Block copolymer micelle nanolithography

Abstract

Au-nanoclusters between 2 and 8 nm in diameter were deposited onto solid substratesin different pattern geometries. The basis of this approach is the self-assembly ofpolystyrene-b-poly[2-vinylpyridine(HAuCl4)]diblock copolymer micelles into uniform monomicellar films onsolid supports such as Si-wafers or glass cover slips. HAuCl4as metallic precursor or a single solid Au-nanoparticle caused by reduction of theprecursor are embedded in the centre of diblock copolymer micelles. Subsequenthydrogen, oxygen or argon gas plasma treatment of the dry film causes depositionof Au-nanoparticles onto the substrate by entire removal of the polymer. TheAu-dot patterns resemble the micellar patterns before the plasma treatment.Separation distances between the dots is controlled by the molecular weight of thediblock copolymers. The limitation of the separation distance between individualdots or the pattern geometry is overcome by combining self-assembly ofdiblock copolymer micelles with pre-structures formed by photo or e-beamlithography. Capillary forces of a retracting liquid film due to solventevaporation on the pre-structured substrate push micelles in the corners of thesedefined topographies. A more direct process is demonstrated by applyingmonomicellar films as negative e-beam resist. Micelles that are irradiated byelectrons are chemically modified and can hardly be dissolved from thesubstrate while non-exposed micelles can be lifted-off by suitable solvents.This process is also feasible on electrical isolating substrates such as glasscover slips if the monomicellar film is coated in addition with a 5 nm thickconductive layer of carbon before e-beam treatment. The applicationof cylindrical block copolymer micelles also allows for the formation of4 nm wide lines which can be 1–50 µmlong and also be organized in defined aperiodic structures.