Controllable Systhesis Of ZnO Nanocrystals And Films

The control of the shape and size of ZnO nanometer sized semiconductor is of great scientific and practical interesting due to its specific size- and shape-dependend properties as well as its wide applications in various fields including room-temperature ultraviolet laser, field-effect transistor, photodetector, gas sensor, photocatalst and solar cells. Numbers of methods, such as the thermal evaporation and wet-chemical growth process, have been developed to obtain the controlled ZnO crystals both in solution and thin films. The wet-chemical approach is one of the most voluble routes because of its low cost and easy preparation of large batches. In this thesis, ZnO nanocrystals of different morphologies either in solution or directly deposited on FTO substrate were grown at low temperature of 90℃.A two-step route, including the deposition of "seeds" on FTO substrate followed by a growth of ZnO film, was used for the growth of ZnO nanocrystal film. The effects of "seeds", ZnO growth time, solution pH and additives on the morphologies of ZnO nanocrystal film were investigated in detail. It is found that vertical ZnO nanorod film can be grown on FTO substrate whenever ZnO or TiO₂ was used as the "seed". When ZnO particle was used as the "seed", a dependent of the morphology of the obtained ZnO rods on the "seed" state was observed. A gradually growth of the ZnO nanorod film was carified by tracing the ZnO film growth process.Further, the pH of the mother solution for the growth of ZnO was found to significantly affect the resulted ZnO nanocrystal film. ZnO nanocrystalline film can only be formed on FTO substrate in the range of 42)₆N₄ solution by using Zn(NO₃)₂ at low temperature. It needs to be noted that ZnO nanocrystals is changed form nanorods to rather complicated flower-like structure by the simple increase of the solution pH and the initial reactant concentration.