Atomic Force Microscopy Study of the Polymeric Nanotemplate Fabricated via a Microphase Separation and Subsequent Selective Etching of (PS-b-PI) Copolymer Thin Film

We have investigated the evolution of surface morphology with thin-film growth of polystyrene (PS)-polyisoprene (PI) diblock copolymer and fabrication of polymer nano-template by atomic force microscopy (AFM). Well-controlled (PS-b-PI) diblock copolymer (PI weight fraction = 0.16, M_w = 85000, and M_w/M_n = 1.01) was prepared by living anionic polymerization. Spin coated copolymer film on both the hydrophobic Si and hydrophilic oxide and nitride substrates showed a typical layer-by-layer growth mode. The (PS-b-PI) diblock copolymer film became spontaneously ordered after overnight annealing inside a vacuum oven above their glass transition temperature, giving hexagonal-close-packed (hep) phase of PI spheres. The well-controlled monolayer film was selectively etched via ozonation to obtain PI sphere voids and then subsequently reacted with CF₄⁺ ions to etch the PS matrix. We obtained the AFM image of the surface morphology of such formed polymer template, whose pattern consisted of 20-nm-size spheres with a periodicity of 45 nm.