| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 90 === ABSTRACT
For potential applications as the insulated alloy nano-wires, this work was planning to examine the feasibility of filling the alloy in carbon nanostructures using alloy oxides as catalysts and to study their growth mechanisms. The alloy-contained carbon nanostructures were synthesized on Si wafer by microwave plasma chemical vapor deposition (MPCVD) using CH4 and N2 as source gases and alloy oxides (Co2NiO4 and CoPdO2) as catalysts. The pure metal coatings (Co, Ni and Pd) on Si wafers were prepared by physical vapor deposition. The coated substrates were followed by oxidation in air furnace to form alloy oxides coatings. The alloy oxide-coated substrates were then pretreated in hydrogen plasma atmosphere to become nano-islands to act as catalysts for nanostructure growth. The alloy oxide-assisted nanostructures were characterized by AFM, SEM, TEM, XRD, EPMA, EDX, Raman spectroscopy and field emission J-V measurement.
The results show that the alloy-filled carbon nanostructures can be obtained by using CoPdO2 as the catalyst instead of Co2NiO4. Where the CoPdO2-assisted nanostructures are tip-growth CNTs or nano-particles, and the Co2NiO4—assisted nanostructures are base-growth CNTs. The results also indicate that the key parameters governing the nanostructures are catalyst materials, hydrogen plasma pretreatment time and deposition temperature. Effect of hydrogen plasma pretreatment time is essentially to prolong the agglomeration effect on the nano-islands of catalyst. Therefore, longer pretreatment time favors a larger island size to form alloy-filled CNTs. Effect of deposition temperature is basically similar to effect of hydrogen plasma pretreatment time. A high deposition temperature favors a higher fluidity of catalyst to fill into the tubes by capillary force.
On field emission properties, the results show that the alloy-filled CNTs have no significant field emission. The turn-on voltage of the CNTs without filling alloy is about 4.8 V/m defined at current density of 1 A/cm2. It is also interesting to note that there are no bamboo-like CNTs in the present conditions, though the presence of N were often reported to be the main parameter to form bamboo-like CNTs.
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