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Abstract
High quality nm-thick Gd2O3 epitaxial films with different thickness have been grown on GaN(001), Si(111), and GaAs(111) substrates. Structural investigation was carried out by in-situ reflection high energy election diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, Gd2O3 films tend to follow the epitaxial relationship of the substrate underneath: Gd2O3(001)H<110>H//GaN(001)H<110>H, Gd2O3(111)C<11 ̅0>C//Si(111)<1 ̅10>, and Gd2O3(001)H<100>H//GaAs(111)<42 ̅2 ̅>. With oxide thickness below the critical thickness, unlike the hexagonal phase Gd2O3 stabilized on GaN (001) and GaAs(111), Gd2O3 would stabilize on Si (111) with cubic phase instead. However, with the increase in Gd2O3 films thickness, the structure of Gd2O3 films on different substrates all transform to monoclinic phase possessing with different rotational domains, following the Gd2O3(2 ̅01)M<020>M//GaN(001)H<110>H, Gd2O3(2 ̅01)M<202>M//Si (111)<21 ̅1 ̅>, and Gd2O3(2 ̅01)M<202>M//GaAs(111)<21 ̅1 ̅> orientational relationship, respectively. The critical thickness for Gd2O3 phase transformation is related to the lattice mismatch between Gd2O3 epitaxial film and the substrate

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