Preparation And Characterization Of ZnO Nanostructures On Si Substrates

The II-VI wide-gap semiconductor, zinc oxide (ZnO) has great promising applications in optical, electronic, catalytic, sensor and biochemical fileds due to its wide direct bandgap of 3.4 eV at room temperature and its large exciton binding energy (60 meV). One-dimensional and two-dimensional ZnO nanostructures show many novel properties, which can be used as building blocks for nanoscale optoelectronic devices such as room-temperature UV nanolaser, light emitting diodes, field-effect transistor and solar cell. Thus it has been the focus of current research in the nano-semiconductor field.Because of the generally expensive equipments, high reaction temperature and strict experimental conditions of preparing ZnO nanostructures by vapor methods, our work focused on wet chemical methods with low cost at remarkably low temperature to prepare ultrathin ZnO films, zero-dimensional dot structured, one-dimensional rod structured and two-dimensional sheet structured nano ZnO on Si substrates. First of all, from the facility point view of film fabrication by spin-coating technique, ZnO films were fabricated. And ZnO nanodots were prepared based on the theory of phase-separation occurred in the ultrathin precursor layer during the spin-coating process. And then, ZnO nanosheets and ZnO nanorods were prepared through the subsequential growth of ZnO films and nanodots on the Si substrates. The morphology variation and controllable growth of ZnO nanostructures were accomplished though different synthesis conditions. The microstructure and properties of these nanostructures were characterized and the formation mechanisms were discussed in the thesis.Accordingly, the main work and main results are summarized as foliowings:1.ZnO nanostructures such as ZnO films, nanodots with adjustable density and nanorings, porous films were prepared on Si substrates by spin-coating technique.2. ZnO nanosheet films and ZnO nanosheet-microsphere layers were prepared at room temperatue through solution growth approach by soaking the ZnO films on Si substrates in the high alkaline Zn(NO₃)₂ aqueous solution with a certain concentration, where the ZnO films pre-fabricated by spin-coating technique were used as seed-layers. The average thickness of ZnO nanosheets was 20～25 nm and the average diameter of ZnO nanosheet-microsphere was about 3.5μm. The two-demensional nanosheet structures showed good UV emitting and hydrophilic property.3. Ordered ZnO nanorod arrays were prepared through low-temperature (90℃) hydrothermal growth of pre-formed ZnO films and nanodots on Si substrates. The average diameters of these nanorods were in the range of 20～40 nm. By changing the morphologies of ZnO films and the density of ZnO nanodots, density-controllable ZnO nanorods and position-selective growth of ZnO nanorods were carried out. The ZnO nanorod arrays showed excellent UV emitting as well as strong hydrophobic property, and the properties of ZnO nanorod arrays were adjustable with their density variation.