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Electric tweezers: Study of positive dielectrophoresis-based positioning and orientation of a nanorod

The manipulation of individual micrometer sized objects has been the focus of significant research efforts over the last few years. Methods based on positive diectrophoresis for the arbitrary manipulation of nanoparticles are being investigated here. This method employs dielectrophoretic forces for the planar control of the motion and orientation of such nanoparticles between a set of microfabricated electrodes. Each electrode is approximated as a set of sources, namely, an unknown point charge and induced dipole. Imposing constraints on the electric field at the location of the particle and requiring self-consistency uniquely determine the sources. They can then be subsequently used to determine the set of electrode voltages that creates an electric field that will produce the prescribed orientation and force on the particle. The drag coefficients of a nanorod are experimentally determined by sequentially applying a constant force both parallel and perpendicular to its axis and observing a resulting motion. With the drag coefficients in hand, the velocity rather than force can be prescribed, and the rod is directed to move accurately at oblique angles to its orientation. The rod is in a constant state of unstable equilibrium and requires negative feedback to maintain a fixed position. The automation of such feedback is being investigated, allowing a controlled travel of the nanostructures over complex paths. This technique can have various potential application in moving and manipulating particles.

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For details regarding this image, please see, B. Edwards, N. Engheta, and S. Evoy "Electric Tweezers: Experimental Studies of Positive Dielectrophoresis-Based Positioning and Orientation of a Nanorod," in Journal of Applied Physics, Vol. 102, 024913 (5 pages) (2007).