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Fabrication of High-Density Carbon-Nanotube Coatings On Microstructured Substrates Zheng Chen Space Power Institute, Auburn University, AL 36830, USA e-mail: [email protected] Yonhua Tzeng and Chao Liu Department of Electrical and Computer Engineering Auburn University, AL 36830, USA e-mail: [email protected] ABSTRACT Fabrication and characterization of carbon nanotubes deposited on microstructured Ni substrate are presented. The highly active surface-area of the microstructured Ni substrate provides highdensity nucleation sites for carbon nanotubes. Coated fine Ni powder also serves as a catalyst for the nanotube growth. Hydrocarbon mixtures were used as the carbon source for the chemical vapor deposition process. Carbon nanotubes deposited on the microstructured Ni substrate were examined by SEM. An ultra high vacuum chamber was used to characterize the field emission properties of carbon nanotube coatings. INTRODUCTION Carbon nanotube (CNT) 1-3 has excellent properties due to its form, which is a tubular form of carbon with a diameter in the range of 1nm to several tenth micrometers. CNT exhibits extraordinary high Young's modulus and tensile strength. It is stiff as diamond. CNT also can have better electrical conductivity than other forms of carbon due to its graphite structure. In addition, CNT has large surface area and high aspect ratio. With these excellent properties, CNT has been found in many applications, such as cold field emitters, electronic device, sensors, energy storage, and mechanical reinforcements for high strength composites. CNT has been successfully grown by several techniques (e.g. chemical vapor deposition CVD and laser ablation) in many laboratories. The size of CNT is in the range of a few to hundred nanometers in diameter and several microns long. The problem to hinder CNT for many practical applications is the slow growth rate, high cost, limited deposited size, weak interface bonding between CNT and substrate, and inability to synthesis CNT with control on the shape and size. Intention of the present investigation is to explore an alternative method to accelerate the CNT growth rate and to improve the control on the bonding strength and growth sites. The approach implemented in this research is to carefully engineer the substrate for CNT growth. The highly active surface of the microstructured Ni substrate provides high-density nucleation sites for CNT and the chemical coated substrate serves as a catalyst for the nanotube growth. SEM and the field emission experiment were used to evaluate the quality of the CNT.

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EXPERIMENTS Ni foil with 5 mil thickness was prepared as substrate through a micro-structuring process* on the surface of the foil to increase its surface area (figure 1). The substrates then were coated with metallic catalysts (e.g. Ni based powder) to enhance the growth rate. The substrates were loaded on a substrate holder in the quartz tube that was then pumped down and subsequently purged with carrier gases such as nitrogen or argon. A resistive heatin