Spatially Separated ZnO Nanopillar Arrays on Pt/Si Substrates Prepared by Electrochemical Deposition

Spatially separated ZnO nanopillars were grown on Pt-thin-film-coated Si substrates by electrochemical deposition in Zn(NO 3 ) 2 aqueous solution. The effects of growth parameters, such as Zn(NO 3 ) 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(NO 3 ) 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% H 2 /95% N 2, 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.