High-k dielectric LaAlO3 (LAO) films on Si(100) were studied by TOF-SIMS and XPS to look for diffusion processes during deposition and additional thermal treatment and for the formation and composition of possible interfacial layers. The measurements reveal the existence Of SiO2 at the LAO/Si interface. Thermal treatment strengthens this effect indicating a segregation of Si. However, thin LAO layers show no interfacial SiO2 but the formation of a La-Al-Si-O compound. In addition, Pt diffusion from the top coating into the LAO layers occurs. Within the LAO layer C is the most abundant contamination (10(21) at/cm(3)). Its relatively high concentration could influence electric characteristics. XPS shows that CO32- is intrinsic to the LAO layer and is due to the adsorption of CO2 of the residual gas in the deposition chamber. (c) 2005 Elsevier B.V. All rights reserved.