Controlled Assembly of Carbon Nanotube Fibrils by Dielectrophoresis
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Controlled Assembly of Carbon Nanotube Fibrils by Dielectrophoresis J. Tang1,2, G. Yang1, J. Zhang1, H.Z. Geng3, B. Gao1, O. Velev4, L.-C. Qin1,3, O. Zhou1,3 1
Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599, U.S.A. 2 National Institute for Materials Science, Tsukuba, Japan 3 Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, NC 27599, U.S.A. 4 Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695, U.S.A.
ABSTRACT Although advances have been made in the synthesis of raw carbon nanotube (CNT) materials, the lack of efficient processes for assembly and integration of CNTs into functional forms has hindered the development of CNT-based devices. Here we report a dielectrophorestic method to manipulate, align and assemble CNTs into onedimensional nanostructures using an alternating-current electric field. Pre-formed CNTs dispersed in water are assembled into micro-electrodes and sub-micron diameter fibrils with variable lengths from 1 µm to over 1 cm. The CNTs within the fibril are bonded by van der Waals forces and are aligned along the fibril axis. This method affords fine control of the fibril length and is capable of parallel fabrication of multiple fibrils using the same material source. The short CNT fibrils can potentially be used as probes for scanning probe microscopes and the long ones as electrodes or conducting nanowires. INTRODUCTION Carbon nanotubes (CNTs) have unique material properties that are promising for a wide range of technological applications. Carbon nanotubes are an extraordinary onedimensional (1D) material and have large aspect ratios, very small diameters, excellent mechanical and electronic properties. These properties enable faithful imaging of deep trenches while good resolution is retained. Since carbon nanotubes elastically buckle rather than fracture when deformed, they can make highly robust probes [1]. CNTs can also be modified at their ends with specific chemical or biological groups for high resolution functional imaging [2]. It has been demonstrated that the resolution and probing depth of a scanning probe microscope (SPM) can be significantly increased by using a CNT probe [3]. There are also considerable interests in fibers, composites, and microelectrodes based on 1D nanostructures [4, 5]. An important step towards the eventual utilization of this novel material is to design high throughput bottom-up processes for assembly of higher-level structures which is currently lacking.
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EXPERIMENTAL The starting materials are short single-walled carbon nanotubes (SWNTs) or multiwalled carbon nanotubes (MWNTs). Single-walled carbon nanotube bundles were synthesized by laser-ablation, purified to remove the impurity phases and processed to shorten the bundles by sonication in an acid solution. The final product has about 90% SWNTs, bundle diameter 30 ~ 50 nm, and bundle length 0.5 ~ 4 µm with individual tubule diameter ~ 1.4 nm, as shown in Fig. 1(a). Multi-wa
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