Carbon nanotube growth from nanoscale clusters formed by ion implantation
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Carbon nanotube growth from nanoscale clusters formed by ion implantation Yongho Choi1, Jennifer Sippel Oakley2, Andrew Rinzler2, and Ant Ural1 1 Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611, U.S.A. 2 Department of Physics, University of Florida, Gainesville, FL 32611, U.S.A
ABSTRACT We have demonstrated that iron ions implanted into silicon dioxide thin films form nanoscale clusters which can act as catalyst for carbon nanotube growth. We have implanted iron ions with an energy of 60 keV and three different doses (1014, 1015, and 1016 cm-2) into silicon dioxide thin films thermally grown on silicon substrates. We then used chemical vapor deposition (CVD) to grow carbon nanotubes on these ion implanted substrates with methane as the precursor gas. We studied the effect of ion implantation dose on the structural properties of the nanoscale clusters, as well as the carbon nanotubes nucleated from these clusters. The nanoscale clusters and grown nanotubes were characterized by Atomic Force Microscopy and Raman spectroscopy. The electrical characteristics of the as-grown nanotubes were also characterized. We found that growth of low density, horizontal, and small diameter carbon nanotubes on silicon dioxide is possible using this nucleation technique.
INTRODUCTION AND BACKGROUND Carbon nanotubes (CNTs), which have attracted a significant amount of research attention in recent years, are promising nanoscale materials as building blocks for new electrical, mechanical, chemical, and biological devices and sensors [1-3]. Carbon nanotubes are unique among solidstate materials in that they can be either metallic or semiconducting depending on their geometrical structure. [4] Nanotubes are generally produced by three main techniques: arc discharge, laser ablation, and chemical vapor deposition (CVD) [5,6]. CVD is a very attractive method to synthesize carbon nanotubes for several reasons: (1) CVD produces pristine, defectfree, and high quality nanotubes without any by-products such as amorphous carbon, (2) It requires no post-growth processing, such as purification, sonication, or filtering, (3) It is scalable to larger substrates and wafer sizes, and (4) It is compatible with silicon microfabrication technologies. The CVD growth technique requires catalyst nanoparticles placed on a substrate for nucleating the growth of carbon nanotubes. The size of these catalyst nanoparticles influences the diameter of the CVD-grown nanotubes [7]. Typically, transition metal nanoparticles, such as nickel, iron, or cobalt, are used as catalyst. One of the fabrication issues is that this catalyst material is typically deposited from liquid solution. In order to control the origin of nanotubes, this catalyst needs to be patterned by lithography. However, it is not possible to pattern liquid based catalyst into very small dimensions and over high aspect ratio topography. In this work, we used ion implantation, a well-established technique in silicon microfabrication [8], and s
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