Nanometric morphological variation of zinc oxide crystals using organic molecules with carboxy and sulfonic groups

The morphological variation of wurtzite-type zinc oxide (ZnO) grown on a substrate in basic aqueous solutions was investigated using a wide variety of organic molecules with carboxy and sulfonic groups. The effect of the organic molecules on the nanometric morphology was classified into several categories. Hexagonal plates exhibiting the (001) planes were obtained by a planarizing effect with the addition of citric, tartaric, and maleic acids, although acetic, salicylic, fumaric, and succinic acids exhibited no effects on the morphology. The production of nanograins was observed by a miniaturizing effect with the addition of a polymeric molecule with carboxy groups and an anionic surfactant with a sulfonic group. Mosaic structures composed of granular crystals and bundles consisting of fibrils elongated in a direction toward the c-axis were produced by the addition of bulky dye molecules having benzene rings and carboxy or sulfonic groups. The influence of the organic molecules was related to the number of the functional groups and the stereochemical structure. The findings of this study suggest that the adsorbability of the organic molecules depending on the chemical structure to the specific crystal faces is essential for the variation of the nanometric morphology.