Monolayer Uniformity of the Nanosphere Mask: Two-dimensional ordered gold nanoparticle arrays with nanosphere lithography.

Nanosphere lithography (NSL) is a simple, effective, and convenient technique for the fabrication of nanoholes, pillar structures, and nanoparticles. An optimal parameter is required for each procedure to fabricate the desired nanostructure, especially for optoelectronic applications to increase their optoelectronic conversion efficiency or some biomedical detection. We produced arrays of gold (Au) nanoparticles with these particles smaller than 100 nm for an application; hence, we focused on precise control in every step. With an innovative method, the step of droplet evaporation in microwells, the monolayer of polystyrene (PS) bead mask achieved great uniformity. By simply adjusting the droplet size and the colloidal concentration, we obtained the largest monolayer area. The monolayer of PS beads on the substrate served as a mask through which Au films were deposited. As a water film occurred on the PS beads that might block the Au deposit onto the substrate, the PS beads had to be treated with an oxygen (O₂) plasma to enlarge the interstices between them. The thickness of the Au deposited was tuned to fabricate annealed nanoparticles smaller than 100 nm. According to this control, the Au nanoparticles were small and formed highly dense arrays.