Coexistence of several structural phases in MOCVD TiO2 layers: evolution from nanometre to micrometre thick films

The morphology and the structure of TiO2 films, grown on Si (1 0 0) substrates by metal organic chemical vapour deposition (MOCVD) was investigated in 5-500 nm thick films. It was shown that the TiO2 layer is mainly amorphous at the first stages of deposition. The growth of nanocrystallites begins inside the amorphous TiO2 layer, and it continues at the expense of the amorphous phase until the crystallized grains occupy the whole layer. Then, the film growth continues with a columnar structure. The coexistence of anatase and rutile phases was evidenced from the beginning of the growth by high resolution transmission electron microscopy and grazing incidence x-ray diffraction. However, the anatase growth overcomes that of rutile, leading to an inhomogeneous phase distribution as a function of the film thickness.