Titanium dioxide thin-film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

The initial stages of TiO2 growth on Si(111) under ultra-high vacuum conditions is studied using core level photoelectron spectroscopy, x-ray absorption spectroscopy, and scanning tunneling microscopy. The TiO2 film was formed by means of chemical vapor deposition of titanium(IV) isopropoxide at a sample temperature of 500 °C. The thickness and composition of the amorphous interface layer and its subsequent transition to crystalline anatase TiO2 are discussed. Three different stages are identified: In the initial stage (film thickness <10 Å), the oxygen atoms are coordinated mainly to Si atoms giving rise to Ti atoms with oxidation states lower than 4+. At this stage, a small amount of carbon (0.15 ML) is observed. The next stage (<25 Å) is best described as an amorphous TiSixOy compound in which the oxidation state of Ti is 4+ and the x and y values vary monotonically with the film thickness, from 2 to 0 and 4 to 2, respectively. Finally (>30 Å) a stoichiometric TiO2 layer starts to form. The TiO2 phase is anatase and the layer consists of particles ∼10 nm wide.