Vacuum-driven assembly of electrostatically levitated microspheres on perforated surfaces

At the onset of a miniaturized device era, several promising methods, primarily wet methods, have been developed to attain large-scale assemblies of microparticles. To improve the speed, versatility and robustness of the current methods for the structured assembly of microparticles, an automatable method capable of forming 2D arrays of microspheres on large silicon surfaces is devised. The method uses surfaces perforated with vacuum-suction holes, capable of aspiring and holding individual particles from a particle cloud generated by subjecting a lump of chargeable particles, e.g., silica, polystyrene, and polymethyl methacrylate (PMMA), to a strong electrical field under ambient air conditions. The microsphere levitation depends on the electrical conductivity and permittivity of the particles. A single or double brush stroke can remove excess particles covering the formed arrays. We find that silica or polystyrene microspheres with a diameter of 5 μm or 10 μm can be assembled on the order of a few seconds, independently of the array size. Owing to the reversible nature of the arresting vacuum force, the assembled layers can be transferred to another surface, such as polydimethylsiloxane (PDMS) sheets, thus providing a key step for future particle printing processes for the fabrication of hierarchical materials, e.g., photonic crystals.