Characterization of asymmetric rhombohedral twin in epitaxial α-Cr2O3 thin films by X-ray and electron diffraction

Epitaxial chromium oxide (α-Cr2O3) films grown by atomic layer deposition at 375 °C from CrO2Cl2 and CH3OH on (1 1¯ 0 2) oriented α-Al2O3 have been studied by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and X-ray reflection (XRR). The thickness of the films ranged from 10 to 310 nm, and the average growth rate was 0.1 nm per deposition cycle. According to the XRD analysis, the orientation relationship in thinner films was (1 1¯ 0 2)[1 1 0]Cr2O3 || (1 1¯ 0 2)[1 1 0]Al2O3. Confirmed by the RHEED and XRD analyses, (1¯ 1 0 2) became the preferred growth plane at the thicknesses above 40 nm. This change has been interpreted as the appearance of an asymmetric rhombohedral twin with the orientation relationship between the layers (1¯ 1 0 2)[1 1 0]top || (1 1¯ 0 2)[1 1 0]bottom and (1¯ 1 0 2)[1 1¯ 1]top || (1 1¯ 0 2)[1¯ 1 1]bottom. The match of the anion and cation sublattices of both layers was characterized in terms of the structural model of the twin interface.