ZnO Nanocrystals: Surprisingly 'Alive'

In the past few years, ZnO has become one of the most elaborately and extensively studied nanocrystalline material. It is often assumed that ZnO nanomaterials are stable in ambient atmosphere. Contrary to this general-but not fully substantiated-belief we show that ZnO nanocrystals in powder form grow unexpectedly in ambient atmosphere at room temperature and the growth is influenced by the vapor pressure of water. Growth kinetics and mechanism, based on chemisorption of water on the surface of ZnO nanocrystals, are proposed. Water vapor not only causes the ZnO nanocrystals to grow but it also improves the crystallinity of the material. This unusual self-healing behavior of ZnO nanocrystals can remarkably influence their properties and affect their numerous applications.