The Effects of Catalyst Grain Sizes on the Diameter of MPECVD Grown Patterned Carbon Nanotubes
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The Effects of Catalyst Grain Sizes on the Diameter of MPECVD Grown Patterned Carbon Nanotubes S. G. Wang, Qing Zhang, G. F. Zhong 1, S. F. Yoon, J. Ahn, D. J. Yang Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. 1 Center Of Excellence, Waseda University, 513 Tsurumaki-cho Waseda Shinjuku-ku Tokyo, Japan, Zip 162-0041,Japan. ABSTRACT The electronic structure and properties of carbon nanotubes (CNTs) strongly depend on their diameter and chirality. The well controlled CNTs diameter is becoming one of the challenges for their applications in microelectronics. In this paper, the patterned CNTs were produced by microwave plasma enhanced chemical vapor deposition technique using a metal catalyst of nickel. The correlation between the CNT diameter and the grain sizes of the nickel catalyst was examined. The experimental results show that nickel films converted to nickel particles when they were heated up. The diameter of CNTs increases with increasing grain sizes of the nickel particles, indicating that the CNT diameter can be controlled by controlling the grain sizes of the nickel catalyst.
INTRODUCTION Carbon nanotubes (CNTs), which were initially discovered by Iijima [1], have attracted a great deal of attention due to their unique structure and properties and would be potential candidates for applications in field effect transistor, sensors and electron field emitters [2-4]. Early studies have shown that the electronic structure and properties of CNTs strongly depend on their diameter and chirality [5,6], which can determine if a CNT is semiconducting or metallic. It has also been reported that the diameter of CNTs affects the gate effect and electron field emission properties when they are employed in carbon nanotube based field effect transistors [2,7] and electron field emission sources [8-10], respectively. Therefore, it is becoming increasingly apparent that one of the challenges for microelectronic applications is the growth control of CNTs, which includes that the diameter, length and density of CNTs can be well controlled in the process of their growth. Many efforts have been made for this purpose and some progresses are encouraging [11-14]. However, the growth mechanisms are still under argument. And fewer papers were reported on the diameter control for patterned CNT growth. In this paper, we present diameter control in patterned CNT growth. The patterned CNTs were produced by microwave plasma enhanced chemical vapor deposition (MPECVD) technique using a nickel catalyst. The growth mechanism of CNTs is also discussed.
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EXPERIMENTAL The patterned CNTs were grown on silicon substrates by MPECVD using an ASTeX microwave enhanced plasma system. Prior to CNT growth, the nickel
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