Fabrication And Characterization Of Patterned ZnO Micro/nano Structures

The fabication of surface-patterned micro/nanostructures mainly relates to the bottom-up processes such as self-assembling systems of various nanoscale buildingblocks and top-down nanoscale lithographic patterning. The top-down methods including conventional Lithography, Electron beam lithography, Ion beam lithography, extreme ultraviolet lithography, and Nanoimprint lithography all have some defects in the application of nano-devices fields due to their own restrictions of technical characteristics.Thus exploring a novel preparation method of surface-patterned nanostructures with high efficiency, low consumption, high-quality, or refining the various existing techniques and to optimizing the combination of existing technology is an important task in current research. This thesis focuses mainly on the following aspects1. Fabrication of surface-patterned ZnO thin films using sol-gel methods and nanoimprint lithography.First, various ordered templates as master mold were replicated by PDMS casting method with the optimized parameters. In the process of nanoimprint, the ZnO sol has been transformed to ZnO gel by the thermal curing nanoimprint technology. The PDMS template worked as a micro reaction vessel and the ZnO sol mixed with PAA instead of the resist layers in nanoimprinting process. Then the patterned ZnO films were directly fabricated without subsequent etching process. The characterization results show that the patterned ZnO films had enhanced transmittance than that of flat sol-gelo films. This surface patterning method is high efficiency and low-cost to fabricate large-scale patterned ZnO film.2. Fabrication of the nanodot-like ZnO array structures using nanoimprint lithography with 2-D polystyrene sphere monolayer as template.The 2-D polystyrene sphere (PS) array films assembled on gas-liquid interface are involved in our experiments as master templates to otain the PDMS soft stamps with two dimensional hemispherical structures.In the nanoimprint process, the ZnO sol had been transformed to ZnO gel by the combination of sol-gel and nanoimprint technology. Different pressures were used in order to research the optimized parameters of imprinting process. The results showed that the influence of pressure parameters was vital during the fabrication of patterned ZnO. The transmission spectra showed that the patterned films had enhanced transmittance. In this work, we solved the problem of high-cost of the fabircation of nanoimprint stamps, and the size of pattern could be designed according to the diameter of PS spheres.3. Fabrication of multifarious patterned ZnO nanowires array structures using surface patterning and low-temperature hydrothermal methods.First, seed layer of zinc oxide substrate was sputtered on the Si substrate by ion beam sputtering with the different substrate temperature. ZnO arrays were fabricated using low temperature hydrothermal treatments on different pattened seed layers. Second, the ordered nano-arrays were successfully fabricated by low-temperature hydrothermal treatments on PMMA mask of different ZnO seed layer aperture which were fabricated by electron beam lithography and ion beam sputtering. Thirdly, the regular porous structures of zinc oxide were fabricated by dual control factors of PS microsphere monolayer template and sodium citrate in low temperature hydrothermal system. These methods are simple and convenient and can be adopted for the preparation of other semiconductor materials with pattened structures.