In Hydromel, researchers in the Nanotechnology Group at the Tyndall National Institute (Cork, Ireland) are addressing this fabrication challenge by developing low cost self-assembly technologies for the assembly of nanowires at technologically relevant substrates, i.e., silicon chips. Two different fabrication methodologies being explored: In the first method, long range forces such as, e.g., electric force fields are used to drive the on-chip self-assembly of freestanding nanowires to form ordered nanowire arrays. In this approach, an AC voltage bias is applied to microelectrodes patterned on a silicon chip substrate and followed by dispensing a suspension droplet of polymer or metal nanowires on top of the chip. The applied voltage establishes an electric field between the electrodes. The field is non-uniform due to the 3-D nature of the electrodes and field is strongest at the electrode edges and decreases to a minimum at the central point between the electrodes. The nanowires in solution become polarised (charge separated) in the presence of the electric field. By tailoring the frequency of the applied electric field and by careful selection of the suspension medium, nanowires ae induced to migrate to the areas of highest field strength thorough a process known as dielectrophoresis. In this manner the nanowires spontaneously self-assemble at the electrode edges and orient in the direction of the electric field to form well ordered nanowire arrays.
