Two-step epitaxial synthesis and layered growth mechanism of bisectional ZnO nanowire arrays

Here a two-step epitaxial synthesis method of bisectional ZnO nanowire arrays (ZNWAs) on silicon substrates has been demonstrated incorporating hydrothermal growth (HG) and CVD process. The as-received well-aligned ZNWAs are confirmed to be single-crystal and growing along 〈001〉 direction, normal to the substrate. Interestingly, they show significant tapering behavior at the conjunctions, which is consistent with theoretical predictions. Therefore a layered growth mechanism is promoted involving the classical two-dimensional nucleation theory. In the proposed mechanism, the HG ZNWA provides nucleation sites for successive growth. The growth mechanism is verified by complementary investigation into conjunction morphology, which is dependent on regional Zn vapor pressure (ZVP) in the CVD process. Three types of conjunction morphologies are differentiated and the difference is explained with the growth model.