Morphological Design of Zinc Oxide Films Grown in Aqueous Solutions

The morphology of wurtzite-type zinc oxide (ZnO) grown from an aqueous solution was successfully controlled by addition of phosphate ions and various organic molecules having carboxy groups. Basically, array of hexagonal needles with a diameter of 50–100 nm was grown on a substrate in the absence of the additives. Hexagonal plates were perpendicularly arranged on the substrate by the adsorption of citric, tartaric and maleic acids. The presence of phosphate ions induced an open cellular structures consisting of zinc oxide nanosheets. Densely packed columns and bundles consisting of nanoscale fibrous crystals were produced by the addition of bulky dye molecules, such as phenolphthalein. The influence of the dye molecules depended on pH of the solution. The morphological variation of ZnO films was ascribed to the selective adsorption of the anionic species on the basal and prism planes of the wurtzite structure.