Wavelength-dependent photosensitivity in a germanium-doped sol-gel hybrid material for direct photopatterning

Abstract

Photosensitivity, as evident in permanent changes in refractive index and volume upon light exposure, is. observed in a germanium-doped methacrylate hybrid material (hybrimer) and found to depend on the wavelength of the UV light. Exposure to short-wavelength UV illumination (220-260 nm) results in very high photosensitivity with changes in refractive index (Delta n approximate to 0.0164) and film thickness (Delta t approximate to -40 % ) that are mainly a result of photopolymerization and Ge-related densification. In contrast, the hybrimer is hardly photosensitive to light in the long UV-wavelength range (350-390 nm). Direct photopatterning of a single circle on the hybrimer film creates a concave lens-like topography upon illumination with UV light of short wavelength and a convex lens-like one upon illumination with UV light of long wavelenght.