Growth of Carbon Nanotubes Using Uniformly Distributed Cobalt Nanoparticles as Catalyst: Controlled Growth and Structura
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Growth of Carbon Nanotubes Using Uniformly Distributed Cobalt Nanoparticles as Catalyst: Controlled Growth and Structural Characterization
Yoon Huh, Jeong Yong Lee*, Sang Kyu Choi1, and Cheol Jin Lee1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea * E-mail: [email protected] 1 Department of Nanotechnology, Hanyang University, Seoul 133-791, Republic of Korea ABSTRACT We have controllably grown carbon nanotubes using uniformly distributed cobalt nanoparticles as catalyst. Cobalt nanoparticles with a uniform size were synthesized by chemical reaction and colloidal solutions including the cobalt nanoparticles were prepared. The cobalt nanoparticles were uniformly distributed on silicon substrates by a spin-coating method. Carbon nanotubes with a uniform diameter were synthesized on the cobalt nanoparticles by thermal chemical vapor deposition of acetylene gas. The density and vertical alignment of carbon nanotubes could be controlled by adjusting the density of Co nanoparticles. INTRODUCTION Since S. Iijima discovered carbon nanotubes (CNTs) in 1991 [1], CNTs have attracted much interest, which may lead to many potential applications due to their unique mechanical and electrical properties [2,3]. One of key factors for growth of CNTs using thermal chemical vapor deposition (CVD) is transition metal as catalyst. To obtain controlled or aligned CNTs using CVD method, it is necessary to control the size and density of metallic nanoparticles on a substrate. The metallic nanoparticles, which serve as catalyst for CNT growth, should be formed from metal layer with a shape of thin film [4-9], by pre-treatment processes such as ammonia etching [4-7] or thermal annealing [8,9]. Even though the size of the catalytic nanoparticles is varied with the thickness of metal film and the conditions of pre-treatment, the nanoparticles are distributed with a wide range of size, resulting in the growth of CNTs with a non-uniform diameter. The uniform distribution of the catalytic nanoparticles on substrate surface is crucial to the synthesis of CNTs with a uniform diameter. For various applications of CNTs, the controlled growth of the CNTs with a uniform diameter should be attained. In our work, CNTs were controllably grown using uniformly distributed cobalt (Co) nanoparticles as catalyst. The Co nanoparticles with a uniform size were synthesized by thermal decomposition process and colloidal solutions were prepared by dispersing the Co nanoparticles
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in toluene. We employed a spin-coating method for uniform distribution of the Co nanoparticles on silicon (Si) substrates. The density of Co nanoparticles was controlled by adjusting the molar concentration of the colloidal solutions. CNTs with a uniform diameter were synthesized on the Co nanoparticles by thermal CVD of acetylene (C2H2) gas. We demonstrated that the density and vertical alignment of CNTs could be controlled by adjusting the density of Co nanoparticles. We investiga
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