Electrophoretic Deposition of Iron Oxide Nanoparticles on Templates

We have investigated guided self-assembly of nanoparticles using a combination of templates and electric fields. Some 11.2 +/- 0.5 nm iron oxide nanoparticles were synthesized and dispersed in toluene. Electrophoretic mobility measurements indicate that most nanoparticles have a small excess charge. Using a parallel plate geometry, a voltage is applied to drive particles toward electrodes submersed in the nanoparticle dispersion. These electrodes are either bare silicon wafers or Si nanopatterned with hydrogen silsesquioxane (HSQ) electron beam resist. We demonstrate how an electric field can guide the nanoparticles to selectively nucleate around patterned features. A model is developed to predict the effect of the electric field on a patterned template and the forces guiding the nanoparticle self-assembly.