Support Controlled Catalytic Chemical Vapor Deposition of Carbon Nanotubes
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1017-DD01-04-EE01-04
Support Controlled Catalytic Chemical Vapor Deposition of Carbon Nanotubes Yunyu Wang1, Bin Li1, Zhiquan Luo1, Li Shi1, Zhen Yao1, Eugene N Bryan2, Robert J Nemanich3, and Paul S Ho1 1 The University of Texas at Austin, Austin, TX, 78712 2 North Carolina State University, Raleigh, NC, 27595 3 Arizona State University, Tempe, AZ, 85287 ABSTRACT Carbon nanotubes (CNTs) have been grown by catalytical chemical vapor deposition (CCVD) with a thin iron layer as the catalyst. High surface tension metal, tantalum (Ta), and low surface tension, SiO2, have been deposited as the supporting layers before depositing the catalysts. SEM, TEM, STEM and EELS have been used to examine the morphology, structure, and chemical profile of iron nanoparticles and CNTs. The results have shown that the catalyst nanoparticle morphologies were distinctly different on two supports. In particular, Fe nanoparticles on SiO2 were found to follow a Vollmer-Weber (VW) growth mode and a StranskiKrastanov (SK) growth mode on Ta. It was also found that CNT growth varied significantly on two supports in terms of morphology, growth rate and growth mode. Dense CNTs were grown on Ta with fast growth rates (> 1µm/min) and vertical alignment for the iron thicknesses of 1.5-9 nm. In contrast, CNTs grown on SiO2 exhibited a slow growth rate (< 100 nm/min) with all deposited iron thicknesses, indicating a severe catalyst poisoning. The results suggested that the catalyst morphology in combination with the presence of an iron wetting layer contributed to the enhanced CCVD growth of CNTs on Ta. INTRODUCTION There are tremendous interests in utilizing CNTs as components of the next-generation microelectronic devices such as transistors, sensors, field emitters and interconnects. However, stringent requirements such as the uniformity, phase purity (chirality), mechanical strength (for CNT films) restrict the application of CNTs in abovementioned devices. For instance, CNTs have shown a remarkable current carrying ability (>109-11A/cm2) [1] and high thermal conductivity [2]. These make them a promising candidate to replace copper as the future interconnect via structure material. However, the low compressive modulus of CNT films [3] makes the CNT via structure mechanically weak, and reinforcement by either filling metals or insulating materials has to be implemented to solve this problem [4]. Besides the film modulus, other properties and structure of CNTs depend greatly on the growth process. Thus, in order to put CNTs into practice, various factors on CNT growth have to be carefully controlled and the microscopic growth mechanism of CNTs has to be fully understood. Significant progress has been made on CNT growth in the last 15 years since its discovery, and the CNTs with controlled orientations, tube diameters, area densities, film thicknesses, and low growth temperatures have already been obtained. Recently, with the motivation to keep increasing the CNT yield as well as controlling SWNT chirality, vast research
on CNT growth has focused o
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