Molecularly interconnected SiO2-GeO2 thin films:: sol-gel synthesis and characterization

SiO2-GeO2 films have been synthesized by the sol-gel method starting from an ethanolic solution of Si(OC2H5)(4) and Ge(OCH3)(4). The coatings have been annealed in air at temperatures ranging between 300 degrees C and 900 degrees C. The compositional and microstructural evolution of the samples under thermal annealing has been investigated by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), Secondary-Ion Mass Spectrometry (SIMS) and Atomic Force Microscopy (AFM). Pure and molecularly homogeneous films have been obtained after 300 degrees C thermal treatment. An amorphous network of interconnected SiO4 and GeO4 tetrahedra has been observed up to 700 degrees C. At higher treatment temperatures the formation of crystalline silica in the cristobalite phase has been detected.