Evolution with temperature of a single sol-gel TIO2 layer on sapphire (α-Al2O3) (0 0 0 1)

TiO2 sol-gel layer has been deposited on single crystal sapphire (0 0 0 1) substrate. Evolution of the layer microstructure with the thermal treatment in the range 100-1100 deg. C has been studied using X-ray diffraction and X-ray reflectometry. TiO2 layer density first increases with temperature up to 800 deg. C and then decreases with the appearance of a high roughness finally leading to anatase islands formation. The single crystal nature of the substrate seems to contribute to hinder the transformation of the anatase phase into the rutile phase and to induce a preferred orientation of the TiO2 islands