Synthesis And Performance Study On Cu₂O And In₂O₃Based Nano-heterojunction Structures

Composites, especially nano-composites are often multifunctional and have high performance comparing with ordinary nano-materials. Therefore, nano-composites have gained more and more research attentions and are leading the orientation of advaced materials in pace with the development of semiconductor micro/nano science and techniques. In this dissertation, we focus on the controllable synthesis, morphology characterization, optical and electrical properties and structure-activity relationships of Cu2O and In2O3based nano-heterojunction structures. The main research contents and innovations are listed below:1. Synthesis of Cu2O/ZnO nano-heterojunction structures and their photoluminescence (PL), photocatalytic (PC) and field emission (FE) properties.Because of the thermolability of Cu2O and the lattice mismatch between Cu2O and ZnO, Cu2O/ZnO nano-heterojunctions are normally made by electrodeposition, electrochemical deposition or sputtering, which impose restrictions on the nanostructure of the heterojunctions that can only exist in the form of film with a simple planar interface, lead to inadequate minority carrier transport length, high recombination rate of the photogenerated electron-hole pairs and low sunlight utilizing efficiency. We report an easy access route for synthesizing ZnO nanoparticles on different Cu2O micro structures by low temperature hydrothermal and thermal annealing process with the assistance of polyethyleneimine (PEI). Our synthesis route is facile to operate and can be applied to manufacturing a variety of compound materials with various morphologies. Despite the new nano-heterostructure, the PL properties of the Cu2O/ZnO nano-heterojunctions are measured and a new light peak is found. The FE and PC properties of the Cu2O/ZnO nano-heterostructures are tested and compared with those of pure Cu2O samples. We find that the as-prepared Cu2O/ZnO nano-heterojunctions have increased FE and PC properties; those nano-heterojunctions with more ZnO nanoparticles has better FE and PC performance than those with fewer. We analysed the origin of the high performances from the aspects of morphology change and nano-size effect. We also gave out a preliminary interpretation of the new PL peak and the enhanced optical/electrical properties by using semiconductor band theory.2. Synthesis of Cu2O/TiO2/ZnO tenary nano-heterojunction structures and their field emission and photocatalytic properties.We designed and successfully prepared Cu2O/TiO2/ZnO tenary nano-heterojunction structures. In the first step, we fabricated Cu2O/TiO2core-shell nanostructure in a low temperature hydrothermal and thermal evaporation process by using Titanium (Ⅳ) oxideacetylacetonate (TiO(acac)2) as precursor. Second, we combined ZnO nanoparticals on Cu2O/TiO2core-shell nanostructure with the assistance of polyethyleneimine (PEI). We tested and compared room temperature field emission and UV-Vis photocatalytic properties of Cu2O, Cu2O/TiO2core-shell nanostructure and CuO/TiO2/ZnO tenary nano-heterojunction structure. The results proved that all the nano composites have enhanced performance as we anticipated. Cu2O/TiO2/ZnO tenary nano-heterojunction structure has better enhancement than Cu2O/TiO2core-shell nanostructure. We gave a theoretical explanation for the enhancement by using semiconductor band theory.3. Synthesis of In2O3/Al2O3core-shell nano-heterojunction structures and their field emission enhancement.We synthesized four kinds of In2O3micro/nano-structures via thermal evaporation method and chose In2O3nano-rods as core, coated Al2O3shell on it using atomic layer deposition (ALD) process. We manufactured samples with diffierent shell thickness, treated them with thermal annealing and H2plasma treatment. We measured room temperature field emission properties of all the samples, systematically analysed the structure-activity relationships of In2O3/Al2O3core-shell nano-heterojunction structures and their field emission properties based on the experiment results.4. Synthesis of Cu2O and In2O3nano structures.We accomplished the controlled preparation of various Cu2O and InO3nano structures via hydrothermal and thermal evaporation methods. We preliminary studied the influence of main process parameters (reaction time, temperature, source material ratio and so on) to samples’ morphologies. Besides, we synthesized a macroscopic In2O3monocrystal microstructure and successfully dispersed it into sigle super-long In2O3micro-rods. In2O3-Ag electrodes of good Ohm contact are fabricated by screen print method and their humidity sensor properties are tested.