Growth Mechanism and Characterizations of ZnO Nanowires

• Main Authors: Fu-chun Tsao, 曹福君
• Other Authors: 紀國鐘
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/66875570945602175270

博士 === 國立中央大學 === 物理研究所 === 95 === In this thesis, the growth mechanism, morphology, structure, and optical properties of the ZnO nanowires grown by chemical vapor deposition (CVD) under different growth conditions were investigated with different growth condition. For ZnO nanowires grown on Si (100) and sapphire, the growth mode is Volmer-Weber mode (VW-mode) due to the large lattice misfit (>30%) between ZnO and substrate. We observed the island-like nanostructures at the bottom of the ZnO nanowires with random direction. The ZnO nanowires grown on GaN template were vertically well-aligned with 1-μm-thick wetting layer. Thus, the growth mode is attributed to the Frankvan der Merwe mode (FdM mode). The ZnO nanowires grown on the GaN template have preferred growth orientation along the c-axis. Photoluminescence (PL) spectrum exhibits only the near-band-edge (NBE) emission without defect-related deep-level emission at room temperature (RT). Characteristics of ZnO nanowires grown with and without employing Au as catalyst are studied. The density of the ZnO nanowires grown with catalyst is 1000 times than that of ZnO nanowires without catalyst. The ZnO nanowires grown with and without Au catalyst can be attributed to the vapor-liquid-solid (VLS) method and vapor-solid processes, respectively. PL spectrum of ZnO nanowires grown with Au catalyst exhibits a strong defect-related deep-level emission. It demonstrated that the ZnO nanowires grown with Au catalyst causes lots of defects in the ZnO nanowires. Size-dependent ZnO nanowires are studied. The diameter is from 37 to 250 nm. From X-ray diffraction results,there exists a tensile strain, along the c-axis, increases with decreasing the diameter of ZnO nanowires. From RT-PL spectrum, the peak of NBE emission shifts to higher energy with decreasing in the diameter of ZnO nanowires. The energy shift could be due to the surface-to-volume ratio effect with different diameter of ZnO nanowires