Nanoscale morphological design of ZnO crystals grown in aqueous solutions

In the past decade, a wide variety of ZnO crystals were prepared through wet chemical processing. However, the fundamentals of the nanoscale morphological variation of ZnO crystals on the crystal growth in aqueous solution systems have not been sufficiently studied. This paper is a review of the various morphologies of ZnO crystals in relation to the preparation conditions, including the source chemicals, the role of seeds or substrates, and the presence of organic molecules as a shape modifier. Versatile guidelines for controlling the nanoscaled morphologies of ZnO crystals in the forms of individual particles and films as assembly of nanocrystals are proposed on the basis of the classification of typical phenomena. The essential parameters, such as the growth rate, growth site, and growth direction of ZnO crystals, are successfully tuned by varying the degree of supersaturation, the presence of seeds or substrates, and the addition of specific organic molecules, respectively.