Investigations into the Impact of the Template Layer on ZnO Nanowire Arrays Made Using Low Temperature Wet Chemical Growth

The impact of various ZnO templates on the alignment and geometry of wet-chemically grown vertical ZnO nanowire (NW) arrays was investigated. The NWs were seeded at nucleation windows which were patterned in poly(methyl methacrylate)-coated ZnO surfaces using electron beam lithography. This growth approach was shown to have the potential for low-cost and low-temperature fabrication of regular, highly aligned, and transparent NW arrays with tunable conductivities on cheap substrates with precise engineering of the NW dimensions and positioning. The compared ZnO templates included a single crystal ZnO substrate, an epitaxial film on a c-sapphire substrate, and polycrystalline films on Si(111), Si(100), and Pt/c-sapphire. Scanning electron microscopy and X-ray diffraction revealed that the alignment, crystal structure, and geometry of the NW arrays were dictated by the crystal structure of the underlying ZnO, while the influence of the surface roughness was negligible. Thus, the choice of seed layer crystallinity gives control over the NW form, alignment, and in-plane crystallographic orientation. In particular, hydrothermal ZnO substrates and epitaidal ZnO layers grown on c-sapphire by pulsed laser deposition gave similar NW arrays with very regular form, strong vertical alignment, and a common relative orientation of their hexagonal crystal facets in the surface plane.