaces of all samples have a cauliflower structure. The structure of the photonic crystals is studied by the method of small-angle synchrotron radiation scattering (SASRS). The SASRS curves exhibit two or three regions with different scattering intensities. Three original techniques for analyzing the data obtained are proposed. Periodicity in the dependence of the logarithm of intensity on the scattering vector at the smallest wavenumbers, related to scattering from nanospheres, is found. The influence of the water/TEOS molar ratio on the size and concentration of these particles is revealed. Particles of two types (nanospheres and subglobules) are observed at low water concentrations (6–8 mol/L), whereas at water concentrations of 13–23 mol/L the particles are of three types (nanospheres, subglobules, and grains). The morphology of the detected particles is estimated.