Patterning of layer-by-layer self-assembled multiple types of nanoparticle thin films by lithographic technique

A lithographic approach to generate clean patterns of multiple types of nanoparticles on one 4-inch silicon wafer is demonstrated in this paper. Each type of nanoparticle is precisely directed to the desired location. The process is mainly based on conventional microelectronic techniques with extremely high reproducibility. This enables the possibility of industrial applications to fabricate devices made of nanocrystals. A thin film of polystyrene spheres, 150 nm in diameter, was first coated on the silicon wafer with layer-by-layer self-assembly, followed by a layer of aluminum deposited on the thin film. A layer of positive photoresist was spun on the surface of aluminum and then patterned by lithographic technique. The unprotected aluminum was removed by wet etching until the polystyrene thin film underneath was exposed to the air. Oxygen plasma was employed to etch the polystyrene thin film all the way to the silicon surface. Subsequently, a thin film of another type of nanoparticle, silica particle 78 nm in diameter, was adsorbed onto the surface with layer-by-layer self-assembly. Eventually, aluminum and photoresist were removed and each type of nanoparticle was located next to each other as the pattern was designed. A scanning electron microscope was used to produce the image of the pattern.