Formation of self-assembled Gd₂O₃ nanowire-like structures during epitaxial growth on Si(001)

The structural and morphological properties of gadolinium oxide (Gd₂O₃) grown at high temperatures with molecular beam epitaxy on Si(001) were investigated for different stages of growth. The Gd₂O₃ layers were grown at 850 °C with different oxygen partial pressures and substrate miscuts. RHEED and XRD investigations indicate an initial formation of silicide and a subsequent transformation into cubic Gd₂O₃ with (110) orientation. The surface exhibits nanowire-like structures oriented orthogonally along with the [110] directions of the substrate, as indicated by AFM. Since on 4° off-cut Si(001) substrates the nanowire-like structures are mainly oriented in only one [110] direction, the orientation of the formed Gd₂O₃ structures seems to be related to the dimer orientation of the (2 × 1) reconstructed Si(001) surface. The density and length of the nanowire-like structures can be tuned by a change in oxygen partial pressure. The results were discussed in terms of different physical effects, where a combination of desorption of silicon and the formation of a silicide layer in the initial stage of growth could be the reason for the growth behaviour, which is also supported through TEM investigations.