Block copolymer micelle nanolithography

Abstract

Au-nanoclusters between 2 and 8 nm in diameter were deposited onto solid substrates in different pattern geometries. The basis of this approach is the self-assembly of polystyrene- b -poly[2-vinylpyridine (HAuCl 4 )] diblock copolymer micelles into uniform monomicellar films on solid supports such as Si-wafers or glass cover slips. HAuCl 4 as metallic precursor or a single solid Au-nanoparticle caused by reduction of the precursor are embedded in the centre of diblock copolymer micelles. Subsequent hydrogen, oxygen or argon gas plasma treatment of the dry film causes deposition of Au-nanoparticles onto the substrate by entire removal of the polymer. The Au-dot patterns resemble the micellar patterns before the plasma treatment. Separation distances between the dots is controlled by the molecular weight of the diblock copolymers. The limitation of the separation distance between individual dots or the pattern geometry is overcome by combining self-assembly of diblock copolymer micelles with pre-structures formed by photo or e-beam lithography. Capillary forces of a retracting liquid film due to solvent evaporation on the pre-structured substrate push micelles in the corners of these defined topographies. A more direct process is demonstrated by applying monomicellar films as negative e-beam resist. Micelles that are irradiated by electrons are chemically modified and can hardly be dissolved from the substrate while non-exposed micelles can be lifted-off by suitable solvents. This process is also feasible on electrical isolating substrates such as glass cover slips if the monomicellar film is coated in addition with a 5 nm thick conductive layer of carbon before e-beam treatment. The application of cylindrical block copolymer micelles also allows for the formation of 4 nm wide lines which can be 1–50 µm long and also be organized in defined aperiodic structures.