Current Dielectrophoresis Research Articles

Assembly and electrical characterization of DNA-wrapped carbon nanotube devices

In this article we report on the electrical characteristics of single wall carbon nanotubes (SWCNTs) wrapped with single-stranded deoxyribonucleic acid (ssDNA). We fabricate these devices using a solution-based method whereby SWCNTs are dispersed in aqueous solution using 20-mer ssDNA, and are placed across pairs of Au electrodes using alternating current dielectrophoresis (ACDEP). In addition to current voltage characteristics, we evaluate our devices using scanning electron microscopy and atomic force microscopy. We find that ACDEP with ssDNA based suspensions results in individual SWCNTs bridging metal electrodes, free of carbon debris, while similar devices prepared using the Triton X-100 surfactant yield nanotube bundles, and frequently have carbon debris attached to the nanotubes. Furthermore, the presence of ssDNA around the nanotubes does not appear to appreciably affect the overall electrical characteristics of the devices. In addition to comparing the properties of several devices prepared on nominally clean Au electrodes, we also investigate the effects of self-assembled monolayers of C14H29-SH alkyl thiol and benzyl mercaptan on the adhesion and electrical transport across the metal/SWCNT/metal devices.

Simultaneous Deposition of Metallic Bundles of Single-walled Carbon Nanotubes Using Ac-dielectrophoresis

A simple and scalable scheme based on alternating current (ac-) dielectrophoresis is used for the simultaneous and site-selective deposition of single bundles of single-walled carbon nanotubes (SWNTs) onto a large number of contacts requiring only one bond wire. This allows for a large number of transport measurements that show that the deposited bundles contain at least one metallic SWNT dominating the transport. With high-voltage pulses, metallic bundles are transformed into Schottky-barrier-type field-effect transistors with p-type, ambipolar, or n-type behavior. From a simple electromechanical model, we derive the fact that ac-dielectrophoresis selectively deposits bundles containing metallic tubes.

Separation of metallic from semiconducting single-walled carbon nanotubes.

We have developed a method to separate metallic from semiconducting single-walled carbon nanotubes from suspension using alternating current dielectrophoresis. Our method takes advantage of the difference of the relative dielectric constants of the two species with respect to the solvent, resulting in an opposite movement of metallic and semiconducting tubes along the electric field gradient. Metallic tubes are attracted toward a microelectrode array, leaving semiconducting tubes in the solvent. Proof of the effectiveness of separation is given by a comparative Raman spectroscopy study on the dielectrophoretically deposited tubes and on a reference sample.