One-Dimensional Nanomaterials: Synthesis, Characterization And Property Study

Since the discovery of carbon nanotubes by Iijima in early 1990's, one-dimensional nanomaterials have attracted much attention due to their unique physical, chemical and biological properties as well as their potential applications in highly active catalysts, magnetic recording media, novel fluorescent materials, building blocks for nanodevices and so on. In this dissertation, we synthesized some one-dimensional nanostructures by different methods, including metal oxide coated carbon nanotubes, carbon coated germanium nanowires and Ga₂O₃ nanowires. The magnetic of metal oxide coated carbon nanotubes and electrical properties of the individual Ga₂O₃ nanowires were also addressed. The significant results achieved in this dissertation are given as follows:1. Methanol-thermal method was proposed as an effective way of completely coating carbon nanotubes with various metal oxides including needle-like Fe₂O₃, uniform La₂O₃ and CeO₂. Based on the system investigation, we predicated that the pre-oxidation of CNTs and the acid-based methanol solution were extremely important in the coating process, and a possible mechanism was also proposed. Preliminary study of magnetic property shows that the coercivity of iron oxide has been enhanced after coating on carbon nanotubes.2. Reacting of GeO₂ with mixed reducing gas of C₂H₄ and NH₃ in the presence of Fe/Al₂O₃ catalysts at 750℃, we synthesized single- crystalline Ge nanowires covered with amorphous carbon in one step. The growth mechanism of the Ge nanowires could be attributed to the well-known vapor-liquid-solid (VLS) catalytic growth process promoted by nanoparticles attached at the end of the nanowires.3. Reacting of metal Ga with water vapor, we synthesized abundant well-crystallized β-Ga₂O₃ nanowires with narrow diameter-distribution. The crystal structure, the composition and the growth mechanism of the Ga₂O₃ nanowires were also intensively investigated. The contact properties of individual Ga₂O₃ nanowires with Pt or Au/Ti electrodes are studied respectively, finding that Pt can form Schottky-barrier junctions and Au/Ti is advantageous to fabricate Ohmic contacts with individual Ga₂O₃ nanowires. The conductivity of n-type semiconducting Ga₂O₃ nanowires is extremely sensitive to NH₃ or NO₂ even at room temperature.