Microelectrophoresis deposition using a nanopipette for three-dimensional structures

A novel and simple technique was developed for fabrication of three-dimensional structures using a nanopipette. The nanopipette was a tapered glass capillary with an aperture sub-micrometer in diameter. It was filled with a colloidal solution including metal nanoparticles. The pipette edge was put in contact with a substrate, and the substrate was moved downward to deposit the metal colloidal solution. The diameter of the pillar was dependent on the aperture size of the pipette. To improve the reproducibility of the fabrication, the amount of deposition of the Au colloidal solution was controlled by a feedback loop that maintained the pre-defined constant current under electrophoresis deposition.