UV photodecomposition of zinc acetate for the growth of ZnO nanowires.

The thermal annealing of zinc precursors to form suitable seed layers for the growth of ZnO nanowires is common. However, the process is relatively long and involves high temperatures which limit substrate choice. In this study the use of a low temperature, ultra-violet (UV) exposure is demonstrated for photodecomposition of zinc acetate precursors to form suitable seed layers. Comparisons are made between ZnO nanowire growth performed on seed layers produced through thermal annealing and exposure to UV. The dependence of growth density and nanowire diameter on UV exposure time is investigated. Growth quality is confirmed with energy dispersive x-ray (EDX) and x-ray diffraction analyses. The chemical composition of the exposed layers is investigated with EDX and x-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) is utilized to investigate morphological changes with respect to UV exposure. The diameter and density of the resultant growth was found to be strongly dependent on the UV exposure time. UV exposure times of only 25-30 s led to maximum density of growth and minimum diameter, significantly faster than thermal annealing. EDX, XPS and AFM analyses of the seed layers confirmed decomposition of the zinc precursor and morphological changes which influenced the growth.

Flexographic printing-assisted fabrication of ZnO nanowire devices.

In this study, the use of flexographic printing was investigated for low cost, high volume production of devices incorporating nanowires through the printing of zinc acetate precursors on a substrate used to form zinc oxide (ZnO) seeds for the growth of nanowires using a hydrothermal growth technique. The printing of precursors allows the selective area growth of ZnO nanowires, which has implications in high-yield production of devices incorporating ZnO nanowires. The work presented here achieved printed line widths of <60 µm with low edge distortion (<3 µm) using a printing plate with a line width of 50 µm. The hydrothermally grown ZnO nanowires show uniform density of growth over the printed area with nanowire diameters between 40 and 60 nm on both silicon and polyimide substrates. Energy-dispersive x-ray spectra showed contamination-free crystals with a 1:1 (zinc to oxygen) stoichiometry. Crystal orientation is along the c-axis with high quality crystalline structure shown using x-ray diffraction spectroscopy and high resolution transmission electron microscopy. A ZnO nanowire gas sensor, fabricated using the flexographic printing technique, is demonstrated. Such a printing-assisted fabrication offers low cost, high volume production of devices incorporating ZnO nanowires, ranging from gas sensors to field emission devices.