Growth and Characterization of Magnetic Nanostructures on Carbon Nanotube Templates
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Growth and Characterization of Magnetic Nanostructures on Carbon Nanotube Templates Yihong Wu, Peiwen Qiao, and Towchong Chong Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 and Data Storage Institute, 5 Engineering Drive 1, Singapore 117608
ABSTRAT We describe the growth of magnetic nanostructures on carbon nanotube templates. The nanotubes were grown by microwave plasma enhanced chemical vapour deposition. The as grown nanotubes were aligned reasonably well around the substrate normal directions. Although the nanotubes were quite straight, there were still some bent and tilt as revealed by the scanning electron microscope observations. Magnetic field has been used to re-align or re-assemble the nanotubes before they were used as the templates to grow magnetic nanostructures. Depending on whether there is a magnetic particle on the top tip of each nanotube and the density of the nanotubes, there are two different consequences of applying a magnetic field to the nanotubes. For nanotubes with magnetic particles attached to their top tips, the post-growth treatment by the magnetic field resulted in re-assembly of the nanotubes into micro-umbrella type of structures. For those without magnetic particles, however, the effect of magnetic field treatment is negligible; but after the deposition of thin magnetic layers, the field treatment made the nanotubes much straighter than what they originally were and aligned almost vertically to the substrates. The re-aligned or re-assembled nanotubes were used as the templates to grow magnetic nanostructures. It was found that most of the magnetic nanostructures exhibited characteristics similar to those of magnetic nanowires.
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INTRODUCTION Since their discovery, carbon nanotubes have attracted much attention due to their unique chemical, mechanical, and electrical properties that may find important applications in nanoscale devices with new performance and functionality [1-13]. In addition to applications as active elements of functional devices, they can also be used as templates to grow other type of nanostructures. Due to the ever increasing demand for bit size reduction in magnetic recording, there is a tremendous interest in the fabrication, characterization, and understanding of the fundamental physics of magnetic nanostructures, which may eventually lead to novel information storage materials and devices. There are several ways to fabricate magnetic nanostructures. These include conventional lithography, self-assembly, energy beam induced recrystallization, nano-printing, template-based technique, and many others. In this work we have employed the template-based technique to growth magnetic nanostructures on carbon nanotube templates [14]. GROWTH OF CARBON NANOTUBES The nanotubes used in this study were grown using microwave plasma enhanced chemical vapor deposition (MPECVD) [6-13]. The reaction gases used were mixtures of methane and hydrogen with a flow rate ratio of 1 to 4. The growth
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