Thin Pr2O3 films have been grown by molecular beam epitaxy on Si(0 0 1) and investigated by in situ reflection high-energy electron diffraction (RHEED). The epitaxial growth results in [1 0 1]-oriented films of cubic Pr2O3 with low interface and surface roughness, as confirmed by subsequent X-ray diffraction and reflectivity measurements. During nucleation of Pr2O3 on double-domain Si(0 0 1) (2 x 1)reconstructed surfaces, a diffuse RHEED pattern with weak streaks evolves. Subsequently, a pattern with modulated streaks appears. According to the analysis of the conventional RHEED patterns and the in-plane symmetry of the reciprocal lattice rods obtained by RHEED azimuthal scans, the modulated streaks are attributed to the reflections resulting froth two orthogonal [1 0 1]-oriented domains of cubic Pr2O3. The [0 1 0] direction of one domain and the [1 0 1] of the other are parallel to Si[1 1 0]. The RHEED patterns resulting from good epitaxy deteriorate when the layer thickness reaches I S net, due to the formation of hexagonal Pr2O3 in the films. The structural features of this phase dominate thereafter. This observation indicates an epitaxial stabilization of the cubic phase at the interface. (c) 2006 Elsevier B.V. All rights reserved.