Structural modifications produced by the incorporation of Ar within the lattice of Fe2O3 thin films prepared by ion beam induced chemical vapour deposition Original Research Article

Iron oxide thin films have been prepared at room temperature by ion beam induced chemical vapour deposition. The films were grown by bombardment of a substrate with O+2 or O+2+Ar+ mixtures, while a Fe(CO)5 volatile precursor was adsorbed on the surface. In both cases, the films were dense and had a low roughness. After preparation, the films prepared with O+2 ions consisted of hematite (α-Fe2O3), although with a low degree of order as revealed by grazing angle X-ray diffraction (GXRD), transmission infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. A progress in the crystallisation process of these films occurred by annealing at 573 and 773 K. In all cases, the crystallographic c axis of the hematite structure was oriented perpendicular to the film surface. Samples prepared with the O+2+Ar+ mixture were amorphous or badly ordered. Rutherford backscattering spectroscopy (RBS) showed that in these films Ar (∼4% atomic) became homogeneously incorporated within the Fe2O3 lattice. These Ar atoms remained incorporated even after annealing at 773 K. At this temperature, a sudden crystallisation of α-Fe2O3 occurred, resulting in the same preferential orientation of the c axis as in the samples prepared in absence of Ar. The extinction of some GXRD peaks for these annealed samples is correlated with the presence of Ar atoms within the α-Fe2O3 lattice. The possibility of controlling the structure of thin films prepared by ion beam assisted methods by incorporation of Ar into their structure is discussed.