Silicate formation at the interface of a calcium-modified lead titanate thin film deposited on Si(100)

A calcium-modified lead titanate (Pb 0.76 Ca 0.24 TiO 3 ) thin film has been prepared by spin-on sol-gel on an Si(100) substrate. The film deposited from a stoichiometric solution was subjected to thermal treatment at 650°C for 720 s with a heating rate of 8°C s -1 . The film presents a perovskite-type structure, as indicated from x-ray diffraction powder pattern data, giving it ferroelectrical properties. The chemical composition at the film surface and at increasing depth into the substrate was studied by XPS combined with 4 keV Ar + depth profiling. Ion bombardment gives rise to compositional and chemical changes in the sample surface, in which case lead and oxygen are sputtered preferentially. After 50 min of 4 keV Ar + bombardment, a steady-state composition is reached. At further depth (>200 min) an increase of the Pb 4f signal indicates a non-homogeneous Pb distribution in the film. At the interface between the ferroelectric film and the Si(100) substrate, silicon is found as Si(IV), as well as chemical shifts of the O 1s and Ca 2p 3/2 peaks to higher binding energies are observed. Both facts support the formation of calcium silicate. At the same time, titanium is reduced from Ti(IV), Ti(III) and Ti(II) to Ti(0).