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In this thesis, a series of novel morphologies of nanostructures such as ZnO tetrapods and quasi-aligned ternary ZnCdO nanorods were synthesized for the first time based on a typical thermal evaporation process. In addition, the growth mechanism and photoluminescence characteristics of ZnO tetrapods were deeply discussed. Also, the growth mechanism and low-temperature optical properties of ternary quasi-aligned ZnO nanorods were investigated. The important results obtained are as follows:
1. Three kinds of tetrapod-like ZnO nanostructureshave been synthesized simultaneously in different regions of the same preparation apparatus by rapidly heating zinc powder, in which two kinds of novel tetrapod-like ZnO nanocrystals with hexagonal needled arms and pyramid tip arms were first reported. Oxygen concentration is deemed as the critical experimental parameter for the formation of different morphologies of ZnO nanostructures. EDS and PL measurements show that the ZnO nanocrystals with hexagonal cylinder arms and pyramid tip arms have high stoichiometric proportions and good crystal qualities, while the ZnO nanocrystal with hexagonal needled arms has a low stoichiometric proportion and relatively poor crystal quality. Annealed in oxygen ambient can slightly improves the crystal quality of the ZnO nanocrystal, while annealed in air and vacuum ambient, its crystalline quality deteriorates.
2. A series of quasi-aligned ZnCdO single-crystal nanorods with different Cd content were prepared for the first time by using thermal evaporation of Zn and CdCl2 on Si substrates with the presence of Au catalyst. The maximum Cd content was up to about 16.7 at. ％, which was significantly larger than the thermodynamic solid solubility limits. Notably, with the Cd content increasing,the ultraviolet (UV) near-band-edge (NBE) emission was red-shifted to 407 nm(3.04 eV) from 386 nm (3.21 eV). The direct modulation of band gap caused by Cd substitution is responsible for the red shift.
3. Raman spectrum revealed that the E2 (high) mode of the ZnCdO nanorods with Cd content of 16.7 at. ％ shifted toward the higher frequency side by 5 cm-1 with respect to that of pure bulk ZnO, corresponding to biaxial compressive stress of 1.14 GPa. The near-band-edge (NBE) emission of ZnCdO red-shifted to 3.04 eV due to Cd substitution. The defect-related emission exhibited anomalous phonon replicas with an energy of 102 meV, which provides a valuable way in current effort to realize the ZnO-based optoelectronic nano-devices.
4. Temperature-dependent PL spectra of the ZnCdO nanorods with Cd content of 16.7 at. ％ show that each spectrum displays an intense near-band-edge (NBE) emission around 3.1 eV, as well as a weak defect-related band around 2.5 eV. At low temperatures, the NBE band consists of three peaks at 3.23, 3.16, and 3.06 eV.From time-integrated and time-resolved PL analyses, we suggest that the peak at 3.06 eV is associated with carriers localized at potential minima induced by Cd spatial inhomogeneous distribution in ZnCdO alloys. The peak at 3.16 eV is attributed to the excitonic emission of ZnCdO while the peak at 3.23 eV is ascribed to bound excitons in ZnO.
5. Ternary ZnCdO single-crystal bramble-like nanostructures with a Cd incorporation of about 6.7 at. ％ were synthesized on Au nanoparticle-deposited Si substrate by vaporizing the mixture of Zn and Cd powder under controllable condition. The super-saturation oxygen concentration plays an important role for the formation of the bramble-like ZnCdO nanostructures.