Spontaneous Stepwise Formation of Polar Crystals with High Sphericity

Abstract

Physicochemical properties and applications of materials are dependent on their morphologies and crystallographic orientations. Therefore, understanding and realization of growth mechanisms are needed for advanced technology. Because (0001) polar facet of ZnO has higher surface energy than surface energy of other facets, the direction to grow is the [0001] direction. Therefore, the spherical growth of ZnO is not thermodynamically favorable. Spontaneous formation of polar crystals with high sphericity, which is formed from the mild solution-based reaction with L-ascorbic acid as a surface energy modifier, was systematically studied and the formation mechanisms of spontaneous stepwise growth of polar crystals with high sphericity was suggested based on the characterization results of cold field-emission (FE)-scanning electron microscopy (SEM) and focused-ion beam (FIB)-transmission electron microscopy (TEM) technique. Because (0001) Zn-terminated polar plane has higher reactivity than other non-polar surfaces on oxygen activity, additional experiments were also performed about hydrogen peroxide production of ZnO sphere and ZnO rod through oxygen reduction reaction (ORR) to see the difference in reactivity on polar and non-polar surface. Through this study, an effective photocatalytic material would be synthesized by better understanding the growth mechanism of polar crystals with high sphericity