Synthesis And Growth Mechanism Of ZnO Nanostructures Via A Solution Method

The development of human history is a process in which people study and explore materials. The evolution from gravel of the Stone Age to crystalline silicon of information society is actually the progress of human civilization. In the new century, novel materials are being increasing demanded and the requirements on their properties are becoming stricter. Due to the quantum size effect and many other unique properties, nanomaterials exhibit many different physical and chemical properties from bulk materials and have greatly potential application in microelectronics, optoelectronics, nonlinear optics, high-density information storage, catalysis, hydrogen storage, biomedicine, sensors and detectors.As a multi-function wide band gap semiconductor material, ZnO not only has excellent optical and electrical properties, but also has many nanostructures with different morphologies. It is significant to study and explore the unique properties of ZnO. At present, different ZnO nanostructures have been synthesized by many research groups, in which ZnO nanocrystals in a high quality are mainly prepared by MOCVD or MBE method. But those technologies require high expenses on equipments, which limits the practical applications of ZnO nanomaterials. Moreover, there is still challenging to realize the controllable growth and optimize the properties of ZnO nanostructures.In this dissertation, a simple solution chemical method is employed to synthesize different ZnO nanostructures and an in-depth study on the nanomaterial properties is performed. The following research works have been carried out:By adjusting the pH value and solution concentration, different ZnO nanostructures including nanostack, nanodisk, nanorod and nanoflower have been obtained. The surface morphologies, crystal structures and optical properties were characterized by SEM, XRD, absorbance and photo luminescence spectroscopy. Based on the comparison of different ZnO nanostructures, the possible applications in devices were also studied. Thermal annealing was applied to improve the nanostructures' quality by optimizing processing conditions. Meanwhile, the influences of thermal treatments on the crystal structures and properties have been discussed.The influence of a substrate on the growth orientation of ZnO nanorods has been studied. On the Au/SiO₂/Si substrate, ZnO nanorod arrays perpendicular to substrate were produced. The nanorods are aligned in high density and have a good uniformity.Growth mechanisms of ZnO nanocrystals in aqueous solutions were discussed. ZnO nanostructures are produced by the growth mode of nucleation followed by the crystal growth. Besides, a method to control the velocity of the nucleation and crystal growth were proposed, so as to realize the controllable morphologies and structures of ZnO nanocrystals.In this dissertation we have done many useful investigations on the growth control and properties research of ZnO nano-material: high quality ZnO nano-material with different morphologies and structure has been synthesized by simple solution chemical growth method; The properties of different ZnO nanostructures have been studied; By analyzing the growth mechanism of ZnO nanocrystal, a method to control the growth of ZnO nanocrystal has been achieved; ZnO nanorod arrays with straight and well oriented growth tendency perpendicular to substrate have been obtained using simply synthesis method, and this structure has great potential application in device, such as the transparent electrode of solar cell.