Shape engineering driven by selective growth of SnO_2 on doped Ga_2O_3 nanowires

Abstract

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 SnO_2/Ga_2O_3 complex nanostructures. Ga_2O_3 nanowires decorated with either crossing SnO_2 nanowires or SnO_2 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 Ga_2O_3 nanowires. Ga_2O_3 nanowires grown along the [001] direction favor the formation of crossing SnO_2 nanowires. Alternatively, SnO_2 forms rhombohedral particles on [110] Ga_2O_3 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 Ga_2O_3 acted as substrates, [110] Ga_2O_3 nanowires grow preferentially. High-resolution transmission electron. microscopy analysis reveals epitaxial relationship lattice matching between the Ga_2O_3 axis and SnO_2 particles, forming skewer-like structures. The addition of chromium oxide to the source materials modifies the growth direction of the trunk Ga_2O_3 nanowires, growing along the [001], with crossing SnO2 wires. The SnO_2/Ga_2O_3 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 Sn_O_2 on its particular shape. Orange emission dominates in SnO_2/Ga_2O_3 crossing wires, while green-blue emission is Observed in SnO_2 particles attached to Ga_2O_3 trunks. The results show that the Ga_2O_3-SnO_2 system appears to be a benchmark for shape engineering to get architectures involving nanowires via the control of the growth direction of the nanowires.