Selectively patterned metal nanodots fabrication by combining block copolymer self-assembly and electron beam lithography

Selectively patterned periodic metal nanodots are prospective for use in photonic, plasmonic and magnetic storage devices. Here, we proposed a simple method to fabricate metal nanodots by block copolymer self-assembly and electron beam lithography. Block copolymer self-assembly is a facile method to fabricate periodic nanostructures such as cylinder and sphere in a large area. These self-assembled nanostructures are useful as templates and scaffolds for the fabrication of periodic metal nanodots. In this study, we used polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) and fabricated perpendicular PMMA cylinders onto substrate in PS matrixes. After UV irradiation and immersion in acetic acid, cylindrical nanopores of PS were fabricated. We performed electron beam lithography onto these PS nanoporous thin films. PS is negative tone resist for electron beam lithography. If the electron dose was enough large for PS resist, nanoporous structures were fabricated only in exposed areas after development by solvent, which dissolves PS. We evaporated Au onto these patterned nanoporous templates and sonicated these metal evaporated films in tetrahydrofuran (THF). In consequence, metal nanodots were fabricated only in exposed areas. The diameter and pitch of these nanodots were approximately 20 nm and 40 nm, respectively. These values were almost equal to block copolymer self-assembled cylinder structures. Finally, we demonstrated a simple method for fabricating periodic metal nanodots only in selective areas.