Tailoring zinc oxide nanowire architectures collectively by catalytic vapor-liquid-solid growth, catalyst-free vapor-solid growth, and low-temperature hydrothermal growth

We present a comprehensive study of the fabrication of zinc oxide (ZnO) nanowires (NWs) with tailored structural morphologies and functional features by utilizing three major growth methods based on vapor-liquid-solid (VLS), vapor-solid (VS), and hydrothermal growth mechanisms. The vertically aligned ZnO NW (ZNW) array can be constructed with tailored length, diameter, and density by controlled catalytic epitaxial VLS growth; the catalyst-free VS growth can create a hierarchical ZNW assembly onto complementary topological frameworks, such as transparent conducting oxides and carbon nanotubes; and the hydrothermal growth practically enables low-temperature growth of conformal ZNWs on large-area and flexible substrates. The growth mechanism and tailoring of the ZNW architectures for each growth strategy were investigated in detail, combined with rational analyses and parametric experiments. This study provides a critical route to the purposeful tailoring of ZNW architectures toward targeted ZnO-driven applications that require specific ZNW morphologies, assembly configurations, and substrate materials for many diverse fields including energy conversion and harvesting, electronics, photonics, and smart and wearable sensors.