Amorphous LaxAlyO films, containing 100, 50, and 30% La, were deposited by atomic layer deposition (ALD) on ultrathin SiO2 films (1 nm). Changes in the depth profile, as a function of composition, and structure were examined by medium energy ion scattering and transmission electron microscopy. The electronic structure of the LaxAlyO films was investigated by X-ray photoelectron spectroscopy as a function of La concentration and postdeposition annealing temperature. In the case of a pure La2O3 film without Al2O3, the SiO2 at the interfacial layer had been converted to SiO2-x and La silicate during the ALD process. However, in case of a La2O3 film with Al2O3, interfacial reactions were significantly suppressed. In particular, silicate formation in the La2O3 films gradually increased with the increasing annealing temperature, while that in La2O3 films incorporated Al2O3 was suppressed up to an annealing temperature of 800 degrees C. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3536503] All rights reserved.