A Continuous Flow Device for the Purification of Semiconducting Nanoparticles by AC Dielectrophoresis
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A Continuous Flow Device for the Purification of Semiconducting Nanoparticles by AC Dielectrophoresis Rustin Golnabi1, Su (Ike) Chih Chi1, Stephen L. Farias1, and Robert C. Cammarata1, 2 1
Department of Materials Science and Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA 2
Department of Mechanical Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA ABSTRACT Single-walled carbon nanotubes (SWCNTs) have attracted significant attention as building blocks for future nanoscale electronics due to their small size and unique electronic properties. However, current SWCNT production techniques generate a mixture of two types of nanotubes with divergent electrical behaviors due to structural variations. Some of the nanotubes act as metallic materials while others display semiconducting properties. This random mixture has prevented the realization of functional carbon nanotube-based nanoelectronics. Here, a method of purifying a continuous flow of semiconducting nanotubes from an initially random mixture of both metallic and semiconducting SWCNTs in suspension is presented. This purification uses A/C dielectrophoresis (DEP), and takes advantage of the large difference of the relative dielectric constants between metallic and semiconducting SWCNTs. Because of a difference in magnitude and opposite directions of a dielectrophoretic force imposed on the random SWCNT solution, metallic SWCNTs deposit onto an electrode while semiconducting SWCNTs remain in suspension [3]. A discussion of these techniques is presented, along with a dielectrophoretic force-utilized microfluidic lab-on-a-chip device that can accomplish purification of semiconducting nanoparticles at high processing rates. The effectiveness of the device is characterized using Raman spectroscopy analysis on separated samples. INTRODUCTION Nanoparticles have continued to be at the forefront of electronics research due to their unique properties and size [1-4]. Semiconducting nanoparticles are especially useful for their various applications in optoelectronics, transistors, biosensors, and drug delivery [5-7]. One of the most investigated and promising nanomaterial is carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) are nanostructures which can be thought of as a single atomic sheet of graphene rolled into a seamless cylinder. They are highly regarded for their high thermal conductivity (over 6000 W/mK), high Young’s modulus (~1 TPa), light weight, and unique electronic properties [8-10]. When synthesized, SWCNTs form in a distribution of structures and sizes, defined by the chiral lattice vector (m, n). Depending on their chirality, carbon nanotubes display either metallic or semiconducting properties and typically grow in a 1:3 ratio of metallic to semiconducting [2]. One of the challenges to implementing carbon nanotubes for commercial applications is this fact that these two types are synthesized together [3]. Many applications require high purity semiconducting nanotu
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