Hf- and Ta-aluminates have been grown by 3 key O-2(+) reactive ion beam mixing (IBM) of X/Al interfaces (X = Hf or Ta). The kinetics of growth, composition and electronic structure of the films formed have been studied using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and factor analysis. A reactive IBM kinetics of two stages has been found by means of factor analysis. In a first stage, HfO2 or a mixture of Ta suboxides and Ta2O5 species are formed for the Hf/Al or Ta/Al interface, respectively. Ta suboxide species are subsequently transformed into Ta2O5 species at the beginning of the second stage. In a second stage. HfO2 or Ta2O5 species are transformed progressively into Hf-O-Al or Ta-O-Al species, respectively, leading to the synthesis of custom designed Hf- and Ta-aluminates. The evolution of the Auger parameters and UPS valence band spectra shows that this transformation is accompanied by changes in the electronic structure of the oxide films formed. (c) 2012 Elsevier B.V. All rights reserved.