The growth mode of α-Fe₂O₃ thin films by DC magnetron sputtering

Hematite (α-Fe₂O₃) thin films were successfully prepared on a clean silicon substrate via the direct current (DC) magnetron sputtering. The composition and microstructure of the films were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). By controlling deposition time, α-Fe₂O₃ thin films with a series of thicknesses from 70 to 3700 nm were prepared at a fixed Ar/O₂ flow ratio. The growth mode was detected from the cross-sections by scanning electron microscopy (SEM). The films surface morphology and roughness were carefully detected by atomic force microscopy (AFM) and optical profiler. It is indicated that the growth model of α-Fe₂O₃ thin films is close to competitive grain growth. Through the scaling analysis, the intrinsic anomalous roughening behavior of α-Fe₂O₃ thin film was confirmed. The grain boundary diffusion dominates the atomic deposition process, which causes the evident local film growth mode. Upon nanoindentation technology, the hardness and elastic modulus of all the films were measured. Mechanical properties were precipitously reduced with increasing film thickness. Such film thickness effect was discussed from the perspective of the evolution of surface structure.