AVS 49th International Symposium
    Nanometer Structures Thursday Sessions
       Session NS-ThA

Paper NS-ThA3
Aligned Dielectrophoretic and Electrophoretic Deposition of Single Wall Carbon Nanotubes

Thursday, November 7, 2002, 2:40 pm, Room C-207

Session: Nanowires
Presenter: P.E. Pehrsson, Naval Research Laboratory
Authors: P.E. Pehrsson, Naval Research Laboratory
J.W. Baldwin, NRC/NRL Postdoctoral Fellow, Naval Research Laboratory
Correspondent: Click to Email
Carbon nanotubes offer real promise for a variety of nanotechnology applications such as resonator arrays for RF electronics, sensors, and other devices. We use dielectrophoresis (DEP) and electrophoresis (EP) to position nanotubes on surfaces and then measure their electrical conductivity. We vary the solution concentration and sonication procedures to control tube aggregation. We also use functionalized single-wall nanotubes (SWNTs), e.g. fluorinated, oxidized or with attached organosilanes. Functionalization can introduce potentially charged species such as carboxylic acid and may also change the nanotube's conductivity and permittivity, both of which may enhance its susceptibility to dielectrophoresis. The resistance across a gap spanned by a few tubes is typically above a M@OMEGA@, but resistance across the gap drops sharply (to 10-20 k@OMEGA@) at higher tube densities, possibly due to formation of a continuous percolation network. Tube purity is critical for good deposition. Contaminant particles in the suspension alter the deposition under specific deposition conditions. Some particles are unassociated with nanotubes and respond to the electric fields like other dielectric particles. Other particles (possibly leftover Ni nanocatalyst or amorphous carbon) are attached to the tubes and may pull them along in response to the fields. We are evaluating the interplay between surface chemistry on the nanotubes and at the electrode/liquid interface and the forces governing DEP and EP. DEP makes particles move in the direction of higher or lower electric field depending on the relative frequency-dependent conductivity and permittivity of the solvent and particle, and the particle size, shape, and surface chemistry. It could ultimately solve two of the biggest problems impeding the exploitation of carbon nanotubes; 1) separation of metallic and semiconducting nanotubes; and 2) removal of non-nanotube contaminants without the need for aggressive acid cleaning.