| Summary: | 博士 === 國立成功大學 === 化學工程學系碩博士班 === 93 === Abstract
Two main research subjects are presented in this thesis. Part I is “Low temperature growth of ZnO nanostructures by chemical vapor deposition”. Part II is “Growth of well-aligned ferromagnetic Zn1-xCoxO nanorods by thermal CVD”.
Part I.
Highly oriented ZnO nanorods have been grown on various substrates, such as fused silica, Si(100), sapphire(110), and sapphire(0001) using a simple catalyst-free CVD method at 500oC in furnace. SEM images indicat that high density and well-aligned ZnO nanorods were grown on fused silica, Si(100) and sapphire(110). XRD diffraction shows that the ZnO nanorods are wurtzite structure and are preferentially oriented in c-axis. TEM analyses indicate that epitaxial ZnO nanorods have been grown on sapphire(110) with the ZnO/sapphire orientational relationship[0001]//[110] and [110]//[0001]. In the case of the Si(100) substrate, an amorphous SiOx interfacial layer exists between ZnO nanorods and Si(100). The well-aligned ZnO nanorods on fused silica substrates exhibit a strong UV emission and absorption at around 386 nm under room temperature. Photoluminescence and Raman spectra indicate that there is a very low concentration of oxygen vacancies in the highly oriented ZnO nanorods. Diameter control of the well-oriented and high-quality ZnO nanorods is achievable by variation of the growth conditions. Angle-dependent x-ray absorption and scanning photoelectron microscopy measurements suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [000-1] direction.
The heterostructures of Zn–ZnO coaxial nanocables and ZnO nanotubes with an average diameter of 30 nm have been synthesized by simple pyrolysis of zinc acetylacetonate. High-resolution transmission electron microscopy analyses reveal that the Zn core and the ZnO sheath of the nanocables have an epitaxial relationship with their longitudinal axis oriented along the <001> direction. ZnO nanotubes with a wall thickness of 4 nm possess a single-crystal structure and appear to be the extension of the ZnO sheath of the coaxial nanocables. It is suggested that the ZnO nanotubes are formed by partial evaporation of Zn core of the Zn–ZnO coaxial nanocables.
Part II.
Diluted magnetic semiconductor Zn1-xCoxO nanorods with a Curie temperature higher than 350 K have been synthesized by in-situ doping of Co in ZnO nanorods using a simple thermal chemical vapor deposition method. Structural analyses indicated that the nanorod possesses the single-crystalline wurtzite structure and there is no segregated cluster of impurity phase appearing throughout the nanorod. The transparence of the Zn1-xCoxO nanorods in the visible region has been examined by UV-visible absorption. The fundamental absorptions of the Zn1-xCoxO nanorods estimated from the absorption spectra do not reveal pronounced difference from that of pure ZnO nanorods.
|
|---|
