Parametric Study of Single-Walled Carbon Nanotubes Using Alcohol Catalytic Chemical Vapor Deposition
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Parametric Study of Single-Walled Carbon Nanotubes Using Alcohol Catalytic Chemical Vapor Deposition H. Emrah Unalan and Manish Chhowalla Ceramic and Materials Engineering Department, Rutgers University Piscataway, NJ 08854 ABSTRACT Single-walled carbon nanotubes (SWNTs) were synthesized both in powder form and on substrates using alcohol catalytic chemical vapor deposition method (ACCVD). A detailed parametric study was conducted. As-grown SWNTs were analyzed using transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. Nucleation and growth of SWNTs occurred within seconds after introduction of the alcohol vapor. The results show that high quality SWNTs with a narrow diameter distribution without amorphous carbon can be grown using Co acetate catalyst doped with Fe acetate above 750°C. Defective nanotubes were observed at low (450°C) and high (950°C) temperatures with the optimum temperature being 850°C. In brief, our work has taken a step towards optimizing SWNTs growth conditions using ACCVD. INTRODUCTION The unique structural, mechanical, and electrical properties of single-wall carbon nanotubes (SWNTs)1 have rendered these structures highly appealing for investigators. The field of nanotube research is reaching maturity through demonstration of opto-electronic devices, field effect transistors, and sensors. One of the major obstacles to SWNT devices is the absence of control over the chirality during growth which determines their electronic and optical properties2. Different methods have been employed for the synthesis of SWNTs such as alcohol catalytic chemical vapor deposition (ACCVD) 3. However, no detailed parametric study of this method has been undertaken. In this work, we present a detailed analysis of the growth properties of SWNTs as a function of growth time, deposition temperature, alcohol flow rate, type of alcohol (i.e. ethanol versus methanol) and catalyst concentration (Fe:Co acetate ratio) to further emphasize their effect on the properties of SWNTs. EXPERIMENTAL DETAILS In the ACCVD method, alcohol vapor (either ethanol or methanol) is used as the carbon source and metal acetates (mixture of Fe and Co-acetate) dissolved in water or alcohol were used as the catalyst materials. Heating the acetates to growth temperature (450°C – 950°C) leads to elimination of the organic layer, creating pure nano-sized catalyst particles which can be used for growth of SWNTs. The SWNTs were grown on a catalyst support bed (such as MgO) and on substrates. Acetates were dissolved in solvent and solution was drop casted onto the MgO bed. The dip coating method was applied to substrates. The growth method is similar to the one described in Ref 4. except for the reduction step. MgO powder supported with catalyst particles were placed into alumina boats whereas a graphite stage was used to support the substrates. One inch quartz tube vacuum furnace was used for growth. The chamber was first evacuated to 150
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