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Recent works in our laboratories investigated the microstructure of titarna films prepared from a colloidal solution and used as planar waveguides. The transmission electron microscopy including high resolution observations together with waveguide Raman spectroscopy, especially in the very low frequency range, showed a strong influence of the heat-treatment procedure on the films' morphology. In addition, atomic force microscopy provided valuable information on their surface roughness.At lower temperatures(450°C), the films' structure consists of a mixture of amorphous TiO and anatase nanocrystals (4.5-5 nm) and its surface is smooth. On the contrary, when increasing the annealing temperature, the nanocrystals grow (50 nm at 1000°C), pores (5-20 nm) are clearly distinguished and the films' waveguiding properties disappear.Here, we discuss the optical behavior of these films and its relationship to microsiructure. It is clearly shown that a high degree of crystallization induces an important porosity, a rough surface and thus dramatically affects the films' waveguiding properties.Finally, we report a relatively simple strategy to stabilize the amorphous phase and control the crystallization in order to improve the optical quality of the waveguides.

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