| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 92 === Abstract
Self-assembled Ag particles on Si0.8Ge0.2 and the growth of ZnO nanowires have been investigated.
Self-assembled method is utilized for the formation of surface structure of Ag nanoparticles on Si0.8Ge0.2. The surface reaction was induced in a furnace with N2 flowing. The resulting surface structure of Ag on SiGe was characterized by scanning electron microscopy (SEM), energy dispersion spectrometer (EDS), and transmission electron microscopy (TEM).
Ag atoms were observed to segregate to the node points of the honeycomb structure after annealing at 800 °C for 90 min. It was found that the Ag particles gradually sank into SiGe substrate. Small particles were found to permeate faster than large particles. Cross-sectional TEM image showed that there is an oxide film covering Ag particles. Small particles are sometimes embedded in the oxide layer. The observation indicated that Ag did not react with SiGe to form compounds. The formation of an oxide layer was found to stabilize the Ag particles.
The growth of ZnO nanowires was found to depend on the catalysis of Au particles. Factors such as ZnO/C ratio, temperature, growth time, pressure of O2, amount of Zn vapor and catalyst, have been varied to investigate their effects on the growth. The resulting nanowires were characterized by SEM, TEM, and high-resolution transmission electron microscopy (HRTEM).
The quantity of ZnO and C affects the concentration of Zn vapor to grow. A high concentration of Zn leads to faster growth. The nanowires were grown via a vapor-liquid-solid growth mechanism. ZnO nanowires grew in length with holding time. For low gas flow, the nanowires were grown under low supersaturation.
For samples prepared with ZnO/C ratio equaling 1 (3.33 g ZnO and 0.5 g C), the temperature 690 °C, holding time 90 min, a constant flow of Ar (25 sccm) and O2 (5 sccm), P equaling 1.5 Torr, with deposited Au as catalyst, ZnO nanodrills were grown on the substrate. The nanodrills are about 10 to 150 nm in average diameter and 1 to 2 micrometers in length. From the HRTEM image of ZnO nanodrills, core-shell structure is evident in the sample. The core and shell were found to be ZnO and Zn. No amorphous material is present at the interface. The results clearly showed that the concentration of Zn affects the growth rate to produce different kinds of ZnO nanowires.
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