Microfabrication for a polystyrene quadrupole by template-assisted self-assembly

Abstract

Abstract It has been widely known that colloidal particles and their arrayed structures play a critical role in various fields because of their versatility. Based on an expectation that quadrupole microstructures would display unique optical characteristics, we focused on the fabrication process for quadrupole structures composed of colloidal particles. The quadrupole structures consisted of polystyrene particles (PSt) with a 1.0 μm diameter were formed by applying the integrated approach with a top-down method and a bottom-up method (i.e., template-assisted self-assembly). Microhole arrays with two different shapes—circular holes and square holes—were fabricated on a Si substrate by using electron beam lithography and reactive ion etching. These top-down processes were followed by a bottom-up process that the Si substrate with fabricated microhole arrays was withdrawn from a PSt aqueous solution. With the microhole arrays as a guide, the PSt particles were forced to array the specific structures in the microholes due to the capillary force and Van der Waals force acting on the particles and substrate. By controlling the solvent drying process, the yield of quadrupole structure was reached approximately 80% in over 300 microholes. Additionally, the distance between two neighboring particles consisting of quadrupole structures could be controlled by the sizes of the microholes, and the obtained particle configurations could be removed onto an adhesive tape.