Vapor-phase Synthesis And Characterization Of Quasi-one-dimensional Nano-oxide

Recent advances in the field of nanotechnology have led to the synthesis and characterization of an assortment of quasi-one-dimensional (Q1D) structures, such as nanowires, nanoneedles, nanobelts and nanotubes. These fascinating materials exhibit novel physical properties owing to their unique geometry with high specific surface. They are the potential building blocks for a wide range of nanoscale electronics, optoelectronics, magnetoelectronics, and sensing devices. In this paper, Al₂O₃/SiO₂ coaxial nanowire heterostructures, Zn₂GeO₄ coated ZnO nanorods and Ge doped ZnO nanocombs and In doped Ga₂O₃ zigzag nanowires have been synthesized by thermal evaporation. The morphology, structure, chemical composition and physical properties of these quasi-one-dimensional nanostructures are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectroscopy. The growth mechanisms of products of different morphologies are further investigated. The relationship between photoluminescence properties and the morphologies is discussed. The following are the main contents and conclusions:1. Synthesis and Characterization of Al₂O₃/SiO₂ coaxial nanowire heterostructures with Periodical Twinning StructuresAl₂O₃/SiO₂ coaxial nanowire heterostructures were synthesized with Al and SiO as raw material by a simple thermal evaporation method. The growth process of the Al₂O₃/SiO₂ coaxial nanowire heterostructures is based on vapor-solid (VS) growth mechanism. Its morphology and microstructures were determined by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The diameter of the nanowires is well-proportioned and generally about 100-150nm. Studies indicate that typical nanostructure consists of single twinning-crystalline Al₂O₃ nanowires (core) with diameter of about 50 nm and amorphous SiO₂ shell. Three emission peaks, namely 364 nm, 398 nm and 442 nm, were observed in the room-temperature photoluminescence measurements.2. Synthesis and photoluminescence properties of aligned Zn₂GeO₄ coated ZnO nanorods and Ge doped ZnO nanocombs Aligned Zn₂GeO₄ coated ZnO nanorods and Ge doped ZnO nanocombs were synthesized on a silicon substrate by a simple thermal evaporation method. The structure and morphology of the as-synthesized nanostructure were characterized using scanning electron microscopy and transmission electron microscopy. For nanocombs the combteeth of one side are longer than that of the other one, but both sides have the same diameter range. The growth of aligned Zn₂GeO₄ coated ZnO nanorods and Ge doped ZnO nanocombs follows a vapor-solid (VS) process. Photoluminescence properties were also investigated at room temperature. The photoluminescence spectrum reveals the nanostructures have a sharp ultraviolet luminescence peak centered at 382nm and a broad green luminescence peak centered at about 494 nm.3. Synthesis of In doped Ga₂O₃ Nanowires and Their LuminescenceIn doped Ga₂O₃ zigzag nanowires and undoped Ga₂O₃ nanowires were successfully synthesized by the simple thermal evaporation method without the presence of catalyst at 1000℃. The growth process of the nanowires is based on vapor-solid (VS) growth mechanism. Its morphology and microstructures were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. Studies indicate that the diameter of the well-proportioned nanowires is about 100nm. But the zigzag shaped nanowires have a diameter of about several hundreds of nanometers. A emission peak centered 457 nm was observed in the room-temperature photoluminescence measurements. The blue bands centered 457 ran can be resulted from oxygen vacancies and oxygen-gallium vacancies centers.