Cation Interdiffusion in Amorphous Oxide Nanolaminates of TiO₂ with GeO₂ and with SiO₂

Amorphous oxide nanolaminates consist of intercalated nanometer thick layers of two different oxides in which the optical and structural properties can be tailored by selecting the layer thicknesses. This study investigates cation interdiffusion in amorphous oxide nanolaminate designs of TiO₂ intercalated with GeO₂ and with SiO₂ after annealing at different temperatures. Nanolaminates are candidates for coatings of gravitational wave detectors to achieve low internal friction. Cation interdiffusion is assessed by X-ray Photoelectron Spectroscopy (XPS), while Grazing Incidence X-ray Diffraction (GIXRD) is used to determine the onset of crystallization. The results indicate cation interdiffusion between TiO₂ and GeO₂ occurs after annealing at 600°C, and similarly between TiO₂ and SiO₂ after annealing at 900°C and 1000°C. The onset of cation interdiffusion takes place at an average of 0.83 of the glass transition temperature (T_g) corresponding to the glass network formers, GeO₂ and SiO₂. The onset of crystallization of TiO₂ in anatase form is observed after annealing to 700°C and 600°C for the TiO₂/GeO₂ and TiO₂/SiO₂ nanolaminates, respectively. The differences in ionic radius and known modifications in the atomic range-order occurring close to the T_g could activate the interdiffusion, while thickness-dependent crystallization is observed for TiO₂.