Aqueous chemical growth of zinc oxide nanowires is a flexible and effective approach to obtain dense arrays of vertically oriented nanostructures with high aspect ratio. Herein we present a systematic study of the different synthesis parameters that influence the ZnO seed layer and thus the resulting morphological features of the free-standing vertically oriented ZnO nanowires. We obtained a homogeneous coverage of transparent conductive substrates with high-aspect-ratio nanowire arrays (length/diameter ratio of up to 52). Such nanostructured vertical arrays were examined to assess their electric and piezoelectric properties, and showed an electric charge generation upon mechanical compressive stress. The principle of energy harvesting with these nanostructured ZnO arrays was demonstrated by connecting them to an electronic charge amplifier and storing the generated charge in a series of capacitors. We found that the generated charge and the electrical behavior of the ZnO nanowires are strictly dependent on the nanowire length. We have shown the importance of controlling the morphological properties of such ZnO nanostructures for optimizing a nanogenerator device.
This study proposes a way to control the wettability of zinc oxide nanowires (NWs) by properly selecting the kind of seed layer used to promote the growth of the wires. ZnO seed layers were synthesized on silicon and conductive substrates by a physical vapor deposition approach and a wet-chemical route, namely, the radio frequency magnetron sputtering and the spin-coating techniques, respectively. ZnO NWs were grown by a hydrothermal method on each kind of seed layer and the results were compared. The morphologies and crystallographic orientations of the seed layers and the resulting NWs were investigated with the aim of correlating the characteristics of the underlying seed layer to those of the resulting NWs. Additional insights were obtained by performing optical contact angle (OCA) measurements on ZnO seed layers to study their wettability behavior immediately after the synthesis processes and two weeks later. Hydrophilic behavior was observed in both sputtered and spin-coated
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