| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 88 === This thesis combines electrochemistry and microwave plasma techniques to prepare carbon-based nanomaterials on various substrates.
Aligned amorphous carbon nanotubes on porous anodic alumina have been synthesized successfully by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using the precursor gases, acetylene and argon. The composite film, with the aligned amorphous carbon nanotubes embedded in the porous anodic alumina, was found to be robust and is expected to have potential application in optic, electronic and optoelectronic devices. It is possible to prepare a large area of such a film by taking advantages of the ECR-CVD process, e.g., high plasma density at low temperature, less ionic damage, contamination-free and high deposition rate. By adjusting the pore size of anodic alumina, amorphous carbon nanotubes of various diameters can be produced in a range from 230 nm down to 30 nm.
Carbon nanofiber films were for the first time synthesized on metallic nanowire array composites using a microwave plasma enhanced chemical vapor deposition (MPECVD) system with a mixture of methane and hydrogen. The results were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and showed that the diameters of carbon nanofibers were of 40-60 nm. This indicates that nickel nanowires not only serve as catalysts to decompose the hydrocarbons and to form carbon nanofibers but also can be functioned as an electrical conductor for other advanced applications. The electron field emission of carbon nanofibers took place at fields above 1.5 V/μm with an observed emission current density up to 1 mA/cm2 at 3 V/μm. This result suggests that carbon nanofiber films are promising candidates for field-emission devices.
Moreover, aligned carbon nanotubes with open ends have been also fabricated on silicon wafer in one step using the MPE-CVD system with a mixture of methane and hydrogen as precursors. High concentration hydrogen plasma and high negative bias voltage to the substrate induce anisotropic etching of carbon nanotubes and can effectively reduce the randomly oriented carbon nanotubes. The mechanism of aligned carbon nanotubes with open ends is proposed in this thesis.
Carbon-encapsulated Ni3Sn2 nanoparticles have been fabricated on silicon wafer by MPE-CVD process, too. The result reveals that pure carbon-encapsulated metal nanoparticles have been exclusively formed without any other carbon nanostructure (e.g. nanotubes or nanofiber) existence. The growth mechanism of carbon-encapsulated metal nanoparticles is also proposed.
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