Shape Engineering Driven by Selective Growth of SnO₂ on Doped Ga₂O₃ Nanowires

Tailoring the shape of complex nanostructures requires control of the growth process. In this work, we report on the selective growth of nanostructured tin oxide on gallium oxide nanowires leading to the formation of SnO₂/Ga₂O₃ complex nanostructures. Ga₂O₃ nanowires decorated with either crossing SnO₂ nanowires or SnO₂ particles have been obtained in a single step treatment by thermal evaporation. The reason for this dual behavior is related to the growth direction of trunk Ga₂O₃ nanowires. Ga₂O₃ nanowires grown along the [001] direction favor the formation of crossing SnO₂ nanowires. Alternatively, SnO₂ forms rhombohedral particles on [110] Ga₂O₃ nanowires leading to skewer-like structures. These complex oxide structures were grown by a catalyst-free vapor-solid process. When pure Ga and tin oxide were used as source materials and compacted powders of Ga₂O₃ acted as substrates, [110] Ga₂O₃ nanowires grow preferentially. High-resolution transmission electron microscopy analysis reveals epitaxial relationship lattice matching between the Ga₂O₃ axis and SnO₂ particles, forming skewer-like structures. The addition of chromium oxide to the source materials modifies the growth direction of the trunk Ga₂O₃ nanowires, growing along the [001], with crossing SnO₂ wires. The SnO₂/Ga₂O₃ junctions does not meet the lattice matching condition, forming a grain boundary. The electronic and optical properties have been studied by XPS and CL with high spatial resolution, enabling us to get both local chemical and electronic information on the surface in both type of structures. The results will allow tuning optical and electronic properties of oxide complex nanostructures locally as a function of the orientation. In particular, we report a dependence of the visible CL emission of SnO₂ on its particular shape. Orange emission dominates in SnO₂/Ga₂O₃ crossing wires while green-blue emission is observed in SnO₂ particles attached to Ga₂O₃ trunks. The results show that the Ga₂O₃-SnO₂ system appears to be a benchmark for shape engineering to get architectures involving nanowires via the control of the growth direction of the nanowires.