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

The structural and morphological properties of gadolinium oxide (GdO) grown at high temperatures with molecular beam epitaxy on Si(001) were investigated for different stages of growth. The GdO 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 GdO 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 GdO 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.