Abstract
A Study of the Growth Mechanism of Carbon Nanotubes and its Applications for the Electrodes of Micro-EDM Polishing Process Ph. D. student：Hsin-Yuan Miao Advisors：Dr. Min-Shen Ouyang Dr. Juh-Tzeng Lue Department of Engineering and System Science National Tsing Hua University Abstract Key words：carbon nanotubes、field emission properties、chemical vapor deposition (CVD)、micro electric discharge machining (micro-EDM)。 In this work we attempt to design and to fabricate the new one dimensional material – carbon nanotubes (CNTs) in a flourish way, and to investigate whether it is suitable for industry applications. The main thrust of this research is to develope a new growth process that results in a fertile CNTs for the exploitation of surface modification by the electric discharge. First of all, we have developed a growth chamber equipped with facilities that can produced the well-aligned CNTs on the different substrate. Then, to utilize the properties of high rigidity and field emission of CNTs, and to combine with the idea of micro electric discharge machining (micro-EDM), it is to expect that making CNTs could as the tool electrode for precise surface polish. The steps of this research are： (1) Carbon nanotubes(CNTs) are successfully grown on alloys made of iron groups and metals by a microwave enhanced hot-filament method with the radio-frequency (rf) field induced self-bias. A precursor of hydrogen etching to produce catalyst nanoparticles on substrate surface is crucial for the CNTs growth. Exploiting bulk-alloy catalysts such as Cu-Ni, Cu-Fe, Cu-Co, and Cu-Ni-Fe-Co for substrates instead of using usual thin film catalysts on Si substrates enunciates a new growth mechanism which debates to the mechanism of dissolving carbons in eutectic nanoparticles and then precipitating graphite near the contact surface of the particle and the substrate. (2) Bunched and multi-circularly wrapped carbon nanotubes (CNT) are observed to grow on alloy substrates based on iron group metals and copper by a microwave enhanced hot-filament method with a dilute gas of ammonia at a proper RF self-bias. The grown size of CNTs embodied in the grain sizes of conducting bulk alloy catalysts such as Cu-Ni, Cu-Fe, Cu-Co, and Cu-Ni-Fe-Co are controlled by a precursor time of hydrogen plasma etching. Species with different structural features and homogenization of CNTs samples are produced crucially attributed to various reactant gases and self-bias induced by the radio frequency field. (3) In this work a miniscule electrode for pursuing the precise surface modification by exploiting multi-wall carbon nanotubes (MWCNT) as the discharge electrodes was studied. The excellent upright growth of carbon nanotubes on copper based alloy substrate by a radio frequency (RF) assisted hot filament chemical vapor deposition (HFCVD) method suggests us to implement MWCNTs as the miniature electrodes for discharge machining. The results reveal that the spoiling rates for the un-polishing of n-type Si wafer ( 10~100 Ω-cm) can up to 30 nm/min with the electrodes to be much endurable to be distorted. It is expected that that MWCNTs can be applied to non-conventional material processing especially in miniature discharge machining.