Spatially separated ZnO nanopillars were grown on Pt-thin-film-coated Si substrates by electrochemical deposition in Zn(NO3)2 aqueous solution. The effects of growth parameters, such as Zn(NO3)2 concentration, cathodic potential, bath temperature, and growth time, were studied with respect to the morphological, structural, and photoluminescence properties of the ZnO nanopillars. The isolated nanopillars fabricated at a relatively low concentration of Zn(NO3)2 (∼5 × 10-4 M) and high temperature (90 °C) had the best structural and optical qualities. The separated ZnO nanopillars were found to exhibit a single-crystal wurtzite structure and to grow along the c axis perpendicularly to the substrate. The as-grown nanopillars had a moderate UV-to-visible emission ratio of ∼4.2, but this value could be substantially improved by annealing. Annealing at 300 °C in all three atmospheres studied (air, 5% H2/95% N2, and vacuum) resulted in a considerable improvement in the UV-to-visible emission ratio (16.7−28.6), although a considerable number of defects were created by annealing at temperatures above 500 °C.

Vertically aligned ZnO nanorods having high optical quality were prepared by a hydrothermal−electrochemical method. The nanorods were synthesized in a Zn(NO3)2 aqueous solution on Si substrates which were coated with a platinum conducting layer and a ZnO seed layer. They possessed a single-crystal würtzite structure and grew along the c-axis, perpendicular to the substrates. The height and diameter of the ZnO nanorods were up to ∼4.3 μm and 90−150 nm, respectively. The morphological, structural, and photoluminescence properties of the ZnO nanorods were examined with respect to the growth temperature (120−180 °C) and the presence of NaOH additive. The nanorods synthesized at high temperature (180 °C) exhibited a strong UV emission and a weak defect-related visible emission leading to a UV−visible ratio of ∼230. This high optical quality was attributed to the increased growth rate of ZnO nanorods (∼4.3 μm/h) which was caused by the high growth temperature (180 °C). This was based on the fact that the ZnO phase is thermodynamically more favorable than the defect-related Zn(OH)2 phase at higher temperature. Since the growth temperature was compatible with polymer materials, our synthetic method may provide a promising way for fabricating high performance optoelectronic devices on flexible polymer substrates.

Precisely positioned and spatially separated ZnO nanorod arrays were fabricated on holographically predefined two-dimensional (2D) SiN x nanohole-array-coated Pt/Si substrates using a simple electrochemical deposition process. The stems of the 2D nanohole-assisted ZnO nanorods had a single-crystal nature and a preferred (002) growth direction but polycrystalline contact with the Pt surface. This approach provides a facile largescale method for fabricating periodic nanohole-supported ZnO nanorods at low growth temperatures (90 °C). The enhanced UV emission from these nanorods was associated with a lower defect density in the nanoholetemplated ZnO nanorods, which was achieved by electrochemical deposition on a 2D nanohole array at a potential of -1.0 V for 30 min.