Control and modeling of the dielectrophoretic assembly of on-chip nanoparticle wires

Suspensions of metallic nanoparticles in water were assembled via the action of an alternating electric field (dielectrophoresis) into wires of micrometer thickness. Two modes of microwire assembly, one through the bulk of the suspension and one as half-cylinders on the glass surface between the electrodes, were identified. The operating conditions responsible for the two assembly modes were recognized. The control of the process parameters allows making, for example, straight single connectors or massively parallel arrays of microwires on the surface of the chip, which can be extracted in dry form. The microwire assembly process was modeled using finite element electrostatic calculations. The direction of growth can be guided by introducing conductive islands or particles in the suspension. The experiments, supported by electrostatic calculations, show that the wires grow in the direction of highest field intensity, "automatically" making electrical connections to the objects between the electrodes. The results point the way to controlled dielectrophoretic assembly of nanoparticles into on-chip electrical connectors, switches, and networks.