Synthesis of Cr-based mixed oxides by reactive ion beam mixing of Cr/X interfaces (X=Al or Si)

The 3 keV $\mathrm{O}₂⁺$ reactive ion beam mixing of Cr/X interfaces (X=Al or Si) has been used to synthesize Cr-based mixed oxide thin films. The kinetics of growth, composition, and electronic structure of those films has been studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and factor analysis. Initially, for low ion doses, Cr2O3 species are formed. Later, with increasing the ion dose, Cr2O3 species are first transformed into Cr3+–O–X species, and subsequently, those Cr3+–O–X species are transformed into Cr6+–O–X species. This sequential transformation, Cr2O3→Cr3+–O–X→Cr6+–O–X, is accompanied by a slight increase of the oxygen concentration and a decrease of the Cr/X ratio in the films formed leading to the synthesis of custom designed Cr-based mixed oxides. The changes observed in the valence band and Auger parameters further support the formation of Cr–X mixed oxide species. Angle resolved X-ray photoelectron spectroscopy shows that for low ion doses, when only Cr2O3 and Cr3+–O–X species coexist, Cr3+–O–X species are located nearer the surface than Cr2O3 species, whereas for higher ion doses, when only Cr3+–O–X and Cr6+–O–X species coexist, the Cr6+–O–X species are those located nearer the surface.