A Study on Applications in Field Emission of Carbon Nanotubes : Growth Mechanism and Purification

• Main Authors: Zhen-Yu Juang, 莊鎮宇
• Other Authors: T. S. Lai
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/16105515999935621840

碩士 === 中原大學 === 物理學系 === 87 === Using graphite as our electrodes of cathode and anode, bulk CNTs （carbon nanotubes） are fabricated by the arc-discharge method under 500 mbar static pressure of helium. The voltage and current applied during the fabrication are 20 — 30 V and 150 A, respectively. We then carried out several measurements of the bulk and the powder, which was gathered from the bulk, after various treatments. Owing to the coexistence of C60 and CNT, coupled with the growth model of C60, we first point out the role of C20 in the production of CNTs. The cross-sectional observation of the fabricated CNT shows that, inside the outer shell of graphite, a double-decked structure of the bulk CNT was observed, kind like a sushi. FESEM （field emission scanning electron microscope） and field emission measurements show that, the outer part of the bulk CNT has a better quality than the center part of the bulk CNT. The radiation image of the bulk CNTs also demonstrates this behavior. A growth mechanism of the CNTs produced by the arc-discharge method was proposed. The double-decked structure of the bulk CNT is closely related to the distributions of the bulk temperature （or current density） and the carbon ions density. Consequently, the observed double-deck structure of the bulk CNT provides an indirect evidence of the distribution of the carbon ions in the arc. Meanwhile, the proposed growth mechanism enables us to predict the longitudinal distributions of the bulk CNT, which was supported by the experimental results. By using ultrasonic wave, via the different specific weight between different carbon structures, we develop a new method of purification of the CNT powder. After the purification, the purity of the CNT powder could be doubled through the observations of FESEM, also, the purification effectively reduce the turn on field to 0.95 V/μm. It was changed about 15% — 25% after purification.