Gas Sensitive Properties Research Of Composite Semiconductor Film Fabricated By Self-assembly

On-line monitoring of harmful gases in industry and home has become an important issue for environmental control. In this respect, semiconductor gas sensors may offer advantages in the form of simple construction, resistance to severe conditions, short response time. To obtain subminiature, intelligent and multi-functional gas sensors, it is important to effectively control thickness, microstructure and composition of film. In this thesis, the granular film with interconnected pore was fabricated by layer-by-layer self-assembly method and it was used for gas sensors. Then the improvement of gas sensitive performance was investigated deeply and the mechanism of gas sensors was analyzed. The major research is as follows.The stable and homogeneous ZnO2 sol was synthesized through reaction of zinc acetate dehydrate and hydrogen peroxide under sunlight radiations, and ZnO2 was annealed to obtain ZnO. Then according to experimental data, reaction equation was deduced and transformation temperature was confirmed. Finally, a green method for sol-gel synthesis of ZnO and ZnO2 powders was developed which is simple, low energy consumption and no pollution. Both the ZnO2 and ZnO have crystal structure and high purity.Generally, ZnO sol is synthesized with alcohol as solvent, so the charges of sol particles are too weak for electrostatic adsorption with oppositely charged polyelectrolytes. Therefore, we adopt an indirect method to fabricate ZnO self-assembled film. First, ZnO2 sol was synthesized with water as solvent. The as-prepared sol particles have strong electrostatic adsorption which makes it easy to construct LbL self-assembled ZnO2 multilayers. Then the ZnO2 multilayers are annealed to obtain ZnO multilayers at temperature above 200 oCThe ZnO film gas sensors were prepared by self-assembly and the gas sensors with interconnected pore were obtained. The layer, microstructure and thickness could be accurately controlled by adjusting preparation parameter. The ZnO gas sensors with different Al dopping method were measured, and it is indicated that ZnO self-assembled film has better performance than thick film to use as gas sensors. Then, gas sensitive mechanism of ZnO self-assembled film was analyzed and the model was established. The composite semiconductor film, ZnO/SnO2 and ZnO/TiO2 composite film, was fabricated by self-assembly. The films have regular alternate layer-by-layer structure. After annealing, SnO2 and TiO2 were doped homogeneously in ZnO which improved gas sensitive properties.In general, the semiconductor gas sensors were fabricated by layer-by-layer electrostatic self-assembly. The obtained film gas sensors have different microstructure and thickness from thick film sensors. The gas sensitive properties were improved.