Dielectrophoretic Deposition of Carbon Nanotubes with Controllable Density and Alignment
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1057-II15-07
Dielectrophoretic Deposition of Carbon Nanotubes with Controllable Density and Alignment Jason Moscatello, Vijaya Kayastha, Archana Pandey, Benjamin Ulmen, and Yoke Khin Yap Department of Physics, Michigan Technological University, 118 Fisher Hall, 1400 Townsend Dr., Houghton, MI, 49931 ABSTRACT Controlled deposition of carbon nanotubes (CNTs) across desired electrodes is important for the fabrication of nanoelectronic devices. Dieletrophoresis (DEP) has been recognized as a convenient and affordable technique for the deposition of nanotubes and nanowires on electrodes. Although DEP has been quite well studied for dielectric particles, the application for depositing nanotubes is still at the early stage of development. Here, we show that multi-walled CNTs can be deposited by DEP with controllable density and degree of alignment. INTRODUCTION Carbon nanotubes are a popular nanomaterial due to their unique structural and electronic properties. These characteristics have facilitated their use in a wide array of devices and applications such as field effect transistors [1-5], chemical and biological sensors [6,7], scanning probe microscopy tips [8 - 10] and field emitters [11, 12]. However, before we can begin to take advantage of the desirable the properties of CNTs, they must be placed in the proper position for each application. Techniques do exist for placement of CNTs, but each comes with its own associated drawbacks. Spin coating of nanotubes, for example, is cheap and simple, but lacks control of position and distribution [5, 13]. Direct growth requires high temperatures and suffers from poor selectivity and non-compatibility [14, 15], while manual attachment is unviable for devices of any significant density due to the enormous amount of time necessary to place individual CNTs. A technique does exist that is quick, cheap and results in well-aligned tubes. This technique, called dielectrophoresis (DEP), involves alignment of solution-dispersed CNTs aligning between electrodes by application of an applied AC electric field. Although DEP has been quite well studied for dielectric particles, the application for depositing nanotubes and nanowires are still at the early stage of development. We have demonstrated that DEP can be used and that the density and alignment of CNTs in the electrode gap is controllable by varying the AC field's strength and frequency. EXPERIMENT Multi-walled CNTs were grown in-house by a dual plasma-enhanced chemical vapor deposition (PECVD) process [16]. This yields CNT directly on a substrate with lengths and widths of roughly 2 µm and 50 nm, respectively. After growth, the 7 mm diameter growth region had its CNTs removed and placed in ethanol for dispersion to a density of roughly 1 x 108 CNTs per mL. This suspension was placed in an ultrasonicating bath for 2 hours in order to disperse the CNTs without surfactant. Electrodes were patterned on glass substrates by pulsed laser deposition of an iron film to a thickness of 50 nm.
Before deposition, the electrodes were connecte
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