Photopatternable and refractive-index-tunable sol–gel-derived silica–titania nanohybrid materials

• Heterogeneously condensed silica–titania nanohybrid materials synthesized by simple sol–gel process.
• Successful photo-fabrication of various typed optical surface structures by high photopatternability.
• Wide ranges of refractive-index tunability and high optical transparency of above 90% in visible wavelength regions.
• Good surface roughness of below 1 nm for optical applications.

Silica–titania nanohybrid materials were synthesized using functionalized organosilanes and organically chelated titanium alkoxide in a simple sol–gel process. The synthesized silica–titania nanohybrid materials exhibited good solution processability and homogeneous dispersion without any phase separation regardless of the ratio of the mixture of the two components. The silica–titania nanohybrid materials exhibited good photoinitiator solubility and effective photocurability with a high degree of degree under ultraviolet (UV) exposure. Because of their high photocurability and solution processability, the silica–titania nanohybrid materials were readily converted into silica–titania nanohybrid films and were used for direct photopatterning without requiring the developing process used in the photomask method. In particular, the refractive indices of the silica–titania nanohybrid materials could be decreased by decreasing the content of chelated titanium alkoxide in the materials. Moreover, the silica–titania nanohybrid films exhibited high transmittance in the visible wavelength range, and their surface roughnesses were very smooth, exhibiting values <1 nm. On the basis of these observations, the fabricated silica–titania nanohybrid materials can be used in solution-processable materials for producing optical and electro-optical elements.