The effects of oxidizers on the diameters of the carbon naotubes grown by chemical vapor deposition method

Abstract

This thesis was focused on growing high quality and small-diameter carbon (C) nanotube (NT) on Fe/Al2O3/SiO2/Si thin film catalyst by ethylene decomposition thermal chemical vapor deposition (CVD) method in the presence of a weak oxidizer (CO2). Moreover, the importance and functional properties of the oxidizer in pretreatment and CNT growth were determined. At first, it was worked in different growth conditions to examine the effects of CO2 in CNT growth. The main parameters were pretreatment time, CO2 gas flow rates during pretreatment and growth, growth temperature. Pretreatment and growth times were kept at 15 min. each and CO2 introduced 5 and 10 min. during pretreatment stage prior to the CNT growth with the flow rates 8:2, 10:2, 10:8 and 10:10 sccm, respectively. Additionally, three different growth temperatures; 750 oC, 760 oC and 770 oC were studied. Secondly, pretreatment time was kept at 15 min. The effects of CO2, which was sent in the system at 8:2, 10:2, 10:8 and 10:10 sccm ratios, on density and height of the catalyst particles were investigated. At last, all catalyst particles and CNTs obtained from the experiments were analyzed by several characterization techniques such as AFM, EDX, SEM, STEM and Raman Spectroscopy, respectively. The optimal values of amount and introduction time of CO2, the ratio of CO2 in growth to that in pretreatment were identified. Moreover, the relation between currently obtained catalyst particles and previously being grown CNTs on them were determined. It was observed that using the appropriate amount of CO2 in pretreatment and growth process positively affected the catalyst sizes and CNT diameter distributions.