XPS depth profile analysis of sol-gel calcium-modified lead titanate thin films

X-ray photoelectron spectroscopy (XPS) combined with 4 keV Ar+ depth profiling has been used for the study of calcium-modified lead titanate thin films obtained by the spin-on sol-gel technique. Amorphous films were prepared on Pt/TiO2/Si(100) substrates. These films were deposited from solutions with a nominal composition of Pb0.76Ca0.24TiO3 and with this composition plus a 10 mol% surplus of Pb. Crystallisation of the films was carried out at 650 degrees C/720 s, with a heating rate of 8 degrees C/s and 650 degrees C/50 s with a heating rate of 30 degrees C/s. The chemical composition at the film surface and in depth of the crystalline films were analysed by XPS. A non-uniform Pb distribution with depth was found for the films crystallised with the slower heating rate, whereas the more rapidly heated films show a homogeneous Pb distribution. The film heated with a rate of 30 degrees C/s and deposited from the stoichiometric solution shows Ph deficiency and Pt diffusion into the film, in the proximity of the Pt electrode. A homogeneous composition throughout the film down to the interface with the Pt electrode was obtained for the film heated with a rate of 30 degrees C/s, but deposited from the solution with 10-mol% Ph excess. This explains the well defined ferroelectric response of this film. (C) 1999 Elsevier Science S.A. All rights reserved.